Research On The Baseband Signal Processing Technique Based On OFDM

Recently, the requirement for wireless communication has increased, with the development of economy, society, technology, and the improvement of people's standard of living. Wireless data transmission whenever and wherever with high speed, high quality is the direction of the development of new generation wireless communication system. The efficiency of frequency spectrum is very important for wireless communication system because of the lack of frequency spectrum resource. However, the efficiency of frequency spectrum for orthogonal frequency division multiplexing (OFDM) is very high for OFDM adopting parallel transmission. And OFDM can almost eliminate inter symbol interference (ISI), which resulted from mufti-path channel for its guard interval and increasing symbol period. So OFDM becomes one of the important technologies of new generation wireless communication.OFDM can be used in conjunction with a multiple-input multiple-output (MIMO) transceiver to increase the diversity gain and/or the system capacity. Thus, MIMO-OFDM is considered a key technology in emerging high-data rate systems.In this paper it is summarized which are the challenge and the development trend on wireless communication technique. The channel estimation technique on OFDM and MIMO-OFDM are introduced specially. Then the fundamental on OFDM and its key technique are discussed. The OFDM model with signal transmitting is depicted. It mainly investigates the constellation mapping, FFT translation in the modulation model. Then we show the mathematics model and the channel character on MIMO system and MIMO-OFDM system. In MIMO-OFDM systems, pilot-symbol-aided or decisiondirected channel estimation must be used to track the instantaneous channel state information at the receiver in order to coherently detect the received signal. Pilot symbols facilitate channel estimation, but in addition to consuming bandwidth, they reduce the transmitted energy for data symbols per OFDM symbol under a fixed total transmit power condition. This suggests a tradeoff between the power allowed to data symbols and the accuracy of the channel estimation in MIMO-OFDM systems when the total transmit power is fixed. To date, there have been numerous previous studies on the problem of optimizing pilot signals for wireless communica- tion systems but none that optimize the PDPR for maximizing the MIMO-OFDM capacity with comparing various pilot schemes. In this paper, the pilot-to-data power ratio (PDPR) for MIMO-OFDM systems with these three different pilot patterns is optimized from an informationtheoretic capacity point of view. The analysis shows that the correlation between different channel links in the estimated channel can be removed by using three different pilot patterns which are termed as IPP, SPP, and OPP, and an optimal PDPR is derived for each of those three cases. Finally, concluding remarks and the perfect conceive in the future are given in the last section.