OFDM multiple sub-channel communication system
A transmitter and corresponding method for transmitting an OFDM signal in a communications channel, including a plurality of base-band OFDM modulators, each for modulating a respective data signal onto a plurality of orthogonal sub-carriers and outputting a respective sub-channel OFDM signal; and a fast convolution filter and up-converter for applying fast convolution filtering and digital up-conversion to the sub-channel OFDM signals to output a combined OFDM signal that includes each of the sub-channel OFDM signals, the fast convolution and up-converter filtering each of the sub-channel OFDM signals and frequency shifting all of the sub-channel signals to respective designated frequencies within the combined OFDM signal. A corresponding receiver is also provided.
1. A receiver for receiving a combined OFDM signal that includes a plurality of sub-channel OFDM signals, the receiver including:
a buffer and FFT for receiving the combined OFDM signal and performing an FFT thereon to output a frequency domain signal, each of the sub-channel OFDM signals occupying assigned frequency ranges within the frequency domain signal;
a plurality of processing chains each associated with a sub-channel and each including:
(i) a fast convolution filter and digital downconverter for extracting from the FFT of the combined OFDM signal the sub-channel OFDM signal occupying the assigned frequency range of the associated sub-channel and performing an IFFT on the extracted sub-channel OFDM signal;
(ii) an OFDM demodulator for demodulating the sub-channel OFDM signal output from the fast convolution and digital downconvertor.
2. The receiver of claim 1 wherein the fast convolution filter and digital downconverter includes:
a frequency window filter for extracting from the FFT of the combined OFDM signal the sub-channel OFDM signal occupying the assigned frequency range of the associated sub-channel;
a fast convolution filter for multiplying the extracted sub-channel OFDM signal with a filter transfer function to remove out-of-band signals;
an IFFT for converting the filtered extracted sub-channel signal to the time domain; and
an output buffer for removing filter transients from the output of the IFFT.
3. The receiver of claim 1 wherein the fast convolution filter and digital downconverter applies overlap-and-save fast convolution filtering to the extracted sub-channel OFDM signal and includes an output buffer for discarding from successive processing blocks in the extracted sub-channel OFDM signal portions that overlap in time with portions of preceding processing blocks.
4. The receiver of claim 1 wherein the fast convolution filter and digital downconverter applies overlap-and-add fast convolution filtering to the extracted sub-channel OFDM signal and includes an output buffer for adding portions of processing blocks in the extracted sub-channel OFDM signal output from the IFFT to portions of preceding processing blocks that overlap in time.
5. A method for receiving a combined OFDM signal that includes a plurality of sub-channel OFDM signals, including:
receiving the combined OFDM signal and performing an FFT thereon to output a frequency domain signal, each of the sub-channel OFDM signals occupying assigned frequency ranges within the frequency domain signal;
for each of the assigned sub-channel frequency ranges, applying fast convolution filtering and digital downconversion to extract from the FFT of the combined OFDM signal the sub-channel OFDM signal occupying the assigned frequency range and performing an IFFT on the extracted sub-channel OFDM signal; and
demodulating in parallel each of the extracted sub-channel OFDM signals to produce respective base-band digital signals each associated with a respective one of the sub-channels.