Enhanced ODMA for Massive Sparse Access: Hybrid Data-Frozen Bit Transmission and Fixed-Point Analysis over Block Fading Channels

2026-07-20

AI Summary

This work addresses the high overhead and inefficiency of conventional pilot-assisted channel estimation in massive sparse multiple access systems. The authors propose an enhanced Orthogonal Division Multiple Access (ODMA) scheme that embeds a small number of frozen symbols within codewords, serving dual roles as pilots and decoding aids, thereby substantially reducing overhead. By integrating low-complexity single-user channel estimation with iterative interference cancellation, the scheme achieves performance approaching that of ideal channel state information (CSI). Furthermore, the paper introduces a multiuser fixed-point analysis method tailored for block-fading channels, which leverages AWGN single-user decoding functions to efficiently predict convergence performance across arbitrary code lengths, rates, and decoding algorithms—eliminating the need for time-consuming Monte Carlo simulations. In a 300-user system, only 5–20 frozen symbols suffice to closely approach perfect CSI performance, offering an efficient design tool for massive connectivity scenarios.

Abstract

This paper proposes a novel on-off division multiple access (ODMA) transmission scheme that enables efficient joint multi-user channel estimation and iterative decoding by inserting a small number of frozen symbols into the codewords. Functionally analogous to pilots, these symbols are sparsely distributed within the codeword. Unlike conventional pilot-based methods, our approach requires only a minimal number of frozen symbols (e.g., $5\sim20$ symbols per user in a 300-user system), which serve dual purposes as both estimation references and decoding aids. By employing low-complexity single-user channel estimation and decoding, combined with simple iterative interference cancellation, the scheme achieves performance equivalent to that with perfectly known user channels, even when accounting for the additional energy and bandwidth costs of the frozen symbols. Furthermore, for the large-scale ODMA sparse multiple access system, this paper proposes a fixed-point analysis method, which can accurately estimate the iterative convergence performance over multi-user block fading channels by only leveraging the decoding functions under the single-user AWGN channel. This method is applicable to performance analysis for arbitrary code lengths, code rates, and decoding algorithms. It eliminates the need for extensive Monte Carlo simulation time, and provides an efficient tool for the design of multi-user codes.

Problem

• massive sparse access
• block fading channels
• joint channel estimation and decoding
• iterative convergence analysis
• ODMA

Innovation

• ODMA
• frozen symbols
• iterative interference cancellation
• fixed-point analysis
• massive sparse access