Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Sequential Processing Strategies in Fronthaul Constrained Cell-Free Massive MIMO Networks

Vida Ranjbar, Robbert Beerten, Marc Moonen, Sofie Pollin

TL;DR

This work addresses spectral efficiency degradation in cell-free massive MIMO networks with sequential fronthaul by introducing two practical mitigation strategies: linearly increasing fronthaul capacity (LF) along the AP chain and Two-Path sequential signal propagation, complemented by vector-wise compression designs (SCNM and WSINM). The LF and Two-Path approaches, with judicious fronthaul allocation, substantially boost sum SE, particularly as the number of users grows, and can reduce the adverse effects of fronthaul compression even under simple equal-user bit allocations. The contributions provide a pathway for more efficient fronthaul-utilization in CFmMIMO and offer extendable ideas to other fronthaul topologies, including future work on optimizing path counts and capacity distributions. Overall, the paper demonstrates that targeted, topology-aware fronthaul design can yield meaningful performance gains in practical, capacity-constrained CFmMIMO deployments.

Abstract

In a cell-free massive MIMO (CFmMIMO) network with a daisy-chain fronthaul, the amount of information that each access point (AP) needs to communicate with the next AP in the chain is determined by the location of the AP in the sequential fronthaul. Therefore, we propose two sequential processing strategies to combat the adverse effect of fronthaul compression on the sum of users' spectral efficiency (SE): 1) linearly increasing fronthaul capacity allocation among APs and 2) Two-Path users' signal estimation. The two strategies show superior performance in terms of sum SE compared to the equal fronthaul capacity allocation and Single-Path sequential signal estimation.

Sequential Processing Strategies in Fronthaul Constrained Cell-Free Massive MIMO Networks

TL;DR

This work addresses spectral efficiency degradation in cell-free massive MIMO networks with sequential fronthaul by introducing two practical mitigation strategies: linearly increasing fronthaul capacity (LF) along the AP chain and Two-Path sequential signal propagation, complemented by vector-wise compression designs (SCNM and WSINM). The LF and Two-Path approaches, with judicious fronthaul allocation, substantially boost sum SE, particularly as the number of users grows, and can reduce the adverse effects of fronthaul compression even under simple equal-user bit allocations. The contributions provide a pathway for more efficient fronthaul-utilization in CFmMIMO and offer extendable ideas to other fronthaul topologies, including future work on optimizing path counts and capacity distributions. Overall, the paper demonstrates that targeted, topology-aware fronthaul design can yield meaningful performance gains in practical, capacity-constrained CFmMIMO deployments.

Abstract

In a cell-free massive MIMO (CFmMIMO) network with a daisy-chain fronthaul, the amount of information that each access point (AP) needs to communicate with the next AP in the chain is determined by the location of the AP in the sequential fronthaul. Therefore, we propose two sequential processing strategies to combat the adverse effect of fronthaul compression on the sum of users' spectral efficiency (SE): 1) linearly increasing fronthaul capacity allocation among APs and 2) Two-Path users' signal estimation. The two strategies show superior performance in terms of sum SE compared to the equal fronthaul capacity allocation and Single-Path sequential signal estimation.
Paper Structure (10 sections, 26 equations, 4 figures)

This paper contains 10 sections, 26 equations, 4 figures.

Table of Contents

  1. Introduction
  2. System model
  3. Fronthaul compression noise
  4. Element-wise compression: Equal inter-user fronthaul capacity allocation
  5. Vector-wise compression: Sum compression noise variance minimization
  6. Vector-wise compression: Weighted sum interference plus noise variance minimization
  7. Fronthaul capacity allocation
  8. Two-Path sequential signal propagation
  9. Simulation results
  10. Conclusion

Figures (4)

  • Figure 1: Sequential uplink signal estimation. User signal estimates are refined following either the blue path until it reaches CPU (Single-Path (SP) signal estimation), or it is refined following two short orange paths, and the two resulting signal estimates from the two paths get fused in the CPU (Two-Path (TP) signal estimation).
  • Figure 2: Impact of limited capacity fronthaul link: sum SE vs number of users. For bit allocation among users, WSINM is considered. $L=12$, $M=120$.
  • Figure 3: Impact of limited capacity fronthaul link: sum SE vs total fronthaul capacity $R_T$. $L=12$, $M=120$ and $K=20$.
  • Figure 4: 3D plot of $f$ as a function of $w$ for different values of $X$.