Limited Feedback in Single and Multi-user MIMO Systems with Finite-Bit ADCs

TL;DR

This paper investigates limited feedback strategies for MIMO systems with finite-bit ADCs, proposing new codebook designs and analyzing how feedback bits impact rate loss across different SNR regimes.

Contribution

It introduces a novel codebook design for beamforming with 1-bit ADCs and analyzes the relationship between feedback bits and rate loss in finite-bit ADC MIMO systems.

Findings

More feedback bits are needed in medium SNR to limit rate loss.

Rate loss is influenced by ADC resolution and feedback bits.

Feedback bits should increase linearly with ADC resolution to minimize rate loss.

Abstract

Communication systems with low-resolution analog-to-digital-converters (ADCs) can exploit channel state information at the transmitter and receiver. This paper presents codebook designs and performance analyses for limited feedback MIMO systems with finite-bit ADCs. A point-to-point single-user channel is firstly considered. When the received signal is sliced by 1-bit ADCs, the absolute phase at the receiver is important to align the phase of the received signals. A new codebook design for beamforming, which separately quantizes the channel direction and the residual phase, is therefore proposed. For the multi-bit case where the optimal transmission method is unknown, suboptimal Gaussian signaling and eigenvector beamforming is assumed to obtain a lower bound of the achievable rate. It is found that to limit the rate loss, more feedback bits are needed in the medium SNR regime than the low and high SNR regimes, which is quite different from the conventional infinite-bit ADC case. Second, a multi-user system where a multiple-antenna transmitter sends signals to multiple single-antenna receivers with finite-bit ADCs is considered. Based on the derived performance loss due to finite-bit ADCs and finite-bit CSI feedback, the number of bits per feedback should increase linearly with the ADC resolution in order to restrict the rate loss.