新颖的WIFI接入点(AP)定位技术,使用智能手机
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Devices RSS(dBm)
Motorola Droid, HTC G1(Android) LG Fathom(WM 6.5) iPhone4 (iOS)
-40 -50 -60 -70
LG Fathom(WM 6.5) HTC G1 (Android)
Protocols
802.11 b/g 802.11n (MIMO)
Strawman design: periodic
• Refine AP direction every 20m
-65
Detected direction
RSS (dBm)
-70 -75 -80 -85 -90
However, nothing is perfect
• Temporal/spatial variation
User Orientation (degree)
1
0.8 0.6 0.4 0.2 0 0 30 60 90 120 150 180
12
For 35% cases, Error > 45˚
Absolute Angular Error (degree)
Our Directional Analysis Model
5
AP Location: Related Work
AP location vs. general wireless network location
How to locate a transmitter? TOA TDOA AOA RSS
6
Conventional AP Location Methods
Insight: The Body Blocking Effect
Can we use this to detect AP location?
No…Effect is not clear enough
Our observation
User facing the AP
User’s back facing the AP
-80 -40
Postures and body shapes of the user RSS(dBm)
7 users in our lab Different phone orientations
Back facing AP User Orientation
iPhone 4
-50 -60 -70 -80
Sliding Sector
60 120 180 240 300 360
User Orientation
Degradation
Detected direction
5 0 -5 -10
0
60
120
180 240 User Orientation
300
14360
Navigation
How does a user navigate using directional hints?
Locating the Blocking Sector
Find the sector with the largest RSS degradation
Sliding window
RSS (dBm)
-65
-70
-75 -80 -85 -90 0
15 10
Sin: average RSS inside the sliding sector Sout: average RSS outside the sliding sector degradation = Sout - Sin
Cisco: WiFi traffic will surpass wired IP traffic in 2015
High density
We need well tuned and managed WiFi networks!
3
AP Location: A Critical Function
User Orientation
15
Implementation
Application layer
Leveraging WiFi scan to read RSS
• Default scan is very slow • Scanning all channels each time
OS layer
Environments
Outdoor LOS/Non-LOS Different distances to AP
802.11b/g 802.11n B
User Rotation based AP Location
AP direction
Directional Antenna Signal Map RSS Gradient 20%+ Violations
Distance RSS Gradient
SB S A
SB S A SB S A
SA
SB
• Fast, very accurate (10˚) • Expensive (hundreds to thousands of dollars)
Signal degradation occurs at a range of directions
d1
d2
Ideal RSS Profile
RSS blocking sector Around 90˚
User Orientation
13
RSS could vary inside the sector, so Min RSS is not accurate
Our adaptive method
Measurement confidence
If confidence is high
Actual direction
0 60 120 180 240 300 360
• The similarity of measured RSS and ideal RSS profile • Walk further between measurements
8
Rotation based Measurement
-60 -65 -70 -75 -80 -85 Facing AP Back facing AP
RSS (dBm)
13dB
0
60
120
180
240
300
360
User Orientation (degree)
The difference is significant
Better network planning
Neighboring AP
Finding rogue APs
4
AP Location: A Critical Function
For network administrators Identify APs causing excessive interference to others Identify unauthorized APs that may provide easy entry for malicious attackers For individual users Locate and get closer to neighborhood WiFi hotspots Build war-driving databases(沿街扫描) Pinpoint neighboring APs so they can better position their own base stations
Simple LOS
1 0.8
NLOS
1 0.8 Offline Analysis Borealis Min RSS GUIDE
CDF CDF
CDF
0.6
0.4 0.2
0.6 0.4 0.2 0
Offline Analysis Borealis Min RSS GUIDE 0 30 60 90 120 150 180
I Am the Antenna: Accurate Outdoor AP Location using Smartphones
MOBICOM 2011
Why AP location
2
Ubiquitous Broadband Access
WiFi network is growing rapidly
User’s body is much larger than the phone User is close to the phone We can emulate a directional antenna just by Rotating with Smartphones
9
Generality of the Effect
0
0 0 30 60 90 120 150 30 60 90 120 150 Absolute Angular Error (degree) 180 180
Absolute Angular Error (degree)
Absolute Angular Error (degree)
18
Error < 30˚ for 80%+ cases in Simple LOS Error < 65˚ for 80%+ cases in NLOS
• Simple method, easy to perform • Very time consuming
• Low measurement overhead • Low accuracy (often error > 45˚)
7
Do we have a better method to quickly and accurately locate the AP?
Testing Scenarios
Simple Line of Sight (Simple LOS) Non Line of Sight (NLOS)
Complex Line of Sight (Complex LOS)
17
Accuracy of Directional Analysis
We compared Borealis to
Modified WiFi driver
• Scanning the interested channel only • Accelerate the process: 10 seconds per rotation (10 times faster) • Save power: WiFi’s energy consumption is 14 times less
Navigation Efficiency
Navigation Overhead:
Defined as the normalized extra distance a user needs to travel
160% 140% 120% 100% 80% 60% 40% 20% 0%
Navigation Overhead
Min RSS direction?
RSS (dBm)
-60 -65 -70 -75 -80 -85 0 60 120 180 240 300 360 ERROR=40˚
user’s back facing AP?
Actual direction
CDF
Using Min RSS direction would cause large errors
Offline Analysis: clustering-based ML method
• Optimized by training set, can be upper bound of directional analysis
GUIDE: RSS gradient based(Online算法) Min RSS: minimum RSS direction based(基准算法)
RSS User Orientation
RSS profile Borealis’ Design
Requirements Accurate Directional Analysis Low Energy Consumption
11
Directional Analysis Is Non-Trivial
Motorola Droid, HTC G1(Android) LG Fathom(WM 6.5) iPhone4 (iOS)
-40 -50 -60 -70
LG Fathom(WM 6.5) HTC G1 (Android)
Protocols
802.11 b/g 802.11n (MIMO)
Strawman design: periodic
• Refine AP direction every 20m
-65
Detected direction
RSS (dBm)
-70 -75 -80 -85 -90
However, nothing is perfect
• Temporal/spatial variation
User Orientation (degree)
1
0.8 0.6 0.4 0.2 0 0 30 60 90 120 150 180
12
For 35% cases, Error > 45˚
Absolute Angular Error (degree)
Our Directional Analysis Model
5
AP Location: Related Work
AP location vs. general wireless network location
How to locate a transmitter? TOA TDOA AOA RSS
6
Conventional AP Location Methods
Insight: The Body Blocking Effect
Can we use this to detect AP location?
No…Effect is not clear enough
Our observation
User facing the AP
User’s back facing the AP
-80 -40
Postures and body shapes of the user RSS(dBm)
7 users in our lab Different phone orientations
Back facing AP User Orientation
iPhone 4
-50 -60 -70 -80
Sliding Sector
60 120 180 240 300 360
User Orientation
Degradation
Detected direction
5 0 -5 -10
0
60
120
180 240 User Orientation
300
14360
Navigation
How does a user navigate using directional hints?
Locating the Blocking Sector
Find the sector with the largest RSS degradation
Sliding window
RSS (dBm)
-65
-70
-75 -80 -85 -90 0
15 10
Sin: average RSS inside the sliding sector Sout: average RSS outside the sliding sector degradation = Sout - Sin
Cisco: WiFi traffic will surpass wired IP traffic in 2015
High density
We need well tuned and managed WiFi networks!
3
AP Location: A Critical Function
User Orientation
15
Implementation
Application layer
Leveraging WiFi scan to read RSS
• Default scan is very slow • Scanning all channels each time
OS layer
Environments
Outdoor LOS/Non-LOS Different distances to AP
802.11b/g 802.11n B
User Rotation based AP Location
AP direction
Directional Antenna Signal Map RSS Gradient 20%+ Violations
Distance RSS Gradient
SB S A
SB S A SB S A
SA
SB
• Fast, very accurate (10˚) • Expensive (hundreds to thousands of dollars)
Signal degradation occurs at a range of directions
d1
d2
Ideal RSS Profile
RSS blocking sector Around 90˚
User Orientation
13
RSS could vary inside the sector, so Min RSS is not accurate
Our adaptive method
Measurement confidence
If confidence is high
Actual direction
0 60 120 180 240 300 360
• The similarity of measured RSS and ideal RSS profile • Walk further between measurements
8
Rotation based Measurement
-60 -65 -70 -75 -80 -85 Facing AP Back facing AP
RSS (dBm)
13dB
0
60
120
180
240
300
360
User Orientation (degree)
The difference is significant
Better network planning
Neighboring AP
Finding rogue APs
4
AP Location: A Critical Function
For network administrators Identify APs causing excessive interference to others Identify unauthorized APs that may provide easy entry for malicious attackers For individual users Locate and get closer to neighborhood WiFi hotspots Build war-driving databases(沿街扫描) Pinpoint neighboring APs so they can better position their own base stations
Simple LOS
1 0.8
NLOS
1 0.8 Offline Analysis Borealis Min RSS GUIDE
CDF CDF
CDF
0.6
0.4 0.2
0.6 0.4 0.2 0
Offline Analysis Borealis Min RSS GUIDE 0 30 60 90 120 150 180
I Am the Antenna: Accurate Outdoor AP Location using Smartphones
MOBICOM 2011
Why AP location
2
Ubiquitous Broadband Access
WiFi network is growing rapidly
User’s body is much larger than the phone User is close to the phone We can emulate a directional antenna just by Rotating with Smartphones
9
Generality of the Effect
0
0 0 30 60 90 120 150 30 60 90 120 150 Absolute Angular Error (degree) 180 180
Absolute Angular Error (degree)
Absolute Angular Error (degree)
18
Error < 30˚ for 80%+ cases in Simple LOS Error < 65˚ for 80%+ cases in NLOS
• Simple method, easy to perform • Very time consuming
• Low measurement overhead • Low accuracy (often error > 45˚)
7
Do we have a better method to quickly and accurately locate the AP?
Testing Scenarios
Simple Line of Sight (Simple LOS) Non Line of Sight (NLOS)
Complex Line of Sight (Complex LOS)
17
Accuracy of Directional Analysis
We compared Borealis to
Modified WiFi driver
• Scanning the interested channel only • Accelerate the process: 10 seconds per rotation (10 times faster) • Save power: WiFi’s energy consumption is 14 times less
Navigation Efficiency
Navigation Overhead:
Defined as the normalized extra distance a user needs to travel
160% 140% 120% 100% 80% 60% 40% 20% 0%
Navigation Overhead
Min RSS direction?
RSS (dBm)
-60 -65 -70 -75 -80 -85 0 60 120 180 240 300 360 ERROR=40˚
user’s back facing AP?
Actual direction
CDF
Using Min RSS direction would cause large errors
Offline Analysis: clustering-based ML method
• Optimized by training set, can be upper bound of directional analysis
GUIDE: RSS gradient based(Online算法) Min RSS: minimum RSS direction based(基准算法)
RSS User Orientation
RSS profile Borealis’ Design
Requirements Accurate Directional Analysis Low Energy Consumption
11
Directional Analysis Is Non-Trivial