Location Based Services Part II: LBS Network Architectures

January 12, 2010

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In the previous blog LBS Part I we discussed about the different Location technologies and their comparisons on different parameters with their advantages/disadvantages. Today we will see how these positioning technologies integrate with the network architecture in different Wireless Standards (3GPP, 3GPP2, OMA, WiMAX, LTE)

We will first start with categorizing the location services by their usage as follows:

The above four categories can be practically implemented in the way the MS communicates through the network with the location server.

The Wireless operators seeing the significant value in LBS delivering a solid ROI, the operator’s engineering team must select one of the two possible deployment methods.

It can be implemented in either Control Plane or User plane mode. Each has its own advantages and disadvantages. This “control-plane” approach, while highly reliable, secure, and appropriate for emergency services, is costly and in many cases, overkill for commercial location-based services. In both 3GPP & 3GPP2 an IP based approach known as “user-plane” allows network operators to launch LBS without costly upgrades to their existing SS7 network and mobile switching elements

Let us consider an LBS implementation architecture as an example in both the modes.

1. Control Plane Architecture

The Control plane architecture consists of following core entities:

  • PDE/SMLC: Position Determination Entity/Serving Mobile Location Center -PDE facilitates determination of the geographical position for a target MS. Input to the PDE for requesting the position is a set of parameters such as PQoS (Position Quality of Service – Accuracy, Yield, Latency) requirements and information about the current radio environment of the Mobile Station (MS)
  • MPC/GMLC: Mobile Positioning Center/Gateway Mobile Location Center – MPC serves as the point of interface to the wireless network for the position determination network. MPC serves as the entity which retrieves, forwards, stores, and controls position information within the position network. MPC selects the PDE to use in position determination and forwards the position estimate to the requesting entity or stores it for subsequent retrieval.
  • LCS Client: LCS client is a logical entity that requests the LCS server to provide information on one or more target MS. LCS client being an logical entity can reside within a PLMN, or outside the PLMNs or even in the UE
  • Geoserver, LBS applications, SCP Service Control point and content

In this configuration, the MPC/GMLC effectively serves as the intermediary and gateway between the applications, running in the Web services space, while the PDE/SMLC runs in the signaling space. It serves as a holding agent for subscriber location information working with MSC<->VLR<->HLR and facilitates push and pull transactions. A “push” transaction might be an application that locates a subscriber and delivers a message, perhaps about a sale at a store nearby, while a “pull” transaction would consist of the subscriber invoking a service, such as Find my Nearest ATM machine. The service set-up and communication is performed via traditional signaling network. The MPC/GMLC also serves as a place to perform general administration functions, such as authentication/security, privacy, billing, provisioning, and so on.

Let us consider an example of position request flow between different entities. This shows an network initiated location request from the LCS in C-plane LBS Architecture.

These type of requests initiated from network side are mostly for network performance measurements, emergency services or for push services querying the MS location.

2. User Plane Architecture

The User Plane consists of following entities:

PS: Position Server – PS provides geographic position information of a target MS to requesting entities. PS serves as the point of interface to the LCS server functionality in the wireless packet data network. PS performs functions such as accepting and responding to the requests for location estimate of a target MS, authentication, service authorization, privacy control, billing, and allocation of PDE resources for positioning.

PDE: Position Determination Entity

3GPP2 U-Plane Architecture

The User plane architecture is similar to control plane but does not include the full functionality of the MPC/GMLC. Instead it allows the handset to invoke services directly with the trusted location applications, via TCP/IP, leaving out traditional SS7 messaging altogether. A scaled-down version of the MPC/GMLC handles authentication/security for the user-plane implementation approach. This method is focused on pull transactions, where the subscriber invokes a location-sensitive service. However, push transactions are possible and supported through the limited MPC/GMLC function. The User plane involves following entities

Let us consider an example of position request flow between different entities. This shows a handset initiated location request from the LCS residing in MS in U-plane LBS Architecture.

U plane LBS location processing request procedure

These requests are initiated from mobile station mostly for location based search requests like restaurants, navigation or for pull services querying the position server.

3. OMA (Open Mobile Alliance) U-Plane Architecture

Open Mobile Alliance (OMA), a mobile communications industry forum is created to bring open standards, platform independence, and global interoperability to the LBS market. More than 360 companies are represented in OMA, including MNOs and wireless vendors, mobile device manufacturers, content and service providers, and other suppliers.

The OMA User Plane consists of following entities and protocols.

  • MLP: Mobile Location Protocol: MLP is a protocol for querying the position of mobile station between location server and a location service client
  • RLP: Roaming Location Protocol: RLP is a protocol between location servers while UE is roaming
  • PCP: Privacy Checking Protocol: PCP is a protocol between location server and privacy checking entity

SUPL (Secure User Plane Location):

SUPL is developed by the Open Mobile Alliance. SUPL is a separate network layer that performs many LBS functions that would otherwise be governed within the C-Plane, and is designed to work with existing mobile Internet systems. With SUPL, MNOs can validate the potential of the LBS market with a relatively small budget and few risks.  SUPL utilizes existing standard to transfer assistance data and positioning data over a user plane bearer. SUPL is an alternative and complementary solution to existing 3GPP and 3GPP2 control plane architecture. SUPL supports all handset based and assisted positioning technologies. SUPL is data bearer independent.

SUPL architecture is composed of two basic elements: a SUPL Enabled Terminal (SET) and a SUPL Location Platform (SLP)

  • SUPL Enabled Terminal (SET): The SET is a mobile device, such as a phone or PDA, which has been configured to support SUPL transactions.
  • SUPL Location Platform (SLP): The SLP is a server or network equipment stack that handles tasks associated with user authentication, location requests, location-based application downloads, charging, and roaming.

SLP consists of following functional entities,

  • SUPL Location Center (SLC) coordinates the operation of SUPL in the network and manages SPCs.
  • SUPL Positioning Center (SPC) provides positioning assistance data to the SET and calculates the SET position.

The core strength of SUPL is the utilization, wherever possible, of existing protocols, IP connections, and data-bearing channels (GSM,GPRS,CDMA,EDGE or WCDMA). SUPL supports C-Plane protocols developed for the exchange of location data between a mobile device and a wireless network including RRLP (3GPP: Radio Resource LCS protocol) and TIA-8014(Telecommunications Industry Association 801-A, Position Determination Service for cdma2000). SUPL also supports MLP (Mobile Location Protocol) and ULP (UserPlane Location Protocol). MLP is used in the exchange of LBS data between elements such as an SLP and a GMLC, or between two SLPs; ULP is used in the exchange of LBS data between an SLP and an SET.

Let us consider an example of position request flow between different entities. This shows a SET initiated location request in OMA-SUPL U-plane LBS Architecture.

SUPL vs. C-Plane

Two functional entities must be added to the C-Plane network in order to support location services: a Serving Mobile Location Center (SMLC), which controls the coordination and scheduling of the resources required to locate the mobile device; and a Gateway Mobile Location Center (GMLC), which controls the delivery of position data, user authorization, charging, and more. Although simple enough in concept, the actual integration of SMLCs and GMLCs into the Control Plane requires multi-vendor, multi-platform upgrades, as well as modifications to the interfaces between the various network elements.

LBS through SUPL is much less cumbersome. The SLP takes on most of the tasks that would normally be assigned to the SMLC and GMLC, drastically reducing interaction with Control Plane elements. SUPL supports the same protocols for location data that were developed for the C-Plane, which means little or no modification of C-Plane interfaces is required. Because SUPL is implemented as a separate network layer, MNOs have the choice of installing and maintaining their own SLPs or outsourcing LBS to a Location Services Provider.

4. LBS Architecture in WiMAX

The WiMAX network architecture for LBS is based on the basic network reference model (NRM) specified by the WiMAX Forum. The model basically differentiates the network architecture into two separate business entities, (NAPs) Network Access Providers which provides radio access and infrastructure whereas (NSPs) Network Service Providers provides IP connectivity with subscription and service delivery functions.

The NAP is typically deployed as one or more access service networks (ASNs). The NSP is typically deployed as one or more Connectivity service network CSN(s). The NAP interfaces with the MS on one side and the CSN on the other.

Below shows the location request initiation from the application either located in device or network.

This is basically MS managed location service. The MS receives location requests from the applications and takes necessary measurements, and determines its location and provides it to the other requesting applications through upper layer messaging. The locations calculations at MS are aided by the periodic geolocation parameters broadcasted of the serving Base Station and the neighboring BS by the serving BS using layer 2 LBS-ADV message defined in IEEE 802.16-2009. The LBS-ADV message delivers the XYZ coordinates, the absolute and relative position of serving and neighboring BS allowing the MS to perform triangulation or trilateration techniques (either EOTDA or RSSI) and further aided by GPS to locate accurately. In this framework no major specific functional support for LBS is required in either the ASN or the CSN. Whereas in a network managed location service requires few functional entities to be added and enhancements to the network such as Location Requester, Location Server, Location Controller, and Location Agent.

Also, The WiMAX network architecture for LBS is designed to accommodate user plane, control plane, and mixed-plane location approaches. The big advantage of user plane location is that the LS can directly get to the MS, and signaling is minimized across the various reference points.  However, for this to the happen, the MS needs to have obtained an IP address and be fully registered with the LS, and application layer support is required in the MS.

In contrast, for the control plane location, the LS does not communicate directly with the MS, and hence there is no hard requirement for the MS to have obtained an IP address. In other words, the control plane location approach relies more on the L2 connectivity of the MS. However, the signaling costs are generally higher in control plane location as the signaling will have to traverse multiple reference points before measurements can be obtained.

The mixed plane method is nothing but the LS invoking both control plane measurements and user plane measurements at the same time. The LS can then perform a hybrid location solution by combining the measurements to get much better accuracy for the location fix. This approach is also fully supported in the WiMAX network. The trade-off here is that this method costs a whole lot more in terms of latency for the fix and the associated signaling, however this will translate to much better accuracy for the MS location indoors where an insufficient number of GPS satellites may be visible

5. LBS in LTE

LTE also generally supports the same types of positioning methods (Cell ID, A-GPS, mobile scan report-based, and hybrid) as in WiMAX. LTE offers user and control plane delivery of GPS assistance data; WiMAX chose to provide only user plane delivery. The rationale was that rapid IP session setup with the LS offered by WiMAX minimizes the need for a control plane solution. In WiMAX, authorization and authentication for LBS service is provided by the AAA, whereas in LTE the gateway mobile location center (GMLC) provides the equivalent functionality. The LTE Location Services specification  is  being developed under the current work plan and targeted for 3GPP Release 9.

This sums up the Location Based Services Architecture covering 3GPP, 3GPP2, WiMAX, LTE and OMA standards.

In the next Part we shall cover the Use Cases, Business Model with current and future trends for LBS.

- Neil Shah

References:

3GPP TS 23.271, “Functional Stage 2 Description of Location Services (LCS)”; http://www.3gpp.org/
Open Mobile Alliance, “Secure User Plane Location V 2.0 Enabler Release Package”; http://member.openmobilealliance.org/
Etemad, K., Venkatachalam, M., Ballantyne, W., Chen, B.,(2009)  “Location Services in WiMAX Networks”, IEEE Communications Magazine.
WiMAX Forum, “Protocols and Procedures for Location Based Services,” v. 1.0.0, May 2009.
OMA, O. M. (2007). Enabler Release Definition for Secure UserPlane for Location (SUPL) . OMA
Faggion, N., S.Leroy, & Bazin, C. (2007). Alcatel Location-based Services Solution. France.
3GPP2. (2000). Location-Based Services Systems LBSS: Stage 1 Description. 3GPP2 S.R0019 . 3GPP2.
3GPP. (2006). 3GPP TS 23.271 V7.4.0 Technical Specification Group Services and System Aspects Functional stage 2 description of Location Services (LCS) (Release 7).

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