# Presentation: 042297

## Frequency Agile Spectrum Access TechnologiesPresentation toFCC Workshop on Cognitive RadiosMay 19, 2003

- Mark McHenry
- Shared Spectrum Company
- 703-761-2818
- mmchenry@sharedspectrum.com

## 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

## 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

## 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

## Typical Spectrum Occupancy Measurement

- No signals

- Medium and short duration signals

- FCC should conduct and publish spectrum occupancy measurements to identify low occupancy bands

## 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

## 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

## 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

## Frequency Agile Coverage “Morphs” To Fit Primary Users

- Hidden-node problem overcome by each Frequency Agile transceiver listening to all Primary users within range

## High Sensitivity Receiver Performance

## Simulation Example

- Primary users are stationary
- XG users are mobile
- Omni-directional antennas
- 420 MHz signal frequency

## Propagation Losses

## TX Power and Interference

- 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)

## Listen-Only Method in the Broadcast Bands

- TV Receiver

- Frequency Agile Transceiver

- TV Transmitter

- Region of Potential Interference

- PT (kW)

- HAAT (m)

- TV Receiver

- L1

- L2

- Differential propagation loss = L1-L2

## 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

## Minimal Interference

- 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

- Joint probability of three conditions
- Agile Receiver doesn’t detect TV signal
- Primary user receives TV signal
- D/U < 15 dB

## Maximum Differential Propagation Value

- 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 dB

- 25 dB

- 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

## Simulation of Differential Propagation

- Test reception points along a ~ 8 km path

- Scenario – Mid-Atlantic Region
- Elevation contours

- TV transmitters

## Large Change in Propagation Loss over a Short Distance is Rare

## 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

## 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_

## 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 TX

- Protected area boundary database information
- Telephone, over-the-air, special beacons, Internet, manually entered

- Guard Distance

## Significant “White Space” Between TV Coverage Areas

- Grade B 50% and 90% contours
- Channel 5 and channel 54

## 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 harvest
- TV bands: 100 km is too large >> Limit TX power to mW’s
- Other bands: Max TX power ?

## 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