DFT Modulated Filter Banks for Multicarrier Transmissions over Wired and Wireless Systems

• Main Authors: Tzung-Hwui Lo, 羅宗惠
• Other Authors: See-May Phoong
• Format: Others
• Language: en_US
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/65183358955524162593

碩士 === 國立臺灣大學 === 電信工程學研究所 === 92 === The OFDM transceiver has enjoyed great success in many wideband communication systems in recent years, and has been adopted in standards for various applications such as ADSL, VDSL, wireless LAN, digital audio and video broadcasting, etc. Two of the attractive features are its low complexity and the ability to combat inter-symbol interference(ISI). Although the OFDM systems are used widely, however it is also well-known that the OFDM transceiver has poor frequency characteristics. To improve the frequency characteristics of transceivers, filter banks (FB) are often proposed as a solution. FBs have the advantage of high stopband attenuation but their complexity is very high. To reduce the implementational cost, we employ DFT modulated filter banks, where the transceivers can be efficiently implemented using fast Fourier transform. In this thesis, FB transceivers with overlapping block transmission are considered. For multi-path fading channels, these FB transceivers suffer from serious ISI. We will show that the SIR (signal to interference ratio) can be formulated in terms of the FB free parameters. Given a fixed receiver (or transmitter) with good frequency characteristics, the transmitter (or receiver correspondingly) can be designed to maximize SIR for multi-path fading channels. The problem of SIR maximization can be formulated into an eigenvector problem. In addition, we also proposed a new method to design these DFT bank transceivers with good transmit and receiver filters. In the new design, the free parameters of the transmitter and receiver are split into 2 parts: one part for frequency response optimization and one part for SIR optimization. An iterative procedure is employed to solve the design problem. Simulation results show that the DFT bank transceivers can enjoy both good frequency characteristics and a moderate SIR value for multi-path fading channels. Moreover, the proposed new method leads to a significant improvement over the original design.