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   On the Optimality of the Stationary Solution of Secrecy Rate Maximization for MIMO Wiretap Channel; ; et al in IEEE Wireless Communications Letters (2021) To achieve perfect secrecy in a multiple-input multiple-output (MIMO) Gaussian wiretap channel (WTC), we need to find its secrecy capacity and optimal signaling, which involves solving a difference of ... [more ▼] To achieve perfect secrecy in a multiple-input multiple-output (MIMO) Gaussian wiretap channel (WTC), we need to find its secrecy capacity and optimal signaling, which involves solving a difference of convex functions program known to be non-convex for the non-degraded case. To deal with this, a class of existing solutions have been developed but only local optimality is guaranteed by standard convergence analysis. Interestingly, our extensive numerical experiments have shown that these local optimization methods indeed achieve global optimality. In this paper, we provide an analytical proof for this observation. To achieve this, we show that the Karush-Kuhn-Tucker (KKT) conditions of the secrecy rate maximization problem admit a unique solution for both degraded and non-degraded cases. Motivated by this, we also propose a low-complexity algorithm to find a stationary point. Numerical results are presented to verify the theoretical analysis. [less ▲] Detailed reference viewed: 36 (0 UL) On privacy notions in anonymous communication; ; Schiffner, Stefan  et alin Proceedings on Privacy Enhancing Technologies (2019), 2019(2), 105--125 Many anonymous communication networks (ACNs) with different privacy goals have been devel- oped. Still, there are no accepted formal definitions of privacy goals, and ACNs often define their goals ad hoc ... [more ▼] Many anonymous communication networks (ACNs) with different privacy goals have been devel- oped. Still, there are no accepted formal definitions of privacy goals, and ACNs often define their goals ad hoc. However, the formal definition of privacy goals benefits the understanding and comparison of different flavors of privacy and, as a result, the improvement of ACNs. In this paper, we work towards defining and comparing pri- vacy goals by formalizing them as privacy notions and identifying their building blocks. For any pair of no- tions we prove whether one is strictly stronger, and, if so, which. Hence, we are able to present a complete hier- archy. Using this rigorous comparison between notions, we revise inconsistencies between the existing works and improve the understanding of privacy goals. [less ▲] Detailed reference viewed: 169 (8 UL)Optimization of weighted individual energy efficiencies in interference networks; Yang, Yang ; in Proc. IEEE Wireless Communications and Networking Conference (2018, April) Detailed reference viewed: 223 (15 UL)Optimal V-BLAST Ordering in Fast Rayleigh Fading: A Linear Assignment Problem; Ottersten, Björn ; in Signal Processing Advances in Wireless Communications (SPAWC), 2011 IEEE 12th International Workshop on (2011) We explore a novel approach to perform decoding-order optimization in the vertical Bell Labs layered space-time (V-BLAST) architecture. Allowing for simultaneous transmission of multiple, separately ... [more ▼] We explore a novel approach to perform decoding-order optimization in the vertical Bell Labs layered space-time (V-BLAST) architecture. Allowing for simultaneous transmission of multiple, separately encoded data streams, the V-BLAST transmit-receive scheme applies to the uplink of a multi-user communication system. A multi-antenna receiver decodes data streams successively, dealing with inter-stream interference by means of cancelling and nulling; interference from previously decoded streams is cancelled by subtraction, and remaining interference is nulled by linear equalization. The order in which the streams are decoded can have a noticeable impact on system performance. We consider the optimization of a fixed decoding order in fast Rayleigh fading, based on long-term channel-fading parameters. For a wide range of performance measures, we show that the fast-fading ordering problem can be treated as a classical linear assignment problem, allowing a solution using existing, efficient algorithms. [less ▲] Detailed reference viewed: 173 (1 UL)Statistical Precoding and Detection Ordering in MIMO Multiple-Access Channels with Decision Feedback Equalization; Ottersten, Björn ; in Communications (ICC), 2011 IEEE International Conference on (2011) We present a novel approach for joint transmitter-receiver design in the uplink of a wireless multiple-input multiple-output communication system. It applies to, e.g., a fast-fading frequency-division ... [more ▼] We present a novel approach for joint transmitter-receiver design in the uplink of a wireless multiple-input multiple-output communication system. It applies to, e.g., a fast-fading frequency-division duplexing system with periodic pilot signaling from each user - a scenario hindering transmitter optimization based on channel state information (CSI), while CSI-based receiver optimization is possible. Each user multiplexes data onto several, independently coded subchannels processed by a linear precoder, and detected at a base station (BS) employing zero-forcing decision feedback (DF) equalization, eliminating all interference prior to detection. We target the problem of jointly designing fixed linear precoders for all users as well as a fixed detection order for the DF receiver based on long-term channel statistics. We propose an efficiently implementable alternating-minimization technique that is verified numerically to converge fast, and to outperform the popular V-BLAST scheme - a computationally more complex ordered-DF receiver with limited applicability by requiring equal-rate subchannels in the system. [less ▲] Detailed reference viewed: 188 (1 UL)On the Impact of Spatial Correlation and Precoder Design on the Performance of MIMO Systems with Space-Time Coding; Ottersten, Björn ; in Acoustics, Speech and Signal Processing, 2009. ICASSP 2009. IEEE International Conference on (2009) The symbol error performance of spatially correlated multi-antenna systems is analyzed herein. When the transmitter only has statistical channel information, the use of space-time block codes still ... [more ▼] The symbol error performance of spatially correlated multi-antenna systems is analyzed herein. When the transmitter only has statistical channel information, the use of space-time block codes still permits spatial multiplexing and mitigation of fading. The statistical information can be used for precoding to optimize some quality measure. Herein, we analyze the performance in terms of the symbol error rate (SER). It is shown analytically that spatial correlation at the receiver decreases the performance both without precoding and with an SER minimizing precoder. Without precoding, correlation should also be avoided at the transmitter side, but with an SER minimizing precoder the performance is actually improved by increasing spatial correlation at the transmitter. The structure of the optimized precoder is analyzed and the asymptotic properties at high and low SNRs are characterized and illustrated numerically. [less ▲] Detailed reference viewed: 156 (0 UL)Feedback Reduction in Uplink MIMO OFDM Systems by Chunk Optimization; ; Ottersten, Björn et alin EURASIP Journal on Applied Signal Processing (2008) Detailed reference viewed: 138 (0 UL)Feedback Reduction in Uplink MIMO OFDM Systems by Chunk Optimization; ; Ottersten, Björn et alin IEEE International Conference on Communications (ICC) (2008) Detailed reference viewed: 133 (0 UL)Performance of TDMA and SDMA based Opportunistic Beamforming; ; Ottersten, Björn in IEEE Transactions on Wireless Communications (2008), 7(11), 40584063 Detailed reference viewed: 60 (0 UL)Guaranteed Performance Region in Fading Orthogonal Space-Time Coded Broadcast Channels; Ottersten, Björn ; et alin EURASIP Journal on Wireless Communications and Networking (2008) Detailed reference viewed: 145 (1 UL) |
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