802.16a-based Adaptive Modulation

Nowadays, WiMAX has been one of the focuses in the telecommunication development and application. Based on IEEE 802.16a, the technology of adaptive modulation under the SUI-2 and SUI-5 channel is researched.Firstly, the basic characters of wireless fading channel are discussed. Then, two ways of channel modeling are researched, including Doppler Filter and SHS.After introducing the channel modeling, the general principles of adaptive modulation are analyzed. There is an established relation between SNR and BER, and it fluctuates with modulation. Thus, adaptive modulation system and threshold based on 802.16a are achieved.Then, adaptive modulation under the flat fading channel are researched and applied to SUI-2 Channel. Because there is no ISI, SNR can be chosen as control parameter. The algorithm of channel estimation and SNR estimation based on ML are discussed. The result shows that adaptive modulation received 7dB SNR Gain.In addition, adaptive modulation under the frequency selective channel are researched and applied to SUI-5 Channel. Because of serious ISI, frequency equalization should be applied. Then error of SNR'estimation is introduced, which influences the performance of adaptive modulation. Therefore, equalization demodulator with LPP is applied and LLR metric is chosen as control parameter. The result shows that adaptive modulation gets 12dB SNR Gain.According to the research of adaptive modulation under two kinds of fading channel, a conclusion, that adaptive modulation is an effective technology to overcome channel fading, is received.