Capacity and QoS analysis for a novel packet based wireless access system

A recently proposed novel approach to asynchronous wireless random packet networking [P. Kota et al., March 2003] promises great enhancements in system performance. In this paper, mathematical and simulation results are presented which confirm the predictions made in [P. Kota et al., March 2003]. It is shown that the penalty in choosing random spreading sequences over orthogonal ones in terms of channel capacity vanishes quickly as the processing gain increases. The superiority of the proposed packet format over spread ALOHA is demonstrated by showing that the new access method is no longer collision limited and packets can overlap without being destroyed using joint detection at the base station receiver. As a result, assuming sufficient multiuser detector resources, outages are shown to be primarily caused by overloading the channel. The problem of exploiting the joint channel capacity can be addressed by the nodes, without complicated interaction with the base station. First results obtained by using a simple positive ACK scheme and low complexity rate finding algorithms in each of the nodes are presented which achieve up to 70% of the channel's theoretical capacity limit.