1. Seattle Spectrum Measurements 900-948 MHz

2. 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

3. Hardware settings

4. System block diagram

5. USRP2 RF Chain (1) 50MHz-2GHz (2) down converted to a center frequency of 126MHz (3) 111-141MHz (4) baseband: 0-1MHz

6. Data Collection Parameters

7. Example Collection

8. Example Collection

9. 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

10. Processing Diagram

11. Receiver Compensation Left half multiplied by: Right Half multiplied by:

12. Harmonic Clipping -Harmonics associates with the USRP are clipped to the noise floor

13. Channel Four After Processing

14. Channel Five After Processing

15. Summary Table

16. 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

17. Noise Floor • Channel three is unoccupied • Sum all of the values in channel three • Divide by number of values • Result 1.047x10^-5

18. Threshold Calculation [1]

19. 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

20. Results • Most activity recorded on Paging bands • These bands are 929-930 and 931-932 MHz

21. 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

22. Unidentified Paging Signals • Unidentified Signals: • 931.8625 • 929.9625 • 931.0875 • 931.9625 • Exact locations inferred from FCC registration data

23. Calibration

24. USRP Noise Figure Plot [2]

25. Calibration Results • New noise level about 2 dB off -174 dBm

26. 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