Research On Channel Estimation And Interference Cancellation Algorithm For Anti - Carrier Interference In OFDM System And VLSI Implementation

With the arrival of the digital age, the new generations of wireless communication standards have been proposed and advanced wireless communication technology have been used. The Orthogonal Frequency Division Multiplexing (OFDM) modulation technology has been used in a lot of wireless communication standards such as European digital TV broadcasting standards (DVB), wireless LAN standards (IEEE802.11), wireless metropolitan area network standards (IEEE802.16) and Long Term Evolution (LTE). Due to the higher spectrum efficiency and being able to overcome the channel delay and frequency selective fading, OFDM technology to become one of the most promising wireless communication technology.OFDM demodulation technique as an irreplaceable technology in next generation wireless communication systems has been studied widely. And channel estimation and channel equalization as a key part in the OFDM demodulation system plays an important role to the system performance.Mobile reception is another important characteristic of wireless communication. In the mobile reception, the OFDM signals go through time-varying channels which destroy the orthogonality between subcarriers and the Intercarrier Interference (ICI) is introduced. The ICI compromises the performance of the OFDM demodulation. In order to support the higher carrier frequency band and high speed mobile reception, the ICI estimation and mitigation technology need to be employed to enhance the performance of the OFDM system.The main work and contribution of this thesis includes:(1) First introduce the OFDM technology and its advantages, then analyze the characteristics of the wireless channel and its modeling. A detailed analysis of the OFDM signals which goes through a time-varying multipath channel is given. The banded structure of the frequency domain ICI matrix is analyzed and simulation results of how the ICI impact on the OFDM demodulation performance is shown.(2) Introduce and analyze some commonly used channel estimation algorithm in OFDM system. And analyze three type of different ICI estimation and mitigation algorithm, and the simulation results of these scheme are given. Reasonable approximate and the statistical characteristics of the ICI energy distribution are used to reduce the complexity and difficult to implement here.(3) DVB-SH digital TV broadcasting standard OFDM mode transmission scheme is studied. A channel estimation and equalization scheme which uses two-dimension interpolation filter is proposed. Simulation results show this scheme allows reliable reception under different channel scenario. Complete the hardware implementations and some modules such as signal to noise ratio estimation are optimized to reducing the computational complexity and the overall hardware resources.(4) For high speed mobile reception, a frequency domain ICI estimation and mitigation scheme is designed for the DVB-SH digital TV broadcasting standard OFDM transmission mode. The proposed scheme uses a simplified feedback decision direct algorithm and effectively reduces the ICI in the received signal to improve the system performance in high-speed mobile reception. After the optimization of the circuit structure, a second time of interpolation filtering is employed to reduce the demand for storage space, reduce the overall cost of hardware implementation of ICI estimation module.(5) DVB-T2digital TV broadcasting standard Multi-Input Single-Output (MISO) mode transmission scheme is studied. Simulation results of the performance gain of the Alamouti code under different channel scenario are given. Then analyze the special pilot pattern in the MISO mode. Then a channel estimation and Alamouti decoding algorithm for the DVB-T2standard is proposed. Simulation results show the scheme allows reliable reception under different MISO channel scenario.(6) Iterative receiver architecture becomes the research hot spot for recent years. Several iterative channel estimation algorithms are studied here. In this these, a Fourier transform (DFT) based iterative channel estimation which uses both the energy and phase information to exploit the sparsity of the estimated channel is proposed for coded OFDM systems over fast fading channels. The receiver exchanges information between the channel estimator and channel decoder in an iterative fashion to obtain accurate channel state information (CSI). Simulations results demonstrate that the proposed iterative channel estimation scheme allows a reliable reception over fast fading channels with normalized Doppler frequency up to10%in a small number of iteration. Furthermore, a modified piecewise linear approximation based iterative ICI estimation and cancellation algorithm is proposed. The ICI mitigation algorithm effectively reduces ICI in the received OFDM signals and the number of iterations, and improves the performance of OFDM systems in extreme high-speed mobile reception.