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  • 151.
    Fahlborg, Daniel
    Linköping University, Department of Electrical Engineering, Communication Systems.
    Measuring one-way Packet Delay in a Radio Network2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Radio networks are expanding, becoming more advanced, and pushing the limits of what is possible. Services utilizing the radio networks are also being developed in order to provide new functionality to end-users worldwide. When discussing 5G radio networks, concepts such as driverless vehicles, drones and near zero communication delay are recurrent. However, measures of delay are needed in order to verify that such services can be provided -- and measuring this is an extensive task. Ericsson has developed a platform for simulating a radio environment surrounding a radio base station. Using this simulator, this project involved measuring one-way packet delay in a radio network, and performing a Quality of Service evaluation of a radio network with a number of network applications in concern. Application data corresponding to video streams, or Voice over IP conversations, were simulated and packet delay measurements were used to calculate and evaluate the Quality of Service provided by a radio network. One of the main conclusions of this project was that packet delay variations are asymmetric in uplink, which suggests usage of non-conventional jitter measurement techniques.

  • 152.
    Fan, Wen
    et al.
    Beijing Jiaotong Univ, Peoples R China.
    Zhang, Jiayi
    Beijing Jiaotong Univ, Peoples R China.
    Björnson, Emil
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Chen, Shuaifei
    Beijing Jiaotong Univ, Peoples R China.
    Zhong, Zhangdui
    Beijing Jiaotong Univ, Peoples R China.
    Performance Analysis of Cell-Free Massive MIMO Over Spatially Correlated Fading Channels2019In: ICC 2019 - 2019 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS (ICC), IEEE , 2019Conference paper (Refereed)
    Abstract [en]

    Cell-free massive multiple-input multiple-output (MIMO) is a promising network architecture for future wireless systems. This paper investigates the uplink performance of cell-free massive MIMO systems employing the least-square (LS) estimator over spatially correlated fading channels. We first derive a generalized closed-form expression of the spectral efficiency as a function of the number of access point (AP) antennas and the spatial correlation matrices. We use this result to analyze the impact that the fronthaul, number of users and number of APs have on the energy efficiency. Compared to traditional colocated massive MIMO using maximum ratio combining (MRC), our analysis shows that the large performance gain of cell-free massive MIMO with low-complexity linear LS estimators.

  • 153.
    Fathi, Mohammad
    et al.
    University of Kurdistan, Iran .
    Karipidis, Eleftherios
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Distributed allocation of subcarrier, power and bit-level in multicell orthogonal frequency-division multiple-access networks2014In: IET COMMUNICATIONS, ISSN 1751-8628, Vol. 8, no 6, p. 781-788Article in journal (Refereed)
    Abstract [en]

    The downlink of multicell orthogonal frequency-division multiple-access (OFDMA) networks is studied, and the adaptive allocation of spectrum, power and rate is addressed. The authors consider networks with adaptive frequency reuse and discrete-level rates. Initially, the joint allocation problem is formulated as a centralised non-linear mixed-integer program (MIP), which is computationally intractable to solve optimally for practical problem sizes. Then, the capability of the receivers is exploited to estimate the subcarrier channel gains and the joint allocation problem is accordingly decomposed into subproblems, each of which is solved by a different base station with linear complexity. In the proposed iterative algorithm, the base stations perform rate and receiver allocation per subcarrier, with concurrent iterations. A filtering method is introduced to further decrease the algorithm complexity. Furthermore, for benchmarking purposes, the authors transform the original non-linear MIP to a linear MIP and find the optimal solution by means of standard branch-and-cut solvers. The merit of the proposed algorithm is demonstrated with numerical comparisons of its performance against the solutions of the linear MIP and the iterative waterfilling algorithm.

  • 154.
    Fathi, Mohammad
    et al.
    University of Kurdistan.
    Karipidis, Eleftherios
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Distributed Resource Optimization in Multicell OFDMA Networks2012In: Proceedings of the IEEE Wireless Communications and Networking Conference (WCNC), IEEE , 2012, p. 1316-1320Conference paper (Refereed)
    Abstract [en]

    We consider the joint allocation of receiver, bit, and power to subcarriers in the downlink of multicell orthogonal frequency-division multiple-access (OFDMA) networks. Assuming that the cells share the entire bandwidth and that the rates are discrete, we formulate the joint allocation problem as a nonlinear mixed integer program (MIP), which however has exponential worst-case complexity. We capitalize on the capability of the receivers to measure the interference-plus-noise on every subcarrier and decompose the joint problem into a set of smaller-scale linear MIPs solved by individual base stations. Accordingly, we propose a distributed algorithm with linear complexity, in which the base stations participate in the problem solution in a round-robin manner. Simulation results demonstrate the effectiveness of the proposed algorithm in comparison with the iterative waterfilling algorithm and the successive optimal solution, by means of standard branch-and-cut solvers, of the individual MIPs.

  • 155.
    Faxén, Linnea
    Linköping University, Department of Electrical Engineering, Communication Systems.
    A Study on Segmentation for Ultra-Reliable Low-Latency Communications2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    To enable wireless control of factories, such that sensor measurements can be sent wirelessly to an actuator, the probability to receive data correctly must be very high and the time it takes to the deliver the data from the sensor to the actuator must be very low. Earlier, these requirements have only been met by cables, but in the fifth generation mobile network this is one of the imagined use cases and work is undergoing to create a system capable of wireless control of factories. One of the problems in this scenario is when all data in a packet cannot be sent in one transmission while ensuring the very high probability of reception of the transmission. This thesis studies this problem in detail by proposing methods to cope with the problem and evaluating these methods in a simulator. The thesis shows that splitting the data into multiple segments and transmitting each at an even higher probability of reception is a good candidate, especially when there is time for a retransmission. When there is only one transmission available, a better candidate is to send the same packet twice. Even if the first packet cannot achieve the very high probability of reception, the combination of the first and second packet might be able to.

  • 156.
    Faxér, Sebastian
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Self-optimization of Antenna Sectorization2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Sectorization is a well-established method of increasing the capacity of telecommunicationnetworks. With modern Active Antenna Systems (AAS) comes the abilityto change sectorization order dynamically, both in horizontal and vertical plane.The purpose of this thesis is to investigate when (and what type of) sectorizationis benficial. A theoretical analysis as well as simulations are performed in orderto determine which quantities to look at when making the decision to apply sectorization.Based on the conclusions from these investigations, a self-optimizingalgorithm that only turns on sectorization when it increases network performanceis developed and evaluated. It is shown that large gains can be achieved by onlyturning on sectorization when the right conditions are met. Further, we show thatadditional gains can be seen if antenna parameters such as downtilt and distributionof transmission power between sectors are set properly. Self-optimizingalgorithms for tuning of these parameters are developed and evaluated as well.NyckelordKeywords

  • 157.
    Fayad, Adel
    Linköping University, Department of Electrical Engineering, Communication Systems.
    Analysis and Compensationfor Clipping-like Distortion of the Transmitted Signal in Massive MIMO Systems2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This project consists of analyzing and finding solutions to the effect of non-linear distortionon the performance of a Massive Multiple Input Multiple Output (MIMO) system interms of Spectral Efficiency (SE) and Symbol Error Rate (SER). Massive MIMO is one ofthe technologies that are considered the backbone of the 5th generation of wireless communicationsand therefore this technology has gathered much interest from researchersand companies alike [19], as it is proven that this kind of system greatly improves thecapacity of the wireless connection [8]. Since Massive MIMO is still a relatively newtechnology and it is yet to be implemented for commercial use, there are several challengesthat arise when trying to implement such a system. One of these problems arisefrom the fact that the Power Amplifiers (PAs) in the transmitters of Massive MIMO systemsare non-linear and thus impose a distortion on the transmitted signals of the system[12]. The thesis aims to study this non-linear effect on the performance of massive MIMOsystems by first modelling the distortion effect on the transmitted signals using two differentnon-linear models. Moreover, closed-form expressions for one of the models areformed to facilitate the simulation of the non-linear model and facilitate the analysis ofthe distortion effect on the performance metrics. Then the established system model issimulated and based on the results, the effect of each of the power amplifier non-lineardistortion models on the performance metrics of the Massive MIMO system is studied.Furthermore, based on the analysis of the simulation results, a compensation mechanismis introduced to the Massive MIMO system in order to mitigate the distortion effect onthe system performance in terms of SER and SE.

  • 158.
    Ferm, Gabriella
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems.
    Jarledal, Jonas
    Linköping University, Department of Electrical Engineering.
    Abis over IP Modelling and Characteristics2009Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In todays GSM network more and more interfaces are run over IP instead of classic synchronized networks. This rises new issues to be solved, for example handling of jitter that use of IP networks introduces. The jitter can be handled by a jitter buffer which ensures that the packets are forwarded in evenly spaced intervals.

    In GSM, data is requested a certain time in advance before delivery to a cellphone. This "time in advance" needs to be adjusted according to the delay of the channel. For an IP network this delay varies (jitter), which means that it would be beneficial to have an algorithm which continuously adjusts how long in advance the packets should be requested. The adjustment is made according to current channel delay and jitter size.

    In this thesis work a model of a general IP network has been developed and isthen used for development of two algorithms for jitter buffer handling. Once the algorithms have been developed they are evaluated and compared to each other and previous solutions to the problem. One of the algorithms is new and the other is an already existing algorithm that has been extended.

    The simplified conclusion is that the behaviors of both algorithms are very similar. They mainly have small packet loss but sometimes the packets are requested earlier than needed and therefore are kept in the buffer a bit longer than necessary. When comparing the two developed algorithms with previous solutions it is visible that they improve the buffer handling a great deal.

  • 159.
    Ferrer-Coll, J
    et al.
    University of Gavle, Sweden .
    Angskog, P
    University of Gavle, Sweden .
    Chilo, J
    University of Gavle, Sweden .
    Stenumgaard, P
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Characterisation of highly absorbent and highly reflective radio wave propagation environments in industrial applications2012In: IET COMMUNICATIONS, ISSN 1751-8628, Vol. 6, no 15, p. 2404-2412Article in journal (Refereed)
    Abstract [en]

    Experience has shown that Bluetooth, Wireless LAN (WLAN), Digital Enhanced Cordless Telecommunications (DECT) and other Industrial, Scientific and Medical (ISM) frequency band wireless technologies developed for office use, have encountered problems when used in critical industrial applications. The development of more reliable wireless solutions requires extensive knowledge of industrial environments with regards to both electromagnetic interference and wave propagation. This study presents the results of the analysis of two important classes of industrial environments having opposite characteristics, one being highly absorbent and the other being highly reflective, with respect to radio wave propagation. The analysis comprises both multipath and path loss characterisation. The results show that wireless solutions with different fundamental properties must be chosen for each of these environments to ensure high reliability. The conclusions of this work can be used as an important reference for further research in this area, as well as the design of new standards and guidelines for selecting wireless solutions in similar industrial environment classes.

  • 160.
    Ferrer-Coll, Javier
    et al.
    University of Gavle, Sweden; KTH Royal Institute Technology, Sweden.
    Ben Slimane, Slimane
    KTH Royal Institute Technology, Sweden.
    Chilo, Jose
    University of Gavle, Sweden.
    Stenumgaard, Peter
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology. Swedish Def Research Agency, Sweden.
    Detection and Suppression of Impulsive Noise in OFDM Receiver2015In: Wireless personal communications, ISSN 0929-6212, E-ISSN 1572-834X, Vol. 85, no 4, p. 2245-2259Article in journal (Refereed)
    Abstract [en]

    In recent years, the use of wireless systems in industrial applications has experienced spectacular growth. Unfortunately, industrial environments often present impulsive noise which degrades the reliability of wireless systems. OFDM is an enhanced technology used in industrial communication to monitor the work and movement of employees using high quality video. However, OFDM is sensitive to high amplitude impulsive noise because the noise energy spreads among all OFDM sub-carriers. This paper proposes a receiver structure consisting of two stages: a detector stage combining Fishers Quadratic discriminant and Gaussian Hypothesis techniques, and a suppression stage optimized by setting well defined thresholds. The receiver structure has been tested by simulations and measurements providing an increment in the probability of detection and improving the system performance.

  • 161.
    Ferrer-Coll, Javier
    et al.
    Högskolan i Gävle.
    Ängskog, Per
    Högskolan i Gävle.
    Chilo, José
    Högskolan i Gävle.
    Stenumgaard, Peter
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Characterization of Electromagnetic Properties in Iron-Mine Production Tunnels2012In: Electronics Letters, ISSN 0013-5194, E-ISSN 1350-911X, Vol. 48, no 2, p. 62-63Article in journal (Refereed)
    Abstract [en]

    Modern underground mines require reliable wireless communication for transmitting voice data, operating surveillance cameras, and monitoring mining equipment such as heavy vehicles. The electromagnetic characteristics of mines therefore have to be considered when determining the type of wireless technology for such critical applications. In this reported work, measurements of radio interference levels, path loss, and multipath propagation are performed in the world's now largest iron ore mine, situated in Sweden, to determine a suitable wireless technology for this mine.

  • 162.
    Ferrer-Coll, Javier
    et al.
    Högskolan i Gävle.
    Ängskog, Per
    Högskolan i Gävle.
    Elofsson, Carl
    Radiobuster, Stockholm, Sweden .
    Chilo, José
    Högskolan i Gävle.
    Stenumgaard, Peter
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Antenna Cross Correlation and Ricean K -Factor Measurements in Indoor Industrial Environments at 433 and 868 MHz2013In: Wireless personal communications, ISSN 0929-6212, E-ISSN 1572-834X, Vol. 73, no 3, p. 587-593Article in journal (Refereed)
    Abstract [en]

    The Ricean K-factor and antenna diversity properties for indoor industrial environments have been characterized for 433 and 868 MHz. The high amount of metallic structures gives a multipath environment that heavily differs from other environments e.g. indoor office environments. The results show that low correlation between receiving antennas can be achieved for shorter antenna distances than in other environments.

  • 163.
    Ferrer-Coll, Javier
    et al.
    Högskolan i Gävle.
    Ängskog, Per
    Högskolan i Gävle.
    Shabai, He
    Högskolan i Gävle.
    Chilo, José
    Högskolan i Gävle.
    Stenumgaard, Peter
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Analysis of Wireless Communications in Underground Tunnels for Industrial Use2012Conference paper (Other academic)
    Abstract [en]

    Wireless communication is expected to improve the safety and the productivity in underground tunnels for industrial use. However the multiple shapes and structures of tunnels affect wireless communication characteristics in terms of signal propagation which is significantly different from terrestrial environments. This paper presents comprehensive broadband measurements and simulations of multipath propagation and path loss in two underground environments. The results can be used in the development of new communication systems in tunnels that provide industrial services.

  • 164.
    Flordelis, Jose
    et al.
    Lund Univ, Sweden.
    Rusek, Fredrik
    Lund Univ, Sweden.
    Tufvesson, Fredrik
    Lund Univ, Sweden.
    Larsson, Erik G
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Edfors, Ove
    Lund Univ, Sweden.
    Massive MIMO Performance-TDD Versus FDD: What Do Measurements Say?2018In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 17, no 4, p. 2247-2261Article in journal (Refereed)
    Abstract [en]

    Downlink beamforming in Massive multiple-input and multiple-output (MIMO) either relies on uplink pilot measurements-exploiting reciprocity and time-division duplexing operation, or on the use of a predetermined grid of beams with user equipments reporting their preferred beams, mostly in frequency-division duplexing operation. Massive MIMO in its originally conceived form uses the first strategy, with uplink pilots, whereas there is currently significant commercial interest in the second, grid-of-beams. It has been analytically shown that with isotropic scattering (independent Rayleigh fading) the first approach outperforms the second. Nevertheless, there remains controversy regarding their relative performance in practical channels. In this contribution, the performances of these two strategies are compared using measured channel data at 2.6 GHz.

  • 165.
    Fors, Karina
    et al.
    Swedish Defence Research Agency (FOI), Linköping, Sweden .
    Wiklundh, Kia
    Swedish Defence Research Agency (FOI), Linköping, Sweden .
    Stenumgaard, Peter
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    A simple measurement method to derive the impulsiveness correction factor for communication performance estimation2013In: IEEE transactions on electromagnetic compatibility (Print), ISSN 0018-9375, E-ISSN 1558-187X, Vol. 55, no 5, p. 834-841Article in journal (Refereed)
    Abstract [en]

    Today, no simple methods are available for measurements of interference signals that give a proper indication of the impact in terms of the bit error probability (BEP) on a digital radio receiver. Such measure should quantify the corresponding impact and the measurements should be relatively easy to perform. By only using the root mean square (RMS) value of the interference average power the BEP can be underestimated with several magnitudes. To address this problem, an impulsiveness correction factor (ICF) has earlier been proposed to adjust for these errors. The ICF opens up for considerably more accurate BEP estimations whereas the simplicity in the calculations is maintained. However, how to determine the ICF for an arbitrary interference source through measurements has not earlier been known. In this paper, we show that the ICF can be obtained in two alternative ways. One way is to use the measured amplitude probability distribution (APD). The other way is to use the peak- and RMS values from standard measurement detectors. Both methods take the interference waveform properties into consideration and the BEP can thus be more accurately estimated.

  • 166.
    Fozooni, Milad
    et al.
    Queen's University of Belfast, North Ireland, UK.
    Matthaiou, Michail
    Queen's University of Belfast, North Ireland, UK.
    Björnson, Emil
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Duong, Trung Q.
    Queen's University of Belfast, North Ireland, UK.
    Performance Limits of MIMO Systems with Nonlinear Power Amplifiers2015In: 2015 IEEE GLOBAL COMMUNICATIONS CONFERENCE (GLOBECOM), Institute of Electrical and Electronics Engineers (IEEE), 2015Conference paper (Refereed)
  • 167.
    Frostensson, Tomas
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Hardware Implementation and Assessment of a Soft MIMO Detector Based On SUMIS2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    To allow faster and more reliable wireless communication a technique is to use multiple antennas in the transmitter and receiver. This technique is called MIMO. The usage of MIMO adds complexity to the receiver that must determine what the transmitter actually sent. This thesis focuses on hardware implementation suitable for an FPGA of a detection algorithm called SUMIS.

    A background to detection and SUMIS in particular is given as a theoretical aid for a better understanding of how an algorithm like this can be implemented. An introduction to hardware and digital design is also presented.

    A subset of the operations in the SUMIS algorithm such as matrix inversion and sum of logarithmic values are analyzed and suitable hardware architectures are presented. These operations are implemented in RTL hardware using VHDL targeted for an FPGA, Virtex-6 from Xilinx.

    The accuracy of the implemented operations is investigated showing promising results alongside of a presentation of the necessary resource usage.

    Finally other approaches to hardware implementation of detection algorithms are discussed and more suitable approaches for a future implementation of SUMIS are commented on. The key aspects are flexibility through software reprogrammability and area efficiency by designing a custom processor architecture. 

  • 168.
    Gabry, Frédéric
    et al.
    Royal Institute of Technology (KTH), Stockholm, Sweden.
    Li, Nan
    Royal Institute of Technology (KTH), Stockholm, Sweden.
    Schrammar, Nicolas
    Royal Institute of Technology (KTH), Stockholm, Sweden.
    Girnyk, Maksym
    Royal Institute of Technology (KTH), Stockholm, Sweden.
    Karipidis, Eleftherios
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Thobaben, Ragnar
    Royal Institute of Technology (KTH), Stockholm, Sweden.
    Rasmussen, Lars K.
    Royal Institute of Technology (KTH), Stockholm, Sweden.
    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, Sweden.
    Secure Broadcasting in Cooperative Cognitive Radio Networks2012In: Proceedings of the Future Network and Mobile Summit Conference, 2012Conference paper (Refereed)
  • 169.
    Gangula, Rajeev
    et al.
    Institut EURECOM.
    Gesbert, David
    Institut EURECOM.
    Lindblom, Johannes
    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.
    On the Value of Spectrum Sharing among Operators in Multicell Networks2013In: Proceedings of the 77th IEEE Vehicular Technology Conference (VTC'13), IEEE , 2013, p. 1-5Conference paper (Refereed)
    Abstract [en]

    This work considers the benefits of allowing spectrum sharing among co-located wireless service providers operating in the same multicell network. Although spectrum sharing was shown to be valuable in some scenarios where the created interference can be eliminated, the benefits have not clearly shown for multicell networks with aggressive reuse. We explore this question and show that spectrum sharing is preferred for just a certain subset of the users defined by their distance from the serving bases, while beyond this distance, an orthogonal division of resources between operators gives better results. The claims are backed with theoretical analysis matching our simulations.

  • 170.
    Gao, Feifei
    et al.
    Tsinghua Univ, Peoples R China.
    Tian, Zhi
    Geogre Mason Univ, VA 22030 USA.
    Larsson, Erik G
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Pesavento, Marius
    Tech Univ Darmstadt, Germany.
    Jin, Shi
    Southeast Univ, Peoples R China.
    Introduction to the Special Issue on Array Signal Processing for Angular Models in Massive MIMO Communications2019In: IEEE Journal on Selected Topics in Signal Processing, ISSN 1932-4553, E-ISSN 1941-0484, Vol. 13, no 5, p. 882-885Article in journal (Other academic)
    Abstract [en]

    n/a

  • 171.
    Gao, Xiang
    et al.
    Lund University, Sweden.
    Edfors, Ove
    Lund University, Sweden.
    Tufvesson, Fredrik
    Lund University, Sweden.
    Larsson, Erik G
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Massive MIMO in Real Propagation Environments: Do All Antennas Contribute Equally?2015In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 63, no 11, p. 3917-3928Article in journal (Refereed)
    Abstract [en]

    Massive MIMO can greatly increase both spectral and transmit-energy efficiency. This is achieved by allowing the number of antennas and RF chains to grow very large. However, the challenges include high system complexity and hardware energy consumption. Here we investigate the possibilities to reduce the required number of RF chains, by performing antenna selection. While this approach is not a very effective strategy for theoretical independent Rayleigh fading channels, a substantial reduction in the number of RF chains can be achieved for real massive MIMO channels, without significant performance loss. We evaluate antenna selection performance on measured channels at 2.6 GHz, using a linear and a cylindrical array, both having 128 elements. Sum-rate maximization is used as the criterion for antenna selection. A selection scheme based on convex optimization is nearly optimal and used as a benchmark. The achieved sum-rate is compared with that of a very simple scheme that selects the antennas with the highest received power. The power-based scheme gives performance close to the convex optimization scheme, for the measured channels. This observation indicates a potential for significant reductions of massive MIMO implementation complexity, by reducing the number of RF chains and performing antenna selection using simple algorithms.

  • 172.
    Gao, Xiang
    et al.
    Department of Electrical Information and Technology, Lund University, Sweden .
    Edfors, Ove
    Department of Electrical Information and Technology, Lund University, Sweden .
    Tufvesson, Fredrik
    Department of Electrical Information and Technology, Lund University, Sweden .
    Larsson, Erik G
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Multi-switch for antenna selection in massive MIMO2015In: 2015 IEEE Global Communications Conference, GLOBECOM 2015, Institute of Electrical and Electronics Engineers (IEEE), 2015, p. 1-6Conference paper (Refereed)
    Abstract [en]

    Massive MIMO has been shown to greatly improve spectral and transmit-energy efficiency. When implementing a massive MIMO system, one challenge is high hardware complexity. A solution is to reduce the number of radio frequency (RF) transceiver chains by performing antenna selection. However, a full RF switch that connects the antennas and RF chains can be highly complex and incurs significant loss in output signal quality, especially when the number of antennas and RF chains are large. We therefore propose a simpler solution - binary switching architecture, which is suboptimal but provides better signal quality, as compared to the full switching network. To evaluate the proposed technique, we compare the sum-rate capacity when using several different configurations of binary switching with the performance of the full switching. Full MIMO performance obtained without antenna selection is also presented as a reference. The investigations in this paper are all based on measured channel data at 2.6 GHz, using a uniform linear array and a cylindrical array, both having 128 antenna elements. It is found that the proposed binary switching gives very competitive performance that are close to the full switching, for the measured channels. The results indicate a potential to simplify massive MIMO hardware by reducing the number of RF chains, and performing antenna selection with simple binary switching architecture.

  • 173.
    Garcia, Nil
    et al.
    Chalmers, Sweden.
    Wymeersch, Henk
    Chalmers, Sweden.
    Larsson, Erik G
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Haimovich, Alexander M.
    New Jersey Institute Technology, NJ 07102 USA.
    Coulon, Martial
    University of Toulouse, France.
    Direct Localization for Massive MIMO2017In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 65, no 10, p. 2475-2487Article in journal (Refereed)
    Abstract [en]

    Large-scale MIMO systems are well known for their advantages in communications, but they also have the potential for providing very accurate localization, thanks to their high angular resolution. A difficult problem arising indoors and outdoors is localizing users over multipath channels. Localization based on angle of arrival (AOA) generally involves a two-step procedure, where signals are first processed to obtain a users AOA at different base stations, followed by triangulation to determine the users position. In the presence of multipath, the performance of these methods is greatly degraded due to the inability to correctly detect and/or estimate the AOA of the line-of-sight (LOS) paths. To counter the limitations of this two-step procedure which is inherently suboptimal, we propose a direct localization approach in which the position of a user is localized by jointly processing the observations obtained at distributed massive MIMO base stations. Our approach is based on a novel compressed sensing framework that exploits channel properties to distinguish LOS from non-LOS signal paths, and leads to improved performance results compared to previous existing methods.

  • 174.
    Geraci, Giovanni
    et al.
    Universitat Pompeu Fabra, Barcelona, Spain.
    Garcia-Rodriguez, Adrian
    Nokia Bell Labs, Dublin, Ireland.
    Galati Giordano, Lorenzo
    Nokia Bell Labs, Dublin, Ireland.
    Lopez-Perez, David
    Nokia Bell Labs, Dublin, Ireland.
    Björnson, Emil
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Understanding UAV Cellular Communications: From Existing Networks to Massive MIMO2018In: IEEE Access, E-ISSN 2169-3536, Vol. 6, no 1, p. 67853-67865Article in journal (Refereed)
    Abstract [en]

    The purpose of this paper is to bestow the reader with a timely study of UAV cellular communications, bridging the gap between the 3GPP standardization status quo and the more forward-looking research. Special emphasis is placed on the downlink command and control (C&C) channel to aerial users, whose reliability is deemed of paramount technological importance for the commercial success of UAV cellular communications. Through a realistic side-by-side comparison of two network deployments – a present-day cellular infrastructure versus a next-generation massive MIMO system – a plurality of key facts are cast light upon, with the three main ones summarized as follows: 1) UAV cell selection is essentially driven by the secondary lobes of a base station’s radiation pattern, causing UAVs to associate to far-flung cells; 2) over a 10 MHz bandwidth, and for UAV heights of up to 300 m, massive MIMO networks can support 100 kbps C&C channels in 74% of the cases when the uplink pilots for channel estimation are reused among base station sites, and in 96% of the cases without pilot reuse across the network; and 3) supporting UAV C&C channels can considerably affect the performance of ground users on account of severe pilot contamination, unless suitable power control policies are in place.

  • 175.
    Geraci, Giovanni
    et al.
    Nokia Bell Labs, Ireland.
    Garcia-Rodriguez, Adrian
    Nokia Bell Labs, Ireland.
    Giordano, Lorenzo Galati
    Nokia Bell Labs, Ireland.
    Lopez-Perez, David
    Nokia Bell Labs, Ireland.
    Björnson, Emil
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Supporting UAV Cellular Communications through Massive MIMO2018In: 2018 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS WORKSHOPS (ICC WORKSHOPS), IEEE , 2018Conference paper (Refereed)
    Abstract [en]

    In this article, we provide a much-needed study of UAV cellular communications, focusing on the rates achievable for the UAV downlink command and control (Camp;C) channel. For this key performance indicator, we perform a realistic comparison between existing deployments operating in single-user mode and next-generation multi-user massive MIMO systems. We find that in single-user deployments under heavy data traffic, UAVs flying at 50 m, 150 m, and 300 m achieve the Camp;C target rate of 100 kbps - as set by the 3GPP - in a mere 35%, 2%, and 1% of the cases, respectively. Owing to mitigated interference, a stronger carrier signal, and a spatial multiplexing gain, massive MIMO time division duplex systems can dramatically increase such probability. Indeed, we show that for UAV heights up to 300m the target rate is met with massive MIMO in 74% and 96% of the cases with and without uplink pilot reuse for channel state information (CSI) acquisition, respectively. On the other hand, the presence of UAVs can significantly degrade the performance of ground users, whose pilot signals are vulnerable to UAV-generated contamination and require protection through uplink power control.

  • 176.
    Geraci, Giovanni
    et al.
    Univ Pompeu Fabra, Spain.
    Garcia-Rodriguez, Adrian
    Nokia Bell Labs, Ireland.
    Giordano, Lorenzo Galati
    Nokia Bell Labs, Ireland.
    Lopez-Perez, David
    Nokia Bell Labs, Ireland.
    Björnson, Emil
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Unerstanding UAV Cellullar Communications: From Existing Networks to Massive MIMO2018In: IEEE Access, E-ISSN 2169-3536, Vol. 6, p. 67853-67865Article in journal (Refereed)
    Abstract [en]

    The purpose of this paper is to bestow the reader with a timely study of UAV cellular communications, bridging the gap between the 3GPP standardization status quo and the more forward-looking research. Special emphasis is placed on the downlink command and control (Camp;C) channel to aerial users, whose reliability is deemed of paramount technological importance for the commercial success of UAV cellular communications. Through a realistic side-by-side comparison of two network deployments - a present-day cellular infrastructure versus a next-generation massive MIMO system - a plurality of key facts are cast light upon, with the three main ones summarized as follows: 1) UAV cell selection is essentially driven by the secondary lobes of a base stations radiation pattern, causing UAVs to associate to far-flung cells; 2) over a 10 MHz bandwidth, and for UAV heights of up to 300 m, massive MIMO networks can support 100 kbps Camp;C channels in 74% of the cases when the uplink pilots for channel estimation are reused among base station sites, and in 96% of the cases without pilot reuse across the network; and 3) supporting UAV Camp;C channels can considerably affect the performance of ground users on account of severe pilot contamination, unless suitable power control policies are in place.

  • 177.
    Gerdin, Markus
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Parameter Estimation in Linear Descriptor Systems2004Licentiate thesis, monograph (Other academic)
    Abstract [en]

    Linear descriptor systems form the natural way in which linear models of physical systems are delivered from an object-oriented modeling tool like Modelica. Linear descriptor systems are also known as linear differential-algebraic equations in the continuous-time case. If some parameters in such models are unknown, one might need to estimate them from measured data from the modeled system. This is a form of system identification called gray box identification. The objective of t his work is to examine how gray box identification can be performed for linear descriptor systems.

    To solve this problem, we use some well-known canonical forms to examine how to transform the descriptor systems into state-space form. In general, the input must be redefined to make the transformation into statespace form possible. To be able to implement the suggested identification methods, we examine how the transformations can be computed using numerical software from the linear algebra package LAPACK.

    Noise modeling is an important part of parameter estimation and system identification, so we also examine how a noise model can be added to linear descriptor systems. The result is that white noise in general cannot be added to all equations of a linear continuous-time descriptor system, since this could lead to differentiation of the noise which is not well defined. It is also noted that a Kalman filter can be implemented if the model is transformed into state-space form.

    We also discuss the problem of finding initial values for the paramet er search. We show how to formulate a biquadratic polynomial, that gives initial values for the parameter search when minimized.

  • 178.
    Gharavol, Ebrahim
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Erik G., Larsson
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Robust joint optimization of MIMO two-way relay channels with imperfect CSI2011Conference paper (Refereed)
    Abstract [en]

    In this paper we deal with the problem of the joint optimization of the precoders, equalizers and relay beamformer of a multiple-input multiple-output two-way relay channel. Unlike the conventional design procedures, we assume that the Channel State Information (CSI) is not known perfectly. The imperfect CSI is described using the norm bounded error framework. We use a system-wide Sum Mean Square Error (SMSE) based problem formulation which is constrained using the transmit power of the terminals and the relay node. The problem at hand, from a worst-case design perspective, is a multilinear, and hence, a nonconvex problem which is also semi-infinite in its constraints. We use a generalized version of the Peterson's lemma to handle the semi-infiniteness and reduce the original problem to a single Linear Matrix Inequality (LMI). However, this LMI is not convex, and to resolve this issue we propose an iterative algorithm based on the alternating convex search methodology to solve the aforementioned problem. Finally simulation results are included to asses the performance of the proposed algorithm.

  • 179.
    Ghazanfar, Amin
    et al.
    Linköping University, Department of Electrical Engineering. Linköping University, Faculty of Science & Engineering.
    Björnson, Emil
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering. Linköping University, The Institute of Technology.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering. Linköping University, The Institute of Technology.
    Power Control for D2D Underlay in Multi-cell Massive MIMO Networks2018In: ITG-Fb. 276: WSA 2018: 22nd International ITG Workshop on Smart Antennas March 14-16, 2018, Bochum, Germany (CD-ROM), Berlin, Offenbach: VDE Verlag , 2018Conference paper (Refereed)
    Abstract [en]

    This paper proposes a new power control and pilot allocation scheme for device-to-device (D2D) communication underlaying a multi-cell massive MIMO system. In this scheme, the cellular users in each cell get orthogonal pilots which are reused with reuse factor one across cells, while the D2D pairs share another set of orthogonal pilots. We derive a closed-form capacity lower bound for the cellular users with different receive processing schemes. In addition, we derive a capacity lower bound for the D2D receivers and a closed-form approximation of it. Then we provide a power control algorithm that maximizes the minimum spectral efficiency (SE) of the users in the network. Finally, we provide a numerical evaluation where we compare our proposed power control algorithm with the maximum transmit power case and the case of conventional multi-cell massive MIMO without D2D communication. Based on the provided results, we conclude that our proposed scheme increases the sum spectral efficiency of multi-cell massive MIMO networks.

  • 180.
    Ghazanfari, Amin
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Power Control for Multi-Cell Massive MIMO2019Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The cellular network operators have witnessed significant growth in data traffic in the past few decades. This growth occurs due to the increases in the number of connected mobile devices, and further, the emerging mobile applications developed for rendering video-based on-demand services. As the frequency bandwidth for cellular communication is limited, significant effort was dedicated to improve the utilization of the available spectrum and increase the system performance via new technologies. For example, 3G and 4G networks were designed to facilitate high data traffic in cellular networks in past decades. Nevertheless, there is a necessity for new cellular network technologies to accommodate the ever-growing data traffic demand. 5G is behind the corner to deal with the tremendous data traffic requirements that will appear in cellular networks in the next decade.

    Massive MIMO (multiple-input-multi-output) is one of the backbone technologies in 5G networks. Massive MIMO originated from the concept of multi-user MIMO. It consists of base stations (BSs) implemented with a large number of antennas to increase the signal strengths via adaptive beamforming and concurrently serving many users on the same time-frequency blocks. As an outcome of using Massive MIMO technology, there is a notable enhancement of both sum spectral efficiency (SE) and energy efficiency (EE) in comparison with conventional MIMO based cellular networks. Resource allocation is an imperative factor to exploit the specified gains of Massive MIMO. It corresponds to properly allocating resources in the time, frequency, space, and power domains for cellular communication. Power control is one of the resource allocation methods to deliver high spectral and energy efficiency of Massive MIMO networks. Power control refers to a scheme that allocates transmit powers to the data transmitters such that the system maximizes some desirable performance metric.

    In the first part of this thesis, we investigate reusing the resources of a Massive MIMO system, for direct communication of some specific user pairs known as device-to-device (D2D) underlay communication. D2D underlay can conceivably increase the SE of traditional Massive MIMO systems by enabling more simultaneous transmissions on the same frequencies. Nevertheless, it adds additional mutual interference to the network. Consequently, power control is even more essential in this scenario in comparison with conventional Massive MIMO systems to limit the interference that is caused between the cellular network and the D2D communication, thereby enabling their coexistence. In this part, we propose a novel pilot transmission scheme for D2D users to limit the interference to the channel estimation phase of cellular users in comparison with the case of sharing pilot sequences for cellular and D2D users. We also introduce a novel pilot and data power control scheme for D2D underlaid Massive MIMO systems. This method aims at assuring that D2D communication enhances the SE of the network in comparison with conventional Massive MIMO systems.

    In the second part of this thesis, we propose a novel power control approach for multi-cell Massive MIMO systems. The new power control approach solves the scalability issue of two well-known power control schemes frequently used in the Massive MIMO literature, which are based on the network-wide max-min and proportional fairness performance metrics. We first explain the scalability issue of these existing approaches. Additionally, we provide mathematical proof for the scalability of our proposed method. Our scheme aims at maximizing the geometric mean of the per-cell max-min SE. To solve this optimization problem, we prove that it can be rewritten in a convex form and then be solved using standard optimization solvers.

    List of papers
    1. Optimized Power Control for Massive MIMO With Underlaid D2D Communications
    Open this publication in new window or tab >>Optimized Power Control for Massive MIMO With Underlaid D2D Communications
    2019 (English)In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 67, no 4, p. 2763-2778Article in journal (Refereed) Published
    Abstract [en]

    In this paper, we consider device-to-device (D2D) communication that is underlaid in a multi-cell massive multiple-input multiple-output (MIMO) system and proposes a new framework for power control and pilot allocation. In this scheme, the cellular users (CUs) in each cell get orthogonal pilots which are reused with reuse factor one across cells, while all the D2D pairs share another set of orthogonal pilots. We derive a closed-form capacity lower bound for the CUs with different receive processing schemes. In addition, we derive a capacity lower bound for the D2D receivers and a closed-form approximation of it. We provide power control algorithms to maximize the minimum spectral efficiency (SE) and to maximize the product of the signal-to-interference-plus-noise ratios in the network. Different from prior works, in our proposed power control schemes, we consider joint pilot and data transmission optimization. Finally, we provide a numerical evaluation, where we compare our proposed power control schemes with the maximum transmit power case and the case of conventional multi-cell massive MIMO without D2D communication. Based on the provided results, we conclude that our proposed scheme increases the sum SE of multi-cell massive MIMO networks.

    Place, publisher, year, edition, pages
    IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2019
    Keywords
    MIMO systems; power control; optimization methods; interference suppression
    National Category
    Telecommunications
    Identifiers
    urn:nbn:se:liu:diva-157237 (URN)10.1109/TCOMM.2018.2890240 (DOI)000465242700012 ()
    Note

    Funding Agencies|European Unions Horizon 2020 research and innovation programme [641985]

    Available from: 2019-06-13 Created: 2019-06-13 Last updated: 2019-10-07
  • 181.
    Ghazanfari, Amin
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Björnson, Emil
    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.
    Optimized Power Control for Massive MIMO With Underlaid D2D Communications2019In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 67, no 4, p. 2763-2778Article in journal (Refereed)
    Abstract [en]

    In this paper, we consider device-to-device (D2D) communication that is underlaid in a multi-cell massive multiple-input multiple-output (MIMO) system and proposes a new framework for power control and pilot allocation. In this scheme, the cellular users (CUs) in each cell get orthogonal pilots which are reused with reuse factor one across cells, while all the D2D pairs share another set of orthogonal pilots. We derive a closed-form capacity lower bound for the CUs with different receive processing schemes. In addition, we derive a capacity lower bound for the D2D receivers and a closed-form approximation of it. We provide power control algorithms to maximize the minimum spectral efficiency (SE) and to maximize the product of the signal-to-interference-plus-noise ratios in the network. Different from prior works, in our proposed power control schemes, we consider joint pilot and data transmission optimization. Finally, we provide a numerical evaluation, where we compare our proposed power control schemes with the maximum transmit power case and the case of conventional multi-cell massive MIMO without D2D communication. Based on the provided results, we conclude that our proposed scheme increases the sum SE of multi-cell massive MIMO networks.

  • 182.
    Ghazanfari, Amin
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Cheng, Hei Victor
    Univ Toronto, Canada.
    Björnson, Emil
    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.
    A FAIR AND SCALABLE POWER CONTROL SCHEME IN MULTI-CELL MASSIVE MIMO2019In: 2019 IEEE INTERNATIONAL CONFERENCE ON ACOUSTICS, SPEECH AND SIGNAL PROCESSING (ICASSP), IEEE , 2019, p. 4499-4503Conference paper (Refereed)
    Abstract [en]

    This paper studies the transmit power optimization in a multi-cell massive multiple-input multiple-output (MIMO) system. To overcome the scalability issue of network-wide max-min fairness (NW-MMF), we propose a novel power control (PC) scheme. This scheme maximizes the geometric mean (GM) of the per-cell max-min spectral efficiency (SE). To solve this new optimization problem, we prove that it can be rewritten in a convex form and then solved using standard tools. To provide a fair comparison with the available utility functions in the literature, we solve the network-wide proportional fairness (NW-PE) PC as well. The NW-PE focuses on maximizing the sum SE, thereby ignoring fairness, but gives some extra attention to the weakest users. The simulation results highlight the benefits of our model which is balancing between NW-PE and NW-MMF.

  • 183.
    Gokceoglu, Ahmet
    et al.
    Tampere University of Technology, Finland.
    Björnson, Emil
    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.
    Valkama, Mikko
    Tampere University of Technology, Finland.
    Spatio-Temporal Waveform Design for Multiuser Massive MIMO Downlink With 1-bit Receivers2017In: IEEE Journal on Selected Topics in Signal Processing, ISSN 1932-4553, E-ISSN 1941-0484, Vol. 11, no 2, p. 347-362Article in journal (Refereed)
    Abstract [en]

    Internet-of-Things (IoT) refers to a high-density network of low-cost, low-bitrate terminals and sensors where low energy consumption is also one central feature. As the power budget of classical receiver chains is dominated by the high-resolution analog-to-digital converters (ADCs), there is a growing interest toward deploying receiver architectures with reduced bit or even 1-bit ADCs. In this paper, we study waveform design, optimization, and detection aspects of multiuser massive MIMO downlink, where user terminals adopt very simple 1-bit ADCs with oversampling. In order to achieve spectral efficiency higher than 1 bit/s/Hz per real dimension, and per receiver antenna, we propose a two-stage precoding structure, namely, a novel quantization precoder followed by maximum-ratio transmission or zero-forcing-type spatial channel precoder which jointly form the multiuser multiantenna transmit waveform. The quantization precoder outputs are designed and optimized, under appropriate transmitter and receiver filter bandwidth constraints, to provide controlled intersymbol interference enabling the input symbols to be uniquely detected from 1-bit quantized observations with a low-complexity symbol detector in the absence of noise. An additional optimization constraint is also imposed in the quantization precoder design to increase the robustness against noise and residual interuser interference (IUI). The purpose of the spatial channel precoder, in turn, is to suppress the IUI and provide high beamforming gains such that good symbol error rates can be achieved in the presence of noise and interference. Extensive numerical evaluations illustrate that the proposed spatio-temporal precoder-based multiantenna waveform design can facilitate good multiuser link performance, despite the extremely simple 1-bitADCsin the receivers, hence being one possible enabling technology for the future low-complexity IoT networks.

  • 184.
    Gokceoglu, Ahmet
    et al.
    Tampere University of Technology, Finland.
    Björnson, Emil
    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.
    Valkama, Mikko
    Tampere University of Technology, Finland.
    Waveform Design for Massive MISO Downlink with Energy-Efficient Receivers Adopting 1-bit ADCs2016In: 2016 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS (ICC), IEEE , 2016Conference paper (Refereed)
    Abstract [en]

    In high-density low-bitrate Internet-of-Things (IoT) use case of 5G networks, the terminals and sensors are to be of extremely low-cost and low energy-consuming. Typically, the analog-to-digital converters (ADCs) dominate the power-budget of receiver chains, in particular if the quantization resolution is high. Hence, receiver architectures deploying 1-bit ADCs are of high interest towards realizing low-cost, high energy-efficiency device solutions. In this paper, we study the waveform design and optimization for a narrowband low-bitrate massive MISO downlink targeting to achieve rates higher than 1 bits/sec (per real-dimension) where the terminal receivers adopt only simple 1-bit quantization (per real-dimension) with oversampling. In this respect, first we show that for a particular precoder structure, the overall link is equivalent to that of an AWGN SISO with controlled intersymbol interference (ISI). The filter design problem for generating the desired ISI in such SISO links has been studied in previous works, however, the only known method in literature is a computationally demanding brute force search method. As a novel contribution, we develop models and tools that elaborate on the conditions to be satisfied for unique detection and existence of solution for the filter coefficients. Then, as a concrete example, the developed models and tools are utilized to show that in the absence of noise, five-times oversampling is required for unique detection of 16-QAM input alphabet. Building on these findings, we then develop novel algorithms that can efficiently design the filter coefficients. Examples and simulations are provided to elaborate on filter coefficient design and optimization, and to illustrate good SER performance of the MISO link with 1-bit receiver even at SNRs down to 5 dB.

  • 185.
    Gomony, Manil Dev
    Linköping University, Department of Electrical Engineering, Communication Systems.
    An adaptive solution for power efficiency and QoS optimization in WLAN 802.11n2010Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The wide spread use of IEEE Wireless LAN 802.11 in battery operated mobile devices introduced the need of power consumption optimization while meeting Quality-of-Service (QoS) requirements of applications connected through the wireless network. The IEEE 802.11 standard specifies a baseline power saving mechanism, hereafter referred to as standard Power Save Mode (PSM), and the IEEE 802.11e standard specifies the Automatic Power Save Delivery (APSD) enhancement which provides support for real-time applications with QoS requirements. The latest amendment to the WLAN 802.11 standard is the IEEE 802.11n standard which enables the use of much higher data rates by including enhancements in the Physical and MAC Layer. In this thesis, different 802.11n MAC power saving and QoS optimization possibilities are analyzed comparing against existing power saving mechanisms.

    Initially, the performance of the existing power saving mechanisms PSM and Unscheduled-APSD (UAPSD) are evaluated using the 802.11n process model in the OPNET simulator and the impact of frame aggregation feature introduced in the MAC layer of 802.11n was analyzed on these power saving mechanisms. From the performance analysis it can be concluded that the frame aggregation will be efficient under congested network conditions. When the network congestion level increases, the signaling load in UAPSD saturates the channel capacity and hence results in poor performance compared to PSM. Since PSM cannot guarantee the minimum QoS requirements for delay sensitive applications, a better mechanism for performance enhancement of UAPSD under dynamic network conditions is proposed.

    The functionality and performance of the proposed algorithm is evaluated under different network conditions and using different contention settings. From the performance results it can be concluded that, by using the proposed algorithm the congestion level in the network is reduced dynamically thereby providing a better power saving and QoS by utilizing the frame aggregation feature efficiently.

  • 186.
    Grundberg, Staffan
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Radio Netwok Test Configuration for Maximum Test Coverage: Model based load generation in system verification of a GSM Base Station Controller2008Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    GSM has been developed during more than a decade and has grown to a very complex system. Due to the wide range of functionality, the high capacity and the complexity of the BSC the testing of stability and performance is time consuming. A simulator is needed for these tests as live networks are not available at this stage in the development process. The performance and stability need to be verified for each new release of functionality.

    This thesis describes a conceptual model of a GSM network. The conceptual model can be used to configure a simulated radio network and to communicate what is simulated on a conceptual level rather than a detailed level.

    The model presented consists of several sub models. The subscriber model describes the actions and movement of subscribers; the cell model describes the radio conditions experienced by a subscriber moving within one cell; and the cell network model describes the geographical and structural properties of the network.

    Together the models are used to compose scenarios with the aim to describe varying radio conditions, varying subscriber behavior and varying cell structures. The aim is that different features of the Ericsson base station controller shall be used in the different scenarios. The scenarios represent different parts of a radio network connected to the same base station controller.

  • 187.
    Gunnarsson, Frida
    et al.
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Björsson, Anders
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Gustafsson, Fredrik
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Knutsson, Björn
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Gunarsson, Fredrik
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Radio Access Network (UTRAN) Modeling for Heterogenous Network Simulations2003Report (Other academic)
    Abstract [en]

    The vision of mobile Internet comprises heterogeneous networks with both wired and wireless infrastructures. The network parts are typically radio access network, core network, service network, Internet, etc. Due to the multitude of nodes and users in such networks and the complicated nature of layered communications protocols, performance analysis through simulations is crucial. The open source network simulation tool, ns-2, is widely used for simulating the behavior of wired, routed networks. This work adds modules to model radio access network nodes that emulate typical behavior of UTRAN (UMTS Terrestrial Radio Access Network) - the 3G standard opted for in Europe and Japan. Furthermore, data communication examples illustrate typical behavior of such a heterogenous network.

  • 188.
    Gustafsson, Fredrik
    et al.
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Gunnarsson, Fredrik
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Gunnarsson, Frida
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Björsson, Anders
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Knutsson, Björn
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Radio Access Network (UTRAN) Modeling for Heterogenous Network Simulations, A Brief Description2003In: Proceedings of the 1st Swedish National Computer Networking Workshop, 2003Conference paper (Refereed)
    Abstract [en]

    The vision of mobile Internet comprises heterogeneous networks with both wired and wireless infrastructures. The network parts are typically radio access network, core network, service network, Internet, etc. Due to the multitude of nodes and users in such networks and the complicated nature of layered communications protocols, performance analysis through simulations is crucial. The open source network simulation tool, ns-2, is widely used for simulating the behavior of wired, routed networks. This work adds modules to model radio access network nodes that emulate typical behavior of UTRAN (UMTS Terrestrial Radio Access Network) - the 3G standard opted for in Europe and Japan. Furthermore, data communication examples illustrate typical behavior of such a heterogenous network.

  • 189.
    Gustafsson, Oscar
    et al.
    Linköping University, Department of Electrical Engineering, Computer Engineering. Linköping University, The Institute of Technology.
    Johansson, Håkan
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Decimation Filters for High-Speed Delta-Sigma Modulators With Passband Constraints: General Versus CIC-Based FIR Filters2015In: 2015 IEEE INTERNATIONAL SYMPOSIUM ON CIRCUITS AND SYSTEMS (ISCAS), IEEE conference proceedings, 2015, p. 2205-2208Conference paper (Refereed)
    Abstract [en]

    For high-speed delta-sigma modulators the decimation filters are typically polyphase FIR filters as the recursive CIC filters can not be implemented because of the iteration period bound. In addition, the high clock frequency and short input word length make multiple constant multiplication techniques less beneficial. Instead a realistic complexity measure in this setting is the number of non-zero digits of the FIR filter tap coefficients. As there is limited control of the passband approximation error for CIC-based filters these must in most cases be compensated to meet a passband specification. In this work we investigate the complexity of decimation filters meeting CIC-like stopband behavior, but with a well defined passband approximation error. It is found that the general approach can in many cases produce filters with much smaller passband approximation error at a similar complexity.

  • 190.
    Gustafsson, Oscar
    et al.
    Linköping University, Department of Electrical Engineering, Computer Engineering. Linköping University, The Institute of Technology. ISY .
    Johansson, Håkan
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology. ISY .
    Wanhammar, Lars
    Linköping University, Department of Electrical Engineering, Computer Engineering. Linköping University, The Institute of Technology.
    MILP design of frequency-response masking FIR filters with few SPT terms2004In: First International Symposium on Control, Communications and Signal Processing, 2004, Tunisia: IEEE , 2004, p. 405-408Conference paper (Refereed)
    Abstract [en]

    In this work we formulate a mixed integer linear programming (MILP) problem that minimizes the number of signed-power-of- two (SPT) terms given a filter specification for linear-phase frequency-response masking (FRM) filters. The proposed method designs the filters in two steps. The model filter and the masking filters are designed separately, but subject to each other. Hence, it is not guaranteed that the global minimum is obtained. However, each solution is optimal given the other filter(s), and iteration may improve the overall solution. The filter design problems are formulated using normalized peak ripple magnitude (NPRM), which for FRM filters introduces some implications, which is also discussed in this work.

  • 191.
    Gustavsson, Jonas
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Department of Electrical Engineering.
    Automated Performance Optimization of GSM/EDGE Network Parameters2009Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The GSM network technology has been developed and improved during several years which have led to an increased complexity. The complexity results in more network parameters and together with different scenarios and situations they form a complex set of configurations. The definition of the network parameters is generally a manual process using static values during test execution. This practice can be costly, difficult and laborious and as the network complexity continues to increase, this problem will continue to grow.This thesis presents an implementation of an automated performance optimization algorithm that utilizes genetic algorithms for optimizing the network parameters. The implementation has been used for proving that the concept of automated optimization is working and most of the work has been carried out in order to use it in practice. The implementation has been applied to the Link Quality Control algorithm and the Improved ACK/NACK feature, which is an apart of GSM EDGE Evolution.

  • 192.
    Gülgün, Ziya
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Yılmaz, Ali Özgür
    Middle East Technical University (METU), Ankara, Turkey.
    Detection Schemes for High Order M-Ary QAM Under Transmit Nonlinearities2019In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 67, no 7, p. 4825-4834Article in journal (Refereed)
    Abstract [en]

    Nonlinearities in various stages of a transmitter may hinder and restrict the transmission rate. As observed in many studies, outermost constellation points are usually more adversely affected by these impairments. To observe these effects, we utilize two power amplifier models that have different effects on transmitted signals. The Rapp model considers only amplitude deformation and the resultant in-phase and quadrature errors can be assumed to be independent on the receiver side. Unlike the Rapp model, the Saleh model exerts both amplitude and phase deformations and the phase deformation introduces correlation between the in-phase and quadrature errors according to our observations. In addition to the correlation, the variances of in-phase and quadrature errors may not be equal to each other. In this paper, we propose receivers that consider error variances of each quadrature amplitude modulation (QAM) symbol. We compare the performances of the receivers with those of other receivers that take average error variances into account for decoding. Furthermore, we propose a practical receiver that directly works on digitized observations based on a look-up table that keeps log-likelihood ratios of the quantized regions in order to reduce computational complexity.

  • 193.
    Haider, Raja Umair
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Fault Detection in WLAN Location Fingerprinting Systems Using Smartphone Inertial Sensors2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Indoor positioning is a rapidly growing research area, enabling new innovative location-aware applications and user-oriented services. Location Fingerprinting (LF) is the positioning technique of coupling a physical location with observed radio signal measurements. In the terms of indoor LF using Wireless Local Area Network (WLAN) it refers to the use of network measurements from the WLAN Access Points (APs) to tag known locations. A data set is created containing reference fingerprints for the area of interest and is known as a radio map. A radio map can later be used to find a user's location in the area of interest. WLAN infrastructures are vulnerable to many kinds of faults and malicious attacks, including, an attacker jamming the signal from an AP, or an AP becoming unavailable during positioning due to power outage. These faults can be collectively characterized as an AP-failure. In LF positioning systems, AP-failure faults can significantly degrade the performance of a LF system due to the difference between the current fingerprints and radio map created with all APs being available. It is desirable to detect such faulty APs, in order to take actions towards fault-mitigation and restoration, in case of a malicious attack. In this work, we have developed a fault detection algorithm that uses inertial sensors (i.e., accelerometer, magnetometer) available in smartphones to detect AP-failure faults in LF systems. Inertial Measurement Unit (IMU) has become an integral part of all high-end smartphones. IMU can be used to infer location information on the smartphone. The main idea is to have two parallel position streams, the LF positioning and the IMU positioning, and to compare the mean positioning error between the two. Since IMU positioning is fairly accurate once provided with starting coordinates, we use it to detect abnormal behaviour in LF positioning system, such as highly erroneous estimates signifying an AP-failure fault present in the system. The performance of the proposed detection algorithm is evaluated with several real-life AP-related faults. The proposed algorithm exhibits low probability of false alarms in the detection of faulty APs. The conclusion is that using IMU based positioning is an effective and robust solution in terms of fault detection in LF systems.

  • 194.
    Heath, Robert W
    et al.
    University of Texas Austin.
    Debbah, Merouane
    Supelec.
    Larsson, Erik G
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    In Kim, Dong
    Sungkyunkwan University.
    Viswanathan, Harish
    Alcatel Lucent Bell Labs.
    Guevenc, Ismail
    DOCOMO Innovat Inc.
    Editorial Material: Introduction to the Issue on Signal Processing in Heterogeneous Networks for Future Broadband Wireless Systems2012In: IEEE Journal on Selected Topics in Signal Processing, ISSN 1932-4553, E-ISSN 1941-0484, Vol. 6, no 3, p. 213-215Article in journal (Other academic)
    Abstract [en]

    n/a

  • 195.
    Helders, Fredrik
    Linköping University, Department of Electrical Engineering, Communication Systems.
    Visualizing Carrier Aggregation Combinations2019Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    As wireless communications is becoming an increasingly important part of ourevery day lives, the amount of transmitted data is constantly growing, creating ademand for ever-increasing data rates. One of the technologies used for boostingdata rates is carrier aggregation, which allows for wireless units to combine multipleconnections to the cellular network. However, there is a limited number ofpossible combinations defined, meaning that there is a need to search for the bestcombination in any given setup. This thesis introduces software capable of organizingthe defined combinations into tree structures, simplifying the search foroptimal combinations as well as allowing for visualizations of the connectionspossible. In the thesis, a proposed method of creating these trees is presented,together with suggestions on how to visualize important combination characteristics.Studies has also been made on different tree traversal algorithms, showingthat there is little need for searching through all possible combinations, but thata greedy approach has a high performance while substantially limiting the searchcomplexity.

  • 196.
    Hinrichsen, Oscar
    Linköping University, Department of Electrical Engineering, Communication Systems.
    An Evaluation of Network Protocols for Bluetooth Low Energy Mesh Networks2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Internet of Things (IoT) is a scenario that theorizes objects and people as potential nodes in an ever-growing wireless network. This idea pushes the development of low-cost wireless technologies that can run on portable power sources for months, or even years. One candidate technique that has shown promising results in this area thru the last years is BluetoothLow Energy (BLE). This thesis studies various techniques to enable and maintain large scale mesh networks over BLE communication. The initial study puts focus on an existing flooding based BLE mesh protocol. The thesis later presents an improved protocol that reduces power consumption with respect to the packet delivery ratio. Other enhancements which are added to the improved protocol are a self-adapting procedure and a packet routing algorithm. Simulations show that the improved protocol can save up to 50 % of the power consumption for a device, compared to the original protocol.

  • 197.
    Ho, Chung Duc
    et al.
    Queens Univ Belfast, North Ireland.
    Ngo, Hien
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering. Queens Univ Belfast, North Ireland.
    Matthaiou, Michail
    Queens Univ Belfast, North Ireland.
    Duong, Trung Q.
    Queens University Belfast, Belfast, Ireland.
    Multi-Way Massive MIMO with Maximum-Ratio Processing and Imperfect CSI2017In: 2017 25TH EUROPEAN SIGNAL PROCESSING CONFERENCE (EUSIPCO), IEEE , 2017, p. 1704-1708Conference paper (Refereed)
    Abstract [en]

    This paper considers a multi-way massive multiple-input multiple-output amplify-and-forward relaying system, where single-antenna users exchange their information-bearing signals with the assistance of one relay station equipped with unconventionally many antennas. The relay first estimates the channels to all users through the pilot signals transmitted from them. Then, the relay uses maximum-ratio processing (i.e. maximum-ratio combining in the multiple-access phase and maximum-ratio transmission in the broadcast phase) to process the signals. A rigorous closed-form expression for the spectral efficiency is derived. We show that by deploying massive antenna arrays at the relay and simple maximum-ratio processing, we can serve many users in the same time-frequency resource, while maintaining a given quality-of-service for each user.

  • 198.
    Holm, Peter D.
    et al.
    Swedish Def Research Agency, SE-58111 Linkoping, Sweden.
    Persson, Daniel
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Wiklundh, Kia
    Swedish Def Research Agency, SE-58111 Linkoping, Sweden.
    Stenumgaard, Peter
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    On multiple-input-multiple-output performance for Terrestrial Trunked Radio systems2014In: IET COMMUNICATIONS, ISSN 1751-8628, Vol. 8, no 14, p. 2484-2488Article in journal (Refereed)
    Abstract [en]

    Measurements for outdoor multiple-input-multiple-output (MIMO) capacity assessment are generally technically complicated, time consuming and expensive activities and few results are therefore published in the literature. Terrestrial Trunked Radio (TETRA) systems suffer from poor capacity and could be significantly improved by MIMO technology. However, performing outdoor channel measurements in relevant environments is very difficult because of interference problems with operating systems. In this study, the authors propose an estimation of the MIMO capacity for TETRA systems, based on outdoor MIMO measurements carried out at 300 MHz.

  • 199.
    Hossain, M. M. Aftab
    et al.
    Aalto Univ, Finland; KTH Royal Inst Technol, Sweden.
    Cavdar, Cicek
    KTH Royal Inst Technol, Sweden.
    Björnson, Emil
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Jantti, Riku
    Aalto Univ, Finland.
    Energy Saving Game for Massive MIMO: Coping With Daily Load Variation2018In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 67, no 3, p. 2301-2313Article in journal (Refereed)
    Abstract [en]

    Massive MIMO (MM) is one of the leading technologies that can cater for very high capacity demand. However, energy consumption of MM systems needs to be load adaptive in order to cope with the significant temporal load variations (TLV) over a day. In this paper, we propose a game-theoretic model for studying load adaptive multicell massive MIMO system where each base station (BS) adapts the number of antennas to the TLV in order to maximize the downlink energy efficiency (EE). The utility function considered here is defined as the number of bits transferred per Joule of energy. In order to incorporate the TLV, the load at each BS is modeled as an M/G/m/m state dependent queue under the assumption that the network is dimensioned to serve a maximum number of users at the peak load. The EE maximization problem is formulated in a game theoretic framework where the number of antennas to be used by a BS is determined through the best response iteration. This load adaptive system achieves around 24% higher EE and saves around 40% energy compared to a baseline system where the BSs always run with the fixed number of antennas that is most energy efficient at the peak load and that can be switched OFF when there is no traffic.

  • 200.
    Hossain, M. M. Aftab
    et al.
    Aalto University, Finland.
    Cavdar, Cicek
    KTH Royal Institute of Technology, Sweden.
    Björnson, Emil
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Jäntti, Riku
    Aalto University, Finland.
    Energy-Efficient Load-Adaptive Massive MIMO2015In: 2015 IEEE GLOBECOM WORKSHOPS (GC WKSHPS), 2015Conference paper (Refereed)
1234567 151 - 200 of 624
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