ORTHOGONAL SIGNAL DEMODULATION

• US 20140003547A1
• Filed: 03/15/2013
• Published: 01/02/2014
• Est. Priority Date: 06/29/2012
• Status: Active Grant

• Current Assignee: Cable Television Laboratories Incorporated
• Original Assignee: Cable Television Laboratories Incorporated
• Inventors: Williams, Thomas H., Campos, Luis Alberto
• Granted Patent: US 9,660,855 B2
• Time in Patent Office: Days
• US Class Current: 375/267
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01
• CPC Class Codes: H04L 27/265 Fourier transform demodulators, e.g. fast Fourier transform [FFT] or discrete Fourier transform [DFT] demodulators H04L27/26524 takes precedence
• CPC Class Codes: H04L 27/26526 with inverse FFT [IFFT] or inverse DFT [IDFT] demodulators, e.g. standard single-carrier frequency-division multiple access [SC-FDMA] receiver or DFT spread orthogonal frequency division multiplexing [DFT-SOFDM]

Abstract

A modulation transmission technique comprises placing orthogonal subcarriers across an arbitrary-wide band of frequencies without a fixed pre-defined center frequency. Receivers demodulate only the sub-group of subcarriers in which they are to receive data. Thus a broadcast service with many audio programs could send signals across a wide band and receivers would only demodulate the audio channel that the user or users wanted to hear. This saves energy which is important for battery powered devices. A transform bandwidth smaller than the transform bandwidth of the transmitter is used that encompasses the receivers pass band, plus the 2 transition bands (upper and lower) of the linear filter. This technique maintains orthogonality between subcarriers. The subcarriers in the pass band are utilized and the subcarriers in the transition bands are discarded. The orthogonal subcarriers may include both orthogonal frequency division multiplexed and pulse amplitude modulated signals. A notch filter may be included in the receiver to remove unwanted non-orthogonal signals such as a television signal or other interference.

Claims

1. A receiver for deriving one of a plurality of stream-blocks of orthogonal subcarriers from time domain symbols from at least one transmitter, said one stream block assigned to a particular data pipe or one or more users, said at least one transmitter having performed inverse Fast Fourier Transform of the plurality of stream-blocks of orthogonal subcarriers to time domain symbols using a transform size that is large enough to contain all of the subcarriers in the plurality of stream-blocks and having performed up conversion of such time domain symbols to a radio frequency center frequency, said receiver comprising:

a converter including an oscillator for down converting said up converted time domain symbols;

a low pass filter that filters the down converted time domain symbols, said low pass filter passing said one stream-block of subcarriers assigned to the particular data pipe, user or users and attenuating subcarriers that are not the subcarriers in such stream-block; and

a Fast Fourier Transform device that transforms said subcarriers that passed the low pass filter from time domain to frequency domain using a transform size that is smaller than the transform size of the inverse Fast Fourier Transform at the at least one transmitter.

2. The receiver of claim 1, said filter having a pass band that matches the frequencies of the stream-block of subcarriers assigned to the particular data pipe, user or users, one or more transition band(s), and a stop band.

3. The receiver of claim 2, further comprising a decoder that decodes subcarriers in said pass band and discards subcarriers in the transition band(s).

4. The receiver of claim 2, wherein subcarriers assigned to at least some of the stream blocks other than the one stream-block of subcarriers assigned to the particular data pipe, user or users fall into said stop band.

5. The receiver of claim 1, wherein said low pass filter has a pass band that is adjustable in response to a control signal.

6. The receiver of claim 1, wherein the transform size of said Fast Fourier Transform device is adjustable in response to a control signal.

7. The receiver of claim 1, wherein a center frequency of the oscillator of the converter is adjustable in response to a control signal.

8. The receiver of claim 1, said oscillator providing a frequency that is different from said radio frequency center frequency of the up conversion in the transmitter.

9. A receiver according to claim 1, wherein said one stream block includes adjacent subcarriers.

13. The group of receivers of claim 9, wherein the Fast Fourier Transform devices of said receivers have different transform sizes.

10. A group of receivers, each receiver for deriving one of a plurality of stream-blocks of orthogonal subcarriers from time domain symbols from at least one transmitter, said one stream block assigned to a particular data pipe or one or more users, said at least one transmitter having performed inverse Fast Fourier Transform of the plurality of stream-blocks of orthogonal subcarriers to time domain symbols using a transform size that is large enough to contain all of the subcarriers in the plurality of stream-blocks and having performed up conversion of such time domain symbols to a radio frequency center frequency, each of said receivers in the group comprising:

a converter including an oscillator for down converting said up converted time domain symbols;

a low pass filter that filters the down converted time domain symbols, said low pass filter passing said one stream-block of subcarriers assigned to the particular data pipe, user or users and attenuating subcarriers that are not the subcarriers in such stream-block; and

a Fast Fourier Transform device that transforms said subcarriers that passed the low pass filter from time domain to frequency domain using a transform size that is smaller than the transform size of the inverse Fast Fourier Transform at the at least one transmitter, wherein at least some of said plurality of stream-blocks of orthogonal subcarriers are simultaneously derived by the group of receivers.

11. The group of receivers of claim 10, wherein center frequencies of the oscillators in said receivers are different.

12. The group of receivers of claim 10, wherein the low pass filters of said receivers have different pass bands and bandwidths.

14. A receiver for deriving one of a plurality of stream-blocks of orthogonal subcarriers from time domain symbols and a signal or interference at a frequency not orthogonal to said stream-blocks of orthogonal subcarriers received from at least one transmitter, said at least one transmitter having performed inverse Fast Fourier Transform of the plurality of stream-blocks of subcarriers and said signal to time domain symbols using a transform size that is large enough to contain all of the subcarriers in the plurality of stream-blocks and said signal and having performed up conversion of such time domain symbols and said signal, said receiver comprising:

a converter including an oscillator for down converting said up converted time domain symbols and said signal;

a first low pass filter that filters the down converted time domain symbols and said signal;

a second filter that has a stop band containing the frequency of the signal or interference that is not orthogonal to said stream-blocks of orthogonal subcarriers; and

a Fast Fourier Transform device that transforms said stream-blocks that passed the low pass filter and the second filter from time domain to frequency domain.

15. A receiver for deriving one of a plurality of stream-blocks of subcarriers from time domain symbols from at least one transmitter, said at least one transmitter having performed inverse Fast Fourier Transform of the plurality of stream-blocks of subcarriers to time domain symbols using a transform size that is large enough to contain all of the subcarriers in the plurality of stream-blocks and having performed up conversion of such time domain symbols to a radio frequency center frequency, wherein the stream-blocks of subcarriers include pulse amplitude modulated signals and orthogonal frequency division multiplexed signals, said receiver comprising:

a converter including an oscillator for down converting said up converted time domain symbols;

a low pass filter that filters the down converted time domain symbols;

a Fast Fourier Transform device that separates and transforms said pulse amplitude modulated signals and orthogonal frequency division multiplexed signals that passed the low pass filter from time domain to frequency domain; and

an inverse Fast Fourier Transform device that transforms the pulse amplitude modulated signals from frequency domain to time domain.

16. A method for deriving one of a plurality of stream-blocks of orthogonal subcarriers from time domain symbols from at least one transmitter, said one stream block assigned to a particular data pipe or one or more users, said at least one transmitter having performed inverse Fast Fourier Transform of the plurality of stream-blocks of orthogonal subcarriers to time domain symbols using a transform size that is large enough to contain all of the subcarriers in the plurality of stream-blocks and having performed up conversion of such time domain symbols to a radio frequency center frequency, said method comprising:

down converting said up converted time domain symbols;

low pass filtering the down converted time domain symbols, said filtering passing said one stream-block of subcarriers assigned to the particular data pipe or user and attenuating subcarriers that are not the subcarriers in such stream-block; and

Fast Fourier transforming said subcarriers that passed the low pass filter from time domain to frequency domain using a transform size that is smaller than the transform size of the inverse Fast Fourier Transform at the at least one transmitter.

17. A method for deriving one or more stream-blocks of orthogonal subcarriers from time domain symbols and a signal or interference at a frequency not orthogonal to said stream-blocks of orthogonal subcarriers received from at least one transmitter, said at least one transmitter having performed inverse Fast Fourier Transform of the plurality of stream-blocks of subcarriers and said signal to time domain symbols using a transform size that is large enough to contain all of the subcarriers in the plurality of stream-blocks and said signal and having performed up conversion of such time domain symbols and said signal, said method comprising:

down converting said up converted time domain symbols and said signal;

low pass filtering the down converted time domain symbols and said signal;

removing from the down converted time domain symbols the signal or interference that is not orthogonal to said stream-blocks of orthogonal subcarriers; and

Fast Fourier transforming said filtered down converted time domain symbols to derive said one or more stream-blocks.

18. A method for deriving one or more stream-blocks of subcarriers from time domain symbols from at least one transmitter, said at least one transmitter having performed inverse Fast Fourier Transform of the plurality of stream-blocks of subcarriers to time domain symbols using a transform size that is large enough to contain all of the subcarriers in the plurality of stream-blocks and having performed up conversion of such time domain symbols to a radio frequency center frequency, wherein the stream-blocks of subcarriers include pulse amplitude modulated signals and orthogonal frequency division multiplexed signals, said method comprising:

down converting said up converted time domain symbols;

low pass filtering the down converted time domain symbols;

Fast Fourier transforming and separating said filtered pulse amplitude modulated signals and said filtered orthogonal frequency division multiplexed signals; and

inverse Fast Fourier transforming the pulse amplitude modulated signals from frequency domain to time domain.