Eigenvalue Based Active User Enumeration for Grant-Free Access Under Carrier Frequency Offsets

TL;DR

This paper presents two eigenvalue-based schemes for active user enumeration in grant-free NOMA systems with carrier frequency offsets, improving estimation accuracy without requiring extensive prior information.

Contribution

The paper introduces novel eigenvalue-based user enumeration methods that handle carrier frequency offsets and operate with or without known noise variance.

Findings

Effective in estimating active users with low normalized root-mean-squared error

Works under conditions with carrier frequency offsets

Operates with or without prior noise variance knowledge

Abstract

This paper investigates a grant-free non-orthogonal multiple access (GF-NOMA) system in the presence of carrier frequency offsets. We propose two schemes for enumerating active users in such a GF-NOMA system, which is equivalent to estimating the sparsity level. Both schemes utilize a short common pilot and the eigenvalues of the sample covariance matrix of the received signal. The two schemes differ in their treatment of noise variance: one exploits known variance information, while the other is designed to function without this knowledge. Simulation results demonstrate the effectiveness of the proposed schemes in terms of the normalized root-mean-squared error.