Research On Adaptive Modulation And Coding Technology In Transform Domain Communication System

With the fast development of communication technologies,the electromagnetic environment is getting more and more intricate,and the spectrum resources are becoming rarer and rarer.Transform domain communication system(TDCS)has the unique advantages of dynamic spectrum sharing access and anti-interference communication.Adaptive coding technology can dynamically switch the parameters of the transmitter according to the channel environment and quality of service requirements to further improve the utilization of system resources.Combining transform domain communication system with adaptive modulation and coding technology can give full play to the respective advantages of adaptive coding technology and transform domain communication,and further improve spectral efficiency.Therefore,in view of the complex electromagnetic environment,this paper studies the adaptive transform domain communication technology.The specific contributions are as follows:Firstly,the SNR estimation technology in TDCS system is studied.In order to achieve effective signal detection and link adaptation,signal-to-noise ratio(SNR)is needed in many communication systems.In this paper,second-and fourth-order moments algorithm,squared signal-to-noise variance algorithm,least square(LS)estimation algorithm,and Boumard signal-to-noise ratio estimation algorithm are studied,and they are extended to TDCS system.Through computer simulation,these SNR estimation algorithms are compared and analyzed in different scenarios of TDCS system.The analysis and simulation show that the LS algorithm is the best under the condition of Gaussian channel,and Boumard algorithm is the best under the condition of multipath fading channel.Under the influence of Doppler frequency shift,LS algorithm has the most stable performance.Secondly,for the communication system with high reliability,this paper proposes a modulation and coding adaptive algorithm based on the target bit error rate,which can ensure the transmission reliability of the communication system to the greatest extent.In this paper,the adaptive modulation and coding scheme of TDCS system is formulated,and the bit error rate curve of each scheme is obtained by using MATLAB simulation,so as to obtain the threshold value when meeting the conditions of triggering switching various modulation and coding schemes and provide the final adaptive decision to meet the system target bit error rate.In addition,this paper analyzes how the SNR estimation error affects the adaptation and how to reduce the SNR estimation error.When the SNR estimation is greater than the real value,the bit error rate(BER)is lower than the target BER in some SNR intervals,leading to poor BER performance of the modulation and coding scheme,which is not conducive to communication data transmission.When the SNR estimation is less than the real value,it will only reduce the transmission rate.Lastly,this paper proposes an adaptive modulation and coding algorithm for TDCS system based on throughput maximization.Compared with the fixed transmission scheme,this algorithm provides a higher data transmission rate.Six kinds of finite Markov channel models with different states are established,corresponding to one modulation and coding scheme respectively.Then MATLAB simulation is completed to get the throughput curves of different schemes.Finally,adaptive decision-making based on throughput maximization is made.The influence of SNR estimation error on adaptive performance is also analyzed.The analysis and simulation show that the SNR estimation error has a certain influence on adaptation in a specific interval.