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Sharing the 5.9 GHz Band Between Unlicensed Devices and DSRC
Jim Lansford, Ph.D. Fellow, Global Standards, CSR & Adjunct, Interdisciplinary Telecomm Program University of Colorado - Boulder
2 © Cambridge Silicon Radio Limited 2015
Use Cases for Wi-Fi in IVI
Internet connectivity (via in-car modem or tethering) Streaming or Fast content downloading at hotspots (Redbox “filling
station”)
Displays (mirroring, A/V content to other screens)
3 © Cambridge Silicon Radio Limited 2015
• The demand for Wi-Fi in vehicles is increasing
rapidly – almost 30% CAGR
• Use cases will require simultaneous internet
tethering and video streaming
• Use cases will also require multiple simultaneous
video streams
• 160MHz bandwidth modes in 802.11ac can’t be used
today without DFS − DFS is problematic in mobile environments
• Poor availability, especially in urban environments
• False alarms
− Detection algorithms interrupt video streaming
• ITS band is not being used significantly today − Extending unlicensed use into 5.9GHz band makes 160MHz
channels available
Why 5.9GHz Spectrum Sharing?
4
Current view/existing spectrum Channelization for 20/40/80 MHz
• The U-NII-1 band (5150-5250MHz) was approved for outdoor use in 2014 • An automobile is considered outdoor use
• U-NII-1 can only be used indoors in Europe and Japan
• U-NII-2A (5250-5350MHz), U-NII-2B, and U-NII-2C (5470-5725MHz) are
problematic for vehicles • Requires Dynamic Frequency Selection (DFS) – poor channel availability
•Thus, only TWO 80MHz channels can be used in the US without DFS for
11ac in cars • U-NII-3 was expanded to 125MHz in May 2014
• Five channels of 40MHz are available
• 160 MHz is not currently available for automotive applications without DFS
• Europe allows 25mW in U-NII-3
• Japan doesn’t allow U-NII-3 for WLAN
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6
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IEEE channel
# 20 MHz
40 MHz
80 MHz
5170
MHz
5330
MHz
5490
MHz
5710
MHz
5735
MHz
5835
MHz
160 MHz
144
169
5
NPRM 13-22 (13-49) Background
• FCC allocated 75MHz of spectrum in the 5.9GHz band (5850-5925MHz) for Dedicated Short Range Communications (DSRC) in October 1999
• In FCC NPRM 13-22 (13-49), the FCC invited comments about sharing the DSRC band, which would be U-NII-4
− DSRC would remain as a primary user of the band
• 802.11ac could be modified to operate in this new U-NII-4 band if approved by the FCC
• FCC did not specify the framework or etiquette by which band sharing would occur, other than unlicensed devices cannot cause “harmful interference”
6
• Ad hoc V2X communication
• Several hundred meter range
• Applications include Safety, Mobility, Commercial, …
• 75 MHz of dedicated spectrum in 5.9 GHz
DSRC Overview
Reserv
ed
5 M
Hz
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
Ch. 178: Control Channel
Advertise services on other channels
Ch. 184: High Power
Public Safety
Ch. 172: Collision Avoidance Safety
FCC DSRC Channel
Designations
7
• IEEE 802.11 convened a “Tiger Team” in August 2013 to address the spectrum sharing issue
− DSRC lower layers are 802.11p – a 10MHz variant of 802.11a
− Open to participation by anyone
• Two proposals presented
− “Detect and Avoid”
− Spectrum repacking
• IEEE Tiger Team completed its work in March
− No consensus position
− Filed a final report with a summary of activities and straw poll results
• No official position from IEEE 802
IEEE “Tiger Team” on spectrum sharing
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Band Plan with Proposed New Spectrum in 5GHz (11ac) - NPRM 13-22/49
• Wide bandwidth channels desired to support high throughput requirements
• At the same time, large number non-overlapping channels desired to support high QoS requirements − To avoid co-channel interference
• Current U-NII spectrum allows only − Six 80 MHz channels
− Two 160 MHz channels
• Additional unlicensed use of 5.35-5.47 GHz and 5.85-5.925 GHz would potentially allow a total of − Nine 80 MHz channels (Three new)
− Four 160 MHz channels (Two new)
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IEEE channel #
20 MHz
40 MHz
80 MHz
160 MHz
UNII-1 UNII-2 UNII-2 UNII-3
5250
MHz
5350
MHz
5470
MHz
5725
MHz
NEW
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92
88
84
80
76
72
68
169
173
177
181
5825
MHz
5925
MHz
NEW
Currently available channels New channels
Possibly shared between DSRC and WLAN
DSRC
9
DSRC and U-NII-4 Devices in 5.9 GHz Band
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50
DSRC
[10 MHz]
Service
Chan 184
DSRC
[10 MHz]
Service
Chan 182
DSRC
[10 MHz]
Service
Chan 180
DSRC
[10 MHz]
Control
Chan 178
DSRC
[10 MHz]
Service
Chan 176
DSRC
[10 MHz]
Service
Chan 172
DSRC
[10 MHz]
Service
Chan 174
Res.
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40
58
55
58
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58
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58
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58
75
58
80
58
85
58
90
58
95
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00
59
05
59
10
59
15
59
20
59
25
58
45
Exp. UNII
[160 MHz]
Center Chan 163
Exp. U-NII-4
[40 MHz]
Center Chan 175
Exp. U-NII-4
[40 MHz]
Center Chan 167
Exp. U-NII-4
[20 MHz]
Center Chan 177
Exp. U-NII-4
[20 MHz]
Cente Chan 173
Exp. U-NII-4
[20 MHz]
Center Chan169
Exp. U-NII-4
[20 MHz]
Center Chan 181
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80
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85
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90
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95
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00
59
05
59
10
59
15
59
20
59
25
58
45
Frequency
(MHz)
Frequency
(MHz)
DSRC Band
[10 MHz Channels]
Proposed
U-NII-4 Expansion
[20 MHz Channels]
Proposed
U-NII-4 Expansion
[40 MHz Channels]
Proposed
U-NII-4 Expansion
[160 MHz Channels]
Exp. U-NII-4
[80 MHz]
Center Chan 171
Proposed
U-NII-4 Expansion
[80 MHz Channels]
DSRC
U-NII-4
U-NII-4
U-NII-4
U-NII-4
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Possible DSRC coexistence techniques (1/2)
802.11ac in the U-NII-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
− Exact CCA detection level is TBD, but must be at least as low as DSRC
chipsets
− Cons: • Preambles of 802.11p are twice as long as 11a/n
• May have to detect all seven channels in parallel − Increased complexity in Wi-Fi chips could make this a non-starter
• Adjacent and alternate channels cannot be sensed by CCA
• May make U-NII-4 unusable in many environments – like DFS
− After detection, what? • Channel transition interval
• Non-occupancy interval
− Summary of Proposal #1: silent for 10 seconds after the last 11p
preamble detect – similar to setting a NAV for CCA_true+10
seconds
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Possible DSRC Sharing Techniques (2/2)
• Repacking the DSRC band − “Important” channels (current 172, 178, 184) would be moved to
upper part of band
− DSRC would not share upper 30MHz – reserved for BSM and other
priority traffic (Europe has partially overlapping 30MHz for ITS)
• Minimal impact to 802.11ac and allows 160MHz channels
• Impacts to existing DSRC equipment and FCC rulemaking − Proposes mixture of 10 and 20MHz channels
− Changes existing ITS channel allocation
DSRC Band
18
1
16
1
16
5
16
9
17
3
17
7
17
7
17
3 DSRC Channels
Wi-Fi Channels
160MHz
80MHz 80MHz
X
Proposed boundary of UNII4
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• Wi-Fi is growing rapidly in automotive
• Video streaming use cases need 802.11ac
• IEEE 802.11 “Tiger Team” examined 5.9GHz band sharing issues
• Tiger Team did not adopt a consensus position
− Two proposals examined by the group
− Draft report not ratified
− Straw poll in Berlin indicated support for band repacking
• Field tests needed
− Could be done under CAMP or other groups
• Regulatory process will play out from here
Summary
13 © Cambridge Silicon Radio Limited 2015
Thank you!
