Protograph EXIT analysis over block fading channels with application to relays

An accurate extrinsic information transfer (EXIT) analysis is developed for protograph low-density parity-check (LDPC) codes over the block fading channel (BFC). The analysis is thus exploited for analyzing the behavior of distributed protograph LDPC ensembles over block fading relay channels. A novel protograph-based construction of low-density parity-check (LDPC) codes for the relay channel is proposed, which provides an enhanced unequal error protection (named unequal diversity, UD) property. The focus is on quasi-static fading channels and on the high-code-rate (R >; 1/2) regimes, for which (according to the Singleton bound) no full diversity can be achieved. In the proposed construction, some nodes (and the corresponding codeword fragments) associated with the code graph enjoy the diversity provided by the relay, whereas the remaining nodes do not experience any diversity. The proposed approach can be thus tailored to transmit information blocks with different priority levels.