Doc.: IEEE 802.18-04-0030-01-0000 Submission July 2004 John Notor, Cadence Design Systems, Inc....

July 2004 doc.: IEEE 802.18-04-0030-01-0000

John Notor, Cadence Design Systems, Inc.Slide 1

Submission

Proposal for Part 15.244 Cognitive Radio Operation in the TV Band

IEEE 802.18 Radio Regulatory TAG

July 2004 doc.: IEEE 802.18-04-xxxx-00-0000


Submission

Outline

• Introduction

• TV Band Incumbents

• Identifying Characteristics of Incumbents

• Elements of Cognitive Radio Operation

• Proposed Cognitive Radio Rules

• Analysis for Personal/Portable Devices

– Operating Range of Personal/Portable Devices

– Detection of DTV Signals

– DFS Sensitivity vs DTV Service Contour Field Strength

– Co-Channel Interference Range Margin

– Terrain Blocking

• Analysis for Fixed Devices

• Wrap Up



Submission

Introduction

• On May 13, 2004, the FCC adopted ET Docket No. 04-186, “Unlicensed Operation in the TV Broadcast Bands” in a Notice of Proposed Rulemaking (NPRM).

• As written, ET-04-186 proposes the following two classes of devices under a new rules section, Part 15.244:

• Personal/Portable Devices

–100 mW peak transmitter power, 400 mW peak EIRP (6 dBi antenna)

–Transmission is permitted only when receiving a control signal indicating which TV channels are vacant from one of the following sources: a TV Broadcast station, an FM Broadcast station, or an unlicensed transmitter

• Fixed Access Devices

–1 W peak transmitter power, 4 W peak EIRP (6 dBi antenna)

–Must meet one of the following criteria

–Include a GPS receiver and means of determining vacant TV channels in the area

–Be installed by professionals to operate only on unused channels.



Submission

Introduction

• Although ET 04-186 seeks comment on the possibility of using spectrum sensing, and other cognitive radio techniques, to identify and avoid TV channels occupied by an incumbent, and select channels for unlicensed operation, the Commission’s proposed rules sections do not permit that approach.

• This presentation does the following:

• Proposes a set of rules for an additional class of devices which permit cognitive radio technologies to be used in unlicensed devices operating in the TV band under Part 15.244.

• Establishes that devices operating under these rules protect the operations of TV band incumbents based on widely available operational data and supporting analysis.



Submission

TV Band Incumbents

• Full Service TV Broadcast Stations (CFR1 Title 47 Part 73).

• Class A TV Broadcast Stations (CFR Title 47 Part 73 subpart J).

• LPTV, TV Translator, TV Booster Stations, Auxiliary Operations, and Wireless Microphones (CFR Title 47 Part 74).

• Private Land Mobile Radio Services (PLMRS) in 13 Metro Areas (CFR Title 47 Part 90), including Public Safety communications systems.

• Commercial Land Mobile Radio Services (CMRS) in 13 Metro Areas (CFR Title 47 Part 20).

• Wireless Medical Telemetry Services (WMTS) (CFR Title 47 Part 95 subpart H).



Submission

TV Band Incumbent Protection from Cognitive Devices

• In order to insure that public safety operations are protected, Ch 14-20 are excluded from the proposed cognitive radio class of operation.

• Wireless Medical Telemetry Services operate on Ch 37 within the TV band, which is excluded by the Commission’s proposed rules from Part 15.244 device operations.

• Wireless microphone operation as a Low Power Auxiliary Station under Part 74 can protected by cognitive techniques, or by rule (assignment to specific channels in each service area, etc). This presentation does not address wireless microphones.

• Wireless video assist devices are provided for as Low Power Auxiliary Devices in Part 74, but no equipment is presently authorized or licensed for operation. This class of equipment should be considered for termination.

• The remaining incumbents are TV broadcast signals, which, because of their unique signatures (analog/NTSC, and digital/ATSC), are readily identifiable.



Submission

Analog TV (NTSC) Spectrum

• Power primarily confined to Video and Audio carriers.

• Distinctive double peaked spectrum makes identification by spectrum profiling relatively easy.

• Relatively high narrowband power levels compared to DTV.



Submission

Digital TV (ATSC) Spectrum

• Power spread over center 5.38 MHz within a TV channnel.

• Pilot tone is a distinctive feature when observed in a narrowband receiver.

• Pilot tone power is 11.3 dB below average power measured in a 6 MHz bandwidth.



Submission

Elements of Cognitive Radio Operation (1)

1. Network Frequency Allocation (NFA):

– Survey and monitor spectrum use patterns.

– Avoid incumbents, operate network on an unused or lightly used channel.

2. Link Power Control (LPC):

– Keep network transmitter power low while maintaining good link quality.

– LPC mitigates interference and promotes frequency reuse with networks located nearby.

3. Incumbent Profile Detection (IPD):

– Detect incumbent users based on specific spectrum signature (supports NFA)

– Example: detecting the presence of a sound/video carriers in NTSC (analog TV) systems or a pilot tone in ATSC (DTV) systems.

4. Collision Detection And Avoidance (CDAA):

– Transmitters wait until the channel is quiet before transmitting (“listen before talk”).

– A receiving node acknowledges valid data by transmitting a response.

– A transmitting node “detects” a collision if it does not receive an acknowledgement before a timeout occurs.

– The protocol implements an appropriate backoff/retry timing mechanism for retransmission when a collision is detected.

1. Notor, J., Radio Architectures for Unlicensed Reuse of Broadcast TV Channels, Communications Design Conference 2003.



Submission

Proposed Cognitive Radio Rules

• These rules extend the FCC’s proposed rules for Part 15.244 devices to authorize cognitive radio techniques.

• Dynamic Frequency Selection (DFS) threshold: a TV channel shall be considered unoccupied when the electric field strength at the receiving antenna is less than the following averaged for 10 ms over the entire 6 MHz channel.

– For Ch 5-6, E(dBu) < -7 dBuV/m/10 kHz

– For Ch 7-13, E(dBu) < 1 dBuV/m/10 kHz

– For Ch 21-51, excluding Ch 37 E(dBu) < 11 dBuV/m/10 kHz

• To operate on a channel whose ambient field strength is greater than the DFS threshold, the cognitive device must, using appropriate Incumbent Profile Detection techniques, verify that the channel is not being occupied by either an analog or a digital TV signal.

• The cognitive radio network shall give priority to operation on empty or lightly occupied channels.



Submission

Proposed Cognitive Radio Rules

• Transmit Power Control (TPC)

– Link Power Control protocols must be included in the cognitive radio devices to minimize transmitter power while supporting reliable communications between any transmitter and any single receiver.

– The LPC protocol operation shall cause the transmitter in any single node to single node link to begin reducing output power when the signal level at the receiver is greater than 20 dB above the receiver’s nominal sensitivity.

– The TPC function shall keep the signal level at the receiver less than 30 dB above the receiver’s nominal sensitivity at least 50% of the time, including the impact of any regular broadcast operations (transmission from a controlling node to all other nodes).

• Listen Before Talk

– The transmitters must operate in burst mode, with a maximum continuous burst length less than 1 second.

– Cognitive radio devices must monitor the operational channel periodically to verify that the channel remains unoccupied by an analog or digital TV signal.



Submission

Analysis for Personal/Portable Devices

• The following analyses establishes the performance limits of cognitive radio operation for personal/portable devices:

– Expected loss exponent (L.E.) for personal/portable operation.

– Detection performance for DTV signals.

– DFS sensitivity margin.

– Co-channel interference range margin.

– Terrain blocking footprint and issues.



Submission

Operating Range of Personal/Portable Devices

Table 1: Range data based on customer survey information (2)

2. Table provided by Southern Communications and Electronics at the following web site:http://www.southernce.com/cgi-bin/SoftCart.exe/range.htm?L+scstore+josy3749+1088643303



Submission


• VHF Loss Exponent estimates based on the operational characteristics of MURS radio handsets (151.820 MHz < fc < 154.600 MHz).

– Sensitivity: 0.2 uV at limit of range, or -121 dBm

– Antenna Gain: 0 dBi

– Tx Power: 2 W (+33 dBm)

– Loss to limit of sensitivity: 33 – (-121) = 154 dB.

– Loss Exponent (LE) = 154/[10*log(d)], where d is the range in m.

• Table 2: Anecdotal range data based on Table 1 with loss exponent:

Est. Range (m) LE Conditions

6436 4.0 Outdoors, clear flat terrain

3620 4.3 Suburban outdoor environments

2011 4.7 Urban outdoor environments

805 5.3 Inside shopping mall



Submission


• UHF Loss Exponent estimates based on the operational characteristics of FRS radio handsets (462.5625 MHz < fc < 467.7125 MHz).

– Sensitivity: 0.2 uV at limit of range, or -121 dBm


– Tx Power: 500 mW (+27 dBm)

– Loss to limit of sensitivity: 27 – (-121) = 148 dB.

– Loss Exponent (LE) = 148/[10*log(d)], where d is the range in m.

• Table 3: Anecdotal range data from various sources with loss exponent:

Data Source Est. Range (m) LE Conditions

Manufacturers 3218 4.2 Over water

McGuinn 2413 4.4 Hotel to hotel, 15th story room to lobby, Disney World

Various 1609 4.6 Normal cluttered outdoor environment

Notor 984 4.9 Outdoors in Willow Glen Neighborhood, San Jose, CA

Other 402 5.7 Inside shopping mall



Submission


• VHF/UHF Loss Exponent (LE) range: 4-5.7

• Loss exponents by environment:

– Clear flat terrain: LE = 4

– Outdoor suburban/urban environment: LE = 4.3 - 4.9

– Indoor to indoor, 15th floor hotel room to hotel lobby: LE = 4.4

– Inside shopping mall: 5.3-5.7

• Operational experience based on loss exponent analysis tracks well between VHF and UHF portable radios.



Submission

Detection of DTV Signals

• DTV is the limiting case re: DFS/IPD for TV signals.

• Receiver Assumptions:

– CNR: 6 dB is sufficient for detection of a narrowband signal like an ATSC pilot tone.

– NF: 5 dB


– Predetection Bandwidth: 10 kHz

– Post Detection Time Constant: 10 ms

– Square Law Detector

• Sensitivity Calculation (CNR = 6 dB)

S = -174 dBm/Hz + 10log(10 kHz) + 5 dB + 6 dB

S = -123 dBm



Submission

Detection of DTV Signals

• For a DFS detection threshold of -123 dBm/10 kHz applied to identifying a DTV signal by detecting the pilot tone, the equivalent clear channel DFS threshold for a DTV signal becomes:

– DTV DFS = -123 dBm + 11.3 dB = -111.7 dBm ~ -112 dBm in a 6 MHz bandwidth

– -112 dBm is below the thermal noise floor for a 6 MHz bandwidth, i.e. Np = -174 dBm + 10log(6 MHz) = -106.2 dBm > -112 dBm, but the analysis remains valid, since the pilot tone can be detected in a 10 kHz bandwidth.

• Assuming a 0 dBi antenna and a 50 Ohm reference impedance, the equivalent DFS threshold in terms of electric field strength in a 6 MHz bandwidth is

– E(dBu) = P(dBm) + 20log[f(MHz)] + 77.2

– For Ch 6, E(dBu) = -112 + 20log[85] + 77.2 = 4 dBuV/m

– For Ch 13, E(dBu) = 12 dBuV/m

– For Ch 51, E(dBu) = 22 dBuV/m



Submission

DFS Sensitivity Margin - Personal/Portable Devices

• The sensitivity margin relative to the minimum in-service DTV field strength for a 30 ft high receive antenna is:

– For Ch 6, margin = 28 – 4 = 24 dB

– For Ch 13, margin = 36 – 12 = 24 dB

– For Ch 51, margin = 41 – 22 = 19 dB

• For a receiver outdoor antenna height of 2 m (nomadic personal/portable device), reduce the sensitivity margin by a 9 dB correction factor (3).

• Table 4 (p.19) shows sensitivity margin calculations for various stations in the FCC database, using the FCC calculator at: http://www.fcc.gov/mb/audio/bickel/curves.html.

• The DFS detector operating outdoors with an antenna height of 2 m can sense a TV channel outdoors at ranges > 21% farther than the service contour (Table 4) in unobstructed terrain.

3. Mehrotra, A., Cellular Radio Performance Engineering, Artech House, 1994, p146



Submission

Table 4: DFS Sensitivity Margin – Personal/Portable Devices

4. The DFS limit is calculated at a 2 m antenna height, assuming a 9 dB loss relative to signal strength at 30 ft (~9 m). So, for Ch 6, DFS Limit =4 dBuV/m + 9 dB =13 dBu. These calculations exclude terrain blockage effects.

Service

Area Contour DFS (4) DFS Range Range

DTV Band HAAT ERP Limit Range Limit Range Margin Margin

Station, Locale Ch (MHz) (m) (kW) (dBu) (km) (dBu) (km) (km) (%)

WCFT-TV, Tuscaloosa, AL 5 76-82 625.4 9.5 28 128.7 12 182.4 53.7 41.7%

KNSO, Merced, CA 5 76-82 575.0 11.0 28 126.5 12 181.7 55.2 43.6%

KYES, Anchorage, AK 6 82-88 277.0 45.0 28 120.5 13 180.5 60.0 49.8%

WEDY, New Haven, CT 6 82-88 88.0 0.4 28 56.0 13 83.9 27.9 49.8%

KMBC-TV, Kansas City, MO 7 174-180 357.0 85.0 36 114.7 19 173.6 58.9 51.4%

KNTV, San Jose, CA 12 204-210 376.6 103.1 36 118.2 20 174.7 56.5 47.8%

WDAF-TV,Kansas City, MO 34 590-596 295.0 1000.0 41 96.2 30 125.1 28.9 30.0%

KLCS, Los Angeles, CA 41 626-632 900.8 162.0 41 115.5 30 140.5 25.0 21.6%

WMSY-TV, Marion, VA 42 638-644 448.0 100.0 41 89.8 30 112.9 23.1 25.7%

KWDK, Tacoma, WA 42 638-644 695.0 144.0 41 107.0 31 129.7 22.7 21.2%

WTVX, Fort Pierce, FL 50 686-692 438.3 704.0 41 106.0 31 132.2 26.2 24.7%

KOPX, Oklahoma City, OK 50 686-692 483.0 200.0 41 97.8 31 120.1 22.3 22.8%

KDTV, San Francisco, CA 51 692.698 701.0 476.3 41 118.5 31 144.1 25.6 21.6%



Submission

Co-Channel Interference Range Margin

• Part 15.244 Device Tx Operating Parameters:

– EIRP: 400 mW, or +26 dBm

– E(dBu) = 104.8 + EIRP(dBm) – 20*log(D) = 131 dBu at D = 1 m.

– Loss exponent (LE): 4 (lower limit of operational experience for portable devices).

• DTV Co-channel D/U: 23 dB at the edge of the service area.

• Maximum allowed co-channel interference field strength at the edge of the service contour (Full service DTV)

– Ch 5-6: 28 – 23 = 5 dBu

– Ch 7-13: 36 – 23 = 13 dBu

– Ch 14-51: 41 – 23 = 18 dBu

• Interference Range (R), LE = 4, to DTV co-channel D/U = 23 dB limit

– Ch 5-6: R = 10[(131 – 5) / 40] = 1.4 km

– Ch 7-13: R = 891 m

– Ch 14-51: R = 668 m



Submission


• FCC propagation calculations indicate that a unlicensed spectrum sensing device operating outdoors can sense a DTV signal 22-60 km outside the service contour of a DTV station, excluding terrain blocking effects.

• The range of a Part 15.244 personal/portable device transmitter operating at a +26 dBm EIRP to the field strength limit for an undesired co-channel signal within a service contour is 668 m to 1.4 km.

• So, DTV services areas are protected by a buffer zone (excluding terrain blockage effects) of greater than 20 km using spectrum sensing techniques.



Submission


DTV Service Area

Edge ofServiceContour

Limit of DFS Sensing Capability

22-60 km

Cognitive Radio Range to 23 dB D/U Limit

R <1.4 km(+26 dBm EIRP, LE = 4)



Submission

Terrain Blocking

• Reduces the available signal level significantly in the blocked area relative to adjacent unblocked areas due to terrain features: mountains, buildings, interior walls. Example terrain blocking losses:

– 40 dB over an 8 km stretch in Virginia for 50% of the cases, much fewer instances of 40 dB change for smaller geographic segments (5)

– 37 dB over a ~ 4 km stretch in Boulder, CO (6) (see p24)

– 27 dB over an ~ 2.4 km stretch (7) in Boulder, CO (see p.25)

– 10 dB for building shadowing losses, and 10-20 dB for building penetration losses (8,9) (see p 26).

Note: For the data in Table 5, the indoor antenna was placed next to a window on the same side of the building where the outdoor signal strength was measured, which tends to produce more optimistic results than otherwise.

• Reduces the range margin at the edge of a service contour over that available in an unblocked situation.

5. McHenry & Byrnes, Shared Spectrum Company Comments to FCC ET-02-380, p96. Holoway, Sanders, & McKenna, NTIA Report 01-387, p24 and Figure 147. Holoway, Sanders, & McKenna, NTIA Report 01-387, p24 and Figure 168. McHenry & Byrnes, Shared Spectrum Company Comments to FCC ET-02-380, p.68. Salehian, Khalil, Comparison Between the Field Strength of DTV Signals Inside and Outside of the Buildings, Communications Research Centre Canada.



Submission

Geographic Terrain Blocking

0.018 V/m

1.3 V/m

37 dB

~ 4 km

Figure 14 reproduced from Holoway, Sanders, & McKenna, NTIA Report 01-387



Submission

Geographic Terrain Blocking

0.055 V/m

1.2 V/m

27 dB

~ 2.4 km

Figure 16 reproduced from Holoway, Sanders, & McKenna, NTIA Report 01-387



Submission

Terrain Blocking By Buildings

Site Number

Outdoor Outdoor Indoor Floor # Outdoor 10 m - Outdoor 2m (dB)

Outdoor 10 m - Indoor (dB)10 meters 2 meters

2 -54.6 -72 -62.2 2 17.4 7.60

3 -71 -77 -70 2 6 -1.00

4 -35.3 -47.2 -51 1 11.9 15.70

-34.6 2 -0.70

5 -47 -67 -60.4 1 20 13.40

-58.1 2 11.10

6 -37.7 -53.2 -46.1 2 15.5 8.40

7 -69.2 -74.3 -67 2 5.1 -2.20

8 -44.9 -63.1 -61.9 1 18.2 17.00

-54.2 2 9.30

9 -50.2 -60.5 -58.9 4 10.3 8.70

Average 13.44 7.94

Notes: Min 5.10 -2.20

1. Sites 1-8 are 1-2 story suburban brick homes. Max 20.00 17.00

2. Site 9 is a tall concrete apartment building. Std Dev 5.63 6.65

Table 5: Outdoor to Indoor Propagation Data (10)

(10) Ibid, adapted from the original CRC Canada report, including the addition of the last two columns of analysis.



Submission

Terrain Blocking Mitigation

• Limit transmit power of personal/portable devices.

– At +26 dBm EIRP, the range of personal/portable devices to the co-channel D/U threshold is < 1.4 km on Ch 5-6, < 900 m on higher frequency channels, i.e., less than the expected shadow footprint (see p.28).

– Using TPC reduces the interference range by reducing network aggregate transmitter power.

– Burst mode operation reduces the impact of transmissions to DTV operation relative to the assumption of continuous operation built into the D/U regulatory limits.

• Require all devices to include DFS/IPD capability, not just access points

– If all devices include DFS/IPD capability, the spectrum sensing footprint is increased, reducing the probability that an occupied channel will go undetected.

– Avoids the possibility of a shadowed master control device accidentally trying to set up the network co-channel with a TV broadcast incumbent.



Submission

Co-Channel Interference in Blocked Terrain

DTV Service Area


Cognitive Radio Range to 23 dB D/U 668 m < R <1.4 km at +26 dBm EIRP

Lb

Shadow Depth (dB) Lb (km)

27 2.4

37 4.0

40 8.0

Terrain Shadow



Submission

Analysis for Fixed Devices

• The following analyses establishes the performance limits of cognitive radio operation for fixed devices:

– DFS sensitivity margin.

– Co-channel interference range margin.

– Terrain blocking footprint and issues.



Submission

DFS Sensitivity Margin – Fixed Devices

• The sensitivity margin relative to the minimum in-service DTV field strength for a 30 ft high receive antenna is:

– For Ch 6, margin = 28 – 4 = 24 dB

– For Ch 13, margin = 36 – 12 = 24 dB

– For Ch 51, margin = 41 – 22 = 19 dB

• Table 6 (p.32) shows sensitivity margin calculations for various stations in the FCC database, using the FCC calculator at: http://www.fcc.gov/mb/audio/bickel/curves.html.

• The DFS detector operating outdoors with an antenna height of 30 ft (~9 m) can sense a TV channel outdoors at ranges > 46% farther than the service contour (Table 6) in unobstructed terrain.



Submission

Table 6: DFS Sensitivity Margin – Fixed Devices

Service DFS DFS

Area Contour DFS DFS 11,12 Range Range

DTV Band HAAT ERP Limit Range Limit Range Margin Margin

Station, Locale Ch (MHz) (m) (kW) (dBu) (km) (dBu) (km) (km) (%)

WCFT-TV, Tuscaloosa, AL 5 76-82 625.4 9.5 28 128.7 3 190.0 61.3 47.6%

KNSO, Merced, CA 5 76-82 575.0 11.0 28 126.5 3 189.8 63.3 50.0%

KYES, Anchorage, AK 6 82-88 277.0 45.0 28 120.5 4 201.3 80.8 67.1%

WEDY, New Haven, CT 6 82-88 88.0 0.4 28 56.0 4 89.3 33.3 59.5%

KMBC-TV, Kansas City, MO 7 174-180 357.0 85.0 36 114.7 10 233.8 119.1 103.8%

KNTV, San Jose, CA 12 204-210 376.6 103.1 36 118.2 11 233.8 115.6 97.8%

WDAF-TV,Kansas City, MO 34 590-596 295.0 1000.0 41 96.2 21 164.3 68.1 70.8%

KLCS, Los Angeles, CA 41 626-632 900.8 162.0 41 115.5 21 171.9 56.4 48.8%

WMSY-TV, Marion, VA 42 638-644 448.0 100.0 41 89.8 21 136.5 46.7 52.0%

KWDK, Tacoma, WA 42 638-644 695.0 144.0 41 107.0 22 156.7 49.7 46.4%

WTVX, Fort Pierce, FL 50 686-692 438.3 704.0 41 106.0 22 166 60.0 56.6%

KOPX, Oklahoma City, OK 50 686-692 483.0 200.0 41 97.8 22 146.3 48.5 49.6%

KDTV, San Francisco, CA 51 692-698 701.0 476.3 41 118.5 22 177.3 58.8 49.6%

11. The FCC calculator won't accept E field levels less than 10 dBu, so for channels 5, 6, 10 dBu was used for the calculation of range.12. DFS Range assumes a 30 ft receiver antenna height for the fixed antenna.



Submission

Interference Range Margin – Fixed Devices

Range to D/U

TV D/U Required D/U limit DFS Range

Channel Center Freq E @ 1 m E limit Loss ITM Range Margin

(MHz) (dBu) (dBu) (dB) (km) (km) (km)

6 85 140.8 5 135.8 31.2 89.3 58.1

12 207 140.8 13 127.8 20.6 233.8 213.2

51 695 140.8 18 122.8 14.3 177.3 163

Table 7: Interference Range Margin

• Table 7 shows the interference range margin for 23 dB D/U, assuming 30 m base station antenna height and 9 m client antenna height.

• The interference range margin is 58 – 213 km (see p34).



Submission


DTV Service Area


Limit of DFS Sensing Capability

89-234 km

Cognitive Radio Range to 23 dB D/U Limit

R < 31 km(+36 dBm EIRP)



Submission

Wrap Up

• Based on the proposed rules, the operational data, and the analysis presented herein, cognitive devices using spectrum sensing techniques can reliably operate in the TV band without causing interference to TV broadcast channels.

• The cognitive radio mode of operation is proposed as an addition to the rules for Part 15.244 devices already proposed by the FCC in the TV Band NPRM.

• The application of cognitive radio technology to TV band unlicensed operation is an important step in realizing the full potential for a wide range of centralized and distributed networks utilizing otherwise unoccupied spectrum.



Submission

Acknowledgements

• The following organizations and individuals were immensely helpful in preparing this presentation:

– The Berkeley Wireless Research Center, especially

– Professor Robert W. Brodersen

– Gary Kelson

– Danielja Cabric’

– The Communications Research Centre Canada, especially

– Gerald Chouinard

– David Rogers

– Khalil Salehian

– Intel Corporation, especially

– Jeffrey Schiffer

– Alan E. Waltho



Submission

Acknowledgements

– Shared Spectrum Corporation, especially

– Mark McHenry

– William Byrnes

– Professor Adam Wolisz, Technische Universitat Berlin

– Michael Lynch, Nortel

– Denis Kuwahara, Boeing

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