VSC-A Multi-Channel Operation Investigation: A report to IEEE 1609

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 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”

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

5. 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

7. 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

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

11. Ch 172 Ch 174 Ch 176 Ch 178 Ch 180 Ch 182 Ch 184 Control messages and Safety messages Session-oriented Safety messages 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

12. 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 Spectrum and Time Usage Maps:always-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

15. Basic Idea: Provide migration path • Add information to WSM header reporting sender’s 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

16. 0 1 1 1 1 0 1 1 1 1 payload payload payload payload payload payload payload payload payload payload Case 1: At least one single-radio car in neighborhood indicates limited capability If at least one car in neighborhood sends packets with bit indicating limited capability, target car (center) sends heartbeat during CCH interval in CCH Heartbeat, with WSM header bit indicating enhanced capability target car Heartbeat, with WSM header bit indicating limited capability Single-radio vehicle SCH interval CCH interval

17. 1 1 1 1 1 1 1 1 1 payload payload payload payload payload payload payload payload payload Case 2: all cars have enhanced capability If all cars in neighborhood have enhanced capability, target car (center) free to send heartbeat anytime in safety channel Heartbeat, with WSM header bit indicating enhanced capability target car SCH interval CCH interval

18. 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)

19. 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