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Decentralizing Coherent Joint Transmission Precoding via Deterministic Equivalents

Yuhao Liu, Xinyu Bian, Yizhou Xu, Tianqi Hou, Wenjie Wang, Yuyi Mao, Jun Zhang

TL;DR

This work tackles downlink inter-cell interference in multi-cell CJT by enabling decentralized precoding that relies on deterministic equivalents (DE) to approximate interference using only channel covariances. The method decouples the global power-minimization problem into per-BS subproblems, avoiding exchange of instantaneous CSI while preserving performance near that of a centralized optimum. A centralized computation step can be used for reference but the DE-based approach eliminates it in practice, requiring only covariance information exchange. Simulations show the decentralized scheme achieves within 2–7% of the optimal centralized power with substantial reductions in signaling and latency, indicating practical viability for scalable CoMP in dense networks and suggesting extensions to multi-stream and lower-complexity solvers.

Abstract

In order to control the inter-cell interference for a multi-cell multi-user multiple-input multiple-output network, we consider the precoder design for coordinated multi-point with downlink coherent joint transmission. To avoid costly information exchange among the cooperating base stations in a centralized precoding scheme, we propose a decentralized one by considering the power minimization problem. By approximating the inter-cell interference using the deterministic equivalents, this problem is decoupled to sub-problems which are solved in a decentralized manner at different base stations. Simulation results demonstrate the effectiveness of our proposed decentralized precoding scheme, where only 2 ~ 7% more transmit power is needed compared with the optimal centralized precoder.

Decentralizing Coherent Joint Transmission Precoding via Deterministic Equivalents

TL;DR

This work tackles downlink inter-cell interference in multi-cell CJT by enabling decentralized precoding that relies on deterministic equivalents (DE) to approximate interference using only channel covariances. The method decouples the global power-minimization problem into per-BS subproblems, avoiding exchange of instantaneous CSI while preserving performance near that of a centralized optimum. A centralized computation step can be used for reference but the DE-based approach eliminates it in practice, requiring only covariance information exchange. Simulations show the decentralized scheme achieves within 2–7% of the optimal centralized power with substantial reductions in signaling and latency, indicating practical viability for scalable CoMP in dense networks and suggesting extensions to multi-stream and lower-complexity solvers.

Abstract

In order to control the inter-cell interference for a multi-cell multi-user multiple-input multiple-output network, we consider the precoder design for coordinated multi-point with downlink coherent joint transmission. To avoid costly information exchange among the cooperating base stations in a centralized precoding scheme, we propose a decentralized one by considering the power minimization problem. By approximating the inter-cell interference using the deterministic equivalents, this problem is decoupled to sub-problems which are solved in a decentralized manner at different base stations. Simulation results demonstrate the effectiveness of our proposed decentralized precoding scheme, where only 2 ~ 7% more transmit power is needed compared with the optimal centralized precoder.
Paper Structure (9 sections, 2 theorems, 17 equations, 1 figure)

This paper contains 9 sections, 2 theorems, 17 equations, 1 figure.

Table of Contents

  1. Introduction
  2. Problem Formulation
  3. System Model
  4. Problem Formulation
  5. Decentralized CJT Precoding
  6. Centralized Calculation of Interference Terms
  7. Approximation of Interference Terms
  8. Simulation Results
  9. Conclusions and Discussions

Key Result

Theorem 1

Let Assumptions (eq:ass2) and (eq:ass3) hold. We have $\max_{i,p} |\lambda_{ip}^* - \overline{\lambda}_{ip}| \to 0$ almost surely where The value of $\overline{m}_{ip}$ is determined as the unique non-negative solution to the following system of equations, computed for $p \in \mathcal{T}, i \in \mathcal{U}$,

Figures (1)

  • Figure 1: Total power consumption versus the number of antennas at each BS.

Theorems & Definitions (2)

  • Theorem 1
  • Theorem 2