An improved code tracking algorithm based on the adaptation of double gains for burst DSSS signals

To enhance the pseudo-range measure performance based on code synchronization of burst direct sequence spread spectrum (DSSS) signals, such as the inbound signal of radio determination satellite service (RDSS) in Compass, a new code tracking algorithm based on minimum mean-square error (MMSE) criterion to adjust double gains of second order tracking loop is proposed. Compared with the derivation of loop transfer function from analog domain in existing papers, our algorithm is derived directly from the structure of digital second order loop, which exhibit the different character of gains of code discriminator and numerical controlled oscillator (NCO). Based on this different character, during each epoch, gains of discriminator and NCO are estimated as two parameters optimization problem, instead of the way which treat these gains as a loop gain totally. Compared with several existing algorithms, simulation results show the excellence of our proposed algorithm on tracking precision and stability.