The Channel Quantization Alternating Algorithm in the Secret Key Generation System

In order to solve the problem that the high bit inconsistent rate between the two parties in the legal communication affects the key length , an improved CQA algorithm that calculating the log likelihood ratio that each bit is '0' or '1' after quantization sample value is proposed. Suppose both parties are Alice and Bob. The algorithm uses Alice's position index and Bob's sampling value to compute the conditional probabilities that each bit is '0' or '1' after quantize Alice's corresponding sample value. The probability log likelihood ratio is then calculated and the hard decision of the log likelihood ratio is used as the quantization result without having to quantize the sampled values by moving the quantization threshold. The simulation results show that the initial inconsistent rate of the improved algorithm is lower than that of the original quantization algorithm and the generated key is longer. When the number of quantization intervals is equal and the correlation coefficient between random variables is less than 0.87, the key length generated by the improved algorithm is increased by at least 0.15bits/symbol; When the number of quantization subintervals of the improved algorithm is 1/2 of the original algorithm and the correlation coefficient is less than 0.83, the key length generated by the improved algorithm is increased by at least 0.1bits/symbol.