Applications of Smartdust in Transport
Over the last few years many different versions of motes have been designed and built by various companies and institutions. The size of these motes varies from roughly the size of a matchbox to the size of a pen tip. MEMS (Micro Electromechanical Systems) technology has been used to miniaturise components with an aim of implementing a mote on a single chip that fits into a volume of no more than a cubic millimetre. These motes have been nicknamed "Smart Dust". In this section various mote designs are looked at which use a variety of communication methods. For the ASTRA project the Mica2 and Mica2Dot motes are used.
Radio Frequency (RF) Mote
The RF mote was an early mote version which was finished in the first part of 1999. The device was designed by Seth Hollar at UC Berkeley. It consisted of an Atmel AT90LS8535 processor, a 916 MHz RF transceiver and 5 sensors (temperature, light, barometric pressure, a 2 axis accelerometer and a 2 axis magnetometer). It operated on a 3V lithium coin cell battery that could sustain a mote for 5 days of continuous operation or 1.5 years at a duty cycle of 1%. The mote used a single radio carrier frequency to transmit data and so only one device was able to transmit at a time. The RF mote had a communication range of about 5 - 30m at a rate of 5Kbps depending on conditions. The RF mote was designed to use a serial operating system where only a single task could occur at any one time.
The Mini mote was designed by Seth Hollar and Christina Adela at UC Berkeley. The mote was a smaller version of the RF mote and had an Atmel AT90S2313 processor and an on-board temperature sensor. The Mini mote was cheaper than the RF mote due to its smaller size and simpler circuit design. It could communicate via a radio link at 10 Kbps over a distance of 20m depending on conditions.
The weC mote was designed by Seth Hollar and James McLurkin at UC Berkeley. The weC mote was an improved version of the Mini mote which has a number of additions and a slightly larger size. On-board it had temperature and light sensors as well as an integrated PCB antenna to improve the motes communication performance. The weC mote had a CPU clock rate of 4 MHz and was capable of being reprogrammed remotely through the sensor network it was part of. This allowed it to be adapted to carry out different tasks from the one it was originally programmed to do without the mote having to be collected from the field. The weC mote used the TinyOS operating system.
The Mica mote was a second generation commercial mote module that is manufactured by Crossbow in the United States. It was mainly used for research and development of low power wireless sensor networks. The Mica mote platform was built around the Atmel Atmega 128L processor which was capable of running at 4 MHz. The Mica mote had 128Kbytes of flash memory, a 4 Mbit serial flash, 4Kbytes of SRAM and a 4Kbyte EEPROM. TinyOS was used to control the mote and its sensors. The mote was able to communicate with the sensor network via a radio link which operated on the 916 or 433 MHz bands and could carry data at 40 Kbps over distances of up to 100 feet. Power was provided from 2 AA batteries and the device had a battery life of roughly 1 year depending on the application. Sensor boards could be attached via a surface mount 51 pin connector that supported analogue input, I2C, SPI, UART and a multiplexed address/data bus.
The Mica2 mote is a third generation commercial mote. Like the Mica mote it is produced by Crossbow and used mainly for research and development. The Mica2 mote features several improvements over the original Mica mote. It uses the same processor as the Mica mote as well as the same surface mount 51 pin connector to attach various sensor boards to the mote. The mote also uses the same batteries as the Mica mote and has a similar battery life. However the Mica2 has 512Kbytes of serial flash which is more than the Mica mote. Also the radio transceiver operates on either the 433 MHz band or the 868/916 MHz bands with a data rate of 38.4 Kbps and a maximum outdoor range of roughly 500 feet. Like the Mica mote the Mica2 uses TinyOS in order to control the mote and its attached sensors. The Mica2 also allows every mote to function as a router and supports remote reprogramming over the sensor network.
The MicaZ Mote is similar to the MICA2 but the radio operates at 2.4GHz resulting in a maximum data rate of 250Kbps.
The Mica2Dot mote is a coin sized mote that is very similar to the Mica2 mote. The mote has the same processor and memory as the Mica2 mote and has the same radio communication capabilities. The Mica2Dot mote operates using a 3V coin cell battery and has reduced input/output capabilities. The mote has a temperature sensor and LED on board as well as a ring of 18 solder less expansion pins to enable extra sensor boards to be added to the setup.
The Spec Mote was developed by a team of researchers at UC Berkeley and is approximately 2mm2 by 2.5mm2 in size. Spec is a fully working single chip mote which has a RISC core and 3Kbytes of memory. Spec uses radio communication on the 902.4 MHz band. In tests Spec has been shown to communicate over 40ft indoors with a data rate of 19.2 Kbps.
The aim of Intel's Deep Networking research project was to develop a mote with more CPU power, digital signal processing, a more reliable radio and better security features. The modular design of the original Berkeley motes was maintained whilst Intel worked on improving battery life and reducing costs. In order to achieve this Intel aimed to maintain the operational duty cycle at 1% or less. The Intel mote consists of an ARM processor, SRAM and flash memory. Communication with other motes is via Bluetooth technology with the platform supporting alternative radio technologies as add on modules. Optional sensor boards and an optional power regulator are also available. The Intel mote software is based on TinyOS but has an Intel mote specific layer with added Bluetooth support, platform device drivers and a network layer for topology establishment and also to allow single and multi-hop routing.
The laser mote uses active laser communication to send sensor data over long distances. The mote runs on 2 AA batteries and contains humidity, light, temperature and pressure sensors. The laser transmitter, a laser module from a laser pointer, needs to be manually pointed towards the receiver. These motes can only send data back to a base station as they have no receiver module on board. These motes have been shown to transmit weather data over a distance of 21 km in the San Francisco Bay area. In this experiment a CCD camera linked to a laptop computer was used as the receiver. However due to the slow speed of the camera data was sent at extremely low data rates but with commercial high speed camera data rates in excess of 1 Kbps are possible.
The CCR mote was designed at UC Berkeley by Seth Hollar and Farrah Santoso. The mote was equipped with a temperature sensor and uses a corner cube reflector (CCR) module to allow passive laser communication. MEMS technology was used to construct the CCR. In order to communicate first of all an interrogator must project a diverged laser beam in the general direction of the motes. This beam contains commands to be executed by the motes. The motes receive this signal and by modulating and reflecting the beam back to the interrogator the mote can send back data if the command requires it to return data. The communication range is a function of the laser beams intensity.