Diversity Order Gain with Noisy Feedback in Multiple Access Channels

TL;DR

This paper investigates how noisy feedback affects the diversity-multiplexing tradeoff in multiuser MIMO systems, showing that even minimal feedback can significantly enhance diversity order.

Contribution

It demonstrates that a single bit of imperfect feedback can double the maximum diversity order in multiuser MIMO systems, and explores the effects of additional feedback bits.

Findings

One bit of feedback doubles the diversity order to 2mn.

Additional feedback bits do not increase the maximum diversity order beyond 2mn.

Higher multiplexing gains can also benefit from increased feedback bits.

Abstract

In this paper, we study the effect of feedback channel noise on the diversity-multiplexing tradeoff in multiuser MIMO systems using quantized feedback, where each user has m transmit antennas and the base-station receiver has n antennas. We derive an achievable tradeoff and use it to show that in SNR-symmetric channels, a single bit of imperfect feedback is sufficient to double the maximum diversity order to 2mn compared to when there is no feedback (maximum is mn at multiplexing gain of zero). Further, additional feedback bits do not increase this maximum diversity order beyond 2mn. Finally, the above diversity order gain of mn over non-feedback systems can also be achieved for higher multiplexing gains, albeit requiring more than one bit of feedback.