# LDPC Coded Multiuser Shaping for the Gaussian Multiple Access Channel

## TL;DR

This paper proposes a joint constellation and LDPC code design for the two-user Gaussian multiple access channel to maximize shaping gain and enable efficient joint decoding, validated through simulations.

## Contribution

It introduces a multilevel coding scheme with jointly designed constellations and LDPC codes optimized via EXIT charts for improved multiuser decoding performance.

## Key findings

- Achieved near-capacity performance with the proposed design.
- Demonstrated effective joint decoding among users.
- Validated the approach through numerical simulations.

## Abstract

The joint design of input constellation and low-density parity-check (LDPC) codes to approach the symmetric capacity of the two-user Gaussian multiple access channel is studied. More specifically, multilevel coding is employed at each user to construct a high-order input constellation and the constellations of the users are jointly designed so as to maximize the multiuser shaping gain. At the receiver, each layer of the multilevel coding is jointly decoded among users, while successive cancellation is employed across layers. The LDPC code employed by each user in each layer is designed using EXIT charts to support joint decoding among users for the prescribed per-layer rate and SNR. Numerical simulations are provided to validate the proposed constellation and LDPC code designs.

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Source: https://tomesphere.com/paper/1905.00405