Rate Analysis of Two-Receiver MISO Broadcast Channel with Finite Rate Feedback: A Rate-Splitting Approach

TL;DR

This paper analyzes rate-splitting schemes for a two-receiver MISO broadcast channel with finite feedback, demonstrating how these schemes reduce feedback overhead while maintaining high sum rates, outperforming traditional methods.

Contribution

It introduces and compares two rate-splitting schemes, RS-S and RS-ST, showing their advantages in feedback overhead reduction and sum rate performance under quantized CSIT.

Findings

RS schemes reduce feedback overhead logarithmically at high SNR.

RS-S maintains constant sum rate loss with less feedback than ZFBF.

RS schemes outperform single-user/multiuser switching in SNR gains.

Abstract

To enhance the multiplexing gain of two-receiver Multiple-Input-Single-Output Broadcast Channel with imperfect channel state information at the transmitter (CSIT), a class of Rate-Splitting (RS) approaches has been proposed recently, which divides one receiver's message into a common and a private part, and superposes the common message on top of Zero-Forcing precoded private messages. In this paper, with quantized CSIT, we study the ergodic sum rate of two schemes, namely RS-S and RS-ST, where the common message(s) are transmitted via a space and space-time design, respectively. Firstly, we upper-bound the sum rate loss incurred by each scheme relative to Zero-Forcing Beamforming (ZFBF) with perfect CSIT. Secondly, we show that, to maintain a constant sum rate loss, RS-S scheme enables a feedback overhead reduction over ZFBF with quantized CSIT. Such reduction scales logarithmically with the constant rate loss at high Signal-to-Noise-Ratio (SNR). We also find that, compared to RS-S scheme, RS-ST scheme offers a further feedback overhead reduction that scales with the discrepancy between the feedback overhead employed by the two receivers when there are alternating receiver-specific feedback qualities. Finally, simulation results show that both schemes offer a significant SNR gain over conventional single-user/multiuser mode switching when the feedback overhead is fixed.