On Some Problems Of OFDM Communication System And Implementation Of Baseband Modulation

Orthogonal frequency division multiplex (OFDM), also named multi-carrier modulation (MCM), has recently received an increasing attention. In OFDM system, ISI (inter-symbol interference) which is caused by frequency selective fading in wideband communication systems is canceled. Moreover, other promising feature is high bandwidth efficiency. For utilizing OFDM in high-speed data transmission system in the future, certain research related to OFDM communication system has been taken in theoretical and practical aspects in this dissertation.OFDM system is summarized in chapter two. ICI and sub-carriers allocation algorithms in OFDM system are analyzed in chapter three and chapter four. Finally, the actual hardware of baseband modulation in the transmitter as well as the hardware emulation is described in chapter five, six and seven.The results show that ICI will be caused by limited spectrum effect of OFDM signal, and that ICI resulted from Doppler shift can be eliminated by synchronization compensation in the receiver. Moreover, frequency tracking algorithms are concluded and the new one is presented in this thesis. In order to sufficiently utilize channel capacity, new sub-carriers allocation algorithms which are lower complex and close to the optimum, are presented. In the perspective of practice, how to implement hardware emulation based on a FPGA development broad is illustrated. The test results indicate that the hardware system could be utilized by high-speed data transmission system with an information throughput of 4×66 megabauds per second (MBps).