STABILITY REQUIREMENTS OF OSCILLATORS USED FOR SYNCHRONIZATION LOOPS IN COMMUNICATION-SYSTEMS

An imperfect clock timing recovery in receivers of modern communicatio n systems degrades the performance of synchronization loops and, hence , the overall system reliability and data transmission quality. In thi s paper, the phase-locked loop (PLL) for the carrier recovery and the delay-locked loop (DLL) for the clock timing recovery of the pseudonoi se (PN) code in direct-sequence spread-spectrum systems are analyzed r egarding the impacts of imperfect oscillators (including phase noise a nd a frequency offset between transmitter and receiver) and channel no ise on the mean exit time. The optimal design considerations to achiev e a maximum mean exit time for second-order synchronization loops can be used to find the required oscillator stability, i.e., the maximum t olerable frequency offset and oscillator phase noise.