Correlation branch selection for extended tracking range delay-locked loops

In spread spectrum systems the delay-locked loop is commonly used to track the spreading code. A problem is to design the delay-locked loop to be both accurate and robust against disturbances which normally requires a tradeoff. The use of extended tracking range delay-locked loops increases the ability of the system to maintain lock even for large Doppler frequency offsets. The extended tracking range is achieved by using more than two correlators to form the error detector characteristic. However, the noise level in the synchronization loop is increased by every additional correlator leading to larger tracking jitter. In this paper an algorithm is proposed which reduces the noise level in the loop considerably. This is done by selecting only those correlation branches with an useful control signal. The investigated performance criteria are the tracking jitter and the mean time to loose lock. Both analytical and simulation results are presented. The extended tracking range delay-locked loop with correlation branch selection shows very promising performance results for both criteria at medium to high signal-to-noise ratios. It approaches the performance of the classical delay-locked loop for the tracking jitter and has a much larger mean time to loose lock than the classical delay-locked loop.