Study Of SNR Estimation And Adaptive Transmission Technique Based On OFDM System

Orthogonal Frequency Division Multiplexing (OFDM) has high spectrum efficiency and capability to mitigate the side-effect of multipath channel. So it has been regarded as a key technology for high data rate transmission. In this dissertation, the SNR estimation and the adaptive transmission technique in OFDM system are studied. The SNR estimation plays an important role in many modern wireless communication systems. It can provide the channel quality information required by the power control and bit assignment algorithms in the adaptive transmission technique. In recent years, adaptive techniques have received more and more attentions, as they can dramatically increase the spectral efficiency and improve the transmission reliability of wireless communication systems.The studies of this dissertation are based on the knowledge of wireless channel and OFDM system. So firstly, the character of wireless channel and the principle of OFDM system are introduced. Then the dissertation begins to introduce the general situation of the development of the SNR estimation algorithms and the definition of SNR. After that, two SNR estimation algorithms that applies to OFDM system are studied deeply, including the simulation and FPGA implementation of the algorithms. The purpose of studying the SNR estimation algorithms in this dissertation is that it's the first important step of implementing the adaptive technique in OFDM system.Finally, the adaptive transmission technique is studied deeply. In this part, the dissertation describes some classical adaptive bit-allocating algorithms firstly. Then, based on the principle of these algorithms, the dissertation proposes a simple scheme of adaptive transmission. The scheme which combines the Trellis Coded Modulation (TCM) technique and adaptive technique can be used in OFDM system to increase transmission efficiency dramatically.