Ultra-Wideband communication technology for sensor network applications

1. Ultra-Wideband communication technology for sensor network applications Julien Ryckaert IMEC Julien.Ryckaert@imec.be

2. The vision of “Ambient Intelligence” “An environment where technology is embedded, hidden in the background” Fred Boekhorst Philips Research, ISSCC ‘02

3. Health Care of the Future Fitness for you!

4. Increase Productivity Home of the Future

5. This vision requires the massive deployment of sensor nodes Network

6. A sensor node is a completely autonomous device Energy clock Sensing Processing Communication

7. Three major challenges in the communication module • Ultra-low power : >2 years autonomy • Ultra-small size : non-invasive • Ultra-low cost : disposable • Low communication performance : <100kbps

8. POWER CONSUMPTION ? PERFORMANCE

9. Power  Energy/bit but… Data rate  Energy/bit In reality, the total Energy consumption must be minimized What does it cost to transfer a bit of information? Power consumption (Energy/time) = Energy/bit Data rate (bits/time)

10. After CEA-LETI 10E4 Energy / bit (nJ/bit) 10E3 10E2 10E1 10E0 WiFi 1Mbps 50 Mbps 250kbps 10 to 150 kbps The active time of the radio must be minimized!!! How does it look like today? Increasing data rate

11. POWER CONSUMPTION UWB ? PERFORMANCE

12. Traditional Communication systems use continuous waves NarrowBand Communication time frequency Each user/application has its own spectrum band

13. Impulse Radio UWB uses short pulses Pulse-based Ultra WideBand communication frequency time Emitted power must be low enough to avoid jamming

14. Activate the radio only when needed Power Active Active Sleep The active time of the radio is reduced: “Radio duty-cycling”

15. Full-7GHz Band -41dBm/MHz … 3.1 1 10.6 F [GHz] Minimum 500MHz band More users FCC: UWB communication must be done in the 3.1-10GHz band -41dBm/MHz FCC 3.1 1 10.6 F [GHz]

16. IEEE standard for low data-rate sensor networks Activate the transmitter only when needed to achieve low-power Burst 3% Active! 97% Inactive

17. Pulse repetition frequency multiple of carrier frequency Fcarrier = N x Fpulse The standard imposes some constraints on the signals • Pulses are BPSK modulated 1 0

18. Overall transmitter architecture CONTROL LOOP (ISSCC 07)

19. Time-domain measurement of the output signal Same energy efficiency as first transmitter!

20. ADC Decision Analog Correlation Very precise timing  Power Hungry Digital Correlation (Matched Filter) ADC Decision Correlation can be done either in Analog or in Digital domain High Sampling rate  Power Hungry

21. I Q Full system block diagram Analog Output CAL ADC I/O bus Digital Controller (System Configuration and Interfacing) LO Timing circuit LNA RFin Serial/Par Out ADC CAL DL DL DL DL Clk/Rst (ISSCC 06) Clk

22. What about power consumption? • State-of-art narrowband solutions (Zigbee): • TX: 10mW • RX: 2mW • UWB solutions: • TX: 0.5-1mW • RX: 0.3mW / 10

23. UWB has other advantages • Positioning by measuring the time of arrival • Security: UWB power spectrum below the background noise DL TX RX TX DT Background noise (kT)

24. Other impulse Radio implementations exist • Example: MIT (US) proposes a similar concept: But uses a proprietary UWB communication interface

25. Therefore the question: should sensor networks be standardized? • Pros: • Interoperability (add nodes in the network) • Market pressure decreases cost • Cons: • Solution biased by the “big ones” • Security • Less interferences (?) Sandardization aspect is an old controversial debate for healthcare wireless systems

26. Conclusions • UWB offers today a 10x improvement on power consumption. • UWB has other interesting advantages in the context of sensor networks: security, positionning,… • An IEEE standard exists today (IEEE 802.15.4a), but its use in wireless healthcare systems is still a debate.