Improved ALOHA-based URA with Index Modulation: Efficient Decoding and Analysis

TL;DR

This paper introduces an improved ALOHA-based unsourced random access scheme for MIMO channels that uses index modulation and a novel decoding approach, achieving better performance and reduced complexity.

Contribution

It proposes a new URA scheme with index modulation and a simplified decoding method, enhancing efficiency and performance over existing approaches.

Findings

The proposed scheme outperforms traditional ALOHA-based URA in simulations.

The simplified superposed codeword decomposer reduces decoding complexity.

Performance analysis confirms the effectiveness of the new method.

Abstract

In this paper, an improved ALOHA-based unsourced random access (URA) scheme is proposed in MIMO channels. The channel coherent interval is divided into multiple sub-slots and each active user selects several sub-slots to send its codeword, namely, the channel access pattern. To be more specific, the data stream of each active user is divided into three parts. The first part is mapped as the compressed sensing (CS) pilot, which also serves for the consequent channel estimation. The second part is modulated by binary phase shift keying (BPSK). The obtained CS pilot and the antipodal BPSK signal are concatenated as its codeword. After that, the codeword of each active user is sent repeatedly based on its channel access pattern, which is determined by the third part of the information bits, namely, index modulation (IM). On the receiver side, a hard decision-based decoder is proposed which includes the CS decoder, maximal likelihood (ML)-based superposed codeword decomposer (SCD), and IM demodulator. To further reduce the complexity of the proposed decoder, a simplified SCD based on convex approximation is considered. The performance analysis is also provided. The exhaustive computer simulations confirm the superiority of our proposal.