Physically-consistent Multi-band Massive MIMO Systems: A Radio Resource Management Model

TL;DR

The paper tackles the challenge of achieving very high data rates in beyond-5G systems by integrating carrier-aggregated multi-band transmission with physically accurate, mutually coupled mMIMO antenna models. It introduces a circuit-theoretic, multi-user, multi-band model and develops a joint optimization framework that simultaneously selects antenna spacing, precoding, sub-carrier windows, and power allocation to maximize sum-rate. A novel block-iterative, water-filling-based inner optimization and a windowing strategy enable efficient handling of hardware and channel constraints, while outer optimization via particle swarm methods guides the spacing. Simulations show significant bandwidth gains from tightly coupled arrays and demonstrate the benefits of joint power allocation across bands, with offline and online implementations offering different complexity-performance trade-offs.

Abstract

Massive multiple-input multiple-output (mMIMO) antenna systems and inter-band carrier aggregation (CA)-enabled multi-band communication are two key technologies to achieve very high data rates in beyond fifth generation (B5G) wireless systems. We propose a joint optimization framework for such systems where the mMIMO antenna spacing selection, precoder optimization, optimum sub-carrier selection and optimum power allocation are carried out simultaneously. We harness the bandwidth gain existing in a tightly coupled base station mMIMO antenna system to avoid sophisticated, non-practical antenna systems for multi-band operation. In particular, we analyze a multi-band communication system using a circuit-theoretic model to consider physical characteristics of a tightly coupled antenna array, and formulate a joint optimization problem to maximize the sum-rate. As part of the optimization, we also propose a novel block iterative water-filling-based sub-carrier selection and power allocation optimization algorithm for the multi-band mMIMO system. A novel sub-carrier windowing-based sub-carrier selection scheme is also proposed which considers the physical constraints (hardware limitation) at the mobile user devices. We carryout the optimizations in two ways: (i) to optimize the antenna spacing selection in an offline manner, and (ii) to select antenna elements from a dense array dynamically. Via computer simulations, we illustrate superior bandwidth gains present in the tightly-coupled colinear and rectangular planar antenna arrays, compared to the loosely-coupled or tightly-coupled parallel arrays. We further show the optimum sum-rate performance of the proposed optimization-based framework under various power allocation schemes and various user capability scenarios.

Figures (17)

• Figure 1: Multi-band mMIMO communication system model.
• Figure 2: Multi-band mMIMO resource allocation.
• Figure 3: Equivalent circuit-theoretic model for a mMIMO communication system with a single sub-carrier.
• Figure 4: Equivalent circuit for TM$_1$ antenna.
• Figure 5: Two TM$_1$ antennas arbitrary oriented in a 2-dimensional plane.