A Large-System Analysis of the Imperfect-CSIT Gaussian Broadcast Channel with a DPC-based Transmission Strategy

TL;DR

This paper analyzes the asymptotic throughput of a large Gaussian broadcast channel with imperfect channel state information, demonstrating that ZFDPC outperforms beamforming and optimizing user selection for maximum throughput.

Contribution

It derives a closed-form expression for the asymptotic throughput of ZFDPC in large systems with finite-rate feedback, highlighting its advantages over beamforming.

Findings

ZFDPC achieves higher throughput than beamforming under finite-rate feedback.

A closed-form asymptotic throughput expression is derived for large systems.

Optimal user selection for maximum throughput is determined.

Abstract

The Gaussian broadcast channel (GBC) with $K$ transmit antennas and $K$ single-antenna users is considered for the case in which the channel state information is obtained at the transmitter via a finite-rate feedback link of capacity $r$ bits per user. The throughput (i.e., the sum-rate normalized by $K$) of the GBC is analyzed in the limit as $K \to \infty$ with $\frac{r}{K} \to \bar{r}$. Considering the transmission strategy of zeroforcing dirty paper coding (ZFDPC), a closed-form expression for the asymptotic throughput is derived. It is observed that, even under the finite-rate feedback setting, ZFDPC achieves a significantly higher throughput than zeroforcing beamforming. Using the asymptotic throughput expression, the problem of obtaining the number of users to be selected in order to maximize the throughput is solved.