SSC Page 1 Frequency Agile Spectrum Access Technologies Presentation to FCC Workshop on Cognitive Radios May 19, 2003 Mark McHenry Shared Spectrum Company

SSC Page 2 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

SSC Page 3 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

SSC Page 4 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

SSC Page 5 Typical Spectrum Occupancy Measurement No signals Medium and short duration signals FCC should conduct and publish spectrum occupancy measurements to identify low occupancy bands

SSC Page 6 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

SSC Page 7 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

SSC Page 8 Adaptive, Receive-Only Spectrum Access Method P max TX = 10*log10(k * T * B) + P Primary – P measured - 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

SSC Page 9 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

SSC Page 10 High Sensitivity Receiver Performance

SSC Page ground vehicles spread over 25 km moving at 25 km/hr 10 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

SSC Page 12 Link closure Interference Longley-Rice Model 420 MHz Free space loss Actual loss Propagation Losses

SSC Page 13 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

SSC Page 14 TV Receiver Frequency Agile Transceiver TV Transmitter Region of Potential Interference P T (kW) HAAT (m) Listen-Only Method in the Broadcast Bands TV Receiver L1 L2 Differential propagation loss = L1-L2

SSC Page 15 Transmit Power Rule P max TX = Po if Primary signal is not detected = Transmission prohibited if Primary signal is detected where, P max TX = Frequency Agile transmitter power level, in dBm Po = specified power value, in dBm

SSC Page 16 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

SSC Page 17 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 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

SSC Page 18 Simulation of Differential Propagation Test reception points along a ~ 8 km path Scenario – Mid-Atlantic Region Elevation contours TV transmitters

SSC Page 19 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

SSC Page 20 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

SSC Page 21 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

SSC Page 22 Geo-Location Method TV Receiver Frequency Agile Transceiver TV Transmitter Region of Potential Interference P T (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

SSC Page 23 Significant “White Space” Between TV Coverage Areas Grade B 50% and 90% contours Channel 5 and channel 54

SSC Page 24 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 ?

SSC Page 25 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