Blind Channel Estimation In OFDM Systems

Orthogonal frequency division multiplexing (OFDM) is the technology with high-speed data transmission capacity, efficient spectrum utilization and anti-multipath interference, which is considered to be one of the core technologies in the fourth generation mobile communication system. In order to achieve high performance of OFDM technology, it is necessary to reserach on the key technologies, such as channel estimation and synchronization, which is composed of time synchronization and frequency synchronization. OFDM time synchronization is used to determine the location of the beginning of OFDM symbols, and frequency synchronization is used to determine the carrier frequency offset between the transmitter and receiver which causes signal attenuation and subcarrier interference. The pilot or trained squences are inserted during transmiting in a traditional way, which can acquire good channel estimation accuracy at the cost of spectrum utilization. It can acquire a higher utilization for the bandwith by blind channel estimation.The thesis researches on channel estimation with comparing and analyzing the existed basic algorithms. Focusing on noise subspace blind channel estimation algorithm, an algorithm based on second-order statistical characteristics of the sub-space method was realized. It is required that the current algorithms are restricted with ideal synchronization. A good performance was achieved by combining maximum likelihood blind synchronization and channel estimation. It is shown by simulation that the normalized root mean square error is no more than 0.1 at 25dB SNR in Guassian and Rayleigh channel.