Asynchronous Massive Access in Multi-cell Wireless Networks Using Reed-Muller Codes

TL;DR

This paper introduces a Reed-Muller code-based scheme for massive device access in multi-cell wireless networks, enabling efficient identification and decoding of messages from numerous devices with improved complexity and error performance.

Contribution

It proposes a novel Reed-Muller sequence-based coding scheme combined with an iterative decoding algorithm for grant-free massive access in 5G networks.

Findings

Supports up to 2^{m(m+3)/2} devices with unique codewords

Achieves better computational complexity than existing algorithms

Provides improved error performance in device identification and message decoding

Abstract

Providing connectivity to a massive number of devices is a key challenge in 5G wireless systems. In particular, it is crucial to develop efficient methods for active device identification and message decoding in a multi-cell network with fading, path loss, and delay uncertainties. This paper presents such a scheme using second-order Reed-Muller (RM) sequences and orthogonal frequency-division multiplexing (OFDM). For given positive integer $m$, a codebook is generated with up to $2^{m(m+3)/2}$ codewords of length $2^m$, where each codeword is a unique RM sequence determined by a matrix-vector pair with binary entries. This allows every device to send $m(m + 3)/2$ bits of information where an arbitrary number of these bits can be used to represent the identity of a node, and the remaining bits represent a message. There can be up to $2^{m(m+3)/2}$ different identities. Using an iterative algorithm, an access point can estimate the matrix-vector pairs of each nearby device, as long as not too many devices transmit in the same frame. It is shown that both the computational complexity and the error performance of the proposed algorithm exceed another state-of-the-art algorithm. The device identification and message decoding scheme developed in this work can serve as the basis for grant-free massive access for billions of devices with hundreds of simultaneously active devices in each cell.