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  • 501.
    Senel, Kamil
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Larsson, Erik G
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Device Activity and Embedded Information Bit Detection Using AMP in Massive MIMO2017In: 2017 IEEE GLOBECOM WORKSHOPS (GC WKSHPS), IEEE , 2017Conference paper (Refereed)
    Abstract [en]

    Future cellular networks will support a massive number of devices as a result of emerging technologies such as Internet-of-Things and sensor networks. Enhanced by machine type communication (MTC), low-power low-complex devices in the order of billions are projected to receive service from cellular networks. Contrary to traditional networks which are designed to handle human driven traffic, future networks must cope with MTC based systems that exhibit sparse traffic properties, operate with small packets and contain a large number of devices. Such a system requires smarter control signaling schemes for efficient use of system resources. In this work, we consider a grant-free random access cellular network and propose an approach which jointly detects user activity and single information bit per packet. The proposed approach is inspired by the approximate message passing (AMP) and demonstrates a superior performance compared to the original AMP approach. Furthermore, the numerical analysis reveals that the performance of the proposed approach scales with number of devices, which makes it suitable for user detection in cellular networks with massive number of devices.

  • 502.
    Senel, Kamil
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Larsson, Erik G
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Grant-Free Massive MTC-Enabled Massive MIMO: A Compressive Sensing Approach2018In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 66, no 12, p. 6164-6175Article in journal (Refereed)
    Abstract [en]

    A key challenge of massive MTC (mMTC), is the joint detection of device activity and decoding of data. The sparse characteristics of mMTC makes compressed sensing (CS) approaches a promising solution to the device detection problem. However, utilizing CS-based approaches for device detection along with channel estimation, and using the acquired estimates for coherent data transmission is suboptimal, especially when the goal is to convey only a few bits of data. First, we focus on the coherent transmission and demonstrate that it is possible to obtain more accurate channel state information by combining conventional estimators with CS-based techniques. Moreover, we illustrate that even simple power control techniques can enhance the device detection performance in mMTC setups. Second, we devise a new non-coherent transmission scheme for mMTC and specifically for grant-free random access. We design an algorithm that jointly detects device activity along with embedded information bits. The approach leverages elements from the approximate message passing (AMP) algorithm, and exploits the structured sparsity introduced by the non-coherent transmission scheme. Our analysis reveals that the proposed approach has superior performance compared with application of the original AMP approach.

  • 503.
    Senel, Kamil
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Joint User Activity and Non-Coherent Data Detection in mMTC-Enabled Massive MIMO Using Machine Learning Algorithms2018In: Proceedings of International ITG Workshop on Smart Antennas (WSA), Berlin, Germany, 2018Conference paper (Refereed)
    Abstract [en]

    Machine-type communication (MTC) services are expected to be an integral part of the future cellular systems. A key challenge of MTC, especially for the massive MTC (mMTC), is the detection of active devices among a large number of devices. The sparse characteristics of mMTC makes compressed sensing (CS) approaches a promising solution to the device detection problem. CS-based techniques are shown to outperform conventional device detection approaches. However, utilizing CS-based approaches for device detection along with channel estimation and using the acquired estimates for coherent data transmission may not be the optimal approach, especially for the cases where the goal is to convey only a few bits of data. In this work, we propose a non-coherent transmission technique for the mMTC uplink and compare its performance with coherent transmission. Furthermore, we demonstrate that it is possible to obtain more accurate channel state information by combining the conventional estimators with CS-based techniques.

  • 504.
    Senel, Kamil
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Tekinay, Sirin
    Isik Univ, Turkey.
    Optimal Power Allocation in NOMA Systems with Imperfect Channel Estimation2017In: GLOBECOM 2017 - 2017 IEEE GLOBAL COMMUNICATIONS CONFERENCE, IEEE , 2017Conference paper (Refereed)
    Abstract [en]

    Non-orthogonal multiple access is a promising technology for the fifth generation systems which exploits the power domain to achieve higher spectral efficiency. The performance of NOMA techniques are usually investigated under an ideal setup with perfect successive interference cancellation. However, the limitations of NOMA techniques under a setup with imperfect successive interference cancellation are not well understood. Contrary to the approaches in the literature, we examine the performance of NOMA under a non-ideal setup and propose two power allocation algorithms. The first algorithm is designed for the max-min problem whereas the second algorithm considers the heterogeneous rate requirements of users and provides solutions based on a novel rate measure. The performance of the algorithms is investigated both theoretically and numerically under a non-ideal setup with channel estimation errors. The theoretical analyses reveal that the algorithms achieve the optimum power allocation for the rate max-min problems. The numerical analyses are not only in agreement with the theoretical analyses, but also show the superiority of the proposed algorithms compared to both the conventional multiple access techniques as well as other NOMA approaches.

  • 505.
    Shalmashi, Serveh
    et al.
    KTH Royal Institute of Technology, Sweden.
    Björnson, Emil
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Kountouris, Marios
    CentraleSupelec, France.
    Sung, Ki Won
    KTH Royal Institute of Technology, Sweden.
    Debbah, Merouane
    CentraleSupelec, France.
    Energy Efficiency and Sum Rate when Massive MIMO meets Device-to-Device Communication2015Conference paper (Refereed)
    Abstract [en]

    This paper considers a scenario of short-range communication, known as device-to-device (D2D) communication, where D2D users reuse the downlink resources of a cellular network to transmit directly to their corresponding receivers. In addition, multiple antennas at the base station (BS) are used in order to simultaneously support multiple cellular users using multiuser or massive MIMO. The network model considers a fixed number of cellular users and that D2D users are distributed according to a homogeneous Poisson point process (PPP). Two metrics are studied, namely, average sum rate (ASR) and energy efficiency (EE). We derive tractable expressions and study the tradeoffs between the ASR and EE as functions of the number of BS antennas and density of D2D users for a given coverage area.

  • 506.
    Shalmashi, Serveh
    et al.
    KTH Royal Institute Technology, Sweden.
    Björnson, Emil
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Kountouris, Marios
    Huawei Technology Co Ltd, France.
    Won Sung, Ki
    KTH Royal Institute Technology, Sweden.
    Debbah, Merouane
    Huawei Technology Co Ltd, France.
    Energy efficiency and sum rate tradeoffs for massive MIMO systems with underlaid device-to-device communications2016In: EURASIP Journal on Wireless Communications and Networking, ISSN 1687-1472, E-ISSN 1687-1499, article id 175Article in journal (Refereed)
    Abstract [en]

    In this paper, we investigate the coexistence of two technologies that have been put forward for the fifth generation (5G) of cellular networks, namely, network-assisted device-to-device (D2D) communications and massive MIMO (multiple-input multiple-output). Potential benefits of both technologies are known individually, but the tradeoffs resulting from their coexistence have not been adequately addressed. To this end, we assume that D2D users reuse the downlink resources of cellular networks in an underlay fashion. In addition, multiple antennas at the BS are used in order to obtain precoding gains and simultaneously support multiple cellular users using multiuser or massive MIMO technique. Two metrics are considered, namely the average sum rate (ASR) and energy efficiency (EE). We derive tractable and directly computable expressions and study the tradeoffs between the ASR and EE as functions of the number of BS antennas, the number of cellular users and the density of D2D users within a given coverage area. Our results show that both the ASR and EE behave differently in scenarios with low and high density of D2D users, and that coexistence of underlay D2D communications and massive MIMO is mainly beneficial in low densities of D2D users.

  • 507.
    Shi, Shuying
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Skoglund, Mikael
    Royal Institute of Technology (KTH), Stockholm.
    Codebook Design and Hybrid Digital/AnalogCoding for Parallel Rayleigh Fading Channels2011In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 59, no 10, p. 5091-5096Article in journal (Refereed)
    Abstract [en]

    Low-delay source-channel transmission over parallel fading channels is studied. In this scenario separate sourceand channel coding is highly suboptimal. A scheme based on hybrid digital/analog joint source-channel coding istherefore proposed, employing scalar quantization and polynomial-based analog bandwidth expansion. Simulationsdemonstrate substantial performance gains.

  • 508.
    Silver, Oscar
    Linköping University, Department of Electrical Engineering, Communication Systems.
    An Indoor Localization System Based on BLE Mesh Network2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

     Internet of Things (iot) is a growing field enabled by many different technologies. One of these technologies is  Bluetooth Low Energy (ble). It is of interest to investigate the potential of ble and one interesting, currently unsupported, feature is mesh networking. This thesis work aims to investigate whether it is possible to design and implement a mesh network protocol using ble. To verify the implemented mesh network protocols functionality an indoor localization system has been implemented upon the BLE mesh network protocol. Furthermore this thesis work investigates if an indoor localization system can benefit from using a mesh network. The results of the investigation is a proof of concept of a functional ble mesh network protocol implemented on hardware and tested in a real environment. Tests show that the implemented localization system has similar accuracy as other rssi based indoor localization systems. The largest advantage found for a mesh based indoor localization is the ability to localize objects outside of the radio propagation range of the user. This feature is enabled by multi-hop messaging in the mesh network.

  • 509.
    Sjobergh, Olof
    et al.
    Royal Institute of Technology (KTH), Stockholm, Sweden.
    Jorswieck, Eduard A.
    Royal Institute of Technology (KTH), Stockholm, Sweden.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Greedy User Selection for Zero-forcing and MMSE Multiuser Beamforming with Channel Estimation Errors2008In: Proceedings of the 33rd IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP'08), IEEE , 2008, p. 3137-3140Conference paper (Refereed)
    Abstract [en]

    In a multi-user MIMO downlink where the base station has only estimates of the channels of the users, the sum-rate of multi-user beamforming saturates at high SNR. However, this is not the case for single-user beamforming. We propose a low-complexity user scheduling algorithm that selects the number of active users based on a closed-form approximation of the average sum-rate, and in particular does not add multiple users in the single-user optimality range. In order to develop this algorithm we derive the expected value of the rate of zero-forcing beamforming and MMSE beamforming with estimated channels and modify the greedy user selection accordingly. The gain of the proposed method is shown in numerical simulations.

  • 510.
    Skärpe, Anders
    Linköping University, Department of Electrical Engineering, Communication Systems.
    Implementation of an SDR in Verilog2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This report presents an implementation of the software part in a software definedradio. The radio is not entirely implemented in software and therefore there arecertain limitations on the received signal. The parts implemented are oscillator,decimation filter, carrier synchronization, time synchronization, package detection,and demodulation. Different algorithms were tested for the different partsto measure the power consumption. To understand how the number of bits usedto represent the signal affects the power consumption, the number of bits wasreduced from 20 bits to 10 bits. This reduction reduced the power consumptionfrom 2.57mW to 1.89mW. A small change in the choice of algorithms was thenmade which reduced the power consumption to 1.86mW. Then the clock rate wasreduced for some parts of the system which reduced the power consumption to1.05mW.

  • 511.
    Sookyoi, Thiti
    Linköping University, Department of Electrical Engineering, Communication Systems.
    Experimental Analysis of Indoor Positioning System Based on Ultra-Wideband Measurements2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Localization is one of the most interesting research areas in wireless networks. It is mostly used for tracking and monitoring applications such as traffic monitoring, search and rescue, navigation and so on. A good quality system can be defined from its accuracy when operating in severe interference environments that contaminate the signals and therefore reduce the system performance. The main issue for localization is channel propagation, e.g., line of sight or non-line of sight channel which should be studied in order to improve the system efficiency.

       In order to perform a localization, most algorithms use two steps: ranging and positioning. For ranging, the two popular techniques that are widely used for distance measurement are received signal strength (RSS) and time of arrival (TOA). RSS ranging technique uses the power of the received signals to identify the distance between a transmitter and a receiver. TOA ranging technique uses time of the signal traveling between a transmitter and a receiver to identify the distance, thus it requires synchronization. The measurements are processed by using a localization algorithm afterwards. However, these techniques suffer from multipath fading and other errors, so there always exists error in the estimated position.

       In this thesis, TOA ranging technique is used for different estimation methods. Simulation results are performed using MATLAB, while the real results are obtained from Pozyx indoor positioning platform. Several estimation algorithms comprising of maximum likelihood (ML), linearized least square (LLS), weighted centroid (WC), and fingerprinting (FP) are studied in detail. The testing area is indoor environment which is suitable for LOS, NLOS and combined situations. The measured data is then used for ranging and localization. We concentrate on comparing and discussing these results in this thesis.

  • 512.
    Stenmark, Fredrik
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Differential Beam-Forming Using Two-Dimensional Antenna Arrays in an LTE FDD System2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Base stations with multiple antenna elements can actively direct signal energy towards a user by means of beam-forming, which results in higher data rates and lower energy consumption compared to a single antenna element. However, beam-forming requires channel state estimates to each antenna element and in an FDD system, these estimates must be fed back to the base station from the user. This feedback infer an inconvenient amount of overhead, especially as the beam gets narrow. Differential beam-forming is a robust technique that, through differential adjustments to the beam shape, allows for narrow and well-directed beams at a low overhead cost. By means of two precoded reference signals from the base station, the user estimates the channel and iteratively reports how the beam-forming should be improved in order to increase the SINR of the sent signal. This thesis develops an algorithm that extends differential beam-forming to the usage of two-dimensional antenna arrays, which allows for adjustments of the beam in two dimensions. Thereby, the received signal strength is potentially increased. The algorithm alternates between differential adjustments to the beam horizontally and vertically, without increased overhead. The algorithm is simulated with different array sizes using an urban and a rural scenario with a horizontal user distribution. However, the biased user distribution has proven to constitute a limiting factor in order to demonstrate the potential benefits of differential beam-forming in two dimensions. The result shows that it is more important to obtain a narrow beam in the dimension where many users are located, in this case the horizontal dimension, than in the orthogonal dimension.

  • 513.
    Stenumgaard, Peter
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    A simple method for dynamic frequency allocation considering the total interference impact on the bit error probability2011In: EMC Europe 2011 York, 2011, p. 654-657Conference paper (Refereed)
    Abstract [en]

    Initiatives to open certain frequency bands for Dynamic Spectrum Access (DSA) are ongoing and examples are WAPECS and White Space Coalition. A key issue in DSA is how to measure both the occupancy and other undesired interference in an open frequency band to make a decision whether or not it can be used for a certain service. A common method to detect unknown interference is to consider the interference power only by using energy detection. This can give large errors since the interference impact can be severely dependent on the interference waveform. In this paper, a frequency allocation method is shown where the total interference waveform properties, in terms of interference impact, are estimated by a simple measurement. An example is shown where the frequency allocation algorithm outperforms a traditional allocation based on pure interference power detection only.

  • 514.
    Stenumgaard, Peter
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Smartphones som störsändare2013In: Electronic Environment, no 4, p. 16-17Article in journal (Other (popular science, discussion, etc.))
    Abstract [sv]

    Under 2013 har det rapporterats i media om att smartphones kan störa stöldlarm för varor i butiker. Det finns flera orsaker till att detta kan hända. En naturlig orsak är att somliga larm baseras på RFID-teknik som arbetar i öppna ISM-band som även somliga smartphones använder för kommunikation på kort distans via så kallad Near Field Communication (NFC).

  • 515.
    Stenumgaard, Peter
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology. Swedish Defence Research Agency (FOI).
    Chilo, José
    Högskolan i Gävle, Sweden.
    Ferrer-Coll, Javier
    Högskolan i Gävle, Sweden.
    Ängskog, Per
    Högskolan i Gävle, Sweden.
    Challenges and Conditions for Wireless Machine-to-Machine Communications in Industrial Environments2013In: IEEE Communications Magazine, ISSN 0163-6804, E-ISSN 1558-1896, Vol. 51, no 6, p. 187-192Article in journal (Refereed)
    Abstract [en]

    Wireless solutions are rapidly growing in machine-to-machine communications in industrial environments. These environments provide challenging conditions in terms of radio wave propagation as well as electromagnetic interference. In this article, results from the characterization of radio channel properties are summarized in order to provide some guidelines for the choice of wireless solutions in industrial environments. In conclusion, it is essential to know the sensitivity of industrial processes to time delay in data transfer. Furthermore, it is important to be aware of the radio interference environment and the manner in which different wireless technologies react upon interference. These steps will minimize the risk of unforeseen expensive disturbances in industrial processes.

  • 516.
    Stenumgaard, Peter
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Eliardsson, Patrik
    Totalförsvarets forskningsinstitut (FOI).
    Alexandersson, Mikael
    Totalförsvarets forskningsinstitut (FOI).
    Gabrielsson, Björn
    Totalförsvarets forskningsinstitut (FOI).
    Larsson, Ann-Kristin
    Swedavia.
    Weilow, Pär
    Swedavia.
    Portabel detektor för övervakning av radiostörningar i samhällskritisk infrastruktur2013In: TAMSEC 2013, 2013, p. 35-Conference paper (Other academic)
    Abstract [sv]

    Den snabbt ökande användningen av trådlös teknik i samhällsviktiga system har lett till en ökad sårbarhet mot radiostörningar. Radiostörningar alstras dels naturligt av alla elektroniska system, dels via illegala störsändare som idag säljs till låg kostnad via Internet. Att kontinuerligt övervaka radiostörningsmiljön vid kritiska system blir därför allt viktigare och i denna presentation visas ett exempel på hur kommersiellt tillgänglig hyllvara kan anpassas för att kostnadseffektivt genomföra kvalificerad övervakning av radiostörningsmiljön vid samhällskritisk infrastruktur.

  • 517.
    Stenumgaard, Peter
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Fors, Karina
    FOI.
    Wiklundh, Kia
    FOI.
    Intersystem Interference Model for Frequency Hopping Systems2012Conference paper (Other academic)
    Abstract [en]

    In this paper a method for calculating the impact of intersystem interference between frequency hopping systems is proposed. The results are given in form of the average bit error probability over all frequencies used by the system. The method includes both the transmitter spectrum with sidebands and the receiver selectivity with sidebands. Furthermore, the effects from partially overlapping frequency hopping bands are included in the model. A strength of the model is that it can be generalized to an arbitrary number of interfering frequency hopping systems. Moreover, in addition to frequency hopping systems, interference on a fix frequency from different kinds of systems can also be included. If measured interference spectra, for example from a computer or a background, are available they can be incorporated in the calculations as well. Results from using the model show that it is important to use correct models of both the transmitter spectrum and receiver sidebands. If the effects from transmitter sidebands and/or receiver selectivity is neglected the resulting bit error probability can be severely underestimated.

  • 518.
    Stenumgaard, Peter
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Fors, Karina
    FOI.
    Wiklundh, Kia
    FOI.
    On the Impulsiveness Correction Factor for Estimation of Performance Degradation of Wireless Systems in Middleton´s Class A Interference2012Conference paper (Other academic)
    Abstract [en]

    To evaluate the performance degradation of a digital communication system, the Middleton’s Class A noise model has shown to be a useful model for real interference sources. By varying the model parameter A and Г, interference from pure Gaussian to a highly impulsive interference can be represented. The digital communication system performance is often determined by using the well-known Gaussian approximation (GA) to determine the bit error probability (BEP) of the system. The GA-approximation has been shown to severely underestimate the BEP for impulsive interference and therefore an earlier proposal, based on a so-called Impulsiveness Correction Factor (ICF) is used to correct the GA-approximation. In earlier work, the ICF has been extended to the case in which the interference signal consists of multiple interference signals. However, a limiting factor in that case is that one of the interference signals has to be dominant in power. In this paper, a simple but useful method is proposed to derive the ICF for a sum of equally distributed Class A-interference signals when none of the signals are dominant in power. This method is a complement to the earlier method and extends the usefulness of the ICF in interference analyses to a wider area of interference signals.

  • 519.
    Stenumgaard, Peter
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Fors, Karina
    FOI.
    Wiklundh, Kia
    FOI.
    Linder, Sara
    FOI.
    Junholm, Leif
    Försvarets Materielverk.
    Electromagnetic Interference on Tactical Radio Systems from Co-located Medical Equipment2013Conference paper (Other academic)
    Abstract [en]

    On military camps for joint international operations, the intersystem-interference situations can be highly unpredictable and scenario changes can occur very fast. For such situations it is highly important to perform intersystem-interference analyses even for electromagnetic interference from other electric equipment than intentional transmitters. One example of such interference source to consider is medical equipment from field hospitals since these can contain a large amount of interfering equipment. In this paper, we show examples of necessary safety distances between medical equipment and tactical radio systems at military camps for international missions. We give an example of how wideband electromagnetic interference can damage the interference reduction measure even for a wideband frequency hopping army combat radio.

  • 520.
    Stenumgaard, Peter
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology. Totalförsvarets forskningsinstitut (FOI).
    Fors, Karina
    Totalförsvarets forskningsinstitut (FOI).
    Wiklundh, Kia
    Totalförsvarets forskningsinstitut (FOI).
    Linder, Sara
    Totalförsvarets forskningsinstitut (FOI).
    Junholm, Leif
    Försvarets Materielverk (FMV).
    Radiostörningsrisker mot blåljusradio från medicinsk utrustning2013In: TAMSEC 2013, 2013, p. 37-Conference paper (Other academic)
    Abstract [sv]

    Den snabbt ökande användningen av trådlös teknik i samhällsviktiga system har lett till en ökad sårbarhet mot radiostörningar. Radiostörningar alstras naturligt av alla elektroniska system. Det är därför mycket viktigt att kontrollera så att de oavsiktliga radiostörningarna inte stör ut samlokaliserade kritiska trådlösa system. Medicinsk utrustning kan alstra radiostörningar och störningsrisken mot blåljusradio har undersökts. Slutsatsen är att vissa typer av medicinska utrustningar kan störa blåljusradio på avstånd upp till ett tiotal meter.

  • 521.
    Stenumgaard, Peter
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Linder, Sara
    Totalförsvarets Forskningsinstitut.
    Wiklundh, Kia
    Totalförsvarets Forskningsinsitut.
    Extension of the impulsiveness correction factor for several modulation schemes and various interfering signals for interference control in dynamic wireless applications2012In: IET Communications, ISSN 1751-8628, E-ISSN 1751-8636, Vol. 6, no 10, p. 1229-1233Article in journal (Refereed)
    Abstract [en]

    The impulsiveness correction factor (ICF) has earlier been proposed as a simple measure for estimating the effect from pulsed interference on binary phase shift keying modulated digital radio systems. The advantage is that with the ICF, large errors introduced by the additive white Gaussian noise interference approximation can be reduced significantly, whereas the simplicity in interference analyses can be maintained. In this study, the ICF is further developed for other modulation schemes, such as M-phase shift keying and M -quadrature amplitude modulation and for a larger set of interference types. The results show that for one pulsed interference signal the ICF is suitable for all investigated modulation schemes. If the interference is a mixtureof modulated and pulsed signals or several pulsed signals the authors suggest and  valuate ways to extend the ICF.

  • 522.
    Stenumgaard, Peter
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Persson, Daniel
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Wiklundh, Kia
    FOI.
    Larsson, Erik G
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    An Early-Warning Service for Emerging Communication Problems in Security and Safety Applications2013In: IEEE Communications Magazine, ISSN 0163-6804, E-ISSN 1558-1896, Vol. 51, no 5, p. 186-192Article in journal (Refereed)
    Abstract [en]

    Experience has shown that unpredictable disruption of communications during emergency operations can have severe consequences both for personal safety and for the ability to conduct a successful operation. An early-warning service for emerging communication disruption due to both unintentional interference and jamming, would therefore be a significant contribution for increased safety and security in such operations. We propose a solution for such an early-warning service both on the terminal and on higher system level. The solution is based on historical recorded data of both local and global information such as signal-to-interference ratio, interference classification, and position. We show by an example that with this service implemented, the operator will have increased time to take actions before a disruption occurs on a specific terminal.

  • 523.
    Stenumgaard, Peter
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Wiklundh, Kia
    FOI, Swedish Defense Research Agency, Linköping.
    Fors, Karina
    FOI, Swedish Defense Research Agency, Linköping.
    Linder, Sara
    FOI, Swedish Defense Research Agency, Linköping.
    Electromagnetic Interference on Tactical Radio Systems from Collocated Medical Equipment on Military Camps2012In: IEEE Communications Magazine, ISSN 0163-6804, E-ISSN 1558-1896, Vol. 50, no 10, p. 64-69Article in journal (Refereed)
    Abstract [en]

    On military camps for joint international operations, the intersystem interference can be highly unpredictable, and situation changes can occur very fast. For such situations it is highly important to perform intersystem interference analyses not only for intentional transmitters but also for electromagnetic interference from other electric equipment. One example of such an interference source to consider is medical equipment in field hospitals since the hospitals can contain a large amount of interfering equipment.  In this article, we show examples of necessary safety distances between medical equipment and tactical radio systems at military camps for international missions. We give an example of how wideband electromagnetic interference can degrade the performance even for a wideband frequency hopping army combat radio.

  • 524.
    Studer, Christoph
    et al.
    Rice University, Houston, TX, USA.
    Erik G., Larsson
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    PAR-aware multi-user precoder for the large-scale MIMO-OFDM downlink2012Conference paper (Refereed)
    Abstract [en]

    We consider an orthogonal frequency-division multiplexing (OFDM)-based downlink transmission scheme for large-scale multi-user (MU) multiple-input multiple-output (MIMO) wireless systems. In order to transmit signals with low peak-to-average (power) ratio (PAR), we propose to exploit the massive degrees-of-freedom available in large-scale MU-MIMO-OFDM systems. Specifically, we jointly perform MU precoding, OFDM modulation, and PAR reduction by solving a convex optimization problem at the base station. Numerical results demonstrate tremendous PAR-reduction capabilities of the proposed method, which eventually enables us to use low-cost RF components for the large-scale MU-MIMO-OFDM downlink.

  • 525.
    Studer, Christoph
    et al.
    Rice University, TX USA .
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    PAR-Aware Large-Scale Multi-User MIMO-OFDM Downlink2013In: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008, Vol. 31, no 2, p. 303-313Article in journal (Refereed)
    Abstract [en]

    We investigate an orthogonal frequency-division multiplexing (OFDM)-based downlink transmission scheme for large-scale multi-user (MU) multiple-input multiple-output (MIMO) wireless systems. The use of OFDM causes a high peak-to-average (power) ratio (PAR), which necessitates expensive and power-inefficient radio-frequency (RF) components at the base station. In this paper, we present a novel downlink transmission scheme, which exploits the massive degrees-of-freedom available in large-scale MU-MIMO-OFDM systems to achieve low PAR. Specifically, we propose to jointly perform MU precoding, OFDM modulation, and PAR reduction by solving a convex optimization problem. We develop a corresponding fast iterative truncation algorithm (FITRA) and show numerical results to demonstrate tremendous PAR-reduction capabilities. The significantly reduced linearity requirements eventually enable the use of low-cost RF components for the large-scale MU-MIMO-OFDM downlink.

  • 526.
    Suraweera, Himal A.
    et al.
    Singapore University of Technology and Design.
    Ngo, Hien Quoc
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Duong, Trung Q.
    Blekinge Institute of Technology, Karlskrona, Sweden .
    Yuen, Chau
    Singapore University of Technology and Design.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Multi-Pair Amplify-and-Forward Relaying with Very Large Antenna Arrays2013In: Proceedings of the IEEE International Conference on Communicatons (ICC), IEEE , 2013, p. 4635-4640Conference paper (Refereed)
    Abstract [en]

    We consider a multi-pair relay channel where multiple sources simultaneously communicate with destinations using a relay. Each source or destination has only a single antenna, while the relay is equipped with a very large antenna array. We investigate the power efficiency of this system when maximum ratio combining/maximal ratio transmission (MRC/MRT) or zero-forcing (ZF) processing is used at the relay. Using a very large array, the transmit power of each source or relay (or both) can be made inversely proportional to the number of relay antennas while maintaining a given quality-of-service. At the same time, the achievable sum rate can be increased by a factor of the number of source-destination pairs. We show that when the number of antennas grows to infinity, the asymptotic achievable rates of MRC/MRT and ZF are the same if we scale the power at the sources. Depending on the large scale fading effect, MRC/MRT can outperform ZF or vice versa if we scale the power at the relay.

  • 527.
    Sven, Ahlberg
    Linköping University, Department of Electrical Engineering, Communication Systems.
    Evaluation of Different Radio-Based Indoor Positioning Methods2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 528.
    Söderström, Emma
    Linköping University, Department of Electrical Engineering, Communication Systems.
    Reducing Effects of Multipath Propagation With a Blind Equalizer2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    When transmitting data from an aircraft being prepared at the apron (the area in front of the hangar) telemetry data is transmitted to ground personnel. The transmitted data is subject to severe distortion due to multipath propagation created by the surroundings, resulting in erroneous detection. By equalizing the signal using the Constant Modulus Algorithm a significant increase in detection performance has been observed, both in simulations and tests on collected data. The most sufficient parameters were chosen after testing a set of different parameter combinations on simulations with single delays. These parameters were then used to equalize simulated multipath as well as collected data. The results show that short delays with low power can be resolved without any equalizer. Longer delays with relatively low power can be resolved using the proposed equalizer but long delays with high power cannot be resolved by the equalizer at all. The thesis shows that it is worth investigating implementation of the equalizer.

  • 529.
    Sörman, Simon
    Linköping University, Department of Electrical Engineering, Communication Systems.
    System Information Distribution in Massive MIMO Systems2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The 5th generation mobile telecommunication system (5G) is currently being specified and developed, with large expectations on throughput and efficiency. While 4G and more specifically LTE might constitute a basis of the design of the network, there are some parts that should be improved. One thing to improve is the static signalling that occurs very frequently in a 4G network, of which system information such as synchronization signals, detection of network frequencies, operators, configurations etc. is a part. It has been shown that the static signalling requires both much energy and time-frequency resources. Since the system information is not intended for a single user it is always broadcast so that any user, and any amount of users can read it when needed. 5G will use a technique called massive MIMO, where the base station is equipped with a large number of antennas which can be used to direct signals in space, called beamforming. This thesis presents a new method for distribution of system information that can utilize the beamforming capabilities of massive MIMO. A simple model together with simulated user channel statistics from urban 4G scenarios are used to show that the new method outperforms the classical method of only broadcasting the information, with respect to time-frequency resources. Especially if there are high requirements on the latency of the system information, the new method results in a large gain.

  • 530.
    Tamoor-ul-Hassan, Syed
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems.
    Demir, Serkan
    Fast Packet Retransmissions in LTE2011Independent thesis Advanced level (degree of Master (Two Years)), 80 credits / 120 HE creditsStudent thesis
    Abstract [en]

    The cellular networks are evolving to meet the future requirements of data rate,coverage and capacity. The fourth generation mobile communication system, LTEhas been developed to meet these goals. LTE uses multiple antenna features andlarger bandwidths in order to accomplish this task. These features will furtherextend the requirements of data rate, coverage, latency and flexibility.

    LTE also utilizes the varying quality of the radio channel and the interferencefrom other transmitters by adapting the data rate to the instantaneous channelquality at all the time. This is typically referred to as Link Adaptation. Thelink adaptation fails from time to time due to the varying channel quality as wellas the interference from other transmitters. In order to counteract these failures,retransmission methods are employed. These methods detect the errors on thereceiver side and signals the transmitter for the retransmission of the erroneousdata. The efficiency of link adaptation increases if combined with a properly designedretransmission scheme at the expense of delays due to retransmissions.

    This master thesis focuses on the study of the retransmission schemes with fasterfeedback, resulting in a reduction in delay. The feedback is generated by makingan early estimate of the decoding outcome and sending it early to the transmitterresulting in faster retransmission. This is important in certain applications wherethe data transmission is intolerant to delays.The thesis work shows by system performance simulations that fast packet retransmission,precisely called Early HARQ Feedback, significantly affects the systemperformance together with the utilization of the link adaptation. The study alsoshows that the link adaptation, in certain scenarios, can be optimized to improvethe system performance. In that respect, it is also possible to increase the numberof retransmissions within the same resource utilization. That optimization is basicallycalled aggressive link adaptation. Consequently, Early HARQ Feedback incombination with aggressive link adaptation provides a large improvement in thedownlink performance of the studied cases.

  • 531.
    Tang, Zhiqiang
    Linköping University, Department of Electrical Engineering, Communication Systems.
    Traffic Scheduling for LTE Advanced2010Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Long Term Evolution (LTE) is becoming the first choice of operators when constructingthe new network infrastructure, because of its high throughput and lowlatency. Although the LTE can offer high speed data service as a benefit of widebandapplication, the large bandwidth also results in huge control signaling cost.This thesis studies how the available radio resources should be allocated todifferent users for the particular purpose. Three proposals are presented in thisthesis. The first two aim at maximizing the overall net capacity. The factors ofchannel conditions and control signaling cost are considered in the first proposalwhereas power control is supplemented as an additional factor in the second one.The third proposal aims at achieving a tradeoff between subframe efficiency andaverage data rate. Channel conditions and control signaling cost are taken intoconsideration.Resource blocks scheduling under a control signaling cost constraint is feasiblewith the knowledge of the channel condition of users. This is obtained from channelstate information directly. The first proposal studies how this scheduling isdone. The second proposal takes power allocation scheme into account. In termsof computational complexity, the methods of internal water-filling and externalwater-filling are described in the second proposal. The simulation results illustratethat the net capacity in the first proposal can be enhanced by about 5% -60% in the second proposal. The exact percentage of increase depends on differentcontrol signaling penalty.The third proposal discusses how to implement flexible subframe length underthe Rayleigh fading channel condition in the LTE system. The objective is toachieve subframe efficiency as high as possible, while maintaining the maximumaverage data rate. The simulation results illustrate that the optimal subframelength depends on control signaling cost penalty as well as on Doppler frequency.Finally, the fairness of the first proposal is compared with the improved versionsof Round Robin, Dynamic Allocation and Proportional Fair scheduling algorithms.The simulation results show that Round Robin and Dynamic Allocationoutperform the first proposal under a certain condition.

  • 532.
    Thalén, Magnus
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    A Study on Random Access Performance in Next Generation Mobile Network Systems2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The next generation of mobile telecommunication, 5G, will be specified in the near future. One of the proposed changes relative to the previous generation, 4G,is the inclusion of a new system control plane (SCP). The purpose of the SCP is to improve system scalability, forward compatibility, peak performance and to enable a higher degree of support for advanced antenna techniques. This is done by logically separating data transmitted explicitly from and to the user, the dynamic transmissions, from the broadcasted transmissions that remain constant regardless of user activity, the static transmissions, and by then redesigning the static part to make it more lean. This is expected to have several positive effects such as considerably more free resources, resulting in energy savings and potentially increased usage of MIMO. Knowing what effect the SCP has upon aspects such as random access is of importance when designing the solution that will go into the standard.

    Simulations show that there is potential in the inclusion of the new SCP. While the simulated 5G candidate systems that include the SCP have an increased delay when running the random access procedure, some aspects of the procedure have been improved. The main differences relative to the simulated 4G system are the performance of the first message in the procedure, which increased, and the performance of the second message in the procedure, which decreased. The deficiencies found in the handling of the second message, however, can be alleviated by using a more proper algorithm and channel design than what was used in this study.

  • 533.
    Thobaben, Ragnar
    et al.
    Royal Institute of Technology (KTH), Stockholm, Sweden.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Sensor-Network Aided Cognitive Radio: On the Optimal Receiver for Estimate-and-Forward Protocols Applied to the Relay Channel2007In: Proceedings of the 41st Asilomar Conference on Signals, Systems and Computers (ACSSC'07), 2007, p. 777-781Conference paper (Other academic)
    Abstract [en]

    Cognitive radio describes a promising concept for improving the utilization of radio spectrum. It allows secondary users to access licensed radio spectrum in an opportunistic fashion, given that the quality of service for primary users is maintained. In this scenario, the detection of unused radio spectrum is the main obstacle: it requires the recognition of lowpower signals in a noisy environment. Therefore, we consider the case where cognitive users are supported by a wireless sensor network (WSN) providing beliefs on the event that the primary user is active. The beliefs provided by the WSN nodes are then combined by the cognitive radio in order to make a final decision. Due to limitations in complexity, power, and bandwidth, the WSN nodes apply the estimate-and-forward protocol to communicate their beliefs and to relay the beliefs of adjacent nodes. For the case where the WSN is subject to noisy communication links, we derive and analyze the optimal receiver which provides the cognitive radio with log-likelihood ratios for the estimated and forwarded hypotheses. The performance of the optimal receiver is compared to the performance of sub-optimal receivers.

  • 534.
    Tsinos, Christos G.
    et al.
    Univ Luxembourg, Luxembourg.
    Kalantari, Ashkan
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Chatzinotas, Symeon
    Univ Luxembourg, Luxembourg.
    Ottersten, Bjorn
    Univ Luxembourg, Luxembourg.
    Symbol-Level Precoding with Low Resolution DACs for Large-Scale Array MU-MIMO Systems2018In: 2018 IEEE 19TH INTERNATIONAL WORKSHOP ON SIGNAL PROCESSING ADVANCES IN WIRELESS COMMUNICATIONS (SPAWC), IEEE , 2018, p. 671-675Conference paper (Refereed)
    Abstract [en]

    While (Multiple Input-Multiple Output) MIMO systems based on large-scale antenna arrays are seen as the solution to the continuously increasing demands in modern wireless systems, they require high hardware complexity and power consumption. To tackle this, solutions based on low resolution Analog-to-Digital Converters (ADCs) / Digital-to-Analog Converters (DACs) have been developed in the literature where they mainly propose quantized versions of typical channel dependent linear precoding solutions. Alternatively, nonlinear Symbol level Precoding techniques have been recently proposed for downlink Multi User (MU)-MIMO systems with low resolution DACs that achieve significantly improved performance in several cases. The existing SLP approaches support only DACs of 1-bit resolution which result in significant performance degradations, especially when constellations with order greater than 4 are employed. To that end, in this work a novel SLP approach is developed that supports systems with DACs of any resolution and it is applicable for any type of constellation. As it is verified by the presented numerical results, the proposed approach exhibits significantly improved performance when constellations with order greater than 4 are employed and require reduced computational complexity, compared to the existing solutions for the 1-bit DAC case.

  • 535.
    Tugfe Demir, Özlem Tugfe
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Tuncer, Temel Engin
    Middle East Tech Univ, Turkey.
    Improved ADMM-based algorithms for multi-group multicasting in large-scale antenna systems with extension to hybrid beamforming2019In: Digital signal processing (Print), ISSN 1051-2004, E-ISSN 1095-4333, Vol. 93, p. 43-57Article in journal (Refereed)
    Abstract [en]

    In this paper, multi-group multicast beamforming is considered for the full digital and hybrid beamforming. The wireless system comprises of a multiple-antenna base station and single-antenna users. Quality-of-service (QoS)-aware design is investigated where the optimization objective is to minimize the total transmitted power subject to the signal-to-interference-plus-noise ratio (SINR) constraint at each user. In addition to the SINR constraints, per-antenna power constraint is included for each antenna of the base station. The original optimization problem for full digital beamforming is transformed into an equivalent form such that the alternating direction method of multipliers (ADMM) can be applied in an effective and computationally inexpensive manner for the large-scale antenna systems. In this new formulation, the beamformer weight vectors are decomposed into two subspaces in order to decrease the number of dual variables and multiplications. The optimum update equations are obtained for the proposed ADMM algorithm. This new reformulation is used for two different hybrid beamforming structures employing phase shifters and vector modulators. Optimum updates are derived for each system. The proposed algorithms decrease computational complexity of the existing ADMM algorithms due to the effective reformulation as well as the direct solution of the nonconvex problem. In the simulation results, it is shown that the proposed methods have better convergence behavior and less computational time than the benchmark algorithms. Furthermore, the proposed method for hybrid beamforming with vector modulators performs better than its counterpart in the literature in terms of transmitted power. (C) 2019 Elsevier Inc. All rights reserved.

  • 536.
    Tugfe Demir, Özlem Tugfe
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Tuncer, Temel Engin
    Middle East Tech Univ, Turkey.
    Robust Optimum and Near-Optimum Beamformers for Decode-and-Forward Full-Duplex Multi-Antenna Relay With Self-Energy Recycling2019In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 18, no 3, p. 1566-1580Article in journal (Refereed)
    Abstract [en]

    In this paper, we consider the full-duplex decode-and-forward wireless-powered relaying system, which employs energy harvesting protocol with power splitting. The robust joint optimum relay transmit beamformer and power splitting factor are obtained for the quality of service (QoS)-aware problem for the first time in the literature. The optimum solution is found by analyzing the Karush-Kuhn-Tucker conditions, thanks to the effective reformulation of the problem in an equivalent and simplified manner. In addition, the signal-to-interference-plus-noise ratio (SINR) maximization problem is investigated in order to find the robust optimum solution. The simulation results verify the optimality of the proposed method compared with the sub-optimum one which is presented by Zhao et al.. In the next part of this paper, the considered system is generalized by employing multiple receive antennas at the relay. Both QoS-aware and SINR maximization problems are considered. The near-optimum relay transmit and receive beamformers as well as power splitting factor are found by optimizing the variables alternately. First, transmit beamformer and power splitting factor are found optimally for a given initial receive beamformer. Then, the optimum receive beamformer is obtained. Relay with multiple-receive antennas is shown to perform better than the single receive antenna relay in terms of SINR and transmission power.

  • 537.
    Tumula, Chaitanya
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Improving 3GPP-LTE Uplink Control Signaling by Repetition Across Frequency Bands2013In: Proceedings of the IEEE International Conference on Communications (ICC), IEEE , 2013, p. 1243-1248Conference paper (Refereed)
    Abstract [en]

    We propose improvements for the physical uplink control channel (PUCCH) format 2 control signaling in 3GPP-LTE systems. These improvements can be useful for low-cost UE design and optimization planned for the future LTE releases. In the proposed method, instead of repeating a single QPSK symbol across the 12 subcarriers in each OFDM symbol of a resource block as done in the current release of the standard, we pick two QPSK symbols from two independent resource blocks and repeat them across 6 subcarriers each. The proposed method has a performance gain of about 5.5 dB and 1.85 dB over the conventional method with one and two receiving antennas at the base station, respectively. These gains can be achieved without the use of any additional transmission power, time-frequency resources or receiver complexity.

    The cell-specific QPSK sequences specified in the standard for PUCCH transmission are chosen according to the conventional repetition across the 12 subcarriers, hence we suggest new cell-specific QPSK sequences which minimize the peak-to-average-power ratio (PAPR) of the PUCCH signal with the proposed method.

  • 538.
    Tumula, Chaitanya
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Improving 3GPP-LTE Uplink Control Signaling Performance Using Complex-Field Coding2013In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 62, no 1, p. 161-171Article in journal (Refereed)
    Abstract [en]

    We study the uplink control signaling in 3GPP-Long Term Evolution (LTE) systems. Specifically, we propose a precoding method that uses complex-field coding (CFC) to improve the performance of the physical uplink control channel (PUCCH) format 2 control signaling. We derive optimal detectors for both the conventional method and the proposed precoding method for different cases of channel state information (CSI) and noise variance information at the receiver. With a single receive antenna, the proposed method offers significant gains compared to the coding currently used in 3GPP-LTE for all the different scenarios considered in this work. However the gains are relatively less with two receive antennas.

  • 539.
    Tumula, Chaitanya
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Optimal Power Allocation for Hybrid ARQ with Chase Combining in i.i.d. Rayleigh Fading Channels2013In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 61, no 5, p. 1835-1846Article in journal (Refereed)
    Abstract [en]

    We consider the optimization of Chase combining (CC)-based hybrid-automatic repeat request (HARQ) schemes with a limit on the maximum number of retransmissions. We formulate two optimization problems: (i) minimizing the packet drop probability (PDP) under a total average transmit power constraint, and (ii) minimizing the average transmit power under a fixed PDP constraint. Towards solving these equivalent optimization problems, we provide a closed-form expression for the outage probability of a CC-HARQ scheme. We then show that solving the optimization problems using an exact expression of the outage probability becomes complex with an increase in the maximum number of retransmissions. We propose an alternative approach in which we approximate the optimization problems by using an approximate outage probability expression and formulate the two optimization problems as two equivalent geometric programming problems (GPPs), which can be solved efficiently even for a large limit on the maximum number of retransmissions.

    The results show that the optimal power allocation solution provides significant gains over the equal power allocation solution. For PDP values below 10-3 , the optimal solution provided by the GPP approach has a performance close to that of the solution provided by solving the optimization problem exactly using nonlinear optimization techniques.

  • 540.
    Tumula, Chaitanya V. K.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Improved Techniques for Retransmission and Relaying in Wireless Systems2011Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The last three decades have seen significant advances in the wireless communication field. As the data rates of wireless systems are increasing, the demand for mobile services also is increasing rapidly. Like other natural resources, radio spectrum suitable for mobile wireless communications is also limited. In order to keep up with this ever increasing demand, there is a requirement of new signal processing algorithms.

    Diversity is a technique used in wireless systems to combat the effects of fading and thereby improve reliability of data transfer. There are many ways in which algorithms can exploit diversity in wireless channels. Hybrid-automatic repeat request (H-ARQ) schemes and relaying mechanisms are two such diversity extracting techniques. Even though these diversity achieving techniques have been well understood in theory, there are many ways in which one can optimize these techniques for specific application scenarios.In this thesis, we focus on improving the performance of retransmission schemes and relaying systems.

    In the first part of the thesis, we improve the performance of H-ARQ schemes in the 3GPP- long term evolution (LTE) system by improving the performance of feedback signaling. We employ complex-field coding to extract the inherent frequency diversity available in the resources. Next, we provide a sub-optimal solution to the outage-optimal power allocation problem in incremental redundancy based H-ARQ system, whose performance is practically the same as that of the optimal solution.

    In the later part of the thesis, we propose a retransmission scheme based on superposition coding (SPC) for the symmetric relaying scenario. We provide packet error probability (PEP) expressions and solutions for the optimal fraction of power allocated for the partners' data. Finally, we study the optimal bits-to-symbol mappings for SPC and its effect on an H-ARQ scheme and the symmetric relaying scenario using SPC.

    List of papers
    1. Improved Error Protection for Uplink Control Signaling in 3GPP-LTE via Complex-Field Coding
    Open this publication in new window or tab >>Improved Error Protection for Uplink Control Signaling in 3GPP-LTE via Complex-Field Coding
    2010 (English)In: Proceedings of the IEEE Vehicular Technology Conference (VTC), 2010Conference paper, Published paper (Refereed)
    Abstract [en]

    We study the uplink control signaling in 3GPP-Long Term Evolution (LTE) systems. Specifically, we propose a precoding method that uses complex-field coding (CFC) to improve the performance of the PUCCH format 2 control signaling. In the case of perfect channel state information (CSI) at the receiver and with a single receive antenna, the proposed method offers significant gains compared to the coding currently used in 3GPP-LTE. However the gains are marginal with two receive antennas. In order to examine the impact of channel estimation errors, we also derive the optimal detector for the case of imperfect receiver CSI, both for conventional coding and for the proposed CFC method.

    Series
    IEEE Vehicular Technology Conference, ISSN 1550-2252
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-53651 (URN)10.1109/VETECS.2010.5493842 (DOI)978-1-4244-2518-1 (ISBN)
    Conference
    IEEE 71st Vehicular Technology Conference, May 16-19, Taipei, Taiwan
    Note
    ©2010 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEEAvailable from: 2010-05-27 Created: 2010-01-27 Last updated: 2016-08-31Bibliographically approved
    2. Outage-Optimal Power Allocation for Hybrid ARQ with Incremental Redundancy
    Open this publication in new window or tab >>Outage-Optimal Power Allocation for Hybrid ARQ with Incremental Redundancy
    2011 (English)In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 10, no 7, p. 2069-2074Article in journal (Refereed) Published
    Abstract [en]

    We consider the optimization of power in incremental redundancy (IR) based hybrid automatic repeat request (HARQ) schemes when the maximum number of(re)transmissions is fixed. We formulate two optimization problems:(i) minimizing the packet drop probability (PDP) undera total average transmit power constraint, and (ii) minimizingthe average transmit power under a fixed PDP constraint.We consider in detail the special case of only two allowed transmissions, and we prove that the two optimization problems are equivalent. For this special case, we also provide a sub-optimal root- finding solution and compare its performance with the optimal solution obtained through an exhaustive search.The results show that the optimal power allocation can provide significant gains over the equal power solution in terms of average transmit power spent. The performance of the proposed root-finding solution is practically the same as that of the optimal solution.

    Place, publisher, year, edition, pages
    IEEE, 2011
    Keywords
    Hybrid ARQ, incremental redundancy, optimal power allocation, outage probability.
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-67132 (URN)10.1109/TWC.2011.041311.101978 (DOI)000293685400010 ()
    Note
    Funding Agencies|Swedish Research Council (VR)||Swedish Foundation for Strategic Research (SSF)||ELLIIT||Knut and Alice Wallenberg Foundation||Available from: 2011-03-31 Created: 2011-03-31 Last updated: 2017-12-11Bibliographically approved
    3. Superposition Modulation Based Symmetric Relaying with Hybrid ARQ: Analysis and Optimization
    Open this publication in new window or tab >>Superposition Modulation Based Symmetric Relaying with Hybrid ARQ: Analysis and Optimization
    2011 (English)In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 60, no 8, p. 3667-3683Article in journal (Refereed) Published
    Abstract [en]

    We present a retransmission scheme based on superposition modulation for the symmetric relaying scenario when the number of retransmissions for a data packet is limited. We consider both diversity combining based as well as code combining based retransmission schemes. Under the assumption that the receiver implements a mechanism that can use all accumulated received mutual information when decoding the message, we derive the packet error probability (PEP) expressions for the proposed retransmission scheme for the case when only one retransmission is allowed. Based on the PEP expressions derived, we provide a closed-form solution for the optimal superposition ratio (the fraction of power used for the relaying operation). Simulation results show that the proposed retransmission scheme offers significant gains compared to a retransmission scheme based on classical decode-and-forward (DF) relaying.

    Place, publisher, year, edition, pages
    IEEE, 2011
    Keywords
    Cooperative communications, hybrid ARQ, superposition modulation, outage probability
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-68288 (URN)10.1109/TVT.2011.2162971 (DOI)000296021300011 ()
    Note
    Funding agencies|Swedish Foundation for Strategic Research and the Excellence Center at Linkoping-Lund in Information Technology||Knut and Alice Wallenberg Foundation through a Royal Swedish Academy of Sciences||Available from: 2011-05-17 Created: 2011-05-17 Last updated: 2017-12-11
    4. Bits-to-Symbol Mappings for Superposition Coding Based HARQ Systems
    Open this publication in new window or tab >>Bits-to-Symbol Mappings for Superposition Coding Based HARQ Systems
    2013 (English)In: Proceedings of the IEEE Wireless Communications and Networking Conference (WCNC), Institute of Electrical and Electronics Engineers (IEEE), 2013, p. 2468-2472Conference paper, Published paper (Refereed)
    Abstract [en]

    We consider the mapping of bits-to-superimposed constellation symbols in terms of the achievable rate on the channel for the HARQ system using superposition coding as proposed in [2]. We show that using a Gray mapping of bits-to-superimposed constellation symbols has better performance thanthe conventional natural mapping that results from superposition in signal space, for all the values of the superposition ratio. We also show through link-level simulations that the predicted gains in terms of achievable rate can be realized in practice using LDPC codes. Furthermore, we show that the optimal superposition ratio for the Gray mapping case results in conventional higher order constellation symbols after the superposition operation.

    Place, publisher, year, edition, pages
    Institute of Electrical and Electronics Engineers (IEEE), 2013
    Series
    IEEE Wireless Communications and Networking Conference. Proceedings, ISSN 1525-3511
    Keywords
    Superposition coding, bits-to-symbol mapping, hybrid ARQ
    National Category
    Communication Systems
    Identifiers
    urn:nbn:se:liu:diva-87279 (URN)10.1109/WCNC.2013.6554948 (DOI)978-1-4673-5938-2 (ISBN)978-1-4673-5937-5 (ISBN)
    Conference
    IEEE Wireless Communications and Networking Conference, WCNC 2013, 7-10 April, Shanghai; China
    Note

    The previous status of this article was Manuscript and the working title was Bits-to-Symbol Mappings for Superposition Coding.

    Available from: 2013-04-03 Created: 2013-01-15 Last updated: 2017-01-13Bibliographically approved
  • 541.
    Tumula V. K., Chaitanya
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    HARQ Systems: Resource Allocation, Feedback Error Protection, and Bits-to-Symbol Mappings2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Reliability of data transmission is a fundamental problem in wireless communications. Fading in wireless channels causes the signal strength to vary at the receiver and this results in loss of data packets. To improve the reliability, automatic repeat request (ARQ) schemes were introduced. However these ARQ schemes suffer from a reduction in the throughput. To address the throughput reduction, conventional ARQ schemes were combined with forward error correction (FEC) schemes to develop hybrid-ARQ (HARQ) schemes. For improving the reliability of data transmission, HARQ schemes are included in the present wireless standards like LTE, LTE-Advanced and WiMAX.

    Conventional HARQ systems use the same transmission power and the same number of channel uses in different ARQ rounds. However this is not optimal in terms of minimizing the average transmit power or the average energy spent for successful transmission of a data packet. We address this issue in the first part of the dissertation, where we consider optimal resource allocation in HARQ systems with a limit on the maximum number of allowed transmissions for a data packet. Specifically, we consider the problem of minimizing the packet drop probability (PDP) under an average transmit power constraint or equivalently minimizing the average transmit power under a fixed PDP constraint. We consider both incremental redundancy (IR)-based and Chase combining (CC)-based HARQ systems in our work. For an IR-HARQ system, for the special case of two allowed transmissions for each packet, we provide a solution for the optimal number of channel uses and the optimal power to be used in each ARQ round. For a CC-HARQ system, we solve the problem of optimal power allocation in i.i.d. Rayleigh fading channels as well as correlated Rayleigh fading channels. For the CC-HARQ case, we also provide a low complexity geometric programming (GP) solution using an approximation of the outage probability expression.

    HARQ systems conventionally use one bit acknowledgement (ACK)/negative ACK (NACK) feedback from the receiver to the transmitter. In the 3GPP-LTE systems, one method for sending these HARQ acknowledgement bits is to jointly code them with the other control signaling information using a specified Reed-Muller code consisting of 20 coded bits. Even though the resources used for sending this control signaling information can inherently provide a diversity gain, the Reed-Muller code with such a short block size is not good at extracting all of the available diversity. To address this issue, in the second part of this dissertation, we propose two new methods: i) based on complex-field coding (CFC), and ii) using repetition across frequency bands, to extract the inherent diversity available in the channel resources and improve the error protection for the HARQ acknowledgement bits along with the other control signaling information. In the second part of the dissertation, we also propose a new signal space diversity (SSD) scheme, which results in transmit signals having constant envelope (CE). The proposed CE-SSD scheme results in a better overall power efficiency due to the reduced back-off requirements on the radio frequency power amplifier. Moreover, the proposed CE-SSD technique can be useful for application scenarios involving transmission of small number of information bits, such as in the case of control signaling information transmission.

    In conventional HARQ systems, during the retransmission phase, the channel resources are exclusively used for the retransmitted data packet. This is not optimal in terms of efficient resource utilization. For efficient utilization of channel resources during the retransmissions, a superposition coding (SPC) based HARQ scheme was proposed in the literature. In an SPC based HARQ system, an erroneous packet is transmitted together with a new data packet by superposition in the Euclidean space. In the final part of this dissertation, we study performance of different bits-to-symbol mappings for such an SPC based HARQ system.

    List of papers
    1. Outage-Optimal Power Allocation for Hybrid ARQ with Incremental Redundancy
    Open this publication in new window or tab >>Outage-Optimal Power Allocation for Hybrid ARQ with Incremental Redundancy
    2011 (English)In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 10, no 7, p. 2069-2074Article in journal (Refereed) Published
    Abstract [en]

    We consider the optimization of power in incremental redundancy (IR) based hybrid automatic repeat request (HARQ) schemes when the maximum number of(re)transmissions is fixed. We formulate two optimization problems:(i) minimizing the packet drop probability (PDP) undera total average transmit power constraint, and (ii) minimizingthe average transmit power under a fixed PDP constraint.We consider in detail the special case of only two allowed transmissions, and we prove that the two optimization problems are equivalent. For this special case, we also provide a sub-optimal root- finding solution and compare its performance with the optimal solution obtained through an exhaustive search.The results show that the optimal power allocation can provide significant gains over the equal power solution in terms of average transmit power spent. The performance of the proposed root-finding solution is practically the same as that of the optimal solution.

    Place, publisher, year, edition, pages
    IEEE, 2011
    Keywords
    Hybrid ARQ, incremental redundancy, optimal power allocation, outage probability.
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-67132 (URN)10.1109/TWC.2011.041311.101978 (DOI)000293685400010 ()
    Note
    Funding Agencies|Swedish Research Council (VR)||Swedish Foundation for Strategic Research (SSF)||ELLIIT||Knut and Alice Wallenberg Foundation||Available from: 2011-03-31 Created: 2011-03-31 Last updated: 2017-12-11Bibliographically approved
    2. Optimal Resource Allocation for IR-HARQ
    Open this publication in new window or tab >>Optimal Resource Allocation for IR-HARQ
    2011 (English)In: Proceedings of the IEEE Swe-CTW, 2011, p. 74-79Conference paper, Published paper (Refereed)
    Abstract [en]

    In this work, we first provide an exact closed-form expression for the packet drop probability (PDP) in incremental redundancy (IR) based hybrid automatic repeat request (HARQ) schemes with a limit on the maximum number of transmissions. In the later part, we extend our work in [5], and consider the optimal resource allocation problem of minimizing the PDP under the constraints of an average transmit power and total number of channel uses. We provide two approaches to solve this optimization problem and compare their performance with the solution given in [5].

    Keywords
    Hybrid ARQ, Incremental redundancy, Optimal resource allocation, Outage probability
    National Category
    Communication Systems
    Identifiers
    urn:nbn:se:liu:diva-71014 (URN)10.1109/Swe-CTW.2011.6082492 (DOI)978-1-4577-1876-2 (ISBN)978-1-4577-1877-9 (ISBN)
    Conference
    IEEE Swedish Communication Technologies Workshop (Swe-CTW)
    Funder
    Swedish Research CouncileLLIIT - The Linköping‐Lund Initiative on IT and Mobile Communications
    Available from: 2011-09-27 Created: 2011-09-27 Last updated: 2016-08-31
    3. Optimal Power Allocation for Hybrid ARQ with Chase Combining in i.i.d. Rayleigh Fading Channels
    Open this publication in new window or tab >>Optimal Power Allocation for Hybrid ARQ with Chase Combining in i.i.d. Rayleigh Fading Channels
    2013 (English)In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 61, no 5, p. 1835-1846Article in journal (Refereed) Published
    Abstract [en]

    We consider the optimization of Chase combining (CC)-based hybrid-automatic repeat request (HARQ) schemes with a limit on the maximum number of retransmissions. We formulate two optimization problems: (i) minimizing the packet drop probability (PDP) under a total average transmit power constraint, and (ii) minimizing the average transmit power under a fixed PDP constraint. Towards solving these equivalent optimization problems, we provide a closed-form expression for the outage probability of a CC-HARQ scheme. We then show that solving the optimization problems using an exact expression of the outage probability becomes complex with an increase in the maximum number of retransmissions. We propose an alternative approach in which we approximate the optimization problems by using an approximate outage probability expression and formulate the two optimization problems as two equivalent geometric programming problems (GPPs), which can be solved efficiently even for a large limit on the maximum number of retransmissions.

    The results show that the optimal power allocation solution provides significant gains over the equal power allocation solution. For PDP values below 10-3 , the optimal solution provided by the GPP approach has a performance close to that of the solution provided by solving the optimization problem exactly using nonlinear optimization techniques.

    Place, publisher, year, edition, pages
    IEEE Press, 2013
    Keywords
    Hybrid-ARQ, diversity combining, optimal power allocation, outage probability, geometric programming.
    National Category
    Communication Systems Telecommunications
    Identifiers
    urn:nbn:se:liu:diva-89650 (URN)10.1109/TCOMM.2013.032013.120422 (DOI)000319752600019 ()
    Funder
    eLLIIT - The Linköping‐Lund Initiative on IT and Mobile CommunicationsSwedish Foundation for Strategic Research Swedish Research Council
    Available from: 2013-04-03 Created: 2013-02-28 Last updated: 2017-12-06Bibliographically approved
    4. Adaptive power allocation for HARQ with Chase combining in correlated Rayleigh fading channels
    Open this publication in new window or tab >>Adaptive power allocation for HARQ with Chase combining in correlated Rayleigh fading channels
    2014 (English)In: IEEE Wireless Communications Letters, ISSN 2162-2337, E-ISSN 2162-2345, Vol. 3, no 2, p. 169-172Article in journal (Refereed) Published
    Abstract [en]

    We consider the problem of minimizing the packet drop probability (PDP) under an average transmit power constraint for Chase combining (CC)-based hybrid-automatic repeat request (HARQ) schemes in correlated Rayleigh fading channels. We propose a method to find a solution to the non-convex optimization problem using an exact expression of the outage probability. However, the complexity of this method is high. Therefore, we propose an alternative approach in which we use an asymptotically equivalent expression for the outage probability and reformulate it as a geometric programming problem (GPP), which can be efficiently solved using convex optimization algorithms.

    Place, publisher, year, edition, pages
    Institute of Electrical and Electronics Engineers (IEEE), 2014
    National Category
    Signal Processing
    Identifiers
    urn:nbn:se:liu:diva-129056 (URN)10.1109/WCL.2013.122113.130793 (DOI)000209681200013 ()
    Note

    The previous status of this article was Manuscript and the working title was Adaptive Power Allocation for Hybrid ARQ with Chase Combining in Correlated Rayleigh Fading Channels.

    Available from: 2016-06-09 Created: 2016-06-09 Last updated: 2017-11-30Bibliographically approved
    5. Improving 3GPP-LTE Uplink Control Signaling Performance Using Complex-Field Coding
    Open this publication in new window or tab >>Improving 3GPP-LTE Uplink Control Signaling Performance Using Complex-Field Coding
    2013 (English)In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 62, no 1, p. 161-171Article in journal (Refereed) Published
    Abstract [en]

    We study the uplink control signaling in 3GPP-Long Term Evolution (LTE) systems. Specifically, we propose a precoding method that uses complex-field coding (CFC) to improve the performance of the physical uplink control channel (PUCCH) format 2 control signaling. We derive optimal detectors for both the conventional method and the proposed precoding method for different cases of channel state information (CSI) and noise variance information at the receiver. With a single receive antenna, the proposed method offers significant gains compared to the coding currently used in 3GPP-LTE for all the different scenarios considered in this work. However the gains are relatively less with two receive antennas.

    Keywords
    3GPP-LTE, uplink control signaling, complex-field coding, perfect CSI, imperfect CSI, optimal detection.
    National Category
    Communication Systems
    Identifiers
    urn:nbn:se:liu:diva-80150 (URN)10.1109/TVT.2012.2215061 (DOI)000318514000016 ()
    Funder
    eLLIIT - The Linköping‐Lund Initiative on IT and Mobile Communications
    Note

    (c) 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: 2012-08-21 Created: 2012-08-21 Last updated: 2017-12-07
    6. Improving 3GPP-LTE Uplink Control Signaling by Repetition Across Frequency Bands
    Open this publication in new window or tab >>Improving 3GPP-LTE Uplink Control Signaling by Repetition Across Frequency Bands
    2013 (English)In: Proceedings of the IEEE International Conference on Communications (ICC), IEEE , 2013, p. 1243-1248Conference paper, Published paper (Refereed)
    Abstract [en]

    We propose improvements for the physical uplink control channel (PUCCH) format 2 control signaling in 3GPP-LTE systems. These improvements can be useful for low-cost UE design and optimization planned for the future LTE releases. In the proposed method, instead of repeating a single QPSK symbol across the 12 subcarriers in each OFDM symbol of a resource block as done in the current release of the standard, we pick two QPSK symbols from two independent resource blocks and repeat them across 6 subcarriers each. The proposed method has a performance gain of about 5.5 dB and 1.85 dB over the conventional method with one and two receiving antennas at the base station, respectively. These gains can be achieved without the use of any additional transmission power, time-frequency resources or receiver complexity.

    The cell-specific QPSK sequences specified in the standard for PUCCH transmission are chosen according to the conventional repetition across the 12 subcarriers, hence we suggest new cell-specific QPSK sequences which minimize the peak-to-average-power ratio (PAPR) of the PUCCH signal with the proposed method.

    Place, publisher, year, edition, pages
    IEEE, 2013
    Keywords
    3GPP-LTE, uplink, control signaling, PUCCH
    National Category
    Communication Systems Telecommunications
    Identifiers
    urn:nbn:se:liu:diva-89654 (URN)10.1109/ICCW.2013.6649427 (DOI)978-146735753-1 (ISBN)
    Conference
    IEEE International Conference on Communications (ICC 2013), 9-13 June 2013, Budapest, Hungary
    Funder
    VinnovaeLLIIT - The Linköping‐Lund Initiative on IT and Mobile Communications
    Available from: 2013-04-03 Created: 2013-02-28 Last updated: 2016-08-31Bibliographically approved
    7. Constant envelope signal space diversity
    Open this publication in new window or tab >>Constant envelope signal space diversity
    2014 (English)In: Proceedings of the 2014 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP), IEEE conference proceedings, 2014, p. 3147-3151Conference paper, Published paper (Refereed)
    Abstract [en]

    We propose a nonlinear signal space diversity (SSD) precoding techniquethat produces transmit signals that have constant envelope(CE) in discrete time, resulting in low peak-to-average power ratio(PAPR) waveforms after pulse-shape filtering. We propose twomethods for construction of CE signal set. While the proposed CESSDscheme is inferior to the conventional SSD designs in termsof coding gain performance, it performs better in terms of overallpower efficiency because of the reduced back-off requirement of thepower amplifier (PA).

    Place, publisher, year, edition, pages
    IEEE conference proceedings, 2014
    Series
    IEEE International Conference on Acoustics, Speech and Signal Processing. Proceedings, ISSN 1520-6149
    Keywords
    Signal space diversity, constant envelope, constellation design, power amplifier efficiency, low PAPR
    National Category
    Communication Systems
    Identifiers
    urn:nbn:se:liu:diva-109639 (URN)10.1109/ICASSP.2014.6854180 (DOI)000343655303036 ()
    Conference
    Acoustics, Speech and Signal Processing (ICASSP), 2014 IEEE International Conference on
    Note

    The previous status of this article was Manuscript.

    Available from: 2014-08-22 Created: 2014-08-22 Last updated: 2017-01-13Bibliographically approved
    8. Bits-to-Symbol Mappings for Superposition Coding Based HARQ Systems
    Open this publication in new window or tab >>Bits-to-Symbol Mappings for Superposition Coding Based HARQ Systems
    2013 (English)In: Proceedings of the IEEE Wireless Communications and Networking Conference (WCNC), Institute of Electrical and Electronics Engineers (IEEE), 2013, p. 2468-2472Conference paper, Published paper (Refereed)
    Abstract [en]

    We consider the mapping of bits-to-superimposed constellation symbols in terms of the achievable rate on the channel for the HARQ system using superposition coding as proposed in [2]. We show that using a Gray mapping of bits-to-superimposed constellation symbols has better performance thanthe conventional natural mapping that results from superposition in signal space, for all the values of the superposition ratio. We also show through link-level simulations that the predicted gains in terms of achievable rate can be realized in practice using LDPC codes. Furthermore, we show that the optimal superposition ratio for the Gray mapping case results in conventional higher order constellation symbols after the superposition operation.

    Place, publisher, year, edition, pages
    Institute of Electrical and Electronics Engineers (IEEE), 2013
    Series
    IEEE Wireless Communications and Networking Conference. Proceedings, ISSN 1525-3511
    Keywords
    Superposition coding, bits-to-symbol mapping, hybrid ARQ
    National Category
    Communication Systems
    Identifiers
    urn:nbn:se:liu:diva-87279 (URN)10.1109/WCNC.2013.6554948 (DOI)978-1-4673-5938-2 (ISBN)978-1-4673-5937-5 (ISBN)
    Conference
    IEEE Wireless Communications and Networking Conference, WCNC 2013, 7-10 April, Shanghai; China
    Note

    The previous status of this article was Manuscript and the working title was Bits-to-Symbol Mappings for Superposition Coding.

    Available from: 2013-04-03 Created: 2013-01-15 Last updated: 2017-01-13Bibliographically approved
  • 542.
    Tumula V. K., Chaitanya
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Larsson, Erik G
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Bits-to-Symbol Mappings for Superposition Coding Based HARQ Systems2013In: Proceedings of the IEEE Wireless Communications and Networking Conference (WCNC), Institute of Electrical and Electronics Engineers (IEEE), 2013, p. 2468-2472Conference paper (Refereed)
    Abstract [en]

    We consider the mapping of bits-to-superimposed constellation symbols in terms of the achievable rate on the channel for the HARQ system using superposition coding as proposed in [2]. We show that using a Gray mapping of bits-to-superimposed constellation symbols has better performance thanthe conventional natural mapping that results from superposition in signal space, for all the values of the superposition ratio. We also show through link-level simulations that the predicted gains in terms of achievable rate can be realized in practice using LDPC codes. Furthermore, we show that the optimal superposition ratio for the Gray mapping case results in conventional higher order constellation symbols after the superposition operation.

  • 543.
    Tumula V. K., Chaitanya
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Optimal Resource Allocation for IR-HARQ2011In: Proceedings of the IEEE Swe-CTW, 2011, p. 74-79Conference paper (Refereed)
    Abstract [en]

    In this work, we first provide an exact closed-form expression for the packet drop probability (PDP) in incremental redundancy (IR) based hybrid automatic repeat request (HARQ) schemes with a limit on the maximum number of transmissions. In the later part, we extend our work in [5], and consider the optimal resource allocation problem of minimizing the PDP under the constraints of an average transmit power and total number of channel uses. We provide two approaches to solve this optimization problem and compare their performance with the solution given in [5].

  • 544.
    Tumula V. K., Chaitanya
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Outage-Optimal Power Allocation for Hybrid ARQ with Incremental Redundancy2011In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 10, no 7, p. 2069-2074Article in journal (Refereed)
    Abstract [en]

    We consider the optimization of power in incremental redundancy (IR) based hybrid automatic repeat request (HARQ) schemes when the maximum number of(re)transmissions is fixed. We formulate two optimization problems:(i) minimizing the packet drop probability (PDP) undera total average transmit power constraint, and (ii) minimizingthe average transmit power under a fixed PDP constraint.We consider in detail the special case of only two allowed transmissions, and we prove that the two optimization problems are equivalent. For this special case, we also provide a sub-optimal root- finding solution and compare its performance with the optimal solution obtained through an exhaustive search.The results show that the optimal power allocation can provide significant gains over the equal power solution in terms of average transmit power spent. The performance of the proposed root-finding solution is practically the same as that of the optimal solution.

  • 545.
    Tumula V. K., Chaitanya
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Retransmission Strategies for Symmetric Relaying Using Superposition Modulation2010In: Proceedings of the IEEE 72nd Vehicular Technology Conference Fall (VTC 2010-Fall), Piscataway, NJ, United States: IEEE , 2010, p. 1-5Conference paper (Refereed)
    Abstract [en]

    In this paper, we study retransmission strategies for the symmetric relaying scenario when the number of retransmissions for a data packet is limited. We propose a retransmission scheme based on superposition modulation and give the exact packet drop probability expression for it when only one retransmission is allowed. We compare the performance of the proposed retransmission scheme with retransmission schemes based on classical decode-and-forward (DF) relaying and non-cooperative transmission. When only two retransmissions are allowed, the proposed scheme has a performance gain of 3 dB in SNR over the retransmission scheme based on classical DF relaying. Through simulations, we also study the effect of varying the superposition ratio for the retransmissions.

  • 546.
    Tumula V. K., Chaitanya
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Superposition Modulation Based Symmetric Relaying with Hybrid ARQ: Analysis and Optimization2011In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 60, no 8, p. 3667-3683Article in journal (Refereed)
    Abstract [en]

    We present a retransmission scheme based on superposition modulation for the symmetric relaying scenario when the number of retransmissions for a data packet is limited. We consider both diversity combining based as well as code combining based retransmission schemes. Under the assumption that the receiver implements a mechanism that can use all accumulated received mutual information when decoding the message, we derive the packet error probability (PEP) expressions for the proposed retransmission scheme for the case when only one retransmission is allowed. Based on the PEP expressions derived, we provide a closed-form solution for the optimal superposition ratio (the fraction of power used for the relaying operation). Simulation results show that the proposed retransmission scheme offers significant gains compared to a retransmission scheme based on classical decode-and-forward (DF) relaying.

  • 547.
    Tumula V. K., Chaitanya
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Wiberg, Niclas
    Ericsson Research.
    Improved Error Protection for Uplink Control Signaling in 3GPP-LTE via Complex-Field Coding2010In: Proceedings of the IEEE Vehicular Technology Conference (VTC), 2010Conference paper (Refereed)
    Abstract [en]

    We study the uplink control signaling in 3GPP-Long Term Evolution (LTE) systems. Specifically, we propose a precoding method that uses complex-field coding (CFC) to improve the performance of the PUCCH format 2 control signaling. In the case of perfect channel state information (CSI) at the receiver and with a single receive antenna, the proposed method offers significant gains compared to the coding currently used in 3GPP-LTE. However the gains are marginal with two receive antennas. In order to examine the impact of channel estimation errors, we also derive the optimal detector for the case of imperfect receiver CSI, both for conventional coding and for the proposed CFC method.

  • 548.
    Tumula V.K., Chaitanya
    et al.
    McGill Univ., Canada.
    Danev, Danyo
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Larsson, Erik G
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Constant envelope signal space diversity2014In: Proceedings of the 2014 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP), IEEE conference proceedings, 2014, p. 3147-3151Conference paper (Refereed)
    Abstract [en]

    We propose a nonlinear signal space diversity (SSD) precoding techniquethat produces transmit signals that have constant envelope(CE) in discrete time, resulting in low peak-to-average power ratio(PAPR) waveforms after pulse-shape filtering. We propose twomethods for construction of CE signal set. While the proposed CESSDscheme is inferior to the conventional SSD designs in termsof coding gain performance, it performs better in terms of overallpower efficiency because of the reduced back-off requirement of thepower amplifier (PA).

  • 549.
    Valverde Martínez, David
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems.
    Parada Otte, Francisco Javier
    Linköping University, Department of Electrical Engineering, Communication Systems.
    Forward Error Correction for Packet Switched Networks2008Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The main goal in this thesis is to select and test Forward Error Correction (FEC) schemes suitable for network video transmission over RTP/UDP. There is a general concern in communication networks which is to achieve a tradeoff between reliable transmission and the delay that it takes. Our purpose is to look for techniques that improve the reliability while the realtime delay constraints are fulfilled. In order to achieve it, the FEC techniques focus on recovering the packet losses that come up along any transmission. The FEC schemes that we have selected are Parity Check algorithm, ReedSolomon (RS) codes and a Convolutional code. Simulations are performed to test the different schemes.

    The results obtained show that the RS codes are the more powerful schemes in terms of recovery capabilities. However they can not be deployed for every configuration since they go beyond the delay threshold. On the other hand, despite of the Parity Check codes being the less efficient in terms of error recovery, they show a reasonable low delay. Therefore, depending on the packet loss probability that we are working with, we may chose one or other of the different schemes. To summarize, this thesis includes a theoretical background, a thorough analysis of the FEC schemes chosen, simulation results, conclusions and proposed future work.

  • 550.
    van Chien, Trinh
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Resource Allocation for Max-Min Fairness in Multi-Cell Massive MIMO2017Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Massive MIMO (multiple-input multiple-output) is considered as an heir of the multi-user MIMO technology and it has recently gained lots of attention from both academia and industry. By equipping base stations (BSs) with hundreds of antennas, this new technology can provide very large multiplexing gains by serving many users on the same time-frequency resources and thereby bring significant improvements in spectral efficiency (SE) and energy efficiency (EE) over the current wireless networks. The transmit power, pilot training, and spatial transmission resources need to be allocated properly to the users to achieve the highest possible performance. This is called resource allocation and can be formulated as design utility optimization problems. If the resource allocation in Massive MIMO is optimized, the technology can handle the exponential growth in both wireless data traffic and number of wireless devices, which cannot be done by the current cellular network technology.

    In this thesis, we focus on two resource allocation aspects in Massive MIMO: The first part of the thesis studies if power control and advanced coordinated multipoint (CoMP) techniques are able to bring substantial gains to multi-cell Massive MIMO systems compared to the systems without using CoMP. More specifically, we consider a network topology with no cell boundary where the BSs can collaborate to serve the users in the considered coverage area. We focus on a downlink (DL) scenario in which each BS transmits different data signals to each user. This scenario does not require phase synchronization between BSs and therefore has the same backhaul requirements as conventional Massive MIMO systems, where each user is preassigned to only one BS. The scenario where all BSs are phase synchronized to send the same data is also included for comparison. We solve a total transmit power minimization problem in order to observe how much power Massive MIMO BSs consume to provide the requested quality of service (QoS) of each user. A max-min fairness optimization is also solved to provide every user with the same maximum QoS regardless of the propagation conditions.

    The second part of the thesis considers a joint pilot design and uplink (UL) power control problem in multi-cell Massive MIMO. The main motivation for this work is that the pilot assignment and pilot power allocation is momentous in Massive MIMO since the BSs are supposed to construct linear detection and precoding vectors from the channel estimates. Pilot contamination between pilot-sharing users leads to more interference during data transmission. The pilot design is more difficult if the pilot signals are reused frequently in space, as in Massive MIMO, which leads to greater pilot contamination effects. Related works have only studied either the pilot assignment or the pilot power control, but not the joint optimization. Furthermore, the pilot assignment is usually formulated as a combinatorial problem leading to prohibitive computational complexity. Therefore, in the second part of this thesis, a new pilot design is proposed to overcome such challenges by treating the pilot signals as continuous optimization variables. We use those pilot signals to solve different max-min fairness optimization problems with either ideal hardware or hardware impairments.

    List of papers
    1. Joint Power Allocation and User Association Optimization for Massive MIMO Systems
    Open this publication in new window or tab >>Joint Power Allocation and User Association Optimization for Massive MIMO Systems
    2016 (English)In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 15, no 9, p. 6384-6399Article in journal (Refereed) Published
    Abstract [en]

    This paper investigates the joint power allocationand user association problem in multi-cell Massive MIMO(multiple-input multiple-output) downlink (DL) systems. Thetarget is to minimize the total transmit power consumptionwhen each user is served by an optimized subset of the basestations (BSs), using non-coherent joint transmission. We firstderive a lower bound on the ergodic spectral efficiency (SE),which is applicable for any channel distribution and precodingscheme. Closed-form expressions are obtained for Rayleigh fadingchannels with either maximum ratio transmission (MRT) or zeroforcing (ZF) precoding. From these bounds, we further formulatethe DL power minimization problems with fixed SE constraintsfor the users. These problems are proved to be solvable aslinear programs, giving the optimal power allocation and BS-user association with low complexity. Furthermore, we formulatea max-min fairness problem which maximizes the worst SEamong the users, and we show that it can be solved as aquasi-linear program. Simulations manifest that the proposedmethods provide good SE for the users using less transmit powerthan in small-scale systems and the optimal user associationcan effectively balance the load between BSs when needed.Even though our framework allows the joint transmission frommultiple BSs, there is an overwhelming probability that only oneBS is associated with each user at the optimal solution.

    Place, publisher, year, edition, pages
    Institute of Electrical and Electronics Engineers (IEEE), 2016
    Keywords
    Massive MIMO, user association, power allocation, load balancing, linear program
    National Category
    Communication Systems
    Identifiers
    urn:nbn:se:liu:diva-131129 (URN)10.1109/TWC.2016.2583436 (DOI)000384241400040 ()
    Funder
    ELLIIT - The Linköping‐Lund Initiative on IT and Mobile Communications
    Available from: 2016-09-11 Created: 2016-09-11 Last updated: 2019-12-09Bibliographically approved
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