| Due to the unique characteristics of underwater acoustic(UWA)channel especially the limited bandwidth,Orthogonal Frequency Division Multiplexing(OFDM)is widely used because of its high spectrum efficiency and ability in anti-multipath fading.However,since the orthogonal frequency division multiplexing technique is composed of multiple subcarriers,it will produce higher peak-to-average ratio with the increase of the number of subcarriers,and then put forward higher requirements for the underwater acoustic power amplifier,leading to low energy efficiency of the communication system.When the underwater power amplifier working in its non-linear area,it will cause distortion of the transmitting signals and affectiong the system's performance in return.Therefore,it is important to study the effect of reducing the peak-to-average ratio algorithms and other communication technologies that with relatively low PAPR.This will promote the development of multi-carrier underwater acoustic communication technology and improve the enegy efficiency of communication systems,which is one of the most important research directions of future underwater acoustic communication.This paper starts from the algorithms of reducing the PAPR in OFDM underwater acoustic communication system.The research work of this paper is arranged as follows:1.The clipping algorithm which belongs to the signal pre-distortion category of reducing PAPR is studied.An improved algorithm based on the clipping which utilize the compressed sensing algorithm to recover the clipping noises is studied,and the comparision is also given between the proposed algorithm and companding,which belongs to the same category with clipping.Then,the iterative compressed sensing algorithm is proposed which combines the the compressed sensing algorithm to recover clipping noise with compreesed sensing channel estimation.Both the simulation and experiment verified the proposed algorithm.2.Another reducing PAPR technology – companding,which belongs to the pre-distortion category as clpping is studied.By studying the commonly used companding transform algorithms in radio and its application in underwater acoustic communication system,the conclusion that the parameters and structure used in radio is not applied to the underwater acoustic field.Therefore,the companding transformation with improved parameters and the performance of the algorithm in underwater acoustic field are studied.The comparision between traditional companding and improved companding are also given.Then,the improved structure of companding based on the improved parameters is studied,which can reducing the quantization noise generated with the compression-expansion procedure.The performance of the proposed algorithm is verified valid by both simulation and experiment.3.The performance of SLM(Selected Mapping)algorithm,which belongs to the probability category of reducing PAPR algorithms is analyzied.The PAPRs of OFDM systems when using SLM with different phase sequences are studied.The traditional SLM algorithm is combined with clipping to study the reducing PAPR performance.Aiming at the complexity problem of the phase factor choosing process of SLM,an improved SLM algorithm is proposed,and combine the improved algorithm with clipping to further optimize the reducing PAPR algorithm's performance.The performance of the improved SLM combining algorithm is verified by simulation and experiment,and the performance of traditional SLM combined with clipping is studied for comparision.4.Researching on the PTS(partial transmission sequence)algorithm which belongs to the probability category of reducing PAPR.The performance of PTS with different number of subblocks and different segmentation modes are studied and analyzed.The large amount of computational complexity and the transmission of sideband information are two mainly drawbacks of PTS algorithm.Then,an improved PTS algorithm which named m-PTS is syudied to solve the phase factor selection process' s shortcomings.However,m sequences are available in a small number of sequences,which will lead to a bottleneck of reducing PAPR algorithm.Based on this,the chaotic sequence used for PTS is proposed which named as c-PTS in this paper.M-PTS and c-PTS are compared and the perfprmance is verified by simulation.5.The modulator structure of emerging multi-carrier technology – GFDM and its application in underwater acoustic communication field are studied.As one of the advantages of GFDM is the low PAPR,this paper studied the PAPR of GFDM system used in underwater acoustic field systemically.GFDM system under different parameters and different modulation matrix structures is studied.Aiming at the difficult problem of channel estimation in GFDM system,underwater acoustic spread spectrum communication systems based on GFDM are proposed,which are GFDM-DS and GFDM-CSS spread spectrum communication system.Simulation and experimental verification of the application of this new multi-carrier communication technology in underwater acoustic communication... |
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