DSRC Spectrum Sharing: Can unlicensed devices share the 5.9 GHz

band without causing interference to DSRC?

IEEE GLOBECOM Industry Forum:

Opportunities and Challenges with Vehicular Networks

John Kenney Toyota InfoTechnology Center, USA

December 10, 2015 jkenney@us.toyota-itc.com

Outline

• What is the issue and why does it matter?

• Who are the stakeholders and what are

they doing?

• What is likely to happen, and when?

2

What is the issue?

• FCC has given DSRC a “Primary”

allocation in 5.850-5.925 GHz

• Wi-Fi community has asked FCC to let

them share the spectrum on the condition

that they cause “no harmful interference”

to DSRC

• Basic question: Is this feasible and if so

how would it work?

3

More details …DSRC

• Initial FCC allocation 1999

• definition of channels and rules in 2003 & 2006

4

5850-

5855

Reserve

5 MHz

CH 172

Service

10 MHz

CH 174

Service

10 MHz

CH 176

Service

10 MHz

CH 178

Control

10 MHz

CH 180

Service

10 MHz

CH 182

Service

10 MHz

CH 184

Service

10 MHz

CH 175

20 MHz

CH 181

20 MHz

5925 MHz5850 MHz

Ch. 172:

Collision Avoidance Safety

Ch. 184: Public Safety

Ch. 178:

Control Channel, advertises services on service channels

DSRC Deployment

• Attention on V2V safety: Ch. 172

– GM Cadillac model year 2017

– NHTSA mandate likely ~2020

• US DOT Pilot Deployments:

– Awarded 2015

– New York, Tampa, Wyoming I-80

– Likely to use channels throughout the band

• DSRC can address ~80% of crash scenarios

• 32,719 US traffic fatalities in 2013

5

USDOT Application Research

6 Source: US Department of Transportation

Most of these use V2I, on channels other than Ch. 172

7

Cooperative Automated Driving

• DSRC devices share sensor information to aid automated

driving application

• High data rate communication with strict performance

requirements, e.g. using DSRC service channels

See: Adaptive Content Control for Communication Amongst Automated Vehicles, F. Fanei et al., IEEE WiVec 2014

US Spectrum is Crowded

8

http://www.ntia.doc.gov/files/ntia/publications/2003-allochrt.pdf

5.850 – 5.925 GHz

The movement toward

spectrum sharing

• Demand for Wi-Fi is high and growing

• Impacts economic growth

• Finding more spectrum for Wi-Fi is considered

strategic by US Government

• FCC approach is to selectively allow Wi-Fi (more

broadly “unlicensed” or U-NII) to share some

spectrum with licensed primary users

• Strict requirement is U-NII does not harmfully

interfere with primary

– Lost and delayed packets degrade DSRC’s ability to

carry out its safety-of-life mission: Harmful Interference

9

U-NII Sharing to Date in 5 GHz

• U-NII2 represents

successful sharing with

radar, e.g. 45 locations

of Terminal Doppler

Weather Radar

• Sharing is based on

“detect & vacate” called

Dynamic Frequency

Selection 10

Source: Cisco Systems

Comparison: Good & Bad News

• Sharing with radar and sharing with DSRC

have similarities and differences:

11

Primary Radar DSRC

Signal Power High Low (10-20 dBm)

Locations Few, static, and known

(?)

Many and mobile

(ubiquitous)

Signal Structure Pulse, specifics not

always known

Well defined preamble,

similar to Wi-Fi

Detect & Vacate? Yes Maybe

Implications for technical sharing proposal discussed below

Major Stakeholders

12

US Congress

US President

Timeline

• Phase 1: February 2012- July 2013

– Congress directs study of 5.9 GHz sharing

– FCC NPRM (asks for comments on many 5 GHz

sharing issues, including 5.9 sharing)

• Phase 2: August 2013 – March 2015

– DSRC Coexistence Tiger Team (sponsored by 802.11)

– DSRC and Wi-Fi stakeholders join in discussion

– Two sharing concepts brought forward

• Phase 3: April 2015 –

– Main focus is testing

– Cisco developed prototypes of their proposal

– Joint testing with automotive stakeholders ongoing

13

Detect & Vacate Concept

Wi-Fi with

DSRC

detector

WiFi

Network

Building

• Wi-Fi devices listen for DSRC

• If no DSRC Wi-Fi ok to operate in 5.9 GHz

• Continues to listen while WLAN operates

• When car appears, Wi-Fi detects DSRC

• If DSRC detected Wi-Fi NOT ok to

operate in 5.9 GHz (minimum TBD

second delay after each DSRC packet)

• Detection leverages DSRC’s heritage as

802.11p

• Note: in-car Wi-Fi will never use 5.9 GHz

Wi-Fi with

DSRC

detector

Building

WiFi

Network

14

Rechannelization Concept

15

Reserv

ed

5 MH

z

CH 172

Service

10 MHz

CH 174

Service

10 MHz

CH 176

Service

10 MHz

CH 178

Control

10 MHz

CH 180

Service

10 MHz

CH 182

Service

10 MHz

CH 184

Service

10 MHz

CH 175 20 MHz

CH 181 20 MHz

5.850 GHz 5.925 GHz

20 MHz 20 MHz 20 MHz

Overlapping Wi-Fi 40 MHz

80 MHz

160 MHz

40 MHz

20 MHz

• Move V2V safety from Ch. 172 to upper band (non-overlap portion)

• Cancel highest 20 MHz Wi-Fi (Ch. 181)

• DSRC use 20 MHz channels in overlap portion instead of 10 MHz

DSRC

Ch. 173

20 MHz

DSRC

Ch. 177

20 MHz

Feedback from

DSRC community

• Detect & Vacate has potential, should be tested

• Fundamentally opposed to Rechannelization

– Cannot protect DSRC from harmful interference

– Detailed critique in 11-14-1101/r1: https://mentor.ieee.org/802.11/dcn/14/11-14-1101-01-0reg-a-response-to-the-re-channelization-

proposal.pptx

– Core idea is to try to share in same time & place

– Note: Rechannelization is a high level concept with

many details not provided

16

Tiger Team R.I.P.

• Wi-Fi interests divided on proposals

• Unable to agree to move ahead with

Detect & Vacate

• IEEE Regulatory Chair ended TT in March

• Final action of Tiger Team was to poll

members on what to do next

– TT voting members approximately equally

split between Wi-Fi and DSRC interests

17

Tiger Team Poll #1:

Do you believe it is technically feasible to protect DSRC

systems from harmful interference if unlicensed (Part 15)

devices share the 5.9 GHz band?

18

Tiger Team Poll #2:

Do you believe [Detect & Vacate] proposed band sharing technique

has merit and, after developing a more complete definition and field

testing, should be considered a basis for a band sharing solution?

19

Tiger Team Poll #3:

Do you believe [Rechannelization] proposed band sharing technique

has merit and, after developing a more complete definition and field

testing, should be considered a basis for a band sharing solution?

20

Compare preference directly:

Team Polls #2 and #3:

21

D&V proposal has merit

Rechannelization proposal

does not have merit

Tiger Team Poll #4:

Which proposal do you support for further specification

development and field testing?

22

Detect & Vacate

Rechannelization

Some combination of both

Testing

• May 6, 2015 FCC Filing by Auto Alliance, Global

Automakers and Cisco:

– “successful efforts to begin testing in the coming

weeks the enhanced … ‘Listen, Detect, and Avoid’

protocol that is under development by Cisco”

• August 21, 2015 FCC Filing by Cisco:

– “Cisco provided a status update on its proof of

concept testing with respect to [DSRC] devices. Cisco

noted that its technology has been reliably able to

listen for DSRC signals at a -95dBm level, which is

the first step in ensuring that unlicensed users of the

bands can detect DSRC. Lab work is proceeding …”

23

Testing Principles

• Encouraged by legislators, stakeholder groups

discussed testing principles: Auto Alliance, Global

Automakers, Intelsat, NCTA, Qualcomm, SES (satellite)

• Letter of agreement sent to FCC, US DOT, US Dept. of

Commerce – Sept. 9, 2015

• Principles include:

– FCC to take testing lead, coordinate testing methods

– Engineers, not lawyers, should decide testing

– Only fully defined proposals with prototypes tested

– All reasonable options to be considered

– Test results of DSRC research should be made public

– Complete testing by end of 2016 if possible

24

European Spectrum Sharing

25

Spectrum Engineering committee SE24

Broadband Radio

Access Networks

(BRAN)

Radio Spectrum

Matters (ERM) Intelligent

Transport

Systems (ITS)

Coordinated ETSI input Direct committee input

ETSI BRAN is preparing TR 103 319:

“Mitigation Techniques to enable

sharing”.

ETSI ITS Liaison to BRAN

notes requirement for

“significant vacate time”

after detection.

What will happen, and when?

• Cannot predict with any confidence

• All parties want resolution

• Possible scenario (not a prediction):

– Details of Detect & Vacate fully defined (e.g. power, timing)

– D&V tested rigorously, shown not to harmfully interfere

– Rechannelization proponents not able to fully define a proposal

that can be shown to avoid harmful interference

– DSRC/Wi-Fi consensus to allow sharing based on D&V. FCC

rule reflects agreement.

– Individual Wi-Fi suppliers decide whether to offer products with

5.9 GHz support based on business decision

• 2016 will be critical for testing and resolution.

26

Summary

• DSRC safety-of-life mission. Primary allocation

from FCC in licensed 5.9 GHz band.

• Wi-Fi stakeholders want to share 5.9 GHz

• Government stakeholders recognize value of

increased Wi-Fi spectrum & need to protect DSRC

• Two sharing concepts.

– D&V: no sharing same time and space. Testing started.

– Rechannelization uses aggressive sharing, cannot

protect DSRC

• Both technical and non-technical forces at play

• Biggest threat to successful DSRC deployment 27

Backup Slides

• Some harmful interference scenarios

28

DSRC Harmful Interference:

Loss of safety message

U-NII

U-NII packet

DSRC pckt

COLLISION DSRC Packet

not received

time

Packet collisions

U-NII packet

DSRC pckt

COLLISION DSRC Packet

not received

29

Lead vehicle transmits DSRC safety message. Host vehicle attempts to receive

safety message. U-NII packet prevents DSRC reception

• Note: Second case mitigated if U-NII has DSRC detector, but first case is not

DSRC Harmful Interference:

Delay of safety message

U-NII

DSRC ready to send packet, backoff DSRC packet sent

time

Indefinite Delay

Inter-frame

space

DSRC pckt

U-NII U-NII U-NII U-NII U-NII

30

Frame Concatenation or

alternating use among

multiple U-NII devices

Lead vehicle’s safety message is delayed indefinitely