advancing wireless link signatures for location distinction
DESCRIPTION
Advancing Wireless Link Signatures for Location Distinction. Mobicom 2008 Junxing Zhang, Mohammad H. Firooz Neal Patwari , Sneha K. Kasera University of Utah Salt Lake City, USA. Outline. Introduction Multipath-Based Link Signatures Multiple Tone Probing Temporal CIR Signature - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: Advancing Wireless Link Signatures for Location Distinction](https://reader035.vdocuments.us/reader035/viewer/2022062501/56816410550346895dd5bbb7/html5/thumbnails/1.jpg)
Advancing Wireless Link Signatures for Location Distinction
Mobicom 2008Junxing Zhang, Mohammad H. Firooz Neal
Patwari, Sneha K. KaseraUniversity of Utah Salt Lake City, USA
![Page 2: Advancing Wireless Link Signatures for Location Distinction](https://reader035.vdocuments.us/reader035/viewer/2022062501/56816410550346895dd5bbb7/html5/thumbnails/2.jpg)
Outline• Introduction• Multipath-Based Link Signatures
– Multiple Tone Probing – Temporal CIR Signature
• Innovative Methods– Refined Metric for multiple Tone Signatures– Complex Temporal Signature
• Framework for Location Distinction• Quantitative Comparisons of Link Signatures• Temporal Behavior of Link Signatures• Conclusion
![Page 3: Advancing Wireless Link Signatures for Location Distinction](https://reader035.vdocuments.us/reader035/viewer/2022062501/56816410550346895dd5bbb7/html5/thumbnails/3.jpg)
Introduction• Location Distinction v.s. Localization
• Proposed wireless link signatures– RSS– Channel Gains of Multi-tonal Probes– Temporal Channel Impulse Response
• The RSS-based method has a consistently lower detection rate and a higher false alarm rate.
Location Distinction Localization
Can thrive in multipath channel Suffer from inaccuracies by multipath
More sensitive to motion (less than 1 meter)
May not be able to determine within a meter of accuracy
Less coverage Larger coverage
![Page 4: Advancing Wireless Link Signatures for Location Distinction](https://reader035.vdocuments.us/reader035/viewer/2022062501/56816410550346895dd5bbb7/html5/thumbnails/4.jpg)
Multipath-Based Link Signatures• Two existing multipath-base link signatures and metrics
– Multiple tone Probing– Temporal CIR Signature
• Comparison and discussion
![Page 5: Advancing Wireless Link Signatures for Location Distinction](https://reader035.vdocuments.us/reader035/viewer/2022062501/56816410550346895dd5bbb7/html5/thumbnails/5.jpg)
Multipath Channel Response• Multipath caused by
– Reflections, diffractions and scattering of the radio waves.– Time-delayed, attenuated and phase-shifted
• Impulse response of multi-path fading channel– Time-variant:
– Time-invariant: (for a packet duration)• Received signal
–
–
Path numberPhase shift
Magnitude gain
Channel frequency response
Channel impulse response (CIR)
![Page 6: Advancing Wireless Link Signatures for Location Distinction](https://reader035.vdocuments.us/reader035/viewer/2022062501/56816410550346895dd5bbb7/html5/thumbnails/6.jpg)
Multipath Channel Response• Recover CIR from received signal
Ps : the power of the sent signal inside the band
![Page 7: Advancing Wireless Link Signatures for Location Distinction](https://reader035.vdocuments.us/reader035/viewer/2022062501/56816410550346895dd5bbb7/html5/thumbnails/7.jpg)
Multiple Tone Probing• Frequency domain• Measures frequency response of multiple carriers
– K carrier waves are simultaneously transmitted to the receiver
• The nth recorded multiple tone signature of the link between transmitter i and receiver j is:–
fK: the carrier frequency of the Kth carrier wave
{H(fK)} used as the multiple tone signature
![Page 8: Advancing Wireless Link Signatures for Location Distinction](https://reader035.vdocuments.us/reader035/viewer/2022062501/56816410550346895dd5bbb7/html5/thumbnails/8.jpg)
Multiple Tone Probing• Metric
– The Nth multiple tone signature h(N) is compared with each previously measured signature in the history Hi,j using average correlation statistic.
• Measurement of similarity – Low -> different, high -> similare
Correlation of the nth and the Nth measurements
Average squared magnitude of the elements of
![Page 9: Advancing Wireless Link Signatures for Location Distinction](https://reader035.vdocuments.us/reader035/viewer/2022062501/56816410550346895dd5bbb7/html5/thumbnails/9.jpg)
Temporal CIR Signature• Time domain• Estimation of the impulse responses a function of time delay and
magnitude
• Metric– Minimum normalized Euclidean distance
– Difference: Low -> similar
The nth sampled link signature measurement of the link between transmitter I and receiver j Tr the sampling interval at
the receiver and S+1 is the number of the samples
![Page 10: Advancing Wireless Link Signatures for Location Distinction](https://reader035.vdocuments.us/reader035/viewer/2022062501/56816410550346895dd5bbb7/html5/thumbnails/10.jpg)
Comparison and Discussion• Qualitative comparison
– Temporal signature can be more robust against small changes in multipath.
– The inclusion of phase information in multiple tone signature effectively increases the richness of the measurement space.
– The temporal link signature has the advantage of operation in the time domain which de-correlates multipath at different delays
– The multiple tone link signature has the advantage of using a complex-valued signature which preserves phase information
![Page 11: Advancing Wireless Link Signatures for Location Distinction](https://reader035.vdocuments.us/reader035/viewer/2022062501/56816410550346895dd5bbb7/html5/thumbnails/11.jpg)
Complex Temporal Signature• Proposed method
– Combines the best features of both the temporal link signature method and the multiple tone probing method.
– enhanced signature:
– The complex link signature retains phase information in a manner similar to the multiple tone link signature.
Comparing to temporal link signature, the magnitude of each gain is not taken
![Page 12: Advancing Wireless Link Signatures for Location Distinction](https://reader035.vdocuments.us/reader035/viewer/2022062501/56816410550346895dd5bbb7/html5/thumbnails/12.jpg)
Issue: Phase Changes• Random Phase Shift:
– Some phase changes in the link signature have nothing to do with any changes in the link
– Clock or carrier frequency shifts
– h ->
Time offset between clocks
Different carrier frequency in receiver and transmitter
![Page 13: Advancing Wireless Link Signatures for Location Distinction](https://reader035.vdocuments.us/reader035/viewer/2022062501/56816410550346895dd5bbb7/html5/thumbnails/13.jpg)
Issue: Phase Changes• Given 2 complex temporal link signatures h and g
– Represent the shift-removed difference with a new Φ2 difference– The Φ2 difference, which minimizes the random phase shift between
two measurements before calculating distance, can be efficiently and explicitly calculated using simple vector operations.
![Page 14: Advancing Wireless Link Signatures for Location Distinction](https://reader035.vdocuments.us/reader035/viewer/2022062501/56816410550346895dd5bbb7/html5/thumbnails/14.jpg)
Quantitative Comparisons of Link Signature
• Comparison:– Multiple tone probing– Temporal channel impulse response– Complex temporal link signatures
• Obtained from CRAWDAD• 5 measurement: 4 for history, 1 for test• ROC plot: receiver operating characteristic
– How the probability of detection varies with the probability of false alarm.
![Page 15: Advancing Wireless Link Signatures for Location Distinction](https://reader035.vdocuments.us/reader035/viewer/2022062501/56816410550346895dd5bbb7/html5/thumbnails/15.jpg)
Normalized Metric
• Normalized Metric– Normalizing each multiple tone signature to its magnitude before the
calculation of the correlation statistic
– Each channel frequency response is normalized to the square root of its average power.
– Avoiding missed detections, when higher h(N) occurs.
=
![Page 16: Advancing Wireless Link Signatures for Location Distinction](https://reader035.vdocuments.us/reader035/viewer/2022062501/56816410550346895dd5bbb7/html5/thumbnails/16.jpg)
Normalized Metric• ROC curves of comparing performance of original and the
normalized metrics in the multiple tone probing method
![Page 17: Advancing Wireless Link Signatures for Location Distinction](https://reader035.vdocuments.us/reader035/viewer/2022062501/56816410550346895dd5bbb7/html5/thumbnails/17.jpg)
Framework for location distinction
N-1 link signatures Metric
Location changed
Threshold
Include it in Discard the oldest
Performance EvaluationPFA : the probability of false alarmPD : the probability of detection
γ
![Page 18: Advancing Wireless Link Signatures for Location Distinction](https://reader035.vdocuments.us/reader035/viewer/2022062501/56816410550346895dd5bbb7/html5/thumbnails/18.jpg)
Comparison (1)• Multiple Tone v.s. Temporal Link Signatures
K increases -> improvementCoherence bandwidth-> not separate enough-> correlation
![Page 19: Advancing Wireless Link Signatures for Location Distinction](https://reader035.vdocuments.us/reader035/viewer/2022062501/56816410550346895dd5bbb7/html5/thumbnails/19.jpg)
Comparison (2)• Three methods
![Page 20: Advancing Wireless Link Signatures for Location Distinction](https://reader035.vdocuments.us/reader035/viewer/2022062501/56816410550346895dd5bbb7/html5/thumbnails/20.jpg)
Multiple Receiver Performance
Multiple tone
Complex temporal
![Page 21: Advancing Wireless Link Signatures for Location Distinction](https://reader035.vdocuments.us/reader035/viewer/2022062501/56816410550346895dd5bbb7/html5/thumbnails/21.jpg)
Temporal Behavior of Link Signatures
• Temporal changes in link behavior can significantly increase the probability of false alarms.
• LOCATION A,B,C,D• Record response vectors comprising 600 complex temporal
responses.• Each impulse response is a vector of 100 complex numbers
![Page 22: Advancing Wireless Link Signatures for Location Distinction](https://reader035.vdocuments.us/reader035/viewer/2022062501/56816410550346895dd5bbb7/html5/thumbnails/22.jpg)
Observation• Isomap 2D embedding coordinates
– Non-linear dimensionality reduction to reduce the 100 dimension vectors to just 1-2 dimension
![Page 23: Advancing Wireless Link Signatures for Location Distinction](https://reader035.vdocuments.us/reader035/viewer/2022062501/56816410550346895dd5bbb7/html5/thumbnails/23.jpg)
Markov Model• Use 1-D embedding of the Isomap algorithm
– Like an amplitude modulation signal -> use AM demodulator to capture the envelope of the pattern
![Page 24: Advancing Wireless Link Signatures for Location Distinction](https://reader035.vdocuments.us/reader035/viewer/2022062501/56816410550346895dd5bbb7/html5/thumbnails/24.jpg)
False alarm case• Different-State False Alarm (DSFA)
– A link signature is measured in state I, but no signature previously measured in state I exists in the history. False alarm is raised.
• Policies of buffer replacement– Policy 1: The history has a FIFO replacement policy.– Policy 2: The history is subdivided into K separate FIFO buffers. One for
each state in the Markov chain
![Page 25: Advancing Wireless Link Signatures for Location Distinction](https://reader035.vdocuments.us/reader035/viewer/2022062501/56816410550346895dd5bbb7/html5/thumbnails/25.jpg)
Two-state Markov Chain Model• Policy 1: evaluate the probability of DFSA
– (1) given we are entering state 1, the probability that we stayed in state 2 N time units ago
– (2) given we are entering state2, the probability that we stayed in state 1 N time units ago
![Page 26: Advancing Wireless Link Signatures for Location Distinction](https://reader035.vdocuments.us/reader035/viewer/2022062501/56816410550346895dd5bbb7/html5/thumbnails/26.jpg)
Results• The rate of convergence is very slow• By using Policy 2, we see virtually no DSFA errors.
![Page 27: Advancing Wireless Link Signatures for Location Distinction](https://reader035.vdocuments.us/reader035/viewer/2022062501/56816410550346895dd5bbb7/html5/thumbnails/27.jpg)
Conclusion• Compare two existing multipath-based location distinction
methods• Improve the multiple tone probing method• Develop a new link signature outperforms the existing two• A measurement campaign to understand and model the
temporal behavior of link signatures to reduce the probaility of false alarms