Outage Probability Analysis of Uplink Cell-Free Massive MIMO Network with and without Pilot Contamination

TL;DR

This paper develops approximate outage probability and ergodic rate expressions for uplink cell-free massive MIMO systems, accounting for pilot contamination and imperfect CSI, using novel distribution approximation and dimension reduction techniques.

Contribution

It introduces new approximation methods for outage probability in CF-mMIMO with and without pilot contamination, including a novel dimension reduction approach for exact expressions.

Findings

Approximate OP closely matches simulations.

Derived closed-form expressions applicable to single-cell MIMO.

Effective dimension reduction simplifies complex integrals.

Abstract

This paper derives approximate outage probability (OP) expressions for uplink cell-free massive multiple-input-multiple-output (CF-mMIMO) systems with and without pilot contamination. The system's access points (APs) are considered to have imperfect channel state information (CSI). The signal-to-interference-plus-noise ratio (SINR) of the CF-mMIMO system is approximated via a Log-normal distribution using a two-step moment matching method. OP and ergodic rate expressions are derived with the help of the approximated Log-normal distribution. For the no-pilot contamination scenario, an exact expression is first derived using conditional expectations in terms of a multi-fold integral. Then, a novel dimension reduction method is used to approximate it by the sum of single-variable integrations. Both the approximations derived for the CF-mMIMO systems are also useful for single-cell collocated massive MIMO (mMIMO) systems and lead to closed-form expression. The derived expressions closely match the simulated numerical values for OP and ergodic rate.