The Research On Channel & Bit Allocation And Channel Estimation In OFDM System

Although the gradually-commercialized 3rd Generation of mobile communicationcan provide Internet and Multimedia Service, it is equipped with some limitations anddisadvantages. As a result, an appropriate multi-media-oriented system and itsrelevant research in theory and technique have been put forward to the order of theday. Therefore, more and more people begin to focus on the next 3G or 4G mobilecommunication, the efficiency of wireless frequency resource, the improvement ofperformance and a unique standard all around the world of one system.As the hotspot of future mobile technologies, OFDM has been widely and deepresearched, in which the Adaptive OFDM is a very important researching field atpresent. Aiming at this very field, the paper first introduces the principles andbackground of adaptive OFDM. Combining the wireless channel and bit allocations,the paper proposes a novel multi-user combined-modulation algorithm of adaptiveOFDM, which can remarkably reduce the total power needed by the system andimprove the efficiency of frequency resource with the assurance of transmission QoS.Simulated in the Adaptive OFDM system with Matlab, the performance of thisalgorithm is compared with present and traditional algorithms, and the results verifythe distinct improvements of performances both in power and SNR as well.Besides, concerning about the vital part of OFDM, i.e. channel estimation, thepaper presents two efficient domain models of channel estimation. And both of themodels are analyzed and simulated in the pre-mentioned adaptive OFDM system, andthe result shows that the models can improve the performance of the system in quite adistinct degree. At last, the paper discusses the application of digital technology,Over-Sampling in OFDM system and analyses the contribution and effect of it to thewhole system.