Retrospective Interference Regeneration Schemes for Relay-Aided K-user MIMO Downlink Networks

Abstract

As a novel method to increase channel capacity of networks, interference alignment (IA) technique has attracted wide attention in fifth-generation wireless networks (5G). However, when it is applied in interference networks, the problem about information delay arises which has not been noticed yet. In this paper, we first propose degree of delay (DoD) to quantify the issue of information delay, and characterize DoD for three typical transmission schemes, i.e., TDMA, beamforming based TDMA (BD-TDMA) and retrospective interference alignment (RIA). By analyzing DoD of these schemes, its value mainly depends on three factors, i.e., delay sensitive factor, queueing delay slot and size of dataset. Therefore, to improve queueing delay slot and reduce DoD, three novel joint IA schemes are proposed for BC networks with different amounts of users. That is, hybrid antenna array based partial interference elimination and retrospective interference regeneration scheme (HAA-PIE-RIR), HAA based improved PIE and RIR scheme (HAA-IPIE-RIR) and HAA based cyclic interference elimination and RIR scheme (HAA-CIE-RIR). The second scheme extends the application scenarios of the first scheme from 2-user to K-user while brings huge computational burden. The third scheme relieves this computational complexity burden but it has somewhat degree of freedom (DoF) loss. Overall, the performances of proposed schemes are all superior to that of traditional IA techniques in DoF and DoD.Index Terms-multi-user MIMO broadcast networks, degree of freedom, degree of delay, hybrid antenna array structure of relay, interference elimination and retrospective interference regeneration.