Remote Data Acquisition for Wireless Sensor Networks

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Remote Data Acquisition for Wireless Sensor
Networks

• Changfei Chen
• Steve Distasi
• Sarah Greenberg

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Topics

• Methods of RDA
• Possible WSN RDA Configurations
• Physical Concerns of RDA

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Methods of Remote Data Acquisition

• Wired System
• Radio Modem (point-to-point)
• Cellular Modem

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Wired System

• Gateway node connected directly to established
  Internet connection

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Wired System Example

• City Sniff
• In-home pollution sensing kit
• Sends environmental data to public database
• Connects to existing wired internet connection

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City Sniff cont.

• Connects Tmote Sky to embedded linux gateway
• BaseStation Tmote connected via USB to gateway
• Gateway is then connected to homes router

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Radio Modem

• Transmit data over long distance (point-to-point)
• Useful for
• Remote Locations
• No wired access
• No cell access

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Radio Modem Example

• Volcanic Monitoring
• Uses FreeWave Radio Modem

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Cellular Modem

• Send/receive data via cellular communication
• SMStext message
• Email
• Direct internet connection
• GSM/GPRS most commonly used standard, CDMA also
  used
• Useful for
• Remote location with cell access
• Mobile sourcescars and boats
• Immediate updates or alerts sent to specific
  person/location

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Cell Modem Example

• Temperature monitoring on fish boats in Ireland
• Users can access the data via web server or SMS
  server
• SMS warning system

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Cell Modem Example

• Klimat
• Monitoring effects of global warming on the
  Baltic Sea
• RDA using GPRS satellite modem

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Limitations

• Power
• Memory
• Frequency
• Transmission Distance

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Power

• Wired
• Usually inside, just plug it in!
• Radio/Cell/Satellite modems
• Large batteries
• Energy harvesting
• Energy saving techniques
• Cyclic sleep modes

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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

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MultiModem GPRS

• Three Modes
• Always-on
• Wake-up on ring
• Dial-on demand

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Memory

• Dependant on gateway device
• Tmotes have little onboard memory, so they have
  limited gateway capabilities.

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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

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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)

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Possible WSN RDA Configurations

• Gateway Concept
• WTF
• Possible Orientations
• Current Solutions
• Cell Modems!lt3
• lwIP µIP

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Gateways

• Provide the connection to the communication
  medium
• Can be a node, or any device with access to the
  WSN.

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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

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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

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Possible Orientations

• WSN to Internet
• Internet to WSN
• WSN to WSN Tunneling

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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.

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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

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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

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Cell Modems!lt3

• GSM/GPRS
• Some Definitions
• Services

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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

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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

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Current Solutions

• lwIP µIP
• lwIP
• Designed for 16-bit microcontrollers
• Uses only tens of kbs of RAM
• Code size of around 40 kbs

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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

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Serial Communication

• RS-232
• USB
• Synchronous and Asynchronous

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Serial CommunicationHardware

• 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

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Serial CommunicationParameters

• 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

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Serial Communication Example Parameters

• Baud rate 115200 bps
• 8 Data Bits
• No parity
• 1 Stop Bit
• No Flow Control

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Serial CommunicationSignals

• Transmitted Data (TxD) 
• Received Data (RxD)
• Ground  (GND)

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Serial CommunicationSignals

• 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

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Flow Control

• Flow control avoids overflow
• Can Eliminate the need for flow control by
• Regulating speeds
• Packet size smaller than buffers

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Demo

• Configure parameters
• Transmit data through modem
• Polling vs. event driven

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Thanks! Any Questions???