On the Low SNR Capacity of Maximum Ratio Combining over Rician Fading Channels with Full Channel State Information

TL;DR

This paper analyzes the low SNR capacity of MRC over Rician channels with full CSI, revealing how capacity scales and can be achieved with minimal feedback, advancing understanding of low SNR wireless communication limits.

Contribution

It derives the low SNR capacity scaling law for Rician fading channels with MRC and demonstrates that one-bit feedback suffices for capacity achievement.

Findings

Capacity scales as (L Omega/(K+L)) SNR log(1/SNR).

One-bit CSI feedback enables optimal capacity with on-off power control.

Framework generalizes existing low-SNR capacity results.

Abstract

In this letter, we study the ergodic capacity of a maximum ratio combining (MRC) Rician fading channel with full channel state information (CSI) at the transmitter and at the receiver. We focus on the low Signal-to-Noise Ratio (SNR) regime and we show that the capacity scales as (L Omega/(K+L)) SNR log(1/SNR), where Omega is the expected channel gain per branch, K is the Rician fading factor, and L is the number of diversity branches. We show that one-bit CSI feedback at the transmitter is enough to achieve this capacity using an on-off power control scheme. Our framework can be seen as a generalization of recently established results regarding the fading-channels capacity characterization in the low-SNR regime.