Orthogonal signal demodulation

• US 9,660,855 B2
• Filed: 03/15/2013
• Issued: 05/23/2017
• 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
• Primary Examiner(s): Marcelo, Melvin
• Assistant Examiner(s): Solinsky, Peter G
• Application Number:
  US13/841,313
• Publication Number:
  US 20140003547A1
• Time in Patent Office: 1,530 Days
• Field of Search: 370208
• 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 demodulation of a transmitted orthogonal frequency multiplexing (OFDM) signal, comprising:

a down converter including an oscillator for down converting time domain symbols from the transmitted OFDM signal, the OFDM signal including a plurality of stream-blocks of adjacent orthogonal subcarriers, each of the adjacent orthogonal subcarriers having different respective center frequencies;

an analog to digital converter, separate from the down converter, for sampling the down converted time domain symbols of the OFDM signal from the down converter;

a low pass filter, separate from the down converter, for filtering the sampled OFDM signal from the analog to digital converter, the low pass filter having a pass band that matches a frequency range of one stream-block of the plurality of stream-blocks;

a serial to parallel converter for converting a serial data stream from the low pass filter into a parallel data streams of adjacent orthogonal subcarriers within the one stream-block of the plurality of stream blocks;

a Fast Fourier Transform device for transforming parallel data streams from the serial to parallel converter into frequency domain data, and for discarding frequency domain data included in the one stream-block corresponding to center frequencies different than a selected center frequency; and

a decoder for decoding frequency domain data from the Fast Fourier Transform device corresponding to the selected center frequency of the adjacent orthogonal sub carriers within the one-stream block.

2. The receiver of claim 1, wherein the low pass filter includes a pass band that is adjustable in response to a control signal.

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

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

5. The receiver of claim 1, wherein the oscillator is capable of providing a frequency that is different from a radio frequency center frequency from an up conversion of the transmitted OFDM signal.

6. The receiver of claim 1, further comprising an inverse fast Fourier transform device for converting frequency domain symbols from the decoder into time domain symbols for transmission.

7. The receiver of claim 6, wherein a number of the time domain symbols converted by the inverse fast Fourier transform is greater than a number of time domain symbols transformed into frequency domain symbols by the Fast Fourier Transform device.

8. A method for demodulating a transmitted orthogonal frequency multiplexing (OFDM) signal, comprising the steps of:

down converting time domain symbols from the transmitted OFDM signal, the OFDM signal including a plurality of stream-blocks of adjacent orthogonal subcarriers, each of the adjacent orthogonal subcarriers having different respective center frequencies;

sampling, after the step of down converting, the down converted time domain symbols of the OFDM signal by an analog to digital converter;

filtering, after the step of sampling, the sampled OFDM signal through a low pass filter having a pass band that matches a frequency range of one stream-block of the plurality of stream-blocks;

converting a serial data stream from the low pass filter into parallel data streams of adjacent orthogonal subcarriers within the one stream-block of the plurality of stream blocks;

transforming, by a Fast Fourier Transform device, the parallel data streams into frequency domain data;

discarding frequency domain data from the Fast Fourier Transform device corresponding to center frequencies different than a selected center frequency;

decoding frequency domain data corresponding to the selected center frequency of the adjacent orthogonal sub carriers within the one-stream block.