Comparison between Modified Bahl, Cocke, Jelinek,  and Raviv (BCJR) and Soft Output Viterbi Algorithm (SOVA) Decoders Over Additive White Gaussian Noise (AWGN) Channel

Abdul Khader Saleh, Khaleel; George Zia, Maha

	Comparison between Modified Bahl, Cocke, Jelinek, and Raviv (BCJR) and Soft Output Viterbi Algorithm (SOVA) Decoders Over Additive White Gaussian Noise (AWGN) Channel
Journal of Engineering and Sustainable Development
Article 1, Volume 11, Issue 3, 2007, Pages 61-75
Authors
Khaleel Abdul Khader Saleh; Maha George Zia
Abstract
Turbo codes are suitable for deep-space communications, because of the codes astonishing performance at low values of signal to noise ratio (SNR) and their ability to achieve near Shannon limit of channel capacity.In this paper the performance of turbo codes in AWGN channel is evaluated under different conditions and circumstances. The deep-space channel is almost exactly modeled as a memoryless additive white Gaussian noise (AWGN) channel that formed the basis for Shannon’s noisy channel coding theorem.A comparison between the modified BCJR* decoder, which uses modified forward-backward metrics and the Soft Output Viterbi Algorithm (SOVA) decoder, is also presented.Simulation results for the turbo encoder-decoder system show that care must be taken in choosing different parameters that govern the turbo encoder- decoder scheme, also the enhancement is required for low rate (rate 1/4) turbo encoder that uses symmetrical component encoder.Finally, it is suggested to use asymmetrical (two different rates and generator polynomial components encoder connected in parallel) turbo encoder, especially for rate (1/4) turbo encoder in order to improve the bit error rate (BER) performance of low rate symmetrical turbo encoder under extremely noisy conditions.

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