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Unified Modeling and Performance Comparison for Cellular and Cell-Free Massive MIMO

Wei Jiang, Hans D. Schotten

TL;DR

This work presents a unified modeling framework for massive MIMO that accommodates a variable number of antennas per access point, bridging cellular and cell-free architectures. It derives generalized uplink and downlink signal models and spectral-efficiency expressions for both matched-filtering and zero-forcing processing, under scenarios with full CSI and with only channel statistics. The study provides extensive numerical comparisons showing that cell-free configurations typically yield higher per-user and sum SE, particularly when CSI is available, and demonstrates practical downlink power control schemes that can approach optimal performance in cellular setups. The results offer actionable insights for the design of scalable, high-performance 6G wireless systems leveraging distributed antenna deployments and flexible AP configurations.

Abstract

Cell-free massive multi-input multi-output (MIMO) has recently gained a lot of attention due to its high potential in sixth-generation (6G) wireless systems. The goal of this paper is to first present a unified modeling for massive MIMO, encompassing both cellular and cell-free architectures with a variable number of antennas per access point. We derive signal transmission models and achievable spectral efficiency in both the downlink and uplink using zero-forcing and maximal-ratio schemes. We also provide performance comparisons in terms of per-user and sum spectral efficiency.

Unified Modeling and Performance Comparison for Cellular and Cell-Free Massive MIMO

TL;DR

This work presents a unified modeling framework for massive MIMO that accommodates a variable number of antennas per access point, bridging cellular and cell-free architectures. It derives generalized uplink and downlink signal models and spectral-efficiency expressions for both matched-filtering and zero-forcing processing, under scenarios with full CSI and with only channel statistics. The study provides extensive numerical comparisons showing that cell-free configurations typically yield higher per-user and sum SE, particularly when CSI is available, and demonstrates practical downlink power control schemes that can approach optimal performance in cellular setups. The results offer actionable insights for the design of scalable, high-performance 6G wireless systems leveraging distributed antenna deployments and flexible AP configurations.

Abstract

Cell-free massive multi-input multi-output (MIMO) has recently gained a lot of attention due to its high potential in sixth-generation (6G) wireless systems. The goal of this paper is to first present a unified modeling for massive MIMO, encompassing both cellular and cell-free architectures with a variable number of antennas per access point. We derive signal transmission models and achievable spectral efficiency in both the downlink and uplink using zero-forcing and maximal-ratio schemes. We also provide performance comparisons in terms of per-user and sum spectral efficiency.
Paper Structure (16 sections, 31 equations, 3 figures)

This paper contains 16 sections, 31 equations, 3 figures.

Table of Contents

  1. Introduction
  2. System Model
  3. Unified Signal Models
  4. Linear Detection in Uplink
  5. Matched Filtering
  6. Full CSI Knowledge
  7. Only Channel Statistics
  8. Zero-Forcing Detection
  9. Linear Precoding in Downlink
  10. Conjugate Beamforming
  11. Zero-Forcing Precoding
  12. Numerical Results
  13. Conclusion
  14. Derivation of Per-User SE with MF
  15. Derivation of Per-User SE with ZF Detection
  16. ...and 1 more sections

Figures (3)

  • Figure 1: The unified model for cellular/cell-free massive MIMO, where $M$ antennas are distributed over $N_{AP}$ APs. If $N_{AP}=1$, it stands for cellular massive MIMO relying on a single base station, as the leftmost diagram shows, while typical cell-free massive MIMO with $N_{AP}=M$ distributed single-antenna APs is shown in the rightmost diagram.
  • Figure 2: Performance comparison in the downlink of massive MIMO systems: (a) the CDF curves in terms of per-user SE using ZFP and CBF, where $M=256$ antennas serve $K=16$ users; and (b) the achievable sum SE in terms of the number of users when $M=256$.
  • Figure 3: Comparison of the CDF in terms of per-user SE in the uplink of massive MIMO systems using ZF and MF detection, where $M=256$ antennas serve $K=16$ users.

Theorems & Definitions (3)

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