Fundamentals of Networking Lab
Seattle Spectrum Measurements
900-948 MHz
Fundamentals of Networking Lab
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
Fundamentals of Networking Lab
Hardware settings
Fundamentals of Networking Lab
System block diagram
Fundamentals of Networking Lab
USRP2 RF Chain
(1) 50MHz-2GHz
(2) down
converted to a
center frequency
of 126MHz
(3) 111-141MHz
(4) baseband: 01MHz
Fundamentals of Networking Lab
Data Collection Parameters
Parameter
Value
Frequency Range
900-950MHz
Channel Bandwidth
8 MHz
Number of Channels
6
Sample Rate
16.67 MS/s
Samples per Channel
2.048x10^9
Collection Times
20 Dec 11 15:00, 21 Dec 11 00:01,
21 Dec 11 07:00, 21 Dec 11 12:00
Total Data Recorded
3.93x10^11 Bytes
6
Fundamentals of Networking Lab
Example Collection
7
Fundamentals of Networking Lab
Example Collection
8
Fundamentals of Networking Lab
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
9
Fundamentals of Networking Lab
Processing Diagram
10
Fundamentals of Networking Lab
Receiver Compensation
-38
-36
-40
-38
-42
-40
-44
-42
-46
-44
-48
-46
-50
-48
-52
-50
-54
-52
0
50
100
150
200
250
300
0
50
100
150
200
250
Left half multiplied by:
Right Half multiplied by:
11
300
Fundamentals of Networking Lab
Harmonic Clipping
-46
-46.5
-47
-47.5
-48
-48.5
-49
X: 146
Y: -49.84
-49.5
-50
-50.5
0
50
100
150
200
250
300
-Harmonics associates with the USRP are clipped to the noise floor
12
Fundamentals of Networking Lab
Channel Four After Processing
Channel Four 924-932MHz
924
10
925
Amateur Radio Service / Location and Monitoring service
Frequency (MHz)
926
5
927
0
928
-5
Specialized Mobile Radio Service
929
Paging
-10
930
Narrowband PCS
-15
931
Paging
932
-20
0
20
40
60
Time (s)
80
100
120
13
Fundamentals of Networking Lab
Channel Five After Processing
Channel Five 932-940MHz
932
0
933
Fixed Microwave / Multiple Address
Service
934
Frequency (MHz)
-5
935
936
-10
937
938
-15
Specialized Mobile Radio Service /
Business-Industrial Land Service
939
-20
940
0
20
40
60
Time (s)
80
100
120
14
Fundamentals of Networking Lab
Summary Table
Property
Value
B/W per channel
8.33333333MHz
Channels per recording time
6
Total recording times
4
Total files
24
Time between rows of the matrix
0.0599 seconds
Total time per channel
119.81 seconds
Total time sweeps
2000
FFT size
416
Noise Floor
1.047E-5
Frequency Per Bin
20KHz
15
Fundamentals of Networking Lab
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
16
Fundamentals of Networking Lab
Noise Floor
•
•
•
•
Channel three is unoccupied
Sum all of the values in channel three
Divide by number of values
Result 1.047x10^-5
17
Fundamentals of Networking Lab
Threshold Calculation
[1]
18
Fundamentals of Networking Lab
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
19
Fundamentals of Networking Lab
Results
• Most activity recorded on Paging bands
• These bands are 929-930 and 931-932 MHz
20
Fundamentals of Networking Lab
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
21
Fundamentals of Networking Lab
Unidentified Paging Signals
• Unidentified Signals:
– 931.8625
– 929.9625
– 931.0875
– 931.9625
• Exact locations inferred from FCC
registration data
22
Fundamentals of Networking Lab
Calibration
23
Fundamentals of Networking Lab
USRP Noise Figure Plot
[2]
24
Fundamentals of Networking Lab
Calibration Results
• New noise level about 2 dB off -174 dBm
Channel Four 924-932MHz
924
-140
925
-145
Frequency (MHz)
926
-150
927
X: 46.66 Y: 928.4
Index: -172.2
RGB: 0, 0, 0.625
928
-155
929
-160
930
-165
931
-170
932
0
20
40
60
Time (s)
80
100
120
25
Fundamentals of Networking Lab
References
1.
2.
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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