The Application Of Turbo Code In Wavelet Packet Transform Based Multicarrier Modulation Communication System

Wavelet packet based multicarrier modulation is a technique combining wavelet analysis theory and multicarrier modulation perfectly. It improves the capability of system and adapts all kinds of environment. The error correcting code in this Wavelet packet based multicarrier modulation system (WPT-MCM) is RS code which is the best linear grouping code with a simple coding structure. RS code is poor in time delay and frame synchronization especially in a channel with high noise.Turbo code is virtually a Parallel/Serial Concatenated Convolutional Code which is composed of two convolutional coders and an interleaver. According to the simulation in AWGN, Turbo code provides 2dB of coding gain and approaches to Shannon limit comparing to RS code and convolutional code. Turbo code has an advantage in time delay and perfoms perfectly in a poor channel condition. The decoding of Turbo depends on soft decision that is suitable for outburst error correcting.In this paper, we supplied Turbo code into a WPT-MCM system as the error correcting code. Turbo code can deal with many problems such as poor randomicity of some triditinal codes and asymmetry of codes. The maintenance of its performance in a poor channel condition is excellent, so it is adaptive to all kinds of channel conditions, which is important to improve the capability of system.At the beginning of the paper, we simplely introduced the structure and theory of Turbo code, then we set the blue print in encoding of PCCC and decoding depending on soft decision, finally, we made a simulation in MATLAB to the whole process of encoding and decoding. After decoding, we got a set of data of BER which can show the good performance of Turbo code. At the end, we brought forward a blue print of combining between Turbo code and RS code as to combine the advantage of both. The problems with sub coders, interleavers and decoding method are still remained to discuss.