A modified code tracking loop based on dual structure

A modified code tracking loop for tracking the pseudo-random noise code in direct sequence spread spectrum signal is proposed. The modified loop differs from the typical through imposing a dual structure which incorporates a coarse loop with large loop parameters and an accurate loop with small loop parameters. The expression of the convergence time for the second-order delay-locked loop (DLL) is derived to measure the time of the convergence process. Two concepts, accuracy improvement and time improvement are defined to exhibit the performance enhancement of the modified loop. Simulation results show that the proposed method can realize a better trade-off between tracking accuracy and convergence time in the whole simulated carrier-to-noise ratio range. Also, the robustness of the modified loop is verified through eliminating the second convergence process which is regarded as the worst issue in the parameter-switching DLL.摘要本文针对直接序列扩频信号提出了一种改进的伪码跟踪环路. 和常规环路相比, 改进的环路采用双环结构, 包括一个参数较大的粗跟踪环和参数较小的精跟踪环. 为了测量收敛过程的时间, 推导了二阶延迟锁定环收敛时间的表达式, 且定义了精度改善量和时间改善量来体现改进环路的性能优势. 仿真结果表明改进环路能够在整个仿真条件下同时获得更优的跟踪精度和更短的收敛时间. 此外, 和参数切换的环路相比, 改进环路消除了二次入锁过程, 提高了环路的稳健性.