Fundamentals of Networking Lab Seattle Spectrum Measurements 900-948 MHz.

Fundamentals of Networking Lab

Seattle Spectrum MeasurementsSeattle Spectrum Measurements

900-948 MHz900-948 MHz


Purpose for the measurementsPurpose 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 settingsHardware settings


System block diagramSystem block diagram


USRP2 RF ChainUSRP2 RF Chain

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


Data Collection ParametersData 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


Example CollectionExample Collection

7


Example CollectionExample Collection

8


Processing StepsProcessing 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


Processing DiagramProcessing Diagram

10


Receiver CompensationReceiver Compensation

11

0 50 100 150 200 250 300-54

-52

-50

-48

-46

-44

-42

-40

-38

0 50 100 150 200 250 300-52

-50

-48

-46

-44

-42

-40

-38

-36

Left half multiplied by:

Right Half multiplied by:


Harmonic ClippingHarmonic Clipping

12

0 50 100 150 200 250 300-50.5

-50

-49.5

-49

-48.5

-48

-47.5

-47

-46.5

-46

X: 146Y: -49.84

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


Channel Four After ProcessingChannel Four After Processing

13

Time (s)

Fre

quen

cy (

MH

z)

Channel Four 924-932MHz

0 20 40 60 80 100 120

924

925

926

927

928

929

930

931

932 -20

-15

-10

-5

0

5

10

Paging

Paging

Narrowband PCS

Specialized Mobile Radio Service

Amateur Radio Service / Location and Monitoring service


Channel Five After ProcessingChannel Five After Processing

14

Time (s)

Fre

quen

cy (

MH

z)

Channel Five 932-940MHz

0 20 40 60 80 100 120

932

933

934

935

936

937

938

939

940 -20

-15

-10

-5

0

Specialized Mobile Radio Service / Business-Industrial Land Service

Fixed Microwave / Multiple AddressService


Summary TableSummary Table

15

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


Channel Occupancy ProbabilityChannel 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


Noise FloorNoise Floor

• Channel three is unoccupied

• Sum all of the values in channel three

• Divide by number of values

• Result 1.047x10^-5

17


Threshold CalculationThreshold Calculation

18

[1]


Pij Across The SpectrumPij 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


ResultsResults

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

20


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

21


Unidentified Paging SignalsUnidentified Paging Signals

• Unidentified Signals:– 931.8625 – 929.9625 – 931.0875 – 931.9625

• Exact locations inferred from FCC registration data

22


CalibrationCalibration

23


USRP Noise Figure PlotUSRP Noise Figure Plot

24

[2]


Calibration ResultsCalibration Results

• New noise level about 2 dB off -174 dBm

25

X: 46.66 Y: 928.4Index: -172.2RGB: 0, 0, 0.625

Time (s)

Fre

quen

cy (

MH

z)

Channel Four 924-932MHz

0 20 40 60 80 100 120

924

925

926

927

928

929

930

931

932

-170

-165

-160

-155

-150

-145

-140


ReferencesReferences1. 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

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

26

Fundamentals of Networking Lab Seattle Spectrum Measurements 900-948 MHz.

Documents

Transcript of Fundamentals of Networking Lab Seattle Spectrum Measurements 900-948 MHz.