IEEE 802.15-09-0613-00-004f Submission Sept 2009 Wolfram Kluge, AtmelSlide 1 Project: IEEE P802.15...
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Transcript of IEEE 802.15-09-0613-00-004f Submission Sept 2009 Wolfram Kluge, AtmelSlide 1 Project: IEEE P802.15...
Sept 2009
Wolfram Kluge, AtmelSlide 1
IEEE 802.15-09-0613-00-004f
Submission
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: [Ranging with IEEE 802.15.4 Narrow-Band PHY]Date Submitted: [14 September, 2009]
Source: [Wolfram Kluge, Dietmar Eggert]Company: [Atmel]Address: [Koenigsbruecker Strasse 61, 01099 Dresden, Germany]E-Mail: [E-Mail: [email protected], [email protected]]
Re: [Response to Call for Final Proposals]Abstract: [Proposal of using IEEE 802.15.4 Narrow-Band PHY for Ranging and Localization]
Purpose: [To present the method of performing ranging in a narrow-band transceiver using phase measurements]
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.
Sept 2009
Wolfram Kluge, AtmelSlide 2
IEEE 802.15-09-0613-00-004f
Submission
IEEE 802.15.4 PHY usage for Active RFID and Ranging
• Widely adopted for wireless sensor networks, home control and industrial automation and similar applications
• Proven technology• Although narrow-band, it is suitable for ranging even under multipath
environments• Less additional hardware needed in existing transceiver design
Sept 2009
Wolfram Kluge, AtmelSlide 3
IEEE 802.15-09-0613-00-004f
Submission
IEEE 802.15.4 PHY extensions needed
• Transmitting carrier for short times (blocking modulation)• Phase measurement unit• State machine to coordinate transmit and receive mode with appropriate timing
can be implemented in hardware or software
Sept 2009
Wolfram Kluge, AtmelSlide 4
IEEE 802.15-09-0613-00-004f
Submission
Advantage of Phase-Based Ranging
• Fits to narrow-band transceiver design – only carrier transmitted
• Any unknown delay in the transceiver (clock skew, filter group delay,…) has no impact on ranging accuracy
• No impact of channel filter group delay
– Example: 2MHz, tg=325ns+/- 5% +/- 16ns systematic error contribution by receiver
– Corresponds to 4.8m systematic range error in ToA systems!
– No impact on phase measurements, since all phases are measured at exactly the same IF frequency
• 10 to 20 times faster than Time-of-Arrival with IEEE 802.15.4 compliant frames
• Needed to perform ranging measurements at multiple frequencies to mitigate multipath effect
• Fast scanning of multiple frequency channels allows tracking of moving objects
• Fast scanning saves power and improves batter life time
Sept 2009
Wolfram Kluge, AtmelSlide 5
IEEE 802.15-09-0613-00-004f
Submission
Choice of TX signal for phase measurements
Phase measurements can be done with 1. Cross-correlation of IEEE 802.15.4 frames
• Utilizing preamble spreading sequence• Complex cross correlation in baseband domain yields phase of received
signal• One frame per frequency at least about 300µs
2. CW carrier • less than 1us needed for phase measurement• Practically 10-20 µs to allow PLL to settle completely Much faster, therefore preferred
Sept 2009
Wolfram Kluge, AtmelSlide 6
IEEE 802.15-09-0613-00-004f
Submission
Active Reflector Principle (1)
RXTX
RXTX
Device B(Reflector)
Device A(Initiator)
• Device A initiates ranging measurement• Device A transmits carrier device B performs phase measurement• changing transmit direction in both devices• Device B transmits carrier device A performs phase measurement• Device B transmits frame with measurement results to Device A• Device A is able to calculate range• Bidirectional traffic needed for devices with asynchronous time base
Sept 2009
Wolfram Kluge, AtmelSlide 7
IEEE 802.15-09-0613-00-004f
Submission
Active Reflector Principle (2)
• PLL is running at same frequency at TX and RX mode• Receiver measures phase between LO signal and received carrier• Phase measurement can be done at any down-converted signal since frequency
conversion maintains phase information• Propose phase measurement at IF frequency in low-IF receiver
Time
Transmit Receive
PLL
Antenna
j
Device A
Sept 2009
Wolfram Kluge, AtmelSlide 8
IEEE 802.15-09-0613-00-004f
Submission
Ranging with Active Reflector
• TX signal phase of device B (reflector) must be the same as of the received signal. hard to implement
Proposal:• Device B measures phase of receives signal relative to own LO signal phase.• Phase difference is transferred to device A used as correction factor.
Sept 2009
Wolfram Kluge, AtmelSlide 9
IEEE 802.15-09-0613-00-004f
Submission
Ranging Procedure (1)
• xxx Time [µs]
TX
TX
RX
TX
RX
Ranging Request
Ranging Ack
N Phase Measurements( N = 80MHz / Df )
Phase Meas.
Results
DistanceCalculation
total time ~ 8ms
B
Device
A
150 µsTstart B
Tstart A
SFD
TX End
PLL settling to Df step
Network Channel
TX Frequency Dev. A [MHz]
2404
2480
Sept 2009
Wolfram Kluge, AtmelSlide 10
IEEE 802.15-09-0613-00-004f
Submission
Ranging Procedure (2)
Device A Transmitting Ranging Request Frame Receiving Ranging Ack Locking AGC Starting timer after RX end Setting PLL to 1st meas. freq. Starting phase meas. sequence Setting PLL to orig. freq. Acking Result Frame Releasing AGC Lock Restoring IF position Distance calculation
Device B Locking AGC after Request
Frame receive Transmitting Ranging Ack Starting Timer after TX end Correcting Frequency offset with
PLL Setting PLL to 1st meas. freq. Starting phase meas. sequence Setting PLL to orig. freq. Transmitting results frame Receiving Ack Releasing AGC Lock
Sept 2009
Wolfram Kluge, AtmelSlide 11
IEEE 802.15-09-0613-00-004f
Submission
Implementation Example of Phase Measurement
• Example: Low-IF receiver• Phase difference measured between IF signal and divided clock signal• Capturing time difference between signal edges (zero crossing of sine signals)• Phase difference independent of time (for zero frequency offset between
devices)
ReceiverTransmitter
Phase Meas.Unit
/8
XtalOsc.
PLL
2
16
22400
15.4 Radio
j
IF Signal
Xtal Reference
Dt
j=2pDt/T
Sept 2009
Wolfram Kluge, AtmelSlide 12
IEEE 802.15-09-0613-00-004f
Submission
Multipath Propagation• Most significant error in ranging measurements• Narrow-band measurement (2MHz bandwidth) very prone to multipath channel
(Corresponds to sampling of channel group delay curve at arbitrary frequency)
Solution: • gathering information over as a wide frequency band as possible• About 80MHz in 2.4GHz ISM band
Flexibility:• Depending on severity of multipath propagation (ratio of LOS signal power to signal power in
delay paths) the number of frequencies used can be chosen
Issue with statistical channel models (like JTC-B)• LOS component amplitude is Rayleigh distributed producing to some percentage a LOS signal
below any detection level.• In this case the channel does not contain the information to get the correct ranging results.
Sept 2009
Wolfram Kluge, AtmelSlide 13
IEEE 802.15-09-0613-00-004f
Submission
Distance Calculation by Averaging for line-of-Sight channel
MHzc
D8021 D
=j
Simple method to cope with multipath effects Adding all Dj to reconstruct phase over 80MHz bandwidth Distance calculation:
Is identical to average group delay
ftg D
D=
j21
fNtc
D g
D= 21
Issue: Df must be small enough to avoidcycle slip for largest distance
Sept 2009
Wolfram Kluge, AtmelSlide 14
IEEE 802.15-09-0613-00-004f
Submission
Distance Calculation by IFFT
• Measuring phase difference and RSSI value for each frequency• Accumulating phase differences to reconstruct phase j(f)• Generating complex baseband signal x(f) = RSSI(f)*exp(jj(f))• IFFT shows channel impulse response.• Selecting 1st tap to identify LOS component• Restriction: 1.875m resolution due to 80MHz bandwidth of ISM band
(double distance measured)
• Higher computational effort than averaging, but more robust under harsh multipath environments (office or industrial environment)
Sept 2009
Wolfram Kluge, AtmelSlide 15
IEEE 802.15-09-0613-00-004f
Submission
Summary
• Ranging with phase measurements fits to narrowband transceiver hardware utilized in IEEE 802.15.4 devices
• Less hardware extensions needed to perform phase measurements
• Distance resolution not prone to transceiver group delay – no transceiver calibration needed
• Ranging at multiple channel frequencies allows mitigation of multipath effects