Low-Density Parity-Check (LDPC) codes are a class of forward error correction (FEC) linear block codes which provide near-capacity performance for power-efficient communications. Optimum decoding requires accurate combining ratio estimation to scale the input signal in an additive white Gaussian noise channel (AWGN). Test data and analysis show that the performance of the optimal LDPC decoding algorithm is severely degraded when encountering pulsed radio frequency interference (RFI) from sources such as ground based radars. This research effort first reveals that the LDPC performance degradation under pulsed RFI is not due to the burst of errors but to the inaccurate combining ratio estimation. Although an ideal combining ratio estimator (symbol-wise) could mitigate the degradation caused by pulsed RFI, it is not practical for implementation. Some near optimal LDPC decoding algorithms which do not require combining ratio estimation are investigated. One near optimum decoding algorithm 'min-scale' is proposed in the robust decoder design to mitigate pulsed RFI. Analysis shows that 'min-scale' only loses about 0.2 dB performance compared to the optimal decoding algorithm under nominal condition; in a pulsed RFI environment, the designed performance can be achieved if the system design has adequate margin. Without combining ratio estimation, the decoder design complexity is reduced and the risk of performance degradation due to combining ratio estimation error is eliminated. This robust decoder design enables reliable communications to space vehicles which may encounter strong pulsed RFI signals from high power radar systems.
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