Abstract
In the encoding of Luby transform (LT) codes, information bits (variable nodes) are randomly connected to the check nodes. Although the check node degrees have been optimized for error-rate performance, the arbitrary connec- tions in the code graph cannot guarantee ecient propagation of the channel information, and may slowdown the convergence speed of the iterative decod- ing. This thesis proposed a design of generator matrix such that the channel information can be eciently propagated through the arranged connections. In addition, the convergence speed for rateless codes can also be accelerated using a variety of di erent decoders. The proposed degree-oriented schedul- ing belief propagation (DOS-BP) updates the decoding messages in the order of check node degrees, and further reduces the required number of iterations. The improvement in the convergence speed can be achieved without sacri- cing the error-rate performance. In the case of Raptor codes, the BER performance can even be improved.