Research On Underwater Acoustic Spread Spectrum Communication Technology Based On Iterative Receiver

Underwater acoustic channel is a typical time-varying channel with narrow available bandwidth,strong background noise,multipath spread and Doppler spread,which makes it difficult to obtain sufficient signal-to-noise ratio（SNR）in conventional receiver communica-tion.In mobile underwater acoustic communication,the communication signal will be seriously affected by the broadband Doppler effect,which causes the compression and expansion of the communication signal in the time domain.The second-order digital phase-locked loop tech-nology can only compensate the carrier phase,but can not compensate it.In order to solve these problems,based on direct sequence spread spectrum technology and wideband Doppler estimation and compensation technology,combined with iterative thinking,this paper studies underwater acoustic communication.Firstly,the conventional receiver based on direct sequence spread spectrum technology is studied.Direct sequence spread spectrum technology has strong anti-interference ability,so it is often used in underwater acoustic communication to overcome inter-symbol interference.When the channel condition is relatively stable,the symbol decision feedback narrowband receiver based on adaptive algorithm is studied,which updates the parameters at the symbol rate and has low computational complexity.When the channel changes rapidly and the channel condition changes greatly in a symbol interval,the chip level hypothesis feedback narrowband receiver based on adaptive algorithm is studied,and the receiver is updated at the chip rate.When there is wideband Doppler frequency shift caused by the relative motion of the transceiver platform,the wideband receiver based on adaptive algorithm for symbol decision feedback and the wideband receiver based on adaptive algorithm for chip level hypothesis feedback are studied respectively.The simulation results based on the time-varying underwater acoustic channel model show that the narrowband receiver can not work in the presence of wideband Doppler frequency shift,while the symbol decision feedback wideband receiver based on adaptive algorithm can achieve a bit error rate of less than when the spreading gain is15,the QPSK mapping mode is used,and SNR is 9d B.Achieve robust underwater acoustic communication with bit error rate lower than10^-4.Secondly,the iterative receiver based on direct sequence spread spectrum technology is studied.In order to improve the performance of the receiver,the SISO Turbo technology is introduced,and the symbol decision feedback narrowband iterative receiver based on adaptive algorithm is studied.The bit interleaved coded modulation-iterative decoding（BICM-ID）narrowband receiver based on adaptive algorithm is further studied.Based on the traditional Turbo idea,the receiver makes full use of the advantage of bit interleaving and divides the iteration into inner and outer iterations.For the signal with wideband Doppler frequency shift interference,the symbol decision feedback wideband iterative receiver based on adaptive algorithm and the BICM-ID wideband receiver based on adaptive algorithm are studied respectively.The simulation results based on the time-varying underwater acoustic channel model show that compared with the conventional receiver,the iterative receiver based on SISO-Turbo technology has a lower bit error rate than10^-3 the conventional receiver in the time-varying underwater acoustic channel.The receiver obtains a gain of about 0.5d B.A receiver based on the BICM-ID technique obtains a gain of about 2d B.Finally,the sea trial data is processed.The results show that the chip level hypothetical feedback receiver based on direct sequence spread spectrum technology can work in the time-varying underwater acoustic channel.The receiver with the wideband Doppler compensation structure can effectively compensate the wideband Doppler frequency shift and realize the underwater acoustic communication between the mobile transceiver platforms;The SISO-Turbo technology and BICM-ID technology introduced in the symbol decision feedback receiver based on direct sequence spread spectrum technology improve the performance of the receiver.