Research On LDPC Code Parameter Identification Technology In FBMC Situation

Channel coding recognition technology means that the receiver uses the received codeword sequence to analyze and identify the encoding style or parameters of the data on the premise of knowing little prior knowledge.This technology has a wide range of applications in intelligent communication and communication confrontation.LDPC code has been widely used in civil and military communication fields because its performance is close to Shannon limit and suitable for high speed transmission.However,most researches on LDPC code recognition technology at home and abroad are not suitable for complex channel models,and there is still space of promotion on recognition rate and recognition speed.Therefore,it is of great significance to study the LDPC coding identification and analysis technology in complex scenes.In this paper,the closed set identification technology of LDPC code parameters is studied based on the communication system model of FBMC offset quadrature amplitude modulation and Rayleigh fading channel.Firstly,in order to get LDPC codeword sequence with FBMC error code characteristics,the modulation and demodulation model of FBMC and Jakes channel model of Rayleigh fading are built.Further,aiming at the characteristics of FBMC inherent virtual part interference,this paper designs pilot symbol based on the idea of precoding interference elimination,reduces the interference between data symbol and pilot symbol,and then completes channel estimation and equalization.Secondly,this paper studies the closed set recognition algorithm of LDPC code parameters,mainly the rank criterion hard decision recognition algorithm and the cosine ratio soft decision recognition algorithm.In this paper,the performance of these two algorithms in FBMC communication system model is simulated and analyzed.It is found that the rank criterion algorithm does not perform well in low SNR and high bit error rate circumstances,and the recognition effect of cosine ratio algorithm for high bit rate LDPC code also needs to be improved.Finally,in order to solve the problem of low recognition rate in low SNR and high bit rate condition,a soft decision recognition algorithm based on improved cosine ratio is proposed.In this algorithm,the channel information estimated by the pilot and the posteriori log likelihood ratio of the FBMC system are used to modify the judger of the parameter identification algorithm of LDPC codes based on cosine ratio,so as to realize the effective closed set identification of IEEE802.16 e LDPC codes.Taking the recognition result of(576,1/2)LDPC code as an example,when the SNR of FBMC system is more than 20,the recognition success rate exceeds 80%.The simulation results also show that the recognition rate of the algorithm is better than that of the cosine ratio algorithm when the SNR is less than 15 d B,and the recognition rate of the high rate LDPC code with the code rate of 5/6 is improved most obviously.