PERFORMANCE ANALYSIS OF ADVANCED WIRELESS SYSTEMS EMPLOYING HARQ BASED OVERLOADED MIMO

Abstract

Co-channel interference amongst multiple transmit streams limits the performance of MIMO systems. In overloaded MIMO systems where number of transmit streams are more than number of receive antennas, the effect of co-channel interference is more pronounced as optimal detection criteria of MIMO systems is violated. Resultantly sophisticated detector design along with retransmissions is required to improve the performance of such MIMO systems. HARQ based retransmission schemes namely CC-HARQ and IR-HARQ are widely used for the purpose of retransmission. However, with each retransmission, average delay associated with the retransmissions increases. Moreover, time slots are also wasted as same data is being transmitted in multiple time slots. In certain delay sensitive systems and the upcoming high throughput and low latency systems, a scheme is required to reduce the retransmissions as by reducing the transmissions, both processing and propagation delay associated with retransmissions is eliminated thereby reducing the delay as well as saving multiple time slots which can effectively be used to transmit new packets. Existing ARQ and HARQ based retransmission schemes retransmit packed based on incorrect decoding of one frame. In this research, multiple schemes are proposed to reduce the number of retransmissions further to reduce average retransmission delay and to increase throughput. Monte Carlo simulations shows that average retransmission delay and throughput spectral efficiency is enhanced by employing proposed scheme. The proposed schemes aim to reduce retransmission which can be employed to achieve low latency target for next generation wireless communication systems.