Space-Time Encoded MISO Broadcast Channel with Outdated CSIT: An Error Rate and Diversity Performance Analysis

TL;DR

This paper analyzes the error rate and diversity-multiplexing tradeoff of space-time encoded MISO broadcast channels with outdated CSIT, revealing conditions where MAT protocol outperforms traditional methods at finite SNR.

Contribution

It provides the first finite SNR error rate and DMT analysis of space-time encoded transmission with delayed CSIT, extending understanding beyond asymptotic DoF results.

Findings

MAT protocol offers 33% DoF gain over TDMA.

MAT is not always better than TDMA at finite SNR.

Full-rate full-diversity codes improve MAT performance.

Abstract

Studies of the MISO Broadcast Channel (BC) with delayed Channel State Information at the Transmitter (CSIT) have so far focused on the sum-rate and Degrees-of-Freedom (DoF) region analysis. In this paper, we investigate for the first time the error rate performance at finite SNR and the diversity-multiplexing tradeoff (DMT) at infinite SNR of a space-time encoded transmission over a two-user MISO BC with delayed CSIT. We consider the so-called MAT protocol obtained by Maddah-Ali and Tse, which was shown to provide 33% DoF enhancement over TDMA. While the asymptotic DMT analysis shows that MAT is always preferable to TDMA, the Pairwise Error Probability analysis at finite SNR shows that MAT is in fact not always a better alternative to TDMA. Benefits can be obtained over TDMA only at very high rate or once concatenated with a full-rate full-diversity space-time code. The analysis is also extended to spatially correlated channels and the influence of transmit correlation matrices and user pairing strategies on the performance are discussed. Relying on statistical CSIT, signal constellations are further optimized to improve the error rate performance of MAT and make it insensitive to user orthogonality. Finally, other transmission strategies relying on delayed CSIT are discussed.