Research On The Estimation Algorithms Of Channel In OFDM System

Orthogonal frequency division multiplexing (OFDM) technology is one of the cores ofthe fourth generation mobile communication technology. It has high transmission rate, andstrong anti-fading ability, etc.. But to obtain these benefits, it is necessary to estimate fadingcharacteristics of wireless channel accurately. So the wireless channel characteristicsestimation technique has become one of the hot spots of the people.At present, OFDM channel estimation techniques can be roughly divided into threecategories: the pilot/training sequence-based channel estimation techniques, blind channelestimation techniques and semi-blind channel estimation techniques.Compared with the pilot-based channel estimation method, blind channel estimationmethod does not need to insert pilot, thus the resources of the channel are saved. This paperanalyzes a kind of blind channel estimation technique which is based on subspace SVDmethod and proposes a method for estimating time-varying channel on the basis of blindchannel estimation technique. In the light of low accuracy of existing methods for estimating,this paper raises an optimization algorithm to carry out weighting using channel’s interrelatedproperty. The algorithm has good adaptability, simple structure and faster convergence. Thesimulation results show that this algorithm can improve the performance of channelestimation effectively. In addition, this paper studies the semi-blind channel estimationalgorithm base on hidden pilots and proposes a time variant OFDM channel estimationalgorithm base on the hidden pilots. In the algorithm the pilots are hidden in the data and sentwith the data at the same time. It saves bandwidth resources and the coherent demodulationcan be used at the receiving end, thus convergence rate is faster. The simulation results showthat the algorithm has high accuracy, while the lower complexity of the algorithm.