Enhanced Semi-Blind Uplink Interference Suppression on Multicell Massive MIMO Systems for Multi Modulus Signals

This paper expands our previously proposed semi-blind uplink interference suppression scheme on multicell multiuser massive MIMO systems to support multi modulus signals. The original proposal applies channel state information (CSI) aided blind adaptive array (BAA) interference suppression after the beamspace preprocessing and decision feedback channel estimation (DFCE). It employed the constant modulus algorithm (CMA) as the BAA scheme which can fully exploit the degree of freedom (DoF) of massive antenna arrays to suppress both inter-user interference (IUI) and inter- cell interference (ICI). Its effectiveness has been verified under the extensive pilot contamination constraint. Unfortunately, CMA basically works well only for the constant envelope signal such as QPSK and thus the proposed scheme should be expanded to cover QAM signals for more general use. This paper newly proposes to apply multi modulus algorithm (MMA) and data-aided sample matrix inversion based minimum mean square error (MMSE-SMI) weight derivation. It can successfully realize interference suppression under the use of multi-level envelope signals such as 16QAM with satisfactorily outage probability performance.

I. Introduction

Massive multiple-input multiple-output (MIMO) is believed to be one of the key technologies to drastically enhance the transmission rate as well as system capacity brought by its significant array gain and spatial multiplexing gain. Since its fundamental concept has been conceived [1], research field now covers a wide variety of topics, e.g. hybrid beamforming [2], complexity reduction [3], mobility robustness [4] and overhead reduction [5]. In any case, a large number of base stations (BSs) having massive antenna arrays will be extensively deployed and this scenario leaves the unavoidable problem still being discussed so called pilot contamination [6]. It is caused by inter-cell interference (ICI) among pilot signals which must be reused due to the limitation of orthogonal training sequence set, see Fig. 1a. Contaminated pilots deteriorate the channel state information (CSI) accuracy. Therefore in uplink data transmission phase (Fig. 1b), CSI-aided postcoding weight cannot well suppress inter-user interference (IUI) for accommodating user terminals (UTs), in addition to ICI.