Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S5/00—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations
  • G01S5/02—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations using radio waves
  • G01S5/0205—Details
  • G01S5/0218—Multipath in signal reception
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S5/00—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations
  • G01S5/02—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations using radio waves
  • G01S5/14—Determining absolute distances from a plurality of spaced points of known location
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W64/00—Locating users or terminals or network equipment for network management purposes, e.g. mobility management

Definitions

• the present invention relates to wireless localization and communications technology. More specifically, the present invention is applicable to improving localization accuracy and communications performance in wireless communication systems.
• ultra- wideband (UWB) technology promises accurate ranging and localization systems capable of resolving individual multipath components (MPCs).
• MPCs multipath components
• TOA time-of-arrival
• Various systems using UWB technology have been disclosed, including those disclosed in the articles: (a) "Analysis of undetected direct path in time of arrival based UWB indoor geolocation," by B. Alavi and K. Pahlavan, published in Proc. IEEE Vehic. Technol. Con/. (VTC), vol. 4, Dallas, TX, Sep. 2005, pp.
• NLOS non-line-of-sight
• a received code division multiple access (CDMA) signal is LOS if: 1) the power ratio of the global maximum path to the local maximum path is greater than a given threshold, and T) the arrival time difference between the first path and the maximum path is less than a given time interval.
• CDMA code division multiple access
• the article "ML time-of-arrival estimation based on low complexity UWB energy detection,” by Rabbachin, I. Oppermann, and B. Denis, published in Proc. IEEE Int. Conf Ultrawideband (ICUWB), Waltham, MA, Sept. 2006. discloses that the NLOS identification for UWB systems may be performed by comparing the normalized strongest path with a fixed threshold. In either scheme, judicious parameter selection (e.g., the threshold or the time interval) is essential.
• information derived from the overall mobile network may be used to mitigate NLOS conditions.
• the article "A non-line-of-sight error mitigation algorithm in location estimation,” by P. C. Chen, published in Proc. IEEE Int. Conf. Wireless Commun. Networking (WCNC), vol. 1, New La, LA, Sept. 1999, pp. 316-320 discloses a residual- based algorithm for NLOS mitigation. That algorithm is based on three or more available base stations, using location estimates and residuals for different combinations of base stations.
• NLOS mitigation techniques using information derived from the mobile network are disclosed in (a) "Robust estimator for non-line-of-sight error mitigation in indoor localization,” by R. Casas, A. Marco, J. J. Guerrero, and J. Falco, published in Eurasip J. Applied Sig. Processing, pp. 1-8, 2006; (b) "Time-of-arrival based localization under NLOS conditions," by Y. T. Chan, W. Y. Tsui, H. C. So, and P. C. Ching, published in IEEE Trans. Vehic. Technol, vol. 55, no. 1, pp. 17-24, Jan. 2006; (c) "A database method to mitigate the NLOS error in mobile phone positioning," by B. Li, A.
• EP 1 ,469,685 discloses a method that uses the multipath components of the received signal in a CDMA system. This technique takes advantage only of the delay information in the strongest path, and the ratio between the global and local maximum paths. The technique relies on appropriately selecting thresholds for these parameters.
• the present invention provides a NLOS identification technique based on amplitude and delay statistics of an UWB channel.
• amplitude and delay statistics for a received signal are captured using the kurtosis of the received signal, the mean excess delay spread and the root mean square (RMS) delay spread of the received multipath components of the received signal.
• RMS root mean square
• Probability density functions of each of these metrics are justified by application to the IEEE 802.15.4a UWB channels and are found to be appropriately modeled by log-normal random variables.
• Ajoint likelihood ratio test selects between the LOS and NLOS hypotheses of the received signal. Given the PDFs of LOS and NLOS conditions (e.g., from previous measurements), the methods of the present invention do not require a large number of measurements.
• the amplitude and delay statistics are assumed to be independent to simplify the likelihood function calculation used in hypothesis testing.
• Figure l(a) illustrates triangulation using on a time-of-arrival (TOA) technique in a wireless network under a NLOS condition, based on measurements at base stations 10, 20 and 30.
• TOA time-of-arrival
• Figure l(b) illustrates processing of received signals at base stations 10, 20 and 30 of Figure l(a).
• Figure 2 illustrates identifying LOS or NLOS conditions using kurtosis 210, mean excess delay 220, and the RMS delay spread 230 from the received signal, in accordance with one embodiment of the present invention.
• (CIR) h(t) of a received signal may be represented by:
• d denotes the actual distance between a fixed terminal (FT) 1 and a mobile terminal
• c denotes the speed of light
• the present invention provides a method that uses statistics of the received multipath components to distinguish between LOS and NLOS conditions.
• statistical data that capture the amplitude and the delay of the received signal (namely, the
• a fixed terminal is a terminal which is non-moving relative to a mobile terminal.
• Examples of a fixed terminal include base stations in a cellular or wireless network and anchor nodes in a sensor network. kurtosis, the mean excess delay, and the RMS delay spread) are used to distinguish between LOS and NLOS conditions.
• the kurtosis is the ratio between the fourth order moment of a random variable to the square of its second order moment (i.e., the variance).
• the kurtosis is defined as "a measure of whether the data are peaked or flat relative to a normal distribution; i.e., data sets with high kurtosis tend to have a distinct peak near the mean, decline rather rapidly, and have heavy tails, while data sets with low kurtosis tend to have a flat top near the mean rather than a sharp peak".
• the kurtosis characterizes how peaked a data is, the kurtosis also characterizes how strong the LOS condition at a multipath CIR.
• the received signal is more likely to be from a LOS source for a CIR with a high kurtosis value.
• ⁇ h ⁇ and ⁇ h ⁇ are the mean and the standard deviation of the absolute value of the CIR, respectively.
• the distribution of K/ can be obtained for both LOS and NLOS conditions using sample channel realizations.
• the IEEE 802.15.4a channels provide histograms of K for eight different channel models (i.e., CMl to CM8), corresponding to indoor residential LOS and NLOS conditions, indoor office LOS and NLOS conditions, outdoor LOS and NLOS conditions, and industrial LOS and NLOS conditions, respectively.
• the histograms may each be modeled by a log-normal PDF given by:
• the histograms of the mean excess delay and RMS delay spread for the eight different channel models from IEEE 802.15.4a justify the assumed log-normal distribution of delay in the received signal, based on the KS test at the 5% significance level.
• likelihood ratio tests can be set up to distinguish between the LOS and NLOS hypotheses. For example, let Pto* i X ) and Pnlo ⁇ W represent the PDFs corresponding to LOS and NLOS conditions, respectively, and let K, T ⁇ m, and ⁇ rms represent the kurtosis, mean excess delay, and RMS delay spread for an observed channel realization h(t), respectively, the following three likelihood ratio tests can each be used to identify LOS/NLOS conditions:
• FIG. l(a) illustrates triangulation using on a TOA technique in a wireless network under a NLOS condition, based on measurements at FTs 10, 20 and 30.
• each FT measures the TOA of the signal received from mobile terminal 5.
• the measurements are then forwarded to a centralized processing station 35.
• mobile terminal 5 may directly estimate its location using the received signals from all the FTs.
• Figure l(b) illustrates processing of received signals at FTs 10, 20 and 30 of Figure l(a).
• the FT receiver first identifies strongest path 9, from which time the receiver searches backwards for first arriving path 7.
• first arriving path 7 represents an actual distance between the transmitter and the receiver.
• NLOS condition i.e., an obstruction exists between the transmitter and the receiver
• first arriving paths 7 arrives at a later time than LOS first arriving paths 11.
• a positive bias is included in the TOA estimate under a NLOS condition, even if the first arriving path is correctly identified.
• threshold 8 is used to qualify the first arriving path, first arriving path 12 is actually be later in time than actual NLOS first arriving path 7.
• the TOA of the received signal is estimated at each FT using arbitrary thresholds.
• the residual depends only on both measurement noise and search-back errors. Search-back errors result from inaccurate identification of the first arriving path.
• the leading edge is easily identified and an accurate estimate of the TOA can be made for each FT. Therefore, under a LOS condition, the estimated mobile terminal location is close to the actual mobile terminal location, and the residual is typically small, assuming sufficient averaging reduces noise variance.
• the residual is considerably large due to the NLOS bias introduced.
• the NLOS bias result from: 1) the delay between the LOS TOA and NLOS TOA, and 2) the delay between the estimated NLOS TOA and actual NLOS TOA.
• the first type of bias may be handled in the triangulation step, rather than the search-back step.
• the LOS or NLOS information of the channel may be obtained from the multipath received signals (e.g., in the form of a likelihood weight) and be used in the triangulation step and as a termination condition for the search- back for LOS FTs.
• Figure 2 illustrates identifying LOS or NLOS conditions using kurtosis 210, mean excess delay 220, or the RMS delay spread 230 from the received signal, in accordance with one embodiment of the present invention.
• kurtosis 210, mean excess delay 220, or the RMS delay spread 230 are calculated from the received signal in the manner described above.
• the likelihood ratio (LR) 250 for each parameter is calculated.
• LR likelihood ratio
• Joint LR 260 is then compared at step 240 to determine whether the signal is LOS or NLOS 240.
• other statistics of the received signal may also be used (e.g., energy of the strongest path, or energy of the signal earlier in time than the strongest path).
• prior art solutions for NLOS identification from the received signal typically require recording of the TOA (or distance) measurements over time.
• the methods according to the present invention do not require a time-history of the measurements, and identification can be performed even using a single channel realization (so long as LOS/NLOS likelihood PDFs are available), as the variations in the TOA is not taken into account.
• the NLOS information in the received MPCs is used.
• the present invention is applicable in numerous ways for improving localization accuracy. NLOS FTs identified by the techniques of the present invention can be eliminated from consideration to avoid the biases of the NLOS FTs to be incorporated into the location estimate. In situations where the number of available FTs is limited in the network, so that measurements cannot simply be discarded, the likelihood functions of LOS FTs can be used as weights in the LS localization algorithm, to minimize the effects of NLOS measurements.
• the LOS/NLOS information identified under the present invention is also applicable for improving symbol detection performance.
• the LOS/NLOS information may be used for selecting the number of Rake fingers to use (e.g., in matched-filter receivers).
• the integration interval e.g., in transmitted reference or in energy detector receivers

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• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• General Physics & Mathematics (AREA)
• Radar, Positioning & Navigation (AREA)
• Remote Sensing (AREA)
• Position Fixing By Use Of Radio Waves (AREA)
• Mobile Radio Communication Systems (AREA)
• Radio Relay Systems (AREA)

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• 2007
  • 2007-08-02 JP JP2009523057A patent/JP4567093B2/ja not_active Expired - Fee Related
  • 2007-08-02 WO PCT/US2007/075084 patent/WO2008017033A2/en active Application Filing
  • 2007-08-02 EP EP07813712A patent/EP2047694A2/en not_active Withdrawn
  • 2007-08-02 KR KR1020087026803A patent/KR101051906B1/ko not_active IP Right Cessation

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