The Value of Staying Current when Beamforming

TL;DR

This paper investigates how the aging of Channel State Information (CSI) affects beamforming performance, quantifying degradation using outage probability and translating results into effective diversity orders for MISO and MIMO systems.

Contribution

It introduces a method to quantify performance loss due to CSI aging and analyzes its impact on various beamforming algorithms including transmit antenna selection.

Findings

CSI aging significantly degrades beamforming performance.

Outage probability effectively measures CSI currency.

Results are applicable to MISO and multiuser MIMO systems.

Abstract

Beamforming is a widely used method of provisioning high quality wireless channels that leads to high data rates and simple decoding structures. It requires feedback of Channel State Information (CSI) from receiver to transmitter, and the accuracy of this information is limited by rate constraints on the feedback channel and by delay. It is important to understand how the performance gains associated with beamforming depend on the accuracy or currency of the Channel State Information. This paper quantifies performance degradation caused by aging of CSI. It uses outage probability to measure the currency of CSI, and to discount the performance gains associated with ideal beamforming. Outage probability is a function of the beamforming algorithm and results are presented for Transmit Antenna Selection and other widely used methods. These results are translated into effective diversity orders for Multiple Input Single Output (MISO) and Multiuser Multiple Input Multiple Output (MIMO) systems.