Seattle spectrum measurements
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Seattle Spectrum Measurements. 900-948 MHz. Purpose for the measurements. Sweeping thru a wideband (bandwidth>900MHz), and use this wideband data to validate our wideband detection architectures and algorithms for cognitive radio

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Seattle Spectrum Measurements

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Seattle spectrum measurements

Seattle Spectrum Measurements

900-948 MHz


Purpose for the measurements

Purpose for the measurements

  • Sweeping thru a wideband (bandwidth>900MHz), and use this wideband data to validate our wideband detection architectures and algorithms for cognitive radio

  • Monitor a set of channels continuously to investigate the temporal correlation for channel modeling


Hardware settings

Hardware settings


System block diagram

System block diagram


Usrp2 rf chain

USRP2 RF Chain

(1) 50MHz-2GHz

(2) down converted to a center frequency of 126MHz

(3) 111-141MHz

(4) baseband: 0-1MHz


Data collection parameters

Data Collection Parameters


Example collection

Example Collection


Example collection1

Example Collection


Processing steps

Processing Steps

  • Initial 832 point FFT and magnitude squared

  • Receiver Characteristic Compensation

  • Harmonic and DC Clipping

  • Result – 2000x416 matrix

    • Rows are time

    • Columns are frequency


Processing diagram

Processing Diagram


Receiver compensation

Receiver Compensation

Left half multiplied by:

Right Half multiplied by:


Harmonic clipping

Harmonic Clipping

-Harmonics associates with the USRP are clipped to the noise floor


Channel four after processing

Channel Four After Processing


Channel five after processing

Channel Five After Processing


Summary table

Summary Table


Channel occupancy probability

Channel Occupancy Probability

  • Estimate the noise floor

  • Calculate threshold for occupation

  • Compare 2000x416 with threshold value

    • one for occupied and zero otherwise

  • Sum over 2000 rows and divide by 2000

  • Result – matrix representing P(i, j)

  • Repeat for different channel and subchannel sizes


Noise floor

Noise Floor

  • Channel three is unoccupied

  • Sum all of the values in channel three

  • Divide by number of values

  • Result 1.047x10^-5


Threshold calculation

Threshold Calculation

[1]


Pij across the spectrum

Pij Across The Spectrum

  • Probabilities of occupancy line up well with FCC spectrum allocation

  • Busy channels occur at paging bands 929-932MHz

  • Additional activity from 935-940 MHz (Business radios


Results

Results

  • Most activity recorded on Paging bands

  • These bands are 929-930 and 931-932 MHz


929 6125 929 6625 931 2125

929.6125, 929.6625, 931.2125

  • Bands support paging at UW and Seattle area

  • 929.6125 Services the UW medical center

  • Use 4-FSK at 6400 bps

  • Flex Protocol – standard protocol for paging in the U.S.

  • Transmission power is 2000 Watts


Unidentified paging signals

Unidentified Paging Signals

  • Unidentified Signals:

    • 931.8625

    • 929.9625

    • 931.0875

    • 931.9625

  • Exact locations inferred from FCC registration data


Calibration

Calibration


Usrp noise figure plot

USRP Noise Figure Plot

[2]


Calibration results

Calibration Results

  • New noise level about 2 dB off -174 dBm


References

References

  • Danijela Cabric, Artem Tkachenko, and Robert W. Brodersen. 2006. Experimental study of spectrum sensing based on energy detection and network cooperation. In Proceedings of the first international workshop on Technology and policy for accessing spectrum (TAPAS '06). ACM, New York, NY, USA, , Article 12 . DOI=10.1145/1234388.1234400 http://doi.acm.org/10.1145/1234388.1234400

  • http://code.ettus.com/redmine/ettus/documents/16


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