الفهرس | Only 14 pages are availabe for public view |
Abstract Error correcting codes is very important in the power limited applications like Satellite communications because it can save power while maintain the same quality of communications. Communication media between a satellite and ground station has a lot of characteristics and the most important parameter here is the long distance, which affects the link budget design for the space link quality and reduces the signal quality. The Bit Error Rate (BER) is used to evaluate the performance of the link. To have a good BER in the satellite link, an efficient channel error correction code should be used. In the thesis, two types of powerful satellite error correcting techniques were studied, turbo code and Low Density Parity Check Code (LDPC). First, the turbo code encoder and decoder design was analyzed by taking into consideration the recommendations from Consultative Committee for Space Data System (CCSDS) for satellite applications. By applying some modifications to the decoding process the performance was improved. This improvement facilitate the using of turbo code in the satellite new missions required very low BER. Also, by redesigning of the interleaver for turbo code the minimum hamming distance of the code words can be increased, which improve the error correcting capabilities and lower the error floor of the code. Moreover, the encoding and decoding algorithm of turbo code was modified to give more satellite mission flexibility in emergency situations which enable the decoder to recover uncompleted received frames and extract valuable information. In some cases, extracted information has an important telemetry data about the state and functionality of the satellite subsystems. Finally, the complexity of turbo code was computed to be in considerations when compared with other types of codes. 6 Beside the turbo code, the performance of LDPC was simulated and compared with the performance of turbo code under different code rates. This comparison is so important, which shows the suitable application for each type of code based on the code rate. Also, the complexity of LDPC was calculated to be in comparison with the complexity of turbo code. This complexity comparison besides the performance comparison gives a second dimension of comparison when the realizing take place. Finally, a complete comparison between Turbo code and LDPC was made for the performance and complexity under different code rates. The entire simulation environment made for turbo code and LDPC was based on Matlab and C language. |