The Adaptive Allocation Tech In OFDM

Broadband wireless communication systems need high data-rate which is limited by inter-symbol interference (ISI) due to the frequency selective fading in channel. Orthogonal Frequency Division Multiplexing (OFDM) technique, widely regarded as a most promising solution, has attracted much attention for its ability of reducing ISI.In OFDM system, due to the independent fading of the channel, different subcarriers can employ different coding and modulation, fully use the resources, to enhance the transmit efficiency. In muiltiuser OFDMA system, due to the frequency selective fading of the channels of different users, adaptively allocating the subcarriers, Bit and power to users can obtain the gain called multiuser diversity, to enhance the transmit efficiency.What is more, MIMO can generate paralyzed channel to transmit multiple data stream in space, enhance the transmit efficiency but not increase the frequency spectrum. MIMO and OFDM can both improve the rate and efficiency of the system. In MIMO_OFDM, the adaptive tech developed, including the antenna.Here, after simply introducing the OFDM system, descript the adaptively distribution tech in OFDM. Introduce the module and algorithm of the three problems for the throughput, bit error rate and transmit power. Then, in complex multiuser system, mainly introduce the Margin Adaptive, give several recently good algorithms and then give the modified and proposed schemes. The Matlab simulation results showed that the modified scheme kept the performance while reducing the computation; the proposed scheme was better than the others and the betterment was more obvious with the load increasing. In MIMO_OFDM system, combined with VBLAST analyze the Rate Adaptive and combined STBC analyze the Margin Adaptive and give the modified scheme.