The Design And Implementation Of OFDM Adaptive Transmission System Based On 802.11g

Orthogonal Frequency Division Multiplexing (OFDM), which employs orthogonal overlapping subcarriers to modulate the signals, has been regarded as a key technology for high data rate transmission due to its ability to overcome many impairments in wireless channel. In recent years, adaptive transmission techniques have received more and more attentions, as they can dramatically increase the spectral efficiency, reduce interference and improve the communication quality of wireless communication system.In the 802.11g protocol, all the subcarriers of OFDM use the same modulation, but each sub-channel's decline is different in the wireless LAN, so under a certain SNR threshold will cause the system error rate increased and spectral efficiency decreased. For this reason, this paper designs a case of OFDM adaptive transimisson based on 802.11g, as well as uses simple block loading algorithm (SBLA) based on subband for reducing the system signaling cost.Firstly, this paper introduces the development trends of wireless communication and status of the history and development of OFDM technology and a detailed exposition of OFDM principle, meanwhile the characteristics of wireless channel and 802.11g protocol are introduced. Then designs the transmission frame format based on the 802.11g protocol used by the system and DSP implementation of the system communication control program, and implements FPGA design of adaptive transmission system in the hardware platform, and ultimately completed a OFDM adaptive transmission demonstration system. Finally, the paper gives the performance results of the system to verify the correctness of system design, and gives the follow-up research projects.