Coexistence issues between 802.11p and 802.11ac in the proposed UNII-4 band

1. Date: 2013-06-14 Coexistence issues between 802.11p and 802.11ac in the proposed UNII-4 band Authors: Jim Lansford (CSR Technology), John Kenney (Toyota ITC)

2. Abstract Discussion of possible coexistence techniques between 802.11p (DSRC/WAVE) and 802.11ac 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)

3. 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 802.11p • No coexistence mechanism with commercial 802.11 (≥ 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 802.11ac • This will be called the “UNII-4” band • DSRC devices are “Primary”; DSRC and U-NII are not peers • Since 802.11p and 802.11ac are both from the 802.11 family and have similarities, band sharing might be simpler than with non-802.11 incumbent technologies (e.g. radar) • DSRC would take precedence in any band sharing proposal Overview Jim Lansford (CSR Technology), John Kenney (Toyota ITC)

4. Based on 802.11a (and 802.11j) • Uses 10 MHz channel option defined with 802.11j (½ clocked from 20 MHz) • Tighter spectral mask • Slightly different MAC (1609.x enhancements) • So it’s NOT just a minor tweak to 802.11g/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. 802.11p overview (1) Safety Applications Non-Safety Applications Safety App. Sublayer Application Layer SAE J2735 SAE J2945 Security Services Message Sublayer Network and Transport Layers - WSMP Transport Layer –TCP/UDP IETF RFC 793/768 IEEE 1609.2 Network Layer – IPv6 IETF RFC 2460 IEEE 1609.3 IEEE 802.2 LLC Sublayer IEEE 1609.4 MAC Sublayer Extension MAC Sublayer DSRC/WAVE Protocol Stack PHY Layer IEEE 802.11p Jim Lansford (CSR Technology), John Kenney (Toyota ITC)

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

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

7. Standardized by IEEE 1609 WG • IEEE 1609.2 – Security • Defines authentication and encryption algorithms, data structures • IEEE 1609.3 – 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 1609.4 – Multi-Channel Operation • Defines time-division for rendezvous on CCH DSRC Middle Layers Jim Lansford (CSR Technology), John Kenney (Toyota ITC)

8. 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 DSRC Traffic Types Jim Lansford (CSR Technology), John Kenney (Toyota ITC)

9. 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) DSRC Device/Vehicle Types Jim Lansford (CSR Technology), John Kenney (Toyota ITC)

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

11. 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 802.11ac Coexistence Mechanisms Jim Lansford (CSR Technology), John Kenney (Toyota ITC)

12. 802.11ac in the UNII-4 band detects 802.11p 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 802.11p 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 801.11ac techniques Jim Lansford (CSR Technology), John Kenney (Toyota ITC)

13. 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? 802.11p techniques Jim Lansford (CSR Technology), John Kenney (Toyota ITC)

14. 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 802.11p and 802.11ac share a band, it creates the opportunity for a single chipset/module with collaborative coexistence like 802.11 – Bluetooth (adaptive frequencies and packet traffic arbitration) • Between adaptive frequency hopping and PTA, 802.11-Bluetooth coexistence is pretty good • 802.11p and 802.11ac aren’t equal in regulatory, so arbitration rules would be different Other issues Jim Lansford (CSR Technology), John Kenney (Toyota ITC)

15. Both 802.11ac and 802.11p 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 802.11ac to adapt for sharing • 802.11ac has to protect 802.11p traffic • 10MHz CCA in 802.11ac 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 Conclusion Jim Lansford (CSR Technology), John Kenney (Toyota ITC)

16. [1] ETSI DSRC standard http://www.etsi.org/deliver/etsi_en/302600_302699/302663/01.02.00_20/en_302663v010200a.pdf [2] Perahia and Stacey presentation on 11ac at Globecom http://www.ieee-globecom.org/2012/private/T3M.pdf [3] Minyoung’s paper on dynamic channel access in 11ac http://202.194.20.8/proc/ICC2011/DATA/03-063-02.PDF References Jim Lansford (CSR Technology), John Kenney (Toyota ITC)