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ABSTRACT: A four terminal Gaussian network composed of a source, a destination, an eavesdropper and a jammer relay is investigated when the jammer relay is causally given the source message. The source aims to increase the achievable secrecy rates, whereas the jammer relay aims to decrease it. To help the eavesdropper and to decrease achievable perfect secrecy rates, the jammer relay can use pure relaying and/or send interference to assist eavesdropping. The problem is formulated as a zero-sum game and the saddle point solutions are found. The results are compared to the case when the jammer relay is not informed about the source message.
Personal Indoor and Mobile Radio Communications (PIMRC), 2010 IEEE 21st International Symposium on; 10/2010
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ABSTRACT: In this paper fading multiple-antenna (MIMO) wiretap channels are investigated under short term power constraints. The secret diversity-multiplexing tradeoff (DMT) is calculated analytically, when the destination and the eavesdropper have receiver side channel state information (CSI) and the source has transmitter side CSI (CSIT). It is shown that the eavesdropper steals transmitter antennas and the secret DMT depends on the effective number of antennas left. This is in contrast to the no CSIT case, where the eavesdropper effectively steals both transmit and receive antennas. A zero-forcing type scheme is shown to achieve the secret DMT when CSIT is available.
Wireless Conference (EW), 2010 European; 05/2010
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ABSTRACT: In this work a four terminal Gaussian network composed of a source, a destination, an eavesdropper and a jammer relay is studied. The jammer relay does not hear the source transmission. It assists the eavesdropper and aims to decrease the achievable secrecy rates. The source, on the other hand, aims to increase the achievable secrecy rates. Assuming Gaussian strategies at the source and the jammer relay, this problem is formulated as a two-player zero-sum continuous game, where the payoff is the achieved secrecy rate. For this game the Nash equilibrium is generally achieved with mixed strategies. The optimal cumulative distribution functions for the source and the jammer relay that achieve the value of the game, which is the equilibrium secrecy rate, are found.
Information Theory Workshop, 2009. ITW 2009. IEEE; 11/2009
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ABSTRACT: In this paper the fading multiple antenna (MIMO) wire-tap channel is investigated. The secret diversity gain and the secret multiplexing gain are defined. Using these definitions, the secret diversity-multiplexing tradeoff (DMT) is calculated analytically when the source node does not have transmitter side channel state information (CSI). It is shown that the wire-tapper steals degrees of freedom from the source-destination channel, and the secret DMT depends on the remaining degrees of freedom. When CSI is available at the source, unlike the case when there are no security constraints, transmitter CSI changes the secret DMT significantly.
Information Sciences and Systems, 2008. CISS 2008. 42nd Annual Conference on; 04/2008
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ABSTRACT: We consider a general multiple-antenna network with multiple sources, multiple destinations, and multiple relays in terms of the diversity-multiplexing tradeoff (DMT). We examine several subcases of this most general problem taking into account the processing capability of the relays (half-duplex or full-duplex), and the network geometry (clustered or nonclustered). We first study the multiple-antenna relay channel with a full-duplex relay to understand the effect of increased degrees of freedom in the direct link. We find DMT upper bounds and investigate the achievable performance of decode-and-forward (DF), and compress-and-forward (CF) protocols. Our results suggest that while DF is DMT optimal when all terminals have one antenna each, it may not maintain its good performance when the degrees of freedom in the direct link are increased, whereas CF continues to perform optimally. We also study the multiple-antenna relay channel with a half-duplex relay. We show that the half-duplex DMT behavior can significantly be different from the full-duplex case. We find that CF is DMT optimal for half-duplex relaying as well, and is the first protocol known to achieve the half-duplex relay DMT. We next study the multiple-access relay channel (MARC) DMT. Finally, we investigate a system with a single source-destination pair and multiple relays, each node with a single antenna, and show that even under the ideal assumption of full-duplex relays and a clustered network, this virtual multiple-input multiple-output (MIMO) system can never fully mimic a real MIMO DMT. For cooperative systems with multiple sources and multiple destinations the same limitation remains in effect.
IEEE Transactions on Information Theory 11/2007; · 3.01 Impact Factor
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ABSTRACT: A four terminal Gaussian network, composed of a single source-destination pair, a relay and a wire-tapper is considered. Unlike the relay channel with a wire-tapper, it is assumed that the relay assists the wire-tapper, not the destination. The relay's objective is to decrease the achievable secrecy rates. However, since the destination is also allowed to listen to the relay's transmission, it also benefits from the relay in terms of achievable rates. Direct transmission, amplify-and-forward (AF), decode-and-forward (DF) and compress-and-forward (CF) relaying schemes are compared in terms of secrecy rates. It is shown that the best relaying strategy depends on relay's location. Comparison of relaying protocols and best power allocation schemes, when the relay assists the source-destination communication, do not readily extend to the case when the relay assists the wire-tapper.
Information Theory Workshop, 2007. ITW '07. IEEE; 10/2007
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ABSTRACT: We study the multiple antenna half-duplex relay channel from the diversity-multiplexing tradeoff (DMT) perspective. We find performance upper bounds and show that compress-and-forward (CF) protocol achieves the upper bound. We argue that although it is hard to find the exact DMT expressions for decode-and-forward (DF) type protocols, they would be suboptimal in the multiple antenna case. We also study the multiple-access relay channel (MARC), and evaluate how CF works in this system. Our results show that CF is a robust strategy, which performs well in different relay networks and multiple antenna scenarios.
Communications, 2007. ICC '07. IEEE International Conference on; 07/2007
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ABSTRACT: In this work a relay channel with a wire-tapper is studied for both discrete memoryless and Gaussian channels. The wire-tapper receives a physically degraded version of the destination's signal. We find inner and outer bounds for the capacity-equivocation rate region. We also argue that when the destination receives a physically degraded version of the relay's signal, inner and outer bounds meet for some special cases.
Information Sciences and Systems, 2007. CISS '07. 41st Annual Conference on; 04/2007
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ABSTRACT: We study the diversity-multiplexing tradeoff (DMT) for the full-duplex relay channel when the source and the destination have multiple antennas, and the relay has 1 or more. We find DMT upper bounds and investigate the achievable performance of decode-and-forward (DF), partial decode-and-forward (PDF), and compress-and-forward (CF) protocols. We study the effect of increased degrees of freedom in the direct link and the source-relay channel when multiple antennas are introduced. Our results suggest that while DF is DMT optimal when all terminals have one antenna each, it cannot maintain its good performance when the degrees of freedom in the direct link is increased. CF proves to be a more robust strategy, which works well in multi-antenna scenarios studied in this paper. We also extend our results for clustered relay networks to find DMT upper bounds and achievable performances
Information Theory, 2006 IEEE International Symposium on; 08/2006
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ABSTRACT: We first examine a system with a single source-destination pair and two relays, each node with a single antenna, and explore whether this virtual multi-input multi-output (MIMO) system can mimic a physical MIMO in terms of diversity-multiplexing tradeoff (DMT). We show that even under the idealistic assumption of full-duplex relays and a clustered network, the relay system can never fully mimic a real MIMO DMT, it is multiplexing gain limited. The limitation comes from the fact that source and destination are connected to relays with finite capacity links. We provide communication strategies that achieve the best DMT of this relay system. We extend our work to cover cooperative systems with multiple sources and multiple destinations and show that the same limitation is still in effect. Our results suggest that while cooperative relaying is able to provide high spatial diversity for low multiplexing gains, it can never mimic a physical MIMO for large multiplexing gains.
Information Sciences and Systems, 2006 40th Annual Conference on; 04/2006
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ABSTRACT: We consider a wireless system consisting of one source, one destination and M relays. Assuming path loss and Rayleigh fading, we use the cutset upper bound to show that no matter where the relays are located, the maximum diversity one can obtain is M+1. However, one can achieve a higher diversity gain, namely └ (M+2/2)<sup>2</sup> ┘ , if └ M/2 ┘ of the relays are clustered with the source and ┌ M/2 ┐ with the destination. This result utilizes the observation that if two wireless nodes are very close, Rayleigh assumption breaks and the proper channel model is additive white Gaussian noise (AWGN). Hence to realize a virtual multiinput multioutput (MIMO) system, clustering is essential.
Information Theory, 2004. ISIT 2004. Proceedings. International Symposium on; 08/2004
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ABSTRACT: We examine a network consisting of one source, one destination and two amplifying and forwarding relays and consider a scenario in which destination and relays can have various processing limitations. For all possible diversity combining schemes at the relays and at the destination, we find diversity order results analytically and confirm our findings through numerical calculations of bit error rate (BER) versus signal-to-noise-ratio (SNR) curves. We compare our results with direct transmission, well known transmit diversity methods and traditional multihop transmission and conclude that diversity reception in multihop networks provides the lowest error rate.
Global Telecommunications Conference, 2003. GLOBECOM '03. IEEE; 01/2004
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ABSTRACT: Broadcast strategy is an encoding technique that enables the reliably decoded rate to adapt to the actual channel state. This can be achieved if the transmitted signal is composed of superimposed information for different fading levels. We apply the broadcast strategy to fading relay channels. The source encodes its information to two levels, the first one is decoded if the channel state is "bad", and, if the channel state is "good", the superimposed information is decoded after the first one. This approach allows the decoding of some partial information at both the relay and the destination, increasing the overall throughput of the system compared to amplify-and-forward (AF) and modified decode-and-forward (MDF), while resulting in two levels of diversity. We also argue that the broadcast approach over the relay channel also results in lower overall distortion when the source is also taken into account.
Military Communications Conference, 2004. MILCOM 2004. IEEE;
