Implementation of 30 kbit/s Iterative Decoding Scheme with FPGA Realization of the Viterbi Decoder
A feasibility study for a low cost, iterative, serially concatenated coding system is performed. The system uses outer (255,223) Reed-Solomon codes and convolutional inner codes with memory 10 and rates 1/4 or 1/6. The corresponding inner decoder is a Viterbi decoder, which can operate in a forced sequence mode when feedback from the Reed-Solomon decoder is available. The Viterbi decoder is realized using two Altera FLEX 10K50 FPGA's. The overall operating speed is 30 kbit/s, and since up to three iterations are performed for each frame and only one decoder is used, the operating speed of the Viterbi decoder becomes 90 kbit/s. For a BER of 10E-5 the enhanced gain compared to the CCSDS recommended system exceeds 1.5 dB and 1.7 dB for the rate 1/4 and the rate 1/6 codes, respectively.