SYSTEM AND METHOD FOR DETECTING TEMPORARILY UNUSED BANDWIDTH IN THE RF SPECTRUM

• US 20090268830A1
• Filed: 05/17/2007
• Published: 10/29/2009
• Est. Priority Date: 05/18/2006
• Status: Active Grant

• Current Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Birru, Dagnachew, Turkenich, Gennady
• Granted Patent: US 8,588,339 B2
• Time in Patent Office: Days
• US Class Current: 375/260
• CPC Class Codes: H04W 16/14 Spectrum sharing arrangements between different networks

Abstract

A method (200) and system (300) for detecting temporarily available bandwidth in a frequency band: select (205) a channel in the frequency band; measure (210) an energy received in the selected channel; compare (215) the measured energy to a first threshold; when the measured energy exceeds the first threshold, determine that the channel is unavailable (220) for transmission, otherwise determine (225) that the channel is available for transmission; correlate (255) a signal received in the channel with a known feature of a signal conforming to a particular transmission format; compare (260) the correlation result to a second threshold; when the correlation result in the channel exceeds the second threshold, determine (265) that a signal conforming to the particular transmission format is present in the channel, otherwise determine (270) that the signal conforming to the particular transmission format is not present in the channel.

Claims

1. A method (200) of detecting temporarily available channels in a frequency band, comprising:

(a) selecting (205) a channel among a plurality of channels in a frequency band;

(b) measuring (210) an energy received in the selected channel;

(c) comparing (215) the measured energy received in the selected channel to a threshold established for the selected channel;

(d) when the measured energy received in the selected channel exceeds the threshold established for the selected channel, determining (220) the selected channel is unavailable for transmission, otherwise determining (225) that the selected channel is available for transmission;

(e) repeating steps (a) through (d) (205-225) for each of a plurality of channels in the frequency band (230);

(f) selecting (250) one of the channels that was determined in step (d) to be unavailable;

(g) correlating (255) a signal received in the selected unavailable channel with a known feature of a signal conforming to a particular transmission format;

(h) comparing (260) the correlation result to a second threshold;

(i) when the correlation result in the selected unavailable channel exceeds the second threshold, determining (265) that a signal conforming to the particular transmission format is present in the selected unavailable channel, otherwise determining (270) that the signal conforming to the particular transmission format is not present in the selected unavailable channel; and

(j) repeating steps (f) through (i) (250-270) for each channel that was determined in step (d) (220) to be unavailable.

2. The method (200) of claim 1, wherein the first threshold is a constant multiplied by an expected input noise energy in the selected channel in the absence of an input signal.

3. The method (200) of claim 2, wherein the expected input noise energy in the selected channel in the absence of an input signal is determined by tuning to a channel where it is known that no signal is present.

4. The method (200) of claim 2, wherein the constant is selected to achieve a desired probability of missed detection, a desired probability of false alarm, and desired probability of detection.

5. The method (200) of claim 1, wherein measuring the energy received in the selected channel comprises averaging the received energy over a selected interval.

6. The method (200) of claim 1, wherein measuring the energy received in the selected channel comprises:

digitizing a signal received in the selected channel;

downconverting the signal to baseband;

passing the signal through a square root raised cosine filter; and

squaring the signal output from the square root raised cosine filter.

7. The method (200) of claim 1, wherein the particular transmission format is one of an 8-VSB transmission format and a Digital Video Broadcast-Terrestrial (DVB-T) transmission format.

8. The method (200) of claim 7, wherein the known feature of a signal conforming to the particular transmission format is one of a PN511 pseudo-random sequence and a cyclic prefix of an orthogonal frequency division multiplex (OFDM) signal.

9. The method (200) of claim 1, wherein step (e) (230) is performed prior to steps (f) through (j) (250-270).

10. The method (200) of claim 1, wherein step (e) (230) is performed after steps (f) through (i) (250-270).

11. The method of claim 1, further comprising repeating steps (f) through (j) (250-270) for a second particular transmission format.

12. A system (300) for detecting temporarily available bandwidth in a frequency band, comprising:

a receiver front-end (310) adapted to select a portion of spectrum in a frequency band;

an energy detector (350) adapted to measure energy present in the selected portion of spectrum;

a first comparator (360) adapted to compare the measured energy in the selected portion of spectrum to a threshold established for the selected portion of spectrum;

a correlator (380) adapted to correlate a signal received in the selected portion of spectrum with a known feature of a signal conforming to a particular transmission format; and

a second comparator (390) adapted to compare the correlation result to a second threshold.

13. The system (300) of claim 12, wherein the receiver front-end (310) comprises:

an RF tuner (315) adapted to tune-in the selected channel;

an analog-to-digital converter (ADC) (320) adapted to digitize an output of the RF tuner for the selected channel;

a downconverter (325) adapted to downconvert the digitized tuner output to baseband; and

a band-limiting filter (330) adapted to filter the digitized baseband signal.

14. The system (300) of claim 12, wherein the threshold established for the selected portion of spectrum is a constant multiplied by an expected input noise energy in the selected portion of spectrum in the absence of an input signal.

15. The system (300) of claim 12, wherein the energy detector (350) measures the energy received in the selected portion of spectrum by averaging the received energy over a selected number of samples.

16. The system (300) of claim 12, wherein the correlator (380) is adapted to correlate the signal received in the selected portion of spectrum with at least one of:

a PN511 pseudo-random sequence of a signal conforming to an 8-VSB transmission format, and a cyclic prefix of an orthogonal frequency division multiplex (OFDM) signal.

17. A method (200) of detecting temporarily available bandwidth in a frequency band, comprising:

(a) selecting (205) a portion of spectrum in a frequency band;

(b) measuring (210) an energy received in the selected portion of spectrum;

(c) comparing (215) the measured energy received in the selected portion of spectrum to a threshold established for the selected portion of spectrum;

(d) when the measured energy received in the selected portion of spectrum exceeds the threshold established for the selected portion of spectrum, determining (220) that the selected portion of spectrum is unavailable for transmission, otherwise determining (225) that the selected portion of spectrum is available for transmission;

(e) correlating (255) a signal received in the selected portion of spectrum with a known feature of a signal conforming to a particular transmission format;

(f) comparing (260) the correlation result to a second threshold;

(g) when the correlation result in the selected portion of spectrum exceeds the second threshold, determining (265) that a signal conforming to the particular transmission format is present in the selected portion of spectrum, otherwise determining (270) that the signal conforming to the particular transmission format is not present in the selected portion of spectrum; and

(h) repeating steps (a) through (g) for each of a plurality of spectrum portions spanning the frequency band.

18. The method (200) of claim 17, wherein the threshold established for the selected portion of spectrum is a constant multiplied by an expected input noise energy in the selected portion of spectrum in the absence of an input signal.

19. The method (200) of claim 17, wherein the known feature of a signal conforming to the particular transmission format is one of a PN511 pseudo-random sequence and a cyclic prefix of an orthogonal frequency division multiplex (OFDM) signal.

20. The method (200) of claim 17, further comprising repeating steps (e) through (h) (255-265) for a second particular transmission format.