FIR Filter Implementation in Frequency Domain For Wireless Communication System

Abstract

Third Generation (3G) communication systems use Wideband Code Division Multiple Access (WCDMA) technique to transmit and receive data. The spectrum of a signal of the type used in WCDMA has adjacent channel side lobes. These side lobes introduce interference into users of the adjacent frequencies who could be of the same operator or could be of other operators. That is why, filtering in the transmitter should be used to overcome the effect of the adjacent channel side lobes. Numerous considerations led to the use of a FIR filter in the WCDMA transmitter, together with a matched filter in the receiver in a way to get a Nyquist filter as the combined filter response. The main property of Nyquist filters is that they result in zero Inter Symbol Interference (ISI) at the optimum sampling point for filtered data. This thesis presents a new method of implementing a high performance Finite Impulse Response (FIR) filter in the frequency domain that is suitable for third generation (3G) communication systems. The method discussed can be used for the implementation of low cost modules capable of performing filtering and Fast Fourier Transforms (FFT) for use with the wide variety of the wireless communication standards available nowadays. With the use of this method the new mobile equipments can support multiple standards in order to offer the most complete set of applications to the users like telephony, mobile internet and mobile television. A comparison between a classical time domain FIR implementation, and frequency domain FIR implementation, in terms of computational complexity, inter symbol interference rejection on the basis of average gain in immunity against ISI, Error Vector Magnitude (EVM) and peak distortion is presented. It is found that frequency domain implementation of FIR filter is better than time domain implementation of FIR filter in all respects. This advantage of FIR filter implementation in frequency domain makes it suitable for its use in 3G communication system.