Grant-Free Non-Orthogonal Multiple Access With Multiple-Antenna Base Station and Its Efficient Receiver Design

Takanori Hara,Koji Ishibashi

doi:10.1109/access.2019.2956817

Abstract

This paper investigates an uplink grant-free non-orthogonal multiple access (NOMA) system with a multiple-antenna base station (BS), in which each user autonomously transmits its own data by multiplying its unique but non-orthogonal spreading sequence, namely code-domain NOMA, and proposes two receivers efficiently performing active user detection (AUD), channel estimation (CE), and data detection, simultaneously. We first propose a receiver based on multiple measurement vector approximate message passing (MMV-AMP), and the threshold for AUD is theoretically analyzed. Numerical results show that the symbol error rate (SER) of our receiver with the designed threshold is comparable to that of grant NOMA in which active users are ideally known. To reduce the complexity, we further propose a receiver based on Boosted AMP, which converts the original multiple-vector reconstruction problem into a smaller-sized vector reconstruction problem. Upon AUD via Boosted AMP, this receiver performs both CE and data detection via well-known linear minimum mean squared error (MMSE). Computer simulations reveal that our low-complexity receiver exhibits SER performance comparable to that of a conventional scheme based on block sparse adaptive subspace pursuit (BSASP), while the complexity is significantly reduced.

Highlights

Internet-of-Things (IoT) has gained considerable attention because of its promising effects on our daily lives and industries [2]; future wireless communications systems need to have the capability to accommodate a massive number of devices
This theoretically designed threshold leads to remarkably improve the performance of multiuser detection (MUD) of measurement vector approximate message passing (MMV-approximate message passing (AMP)), and computer simulations show that the symbol error rate (SER) performance of our proposed receiver surprisingly achieves the performance of linear minimum mean squared error (MMSE) with the perfect knowledge of active users, namely grant-based code-domain non-orthogonal multiple access (NOMA)
To further reduce the complexity, we propose a receiver based on boosted approximate message passing (Boosted AMP), which utilizes the combination of measurement vector (MMV)-AMP and the conversion inspired by reduce MMV and boost (ReMBo) [20]

Summary

INTRODUCTION

Internet-of-Things (IoT) has gained considerable attention because of its promising effects on our daily lives and industries [2]; future wireless communications systems need to have the capability to accommodate a massive number of devices. Grant-free code-domain nonorthogonal multiple access (NOMA) based on compressed sensing has been actively investigated in the literature [10] In this approach, every user transmits its own data spread by a pre-assigned unique sequence that must have the low coherence property [11], and this structure enables the BS to detect who transmitted the data among all users using an efficient compressed sensing algorithm because AUD can be interpreted as a sparse recovery problem caused by the inherent sporadic traffic property of mMTC. We address the theoretical design of the threshold for AUD to further improve the overall performances of GF-NOMA systems This theoretically designed threshold leads to remarkably improve the performance of MUD of MMV-AMP, and computer simulations show that the SER performance of our proposed receiver surprisingly achieves the performance of linear MMSE with the perfect knowledge of active users, namely grant-based code-domain NOMA. The L1 × L2 matrix in which all elements are zeros is expressed as OL1×L2

SYSTEM MODEL

RECEIVER BASED ON MMV-AMP

PERFORMANCE ANALYSES AND THRESHOLD DESIGN FOR AUD

BOOSTED AMP

NUMERICAL RESULTS

CONCLUSION