An adaptive differentially coherent detection and phase compensation algorithm in underwater acoustic communication

In underwater acoustic communication, carrier tracking is adversely affected by Doppler and time-variation of the channel, which caused bad performance of the receiver. Differentially coherent detection based on the premise that there is no intersymbol interference (ISI) and the bad performance is produced when carrier frequency shift is enormous. In order to solve this problem, we propose an adaptive differentially coherent detection (ADCD) algorithm and its phase compensation. In the proposed algorithm, a linear equalizer and a differentially coherent detector are combined to reduce the mean squared error (MSE) of the detection. A new way for phase compensation is proposed to track the variation of the signal phase and improve the performance to resist the carrier frequency shift. 4DPSK simulation tests are conducted using 10 km real underwater acoustic channel. Results show that conventional coherent detection (CD) algorithm can get right decision, only when the normalized frequency shift is less than 0.01. However, the needed input signal noise ratio (SNR) is 2~4 dB less than ADCD, when the proposed phase compensation is used in ADCD at the condition of the normalized frequency shift is 0.02~0.04.