Dominic C. O Brien,Jing Jing Liu , Design and Implementation of Optical Wireless Communications with Optically Powered Smart Dust Motes Dominic C. O Brien,Jing Jing Liu ,

CONTENTS 1.Introduction 2.Micromachine communication network 3.Base station design 4.Smart dust motes 5.System results 6.Conclusion 7.References

INTRODUTION Providing connection with micro machines and smart dust are challenging Integrated circuits with wireless connection are preferred Optical wireless communications is an attractive option for low data rate communications modulated retro- reflectors are used Low speed communication for smart dust without tracking

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OVERVEIW according to fig1 Base Station is situated above a number of Smart Dust Motes. Light from the BS falls on a particular mote using holographic beemsteering system. The light illuminates the SDM, and modulated to provide a downlink from the BS to the SDM A Modulated Retro-Reflector on the SDM reflects light back to the BS. modulated radiation is detected using an imaging receiver that consists of a high frame-rate CMOS camera and associated image processing

BASE STATION DESIGN BS illuminate the SDM to provide power, intensity for the SDM downlink and power for uplink to operate. Holographic beam steering used for maximizing intensity. possibility to alter the divergence of beams, and correct for aberrations.

Base station

Optical design and link budget modeling Optical system layout

Light from a 670nm laser is polarized and illuminates the SLM. The SLM is arranged for binary phase modulation. Resulting wave front is Fourier transformed using a Fourier Lens. Two lenses are used to magnify the steering angle, to create a total view of 30 degrees. The simple optical system used creates aberrated, enlarged, spots

B. Intensity and link budgets Three constraints for correct operation of SDM 1.illumination intensity from the beam to power the SDM 2. sufficient link margin for the downlink 3.sufficient link margin for the uplink.

The intensity at the SDM is m:order of beam from BS PT:transmitted power r:distance from BS to SDM

Light passes through the aperture of the modulator, is retro-reflected and passes back through it once more power that passes back through the aperture to be ’re-emitted’and propagate back to the BS, Πa^2LC :area ofmodulator R:reflection coefficient of retro reflector

C. System Operation 1.Acquisition and tracking 2.Downlink 3.Uplink 4.Network operation

SMART DUST MOTES The SDM consists of power photodiode communications receiver Modulated retro reflector LC cells: to form the modulator LC drive directory Retroreflectors

Layout of smart dust integrated circuit Layout of smart dust integrated circuit. The large areas in the centre are different types of power photodiode. The IC is 5x5mm in size.

Modulated retro-reflector

SYSTEM RESULTS Downlink and SDM operation SDM was illuminated with a downlink waveform of avg intensity 3.5 μW/mm^2 1nF external storage capacitor is connected 100pF capacitor connected in place of the LC modulator SDM contained bias generating circuits did not operate as predicted due to process calibration issues so several biases in the circuit are externally generated

The measured response of a optically powered mote This shows the SDM operating correctly, and that the successive signals are translated to operating voltages required for LC cell. Switching energy is 16pJ/bit for 100pJ. Electrical power consumption is approximately 100nA at .4V or40nW.

B. Base station tracking Tracking error was reduced by making precorrection to steering angle Measuring performance of correction using rectangular calibration board. consisting of 90 equally spaced retro- reflectors. Each target was acquired and tracked and the mean tracking error reduced by 11%

C Uplink operation shows a waveform of a 32bit/s Manchester coded waveform received by the base station at a distance of 15 m under low ambient light conditions and a sampling (frame) rate of 250 samples/s

The link was operated in a dark room with different LC voltages at a range of 3m. The received waveforms that are recorded are degraded by Inter-symbol Interference (ISI) Data recovery achieved by using a band pass filter. present the SDM and the uplink have been separately tested, and both show correct operation

CONCLUSION optical wireless technique can communicate with and power small silicon based systems. Communication over 10s of metres is possible using the interrogating beam. total power consumption of the mote is approximately 40nW. integrating the communications modulator and the si to create a compact dust mote In the longer term work will focuson increasing the functionality of the system,

REFERENES [1] Specknet collaboration,www.specknet.org, Accessed Jan 2009. [2] J. M. Kahn, R. H. Katz, and K. S. Pister, Next century challenges: mobilenetworking for ”Smart Dust”’ 1999. [3] Semiconductor Industry Association www.sia-online.org, Accessed May2009.