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Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)

Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [Preliminary IMEC Proposal] Date Submitted: [10 March, 2009] Source: [Guido Dolmans, Li Huang, Yan Zhang] Company [Holst Centre / IMEC-NL]

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Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)

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  1. Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title:[Preliminary IMEC Proposal] Date Submitted: [10 March, 2009] Source: [Guido Dolmans, Li Huang, Yan Zhang] Company [Holst Centre / IMEC-NL] Address [High Tech Campus 31, Eindhoven, the Netherlands] Voice:[+31 40 2774094], FAX: [+44 40 2746400], E-Mail:[guido.dolmans@imec-nl.nl] Abstract: [This presentation puts forward a preliminary proposal for IEEE 802.15.6 PHY and partly MAC.] Purpose: [For discussion by the group in order to provide applications scenarios, develop channel models and discuss radio architectures for IEEE P802.15.6.] Notice: This document has been prepared to assist the IEEE P802.15. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P802.15. Guido Dolmans, IMEC-NL

  2. Outline • WBAN PHY proposal • Dual-radio (ISM Band Main Radio and ISM Band Wake-up) WBAN Overview • ISM band Transceiver • Wake-up Receiver • Conclusions Guido Dolmans, IMEC-NL

  3. 802.15.6 Technical Requirements • Miniaturized sensor nodes – small form factor • Limited range (3 meters, extendable to 5 meters) • Significant path loss • Energy scavenging / battery-less operation • Scalable data rate: 10 kbps - 10 Mbps • Extremely low consumption power (0.1 to 1 mW) • Different classes of QoS for high reliability, low latency, asymmetric traffic • Energy efficient, low complexity MAC and upper layers • High security/privacy required for certain applications Guido Dolmans, IMEC-NL

  4. Dual-Radio System MAIN WBAN TRX RADIO Requirements of hardware event-driven triggered wake-up: • A node should wake up almost instantly when it receives a wake-up packet (low latency 802.15.6 QoS)  Wake-up radio not duty cycled • Energy consumption used for channel monitoring with dedicated wakeup receiver should be less than that with cycled main radio. • Performance: Node should not wake up when the event of interest does not happen (‘false alarms’) • Performance: Node should not miss wake-up calls (‘miss detection’) enable Wake-up radio Guido Dolmans, IMEC-NL

  5. PHY 2.4 GHz ISM band with wake-up radios • Proposal: ISM band 2.4 – 2.485 GHz with possible 2.36 – 2.4GHz MBAN extension. Wake-up control channel in the extended part  less false alarms in a clean band. Hardware of two radios can be shared. • Proposal PHY operation: duty-cycled main radio with reliable wake-up scheme for achieving key requirements of IEEE 802.15.6 WBAN • Single-radio MAC architecture: a single radio receiver is used for both data communication and traffic monitoring. The corresponding wake-up scheme could be synchronous (e.g. beacon-enable 802.15.4) or asynchronous (e.g. non beaconed 802.15.4). • Dual-radio wakeup architecture: adding a ULP wake-up receiver (WuRx) in addition to the main radio so that the main radio could stay in sleep mode if no data communication occurs. • Wakeup overrules MAC in case of strict latency requirements. When buffers are full, enable wake-up, otherwise follow scheduled MAC. • Wakeup overrules MAC in case of high energy efficiency requirements. Guido Dolmans, IMEC-NL

  6. Dual Radio: WuRx Enabled WBAN Communication (1) • Ultra-low power wake-up receivers (WuRx): • A bit-rate scalable (10 kbps – 1 Mbps) OOK wake-up receiver is used to monitor the channel and to identify the wake-up calls. • Fits with asymmetric links  strong wake-up trigger signals  low cost and low power wakeup receiver for body area network nodes. • Always on and power up the main (data) radio when needed, aiming at two QoS requirements: low access latency and low energy consumption. Guido Dolmans, IMEC-NL

  7. Dual Radio: WuRx Enabled WBAN Communication (2) Dual-radio (high performance main radio TRX + ULP WuRx) architecture fits perfectly with event-driven applications: • Minimize access latency; • Simplify protocol design; • Improve energy efficiency; Guido Dolmans, IMEC-NL

  8. Dual-radio architecture is superior in that: Power consumption of data communication scales with network traffic; Relaxed requirements for synchronization; Low access latency; Relaxed power budget for main radio; But : Trade-offs between ULP and performance – could be solved by proper Tx/Rx link-budget; WuRx sets a lower-bound of power consumption in idle state– could be mitigated by applying duty-cyling to the WuRx; Co-optimization of MAC/PHY layer is critical in fully exploiting the flexibility offered by dual-radio architecture Dual Radio: WuRx Enabled WBAN Communication (3) 8 Guido Dolmans, IMEC-NL

  9. Outline • WBAN proposal • Dual-radio (ISM Main and ISM Wake-up) WBAN Overview • ISM band Transceiver • Wake-up Receiver • Conclusions Guido Dolmans, IMEC-NL

  10. WBAN Transceiver band overview • Proposal: WBAN average radio energy consumption limited to 1 nJ/bit. For 200 kbps, this is equivalent to 200 µW. • This can be achieved (easily) with simple radio structures, e.g. a super-regenerative radio. • OOK transmitter, e.g. 5 MHz channels. • Proposal to use world-wide available ISM band 2.4 – 2.485 GHz with MBAN extension (2.36 – 2.4 GHz). Architecture of a super-regenerative receiver Guido Dolmans, IMEC-NL

  11. For noncoherent detection: BER = 10-3 SNR = 11dB BER = 10-6  SNR = 14dB WBAN Receiver Baseband Guido Dolmans, IMEC-NL

  12. Digital Baseband: Matched Filter (1) • It is well-know that the optimum receiver for an AWGN channel is the matched filter receiver. • Square root raised cosine (RRC) filter is used as the matched filter (in pair with the pulse shaping filter at the transmitter). Digital RRC filter design: • Oversampling rate • Filter order • Roll-off factor • Resolution of filter coefficient Guido Dolmans, IMEC-NL

  13. 2.5 dB 2.5 dB gain is achieved with the matched filter in case of AWGN channel. Digital Baseband: Matched Filter (2) Guido Dolmans, IMEC-NL

  14. SNR and Receiver Sensitivity (1) • For BER=10-3, incoherent OOK modulation, Eb/No= 11 dB magnitude • R/B : ½ for typical modulations. 1 for DSSS • SNR= 8db+ 2db (additional losses)=10 db = = system BW, twice the data rate for typical modulation schemes Guido Dolmans, IMEC-NL

  15. SNR and Receiver Sensitivity (2) • Receiver sensitivity without the addition of Noise Figure (NF): 10 Mbps 10 Kbps • The minimum detectable signal: • MDS= Noisefloor +SNR +NF +Fade Margin+ L Transmit power, PT: -10 dBm, 0 dBm, 10 dBm. GTXand GRX are the transmit and receiver antenna gain: 0-3 dBI Fade margin 15 dB Propagation loss, Lfs Additional Losses-matched filter loss, board/digital losses: L=7 dB Guido Dolmans, IMEC-NL

  16. SNR and Receiver Sensitivity (3) • For 10 MHz data rate • For 1m distance: For -10dbm transmit power: • MDS=PT -Fade Margin - LFS+ GTX + GRX -L=-10-15-40-7=-72 dB. • NF target =MDS-Noisefloor –SNR= =-72+90.9= 18.9 dB • Sensitivity target = -86 dBm Guido Dolmans, IMEC-NL

  17. Outline • WBAN proposal • Dual-radio (ISM Main and ISM Wake-up) WBAN Overview • ISM band Transceiver • Wake-up Receiver • Conclusions Guido Dolmans, IMEC-NL

  18. Dual Radio: benefits for low latencies and high energy efficiency Energy efficiency maximization w.r.t. to the latency requirements for different network settings (Pmiss=Pfalse=0.1) If the requirements of false alarm and miss detection become stricter curves will become flatter  the scheme with separate wake-up receiver is applicable to more scenarios. Guido Dolmans, IMEC-NL

  19. Wake-Up Transceiver Duty-Cycled Wake-Up (based on IEEE 802.15.4 frame structure) Full Wake-Up Guido Dolmans, IMEC-NL

  20. Data Transfer Model: From BNC to BN BNC BN • Initialized by BNC • BNC is on or self triggered to the main radio mode • BN is in the wake up or the main radio mode • First, BNC sends Request-To-Send (RTS) or wake up signal to BN through the Beacon • Second, BN sends ACK • Third, BNC sends data to BN • Fourth, BN sends ACK back if applicable Beacon ACK Data ACK if applicable Guido Dolmans, IMEC-NL

  21. Data Transfer Model: From BN to BNC BNC BN • Initialized by BN • BN is on or self triggered to the main radio mode • BNC is in the wake up or the main radio mode • First, BN senses SFB over the maximum superframe duration. If SFB is not sensed, a wake up signal from BN is sent. • Second, after SFB is sensed, BN sends RTS. • Third, BNC sends ACK. • Fourth, BNC sends data to BN • Fifth, BN sends ACK back if applicable Wake Up Signal if applicable Beacon Data Send Request ACK Data ACK if applicable Guido Dolmans, IMEC-NL

  22. Digital Wakeup Receiver Baseband • Matched filter is used to improve the BER performance in case of OOK modulation and AWGN channel (see previous slides). • Manchester code is a line code with self-synchronization performance. • Correlator is used to measure the likelihood between the received address code and the local address code. • Power consumption estimateof the digital wakeup baseband is 6 µW. Analog RF and baseband estimate is 50 µW. Guido Dolmans, IMEC-NL

  23. Wakeup Packet The wakeup packet consists of a preamble part and an address code part. After specifying the main radio design, another part used for channel configuration can be added at the end of the packet. • The first part of the preamble is used to implement amplitude estimation and timing synchronization. • The second part of the preamble is used to do packet synchronization. • Address code is Manchester encoded to improve robustness. Guido Dolmans, IMEC-NL

  24. Simulation Results Different address codes are used in the simulation for comparison. Case 1: PN code is used as address code Case 2: Walsh-Hadamard sequence is used as address code Walsh-Hadamard sequence is featured by good cross-correlation performance. Guido Dolmans, IMEC-NL

  25. More options than wake-up receivers Motivation Sensor node: extremely tight power budget Master device: slightly more relaxed power budget Shifting as much complexity as possible to the master device Possible Solutions Temporal Diversity (oversampling) Networking Diversity (multiple routes) Spatial Diversity (multiple antennas) Guido Dolmans, IMEC-NL

  26. Conclusions • Asymmetric link budget: use wake-up radios and receive diversity • 2.4 – 2.485 GHz ISM band with MBAN extension from 2.36 GHz – 2.4 GHz • Cycled main radio: 5 MHz channels, superregenerative architecture TRX for 1 nJ/bit (200 µW for 200 kbps), NF = 20 dB, Sensitivity = -85 dBm. • Always-on wakeup radio: Low latency and low energy QoS. Power consumption below 60 µW. Sensitivity = -75 dBm (strong beacons) or -85 dBm (weak beacons). Guido Dolmans, IMEC-NL

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