Method, apparatus and computer program for sensing spectrum in a cognitive radio environment

• US 20090253376A1
• Filed: 04/07/2008
• Published: 10/08/2009
• Est. Priority Date: 04/07/2008
• Status: Active Grant

• Current Assignee: Nokia Technologies Oy (Nokia Corporation)
• Original Assignee: Nokia Corporation
• Inventors: Kukkonen, Janne, Ikonen, Petri, Parssinen, Aarno
• Granted Patent: US 8,718,559 B2
• Time in Patent Office: Days
• US Class Current: 455/62
• CPC Class Codes: H04W 16/14 Spectrum sharing arrangements between different networks
• CPC Class Codes: H04W 24/00 Supervisory, monitoring or testing arrangements
• CPC Class Codes: H04W 72/02 Selection of wireless resources by user or terminal
• CPC Class Codes: H04W 72/542 using measured or perceived quality

Abstract

To find frequency slots over which a cognitive radio can send an opportunistic transmission, a wideband spectrum is searched with a lower resolution to identify bandwidth slices having low or no signal levels. The identified bandwidth slices are searched with a higher resolution and candidate frequency slices are selected as those bandwidth slices having the least signal levels after the higher resolution searching, and ranked from the lowest signal level to the highest. A spectrum detection algorithm is executed on the selected candidate frequency slices in the order of the rank until it is decided that one of them has sufficiently free spectrum. A transmission is then opportunistically sent on the decided candidate frequency slice. Ongoing to the searching, intermittent signals are detected and a band about them is searched with the lower resolution to determine if the band about the detected intermittent signal is an identified bandwidth slice. Various techniques are shown for how the fine search is conducted.

Claims

1. A method comprising:

searching a wideband spectrum with a first resolution to identify bandwidth slices having low or no signal levels;

searching the identified bandwidth slices with a second resolution that is higher than the first resolution and selecting as candidate frequency slices those bandwidth slices having least signal levels after the second resolution searching;

executing a spectrum detection algorithm on at least one of the selected candidate frequency slices and deciding that it has sufficiently free spectrum; and

transmitting in the decided candidate frequency slice.

2. The method of claim 1 further comprising:

after searching the identified bandwidth slices with the second resolution, ranking the candidate frequency slices in priority from lowest to highest signal level;

and wherein executing the spectrum detection algorithm is on the ranked candidate frequency slices in the order of the rank until it is decided that one of the candidate frequency slices has sufficiently free spectrum.

3. The method of claim 1, wherein searching the identified bandwidth slices with the second resolution comprises narrowing a frequency range of at least one of the identified bandwidth slices.

4. The method of claim 1, wherein transmitting comprises opportunistically transmitting in the decided candidate frequency slice.

5. The method of claim 1, wherein searching the identified bandwidth slices with the second resolution comprises at least two of the set:

narrowing a filter bandwidth;

tuning a local oscillator frequency;

increasing analog to digital converter resolution while reducing bandwidth of one of the identified bandwidth slices;

changing sampling rate at an analog to digital converter;

tuning fast Fourier transform parameters; and

canceling radio frequency interferers.

6. The method of claim 1 wherein searching the wideband spectrum with the first resolution is done faster than searching the identified bandwidth slices with the second resolution.

7. The method of claim 1, further comprising controlling radio frequency gain of the search of the wideband spectrum and the search of the identified bandwidth slices with a radio frequency envelope detector to reduce dynamic range of analog to digital conversions done in the said searches.

8. The method of claim 1, wherein searching the wideband spectrum with the first resolution is executed in parallel over multiple frequency bins that span the wideband spectrum.

9. The method of claim 1, further comprising:

detecting intermittent signals with an envelope detector and searching a band about any detected intermittent signal with the first resolution to determine if the band about the detected intermittent signal is an identified bandwidth slice.

10. The method of claim 1 executed by a handheld mobile terminal.

11. An apparatus comprising:

a coarse power detector configured to search a wideband spectrum with a first resolution to identify bandwidth slices having low or no signal levels;

a fine power detector configured to search the identified bandwidth slices with a second resolution that is higher than the first resolution and to select as candidate frequency slices those bandwidth slices having least signal levels after the second resolution searching;

a spectrum detector configured to execute a spectrum detection algorithm on at least one of the selected candidate frequency slices;

a processor configured to decide that the at least one of the selected candidate frequency slices has sufficiently free spectrum; and

a transmitter configured to transmit in the decided candidate frequency slice.

12. The apparatus of claim 11, wherein:

the processor is configured to rank the candidate frequency slices in priority from lowest to highest signal level;

the spectrum detector is configured to execute the spectrum detection algorithm on the ranked candidate frequency slices in the order of the rank until the processor decides that one of the candidate frequency slices has sufficiently free spectrum.

13. The apparatus of claim 11, wherein the fine power detector is configured to narrow a frequency range of at least one of the identified bandwidth slices while searching the identified bandwidth slices.

14. The apparatus of claim 11, wherein the transmitter is configured to opportunistically transmit in the decided candidate frequency slice.

15. The apparatus of claim 11, wherein the fine power detector is configured to search the identified bandwidth slices with the second resolution by at least two of the set:

narrowing a filter bandwidth;

tuning a local oscillator frequency;

increasing analog to digital converter resolution while reducing bandwidth of one of the identified bandwidth slices;

changing sampling rate at an analog to digital converter;

tuning fast Fourier transform parameters; and

canceling radio frequency interferers.

16. The apparatus of claim 11, wherein the coarse power detector is configured to search the wideband spectrum with the first resolution faster than the fine power detector searches the identified bandwidth slices with the second resolution.

17. The apparatus of claim 11, further comprising a radio frequency envelope detector configured to reduce dynamic range of analog to digital conversions done within the coarse power detector and within the fine power detector by controlling radio frequency gain of the coarse power detector and of the fine power detector.

18. The apparatus of claim 11, wherein the coarse power detector comprises circuitry that executes in parallel the first resolution search over frequency bins of the wideband spectrum.

19. The apparatus of claim 11, further comprising:

an envelope detector configured to detect intermittent signals; and

wherein the coarse power detector is configured to search frequency bands about the detected intermittent signals with the first resolution to determine if the band about the detected intermittent signal is an identified bandwidth slice.

20. The apparatus of claim 11, the apparatus comprising a handheld mobile terminal.

21. The apparatus of claim 11, the apparatus comprising an integrated circuit.

22. A computer readable memory embodying a program of machine-readable instructions executable by a digital data processor to perform actions directed toward searching spectrum for a frequency band available for transmission, the actions comprising:

searching a wideband spectrum with a first resolution to identify bandwidth slices having low or no signal levels;

searching the identified bandwidth slices with a second resolution that is higher than the first resolution and selecting as candidate frequency slices those bandwidth slices having least signal levels after the second resolution searching; and

executing a spectrum detection algorithm on at least one of the selected candidate frequency slices and deciding that it has sufficiently free spectrum.

23. The computer readable memory of claim 22, further comprising:

after searching the identified bandwidth slices with the second resolution, ranking the candidate frequency slices in priority from lowest to highest signal level;

and wherein executing the spectrum detection algorithm is on the ranked candidate frequency slices in the order of the rank until it is decided that one of the candidate frequency slices has sufficiently free spectrum.

24. The computer readable memory of claim 22, wherein searching the identified bandwidth slices with a second resolution comprises narrowing a frequency range of at least one of the identified bandwidth slices.

25. The computer readable memory of claim 22, further comprising opportunistically transmitting in the decided candidate frequency slice.

26. The computer readable memory of claim 22, wherein searching the identified bandwidth slices with the second resolution comprises at least two of the set:

narrowing a filter bandwidth;

tuning a local oscillator frequency;

increasing analog to digital converter resolution while reducing bandwidth of one of the identified bandwidth slices;

changing sampling rate at an analog to digital converter;

tuning fast Fourier transform parameters; and

canceling radio frequency interferers.

27. The computer readable memory of claim 22, further comprising controlling radio frequency gain of the search of the wideband spectrum and the search of the identified bandwidth slices with a radio frequency envelope detector to reduce dynamic range of analog to digital conversions done in the said searches.

28. The computer readable memory of claim 22, wherein searching the wideband spectrum with the first resolution is executed in parallel over multiple frequency bins that span the wideband spectrum.

29. The computer readable memory of claim 22, further comprising:

detecting intermittent signals with an envelope detector and searching a band about any detected intermittent signal with the second resolution to determine if the band about the detected intermittent signal is an identified bandwidth slice.

30. An apparatus comprising:

first searching means for searching a wideband spectrum with a first resolution to identify bandwidth slices having low or no signal levels;

second searching means for searching the identified bandwidth slices with a second resolution that is higher than the first resolution and selecting as candidate frequency slices those bandwidth slices having least signal levels after the second resolution searching;

detect means for detecting spectrum of at least one of the selected candidate frequency slices;

processing means for deciding that the at least one of the selected candidate frequency slices has sufficiently free spectrum; and

transmit means for transmitting in the decided candidate frequency slice.