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Numrering	Referens	Omslagsbild	Hitta
1.	Abrardo, Andrea, et al. (författare) MMSE Receiver Design and SINR Calculation in MU-MIMO Systems With Imperfect CSI 2019 Ingår i: IEEE Wireless Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-2337 .- 2162-2345. ; 8:1, s. 269-272 Tidskriftsartikel (refereegranskat)abstract The performance of the uplink of multiuser multiple input multiple output systems depends critically on the receiver architecture and on the quality of the acquired channel state information. A popular approach is to design linear receivers that minimize the mean squared error (MSE) of the received data symbols. Unfortunately, most of the literature does not take into account the presence of channel state information errors in the MSE minimization. In this letter we develop a linear minimum MSE (MMSE) receiver that employs the noisy instantaneous channel estimates to minimize the MSE, and highlight the dependence of the receiver performance on the pilot-to-data power ratio. By invoking the theory of random matrices, we calculate the users' signal-to-interference-plus-noise ratio as a function of the number of antennas and the pilot-to-data power ratio of all users. Numerical results indicate that this new linear receiver outperforms the classical mismatched MMSE receiver.
2.	Akhlaghpasand, Hossein, et al. (författare) Jamming Detection in Massive MIMO Systems 2018 Ingår i: IEEE Wireless Communications Letters. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2162-2337 .- 2162-2345. ; 7:2, s. 242-245 Tidskriftsartikel (refereegranskat)abstract This letter considers the physical layer security of a pilot-based massive multiple-input multiple-output (MaMIMO) system in presence of a multi-antenna jammer. We propose a new jamming detection method that makes use of a generalized likelihood ratio test over some coherence blocks. Our proposed method utilizes intentionally unused pilots in the network. The performance of the proposed detector improves by increasing the number of antennas at the base station, the number of unused pilots and also by the number of the coherence blocks that are utilized. Simulation results show that in the MaMIMO regime, perfect detection is achievable even with a small number of unused pilots.
3.	Antonioli, Roberto P., et al. (författare) User Scheduling for Sum-Rate Maximization Under Minimum Rate Constraints for the MIMO IBC 2019 Ingår i: IEEE Wireless Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-2337 .- 2162-2345. ; 8:6, s. 1591-1595 Tidskriftsartikel (refereegranskat)abstract While the problem of sum-rate maximization of the multiple-input-multiple-output interference broadcast channel (MIMO IBC) has been extensively studied, most of the proposed solutions do not ensure a minimum rate for each scheduled user. In practice, many services require a minimum rate from the underlying communication links. Therefore, in this letter, we consider a sum-rate maximization problem with per-link minimum rate constraints for the MIMO IBC. The key idea is scheduling a suitable subset of the communication links for simultaneous transmissions, such that a minimum rate for each scheduled link can be ensured. To this end, we pose the sum-rate maximization problem as a combinatorial optimization problem, in which we introduce binary variables to the classical transceiver design problem. We propose a centralized solution based on branch-and-bound and a low-complexity semi-distributed scheme, in which a centralized unit is responsible for scheduling decisions, while the transceiver computations are distributed. Simulations show that the proposed solutions handle the user scheduling effectively, while the proposed semi-distributed scheme performs closely to the centralized scheme.
4.	Ardah, Khaled, et al. (författare) A Novel Cell Reconfiguration Technique for Dynamic TDD Wireless Networks 2018 Ingår i: IEEE Wireless Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-2337 .- 2162-2345. ; 7:3, s. 320-323 Tidskriftsartikel (refereegranskat)abstract In dynamic time division duplexing (DTDD) systems, the uplink (UL) and downlink (DL) resources can be configured to adapt to changing traffic conditions. Therefiwe, DTDD systems are advantageously deployed in scenarios in which the UL and DL traffic demands are asymmetric and timevarying. Unfortunately, multicell DTDD systems give rise to base station-to-base station and user equipment-to-user equipment interference, that can severely degrade the system performance. Previous works on DTDD either assumed that the UL/DL configurations are given, or they did not take into account the negative impact of multicell DTDD interference. In this letter, we propose a novel cell reconfiguration technique that considers both the prevailing traffic conditions and multicell interference levels. The proposed technique is based on an efficient solution of a mixed integer linear program, whose objective is to maximize the overall system throughput taking into account users' traffic preferences. Realistic system level simulations indicate that the proposed scheme outperforms not only the static TDD system but also other reference schemes, that disregard the DTDD specific interference effects.
5.	Azimi-Abarghouyi, Seyed Mohammad, et al. (författare) Decentralized Compute-and-Forward for Ad Hoc Networks 2016 Ingår i: IEEE Wireless Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-2345 .- 2162-2337. ; 5:6, s. 652-655 Tidskriftsartikel (refereegranskat)abstract In this letter, we introduce a decentralized compute-and-forward (DCMF) protocol to solve the rank failure problem in compute-and-forward (CMF) ad hoc multi-user multi-relay networks without a central coordinator. In sufficiently strong inter-relay links, we show that the DCMF scheme can reach the same achievable rate as in the successive centralized CMF (SCCMF), which is a modified version of the previously introduced centralized CMF in using our proposed successive method for a fair comparison. We evaluate the outage probability and rate of the proposed strategy, and compare the results with those of the conventional CMF and decode-and-forward, and the SCCMF.
6.	Barros da Silva Jr., José Mairton, et al. (författare) A Binary Power Control Scheme for D2D Communications 2015 Ingår i: IEEE Wireless Communications Letters. - : IEEE. - 2162-2337 .- 2162-2345. ; 4:6, s. 669-672 Tidskriftsartikel (refereegranskat)abstract Binary power control (BPC) is known to maximize the capacity of a two-cell interference limited system and performs near optimally for larger systems. However, when device-to-device (D2D) communication underlaying the cellular layer is supported, an objective function that considers the power consumption is more suitable. We find that BPC remains optimal for D2D communications when the weight of the overall power consumption in the utility function is bounded. Building on this insight, we propose a simple near-optimal extended BPC scheme and compare its performance with a recently proposed utility optimal iterative scheme using a realistic multicell simulator. Our results indicate that a near optimal D2D performance can be achieved without lengthy iterations or complex signaling mechanisms.
7.	Cavalcante, Eduardo de Olivindo, et al. (författare) Distributed Beamforming in Dynamic TDD MIMO Networks With BS to BS Interference Constraints 2018 Ingår i: IEEE Wireless Communications Letters. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2162-2337 .- 2162-2345. ; 7:5, s. 788-791 Tidskriftsartikel (refereegranskat)abstract This letter proposes distributed beamforming as a means of reducing interference in dynamic time division duplexing multiple input multiple output networks. Specifically, we formulate an optimization task, whose objective is to minimize the base station (BS) transmit power, while satisfying a predefined signal-to-interference-plus-noise ratio threshold for each downlink user equipment and keeping the BS to BS interference power below a tolerable level. An iterative decentralized solution requiring reduced signaling load based on primal decomposition is proposed. This decentralized algorithm is shown to iterate towards the centralized solution, while feasible but suboptimal solutions can be obtained at any iteration.
8.	Chen, Zheng, et al. (författare) When Is the Achievable Rate Region Convex in Two-User Massive MIMO Systems? 2018 Ingår i: IEEE Wireless Communications Letters. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2162-2337 .- 2162-2345. ; 7:5, s. 796-799 Tidskriftsartikel (refereegranskat)abstract This letter investigates the achievable rate region in massive multiple-input-multiple-output systems with two users, with a focus on the i.i.d. Rayleigh fading and line-of-sight (LoS) scenarios. If the rate region is convex, spatial multiplexing is preferable to orthogonal scheduling, while the opposite is true for non-convex regions. We prove that the uplink and downlink rate regions with i.i.d. Rayleigh fading are convex, while the convexity in LoS depends on parameters such as angular user separation, number of antennas, and signal-to-noise ratio (SNR).
9.	Deng, Tao, et al. (författare) Device caching for network offloading : Delay minimization with presence of user mobility 2018 Ingår i: IEEE Wireless Communications Letters. - 2162-2337 .- 2162-2345. ; 7:4, s. 558-561 Tidskriftsartikel (refereegranskat)
10.	Do, Tan Tai, et al. (författare) Massive MIMO Pilot Retransmission Strategies for Robustification Against Jamming 2017 Ingår i: IEEE Wireless Communications Letters. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2162-2337 .- 2162-2345. ; 6:1, s. 58-61 Tidskriftsartikel (refereegranskat)abstract This letter proposes anti-jamming strategies based on pilot retransmission for a single user uplink massive MIMO under jamming attack. A jammer is assumed to attack the system both in the training and data transmission phases. We first derive an achievable rate which enables us to analyze the effect of jamming attacks on the system performance. Counter-attack strategies are then proposed to mitigate this effect under two different scenarios: random and deterministic jamming attacks. Numerical results illustrate our analysis and benefit of the proposed schemes.
11.	Fang, Chao, 1991, et al. (författare) Equal Gain Combining in Poisson Networks With Spatially Correlated Interference Signals 2016 Ingår i: IEEE Wireless Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-2345 .- 2162-2337. ; 5:6, s. 628-631 Tidskriftsartikel (refereegranskat)abstract We study the successful reception probability and the area spectral efficiency (ASE) of equal gain receivers in a network where transmitters are distributed according to a Poisson point process. Considering spatially correlated interference signals, we derive exact analytical expression of the successful reception probability for two receive antennas and tight approximations for more than two receive antennas. Also, we give an approximation for the optimal transmitter density maximizing the ASE. The results show that the fully-correlated case where interference on different antennas are from the same set of transmitters gives pessimistic successful reception probability, while the uncorrelated case is optimistic.
12.	Gabry, Frédéric, et al. (författare) Energy Efficiency Analysis of Cooperative Jamming in Cognitive Radio Networks with Secrecy Constraints 2015 Ingår i: IEEE Wireless Communications Letters. - 2162-2337 .- 2162-2345. ; 4:4, s. 437-440 Tidskriftsartikel (refereegranskat)abstract We investigate energy-efficient cooperation for secrecy in cognitive radio networks. In particular, we consider a four-node cognitive scenario where the secondary receiver is treated as a potential eavesdropper with respect to the primary transmission. The cognitive transmitter should ensure that the primary message is not leaked to the secondary user by using cooperative jamming. We investigate the optimal power allocation and power splitting at the secondary transmitter for our cognitive model to maximize the secondary energy efficiency (EE) under secrecy constraints. We formulate and analyze an important EE Stackelberg game between the two transmitters aiming at maximizing their utilities. We illustrate the analytical results through our geometrical model, highlighting the EE performance of the system and the impact of the Stackelberg game.
13.	Gerami, Majid, et al. (författare) Partial Repair for Wireless Caching Networks With Broadcast Channels 2015 Ingår i: IEEE Wireless Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-2337 .- 2162-2345. ; 4:2, s. 145-148 Tidskriftsartikel (refereegranskat)abstract We investigate the repair problem for wireless caching networks when parts of stored packets in cashing nodes are lost. We first develop theoretical lower bounds on the number of necessary transmission packets over error-free broadcast channels for repair. Then we discuss the impact of the distribution of the lost packets among caching nodes. Finally, we study the construction of repair codes and propose the optimal exact repair for some special scenarios.
14.	Girnyk, Maksym A., et al. (författare) On the asymptotic sum rate of downlink cellular systems with random user locations 2015 Ingår i: IEEE Wireless Communications Letters. - 2162-2337 .- 2162-2345. ; 4:3, s. 333-336 Tidskriftsartikel (refereegranskat)abstract We consider a downlink cellular communication system with a multi-antenna base station (BS). A regularized zero forcing precoder is employed at the BS to manage the inter-user interference within the cell. Using methods from random matrix theory, we derive a deterministic approximation for the achievable ergodic sum rate, taking into account the randomness from both fading and random user locations. The obtained approximation describes well the behavior of finite-sized systems and enables efficient optimization of the precoder matrix.
15.	Guntupalli, Lakshmikanth, et al. (författare) Multiple Packet Transmissions in Duty Cycling WSNs : A DTMC Based Throughput Analysis 2018 Ingår i: IEEE Wireless Communications Letters. - : IEEE. - 2162-2337 .- 2162-2345. ; 7:3, s. 480-483 Tidskriftsartikel (refereegranskat)abstract Multiple packet transmissions (MPT) improve performance by transmitting multiple packets in a single operational cycle. Asynchronous duty cycling (DC) medium access control (MAC) protocols such as receiver initiated MAC protocol (RI-MAC) transmit multiple packets in one cycle. In this paper, we develop two associated discrete time Markov chain (DTMC) models to model MPT that can be achieved via multiple node competitions. Furthermore, we present the way of incorporating those developed models with each other for evaluating performance of RI-MAC with MPT. Using the solution of DTMC models, network throughput of MPT is calculated and compared with the one achieved by single packet transmission MAC (e.g., S-MAC) protocol. Validation of analytical results through discrete-event simulations confirms the accuracy of modeling and discloses the operation of MPT in RI-MAC protocol.
16.	Gustafson, Carl, et al. (författare) Statistical Modeling and Estimation of Censored Pathloss Data 2015 Ingår i: IEEE Wireless Communications Letters. - 2162-2337 .- 2162-2345. ; 4:5, s. 569-572 Tidskriftsartikel (refereegranskat)abstract Pathloss is typically modeled using a log-distance power law with a large-scale fading term that is log-normal. However, the received signal is affected by the dynamic range and noise floor of the measurement system used to sound the channel, which can cause measurement samples to be truncated or censored. If the information about the censored samples is not included in the estimation method, as in ordinary least squares estimation, it can result in biased estimation of both the pathloss exponent and the large scale fading. This can be solved by applying a Tobit maximum-likelihood estimator, which provides consistent estimates for the pathloss parameters. This letter provides information about the Tobit maximum-likelihood estimator and its asymptotic variance under certain conditions.
17.	haghifam, mahdi, et al. (författare) Joint Sum Rate and Error Probability Optimization: Finite Blocklength Analysis 2017 Ingår i: IEEE Wireless Communications Letters. - 2162-2345 .- 2162-2337. ; 6:6, s. 726-729 Tidskriftsartikel (refereegranskat)abstract We study the tradeoff between the sum rate and the error probability in downlink of wireless networks. Using the recent results on the achievable rates of finite-length codewords, the problem is cast as a joint optimization of the network sum rate and the per-user error probability. We develop an efficient algorithm based on the divide-and-conquer technique to simultaneously maximize the network sum rate and minimize the maximum users’ error probability and to evaluate the effect of the codeword length on the system performance. The results show that, in delay-constrained scenarios, optimizing the per-user error probability plays a key role in achieving high throughput.
18.	Ivanov, Mikhail, 1986, et al. (författare) Unequal Error Protection in Coded Slotted ALOHA 2016 Ingår i: IEEE Wireless Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-2345 .- 2162-2337. ; 5:5, s. 536-539 Tidskriftsartikel (refereegranskat)abstract We analyze the performance of coded slotted ALOHA systems for a scenario where users have different error protection requirements and correspondingly can be divided into user classes. The main goal is to design the system so that the requirements for each class are satisfied. To that end, we derive analytical error floor approximations of the packet loss rate for each class in the finite frame length regime, as well as the density evolution in the asymptotic case. Based on this analysis, we propose a heuristic approach for the optimization of the degree distributions to provide the required unequal error protection. In addition, we analyze the decoding delay for users in different classes and show that better protected users experience a smaller average decoding delay.
19.	Kashyap, Salil, et al. (författare) Power Gain Estimation and Its Impact on Binary Power Control in Underlay Cognitive Radio 2015 Ingår i: IEEE Wireless Communications Letters. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2162-2337 .- 2162-2345. ; 4:2, s. 193-196 Tidskriftsartikel (refereegranskat)abstract We propose a novel minimum mean square error estimator that estimates the channel power gain of the link from the secondary transmitter to the primary receiver (PRx). It lowers the root mean square error compared to several other estimators used in the underlay cognitive radio literature that first estimate the channel amplitude. We then analyze its system impact for two types of interference constraints. To this end, for the optimal binary transmit power control policy, we derive closed-form expressions for the average interference and the probability that the interference at the PRx violates a peak interference constraint with the proposed estimator. We show that the proposed estimator performs closer to the perfect channel state information scenario compared to the other estimators.
20.	Keskin, Furkan, 1988, et al. (författare) Jamming Strategies in Wireless Source Localization Systems 2019 Ingår i: IEEE Wireless Communications Letters. - 2162-2345 .- 2162-2337. ; 8:4, s. 1141-1145 Tidskriftsartikel (refereegranskat)abstract We consider optimal jamming strategies in wireless source localization systems, where anchor nodes estimate positions of target nodes in the presence of jammers that emit zero-mean Gaussian noise. The Cramér-Rao lower bound (CRLB) for target location estimation is derived and the problem of optimal power allocation for jammer nodes is formulated to maximize the average CRLB for target nodes under total and peak power constraints. Exploiting the special problem structure and successive convex approximation techniques, we develop an iterative algorithm that transforms the original non-convex problem into a sequence of convex geometric programs. In addition, we present a closed-form solution that is asymptotically optimal. Numerical results demonstrate the improved jamming performance of the proposed solutions over the uniform power allocation strategy.
21.	Larsson, Erik G., 1974-, et al. (författare) Out-of-Band Radiation From Antenna Arrays Clarified 2018 Ingår i: IEEE Wireless Communications Letters. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2162-2337 .- 2162-2345. ; 7:4, s. 610-613 Tidskriftsartikel (refereegranskat)abstract Non-linearities in radio-frequency transceiver hardware, particularly in power amplifiers, cause distortion in-band and out-of-band. Contrary to claims made in recent literature, in a multiple-antenna system this distortion is correlated across the antennas in the array. A significant implication of this fact is that out-of-band emissions caused by non-linearities are beamformed, in some cases into the same direction as the useful signal.
22.	Larsson, Peter (författare) Golden Angle Modulation 2018 Ingår i: IEEE Wireless Communications Letters. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2162-2337 .- 2162-2345. ; 7:1, s. 98-101 Tidskriftsartikel (refereegranskat)abstract Quadrature amplitude modulation (QAM), with its uniform distribution, exhibits an asymptotic shaping-loss of pi e/6 (approximate to 1.53 dB) with increasing signal-to-noise-ratio compared to the additive white Gaussian noise Shannon capacity. With inspiration gained from special (leaf, flower petal, and seed) packing arrangements (spiral phyllotaxis) found among plants, a novel, shape-versatile, circular symmetric, modulation scheme, the golden angle modulation (GAM) is introduced. Disc-shaped, and complex Gaussian approximating bell-shaped, GAM-signal constellations are considered. For bell-GAM, a high-rate approximation, and a mutual information optimization formulation, are developed. Bell-GAM overcomes the asymptotic shaping-loss seen in QAM, and offers Shannon capacity approaching performance. Transmitter resource limited links, such as space probe-to-earth, and mobile-to-basestation, are cases where GAM could be particularly valuable.
23.	Larsson, Peter, et al. (författare) The Golden Quantizer : The Complex Gaussian Random Variable Case 2018 Ingår i: IEEE Wireless Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-2337 .- 2162-2345. ; 7:3, s. 312-315 Tidskriftsartikel (refereegranskat)abstract The problem of quantizing a circularly symmetric complex Gaussian random variable is considered. For this purpose, we design two non-uniform quantizers, a high-rate- and a Lloyd-Max-quantizer, that are both based on the (golden angle) spiral-phyllotaxis packing principle. We find that the proposed schemes have lower mean-square error distortion compared to (non)-uniform polar/rectangular-quantizers, and near-identical to the best performing trained vector quantizers. The proposed quantizer scheme offers a structured design, a simple natural index ordering, and allows for any number of centroids.
24.	Makki, Behrooz, 1980, et al. (författare) Finite Block-length Analysis of Large-but-finite MIMO Systems 2019 Ingår i: IEEE Wireless Communications Letters. - 2162-2345 .- 2162-2337. ; 8:1, s. 113-116 Tidskriftsartikel (refereegranskat)abstract This letter studies the performance of point-to-point multiple-input-multiple-output (MIMO) systems in the presence of large but finite numbers of transmit and receive antennas. We use some recent results on the achievable rates of finite-length codes to analyze the system performance in the cases with short packets. The results are presented for different fading models. With codewords of finite length, we derive closed-form expressions for the error probability/throughput and determine the minimum number of antennas which are required to satisfy different error probability/throughput requirements. As we show, while the error-constrained required number of antennas is sensitive to the length of short codewords, its effect is negligible for codewords of moderate/long length.
25.	Makki, Behrooz, 1980, et al. (författare) Finite Block-Length Analysis of Spectrum Sharing Networks: Interference-Constrained Scenario 2015 Ingår i: IEEE Wireless Communications Letters. - 2162-2345 .- 2162-2337. ; 4:4, s. 433-436 Tidskriftsartikel (refereegranskat)abstract This letter studies the interference-constrained performance of spectrum sharing networks using adaptive power allocation. The throughput of the secondary user is derived in different cases with constraints on the primary user average or instantaneous received interference power. The analysis is based on some recent results on the achievable rates of finite-length codes and shows the effect of the codeword length on the performance of spectrum sharing networks. The results indicate that, with codewords of finite length and different primary user's interference constraints, there is potential for spectrum sharing, if the transmission power is properly adapted.
26.	Makki, Behrooz, 1980, et al. (författare) Wireless Energy and Information Transmission in FSO and RF-FSO Links 2018 Ingår i: IEEE Wireless Communications Letters. - 2162-2345 .- 2162-2337. ; 7:1, s. 90-93 Tidskriftsartikel (refereegranskat)abstract We propose and analyze a wireless energy and information transmission scheme in free-space optical (FSO) links. The results are presented for both quasi-static and fast-fading conditions. We derive closed-form expressions for throughput, outage probability and optimal power allocation optimizing the system throughput/outage probability. Finally, we complement the FSO link with an additional radio frequency (RF) link to create a hybrid RF-FSO system and reduce the system outage probability. The results show that joint implementation of the RF and FSO links leads to considerable performance improvement, compared to the cases with only FSO-based communication.
27.	Mishra, Deepak, et al. (författare) Jointly Optimal Spatial Channel Assignment and Power Allocation for MIMO SWIPT Systems 2018 Ingår i: IEEE Wireless Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-2337 .- 2162-2345. ; 7:2, s. 214-217 Tidskriftsartikel (refereegranskat)abstract The joint design of spatial channel assignment and power allocation in multiple input multiple output (MIMO) systems capable of simultaneous wireless information and power transfer is studied. Assuming availability of channel state information at both communications ends, we maximize the harvested energy at the multi-antenna receiver, while satisfying a minimum information rate requirement for the MIMO link. We first derive the globally optimal eigenchannel assignment and power allocation design, and then present a practically motivated tight closed-form approximation for the optimal design parameters. Selected numerical results verify the validity of the optimal solution and provide useful insights on the proposed designs as well as the Pareto-optimal rate-energy tradeoff.
28.	Ngo, H. Q., et al. (författare) Correction to "massive MIMO with Optimal Power and Training Duration Allocation" 2015 Ingår i: IEEE Wireless Communications Letters. - 2162-2345 .- 2162-2337. ; 4:2, s. 225-225 Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract © 2012 IEEE. We correct the proofs of Propositions 1 and 2 in [1].
29.	Pirzadeh, Hessam, et al. (författare) Subverting Massive MIMO by Smart Jamming 2016 Ingår i: IEEE Wireless Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-2337 .- 2162-2345. ; 5:1, s. 20-23 Tidskriftsartikel (refereegranskat)abstract We consider uplink transmission of a massive multiuser multiple-input multiple-output (MU-MIMO) system in the presence of a smart jammer. The jammer aims to degrade the sum spectral efficiency of the legitimate system by attacking both the training and data transmission phases. First, we derive a closed-form expression for the sum spectral efficiency by taking into account the presence of a smart jammer. Then, we determine how a jammer with a given energy budget should attack the training and data transmission phases to induce the maximum loss to the sum spectral efficiency. Numerical results illustrate the impact of optimal jamming specifically in the large limit of the number of base station (BS) antennas.
30.	Ramazanali, Hawar, et al. (författare) Mean Queuing Delay in LTE DRX 2016 Ingår i: IEEE Wireless Communications Letters. - Piscataway : Institute of Electrical and Electronics Engineers (IEEE). - 2162-2337 .- 2162-2345. ; 5:4, s. 444-447 Tidskriftsartikel (refereegranskat)abstract Energy-efficiency is a crucial requirement for future 5G radio devices. Discontinuous reception (DRX) is a mechanism for power saving in LTE/LTE-A standard. In this letter, a method is developed to compute the mean queuing delay induced by the DRX. In contrast to existing semi-Markovian models, an approach, which combines Markov chains and regenerative processes, is proposed. © 2012 IEEE
31.	Ren, Ping, et al. (författare) Performance Tradeoffs of Joint Radar-Communication Networks 2019 Ingår i: IEEE Wireless Communications Letters. - : IEEE. - 2162-2337 .- 2162-2345. ; 8:1, s. 165-168 Tidskriftsartikel (refereegranskat)abstract This letter considers a network where nodes share a wireless channel to work in turn as pulse radars for target detection and as transmitters for data exchange. Radar detection range and network throughput are studied using stochastic geometry tools. We derive closed-form expressions that identify the key tradeoffs between radar and communication operations. Results reveal interesting design hints, and stress a marked sensitivity of radar detection to communication interference.
32.	Sadeghi, Meysam, et al. (författare) Adversarial Attacks on Deep-Learning Based Radio Signal Classification 2019 Ingår i: IEEE Wireless Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-2337 .- 2162-2345. ; 8:1, s. 213-216 Tidskriftsartikel (refereegranskat)abstract Deep learning (DL), despite its enormous success in many computer vision and language processing applications, is exceedingly vulnerable to adversarial attacks. We consider the use of DL for radio signal (modulation) classification tasks, and present practical methods for the crafting of white-box and universal black-box adversarial attacks in that application. We show that these attacks can considerably reduce the classification performance, with extremely small perturbations of the input. In particular, these attacks are significantly more powerful than classical jamming attacks, which raises significant security and robustness concerns in the use of DL-based algorithms for the wireless physical layer.
33.	Vu, T. X., et al. (författare) Energy Minimization for Cache-Assisted Content Delivery Networks With Wireless Backhaul 2018 Ingår i: IEEE Wireless Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-2337 .- 2162-2345. ; 7:3, s. 332-335 Tidskriftsartikel (refereegranskat)abstract Content caching is an efficient technique to reduce delivery latency and system congestion during peak-traffic time by bringing data closer to end users. In this letter, we investigate energy-efficiency performance of cache-assisted content delivery networks with wireless backhaul by taking into account cache capability when designing the signal transmission. We consider multi-layer caching and the performance in cases when both base station and users are capable of storing content data in their local cache. Specifically, we analyze energy consumption in both backhaul and access links under two uncoded and coded caching strategies. Then two optimization problems are formulated to minimize total energy cost for the two caching strategies while satisfying some given quality of service constraint. We demonstrate via numerical results that the uncoded caching achieves higher energy efficiency than the coded caching in the small user cache size regime.
34.	Zang, Guangda, et al. (författare) Optimal Hybrid Beamforming for Multiuser Massive MIMO Systems With Individual SINR Constraints 2019 Ingår i: IEEE Wireless Communications Letters. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2162-2337 .- 2162-2345. ; 8:2, s. 532-535 Tidskriftsartikel (refereegranskat)abstract In this letter, we consider optimal hybrid beamforming design to minimize the transmission power under individual signal-to-interference-plus-noise ratio (SINR) constraints in a multiuser massive multiple-input-multiple-output (MIMO) system. This results in a challenging non-convex optimization problem. We consider two cases. In the case where the number of users is smaller than or equal to that of radio frequency (RF) chains, we propose a low-complexity method to obtain a globally optimal solution and show that it achieves the same transmission power as an optimal fully-digital beamformer. In the case where the number of users is larger than that of RF chains, we propose a low-complexity globally convergent alternating algorithm to obtain a stationary point.
35.	Zhang, Jianjun, et al. (författare) Hybrid Precoding for Multi-Subarray Millimeter-Wave Communication Systems 2018 Ingår i: IEEE Wireless Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-2337 .- 2162-2345. ; 7:3, s. 440-443 Tidskriftsartikel (refereegranskat)abstract This letter studies analog and digital hybrid precoding for millimeter wave communication systems with multiple subarray architecture. To reap the benefit of multiple subarrays with less number of RF chains, subarray selection needs to be jointly optimized, which leads to a mixed integer nonlinear problem and hard to solve. To find a good solution, we propose an efficient hybrid precoding algorithm by leveraging the constraint-introducing-and-penalty (CIP) approach. Simulation results show that the spectral efficiency achieved by the proposed algorithm is larger than that of existing hybrid precoding algorithms.
36.	Zhang, Jiayi, et al. (författare) Spectral Efficiency of Multipair Massive MIMO Two-Way Relaying With Hardware Impairments 2018 Ingår i: IEEE Wireless Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-2337 .- 2162-2345. ; 7:1, s. 14-17 Tidskriftsartikel (refereegranskat)abstract We consider a multipair massive multiple-input multiple-output (MIMO) two-way relaying system, where multiple pairs of single-antenna devices exchange data with the help of a relay employing a large number of antennas N. The relay consists of low-cost components that suffer from hardware impairments. A large-scale approximation of the spectral efficiency with maximum ratio processing is derived in closed form, and the approximation is tight as N -> infinity. It is revealed that for a fixed hardware quality, the impact of the hardware impairments vanishes asymptotically when N grows large. Moreover, the impact of the impairments may even vanish when the hardware quality is gradually decreased with N, if a scaling law is satisfied. Finally, numerical results validate that multipair massive MIMO two-way relaying systems are robust to hardware impairments at the relay.
37.	Bengtsson, Erik L, et al. (författare) A Case Study on the Influence of Multiple Users on the Effective Channel in a Massive MIMO System 2019 Ingår i: IEEE Wireless Communications Letters. - 2162-2337. ; , s. 1-6 Tidskriftsartikel (refereegranskat)abstract We investigate the importance of weak clusters when modeling a wireless massive MIMO channel. We do this by studying the influence of densely spaced terminals and the number of base-station antennas for a zero-forcing precoded massive MIMO system. In particular, we focus on the influence on the correlation and imbalance between the signals at the terminal antennas, the effective channel-gain, the eigenvalue distributions and the number of clusters.The study is based on measured radio-channels from terminal prototypes with integrated antennas connected to a massive MIMO testbed.We further evaluate the advantage of using block-diagonalized zero-forcing compared to conventional zero-forcing in a massive MIMO system. Unexpectedly, terminals with low antenna envelope correlation coefficient may benefit significantly from block-diagonal zero-forcing in a massive MIMO system.The main conclusion is that weaker clusters are important when modeling multi-user scenarios.
38.	Dahman, Ghassan, et al. (författare) On the probability of non-shared multipath clusters in cellular networks 2015 Ingår i: IEEE Wireless Communications Letters. - 2162-2345. ; :99 Tidskriftsartikel (refereegranskat)abstract In Space Division Multiple Access (SDMA) systems, users are separated based on their positions. The base-station (BS) signals typically reach the users through multipath clusters. The goal of this work is to find the probability that a randomly selected user will receive the signal from the BS via at least one nonshared (by any other user) multipath cluster. This probability, referred to as PSuccess, provides (under some conditions) the limit of the probability that the BS is able to communicate successfully with a randomly selected user using SDMA without causing significant interference to other users. In order to find PSuccess, we first derive a model describing the probability distribution function (pdf) of the non-overlapping area of a set of circles, that have the same radius and are spatially distributed according to a Poisson distribution. Then, the proposed model for this pdf is used to express PSuccess as a function of the user’s intensity and the clusters’ intensity. Simulations, using the COST 2100 model, for outdoor and indoor scenarios, are used to validate the derived expression for PSuccess with a very good agreement, where the maximum error was 0:04.
39.	Harris, Paul, et al. (författare) Achievable Rates and Training Overheads for a Measured LOS Massive MIMO Channel 2018 Ingår i: IEEE Wireless Communications Letters. - 2162-2337. ; 7:4, s. 594-597 Tidskriftsartikel (refereegranskat)abstract This paper presents achievable uplink (UL) sum-rate predictions for a measured line-of-sight (LOS) massive multiple-input, multiple-output (MIMO) (MMIMO) scenario and illustrates the trade-off between spatial multiplexing performance and channel de-coherence rate for an increasing number of base station (BS) antennas. In addition, an orthogonal frequency division multiplexing (OFDM) case study is formed which considers the 90% coherence time to evaluate the impact of MMIMO channel training overheads in high-speed LOS scenarios. It is shown that whilst 25% of the achievable zero-forcing (ZF) sum-rate is lost when the resounding interval is increased by a factor of 4, the OFDM training overheads for a 100-antenna MMIMO BS using an LTE-like physical layer could be as low as 2% for a terminal speed of 90m/s.
40.	Karttunen, Aki, et al. (författare) Censored Multipath Component Cross-Polarization Ratio Modeling 2017 Ingår i: IEEE Wireless Communications Letters. - 2162-2337. ; 6:1, s. 82-85 Tidskriftsartikel (refereegranskat)abstract In wireless channel measurements, the relatively weak cross-polarized multipath components (MPCs) are typically severely affected by the measurement noise level. As shown in this letter, the typical cross-polarization ratio (XPR) model parameter estimation, which ignores the existence of censored samples, may lead to significant errors. We demonstrate how to achieve accurate parameter estimates with a maximum likelihood estimator that properly takes into account both the measured XPRs and the censored samples. Also, a new XPR model is presented in which the average XPR is modeled as a function of the MPC excess loss. The new model is shown to be insensitive to the channel measurement noise level. A practical example with measured data in an indoor environment at 60 GHz demonstrates the utility of the approach.
41.	Sarajlić, Muris, et al. (författare) Fully Decentralized Approximate Zero-Forcing Precoding for Massive MIMO Systems 2019 Ingår i: IEEE Wireless Communications Letters. - 2162-2337. ; 8:3, s. 773-776 Tidskriftsartikel (refereegranskat)abstract We analyze the downlink of a massive multiuser multiple input, multiple output (MIMO) system where antenna units at the base station are connected in a daisy chain without a central processing unit and only possess local channel knowledge. For this setup, we develop and analyze a linear precoding algorithm for suppressing interuser interference. It is demonstrated that the algorithm is close to zero-forcing precoding in terms of performance for a large number of antennas. Moreover, we show that with careful scheduling of processing across antennas, requirements for interconnection throughput are reduced compared with the fully centralized solution. Favorable tradeoff between performance and interconnection throughput makes the daisy chain a viable candidate topology for real-life implementations of base stations in MIMO systems where the number of antennas is very large.

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