Research On Multiplexing And Demultiplexing Technology For The Downlink Of MF-TDMA/QOTDM

Broadband satellite communication system based on MF-TDMA,which adopts the non-regenerating processing mode on satellite generally, having the advantages of low facility complexity and power consumption,as well as channel resources can be flexibly applied for many different users.Effective reducing the load of the satellite and prolong the service life of the satellite.The downlink uses sample mixed continuous wave time-division multiplexing transmission method in this thesis,solving the problem of complex envelop signals of multiple narrowband signals to time-division multiplexing transmission,that can make any number of multi-channel multiplex signals to a continuous signal for transmission.How to realize the synchronization is the key problem for QOTDM multiplexing technology.This thesis mainly studies the sample synchronization and carrier synchronization problem in the process of multiplexing and demultiplexing for the downlink.In this thesis, the main research work is as follows:1. This thesis proposes an improved multiplexing scheme of a combination of OFDM and QOTDM for the downlink transmission,the scheme divides 48 roads signals into 12 groups,each groups do 4 points of IFFT,forming 12 roads multi-carrier signals, reducing the roads of multiplexing and the pressure for demultiplexing on the receiving terminal,and then adds two lines of the same PN codes of QOTDM multiplexing.2. According to QOTDM technology demand the receiver terminal has a very high sample synchronization precision requirement,designing a set of the group delay filters,through different phase frequency characteristics of the group delay filters to adjust the sample,to achieve the purpose of sample synchronization precisely,which makes the sample accuracy to reach 5% of the sample point sampling interval,and relatively simple to implement and overcome the problem of high complexity and hardware implementation difficulties of sample point interpolation method and adaptive matched filter method.When BER is equal to10-3,compared with the theoretical curve deterioration of 0.5d B.3. At the receiving terminal,the thesis puts forward a method of correcting carrier frequency deviation.The method according to data-aided method to correct the carrier frequency deviation,using the phase difference between the two lines of PN codes obtaining a frequency deviation estimated value,then based on the weighted factor to adjust the estimate,getting a similar value of carrier frequency deviation to correct frequency deviation.which can only achieve the goal of carrier coarse synchronization.When BER is equal to10-3, compared with the theoretical curve deterioration of 1.6 d B.4. Completing the scheme design of downlink transmission system for QOTDM multiplexing and demultiplexing,and the simulation and FPGA design of all modules.Verifies the correctness of the FPGA design by Model Sim finally.