Transcript Overview - UNT | University of North Texas

ENVIRONMENTAL MONITORING:
FROM SENSORS TO DATABASE
Jerry Yang
Overview
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
Design Requirement
System Framework
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Wireless Sensor Networks
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Telecommunication system
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Single Board Computer
GPRS modem
Networking sensors, data loggers and data servers
Database and Client Interfaces
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Communications Protocols
Data Interpolating
Energy Harvesting
Over-the-Air Programming
Database
Data Visualization
Conclusion and Future Work
Project Object

Design and implement a fully functional environmental
monitoring system
Collect and report temporal and spatial soil moisture data
with required accuracy
 Provide near-real-time data about monitored variables to
the public
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Monolithic weather stations
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Wired Sensors (Data loggers)
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limited Spatial Coverage
Field Study
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Data is acquired every month
Go Wireless
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Wireless Sensors could fulfill this mission
 Unprecedented
temporal and spatial granularities
 Near-real-time data is accessible via the Internet
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Besides…
 Robust
and accurate through dense deployment
 Minimize disturbance to the monitored site
 Cover larger area (Multihop)
 Low installation cost
 Ease of deployment and relocation
System Architecture
Data loggers
In the Field:
Download Data
Client Data Browsing
and Processing
Internet
Database Server
In the Lab:
Upload Data
System Architecture
Data loggers
Wireless Sensor Nodes
Base Station Node
Gateway
(Single Board Computer)
Client Data Browsing
and Processing
GPRS Link
Internet
GPRS Modem
Database Server
An introduction to WSNs
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A wireless sensor mote is a battery-operated
embedded system including various hardware and
software components. For MicaZ motes:
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Processing Unit
7.37MHz micro-controller
 4KB RAM 512KB Flash
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Sensors
16-bit ADC with MDA 300 Data Acquisition Board
 EC-5 Soil Moisture Sensors
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Transceiver
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2.4 GHz, IEEE 802.15.4 compliant, 250 kbps
Powered by 2 AA batteries
Constraints of Sensor Motes
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Limited processing, storage and communication capabilities
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100 nodes @250bps = 25kbps (data sampled every second)
WILL be solved in the near future
Streaming Data
to/from the
Physical World
year
Fundamental Problem
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Sensor network is un-tethered, and will be operating for
a long time.

Replacing batteries is difficult and expensive if not
impossible
For MicaZ, typical current drawing is 30mA. Powered by 2.4V
3000mAh Batteries, a MicaZ mote could run for 100 hours
continuously.
 Communicating 1 bit data over the wireless medium consumes far
more energy than processing it.

Operating Current (mA)
ATMega128L, full operation
ATMega128L, sleep
Radio, receive
Radio, transmit (0dBm)
Radio, sleep
MicaZ
12 (7.37 MHz)
0.010
19.7
17
0.001
Software Support
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TinyOS and NesC
 An open-source operating system designed for
wireless embedded sensor networks
 Component-based architecture which enables rapid
innovation and implementation while minimizing code
size
 Event-driven execution model
Communication Protocols
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Design requirement
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Energy Efficient
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Robust, scalable and adaptive
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Dynamic topology changes due to unstable links, node failures and network
disconnections
Unique characteristics of our project
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Radio communication is the most expensive operation in terms of energy
usage
Long-term operation with very low data rate
A single sink node
At most of the time, data flow is uni-directional
Layered Architecture
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Physical/Link Layer
Medium Access Control
Routing
Physical/Link Layer
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Radio Propagation
 Path
Loss - signal strength attenuates as distance to a
constant exponent
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However, radio connectivity is not a simple disk
 Shadowing
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(due to obstructions) and Multipath Fading
Wireless Channel Characteristics
 Great
spatial variability
 Non-isotropic propagation
 Asymmetric links are common due to hardware
calibration
Link Quality Over Space
Packet reception over distance has a heavy tail. There is a
non-zero probability of receiving packets at distances much
greater than the average cell range
169 motes, 13x13 grid, 2 ft spacing, open area, RFM radio,
simple CSMA
Medium Access Control
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MAC protocol decides when and how nodes access the
shared wireless channel
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Collision avoidance
Duty-cycle control
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MAC layer protocols directly controls radio activities, significantly
affect the overall node lifetime
MAC in Wireless Networks
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Contention-based protocols
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CSMA/CA – node compete for a single channel
On-demand allocation provides more flexibility and adaptivity
Scheduled protocols
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C/T/FDMA – divide wireless channel into different sub-channels
Collision-free and energy-efficient
MAC for Sensors
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Sources of energy waste in radio communication
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Idle listening
Costs as much power as transmitting or receiving
 dominant factor of energy consumption especially in low data
rate systems
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Collision – retransmit when packets collide
Build on CSMA but also adopt TDMA-like
sleep/wakeup duty cycle
S-MAC, T-MAC, B-MAC, Z-MAC
 Reduce idle listen and minimize collision
 Improve power efficiency while retaining flexibility
 Sacrifice throughput, increase latency
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MAC Protocol Design
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We implement a tree-structure data report hierarchy, rooted at the
sink node
A global clock is also maintained by time synchronization
All nodes begin with a Sync slot
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Synchronize time, manage neighbor list, select parent
Parent nodes then allocate time slots for their children
All nodes are awake, but only broadcasting very short control packets
A node will report its latest readings to its parent in transmit slot,
while the parent node will become active and listen to the channel
Nodes sleep for the rest of time
Parent
…
Sync
Sleep
Rcv 1
Child 1
…
Sync
Sleep
Transmit
Child 2
…
Sync
Sleep
Rcv2
Sleep
Transmit
Sleep
Transmit
Sleep
Sleep
Network Layer - Routing
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Establishing and maintain the multi-hop routing
hierarchy
Link Quality Estimation
Neighbor Management
 Discover,
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update, remove neighboring nodes
Parent selection
 Shortest
Path, Minimal Transmission, Geo-Routing,
Energy-Aware routing
Link Quality Versus Distance
Packet Reception Rate vs Distance
100
-25dBm
-15dBm
90
80
PRR (%)
70
60
50
40
30
20
10
0
1
2
3
4
5
6
Distance (feet)
7
8
9
10
Time Synchronization
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Why do we need network-wise clock?
Time stamp data samples
 Set up radio schedule
 TOA, TDOA in Localization
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Pair-wise Synchronization
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Estimate communication delays
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Estimate clock skew
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Send time, access time, propagation time, receive time, etc.
Perform linear regression on past local/global time pairs
Multihop Synchronization
Minimize control overhead
Application Layer
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Energy Efficient Map Interpolation for Sensor
Fields using Kriging (E2K)
 an
energy efficient and error bounded framework for
interpolating maps from sensor fields
 Environmental dynamics, such as temperature and soil
moisture, are continuous
 Should be represented as a continuous surface over the
sensor fields through interpolating
 Spatial and temporal autocorrelation could be utilized
to reduce sample points
Data Interpolating
Data Interpolating
Localization
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Knowing the exact location where information was
collected is critical
A
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reading is represented by vectors (x,y,t,v)
Self-localization vs Tracking
Ranging Methods
 Radio,
acoustic/ultrasound, laser, etc.
 RSS, TOA, TDOA
 Lateration and Triangulation
Solar Harvesting Sub-System
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Energy Storage Module
Ultra Capacitors and Rechargeable Batteries
 Choosing Batteries
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NiMH, NiCd, Li-ion
Solar Harvesting Module
Solar Cells
 Regulators and Switches
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Circuit Design
Smart Battery Monitoring
Energy-Aware Protocol and Considerations
Over-the-Air Programming
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Loading a new application or upgrading an existing
application on a sensor node
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via a serial port or some physical connections to the node
Reprogram nodes one by one
However, physical access to nodes is in many cases
extremely limited following deployment
Even when access were possible, manually updating
hundreds or thousands of nodes would be a tedious task
indeed
Network reprogramming protocols have recently emerged
as a way to distribute application updates without requiring
physical access to sensor nodes.
Multi-hop Over-the-Air Programming
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MOAP divides a program image into packets, and these packets are
distributed through the network. Once received, packets are placed in
stable storage until the entire update has been completed.
In MOAP, sources advertise updated code images to their neighbors. A
node having received a full image become publishers and propagate the
image to other nodes out of range of the original source.
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This process is applied iteratively until the update has propagated across the
network.
Packet loss and retransmission
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Receiver uses a sliding window to keep track of lost packets.
When a missing packet is detected, the receiver sends a uni-cast retransmission
request.
If the source does not respond within a certain amount of time, the receiver
broadcasts a retransmission request to which all nodes within range reply.

This allows the receiver to choose a new source in case the original source fails.
Duplicate requests arriving at a source within a given time period are suppressed.
Cross Layer Protocol Design
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No standard protocol for sensor nets
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Resource constraints even demand cross-layer
integration
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Sensor protocol design is task-specific
While some protocols can achieve very high performance in
terms of the metrics related to each of the individual layer,
they are not jointly optimized in order to maximize the
overall network performance and minimize energy
expenditure
When designing communication schemes, we can not
simply pick the best protocol in each layer and pile
them up.
Tele-Communication System
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The needs for telemetry
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Provides near-real-time data feeding
Enables remote control of sensor nets and data loggers
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Single Board Computer (SBC)
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Change monitoring parameters
Update sensor motes/data logger programs after deployment
200Mhz ARM processor, 64MB RAM, 1GB SD Card
Linux support
Bridge between sensors and Internet
Local Database Server
GPRS modem
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PPP and PPP Daemon
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a data link protocol commonly used to establish a direct connection between two nodes
over serial cable, phone line, cellular phone, or dial-up network to get access to the
Internet
Conclusion
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Data flows from sensors to remote database
System Architecture
Research areas
 Energy-Aware
Design
 Cross Layer Protocol Design
 Over the air programming
 Localization
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Questions?