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Sökning: WFRF:(Jorswieck Eduard A.)

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1.
  • Sezgin, A., et al. (författare)
  • Tight upper bound on the outage probability of QSTBC
  • 2006
  • Ingår i: IEEE Communications Letters. - 1089-7798 .- 1558-2558. ; 10:11, s. 784-786
  • Tidskriftsartikel (refereegranskat)abstract
    • Recently, the statistical properties of the equivalent channel representation of a multiple-input-multiple output (MIMO) system employing rate one quasi-orthogonal space-time block codes (QSTBC) for nT = 2", n > 2 transmit antennas was characterized. It was shown, that these QSTBC were capable of achieving a significant fraction of the outage mutual information of a MIMO system. In this letter, based on the Minkowski's determinant inequality and the Meijer's G-function we derive an upper bound for the fraction of outage probability achieved with QSTBC for the general case of nT = 2n,n > 2 transmit antennas. Simulations results show that this bound gets tight for all signal-to-noise-ratios (SNR) values by increasing the number of receive antennas.
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2.
  • Björnson, Emil, 1983-, et al. (författare)
  • Impact of Spatial Correlation and Precoding Design in OSTBC MIMO Systems
  • 2010
  • Ingår i: IEEE Transactions on Wireless Communications. - : IEEE. - 1536-1276 .- 1558-2248. ; 9:11, s. 3578-3589
  • Tidskriftsartikel (refereegranskat)abstract
    • The impact of transmission design and spatial correlation on the symbol error rate (SER) is analyzed for multi-antenna communication links. The receiver has perfect channel state information (CSI), while the transmitter has either statistical or no CSI. The transmission is based on orthogonal space-time block codes (OSTBCs) and linear precoding. The precoding strategy that minimizes the worst-case SER is derived for the case when the transmitter has no CSI. Based on this strategy, the intuitive result that spatial correlation degrades the SER performance is proved mathematically. In the case when the transmitter knows the channel statistics, the correlation matrix is assumed to be jointly-correlated (a generalization of the Kronecker model). The eigenvectors of the SER-optimal precoding matrix are shown to originate from the correlation matrix and the remaining power allocation is a convex problem. Equal power allocation is SER-optimal at high SNR. Beamforming is SER-optimal at low SNR, or for increasing constellation sizes, and its optimality range is characterized. A heuristic low-complexity power allocation is proposed and evaluated numerically. Finally, it is proved analytically that receive-side correlation always degrades the SER. Transmit-side correlation will however improve the SER at low to medium SNR, while its impact is negligible at high SNR.
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3.
  • Boche, H., et al. (författare)
  • Calculus for multiuser MIMO performance measures
  • 2006
  • Ingår i: Conf. Rec. Asilomar Conf. Signals Syst. Comput.. - 1424407850 - 9781424407859 ; , s. 369-373
  • Konferensbidrag (refereegranskat)abstract
    • In this paper, we review and combine recent results from multiuser MIMO MSE-based performance optimization and from concave and convex interference function calculus. First, a generalized MIMO MAC weighted MSE-based performance measure is developed using matrix-monotone functions. Next, the connection to interference functions is established. The representation of convex and concave interference functions are reviewed. Finally, the transition of a multiuser MIMO performance measure to the interference functions in terms of weighted sum optimization is shown.
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4.
  • Boche, Holger, et al. (författare)
  • Game Theory in Signal Processing and Communications
  • 2009
  • Ingår i: EURASIP Journal on Advances in Signal Processing. - : Springer. - 1687-6172 .- 1687-6180.
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • Game theory is a branch of mathematics aimed at the modeling and understanding of resource conflict problems. Essentially, the theory splits into two branches: noncooperative and cooperative game theory. The distinction between the two is whether or not the players in the game can make joint decisions regarding the choice of strategy. Noncooperative game theory is closely connected to minimax optimization and typically results in the study of various equilibria, most notably the Nash equilibrium. Cooperative game theory examines how strictly rational (selfish) actors can benefit from voluntary cooperation by reaching bargaining agreements. Another distinction is between static and dynamic game theory, where the latter can be viewed as a combination of game theory and optimal control. In general, the theory provides a structured approach to many important problems arising in signal processing and communications, notably resource allocation and robust transceiver optimization. Recent applications also occur in other emerging fields, such as cognitive radio, spectrum sharing, and in multihop-sensor and adhoc networks.
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5.
  • Butt, M.Majid, et al. (författare)
  • Maximizing energy efficiency for loss tolerant applications : The packet buffering case
  • 2013
  • Ingår i: 2013 IEEE 24th International Symposium on Personal Indoor and Mobile Radio Communications (PIMRC). - 9781467362351 ; , s. 2663-2667
  • Konferensbidrag (refereegranskat)abstract
    • Energy efficient communication has emerged as one of the key areas of research due to its impact on industry and environment. Any potential degree of freedom (DoF) available in the system should be exploited smartly to design energy efficient systems. This paper proposes a framework for achieving energy efficiency for the data loss tolerant applications by exploiting the multiuser diversity and DoFs available through the packet loss pattern. For a real time application, there is a constraint on the maximum number of packets to be dropped successively that must be obeyed. We propose a channel-aware energy efficient scheduling scheme which schedules the packets such that the constraint on the average packet drop rate and the maximum number of successively dropped packets is fulfilled for the case when a finite number of unscheduled packets can be buffered. We analyze the scheme in the large user limit and show the energy gain due to buffering on the proposed scheme.
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6.
  • Clerckx, Bruno, et al. (författare)
  • Is NOMA Efficient in Multi-Antenna Networks? : A Critical Look at Next Generation Multiple Access Techniques
  • 2021
  • Ingår i: IEEE Open Journal of the Communications Society. - : Institute of Electrical and Electronics Engineers (IEEE). - 2644-125X. ; 2, s. 1310-1343
  • Tidskriftsartikel (refereegranskat)abstract
    • In the past few years, a large body of literature has been created on downlink Non-Orthogonal Multiple Access (NOMA), employing superposition coding and Successive Interference Cancellation (SIC), in multi-antenna wireless networks. Furthermore, the benefits of NOMA over Orthogonal Multiple Access (OMA) have been highlighted. In this paper, we take a critical and fresh look at the downlink Next Generation Multiple Access (NGMA) literature. Instead of contrasting NOMA with OMA, we contrast NOMA with two other multiple access baselines. The first is conventional Multi-User Linear Precoding (MU-LP), as used in Space-Division Multiple Access (SDMA) and multi-user Multiple-Input Multiple-Output (MIMO) in 4G and 5G. The second, called Rate-Splitting Multiple Access (RSMA), is based on multi-antenna Rate-Splitting (RS). It is also a non-orthogonal transmission strategy relying on SIC developed in the past few years in parallel and independently from NOMA. We show that there is some confusion about the benefits of NOMA, and we dispel the associated misconceptions. First, we highlight why NOMA is inefficient in multi-antenna settings based on basic multiplexing gain analysis. We stress that the issue lies in how the NOMA literature, originally developed for single-antenna setups, has been hastily applied to multi-antenna setups, resulting in a misuse of spatial dimensions and therefore loss in multiplexing gains and rate. Second, we show that NOMA incurs a severe multiplexing gain loss despite an increased receiver complexity due to an inefficient use of SIC receivers. Third, we emphasize that much of the merits of NOMA are due to the constant comparison to OMA instead of comparing it to MU-LP and RS baselines. We then expose the pivotal design constraint that multi-antenna NOMA requires one user to fully decode the messages of the other users. This design constraint is responsible for the multiplexing gain erosion, rate and spectral efficiency loss, ineffectiveness to serve a large number of users, and inefficient use of SIC receivers in multi-antenna settings. Our analysis and simulation results confirm that NOMA should not be applied blindly to multi-antenna settings, highlight the scenarios where MU-LP outperforms NOMA and vice versa, and demonstrate the inefficiency, performance loss, and complexity disadvantages of NOMA compared to RSMA. The first takeaway message is that, while NOMA is suited for single-antenna settings (as originally intended), it is not efficient in most multi-antenna deployments. The second takeaway message is that another non-orthogonal transmission framework, based on RSMA, exists which fully exploits the multiplexing gain and the benefits of SIC to boost the rate and the number of users to serve in multi-antenna settings and outperforms both NOMA and MU-LP. Indeed, RSMA achieves higher multiplexing gains and rates, serves a larger number of users, is more robust to user deployments, network loads and inaccurate channel state information and has a lower receiver complexity than NOMA. Consequently, RSMA is a promising technology for NGMA and future networks such as 6G and beyond.
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7.
  • Gabry, Frederic (författare)
  • Cooperation for Secrecy in Wireless Networks
  • 2012
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The growth of wireless networks has been considerable over the last decades. Due to the broadcast nature of these networks, security issues have taken a critical role in today’s communications. A promising direction towards achieving secure communications is information theoretic secrecy, which is an approach exploiting the randomness of the channels to ensure secrecy. Based on this approach, there has been a recent surge of interest in a potential cooperation between users to enhance the secrecy of communications. In this thesis we investigate the interaction between cooperation and secrecy. In particular the contributions of the thesis can be divided into two parts.In the first part, we study cooperative strategies for secrecy for wireless channels. Our goal is to evaluate the effect of fading and limited CSI on the eavesdropper’s channels. In that purpose we consider a scenario where a helper aims at increasing the secrecy of the communication between a source and destination in the presence of an eavesdropper. Several strategies are discussed for the helper, namely decode-and-forward, amplify-and-forward, and cooperative jamming. We introduce the secrecy outage probability, the conditional secrecy outage probability and the secure throughput as secrecy measures. For each measure, we investigate and compare the secrecy performance of cooperation. We furthermore elaborate a system optimization in terms of strategy selection, node positioning, power allocation and rate design.In the second part, we consider cooperation in the 4-node scenario against a more sophisticated adversary: an active eavesdropper, which can either passively eavesdrop, or jam the transmission. A game-theoretic perspective is a natural way to analyze the competitive interaction between the helper and the eavesdropper. Therefore we define several secrecy games, for which we find the Nash and Stackelberg equilibria as well as the corresponding secrecy rate outcomes. Another important consideration in this scenario is the interaction between the source and the helper, which we model and solve as a Stackelberg game, and we illustrate its impact on the achievable secrecy rates.
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8.
  • Gerbracht, Sabrina, et al. (författare)
  • Non-regenerative two-hop wiretap channels using interference neutralization
  • 2012
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • In this paper, we analyze the achievable secrecy rates in the two-hop wiretap channel with four nodes, where the transmitter and the receiver have multiple antennas while the relay and the eavesdropper have only a single antenna each. The relay is operating in amplify-and-forward mode and all the channels between the nodes are known perfectly by the transmitter. We discuss different transmission and protection schemes like artificial noise (AN). Furthermore, we introduce interference neutralization (IN) as a new protection scheme. We compare the different schemes regarding the high-SNR slope and the high-SNR power offset and illustrate the performance by simulation results. It is shown analytically as well as by numerical simulations that the high SNR performance of the proposed IN scheme is better than the one of AN.
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9.
  • Giovanidis, A., et al. (författare)
  • Maximization of the single user rate in OFDMA assuming equal power on allocated subcarriers
  • 2007
  • Ingår i: 2007 IEEE 65th Vehicular Technology Conference. - : IEEE. - 1424402662 - 9781424402663 ; , s. 2751-2755
  • Konferensbidrag (refereegranskat)abstract
    • The problem of optimal power allocation for a single user in an OFDMA system is considered for uplink, under the assumption that the total power is divided equally to a selected subset of subcarriers. This scenario suggests reduced feedback information for power control from base station to the user since only the information over modulation on each subcarrier is necessary. Assuming knowledge of the instantaneous users' channel gains, the rate optimization problem reduces to a subcarrier allocation problem, discribed by a discrete function with the set of possible allocated subcarriers as domain and the set of achievable sum rates as range. A continuous equivalent of the function is used to derive properties that also hold in the discrete case. The function is in general not concave and concavity holds only for high CNR regions - over a specified bound. In all cases however it is proved that the maximum is unique and a simple and efficient algorithm is proposed for subcarrier allocation which always provides the optimal solution concerning the subcarriers to be loaded. The cost in achievable capacity from the use of equal-power compared to actual waterfilling is calculated, which is shown to be small while the gain in frequency resources and feedback reduction is important.
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10.
  • Janda, Carsten Rudolf, et al. (författare)
  • Wiretap-Channels under Constrained Active and Passive Attacks
  • 2015
  • Ingår i: 2015 IEEE CONFERENCE ON COMMUNICATIONS AND NETWORK SECURITY (CNS). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781467378765 ; , s. 16-21
  • Konferensbidrag (refereegranskat)abstract
    • In this paper, the pessimistic multi letter common randomness assisted secrecy capacity for the Arbitrarily Varying Wiretap Channel (AVWC) under input and state constraints is derived.
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11.
  • Jarmyr, Simon, 1982-, et al. (författare)
  • Statistical Precoding With Decision Feedback Equalization Over a Correlated MIMO Channel
  • 2010
  • Ingår i: IEEE Transactions on Signal Processing. - : IEEE. - 1053-587X .- 1941-0476. ; 58:12, s. 6298-6311
  • Tidskriftsartikel (refereegranskat)abstract
    • The decision feedback (DF) transceiver, combining linear precoding and DF equalization, can establish point-to-point communication over a wireless multiple-input multiple-output channel. Matching the DF-transceiver design parameters to the channel characteristics can improve system performance, but requires channel knowledge. We consider the fast-fading channel scenario, with a receiver capable of tracking the channel-state variations accurately, while the transmitter only has long-term, channel-distribution information. The receiver design problem given channel-state information is well studied in the literature. We focus on transmitter optimization, which amounts to designing a statistical precoder to assist the channel-tailored DF equalizer. We develop a design framework that encompasses a wide range of performance metrics. Common cost functions for precoder optimization are analyzed, thereby identifying a structure of typical cost functions. Transmitter design is approached for typical cost functions in general, and we derive a precoder design formulation as a convex optimization problem. Two important subclasses of cost functions are considered in more detail. First, we explore a symmetry of DF transceivers with a uniform subchannel rate allocation, and derive a simplified convex optimization problem, which can be efficiently solved even as system dimensions grow. Second, we explore the tractability of a certain class of mean square error based cost functions, and solve the transmitter design problem with a simple algorithm that identifies the convex hull of a set of points in R-2. The behavior of DF transceivers with optimal precoders is investigated by numerical means.
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12.
  • Jorswieck, Eduard A., et al. (författare)
  • Complete Characterization of the Pareto Boundary for the MISO Interference Channel
  • 2008
  • Ingår i: IEEE Transactions on Signal Processing. - 1053-587X .- 1941-0476. ; 56:10, s. 5292-5296
  • Tidskriftsartikel (refereegranskat)abstract
    • In this correspondence, we study the achievable rate region of the multiple-input single-output (MISO) interference channel, under the assumption that all receivers treat the interference as additive Gaussian noise. Our main result is an explicit parametrization of the Pareto boundary for an arbitrary number of users and antennas. The parametrization describes the boundary in terms of a low-dimensional manifold. For the two-user case we show that a single real-valued parameter per user is sufficient to achieve all points on the Pareto boundary and that any point on the Pareto boundary corresponds to beamforming vectors that are linear combinations of the zero-forcing (ZF) and maximum-ratio transmission (MRT) beamformers. We further specialize the results to the MISO broadcast channel (BC). A numerical example illustrates the result.
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13.
  • Jorswieck, Eduard A., et al. (författare)
  • Delay-limited capacity : Multiple antennas, moment constraints, and fading statistics
  • 2007
  • Ingår i: IEEE Transactions on Wireless Communications. - 1536-1276 .- 1558-2248. ; 6:12, s. 4204-4208
  • Tidskriftsartikel (refereegranskat)abstract
    • Different performance measures are an important mean in order to analyze and design wireless communications systems. Examples of common performance measures are the ergodic capacity, the outage capacity, and the average mean-square error (MSE). In this work, we study the delay-limited capacity (DLC). The DLC depends on the properties of the fading channel, e.g. on the spatial correlation and on the line-of-sight (LOS) component. In this letter, we derive the DLC for the general class of parallel fading channels, including the multiple antenna channels under moment and long-term power constraint. We prove that the DLC is Schur-concave with respect to the spatial correlation in single-input multiple-output (SIMO), and multiple-input single-output (MISO). Bounds for the DLC of multiple-input multiple-output (MIMO) and parallel fading channels are derived and the impact of the the mean component and spatial correlation on these bounds is characterized.
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14.
  • Jorswieck, Eduard A., et al. (författare)
  • Ergodic capacity achieving transmit strategy in MIMO systems with statistical and short-term norm CSI
  • 2007
  • Ingår i: 2007 IEEE International Conference on Acoustics, Speech, and Signal Processing. - : IEEE. ; , s. 393-396
  • Konferensbidrag (refereegranskat)abstract
    • The type and quality of the channel state information at the transmitter of a fading multiple-input multiple-output system greatly affects the ergodic capacity of the wireless link. In order to compare and unify the different proposals of transmit strategies for different scenarios, recently classes of MIMO channels are introduced that share a common optimal transmit strategy. In this work, we derive the ergodic capacity achieving transmit strategy for the class of unitary invariant norm feedback which complements statistical channel information at the transmitter. The impact of the short-term feedback quality is illustrated by the beamforming optimality range. The higher the feedback norm is the more likely is single stream beamforming to be optimal.
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15.
  • Jorswieck, Eduard A., 1975-, et al. (författare)
  • Feedback reduction in uplink MIMO OFDM systems by chunk optimization
  • 2008
  • Ingår i: EURASIP Journal on Advances in Signal Processing. - : Springer Science and Business Media LLC. - 1687-6172 .- 1687-6180.
  • Tidskriftsartikel (refereegranskat)abstract
    • The performance of multiuser MIMO systems can be significantly increased by channel-aware scheduling and signal processing at the transmitters based on channel state information. In the multiple antenna uplink multicarrier scenario, the base station decides centrally on the optimal signal processing and spectral power allocation as well as scheduling. An interesting challenge is the reduction of the overhead in order to inform the mobiles about their transmit strategies. In this work, we propose to reduce the feedback by chunk processing and quantization. We maximize the weighted sum rate of a MIMO OFDM MAC under individual power constraints and chunk size constraints. An efficient iterative algorithm is developed and convergence is proved. The feedback overhead as a function of the chunk size is considered in the rate computation and the optimal chunk size is determined by numerical simulations for various channel models. Finally, the issues of finite modulation and coding schemes as well as quantization of the precoding matrices are addressed.
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16.
  • Jorswieck, Eduard A., 1975-, et al. (författare)
  • Framework for Analysis of Opportunistic Schedulers : Average Sum Rate vs. Average Fairness
  • 2008
  • Ingår i: Proceedings of the 6th International Symposium on Modeling and Optimization in Mobile, Ad Hoc, and Wireless Networks, WiOpt 2008. - 9789639799189 ; , s. 100-105
  • Konferensbidrag (refereegranskat)abstract
    • Channel aware and opportunistic scheduling algorithms exploit the channel knowledge and fading to increase the average throughput. The maximum throughput scheduler (MTS) transmits only to the best user at a time. It is unfair to users at the cell edge. Obviously, there is a tradeoff between average throughput and fairness in the system. In this work, we study four representative schedulers, namely the MTS, the proportional fair scheduler (PFS), the (relative) opportunistic round robin scheduler (ORS), and the round robin scheduler (RRS). We show that the average sum rate performance and the average worst-case delay depend strongly on the user distribution within the cell. MTS gains from asymmetrically distributed users whereas the other three schedulers suffer. On the other hand, the average fairness of MTS and PFS decreases with asymmetrical user distribution. The key contribution of this paper is to put these tradeoffs and observations on a solid theoretical basis. The scaling laws of the average sum rate with the number of users as well as of the average worst-case delay are derived. Both the PFS and the ORS provide a reasonable performance in terms of throughput and fairness. However, PFS outperforms ORS for symmetrical user distributions, whereas ORS outperforms PFS for asymmetrical user distributions.
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17.
  • Jorswieck, Eduard A., et al. (författare)
  • Game Theory in Signal Processing and Communications
  • 2009
  • Ingår i: IEEE signal processing magazine (Print). - : IEEE. - 1053-5888 .- 1558-0792. ; 26:5
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • Game theory is a branch of mathematics aimed at the modeling and understanding of resource conflict problems. Essentially, the theory splits into two branches: noncooperative and cooperative game theory. The distinction between the two is whether or not the players in the game can make joint decisions regarding the choice of strategy. Noncooperative game theory is closely connected to minimax optimization and typically results in the study of various equilibria, most notably the Nash equilibrium. Cooperative game theory examines how strictly rational (selfish) actors can benefit from voluntary cooperation by reaching bargaining agreements. Another distinction is between static and dynamic game theory, where the latter can be viewed as a combination of game theory and optimal control. In general, the theory provides a structured approach to many important problems arising in signal processing and communications, notably resource allocation and robust transceiver optimization. Recent applications also occur in other emerging fields, such as cognitive radio, spectrum sharing, and in multihop-sensor and adhoc networks.
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18.
  • Jorswieck, Eduard A., et al. (författare)
  • Guaranteed performance region in fading orthogonal space-time coded broadcast channels
  • 2007
  • Ingår i: 2007 IEEE INTERNATIONAL SYMPOSIUM ON INFORMATION THEORY PROCEEDINGS. - NEW YORK : IEEE. - 9781424413973 ; , s. 96-100
  • Konferensbidrag (refereegranskat)abstract
    • Recently, the capacity region of the MIMO broadcast channel (BC) was completely characterized and duality between MIMO multiple access channel (MAC) and MIMO BC with perfect channel state information (CSI) at transmitter and receiver was established. In this work, we propose a MIMO BC approach in which only information about the channel norm is available at the base and hence no dirty paper precoding (DPC) can be applied. However, a certain set of individual performances in terms of MSE or zero-outage rates can be guaranteed at any time by applying an orthogonal space time block code (OSTBC). The guaranteed MSE region without superposition coding is characterized in closed form and the impact of diversity, fading statistics, and number of transmit antennas is analyzed. The guaranteed MSE region with superposition coding is also studied. Finally, the guaranteed sum MSE is briefly discussed.
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19.
  • Jorswieck, Eduard A., 1975-, et al. (författare)
  • Guaranteed performance region in fading orthogonal space-time coded broadcast channels
  • 2008
  • Ingår i: EURASIP Journal on Wireless Communications and Networking. - : Springer Science and Business Media LLC. - 1687-1472 .- 1687-1499.
  • Tidskriftsartikel (refereegranskat)abstract
    • Recently, the capacity region of the MIMO broadcast channel (BC) was completely characterized and duality between MIMO multiple access channel (MAC) and MIMO BC with perfect channel state information (CSI) at transmitter and receiver was established. In this work, we propose a MIMO BC approach in which only information about the channel norm is available at the base and hence no joint beamforming and dirty paper precoding (DPC) can be applied. However, a certain set of individual performances in terms of MSE or zero-outage rates can be guaranteed at any time by applying an orthogonal space-time block code (OSTBC). The guaranteed MSE region without superposition coding is characterized in closed form and the impact of diversity, fading statistics, and number of transmit antennas and receive antennas is analyzed. Finally, six CSI and precoding scenarios with different levels of CSI and precoding are compared numerically in terms of their guaranteed MSE region. Depending on the long-term SNR, superposition coding as well as successive interference cancellation (SIC) with norm feedback performs better than linear precoding with perfect CSI.
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20.
  • Jorswieck, Eduard A, et al. (författare)
  • Introduction to the Issue on Game Theory in Signal Processing
  • 2012
  • Ingår i: IEEE Journal on Selected Topics in Signal Processing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1932-4553 .- 1941-0484. ; 6:2, s. 73-75
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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21.
  • Jorswieck, Eduard A., et al. (författare)
  • Linear Precoding in Multiple-antenna Broadcast Channels : Efficient Computation of the Achievable Rate Region
  • 2008
  • Ingår i: Proceedings of the International ITG Workshop on Smart Antennas (WSA'08). - 9781424417568 ; , s. 21-28
  • Konferensbidrag (refereegranskat)abstract
    • This paper studies the achievable rate region of the two-use rmultiple antenna broadcast channel with linear precoding. It consists of two parts: In the first part, the set of beamformingvectors which achieve points on the Pareto boundary are characterized by a single real valued parameter per user. It is shown that a certain linear combination of the zero-forcing (ZF) beamforming vector and the maximum ratio-transmission (MRT) beamforming vector can achieve all Pareto boundary points of the rate region. In the second part, an iterative algorithm is proposed to compute the maximum sum-rate. Based on the characterization of the Pareto boundary, we develop an outer approximation algorithm for monotonic optimization using polyblocks. Numerical examples provide comparisons between rate and capacity regions as well as between the maximum sum-rate and maximum capacity operating points.
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22.
  • Jorswieck, Eduard A., et al. (författare)
  • Majorization and Matrix-monotone Functions in Wireless Communications
  • 2007
  • Bok (övrigt vetenskapligt/konstnärligt)abstract
    • This short tutorial presents two mathematical techniques namely Majorization Theory and Matrix-Monotone Functions, reviews their basic definitions and describes their concepts clearly with many illustrative examples. In addition to this tutorial, new results are presented with respect to Schur-convex functions and regarding the properties of matrix-monotone functions.  The techniques are applied to solve communication and information theoretic problems in wireless communications. The impact of spatial correlation in multiple antenna systems is characterized for many important performance measures, e.g., average mutual information, outage probability, error performance, minimum and wideband slope, zero-outage capacity, and capacity region. The impact of user distribution in cellular systems is characterized for different scenarios including perfectly informed transmitters and receivers, regarding, e.g., the average sum rate, the outage sum rate, maximum throughput. Finally, a unified framework for the performance analysis of multiple antenna systems is developed based on matrix-monotone functions. The optimization of transmit strategies for multiple antennas is carried out by optimization of matrix-monotone functions. The results within this framework resemble and complement the various results on optimal transmit strategies in single-user and multiple-user multiple-antenna systems.
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23.
  • Jorswieck, Eduard A., et al. (författare)
  • Monotonic Optimization Framework for the MISO IFC
  • 2009
  • Ingår i: Proceedings of the 34th IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP'09). - : IEEE. - 9781424423538 ; , s. 3633-3636
  • Konferensbidrag (refereegranskat)abstract
    • Resource allocation and transmit optimization for the multiple-antenna Gaussian interference channel are important but difficult problems. Recently, there has been a large interest in algorithms that find operating points which are optimal in the sum-rate, proportional-fair, or minimax sense. Finding these points entails solving a nonlinear, non-convex optimization problem. In this paper, we develop an algorithm that solves these problems exactly, to within a prescribed level of accuracy and in a finite number of steps. The main idea is to rewrite the objective functions so that methods for monotonic optimization can be used. More precisely, we write each objective function as a difference between two functions which are strictly increasing over a normal constraint set. The so-obtained reformulated, equivalent problem can then be solved efficiently by using so-called polyblock optimization. Numerical examples illustrate the advantages of the proposed framework compared to an exhaustive grid search.
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24.
  • Jorswieck, Eduard A., et al. (författare)
  • Monotonic Optimization Framework for theTwo-User MISO Interference Channel
  • 2010
  • Ingår i: IEEE Transactions on Communications. - 0090-6778 .- 1558-0857. ; 58:7, s. 2159-2169
  • Tidskriftsartikel (refereegranskat)abstract
    • Resource allocation and transmit optimization for the multiple-antenna Gaussian interference channel are important but difficult problems. The spatial degrees of freedom can be exploited to avoid, align, or utilize the interference. In recent literature, the upper boundary of the achievable rate region has been characterized. However, the resulting programming problems for finding the sum-rate, proportional fair, and minimax (egalitarian) operating points are non-linear and non-convex. In this paper, we develop a non-convex optimization framework based on monotonic optimization by outer polyblock approximation. First, the objective functions are represented in terms of differences of monotonic increasing functions. Next, the problems are reformulated as maximization of increasing functions over normal constraint sets. Finally, the idea to approximate the constraint set by outer polyblocks is explained and the corresponding algorithm is derived. Numerical examples illustrate the advantages of the proposed framework compared to an exhaustive grid search approach.
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25.
  • Jorswieck, Eduard A., et al. (författare)
  • Multiuser gaussianity and constellation randomization for the MIMO multiple access channel : A unified view
  • 2007
  • Ingår i: 2007 IEEE 8th Workshop On Signal Processing Advances In Wireless Communications, Vols 1 And 2. - : IEEE. - 9781424409549 - 9781424409556 ; , s. 126-130
  • Konferensbidrag (refereegranskat)abstract
    • In recent analyses of multiuser MIMO systems and their capacity achieving transmit strategies, Gaussian codebooks; are usually used. For the case in which the input signals are constrained to belong to a finite constellation, we study and explain two effects, namely Multiuser Gaussianity (MuG) and constellation randomization (CoRa). MuG means that the more users transmit simultaneously, the higher is the similarity of the received density to the optimal Gaussian one. Hence, the instantaneous mutual information is increased by MuG. This leads to a tradeoff between multiuser diversity and MuG. On the other hand, CoRa is done by linear precoding by random unitary matrices. Based on the observations from MuG, we explain why the outage capacity is increased by CoRa. The effects are illustrated by various numerical simulations.
  •  
26.
  • Jorswieck, Eduard A., 1975-, et al. (författare)
  • Performance of TDMA and SDMA based Opportunistic Beamforming
  • 2008
  • Ingår i: IEEE Transactions on Wireless Communications. - : Institute of Electrical and Electronics Engineers (IEEE). - 1536-1276 .- 1558-2248. ; 7:11, s. 4058-4063
  • Tidskriftsartikel (refereegranskat)abstract
    • In this work, we analyze opportunistic beamforming with finite number of single-antenna users under the constraint that the feedback overhead from the mobiles to the base is constant. First, we characterize the impact of the fading variances of the users and the spatial correlation on the sum rate of TDMA based opportunistic beamforming using majorization theory. Further, we describe quantitatively the high-SNR behavior in terms of throughput slope and power offset. Next, the impact of the fading variances of the users on an upper bound of the sum rate for space division multiple access (SDMA) based opportunistic beamforming is derived which is tight for high SNR. We propose to adapt the number of active beams to the SNR and the number of active users in a cell and illustrate the corresponding optimization problem by simulations.
  •  
27.
  • Jorswieck, Eduard A., et al. (författare)
  • Resource Sharing in Wireless Networks : The SAPHYRE Approach
  • 2010
  • Ingår i: Proceedings of the Future Network and Mobile Summit Conference. - 9781905824168 ; , s. 1-8
  • Konferensbidrag (refereegranskat)abstract
    • Physical resource sharing between wireless operators and service providers is necessary in order to support efficient, competitive, and innovative wireless communication markets. By sharing resources, such as spectrum or infrastructure, which are usually exclusively allocated interference is created on the physical layer. Therefore, the economic gains, regulatory overhead, and engineering efforts need to be addressed by a consolidated cross-layer approach. This paper describes briefly the approach taken by the EU FP7 project SAPHYRE.
  •  
28.
  • Jorswieck, Eduard A., et al. (författare)
  • Spectrum Sharing Improves the Network Efficiency for Cellular Operators
  • 2014
  • Ingår i: IEEE Communications Magazine. - : IEEE Communications Society. - 0163-6804 .- 1558-1896. ; 52:3, s. 129-136
  • Tidskriftsartikel (refereegranskat)abstract
    • The article describes the potential gain by spectrum sharing between cellular operators in terms of network efficiency. The focus of the study is on a specific resource sharing scenario: spectrum sharing between two operators in cellular downlink transmission. If frequency bands are allocated dynamically and exclusively to one operator - a case called orthogonal spectrum sharing - significant gains in terms of achievable throughput (spectrum sharing gains between 50 percent and 100 percent) and user satisfaction are reported for asymmetric scenarios at link and system level as well as from two hardware demonstrators. Additionally, if frequency bands are allocated simultaneously to two operators - a case called non-orthogonal spectrum sharing - further gains are reported. In order to achieve these, different enablers from hardware technologies and base station capabilities are required. However, we argue that all requirements are fulfilled in 3GPP and newer mobile standards. Therefore, the results and conclusions of this overview article encourage to seriously consider the inter-operator spectrum sharing technologies.
  •  
29.
  • Jorswieck, Eduard A., 1975-, et al. (författare)
  • The MISO interference channel from a game-theoretic perspective : A combination of selfishness and altruism achieves Pareto optimality
  • 2008
  • Ingår i: 2008 IEEE International Conference On Acoustics, Speech And Signal Processing. - : IEEE. - 9781424414833 ; , s. 5364-5367
  • Konferensbidrag (refereegranskat)abstract
    • We study the MISO interference channel from a game-theoretic perspective. Recently, it was shown that the rates at the non-cooperative Nash equilibrium (NE) strategy are poor especially in the medium and high SNR regimes. A reasonable outcome of the cooperative approach, close to the Pareto boundary of the achievable rate region, was shown to be the zero-forcing (ZF) strategy. In this work, we prove that any point on the Pareto boundary can be achieved by a certain linear combination of the NE and ZF strategies. A scalar weight per user chooses between "selfish" (NE) and altruistic (ZF) behavior. Thereby, the difficult beamforming optimization is reduced to a simple weight optimization. Different optimal operating points, e.g. maximum weighted sum-rate, the Nash-bargaining solution, or the Egalitarian solution, can be obtained by a computationally efficient iterative algorithm. The results are characterized by instantaneous achievable rate regions and the corresponding operating points.
  •  
30.
  • Jorswieck, Eduard A., 1975-, et al. (författare)
  • Throughput versus Fairness : Channel-Aware Scheduling in Multiple Antenna Downlink
  • 2009
  • Ingår i: EURASIP Journal on Wireless Communications and Networking. - : Springer Science and Business Media LLC. - 1687-1472 .- 1687-1499. ; , s. 271540-
  • Tidskriftsartikel (refereegranskat)abstract
    • Channel aware and opportunistic scheduling algorithms exploit the channel knowledge and fading to increase the average throughput. Alternatively, each user could be served equally in order to maximize fairness. Obviously, there is a tradeoff between average throughput and fairness in the system. In this paper, we study four representative schedulers, namely the maximum throughput scheduler (MTS), the proportional fair scheduler (PFS), the (relative) opportunistic round robin scheduler (ORS), and the round robin scheduler (RRS) for a space-time coded multiple antenna downlink system. The system applies TDMA based scheduling and exploits the multiple antennas in terms of spatial diversity. We show that the average sum rate performance and the average worst-case delay depend strongly on the user distribution within the cell. MTS gains from asymmetrical distributed users whereas the other three schedulers suffer. On the other hand, the average fairness of MTS and PFS decreases with asymmetrical user distribution. The key contribution of this paper is to put these tradeoffs and observations on a solid theoretical basis. Both the PFS and the ORS provide a reasonable performance in terms of throughput and fairness. However, PFS outperforms ORS for symmetrical user distributions, whereas ORS outperforms PFS for asymmetrical user distribution.
  •  
31.
  • Järmyr, Simon, et al. (författare)
  • Statistical Framework for Optimization in the Multi-User MIMO Uplink With ZF-DFE
  • 2014
  • Ingår i: IEEE Transactions on Signal Processing. - 1053-587X .- 1941-0476. ; 62:10, s. 2730-2745
  • Tidskriftsartikel (refereegranskat)abstract
    • We consider performance optimization in the uplink of a multiuser multiantenna communication system. Each user multiplexes data onto several independently encoded data streams, which are spatially precoded and conveyed over a fading narrowband multiple-input multiple-output (MIMO) channel. All users' data streams are decoded successively at the receiving base station using zero-forcing decision feedback equalization (ZF-DFE). We target the joint optimization of a decoding order and linear precoders for all users based on long-term channel information. For a class of general MIMO channel models, including the separable-correlation and double-scattering models, we show that the choice of precoder for a certain user does not affect the performance of the others. This leads to a particularly straightforward characterization of general user utility regions as a polyblock, or a convex polytope if time-sharing is allowed. We formulate the decoding-ordering problem under transmit-correlated Rayleigh fading as a linear assignment problem, enabling the use of existing efficient algorithms. Combining decoding ordering with single-user precoder optimization by means of alternating optimization, we propose an efficient iterative scheme that is verified numerically to converge fast and perform close to optimally, successfully reaping the benefits of both precoding and ordering in the MIMO uplink.
  •  
32.
  • Karipidis, Eleftherios, 1978-, et al. (författare)
  • Transmit Beamforming for Inter-Operator Spectrum Sharing
  • 2011
  • Ingår i: Proceedings of the Future Network and Mobile Summit Conference.
  • Konferensbidrag (refereegranskat)abstract
    • We study the nonorthogonal spectrum sharing scenario, in which coexisting transmitters of different operators concurrently utilize the same frequency band. The transmitters (and possibly the receivers) are equipped with multiple antennas. In EU FP7 project SAPHYRE, we propose various transmit beamforming techniques to manage the interference in the physical layer. We show that operating points that are more efficient than orthogonal spectrum sharing can be reached, when the operators cooperatively design their beamforming vectors to minimize the interference.
  •  
33.
  • Larsson, Erik G., 1974-, et al. (författare)
  • Asymptotically Optimal Transmit Strategies for the Multiple Antenna Interference Channel
  • 2008
  • Ingår i: Proceedings of the 46th Annual Allerton Conference on Communication, Control, and Computing (Allerton'08). ; , s. 708-714
  • Konferensbidrag (refereegranskat)abstract
    • We consider the interference channel with multiple antennas at the transmitter. We prove that at high signal-to-noise ratio (SNR), the zero-forcing transmit scheme is optimal in the sum-rate sense. Furthermore we prove that at low SNR, maximum-ratio transmission is optimal in the sum-rate sense. We also provide a discussion of the connection to classical results on spectral efficiency in the wideband regime. Finally, we propose a non-convex optimization approach based on monotonic optimization to solve the sum rate maximization problem.
  •  
34.
  • Larsson, Erik G., et al. (författare)
  • Game Theory and the Flat-Fading Gaussian Interference Channel : Analyzing Resource Conflicts in Wireless Networks
  • 2009
  • Ingår i: IEEE signal processing magazine (Print). - 1053-5888 .- 1558-0792. ; 26:5, s. 18-27
  • Tidskriftsartikel (refereegranskat)abstract
    • In this article, we described some basic concepts from noncooperative and cooperative game theory and illustrated them by three examples using the interference channel model, namely, the power allocation game for SISO IFC, the beamforming game for MISO IFC, and the transmit covariance game for MIMO IFC. In noncooperative game theory, we restricted ourselves to discuss the NE and PoA and their interpretations in the context of our application. Extensions to other noncooperative approaches include Stackelberg equilibria and the corresponding question "Who will go first?" We also correlated equilibria where a certain type of common randomness can be exploited to increase the utility region. We leave the large area of coalitional game theory open.
  •  
35.
  •  
36.
  • Lin, Pin-Hsun, et al. (författare)
  • Multi-Phase Smart Relaying and Cooperative Jamming in Secure Cognitive Radio Networks
  • 2016
  • Ingår i: IEEE Transactions on Cognitive Communications and Networking. - : Institute of Electrical and Electronics Engineers (IEEE). - 2332-7731. ; 2:1, s. 38-52
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper, we investigate cooperative secure communications in a four-node cognitive radio network where the secondary receiver is treated as a potential eavesdropper with respect to the primary transmission. The secondary user is allowed to transmit his own signals under the condition that the primary user's secrecy rate and transmission scheme are intact. Under this setting, we derive the secondary user's achievable rates and the related constraints to guarantee the primary user's weak secrecy rate, when Gelfand-Pinsker coding is used at the secondary transmitter. In addition, we propose a multiphase transmission scheme to include: 1) the phases of the clean relaying with cooperative jamming and 2) the latency to successfully decode the primary message at the secondary transmitter. A capacity upper bound for the secondary user is also derived. Numerical results show that: 1) the proposed scheme can outperform the traditional ones by properly selecting the secondary user's parameters of different transmission schemes according to the relative positions of the nodes and 2) the derived capacity upper bound is close to the secondary user's achievable rate within 0.3 bits/channel use, especially when the secondary transmitter/receiver is far/close enough to the primary receiver/transmitter, respectively. Thereby, a smart secondary transmitter is able to adapt the relaying and cooperative jamming to guarantee primary secrecy rates and to transmit its own data at the same time from relevant geometric positions.
  •  
37.
  • Lindblom, Johannes, et al. (författare)
  • Parameterization of the MISO IFC Rate Region: The Case of Partial Channel State Information
  • 2010
  • Ingår i: IEEE Transactions on Wireless Communications. - 1536-1276 .- 1558-2248. ; 9:2, s. 500-504
  • Tidskriftsartikel (refereegranskat)abstract
    • We study the achievable rate region of the multiple-input  single-output (MISO) interference channel (IFC), under the  assumption that all receivers treat the interference as additive  Gaussian noise. We assume the case of two users, and that the  channel state information (CSI) is only partially known at the  transmitters. Our main result is a characterization of  Pareto-optimal transmit strategies, for channel matrices that  satisfy a certain technical condition. Numerical examples are  provided to illustrate the theoretical results.
  •  
38.
  • Lindblom, Johannes, et al. (författare)
  • Parametrization of the MISO Interference Channel with Transmit Beamforming and Partial Channel State Information
  • 2008
  • Ingår i: Proceedings of the 42nd Asilomar Conference on Signals, Systems and Computers (ACSSC'08). - 9781424429400 ; , s. 1103-1107
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • We study the achievable rate region of the multipleinputsingle-output (MISO) interference channel (IFC), under theassumption that all receivers treat the interference as additiveGaussian noise. The main result is a parameterization of thePareto boundary for the case where there are two users, thetransmitters use beamforming, and the channel state information(CSI) is only partially known at the transmitters. The result isillustrated by two numerical results.
  •  
39.
  • Mochaourab, Rami, et al. (författare)
  • Coalitional Games in MISO Interference Channels : Epsilon-Core and Coalition Structure Stable Set
  • 2014
  • Ingår i: IEEE Transactions on Signal Processing. - : IEEE Signal Processing Society. - 1053-587X .- 1941-0476. ; 62:24, s. 6507-6520
  • Tidskriftsartikel (refereegranskat)abstract
    • The multiple-input single-output interference channel is considered. Each transmitter is assumed to know the channels between itself and all receivers perfectly and the receivers are assumed to treat interference as additive noise. In this setting, noncooperative transmission does not take into account the interference generated at other receivers which generally leads to inefficient performance of the links. To improve this situation, we study cooperation between the links using coalitional games. The players ( links) in a coalition either perform zero forcing transmission or Wiener filter precoding to each other. The epsilon-core is a solution concept for coalitional games that takes into account the overhead required in coalition deviation. We provide necessary and sufficient conditions for the strong and weak epsilon-core of our coalitional game not to be empty with zero forcing transmission. Since, the epsilon-core only considers the possibility of joint cooperation of all links, we study coalitional games in partition form in which several distinct coalitions can form. We propose a polynomial-time distributed coalition formation algorithm based on coalition merging and prove that its solution lies in the coalition structure stable set of our coalition formation game. Simulation results reveal the cooperation gains for different coalition formation complexities and deviation overhead models.
  •  
40.
  • Oechtering, Tobias J., et al. (författare)
  • On the Optimal Transmit Strategy for the MIMO Bidirectional Broadcast Channel
  • 2009
  • Ingår i: IEEE Transactions on Communications. - 0090-6778 .- 1558-0857. ; 57:12, s. 3817-3826
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
  •  
41.
  • Osseiran, Afif, et al. (författare)
  • A MIMO framework for 4G systems : WINNER concept and results
  • 2007
  • Ingår i: 2007 IEEE 8th Workshop on Signal Processing Advances in Wireless Communications. - : IEEE. - 9781424409549 ; , s. 798-802
  • Konferensbidrag (refereegranskat)abstract
    • In this paper, the MIMO framework within WINNER for fourth generation radio systems is further developed and assessed for various deployment scenarios. The emphasis is on radio network system aspects of multi-antenna techniques where preferred configurations for three basic deployment scenarios are given. In the wide area scenario which aims to provide ubiquitous coverage for rural, suburban and urban areas, the scheme selection depends on the user density of spatially separated users. It ranges from grid of fixed beams (GoB) (TDMA based) in case of few users to SDMA with a fixed linear precoding codebook, and finally to adaptive beams with SDMA for highly dense system. In the metropolitan area scenario which is targeting system deployments in large urban environments, multi-user (MU) MIMO precoding performs very well for slow moving users. For higher velocities, per antenna rate control (PARC) or adaptive linear dispersion codes (LDCs) are better choices. In the local area scenario which is characterized by isolated sites, the combination of SDMA and spatial multiplexing achieved by MU-MIMO precoding provides high spectral efficiency.
  •  
42.
  • Peng, Bile, 1985, et al. (författare)
  • Communication Scheduling by Deep Reinforcement Learning for Remote Traffic State Estimation with Bayesian Inference
  • 2022
  • Ingår i: IEEE Transactions on Vehicular Technology. - 0018-9545 .- 1939-9359. ; 71:4, s. 4287-4300
  • Tidskriftsartikel (refereegranskat)abstract
    • Traffic awareness is the prerequisite of autonomous driving. Given the limitation of on-board sensors (e.g., precision and price), remote measurement from either infrastructure or other vehicles can improve traffic safety. However, the wireless communication carrying the measurement result undergoes fading, noise and interference and has a certain probability of outage. When the communication fails, the vehicle state can only be predicted by Bayesian filtering with a low precision. Higher communication resource utilization (e.g., transmission power) reduces the outage probability and hence results in an improved estimation precision. The power control subject to an estimate variance constraint is a difficult problem due to the complicated mapping from transmit power to vehicle-state estimate variance. In this paper, we develop an estimator consisting of several Kalman filters (KFs) or extended Kalman filters (EKFs) and an interacting multiple model (IMM) to estimate and predict the vehicle state. We propose to apply deep reinforcement learning (DRL) for the transmit power optimization. In particular, we consider an intersection and a lane-changing scenario and apply proximal policy optimization (PPO) and soft actor-critic (SAC) to train the DRL model. Testing results show satisfactory power control strategies confining estimate variances below given threshold. SAC achieves higher performance compared to PPO.
  •  
43.
  • Sezgin, A., et al. (författare)
  • Interaction between scheduling and user locations in an OSTBC coded downlink system
  • 2008
  • Ingår i: 7th International ITG Conference on Source and Channel Coding, SCC 2008. - : Institute of Electrical and Electronics Engineers (IEEE). - 9783800730773
  • Konferensbidrag (refereegranskat)abstract
    • We study the MIMO broadcast channel (BC) with perfect channel state information (CSI) at the mobiles and different types of CSI at the base station, i.e. without CSI, with long-term CSI and with CQI. The antennas at the base station are used to apply an orthogonal space-time block code (OSTBC). At the receiver a linear MMSE detector is employed. We first study the optimal transmit and scheduling strategies for these three cases using the weighted sum minimum mean-square error (WSMSE) as the performance criterion. Afterwards, we analyze the impact of the user locations on the achievable minimum WSMSE. Depending on the scheduling strategy (minimum or maximum fairness), having the users rather more spread out within the cell is either helpful or harmful in order to minimize the WSMSE.
  •  
44.
  • Sezgin, A., et al. (författare)
  • LDC in MIMO Ricean channels : Optimal transmit strategy with MMSE detection
  • 2008
  • Ingår i: IEEE Transactions on Signal Processing. - 1053-587X .- 1941-0476. ; 56:1, s. 313-328
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper, we study a MIMO system with a transmitter using a linear dispersion code (LDC) and a linear minimum mean square-error (MMSE) detector at the receiver in a Ricean flat-fading environment. We assume that the receiver has perfect channel state information and the transmitter knows only the mean channel matrix either by feedback or channel estimation. The focus of our work is the analysis of the optimal transmit strategy using different types of LDC. On the one hand, we consider spatial multiplexing schemes that achieve high data rates, but sacrifice diversity. On the other hand, we have schemes that achieve full diversity like quasi-orthogonal space-time block codes or orthogonal space-time block code. Depending on the LDC in use, the optimization problem is either convex or nonconvex. For both of these classes of LDC, we first derive the properties of the average normalized MSE and then analyze the impact of the mean component on the MSE, the optimal transmit strategy and the optimal power allocation. Finally, we derive some bounds on the error rate performance for different scenarios with the MMSE receiver.
  •  
45.
  • Sezgin, Aydin, et al. (författare)
  • On the relation of OSTBC and code rate one QSTBC : Average rate, BER, and coding gain
  • 2008
  • Ingår i: IEEE Transactions on Signal Processing. - 1053-587X .- 1941-0476. ; 56:10, s. 4879-4891
  • Tidskriftsartikel (refereegranskat)abstract
    • Recently, the statistical properties of the equivalent channel representation of a multiple-input-multiple output (MIMO) system employing code rate one quasi-orthogonal space-time block codes (QSTBC), which are constructed by using orthogonal space-time block codes (OSTBC) as building elements, was characterized. Based on these characterizations we analyze the average rate (or mean mutual information), the bit-error-rate performance, and the coding gain achieved with QSTBC for any number of receive and n(T) = 2(n), n >= 2 transmit antennas. First, we study constellation rotation using a systematic approach in order to maximize the coding gain and to achieve full diversity QSTBC. Moreover, we present an upper bound on the coding gain. We derive a lower and upper bound on the BER-performance for QSTBC. Furthermore, we analyze the average rate achievable with QSTBC in case of an uninformed transmitter and also the case, in which the transmitter knows the mean channel matrix whereas the receiver has perfect CSI. Along with the analysis, we compare all the results of these performance measures with the results achieved with OSTBC, revealing important connections between OSTBC and QSTBC. For example, the coding gain of a QSTBC is upper bounded by the coding gain of the underlying OSTBC. Also, the BER of a QSTBC for n(T),T transmit and n(R) receive antennas is tightly lower bounded by the BER of a full-diversity providing intersymbol-interference free system. In addition to that, we show that gains in terms of average rate by using a QSTBC (and, thus, with higher n(T)) instead of the underlying OSTBC are only attainable, if the available channel state information at the transmitter (CSIT) is utilized. Finally, we illustrate our theoretical results using numerical simulations.
  •  
46.
  • Sezgin, Aydin, et al. (författare)
  • Performance Optimization of Open-Loop MIMO Systems With Orthogonal Space?Time Block Codes
  • 2007
  • Ingår i: IEEE Signal Processing Letters. - : IEEE Signal Processing Society. - 1070-9908. ; 14:1, s. 13-16
  • Tidskriftsartikel (refereegranskat)abstract
    • In order to obtain full spatial divversity available in a multiple-input multiple-output (MIMO) system, orthogonal space?time block codes (OSTBC) are employed due to their low decoding complexity. However, the drawback of OSTBC is that the code rate decreases with increasing number of transmit antennas. Using a recent result on the properties of Gaussian quadratic forms, we show that an OSTBC for an odd number of transmit antennas is always outperformed in terms of different performance measures, namely, the outage probability, the outage mean-squared error (MSE), and the raw bit-error rate (BER), by an OSTBC for an even number of transmit antennas, which has a strong impact on the design and application of OSTBC.
  •  
47.
  • Sjöbergh, Olof, et al. (författare)
  • Greedy user selection for zero-forcing and MMSE multiuser beamforming with channel estimation errors
  • 2008
  • Ingår i: ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings. - : IEEE. - 9781424414833 ; , s. 3137-3140
  • Konferensbidrag (refereegranskat)abstract
    • in a multi-user MIMO downlink where the base station has only estimates of the channels of the users, the sum-rate of multi-user beamforming saturates at high SNR. However, this is not the case for single-user beamforming. We propose a low-complexity user scheduling algorithm that selects the number of active users based on a closed-form approximation of the average sum-rate, and in particular does not add multiple users in the single-user optimality range. In order to develop this algorithm we derive the expected value of the rate of zero-forcing beamforming and MMSE beamforming with estimated channels and modify the greedy user selection accordingly. The gain of the proposed method is shown in numerical simulations.
  •  
48.
  • Svedman, Patrick, et al. (författare)
  • Reduced Feedback SDMA Based on Subspace Packings
  • 2009
  • Ingår i: IEEE Transactions on Wireless Communications. - : IEEE. - 1536-1276 .- 1558-2248. ; 8:3, s. 1329-1339
  • Tidskriftsartikel (refereegranskat)abstract
    • Herein, we treat Space Division Multiple Access (SDMA) based on partial channel state information and limited feedback. We propose a novel framework utilizing subspace packings, where beamforming, feedback, and scheduling are integrated. Advantages of the proposed framework are that the fed back supportable rates are based on the post-scheduling SINR and that the feedback implicitly contains information about the spatial compatibility of the users. The feasibility region of packings of different dimensions is indicated by the allocation outage probability which is derived. Grassmannian subspace packings, DFT-based packings, and non-orthogonal Grassmannian packings are formulated and studied as candidates. Numerical simulations show better performance for the proposed scheme compared to conventional channel quantization at the receiver with zero-forcing transmission in i.i.d. Rayleigh fading. Finally, we propose and evaluate a beam-graph method to further reduce the feedback load, that can be used in the context of tracking quantized beamformers.
  •  
49.
  • Zhang, Xi, et al. (författare)
  • MSE based optimization of multiuser MIMO MAC with partial CSI
  • 2006
  • Ingår i: 2006 Fortieth Asilomar Conference on Signals, Systems and Computers. - 9781424407842 ; , s. 374-378
  • Konferensbidrag (refereegranskat)abstract
    • This paper studies the optimal transmission design for multiple antenna multiple access channels with linear MMSE receiver at the base station and partial channel state information at the mobiles. The performance criterium for optimization is based on a Schur-concave function that works on the average individual MSEs of all users. The optimal beamforming matrix of each user corresponds to the eigenvector matrix of his channel correlation matrix. The remaining power allocation problem can be solved at reduced complexity. It is also direct to extend the results to Schur-convex functions. The results are illustrated by numerical simulations.
  •  
50.
  • Zhang, Xi, et al. (författare)
  • On the Asymptotic Optimality of Opportunistic Norm-Based User Selection with Hard SINR Constraint
  • 2009
  • Ingår i: EURASIP Journal on Advances in Signal Processing. - : Springer Science and Business Media LLC. - 1687-6172 .- 1687-6180.
  • Tidskriftsartikel (refereegranskat)abstract
    • Recently, user selection algorithms in combination with linear precoding have been proposed that achieve the same scaling as the sum capacity of the MIMO broadcast channel. Robust opportunistic beamforming, which only requires partial channel state information for user selection, further reduces feedback requirements. In this work, we study the optimality of the opportunistic norm-based user selection system in conjunction with hard SINR requirements under max-min fair beamforming transmit power minimization. It is shown that opportunistic norm-based user selection is asymptotically optimal, as the number of transmit antennas goes to infinity when only two users are selected in high SNR regime. The asymptotic performance of opportunistic norm-based user selection is also studied when the number of users goes to infinity. When a limited number of transmit antennas and/or median range of users are available, only insignificant performance degradation is observed in simulations with an ideal channel model or based on measurement data.
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