Multiuser Detector for Uplink Grant Free NOMA Systems Based on Modified Subspace Pursuit Algorithm

Multiuser detection schemes are essential in any multiuser user access technology. Their importance cannot be over emphasized in a non-orthogonal multiple access (NOMA) system, a multiuser access technology that has been proposed for the fifth generation (5G) wireless networks. This paper proposed a multiuser detection (MUD) scheme, named the modified subspace pursuit (SP)-based MUD, for use in uplink grant free NOMA systems. In developing the scheme, temporary correlation of active user sets between adjacent time slots together with side information, a-priori knowledge of the active user support set's estimate, are exploited. The proposed MUD performs signal detection in a continuous time slots while user activities changes within a transmission frame in contrast to the traditional orthogonal matching pursuit (OMP)-based MUD that performs similar detection with the assumption that user activity remains unchanged within a whole frame. Computer simulation results show that the proposed modified SP-based MUD achieves better performance in comparison with the performances of the traditional OMP-based MUD and its variant, the computational efficient OMP-based MUD considered in this paper.