Performance analysis of a decision-feedback coherent code tracking loop for pilot-symbol-aided DS/SS systems

In this paper, the performance of a decision-feedback coherent code tracking loop for pilot-symbol-aided (PSA) direct-sequence spread-spectrum systems, considering the effect of both symbol and channel estimation errors, is analyzed. An analytical closed-form expression on the steady-state jitter variance in additive white Gaussian noise (AWGN) environments using the linear analysis model is first derived. Then, the upper and lower bounds of the jitter variance in fading environments are obtained based on the analysis of the loop bandwidth variation according to the input signal level. Finally, a second-order coherent tracking loop is designed, and its performance in both AWGN and fading environments is evaluated, along with verification by computer simulations. It is demonstrated that analytical results are very close to the simulation results in AWGN environments and that the jitter variance in fading environments is located between analytical upper and lower bounds with its position depending on the fading rate.