Upload
ashlee-perry
View
213
Download
0
Embed Size (px)
Citation preview
The Design of a Portable Kit of Wireless Sensors for Naturalistic
Data Collection
Emmanuel Munguia Tapia, Stephen S. Intille,
Louis Lopez, and Kent LarsonMassachusetts Institute of Technology
@ Pervasive2006
概要• MITes (MIT environmental sensors)
– 無線センサデバイスシリーズ– 日常の活動に関するデータ収集が目的
– 目標• 使いやすい• 設置しやすい• 低コスト• 家など non-laboratory な環境でも使える
– 紹介・現段階の評価 (placelab で利用 )
MITes センサ群• 環境側に設置するセンサ
– 動作(Ball, Mercury, Reed Switches)
– 使用状況取得を目的とした動作センサ ( 加速度 )
– 照度
– 温度
– 隣接・距離
– 電力消費量
• ウェアラブルセンサ– カラダの動作(加速度)
– 心拍数
– 紫外線量
– RFID リーダ・リストバンド
– 位置情報
Introduction
• 現代 pervasive computing の課題– コストの壁– non-laboratoryな環境で使えるような柔軟性の欠
如– しかし、ムーア氏いわく・・・
小さくてコストが低くて使いやすいモノの時代がくる
• 日常生活の活動を取得するためのセンサ– 目標を満たしたセンサ群はまだ現れていない– 分かりやすく、設置しやすく、低コストで、家などで
使える MITes を提案し、実際に作ってみた
家に設置するための Design Goals
1. Ease of Installation
2. Ease of Use
3. Adequate performance in natural settings
4. Affordability
Usability Goals
(What)
Sensor Design Goals (How) Benefit to Researcher(R) and Subject (S) (Why)
Ease ofinstallatio
n
Light weight, and small sensor nodes (portable) Self-contained single point of contact to body/home Single receiver to collect data from multiple sensors Real-time simultaneous data -acquisition from high and low sampling rate sensors No pre-configuration required or threshold setting Good indoor Tx/Rx range and easy to detect if in range
Minimizes installation time (R) Subjects can install sensors themselves (R/S) Subjects can re-install sensors if they dislodge, simplifying maintenance for researchers during studies (R/S)
Ease of use
Real-time simultaneous data acquisition from multiple high and low sampling sensors with single receiver Each sensor does one thing well Convenient battery life Robustness to environmental noise
Facilitates maintenance (R/S) Low training overhead (R/S) Facilitates the addition of new sensors(R) Reduces failure points (R) Decreases probability of data loss (RS)
Adequate longitudinal performance in natural settings
Convenient battery life/low power Robustness to environmental noise Self-contained, resistant packaging Good indoor Tx/Rx range and easy to detect if in range Performance valuated in a natural setting (Section 5.1)
Decreases probability of data loss (R/S) Facilitates design of data collection (R)
Affordable for researchers
Design with low-cost components Each sensor does one thing well
Deployment of hundreds of sensors (R)
1. Ease of Installation (設置しやすく)
• Minimization of Installation time– 家にだいたいセンサノードを200個置くとする– これまで (5-10min./node) x 200 = 16-32 man-hours
– センサの設置方法を簡易化する– 4点固定→1点固定(動いているかどうか知りたいだけ)
– これからは (5-60sec./node) x 200 = 1-2.5 man-hours
• 既存のモノは・・・– サイズがでかい( snap-on boards, AA battery, antenna )– 電波が弱い (low freq)
2. Ease of Use (使いやすく)• Robust communication protocols
• Good communication range– 余計な中継ノードを必要としない
• Infrequent (& easy) battery replace
• Add & removing sensors with little or no configuration.
• 既存のモノは・・・– ネットワークの構造・設定が複雑– low-rate for event detecting, high-rate for wearable sensors– 簡単に複数の種類のセンサのデータをまとめて見る手段がない
3. Adequate performance in natural settings (自然環境への適応)
• 温室育ちのセンサではダメ
• 頑強なケース
• 電波や騒音などのノイズに対する抵抗力
• 既存のモノは・・・– あまり論文にのっていない– 研究室向けのモノが多い
Affordability
• 安くないといけない
• 既存のモノは– $15,600(Motes x 200)– $26,000(+2 軸加速度 )
– ECO System は合格ライン
– u-part はライバルだけど– 自然環境での実験が行われていない
MITes ノードの概要
• 3.2 x 2.5 x 0.6cm• 8.1g (battery incl.)
• 低コスト防水ケース• 長いアンテナ無 (2.4GHz 帯 )• 超寿命 (mobileMITes>24hr,others>week)• $6 per Unit
• Receiver→USB or RS232→NotePC• C# and JAVA available
Sensor Design Goals (What) Implementation (How) Benefit to Researcher (R) and Subject (S) (Why)
Light weight and small form factor
Low-profile highly integrated chip components, 3cm Microstrip antenna (possible with 2.4GHz), 3.2x2.5x.0.6cm PCB design, 20mm coin cell battery Total board size of 3.2x2.5x.0.6cm Total weight (including battery) of 8.1g
Facilitates installation (R) Minimizes sensor dislodgement (S) Improves portability (R) Comfortably wearable (S) Sensors fit on most household objects (R/S)
Self-contained and resistant packaging Sensors embedded in low-cost water resistant plastic cases Facilitates installation (R) Physically robust (R)
Self-contained, with single point of contact to body/home
Single, self-contained acceleration sensor to measure object usage No dangling antennas Minimize external sensors whenever possible
Rapid installation (R) Easy to reattach if dislodged (R/S) Attach with only a small bit of putty (R/S) No parts to break/yank (R/S)
Real-time simultaneous data acquisition from multiple high and low sampling sensors with a single receiver
FDMA in wearable/high sampling rate sensors, and single channel shared by low sampling environmental sensors Combination of TDMA and FDMA at receiver to collect data from sensors
Data acquisition from environmental and wearable sensors (R) Reduced costs – only one system needed (R) Rapid installation (R) Real-time applications possible (R/S) Many wearable sensors can be used without bulky receiver devices or wires (S)
No pre-configuration required or threshold setting
Simple star network topology A featherweight MAC protocol with only one parameter that is fixed (num. of retransmissions) (See Section 4.3) Receiver outputs simple data format via serial port or USB serial for easy programming
Minimizes installation time (R) Subjects can install sensors themselves (R/S) Facilitates first time setup of system (R) Decreases points of failure (R)
Good indoor Tx/Rx range and easy to detect if in range
Transceiver with 0dB output power PCB design that maximizes antenna ground plane Optimally cut /4 monopole microstrip antenna Extensive field measurements of outdoors and indoors range (see Section 5.1)
Reduces cost since a typical home requires few receivers (R) Facilitates deployment (R) Facilitate subject mobility (S)
Convenient battery life (mobile MITES > 24 hr; receiver if attached to mobile device >24 hr; other sensors > weeks)
Node Low power components Low duty cycles Embedded intelligence at the sensor node to broadcast information only when necessaryOverall System Simple star topology – no overhead A Featherweight MAC protocol – no overhead
Long data collection deployments (R) Reduce battery replacements (S) Acceptable weight when worn (S) Fits in pocket when receiver embedded in mobile device (S)
No dangling antenna /4 Microstrip monopole onboard antenna and high Tx/Rx frequency of 2.4GHz Facilitates installation (R) Minimizes sensor dislodgement/breakage (S) Easy to carry/pack (R) Comfortable and aesthetical form factor (S)
Robustness to environmental noise EMI reduction bead cores Tantalum capacitors where required Noise efficient PCB design
Decreases probability of data loss (R/S) Decreases probability sensor failure (R/S) Permits deployment in natural settings when noisy appliances are being used (R/S)
Design with low-cost components $3 integrated C and transceiver (RF24E1), $0.01 microstrip antenna, $0.30 CR2032 coin cell battery
Easy to add as many sensors as desired (R)
Each sensor does one thing well One sensor optimized per task (reducing complexity and cost of individual sensor) Reduces learning-curve/implementation complexity (R)
通信 1/2
• Low Rate<10Hz , High Rate>10Hz
• Combining FDMA & TDMA– FDMA→HighRate TDMA→LowRate
• Data format– Head 2B, channel1B, Payload 4B 計 7bytes
• Star network topology with feather weight MAC
通信 2/2
• 500 個のノードで実験• 各ノードの発信レートとパケットロスの関係• 発信回数とパケット伝達確率の関係
• レートを 5sec. にすると 97 %のパケットが伝達
• レートを 0.5sec. にすると 60 %のパケットが伝達• 6回の再送信で 100 %のパケットを伝達
2 3 4 5 6 7 80
0.2
0.4
0.6
0.8
1Reception probability vs. number of retransmissions
Number of retransmissions
Re
cep
tion
pro
ba
bili
ty
Ploss=0.016
Ploss=0.2
Ploss=0.4
Ploss=0.6
Ploss=0.8
Ploss=0.9
50 100 150 200 250 300 350 400 4500.6
0.65
0.7
0.75
0.8
0.85
0.9
0.95
1
Reception probability vs. number of sensors
Number of sensorsR
ece
ptio
n p
rob
ab
ility
0.5 Sec
1 Sec
5 Sec
10 Sec
(a) Plot of RxP
vs. number of retransmissions
(b) Plot of RxP
vs. number of sensors in the system.
Multi-modal Sensor Types
• RS232, I2C, SPI output のセンサなら拡張 OK
• Mobile, Current sensing, Ultraviolet exposure, Temperature, Light, Heart rate, Location beacons, Proximity, RFID wrist-band
MITES Type Measures Sensor Range Res Battery life (days)
Cost ($)
Object usage Object manipulation Accelerometer. ADXL202
2g 2-axis 0.005 46, 10Hz 28.43
Mobile OnbodyAcceleration (Acc)
Accelerometer. ADXL202/10
2g or 10g 3-axis 0.005 1.5, 200Hz 44.3
Temperature Temperature MAX6677 –40C to 125C ±1.5 1309, 1Hz 20.3*
Light Ambient light intensity
DigitalTSL235R
0.003-1ku W/cm2at 320-1050nm
16bit 620, 1Hz 21.0*
Current sensing Current consumption
Split-core current transformer
30mA to 28A 10bit 14, 1Hz 75.5*
Heart rate Beats per minute WearLink Polar chest strap/receiver
30-240 bmp 1 2.5 @1-255bmp9Vbattery
95.5*
Ultraviolet exposure
Onbody UV exposure
UV PhotodiodeEryf by Sglux
0-28UV 0.027 2.58, 1Hz 93.5*
Location beacons Rough location with respect to a receiver node
Tx beacon and Rx node counting packets received
2.5, 3.8, 4.8, and 9.4m outdoors0.7, 3, 4.5, and 6mindoors
- 5, 12Hz 48.5*
Proximity Proximity to area(binary output)
PIR motionKC7783R
Circle with 0-2.6m varying radius(by replacing lid)
1 47.5, 2Hz9Vbattery
33.1*
RFID wristband Acc + RFID tagged objects
ADXL202/10M1 Mini SkyTek
10cm - 0.2, 5Hz 4.7 Li-Po.
181*
Table 3. Summary of MITes types available and performance parameters.
Evaluation1 屋外無線実験
• Line of sight range (LOS)• 屋外で実験• 180 packets per sec. 発信してパケ落ちを計
測• 無線 channel0(2.4GHz)
MITes microstrip ($0.01)
Linx Chip($1.5)ANT2.45CHP
Yageo chip ($3)
Monopole Gigant ($35)
Parallel orient. 106.6 m 60.96 m 15.24 m 114.3 m
Random disp. 38.1 m 15.24 m 7.62 m 30.48 m
Titanis is a /4 monopole antenna manufactured by Gigant corp
Microstrip /4 monopole embedded antenna
The Linx embedded chip antenna
The Yagui embedded chip antenna
Figure X. MITes Antennas installation and antenna types
Titanis Yagui (Blue) Linx (white)
Central frequency 2.4-2.5GHz 2.45GHz 2.45GHz
Bandwidth 310MHz > 100MHz 180MHz
Impedance 50 50 50
Polarization Linear Linear Linear
Maximum power Not specified in datasheet 1W Not specified in datasheet
Efficiency (Typ) 65%
Gain 4.2dBi 0dBi 0.8dBi
VSWR < 1.5:1 < 2 Not specified in datasheet
Temperature (C) -40 to 85 -55 to 125 -25 to 85
Antenna type Swivel Embedded Embedded
Size 20x19.5x62.5mm 8x3.5x.9mm 6.5x2.2x1.0mm
Weight 7.5g Not specified in datasheet
Not specified in datasheet
Table 1. Presents the different antenna properties or parameters that are important to consider while selecting an antenna.
0 50 100 1500
20
40
60
80
100Tx/Rx Range outdoors LOS antennas parallel
Distance in meters
Per
cent
age
of p
acke
ts r
ecei
ved
GigantMITesLinxYageo
20 40 60 80 100 1200
20
40
60
80
Tx/Rx Range LOS antennas in random disposition
Distance in metersP
erce
ntag
e of
pac
kets
rece
ived
GigantMITesLinxYageo
(a) LOS range outdoors with antennas parallel.
( b ) LOS range with the Tx antenna in a random disposition.
Evaluation2 無線ノイズ実験
• 自然界のノイズを入れてみる• 無線 LAN + α の時のパケ落ち率
• + 掃除機 3.7 %落ち• + 電子レンジ 4.3 %落ち• + 電話(子機) 1.2 %落ち
Evaluation3 電池・インスタレーション実験
• 平均発信回数寿命– 新品 CR2032 を使って 20.85million 回発信
• 平均インスタレーション所要時間– 75 個 /45 分 100 個 /60 分– 36sec. per node