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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 [email protected]
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