Abstract: Based on the definition of cable modem and the comparison of several demodulators, a novel burst mode differential quadrature phase shift keying (DQPSK) demodulator for the up-stream channel of hybrid fiber-coax networks is given. The scheme achieves bit-timing recovery prior to carrier recovery. Simulation results demonstrate that the proposed scheme can greatly reduce the required preamble length and its bit error rate (BER) performance in the AWGN channel is close to the theoretical performance of static DQPSK demodulator.