| Long distance VHP wireless communication transmission requires only moderate transmission power and reasonable equipment cost,also the channel is very difficult to be destroyed. These characteristics make its development very promising. However,due to the nature of its channel,it also has the deficiencies such like low reliability and poor performance. These limit its application in ever-increasing communication demand. This thesis focuses on some technical difficulties encountered in the long distance wireless communication and tackles the task by applying OFDM (Orthogonal Frequency-division Multiplexing) techniques in the communication system. This hence improves the overall communication system's performance by overcoming the effects such like Multi-path fading and Doppler spread in the frequency domain.Orthogonal Frequency Division Multiplexing (OFDM) is a multi-carrier digital modulation technique. Its conception has come out for a long time,however,it is recently that it's recognized as an proposed method in broadband bi-direction wireless data communications with the development of multimedia services. With the development of DSP chip techniques and the introduction of some mature techniques,such as FFT/IFFT,the application of 64/128/256 QAM in high-speed modem,TCM,adaptive channel equalization,the insertion of Guard Interval and so on,people are starting to focus on the application of OFDM in the field of mobile communications.Base on the study of long distance wireless communication channel characteristics,the thesis gives an analysis on the existing problems and proposes a solution:Implanting the OFDM technique in communication system modulator. In the thesis,detailed design architecture is given,together with a comparison among the different algorithms. A final solution in favor to the long distance wireless mobile communication system is suggested after an overall consideration of both performance and cost.In the chapter one,the thesis gives a brief introduction of the long distance wireless communication. Some problems encountered are analyzed. OFDM theory and its advantages and disadvantages are also introduced here. Anticipation of the OFDM technique is given in the late of the chapter with some related standards.Chapter two gives a study on the characteristics of the long distance wireless communication channel,based on this proposes the channel model which this thesis would discuss.Based on the discussion of chapter two,chapter three gives the baseband transmission architecture of OFDM communication system. Detailed analysis of channel estimation model of OFDM system and compassion between several implementation scheme are presented,including the simulation result. According to these,the channel estimation algorithm and the detailed transmitting frame structure parameters are proposed for the application. At the same time,this chapter also researches on the theory analysis and implementation approaches of other key modules,such as modulation,demodulation,channel coding,timing and synchronization.According to the technical theory of OFDM and the analysis results of the former three chapters,chapter four gives the detailed theoretical diagram of the transmission end and receiving end of OFDM communication system. The transmission parameters are also decided. An transmission frame architecture and OFDM character architecture applicable to OFDM discussion on theoretical analysis on the estimate channel modules,five,the article introduces thelong distance wireless communication are also presented. Finally,this chapter gives a brief introduction of the design of the hardware platform for the long distance wireless mobile communication system as well as the data transmission flaw. |
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