Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Channel Orthogonalization in Panel-Based LIS

Juan Vidal Alegría, Ove Edfors

TL;DR

Problem: enabling orthogonal space-division multiplexing in panel-based LIS by using a subset of active panels and low-power receive-and-transmit (RRTx) to create an orthogonal channel in time and space. Approach: design the RRTx processing to achieve perfect orthogonality, and optimize the remaining degrees of freedom on the Stiefel manifold to minimize processing power, leveraging an SVD-based decomposition of the direct channel. Contributions: a closed-form global minimizer for the RRTx power under the orthogonality constraint, explicit feasibility conditions for the orthogonalization, and numerical results showing substantial power savings and improved user fairness compared with RIS-based or fully-active baselines. Impact: delivers a scalable, energy-efficient framework for OS DM in LIS with panel granularity and per-subcarrier BB processing.

Abstract

Large intelligent surface (LIS) has gained momentum as a potential 6G-enabling technology that expands the benefits of massive multiple-input multiple-output (MIMO). On the other hand, orthogonal space-division multiplexing (OSDM) may give a promising direction for efficient exploitation of the spatial resources, analogous as what is achieved with orthogonal frequency-division multiplexing (OFDM) in the frequency domain. To this end, we study how to enforce channel orthogonality in a panel-based LIS (P-LIS) scenario. Our proposed method consists of having a subset of active LIS-panels coherently serving a set of users, and another subset of LIS-panels operating in a novel low-power mode by implementing a receive and re-transmit (RRTx) process. This results in an inter-symbol interference (ISI) channel, where we characterize the RRTx processing required to achieve simultaneous orthogonality in time and space. We then employ the remaining degrees of freedom (DoFs) from the orthogonality constraint to minimize the RRTx processing power, where we derive a closed-form global minimizer, allowing for efficient implementation of the proposed scheme.

Channel Orthogonalization in Panel-Based LIS

TL;DR

Problem: enabling orthogonal space-division multiplexing in panel-based LIS by using a subset of active panels and low-power receive-and-transmit (RRTx) to create an orthogonal channel in time and space. Approach: design the RRTx processing to achieve perfect orthogonality, and optimize the remaining degrees of freedom on the Stiefel manifold to minimize processing power, leveraging an SVD-based decomposition of the direct channel. Contributions: a closed-form global minimizer for the RRTx power under the orthogonality constraint, explicit feasibility conditions for the orthogonalization, and numerical results showing substantial power savings and improved user fairness compared with RIS-based or fully-active baselines. Impact: delivers a scalable, energy-efficient framework for OS DM in LIS with panel granularity and per-subcarrier BB processing.

Abstract

Large intelligent surface (LIS) has gained momentum as a potential 6G-enabling technology that expands the benefits of massive multiple-input multiple-output (MIMO). On the other hand, orthogonal space-division multiplexing (OSDM) may give a promising direction for efficient exploitation of the spatial resources, analogous as what is achieved with orthogonal frequency-division multiplexing (OFDM) in the frequency domain. To this end, we study how to enforce channel orthogonality in a panel-based LIS (P-LIS) scenario. Our proposed method consists of having a subset of active LIS-panels coherently serving a set of users, and another subset of LIS-panels operating in a novel low-power mode by implementing a receive and re-transmit (RRTx) process. This results in an inter-symbol interference (ISI) channel, where we characterize the RRTx processing required to achieve simultaneous orthogonality in time and space. We then employ the remaining degrees of freedom (DoFs) from the orthogonality constraint to minimize the RRTx processing power, where we derive a closed-form global minimizer, allowing for efficient implementation of the proposed scheme.
Paper Structure (6 sections, 2 theorems, 29 equations, 3 figures)

This paper contains 6 sections, 2 theorems, 29 equations, 3 figures.

Table of Contents

  1. Introduction
  2. System Model
  3. ISI Channel Orthogonalization
  4. Power Minimization
  5. Numerical Results
  6. Conclusions

Key Result

Lemma 1

Consider two arbitrary positive-definite matrices $\widecheck{\boldsymbol{G}}_1$ and $\widecheck{\boldsymbol{G}}_2$, each of them containing distinct eigenvalues, and where we may assume without loss that the dimension of $\widecheck{\boldsymbol{G}}_1$ is larger than that of $\widecheck{\boldsymbol{ where $\widecheck{\boldsymbol{U}}_1$ and $\widecheck{\boldsymbol{U}}_2$ are the unitary matrices fr

Figures (3)

  • Figure 1: Illustration of the scenario at time-slot $t$.
  • Figure 2: RRTx processing power (left) for minimum channel gain per UE (right) with respect to the channel gain ratio.
  • Figure 3: Ergodic UE capacity with respect to channel gain ratio for $M=8$ antennas per panel and $K=2$ UEs.

Theorems & Definitions (2)

  • Lemma 1
  • Lemma 2