Abstract—We develop and analyze low-complexity cooperative diversity protocols that combat fading induced by multipath propagation in wireless networks. The underlying techniques exploit space diversity available through cooperating terminals’ relaying signals for one another. We outline several strategies employed by the cooperating radios, including fixed relaying schemes such as amplify-and-forward and decode-and-forward, selection relaying schemes that adapt based upon channel measurements between the cooperating terminals, and incremental relaying schemes that adapt based upon limited feedback from the destination terminal. We develop performance characterizations in terms of outage events and associated outage probabilities, which measure robustness of the transmissions to fading, focusing on the high signal-to-noise ratio (SNR) regime. Except for fixed decode-and-forward, all of our cooperative diversity protocols are efficient in the sense that they achieve full diversity (i.e., second-order diversity in the case of two terminals), and, moreover, are close to optimum (within 1.5 dB) in certain regimes. Thus, using distributed antennas, we can provide the powerful benefits of space diversity without need for physical arrays, though at a loss of spectral efficiency due to half-duplex operation and possibly at the cost of additional receive hardware. Applicable to any wireless setting, including cellular or ad hoc networks—wherever space constraints preclude the use of physical arrays—the performance characterizations reveal that large power or energy savings result from the use of these protocols. Index Terms—Diversity techniques, fading channels, outage probability, relay channel, user cooperation, wireless networks. I.

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For the multiple level relay channel, an achievable rate formula, and a simple coding scheme to achieve it, are presented. Generally higher rates can be achieved with this coding scheme in the multiple level relay case than previously known. For a class of degraded channels, this achievable rate is shown to be the exact capacity. An application of the coding scheme to the allcast problem is also discussed.

This chapter rethinks the link abstraction for wireless networks in the context of coopera-tive communications, which has recently received interest as an untapped means for improv-ing performance of relay transmission systems operating over the ever-challenging wireless medium. The common theme of most research in this area is to optimize physical layer per-formance measures without considering in much detail how cooperation interacts with higher layers and improves network performance measures. Because these issues are important for enabling cooperative communications to practice in real-world networks, especially for the increasingly important class of mobile ad hoc networks (MANETs), the goals of this paper are to survey basic cooperative communications and outline two potential architectures for cooperative MANETs. The first architecture relies on an existing clustered infrastructure: cooperative relays are centrally controlled by cluster heads. In another without explicit clustering, cooperative links are formed by request of a source node in an ad hoc, decentralized fashion. In either case, cooperative communication considerably improves the network con-nectivity. Although far from a complete study, these architectures provide modified wireless link abstractions and suggest tradeoffs in complexity at the physical and higher layers.

In a world where different systems have to share the same spectrum, the received (interfering) power may be a more relevant constraint than the maximum transmit power. Motivated by such a spectrum-sharing approach, this paper investigates the behavior of capacity under received-power constraints, modeling for example the maximum interference that one system may inflict on another. The insight of the paper is that while in the point-to-point case, transmit and received-power constraints are largely equivalent, they can lead to quite different conclusions in network cases, including relay networks, multiple access channels with dependent sources and feedback, and collaborative communication scenarios. 1

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Abstract — Future infrastructure based wireless systems are likely to use relaying due to energy savings, simpler roll-out of cellular networks, simpler increase of coverage and so forth. To increase the performance of relaying based systems cooperative relaying has emerged as an additional option to exploit spatial diversity. In order to allow for a fair comparison between singlehop and multi-hop schemes, an N-fold more spectrally efficient use of each link needs to be assumed for the multi-hop case. We propose a novel protocol relying on two relaying nodes which does not require the need for an increase in spectral efficiency in comparison to direct transmission. However, we achieve a better performance in the low SNR/high rate regime (which is of interest in many cellular networks, e. g. UMTS) at the expense of a worse performance in the high SNR/low rate regime. The proposal is compared to direct transmission, conventional relaying, transmit diversity and a distinct cooperative relaying scheme considering their outage probability. I.

In their fundamental paper, Cover and El Gamal presented three basic coding strategies – decode-and-forward, compress-and-forward and a mixed strategy based on partial decode-and-forward and compress-and-forward – which are still the basis for many recent relaying protocols. So far, only parts of their work are applied to networks of relay nodes, e. g., the decode-and-forward as well as compress-and-forward approach. This work generalizes a mixed approach of partial decode-andforward and compress-and-forward to networks of relay nodes. We further highlight how the “successive refinement problem” and the “broadcast channel problem with degraded message sets” are applied in our approach. Finally, we formulate achievable rates for the discrete memoryless relay channel consisting of two relay nodes.

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