CICAS-V Progress Briefing

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VSC-A Multi-Channel Operation Investigation An
update to IEEE 1609 VSC-A Vehicle Safety
Communications - Application
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VSC-A Motivation

• Concern about congestion on CCH during CCH
  interval
• Take into account FCC designation of Channel 172
  for safety communication
• VSC-A looking at alternative safety communication
  approaches, narrowing focus to a few
• 3 alternatives discussed in this presentation
• 1 comes from our Phase 1 study, which uses the
  WSM header as defined in d1.2
• The other two come from our Phase 2 study, which
  requires the addition of one or more bits to the
  header

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Phase 1 StudyTaxonomy of Channel Switching
Scenarios
Safety on CCH
Safety on Ch. 172
1609.4
Always-on Safety Channel
Always-on Safety Channel
3-way switch
1 radio
2 radios
1 radio
2 radios
1 radio
2 radios
2 radios
1 radio
Interested in this approach
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Phase 1 Spectrum and Time Usage Maps
foralways-on Ch 172, single and dual radio cases

• Spectrum Map

Radio 1
Radio 2 optional
Time Map
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Phase 2 StudyWhat can we do with extra O-T-A
information?

• Add information to WSM header reporting senders
  multi-channel intent/capability
• Vehicles monitor neighbors advertised info.
  Adapt behavior based on make-up of neighborhood
• Goals
• allow more flexible co-existence of vehicle
  types
• use an always-on safety channel to reduce
  congestion most of the time
• Weve looked at several variations, and are
  interested in two

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Example, Case 1 At least one car in neighborhood
needs BSM in CCH interval
Heartbeat, with WSM header bit indicating
enhanced capability
target car
Heartbeat, with WSM header bit indicating limited
capability
Vehicle needs BSM in CCH interval

• If at least one car in neighborhood sends packets
  with bit indicating limited capability, target
  car (center) sends BSM on CCH during CCH
  interval. Each cars sending behavior dictated
  by its local neighborhood

SCH interval
CCH interval
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Example, Case 2 all cars in neighborhood can
monitor safety channel for entire sync period
Heartbeat, with WSM header bit indicating
enhanced capability
target car

• If all cars in neighborhood are monitoring safety
  channel all the time, target car (center) free to
  send BSM anytime in safety channel

SCH interval
CCH interval
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Two questions (at least)

• What does the bit (or bits) mean? Semantics
• Which channel is used as the always-on safety
  channel?

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Two combinations of interest

• (Capability Bit, Channel 172 safety channel)
• (Intention Bit, CCH safety channel)

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(Capability Bit, Channel 172 safety ch.)

• Single-radio vehicle
• Sends BSM on CCH during CCH interval
• Needs to receive BSM on CCH during CCH interval
• Sets bit to 1 in all outgoing WSMs to indicate
  capability
• Dual-radio vehicle
• Always sends BSM on Ch. 172 (no time division)
• If single-radio vehicle in neighborhood, ALSO
  sends BSM on CCH during CCH interval
• Receives BSMs on both Ch. 172 and CCH/CCH Int.
• Sets bit to 0 in all outgoing WSMs to indicate
  capability

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(Intention Bit, CCH safety channel)

• Single-radio vehicle
• Might stay on CCH all the time, or switch to SCH
  during SCH interval (e.g. if interested in
  service)
• Only sets header bit to 1 to indicate intention
  to switch to an SCH on next SCH interval, else
  sets bit to 0.
• Dual-radio vehicle leaves one radio on CCH all
  the time, always sets header bit to 0 to indicate
  intention
• All vehicles
• If a neighbor (or itself) sets header bit,
  vehicle sends BSM on CCH during CCH interval
• Else, vehicle sends BSM on CCH at any time
• Vehicle listens for BSMs on CCH whenever it is on
  CCH

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Congestion under (capability, Ch 172) option
Single-radio vehicle sets header bit to 1, i.e.
b1 vehicle
Dual-radio vehicle (b0) with b1 neighbor
Dual-radio vehicle (b0) within 2 hops of b1
Dual-radio vehicle (b0) more than 2 hops from b1
4 receiving vehicles of interest drawn. Next
slide shows BSMs from additional sending vehicles
that are not drawn
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Congestion under (capability, Ch 172) option
Ch 172 load uniform, CCH load high near b1
CCH Interval
SCH Interval
CCH
Ch 172
CCH
Ch 172
CCH
Ch 172
CCH
Ch 172
BSM from b1 vehicle
BSM from a b0 vehicle w/in 2 hops
BSM from a b0 vehicle with b1 neighbor
BSM from a b0 vehicle gt 2 hops
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Congestion under (intention, CCH) option
RSU
Single-radio vehicle that sets header bit to 1,
i.e. b1 vehicle Only sets bit when intending to
access service (e.g. near RSU)
Single or Dual-radio vehicle (b0) with b1 neighbor
Single or Dual-radio vehicle (b0) within 2 hops
of b1
Single or Dual-radio vehicle (b0) more than 2
hops from b1
4 receiving vehicles of interest drawn.Next
slide shows BSMs from additional sending vehicles
that are not drawn
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Congestion under (intention, CCH) option
RSU
Channel load spreads out
CCH Interval
SCH Interval
BSM from b1 vehicle
BSM from b0 vehicle w/in 2 hops
BSM from b0 vehicle with b1 neighbor
BSM from b0 vehicle gt 2 hops
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Integrated congestion control

• Note that congestion control can be integrated
  into either approach
• Ex (Capability, Ch 172) if load on CCH during
  CCH interval gets high, BSM rate can be reduced
  there, while staying 10 Hz on Ch. 172. Separate
  rate decisions optimize performance on each
  channel
• Ex (Intention, CCH) A vehicle may be
  rate-limited during CCH interval, and might send
  excess in SCH interval to a total of 10 Hz

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Summary of these options

• No Bit
• Simplest. No header bits, decisions, boundary
  conditions
• GID SPAT need to be on Ch. 172
• Single-radio supports safety only
• Allows CCH/SCH interval split more favorable to
  services
• Capability Bit
• Allows migration from single-radio channel
  switching to dual-radio-dominated environment
• BSMs between dual-radio vehicles not subject to
  CCH interval congestion
• Intention Bit
• Like Capability Bit on migration
• Works best where vehicles not switching to SCH
  (e.g. no RSU).
• All vehicles within range of B1 vehicle
  affected by CCH interval congestion

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Bit field definition

• We need to distinguish between two types of
  vehicle
• Do we also need to distinguish a WSM from an RSU?
• Possible 2-bit code

00 b0 vehicle
01 b1 vehicle
10 RSU
11 reserved
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Where in WSM header?
WSM Header
PSID
WSM Data (payload)
WSMP Version
WSM Length
WSM Element ID
Extension Fields
1 byte
variable
4 bytes
2 bytes
variable
1 byte

• Could use bit(s) from Version field
• Could allocate a separate byte
• Needs to be present in all WSMs, so extension
  field is not a good choice

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Next steps

• VSC-A continue narrowing options. Select
  preferred approach based on technical and policy
  evaluation
• IEEE 1609 provide feedback to VSC-A. Continue
  dialog
• IEEE 1609 begin to consider allocating bits in
  WSM header

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• Backup Slides

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FCC Memorandum Opinion and OrderJuly 26, 2006
(FCC 06-110)

• We designate Channel 172 (frequencies
  5.855-5.865 GHz) exclusively for
  vehicle-to-vehicle safety communications for
  accident avoidance and mitigation, and safety of
  life and property applications
• we agree that vehicle-to-vehicle collision
  avoidance and mitigation applications are
  exceptionally time-sensitive and should not be
  conducted on potentially congested channels.
• the delay associated with shared use of a
  time-critical DRSC channel could be literally
  life-threatening in the context of collision
  avoidance

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Taxonomy of Channel Switching Scenarios
Safety on CCH
Safety on Ch. 172
1609.4
Always-on Safety Channel
Always-on Safety Channel
3-way switch
1 radio
2 radios
1 radio
2 radios
1 radio
2 radios
2 radios
1 radio
No Obvious Migration Path
Good Initial Deployment
Long Term Advantages
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Spectrum and Time Usage Maps1609.4, single and
dual radio cases
Multi-Channel continued

• Spectrum Map

Radio 1
Radio 2 optional
Time Map