BCJR detection for GMSK modulation
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.
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