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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: Ubisense UWB PHY Proposal to 802.15TG4f Date Submitted: 11 th September 2009 Source: Andy Ward, Ubisense Address: St Andrew’s House, St Andrew’s Road, Chesterton, Cambridge, CB4 1DL, ENGLAND

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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: Ubisense UWB PHY Proposal to 802.15TG4f Date Submitted: 11th September 2009 Source: Andy Ward, Ubisense Address: St Andrew’s House, St Andrew’s Road, Chesterton, Cambridge, CB4 1DL, ENGLAND Voice: +44 1223 535170, FAX: +44 1223 535167, E-Mail: andy.ward@ubisense.net Re: TG4f Call for Preliminary Proposals and Final Proposals, IEEE P802.15-09-0419-01-004f Abstract: UWB PHY-layer proposal for 802.15.4f Purpose: To be considered by 802.15TG4f 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. Andy Ward, Ubisense

  2. UWB PHY-layer proposal for 802.15.4f Andy Ward Ubisense Andy Ward, Ubisense

  3. Overview • Discuss PHYs for supporting RTLS • Relates to CFA responses: • IEEE802.15-09-0198-00-004f • IEEE802.15-09-0174-00-004f • IEEE802.15-09-0403-00-004f Andy Ward, Ubisense

  4. Target system characteristics • Industrial user base • Mobile tags • Likely to be transmitter, for complexity/power reasons • Very likely to be most numerous system component • Very cost-sensitive • Off-the-shelf design desirable for manufacturers • Fixed, managed infrastructure • Likely to be receiver, no complexity/power concerns • Connected to standard wired/wireless data network • No requirement for ad-hoc / peer-peer support • Likely to be few in number • Less cost-sensitive • Differentiator from other RFID systems is accurate location • Data transfer is at most a secondary concern Andy Ward, Ubisense

  5. Primary PHY target characteristics • Location-centric • Global regulatory compliance • Coexistence with existing spectrum use • High performance • Low cost / complexity • Baseline PHY with optional extensions • Flexible Andy Ward, Ubisense

  6. UWB PHY Background Andy Ward, Ubisense

  7. Background on UWB PHY • Provides highest location accuracy • Required by highlighted CFA responses • One-way asymmetric beacon architecture desirable • Lowest-complexity tag • Proven potential for high performance • Proprietary systems already deployed worldwide Andy Ward, Ubisense

  8. Global UWB bands Power • At first sight, plenty of overlaps between UWB bands… Japan Korea China EU US Wideband (FCC Part 15.250) US UWB (FCC Parts 15.517 / 15.519) Canada f / GHz 4.8 10.6 Andy Ward, Ubisense

  9. Typical EU UWB tag spectrum Typical US wideband tag spectrum ‘Compromise’ tag spectrum => Narrow bandwidth, low total power! FCC Part 15.250 Practical problems with combining bands • …but high attenuation often required at band edges • Want wide-bandwidth signal for best location accuracy & total power • Hard to achieve with low-complexity transmitter & low-cost filtering Power / dBm -41.3 -51.3 -65 EU 2007/131/EC -70 f / GHz 4.8 10.6 Andy Ward, Ubisense

  10. Other restrictions on UWB systems • UWB use often comes with onerous restrictions, e.g. • EU: No fixed outdoor transmitters (2007/131/EC) • Canada: 10s Rx ack needed for outdoor systems (RSS-220) • Singapore: 10s Rx ack needed (iDA TS-UWB) • Japan: No mobile beacon-only UWB (ARIB STD T-91) • Not always possible for tag to be beacon-only • Not always possible to do bidirectional UWB Andy Ward, Ubisense

  11. Global compliance for UWB RFID systems • Multiple distinct bands to cover all territories/applications • Band 0: 5.925-7.25GHz (US wideband) • Band 1: 6-8.5GHz (EU, China, US UWB, Canada) • Band 2: 7.25-10.2GHz (Korea, Japan, US UWB, Canada) • Auxilliary non-UWB 2.4GHz PHY desirable for: • Band selection for multi-band devices • Regulatory compliance assistance for UWB PHY • Use of auxilliary PHY not mandatory • E.g. US-only wideband class device • Auxilliary PHY is described elsewhere Andy Ward, Ubisense

  12. Location Enabler signal (1) • In occluded environments, LOS propagation is rare • This isn’t necessarily a problem for communications, but it is for location • The more information we can get out of a LOS / near-LOS path, the better Andy Ward, Ubisense

  13. Location Enabler signal (2) • Measuring basic time-of-arrival of signal is easy • Measuring angle-of-arrival takes a bit longer • Measuring better time-of-arrival takes longer too • Therefore, add an optional extra signal period for improved location measurements • Better location accuracy and robustness; but… • Higher power consumption and lower throughput; but… • Manufacturers/users can decide on the trade-off Andy Ward, Ubisense

  14. UWB PHY Details Andy Ward, Ubisense

  15. Modulation, pulse repetition rate, symbol mapping • OOK modulation of data • Simple to implement in transmitter • Can be decoded by either coherent or non-coherent receiver • 1.625Mpps pulse repetition rate • Will (just) be average power limited • Power-of-two division from standard 26MHz GSM crystal • Cheapest source of really good timing for angle-of-arrival / coherent receiver support • Many 2.4GHz auxilliary PHY chipsets use same 26MHz frequency for same reason • Obviously can use a lower multiple of 1.625MHz / cheaper crystal if none of this is relevant • OOK symbol to pulse mapping is 1:3 • An OOK ‘1’ is “pulse-pulse-pulse”, an OOK ‘0’ is “no pulse-no pulse-no pulse” • Non-coherent receiver wins by voting on received triplets (triple modular redundancy) • Coherent receiver wins by integrating bits for 4.8dB SNR improvement • Power overhead isn’t as high as it first looks for small packets • Time taken to turn crystal on and get going is not insignificant Andy Ward, Ubisense

  16. Band 0 PSD (US wideband) • All figures e.i.r.p.radiated • Operates under FCC Part 15.250 Andy Ward, Ubisense

  17. Band 1 PSD (EU, China, US UWB, Canada) • All figures e.i.r.p.radiated • Operates under • FCC Part 15.517/15.519 (US) • Decision 2007/131/EC (EU) • RSS-220 (Canada) • Singapore (iDA TS-UWB) • New Zealand (General User Radio Licence for Ultra Wide Band Communication Devices 2008) • China (MII draft proposal) Andy Ward, Ubisense

  18. Band 2 PSD (Korea, Japan, US UWB, Canada) • All figures e.i.r.p.radiated • Operates under • FCC Part 15.517/15.519 (US) • RSS-220 (Canada) • Korea (RRL announcement 2007-22) • Japan (STD-T91, assuming relaxation of minimum data rate regulation) Andy Ward, Ubisense

  19. SHR/PHR definition • Suggested preamble /SFD sequence • Four octets of 11111111 (preamble / coherent RX acquisition) • One octet of 00010101 (coherent RX alignment) • One octet of 01001101 (true start of frame delimiter) • These are symbols – remember that there are three pulses / pulse periods per symbol Andy Ward, Ubisense

  20. Required MAC changes • Add “Blink” frame type for transmit-only tags using UWB PHY • See GuardRFID preliminary proposal • IEEE 802.15-09-0591-00-004e • See Decawave proposal • IEEE 802.15-09-0596-00-004e • “Blink” transmissions should not perform CCA • Transmit-only tags • Already in 802.15.4a? Andy Ward, Ubisense

  21. 2 Octets 1 8 2 Frame Control Sequence Number Source Address CRC Simple blink PPDU • Minimal zero-payload PDSU • Total of 21 octets, 168 symbols • Total packet time (3 pulses/symbol, 1.625Mpps) = 310.2us Andy Ward, Ubisense

  22. 2 Octets 1 8 2 2 Frame Control Sequence Number Source Address Payload CRC Blink PPDU with Location Enabler • Just enough payload to tell receiver that Location Enabler information is appended to packet • ‘Postamble’ is used for more detailed signal measurements • Should go after the packet because it is not data, and isn’tcovered by the frame check sequence • Total of 23 octets (184 symbols) + LEI packet • Total of 1064 pulse periods • Total packet time = (1064 pulses / 1.625Mpps) = 654.7us Location Enabler Information (512 pulses) Andy Ward, Ubisense

  23. Using both UWB & 2.4GHz PHYs together • Regulatory compliance • Many UWB regimes require some sort of two-way link • UWB band change • Globally-compliant tags will have to switch bands (US wideband, US/EU/China UWB, Korea/Japan UWB) • Security • Many security protocols involve two-way transfer • Rate change • Variable tag update rates • Mode change • Enable/disable extensions to UWB packet to aid location Andy Ward, Ubisense

  24. 2.4GHz link supporting UWB PHY (1) • Regulatory support for UWB PHY 1: UWB – Part 15.517 2: Data request “Can you hear me?” 3: Data response “Yes – keep going”, or “No – cease transmission” Andy Ward, Ubisense

  25. 2.4GHz link supporting UWB PHY (2) • PHY handover in global tag • Probably needs bidirectional 2.4GHz • Can’t just transmit UWB since correct band is unknown! 3: UWB – Part 15.517 3: UWB – ARIB STD T91 1: Beacon request 1: Beacon request JAPAN UWB US UWB 2: 2.4GHz beacon frame 2: 2.4GHz beacon frame Andy Ward, Ubisense

  26. Coexistence • Coexistence with general radio systems is assured by limitation of TX power by UWB regulations • Only IEEE 802.15 system in same band(s) will be 802.15.4a-compliant Andy Ward, Ubisense

  27. Example link budget • Assume: • PTx (transmitter power): 13dBm • GTx (transmitter gain): 0dBi • GRx (receiver gain): 8dBi • BWRx (receiver bandwidth): 750MHz • M (required receiver margin): 10dB • NF (receiver noise figure): 3dB • Calculate: • Noise power: -85.3dBm • Operating margin (=PTx+GTx+GRx-M-NF-NoisePower): 93.25dB • Therefore: • Operating range for ~7GHz system non-coherent system: 157m • Operating range for same system with coherent receiver (+4.8dB): 272m Andy Ward, Ubisense

  28. 2 Octets 1 8 2 Frame Control Sequence Number Source Address CRC Power consumption example • Minimal zero-payload PDSU • Total of 21 octets, 168 symbols • Total packet time (3 pulses/symbol, 1.625Mpps) = 310.2us • Average active power of UWB pulse generator: ~ 0.021mW • 13mW peak, duty cycle of 1ns ‘on’ in 615.3ns pulse repetition period • Average active power of controlling microprocessor + crystal: ~6.3mW • 3mA current drain at 2.1V • Startup time of crystal: ~400us • Therefore, total energy consumption per blink = ((0.021mW+6.3mW)*310.2us)+(6.3mW*400us) = 4.5uJ • For comparison, consider the same system but using one pulse per symbol. In this case, the total packet time is 103.4us, so the total energy consumption per blink = ((0.021mW+6.3mW)*103.4us)+(6.3mW*400us) = 3.2uJ. Therefore, the overhead of triple modular redundancy is only 41%, not 200% as might be expected. Andy Ward, Ubisense

  29. ‘Blink only’ tag throughput • Real-life throughput obviously depends on channel loading • Channel loading depends in turn on # tags, blink rate • Device is only transmitting for a small fraction of the packet time • Quite possible for two tags to transmit overlapping packets successfully • Assume 310.2us per blink • 64-bit ID, no payload • No acknowledgement of blink required • Assume 50ns delay spread • Maximum possible theoretical throughput is ~40000 tag blinks / sec. • For 1000 tags, using P-Aloha modified for low UWB duty cycle • 1s blink rate: 95% packet success rate • 2s blink rate: 98% message delivery probability • For 5000 tags, using P-Aloha modified for low UWB duty cycle • 1s blink rate: 78% packet success rate • 2s blink rate: 88% message delivery probability Andy Ward, Ubisense

  30. Summary • We propose: • (Here) A primary UWB PHY for best RTLS performance • (Elsewhere) A complimentary 2.4GHz PHY • Both PHYs are useful independently • They can be used together advantageously • We welcome collaboration with other proposers. Andy Ward, Ubisense

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