Classes de códigos LDPC estruturados adequadas para codificação cooperativa

Abstract

The Cooperative Comunication makes use of the wireless broadcasting nature, using intermediate nodes as relay and produces diversity between a point-to-point communication link.One of the communication methods is the cooperative codiĄcation, that can be implemented by using low density parity check (LDPC) codes. These kinds of codes presents performance that are very close to the theorical capacity in channels disturbed by additive white Gaussian noise (AWGN). ItŠs possible to design LDPC codes with good coding and decoding properties in such a way that they become efficient to implement cooperative coding. Three of the classes that will be carefully studied on this work are: LDPC codes with parity checking matrix H constructed from Barker sequences, LDPC codes with H matrix constructed from submatrices deĄned with cyclic rotations by prime numbers of an identity matrix I and codes with H matrix constructed with submatrices deĄned from Latin squares.The cooperative coding scheme used in this thesis consists of three devices: a source, a relay and a receiver. The source generates and broadcasts its encoded data to the relay and the receiver. The relay receives the signal sent by the source corrupted by noise and channel interference, decodes the source data, recodes and retransmits them to the receiver. The relay may or may not use the same encoder used by the source. At the receiver, the signals received from the source and the relay are combined and decoded to obtain the best estimate of the data sent by the source. This thesis presents methods of performing channel encoding in the relay accommodating as little redundancy as possible, without compromising the error correction capability of the receiver. Thus, the LDPC codes used here have the modular structure in their parity check matrices. In other words, classes of LDPC codes having the parity check matrix consisting of blocks are used in order to be able to simply change their coding rate. This strategy allows the relay to transmit incremental redundancy to the source codeword and the receiver can perform the decoding of the information transmitted by the source efficiently but without overloading the relay in terms of frequency band usage.The results obtained by computational simulation show that it is possible to obtain significant gains with the implementation of these cooperative coding schemes over the sourcereceiver communication scheme, without the aid of the relay.