Post on 09-Jul-2015
Remote Data
Acquisition for Wireless
Sensor Networks
Changfei Chen
Steve Distasi
Sarah Greenberg
Topics
Methods of RDA
Possible WSN RDA Configurations
Physical Concerns of RDA
Methods of Remote Data
Acquisition
Wired System
Radio Modem (point-to-point)
Cellular Modem
Wired System
Gateway node connected directly to
established Internet connection
Wired System Example
City Sniff
In-home pollution sensing kit
Sends environmental data to public database
Connects to existing wired internet connection
City Sniff cont.
Connects Tmote Sky to
embedded linux gateway
BaseStation Tmote
connected via USB to
gateway
Gateway is then connected
to home’s router
Radio Modem
Transmit data over long distance (point-to-point)
Useful for…
Remote Locations
No wired access
No cell access
Radio Modem Example
Volcanic Monitoring
Uses FreeWave Radio Modem
Cellular Modem
Send/receive data via cellular communication
SMS—text message
Direct internet connection
GSM/GPRS most commonly used standard, CDMA also used
Useful for…
Remote location with cell access
Mobile sources—cars and boats
Immediate updates or alerts sent to specific person/location
Cell Modem Example
Temperature
monitoring on fish
boats in Ireland
Users can access the
data via web server or
SMS server
SMS warning system
Cell Modem Example Klimat
Monitoring effects of global warming on the Baltic
Sea
RDA using GPRS satellite modem
Limitations
Power
Memory
Frequency
Transmission Distance
Power
Wired
Usually inside, just plug it in!
Radio/Cell/Satellite modems
Large batteries
Energy harvesting
Energy saving techniques
Cyclic sleep modes
XTend-PKG 900 MHz USB RF
Modem
•Receive current: 110mA
•Transmit current (1mW-1W transmit power):
110-900mA
•Three Modes:
•Pin sleep: 17mA
•Serial port sleep: 45mA
•Cyclic sleep (Various intervals): 19-39mA
MultiModem GPRS
•Three Modes:
•Always-on
•Wake-up on ring
•Dial-on demand
Memory
Dependant on gateway device
Tmotes have little onboard memory, so
they have limited gateway capabilities.
Operating Frequencies of
modems
Radio Modem – 900 MHz
Cellular Modem
GSM:
900MHz, 1800MHz;
850MHz, 1900MHz. (US., Canada)
Uses 1900MHz
Uplink: 1850-1910MHz
Downlink: 1930-1990MHz
Transmission Distance
XTend RF Modem & MultiModem GPRS
Transmission Power can be up to 1 Watt
Indoor/Urban range (2.1 dB dipole
antenna): Up to 3000 feet (900m)
Outdoor RF line-of-sight range (High gain
antenna): Up to 40 miles (64 km)
Outdoor RF line-of-sight range (2.1 dB
dipole antenna): Up to 14 miles (22 km)
Possible WSN RDA
Configurations
Gateway Concept
WTF
Possible Orientations
Current Solutions
Cell Modems!<3
lwIP & µIP
Gateways
Provide the connection to the
communication medium
Can be a node, or any device with access
to the WSN.
Gateway Challenges
Is it just a router?
Do we want the ability to address individual
nodes?
Goes against the idea that and individual
node is irrelevant
Gateway Challenges
Application-level gateway
Requester sends properly formatted
message to the gateway node
Masks the data-centric exchange in the
WSN behind an identity-centric exchange
of the internet
Possible Orientations
WSN to Internet
Internet to WSN
WSN to WSN
Tunneling
INTERNET
Possible Configurations
WSN to Internet
A sensor node in your house wants to send an
alert that your house is on fire.
Gateway must convert intra-WSN event
notification message to an Internet application
message.
Possible Configurations
Internet to WSN
You wish to access the Votey WSN from
your home terminal
Gateway must translate this request into
proper intra-sensor network protocols
Possible Configurations
WSN to WSN Tunneling
Gateways act as simple extensions from
one WSN to another
Such tunnels need not be made of fixed
gateways
Cell Modems!<3
GSM/GPRS
Some Definitions
Services
Global System for Mobile
communications (GSM)
Implements 2 Circuit-Switching data
protocols
Circuit Switched Data (CSD)
High Speed Circuit Switched
Data(HSCSD)
Reserves a certain amount of bandwidth
between two points for the life of a
connection
General Packet Radio Service
(GPRS)
Packet-Switching data protocol
Sends data in packets along channels not
being used for circuit-switching
Multiple GPRS users share a single
unused channel - using it only in short
bursts
Current Solutions
lwIP & µIP
lwIP
Designed for 16-bit microcontrollers
Uses only tens of kbs of RAM
Code size of around 40 kbs
Current Solutions
lwIP & µIP
µIP
Designed for 8-bit and 16-bit
microcontrollers
Ram usage on the order of a few hundred
bytes
Code size on the order of a few kbs
Serial Communication
RS-232
USB
Synchronous and Asynchronous
Serial Communication
Hardware
UART (Universal Asynchronous
Receiver Transmitter) -- Translates data
between parallel and serial forms
Included in Tmote microcontroller
RX, TX, and FIFO buffers
Line driver -- Converts circuit level
voltages to line voltages and vice versa
USB controller
Serial Communication
Parameters
Baud Rate
Start Bit
Data Bits – 5 to 8
Parity – Error check (Even, Odd, none)
Stop Bit(s)
Flow Control (DTR/DSR, RTS/CTS, Xon/Xoff, none)
Start and Stop bits not necessary for synchronous communication
Serial Communication
Example Parameters
Baud rate = 115200 bps
8 Data Bits
No parity
1 Stop Bit
No Flow Control
Serial Communication
Signals
Transmitted Data (TxD)
Received Data (RxD)
Ground (GND)
Serial Communication
Signals
Request To Send (RTS)
Asserted (set to 0) by sender to prepare receiver to receive data.
Clear To Send (CTS)
Asserted by receiver to acknowledge RTS and allow transmission.
Data Terminal Ready (DTR)
Asserted by device to indicate that it is ready to be connected. If the device is a modem, this may "wake up" the modem, bringing it out of a power saving mode.
Data Set Ready (DSR)
Asserted by host to indicate an active connection.
Data Carrier Detect (DCD)
Asserted by host when a connection has been established with remote equipment.
Ring Indicator (RI)
Asserted by host when it detects ring signal from the telephone line
Flow Control
Flow control avoids overflow
Can Eliminate the need for flow control
by…
Regulating speeds
Packet size smaller than buffers
Demo
Configure parameters
Transmit data through modem
Polling vs. event driven
Thanks! Any Questions???