Multi-mode Transmission for the MIMO Broadcast Channel with Imperfect Channel State Information

TL;DR

This paper introduces an adaptive multi-mode transmission strategy for MIMO broadcast channels with imperfect CSI, optimizing spectral efficiency by balancing multiple factors and outperforming single-user schemes under certain conditions.

Contribution

It presents a novel adaptive transmission mode selection method that accounts for feedback delay and quantization errors, enhancing throughput with limited feedback.

Findings

Achieves higher throughput than single-user MIMO at moderate SNR.

Provides near-opportunistic scheduling performance with limited feedback.

Derives closed-form rate approximations for different transmission modes.

Abstract

This paper proposes an adaptive multi-mode transmission strategy to improve the spectral efficiency achieved in the multiple-input multiple-output (MIMO) broadcast channel with delayed and quantized channel state information. The adaptive strategy adjusts the number of active users, denoted as the transmission mode, to balance transmit array gain, spatial division multiplexing gain, and residual inter-user interference. Accurate closed-form approximations are derived for the achievable rates for different modes, which help identify the active mode that maximizes the average sum throughput for given feedback delay and channel quantization error. The proposed transmission strategy is combined with round-robin scheduling, and is shown to provide throughput gain over single-user MIMO at moderate signal-to-noise ratio. It only requires feedback of instantaneous channel state information from a small number of users. With a feedback load constraint, the proposed algorithm provides performance close to that achieved by opportunistic scheduling with instantaneous feedback from a large number of users.