Channel Dependent Mutual Information in Index Modulations

TL;DR

This paper introduces approximations for mutual information in index modulations, enabling real-time link adaptation in time-varying channels by providing a simple closed-form expression.

Contribution

It proposes novel approximations for mutual information in index modulations, facilitating real-time computation and adaptive transmission in dynamic channels.

Findings

Closed-form expressions for mutual information in index modulations.

Enabling real-time link adaptation in time-varying channels.

Reduction of computational complexity for mutual information calculation.

Abstract

Mutual Information is the metric that is used to perform link adaptation, which allows to achieve rates near capacity. The computation of adaptive transmission modes is achieved by employing the mapping between the Signal to Noise Ratio and the Mutual Information. Due to the high complexity of the computation of the Mutual Information, this process is performed off-line via Monte Carlo simulations, whose results are stored in look-up tables. However, in Index Modulations, such as Spatial Modulation or Polarized Modulation, this is not feasible since the constellation and the Mutual Information are channel dependent and it would require to compute this metric at each time instant if the channel is time varying. In this paper, we propose different approximations in order to obtain a simple closed-form expression that allows to compute the Mutual Information at each time instant and thus, making feasible the link adaptation.