GPS World, March 2011

EXPERT ADVICE FIGURE 7 LPPe reversed mode for capability and location information exchange cation Information message as shown in Figure 4 Extensions OMA LPPe introduces several enhancements for various positioning methods as well as completely new methods Additions in the A GNSS domain include local atmosphere models In 3GPP LPP the models are limited to ionosphere ones and therein to the broadcast types as in GPS Galileo and QZSS broadcasts The OMA LPPe introduces a localized Klobuchar model which allows for presenting the delay corrections in the well known Klobuchar model but for a limitedvalidity area and time for more accurate delay compensation In addition ionosphere storm warnings can be carried to the UE at the chosen resolution This information allows UE to deduce the reason for high measurement residuals Troposphere models have not previously been in the scope of the standardized assistance protocols The troposphere model in LPPe carries the hydrostatic and wet zenith delays their change rates in the height dimension for approximating the zenith delays at the UE altitude Niel mapping functions for hydrostatic and wet components and composite spatial gradients Alternatively the surface meteorological parameters pressure temperature can be carried to the UE and the calculation of the troposphere delay is left for the UE Another troposphere model is the altitude pressure relationship for the UEs with a barometer This altitude assistance increases availability by introducing an independent source of altitude information Whereas the 3GPP LPP carries the ephemerides almanacs signals supported by the satellites and the GLONASS frequency mappings OMA LPPe introduces satellite mechanical informational differential code biases and new navigation models The mechanical information consists of mass effective reflectivity area and phase center offsets for the in UE orbit prediction purposes In the navigation model domain the additions include SP3 type orbit representation and the orbit clock model degradation models for improved error modeling Practically all the new assistance data types support precise point positioning approaches for future GNSS services Lastly one of the major LPPe A GNSS features is the continuous carrier phase CCP assistance for realtime kinematic applications The CCP data format supports straightforward mapping from RTCM 104031 to ensure interoperability The LPPe CCP mechanism utilizes the LPPe level periodic assistance data procedure and supports multiple reference stations as well as mobility that is changes in the set of active reference stations on thefly To enable the use of LPP LPPe in all the networks the legacy hyperbolic methods E OTD and OTDOA IPDL for GSM and UTRA networks respectively are supported and the data content are copy pastes from RRLP and RRC to ensure interoperability Support for UE based LTE OTDOA is also included A major part of LPPe specification is devoted to the various ECID methods These cover GSM UTRA LTE and WLAN networks both in UE assisted and UE based modes In LPPe terminology the shortrange nodes SRNs refer to Bluetooth Bluetooth Low Energy and near field communication NFC tags which are considered separately from the primary communications networks cellular networks and WLAN Similarly to the ECID methods the SRNs can be used for positioning in either UE assisted or UE based modes In the UE based mode in which the SRN locations need to be carried to the UE the philosophy is that the SRNs are logically arranged into groups one group of SRNs can be the set of SRNs in one building or in one floor in the building The assistance data is considered in the units of these groups in conjunction with the group data version that allows for handling situations in which the arrangement of the SRNs in the building changes and the data in the UE needs to be refreshed Finally no single positioning and assistance protocol can address all needs Thus both LPPe assistance data exchange and LPPe location information exchange include black box containers for vendors and operators to carry their own proprietary assistance data and location information in a standardized framework The benefit of this approach is that the same standardized protocol framework used in commercial deployments can be used for rapid prototyping and providing differentiating positioning performance without the need for defining proprietary protocols from scratch Conclusion The framework introduced by 3GPP LPP and extended in LPPe brings longsought convergence in the control and user plane positioning protocols This ensures that in the user plane domain the dominant domain for positioning services in consumer LBS vendors can utilize exactly the same protocol as in the control plane This reduces implementation testing and deployments costs and will make the LPP LPPe the de facto standardized positioning protocol in the mobile domain LAURI WIROLA has a Ph D in electrophysics from Tampere University of Technology in Finland He manages indoor positioning activities at Nokia Services Location www gpsworld com March 2011 GPS World 13