Performance Analysis of Cell-Free Massive MIMO Systems: A Stochastic Geometry Approach

Abstract

Cell-free (CF) massive multiple-input-multiple-output (MIMO) has emerged as an alternative deployment for conventional cellular massive MIMO networks. Prior works relied on the strong assumption (quite idealized) that the APs are uniformly distributed, and actually, this randomness was considered during the simulation and not in the analysis. However, in practice, ongoing and future networks become denser and increasingly irregular. Having this in mind, we consider that the AP locations are modeled by means of a Poisson point process (PPP) which is a more realistic model for the spatial randomness than a grid or uniform deployment. In particular, by virtue of stochastic geometry tools, we derive both the downlink coverage probability and achievable rate. Notably, this is the only work providing the coverage probability and shedding light on this aspect of CF massive MIMO systems. Focusing on the extraction of interesting insights, we consider small-cells (SCs) as a benchmark for comparison. Among the findings, CF massive MIMO systems achieve both higher coverage and rate with comparison to SCs due to the properties of favorable propagation, channel hardening, and interference suppression. Especially, we showed for both architectures that increasing the AP density results in a higher coverage which saturates after a certain value and increasing the number of users decreases the achievable rate but CF massive MIMO systems take advantage of the aforementioned properties, and thus, outperform SCs. In general, the performance gap between CF massive MIMO systems and SCs is enhanced by increasing the AP density. Another interesting observation concerns that a higher path-loss exponent decreases the rate while the users closer to the APs affect more the performance in terms of the rate.

arXiv comment14 pages, accepted in IEEE TVT

References in corpus (9)

• Massive MIMO for Next Generation Wireless Systems
• A Tractable Approach to Coverage and Rate in Cellular Networks
• Power Scaling of Uplink Massive MIMO Systems with Arbitrary-Rank Channel Means
• Massive MIMO with Non-Ideal Arbitrary Arrays: Hardware Scaling Laws and Circuit-Aware Design
• Downlink MIMO HetNets: Modeling, Ordering Results and Performance Analysis
• Aspects of Favorable Propagation in Massive MIMO
• Rate-Splitting to Mitigate Residual Transceiver Hardware Impairments in Massive MIMO Systems
• How Much Do Downlink Pilots Improve Cell-Free Massive MIMO?
• Towards a Realistic Assessment of Multiple Antenna HCNs: Residual Additive Transceiver Hardware Impairments and Channel Aging