Generalized Code Index Modulation Aided AFDM for Spread Spectrum Systems

TL;DR

This paper introduces a generalized code index modulation scheme for AFDM in spread spectrum systems, enhancing energy efficiency and performance in high-mobility channels with a low-complexity detection algorithm.

Contribution

It proposes a novel GCIM-AFDM-SS scheme that encodes information via spreading code indices and symbols, with a low-complexity detector and theoretical BER bounds.

Findings

Outperforms classical AFDM-SS and IM-AFDM systems

Demonstrates improved BER performance in simulations

Provides a low-complexity detection algorithm

Abstract

The recently proposed affine frequency division multiplexing (AFDM) is a new transmission waveform that has shown excellent performance in high-mobility environments, making it a sensible option for the next-generation wireless networks. In this paper, we investigate an energy-efficient generalized code index modulation scheme for AFDM by leveraging spread spectrum, referred to as GCIM-AFDM-SS, to combat the interference caused by the doubly dispersive channels. Specifically, the information bits are conveyed by the transmitted symbols as well as the indices of the selected spreading codes in our proposed GCIM-AFDM-SS scheme. To avoid extensive computations, we also develop a lowcomplexity maximal ratio combining (MRC) detector algorithm, which recovers the spreading codes first and demodulates the symbols afterwards. Moreover, an upper bound on the bit error rate (BER) of the proposed GCIM-AFDM-SS system with maximum-likelihood (ML) detection is derived. Numerical results demonstrate the superiority of the proposed GCIM-AFDM-SS system over the classical AFDM spread spectrum (AFDM-SS) and the existing index modulated AFDM (IM-AFDM) systems.