Filtered fast Fourier transmultiplexer and method

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT With reference to FIG.
2 a multi-channel digital transceiver 200 is coupled to a communication network 250.
It will be appreciated that transceiver 200 may be advantageously utilized in nearly any multi-channel communication system such as cellular radiotelephone communication systems, cable television (CATV) telephony systems, and the like.
Transceiver 200 includes in a receive path a receive antenna 202, a RF bandpass filter 204, a RF-to-intermediate frequency (IF) mixer 206, an IF bandpass filter 208, an IF-to-baseband mixer 210, an anti-alias filter 212, an analog-to-digital converter (ADC) 214, and a filtered fast Fourier transmultiplexer (FFFT) 216.
In a transmit path, transceiver 200 includes an inverse-FFFT 218, a digital-to-analog converter (DAC) 220, anti alias filter 222, a baseband-to-IF mixer 224, IF bandpass filter 226, an IF-to-RF mixer 228, an RF bandpass filter and amplifier 230 and transmit antenna 232.
In operation in receive mode, multi-channel communication signals are received at antenna 202 and processed along the receive path to FFFT 216 which operates to downconvert the channels contained within the multi-channel communication signal to produce a block of N communication channels which are then coupled to communication system 250.
Similarly in transmit, a block of N communication channels are communicated from communication system 250 to inverse FFFT 218 which operates to upconvert the individual communication channels into a multi-channel communication signal which is then processed along the transmit path and ultimately radiated from transmit antenna 230.
With reference to FIG.
3, a preferred implementation of FFFT 216 is shown; it being understood that a similar structure although reverse of FFFT 216 is the preferred implementation of inverse FFFT 218.
FFFT 216 structure generally resembles a decimation in time Cooley-Tukey FFT structure with filters on each branch.
As shown in FIG.
3, FFFT 216 includes a commutator 302 which commutates an input multi-channel communication signal to a first filter stage 304 having a plurality of filters 306-312 and via delay element 303 to a second filter stage 314 having a plurality of filters 316-322