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

Email

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???