Research On Channel Estimation Method In WRAN System

With the rapid development of wireless communication, wireless spectrum resources become increasingly scarce. However, the users authorized to have access to a lot of resources in the VHF and UHF band such as radio and television are not able to effectively use the spectrum. As a result, there is a lot of TV white space(TVWS) appearing in the TV band. To take full advantage of TVWS, Institute of Electrical and Electronics Engineers(IEEE) proposed the Wireless Regional Area Network(WRAN) in 2011. The WRAN system is designed to utilize TVWS to provide wireless broadband access for low population density areas such as rural and remote areas without interfering with authorized users.The physical layer of the WRAN system makes use of Orthogonal Frequency Division Multiplexing(OFDM). In the OFDM receiver with coherent demodulation, the accuracy of channel estimation is directly related to the performance of the entire system, which has an important significance to research.A research on the channel estimation method in WRAN system is carried out by this thesis. The main work of this thesis includes the following aspects:1. The simulation platform of WRAN system based on the VS2010 is established in C language. By comparing the error performance of simulation platform in additive white Gaussian noise(AWGN) channel, with the theoretical error formula, the correctness of the simulation platform is initially verified.2. Using the preamble sequences inserted in each frame of WRAN system, the channel estimation method based on the preamble sequences is studied. This study aims at improving the accuracy of initial channel estimation with high-density training sequence. To this end, the polynomial interpolation method of low complexity in frequency domain and the CIR detection method in time domain are studied. Against the shortcomings of the maximum length multipath delay method in filtering noise, an improved channel impulse response(CIR) detection method based on dual-sliding window is proposed. This method can improve the accuracy of channel estimation with detecting small power CIR components.3. Using the pilot sequence inserted in each OFDM symbol of WRAN frame besides preamble, the channel estimation method based on pilot sequence is studied. This study focuses on the FIR filter interpolation method with real coefficient. By analysing the defect of the real coefficient FIR interpolation method against long delay SFN channel, an improved adaptive complex interpolation channel estimation method is proposed. This method turns the real interpolation coefficient into complex interpolation coefficients through phase rotation, greatly enhancing the capability of combating multipath delay of WRAN system. Moreover, the adaptive approach can flexibly match the real maximum delay spread, and can improve the performance of channel estimation.