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Fronthaul Network Planning for Hierarchical and Radio-Stripes-Enabled CF-mMIMO in O-RAN

Anas S. Mohammed, Krishnendu S. Tharakan, Hussein A. Ammar, Hesham ElSawy, Hossam S. Hassanein

Abstract

The deployment of ultra-dense networks (UDNs), particularly cell-free massive MIMO (CF-mMIMO), is mainly hindered by costly and capacity-limited fronthaul links. This work proposes a two-tiered optimization framework for cost-effective hybrid fronthaul planning, comprising a Near-Optimal Fronthaul Association and Configuration (NOFAC) algorithm in the first tier and an Integer Linear Program (ILP) in the second, integrating fiber optics, millimeter-wave (mmWave), and free-space optics (FSO) technologies. The proposed framework accommodates various functional split (FS) options (7.2x and 8), decentralized processing levels, and network configurations. We introduce the hierarchical scheme (HS) as a resilient, cost-effective fronthaul solution for CF-mMIMO and compare its performance with radio-stripes (RS)-enabled CF-mMIMO, validating both across diverse dense topologies within the open radio access network (O-RAN) architecture. Results show that the proposed framework achieves better cost-efficiency and higher capacity compared to traditional benchmark schemes such as all-fiber fronthaul network. Our key findings reveal fiber dominance in highly decentralized deployments, mmWave suitability in moderately centralized scenarios, and FSO complements both by bridging deployment gaps. Additionally, FS7.2x consistently outperforms FS8, offering greater capacity at lower cost, affirming its role as the preferred O-RAN functional split. Most importantly, our study underscores the importance of hybrid fronthaul effective planning for UDNs in minimizing infrastructural redundancy, and ensuring scalability to meet current and future traffic demands.

Fronthaul Network Planning for Hierarchical and Radio-Stripes-Enabled CF-mMIMO in O-RAN

Abstract

The deployment of ultra-dense networks (UDNs), particularly cell-free massive MIMO (CF-mMIMO), is mainly hindered by costly and capacity-limited fronthaul links. This work proposes a two-tiered optimization framework for cost-effective hybrid fronthaul planning, comprising a Near-Optimal Fronthaul Association and Configuration (NOFAC) algorithm in the first tier and an Integer Linear Program (ILP) in the second, integrating fiber optics, millimeter-wave (mmWave), and free-space optics (FSO) technologies. The proposed framework accommodates various functional split (FS) options (7.2x and 8), decentralized processing levels, and network configurations. We introduce the hierarchical scheme (HS) as a resilient, cost-effective fronthaul solution for CF-mMIMO and compare its performance with radio-stripes (RS)-enabled CF-mMIMO, validating both across diverse dense topologies within the open radio access network (O-RAN) architecture. Results show that the proposed framework achieves better cost-efficiency and higher capacity compared to traditional benchmark schemes such as all-fiber fronthaul network. Our key findings reveal fiber dominance in highly decentralized deployments, mmWave suitability in moderately centralized scenarios, and FSO complements both by bridging deployment gaps. Additionally, FS7.2x consistently outperforms FS8, offering greater capacity at lower cost, affirming its role as the preferred O-RAN functional split. Most importantly, our study underscores the importance of hybrid fronthaul effective planning for UDNs in minimizing infrastructural redundancy, and ensuring scalability to meet current and future traffic demands.

Paper Structure

This paper contains 27 sections, 34 equations, 17 figures, 2 tables, 2 algorithms.

Table of Contents

  1. Introduction
  2. System Model for Hybrid Fronthaul Networks
  3. Hybrid Fronthaul Network Architecture
  4. FS-Options Capacity Requirements
  5. Functional Split 8 (FS8)
  6. Functional Split 7.2x (FS7.2x)
  7. Non-Homogeneous Traffic and the Control Plan
  8. Fiber-Based Fronthaul Link Capacity
  9. mmWave-based Fronthaul Link Capacity
  10. FSO-Based Fronthaul Link Capacity
  11. Hierarchical and Radio-Stripes-Enabled CF-mMIMO Network Configuration
  12. Preliminary Network Construction Methodology
  13. Constructing Radio-Stripes-Based CF-mMIMO Network
  14. Constructing Hierarchical-Based CF-mMIMO Network
  15. Fronthaul TCO Optimization Formulation
  16. ...and 12 more sections

Figures (17)

  • Figure 1: Illustration of the different fronthaul topologies employed for UDNs schemes; (a) Conventional small-cell architecture with dedicated P2P fronthaul links, (b) RS topology and (c) HS topology.
  • Figure 2: Distribution of processing tasks in FS7.2x and FS8.
  • Figure 3: Sample realization of the optimized RS network.
  • Figure 4: Sample realization of the optimized HS network.
  • Figure 5: Optimized fronthaul mixed-technology selection in RS with FS7.2x under different levels of decentralized processing.
  • ...and 12 more figures

Theorems & Definitions (4)

  • Remark 1
  • Remark 2
  • Remark 3
  • Remark 4