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Response to CID 472 Concerning the San Francisco Presentation. Authors:. Date: 2008-11-04. Abstract.

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response to cid 472 concerning the san francisco presentation
Response to CID 472 Concerning the San Francisco Presentation


Date: 2008-11-04

Carl Kain, Noblis (USDoT)


This presentation provides a response to CID 472 (and all related comments) from Andrew Miles addressing his concern that 802.11p will not work based on a VSC presentation made in San Francisco. That presentation gave preliminary results from an experiment designed to quantify adjacent channel interference for a certain class of vehicle to vehicle applications with a specific transceiver implementation.

Carl Kain, Noblis (USDoT)

andrew s comment
Andrew’s Comment
  • During the San Francisco meeting, a presentation was given that claims experiments show adjacent channel interference is a significant problem when 11p is used in a way similar to the way it is used by IEEE 1609I requested:Please either explain how 11p can be used in its current form or make appropriate modification to either 11p and/or IEEE 1609 so that 11p can be used:

Carl Kain, Noblis (USDoT)

some background for the response
Some Background for the Response
  • 802.11p, when used in the 5.9 GHz band in the USA, is being designed for any Intelligent Transportation Systems application, both vehicle to vehicle, and vehicle to roadside.
  • It can be used for any applications (not just ITS) regulatory agencies might allow in any band in any country.
  • The presentation Andrew saw was from the Vehicle Safety Consortium, only one of many potential stakeholders
    • This group researches a specific type of vehicle to vehicle safety applications (their area of interest)
    • Their main concern is in the specific case of this subset of applications, with a multichannel transceivers on the vehicle (this is not the only option), the transceivers are operated in an uncoordinated manner (this is not the only option) and there has to be certain geometries with units that may be using an adjacent channel simultaneously, and only when it is in extremely close proximity.
  • IEEE 1609 is an upper layer standard that can be used as part of the DSRC protocol suite (it is not mandatory) and it actually provides a solution to the CCI problem discussed in the experiment that was briefed in San Francisco.
  • There are many vehicle to roadside and vehicle to vehicle applications where CCI is not an issue, and 802.11p should work fine.

Carl Kain, Noblis (USDoT)

sample applications for 802 11p
Here is a partial sample of uses planned for this technology:

Emergency Vehicle Approaching warning

Emergency Vehicle At Scene warning

Highway Variable Signage- Work Zone warning- School zone warning- Exit facility information- Icy Bridges- Low overhead (bridge, parking garage, storage) - Wrong Way Warning

Curve speed warning (rollover warning)

Road condition warning to other vehicles- Road feature notification- Environmental sensing notification

Traffic signal violation warning (in-vehicle warning)

Road Surface Conditions to TOC (potholes)

Vehicle Probes Provide Weather Data

SOS services

Enhanced Route Guidance and Navigation- Off-board navigation- Dynamic traffic information- Optimize routing- Incident information

Fleet Management- Driver advisories and information- Location tracking and scheduling- Optimize routing- Mission downloading

Sample Applications for 802.11p

Carl Kain, Noblis (USDoT)

sample applications continued
Crash Data to Transportation Operations Center (TOC)

Origin & Destination (OD) Data to TOC

Crash Data to Public Service Answering Point (PSAP)

Post-crash Incident warning to other vehicles

Diagnostic Downloads

Directory Search - Point of Interest

Data transfer / Info-fueling

Data Downloads- Entertainment media- Software upgrades- Map updates

Access Control - parking gates- Commercial vehicle electronic clearance- Border crossing

Electronic payments- Fast Food driver through, gas- Parking fees- toll fees

Highway/rail collision warning- Optimize gate down time

Intersection collision warning

Stop Sign Movement Assistance

Stop Sign Violation Warning

Lane change warning

Sample Applications Continued

Carl Kain, Noblis (USDoT)

sample applications continued1
Safety Recall Notice

Emergency vehicle signal preemption

Safety Event Recorder

Emergency Electronic Brake Lights

Car Dealer Service processing

On-Board Safety Data Transfer

Rental Car processing

Vehicle Safety Inspection

Dynamic Interactive Emissions Tests

Remote Traffic Camera

Just-In-Time Repair Notification

Pre-crash sensing

Cooperative Adaptive Cruise Control (ACC)- Platooning

Cooperative collision warning- Cooperative Forward Collision Warning

Emergency Vehicle Video Relay

Visibility Enhancer

Cooperative glare reduction- Adaptive Headlight adjust

Parking Spot Locator

Internet Audio & Video

Receiving / Sending E-mail

Stolen Vehicle Tracking

Web Browsing

Mechanical Failure Warning

Sending Vehicle Data To Service Provider

Adaptive Drive train Management

Advertisements (e.g. dealership)

Instant messaging (between vehicles)

Acquisition of Customer Data & Preferences

Speed Limit Assistant

Blind spot warning- Blind merge warning

Highway merge assistant

Sample Applications Continued

Carl Kain, Noblis (USDoT)

sample applications continued2
Left turn assistant

Pedestrian Crossing Information at Designated Intersections

Emergency Vehicle Initiated Traffic Pattern Change

Transit Vehicle Data Transfer (gate/yard)

Transit Vehicle Priority at Traffic Signal

Intelligent On-Ramp Metering

Intelligent Traffic Flow Control- Vehicle Occupant count

In-Vehicle Amber (Crime) Alert

Driver's Daily Log

Hazardous Material Cargo Tracking

Locomotive Data Transfer

Low bridge - Alternate routing

Weigh Station Clearance

Limited Height Warning- Overhead storage reminder- Low Parking Structure- Low bridge

Concierge Services- Hotel and restaurant reservations- Shopping- Airline scheduling- Parking reservations

Evacuation planning

Instant carpool matching

Interactive Emission testing/reporting

eGovernment Services and Announcements - Permitting commercial loads

Vehicles as Traffic Probes

Sample Applications Continued

Carl Kain, Noblis (USDoT)

sample applications concluded
Sample Applications Concluded
  • The previous list is not complete or exhaustive, and is subject to additions at the creativity of the application designers.

Carl Kain, Noblis (USDoT)

  • There are dozens of 802.11p applications where the VSC concerns of cross channel interference as presented in San Francisco do not apply
  • The VSC presentation was quality, informative, preliminary research on what they need to do for the subset of applications (perhaps as few as seven applications at this time) to get ANY radio system to work
    • cross channel interference (per their report), is really adjacent channel interference that exists in all radio services and is a design issue not unique to 802.11, however the San Francisco report quantifies it for certain circumstances in 802.11
  • There are multiple techniques to mitigate the CCI problem that the VSC is aware of and is currently performing research on.

Carl Kain, Noblis (USDoT)

vsc preliminary assessment
VSC Preliminary Assessment
  • Draft 802.11p will work in conjunction with trial use IEEE 1609.x standards and existing FCC regulations.  Under IEEE 1609.4, safety and control messages are sent on the Control Channel (CCH) during the CCH interval.  No transmissions are allowed on a non-CCH channel during the CCH interval, so safety and control messages are not subject to any cross-channel interference (CCI) of the type discussed in 11-07-2133. 
  • Non-safety messages sent on a Service Channel (SCH) are potentially subject to CCI from transmissions on other SCHs.  However, the non-critical nature of these messages means that making 802.11p "work" amounts to reducing CCI-induced packet loss to acceptable levels.  Note that most of the results in 11-07-2133 were from tests in which the interferer was active essentially all the time, and thus PER values would be expected to be lower in realistic environments.

Carl Kain, Noblis (USDoT)

vsc preliminary assessment cont d
VSC Preliminary Assessment Cont’d
  • There are a variety of tools available for controlling CCI-induced packet loss on SCHs for non-critical messages, including:
    • 1) FCC licenses of SCH spectrum to road-side equipment (RSE): in most cases the density of RSEs will be low enough that their transmission ranges either will not overlap, or they will be assigned to channels far enough apart so that the transmissions of devices on a channel assigned to one RSE contribute negligibly to the CCI experienced by devices operating on a channel assigned to another RSE. 
    • 2) Message rate redundancy: a given message can be transmitted more than once to increase the probability that it is received correctly at least once.  This tool is expected to be used in DSRC communication, especially for messages destined to a group address, for which no ACK will be sent.  Even where no CCI effects will be felt, e.g. safety messages on the CCH, the nominal message rate will exceed that needed by the application layer in order to compensate for physical layer bit errors and MAC collisions inherent to 802.11 environments. Message rates are not subject to any DSRC standards. 
    • 3) 802.11p is adding enhanced channel rejection levels, compared to baseline 802.11, to further reduce the effects of CCI. For CCI sensitive applications, this should be used.
    • 4) if two radios are deployed in one vehicle, their operation can be coordinated so that they do not needlessly interfere with each other.  For example, if one radio is in the process of receiving a packet on one channel, the second radio can opt to defer transmission on a different channel until the first reception is complete.  Dual-radio coordination is not subject to standardization. 
  • Taken together, these tools can reduce the level of CCI-induced packet errors to an acceptably low level for non-critical messages.  

Carl Kain, Noblis (USDoT)

vsc preliminary assessment concluded
VSC Preliminary Assessment concluded
  • The conclusion is that critical safety messages will not experience CCI due to 1609.4 time division, and non-critical messages will employ CCI-mitigation tools so that draft 802.11p will work as currently defined."

Carl Kain, Noblis (USDoT)

what specifically is being done to minimize effects in regulations and in the standards
What Specifically is Being Done to Minimize Effects in Regulations and in the Standards?
  • ITS is a licensed service in the USA
    • The vehicle safety channel and the control channel are not adjacent; the public safety channel and control channel are also not adjacent
    • Roadside units are licensed and the locations, antenna data, ERP, channel assignments being used etc. will be in the publicly available Universal License System database. Systems will be engineered to avoid using adjacent channels on RSUs in close proximity, as they routinely are in all licensed radio services.
  • Modifications to 802.11 (TGp)
    • More stringent adjacent channel rejection and non-adjacent channel rejection
    • The specification of tighter transmission masks
  • Features in IEEE 1609
    • 802.11 radio can be controlled from upper layers whereby communications is established on control channel and STAs are instructed to switch to service channel to ensure transmissions occur only on one channel at a time
  • Experimentation results such as those presented in San Francisco (11-07-2133) are guidance to application designers to consider the physics and operation of wireless devices when implementing any of the over 100 potential ITS applications using the 802.11p standard.

Carl Kain, Noblis (USDoT)

bottom line
Bottom Line
  • The consortium that made the San Francisco presentation feels the 802.11 amendment will work in its current form
    • Additional improvements are being made to the IEEE 1609 trial use standards, which are currently being modified to ballot as full use standards.
  • The San Francisco presentation was on some basic research to quantify a potential problem using worst case conditions.
    • 802.11 p has stringent transmit masks and tighter adjacent channel interference rejection values to reduce CCI to more acceptable levels.
    • The duty cycles were artificially high and multi-channel receivers were used (there are other implementations)
  • The VSC is funded to perform further research on implementations of certain specific vehicle to vehicle safety applications, and at this time, does not feel CCI is an insurmountable problem
  • There are dozens of applications where the CCI issue does not apply
  • There are provisions in both 802.11p and IEEE 1609 that give application designers several ways to obtain acceptable performance.

Carl Kain, Noblis (USDoT)

  • Correspondence with the VSC
    • Special thanks to John Kenney for providing additional insight into the details behind the test results given in San Francisco.

Carl Kain, Noblis (USDoT)