The effect of data modulation on sigma delta and modified delay-locked loop operation

Computer simulations were used to examine the effects of data modulation on the discriminator output of the sigma-delta and modified noncoherent delay-locked loops. The results show how data-modulation-induced transients in the received signal detract from the performance of the tracking loops by forcing discriminator IF (intermediate frequency) filters into a continuous transient state. Furthermore, the loops are somewhat vulnerable to an internal gain imbalance resulting from an improper choice of the code phase used for spreading the data bits. A measurement approach is applied to both loops to combat the effect of data modulation.<>