Joint design of code, constellation and power allocation in BICM LDPC coded systems

Abstract:
The performance of a system using low density parity check (LDPC) codes depends on the proper matching of several parameters: degree profile of the code, constellation size and constellation labelling and the power allocated to each transmitted symbol. In this paper we propose a unified formulation for the optimisation of all these parameters, so that some or all of them can be jointly designed to maximise the spectral efficiency for a certain transmitted power or to minimise the transmitted power that guarantees a certain spectral efficiency. The proposed algorithm is based on the EXIT chart analysis of the LDPC code and it can be applied to two different set ups: (I) scenarios where the transmitter has perfect channel knowledge, so the proposed algorithm can be regarded as an extension of waterfilling and bit-loading policies that takes into account the specific channel code stage, and to (II) scenarios where the transmitter only knows the average channel quality, so the proposed algorithm can be regarded as a generalisation of the previously proposed irregular codes and irregular modulation schemes. Besides, it can be applied to the optimisation of BICM and BICM-ID.