|M.Sc Student||Peter Brokhman|
|Subject||Implementation of Serial Concatenated Continuous Phase|
Modulation System in FPGA
|Department||Department of Electrical Engineering||Supervisor||Mr. Kalet Yitzhak|
Continuous Phase Modulation (CPM) signals are widely used in radio, mobile and satellite communications. In this work, the implementation of an iterative decoder of a serially concatenated signal, using an outer convolutional code and an inner CPM modulation, separated by a random interleaver, is examined. The work is based on a previous work by Shachar Kons. The combined use of a convolutional code and a CPM modulation, separated by a random interleaver is known to produce high coding gain. We examine this serial concatenation for an MSK signal. A maximum a posteriori Soft-Input Soft-Output decoder is implemented for the decoding of the combined coded MSK signal. A decoder in the logarithmic domain is used for practical implementations. The overall iterative decoding process of the concatenated system is presented. The sliding- window technique is used in the decoder implementation.
The system is designed in fixed-point representation and written in the Verilog HDL. The system is implemented using a field-programmable gate array (FPGA)
Finally, the bit-error rate (BER) probability of the implemented system is found and compared to the simulation results of Kons. The BER results of the implemented system are about 0.7 dB worse than the results of the simulation system using floating point representation. The difference is due to the limited precison of the fixed point representation. The performance for four or more iterations in the fixed point system, is almost the same.
In summary, we have implemented a serial coded MSK system with coding gain of almost six dB at the BER of 10-5.