Network assisted diversity for random access wireless data networks

Contention based protocols inevitably lead to packet collisions and therefore underutilization of the channel resources. Collided packets however contain mixtures of useful user packets and should not necessarily be discarded. In this paper, a signal processing viewpoint is adopted in the development of alternative random access protocols which (at high SNR) introduce no throughput penalties. The approach is based on utilizing the network to create diversity through selective retransmissions of the corrupted packets. The user packets are then retrieved using conventional source separation techniques. The resulting protocol requires k time slots to transmit k collided users and does not affect the channel throughput in a negative way. Performance issues are studied in the paper, related to the implementation of the collision detection algorithm. The protocol´s parameters are optimized to maximize the system throughput.