Channel Equalization Of Very Low Frequency

Very Low Frequency is a unique frequency band in the radio spectrum.Unlike other high frequency bands,the VLF has the following characteristics: low attenuation,long propagation distance,and strong anti-interference ability,penetration into seawater and soil and transmission in it.So VLF is widely used in underwater and deep underground communication fields.In spite of the advantages mentioned above,it is also faced with the problems such as large transmission system,large channel fading and low signal to noise ratio at the receiver.In this paper,the fading of the wireless VLF channel is analyzed.And based on direct sequence spread spectrum and the minimum frequency shift keying communication mode,combined with the single carrier frequency domain equalization,it is studied that to reduce or eliminate inter symbol interference in order to enhance the system's performance of BER(Bit Error Rate).The main contents of this paper include the following aspects:Firstly,the characteristics of VLF propagation are introduced theoretically,and the communication channel is modeled according to its characteristics.Detailed analysis of MSK and DS-MSK modulation and demodulation,and the BER performance simulation is performed.Then,through the analysis of the principle and structure of SC-FDE system model,the SC-FDE model applied in MSK modulation,the adding tail bits to maintain MSK phase continuity,and application of discrete Fourier transform required for Laurent' s decomposition solutions is researched.Classification of channel equalization principle is introduced,focusing on the SC-FDE linear equalization algorithm,including the commonly used ZF and MMSE equalization.The SC-FDE linear equalizer coefficients based on MSK and DS-MSK modulation are derived,and the BER performance simulation is performed.The SC-FDE linear equalization under DS-MSK modulation is improved to further reduce the complexity,and the computational complexity and time domain equalization are compared and analyzed.Finally,according to the existing SC-FDE decision feedback equalization algorithm,the feedforward and feedback coefficients of the SC-FDE decision feedback equalizer for MSK are derived,and the simulation results are verified.The decision feedback equalization of DS-MSK is improved,which is based on the hypothesis-feedback equalization.And a variety of SC-FDE equalization algorithms are analyzed and compared,including error performance and computational complexity two aspects.