Fast method for wideband spectrum sensing

• US 9,635,508 B2
• Filed: 08/07/2014
• Issued: 04/25/2017
• Est. Priority Date: 01/14/2014
• Status: Active Grant

• Current Assignee: United States Of America As Represented By The Secretary Of The Army (Government of the United States of America)
• Original Assignee: The United States Of America As Represented By The Secretary Of The Army
• Inventors: Martone, Anthony F., Ranney, Kenneth I.
• Primary Examiner(s): Patel, Parth
• Application Number:
  US14/453,761
• Publication Number:
  US 20150201420A1
• Time in Patent Office: 992 Days
• Field of Search: 370252
• CPC Class Codes: H04L 27/0006 Assessment of spectral gaps suitable for allocating digitally modulated signals, e.g. for carrier allocation in cognitive radio for spectrum sharing between different networks H04W16/14
• CPC Class Codes: H04W 4/025 using location based information parameters

Abstract

Embodiments of the present invention relate cognitive radar and RF technologies, and more particularly, to spectrum sensing processing for rapidly monitoring the RF spectrum for channel availability and activity. The goal is to find and use unoccupied RF channels to broadcast and receive information. According to one embodiment, a method for analyzing a received RF signal to determine unused channels, or frequencies, therein, comprises: analyzing a received RF signal to determine anchor points that represent high energy frequency locations; calculating distances between the determined anchor points; identifying and eliminating clusters or isolated anchor points defined as a high energy region of interference based on the calculated distances; and selecting at least one remaining unoccupied frequency for transmitting or receiving a RF signal. The method may further include performing an optional quality or risk assessment on remaining frequencies of the waveform, and eliminating high risk frequencies from consideration in some instances.

Claims

1. A method for analyzing a received RF signal to determine unused channels, or frequencies, therein, the method comprising:

analyzing a RF signal received by an antenna to determine anchor points that represent high energy frequency locations;

calculating distances in terms of frequency between the determined adjacent anchor points;

identifying and eliminating clusters of anchor points in which the calculated distances indicate an adjacent high energy region of interference and any isolated anchor point; and

selecting at least one remaining unoccupied frequency for transmitting or receiving a RF signal,

wherein the at least one remaining unoccupied frequency available for selection is unknown before the received RF signal is analyzed.

2. The method of claim 1, wherein (i) any unused determined frequency is substantially devoid of noise;

and (ii) the surrounding energy of the unused determined frequency is minimal.

3. The method of claim 1, wherein prior to determining anchor points, (i) time-domain data of the received RF signal is converted to the frequency domain via the fast Fourier transform (FFT);

and (ii) energy estimates are determined for the frequency domain samples.

4. The method of claim 1, wherein the anchor points are determined using a binary hypothesis test.

5. The method of claim 4, wherein the binary hypothesis test is defined as follows:

6. The method of claim 4, wherein distances between the anchor points are calculated as d_i=I_i+1−

I_i forming the set D={d₁, d₂, . . . d<sub>L−

1</sub>}.

7. The method of claim 6, wherein, a cluster is defined as a sequence of anchor points, {I_i, I_i+1, . . . I_i+V}⊂

I, whose distances satisfy {d_i≦

ε

, d_i+1≦

ε

, . . . d_j≦

ε

}, where ε

is the maximum distance needed to form a cluster, and V<

L.

8. The method of claim 7, wherein eliminating the clusters comprises removing the clusters thereby forming the set of groups G={G₁, . . . , G_W}, where each group is separated by a gap created by the deleted indices, and the group G_i={g_i,1, . . . g_i,Z(i)}⊂

G is defined as a set of Z(i) sequential indices.

9. The method of claim 1, further comprising:

performing a risk assessment on remaining frequencies of the input RF signal and eliminating high risk frequencies from consideration.

10. The method of claim 9, wherein risk is assessed by techniques selected from the group consisting:

defining a guard band to provide a buffer for anticipated sidelode interference from the edge of an adjacent eliminated cluster or isolated anchor points sufficient, and then determining if power levels in the guard band are above or below a threshold;

determining if power levels at or near the edge of an adjacent eliminated cluster or isolated anchor point is above or below a threshold;

determining if the average power level for unoccupied frequencies is above or below a threshold; and

determining if the bandwidth between adjacent eliminated clusters or isolated anchor points is above or below a threshold.

11. The method of claim 10, further comprising selecting a remaining frequency having a minimal risk assessment.

12. The method of claim 1, wherein the overall computational complexity of the entire method is of the order of magnitude of the number of frequencies of the received RF signal which were considered.

13. A system for analyzing a received RF signal to determine unused channels, or frequencies, therein, the system having at least one processor and one or more modules executable by the at least one processor, and comprising:

a fast spectrum sensing module configured to execute the method of claim 1.

14. The system of claim 13, further comprising:

an antenna which receives an RF signal;

a front-end module configured to process the received RF signal;

an analog digital converter (ADC) configured to digitize the processed signal;

a discrete Fourier transform (DFT) module configured to transform the digitized signal into a set of frequency domain samples; and

an estimate power module configured to estimate the power of the signal at various frequencies.

15. The system of claim 13, wherein power samples X=={x₁, . . . x_N} corresponding to frequencies f={f₁, . . . f_N} are inputs to the fast spectrum sensing module.

16. The system of claim 14, wherein the received signal is processed by the front-end module with a center frequency f_c, having a bandwidth B.

17. The system of claim 14, wherein the processed signal from the front end module is digitized using the ADC with a sampling frequency F_s and a dynamic range P_dr to generate a resulting set of N real, time-domain samples as y={y₁, . . . y_N}.

18. The system of claim 14, wherein the digitized signal from the ADC is transformed to the frequency domain in the DFT module implementing a discrete Fourier transform function which results in a set of frequency domain samples in the fundamental band, defined as η

={η

₁, . . . η

_N} which correspond to the frequencies f={f₁, . . . f_N}.

19. The system of claim 14, wherein the power of the signal at various frequencies f_k is estimated in the estimate power module as x_k=|η

_k|², where f_kε

f, in which f is a frequency, η

is a fundamental band, and k is a particular frequency value or frequency bin of interest.

20. A non-transitory computer-readable storage medium having computer-readable instructions, that when executed by a processor, implement the method for analyzing a received RF signal to determine unused channels, or frequencies, of claim 1.