Mobile Positioning in Wireless Mobile Networks

Transcription

1 Mobile Positioning in Wireless Mobile Networks Peter Brída Department of Telecommunications and Multimedia Faculty of Electrical Engineering University of Žilina SLOVAKIA

2 Outline Why Mobile Positioning? Mobile Positioning Conclusion Discussion 2

3 Why Mobile Positioning? Dependency on network platform Network properties Devices mobility Capabilities of individual devices Hardware limitations (e.g. battery, antennas) Improvement of the wireless networks performance Radio resource management algorithms Location-aware network protocols (the number of control packets can be reduced) Effective communication Services Emergency Calls 112 LBS (Location Based Services) Intelligent Transport Systems 3

4 Terms Location - the position of an object in physical space with respect to a specific frame of reference that varies across applications. (x,y,z,t) Mobile station Reference station (node) Blindfolded station (node) Positioning (Localization) Process 4

5 Abstraction of Position Absolute position is given in respect to an inertial system and a reference point in this inertial system Relative position can only be given in respect to other points resolving the distances and the geometric configuration (e.g. the topology) 5

6 Mobile Positioning Process 6

7 Principle of Mobile Positioning 7

8 Positioning Classification 1/4 Where measurements and calculation is done Mobile Based Positioning - Self Positioning Mobile Assisted Positioning Network Based Positioning - Remote Positioning Mobile Assisted Positioning Hybrid Positioning Modification (device, network) 8

9 Positioning Classification 2/4 Measurement principle Multilateral Unilateral Bilateral Multilateral several reference devices make simultaneous (or almost simultaneous) measurements, network based positioning requires co-ordination of simultaneous measurements at multiple sites Unilateral mobile device measures signals, which are transmitted by several reference devices, mobile based or mobile assisted implementation Bilateral multiple measurements are not needed: either mobile device measures signal from a single reference device or reference device measures signal from mobile device optimal for rural coverage since only one reference device is involved 9

10 Positioning Classification 3/4 Range Based Positioning indirect measurements of distance or angle between reference devices and blindfolded device Range Free Positioning by exploiting the radio connectivity information among neighboring mobile devices, or by exploiting the sensing capabilities of the mobile devices. reference device based methods (connection, proximity) reference device free methods (fingerprinting) 10

11 Environment INDOOR OUTDOOR Platform satellite cellular ad hoc sensor Positioning Classification 4/4 Principles, methods are same for all platforms Implementation of methods 11

12 Localization Methods Cell identification Received signal strength Time based methods Angle of arrival Fingerprinting Proximity DV-Hop DV-Distance 12

13 Cell Identification Advantages: It doesn t require any modifications in network infrastructure and mobile station Disadvantage: tb.c 3, TA = = = 553,5 m 2 2 tb K1 b duration c K speed of light [s, m.s ] 1 Low accuracy 13

14 Received Signal Strength Method Advantages: It doesn t require important investments in network infrastructure It doesn t require any changes in mobile terminal Higher accuracy than Cell ID (the most often used method) Disadvantage: f P(dB ) = 10α log 10 β log(4πd ) c Lower accuracy than more modern methods, though much more expensive than RSS 14

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16 Time Based Methods t i = r i c = 2 2 ( x x) + ( y y) c i i 16

17 Time Based Methods Advantage: Higher accuracy than other methods Disadvantages: It requires modifications of network infrastructure and also in mobile terminal Precise synchronization is necessary ( t t ) c = r r = R = ( x x) 2 + ( y y) 2 ( x x) 2 + ( y y ) 2 i j i j ij i i j j 17

18 Angle of Arrival Method Advantage: It is able to locate a MS by means of two BTSs Disadvantages: The accuracy diminishes with increasing distance between the MS and BTSs It requires antenna array 18

19 Phase off-line Fingerprinting Method predicting (simulation) measuring on-line Advantage: It is immune against multipath propagation Disadvantages: Big demanding effort during radio signal strength prediction (measuring) 19

20 Proximity Based Methods Common proximity Centroid proximity Weighted proximity Advantage: Small demand on positioning system low-cost solution Disadvantages: Poor accuracy 20

21 DV-Hop Method The most basic method for ad hoc networks Three phases all nodes in the network determine distances to the reference nodes (in hops) the hop counts are converted into distances (multiplying the hop count by an average hop distance) Distance and the number of hops between reference nodes are known Average hop distance is flooded into the network blindfolded node determines own position (distances to three or more reference nodes, in meters, which can be used to perform the trilateration) Advantage: small demand on node low-cost solution works well in dense and regular topologies the accuracy is not influenced by radio channel properties Disadvantages: poor accuracy works bad in sparse or irregular networks - no all hops are same length 21

22 DV-Distance Method The improvement of DV-Hop method A distance between nodes is directly expressed in meters It is obtained by the cumulative traveling distance (in meters) Each receiving node adds the measured range to the path length and forwards the message range may be measured either by means of received signal strength or by time of arrival The final result is that each node will have stored the position and minimum path length to reference nodes. Blindfolded node determines own position (trilateration) Advantage: small demand on node low-cost solution Disadvantages: higher accuracy compare to DV-Hop the accuracy is influenced by radio channel properties 22

23 Localization Accuracy Metrics RMSE (Root Mean Square Error) RMSE = ( x x ) + ( y y ) 2 r est 2 r est CEP (Circular Error Probability) For a 2D system, the CEP is defined as the radius of a circle which contains the given number of the random vector realizations with the mean as its center. 23

24 Source of Positioning Error Radio channel character Multipath propagation Non line of sight propagation Selection of reference nodes used for position estimation Mutual position of reference nodes Distance to blindfolded nodes Calculation algorithm Statistical Geometrical 24

25 Niečo popísať o zlých polohách uzlov pri trilaterácií... 25

26 Positioning Systems GNSS (Global Navigation Satellite System) GPS (Global Positioning System) AGNSS (Assisted Global Navigation Satellite System) 26

27 Assisted Global Navigation Satellite System AGNSS probably the best solution to meet the accuracy requirements compensates for the major faults GNSS and cellular positioning Time To First Fix TTFF mobile based mode mobile assisted mode 27

28 Global Positioning System GPS 1/2 global satellite radio positioning and navigation system Global it is possible to use it for 24 hours per day Satellite the satellites are used as transmitters, rotation around Earth Radio radio signal is used for positioning Positioning it is possible to determine own position in space Navigation system serves for orientation in space WGS84 Distance measuring based system SPS a PPS 28

29 Global Positioning System GPS 2/2 GPS architecture Space segment Control segment User segment 29

30 Nominal: 21 satellites + 3 active standby 31 satellites at the present 6 orbital planes - MEO Altitude km Inclination to equator 55º Period of one rotation around the Earth 11h58min Two frequencies L1 = MHz L2 = MHz L5 = MHz (GPS II) Space Segment 30

31 Master control station Monitoring stations Control Segment 31

32 CDMA system two frequencies L1 = MHz L2 = MHz BPSK Two modulation codes C/A (Coarse/Acquisition) 1.023Mb/s sensitivity L1» -160dBW P (Precise) - Y code 10.23Mb/s sensitivity L1» -163dBW a L2» -166dBW GPS Signals 32

33 The ephemeris data - the satellite's own precise orbit The ephemeris is updated every 2 hours and is generally valid for 4 hours The almanac consists of coarse orbit and status information for each satellite in the constellation, an ionospheric model, and information to relate GPS derived time to Coordinated Universal Time (UTC) Navigation Message 33

34 Position Calculation 34

35 Error Sources 35

36 Differential GPS 36

37 European Geostationary Navigation Overlay Service EGNOS 37

38 GNSS Vision independent systems 120 satellites GNSS High accuracy and reliability SDR receiver 38

39 Conclusion 39

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