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• 401.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology. Bell Laboratories, Alcatel-Lucent Murray Hill, NJ 07974, USA.
Aspects of Favorable Propagation in Massive MIMO2014In: European Signal Processing Conference (EUSIPCO), EURASIP , 2014, p. 76-80Conference paper (Refereed)

Favorable propagation, dened as mutual orthogonality among the vector-valued channels to the terminals, is one of the key properties of the radio channel that is exploited in Massive MIMO. However, there has been little work that studies this topic in detail. In this paper, we first show that favorable propagation offers the most desirable scenario in terms of maximizing the sum-capacity. One useful proxy for whether propagation is favorable or not is the channel condition number. However, this proxy is not good for the case where the norms of the channel vectors are not equal. For this case, to evaluate how favorable the propagation oered by the channel is, we propose a distance from favorable propagation measure, which is the gap between the sum-capacity and the maximum capacity obtained under favorable propagation. Secondly, we examine how favorable the channels can be for two extreme scenarios: i.i.d. Rayleigh fading and uniform random line-of-sight(UR-LoS). Both environments offer (nearly) favorable propagation. Furthermore, to analyze the UR-LoS model, we propose an urns-and-balls model. This model is simple and explains the singular value spread characteristic of the UR-LoS model well.

• 402.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology. Bell Laboratories, Alcatel-Lucent, NJ, USA.
Energy and Spectral Efﬁciency of Very Large Multiuser MIMO Systems2013In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 61, no 4, p. 1436-1449Article in journal (Refereed)

A multiplicity of autonomous terminals simultaneously transmits data streams to a compact array of antennas. The array uses imperfect channel-state information derived from transmitted pilots to extract the individual data streams. The power radiated by the terminals can be made inversely proportional to the square-root of the number of base station antennas with no reduction in performance. In contrast if perfect channel-state information were available the power could be made inversely proportional to the number of antennas. Lower capacity bounds for maximum-ratio combining (MRC), zero-forcing (ZF) and minimum mean-square error (MMSE) detection are derived. An MRC receiver normally performs worse than ZF and MMSE. However as power levels are reduced, the cross-talk introduced by the inferior maximum-ratio receiver eventually falls below the noise level and this simple receiver becomes a viable option. The tradeoff between the energy efficiency (as measured in bits/J) and spectral efficiency (as measured in bits/channel use/terminal) is quantified for a channel model that includes small-scale fading but not large-scale fading. It is shown that the use of moderately large antenna arrays can improve the spectral and energy efficiency with orders of magnitude compared to a single-antenna system.

• 403.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology. Bell Laboratories, Alcatel-Lucent, Murray Hill, NJ 07974, USA.
Massive MU-MIMO Downlink TDD Systems with Linear Precodingand Downlink Pilots2013In: 51st Annual Allerton Conference on Communication, Control, and Computing (Allerton), 2013, IEEE , 2013, p. 293-298Conference paper (Refereed)

We consider a massive MU-MIMO downlink time-division duplex system where a base station (BS) equipped with many antennas serves several single-antenna users in the same time-frequency resource. We assume that the BS uses linear precoding for the transmission. To reliably decode the signals transmitted from the BS, each user should have an estimate of its channel. In this work, we consider an efficient channel estimation scheme to acquire CSI at each user, called beamforming training scheme. With the beamforming training scheme, the BS precodes the pilot sequences and forwards to all users. Then, based on the received pilots, each user uses minimum mean-square error channel estimation to estimate the effective channel gains. The channel estimation overhead of this scheme does not depend on the number of BS antennas, and is only proportional to the number of users. We then derive a lower bound on the capacity for maximum-ratio transmission and zero-forcing precoding techniques which enables us to evaluate the spectral efficiency taking into account the spectral eciency loss associated with the transmission of the downlink pilots. Comparing with previous work where each user uses only the statistical channel properties to decode the transmitted signals, we see that the proposed beamforming training scheme is preferable for moderate and low-mobility environments.

• 404.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology. Bell Laboratories, Alcatel-Lucent, NJ, USA .
The Multicell Multiuser MIMO Uplink with Very Large Antenna Arrays and a Finite-Dimensional Channel2013In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 61, no 6, p. 2350-2361Article in journal (Refereed)

We consider multicell multiuser MIMO systems with a very large number of antennas at the base station (BS). We assume that the channel is estimated by using uplink training. We further consider a physical channel model where the angular domain is separated into a ﬁnite number of distinct directions. We analyze the so-called pilot contamination effect discovered in previous work, and show that this effect persists under the ﬁnite-dimensional channel model that we consider. In particular, we consider a uniform array at the BS. For this scenario, we show that when the number of BS antennas goes to inﬁnity, the system performance under a ﬁnite-dimensional channel model with P angular bins is the same as the performance under an uncorrelated channel model with P antennas. We further derive a lower bound on the achievable rate of uplink data transmission with a linear detector at theBS. We then specialize this lower bound to the cases of maximum-ratio combining (MRC) and zero-forcing (ZF) receivers, for a ﬁnite and an inﬁnite number of BS antennas. Numerical results corroborate our analysis and show a comparison between the performances of MRC and ZF in terms of sum-rate.

• 405.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
Bell Laboratories, Alcatel-Lucent, Murray Hill, NJ 07974, USA. Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
Analysis of the Pilot Contamination Effect in Very Large Multicell Multiuser MIMO Systems for Physical Channel Models2011In: Proceedings of the IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP), IEEE conference proceedings, 2011, p. 3464-3467Conference paper (Refereed)

We consider multicell multiuser MIMO systems with a very large numberof antennas at the base station. We assume that the channel is estimated by using uplink training sequences, and we consider a physical channel model where the angular domain is separated into a finite number of directions. We analyze the so-called pilot contamination effect discovered in previous work, and show that this effect persists under the finite-dimensional channel model that we consider.  We further derive closed-form bounds on the achievable rate of uplink data transmission with maximum-ratio combining, for a finite and an infinite number of base station antennas.

• 406.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
Chalmers University of Technology, Gothenburg, Sweden. Blekinge Institute of Technology, Karlskrona, Sweden. Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
Uplink Performance Analysis of Multicell MU-SIMO Systems with ZF Receivers2013In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359Article in journal (Refereed)

We consider the uplink of a multicell multiuser single-input multiple-output system where the channel experiences both small and large-scale fading. The data detection is done by using the linear zero-forcing technique, assuming the base station (BS) has perfect channel state information of all users in its cell. We derive  new, exact analytical expressions for the uplink rate, symbol error rate, and outage probability per user, as well as alower bound on the achievable rate. This bound is very tight and becomes exact in the large-number-of-antennas limit. We further study the asymptotic system performance in the regimes of high signal-to-noise ratio (SNR), large number of antennas, and large number of users per cell. We show that at high SNRs, the system is interference-limited and hence, we cannot improve the system performance by increasing the transmit power of each user. Instead, by increasing the number of BS antennas, the effects of interference and noise can be reduced, thereby improving the system performance. We demonstrate that, with very large antenna arrays at the BS, the transmit power of each user can be made inversely proportional to the number of BS antennas while maintaining a desired quality-of-service. Numerical results are presented to verify our analysis.

• 407.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
Queen's University Belfast, Belfast, BT3 9DT, U.K.. Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
Massive MIMO with Optimal Power and Training Duration Allocation2014In: IEEE Wireless Communications Letters, ISSN 2162-2337, E-ISSN 2162-2345, Vol. 3, no 6, p. 605-608Article in journal (Refereed)

We consider the uplink of massive multicell multiple-input multiple-output systems, where the base stations (BSs), equipped with massive arrays, serve simultaneously several terminals in the same frequency band. We assume that the BS estimates the channel from uplink training, and then uses the maximum ratio combining technique to detect the signals transmitted from all terminals in its own cell. We propose an optimal resource allocation scheme which jointly selects the training duration,training signal power, and data signal power in order to maximize the sum spectral efficiency, for a given total energy budget spent in a coherence interval. Numerical results verify the benets of the optimal resource allocation scheme. Furthermore, we show that more training signal power should be used at low signal-to-noise ratio(SNRs), and vice versa at high SNRs. Interestingly, for the entire SNR regime, the optimal training duration is equal to the number of terminals.

• 408.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
Department of Signals and Systems, Chalmers University of Technology, Gothenburg, Sweden. Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
Performance Analysis of Large Scale MU-MIMO with Optimal Linear Receiver2012In: Proceedings of the IEEE Swedish Communication Technologies Workshop (Swe-CTW), IEEE , 2012, p. 59-64Conference paper (Refereed)

We consider the uplink of multicell multiuser MIMO(MU-MIMO) systems with very large antenna arrays at the base station (BS). We assume that the BS estimates the channel through uplink training, and then uses this channel estimate to detect the signals transmitted from a multiplicity of autonomous users in its cell. By taking the correlation between the channel estimate and the interference from other cells into account, we propose an optimal linear receiver (OLR) which maximizes the received signal-to-interference-plus-noise (SINR). Analytical approximations of the exact and lower bound on the achievable rate are then derived. The bound is very tight, especially at large number of BS antennas. We show that at low SINR, maximal-ratio combing (MRC) receiver performs as well as OLR, however at high SINR, OLR outperforms MRC. Compared with the typical minimum mean-square error receiver, our proposed OLR improves systematically the system performance, especially when the interference is large.

• 409.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
University of Peradeniya, Peradeniya 20400, Sri Lanka . Queen's University Belfast, Belfast, BT3 9DT, U.K.. Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
Multipair Full-Duplex Relaying with Massive Arrays and Linear Processing2014In: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008, Vol. 32, no 9, p. 1721-1737Article in journal (Refereed)

We consider a multipair decode-and-forward relay channel, where multiple sources transmit simultaneously their signals to multiple destinations with the help of a full-duplex relay station. We assume that the relay station is equipped with massive arrays, while all sources and destinations have a single antenna. The relay station uses channel estimates obtained from received pilots and zero-forcing (ZF) or maximum-ratio combining/maximum-ratio transmission (MRC/MRT) to process the signals. To signicantly reduce the loop interference effect, we propose two techniques: i) using a massive receive antenna array; or ii) using a massive transmit antenna array together with very low transmit power at the relay station. We derive an exact achievable rate expression in closed-form for MRC/MRT processing and an analytical approximation of the achievable rate for ZF processing. This approximation is very tight, particularly for a large number of relay station antennas. These closed-form expressions enable us to determine the regions where the full-duplex mode outperforms the half-duplex mode, as well as to design an optimal power allocation scheme. This optimal power allocation scheme aims to maximize the energy efficiency for a given sum spectral efficiency and under peak power constraints at the relay station and sources. Numerical results verify the effectiveness of the optimal power allocation scheme. Furthermore, we show that, by doubling the number of transmit/receive antennas at the relay station, the transmit power of each source and of the relay station can be reduced by 1.5 dB if the pilot power is equal to the signal power, and by 3 dB if the pilot power is kept fixed, while maintaining a given quality of service.

• 410.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering. Queens Univ Belfast, Sch Elect Elect Engn & Comp Sci, Belfast BT3 9DT, Antrim, North Ireland.
Maynooth Univ, Dept Elect Engn, Maynooth, Kildare, Ireland. Queens Univ Belfast, Sch Elect Elect Engn & Comp Sci, Belfast BT3 9DT, Antrim, North Ireland. Queens Univ Belfast, Sch Elect Elect Engn & Comp Sci, Belfast BT3 9DT, Antrim, North Ireland. Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
Energy Efficiency Optimization for Cell-Free Massive MIMO2017In: 2017 IEEE 18TH INTERNATIONAL WORKSHOP ON SIGNAL PROCESSING ADVANCES IN WIRELESS COMMUNICATIONS (SPAWC), 2017Conference paper (Refereed)

This paper considers a time-division duplex cell-free massive multiple-input multiple-output downlink with imperfect channel station information and conjugate beamforming scheme. The total energy efficiency is investigated taking into account the hardware power consumption and the backhaul power consumption. We propose an optimal power allocation algorithm which aims to maximize the total energy efficiency, under a per-access point power constraint and a per-user spectral efficiency constraint. This optimization problem can be approximately solved via a sequence of second-order cone programs. Compared with the case of without power control, our proposed power allocation scheme can double the total energy efficiency. Furthermore, we show that, when the number of access points is large, the backhaul power consumption affects significantly the total energy efficiency.

• 411.
Institute of Electronics, Communications and Information Technology, Queen’s University Belfast, Belfast, U.K..
School of Electrical and Electronic Engineering, University College Dublin, Dublin 4, Ireland. Institute of Electronics, Communications and Information Technology, Queen’s University Belfast, Belfast, U.K.. Institute of Electronics, Communications and Information Technology, Queen’s University Belfast, Belfast, U.K.. Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
On the Total Energy Efficiency of Cell-Free Massive MIMO2018In: IEEE Transactions on Green Communications and Networking, ISSN 2473-2400, Vol. 2, no 1, p. 25-39Article in journal (Refereed)

We consider the cell-free massive multiple-input multiple-output (MIMO) downlink, where a very large number of distributed multiple-antenna access points (APs) serve many single-antenna users in the same time-frequency resource. A simple (distributed) conjugate beamforming scheme is applied at each AP via the use of local channel state information (CSI). This CSI is acquired through time-division duplex operation and the reception of uplink training signals transmitted by the users. We derive a closed-form expression for the spectral efficiency taking into account the effects of channel estimation errors and power control. This closed-form result enables us to analyze the effects of backhaul power consumption, the number of APs, and the number of antennas per AP on the total energy efficiency, as well as, to design an optimal power allocation algorithm. The optimal power allocation algorithm aims at maximizing the total energy efficiency, subject to a per-user spectral efficiency constraint and a per-AP power constraint. Compared with the equal power control, our proposed power allocation scheme can double the total energy efficiency. Furthermore, we propose AP selections schemes, in which each user chooses a subset of APs, to reduce the power consumption caused by the backhaul links. With our proposed AP selection schemes, the total energy efficiency increases significantly, especially for large numbers of APs. Moreover, under a requirement of good quality-of-service for all users, cell-free massive MIMO outperforms the colocated counterpart in terms of energy efficiency.

• 412.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
Department of Electrical and Electronics Engineering, University of of Peradeniya, Peradeniya, Sri Lanka. School of Electronics, Electrical Engineering and Computer Science, Queens University of Belfast, Belfast, United Kingdom; Department of Signals and Systems, Chalmers University of of Technology, Gothenburg, Sweden. Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
Multipair massive MIMO full-duplex relaying with MRC/MRT processing2014In: 2014 IEEE International Conference on Communications, ICC 2014, IEEE Computer Society , 2014, no 6884081, p. 4807-4813Conference paper (Refereed)

We consider a multipair relay channel, where multiple sources communicate with multiple destinations with the help of a full-duplex (FD) relay station (RS). All sources and destinations have a single antenna, while the RS is equipped with massive arrays. We assume that the RS estimates the channels by using training sequences transmitted from sources and destinations. Then, it uses maximum-ratio combining/maximum-ratio transmission (MRC/MRT) to process the signals. To significantly reduce the loop interference (LI) effect, we propose two massive MIMO processing techniques: i) using a massive receive antenna array; or ii) using a massive transmit antenna array together with very low transmit power at the RS. We derive an exact achievable rate in closed-form and evaluate the system spectral efficiency. We show that, by doubling the number of antennas at the RS, the transmit power of each source and of the RS can be reduced by 1.5 dB if the pilot power is equal to the signal power and by 3 dB if the pilot power is kept fixed, while maintaining a given quality-of-service. Furthermore, we compare FD and half-duplex (HD) modes and show that FD improves significantly the performance when the LI level is low. © 2014 IEEE.

• 413.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology. Bell Laboratories, Alcatel-Lucent, Murray Hill, NJ 07974, USA.
Uplink Power Efficiency of Multiuser MIMO with Very Large Antenna Arrays2011In: Proceedings of Allerton Conference on Communication, Control, and Computing, IEEE , 2011, p. 1272-1279Conference paper (Refereed)

A multiplicity of autonomous terminals simultaneously transmits data streams to a compact array of antennas. The array uses imperfect channel-state information derived from transmitted pilots to extract the individual data streams. The power radiated by the terminals can be made inversely proportional to the square-root of the number of base station antennas with no reduction in performance. In contrast if perfect channel-state information were available the power could be made inversely proportional to the number of antennas. A maximum-ratio combining receiver normally performs worse than a zero-forcing receiver. However as power levels are reduced, the cross-talk introduced by the inferior maximum-ratio receiver eventually falls below the noise level and this simple receiver becomes a viable option.

• 414.
Queens University of Belfast, North Ireland.
Queens University of Belfast, North Ireland. Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering. Queens University of Belfast, North Ireland. St Cyril & Methodius Univ, Skopje, Macedonia. Guangdong University of Petrochem Technology, Peoples R China.
Secure 5G Wireless Communications: A Joint Relay Selection and Wireless Power Transfer Approach2016In: IEEE Access, E-ISSN 2169-3536, Vol. 4, p. 3349-3359Article in journal (Refereed)

In this paper, we investigate the secrecy performance of an energy harvesting relay system, where a legitimate source communicates with a legitimate destination via the assistance of multiple trusted relays. In the considered system, the source and relays deploy the time-switching-based radio frequency energy harvesting technique to harvest energy from a multi-antenna beacon. Different antenna selection and relay selection schemes are applied to enhance the security of the system. Specifically, two relay selection schemes based on the partial and full knowledge of channel state information, i. e., optimal relay selection and partial relay selection, and two antenna selection schemes for harvesting energy at source and relays, i. e., maximizing energy harvesting channel for the source and maximizing energy harvesting channel for the selected relay, are proposed. The exact and asymptotic expressions of secrecy outage probability in these schemes are derived. We demonstrate that applying relay selection approaches in the considered energy harvesting system can enhance the security performance. In particular, optimal relay selection scheme outperforms partial relay selection scheme and achieves full secrecy diversity order, regardless of energy harvesting scenarios.

• 415.
Linköping University, Department of Electrical Engineering, Communication Systems.
Reliable Communication of Time- and Security-Sensitive Information over a Single Combat Vehicle Network2019Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis

A common trend, in general as well as in the field of combat vehicles, is the rapidly increasing demand for data network capacity and even more in transferred data. To handle this increased demand, different countries with their armed forces and equipment manufacturers evaluate methods to increase the data transmission capacity in combat vehicles. The different types of transmitted data are of different criticality and have different security demands. An easy solution to this is to have separated networks for each type of traffic, but that is quite expensive and uses a lot of hardware. This thesis focuses on a different solution, with a shared network for all types of data transmissions.

This is done by evaluating different types of data networks and add-on protocols and then testing the networks practically with varying transmission rates. In the thesis, all the practical testing is done with data networks according to the Ethernet standard, which is the standard evaluated with a throughput that is high enough for the use case. Ethernet as a standard is not suitable for critical data traffic and therefore add-on protocols for Ethernet to optimize the system for critical data traffic are tested. With these optimizations made, Ethernet can be considered more suitable for critical traffic, but this depends entirely on the system requirements.

• 416.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
Double Differential TOA Positioning for GSM2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis

For most time-based positioning techniques, synchronization between the objectsin the system is of great importance. GPS (global positioning system) signalshave been found very useful in this area. However, there are some shortcomingsof these satellite signals, making the system vulnerable. The aim of this masterthesis is to investigate an alternative method for synchronization, independent ofGPS signals, which could be used as a complement. The proposed method takesadvantage of the broadcast signals from telecommunication towers, and use themfor calculation of the synchronization error between two receivers. By looking atthe time difference between arrival times at the receivers, and compare it to thetrue time difference, the synchronization error can be found. A precondition isthat the locations of the receivers as well as the tele tower are known beforehand,so that the true time difference can be calculated using geometry.The arrival times are determined through correlation between the received signalsand known training bits, which are a part of the transmission sequence. Forverification, experiments were made on localization of a mobile phone in theGSM (global system of mobile communications) network.This researchwas a collaboration with FOI, the Swedish Defense Research Agency,where most of the work was done.

• 417.
Linköping University, Department of Electrical Engineering, Communication Systems.
All-Digital Aggregator for Multi-Standard Video Distribution2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis

In video transmission there is a need to compose a wide-band signal from a numberof narrow-band sub-signals. A flexible solution offers the possibility to place any narrow-band sub-signal anywhere in the wide-band signal, making better use of the frequency space of the wide-band signal. A multi-standard supportive solution will also consider the three standard bandwidths of digital and analog video transmissions, both terrestrial and cable (6; 7 and 8 MHz), in use today.

This thesis work will study the efficiency of a flexible aggregation solution, in terms of computational complexity and error vector magnitude (EVM). The solution uses oversampled complex modulated filter banks and inner channelizers, to reduce the total workload on the system.

Each sub-signal is channelized through an analysis filter bank and together all channelized sub-signals are aggregated through one synthesis filter bank to form the wide-band composite signal. The EVM between transmitted and received sub-signals are investigated for an increasing number of sub-signals.

The solution in this thesis work is performing good for the tested number of up to 100 narrow-band sub-signals. The result indicates that the multi-standard flexible aggregation solution is efficient for an increasing number of transmitted sub-signals.

• 418.
Linköping University, Department of Electrical Engineering, Communication Systems.
Is the Cyclic Prefix Needed in Massive MIMO?2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis

Massive multiple-input-multiple-output (MIMO) is a wireless communication technologythat usesa large number of antennas at the base station and servesmultiple terminals over the same time-frequency resource.This technique can achievehigher data rates than existing communication technology, which only serves one terminal per resource. That is why Massive MIMO is considered a promising candidate for 5G. Orthogonal frequency division multiplexing (OFDM) can be used for transmitting information at different sub-channels. The cyclic prefix (CP) is a repetition of the last samples in a symbol, which is appended at the beginning of the symbol.It serves as a guard interval between consecutive symbols to avoid inter-symbol interference (ISI) and to make sub-channels orthogonal. In this thesis it is proposed to shorten the CP length in Massive MIMO. The shortening of the CP length will increase the effective spectral efficiency but also create additional interference. This trade-off is investigated. A simulation based study is performed to analyse the effective achievable rate of anuplink Massive MIMO system in a single-cell scenario when 10000 Gaussian symbols are transmitted.In the simulation, the number of sub-channels is 128. They are transmitted through a channel with 10 taps. With the classical CP length9samples and a massive MIMO base stationwith 50 antennas serving 3 terminals,the effective achievable rate was 3.863 bits/s/Hz. It was found thatthe effective achievable rate is maximized when the CP length is shortened to 6 samples; the effective achievable rate then became 4.112 bits/s/Hz.In the same system when 100 antennas are used, the corresponding effective achievable rates are 4.791 bits/s/Hz and 4.895 bits/s/Hz with an optimum CP lengthof5 samples. It is shown that the optimum CP length in Massive MIMO is not equal to the number of taps minus one which is the conventional choice. Yes, the CP is needed in Massive MIMO, but it can be shorter than conventionally.

• 419.
Linköping University, Department of Electrical Engineering, Communication Systems.
Enhancements in LTE OTDOA Positioning for Multipath Environments2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis

By using existing radio network infrastructure, a user can be positioned even where GPS and other positioning technologies lack coverage. The LTE Positioning Protocol (LPP) supports user Reference Signal Time Difference (RSTD) reports based on the Time of Arrival (TOA) for a Positioning Reference Signal (PRS). In the current reporting format, only one RSTD for each base station is considered, but for indoor environments this is easily biased due to fading and multipath issues, resulting in a Non-Line of Sight (NLOS) bias. With a rich User Equipment (UE) feedback that can represent the multipath channel for each Base Station (BS), the positioning accuracy can be increased. This thesis develops and evaluates a UE reporting format representing multiple TDOA candidates, and a probabilistic positioning algorithm, in terms of positioning accuracy and amount of data reported. By modeling time measurements as Gaussian Mixture (GM), the time information can be compressed with arbitrary resolution and used in a Maximum-Likelihood (ML) estimation to find the position. Results were obtained through simulation in a radio network simulator and post-processing of simulation data in Matlab. The results suggest that several TOA candidates improve the positioning accuracy, but that the largest improvement comes from a noise based threshold by increasing LOS detectability reducing the NLOS bias, while suppressing noise. The results also suggest that the accuracy for the method can be further improved by combining multiple time measurement occasions.

• 420.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
Signal theory2011 (ed. 1)Book (Other academic)

Signal theory provides a mathematical toolbox for modeling and analysis of physical systems. Stochastic processes are used to model more or less unknown signals. Signal theory has applications in communication engineering, signal processing, automatic control, medical engineering, and more.

This book starts off by reviewing the needed background from probability theory and signals & systems. Then stochastic processes are introduced, both in discrete and continuous time, together with the important tools auto-correlation function and power-spectral density. Separate chapters focus on analyzing linear filters, sampling & reconstruction, some nonlinearities and modulation in terms of stochastic processes. The modulation chapter includes noise analyses of the considered modulation methods assuming that thermal noise dominates the picture. A separate chapter briefly covers multi-dimensional signals and systems as a preparation for image processing. A chapter on spectral estimation is included, which could be used as a basis for computer-based laborations. Problems are given at the end of each chapter. Hints and answers to most of those problems are provided in appendices.

The book is suitable for an advanced course on engineering aspects of stochastic processes. It is written with an electrical engineering student in mind, but should be useful in other engineering disciplines as well. We do not dwell on the innermost details of stochastic processes. Instead we focus on the ability to deal with stochastic processes in situations that could very well be models of real-world problems. This book provides tools and understanding that can be used as a preparation for in-depth studies of subjects such as communication engineering, image and signal processing or analysis, and automatic control, just to mention a few.

This book is intended for engineering students with a background in probability theory on one hand and signals and systems on the other hand. No prior knowledge of stochastic processes is assumed.

• 421.
Linköping University, Department of Electrical Engineering, Communication Systems.
Network-Based Positioning Using Last Visited Cells Report2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis

The positioning performance with the LVC (Last Visited Cells) report is evaluated and compared with extended reports with signal strength data. The LVC report contains cell identities and time spent in the last cells listened to. This is an off-line data source and the purpose of the positioning is to extract information about users’ whereabouts, which for example can be used to optimize the cellular network or vehicular traffic. The positioning evaluation is done in Matlab with a log-distance model, a fingerprinting algorithm, and a new LVC specific algorithm. A particle filter and a particle smoother is used to process simulated LVC reports and extended reports with different amount of information. The results are compared and evaluated with regard to the positioning accuracy and the information density of the reports.

• 422.
Linköping University, Department of Electrical Engineering, Communication Systems.
Linköping University, Department of Electrical Engineering, Communication Systems.
5G Simulation Framework2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis

From the first generation, 1G, to the fourth generation, 4G, the development and technological advancements in telecommunications network systems have been remarkable. Faster and better connections have opened up for new markets, ideas and possibilities, to that extent that there now is a demand that surpasses the supply. Despite all these advancements made in the mobile communications field most of the concept of how the technology works and its infrastructure has remained the same. This however, is about to change with the introduction of the fifth generation (5G) mobile communication.

With the introduction of 5G much of the technology introduced will be different from that of previous generations. This change extends to include the entire infrastructure of the mobile communications system. With these major changes, many of the tools available today for telecommunications network evaluation do not really suffice to include the 5G network standard. For this reason, there is a need to develop a new kind of tool that will be able to include the changes brought by this new network standard.

In this thesis a simulation framework adapted for the next generation telecommunication standard 5G is set to be developed. This framework should include many of the characteristics that set 5G aside from previous generations.

• 423.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
Linear Precoding Performance of Massive MU-MIMO downlink System2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis

Nowadays, multiuser Multiple-In Multiple-Out systems (MU-MIMO) are used in a new generation wireless technologies. Due to that wireless technology improvement is ongoing, the numbers of users and applications increase rapidly. Then, wireless communications need the high data rate and link reliability at the same time. Therefore, MU-MIMO improvements have to consider 1) providing the high data rate and link reliability, 2) support all users in the same time and frequency resource, and 3) using low power consumption. In practice, the interuser interference has a strong impact when more users access to the wireless link. Complicated transmission techniques such as interference cancellation should be used to maintain a given desired quality of service. Due to these problems, MU-MIMO with very large antenna arrays (known as massive MIMO) are proposed. With a massive MU-MIMO system, we mean a hundred of antennas or more serving tens of users. The channel vectors are nearly orthogonal, and then the interuser interference is reduced significantly. Therefore, the users can be served with high data rate simultaneously. In this thesis, we focus on the performance of the massive MU-MIMO downlink where the base station uses linear precoding techniques to serve many users over Rayleigh and Nakagami-m fading channels.

• 424.
Imperial Coll London, England; University of Edinburgh, Scotland.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering. Queen’s University Belfast, Belfast, Northern Ireland. University of Edinburgh, UK.
Performance of Massive MIMO Uplink With Zero-Forcing Receivers Under Delayed Channels2017In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 66, no 4, p. 3158-3169Article in journal (Refereed)

In this paper, we analyze the performance of the up-link communication of massive multicell multiple-input multiple-output (MIMO) systems under the effects of pilot contamination and delayed channels because of terminal mobility. The base stations (BSs) estimate the channels through the uplink training and then use zero-forcing (ZF) processing to decode the transmit signals from the users. The probability density function (pdf) of the signal-to-interference-plus-noise ratio (SINR) is derived for any finite number of antennas. From this pdf, we derive an achievable ergodic rate with a finite number of BS antennas in closed form. Insights into the impact of the Doppler shift (due to terminal mobility) at the low signal-to-noise ratio (SNR) regimes are exposed. In addition, the effects on the outage probability are investigated. Furthermore, the power scaling law and the asymptotic performance result by infinitely increasing the numbers of antennas and terminals (while their ratio is fixed) are provided. The numerical results demonstrate the performance loss for various Doppler shifts. Among the interesting observations revealed is that massive MIMO is favorable even under channel aging conditions.

• 425.
Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering. University of Patras, Greece.
Throughput and Delay Analysis of Wireless Caching Helper Systems with Random Availability2018In: IEEE Access, E-ISSN 2169-3536, Vol. 6, p. 9667-9678Article in journal (Refereed)

In this paper, we investigate the effect of bursty traffic and random availability of caching helpers in a wireless caching system. More explicitly, we consider a general system consisting of a caching helper with its dedicated user in proximity and another non-dedicated user requesting for content. Both the non-dedicated user and the helper have limited storage capabilities. When the user is not able to locate the requested content in its own cache, then its request shall be served either by the caching helper or by a large data center. Assuming bursty request arrivals at the caching helper from its dedicated destination, its availability to serve other users is affected by the request rate, which will further affect the system throughput and the delay experienced by the non-dedicated user. We characterize the maximum weighted throughput and the average delay per packet of the considered system, taking into account the request arrival rate of the caching helper, the request probability of the user and the availability of the data center. Our results provide fundamental insights in the throughput and delay behavior of such systems, which are essential for further investigation in larger topologies.

• 426.
Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
University of Patras, Greece. Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
Network-level Cooperation in Random Access IoT Networks with Aggregators2018In: International Teletraffic Congress (ITC 30), 2018Conference paper (Refereed)

In this work, we consider a random access IoT wireless network assisted by two aggregators. The nodes and the aggregators are transmitting in a random access manner under slotted time, the aggregators use network-level cooperation. We assume that all the nodes are sharing the same wireless channel to transmit their data to a common destination. The aggregators with out-of-band full duplex capability, are equipped with queues to store data packets that are transmitted by the network nodes and relaying them to the destination node. We characterize the throughput performance of the IoT network. In addition, we obtain the stability conditions for the queues at the aggregators and the average delay of the packets.

• 427.
Univ Ferrara, Italy.
Boegli Gravures SA, Switzerland. Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering. Rice Univ, TX 77251 USA.
Guest Editorial Special Issue on the 2017 IEEE International Symposium on Circuits and Systems (ISCAS 2017)2018In: IEEE Transactions on Circuits and Systems Part 1: Regular Papers, ISSN 1549-8328, E-ISSN 1558-0806, Vol. 65, no 3, p. 857-858Article in journal (Other academic)

n/a

• 428.
Linköping University, Department of Electrical Engineering, Communication Systems.
Linköping University, Department of Electrical Engineering, Communication Systems.
Self-Organized TDMA protocol for Tactical Data Links2011Independent thesis Advanced level (degree of Master (Two Years)), 30 credits / 45 HE creditsStudent thesis

A Tactical Data Link (TDL) system has been deployed in many military missions as a winning strategy. The performance of a TDL system is governed by the MAC protocol. The MAC protocol that is able to provide more flexibility and high quality of services is more desirable. However, most MAC protocols implemented in current TDL systems are based on a preprogramming TDMA protocol, in which a time slot schedule is fixed. This thesis presents the new self-organized TDMA protocol based on the existing self-organized slot assignment algorithms and the practical military scenarios as the alternative solution to the current preprogramming TDMA protocol. The self-organized TDMA protocol presented in this thesis is based on the Node Activation Polling Access (NAPA), Virtual Slot (VSLOT), and message based slot assignment algorithms. To evaluate the performance of the designed self-organized TDMA protocol over the preprogramming TDMA protocol, the simulation models for both protocols were implemented and simulated with NS-2 under the specific study scenarios. The results show that the self-organized TDMA protocol offers more flexibility and higher performance than the preprogramming TDMA protocol. In addition, the aspects of stability and security for the self-organized TDMA protocol were discussed. The overall conclusion is that the self-organized TDMA protocol could be a viable alternative for a future TDL system.

• 429.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
Range Based Indoor Localization in Wireless Sensor Networks with Telos2013Independent thesis Advanced level (degree of Master (One Year)), 20 credits / 30 HE creditsStudent thesis

Localization of individual nodes in a wireless network is useful in many applications, e.g for tracking patients in hospitals. Using the Received Signal Strength Indicator, RSSI, for this purpose has been explored in numerous studies. It is energy efficient and rarely requires customised hardware of configuration. The possibility to use pre-configured, off-the-shelf products is especially important in large scale sensor network deployments. Using RSSI has, however, many drawbacks, since the radio signal is heavily affected by the surrounding envi- ronment. Most studies in this area discuss the impact of multipath effects. Our study on range based distance estimations, using the Telos hardware, shows that individual profiling requirements and antenna quality are equally challenging.

Still, RSSI based indoor localization systems remains an active field of research. A multitude of approaches and algorithms have been proposed to gain accuracy in position estimations. The most common of these techniques are explored in this report. Based on previous work at The Polytechnic University of Catalonia, the Telos hardware has been integrated successfully with existing software to form local wireless sensor networks for indoor localization. We present applications developed on top of TinyOS, an operating system for embedded systems. These applications serve as a platform for related future work at The Polytechnic University of Catalonia and elsewhere.

• 430.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
Chalmers University, Department of Signals and Systems.
On Multiple Description Coding of Sources with Memory2010In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 58, no 8, p. 2242-2251Article in journal (Refereed)

We propose a framework for multiple description coding (MDC) of sources with memory. A new source coding method for lossless transmission of correlated sources, power series quantization (PSQ), was recently suggested. PSQ uses a separate linear or non-linear predictor for each quantizer region, and has shown increased performance compared toseveral common quantization schemes for sources with memory. We propose multiple description PSQ as a special case within our framework. The suggested scheme is shown to increase performance compared with previous state-of-the-art MDC methods.

• 431.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
Chalmers.
Power Series Quantization for Noisy Channels2010In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 58, no 5, p. 1405-1414Article in journal (Refereed)

A recently proposed method for transmission of correlated sources under noise-free conditions, power series quantization (PSQ), uses a separate linear or nonlinear predictor for each quantizer region, and has shown to increase performance compared to several common quantization schemes for sources with memory. In this paper, it is shown how to apply PSQ for transmission of a source with memory over a noisy channel. A channel-optimized PSQ (COPSQ) encoder and codebook optimization algorithms are derived. The suggested scheme is shown to increase performance compared with previous state-of-the-art methods.

• 432.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
S2, Chalmers University. Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
Amplifier-Aware Multiple-Input Multiple-Output Power Allocation2013In: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 17, no 6, p. 1112-1115Article in journal (Refereed)

We propose multiple-input multiple-output (MIMO)transmitter power allocation which takes dissipation in the power amplifiers into account. We derive the equations of the generalproblem with full channel state information (CSI), discuss its challenges, and supply solutions in two special cases, namely fora multiple-input single-output channel with a linear beamformer constraint, and for a parallel MIMO channel. The proposed algorithms show substantial gains in terms of rate and total consumed power compared to previous state of the art over awide range of parameter settings, and have low computational complexities.

• 433.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
School of Electrical Engineering, KTH. School of Electrical Engineering, KTH. Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
Joint Source-Channel Coding for the MIMO Broadcast Channel2012In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 60, no 4, p. 2085-2090Article in journal (Refereed)

We investigate the problem of broadcasting analog sources to several users using short codes,employing several antennas at both the transmitter and the receiver, and channel-optimized quantization.Our main objective is to minimize the sum mean square error distortion. A joint multi-user encoder, aswell as a structured encoder with separate encoders for the different users, are proposed. The ﬁrst encoderoutperforms the latter, which in turn offers large improvements compared to state-of-the-art, over a widerange of channel signal-to-noise ratios. Our proposed methods handle bandwidth expansion, i.e., usageof more channel than source dimensions, automatically. We also derive a lower bound on the distortion.

• 434.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
School of Electrical Engineering, KTH. School of Electrical Engineering, KTH. Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
Joint Source-Channel Coding for the MIMO Broadcast Channel2012Data set

We investigate the problem of broadcasting analog sources to several users using short codes,employing several antennas at both the transmitter and the receiver, and channel-optimized quantization.Our main objective is to minimize the sum mean square error distortion. A joint multi-user encoder, aswell as a structured encoder with separate encoders for the different users, are proposed. The ﬁrst encoderoutperforms the latter, which in turn offers large improvements compared to state-of-the-art, over a widerange of channel signal-to-noise ratios. Our proposed methods handle bandwidth expansion, i.e., usageof more channel than source dimensions, automatically. We also derive a lower bound on the distortion.

• 435.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
Partial Marginalization Soft MIMO Detection with Higher Order Constellations2011In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 59, no 1, p. 453-458Article in journal (Refereed)

A new method for multiple-input multiple-output (MIMO) detection with soft-output, the partial marginalization (PM) algorithm, was recently proposed. Advantages of the method are that it is straightforward to parallelize, and that it offers a fully predictable runtime. PM trades performance for computational complexity via a user-defined parameter. In the limit of high computational complexity, the algorithm becomes the MAP demodulator. The PM algorithm also works with soft-input, but until now it has been unclear how to apply it for other modulation formats than binary phase-shift keying (BPSK) per real dimension. In this paper, we explain how to extend PM with soft-input to general signaling constellations, while maintaining the low complexity advantage of the original algorithm.

• 436.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology. Royal Institute of Technology, Stockholm, Sweden.
Joint Source-Channel Decoding over MIMOChannels Based on Partial Marginalization2012In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 60, no 12, p. 6734-6739Article in journal (Refereed)

We investigate fast joint source-channel decoding employed for communication over frequency-flat and frequency selective block-fading multiple-input multiple-output channels. Our setting has applications for communication with short codes under low-latency constraints. The case of no transmitter channel state information is considered.

We propose a partial marginalization decoder that allows performance to be traded for computational complexity, by adjusting a user parameter. By tuning this parameter to its maximum value, the minimum mean square error (MMSE)decoder is obtained. In the conducted simulations, the proposed scheme almost achieves the MMSE performance for a wide range of the channel signal-to-noise ratios, with significant reductions in computational complexity.

• 437.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
Chalmers University of Technology, Gothenburg, Sweden. Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
Amplifier-Aware Multiple-Input Single-Output Capacity2014In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 62, no 1, p. 913-919Article in journal (Refereed)

We investigate multiple-input single-output channel capacity taking dissipation in the power amplifiers into account. We consider the case of a fixed channel with full channel state information (CSI) at both the transmitter and receiver. The capacity expression is given on closed form, and we show that the optimal solution is antenna selection. An algorithm for finding minimum consumed power for any given mutual information is further developed, and we show that the power-mutual information pair is capacity-achieving. We also investigate the ergodic Rayleigh fading channel with full CSI at the receiver and no instantaneous CSI at the transmitter. We devise a numerical approach which finds the global optimum given a quantization of the space of possible allocated powers. We further show that down to the simulation precision, the ergodic Rayleigh fading solution again is antenna selection. It is shown that the allocation algorithms have low computational complexity and give significant rate and total consumed power gains in comparison to previous state of the art.

• 438.
Linköping University, Department of Electrical Engineering, Communication Systems.
Performance Assessment of Massive MIMO Systems for Positioning and Tracking of Vehicles in Open Highways2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis

The next generation of mobile networks (5G) is currently being standardized, and massive MIMO (Multiple-Input-Multiple-Output) is a strong candidate to be part of this standard. Other than providing higher data rates and lower latency, high accuracy positioning is also required. In this thesis, we evaluate the achievable performance of positioning using massive MIMO systems in open highway scenarios. Relevant theory from sensor array signal processing and Bayesian filtering is presented, and is used in a simulation environment on large antenna arrays representing massive MIMO base stations. Positioning is done by utilizing the uplink pilot reference signals, where the Direction of Arrival (DOA) of the pilot signal is estimated, and then used for position estimation. Estimation of the DOA is done by both a maximum-likelihood method and by using an Extended Kalman Filter (EKF). A positioning error of less than 8 m is achieved with absolute certainty when the vehicle is less than 300 m from the base station. It is also concluded that this result could be improved by using more sophisticated filtering algorithms.

• 439.
Blekinge Institute of Technology Karlskrona, Sweden; University of of Reading, United Kingdom.
Blekinge Institute of Technology Karlskrona, Sweden. Blekinge Institute of Technology Karlskrona, Sweden. Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
Performance of cognitive radio networks with finite buffer using multiple vacations and exhaustive service2014In: 2014, 8th International Conference on Signal Processing and Communication Systems, ICSPCS 2014 - Proceedings, Institute of Electrical and Electronics Engineers Inc. , 2014, no 7021133Conference paper (Refereed)

In this paper, we analyze the performance of a cognitive radio network where the secondary transmitter, besides its own transmission, occasionally relays the primary signal. It is assumed that the secondary transmitter employs the exhaustive service mode to transmit the secondary signal and multiple vacations to relay the primary signal. When assisting the primary transmitter, we assume that the secondary transmitter utilizes the decode-and-forward protocol to process the primary signal and forwards it to the primary receiver. Furthermore, the secondary transmitter has a finite buffer, the arriving packets of the secondary network are modeled as a Poisson process, and all channels are subject to Nakagami-m fading. Modeling the system as an M/G/1/K queueing system with exhaustive service and multiple vacations, using an embedded Markov chain approach to analyze the system, we obtain several key queueing performance indicators, i.e., the channel utilization, blocking probability, mean number of packets, and mean serving time of a packet in the system. The derived formulas are then utilized to evaluate the performance of the considered system.

• 440.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.

Firstly, we consider a class of nonuniformly sampled signals that occur as a result of static timing mismatch errors or due to channel mismatches in TI-ADCs. For this type of nonuniformly sampled signals, we propose three reconstructors which utilize a two-rate approach to derive the corresponding single-rate structure. The two-rate based reconstructors move part of the complexity to a symmetric filter and also simplifies the reconstruction problem. The complexity reduction stems from the fact that half of the impulse response coefficients of the symmetric filter are equal to zero and that, compared to the original reconstruction problem, the simplified problem requires only a simpler reconstructor.

Next, we consider the class of nonuniformly sampled signals that occur when a TI-ADC is used for sub-Nyquist cyclic nonuniform sampling (CNUS) of sparse multi-band signals. Sub-Nyquist sampling utilizes the sparsities in the analog signal to sample the signal at a lower rate. However, the reduced sampling rate comes at the cost of additional digital signal processing that is needed to reconstruct the uniform-grid sequence from the sub-Nyquist sampled sequence obtained via CNUS. The existing reconstruction scheme is computationally intensive and time consuming and offsets the gains obtained from the reduced sampling rate. Also, in applications where the band locations of the sparse multi-band signal can change from time to time, the reconstructor should support online reconfigurability. Here, we propose a reconstruction scheme that reduces the computational complexity of the reconstructor and at the same time, simplifies the online reconfigurability of the reconstructor.

Finally, we consider a class of nonuniformly sampled signals which occur at the output of TI-ADCs that use some of the input sampling instants for sampling a known calibration signal. The samples corresponding to the calibration signal are used for estimating the channel mismatch parameters. In such TI-ADCs, nonuniform sampling is due to the mismatches between the channel ADCs and due to the missing input samples corresponding to the sampling instants reserved for the calibration signal. We propose three reconstruction schemes for such nonuniformly sampled signals and show using design examples that, compared to a previous solution, the proposed schemes require substantially lower computational complexity.

1. Two-rate based low-complexity time-varying discrete-time FIR reconstructors for two-periodic nonuniformly sampled signals
Open this publication in new window or tab >>Two-rate based low-complexity time-varying discrete-time FIR reconstructors for two-periodic nonuniformly sampled signals
2012 (English)In: Sampling Theory in Signal and Image Processing, ISSN 1530-6429, Vol. 11, no 2-3, p. 195-220Article in journal (Refereed) Published
##### Abstract [en]

This paper deals with time-varying finite-length impulse response (FIR) filters used for reconstruction of two-periodic nonuniformly sampled signals. The complexity of such reconstructorsincreases as their bandwidth approaches the whole Nyquist band. Reconstructor design that yields minimum reconstructor order requires expensive online redesign while those methods that simplify online redesign result in higher reconstructor complexity. This paper utilizes a two-rate approach to derive a single-rate structure where part of the complexity of the reconstructor is moved to a symmetric filter so as to reduce the number of multipliers. The symmetric filter is designed such that it can be used for all time-skew errors within a certain range, thereby reducing the number of coefficients that need online redesign. The basic two-rate based reconstructor is further extended to completely remove the need for online redesign at the cost of a slight increase in the total number of multipliers.

##### Place, publisher, year, edition, pages
Sampling Publishing, 2012
##### Keywords
Finite-length impulse response (FIR) filters, least-squares design, two-rate approach, periodic nonuniform sampling, time-interleaved analog-to-digital converters (TI-ADCs), reconstruction filters
##### National Category
Signal Processing
##### Identifiers
urn:nbn:se:liu:diva-105470 (URN)2-s2.0-84896442526 (Scopus ID)
##### Funder
Swedish Research Council Available from: 2014-03-25 Created: 2014-03-25 Last updated: 2017-12-05
2. Efficient signal reconstruction scheme for M-channel time-interleaved ADCs
Open this publication in new window or tab >>Efficient signal reconstruction scheme for M-channel time-interleaved ADCs
2013 (English)In: Analog Integrated Circuits and Signal Processing, ISSN 0925-1030, E-ISSN 1573-1979, Vol. 77, no 2, p. 113-122Article in journal (Refereed) Published
##### Abstract [en]

In time-interleaved analog-to-digital converters (TI-ADCs), the timing mismatches between the channels result in a periodically nonuniformly sampled sequence at the output. Such nonuniformly sampled output limits the achievable resolution of the TI-ADC. In order to correct the errors due to timing mismatches, the output of the TI-ADC is passed through a digital time-varying finite-length impulse response reconstructor. Such reconstructors convert the nonuniformly sampled output sequence to a uniformly spaced output. Since the reconstructor runs at the output rate of the TI-ADC, it is beneficial to reduce the number of coefficient multipliers in the reconstructor. Also, it is advantageous to have as few coefficient updates as possible when the timing errors change. Reconstructors that reduce the number of multipliers to be updated online do so at a cost of increased number of multiplications per corrected output sample. This paper proposes a technique which can be used to reduce the number of reconstructor coefficients that need to be updated online without increasing the number of multiplications per corrected output sample.

##### Place, publisher, year, edition, pages
Springer, 2013
##### Keywords
Finite-length impulse response (FIR) filters, Least-squares design, Two-rate approach, Periodically nonuniform sampling, Time-interleaved analog-to-digital converters (TI-ADCs), Reconstruction filters
##### National Category
Signal Processing
##### Identifiers
urn:nbn:se:liu:diva-100965 (URN)10.1007/s10470-013-0115-x (DOI)000326453400004 ()
##### Funder
Swedish Research Council Available from: 2013-11-15 Created: 2013-11-15 Last updated: 2017-12-06Bibliographically approved
3. Low-complexity two-rate based multivariate impulse response reconstructor for time-skew error correction in m-channel time-interleaved ADCs
Open this publication in new window or tab >>Low-complexity two-rate based multivariate impulse response reconstructor for time-skew error correction in m-channel time-interleaved ADCs
2013 (English)In: IEEE International Symposium on Circuits and Systems (ISCAS), 2013, IEEE , 2013, p. 2936-2939Conference paper, Published paper (Refereed)
##### Abstract [en]

Nonuniform sampling occurs in time-interleaved analog-to-digital converters (TI-ADC) due to timing mismatches between the individual channel analog-to-digital converters (ADCs). Such nonuniformly sampled output will degrade the achievable resolution in a TI-ADC. To restore the degraded performance, digital time-varying reconstructors can be used at the output of the TI-ADC, which in principle, converts the nonuniformly sampled output sequence to a uniformly sampled output. As the bandwidth of these reconstructors increases, their complexity also increases rapidly. Also, since the timing errors change occasionally, it is important to have a reconstructor architecture that requires fewer coefficient updates when the value of the timing error changes. Multivariate polynomial impulse response reconstructor is an attractive option for an M-channel reconstructor. If the channel timing error varies within a certain limit, these reconstructors do not need any online redesign of their impulse response coefficients. This paper proposes a technique that can be applied to multivariate polynomial impulse response reconstructors in order to further reduce the number of fixed-coefficient multipliers, and thereby reduce the implementation complexity.

IEEE, 2013
##### Series
IEEE International Symposium on Circuits and Systems, ISSN 0271-4310
##### National Category
Engineering and Technology
##### Identifiers
urn:nbn:se:liu:diva-106537 (URN)10.1109/ISCAS.2013.6572494 (DOI)000332006803036 ()978-1-4673-5760-9 (ISBN)
##### Conference
IEEE International Symposium on Circuits and Systems (ISCAS), 19-23 May 2013, Beijing, China
Available from: 2014-05-12 Created: 2014-05-09 Last updated: 2015-05-22Bibliographically approved
4. Efﬁcient Recovery of Sub-Nyquist Sampled Sparse Multi-Band Signals Using Reconﬁgurable Multi-Channel Analysis and Modulated Synthesis Filter Banks
Open this publication in new window or tab >>Efﬁcient Recovery of Sub-Nyquist Sampled Sparse Multi-Band Signals Using Reconﬁgurable Multi-Channel Analysis and Modulated Synthesis Filter Banks
2015 (English)In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 63, no 19, p. 5238-5249Article in journal (Refereed) Published
##### Abstract [en]

Sub-Nyquist cyclic nonuniform sampling (CNUS) of a sparse multi-band signal generates a nonuniformly sampled signal. Assuming that the corresponding uniformly sampled signal satisfies the Nyquist sampling criterion, the sequence obtained via CNUS can be passed through a reconstructor to recover the missing uniform-grid samples. In order to recover the missing uniform-grid samples, the sequence obtained via CNUS is passed through a reconstructor. At present, these reconstructors have very high design and implementation complexity that offsets the gains obtained due to sub-Nyquist sampling. In this paper, we propose a scheme that reduces the design and implementation complexity of the  reconstructor. In contrast to the existing reconstructors which use only a multi-channel synthesis filter bank (FB), the proposed reconstructor utilizes both analysis and synthesis FBs which makes it feasible to achieve an order-of-magnitude reduction of the complexity. The analysis filters are implemented using polyphase networks whose branches are allpass filters with distinct fractional delays and phase shifts. In order to reduce both the design and the implementation complexity of the  synthesis FB, the synthesis filters are implemented using a cosine-modulated FB. In addition to the reduced complexity of the reconstructor, the proposed multi-channel recovery scheme also supports online reconfigurability which is required in flexible (multi-mode) systems where the user subband locations vary with time.

IEEE, 2015
##### Keywords
Sub-Nyquist sampling, sparse multi-band signals, reconstruction, nonuniform sampling, time-interleaved analog-to-digital converters, ﬁlter banks
##### National Category
Communication Systems
##### Identifiers
urn:nbn:se:liu:diva-117824 (URN)10.1109/TSP.2015.2451104 (DOI)000360852200017 ()
Available from: 2015-05-08 Created: 2015-05-08 Last updated: 2017-12-04Bibliographically approved
5. A sub-band based reconstructor for M-channel time-interleaved ADCs with missing samples
Open this publication in new window or tab >>A sub-band based reconstructor for M-channel time-interleaved ADCs with missing samples
2014 (English)In: 2014 IEEE INTERNATIONAL CONFERENCE ON ACOUSTICS, SPEECH AND SIGNAL PROCESSING (ICASSP), IEEE conference proceedings, 2014Conference paper, Published paper (Refereed)
##### Abstract [en]

This paper proposes a scheme for the recovery of a uniformly sampled sequence from the output of a time-interleaved analog-to-digital converter (TI-ADC) with static time-skew errors and missing samples. Nonuniform sampling occurs due to timing mismatches between the individual channel ADCs and also due to missing input samples as some of the sampling instants are reserved for estimating the mismatches in the TI-ADC. In addition to using a non-recursive structure, the proposed reconstruction scheme supports online reconfigurability and reduces the computational complexity of the reconstructor as compared to a previous solution.

##### Place, publisher, year, edition, pages
IEEE conference proceedings, 2014
##### Series
International Conference on Acoustics Speech and Signal Processing ICASSP, ISSN 1520-6149
##### National Category
Signal Processing
##### Identifiers
urn:nbn:se:liu:diva-103931 (URN)10.1109/ICASSP.2014.6854378 (DOI)000343655304030 ()978-1-4799-2893-4 (ISBN)
##### Conference
IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP 2014), Florence, Italy, May 4-9, 2014
Available from: 2014-02-03 Created: 2014-02-03 Last updated: 2015-05-22Bibliographically approved
6. Two reconstructors for M-channel time-interleaved ADCs with missing samples
Open this publication in new window or tab >>Two reconstructors for M-channel time-interleaved ADCs with missing samples
2014 (English)In: IEEE 12th International New Circuits and Systems Conference (NEWCAS), 2014, IEEE conference proceedings, 2014, p. 41-44Conference paper, Published paper (Refereed)
##### Abstract [en]

In this paper, we explore two nonrecursive reconstructors which recover the uniform-grid samples from the output of a time-interleaved analog-to-digital converter (TI-ADC) that uses some of the sampling instants for estimating the mismatches in the TI-ADC. Nonuniform sampling occurs due to timing mismatches between the individual channel ADCs and also due to missing input samples. Compared to a previous solution, the reconstructors presented here offer substantially lower computational complexity.

##### Place, publisher, year, edition, pages
IEEE conference proceedings, 2014
##### National Category
Signal Processing
##### Identifiers
urn:nbn:se:liu:diva-106048 (URN)10.1109/NEWCAS.2014.6933980 (DOI)000363906700011 ()
##### Conference
12th IEEE International New Circuits and Systems Conference (NEWCAS), Trois-Rivières, Canada, June 22-25, 2014.
Available from: 2014-04-19 Created: 2014-04-19 Last updated: 2015-12-03Bibliographically approved
7. Prefilter-Based Reconfigurable Reconstructor for Time-Interleaved ADCs With Missing Samples
Open this publication in new window or tab >>Prefilter-Based Reconfigurable Reconstructor for Time-Interleaved ADCs With Missing Samples
2015 (English)In: IEEE Transactions on Circuits and Systems - II - Express Briefs, ISSN 1549-7747, E-ISSN 1558-3791, Vol. 62, no 4, p. 392-396Article in journal (Refereed) Published
##### Abstract [en]

This brief proposes a reconstruction scheme for the compensation of frequency-response mismatch errors at the output of a time-interleaved analog-to-digital converter (TI-ADC) with missing samples. The missing samples are due to sampling instants reserved for estimating the channel mismatch errors in the TI-ADC. Compared with previous solutions, the proposed scheme offers substantially lower computational complexity.

##### Place, publisher, year, edition, pages
IEEE Press, 2015
##### Keywords
Reconstruction, frequency-response mismatch errors, time-interleaved analog-to-digital converters, reconﬁgurable reconstructors
##### National Category
Communication Systems
##### Identifiers
urn:nbn:se:liu:diva-117769 (URN)10.1109/TCSII.2014.2387651 (DOI)000352306200016 ()
Available from: 2015-05-08 Created: 2015-05-08 Last updated: 2017-12-04Bibliographically approved
• 441.
Linköping University, The Institute of Technology. Linköping University, Department of Electrical Engineering, Communication Systems.
Linköping University, The Institute of Technology. Linköping University, Department of Electrical Engineering, Communication Systems.
Efﬁcient Recovery of Sub-Nyquist Sampled Sparse Multi-Band Signals Using Reconﬁgurable Multi-Channel Analysis and Modulated Synthesis Filter Banks2015In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 63, no 19, p. 5238-5249Article in journal (Refereed)

Sub-Nyquist cyclic nonuniform sampling (CNUS) of a sparse multi-band signal generates a nonuniformly sampled signal. Assuming that the corresponding uniformly sampled signal satisfies the Nyquist sampling criterion, the sequence obtained via CNUS can be passed through a reconstructor to recover the missing uniform-grid samples. In order to recover the missing uniform-grid samples, the sequence obtained via CNUS is passed through a reconstructor. At present, these reconstructors have very high design and implementation complexity that offsets the gains obtained due to sub-Nyquist sampling. In this paper, we propose a scheme that reduces the design and implementation complexity of the  reconstructor. In contrast to the existing reconstructors which use only a multi-channel synthesis filter bank (FB), the proposed reconstructor utilizes both analysis and synthesis FBs which makes it feasible to achieve an order-of-magnitude reduction of the complexity. The analysis filters are implemented using polyphase networks whose branches are allpass filters with distinct fractional delays and phase shifts. In order to reduce both the design and the implementation complexity of the  synthesis FB, the synthesis filters are implemented using a cosine-modulated FB. In addition to the reduced complexity of the reconstructor, the proposed multi-channel recovery scheme also supports online reconfigurability which is required in flexible (multi-mode) systems where the user subband locations vary with time.

• 442.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
Feasibility Study for Wireless Control on The Countermeasure Dispenser System2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis

Electrical wiring on board aircraft has raised serious weight and safety concerns in the aerospace industry. Wires are antenna. It may also cause interference to radio-based systems on the aircraft, or, in the case of military aircraft, create a "signature" that can be detected by enemy receivers. Wireless application in avionic system helps reducing the total weight and reconfigurable of the aircraft; hence, lower the fuel costs, installation cost and maintenance costs, as well as the “signature” of the aircraft. The focus of this thesis, therefore, is to study the feasibility of different wireless standards, namely Wi-Fi, Bluetooth and ultra-wide band (UWB), on replacing the wired data connection in the EW countermeasure or chaff/flare dispenser systems.

The study was constructed under the supervision of the department of Electronic Defense System, Saab AB in Järfalla, Stockholm. The discussion will be based on the resource availability, the reliability, the stability and the security of the wireless system relative to an avionic application; i.e., whether wireless links will negatively affect the overall reliability and safety of the aircrafts. Due to the theoretical studies and results from the simulation, we studied the feasibility issue and concluded that UWB is the most appropriate choice of wireless communication for non-critical aerospace applications, comparing with Wi-Fi and Bluetooth. UWB links can have reasonable immunity to interferences, low interference to other on-board wireless systems, and good security performance.

• 443.
IUST, Sch Elect Engn, Tehran 1684613114, Iran.
IUST, Sch Elect Engn, Tehran 1684613114, Iran. Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
Subverting Massive MIMO by Smart Jamming2016In: IEEE Wireless Communications Letters, ISSN 2162-2337, E-ISSN 2162-2345, Vol. 5, no 1, p. 20-23Article in journal (Refereed)

We consider uplink transmission of a massive multiuser multiple-input multiple-output (MU-MIMO) system in the presence of a smart jammer. The jammer aims to degrade the sum spectral efficiency of the legitimate system by attacking both the training and data transmission phases. First, we derive a closed-form expression for the sum spectral efficiency by taking into account the presence of a smart jammer. Then, we determine how a jammer with a given energy budget should attack the training and data transmission phases to induce the maximum loss to the sum spectral efficiency. Numerical results illustrate the impact of optimal jamming specifically in the large limit of the number of base station (BS) antennas.

• 444.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
On the performance of Massive MIMO systems with single carrier transmission and phase noise2013Licentiate thesis, comprehensive summary (Other academic)

In the last decade we have experienced a rapid increase in the demand for high data rates over cellular networks. This increase has been partly satisfied by the introduction of multi-user multiple-input multiple-output (MU-MIMO). In such systems, the base station (BS) is equipped with multiple antennas and the users share the time-frequency resources. However, modern communication systems are highly power inefficient. Further, the increase in demand for higher data rates is expected to accelerate in the years to come due to the popularity of mobile devices like smartphones and tablets. Hence, next generation cellular systems arerequired to exhibit high energy efficiency as well as low power  consumption. Recently, it has been shown that the deployment of a large excess of base station (BS) antennas in comparison to the served users can be a promising candidate to meet these contradictory requirements. These systems are termed as Massive MIMO. When the number of BS antennas grows large, the channels between different users become orthogonal and low complexity transceiver processing exhibits sum-rate performance that is close to optimal. In order to realize the promised gains of Massive MIMO systems, it is required that power efficient and inexpensive components are used. In contemporary cellular systems, multi-carrier transmission is used since it facilitates simple equalization at the receiver side. However, multi-carrier signals exhibit high peak-to-average-power-ratio (PAPR) and require expensive highly linear power amplifiers. Power amplifiers in this regime are also very power inefficient. On the other hand single carrier signals exhibit lower PAPR and are suitable for signal design that is more robust to non-linear power amplifiers. Further, single-carrier signals are less vulnerable to hardware impairments, such as phase noise. In this thesis we study the fundamental limits of Massive MIMO systems in terms of sum-rate performance with single-carrier transmission and phase noise and provide important insight on the design of Massive MIMO under these scenarios.

1. On the Optimality of Single-Carrier Transmission in Large-Scale Antenna Systems
Open this publication in new window or tab >>On the Optimality of Single-Carrier Transmission in Large-Scale Antenna Systems
2012 (English)In: IEEE Wireless Communications Letters, ISSN 2162-2337, E-ISSN 2162-2345, Vol. 1, no 4, p. 276-279Article in journal (Other academic) Published
##### Abstract [en]

A single carrier transmission scheme is presentedfor the frequency selective multi-user (MU) multiple-input singleoutput(MISO) Gaussian Broadcast Channel (GBC) with a basestation (BS) having M antennas and K single antenna users.The proposed transmission scheme has low complexity andfor M ≫ K it is shown to achieve near optimal sum-rateperformance at low transmit power to receiver noise power ratio.Additionally, the proposed transmission scheme results in anequalization-free receiver and does not require any MU resourceallocation and associated control signaling overhead. Also, thesum-rate achieved by the proposed transmission scheme is shownto be independent of the channel power delay profile (PDP). Interms of power efficiency, the proposed transmission scheme alsoexhibits an O(M) array power gain. Simulations are used toconfirm analytical observations.

##### Place, publisher, year, edition, pages
Institute of Electrical and Electronics Engineers (IEEE), 2012
##### National Category
Communication Systems
##### Identifiers
urn:nbn:se:liu:diva-80173 (URN)10.1109/WCL.2012.041612.120046 (DOI)
##### Note

© Copyright 2012 IEEE Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works.

Available from: 2012-08-22 Created: 2012-08-22 Last updated: 2017-12-07Bibliographically approved
2. Uplink Performance of Time-Reversal MRC in Massive MIMO Systems subject to Phase Noise
Open this publication in new window or tab >>Uplink Performance of Time-Reversal MRC in Massive MIMO Systems subject to Phase Noise
2015 (English)In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 14, p. 711-723Article in journal (Refereed) Published
##### Abstract [en]

Multi-user multiple-input multiple-output (MU-MIMO) cellular systems with an excess of base station (BS) antennas (Massive MIMO) offer unprecedented multiplexing gains and radiated energy efficiency. Oscillator phase noise is introduced in the transmitter and receiver radio frequency chains and severely degrades the performance of communication systems. We study the effect of oscillator phase noise in frequency-selective Massive MIMO systems with imperfect channel state information (CSI) and M BS antennas. In particular, we consider two distinct operation modes, namely when the phase noise processes at the BS antennas are identical (synchronous operation) and when they are independent (non-synchronous operation). We analyze a linear and low-complexity time-reversal maximum-ratio combining (TR-MRC) reception strategy. For both operation modes we derive a lower bound on the sum-capacity and we compare the performance of the two modes. Based on the derived achievable sum-rate, we show that with the proposed receive processing an O($\sqrt{M}$) array gain is achievable. Due to the phase noise drift the estimated effective channel becomes progressively outdated. Therefore, phase noise effectively limits the length of the interval used for data transmission and the number of scheduled users. The derived achievable rates provide insights into the optimum choice of the data interval length and the number of scheduled users.

IEEE, 2015
##### National Category
Communication Systems
##### Identifiers
urn:nbn:se:liu:diva-97477 (URN)10.1109/TWC.2014.2359018 (DOI)000349674800010 ()
##### Note

Manuscript received March 5, 2014; revised July 10, 2014; accepted September 6, 2014. Date of publication September 18, 2014; date of current version February 6, 2015. This work was supported in part by the Swedish Foundation for Strategic Research and in part by ELLIIT. The work of S. K. Mohammed was supported by the Science and Engineering Research Board, Department of Science and Technology, Government of India. This paper was presented in part at the 50th Allerton Conference on Communication, Control and Computing, Urbana-Champaign, IL, USA, October 2012. The associate editor coordinating the review of this paper and approving it for publication was L. Sanguinetti.

Available from: 2013-09-13 Created: 2013-09-13 Last updated: 2017-12-06Bibliographically approved
3. Achievable Rates of ZF Receivers in Massive MIMO with Phase Noise Impairments
Open this publication in new window or tab >>Achievable Rates of ZF Receivers in Massive MIMO with Phase Noise Impairments
2013 (English)In: 2013 ASILOMAR CONFERENCE ON SIGNALS, SYSTEMS AND COMPUTERS, 2013, p. 1004-1008Conference paper, Published paper (Refereed)
##### Abstract [en]

The effect of oscillator phase noise on the sum-rate performance of large multi-user multiple-input multiple-output (MU-MIMO) systems, termed as Massive MIMO, is studied. A Rayleigh fading MU-MIMO uplink channel is considered, where channel state information (CSI) is acquired via training. The base station (BS), which is equipped with an excess of antenna elements, M, uses the channel estimate to perform zero-forcing (ZF) detection. A lower bound on the sum-rate performance is derived. It is shown that the proposed receiver structure exhibits an O($\sqrt{M}$) array power gain. Additionally, the proposed receiver is compared with earlier studies that employ maximum ratio combining and it is shown that it can provide significant sum-rate performance gains at the medium and high signal-to-noise-ratio (SNR) regime. Further, the expression of the achievable sum rate provides new insights on the effect of various parameters on the overall system performance.

##### Series
ASILOMAR CONFERENCE ON SIGNALS, SYSTEMS AND COMPUTERS, ISSN 1058-6393
##### National Category
Communication Systems
##### Identifiers
urn:nbn:se:liu:diva-97478 (URN)10.1109/ACSSC.2013.6810441 (DOI)000341772900184 ()978-1-4799-2390-8 (ISBN)
##### Conference
47th Asilomar Conference on Signals, Systems and Computers
Available from: 2013-09-13 Created: 2013-09-13 Last updated: 2016-09-13Bibliographically approved
• 445.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
Phase Noise and Wideband Transmission in Massive MIMO2016Doctoral thesis, comprehensive summary (Other academic)

In the last decades the world has experienced a massive growth in the demand for wireless services. The recent popularity of hand-held devices with data exchange capabilities over wireless networks, such as smartphones and tablets, increased the wireless data traffic even further. This trend is not expected to cease in the foreseeable future. In fact, it is expected to accelerate as everyday apparatus unrelated with data communications, such as vehicles or household devices, are foreseen to be equipped with wireless communication capabilities.

Further, the next generation wireless networks should be designed such that they have increased spectral and energy efficiency, provide uniformly good service to all of the accommodated users and handle many more devices simultaneously. Massive multiple-input multiple-output (Massive MIMO) systems, also termed as large-scale MIMO, very large MIMO or full-dimension MIMO, have recently been proposed as a candidate technology for next generation wireless networks. In Massive MIMO, base stations (BSs) with a large number of antenna elements serve simultaneously only a few tens of single antenna, non-cooperative users. As the number of BS antennas grow large, the normalized channel vectors to the users become pairwise asymptotically orthogonal and, therefore, simple linear processing techniques are optimal. This is substantially different from the current design of contemporary cellular systems, where BSs are equipped with a few antennas and the optimal processing is complex. Consequently, the need for redesign of the communication protocols is apparent.

The deployment of Massive MIMO requires the use of many inexpensive and, potentially, off-the-shelf hardware components. Such components are likely to be of low quality and to introduce distortions to the information signal. Hence, Massive MIMO must be robust against the distortions introduced by the hardware impairments. Among the most important hardware impairments is phase noise, which is introduced by local oscillators (LOs) at the BS and the user terminals. Phase noise is a phenomenon of particular importance since it acts multiplicatively on the desired signal and rotates it by some random and unknown argument. Further, the promised gains of Massive MIMO can be reaped by coherent combination of estimated channel impulse responses at the BS antennas. Phase noise degrades the quality of the estimated channel impulse responses and impedes the coherent combination of the received waveforms.

In this dissertation, wideband transmission schemes and the effect of phase noise on Massive MIMO are studied. First, the use of a low-complexity single-carrier precoding scheme for the broadcast channel is investigated when the number of BS antennas is much larger than the number of served users. A rigorous, closed-form lower bound on the achievable sum-rate is derived and a scaling law on the potential radiated energy savings is stated. Further, the performance of the proposed scheme is compared with a sum-capacity upper bound and with a bound on the performance of the contemporary multi-carrier orthogonal frequency division multiplexing (OFDM) transmission.

Second, the effect of phase noise on the achievable rate performance of a wideband Massive MIMO uplink with time-reversal maximum ratio combining (TRMRC) receive processing is investigated. A rigorous lower bound on the achievable sum-rate is derived and a scaling law on the radiated energy efficiency is established. Two distinct LO configurations at the BS, i.e., the common LO (synchronous) operation and the independent LO (non-synchronous) operation, are analyzed and compared. It is concluded that the non-synchronous operation is preferable due to an averaging of the independent phase noise sources. Further, a progressive degradation of the achievable rate due to phase noise is observed. A similar study is extended to a flat fading uplink with zero-forcing (ZF) receiver at the BS.

The fundamental limits of data detection in a phase-noise-impaired uplink are also studied, when the channel impulse responses are estimated via uplink training. The corresponding maximum likelihood (ML) detector is provided for the synchronous and non-synchronous operations and for a general parameterization of the phase noise statistics. The symbol error rate (SER) performance at the high signal-to-noise ratio (SNR) of the detectors is studied. Finally, rigorous lower bounds on the achievable rate of a Massive MIMO-OFDM uplink are derived and scaling laws on the radiated energy efficiency are stated.

1. On the Optimality of Single-Carrier Transmission in Large-Scale Antenna Systems
Open this publication in new window or tab >>On the Optimality of Single-Carrier Transmission in Large-Scale Antenna Systems
2012 (English)In: IEEE Wireless Communications Letters, ISSN 2162-2337, E-ISSN 2162-2345, Vol. 1, no 4, p. 276-279Article in journal (Other academic) Published
##### Abstract [en]

A single carrier transmission scheme is presentedfor the frequency selective multi-user (MU) multiple-input singleoutput(MISO) Gaussian Broadcast Channel (GBC) with a basestation (BS) having M antennas and K single antenna users.The proposed transmission scheme has low complexity andfor M ≫ K it is shown to achieve near optimal sum-rateperformance at low transmit power to receiver noise power ratio.Additionally, the proposed transmission scheme results in anequalization-free receiver and does not require any MU resourceallocation and associated control signaling overhead. Also, thesum-rate achieved by the proposed transmission scheme is shownto be independent of the channel power delay profile (PDP). Interms of power efficiency, the proposed transmission scheme alsoexhibits an O(M) array power gain. Simulations are used toconfirm analytical observations.

##### Place, publisher, year, edition, pages
Institute of Electrical and Electronics Engineers (IEEE), 2012
##### National Category
Communication Systems
##### Identifiers
urn:nbn:se:liu:diva-80173 (URN)10.1109/WCL.2012.041612.120046 (DOI)
##### Note

© Copyright 2012 IEEE Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works.

Available from: 2012-08-22 Created: 2012-08-22 Last updated: 2017-12-07Bibliographically approved
2. Uplink Performance of Time-Reversal MRC in Massive MIMO Systems subject to Phase Noise
Open this publication in new window or tab >>Uplink Performance of Time-Reversal MRC in Massive MIMO Systems subject to Phase Noise
2015 (English)In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 14, p. 711-723Article in journal (Refereed) Published
##### Abstract [en]

Multi-user multiple-input multiple-output (MU-MIMO) cellular systems with an excess of base station (BS) antennas (Massive MIMO) offer unprecedented multiplexing gains and radiated energy efficiency. Oscillator phase noise is introduced in the transmitter and receiver radio frequency chains and severely degrades the performance of communication systems. We study the effect of oscillator phase noise in frequency-selective Massive MIMO systems with imperfect channel state information (CSI) and M BS antennas. In particular, we consider two distinct operation modes, namely when the phase noise processes at the BS antennas are identical (synchronous operation) and when they are independent (non-synchronous operation). We analyze a linear and low-complexity time-reversal maximum-ratio combining (TR-MRC) reception strategy. For both operation modes we derive a lower bound on the sum-capacity and we compare the performance of the two modes. Based on the derived achievable sum-rate, we show that with the proposed receive processing an O($\sqrt{M}$) array gain is achievable. Due to the phase noise drift the estimated effective channel becomes progressively outdated. Therefore, phase noise effectively limits the length of the interval used for data transmission and the number of scheduled users. The derived achievable rates provide insights into the optimum choice of the data interval length and the number of scheduled users.

IEEE, 2015
##### National Category
Communication Systems
##### Identifiers
urn:nbn:se:liu:diva-97477 (URN)10.1109/TWC.2014.2359018 (DOI)000349674800010 ()
##### Note

Manuscript received March 5, 2014; revised July 10, 2014; accepted September 6, 2014. Date of publication September 18, 2014; date of current version February 6, 2015. This work was supported in part by the Swedish Foundation for Strategic Research and in part by ELLIIT. The work of S. K. Mohammed was supported by the Science and Engineering Research Board, Department of Science and Technology, Government of India. This paper was presented in part at the 50th Allerton Conference on Communication, Control and Computing, Urbana-Champaign, IL, USA, October 2012. The associate editor coordinating the review of this paper and approving it for publication was L. Sanguinetti.

Available from: 2013-09-13 Created: 2013-09-13 Last updated: 2017-12-06Bibliographically approved
3. Achievable Rates of ZF Receivers in Massive MIMO with Phase Noise Impairments
Open this publication in new window or tab >>Achievable Rates of ZF Receivers in Massive MIMO with Phase Noise Impairments
2013 (English)In: 2013 ASILOMAR CONFERENCE ON SIGNALS, SYSTEMS AND COMPUTERS, 2013, p. 1004-1008Conference paper, Published paper (Refereed)
##### Abstract [en]

The effect of oscillator phase noise on the sum-rate performance of large multi-user multiple-input multiple-output (MU-MIMO) systems, termed as Massive MIMO, is studied. A Rayleigh fading MU-MIMO uplink channel is considered, where channel state information (CSI) is acquired via training. The base station (BS), which is equipped with an excess of antenna elements, M, uses the channel estimate to perform zero-forcing (ZF) detection. A lower bound on the sum-rate performance is derived. It is shown that the proposed receiver structure exhibits an O($\sqrt{M}$) array power gain. Additionally, the proposed receiver is compared with earlier studies that employ maximum ratio combining and it is shown that it can provide significant sum-rate performance gains at the medium and high signal-to-noise-ratio (SNR) regime. Further, the expression of the achievable sum rate provides new insights on the effect of various parameters on the overall system performance.

##### Series
ASILOMAR CONFERENCE ON SIGNALS, SYSTEMS AND COMPUTERS, ISSN 1058-6393
##### National Category
Communication Systems
##### Identifiers
urn:nbn:se:liu:diva-97478 (URN)10.1109/ACSSC.2013.6810441 (DOI)000341772900184 ()978-1-4799-2390-8 (ISBN)
##### Conference
47th Asilomar Conference on Signals, Systems and Computers
Available from: 2013-09-13 Created: 2013-09-13 Last updated: 2016-09-13Bibliographically approved
4. ML Detection in Phase Noise Impaired SIMO Channels with Uplink Training
Open this publication in new window or tab >>ML Detection in Phase Noise Impaired SIMO Channels with Uplink Training
2016 (English)In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 64, no 1, p. 223-235Article in journal (Refereed) Published
##### Abstract [en]

The problem of maximum likelihood (ML) detection in training-assisted single-input multiple-output (SIMO) systems with phase noise impairments is studied for two different scenarios, i.e. the case when the channel is deterministic and known (constant channel) and the case when the channel is stochastic and unknown (fading channel). Further, two different operations with respect to the phase noise sources are considered, namely, the case of identical phase noise sources and the case of independent phase noise sources over the antennas. In all scenarios the optimal detector is derived for a very general parameterization of the phase noise distribution. Further, a high signal-to-noise-ratio (SNR) analysis is performed to show that symbol-error-rate (SER) floors appear in all cases. The SER floor in the case of identical phase noise sources (for both constant and fading channels) is independent of the number of antenna elements. In contrast, the SER floor in the case of independent phase noise sources is reduced when increasing the number of antenna elements (for both constant and fading channels). Finally, the system model is extended to multiple data channel uses and it is shown that the conclusions are valid for these setups, as well.

IEEE, 2016
##### National Category
Signal Processing
##### Identifiers
urn:nbn:se:liu:diva-122617 (URN)10.1109/TCOMM.2015.2498163 (DOI)000368353700021 ()
##### Note

Funding agencies: Swedish Foundation for Strategic Research (SSF); ELLIIT

Available from: 2015-11-12 Created: 2015-11-12 Last updated: 2019-06-28Bibliographically approved
5. Performance of the Massive MIMO Uplink with OFDM and Phase Noise
Open this publication in new window or tab >>Performance of the Massive MIMO Uplink with OFDM and Phase Noise
2016 (English)In: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 20, no 8, p. 1595-1598Article in journal (Refereed) Published
##### Abstract [en]

The performance of multi-userMassiveMIMO-OFDMuplink systems in the presence of base station (BS) phase noise impairments is investigated. Closed-form achievable rate expressions are rigorously derived under two different operations, namely the case of a common oscillator (synchronous operation) at the BS and the case of independent oscillators at each BS antenna (non-synchronous operation). It is observed that the non-synchronous operation exhibits superior performance due to the averaging of intercarrier interference. Further, radiated power scaling lawsare derived, which are identical to the phase-noise-free case.

IEEE, 2016
##### National Category
Communication Systems
##### Identifiers
urn:nbn:se:liu:diva-127398 (URN)10.1109/LCOMM.2016.2581169 (DOI)000384642900028 ()
##### Note

Funding agencies: Swedish Foundation for Strategic Research (SSF); ELLIIT

Available from: 2016-04-26 Created: 2016-04-26 Last updated: 2019-06-28Bibliographically approved
• 446.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
ML Detection in Phase Noise Impaired SIMO Channels with Uplink Training2016In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 64, no 1, p. 223-235Article in journal (Refereed)

The problem of maximum likelihood (ML) detection in training-assisted single-input multiple-output (SIMO) systems with phase noise impairments is studied for two different scenarios, i.e. the case when the channel is deterministic and known (constant channel) and the case when the channel is stochastic and unknown (fading channel). Further, two different operations with respect to the phase noise sources are considered, namely, the case of identical phase noise sources and the case of independent phase noise sources over the antennas. In all scenarios the optimal detector is derived for a very general parameterization of the phase noise distribution. Further, a high signal-to-noise-ratio (SNR) analysis is performed to show that symbol-error-rate (SER) floors appear in all cases. The SER floor in the case of identical phase noise sources (for both constant and fading channels) is independent of the number of antenna elements. In contrast, the SER floor in the case of independent phase noise sources is reduced when increasing the number of antenna elements (for both constant and fading channels). Finally, the system model is extended to multiple data channel uses and it is shown that the conclusions are valid for these setups, as well.

• 447.
School of Electrical Engineering and ACCESS Linnaeus Center, KTH Royal Institute of Technology, Stockholm, Sweden.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
On the effect of imperfect timing synchronization on pilot contamination2017In: 2017 IEEE International Conference on Communications (ICC) / [ed] Debbah M.,Gesbert D.,Mellouk A., IEEE, 2017Conference paper (Refereed)

The phenomenon of pilot contamination (PC) in multi-cell Massive MIMO systems is investigated in the presence of imperfect timing synchronization (TS). In particular, a basic setup is considered, where a base station (BS) is perfectly synchronized with the user of its cell, but there is imperfect TS between the BS and the user in another cell, possibly due to different propagation distances. A discrete-time system model is derived based on the continuous-time system model. The discrete-time system model accurately captures the phenomenon of imperfect TS in terms of the timing mismatch and the pulse shaping filter impulse responses. The derived discrete-time system model is used to study the achievable rates of a two-cell Massive MIMO uplink. It is shown that the structure imposed to the pilot contaminating signal due to the imperfect TS can be leveraged to mitigate the effect of PC. The level of PC suppression is quantified as a function of the timing mismatch and the characteristics of the transmit/receive pulse shaping filters.

• 448.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology. Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
Optimal Detection in Training Assisted SIMO Systems with Phase Noise Impairments2015In: 2015 IEEE International Conference on Communications (ICC), IEEE Press, 2015, p. 2597-2602Conference paper (Refereed)

Abstract—In this paper, the problem of optimal maximum likelihood detection in a single user single-input multiple-output (SIMO) channel with phase noise at the receiver is considered. The optimal detection rules under training are derived for two operation modes, namely when the phase increments are fully correlated among the M receiver antennas (synchronous operation) and when they are independent (non-synchronous operation). The phase noise increments are parameterized by a very general distribution, which includes the Wiener phase noise model as a special case. It is proven that phase noise creates a symbol-error-rate (SER) floor for both operation modes. Inthe synchronous operation this error floor is independent of M, while it goes to zero exponentially withM in the non-synchronous operation.

• 449.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
Performance of the Massive MIMO Uplink with OFDM and Phase Noise2016In: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 20, no 8, p. 1595-1598Article in journal (Refereed)

The performance of multi-userMassiveMIMO-OFDMuplink systems in the presence of base station (BS) phase noise impairments is investigated. Closed-form achievable rate expressions are rigorously derived under two different operations, namely the case of a common oscillator (synchronous operation) at the BS and the case of independent oscillators at each BS antenna (non-synchronous operation). It is observed that the non-synchronous operation exhibits superior performance due to the averaging of intercarrier interference. Further, radiated power scaling lawsare derived, which are identical to the phase-noise-free case.

• 450.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology. Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
Achievable Rates of ZF Receivers in Massive MIMO with Phase Noise Impairments2013In: 2013 ASILOMAR CONFERENCE ON SIGNALS, SYSTEMS AND COMPUTERS, 2013, p. 1004-1008Conference paper (Refereed)

The effect of oscillator phase noise on the sum-rate performance of large multi-user multiple-input multiple-output (MU-MIMO) systems, termed as Massive MIMO, is studied. A Rayleigh fading MU-MIMO uplink channel is considered, where channel state information (CSI) is acquired via training. The base station (BS), which is equipped with an excess of antenna elements, M, uses the channel estimate to perform zero-forcing (ZF) detection. A lower bound on the sum-rate performance is derived. It is shown that the proposed receiver structure exhibits an O($\sqrt{M}$) array power gain. Additionally, the proposed receiver is compared with earlier studies that employ maximum ratio combining and it is shown that it can provide significant sum-rate performance gains at the medium and high signal-to-noise-ratio (SNR) regime. Further, the expression of the achievable sum rate provides new insights on the effect of various parameters on the overall system performance.

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