Research On Performance Of LTE-HARQ System Based On Mixed Carrier Signal

With the development of society and communication technology, users have higher requirements for the quality of communication which requires the communication system to have good performance under the various circumstances. With the standard of 3GPP, the communication system transports the signals with the method of OFDM which changes the signals to multi-carrier signals. But the OFDM method loses the advantages in the doubly dispersive channel and the communication system will sacrifice its capacity to maintain the balance of the system. However, the hybrid-carrier signals which using the method of FRFT have excellent performance over the doubly dispersive channel. In the recent years, the research of mixed carrier signals is becoming the hot spot of communication technology. Based on the system of LTE-HARQ, the research of mixed carrier signals has the significant meaning in theory and practice.This paper mainly intends to analyze the performance of LTE-HARQ communication system in the doubly dispersive channel based on mixed carrier signal. Firstly, the definition and properties of FRFT are compared to the traditional FFT and the realization of FRFT is analyzed. The method of 4-Weighted Fractional Fourier Transform(4-WFRFT) is raised to realize the FRFT. Then the definition and properties of WFRFT method as well as the application of mixed carrier in communication system are analyzed. The continuous time model of OFDM system with the method of WFRFT is built. Secondly, the LTE-HARQ communication system is analyzed and the main system models are showed. Under the variety of multipaths and Doppler frequency shifts, the numbers of retransmission, throughput and block error rate are analyzed in the Jakes model channel. The result shows the performance decreasing of LTE-HARQ system in the doubly dispersive channel. At last, the deduction of discrete-time model of OFDM system with the method of WFRFT and the channel matrix model of the Jakes model are built. The form of mixed carrier signal throughout the channel is analyzed. With the simulation results, the LTE-HARQ communication system based on mixed carrier signal has better performance over the old system in doubly dispersive channel.