# A modified probabilistic amplitude shaping scheme to use sign-bit-like shaping with a BICM

## TL;DR

This paper introduces a modified probabilistic amplitude shaping method that enables sign-bit-like shaping within a BICM framework, demonstrated through simulations with 5G NR LDPC codes.

## Contribution

It presents a novel modification allowing sign-bit shaping to be integrated into BICM systems, expanding its applicability beyond multilevel coded modulations.

## Key findings

- Successful implementation of sign-bit-like shaping with BICM.
- Simulation results show improved performance in 5G NR LDPC schemes.
- Minor modifications enable compatibility of sign-bit shaping with BICM.

## Abstract

On the one hand, sign-bit shaping is a popular shaping scheme where the conditional probability of the sign bit is made non-equiprobable. On the other hand, probabilistic amplitude shaping (PAS) is a popular coding scheme, to combine shaping and a bit-interleaved coded modulation (BICM), where the sign bit should not be involved in the shaping. Indeed, with the PAS scheme the sign bit is the parity bit, i.e., the output of the systematic error-correcting code. As a result, sign-bit shaping has been used with multilevel coded modulations rather than BICM. In this paper, we show that with minor modifications it is possible to use sign-bit-like shaping with a BICM. Simulation results are provided with the 5G NR LDPC BICM scheme.