A novel U-turn counting hangup detection algorithm for SDPSK modulation

In this letter a new hangup detection algorithm for symmetric differential phase-shift keying (SDPSK) modulation is proposed. Hangup is detected by ob serving phase transition patterns in the received SDPSK signal trajectory. The average pull-in times with and without the proposed hangup detector are compared. Simulation results show that the proposed algorithm significantl y reduces the average pull-in time when the initial timing error is near th e unstable null. We also show that the proposed algorithm is very robust ag ainst carrier frequency offsets.