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Decentralized Multi-Antenna Architectures with Unitary Constraints

Juan Vidal Alegría, Ove Edfors

TL;DR

This work studies decentralized multi-antenna architectures under unitary constraints within the WAX framework to enable energy-efficient processing. It derives the structure of information-lossless semi-unitary transformations and proposes an iterative, SVD-based method to minimize the information loss between decentralized and centralized processing by jointly optimizing the block-diagonal filters, the combining module, and unitary rotation variables. The proposed algorithm converges to near information-lossless performance and outperforms projection-based baselines, with the potential to achieve full information losslessness for sufficiently large interconnection bandwidth $T$. The results highlight a degraded yet practical trade-off between interconnection bandwidth and processing complexity under unitary constraints, motivating further exploration of this degraded region and energy-efficient hardware realizations.

Abstract

The increase in the number of base station (BS) antennas calls for efficient solutions to deal with the increased interconnection bandwidth and processing complexity of traditional centralized approaches. Decentralized approaches are thus gaining momentum, since they achieve important reductions in data/processing volume by preprocessing the received signals before forwarding them to a central node. The WAX framework offers a general description of decentralized architectures with arbitrary interplay between interconnection bandwidth and decentralized processing complexity, but the applicability of this framework has only been studied assuming unrestricted baseband processing. We consider an adaptation of the WAX framework where the decentralized processing has unitary restriction, which allows for energy-efficient implementations based on reconfigurable impedance networks at the cost of some performance loss. Moreover, we propose an effective method to minimize the performance gap with respect to centralized processing. The previous method gives a first step towards characterizing the information-lossless trade-off between interconnection bandwidth and processing complexity in decentralized architectures with unitary constraints.

Decentralized Multi-Antenna Architectures with Unitary Constraints

TL;DR

This work studies decentralized multi-antenna architectures under unitary constraints within the WAX framework to enable energy-efficient processing. It derives the structure of information-lossless semi-unitary transformations and proposes an iterative, SVD-based method to minimize the information loss between decentralized and centralized processing by jointly optimizing the block-diagonal filters, the combining module, and unitary rotation variables. The proposed algorithm converges to near information-lossless performance and outperforms projection-based baselines, with the potential to achieve full information losslessness for sufficiently large interconnection bandwidth . The results highlight a degraded yet practical trade-off between interconnection bandwidth and processing complexity under unitary constraints, motivating further exploration of this degraded region and energy-efficient hardware realizations.

Abstract

The increase in the number of base station (BS) antennas calls for efficient solutions to deal with the increased interconnection bandwidth and processing complexity of traditional centralized approaches. Decentralized approaches are thus gaining momentum, since they achieve important reductions in data/processing volume by preprocessing the received signals before forwarding them to a central node. The WAX framework offers a general description of decentralized architectures with arbitrary interplay between interconnection bandwidth and decentralized processing complexity, but the applicability of this framework has only been studied assuming unrestricted baseband processing. We consider an adaptation of the WAX framework where the decentralized processing has unitary restriction, which allows for energy-efficient implementations based on reconfigurable impedance networks at the cost of some performance loss. Moreover, we propose an effective method to minimize the performance gap with respect to centralized processing. The previous method gives a first step towards characterizing the information-lossless trade-off between interconnection bandwidth and processing complexity in decentralized architectures with unitary constraints.
Paper Structure (10 sections, 2 theorems, 25 equations, 2 figures)

This paper contains 10 sections, 2 theorems, 25 equations, 2 figures.

Table of Contents

  1. Introduction
  2. System model
  3. Background
  4. Problem formulation
  5. Information loss minimization
  6. Information-lossless semi-unitary transformations
  7. Information-lossless processing distance minimization
  8. Baseline approach
  9. Numerical Results
  10. Conclusion

Key Result

Theorem 1

Let $\boldsymbol{F}_\mathrm{L}\in \mathcal{S}(M,T)$ be an arbitrary semi-unitary information-lossless $M\times T$ transformation, i.e., such that $I(\boldsymbol{F}_\mathrm{L}^\mathrm{H}\boldsymbol{y};\boldsymbol{s})=I(\boldsymbol{y};\boldsymbol{s})$ for the signal model eq:mimo with $K\leq T\leq M$. where $\widetilde{\boldsymbol{U}}_{\boldsymbol{H}}\in \mathcal{S}(M,K)$ is a given semi-unitary mat

Figures (2)

  • Figure 1: General decentralized framework under study.
  • Figure 2: Capacity ratio for $M=12$ and $K=4$.

Theorems & Definitions (2)

  • Theorem 1
  • Lemma 1