Simulation of Sequential Decoding with Phase-Locked Demodulation

Convolutional encoding with biphase modulation is an attractive combination of modulation/coding for the Gaussian channel, but a means of tracking carrier phase must be provided. The performance of combined sequential decoding and suppressed carrier (Costas loop) tracking in the receiver is difficult to analyze but can be obtained by computer simulations. Results of such simulations are presented in the form of a Pareto fit to the computation distributions for various tracking loop bandwidths and demodulator quantization (soft decisions). These distributions are applied to predict probability of error performance for typical decoder parameters (buffer size, speed factor). The anticipated advantage of quantized demodulation is observed. However, narrow tracking bandwidths are required, with sufficient interleaving to overcome effects of correlated phase perturbations due to noise.