Design And Implementation Of High-speed Underwater Acoustic Communication Modem And Software Radio

GNSS based global terrestrial navigation and positioning technology has made great progress and achieved centimeter positioning accuracy,while underwater navigation and positioning technology is in the stage of rapid development in China,so it is imperative to expand GNSS positioning technology into the ocean field.The effective method of underwater long-distance communication is underwater acoustic communication(UAC).UAC Modem is the key node of underwater communication.The design of UAC Modem suitable for communication and positioning is the premise and basis for the popularization of underwater GNSS technology.Based on the above background and project requirements,this paper designed a prototype of high-speed UAC Modem,including hardware design,algorithm design and other details.The main work is as follows:(1)Design hardware circuit of UAC Modem according to project index,including DSP Data Processing Circuit Board,Power Amplification Circuit Board,and Duty Circuit Board.The principle of circuit design is expounded and the index is calculated,and the circuit index is tested and analyzed.The overall size of the Modem prototype(excluding the enclosure)is 6.5 cm in width and 17 cm in height,and the volume of communication nodes is effectively controlled.(2)The receiver of UAC Modem adopts software radio.The demodulation algorithms of QPSK and CDMA are analyzed and simulated,it mainly includes doppler acquisition,carrier recovery,code tracking,channel equalization and so on.Carrier doppler frequency shift estimation is necessary in UAC.In this paper,the doppler estimation is carried out by using the theory of matching filter peak of pseudo random code.The demodulation loop in CDMA spread spectrum communication includes Costas carrier tracking loop and delay locking code tracking loop.QPSK high-speed underwater acoustic communication does not need code tracking,and the demodulation performance depends on the decision feedback equalizer with embedded digital PLL.The equalizer iterates the greedy algorithm in sparse channel processing and simulates the equalization algorithm.At the same time,the constant modulus blind equalization technology is introduced and simulates the equalizer performance,this provides an alternative scheme for blind equalization.(3)When carrying out UAC algorithm on the embedded system,the algorithm needs to be improved according to the system hardware equipment,it mainly involves the algorithm and technology of DSP terminal.In this paper,part of the transmitter circuit is simplified design,and a pulse sampling based SPWM generation system is proposed,effectively reducing the size of the hardware.DSP uses SPI port to drive ADC for data collection,the generation of driving signal and the transfer of data after sampling all adopt DMA technology.This paper introduces the whole process of parameter calculation and configuration of DSP SPI and EDMA registers.An AGC process based on median filter is proposed to stabilize the amplitude of received signal.This paper expounds every detail from hardware design to embedded software in design process of UAC Modem,and successfully designed the Modem prototype.This paper provides a detailed reference for the hardware design of UAC Modem and software transmitter and software receiver of UAC based on embedded system.