| 1. |
- Sezgin, A., et al.
(author)
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Tight upper bound on the outage probability of QSTBC
- 2006
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In: IEEE Communications Letters. - 1089-7798 .- 1558-2558. ; 10:11, s. 784-786
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Journal article (peer-reviewed)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.
(author)
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Impact of Spatial Correlation and Precoding Design in OSTBC MIMO Systems
- 2010
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In: IEEE Transactions on Wireless Communications. - : IEEE. - 1536-1276 .- 1558-2248. ; 9:11, s. 3578-3589
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Journal article (peer-reviewed)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.
(author)
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Calculus for multiuser MIMO performance measures
- 2006
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In: Conf. Rec. Asilomar Conf. Signals Syst. Comput.. - 1424407850 - 9781424407859 ; , s. 369-373
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Conference paper (peer-reviewed)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.
(author)
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Game Theory in Signal Processing and Communications
- 2009
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In: EURASIP Journal on Advances in Signal Processing. - : Springer. - 1687-6172 .- 1687-6180.
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Journal article (other academic/artistic)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.
(author)
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Maximizing energy efficiency for loss tolerant applications : The packet buffering case
- 2013
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In: 2013 IEEE 24th International Symposium on Personal Indoor and Mobile Radio Communications (PIMRC). - 9781467362351 ; , s. 2663-2667
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Conference paper (peer-reviewed)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.
(author)
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Is NOMA Efficient in Multi-Antenna Networks? : A Critical Look at Next Generation Multiple Access Techniques
- 2021
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In: IEEE Open Journal of the Communications Society. - : Institute of Electrical and Electronics Engineers (IEEE). - 2644-125X. ; 2, s. 1310-1343
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Journal article (peer-reviewed)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
(author)
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Cooperation for Secrecy in Wireless Networks
- 2012
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Licentiate thesis (other academic/artistic)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.
(author)
-
Non-regenerative two-hop wiretap channels using interference neutralization
- 2012
-
Conference paper (other academic/artistic)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.
(author)
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Maximization of the single user rate in OFDMA assuming equal power on allocated subcarriers
- 2007
-
In: 2007 IEEE 65th Vehicular Technology Conference. - : IEEE. - 1424402662 - 9781424402663 ; , s. 2751-2755
-
Conference paper (peer-reviewed)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.
(author)
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Wiretap-Channels under Constrained Active and Passive Attacks
- 2015
-
In: 2015 IEEE CONFERENCE ON COMMUNICATIONS AND NETWORK SECURITY (CNS). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781467378765 ; , s. 16-21
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Conference paper (peer-reviewed)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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