SMALL SIDE-LOBE FILTER DESIGN FOR MULTITONE DATA-COMMUNICATION APPLICATIONS

An approach for realizing filter banks having improved sidelobe perfor mance compared to approaches such as those based on inverse Fourier tr ansforms (IFT's), especially for greater frequency differences from th e passband frequencies, is presented. The approach is based on using a weighted-sum of near-adjacent IFT filters to realize the individual c hannel-bank filters, but with constraints added that results in signif icantly improved stopband performance while still achieving small reco nstruction errors. The proposed channel banks are suitable for realizi ng multitone digital data communication systems, such as Asymmetric Di gital Subscriber Line (ADSL) systems, where stopband performance is cr itical. Under the conditions of maximal decimation, the reconstruction is not perfect, but aliasing errors are small enough to be negligible in practical communication systems. For some cases, the filter coeffi cients can be determined exactly without using optimization. Given the frequency-weighting coefficients reported herein, near-optimal multir ate filter banks may be designed exactly without optimization for all even n.