A Pragmatic Approach to Cooperative Diversity Communication
Lee,David
University Southern California, Communication Sciences Institute
Chugg,Keith
University Southern California, Communication Sciences Institute
Cooperative diversity techniques promise to provide spatial diversity by allowing multiple source radios ("team radios") to send data to an intended sink radio. These methods assume that each of the team radios have knowledge of their channel (channel state information (CSI)) to the sink radio. Furthermore, it is assumed that the team radios can control their transmissions accurately enough to ensure that all team radio signals arrive aligned coherently in phase and frequency. Such a system would likely require the sink node to have knowledge of the number of team radios, very accurate channel estimation and very stable oscillators and RF circuitry. Thus, this promising approach would be extremely challenging to implement.
We propose a method for cooperative diversity that does not require the transmitters to have CSI. Also, the sink radio need not know the number of team radios or estimate their individual channels. The approach is based on modern error correction coding and phase (or phase and amplitude) dithering. Each of the team radios, dithers its signal so that a static, destructive interference pattern is not encountered at the sink radio. The modern code is used to obtain diversity over the time-varying interference patterns induced by the dithering.
Modulation constrained information rate analysis for this approach is presented for various modulation schemes operating with practical amplitude and phase dithering patterns. The loss relative to the ideal cooperative diversity scheme is minimal. Simulation results using the 3gpp turbo code are compared with the information-theoretic analysis, validating the technical approach. The simulation is further used to examine the performance of block-oriented phase dithering within a quasi-static Rayleigh fading channel.
David K. Lee received the B.S. and M.S. degrees in Electrical Engineering from Kansas State University, Manhattan, Kansas in 1994 and 1996, respectively. He is currently a doctoral candidate at the University of Southern California (USC), Los Angeles, CA where his research interests are in the areas of iterative detection and wireless communication. Since 1996, he has been with General Dynamics (formerly Motorola Space Systems) in Scottsdale, AZ where he currently works as a senior communication systems engineer.