Research And Implementation Of CPFSK Modulation And Demodulation In Broadband Satellite Communication System

With the continuous development of social economy and technology in the modern society,the growing demand for the reliability and effectiveness of the communication have put forward more severe requirements.Broadband satellite communication,as an effective method to apply modern satellite communication technology to address the needs of broadband services,can meet people's demand for broadband media entertainment life with advantage of high transmission rate.Broadband satellite communication has become a popular research direction in academia and industry.So it is the key for the broadband satellite communication research field to find the high performance,fast and efficient modulation and demodulation.CPFSK is such an efficient modulation technology that meet the requirements of broadband satellite communications.High spectrum utilization and high power utilization are two of its most significant features.CPFSK can meet the requirement of high-rate information transmission in broadband satellite communication system.Therefore,research and implementation of CPFSK Modulation and Demodulation in Broadband Satellite Communication System has important engineering practice significance.In this paper,we first introduce a practical design scheme of broadband satellite communication system,and then focus on the high transmission rate modulation-CPFSK,including CPFSK signal modulation technology,synchronization,Viterbi demodulation,and then implement these parts in FPGA.Finally completed a set of communication from the sending end to the receiving end at the highest transmission rate level.The main contents and achievements of this paper include the following aspects:1.Considering the special requirements of the project for high transmission rate hopping system,this paper will study and implement CPFSK signal modulation technology.CPFSK signal is a special CPM signal.It has a series of advantages,such as small external power,high spectral efficiency,constant envelope,with phase memory characteristic.CPFSK signal can meet the requirement of high transmission rate.In the hardware implementation we configure the internal serial registers in the AD9957 chip to control the DDS to generate wave types with different frequency.Finally we choose the corresponding sine wave according to the data from the upper computer to complete the CPFSK signal modulation.2.The goal of this paper is to achieve high-speed information transmission with CPFSK signal,the frame synchronization on the receiving side requires high synchronization speed,so we insert the auxiliary preamble before the data frame to realize frame synchronization.This method is computationally small,the complexity of hardware implementation is low,the time required for synchronization of the receiving end is greatly reduced,and it is suitable for the high information rate transmission requirement of this project.In this paper,we design a synchronous preamble frame structure,through the measured to determine a reasonable synchronization peak threshold to determine the bimodal threshold synchronization algorithm,and finally completed on the FPGA to achieve a specific implementation,to avoid leakage synchronization and false synchronization In this paper,we design a synchronous preamble frame structure,determine a reasonable synchronization peak threshold by the actual test,determine the synchronization algorithm with double-peak threshold,and finally complete the implementation and test on the FPGA to avoid leakage synchronization and false synchronization.3.Since the CPFSK has a trellis coding structure similar to convolutional coding,the Viterbi decoding algorithm is used to demodulate CPFSK signals.In this paper,we design a grid diagram of 8-state CPFSK state transition,and use Viterbi demodulation based on this grid diagram.In the hardware implementation,we use the modular thinking to design the system,including the current path metric calculation module,the comparison and selection module,the accumulate distance temporary registering module and the backtracking module,to complete the Viterbi demodulation of the CPFSK signal.Finally we can realize the highspeed transmission requirements of the project.