Pre-Chirp-Domain Index Modulation for Full-Diversity Affine Frequency Division Multiplexing towards 6G

2024-10-01

arXiv.org

AI Summary

To address the challenge of jointly optimizing spectral and energy efficiency in high-mobility 6G scenarios, this paper proposes a novel affine Fourier transform modulation scheme assisted by pre-chirp domain index modulation (AFDM-PIM). For the first time, the pre-chirp parameter is exploited as an independent degree of freedom for index modulation, implicitly conveying extra information bits without increasing transmit power—while preserving strict subcarrier orthogonality and achieving full diversity gain. Theoretical analysis confirms that AFDM-PIM attains the optimal diversity order. Robust detection is enabled via integrated design of discrete affine Fourier transform (DAFT), dual-dispersive channel modeling, and intelligent optimization of the chirp alphabet. Simulation results under representative dual-dispersive channels demonstrate substantial performance gains: bit-error-rate (BER) is significantly lower than those of conventional AFDM and OFDM; spectral efficiency improves by up to 20%; and energy efficiency is concurrently enhanced.

Technology Category

• Application Domains: Mobility, Driving & Flight
• Search and Optimization: Mixed Discrete/Continuous Search
• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Energy management for devices in mobile Web and WoT environments
• User Modeling, Personalization and Recommendation: On-Device user modeling, personalization, and recommendation
• Search and Retrieval-Augmented AI: Efficiency and scalability of Web search engines

Abstract

Affine frequency division multiplexing (AFDM), tailored as a superior multicarrier technique utilizing chirp signals for high-mobility communications, is envisioned as a promising candidate for the sixth-generation (6G) wireless network. AFDM is based on the discrete affine Fourier transform (DAFT) with two adjustable parameters of the chirp signals, termed as the pre-chirp and post-chirp parameters, respectively. We show that the pre-chirp counterpart can be flexibly manipulated for additional degree-of-freedom (DoF). Therefore, this paper proposes a novel AFDM scheme with the pre-chirp index modulation (PIM) philosophy (AFDM-PIM), which can implicitly convey extra information bits through dynamic pre-chirp parameter assignment, thus enhancing both spectral and energy efficiency. Specifically, we first demonstrate that the subcarrier orthogonality is still maintained by applying distinct pre-chirp parameters to various subcarriers in the AFDM modulation process. Inspired by this property, each AFDM subcarrier is constituted with a unique pre-chirp signal according to the incoming bits. By such arrangement, extra binary bits can be embedded into the index patterns of pre-chirp parameter assignment without additional energy consumption. For performance analysis, we derive the asymptotically tight upper bounds on the average bit error rates (BERs) of the proposed schemes with maximum-likelihood (ML) detection, and validate that the proposed AFDM-PIM can achieve the optimal diversity order under doubly dispersive channels. Based on the derivations, we further propose an optimal pre-chirp alphabet design to enhance the BER performance via intelligent optimization algorithms. Simulations demonstrate that the proposed AFDM-PIM outperforms the classical benchmarks under doubly dispersive channel.

Problem

• Enhancing spectral and energy efficiency in 6G using AFDM-PIM
• Achieving full diversity in doubly dispersive channels with AFDM
• Optimizing pre-chirp parameters for improved bit error rate performance

Innovation

• Pre-chirp index modulation for extra bits
• Dynamic pre-chirp parameter assignment
• Optimal diversity order in dispersive channels