Next Century Challenges: Mobile Networking for “Smart Dust”Abstract:Main aim of the paper:Introduction:What is the Smart Dust project:Smart Dust Technology:Major Challenges:Slide 8Developing a communications architecture for ultra low-power is a more critical challenge.RF Technique:Slide 11Optical Transmission Technique:3. The short wavelength of the visible or near infrared light makes it possible for a millimeter scale device to emit a narrow beam.There are two requirements for successful decoding of these simultaneous transmissions:The CCR is shown here:CCRSlide 17Slide 18The BTS contains a laser whose beam illuminates an area containing dust motes.When the application requires dust motes to use active optical transmitters, MEMS technologyThe active transmitters should be used for short- duration burst-mode communication only.Mobile Networking ChallengesLine-of-sight requirementIn such cases BTS continuously senses the dust motes.Link DirectionalitySlide 26Active dust mote transmitterFollowing points are considered in developing beam-steering algorithms:-In all of the above cases the dust motes transmitter and receiver have different spreads. This leads to non reciprocal link characteristics.Collision during active peer-to-peer communication is a potential problem in Smart Dust Networks.Trade-offs Between Bit rate, Distance and Energy per BitWhere,The expression assumes the following:-The average transmitted power is Pt = Eb/RbSlide 35Applicationseg. Instrumentation of semiconductor processing chambers, wind tunnels, rotating machinery etc.Scenario: Multi-Sensor Emergent BehaviorTechnology Approaches for Realizing the Scenario:If line of sight path is blocked then mote will need to use ad hoc, multihop techniques to communicate with the BTS or nearby sensor nodes.The main challenge is building a multihop route in this environment.Slide 42Related ProjectsSummary and Conclusion1Next Century Challenges:Next Century Challenges:Mobile Networking forMobile Networking for“Smart Dust”“Smart Dust”2Abstract:Abstract:Advances in hardware technology has enabled very compact ,autonomous and mobile nodes, each having one or more sensors, computation and communication capabilities, and a power supply.There is a need for networking all these devices.3Main aim of the paper:Main aim of the paper:To review the key elements of “Smart Dust”.To outline the research challenges they present to the mobile networking and systems community.The paper also explores the limit on size and power consumption of sensor nodes.4Introduction:Introduction:Networking of wireless sensors has become possible due to the following three technologies: 1. Digital Circuitry 2. Wireless Communication 3. Micro ElectroMechanical Systems (MEMS) In all these areas the main focus has been on reduction in size, power consumption and cost.5What is the What is the Smart DustSmart Dust project: project: Being developed at UC Berkeley by Prof. Pister and Prof Kahn.It explores the limits on size and power consumption in autonomous sensor nodes.Size reduction is important in order to make the nodes as inexpensive as possible and also easy to deploy.The researchers believe that these nodes will be of the order of a few cubic millimeters and are called “Smart Dust”.6Smart Dust Technology:Smart Dust Technology:A Smart Dust mote consists of:MEMS sensors.A semi-conductor laser diode and MEMS beam- steering mirror for active optical transmission.A MEMS corner-cube retroreflector (CCR) for passive optical transmission.An Optical receiver.Signal Processing and Control Circuitry.A power source based on thick-film batteries and solar cells.7Major Challenges:Major Challenges:To incorporate all these functions while maintaining a low power consumption.Maximizing operating life given the limited volume of energy storage.The functionality can be achieved only if the total power consumption of a dust mode is limited to microwatt levels, and if careful power management strategies are utilized. A Smart Dust mote is shown in next figure.89Developing a communications architecture for Developing a communications architecture for ultra low-power is a more critical challenge.ultra low-power is a more critical challenge.There are primarily two communication technologies:Radio Frequency (RF) TechniqueOptical Transmission TechniqueEach technique has certain advantages and disadvantages.10RF Technique:RF Technique:Presents problem because dust motes offer very limited space for antennas, thereby demanding extremely short-wavelength( or high frequency) transmission.Communication not compatible with low power transmission.The radio receivers are complex circuits making it difficult to reduce their power consumption to the required microwatt level.11Require:1. Modulation2. Bandpass filtering3. Demodulation circuitry 4. Additional circuitry is required if the transmissions of a large number of motes are to be multiplexed using time, frequency or code division multiple access.12Optical Transmission Optical Transmission Technique:Technique:Kahn and Pistor showed 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 the optical links:1. Optical transceivers require only simple baseband analog and digital circuitry.2. They don’t require modulators, active bandpass filters or demodulators.13 3. The short wavelength of the visible or 3. The short wavelength of the visible or near infrared light makes it possible for a near infrared light makes it possible for a millimeter scale device to emit a narrow millimeter scale device to emit a narrow beam.beam. 4. 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.14a. Dust motes should not block one another’s line of sight to the BTS. Such blockage is unlikely due to the small size of dust motes.b. Images of different dust motes be formed on different pixels in the BTS imaging receiver.5. Another advantage is that the dust motes use passive optical transmission techniques i.e to transmit modulated optical signals without supplying any optical power. This structure is a corner-cube
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