Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Heterogeneous System Design for Cell-Free Massive MIMO in Wideband Communications

Wei Jiang, Hans D. Schotten

TL;DR

This work introduces a heterogeneous CFmMIMO framework (HmMIMO) that combines a central BS-based CBS with distributed APs to serve near and far users in wideband OFDM channels. By classifying users into near (NU) and far (FU) groups and activating only the closest APs for each FU, the scheme enables DL pilots and coherent reception for FUs while keeping NUs coherently detectable at the CBS, reducing fronthaul and deployment costs. Theoretical SE analyses and extensive simulations show that HmMIMO achieves higher sum capacity than CFmMIMO, UCmMIMO, and mMIMO, while maintaining comparable user-experienced rates. Practically, the approach lowers AP installation costs and fronthaul signaling, offering improved scalability for wideband CFmMIMO deployments.

Abstract

Cell-free massive multi-input multi-output (CFmMIMO) offers uniform service quality through distributed access points (APs), yet unresolved issues remain. This paper proposes a heterogeneous system design that goes beyond the original CFmMIMO architecture by exploiting the synergy of a base station (BS) and distributed APs. Users are categorized as near users (NUs) and far users (FUs) depending on their proximity to the BS. The BS serves the NUs, while the APs cater to the FUs. Through activating only the closest AP of each FU, the use of downlink pilots is enabled, thereby enhancing performance. This heterogeneous design outperforms other homogeneous massive MIMO configurations, demonstrating superior sum capacity while maintaining comparable user-experienced rates. Moreover, it lowers the costs associated with AP installations and reduces signaling overhead for the fronthaul network.

Heterogeneous System Design for Cell-Free Massive MIMO in Wideband Communications

TL;DR

This work introduces a heterogeneous CFmMIMO framework (HmMIMO) that combines a central BS-based CBS with distributed APs to serve near and far users in wideband OFDM channels. By classifying users into near (NU) and far (FU) groups and activating only the closest APs for each FU, the scheme enables DL pilots and coherent reception for FUs while keeping NUs coherently detectable at the CBS, reducing fronthaul and deployment costs. Theoretical SE analyses and extensive simulations show that HmMIMO achieves higher sum capacity than CFmMIMO, UCmMIMO, and mMIMO, while maintaining comparable user-experienced rates. Practically, the approach lowers AP installation costs and fronthaul signaling, offering improved scalability for wideband CFmMIMO deployments.

Abstract

Cell-free massive multi-input multi-output (CFmMIMO) offers uniform service quality through distributed access points (APs), yet unresolved issues remain. This paper proposes a heterogeneous system design that goes beyond the original CFmMIMO architecture by exploiting the synergy of a base station (BS) and distributed APs. Users are categorized as near users (NUs) and far users (FUs) depending on their proximity to the BS. The BS serves the NUs, while the APs cater to the FUs. Through activating only the closest AP of each FU, the use of downlink pilots is enabled, thereby enhancing performance. This heterogeneous design outperforms other homogeneous massive MIMO configurations, demonstrating superior sum capacity while maintaining comparable user-experienced rates. Moreover, it lowers the costs associated with AP installations and reduces signaling overhead for the fronthaul network.
Paper Structure (13 sections, 25 equations, 3 figures)

This paper contains 13 sections, 25 equations, 3 figures.

Table of Contents

  1. Introduction
  2. System Model
  3. The Communication Protocols
  4. User Classification
  5. Resource Allocation
  6. Uplink Channel Estimation
  7. Uplink Data Transmission
  8. Downlink Data Transmission and Channel Estimation
  9. Performance Analysis
  10. Uplink Performance
  11. Downlink Performance
  12. Numerical Results
  13. Conclusions

Figures (3)

  • Figure 1: The system model of HmMIMO consists of a CBS, APs, and UEs.
  • Figure 2: Illustration of the OFDM time-frequency resource grid with two RB examples, each consisting of $8$ subcarriers spanning $24$ OFDM symbols. Users simultaneously transmit across all RBs with UL pilots, while DL resources for NUs, exemplified by the upper RB, lack pilot insertion. Conversely, the activated $K$ FUs can insert DL pilots, as shown by the lower RB.
  • Figure 3: Performance comparison of HmMIMO, CFmMIMO, UCmMIMO, and mMIMO, including (a) the CDF curves of UL sum capacity; (b) the CDF curves of UL per-user SE; (c) the CDF curves of DL per-user SE; and (d) the CDF curves of DL sum capacity;.