Research On Iterative Stopping Criterion In Low Complexity OFDM-Turbo Receiving System

In recent years,with the development of underwater acoustic communication technology and more and more complicated communication scenarios,on the one hand,people have higher and higher requirements for communication quality,and on the other hand,they have required faster and faster communication rates,which are more demanding for the environment.In underwater scenes,high-quality communication transmission systems have become the focus of research.Orthogonal frequency division multiplexing(Orthogonal Frequency Division Multiplexing,OFDM)technology has the natural advantages of resisting multipath fading and high spectrum utilization,and has become one of the most important modulation technologies for wireless communications,especially broadband wireless communications.At the same time,due to the complexity of the channel,a high-performance receiver has also become a research focus.A high-performance receiver can effectively equalize and decode received data at the receiving end,so that the receiving end can obtain high-quality received data.Turbo equalization as a high-performance equalization method is very suitable for communication systems that require high transmission quality.At the same time,the iterative equalization method of Turbo equalization introduces higher algorithm complexity,so reducing Turbo equalization complexity has also become an important research direction.Based on the OFDM-Turbo receiving system,this paper studies the iteration stop criterion based on Degree of Symbol Offset(DOSO),and verifies the feasibility of the algorithm through simulation analysis and comparison.The main work overview of this paper is as follows:1.Introduce the basic implementation method and communication processing flow ofOFDM communication system,the basic principle of Turbo equalization,and the specific implementation method of OFDM-Turbo receiving system.Introduced the Turbo code decoding structure and the related iteration stopping criterion.2.Analyze the statistical characteristics of the external information output by the decoder and the equalizer in Turbo equalization.Based on the statistical characteristics,two relevant iteration stop criteria are introduced,namely,the iteration based on external information statistics(EIS)Stop criterion and iterative stop criterion based on Symbol Reliable Measure(SRM).3.It proposes the DOSO iteration stop criterion based on the degree of symbol shift in Turbo equalization,and introduces the algorithm flow and specific implementation of the criterion in detail.This criterion determines the corrective effect of the symbol by observing the distance between the mean value of the symbol obtained after each iteration and the modulation constellation point,and the degree of change in the distance between the two iterations before and after,by setting a reasonable threshold to terminate the iteration in advance process.In the background of OFDM-Turbo receiving system,simulation experiments were carried out to verify the performance of the algorithm on the one hand,and compare it with the EIS iteration stop criterion and SRM iteration stop criterion on the other hand,proving the performance advantages of the algorithm.4.Based on the DOSO iteration stopping criterion,three improvement schemes are proposed on the basis of the DOSO criterion.(a)DOSO iterative stop criterion based on double thresholds,which sets upper and lower thresholds for the threshold used for iterative stop,which can effectively improve the low SNR environment without almost reducing the bit error rate Algorithm complexity.(b)DOSO iteration stop criterion based on symbol selective iteration,under this criterion,all symbols will be judged after each iteration processing is completed,and only the unreliable symbols will be subjected to the subsequent iteration process.(c)DOSO iteration stopping criterion based on adaptive threshold.Under this criterion,the parameter threshold used to terminate the iteration will be dynamically adjusted as the iteration process is adjusted to meet the needs of different signal-to-noise ratio environments.The three criteria can further reduce the algorithm complexity of DOSO criteria to varying degrees.And simulation experiments were carried out on these three criteria to verify the feasibility and effectiveness of the scheme.5.Lake experiments and demodulation analysis were carried out on the above four improvement schemes to further verify the feasibility of the scheme.