An Algorithm for Grant-Free Random Access in Cell-Free Massive MIMO

TL;DR

This paper proposes a new algorithm for device activity detection in grant-free random access within cell-free massive MIMO networks, enabling efficient support for massive machine-type communications with broad coverage.

Contribution

It introduces a maximum likelihood detection algorithm based on coordinate descent for cell-free massive MIMO, addressing activity detection in mMTC scenarios.

Findings

Supports low-powered mMTC devices

Provides broad coverage for massive access

Offers an affordable complexity detection algorithm

Abstract

Massive access is one of the main use cases of beyond 5G (B5G) wireless networks and massive MIMO is a key technology for supporting it. Prior works studied massive access in the co-located massive MIMO framework. In this paper, we investigate the activity detection in grant-free random access for massive machine type communications (mMTC) in cell-free massive MIMO network. Each active device transmits a pre-assigned non-orthogonal pilot sequence to the APs and the APs send the received signals to a central processing unit (CPU) for joint activity detection. We formulate the maximum likelihood device activity detection problem and provide an algorithm based on coordinate descent method having affordable complexity. We show that the cell-free massive MIMO network can support low-powered mMTC devices and provide a broad coverage.