An Efficient Frequency Domain Equalization Method for Channelizer-based Software Defined Radios

In this paper we present an efficient method for equalizing the wireless channel in DSP-based radio architectures. Equalization is usually performed in the time domain via transversal filters. Our proposal performs the channel equalization in the frequency domain by adjusting scalar gains and phases of each path of a perfect reconstruction filter bank. In this process the spectral products form a composite channel-equalizer and matched filter frequency response with uniform gain and phase profiles. This process cancels severe signal distortion caused by the multipath channel. The appropriate gain and phase profiles can be obtained adaptively or from a channel probe. In this paper the frequency domain equalization method is applied in fully digital receivers containing perfect reconstruction (PR) polyphase filter banks designed to synthesize arbitrary filter responses. The output ports of an M-path analysis channelizer present samples of the narrow band complex envelope from spectral segments spanning the entire signal bandwidth. Appropriate scalar gains and phase shifts are applied to each path to reverse the distortion caused by the wireless channel. An estimation block guides the selection of the proper parameter values. Trade-off considerations between total workload and receiver performance influence the selection of the number of IFFT spectral sample points in the analysis channelizer. The channelizer spectral response interacts with the applied gains to form a “connect the dots” piece-wise linear approximation to any specified frequency response. Theoretical analysis and simulation results, which prove the efficacy of the proposed method, are provided in this paper along with suggestions for further research and development work.