Abstract:

In digital communications, 90° or 180° phase ambiguity between the receiver and transmitter carrier is a serious problem for the coherent demodulation. To remove their phase ambiguity, differential quadrature phase shift keying (DQPSK) is proposed at the cost of a remarkable 2.3 dB performance degradation. Based on the iterative decoding (ID) scheme, an efficient joint convolutional code (CC)-coded DQPSK method is proposed to close the gap between quadrature phase shift keying (QPSK) and DQPSK. Using the extrinsic information transfer (EXIT) chart technique, the generator polynomial of the convolutional code is optimized. Simulation results show out that the proposed differential encoding method can overcome the phase ambiguity, and achieve a 3.5 dB signal-to-noise ratio (SNR) per bit gain compared with the CC-QPSK scheme by ID. Through optimization algorithm, the CC with an optimized generator polynomials outperforms the CC used in IEEE 802.11n protocol by 0.3 dB, and by 1.1 dB compared with the Turbo code in the 3rd generation partnership project long term evolution (3GPP LTE) protocol.