Cooperative communication using protograph-based low-density parity-check codes

We propose a novel two-user cooperation scheme that employs protograph-based low-density parity-check (LDPC) codes. The proposed scenario is based on time division where each user transmits its message to the base station (BS) in two successive intervals. In the first interval, the user sends its message to the BS as well as its partner user. If the partner user successfully decodes the received signal, the two users cooperatively send the main user´s message using the Alamouti scheme during the second interval. Otherwise, the main user simply retransmits its message to the BS. The users change roles during the next two intervals. Furthermore, the users encode their information over a class of protograph-based LDPC codes called the Accumulate-Repeat-4-Jagged-Accumulate (AR4JA) codes that allow flexible selections of rate and length. Using this technique, a three-level diversity is achieved when there exists a strong interuser link, whereas when the interuser channel has a poor quality, at least a two-level diversity is achieved.