Full-spreading non-orthogonal multiple access (FS-NOMA) is one category of the candidate technologies designed to support massive connectivity in wireless communication systems. Before it can handle the massive volume of user connections, it is important for the FS-NOMA to develop a receiver that successfully decodes target data from non-orthogonally overlapped receiving signals. However, the decoding performance of conventional interference-cancellation (IC)-based receivers is far from optimal because of error-propagation problems. To improve the decoding performance, we propose a novel FS-NOMA receiver based on the tabu-search (TS) algorithm which is a sort of machine-learning algorithm. Specifically, a novel TS mechanism and a diversification scheme are proposed to overcome the inherent adverse conditions of FS-NOMA systems which lead the TS algorithm to local optima. Simulation results demonstrate that the proposed TS-based receiver has decoding performance that is superior to that of the conventional IC-based receiver. The results also show that the proposed receiver accommodates a higher number of user connections with a given packet drop rate threshold.

Introduction

It has been forecasted from both industry and academy that the ‘massive connectivity’ will play a pivotal role in future wireless networks [1]–[۴]. In industrial fields, general electric (GE) has estimated that 50 billion connected devices could create $10 trillion in monetary value for smart factories [5]. In cellular networks, the 3rd generation partnership project (3GPP) standardization group has defined massive machine type communications (mMTC) as one of the core scenarios of 5-th generation (5G) communication systems [6], [7]. Within the context of extending connectivity, nonorthogonal multiple access (NOMA) technologies have been investigated in the literature [8], [9]. Motivated by the fact that the connectivity of the conventional orthogonal multiple access (OMA) systems is restricted by the available number of orthogonal resources, NOMA systems intentionally allow multiple devices to access the same resource. NTT Docomo introduced power domain NOMA (PD-NOMA) as an initial attempt at non-orthogonal exploitation of communication resources [10]. The PD-NOMA focuses on extending the capacity region by manipulating the power of the transmitting devices [11]. Meanwhile, interleave-division multiple access (IDMA) has been investigated as a way to improve spectral efficiency by exploiting the diversity derived from the interleaving operation [12]. In particular, it has recently been revealed that IDMA with the elementary signal estimator (ESE) receiver can achieve capacity if the infinite length channel code is applied [13].