Underwater sound OFDM (orthogonal frequency division multiplexing) Doppler estimation method based on cyclic prefixes

Abstract

The invention provides an underwater sound OFDM (orthogonal frequency division multiplexing) Doppler estimation method based on cyclic prefixes, which is characterized in that (1) A frame header part of an OFDM underwater sound communication system comprises a chirp signal and a simple-frequency signal, and the cyclic prefixes are added on a data symbol part; (2) FFT (Fast Fourier Transform) frequency measurement estimation is carried out on the received simple-frequency signal, a sending frequency is compared so as to obtain preliminary estimation of Doppler frequency offset factors, and the preliminary estimated value is used as an initial value for next Doppler estimation based on the cyclic prefixes; and (3) the inherent cyclic prefixes of the orthogonal frequency division multiplexing symbols and copy parts thereof are subjected to related two-dimensional search under different window lengths and window initial positions, and a Doppler frequency offset factor of each symbol is estimated. The underwater sound OFDM Doppler estimation method based on the cyclic prefixes overcomes the defects of inaccurate synchronization caused by Doppler and weakened relativity of the cyclic prefixes, and realizes fine synchronization of OFDM symbols and Doppler factor estimation. In addition, under the condition that the length of the cyclic prefixes is definite, the accuracy of Doppler frequency offset factor estimation is improved through sampling the OFDM symbols (including cyclic prefix parts).

Description

technical field [0001] The invention relates to an underwater acoustic mobile communication method. In particular, it relates to a method for estimating a Doppler frequency offset factor of a broadband signal. Background technique [0002] Due to the low speed of sound in water, the Doppler frequency deviation of different frequencies of the broadband underwater acoustic signal is quite different, so it is impossible to simply perform consistent Doppler frequency deviation compensation on the received signal. In addition, the underwater acoustic channel has a large multipath delay and a high background noise level, which will also affect the Doppler estimation. Therefore, it is necessary to study a Doppler estimation algorithm suitable for underwater acoustic channels. [0003] In the public document Byung-Chul Kim and I-Tai Lu.Parameter Study of OFDM Underwater Communications System[C] / / in Proc.OCEANS 2000MTS.Providence, USA, 2000: 1251-1255, the cyclic prefix in the OFDM...

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Problems solved by technology

[0003] In the public document Byung-Chul Kim and I-Tai Lu.Parameter Study of OFDM Underwater Communications System[C] / / in Proc.OCEANS 2000MTS.Providence, USA, 2000: 1251-1255, the cyclic prefix in the OFDM symbol and its copy Part of the cross-correlation characteristic estimates the Doppler factor, but there are two problems in practical application: First, the algorithm intercepts the cyclic prefix and performs sliding correlation with the subsequent signal under the assumption that the symbol synchronization is accurate. Due to the influence of Doppler, the symbol synchronization is often inaccurate, so the cyclic prefix signal cannot be accurately intercepted; second, the algorithm only considers the change of the interval between the cyclic prefix and its copy (that is, the number of OFDM symbol sampling points) affected by Doppler, and does not consider the cyclic prefix. The length of the prefix itself changes, resulting in a decrease in related performance

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