| The ocean is an important strategic space and reserve resource treasure house.With the continuous enhancement of China's comprehensive national strength,the international competition in the field of deep sea is becoming increasingly fierce.Therefore,it is the key to develop marine high-tech and enhance national competitiveness.Based on the principle of electromagnetic induction coupling,a closed loop composed of a single anchor chain and sea water is used to realize the non-contact transmission of underwater multi node data.However,due to the complexity of the sea water channel and the relatively backward ASK/DPSK modulation technology,the transmission rate and reliability of the signal are greatly affected.Therefore,this paper mainly starts from these two aspects,aiming at the characteristics of the long-distance underwater inductive coupling multi-path transmission channel,designs the algorithm and solution for the multi-node information transmission suitable for the water depth of 300 meters.First of all,in order to analyze the channel characteristics more accurately,the conductivity curves of seawater at different temperature and concentration with frequency are measured by impedance analyzer,and the electric flow signals received at different frequencies are determined by COMSOL multi physical simulation software and measurement results.After normalization,300 meters of water is determined according to the set-20 d B attenuation threshold and t he effective bandwidth of deep sea water channel is 2MHz.Secondly,because of the multi-path effect of electrical signals in the sea water channel,the attenuation effect of sea water on electrical signals of different frequencies is also different,and the multi-path effect is more obvious with the gradual increase of signal frequency.Therefore,this paper improves the traditional multicarrier algorithm,divides the signal into multiple channels and adds the real part and the virtual part of the signal to shorten the transmission time by half compared with the traditional algorithm,and can effectively resist the multipath effect and reduce the signal error rate.In addition,this paper also uses the amplitude limiting method to reduce the PAPR,and compares and analyzes the channel capacity under different mapping modes.However,in the traditional time division multiplexing(TDMA)transmission mode,underwater sensor nodes carry out data transmission according to the time sequence,with low time resolution and lowbandwidth utilization.Therefore,this paper proposes a new multicarrier algorithm solution,which combines OFDM and FDMA,uses OFDM Technology in the nodes,and uses FDMA technology among the nodes.In this paper,the water injection principle is used to further optimize the algorithm to allocate the 2MHz bandwidth to the users of each node reasonably,and the filter bank is used to strip the information of each user at the receiving end.The results of this study provide an optimized solution for the transmission performance of the inductive coupled data transmission system,which provides a theoretical basis for solving the long distance underwater multi node joint transmission. |
PDF Full Text Request