Based On The Simulation Of Stratospheric Communication System Baseband Module

Stratospheric communication platform is equivalent to put the base station in the high altitude about 20km to 50km, its covering area expands to 300km to 500km. compared with ground platform, the stratospheric communication platform have wider visible area, longer communication distance and smaller channel attenuation,so the emission power can be reduced obviously, same as the fee of basic establishment construction and the radiated pollution to the base stations around.MF-TDMA also called "multifrequency time division multiple access", adopt both FDMA and TDMA. the carrier frequency and distributed bandwidth can satisfy the transmitting requirement of mulitimedia flexibly. the time slot and burst rate can change according to demand of network control center. MF-TDMA with high access data rate and the flexibilty of network distribution, can satisfy the integrated sevices transmitting requirment of the future communication.Aimed at burst communication, this dissertation works on the simulation of the MF-TDMA system and the realization of some key modules, such as DDC module, symbol timing synchronization and carrier synchronization.First of all, this paper intorduces the concepts and chracteristics of the stratospheric communication and MF-TDMA, then brings forward the transmitting architecture and receving architecture. The signal in MF-TDMA system is just a short time slice usually called time slot, different clients occupy different time slots with short time duration. so there is a new time requirement about the signal capture of receiver and establishment of synchronization.In the part of the DDC module, firstly, this paper introduces the pricinple and architecture of the DDC, including NCO, HB filter, CIC filter and low band pass filter. secondly, this paper carries out the design according to the requirement of the system, adopting CORDIC pipeline to realize the NCO, using 5 classes CIC filter and 2 classes HB filter, introducing the DA arithmetic to optimize the LPF.In the part of the symbol timing synchronization module, this paper introduces the theories and architecture of the symbol timing synchronization, because of the bursting characteristic, this paper adopts the open loop model and designs the three major parts including timing error estimation, interpolation control and interpolated filter based on the farrow structure.In the part of the carrier synchronization module, this paper introduces the MLE of related sychronization parameters, then brings forward the frequency offset estimation algorithm and phase offset estimation algorithm, at last, it designs the implementation architectures of the two modules.Finally, this paper carries out the simulation of the MF-TDMA module, and discusses the performance of the system.