Reconfigurable Farrow Structure-Based FRM Filters for Wireless Communication Systems

Recent trends in mobile technology are toward supporting multi-standard communication systems on the same device. This requires their design to be based on some kind of reconfigurable techniques. Also, in cognitive applications, intelligent bandwidth allocation for efficient spectrum utilization requires altering the bandwidth within the same communication channel. Digital filters with non-uniform and varying bandwidths can be used to channelize different frequencies. Efficient designs of such filters are proposed in this paper. Frequency response masking (FRM)-based design is used, where the masking filters can be tuned to a desired set of frequencies by using a variable bandwidth (VBW) digital filter, configured as Farrow structure. For each of the chosen bandwidth, a corresponding masking filter response can be obtained, using the Farrow structure. A novel extension of FRM is proposed in this paper, using two approaches, to realize more than one sharp filter response from the same prototype linear-phase low-pass filter. In both approaches, the masking filters of the FRM filter are realized using Farrow structure. In the first approach, only a set of two Farrow structure filters are required to realize all the required channels. The channel selection is then carried out by varying a single parameter on each of the two masking filters. In the second approach, every channel is realized using a set of two Farrow structure filters and the channel is selected by means of hardware switching techniques. In addition to reconfigurability, hardware implementation complexity of Farrow structure-based VBW is lower compared to the direct FIR filter structure when designed for large set of bandwidths.