Affine Frequency Division Multiplexing With Index Modulation

TL;DR

This paper introduces AFDM-IM, a novel index modulation scheme for affine frequency division multiplexing, enhancing high-mobility communication performance by leveraging subsymbol activation in the DAF domain.

Contribution

It proposes a new AFDM-IM scheme with efficient index modulation strategies and derives a tight BER bound considering channel estimation errors.

Findings

AFDM-IM outperforms benchmark schemes in linear time-varying channels.

Index bits exhibit stronger diversity protection than modulated bits.

The scheme maintains robust performance even without full diversity condition.

Abstract

Affine frequency division multiplexing (AFDM) is a new multicarrier technique based on chirp signals tailored for high-mobility communications, which can achieve full diversity. In this paper, we propose an index modulation (IM) scheme based on the framework of AFDM systems, named AFDM-IM. In the proposed AFDM-IM scheme, the information bits are carried by the activation state of the subsymbols in discrete affine Fourier (DAF) domain in addition to the conventional constellation symbols. To efficiently perform IM, we divide the subsymbols in DAF domain into several groups and consider both the localized and distributed strategies. An asymptotically tight upper bound on the average bit error rate (BER) of the maximum-likelihood detection in the existence of channel estimation errors is derived in closed-form. Computer simulations are carried out to evaluate the performance of the proposed AFDM-IM scheme, whose results corroborate its superiority over the benchmark schemes in the linear time-varying channels. We also evaluate the BER performance of the index and modulated bits for the AFDM-IM scheme with and without satisfying the full diversity condition of AFDM. The results show that the index bits have a stronger diversity protection than the modulated bits even when the full diversity condition of AFDM is not satisfied.