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  • 101.
    Mishra, Deepak
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Johansson, Håkan
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Optimal Channel Estimation for Hybrid Energy Beamforming Under Phase Shifter Impairments2019In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 67, no 6, p. 4309-4325Article in journal (Refereed)
    Abstract [en]

    Smart multiantenna wireless power transmission can enable perpetual operation of energy harvesting (EH) nodes in the Internet-of-Things. Moreover, to overcome the increased hardware cost and space constraints associated with having large antenna arrays at the radio frequency (RF) energy source, the hybrid energy beamforming (EBF) architecture with single RF chain can be adopted. Using the recently proposed hybrid EBF architecture modeling the practical analog phase shifter impairments (API), we derive the optimal least-squares estimator for the energy source to an EH user channel. Next, the average harvested power at the user is derived while considering the nonlinear RF EH model and a tight analytical approximation for it is also presented by exploring the practical limits on the API. Using these developments, the jointly global optimal transmit power and time allocation for channel estimation (CE) and EBF phases, that maximizes the average energy stored at the EH user is derived in closed form. Numerical results validate the proposed analysis and present nontrivial design insights on the impact of API and CE errors on the achievable EBF performance. It is shown that the optimized hybrid EBF protocol with joint resource allocation yields an average performance improvement of 37% over benchmark fixed allocation scheme.

  • 102.
    Mishra, Deepak
    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.
    Sum Throughput Maximization in Multi-Tag Backscattering to Multiantenna Reader2019In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 67, no 8, p. 5689-5705Article in journal (Refereed)
    Abstract [en]

    Backscatter communication (BSC) is being realized as the core technology for pervasive sustainable Internet-of-Things applications. However, owing to the resource limitations of passive tags, the efficient usage of multiple antennas at the reader is essential for both downlink excitation and uplink detection. This paper targets at maximizing the achievable sum-backscattered throughput by jointly optimizing the transceiver (TRX) design at the reader and backscattering coefficients (BCs) at the tags. Since this joint problem is nonconvex, we first present individually optimal designs for the TRX and BC. We show that with precoder and combiner designs at the reader, respectively, targeting downlink energy beamforming and uplink Wiener filtering operations, the BC optimization at tags can be reduced to a binary power control problem. Next, the asymptotically optimal joint-TRX-BC designs are proposed for both low- and high-signal-to-noise ratio regimes. Based on these developments, an iterative low-complexity algorithm is proposed to yield an efficient jointly suboptimal design. Thereafter, we discuss the practical utility of the proposed designs to other application settings, such as wireless powered communication networks and BSC with imperfect channel state information. Finally, selected numerical results, validating the analysis and shedding novel insights, demonstrate that the proposed designs can yield significant enhancement in the sum-backscattered throughput over existing benchmarks.

  • 103.
    Mollén, Christopher
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering. Ericsson, Sweden; Ericsson, Peoples R China; Eidgenoss TH Zurich, Switzerland; Univ Texas Austin, TX 78712 USA; Apple, CA 92307 USA.
    Gustavsson, Ulf
    Ericsson Res, Sweden.
    Eriksson, Thomas
    Chalmers Univ Technol, Sweden.
    Larsson, Erik G
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Impact of Spatial Filtering on Distortion From Low-Noise Amplifiers in Massive MIMO Base Stations2018In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 66, no 12, p. 6050-6067Article in journal (Refereed)
    Abstract [en]

    In massive multiple-input-multiple-output base stations, power consumption and cost of the low-noise amplifiers (LNAs) can be substantial because of the many antennas. We investigate the feasibility of inexpensive, power efficient LNAs, which inherently are less linear. A polynomial model is used to characterize the nonlinear LNAs and to derive the second-order statistics and spatial correlation of the distortion. We show that, with spatial matched filtering (maximum-ratio combining) at the receiver, some distortion terms combine coherently, and that the signal-to-interference-and-noise ratio of the symbol estimates therefore is limited by the linearity of the LNAs. Furthermore, it is studied how the power from a blocker in the adjacent frequency band leaks into the main band and creates distortion. The distortion term that scales cubically with the power received from the blocker has a spatial correlation that can be filtered out by spatial processing and only the coherent term that scales quadratically with the power remains. When the blocker is in free-space line-of-sight and the LNAs are identical, this quadratic term has the same spatial direction as the desired signal, and hence cannot be removed by linear receiver processing.

  • 104.
    Mollén, Christopher
    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.
    Eriksson, Thomas
    Chalmers tekniska högskola, Sweden.
    Waveforms for the Massive MIMO Downlink: Amplifier Efficiency, Distortion and Performance2016In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 46, no 12, p. 5050-5063Article in journal (Refereed)
    Abstract [en]

    In massive multiple-input multiple-output (MIMO), most precoders result in downlink signals that suffer from high peak-to-average ratio (PAR), independently of modulation order and whether single-carrier or orthogonal frequency-division multiplexing (OFDM) transmission is used. The high PAR lowers the power efficiency of the base-station amplifiers. To increase the power efficiency, low-PAR precoders have been proposed. In this paper, we compare different transmission methods for massive MIMO in terms of the power consumed by the amplifiers. It is found that: 1) OFDM and single-carrier transmission have the same performance over a hardened massive MIMO channel and 2) when the higher amplifier power efficiency of low-PAR precoding is taken into account, conventional and low-PAR precoders lead to approximately the same power consumption. Since downlink signals with low PAR allow for simpler and cheaper hardware, than signals with high PAR, therefore, the results suggest that low-PAR precoding with either single-carrier or OFDM transmission should be used in a massive MIMO base station.

  • 105.
    Moosavi, Reza
    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.
    Fast Blind Recognition of Channel Codes2014In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 62, no 5, p. 1393-1405Article in journal (Refereed)
    Abstract [en]

    We present a fast algorithm that, for a given input sequence and a linear channel code, computes the syndrome posterior probability (SPP) of the code, i.e., the probability that all parity check relations of the code are satisfied. According to this algorithm, the SPP can be computed blindly, i.e., given the soft information on a received sequence we can compute the SPP for the code without first decoding the bits. We show that the proposed scheme is efficient by investigating its computational complexity.

    We then consider two scenarios where our proposed SPP algorithm can be used. The first scenario is when we are interested in finding out whether a certain code was used to encode a data stream. We formulate a statistical hypothesis test and we investigate its performance. We also compare the performance of our scheme with that of an existing scheme. The second scenario deals with how we can use the algorithm for reducing the computational complexity of blind decoding process, the process that, for instance, is used by terminals in LTE for detection of control information. We propose a heuristic sequential statistical hypotheses test to use the fact that in real applications, the data arrives sequentially, and we investigate its performance using system simulations.

  • 106. Nasir, A. A.
    et al.
    Mehrpouyan, H.
    Durrani, S.
    Blostein, S. D.
    Kennedy, R. A.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Optimal Training Sequences for Joint Timing Synchronization and Channel Estimation in Distributed Communication Networks2013In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 61, no 7, p. 3002-3015Article in journal (Refereed)
    Abstract [en]

    For distributed multi-user and multi-relay cooperative networks, the received signal may be affected by multiple timing offsets (MTOs) and multiple channels that need to be jointly estimated for successful decoding at the receiver. This paper addresses the design of optimal training sequences for efficient estimation of MTOs and multiple channel parameters. A new hybrid Cramer-Rao lower bound (HCRB) for joint estimation of MTOs and channels is derived. Subsequently, by minimizing the derived HCRB as a function of training sequences, three training sequence design guidelines are derived and according to these guidelines, two training sequences are proposed. In order to show that the proposed design guidelines also improve estimation accuracy, the conditional Cramer-Rao lower bound (ECRB), which is a tighter lower bound on the estimation accuracy compared to the HCRB, is also derived. Numerical results show that the proposed training sequence design guidelines not only lower the HCRB, but they also lower the ECRB and the mean-square error of the proposed maximum a posteriori estimator. Moreover, extensive simulations demonstrate that application of the proposed training sequences significantly lowers the bit-error rate performance of multi-relay cooperative networks when compared to training sequences that violate these design guidelines.

  • 107.
    Nasiri Khormuji, Majid
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Zaidi, Ali A.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Interference Management Using Nonlinear Relaying2010In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 58, no 7, p. 1924-1930Article in journal (Refereed)
    Abstract [en]

    We consider the three-node Gaussian relay channel where the relay observes a noisy version of the interference present in the source-destination link. We investigate three fundamental relaying approaches: linear relaying, memoryless nonlinear relaying, and compress-and-forward (CF). For interference-limited cases, we illustrate that optimized memoryless nonlinear relaying almost achieves the capacity.

  • 108.
    Negusse, Senay
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Phase-noise mitigation in OFDM by best match trajectories2015In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 63, no 5, p. 1712-1725Article in journal (Refereed)
    Abstract [en]

    This paper proposes a novel approach to phasenoise compensation. The basic idea is to approximate the phasenoise statistics by a finite number of realizations, i.e., a phasenoise codebook. The receiver then uses an augmented received signal model, where the codebook index is estimated along with other parameters. The realization of the basic idea depends on the details of the air interface, the phase-noise statistics, the propagation scenario and the computational constraints. In this paper, we will focus on a MQAM-OFDM system with pilot subcarriers within each OFDM symbol. The channel is frequency selective, fading and unknown. A decision-feedback method is employed to further enhance performance of the system. Simulation results are shown for uncoded and coded systems to illustrate the performance of the algorithm, which is als o compared with previously employed methods. Our simulation s show that for a 16-QAM coded OFDM system over a frequency selective Rayleigh fading channel affected by phase noise with root-mean-square (RMS) of 14.4 degrees per OFDM symbol, the proposed algorithm is 1.5dB from the ideal phase-noise free case at a BER of 10 − 4 . The performance of the best reference scheme is 2.5dB from the ideal case at BER of 10 − 4 . The proposed scheme is also computationally attractive.

  • 109.
    Nekouei, Ehsan
    et al.
    Univ Melbourne, Dept Elect & Elect Engn, Parkville, Vic 3010, Australia.
    Inaltekin, Hazer
    Antalya Int Univ, Dept Elect & Elect Engn, Antalya, Turkey.
    Dey, Subhrakanti
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Power control and asymptotic throughput analysis for the distributed cognitive uplink2014In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 64, no 1, p. 41-58Article in journal (Refereed)
    Abstract [en]

    This paper studies optimum power control and sum-rate scaling laws for the distributed cognitive uplink. It is first shown that the optimum distributed power control policy is in the form of a threshold based water-filling power control. Each secondary user executes the derived power control policy in a distributed fashion by using local knowledge of its direct and interference channel gains such that the resulting aggregate (average) interference does not disrupt primary's communication. Then, the tight sum-rate scaling laws are derived as a function of the number of secondary users N under the optimum distributed power control policy. The fading models considered to derive sum-rate scaling laws are general enough to include Rayleigh, Rician and Nakagami fading models as special cases. When transmissions of secondary users are limited by both transmission and interference power constraints, it is shown that the secondary network sum-rate scales according to 1/en(h) log log (N), where n(h) is a parameter obtained from the distribution of direct channel power gains. For the case of transmissions limited only by interference constraints, on the other hand, the secondary network sum-rate scales according to 1/e gamma(g) log (N), where gamma(g) is a parameter obtained from the distribution of interference channel power gains. These results indicate that the distributed cognitive uplink is able to achieve throughput scaling behavior similar to that of the centralized cognitive uplink up to a pre-log multiplier 1/e, whilst primary's quality-of-service requirements are met. The factor 1/e can be interpreted as the cost of distributed implementation of the cognitive uplink.

  • 110.
    Nekouei, Ehsan
    et al.
    Univ Melbourne, Dept Elect & Elect Engn, Melbourne, Vic 3010, Australia..
    Inaltekin, Hazer
    Antalya Int Univ, Dept Elect & Elect Engn, TR-07190 Antalya, Turkey..
    Dey, Subhrakanti
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Throughput Analysis for the Cognitive Uplink Under Limited Primary Cooperation2016In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 64, no 7, p. 2780-2796Article in journal (Refereed)
    Abstract [en]

    This paper studies the achievable throughput performance of the cognitive uplink under a limited primary cooperation scenario wherein the primary base station cannot feed back all interference channel gains to the secondary base station. To cope with the limited primary cooperation, we propose a feedback protocol called K-out-of-N feedback protocol, in which the primary base station feeds back only the K-N smallest interference channel gains, out of N of them, to the secondary base station. We characterize the throughput performance under the K-out-of-N feedback protocol by analyzing the achievable multiuser diversity gains (MDGs) in cognitive uplinks for three different network types. Our results show that the proposed feedback mechanism is asymptotically optimum for interference-limited (IL) and individual-power-and-interference-limited (IPIL) networks for a fixed positive K-N. It is further shown that the secondary network throughput in the IL and IPIL networks (under both the full and limited cooperation scenarios) logarithmically scales with the number of users in the network. In total-power-and-interference-limited (TPIL) networks, on the other hand, the K-out-of-N feedback protocol is asymptotically optimum for K-N = N-delta, where delta is an element of (0, 1). We also show that, in TPIL networks, the secondary network throughput under both the limited and full cooperation scales logarithmically double with the number of users in the network. These results indicate that the cognitive uplink can achieve the optimum MDG even with limited cooperation from the primary network. They also establish the dependence of pre-log throughput scaling factors on the distribution of fading channel gains for different network types.

  • 111.
    Ngo, Hien Quoc
    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.
    Marzetta, Thomas L.
    Bell Laboratories, Alcatel-Lucent, NJ, USA.
    Energy and Spectral Efficiency of Very Large Multiuser MIMO Systems2013In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 61, no 4, p. 1436-1449Article in journal (Refereed)
    Abstract [en]

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

  • 112.
    Ngo, Hien Quoc
    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.
    Marzetta, Thomas L.
    Bell Laboratories, Alcatel-Lucent, NJ, USA .
    The Multicell Multiuser MIMO Uplink with Very Large Antenna Arrays and a Finite-Dimensional Channel2013In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 61, no 6, p. 2350-2361Article in journal (Refereed)
    Abstract [en]

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

  • 113.
    Nilsson, Rickard
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Sjöberg, Frank
    Luleå tekniska universitet.
    Leblanc, James
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    A rank-reduced LMMSE canceller for narrowband interference suppression in OFDM-based systems2003In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 51, no 12, p. 2126-2140Article in journal (Refereed)
    Abstract [en]

    We present a narrowband interference (NBI) canceller that suppresses spectral leakage in an orthogonal frequency-division multiplexing (OFDM)-based system caused by a narrowband (NB) signal. We assume that the spectrum of the NB signal is within the spectrum of the OFDM signal. This can be the case, e.g., on digital subscriber lines (DSL) and in new unlicensed frequency bands for radio transmission. The canceller makes linear minimum mean-square error estimates of the spectral leakage by measuring the NBI on a few modulated or unmodulated OFDM subcarriers. It uses a model of the NB signal's power spectral density as a priori information. Using a frequency invariant design, it is possible to cancel NBI from signals that are changing their frequency location with significantly reduced complexity overhead. The operational complexity of the canceller can be lowered by using the theory of optimal rank reduction and using the time-bandwidth product of the NB signal. Analytical performance evaluations, as well as Monte Carlo simulations, show that, without perfect a priori information, this canceller can suppress the spectral leakage from a strong NB signal (e.g., with equal power as the OFDM signal) to well below the background noise floor for typical applications where it causes negligible signal-to-noise ratio and symbol error rate degradation.

  • 114. Nomikos, Nikolaos
    et al.
    Charalambous, Themistoklis
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Krikidis, Ioannis
    Skoutas, Dimitrios N.
    Vouyioukas, Demosthenes
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    A Buffer-Aided Successive Opportunistic Relay Selection Scheme With Power Adaptation and Inter-Relay Interference Cancellation for Cooperative Diversity Systems2015In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 63, no 5, p. 1623-1634Article in journal (Refereed)
    Abstract [en]

    In this paper, we present a relay selection scheme which combines the spectral efficiency of successive opportunistic relaying with the robustness of single-link relay selection. More specifically, we propose a scheme that minimizes the total energy expenditure per time slot under an inter-relay interference cancellation scheme. The new relay selection policy is analyzed in terms of outage probability and diversity by modeling the evolution of relay buffers as a Markov Chain. We construct the state transition matrix of the Markov Chain and obtain its stationary distribution, which in turn, yields the outage probability. The proposed scheme outperforms relevant state-of-the-art relay selection schemes in terms of throughput, diversity, energy efficiency and average delay, as demonstrated via representative numerical examples.

  • 115.
    Oechtering, Tobias J.
    et al.
    Technical University of Berlin, Heinrich-Hertz Chair for Mobile Communication, Berlin, Germany.
    Boche, Holger
    Stability region of an optimized bidirectional regenerative half-duplex relaying protocol2008In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 56, no 9, p. 1519-1529Article in journal (Refereed)
    Abstract [en]

    In this work, we study a cross-layer design of a spectrally efficient bidirectional relay communication in a three-node network using superposition encoding at the relay node. On the physical layer, a half-duplex relay node decodes-and-forwards the messages of two nodes in a two-phase protocol with optimal time-division. On the data link layer, we assume ergodic arrival processes at node 1 and 2 which have queues with infinite buffer length. At the beginning of each time-slot a centralized controller chooses the service rate pair which achieves the weighted rate sum maximum of the instantaneous achievable rate region for the block-fading channel state of the next time-slot with weights equal to the current buffer levels. To this end, the controller adjusts the time-division and relay power distribution. The policy is throughput optimal since the stability region is equal to the bidirectional ergodic rate region. This is because whenever the mean queue length is large, a negative drift of a quadratic Lyapunov function on the buffer levels can be proved.

  • 116.
    Oechtering, Tobias J.
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Jorswieck, Eduard A.
    Dresden University of Technology (TUD), Germany.
    Wyrembelski, Rafael F.
    Technische Universität Berlin, Heinrich- Hertz-Chair for Mobile Communications, Berlin, Germany.
    Boche, Holger
    Fraunhofer German-Sino Lab for Mobile Communications, Berlin, Germany.
    On the Optimal Transmit Strategy for the MIMO Bidirectional Broadcast Channel2009In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 57, no 12, p. 3817-3826Article in journal (Refereed)
    Abstract [en]

    In this work the transmit covariance matrix optimization problem for the discrete memoryless MIMO Gaussian bidirectional broadcast channel is studied. A half-duplex relay node establishes bidirectional communication between two nodes using a decode-and-forward protocol. In the initial multiple access phase both nodes transmit their messages to the relay node. In the succeeding phase the relay broadcasts an optimal re-encoded message so that both nodes can decode the other's message using their own message as side information. The capacity region of the bidirectional broadcast channel is completely characterized by a weighted rate sum maximization problem, which can be solved by a simple iterative fixed point algorithm. If an efficient transmit covariance matrix is invariant with respect to the joint subspace spanned by the channels, then different combinations of the part transmitted on the orthogonal subspaces result in equivalent transmit strategies with different ranks. A closed-form procedure to obtain the optimal transmit covariance is derived for the case where the rank of the channels is equal to the number of antennas at the relay node and a full-rank transmission is optimal. It shows the complicated structure of the optimal eigenspace, which depends on the weights and the mean transmit power constraint. For parallel channels the optimal solution is completely characterized and discussed, which also solves the optimal power allocation problem for a single-antenna OFDM system.

  • 117.
    Ottosson, Tony
    et al.
    Department of Signals and Systems, Chalmers University of Technology.
    Skoglund, Mikael
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Joint source-channel and multiuser decoding for Rayleigh fading CDMA Channels2000In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 48, no 1, p. 13-16Article in journal (Refereed)
    Abstract [en]

    We consider joint source-channel and multiuser decoding for frequency-selective Rayleigh fading code-division multiple-access channels. The block source-channel encoder is defined by a vector quantizer, We investigate optimal (minimum mean-square error) decoding and user-separated decoding of lower complexity, The studied decoders are soft in the sense that they utilize all soft information available at the receiver. Simulations indicate significant performance gains of the introduced decoders compared with a tandem approach that uses maximum-likelihood multiuser detection plus table-lookup decoding.

  • 118.
    Pappas, Nikolaos
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Kountouris, Marios
    Huawei Technol Co Ltd, France.
    Ephremides, Anthony
    Univ Maryland, MD 20742 USA.
    Angelakis, Vangelis
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Stable Throughput Region of the Two-User Broadcast Channel2018In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 66, no 10, p. 4611-4621Article in journal (Refereed)
    Abstract [en]

    In this paper, we consider the two-user broadcast channel and we characterize its stable throughput region. We start the analysis by providing the stability region for the general case without any specific considerations on transmission and reception mechanisms. We also provide conditions for the stable throughput region to be convex. Subsequently, we study the case where the transmitter uses superposition coding and we consider two special cases for the receivers. The first one is when both receivers treat interference as noise. The second is when the user with a better channel uses successive decoding and the other receiver treats interference as noise.

  • 119.
    Parkvall, Stefan
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Strom, Erik G
    Department of Signals and Systems, Chalmers University of Technology, 412 96 G¨oteborg, Sweden.
    Milstein, Laurence B
    Wireless Communication, University of California, San Diego, La Jolla, CA 92093 USA.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Asynchronous near-far resistant DS-CDMA receivers without a priori synchronization1999In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 47, no 1, p. 78-88Article in journal (Refereed)
    Abstract [en]

    In this paper, several receivers for data demodulation in an asynchronous direct-sequence code-division multiple access (DS-CDMA) system operating without prior knowledge of the propagation delays are proposed and compared. Special attention is paid to the near-far problem, and the proposed schemes are numerically shown to he near-far resistant, The near-far resistance is obtained by estimating the a priori unknown propagation delay using a subspace-based technique. Quantities obtained in the estimation procedure are used to design a filter used for suppression of interference, according to the minimum mean square error criterion. Either a decision feedback technique or a simple two-state Viterbi algorithm is subsequently used for the data demodulation in the uncoded case, By extending the trellis used in the Viterbi algorithm, error correcting coding is easily implemented.

  • 120.
    Persson, Daniel
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Eriksson, Thomas
    Chalmers University, Department of Signals and Systems.
    On Multiple Description Coding of Sources with Memory2010In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 58, no 8, p. 2242-2251Article in journal (Refereed)
    Abstract [en]

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

  • 121.
    Persson, Daniel
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Eriksson, Thomas
    Chalmers.
    Power Series Quantization for Noisy Channels2010In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 58, no 5, p. 1405-1414Article in journal (Refereed)
    Abstract [en]

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

  • 122.
    Persson, Daniel
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Thomas, Eriksson
    Chalmers University of Technology, Gothenburg, Sweden.
    Larsson, Erik G.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Amplifier-Aware Multiple-Input Single-Output Capacity2014In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 62, no 1, p. 913-919Article in journal (Refereed)
    Abstract [en]

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

  • 123. Piazza, R.
    et al.
    Shankar, M.R. Bhavani
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering and Computer Science (EECS), Information Science and Engineering.
    Multi-Gateway Data Predistortion for Non-Linear Satellite Channels2015In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 63, no 10, p. 3789-3802Article in journal (Refereed)
  • 124.
    Pitarokoilis, Antonios
    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.
    ML Detection in Phase Noise Impaired SIMO Channels with Uplink Training2016In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 64, no 1, p. 223-235Article in journal (Refereed)
    Abstract [en]

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

  • 125.
    Pitaval, Renaud-Alexandre
    et al.
    Huawei Technologies Sweden AB.
    Popović, Branislav M.
    Huawei Technologies Sweden AB.
    Van de Beek, Jaap
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    N-continuous SC-FDMA and its Polarized Transmission and Reception2017In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 65, no 11, p. 4911-4925Article in journal (Refereed)
    Abstract [en]

    This paper investigates the application of N -continuous spectral projection precoding design to single-carrier frequency-division multiple access (SC-FDMA). It first considers a general orthogonal projection-based precoded system with an improved iterative receiver and analyzes its ultimate performance in an additive white Gaussian noise channel, both in terms of achievable throughput and symbol-error rates. For N -continuous SC-FDMA, the distribution of the symbol errors is very much asymmetric; a few base pulses carry the lion share of the self-induced interference, resulting in a zero throughput. We show that an optimized transmission and reception scheme based on a polarized use of the base pulses can satisfactorily deal with this asymmetry, and the end-to-end throughput can be recovered to be close to optimal. Applying a similar scheme to N -continuous OFDM enables also an improved performance in the high-SNR regime, where the interference effect strikes the most.

  • 126. Pobloth, H.
    et al.
    Vafin, R.
    Kleijn, W. Bastiaan
    KTH, School of Electrical Engineering (EES), Sound and Image Processing.
    Multivariate block polar quantization2005In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 53, no 12, p. 2043-2053Article in journal (Refereed)
    Abstract [en]

    We introduce multivariate block polar quantization (MBPQ). MBPQ minimizes the weighted squared-error distortion for a set of complex variables representing one block of a signal under a resolution constraint for the entire block. MBPQ performs below the lower bound for classical bivariate quantization, both for Gaussian complex variables and for complex variables found from sinusoidal analysis of audio data. Still, it is of similar complexity as traditional polar quantizers. In the case of audio data, we found a performance gain of about 2.5 dB over the best performing conventional resolution-constrained polar quantization (an extension of unrestricted polar quantization).

  • 127.
    Qi, Nan
    et al.
    KTH. Northwestern Polytechnical University, China.
    Xiao, Ming
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Tsiftsis, Theodoros A.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Cao, Phuong
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Li, Lixin
    Energy-Efficient Cooperative Network Coding With Joint Relay Scheduling and Power Allocation2016In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 64, no 11, p. 4506-4519Article in journal (Refereed)
    Abstract [en]

    The energy efficiency (EE) of a multi-user multi-relay system with the maximum diversity network coding (MDNC) is studied. We explicitly find the connection among the outage probability, energy consumption, and EE, and formulate the maximizing EE problem under the outage probability constraint. Relay scheduling (RS) and power allocation (PA) are applied to schedule the relay states (transmitting, sleeping, and so on) and optimize the transmitting power under the practical channel and power consumption models. Since the optimization problem is NP hard, to reduce computational complexity, the outage probability is first tightly approximated to a log-convex form. Furthermore, the EE is converted into a subtractive form based on the fractional programming. Then, a convex mixed-integer nonlinear problem is eventually obtained. With a generalized outer approximation algorithm, RS and PA are solved in an iterative manner. The Pareto-optimal curves between the EE and the target outage probability show the EE gains from PA and RS. Moreover, by comparing with the no network coding (NoNC) scenario, we conclude that with the same number of relays, MDNC can lead to EE gains. However, if RS is implemented, NoNC can outperform MDNC in terms of the EE when more relays are needed in the MDNC scheme.

  • 128.
    Raeesi, Orod
    et al.
    Tampere Univ Technol, Finland.
    Gokceoglu, Ahmet
    Tampere Univ Technol, Finland.
    Zou, Yaning
    Tech Univ Dresden, Germany.
    Björnson, Emil
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Valkama, Mikko
    Tampere Univ Technol, Finland.
    Performance Analysis of Multi-User Massive MIMO Downlink Under Channel Non-Reciprocity and Imperfect CSI2018In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 66, no 6, p. 2456-2471Article in journal (Refereed)
    Abstract [en]

    This paper analyzes the performance of linearly precoded time division duplex based multi-user massive MIMO downlink system under joint impacts of channel non-reciprocity (NRC) and imperfect channel state information. We consider a generic and realistic NRC model that accounts for transceiver frequency-response as well as mutual coupling mismatches at both user equipment (UE) and base station (BS) sides. The analysis covers two most prominent forms of linear precoding schemes, namely, zero-forcing (ZF) and maximum-ratio transmission (MRT), and assumes that only the statistical properties of the beamformed channel are used at the UE side to decode the received signal. Under the approximation of i.i.d. Gaussian channels, closed-form analytical expressions are derived for the effective signal to interference and noise ratios (SINRs) and the corresponding capacity lower bounds. The expressions show that, in moderate to high SNR, the additional interference caused by imperfect NRC calibration can degrade the performance of both precoders significantly. Moreover, ZF is shown to be more sensitive to NRC than MRT. Numerical evaluations with practical NRC levels indicate that this performance loss in the spectral efficiency can be as high as 42% for ZF, whereas it is typically less than 13% for MRT. It is also shown that due to the NRC, the asymptotic large-antenna performance of both precoders saturate to an identical finite level. The derived analytical expressions provide useful tools and valuable technical insight, e.g., into calculating the NRC calibration requirements in BSs and UEs for any given specific performance targets in terms of effective SINR or the system capacity bound.

  • 129.
    Rasmussen, Lars Kildehöj
    et al.
    National University of Singapore.
    Lim, Teng Joon
    National University of Singapore.
    Aulin, Tor M.
    Chalmers University of Technology.
    Breadth-first maximum likelihood detection in multiuser CDMA1997In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 45, no 10, p. 1176-1178Article in journal (Refereed)
  • 130.
    Rasmussen, Lars Kildehöj
    et al.
    National University of Singapore.
    Lim, Teng Joon
    National University of Singapore.
    Johansson, Ann-Louise
    Chalmers University of Technology.
    A matrix-algebraic approach to successive interference cancellation in CDMA2000In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 48, no 1, p. 145-151Article in journal (Refereed)
  • 131.
    Rasmussen, Lars Kildehöj
    et al.
    Georgia Institute of Technology.
    Wicker, Stephen B.
    Georgia Institute of Technology.
    TRELLIS-CODED, TYPE-I HYBRID-ARQ PROTOCOLS BASED ON CRC ERROR-DETECTING CODES1995In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 43, no 10, p. 2569-2575Article in journal (Refereed)
  • 132.
    Sandberg, Sara
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Deetzen, Neele von
    Jacobs University, Bremen.
    Design of bandwidth-efficient unequal error protection LDPC codes2010In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 58, no 3, p. 802-811Article in journal (Refereed)
    Abstract [en]

    This paper presents a strategy for the design of bandwidth-efficient LDPC codes with unequal error protection. Bandwidth efficiency is obtained by appropriately designing the codes for higher order constellations, assuming an AWGN channel. The irregularities of the LDPC code are designed, using the Gaussian approximation of the density evolution, to enhance the unequal error protection property of the code as well as account for the different bit error probabilities given by the higher order constellation. The proposed code design algorithm is flexible in terms of the number and proportions of protection classes. It also allows arbitrary modulation schemes. Our method combines the design of unequal error protection LDPC codes for the binary input AWGN channel with the code design for higher order constellations by dividing the variable node degree distribution into sub-degree distributions for each protection class and each level of protection from the modulation. The results show that appropriate code design for higher order constellations reduces the overall bit-error rate significantly. Furthermore, the unequal error protection capability of the code is increased, especially for high SNR.

  • 133.
    Sarkis, Gabi
    et al.
    McGill University, Canada .
    Hemati, Saied
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Mannor, Shie
    Technion Israel Institute Technology, Israel .
    Gross, Warren J.
    McGill University, Canada .
    Stochastic Decoding of LDPC Codes over GF(q)2013In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 61, no 3, p. 939-950Article in journal (Refereed)
    Abstract [en]

    Despite the outstanding performance of non-binary low-density parity-check (LDPC) codes over many communication channels, they are not in widespread use yet. This is due to the high implementation complexity of their decoding algorithms, even those that compromise performance for the sake of simplicity. less thanbrgreater than less thanbrgreater thanIn this paper, we present three algorithms based on stochastic computation to reduce the decoding complexity. The first is a purely stochastic algorithm with error-correcting performance matching that of the sum-product algorithm (SPA) for LDPC codes over Galois fields with low order and a small variable node degree. We also present a modified version which reduces the number of decoding iterations required while remaining purely stochastic and having a low per-iteration complexity. less thanbrgreater than less thanbrgreater thanThe second algorithm, relaxed half-stochastic (RHS) decoding, combines elements of the SPA and the stochastic decoder and uses successive relaxation to match the error-correcting performance of the SPA. Furthermore, it uses fewer iterations than the purely stochastic algorithm and does not have limitations on the field order and variable node degree of the codes it can decode. less thanbrgreater than less thanbrgreater thanThe third algorithm, NoX, is a fully stochastic specialization of RHS for codes with a variable node degree 2 that offers similar performance, but at a significantly lower computational complexity. less thanbrgreater than less thanbrgreater thanWe study the performance and complexity of the algorithms; noting that all have lower per-iteration complexity than SPA and that RHS can have comparable average per-codeword computational complexity, and NoX a lower one.

  • 134.
    Schiessl, Sebastian
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Information Science and Engineering.
    Al-Zubaidy, Hussein
    KTH, School of Electrical Engineering and Computer Science (EECS), Information Science and Engineering.
    Skoglund, Mikael
    KTH, School of Electrical Engineering and Computer Science (EECS), Information Science and Engineering.
    Gross, James
    KTH, School of Electrical Engineering and Computer Science (EECS), Information Science and Engineering.
    Delay Performance of Wireless Communications With Imperfect CSI and Finite-Length Coding2018In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 66, no 12, p. 6527-6541Article in journal (Refereed)
    Abstract [en]

    With the rise of critical machine-to-machine applications, next generation wireless communication systems must meet challenging requirements with respect to latency and reliability. A key question in this context relates to channel state estimation, which allows the transmitter to adapt the code rate to the channel state. In this paper, we characterize the tradeoff between the training sequence length and data codeword length: shorter channel estimation leaves more time for the payload transmission but reduces the estimation accuracy and causes more decoding errors. Using lower coding rates can mitigate this effect, but may result in a higher backlog of data at the transmitter. In order to optimize the training sequence length and the rate adaptation scheme with respect to the delay performance, we employ queuing analysis on top of accurate models of the physical layer. We obtain an analytically tractable solution to the problem by deriving a closed-form approximation for the decoding error probability due to imperfect channel knowledge and finite-blocklength channel coding. The optimized training sequence length and rate adaptation strategy can reduce the delay violation probability by an order of magnitude, compared with suboptimal strategies that do not consider the delay constraints.

  • 135.
    Schrammar, Nicolas
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Transmission Strategies for Wireless Relay Networks Obtained from Linear Finite-Field Deterministic Models2012In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 60, no 8, p. 2167-2176Article in journal (Refereed)
    Abstract [en]

    In this paper we show how the recently proposed linear finite-field deterministic model (LFFM) can be used to design transmission strategies for the corresponding AWGN model of wireless relay networks. The transmission scheme in the AWGN model uses hierarchical modulation to transmit information on multiple layers. We show that a transmission strategy in the LFFM can be translated to the AWGN model if it is coordinated, that is, if the amount of interference is limited in a certain way. We consider two types of coordination, full and partial, with different restrictions on the transmission scheme. In both cases we show that the rate in the AWGN model is at most a constant gap below the rate in the LFFM, which provides a link between the models. Closed-form upper bounds on the gap are derived based on the analysis of noise and interference forwarding. The bounds are evaluated numerically, and the dependency on the system parameters and the parameters of coordination are discussed. The trade-off between full and partial coordination and the corresponding parameters are illustrated.

  • 136.
    Schrammar, Nicolas
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Wang, Chao
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Rasmussen, Lars Kildehøj
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    New Achievable Rates for Gaussian Partially Cognitive Interference Channels With Multiple Cognitive Pairs2014In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 62, no 6, p. 2051-2060Article in journal (Refereed)
    Abstract [en]

    This paper characterizes achievable rate regions for the Gaussian partially cognitive interference channel with multiple cognitive pairs (K-PCIFC), where the cognitive transmitters know one part of the primary transmitter's message. We explore a novel methodology using the deterministic discrete superposition model (DSM). We find codes and their achievable rate regions in the DSM, and we show that they yield achievable rate regions in the Gaussian model. Our coding scheme in the DSM can be applied in general scenarios. We devise an achievable rate region for the K-PCIFC, which is within a constant gap to known outer bounds for K = 2 in the weak interference regime. From our expressions we derive guidelines for designing the cognitive link between the primary transmitter and the cognitive transmitters. Furthermore, we show that the gain from cognition diminishes for increasing K.

  • 137.
    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.

  • 138.
    Shokri-Ghadikolaei, Hossein
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Fischione, Carlo
    KTH, School of Electrical Engineering (EES), Automatic Control.
    The Transitional Behavior of Interference in Millimeter Wave Networks and Its Impact on Medium Access Control2015In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 64, no 2, p. 723-740Article in journal (Refereed)
    Abstract [en]

    Millimeter wave (mmWave) communication systems use large number of antenna elements that can potentially overcome severe channel attenuation by narrow beamforming. Narrow-beam operation in mmWave networks also reduces multiuser interference, introducing the concept of noise-limited wireless networks as opposed to interference-limited ones. The noise-limited or interference-limited regime heavily reflects on the medium access control (MAC) layer throughput and on proper resource allocation and interference management strategies. Yet, these regimes are ignored in current approaches to mmWave MAC layer design, with the potential disastrous consequences on the communication performance. In this paper, we investigate these regimes in terms of collision probability and throughput. We derive tractable closed-form expressions for the collision probability and MAC layer throughput of mmWave ad hoc networks, operating under slotted ALOHA. The new analysis reveals that mmWave networks may exhibit a non-negligible transitional behavior from a noise-limited regime to an interference-limited one, depending on the density of the transmitters, density and size of obstacles, transmission probability, operating beamwidth, and transmission power. Such transitional behavior necessitates a new framework of adaptive hybrid resource allocation procedure, containing both contention-based and contention-free phases with on-demand realization of the contention-free phase. Moreover, the conventional collision avoidance procedure in the contention-based phase should be revisited, due to the transitional behavior of interference, to maximize throughput/delay performance of mmWave networks. We conclude that, unless proper hybrid schemes are investigated, the severity of the transitional behavior may significantly reduce throughput/delay performance of mmWave networks.

  • 139.
    Shokri-Ghadikolaei, Hossein
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Fischione, Carlo
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Fodor, Gabor
    KTH, School of Electrical Engineering (EES), Automatic Control. Ericsson Res, Sweden.
    Popovski, Petar
    Aalborg Univ, Denmark.
    Zorzi, Michele
    Univ Padua, Italy.
    Millimeter Wave Cellular Networks: A MAC Layer Perspective2015In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 63, no 10, p. 3437-3458Article in journal (Refereed)
    Abstract [en]

    The millimeter wave (mmWave) frequency band is seen as a key enabler of multi-gigabit wireless access in future cellular networks. In order to overcome the propagation challenges, mmWave systems use a large number of antenna elements both at the base station and at the user equipment, which lead to high directivity gains, fully-directional communications, and possible noise-limited operations. The fundamental differences between mmWave networks and traditional ones challenge the classical design constraints, objectives, and available degrees of freedom. This paper addresses the implications that highly directional communication has on the design of an efficient medium access control (MAC) layer. The paper discusses key MAC layer issues, such as synchronization, random access, handover, channelization, interference management, scheduling, and association. The paper provides an integrated view on MAC layer issues for cellular networks, identifies new challenges and tradeoffs, and provides novel insights and solution approaches.

  • 140.
    Si, Zhongwei
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Thobaben, Ragnar
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Bilayer LDPC Convolutional Codes for Decode-and-Forward Relaying2013In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 61, no 8, p. 3086-3099Article in journal (Refereed)
    Abstract [en]

    In this paper we present bilayer LDPC convolutional codes for half-duplex relay channels. Two types of codes, bilayer expurgated LDPC convolutional codes and bilayer lengthened LDPC convolutional codes, are proposed for decode-and-forward (DF) relaying. In the case of the binary erasure relay channel, we prove analytically that both code constructions achieve the capacities of the source-relay link and the source-destination link simultaneously, provided that the channel conditions are known when designing the codes. Meanwhile, both codes enable the highest transmission rate possible with DF relaying for a wide range of channel parameters. In addition, the regular degree distributions can easily be computed from the channel parameters, which significantly simplifies the code optimization. The code construction and performance analysis are extended to the general binary memoryless symmetric channel, where a capacity-achieving performance is conjectured. Numerical results are provided for both types of codes with finite node degrees over binary erasure channels and binary-input additive white Gaussian noise channels, which verify the aforementioned theoretical analysis.

  • 141.
    Sjöberg, Frank
    et al.
    Luleå tekniska universitet.
    Isaksson, Mikael
    Telia Research AB.
    Nilsson, Rickard
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Ödling, Per
    Lunds universitet.
    Wilson, Sarah Kate
    Luleå tekniska universitet.
    Börjesson, Per-Ola
    Lunds universitet.
    Zipper - a duplex method for VDSL based on DMT1999In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 47, no 8, p. 1245-1252Article in journal (Refereed)
    Abstract [en]

    We present a new duplex scheme, called Zipper, for discrete multitone (DMT)-based very high bit-rate digital subscriber line (VDSL) systems on copper wires. This scheme divides the available bandwidth by assigning different subcarriers for the upstream and downstream directions. It has high flexibility to divide the capacity between the up and downstream, as well as good coexistence possibilities with other systems such as ADSL. Simulation results show the high bit-rate performance in different environments such as mixed ADSL and VDSL traffic under radio frequency interference and with different background noise sources

  • 142.
    Skoglund, Mikael
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Larsson, Erik G.
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Optimal Modulation for Known Interference2008In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 56, no 11, p. 1892-1899Article in journal (Refereed)
    Abstract [en]

    We present a symbol-by-symbol approach to the problem of canceling known interference at the transmitter in a communication system. In the envisioned system, the modulator maps an information symbol (taken from a finite alphabet) and an interference symbol (from the complex field) onto a transmitted constellation point. Our scheme is based on joint optimization of a modulator and demodulator, subject to a constraint on the average transmit power. The demodulator picks the information symbol (as a function of the received symbol) that minimizes the average error probability. We emphasize that our focus is on transmission in a single (complex) dimension, and hence the proposed technique is a "modulation" rather than a "coding" scheme. We illustrate that the new scheme outperforms Tomlinson-Harashima precoding, which is a classical but suboptimal solution to the one-dimensional known-interference precoding problem. In our simulations, the new approach is able to perform close to the no-interference bound.

  • 143.
    Skoglund, Mikael
    et al.
    Royal Institute of Technology (KTH).
    Larsson, Erik G.
    Royal Institute of Technology (KTH).
    Optimal Modulation for Known Interference2008In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 56, no 11, p. 1892-1899Article in journal (Refereed)
    Abstract [en]

    We present a symbol-by-symbol approach to the problem of canceling known interference at the transmitter in a communication system. In the envisioned system, the modulator maps an information symbol (taken from a finite alphabet) and an interference symbol (from the complex field) onto a transmitted constellation point. Our scheme is based on joint optimization of a modulator and demodulator, subject to a constraint on the average transmit power. The demodulator picks the information symbol (as a function of the received symbol) that minimizes the average error probability. We emphasize that our focus is on transmission in a single (complex) dimension, and hence the proposed technique is a “modulation” rather than a “coding” scheme. We illustrate that the new scheme outperforms Tomlinson–Harashima precoding, which is a classical but suboptimal solution to the one-dimensional known-interference precoding problem. In our simulations, the new approach is able to perform close to the no-interference bound.

  • 144.
    Skoglund, Mikael O.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Bit-estimate based decoding for vector quantization over noisy channels with intersymbol interference2000In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 48, no 8, p. 1309-1317Article in journal (Refereed)
    Abstract [en]

    We introduce new techniques for quantization over noisy channels with intersymbol interference. We focus on the decoding problem, and present a decoder structure that allows the decoding to be based on soft minimum mean-square-error estimates of the transmitted bits. The new bit-estimate based decoder provides a structured lower-complexity approximation of optimal decoding for general codebooks, and for so-called linear mapping codebooks, it is shown that its implementation becomes particularly simple, We investigate decoding based on optimal bit-estimates, and on suboptimal estimates of lower computational complexity. We also consider encoder optimization and combined source-channel code design. Numerical simulations demonstrate that bit estimate based de coding is able to outperform a two-stage decision-based approach implemented using Viterbi sequence detection plus table look-up source decoding. The simulations also show that decoding based on suboptimal bit-estimates performs well, at a considerably lowered complexity.

  • 145.
    Stathakis, Efthymios
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Rasmussen, Lars K.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. Univ S Australia, Inst Telecommun Res, Mawson Lakes 5095, Australia.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Closed-Form Capacity Result for Interference-Limited Environments With Mixed Fading2015In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 63, no 6, p. 2374-2387Article in journal (Refereed)
    Abstract [en]

    We study a multinode network, where a multiantenna transmitter T-x communicates with its desired receiver R-x, whereas a cluster P (sic) {P-x,P- n, n = 1,..., N} of unintended nodes is disturbed by the T-x-R-x (TR) communication. To prevent severe performance degradation, we impose a constraint on the total interference that is inflicted at the nodes of P. The TR link contains a line-of-sight component, whereas the propagation environment for each T-x-P-x, n link is shadowed. The T-x node is preprocessing the information sequence by means of a precoding matrix that is optimized to achieve the ergodic capacity under a constraint on the maximum admissible ergodic interference power, arriving on P. In this paper, we show that the optimum precoding strategy involves the transmission of a single stream over the precoding direction, i.e., the eigenvector of the precoding matrix, which corresponds to beamforming along the instantaneous direction of the TR-link channel. The solution of the remaining power allocation problem yields the optimal precoding matrix. For this setup, we provide an efficient stochastic characterization of the network, which allows us to obtain an analytical expression for the TR-link ergodic capacity; this problem has been previously open, even for the case of a single-antenna node T-x and a single-element set P. We complement the analysis by deriving the TR-link signal-to-noise ratio and the average bit error rate, which are associated with our transmission scheme. Numerical results corroborate the theoretical analysis and reveal an interplay between the network parameters and their impact on the TR-link performance.

  • 146.
    Stathakis, Efthymios
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Rasmussen, Lars K.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    On Beamforming and Orthogonal Space-Time Coding in Cognitive Networks with Partial CSI2013In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 61, no 3, p. 961-972Article in journal (Refereed)
    Abstract [en]

    We consider a pair of secondary users that coexist, in a cognitive network, with multiple primary user pairs. The secondary link is supplied with partial network side information (NSI), which comprises message side information and partial channel side information (CSI), available in different levels at both the transmitter and the receiver of the cognitive link. The cognitive transceiver design has to obey predefined quality-of-service (QoS) criteria, that need to be maintained at the primary receivers, and at the same time properly handle the incoming interference from each primary transmitter in order to establish reliable communication. In this framework, we investigate the design and performance of the combined beamforming and orthogonal space-time block coding (BOSTBC) strategy, whose merits are well-documented, as a candidate transmission scheme for the secondary link. We study both aspects, QoS and interference, of the composite problem and characterize how they affect the beamformer design and the cognitive link performance, in the presence of partial NSI. Further, we propose a CSI quality-dependent model for the QoS criteria which yields an interesting trade-off between the cognitive link design and the primary QoS. Numerical results illustrate the system performance in this framework.

  • 147.
    Ström, Erik G
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Parkvall, Stefan
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Miller, Scott L
    Department of Electrical Engineering, University of Florida, Gainesville, FL 3261 1 USA.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Propagation delay estimation in asynchronous direct-sequence code-division multiple access systems1996In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 44, no 1, p. 84-93Article in journal (Refereed)
    Abstract [en]

    In an asynchronous direct-sequence code-division multiple access CDS-CDMA) communication system, the parameter estimation problem, i.e., estimating the propagation delay, attenuation and phase shift of each user's transmitted signal, may be complicated by the so-called near-far problem. The near-far problem occurs when the amplitudes of the users' received signals are very dissimilar, as the case might be in many important applications, In particular, the standard method for estimating the propagation delays will fail in a near-far situation, Several new estimators, the maximum likelihood, an approximative maximum likelihood and a subspace-based estimator, are therefore proposed and are shown to be robust against the near-far problem, No knowledge of the transmitted bits is assumed, and the proposed estimators can thus be used for both acquisition and tracking. In addition, the Cramer-Rao bound is derived for the parameter estimation problem.

  • 148.
    Svedman, Patrick
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Wilson, Sarah Kate
    Department of Electrical Engineering, Santa Clara University, Santa Clara, USA.
    Cimini, Leonard J., Jr.
    e Electrical and Computer Engineering Department, University of Delaware, Newark, USA..
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Opportunistic beamforming and scheduling for OFDMA systems2007In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 55, no 5, p. 941-952Article in journal (Refereed)
    Abstract [en]

    Orthogonal frequency-division multiple access (OFDMA) is an attractive technique for exploiting multiuser diversity in the downlink of a cellular system. This paper addresses three problems in multiuser diversity for OFDMA systems. First, we propose a way to significantly reduce the amount of channel state information (CSI) feedback without sacrificing performance too much, by selective and adaptive feedback. Second, we propose a way to increase the cell throughput and fairness by appying an opportunistic beamforming scheme to orthogonal frequency-division multiplexing. This beamforming scheme increases the frequency fading rate, which increases the multiuser diversity effect. Thirdly, we deal with the issue of fairness and quality-of-service (QoS) in opportunistic systems by proposing a modified proportional fair (PF) scheduler for OFDMA. Key features in the scheduler are that it incorporates QoS classes into the PF scheduler and that it has a tunable fairness level. Extensive simulation results are presented to evaluate. the performance of the proposed schemes. The opportunistic beamforming scheme performed well in comparison with several other schemes. The modified PF scheduler was able to give users different QoS, based on their requirements, while still exploiting multiuser diversity.

  • 149.
    Svedman, Patrick
    et al.
    KTH.
    Wilson, Sarah Kate
    Cimini, Leonard J., Jr.
    Ottersten, Björn
    KTH, Superseded Departments (pre-2005), Speech, Music and Hearing.
    Opportunistic beamforming and scheduling for OFDMA systems (vol 55, pg 941, 2007)2007In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 55, no 6, p. 1266-1266Article in journal (Refereed)
  • 150.
    Takeuchi, Keigo
    et al.
    University of Electro-Communications, Department of Communication Engineering and Informatics.
    Müller, Ralf R.
    University Erlangen-Nürnberg.
    Vehkaperä, Mikko
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Iterative LMMSE Channel Estimation and Decoding Based on Probabilistic Bias2013In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 61, no 7, p. 2853-2863Article in journal (Refereed)
    Abstract [en]

    Iterative channel estimation and decoding based on probabilistic bias is investigated. In order to control the occurrence probability of transmitted symbols, biased convolutional codes (CCs) are proposed. A biased CC is obtained by puncturing the parity bit of a conventional (unbiased) CC and by inserting a fixed bit at the punctured position when the state is contained in a certain subset of all possible states. A priori information about the imposed bias is utilized for the initial linear minimum mean-squared error (LMMSE) channel estimation. This paper focuses on biased turbo codes that are constructed as the parallel concatenation of two biased CCs with interleaving, and proposes an iterative LMMSE channel estimation and decoding scheme based on approximate belief propagation. The convergence property of the iterative LMMSE channel estimation and decoding scheme is analyzed via density evolution (DE). The DE analysis allows one to design the magnitude of the bias according to the coherence time, in terms of the decoding threshold. The proposed scheme is numerically shown to outperform conventional pilot-based schemes in the moderate signal-to-noise ratio (SNR) regime, at the expense of a performance degradation in the high SNR regime.

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