Design of Serially-Concatenated Low-Density Generator Matrix codes using EXIT charts

Inhalt:
Serially-Concatenated Low-Density Generator Matrix (SCLDGM) codes are an attractive scheme to approach channel capacity on several channel models. Performance of SCLDGM codes depends basically on the rates of the two component codes, as well as on the connection degrees of the bits involved in a codeword. SCLDGM codes proposed so far have been constructed setting the values of these parameters heuristically. In this paper we present two SCLDGM codes constructed using an optimization procedure based on tracking the decoding behaviour of the Sum-Product Algorithm (SPA) by means of EXtrinsic Information Transfer (EXIT) functions. We present results for both Binary-Input AWGN (BIAWGN) and Rayleigh fading channels. In both cases the optimized SCLDGM codes exhibit better performance than other recent schemes, such as Irregular Repeat-Accumulate (IRA) codes, at similar coding/decoding computational cost.