CICAS-V Progress Briefing

1
VSC-A Multi-Channel Operation Investigation A
report to IEEE 1609 VSC-A Vehicle Safety
Communications - Application
2
VSC-A Project Statement of Work

• Subtask 5.2.6 Channel 172 Usage
• In light of the recent FCC memorandum
  designating DSRC channel 172 exclusively for
  vehicle-to-vehicle safety communication the
  VSC-A team proposes to study methods for
  optimizing the use of channel 172 for VSC-A
  applications. An analysis will be conducted to
  determine potential approaches . This analysis
  will also take into account the current and
  related activities (channel switching) in IEEE
  1609.4. VSC-A team to determine and recommend
  an optimal usage approach for this channel.
  (emphasis added)

3
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

4
VSC-A Multi-Channel Work

• Two pronged study
• Quantitative analysis of 1609.4 50/50 Channel
  Switching performance not part of this
  presentation
• Consideration of alternative approaches
• Includes qualitative comparison with 1609.4

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Constraints applied to alternatives (initial
study)

• Single-radio must be sufficient for safety
  second radio may optionally be deployed.
  Dual-radio deployments assume they co-exist with
  single-radio deployments
• No additional over-the-air protocol information
• Each vehicle attempts to hear all safety messages

6
Criteria for evaluating Multi-Channel scenarios

• How well does single radio support safety
  applications and non-safety applications?
• Does optional second radio provide demonstrable
  benefit?
• Is channel 172 used for V-V Safety
  communications?
• Criteria importance not assumed equal criteria
  are subjective

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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
8
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
Defer
Focus
Focus
Will not pursue further
9
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
Good Initial Deployment
Long Term Advantages
10
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
11
Spectrum and Time Usage Maps1609.4, single and
dual radio cases

• Spectrum Map

Radio 1
Radio 2 optional
Time Map
12
Spectrum and Time Usage Mapsalways-on Ch 172,
single and dual radio cases

• Spectrum Map

Radio 1
Radio 2 optional
Time Map
13
Qualitative Comparison

• 1609.4 single-radio has broad functionality
• 1609.4 single-radio capacity for safety very
  limited
• 1609.4 dual-radio does not add much capability
• Ch 172 single-radio has 2x capacity for safety
• Ch 172 single-radio does not support control or
  non-safety
• Ch 172 dual-radio has attractive trade-off
  between safety capacity and non-safety support
• No obvious migration between 1609.4 single-radio
  and Ch 172 dual-radio

14
Reconsider constraints applied to alternatives
ongoing study
Keep This

• Single-radio must be sufficient for safety
  second radio may optionally be deployed and
  assumes it co-exists with single-radio
  deployments
• No additional over-the-air protocol information
• Each vehicle attempts to hear all safety messages

Relax This
Keep This but single-radio and dual-radio have
different capabilities
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Basic Idea Provide migration path

• Add information to WSM header reporting senders
  multi-channel intent/capability
• Simplest case 1-bit indicates if sender is
  single-radio
• More sophisticated cases possible as well
• Dual-radio vehicle monitors neighbors
• Adapts behavior based on presence/absence of
  single-radio neighbors
• Simplest case if at least one single-radio
  neighbor, revert to 1609.4, else use always-on
  safety channel

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Case 1 At least one single-radio car in
neighborhood indicates limited capability
Heartbeat, with WSM header bit indicating
enhanced capability
target car
Heartbeat, with WSM header bit indicating limited
capability
Single-radio vehicle

• If at least one car in neighborhood sends packets
  with bit indicating limited capability, target
  car (center) sends heartbeat during CCH interval
  in CCH

SCH interval
CCH interval
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Case 2 all cars have enhanced capability
Heartbeat, with WSM header bit indicating
enhanced capability
target car

• If all cars in neighborhood have enhanced
  capability, target car (center) free to send
  heartbeat anytime in safety channel

SCH interval
CCH interval
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Basic Idea Provide migration path

• VSC-A considering several flavors of this
  approach
• Goal is to provide single-radio vehicles with
  best safety that 1609.4 can support
• Provide dual-radio vehicles with more access to
  safety information, using extra capacity not
  available to single-radio vehicles during times
  of congestion
• Header information can also be used to indicate
  intent to access a service
• This idea makes most sense if, eventually, most
  vehicles have enhanced capability (i.e.
  dual-radios)

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VSC-A next steps

• Continue exploring alternatives
• Simulation study to determine performance of
  candidates
• Implement in vehicle testbed to prove feasibility
• Dialog with IEEE 1609.4
• Select preferred approach based on technical and
  policy evaluation