Download 18-04-0003-00-0000-unlicensed-use-tv-bands

January 2004
doc.: IEEE 802.18-04-0003-00-0000
802.18 Study Group 1
Unlicensed Reuse of Broadcast TV Channels
Submission
Slide 1
John Notor, Cadence Design Systems, Inc.
January 2004
doc.: IEEE 802.18-04-0003-00-0000
Outline
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Introduction
Overview of the Opportunity
Approaches to TV Channel Reuse
Identifying Incumbent Users
Service Profiles
Air Interface Options
Four Protocols for Spectrum Etiquette
Cognitive vs Non-Cognitive Radios
Wrap Up
Submission
Slide 2
John Notor, Cadence Design Systems, Inc.
January 2004
doc.: IEEE 802.18-04-0003-00-0000
Introduction
• On December 20, 2002, the Federal Communications Commission (FCC)
released a Notice of Inquiry (NOI)1 regarding "...the feasibility of allowing
unlicensed devices to operate in TV broadcast spectrum at locations and
times when spectrum is not being used...".
• The FCC’s NOI on TV band reuse envisions:
– New opportunities for more commercial utilization of existing spectrum.
– The right mix of radio technologies to avoid interfering with incumbent
users (i.e., TV broadcasters).
• Without attempting to predict the outcome of the FCC proceedings, this
presentation explores the architectural issues related to exploiting unused
TV spectrum from a radio design perspective.
1. “Notice of Inquiry: Additional Spectrum for Unlicensed Devices Below 900 MHz and in the 3 GHz Band”, ET Docket
No. 02-380, December 11, 2002
Submission
Slide 3
John Notor, Cadence Design Systems, Inc.
January 2004
doc.: IEEE 802.18-04-0003-00-0000
Overview of the Opportunity
• According to the FCC NOI:
“During and after the digital television transition, there will be a number
of TV channels in a given geographic area not being used … because
such stations will not be able to operate without causing interference to
co-channel or adjacent channel stations.”
• Unused TV channels in any geographic area could be reused by unlicensed
systems under an appropriate (TBD) regulatory regime.
• A central feature of the reuse strategy is the protection of incumbent users
from interference by unlicensed devices.
Submission
Slide 4
John Notor, Cadence Design Systems, Inc.
January 2004
doc.: IEEE 802.18-04-0003-00-0000
Overview of the Opportunity (con)
• The current Digital TV (DTV) plan:
– Only channels 2-51 will be available for DTV broadcasts after the
transition to digital.
– All analog TV broadcasts will be shut down.
– Spectrum for channels 52-69 will be reallocated to other uses:
• Channels 52-67 (700 MHz band: 698-794 MHz) are currently being
auctioned off for other services:
– Lower 700 MHz auction (Ch 52-59: 698-746 MHz) complete
except blocks A, B, & E, which are currently not scheduled.
– Upper 700 MHz auction (Ch 60-67: 746-794 MHz) currently not
scheduled.
– Scheduled DTV roll-out to be complete by the end of 2006.
Submission
Slide 5
John Notor, Cadence Design Systems, Inc.
January 2004
doc.: IEEE 802.18-04-0003-00-0000
Approaches To TV Channel Reuse
• The Basic principles of reuse:
– Select a channel unoccupied by an incumbent to establish the network.
– Minimize impact to other unlicensed networks using the same channel
by
• Keeping aggregate network transmit power low to avoid
interference with other nearby networks.
• Implementing a burst mode transmission scheme to allow other
networks access to the channel.
– Mitigate interference from other unlicensed networks occupying the
same channel by using spectrum spreading, error correction, and data
retransmission signaling schemes.
• The Ideal Solution: a “cognitive radio” system, i.e., a radio system with the
ability to adapt to it’s communications environment automatically.
Submission
Slide 6
John Notor, Cadence Design Systems, Inc.
January 2004
doc.: IEEE 802.18-04-0003-00-0000
Identifying Incumbent Users
• Accurate identification of incumbent users in a given geographic area is the
key to interference management and channel reuse.
• Some approaches to creating a database of unused or infrequently used
channels:
– Geolocation: use GPS or some other location technology along with a
pre-programmed database.
– Autonomous detection: scan all channels, identify any incumbent users
based on signal characteristics, and create a database automatically.
– Preprogram network devices: manual or operator-initiated broadcast
programming of each device to create the database.
• A fully cognitive radio system would implement autonomous detection as the
most adaptive approach.
• In some situations, geolocation or preprogramming may be cheaper.
Submission
Slide 7
John Notor, Cadence Design Systems, Inc.
January 2004
doc.: IEEE 802.18-04-0003-00-0000
Service Profiles
• The TV Channel Bandwidth is now and will continue to be 6 MHz.
• 6 MHz will support a wide variety of unlicensed communications services:
– Narrowband symmetrical voice and/or data access (Example: 240
narrowband channels at 25 kHz channel spacing)
– Broadband symmetrical data access (1–30 Mbps), supporting
broadband networking, local teleconferencing, Voice Over IP, and
similar Internet-style applications.
– Short range proprietary video services including security monitoring,
campus educational services, and other similar applications.
– Low to medium rate burst mode telemetry services which take
advantage of transient channel availability.
• The FCC might allow radio systems to aggregate two or more unassigned
TV channels to support higher data rates for video distribution, shared
multi-media experiences (games, group training in simulated environments,
etc.).
Submission
Slide 8
John Notor, Cadence Design Systems, Inc.
January 2004
doc.: IEEE 802.18-04-0003-00-0000
Air Interface Options
• Multiple access air interface choices for TV Channel reuse are constrained
by the likely operating environment:
– Competing Players: uncoordinated heterogeneous systems sharing the
same channelized spectrum: telemetry, narrowband voice, broadband
data, etc.
– The usual multiple access suspects – TDMA, FDMA, CDMA – require
disciplined, highly coordinated sharing protocols within a common
network structure – not a fit for an unlicensed scenario.
Submission
Slide 9
John Notor, Cadence Design Systems, Inc.
January 2004
doc.: IEEE 802.18-04-0003-00-0000
Air Interface Options (con)
• A “Listen-Before-Talk” communications etiquette using a burst mode
transmission scheme works best for uncoordinated networks.
– No requirement for disciplined timing across heterogeneous networks.
– Uses RSSI2 or other techniques to determine if a channel is quiet, i.e.,
available for use.
– Includes some kind of receive acknowledgement mechanism to identify
data corruption due to collisions between network signals.
– Depends on random backoff/retry mechanisms to minimize the
probability of a collision when retransmitting data.
2. RSSI: Received Signal Strength Indicator, a mechanism for determining the signal level at the receiver input.
Submission
Slide 10
John Notor, Cadence Design Systems, Inc.
January 2004
doc.: IEEE 802.18-04-0003-00-0000
Four Protocols for Spectrum Etiquette
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3.
Network Frequency Allocation (NFA, aka “DFS”):
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Survey and monitor spectrum use patterns.
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Avoid incumbents, operate the network on an unused or lightly used
channel.
Link Power Control (LPC, aka “TPC”):
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Keep network transmitter power low while maintaining good link
quality.
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LPC mitigates interference and promotes frequency reuse with
networks located nearby.
Incumbent Profile Detection (IPD, historically subsumed under DFS):
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Detect incumbent users based on specific spectrum signature
(supports NFA)
• Example: detecting the presence of a sound carrier in NTSC
(analog TV) systems or a pilot tone in ATSC (DTV) systems.
Submission
Slide 11
John Notor, Cadence Design Systems, Inc.
January 2004
doc.: IEEE 802.18-04-0003-00-0000
Four Protocols for Spectrum Etiquette (con)
4.
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Collision Detection And Avoidance (CDAA, aka “CCA”):
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Transmitters wait until the channel is quiet before transmitting
(“listen before talk”).
–
A receiving node acknowledges valid data by transmitting a
response.
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A transmitting node “detects” a collision if it does not receive an
acknowledgement for a data transmission.
–
The protocol implements an appropriate backoff/retry timing
mechanism for retransmission when a collision is detected.
Note: These protocols resemble those presently adopted or proposed for
IEEE 802.11x wireless networks (“DFS”, “TPC”, “CCA”), but are
generalized here to avoid confusion with the specifics of pre-existing
implementations.
Submission
Slide 12
John Notor, Cadence Design Systems, Inc.
January 2004
doc.: IEEE 802.18-04-0003-00-0000
Cognitive vs. Non-Cognitive Radios
• A fully cognitive network should have the ability to do the following:
1. Tune to any TV channel in the band (up to 50 channels after the
DTV changeover).
2. Establish links and operate in all or part of a 6 MHz channel.
3. Implement NFA, LPC, IPD, and CDAA protocols.
4. Implement adaptive transmission bandwidths, data rates, and error
correction schemes to obtain the best throughput possible.
5. Implement adaptive antenna steering to focus transmitter power in
the direction required and optimize received signal strength.
• For data network applications where reliability and throughput are
overriding system values, the fully cognitive approach is the best.
Submission
Slide 13
John Notor, Cadence Design Systems, Inc.
January 2004
doc.: IEEE 802.18-04-0003-00-0000
Cognitive vs. Non-Cognitive Radios (con)
• The simplest non-cognitive approach to TV channel reuse requires the
ability to do the following:
1. Operate on one or more unoccupied channels selected by the system
operator during network deployment.
2. Implement IPD and CDAA protocols.
3. Operate with low transmit power by design.
4. Use a simple antenna system.
• For applications like telemetry, or applications fielded in remote areas with
little chance of interference, the non-cognitive approach makes the most
economic sense.
Submission
Slide 14
John Notor, Cadence Design Systems, Inc.
January 2004
doc.: IEEE 802.18-04-0003-00-0000
Wrap Up
• This presentation identifies radio network strategies and protocols which
support frequency reuse of TV spectrum by unlicensed devices as
suggested by the FCC’s NOI.
• These same strategies and protocols are generally applicable to any sharing
environment where licensed and unlicensed radio systems interoperate on a
non-interfering basis.
• Fully cognitive unlicensed radio systems support high data rate, moderately
high throughput networks in densely occupied spectrum environments.
• In rural areas, and other low density spectrum environments, simple, low
cost, non-cognitive radios can reuse fallow spectrum effectively.
Submission
Slide 15
John Notor, Cadence Design Systems, Inc.