Positioning Techniques. João F. Galera Monico - UNESP Tuesday 12 Sep

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2 Positioning Techniques João F. Galera Monico - UNESP Tuesday 12 Sep

3 Positioning methods Absolute Positioning Static and kinematic SPP and PPP Relative Positioning Static Static rapid Semi kinematic Kinematic RTK and NRTK

4 Single Point Positioning (SPP) Code based - pseudorange Knowing the satellite coordinates, it is possible to compute the coordinates of the user antenna in the same frame From a geometrical point of view, only three satellites would be enough However, the receiver clock is not synchronized with the satellites system clock An extra satellite is required

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6 Considering the code pseudorange measurements (SF) TGD Correction (GPS Galileo - QZSS) SF C/A users has to apply additional P1-C1 This estimable receiver clock is a combination of the true receiver clock error plus the (frequency-dependent) receiver hardware delay

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8 (SPP) The linearized system will be given by: s=1,2, n>4

9 n-u = s-4

10 Comments on SPP Satellite positioning from broadcast ephemeris Accuracy in the level of 10 to 15 m Often referred as navigation solution solution for most of mobile It can also be computed with dual frequency data

11 Precise Point Positioning (PPP) Undifferenced, precise point positioning (PPP) techniques aim to provide absolute positions in a precision global reference frame. It uses pseudoranges and carrier phase observations in combination with precise (IGS) products. Precise orbits and clocks Single-frequency and multifrequency PPP One or more constellation.

12 Precise Point Positioning The precise (IGS) products (precise satellite clocks) are based on the ionosphere-free combination, similar to the broadcast satellite clock for most constellations. For single-frequency PPP, corrections for the satellite DCBs are required. but these are also provided by the IGS or its analysis centers. (Tgd) For Single-frequency PPP users ionospheric corrections are essential and these can be obtained from the IGS as well, in the GIM format. Can also be estimated

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14 Precise Point Positioning GLONASS PPP (and also RTK) requires a-priori correction of the receiver- and frequencydependent interchannel or interfrequency biases, at least for the phase data (L. Wanninger: Carrier-phase inter-frequency biases of GLONASS receivers, J. Geod. 86(2), (2012) ). Importante para solução das ambiguidades All other cited errors have to be appropriated treated.

15 PPP Concept (a) CORS (global or regional) network determines GNSS parameters; (b) satellite-dependent parameters are uploaded by the network and downloaded by a user; (c) the user applies the corrections to his data, enabling singlereceiver precise positioning Dennis Odijk

16 Single Frequency (SF) PPP It is assumed that identical offsets for the satellite clock and hardware bias apply to both code and phase observations, as well as a- priori corrections for tropospheric and ionospheric delays. And as the satellite clock offsets are based on the Ion-Free combination (as is the case with precise IGS products), the correction terms for code and phase then can be given as:

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20 SF PPP The ambiguities is not integer has bias Rank defect The Ionosphere was taken from a model (GIM for instance) We can also estimate the Ionosphere and include constraints if available. Accuracy in the level of dm after about 30 minutes of data collection.

21 Dual Frequency (DF) PPP

22 DF PPP With these modifications, the steps to get the ION-FREE solution is equal to the SF PPP Including the ionosphere as unknown, without combine the observations, is another option (the state of the art of PPP). At such case, the ionosphere will be estimated, and can be constrained if information is available.

23 International GNSS Service (IGS) RT IGS Real Time was developed to provide Real Time PPP Several products available. Corrections to the broadcast ephemeris and clocks

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27 PPP with Ambiguity Resolution (AR) Several models were developed Consist in the determination of fractional part of the satellite phase biases using a network of receivers It has to be provided to the user Such fractional part (bias) is for some extend constant (at least for few hours/days).

28 Ambiguity Fractional Part (FCB)

29 Ion-free versus uncombined PPP Iono-free combination, could make the inclusion of triple frequency observations to be cumbersome, since many possible dualcombinations exist. In order to provide a suitable representation for triple frequency receivers uncombined phase biases model compatible with the RTCM SSR framework may be better RTCM (Real-Time Maritime Services) SSR (State Space Representation)

30 The PPP-Wizard software package uses uncombined phase biases model ( PPP-RTK integer PPP improved by atmospheric corrections from local/regional RTK networks

31 PPP-AR

32 SSR Computation In RTK or NRTK systems, the main errors affecting the GNSS measurements are monitored by a GNSS reference station or a CORS dense network, and provided to the users as range corrections OSR (Observation-Space-Representation) OSR is not able to dissociate the different errors impacting GNSS measurements

33 SSR Computation State-Space-Modeling (SSM) is the representation of all relevant physical effects by a mathematical model The parameters that are estimated in real-time using CORS network Knowing the temporal and spatial behavior of these effects, it is possible to optimize the use of all observations coming from the CORS network

34 SSR Computation The state vector of such State-Space- Representation (SSR) is provided by the integrated and optimized SSM. This representation is applicable to PPP-RTK

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37 Real Time PPP activity Install the BNC (BKG Ntrip Client) Get access to data and one kind of IGS corrections Choose a station available in real time and perform real time PPP. "IGS-IP" <igs-ip@bkg.bund.de> Provide Analysis and comment of the results

38 Real Time Kinematic (RTK) Concept: a base station provide corrections (observations) to a rover receiver in real time. It is mainly carrier based (DD observables) The aim is to reduce and remove errors common to a base station and rover pair All data processing is carried out at the rover. Ambiguity fixed Accuracy of up to 1 cm + 1 ppm.

39 Real Time Kinematic (RTK) It is a relative positioning method (2017) Springer Handbook of Global Navigation Satellite Systems Editors: Teunissen, Peter J.G., Montenbruck, Oliver (Eds.)

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41 Drawback of RTK Deteriorate with distance from base station troposphere (2017) Springer Handbook of Global Navigation Satellite Systems Editors: Teunissen, Peter J.G., Montenbruck, Oliver (Eds.)

42 From RTK to Network RTK (NRTK) It is based on the use of several widely spaced permanent stations. Depending on the implementation, positioning data from the permanent stations is regularly communicated to a central processing station. On demand from RTK user terminals, which transmit their approximate location to the central station, the central station calculates and transmits correction information or corrected position to the RTK user terminal.

43 The benefit of this approach is an overall reduction in the number of RTK base stations required. Depending on the implementation, data may be transmitted over cellular radio links or other wireless medium.

44 The distance dependent errors can be accurately modeled using the measurements of an array of GNSS reference stations surrounding the rover site. Therefore, the solution to the distance limitation of RTK lies in multibase techniques which became popular under the name network RTK, sometime abbreviated to NRTK.

45 Network RTK technique enabled the establishment of positioning services which serve larger regions or whole countries. One possibility is to create a VRS (Virtual Reference Station) close to the user The user than perform the relative positioning.

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47 φ c λ c h c φ c λ c h c φ c λ c h c Stations Bidirectional Link RTCM-VRS VRS NMEA Relative positioning φ c λ c h c φ c λ c h c φ c λ c h c

48 RTK experiment - Usina Guarani Mendonça; Monico; Motoki (2012)

49 São Paulo State NRTK.

50 Statistical results from an experiment of station Tupã (SP-Brazil). Estação de Coleta TUPÃ Base/RTK Tempo de Pontos Início Fim inicialização coletados VRS 1min 24 seg 13:07:01 as 13:18: ARAC (GNSS) 84,13km 8 min 4 seg 13:24:52 as 13:43: VRS 2 min 23 seg 13:47:55 as 14:08: ARAC_S (GPS) 84,13 km 12 min 19 seg 14:18:35 as 14:44:30 205

51 Comments on NTRK It works quite well for very stable ionosphere We can say the same for PPP and PPP-RTK In the equatorial region during some period we have problems due to the behavior of the ionosphere, mainly due to the Ionosphere Scintillation after the sunset.

52 Comments on NTRK Several research can be carried out on these topics.