1. January 2013
doc.: IEEE /0153r0
May 2013
Coexistence issues between p and ac in the proposed UNII-4 band
Authors:
Date:
Jim Lansford (CSR Technology), John Kenney (Toyota ITC)
Clint Chaplin, Chair (Samsung)

2. January 2013
doc.: IEEE /0153r0
May 2013
Abstract
Discussion of possible coexistence techniques between p (DSRC/WAVE) and ac extended into the proposed UNII-4 band
Disclaimer: This presentation is for discussion purposes only, and does not represent the official position of the presenters’ employers or any industry group
Jim Lansford (CSR Technology), John Kenney (Toyota ITC)
Clint Chaplin, Chair (Samsung)

3. Overview DSRC was designed for the 5.9GHz ITS band
May 2013
Overview
DSRC was designed for the 5.9GHz ITS band
Licensed under FCC Part 90 and 95
Uses “communication outside the context of a BSS” defined in p
No coexistence mechanism with commercial (≥ 20 MHz channels)
FCC designates certain channels, e.g. V2V safety, control, public safety
802.11ac was designed with coexistence mechanisms for mixed 20/40/80/dual 80/160 environments
In NPRM 13-22, the FCC has proposed spectrum sharing between the 5.9GHz ITS band and unlicensed technologies such as ac
This will be called the “UNII-4” band
DSRC devices are “Primary”; DSRC and U-NII are not peers
Since p and ac are both from the family and have similarities, band sharing might be simpler than with non incumbent technologies (e.g. radar)
DSRC would take precedence in any band sharing proposal
Jim Lansford (CSR Technology), John Kenney (Toyota ITC)

4. Non-Safety Applications
May 2013
802.11p overview (1)
Based on a (and j)
Uses 10 MHz channel option defined with j (½ clocked from 20 MHz)
Tighter spectral mask
Slightly different MAC (1609.x enhancements)
So it’s NOT just a minor tweak to g/n/ac
Differences in layers above PHY and MAC as well
Special FCC channel designations:
Ch. 172 is for vehicle collision avoidance communication
Ch.178 is the control channel
Ch. 184 is for long distance public safety communication
Europe: Similar band/channelization
Japan: Uses 11p PHY in 700 MHz, but higher layers quite different.
IEEE
Non-Safety Applications
IETF RFC 2460
Safety Applications
IEEE
802.2
PHY Layer
MAC Sublayer
MAC Sublayer Extension
LLC Sublayer
Application Layer
Network and Transport Layers - WSMP
Safety App. Sublayer
IEEE p
IEEE
SAE J2735
SAE J2945
IETF RFC 793/768
Transport Layer –TCP/UDP
Network Layer – IPv6
IEEE
Security Services
Message Sublayer
DSRC/WAVE Protocol Stack
Jim Lansford (CSR Technology), John Kenney (Toyota ITC)

5. 802.11p overview (2) DSRC Use Cases May 2013
Jim Lansford (CSR Technology), John Kenney (Toyota ITC)

6. DSRC Spectrum May 2013 Shared Public Safety /Private Service
Designated Public Safety
Control
Channel
Medium Range
Service
Short Range
Service
V2V and
Safety of Life
Long Range
Intersections
Power Limits
(dBm EIRP)
44.8
44.8 dBm
40.0
Public limit
Private limit
40 dBm
33.0
33 dBm
23.0
23 dBm
Frequency(GHz)
5.850
5.855
5.865
5.875
5.885
5.895
5.905
5.915
5.925
Ch 172
BSMs
Ch 174
Ch 176
Ch 178
CCH
Ch 180
Ch 182
Ch 184
Public Safety
Jim Lansford (CSR Technology), John Kenney (Toyota ITC)

7. DSRC Middle Layers Standardized by IEEE 1609 WG IEEE 1609.2 – Security
May 2013
DSRC Middle Layers
Standardized by IEEE 1609 WG
IEEE – Security
Defines authentication and encryption algorithms, data structures
IEEE – Networking Services
Defines WAVE Short Message Protocol (WSMP) – lightweight alternative to UDP/IP
Defines WAVE Service Advertisement (WSA) – sent on CCH to advertise services in an area
IEEE – Multi-Channel Operation
Defines time-division for rendezvous on CCH
Jim Lansford (CSR Technology), John Kenney (Toyota ITC)

8. DSRC Traffic Types Communication at MAC sub-layer can be:
May 2013
DSRC Traffic Types
Communication at MAC sub-layer can be:
Unicast or Broadcast
Single hop or multi-hop
SAE standards define message formats and application requirements
SAE J2735 DSRC Message Set Dictionary
Basic Safety Message
14 other message types
SAE J2945 DSRC Minimum Performance Requirements
Data element accuracy and age (vehicle sensors)
Transmission behavior (message frequency, modulation, Tx power)
Protocol dialogues
Jim Lansford (CSR Technology), John Kenney (Toyota ITC)

9. DSRC Device/Vehicle Types
May 2013
DSRC Device/Vehicle Types
Light Vehicle
Factory integrated (rich sensor data)
“Aftermarket Safety Device” (ASD, usually relies on GPS)
“Vehicle Awareness Device” (VAD, Tx only, full CSMA/CA MAC)
Emergency Vehicle
Police, Fire, Ambulance – special Tx permissions
Commercial
Transit
Tracked (train, including light rail)
Motorcycle
Vulnerable Road User (road worker, pedestrian, bicycle)
Jim Lansford (CSR Technology), John Kenney (Toyota ITC)

10. 802.11p PPDU Structure Same as 802.11a, but twice the length May 2013
Jim Lansford (CSR Technology), John Kenney (Toyota ITC)

11. 802.11ac Coexistence Mechanisms
May 2013
802.11ac Coexistence Mechanisms
This figure above from [2] illustrates how 20MHz systems can do CCA
The figure below from [3] shows how an 80MHz system does CCA on multiple 20MHz preambles
Jim Lansford (CSR Technology), John Kenney (Toyota ITC)

12. May 2013
801.11ac techniques
802.11ac in the UNII-4 band detects p preambles during CCA
Pros:
Leverages existing primary/secondary-n CCA
802.11p/DSRC doesn’t have to do anything
Better solution than energy detection
False alarms from energy detection are very undesirable
Cons:
Preambles of p are twice as long as 11a/n
High power channels (178 and 184) will possibly cause adjacent and alternate channel interference that CCA may not detect
After detection, what?
Channel transition interval
Non-occupancy interval
Jim Lansford (CSR Technology), John Kenney (Toyota ITC)

13. 802.11p techniques Transmit an “intolerance” bit
May 2013
802.11p techniques
Transmit an “intolerance” bit
No particular advantage – 11ac would have to be able to process 11p frames to do this, so 11ac might as well do CCA
Use of Service Channels in the upper part of the band (Ch 180/182) first
Doesn’t solve channel 172 problem
Others?
Jim Lansford (CSR Technology), John Kenney (Toyota ITC)

14. May 2013
Other issues
There has been some discussion about moving the collision avoidance channel (CH 172) to the upper part of the band
Puts two high powered signals in adjacent channels
Major change to existing DSRC channel definition
Requires significant re-testing of DSRC safety functions
The good news: If p and ac share a band, it creates the opportunity for a single chipset/module with collaborative coexistence like – Bluetooth (adaptive frequencies and packet traffic arbitration)
Between adaptive frequency hopping and PTA, Bluetooth coexistence is pretty good
802.11p and ac aren’t equal in regulatory, so arbitration rules would be different
Jim Lansford (CSR Technology), John Kenney (Toyota ITC)

15. Conclusion Both 802.11ac and 802.11p are baked
May 2013
Conclusion
Both ac and p are baked
802.11p wasn’t designed for band sharing
802.11ac can’t process 10MHz channels
802.11p is the primary user in the band
Puts the burden on ac to adapt for sharing
802.11ac has to protect p traffic
10MHz CCA in ac is one way forward
Double length preamble
Up to 7 possible channels to monitor
Adjacent/alternate channels are problematic
NPRM process is rolling
Industry must come to consensus soon
Jim Lansford (CSR Technology), John Kenney (Toyota ITC)

16. References [1] ETSI DSRC standard
May 2013
References
[1] ETSI DSRC standard
[2] Perahia and Stacey presentation on 11ac at Globecom
[3] Minyoung’s paper on dynamic channel access in 11ac
Jim Lansford (CSR Technology), John Kenney (Toyota ITC)