802.18 Study Group 1 Unlicensed Reuse of Broadcast TV Channels

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802.18 Study Group 1Unlicensed Reuse of
Broadcast TV Channels
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Outline

• 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

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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 FCCs 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
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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.

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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.

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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
  its communications environment automatically.

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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.

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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 (130 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.).

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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.

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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.
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Four Protocols for Spectrum Etiquette

• Network Frequency Allocation (NFA, aka DFS)
• Survey and monitor spectrum use patterns.
• Avoid incumbents, operate the network on an
  unused or lightly used channel.
• Link Power Control (LPC, aka TPC)
• Keep network transmitter power low while
  maintaining good link quality.
• LPC mitigates interference and promotes frequency
  reuse with networks located nearby.
• Incumbent Profile Detection (IPD, historically
  subsumed under DFS)
• 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.

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Four Protocols for Spectrum Etiquette (con)

• Collision Detection And Avoidance (CDAA, aka
  CCA)
• 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 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.

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Cognitive vs. Non-Cognitive Radios

• A fully cognitive network should have the ability
  to do the following
• Tune to any TV channel in the band (up to 50
  channels after the DTV changeover).
• Establish links and operate in all or part of a 6
  MHz channel.
• Implement NFA, LPC, IPD, and CDAA protocols.
• Implement adaptive transmission bandwidths, data
  rates, and error correction schemes to obtain the
  best throughput possible.
• 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.

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Cognitive vs. Non-Cognitive Radios (con)

• The simplest non-cognitive approach to TV channel
  reuse requires the ability to do the following
• Operate on one or more unoccupied channels
  selected by the system operator during network
  deployment.
• Implement IPD and CDAA protocols.
• Operate with low transmit power by design.
• 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.

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Wrap Up

• This presentation identifies radio network
  strategies and protocols which support frequency
  reuse of TV spectrum by unlicensed devices as
  suggested by the FCCs 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.