Research On The Receiving Technology For Long Wave Communication Signal

The long wave radio has been widely used in the remote communication,due to its stable propagation characteristic.Moreover,the long wave radio has also been chosen for the coast based submarine communication because of its prominent anti-jamming and penetration capability.The adopted frequency band is 30Hz-30 KHz in the coast based submarine communication,where atmospheric noise is the dominant interference to the received signal.It is noteworthy that the strong interference impulse in the atmospheric noise has the short time of duration and the large amplitude.In this paper,we give the propagation model of the long wave radio in sea water,and analyze the effect of the sea water on the impulsive noise based on the existing impulsive noise model.Furthermore,the clipper is used to suppress the atmospheric noise,for which the optimal bandwidth of the pre-filter and the optimal threshold of the clipper are also offered by numerical simulations.The optimal clipper threshold can also be determined based on the estimation of the parameters of the atmospheric noise.Meanwhile,we give the multiple symbols based differential demodulation algorithm of the minimum shift keying(MSK),and compare the performances of signal demodulation under different modulation parameters,which can guide us to choose the appropriate modulation parameters.The contributions of this paper contain that 1)give the propagation model of the long wave radio in sea water,2)design the algorithm to suppress the impulsive noise,and 3)investigate the demodulation method of the MSK.The contents of different chapters of this paper are given in the following.In the chapter two,we first compare different atmospheric noise models.As a result,the alpha-stable distribution is adopted to model the atmospheric noise,and the method to generate the atmospheric noise is given as well.The propagation model of the long wave radio in sea water is further determined.The effect of the sea water on the atmospheric noise is also given based on the propagation characteristic of the long wave in sea water.The effect of the sea wave on the received signal is finally studied.In the chapter three,we first focus on the method to recover the impulsive property of the atmospheric noise.Some commonly used non-linearity are introduced,and the optimal bandwidth of the pre-filter and the optimal threshold of the clipper are also offered by simulations.We finally analyze the algorithm to determine the clipper threshold.The key of the proposed algorithm lies in the estimation of the characteristic exponent of the atmospheric noise.In the chapter four,two basic modulation in long-wave radio communications,i.e.,FSK and MSK,are first introduced,and the multiple symbols based differential demodulation of the MSK is further derived under our adopted received signal model.Additionally,the appropriate modulation parameters and demodulation algorithms can be chosen based on different channel models and non-linearity.In the chapter five,the work of the paper was summarized,by using the estimated atmospheric noise characteristic index to determine the clipper threshold method,the long-wave radio receiver can receive the signal underwater better with the receiving environment changes in time to adjust the clipper threshold.It can meet the needs of different communication environments;And the follow-up work carried out the prospect.