VSC-A Multi-Channel Operation Investigation: An update to IEEE 1609

1. VSC-A Multi-Channel Operation Investigation: An update to IEEE 1609 * VSC-A: Vehicle Safety Communications - Application

2. 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

3. Phase 1 Study: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 1 radio 2 radios Interested in this approach

4. Ch 172 Ch 174 Ch 176 Ch 178 Ch 180 Ch 182 Ch 184 Control messages Safety messages DSRC Services DSRC Services DSRC Services DSRC Services DSRC Services time CCH interval CCH interval SCH interval SCH interval time 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

5. Phase 2 Study:What can we do with extra O-T-A information? • Add information to WSM header reporting sender’s 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 • We’ve looked at several variations, and are interested in two

6. 1 0 0 0 0 1 0 0 0 0 payload payload payload payload payload payload payload payload payload payload Example, Case 1: At least one car in neighborhood 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 car’s sending behavior dictated by its local neighborhood Heartbeat, with WSM header bit indicating enhanced capability target car Heartbeat, with WSM header bit indicating limited capability Vehicle needs BSM in CCH interval SCH interval CCH interval

7. 0 0 0 0 0 0 0 0 0 payload payload payload payload payload payload payload payload payload Example, Case 2: all cars in neighborhood can monitor safety channel for entire sync period If all cars in neighborhood are monitoring safety channel all the time, target car (center) free to send BSM anytime in safety channel Heartbeat, with WSM header bit indicating enhanced capability target car SCH interval CCH interval

8. Two questions (at least) • What does the bit (or bits) mean? Semantics • Which channel is used as the always-on safety channel?

9. Two combinations of interest • (Capability Bit, Channel 172 safety channel) • (Intention Bit, CCH safety channel)

10. (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

11. (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

12. 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

13. 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 > 2 hops

14. Y 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

15. Y 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 > 2 hops

16. 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

17. 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

18. 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:

19. Where in WSM header? WSM Header • 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 WSMP Version PSID Extension Fields WSM Element ID WSM Length WSM Data (payload) 1 byte variable 4 bytes variable 2 bytes 1 byte

20. 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

21. Backup Slides

22. FCC Memorandum Opinion and Order:July 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”

23. 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 1 radio 2 radios No Obvious Migration Path Good Initial Deployment Long Term Advantages

24. Multi-Channel continued Ch 172 Ch 174 Ch 176 Ch 178 Ch 180 Ch 182 Ch 184 Control messages and Basic Safety messages Safety “services” (e.g. pre-crash?) DSRC Services DSRC Services DSRC Services DSRC Services DSRC Services CCH interval SCH interval CCH interval SCH interval CCH interval CCH interval SCH interval SCH interval time time Spectrum and Time Usage Maps:1609.4, single and dual radio cases Spectrum Map Radio #1 Radio #2 optional Time Map