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PeopleTones: a system for the detection and notification of buddy proximity on mobile phones
Kevin A. LiTimothy SohnSteven Huang
William G. GriswoldUniversity of California, San
Diego
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ubiquitous
ample computational power
a few sensors
a few actuators
proactive context-awareness
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messaging
You are driving by Safeway. Reminder: Buy steak.
location-based reminders
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The slopes on Beaver Run have opened!
unobtrusive notifications
Bzzzzt!
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crappy sensors crappy actuators
cheap sensors could lead to many false notifications
cheap actuators could lead to misunderstood cues
proactive notification + commodity hardware flood of meaningless notifications
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two proximity states: far and near (< 2 city blocks)
when a buddy becomes near,
play her sound or vibration cue
runs on commodity hardware (Windows Smartphone)
PeopleTones
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“It was so cool to see who was home by the time I got home. I could tell if Jenny was home when I passed by University. So if we were going to go eat or something I could ask her. Oh she’s home, so let’s call her and see if she wants to eat.”
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focus on application goals to avoid over-engineered, impractical solution
proximity is easier than location
acceptable if notifications missed or not understood
approach
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privacy-friendly proximity detection algorithm
technique for reducing sensor noise without sapping power
method for generating a language of understandable vibrotactile cues
exploratory study of buddy proximity cues
contributions
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proximity detection
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[LaMarca et al. 2005]
build on location?
GPS doesn’t work indoors, in urban canyons
tower-based systemsmust keep database current
require wardriving
how about tower overlap?NearMe [Krumm 2004]
iPhoneiPhone
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initial data collection
used a GSM phone to record the cell towers it saw every 5 minutes
3 GSM phones, kept 1 stationary
gather data at a variety of distances (0 - 1.2 miles)
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initial measurements
a and b are the sets of cell towers seen by each phone
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0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.2 0.4 0.6 0.8 1 1.2
Ratio
of C
ell T
ower
s
Distance (miles)
Suburbs 1Suburbs 2Downtown
initial measurements
a and b are the sets of cell towers seen by each phone
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evaluatingproximity algorithm
can our overlap-ratio algorithm detect proximity accurately enough to support nice-to-know information?
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requirements
cannot be annoying
when the system detects a buddy is near,
they should really be near
OK to not detect every time
if a buddy is nearby and stationary, we’ll have multiple chances
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the datasetused the dataset collected by wardriving seattle
[Chen et. al., 2006]
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coverage
Suburb
Downtown
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precision
100% precision every report is valid
recall
100% recall every near incident is detected
metric: precision and recall
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how do we extract the relevant data?
only care about when two phones are near or far from each other
why not pull out each set of data by different distance thresholds?
turns out mobile phone tower readings fluctuate over time (e.g., due to load balancing)
we can crosscut the dataset to approximate precision and recall for different scenarios
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nearby
extract pairs of readings taken within 90s
569,264 pairs from Suburb
379,285 pairs from Downtown
calculate precision and recall for different ratio threshold values
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nearby precision
100% precision every report was valid
100% recall every near incident was detected
suburb downtown
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0.75
0.8
0.85
0.9
0.95
1
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Prec
ision
Distance (km)
0.3
0.4
0.5
nearby precision
suburb downtown
100% precision every report was valid
100% recall every near incident was detected
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0.75
0.8
0.85
0.9
0.95
1
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Prec
ision
Distance (km)
0.3
0.4
0.5
0.80.820.840.860.88
0.90.920.940.960.98
1
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Prec
ision
Distance (km)
0.3
0.4
0.5
nearby precision
suburb downtown
100% precision every report was valid
100% recall every near incident was detected
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nearby recall
Ratio Recall(Downtown)
Recall (Suburb)
0.1km 1.0 km 0.1 km 1.0 km
0.3 0.74 0.66 0.67 0.66
0.4 0.50 0.41 0.42 0.40
0.5 0.39 0.30 0.30 0.29
100% precision every report was valid
100% recall every near incident was detected
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reducingsensor noise
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initialapproaches
wait for 2 consecutive-same-readings– Too many false positives
wait for 3 consecutive-same-readings– Too much delay
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2-bit-filter(“eventually 3 more”)
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filterevaluation
for noise filtering, interested in transitions from far to near and vice-versa
extract seattle wardrive readings at 30s intervals
try three algorithms on this subset, baseline is single report
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filterevaluation
Filter False Positive Reduction
1-same (baseline) 0%
2-same-filter 53.8%
3-same-filter 80.9%
2-bit-filter 84.9%
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adaptive sampling rate
sampling once every 20s kills the phone in less than a day
increasing sampling rate to once per 90s helps but introduces a worst-case delay of 270s
sample at 90s when in steady state, 20s when transitioning
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buddy cues
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mapping musicto vibrations
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problem
we want to convert music to vibrations…
…but the phone’s vibrator only turns on and off
…at single frequency, single amplitude
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pulse width modulation
electric motors do this to save power
in the case of vibrotactile motors this also decreases its rotational frequency
perceived as different vibration levels
can produce 10 levels of 20ms pulses
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capturing the essence of music
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overview of approach
just using beat doesn’t always work
mapping lyrics doesn’t work well
basic idea: convey the current energy level of the music
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remove noise
isolate 6.6kHz to 17.6kHz components using 8th order Butterworth Filter
use amplitude threshold, to keep only components greater than the average
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takerunning sum
take running sum of absolute value, generate 1 value every 20ms
this keeps length consistent
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exaggeratefeatures
compose output from previous step with power function:
Axn , x is sample,
A and n are constants, 10<=A<15, 1<=n<=2
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Beethoven’s 5th Symphony
matching vibration sequence
Michael Jackson – Smooth Criminal
matching vibration sequence
examples(requires imagination)
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so far…
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would the techniques we used for proximity detection, sensor noise filtering and vibrotactile cues work in the wild?
can peripheral cues be deployed on mobile phones despite poor sensors and actuators?
(what experiences can such a system enable?)
field study
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two proximity states, far and near (< 2 blocks)
when a buddy is near, play their song
if phone is in vibrate mode, play a matching vibrotactile sequence
PeopleTones
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participants
3 groups of friends, 2 weeks
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could you tell who it was?
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could you tell who it was?
0% 20% 40% 60% 80% 100%
My Choice
Your Choice
Nature
Yes
Ignored
No
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0% 20% 40% 60% 80% 100%
My Choice
Your Choice
Nature
Acted on or Nice to KnowDidn’t Notice or not that usefulAnnoyed
user response to the cue
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designing peripheral cues for the wild
higher comprehension rate when users select their own cues
obtrusiveness of music cues was not a concern
mapping music to vibration was most successful for people who knew the songs well
semantic association is key to learnability
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userexperience
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“One time at the library, I wanted to eat with someone and so I went outside to call someone. The phone vibrated. I just called the person to meet up.”
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lessons
cues were sensible, but not socially obtrusive
proximity algorithm worked well in the wild
emphasizing elimination of false positives was effective in combination with 2-bit counter
dwelling/lingering led to successful recall
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whole can be greaterthan its parts
despite crappy sensors and actuators, mobile phones can achieve adequate context awareness and notification
with careful system-level design these can be brought together into a useful proactive context-aware application like PeopleTones
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PeopleTones: a system for the detection and notification of buddy proximity on mobile phones
Kevin A. LiTimothy SohnSteven Huang
William G. GriswoldUniversity of California, San
Diego
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EXTRA SLIDES
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measuring vibrations
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0 5 10 15 20 25 30 35 40 45 50
Time (ms)
Vo
lts
(V
)0
1
.5
3.0
4.5
6.
0
0 5 10 15 20 25 30 35 40 45 50
Time (ms)
Vo
lts
(V
)0
1
.5
3.0
4.5
6.
0
0 5 10 15 20 25 30 35 40 45 50
Time (ms)
Vo
lts
(V
)0
1
.5
3.0
4.5
6.
0
0 5 10 15 20 25 30 35 40 45 50
Time (ms)
Vo
lts
(V
)0
1
.5
3.0
4.5
6.
0
Duty Cycle = 100%
Duty Cycle = 60%
Duty Cycle = 18%
Duty Cycle = 37%
zzz
z
z zvibrotactilesignals
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far apart
unfortunately, there are few points in dataset that are both far apart and proximate in time
expected atypical results
used the entire dataset
55,181,015 pairs from Suburb
36,769,390 pairs from Downtown
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far apart precision
suburb downtown
100% precision every report was valid
100% recall every near incident was detected
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far apart precision
0.75
0.8
0.85
0.9
0.95
1
0.1 0.3 0.5 0.7 0.9 1.1 1.3 1.5 1.7 1.9 2.1 2.3
Prec
ision
Distance (km)
0.3
0.4
0.5
suburb downtown
100% precision every report was valid
100% recall every near incident was detected
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0.88
0.9
0.92
0.94
0.96
0.98
1
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Prec
ision
Distance (km)
0.3
0.4
0.5
far apart precision
0.75
0.8
0.85
0.9
0.95
1
0.1 0.3 0.5 0.7 0.9 1.1 1.3 1.5 1.7 1.9 2.1 2.3
Prec
ision
Distance (km)
0.3
0.4
0.5
suburb downtown
100% precision every report was valid
100% recall every near incident was detected
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far apart recall
Ratio
Recall(Downtown)
Recall (Suburb)
0.1km 1.0km 0.1km 2.4km
0.3 0.12 0.08 0.09 0.06
0.4 0.05 0.04 0.03 0.02
0.5 0.03 0.02 0.02 0.01
100% precision every report was valid
100% recall every near incident was detected
![Page 63: PeopleTones: a system for the detection and notification of buddy proximity on mobile phones Kevin A. Li Timothy Sohn Steven Huang William G. Griswold](https://reader035.vdocuments.us/reader035/viewer/2022062421/56649cc05503460f949879c2/html5/thumbnails/63.jpg)
“It was so cool to see who was home by the time I got home. I could tell if Jenny was home when I passed by University. So if we were going to go eat or something I could ask her. Oh she’s home, so let’s call her and see if she wants to eat.”
![Page 64: PeopleTones: a system for the detection and notification of buddy proximity on mobile phones Kevin A. Li Timothy Sohn Steven Huang William G. Griswold](https://reader035.vdocuments.us/reader035/viewer/2022062421/56649cc05503460f949879c2/html5/thumbnails/64.jpg)
“One time at the library, I wanted to eat with someone and so I went outside to call someone. The phone vibrated. I just called the person to meet up.”
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generating vibrations
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same location
Extract pairs of readings taken within 5s
28,625 pairs from Suburb
19,087 pairs from Downtown
GPS confirmed 99.9% within 100m of each other
![Page 67: PeopleTones: a system for the detection and notification of buddy proximity on mobile phones Kevin A. Li Timothy Sohn Steven Huang William G. Griswold](https://reader035.vdocuments.us/reader035/viewer/2022062421/56649cc05503460f949879c2/html5/thumbnails/67.jpg)
Ratio Recall
(Downtown)Recall
(Suburb)
0.1 0.96 0.96
0.2 0.84 0.85
0.3 0.83 0.83
0.4 0.57 0.58
0.5 0.44 0.44
same location recall
100% precision => every report was valid
100% recall => every near incident was detected
![Page 68: PeopleTones: a system for the detection and notification of buddy proximity on mobile phones Kevin A. Li Timothy Sohn Steven Huang William G. Griswold](https://reader035.vdocuments.us/reader035/viewer/2022062421/56649cc05503460f949879c2/html5/thumbnails/68.jpg)
You are driving by Safeway. Reminder: Buy steak.
eyes-freenotifications
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[LaMarca et al. 2005]
build on location?GPS doesn’t work indoors, in urban
canyons
tower-based systemsmust keep database currenttower adaptation (e.g., load balancing)
![Page 70: PeopleTones: a system for the detection and notification of buddy proximity on mobile phones Kevin A. Li Timothy Sohn Steven Huang William G. Griswold](https://reader035.vdocuments.us/reader035/viewer/2022062421/56649cc05503460f949879c2/html5/thumbnails/70.jpg)
location sensingon iphone
![Page 71: PeopleTones: a system for the detection and notification of buddy proximity on mobile phones Kevin A. Li Timothy Sohn Steven Huang William G. Griswold](https://reader035.vdocuments.us/reader035/viewer/2022062421/56649cc05503460f949879c2/html5/thumbnails/71.jpg)
“It was so cool to see who was home by the time I got home. I could tell if Jenny was home when I passed by University. So if we were going to go eat or something I could ask her. Oh she’s home, so let’s call her and see if she wants to eat.”
![Page 72: PeopleTones: a system for the detection and notification of buddy proximity on mobile phones Kevin A. Li Timothy Sohn Steven Huang William G. Griswold](https://reader035.vdocuments.us/reader035/viewer/2022062421/56649cc05503460f949879c2/html5/thumbnails/72.jpg)
2-bit-filter