dsrc and wi-fi baseline cross-channel interference test ......interference test and measurement ....
TRANSCRIPT
DSRC and Wi-Fi Baseline Cross-channel Interference Test and Measurement
SAE Government Industry MeetingWashington DC,
January 2020
2Background• FCC considering reallocation of the 5.9
GHz Safety Band
• NHTSA and CAMP conducted research to evaluate potential interference on DSRC from 802.11ac (Wi-Fi) devices operating in adjacent bands
Lower 45 MHz of the DSRC band
802.11acCH 171
(80 MHz)
DSRC CH 174
DSRC CH 176
DSRC CH 178
DSRC CH 180
DSRC CH 182
DSRC CH 184
802.11acCH 173
(20 MHz)
802.11acCH 177
(20 MHz)
802.11acCH 175(40 MHz)
5860
5865
5870
5875
5880
5885
5890
5895
5900
5905
9105
5915
5920
5925
5855
DSRCCH 172
5850Cross-channel Interference
802.11acCH 163
(160 MHz)
5875802.11ac
(Wi-Fi)DSRC180
DSRC182
DSRC184
177: 20 MHz X X X
175: 40 MHz X X X
171: 80 MHz X X X
163: 160 MHz X X X
3Test Procedure and Set Up• All devices compliant with FCC rules
• Wi-Fi devices adjusted to 36 dBm EIRP –highest allowable per FCC rules
• DSRC devices adjusted to 17 dBM transmit power—resulting a very strong signal strength condition (~68 dbm compared to -92dbm minimum specification)
• Vehicles positioned 75m apart, fixed.
• Maximum range tested (1,000 -1,075 m)
• Captured Packet Error Rate (PER), Channel Busy Percentage (CBP), Received Signal Strength Indicator (RSSI), and Information Age (IA) during each test.
4Experimental Set-Up
75 m
75 m
75 m
0 - 75 m
25 - 100 m
Up to 1075 m
75 m
50 - 125 m
802.11ac Device(In building w/ ~6 m LMR400 cable to antenna)
802.11ac Antenna (~5 ½ m off the ground)
Near Vehicle
Far Vehicle
DSRC antenna
5Results Preview….Highly variable, dependent on distance and channel
• Packet Error Rate (PER) does not decay uniformly with distance
• Close channels (180/177) showed greatest interference as expected
• Cross-channel effects generally disappear after 250m
6Sample Results: PER at various ranges
0
20
40
60
80
100
25 50 75 100 125 150 175 200 225 250 275 300
PER
(%)
Distance (m)
DSRC Channel 180Ch 163 Near Ch 163 Far
Ch 171 Near Ch 171 Far
Error Limit
7Sample Results: PER at various ranges
0
20
40
60
80
100
0 25 50 75 100 125 150 175 200 225 250 275 300
PER
(%)
Distance (m)
DSRC Channel 182Ch 163 Near Ch 163 Far
Ch 171 Near Ch 171 Far
Error Limit
8Sample Results: PER at various ranges
0
20
40
60
80
100
0 25 50 75 100 125 150 175 200 225 250 275 300
PER
(%)
Distance (m)
DSRC Channel 184Ch 163 Near Ch 163 Far
Ch 171 Near Ch 171 Far
Error Limit
9Sample Results: PER at various ranges
0
20
40
60
80
100
25 50 75 100 125 150 175 200 225 250 275 300
PER
(%)
Distance (m)
Wi-Fi Channel 163 (near)Ch 180 Near Ch 182 Near
Ch 184 Near Error Limit
10Sample Results: PER at various ranges
0
20
40
60
80
100
25 50 75 100 125 150 175 200 225 250 275 300
PER
(%)
Distance (m)
Wi-Fi Channel 163 (far)Ch 180 Far Ch 182 Far
Ch 184 Far Error Limit
11Sample Results: PER at various ranges
0
20
40
60
80
100
25 50 75 100 125 150 175 200 225 250 275 300
PER
(%)
Wi-Fi Channel 163 (near)Ch 180 Near Ch 182 Near
Ch 184 Near Error Limit
0
20
40
60
80
100
25 50 75 100 125 150 175 200 225 250 275 300
PER
(%)
Distance (m)
Wi-Fi Channel 163 (far)Ch 180 Far Ch 182 Far
Ch 184 Far Error Limit
12Conclusions and Potential Next Steps• Cross-channel interference characterization was successfully measured along
multiple DSCR and 802.11ac channels
• No attempt was made to model wireless LAN network traffic patterns
• Potentially performance disrupting interference was found up to a range of 400m, but 100m-200m was more typical
• As expected, closer channels generally showed greater interference potential
• Needs:• Evaluate impact of multiple 802.11ac network traffic patterns (video streaming, LAN,
more clients, etc) • Evaluate impacts in more congested V2X environments, and,
• Evaluate impact of 802.11ac traffic on C-V2X devices and operation
13You can find the report at….
• https://www.nhtsa.gov/about-nhtsa/briefing-room
Robert KreebChief, Electronic Systems Safety [email protected]