| WLAN is generally considered as the 'last mile' in the connection of computers and wired networks. In 1997, IEEE started to frame and to approve WLAN standards called IEEE 802.11. Since then, research about this field has been developed rapidly. And Orthogonal Frequency Division Multiplexing (OFDM) in IEEE 802.11a has been given more and more attention because of its various advantages in cancelling the severe effects of frequency selective fading. In recent years, OFDM has been a hot topic in the development area of broadband wireless communication. Under the background, and based on IEEE 802.11a Standard, this thesis presents research and simulation for communication system of based-band signal in OFDM.In order to solve some problems of OFDM system, for example, its complexity is high, computing speed is slow, and portability is poor, with IEEE802.11a Standard of Wireless Local Area Networks, we do further research in based-band computation algorithm. According to the idea of Object Oriented Programming, we design the whole program and write the code for each module. These modules includ random number generator, convolutional coding, generating punctured codes, viterbi decoder, interleaving and deinterleaving, subcarrier mapping, IFFT/FFT, inserting pilot and preamble sequence, adding Gaussian white nosie and so on. In the end, we also design a man-machine dialog box for the system. And, based on Visual C++6.0 platform, we complete a simulation software for based-band computation of OFDM system. And then, with the Monte-Carlo method, we give some analysis on the reliability of the system with or without channel code. Also, we research the effects of differ punctured figures on BER. At last, we optimize the system, and improve FFT and viterbi algorithm in order to enhance the operational efficiency. In this paper, we build the simulation platform with C++ language, which is much better than that with other explanatory languages such as Matlab. Also, the program has good generality. |
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