Performance Analysis of Heterogeneous Feedback Design in an OFDMA Downlink with Partial and Imperfect Feedback

TL;DR

This paper analyzes the performance of heterogeneous feedback design in OFDMA downlink systems, considering partial and imperfect feedback, and proposes strategies to optimize system throughput and robustness.

Contribution

It develops an analytical framework for heterogeneous partial feedback in OFDMA, including effects of imperfections and outage, with closed-form sum rate expressions and adaptation strategies.

Findings

Heterogeneous subband sizes improve feedback efficiency.

Imperfect feedback reduces system sum rate and goodput.

Adaptive strategies can mitigate the impact of feedback imperfections.

Abstract

Current OFDMA systems group resource blocks into subband to form the basic feedback unit. Homogeneous feedback design with a common subband size is not aware of the heterogeneous channel statistics among users. Under a general correlated channel model, we demonstrate the gain of matching the subband size to the underlying channel statistics motivating heterogeneous feedback design with different subband sizes and feedback resources across clusters of users. Employing the best-M partial feedback strategy, users with smaller subband size would convey more partial feedback to match the frequency selectivity. In order to develop an analytical framework to investigate the impact of partial feedback and potential imperfections, we leverage the multi-cluster subband fading model. The perfect feedback scenario is thoroughly analyzed, and the closed form expression for the average sum rate is derived for the heterogeneous partial feedback system. We proceed to examine the effect of imperfections due to channel estimation error and feedback delay, which leads to additional consideration of system outage. Two transmission strategies: the fix rate and the variable rate, are considered for the outage analysis. We also investigate how to adapt to the imperfections in order to maximize the average goodput under heterogeneous partial feedback.