Title: Randomized Space-Time Coding for Distributed Cooperative Communication
Authors: Birsen Sirkeci-Mergen, Anna Scaglione (Poster I, 15)

ABSTRACT

We study the design of distributed space-time codes for cooperative communication. We assume that each node is equipped with a single antenna; however, the cooperating nodes act as a virtual multi-antenna system. Our design objective is to obtain diversity and coding gains while eliminating the need for communication among nodes or from the nodes to a central control unit. For this purpose, we introduce randomized strategies that decentralize the transmission of a space time code from a set of distributed relays. In our methods, as in other cooperative transmission strategies, the relay signals are encoded so as to provide diversity and coding gains. However, through code randomization we allow the nodes to achieve such gains in a decentralized fashion. The simple idea we propose is to let each node transmit a random linear combination of the codewords that would be transmitted by all the antennas in a centralized space time coding scheme. We provide code design criteria and analyze the performance of different strategies which correspond to different choices for the statistics of the random coefficients. We show that the proposed scheme achieves full diversity (N) if N < L, where N is the number of cooperating nodes and L is the number of virtual transmit antennas. For N > L, the achieved diversity order saturates at L. Interestingly, in certain cases (e.g. N=L=2), we show that the achieved diversity order is fractional (d* = 1.5).