Impact of Interference Subtraction on Grant-Free Multiple Access with Massive MIMO

Abstract

In next generation Internet-of-Things, the overhead introduced by grant-based multiple access protocols may engulf the access network as a consequence of the unprecedented number of connected devices. Grant-free access protocols are therefore gaining an increasing interest to support massive access from machine-type devices with intermittent activity. In this paper, coded random access (CRA) with massive multiple input multiple output (MIMO) is investigated as a solution to design highly-scalable massive multiple access protocols, taking into account stringent requirements on latency and reliability. With a focus on signal processing aspects at the physical layer and their impact on the overall system performance, critical issues of successive interference cancellation (SIC) over fading channels are first analyzed. Then, SIC algorithms and a scheduler are proposed that can overcome some of the limitations of the current access protocols. The effectiveness of the proposed processing algorithms is validated by Monte Carlo simulation, for different CRA protocols and by comparisons with developed benchmarks.

Massive Grant-Free Access With Massive MIMO and Spatially Coupled Replicas

“…The process continues until the buffer is empty. Discussion: Approximations ( 6) and ( 7) are justified in [13] and [33] and analyzed in [34] with the use of a massive MIMO BS. In particular, they heavily rely on the statistical orthogonality of the propagation vectors.…”

“…In order not to stick to a particular ACK implementation, we consider N a = 0 in the following section. Nevertheless, when schemes using ACKs will be compared to scheme without ACKs some considerations will be drawn using (34).…”

“…As a particular class of grant-free access schemes, uncoordinated protocols based on the coded random access (CRA) paradigm [18], [19], [20], [21], [22], [23], [24], also known as "modern random access", ensure high reliability and are currently regarded as a candidate for 6G owing to their ability to bridge random access with iterative decoding of codes on sparse graphs [25]. Additional features envisaged for next MMA schemes for the future IoT are the extreme simplicity and very high energy efficiency on the device side, as well as the capability of the protocol to exploit massive MIMO base stations or cell-free architectures [12], [13], [14], [16], [26], [27], [28], [29], [30], [31], [32], [33], [34].…”