Transcript Slides - SIGMOBILE

I Am the Antenna:
Accurate Outdoor AP Location
using Smartphones
Zengbin Zhang, Xia Zhou, Weile Zhang*, Yuanyang Zhang
Gang Wang, Ben Y. Zhao, Haitao Zheng
Department of Computer Science,
University of California, Santa Barbara, USA
*School of Electronic and Information Engineering,
Xian Jiaotong University, China
Ubiquitous Broadband Access
 WiFi network is growing rapidly
 Cisco: WiFi traffic will surpass wired IP traffic in 2015
 High density
 We need well tuned and managed WiFi networks!
2
AP Location: A Critical Function
 Better network
planning
Neighboring AP
 Finding rogue APs
3
Conventional AP Location Methods
Directional Antenna
RSS Gradient
20%+ Violations
Signal Map
Distance
RSS Gradient
SB  SA
SB  SA
SB  SA
SA
• Fast, very accurate (10˚)
• Expensive (hundreds to
thousands of dollars)
• Simple method, easy to
perform
• Very time consuming
SB
• Low measurement
overhead
• Low accuracy (often
error > 45˚)
Do we have a better method to quickly and accurately locate
the AP?
4
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
5
Rotation based Measurement
Facing AP
RSS (dBm)
-60
Back facing AP
-65
13dB
-70
-75
-80
-85
0
60
120
180
240
300
User Orientation (degree)
360
 The difference is significant
 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
6
Generality of the Effect
 Devices
 Protocols
RSS(dBm)
 Motorola Droid, HTC G1(Android)
 LG Fathom(WM 6.5)
 iPhone4 (iOS)
-40
 802.11 b/g
 802.11n (MIMO)
 Outdoor LOS/Non-LOS
 Different distances to AP
-70
-40
RSS(dBm)
 Environments
-60
-80
 Postures and body shapes of the
user
 7 users in our lab
 Different phone orientations
-50
LG Fathom(WM 6.5)
HTC G1 (Android)
Back facing AP
User Orientation
iPhone 4
-50
-60
-70
-80
802.11b/g
802.11n Back facing AP
User Orientation
7
Outline
Motivation
Accurate AP Location
Evaluation
Conclusion
8
User Rotation based AP Location
RSS
AP direction
User Orientation
RSS profile
Borealis’ Design
Requirements
Accurate
Directional Analysis
Low
Energy Consumption
9
Directional Analysis Is Non-Trivial
 Min RSS direction?
user’s back facing AP?
RSS (dBm)
-60
-65
-70
ERROR=40˚
-75
Actual direction
-80
-85
0
120
180
240
300
360
User Orientation (degree)
1
0.8
CDF
 Using Min RSS
direction would cause
large errors
60
0.6
For 35% cases,
Error > 45˚
0.4
0.2
0
0
30
60
90
120
150
180
Absolute Angular Error (degree)
10
Our Directional Analysis Model
 Signal degradation occurs at a range of directions

d1

d2
RSS
Ideal RSS Profile
blocking
sector
RSS could vary inside
the sector, so Min RSS is
not accurate
Around 90˚
User Orientation
11
Locating the Blocking Sector
 Find the sector with the largest RSS degradation
 Sliding window
 Sout: average RSS outside
the sliding sector
RSS (dBm)
 Sin: average RSS inside
the sliding sector
-65
-70
-75
-80
Sliding
Sector
-85
-90
0
120
180
240
300
360
User Orientation
15
Degradation
10
 degradation = Sout - Sin
60
Detected direction
5
0
-5
-10
0
60
120
180
240
User Orientation
300
12360
Navigation
 How does a user navigate using directional hints?
 Strawman design: periodic
Detected direction
• Refine AP direction every 20m
• Temporal/spatial variation
 Our adaptive method
RSS (dBm)
 However, nothing is perfect
-65
-70
-75
-80
-85
Actual direction
-90
 Measurement confidence
0
60
120
180
240
300
User Orientation
• The similarity of measured RSS and ideal RSS profile
 If confidence is high
• Walk further between measurements
13
360
Implementation
 Application layer
 Leveraging WiFi scan to read RSS
• Default scan is very slow
• Scanning all channels each time
 OS layer
 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
14
Testing Scenarios
Simple Line of Sight (Simple LOS)
Non Line of Sight (NLOS)
Complex Line of Sight (Complex LOS)
15
Accuracy of Directional Analysis
 We compared Borealis to
 Offline Analysis: clustering-based ML method
• Optimized by training set, can be upper bound of directional analysis
 GUIDE: RSS gradient based
 Min RSS: minimum RSS direction based
NLOS
1
1
0.8
0.8
0.6
Offline Analysis
Borealis
Min RSS
GUIDE
0.4
0.2
0
CDF
CDF
CDF
Simple LOS
0.6
Offline Analysis
0.4
Borealis
Min RSS
0.2
GUIDE
0
00
30
60
90
120
150
30
60
90
120
150
Absolute Angular Error (degree)
Absolute Angular Error (degree)
180
180
0
30
60
90
120
150
180
Absolute Angular Error (degree)
Error < 30˚ for 80%+ cases in Simple LOS Error < 65˚ for 80%+ cases in NLOS
16
Navigation Efficiency
 Navigation Overhead:
 Defined as the normalized extra distance a user needs to travel
Navigation Overhead
Navigation Overhead
160%
140%
120%
100%
80%
60%
40%
20%
0%
Periodic
Adaptive
134%
107%
74%
48%
37%
18%
Simple LOS
Complex
LOS
NLOS
NLOS Examples
17
Locating Indoor APs?
 Most APs are mounted inside buildings
 We mounted the AP on a table in our lab
 Try to locate it outside in Complex LOS/NLOS environment
11
0.8
0.8
CDF
CDF
0.6
0.6
Outdoor AP, Borealis
0.4
0.4
Indoor AP, Borealis
Outdoor AP, GUIDE
0.2
0.2
00
Indoor AP, GUIDE
00
30
30
60
60
90
90
120
120
150
150
180
180
Absolute
Angular
Error (degree)
Absolute
Angular
Error (degree)
Borealis is fully capable of finding Indoor APs
18
Conclusion
 AP location is an important function
 Very beneficial in AP deployment and management
 Borealis: an efficient and accurate solution for WiFi AP
location
 Leveraging the body blocking effect on smartphones
 Feasible even in complex environments
 Body blocking effect is general
 i.e. works on GNU Radios in 900MHz/1900MHz/5GHz
 Borealis can be applied to locate other types of transmitters
19
Thank you!
Questions?
20