A Study Of The Adaptive Transmission Scheme In Scattering Channel

Troposcatter communication has become the main means of long-distance communication in various countries because of its strong confidentiality and stable channel.Adaptive modulation and coding technology can increase system throughput by counteracting the time-varying characteristics of tropospheric channel effectively.This paper designs an adaptive transmission scheme for tropospheric scatter channel.Firstly,the main characteristics of the tropospheric scatter channel are analyzed.Then,a tropospheric scatter channel model is established with reference to the typical tropospheric multipath channel type.Finally,a tropospheric scatter channel adaptive transmission scheme is designed based on the channel model.This scheme mainly consists of two parts: a multi-rate transmission scheme and a MCS switching control scheme.In the first part,the advantages of the SC-FDMA system are first analyzed compared to the current scatter communication system.Then the system structure and data frame structure are introduced,and the selection basis of related parameters is given.At the same time,the design process of multi-rate MCS scheme is also explained.Finally,key technologies in the scheme are studied.These key technologies mainly include frame synchronization,frequency offset estimation,channel estimation and equalization,combining and SNR estimation.By comparing the performance of different synchronization methods,the length and structure of the frame synchronization sequence are designed.According to the repetitive structure of the received data,new frequency offset estimation and SNR estimation methods are proposed,and these methods perform better than the traditional methods.Based on the DFT channel estimation algorithm,the different channel interpolation methods and different frequency domain equalization algorithms are compared,and the best channel estimation and equalization method is selected.In the second part,the traditional control scheme based on the lookup table is introduced firstly,such as EESM.The calculation method of tuning factor in EESM is given in detail,and the performance of different algorithms in the system is analyzed.Then,in order to overcome the inaccuracy of channel quality feedback in traditional schemes,two classic algorithms in machine learning,SVM and K-NN,are introduced.Not only the basic principles of the two algorithms are introduced,but also the process of controlling MCS switching are described in detail.The effect of different training sets number on the performance of the SVM algorithm was simulated and analyzed.The influence of different K values on the performance of the K-NN algorithm was also analyzed.Finally,a 4-dimensional feature parameter based on K-NN algorithm is proposed for the adaptive transmission scheme designed in this paper.This algorithm can obtain the performance similar to the 32-dimensional feature parameter,and is superior to other algorithms.