BCJR detection for GMSK modulation

by Wu, Ching-Tang

Abstract (Summary)
CPM advantageous in spectral efficiency because of its continuity of the phase in modulation. One of the CPM example is GMSK, which has been applied to the wireless GSM system. The conventional demodulaton og CPM is achieved by Viterbi algorithm. This is because of the state transition structure for the dynamic description of phase of the CPM signal. Furthermore, the state transition can be presented by a trellis diagram, which can be efficiently solved by Viterbi algorithm based upon the strategy of selecting best survivor path to a maximum likelihood criterion. The best survivor path is measured by the Euclidean distance in modulation in this thesis. Another demodulation method proposed by us is the famous BCJR algorithm. BCJR which is based upon the posteriori probabilities is a alternative method for decoding the convolution code. We compare the BCJR and Viterbi algorithm for the demodulation of the GMSK system. Experiment results demonstrate that BCJR has a better error probability than the Viterbi algorithm. Also, we compare different GMSK system for different overlapping length and modulation index. The best combination of L and h suggested by pur experiments is the case of L=3, and h=3/4.
Bibliographical Information:

Advisor:Ben-Shung Chow; Ju-Ya Chen; Tzyy-Sheng Horng

School:National Sun Yat-Sen University

School Location:China - Taiwan

Source Type:Master's Thesis

Keywords:viterbi cpm bcjr gmsk


Date of Publication:09/02/2003

© 2009 All Rights Reserved.