OFDM-MFSK underwater acoustic communication broadband Doppler estimation and compensation method of known sub-carrier frequency

Abstract

The invention discloses an OFDM-MFSK underwater acoustic communication broadband Doppler estimation and compensation method of known sub-carrier frequency, and belongs to the field of the underwater acoustic communication. The content disclosed by the invention is specifically as follows: a transmitting end adds a plurality of sub-carries and inserts a pulse pair signal into each OFDM-MFSK data symbol; a receiving end intercepts the pulse pair signal and data, and performs coarse estimation on the Doppler factor, and determines the Doppler frequency deviation search range of each known frequency sub-carrier; performing over-sampling processing on each OFDM-MFSK data block, and computing a mean Doppler factor of the current data block; and then computing new locations of all sub-carriers ofthe whole data block after being influenced by the Doppler, and finishing the broadband Doppler compensation by extracting the corresponding data. By using the method disclosed by the invention, theaccurate estimation and compensation of the broadband Doppler in the underwater OFDM-MFSK communication system can be realized only through once data over-sampling, the process of resampling the datain the traditional Doppler estimation and compensation method is avoided, and the computing efficiency is improved.

Description

technical field [0001] The invention relates to a broadband Doppler estimation and compensation method for OFDM-MFSK underwater acoustic communication with known subcarrier frequency, belonging to the field of underwater acoustic communication. Background technique [0002] OFDM-MFSK is a modulation technology that combines multi-carrier technology and MFSK. The transmitting end of OFDM-MFSK divides all subcarriers into groups of M elements, uses MFSK to map information, and the receiving end uses a non-coherent method. The detection of the MFSK signal avoids the process of channel estimation and equalization. OFDM-MFSK is compatible with the high communication rate of multi-carrier modulation technology, and retains the robust performance of MFSK modulation. Compared with Orthogonal Frequency Division Multiplexing (OFDM) modulation, it can better balance the transmission rate and robust performance. In underwater acoustic communication, the relative motion between the sour...

AI Technical Summary

Problems solved by technology

The single-frequency pulse method calculates the Doppler factor by estimating the frequency offset, but the severe frequency selectivity of the underwater acoustic channel causes a serious loss of the signal-to-noise ratio of the single-frequency signal during use, resulting in errors in the measurement results. At the same time, in order to obtain a higher Estimation accuracy, the general single-frequency signal is longer, which will reduce the power efficiency of the system

The linear frequency modulation block method refers to inserting a linear frequency modulation signal (LFM) at the beginning and end of a frame of data in the communication system, and estimating the average Doppler factor of the entire frame of data by measuring the time compression and expansion of the transmitted signal. However, when the system transmits data for a long time , the receiving end must store all one frame of data to complete the Doppler compensation, which brings a large hardware storage overhead and a long communication delay, which is not conducive to the actual engineering application of the system, and when the channel changes badly When it is faster, the correlation peak and maximum value of the first and last chirp signals will appear on different multi-path paths, resulting in inaccurate timing and large deviations in Doppler estimation results

The empty subcarrier method is to insert several empty subcarriers with known positions in each data symbol, and use the energy at the empty subcarrier and the principle of the minimum under the correct Doppler factor to achieve accurate estimation of the Doppler factor. Stable estimation results can be obtained under time-varying channels, but the disadvantage is that the calculation amount is large, and multiple DFT operations need to be performed based on the search step size of the Doppler factor, and finally the current data is resampled according to the estimated Doppler factor

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