Extended version of sphere decoding with MMSE based enumeration for DL MU-MIMO systems

In this paper, we propose an extended version of sphere decoder (ESD) with the MMSE based enumeration for DL MU-MIMO systems. In previous work, we proposed the ESD which detects interference signals additionally. The ESD can achieve near-optimal performance, but it has much higher complexity than the existing SD. Therefore, this paper presents the improved enumeration based on MMSE. The proposed algorithm can reduce the complexity of ESD significantly while having low performance degradation.

I. Introduction

In recent communication area, downlink (DL) multi-user multiple-input multiple-output (MU-MIMO) system has received many attentions. The DL MU-MIMO system is the data communication from base station (BS) toward multiple users. BS and each user has more than one transmit and receive antennas respectively. Under the limited feedback systems, because the information of channel state is limited, precoding does not perform perfectly [1]. As a result, performance degradation and error floor are caused. For this problem, in previous work, we already proposed an extended version of sphere decoding (ESD) which detects the interference signal additionally [2], [3]. Although it can achieve near optimal performance, it has high complexity. Therefore, in this paper, we propose more strict enumeration based on the minimum mean-square error (MMSE) to reduce high complexity of ESD.