January 2004
Bill Byrnes, Shared Spectrum Co.
doc.: IEEE 802.18-04-0004-00-000
Submission
Frequency Agile Spectrum Access Technologies
This Presentation was originally made to anFCC Workshop on Cognitive Radios
May 19, 2003 by one of Bill’s colleagues.
(Bill was kind enough to share this information with 802.18 SG1 in the interest of promoting discussion.)
January 2004
Bill Byrnes, Shared Spectrum Co.
doc.: IEEE 802.18-04-0004-00-000
Submission
Agenda
• Requirements
• Spectrum occupancy characteristics– Significant amount of “low hanging fruit”
• Spectrum access methods– Listen-Before Talk
• “TDMA” spectrum
• Broadcast spectrum
– Probe
– Geo-location/database
January 2004
Bill Byrnes, Shared Spectrum Co.
doc.: IEEE 802.18-04-0004-00-000
Submission
Frequency Agile Radio Requirements
• Create insignificant interference – Secondary operation with minimal requirement for coordination
with primary system licensees– Unlicensed with equipment certifications on a system basis to
assure avoidance of interference
• Operate in multiple bands– Assured capacity
• Offer cost/capacity/link range/deployment benefits– Access more (5 X?) spectrum than any current system– Operate in VHF/UHF TV band– Rapid spectrum agreements for itinerate use
January 2004
Bill Byrnes, Shared Spectrum Co.
doc.: IEEE 802.18-04-0004-00-000
Submission
Spectrum Occupancy Is Low
• “In many bands, spectrum access is a more significant problem than physical scarcity of spectrum, in large part due to legacy command-and-control regulation that limits the ability of potential spectrum users to obtain such access.”1
• Shared Spectrum’s measurements indicate– Many bands have no detectable occupancy
– Some bands have low occupancy
– Some bands have high occupancy
Note 1: FCC Spectrum Policy Task Force Report, page 3
January 2004
Bill Byrnes, Shared Spectrum Co.
doc.: IEEE 802.18-04-0004-00-000
Submission
Typical Spectrum Occupancy Measurement
No signals Medium and short duration signals
FCC should conduct and publish spectrum
occupancy measurements to
identify low occupancy bands
January 2004
Bill Byrnes, Shared Spectrum Co.
doc.: IEEE 802.18-04-0004-00-000
Submission
Initially Harvest the Low Hanging Fruit
• Measurements show a large quantity of long duration, large area spectrum holes
• “Simple” spectrum access methods are sufficient– Minimal coordination between transceivers– Moderate computational costs
• Later evolve algorithms to handle more complex situations– Short duration, small spectrum holes– Optimize frequency assignments for increased capacity
January 2004
Bill Byrnes, Shared Spectrum Co.
doc.: IEEE 802.18-04-0004-00-000
Submission
Agenda
• Requirements
• Spectrum occupancy characteristics– Significant amount of “low hanging fruit”
• Spectrum access methods– Listen-Before Talk
• “TDMA” spectrum
• Broadcast spectrum
– Probe
– Geo-location/database
January 2004
Bill Byrnes, Shared Spectrum Co.
doc.: IEEE 802.18-04-0004-00-000
Submission
Adaptive, Receive-Only Spectrum Access Method
• Pmax TX = 10*log10(k * T * B) + PPrimary – Pmeasured - Margin
– Margin = 10 to 20 dB, required for cummulative effects, rapid propagation changes, false alarm minimization
– T – Interference Noise Temperature, in K
– B = signal bandwidth, in Hz
Primary network
Secondary transceiver
1) Assume a transmit power level value (Pprimary)
2) Measure receive power level (Pmeasured)
3) The difference is the propagation loss (Pprimary – Pmeasured)
Pmax TX = Pallowable interference + Pprimary – Pmeasured
Primary network
Secondary transceiver
1) Assume a transmit power level value (Pprimary)
2) Measure receive power level (Pmeasured)
3) The difference is the propagation loss (Pprimary – Pmeasured)
Pmax TX = Pallowable interference + Pprimary – Pmeasured
January 2004
Bill Byrnes, Shared Spectrum Co.
doc.: IEEE 802.18-04-0004-00-000
Submission
Primary Transceivers
Frequency Agile Transceivers
Interference/Connectivity Limit
Exclusion Zone
Frequency Agile Coverage “Morphs” To Fit Primary Users
Hidden-node problem overcome by each Frequency Agile transceiver listening to all Primary users within range
January 2004
Bill Byrnes, Shared Spectrum Co.
doc.: IEEE 802.18-04-0004-00-000
Submission
High Sensitivity Receiver Performance
Cyclic Correlation Output SNR
0
10
20
30
40
50
60
70
-40 -30 -20 -10 0 10 20 30 40
Input SNR
Ou
tpu
t S
NR
T=1 sec
T=100 ms
T=10 ms
T=1 ms
T=.1 ms
January 2004
Bill Byrnes, Shared Spectrum Co.
doc.: IEEE 802.18-04-0004-00-000
Submission
10 ground vehicles spread over 25 km moving at 25
km/hr10 stationary ground vehicles spread over 25 km
•West Virginia location•3 m antenna height
Simulation Example
•Primary users are stationary•XG users are mobile•Omni-directional antennas•420 MHz signal frequency
January 2004
Bill Byrnes, Shared Spectrum Co.
doc.: IEEE 802.18-04-0004-00-000
Submission
Link closure
Interference
•Longley-Rice Model•420 MHzFree space loss
Actual loss
Propagation Losses
January 2004
Bill Byrnes, Shared Spectrum Co.
doc.: IEEE 802.18-04-0004-00-000
Submission
Frequency Agile network reduces TX power
automatically
Network needs switch to another frequency at low TX power levels
XG TX Power (dBm)
Target interference level of –100 dBm
Primary Interference Level (dBm)
TX Power and Interference
January 2004
Bill Byrnes, Shared Spectrum Co.
doc.: IEEE 802.18-04-0004-00-000
Submission
TV Receiver
Frequency Agile Transceiver
TV Transmitter
Region of Potential Interference
PT (kW)
HAAT (m)
Listen-Only Method in the Broadcast Bands
TV Receiver
L1
L2
Differential propagation loss = L1-L2
January 2004
Bill Byrnes, Shared Spectrum Co.
doc.: IEEE 802.18-04-0004-00-000
Submission
Transmit Power Rule
Pmax TX = Po if Primary signal is not detected
= Transmission prohibited if Primary signal is detected
where, Pmax TX = Frequency Agile transmitter power level, in dBm
Po = specified power value, in dBm
January 2004
Bill Byrnes, Shared Spectrum Co.
doc.: IEEE 802.18-04-0004-00-000
Submission
TV Receiver with Grade B reception
Frequency Agile Transceiver
TV Transmitter
Terrain Blockage
Building Blockage
LOS Location
LOS to Frequency Agile Transceiver
Multi-Path Effects
Minimal Interference
•Joint probability of three conditions–Agile Receiver doesn’t detect TV signal–Primary user receives TV signal–D/U < 15 dB
January 2004
Bill Byrnes, Shared Spectrum Co.
doc.: IEEE 802.18-04-0004-00-000
Submission
Minimum Detectable Signal (-121 dBm)
Minimum Signal Strength– “Grade B” (-81 dBm)
Min D/U =15 dB
Acceptable Interference = Thermal Noise (-96 dBm)
Received Power (dBm)
40 dB25 dB
Maximum Differential Propagation Value
Maximum differential propagation value = 40 dB
Maximum practical sensitivity improvement due to special detection processing
Signal level at TV receiver
Signal level at Frequency Agile receiver
January 2004
Bill Byrnes, Shared Spectrum Co.
doc.: IEEE 802.18-04-0004-00-000
Submission
Simulation of Differential Propagation
Test reception points along a ~ 8 km path
Scenario – Mid-Atlantic Region Elevation contours
TV transmitters
January 2004
Bill Byrnes, Shared Spectrum Co.
doc.: IEEE 802.18-04-0004-00-000
Submission
Large Change in Propagation Loss over a Short Distance is Rare
Signal from TV station A
Signal from TV station B
~30 dB change in propagation loss over a small distance
January 2004
Bill Byrnes, Shared Spectrum Co.
doc.: IEEE 802.18-04-0004-00-000
Submission
Low Power Transmitters Have a Small Interference Range
Noise
Obstructed propagation
Free-space propagation
Maximum interference range
of 4 km in free-space
Maximum interference range of 600 m in
obstructed conditions
1 mW transmit power
January 2004
Bill Byrnes, Shared Spectrum Co.
doc.: IEEE 802.18-04-0004-00-000
Submission
Spectrum Probing Method
75 km to 200 km spacing
Frequency Agile transceiver
Broadcast Receiver
1) Transmit (Pt) at a very low power
3) Measure Pr of the very weak signal using high processing gain
2) Very weak signal doesn’t interfere with primary user
4) Pt minus Pr is the propagation loss
5) Repeat with N nodes to estimate minimum propagation loss into area
Frequency Agile monitors
January 2004
Bill Byrnes, Shared Spectrum Co.
doc.: IEEE 802.18-04-0004-00-000
Submission
Geo-Location Method
TV Receiver
Frequency Agile Transceiver
TV Transmitter
Region of Potential Interference
PT (kW) HAAT (m)
TV Receiver
Protected Area
Position information
•GPS, telephone
Beacon TXProtected area boundary database information
•Telephone, over-the-air, special beacons, Internet, manually entered
Guard Distance
January 2004
Bill Byrnes, Shared Spectrum Co.
doc.: IEEE 802.18-04-0004-00-000
Submission
Significant “White Space” Between TV Coverage Areas
Grade B 50% and 90% contoursChannel 5 and channel 54
January 2004
Bill Byrnes, Shared Spectrum Co.
doc.: IEEE 802.18-04-0004-00-000
Submission
How Large A Guard Distance?
Noise
Maximum interference range of > 100 km in
free-space
Maximum interference
range of 2 km in obstructed
conditions
1 W transmit power
Large guard distances reduce spectrum harvestTV bands: 100 km is too large >> Limit TX power to mW’s
Other bands: Max TX power ?
January 2004
Bill Byrnes, Shared Spectrum Co.
doc.: IEEE 802.18-04-0004-00-000
Submission
Summary• Multiple, robust spectrum access methods
– Listen-Before Talk• “TDMA” spectrum• Broadcast spectrum
– Geo-location/database
• FCC should conduct and publish spectrum occupancy measurements– Many spectrum holes are large and have long duration
• FCC should allow experimental interactive operations– All access methods including Probe– TV and other bands
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