Selective Retransmission Based Efficient Multiuser Detection For Overloaded Mimo Ofdm System

In wireless communication systems, multiple input multiple output (MIMO) and orthogonal frequency division multiplexing (OFDM) technologies offer reliable communication with high capacity and coverage rate. In a multiuser MIMO systems, co-channel interference increases drastically when a large number of users are added to the channel. However, it is practically not feasible to provide a separate physical receive antenna to each user, which leads the system into an overloaded condition. Although, the optimal and suboptimal multiuser detection (MUD) algorithms perform better in MIMO system but these algorithms perform poorly in an overloaded MIMO system (N-Rx < N-Tx). To overcome this problem, we proposed a receiver design that allows the application of conventional optimal and suboptimal MUD algorithms in overloaded system. In proposed receiver design, virtual receive antennas (VRA) are created using hybrid automatic repeat request (HARQ) retransmissions, and thereafter chase combining of (re)transmitted vectors is performed to convert an overloaded system into a critically (N-Rx = N-Tx) or under loaded (N-Rx > N-Tx) system. In addition, we introduce a selective retransmission (SR) scheme for the retransmission of erroneous OFDM subcarriers at modulation level. The SR scheme increases the throughput by reducing HARQ retransmissions. Simulation results validate the performance of our proposed scheme in terms of throughput enhancement with reduced bit error rate (BER) and packet drop rate.