Various results to date have demonstrated the advantages of one or several relay nodes assisting transmissions in a wireless network. In many practical scenarios, not all nodes in the network are simultaneously involved in every transmission; therefore, protocols are needed to form groups or subsets of nodes for the purposes of cooperation. We consider this problem in the context of regenerative nodes and non-altruistic cooperation (all nodes have data of their own to transmit). For a network-wide diversity advantage, the protocol must provide each transmitting node with enough "partners" that can decode its message with high-enough probability. Assuming that the nodes cannot communicate their control decisions (distributed scenario), and that each node chooses to help n other nodes, we point out a simple, static selection strategy that guarantees diversity n+1 for all transmissions. We then consider centralized control strategies and study the additional gains that arise from a central control, under various amounts of information being available to the central controller.

Cooperative communication is an emerging paradigm where multiple mobiles share their resources (bandwidth and power) to achieve better overall performance. Coded cooperation is a mechanism where cooperation is combined with-and operates through-channel coding, as opposed to the repetition-based methods. This work develops expressions for outage probability of coded cooperation. In this work, each node acts as both a data source as well as a relay, i.e., only active (transmitting) nodes are available to assist other nodes, and each node operates under overall (source + relay) power and bandwidth constraints. Outage expressions confirm that full diversity is achieved by coded cooperation. This shows that despite superficial similarities, coded cooperation is distinct from decode-and-forward, which has been shown to have diversity one. The outage probability expressions developed in this work characterize coded performance at various rates. Furthermore, outage probabilities yield bounds that are arguably more insightful than the bit-error rate (BER) results previously available for coded cooperation. Numerical comparisons shed light on the relative merits of coded cooperation and various repetition-based methods, under various inter-user and uplink channel conditions.

Motivated by the recent works on the relay channel and cooperative diversity, this letter introduces coded cooperation, where cooperation is achieved through channel coding methods instead of a direct relay or repetition. Each codeword is partitioned into two subsets that are transmitted from the user's and partner's antennas, respectively. Coded cooperation achieves impressive gains compared to a non-cooperative system while maintaining the same information rate, transmit power, and bandwidth. We develop bounds on BER and FER and illustrate the advantage of coded cooperation under a number of different scenarios.

Cooperative communication has recently emerged as an effective form of signaling in wireless fading channels. This work examines cooperative communication in multi-user networks, where the geometry of information flow becomes an issue, i.e. who should cooperate with whom? In particular, one is interested in algorithms that do not require global network information, which is often unavailable due to latency, limited memory, or other constraints. In this work we propose and study distributed protocols for partner selection in cooperative networks. In this class of protocols, wireless users act individually and independently in establishing cooperative communication, without the aid of a central authority. Such a setup is especially of interest in ad-hoc networks, or networks of wireless sensors. We perform outage analysis for the proposed protocols, showing that full diversity in the number of cooperating users is achieved. The cooperative network with the proposed protocols performs significantly better than the non-cooperative counterpart.

Coded cooperation is a new framework recently proposed for cooperative communication. In this work, we present outage probability results for coded cooperation, and demonstrate that full diversity is achieved. In addition, we compare the outage behavior of coded cooperation with other repetition-based cooperative schemes.

In a multi-user environment, coded cooperation creates transmit diversity for small mobiles (e.g. handsets) that cannot support more than one antenna. Coded cooperation allows these mobiles to share their antennas via a simple and effective coding method. In this work we present an analytical methodology for evaluating the performance of coded cooperation. We develop tight bounds for bit and block error capabilities, showing in the process that coded cooperation achieves maximal diversity. We demonstrate the validity of these bounds via simulations.

Linebarger et al. (see Proceedings of Thirty-First Asilomar Conference on Signals, Systems & Computers, Pacific Grove, California, USA, vol.1, p.123-27, 1997) introduced a new, optimal approach to low rank transform domain adaptive filtering is , using a least squares, matrix based framework. Further, Raghothaman (see Proceedings of 8th IEEE DSP Workshop, Utah, USA, 1998) provides a computationally efficient algorithm to solve the formulation of the problem proposed by Linebarger. In this paper, we examine an alternative method for applying an optimal low rank transform, within the framework derived by Linebarger, to convert an overdetermined, full rank system into a low rank system. In addition, we propose a computationally efficient algorithm for the implementation of our method, using the DCT as the unitary transformation. Finally, we evaluate the performance of our algorithm via simulation in an acoustic echo canceller application, and show that the performance of our method is superior to existing low rank methods, NLMS and affine projection.