Smart Dust Paper Presentation

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Abstract:Smart dust is an emerging technology made up from tiny, wireless sensors or motes. These large scale networks of

wireless sensors are becoming increasingly tractable. Advances in hardware technology and engineering design have

led to dramatic reductions in size, power consumption and cost for digital circuitry, wireless communications and

Micro Electro Mechanical Systems (MEMS). This has enabled very compact, autonomous and mobile nodes, each

containing one or more sensors, computation and communication capabilities, and a power supply. This paper gives a

profound description about the technology and also the working of a mote, which are very tiny wireless sensors and

also about the history. It also gives a detailed description about types of transmission between sensors and the

antennas. The optical mode of transmission is most effective one. It also states the various challenges faced for the

development of mobile networking protocols for Smart Dust. The missing ingredient is the networking and

applications layers needed to harness this revolutionary capability into a complete system. Thus we review the key

elements of the emergent technology of "Smart Dust" and outline the research challenges they present to the mobile

networking and systems community, which must provide coherent connectivity to large numbers of mobile network

nodes co-located within a small volume.

Introduction:As the research community searches for the processing platform beyond the personal computer, networks of wireless sensors

have become quite interesting. Many researchers have shown that it is possible to integrate sensing, communication, and

power supply into an inch scale using only off the scale technology. These have been enabled by a rapid convergence of three

key technologies namely digital circuitry, wireless communications, and micro Electromechanical Systems.

Smart dust is an emerging technology made up from tiny, wireless sensors or motes. Eventually these devices will be smart

enough to talk with other sensors yet small enough to fit on the head of the pin. Each mote is a very tiny computer with a

power supply, one or more sensors and the communication system. Smart dust motes are typically outfitted with

environmental sensors which can monitor things like temperature, humidity, lighting, position and acceleration.



Fig1: Image of smart dust particle surrounding a drop of hydrophobic liquid in water.

Smart dust has theoretical applications in virtually every field of science and industry. Research in the technologies is

well-funded and sturdily based, and it is generally accepted that it is simply a matter of time before smart dust exists in a

functional manner. Opponents question the risks to personal privacy, but proponents hold that the downsides are strongly

outweighed by the positive benefits.

The Defense Advanced Research Projects Agency (DARPA) has been funding smart dust research heavily since the late

1990s, seeing virtually limitless applications in the sphere of modern warfare. So far the research has been promising; with

prototype smart dust sensors as small as 5mm. Costs have been promising; with prototype smart dust sensors as small as

5mm. Costs have been dropping rapidly with technological innovations, bringing individual motes down to a very low rate.

History of smart dust:Smart dust was conceived in 1998 by Dr.Kris pister of the UC Berkeley. He set out to build a device with a sensor, a

communication device and a small computer integrated in to small package. In the early stages of project the team gained

experience by building relatively large motes. One such mote called RF mote has sensors for temperature humidity, barometric

pressure, light intensity, tilt and vibration and magnetic field and is capable of communicating distance of 60 feet using RF

communication. They faced trade-off between miniaturization and long battery life. One approach was taken by Dr. David

Culler to prolong the battery life is to design a software that enables the mote to sleep most of the time but yet wake up

regularly to take readings and communicate. This helps in energy conservation during sleep hours.

The UC Berkeley team equipped some of the early motes with optical communication system to reduce power consumption.

Another energy saving approach is the passive transmission which does not have a on-broad light source but it uses a series of

mirror controlled by electric charge. When the laser is pointed towards the



Fig2: Early Smart dust

Mote, it rapidly adjusts the position of the mirrors to send messages encoded in pulse of light, the message could be read by a

special optical device. But the disadvantage with this type of system is that it cannot directly communicate with one another.

It rely on the central station equipped with the light source to send and receive data from other motes. But later Professor

David Culler and a team of researches created the TinyOS operating system which once installed in a mote; it operates the

device, managing its power consumption and facilitating communication with other motes.

Working of a mote:The primary constraint in the design of the a severe constraint on energy since we do not have much room for batteries or

large solar cells. Thus, the motes must operate efficiently and conserve energy whenever possible. Most of the time, the

majority of the mote is powered off with only a clock and a few timers running. When a timer expires, it

Powers up a part of the mote to carry out a job, then powers off. A few of the timers control the sensors that measure one of

a number of physical or chemical stimuli such as



temperature, ambient light, vibration, acceleration, or air pressure. When one of these timers expires, it powers up the

corresponding sensor, takes a sample, and converts it to a digital word. If the data is interesting, it may either be stored

directly in the SRAM or the microcontroller is powered up to perform more complex operations with it. When this task is



complete, everything is again powered down and the timer begins counting again.Fig 3: Smart dust particles

Another timer controls the receiver. When that timer expires, the receiver power up and looks for an incoming packet. If it

doesn't see one after a certain length of time, it is powered down again. The mote can receive several types of packets,

including ones that are new program code that is stored in the program memory. This allows the user to change the behavior

of the mote remotely. Packets may also include messages from the base station or other motes. When one of these is received,

the microcontroller is powered up and used to interpret the contents of the message. The message may tell the mote to do

something in particular, or it may be a message that is just being passed from one mote to another on its way to a particular

destination. In response to a message or to another timer expiring, the microcontroller will assemble a packet containing

sensor data or a message and transmit it using either the corner cube retro reflector or the laser diode, depending on which it

has. The corner cube retro reflector transmits information just by moving a mirror and thus changing the reflection of a laser

beam from the base station. This technique is substantially more energy efficient than actually generating some radiation. With

the laser diode and a set of beam scanning mirrors, we can transmit data in any direction desired, allowing the mote to

communicate with other Smart Dust motes.

Smart dust technology:Integrated into a single package are MEMS sensors, a semiconductor laser

fig 4: Motes with all its components

Diode and MEMS beam steering mirror for active optical transmission, a MEMS corner-cube retro reflector for passive

optical transmission, an optical receiver, signal processing and control circuitry, and a power source based on thick-film

batteries and solar cells. This remarkable package will have the ability to sense and communicate, and be self-powered. A

major challenge is to incorporate all these functions while maintaining very low power consumption, thereby maximizing

operating life given the limited volume available for energy storage. Within the design goal of a cubic millimeter volume, using



the best available battery technology, the total stored energy is in the order of 1 J. If this energy is consumed continuously

over a day, the dust mote power consumption cannot exceed roughly 10 jiW. For comparison, this is roughly the shutdown

power of individual low power ICs found in today's laptop computers. The functionality envisioned for Smart Dust can be

achieved only if the total power consumption of a dust mote is limited to microwatt levels, and if careful power management

strategies are utilized. To enable dust motes to function over the span of days, solar cells could be employed to scavenge as

much energy as possible when the sun shines or when room lights are turned on. With energy as the most precious resource,

and time not as likely to be critical, elementary operations and ultimately algorithms are likely to be judged in terms of their

energy cost, rather than power consumption.

Types of transmission:

Techniques for performing sensing and computation at low power are reasonably well understood. Developing

communications architecture for ultra-low-power represents a more critical challenge. The primary candidate communication

technologies are based on RF or optical transmission techniques.

Fig.5: Design of a free-space optical network in which a base-station transceiver communicates simultaneously with

a collection of many dust motes.

RF transmission technique:

In RF dust motes offer very limited space for antennas, thereby demanding extremely short-wavelength i.e., high frequency

transmission. Communication in this regime is not currently compatible with low power operation. Furthermore, radio

transceivers are relatively complex circuits, making it difficult to reduce their power consumption to the required microwatt

levels. They require modulation, band pass filtering and demodulation circuitry, and additional circuitry is required if the

transmissions of a large number of dust motes are to be multiplexed using time-, frequency- or code-division multiple access.

Optical transmission techniques:



An attractive alternative is to employ free-space optical transmission. Studies have shown that when a line-of-sight path is

available, well-designed free-space optical links require significantly lower energy per bit than their RF counterparts. There are

several reasons for the power advantage of optical links. Optical transceivers require only simple

base band analog and digital circuitry; no modulators, active band pass filters or demodulators are needed. The short

wavelength of visible or near-infrared light of the order of lum makes it possible for a millimeter scale device to emit a narrow

beam i.e., high antenna gain can be achieved. As another consequence of this short wavelength, a base- station transceiver

(BTS) equipped

with a compact imaging receiver can decode the simultaneous transmissions from a large number of dust motes at different

locations within the receiver field of view, which is a form of space-division multiplexing. Successful decoding of these

simultaneous transmissions requires that dust motes not block one another's line of sight to the BTS. Such blockage is

unlikely, in view of the dust motes small size. A second requirement for decoding of simultaneous transmission is that the

images of different dust motes be formed on different pixels in the BTS imaging receiver. To get a feeling for the required

receiver resolution, consider the following example. Suppose that the BTS views a 17 m

* 17 m area containing Smart Dust, and that it uses a high-speed video camera with a 256

*256 pixel imaging array. Each pixel views an area about 6.6 cm2. Hence, simultaneous transmissions can be decoded as long

as the dust motes are separated by a distance roughly the size of a pack of cigarettes. Another advantage of free-space optical

transmission is that a special MEMS structure makes it possible for dust motes to use passive optical transmission techniques,

i.e., to transmit modulated optical signals without supplying any optical power. This structure is a, or CCR.

Applications:

These small sensors can have various applications, it can be used at

Defense-related sensor networks: - These can be used in battle field surveillance which can help in the detection of any

explosives planted in the field by the enemy and they can also be used for spying on other countries to know their secret

movements. It is also used in Military for treaty monitoring, transportation monitoring and stud hunting. Thus smart dust

ensures safety to the country.

Virtual keyboard :- As Smart dust can sense the smallest motion it can be of great help to the physically handicapped. It can

be very useful to them in communicating with computers with the movement of fingers. By gluing a dust mote on each

fingernails, the accelerators in it will sense the orientation and motion of each fingertips and thus communicate with the

computer.

Inventory control: - The position of the products and its shape at any time anywhere can be known. Sort of like

FedEx tracking on steroids for all products in your production stream from raw materials to delivered goods.

Product quality monitoring: — They can also check the temperature, humidity of meat and dairy products and help in

preserving them. It also monitors temperatures, vibrations and impact of consumer electronics. And also gives failure analysis



and diagnostic information, like monitoring vibration of bearings for frequency signatures indicating imminent failure.

Smart office spaces: - The Center for the Built Environment has fabulous plans for the office of the future in which

environmental conditions are tailored to the desires of every individual. Maybe soon we'll all be wearing temperature,

humidity, and Environmental comfort sensors sewn into our clothes, continuously talking to our workspaces which will

deliver conditions tailored to our needs.

Interfaces for the Disabled :-By putting motes on a quadriplegic are face, to monitor blinking & facial twitches - and send

them as commands to a wheelchair or a computer or to other devices. This could be generalized to a whole family of

interfaces for the disabled.

Conclusion:

The research community is searching for a new environment in which to generate innovative ideas and prove their

effectiveness. A new paradigm beyond desktop computing is capturing the imaginations of systems designs: the so-called

post-PC era. A wireless sensor network is one area that promises to yield important applications and demands new

approaches to traditional networking problems.

We have described Smart Dust, an integrated approach to networks of millimeter scale sensing/communicating nodes. Smart

Dust can transmit passively using novel optical reflector technology. This provides an inexpensive way to probe a sensor or

acknowledge that information was received. Smart dust provides a very challenging platform in which to investigate

applications that can harness the emergent behavior of ensembles of simple nodes. Dealing with partial disconnections while

establishing communications via dynamic routing over rapidly changing unidirectional links poses critical research challenges

for the mobile networking Community.

References:1. Mobile Networking for "Smart Dust" by J.M. Kahn, R. H. Katz (ACM Fellow), K. S. J. Pister.

2. Smart dust UHISRC Technology briefing by Doug Steel.

Smart Dust Paper Presentation

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