Variable-Rate M-PSK Communications without Channel Amplitude Estimation

TL;DR

This paper proposes a variable-rate M-PSK modulation scheme for fading channels that does not require channel gain estimation, using S+N sampling to adapt modulation order and improve spectral efficiency with low complexity receivers.

Contribution

It introduces a novel VR M-PSK scheme based on S+N sampling, eliminating the need for channel gain estimation in adaptive modulation over fading channels.

Findings

S+N sampling effectively replaces S/N for modulation adaptation

The scheme enhances spectral efficiency under error constraints

Application demonstrated in EGC diversity receivers

Abstract

Channel estimation at the receiver side is essential to adaptive modulation schemes, prohibiting low complexity systems from using variable rate and/or variable power transmissions. Towards providing a solution to this problem, we introduce a variable-rate (VR) M-PSK modulation scheme, for communications over fading channels, in the absence of channel gain estimation at the receiver. The choice of the constellation size is based on the signal-plus-noise (S+N) sampling value rather than on the signal-to-noise ratio (S/N). It is analytically shown that S+N can serve as an excellent simpler criterion, alternative to S/N, for determining the modulation order in VR systems. In this way, low complexity transceivers can use VR transmissions in order to increase their spectral efficiency under an error performance constraint. As an application, we utilize the proposed VR modulation scheme in equal gain combining (EGC) diversity receivers.