Multiuser Detection of Co-Channel Systems Using Combination of Basic Network Coding and HARQ

Abstract

A multiuser system where signals are simultaneously transmitted within the same bandwidth helps in achieving higher capacity. However, such a system is quite vulnerable to co-channel interference, due to presence of multiple users in the system. Signal detection becomes highly challenging when number of transmit antennas exceeds the number of receive antennas, thereby creating an over-loaded wireless system. In this case, Maximum Likelihood (ML) detection offers optimal performance as compared to suboptimal methods. However, ML detection is prohibitively complex especially once the number of transmit antenna increase. This work proposes a receiver architecture to handle multi user overloaded systems using a combination of Network Coding (NC) and Hybrid Automatic Repeat reQuest (HARQ) protocol to transform an overloaded system into a simplified co-channel system. An overloaded system is created using stacked HARQ retransmissions and NC techniques. This enables application of conventional low complexity detectors in such systems. Monte Carlo Simulations prove that the proposed approach results in significant gains in terms of Error Rates and throughput, while keeping the dropped packet rate quite low at an affordable complexity.