Research On Equalization In Different Carrier Schemes

In this paper, we research the broadband wireless access problem in double-selective fading channels which involves time dispersion and frequency dispersion, and focus on anti-fading performance of various carrier schemes. Since the high speed wireless channel is vulnerable to multipath effect, as a result, the system will have serious inter-symbol interference. In order to eliminate inter-symbol interference, reduce the error bit rate in communication system, equalization is widely used in high speed wireless communication system. The IEEE802.16a physical layer standard involves key technologies in the representatives of the proposed multi-carrier orthogonal frequency division multiplexing (OFDM) systems and frequency-domain equalization of single carrier (SC-FDE) two options. Meanwhile, the two solutions are the core of the fourth generation mobile communication technology. As a result, the research on these two schemes is very important for the development of wireless communication. Beside them, a single multi-carrier mixed carrier system based on 4-weighted fractional Fourier transform (4-WFRFT) debuts stage.As representative of a brand new hybrid system, it should be studied in detail with a comparison to OFDM and SC-FDE technology. The paper first described the basic characteristics of wireless channel, given time-varying multipath channel impulse response model. And on this basis, equalization is introduced to overcome the channel fading and interference channel. After a brief description of equalization and equalization classification, equalization technology is analyzed from three aspects: the equalizer structure, equalization criteria, adaptive equalization algorithms in detail. Due to poor time-varying channel, fast adaptive algorithm for equalizer is essential, so we introduced two adaptive algorithms: LMS steepest descent algorithm and RLS algorithm. Then theoretical analysis and simulation are conducted also the comparison of the two algorithms is analyzed. Then the model and features of OFDM, SC-FDE, 4-WFRFT three carrier schemes are analyzed , and 4-WFRFT theory and its applications in communication system are described in detail. The diagrams of 4-WFRFT basic principles and systems are given, focusing on analysis of advantages the 4-WFRFT hybrid carrier scheme as a new technology may have. Finally, the single carrier QPSK modulation in several channels with different equalizer structures and adaptive algorithms simulation is simulated, the performance is analyzed. Then introduced the frequency domain equalization principle, and the frequency equalization performance of OFDM, SC-FDE, 4-WFRFT hybrid carrier schemes is simulated in time dispersive channel to show the different, then theoretical analysis of BER is given. After that, a simplified double-selective fading channel is established and compared three types of system. The simulation shows 4-WFRFT hybrid scheme on the double selective fading channels are more resistant to distortion, and it is thus prospective.