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A Channel Knowledge Map-Driven Two-Stage Coordinated User Scheduling in Multi-Cell Massive MIMO Systems

Jiayang Wan, Hongwei Hou, Jiawei Zhuang, Wenjin Wang, Shi Jin

Abstract

This paper investigates narrowband coordinated user scheduling in multi-cell massive multiple-input multiple-output (MIMO) systems. We formulate the problem under a spectral-efficiency maximization criterion, revealing inherent challenges in computational complexity and signaling overhead. To address these, we develop a user-scheduling-oriented CKM (US-CKM) and a US-CKM-driven two-stage coordinated scheduling framework. By exploiting the mapping between location information and statistical channel state information (SCSI), the system enables rapid SCSI retrieval and persistent reuse, substantially reducing CSI acquisition overhead. Embedding statistical channel correlation into the CKM further characterizes interuser interference patterns. The framework designs an intra-cell active-user selection scheme for the first stage and an inter-cell coordinated scheduling scheme for the second, both based on US-CKM entries. The first stage identifies users with favorable channel gains and low intra-cell interference, reducing the candidate set with marginal sum-rate loss. The second stage suppresses inter-cell interference (ICI) by exploiting cross-cell channel correlations. To enhance robustness against imperfect SCSI in dynamic scattering environments, we augment the framework with a reliability-guided mechanism. Instead of uniform treatment, we evaluate entry stability using a grid reliability metric quantifying channel measurement variance at sampling locations. Low-reliability grids are identified, and their instantaneous CSI is acquired in real time to integrate with existing SCSI. This process refines channel gain and spatial correlation characteristics, ensuring robust performance under imperfect conditions.

A Channel Knowledge Map-Driven Two-Stage Coordinated User Scheduling in Multi-Cell Massive MIMO Systems

Abstract

This paper investigates narrowband coordinated user scheduling in multi-cell massive multiple-input multiple-output (MIMO) systems. We formulate the problem under a spectral-efficiency maximization criterion, revealing inherent challenges in computational complexity and signaling overhead. To address these, we develop a user-scheduling-oriented CKM (US-CKM) and a US-CKM-driven two-stage coordinated scheduling framework. By exploiting the mapping between location information and statistical channel state information (SCSI), the system enables rapid SCSI retrieval and persistent reuse, substantially reducing CSI acquisition overhead. Embedding statistical channel correlation into the CKM further characterizes interuser interference patterns. The framework designs an intra-cell active-user selection scheme for the first stage and an inter-cell coordinated scheduling scheme for the second, both based on US-CKM entries. The first stage identifies users with favorable channel gains and low intra-cell interference, reducing the candidate set with marginal sum-rate loss. The second stage suppresses inter-cell interference (ICI) by exploiting cross-cell channel correlations. To enhance robustness against imperfect SCSI in dynamic scattering environments, we augment the framework with a reliability-guided mechanism. Instead of uniform treatment, we evaluate entry stability using a grid reliability metric quantifying channel measurement variance at sampling locations. Low-reliability grids are identified, and their instantaneous CSI is acquired in real time to integrate with existing SCSI. This process refines channel gain and spatial correlation characteristics, ensuring robust performance under imperfect conditions.
Paper Structure (31 sections, 34 equations, 8 figures, 4 tables, 4 algorithms)

This paper contains 31 sections, 34 equations, 8 figures, 4 tables, 4 algorithms.

Table of Contents

  1. Introduction
  2. Prior Work
  3. Motivation and Main Contributions
  4. System Model and Problem Formulation
  5. Signal Model
  6. Problem Formulation
  7. Two-Stage Scheduling Algorithm via SCSI
  8. Grid-Based US-CKM Construction
  9. Stage I: Intra-Cell Active User Selection
  10. AES Algorithm
  11. GIS Algorithm
  12. Stage II: Inter-Cell Coordinated Scheduling
  13. Review of SUS algorithm
  14. SUS-inspired multi-cell user selection algorithm
  15. Robustness-Enhanced Two-Stage Scheduling Algorithm
  16. ...and 16 more sections

Figures (8)

  • Figure 1: Illustration of the multi-cell uplink MIMO system.
  • Figure 2: Illustration of grid-based US-CKM. The upper right is a one-dimensional table representing statistical channel gains obtained for all grids, and the lower right is a two-dimensional table representing statistical channel correlations between all grids.
  • Figure 3: Flowchart of robustness-enhanced two-stage user scheduling algorithm.
  • Figure 4: Visualization of grid-based US-CKM.
  • Figure 5: The sum-rate performance for different active user selection algorithms under different user distributions.
  • ...and 3 more figures

Theorems & Definitions (2)

  • Remark 1
  • Remark 2