Introduction

Although Service Providers initially offered only network access facilities (fixed/mobile - data, voice, etc.), they have added new, attractive services to their commercial offer, including services utilizing location-based awareness. Since the convergence of various mobile data technologies with the fixed network edge geographically extended Internet access availability to users, it has been increasingly interesting to offer users particular services related to their geolocation.

Location-based services (LBS) have been developed that benefit from the network resources, determining the user's closest facilities (Figure 1), places of interest, traffic directions, etc. It's even possible to use LBS for parental control of children, assistance for the physically or mentally handicapped, online gaming or social networking. The original intention to create an Internet cloud environment generally helped to provide virtualization of a user. In this “simulated” background, LBS brings back to the cloud the presence of the user in a particular real place (when this information is required or beneficial as a value-add).

FIGURE 1:

LBS in practice – places of interest related to the user's location (SOURCE: AT&T)

Applications of Location-Based Services

For the application of LBS, a correlation of the user's location (determined in several possible ways) with the map or another space presentation is needed. A map could be loaded over the packet data connection (usually 2.5G/3G mobile), or it might be preloaded within the device application. Some of the possible applications are shown in Figure 2. When the user's location is determined, LBS acts on that information and offers a particular service.

One of the most common applications could help in obtaining the necessary information on resources and places of interest according to the user's nearest location (restaurants, hotels, etc.). Another application might be tracking objects (such as mobile devices) or people (such as children). Another useful group of services could provide navigation or traffic support (traffic jam alerts, available parking spaces). Emergency calls could utilize the actual geolocation to route the call to the closest 911 emergency center. For communication facilities, another application might be location-aware routing of VoIP calls. Several new options are emerging, such as forwarding to voice mail or other numbers based on location. That option might prove useful in particular institutions such as hospitals, theaters, museums and other places with posted “No cellular use” signs. “Buddy finder” is a popular application, indicating to the user whether any friends from the user's contact list are in the vicinity. Gaming could be proposed with people in the area of the user's choice. Advertising messaging has a frame of potential activities. LBS and location-awareness of the user can be utilized to introduce an additional level of security when the user might attempt a service access; for example, an additional check might be instituted when opening a web page to access Internet banking, based on the user's geographical position.

FIGURE 2:

Possible LBS applications

Location-Based Services Technology Evolution

To determine the location of the user's equipment, you can use several possible technologies. Generally, localization is considered to be mostly applicable to the mobile user, but there is no reason to exclude users in relatively stationary positions from such services, when you can use the same access credentials on a different last-mile point – ADSL/cable. In this article, we will consider the methods used by Service Providers, and not those based on the 802.11 standard and Radio Frequency Identification (RFID). Instead, we will examine the methods based on the built-in Global Positioning System (GPS) capabilities or the Assisted Global Positioning System (A-GPS), the technology that uses cell tower information. The GPS is generally already incorporated into modern smartphones (see Table 1 for the comparison).

TABLE 1:

Differences in LBS technologies

Sometimes the option based on the cell tower satisfies the requirements, and the coverage area (identified by cell ID) is only a reference. Table 2 shows the three measurement techniques used for the location services. The third (optional) method is more complex than the first two, and involves either of the first two methods together with a GPS measurement (described in detail in the later section “Assisted Global Positioning System”).

TABLE 2:

Measurement techniques for LBS applied in Universal Mobile Telecommunications System (UMTS) Release ’99 (R99)

Location-Based Services Positioning Techniques

Positioning techniques are classified into two categories: those that are based on GPS technology, and supplementary techniques that are not only based on GPS, but combined with network resources. Figure 3 shows these positioning techniques in relationship to the use of GPS. The GPS-based techniques use Trilateration positioning, and the techniques that are not GPS-based use either Proximity or Triangulation positioning. One of these two techniques is then combined with the GPS-based positioning resource provided by the network, creating the network-assisted GPS-based technique.

FIGURE 3:

Positioning techniques

Proximity positioning type

In GSM/UMTS technology, the signal strength is the main criteria for the mobile user to be handled by a proper cell, so the closest tower identified with the cell ID usually provides the strongest radio signal. If we provide such localization, the possible location is extended to the whole mobile cell.

Triangulation positioning type

However, in the UMTS Release ’99 specification, there is an additional algorithm on the border of the three neighboring cells (triangle of Node-B antennas in Figure 4), called Observed Time Difference of Arrival (OTDOA). The Round-Trip Time (RTT) from at least three neighboring Node-Bs is calculated and compared. (Important: All Node-Bs must be synchronized.) During common idle periods, when the neighboring Node-Bs do not transmit, there is a random or periodic exchange of signals used for location estimation. The disadvantage of this method is the complexity and signalling overhead added to the network.

FIGURE 4:

Triangulation with OTDOA method of location estimation in GSM/UMTS

LTE 4G includes an improved localization method called Uplink Time Difference of Arrival (UTDOA).An advancement is achieved in an improved triangulation method. UTDOA does not imply any additional software upgrade of a mobile phone.

Trilateration positioning type

GPS currently uses 31 active satellites in orbit (Figure 5). In GPS-based positioning, trilateration is the process of comparing the distances derived from the measured times (within 100-billionths of a second) from at least three synchronized satellites. Each satellite contains multiple atomic clocks for the synchronization. Many mobile base stations use this GPS time resource to keep their networks synchronized. The distance between the GPS equipment and the satellites is calculated by multiplying the measured time by the signal velocity. Three satellites create three virtual spheres around themselves, which, in their crossing areas, determine a very accurate estimated location. GPS uses the frequency of 1575.42 MHz UHF for civilian purposes. GPS transmits a spectrum signal together with the following three pieces of information:

Pseudorandom code – Used to identify the transmitting satellite

Almanac data – Informs the GPS receiver where each GPS satellite should be at any time throughout the day

Ephemeris data – Used for actual positioning, since it contains important information about the satellite's status (a satellite is tagged as “healthy” or “unhealthy”), as well as the current date and time

The disadvantages of the trilateration method are a long Time to First Fix (TTFF) - from 30 seconds to 10 minutes – as well as problems with coverage and high power usage.

FIGURE 5:

GPS satellites around the earth (SOURCE: WWW.GPS.ORG)

Assisted Global Positioning System

This technique, which provides an alternative to GPS, is used as a less expensive but also less accurate method of positioning (when GPS capability is not built in or not a backup option, or no GPS signal is available) to determine a user position based on the Service Provider's infrastructure. (No user investment in a GPS-enabled smartphone is necessary.) To create such an alternative positioning resource to the GPS requires several commitments. It must handle 911 calls correctly even when no GPS signal is available (indoors, under dense trees, between high buildings), or when no GPS capability is implemented (older phones).

Figures 6 and 7 show the functional diagram and the message flow of the A-GPS implementation in the 3G network. Received Signal Code Power (RSCP) measurement is reported within the radio signaling, providing the necessary position information to the Serving Mobile Location Center (SMLC). Cell site identification is combined with the information from the referential receiver with a good satellite signal. SMLC forwards the processed position to the Serving Radio Network Controller (SRNC). SRNC and the external LCS client can exchange Location Request and Location Response messages, delivering the User's location.

In addition to the standard network elements – Node-B, Radio Network Controller (RNC), Home Location Register (HLR), Mobile Switching Center (MSC), Visitor Location Register (VLR), Serving GPRS Support Node (SGSN), Global System for Mobile Communications (GSM) System Control Function (gsmSCF), Public Land Mobile Network (PLMN) – are some new network elements:

Serving Radio Network Controller (SRNC) – Radio Network Controller enabled for the location services (LCS).

Serving Mobile Location Center (SMLC) – or Position Determination Entity (PDE) or LCS server - facilitates determination of the geographical position for the target mobile stations (MS).

External Location Services (LCS) Client – Logical entity that requests (when network-initiated) that the LCS server (SMLC) provide the information on one or more target mobile stations (GeoServer, LBS applications). It can reside within the PLMN, outside it, or within the MS.

Gateway Mobile Location Center (GMLC) – 3rd Generation Partnership Project (3GPP) compliant node, responsible for Location Method Selection (after receiving a network-initiated request from the external LCS client), and serving as an interface.

Position Calculation Function (PCF) – This capability could be implemented either within MS (MS-based), or in SMLC (MS-assisted). It is based on parameters such as Position Quality of Service (PQoS – accuracy, yield, latency) and the information in the current radio environment from the MS. It handles location requests (user-initiated or network-initiated, as ion Figure 7) sent through SRNC, and correlates data received from the MS – measurement (MS-assisted) or report (MS-based) – with the reference signal from the GPS receiver. SMLC can assist in providing the information to acquire satellites quickly.

FIGURE 6:

Functional diagram of network with A-GPS facilities (SOURCE: ETSI TS 123 002 V3.3.0 (2000-03))

3GPP – 3rd Generation Partnership Project is a standardization benefited from the collaboration between groups of telecommunications associations

UTRAN – Universal Terrestrial Radio Access Network

Iub – 3GPP standardized logical interface between Node-B and Radio Network Controller (RNC)

Iur – 3GPP standardized logical interface between RNCs in the same network

Iu – 3GPP standardized logical interface between RNCs and the Circuit Switched or Packet Switched Core Network

Lg – 3GPP standardized logical interface between the Circuit Switched or Packet Switched Core Network and the Gateway Mobile Location Center (GMLC)

Lh – 3GPP standardized logical interface between GMLC and Home Subscriber Server (HSS)

Le – 3GPP standardized logical interface between GMLC and Location Service Client (LCS)

Lc – 3GPP standardized logical interface between GMLC and GSM Specialized Resource Function (gsmSRF)

FIGURE 7 :

Messages for the network-initiated location request (SOURCE: ETSI TS 123 123 002 V3.3.0 (2000-03))

Conclusion

If the market growth and forecast for the consumer LBS market are analyzed (Figure 8, Figure 9), the undoubted conclusion is the necessity of bringing such intelligence into the cloud. The market analysis prepared by Pyramid Research predicts that LBS revenues in the U.S. will reach $10.3 billion in 2015; Frost & Sullivan predicts $3 billion in 2013. Out of that number, 60% will be location-based advertising. The fastest growth is foreseen in the U.S. market, which has the largest amount of GPS-enabled equipment.

The widespread implementation of GPS-enabled smartphones (with implemented maps, and applied target-resource databased) presents a wide-open door for a huge set of new applications. Although this might immediately seem to indicate a revenue increase for Service Providers, LBS with GPS capabilities reduce the exclusivity of the user's location information. Therefore, Service Providers must offer their own developed navigation facilities, consequently increasing sales of mobile devices, Average Revenue per User (ARPU), and number of users.

FIGURE 8:

Consumer LBS, revenue by region (in USD millions), economic crisis years 2008–2009 (SOURCE:GARTNER)

FIGURE 9:

U.S. LBS users in millions, 2009–2010 (SOURCE: SNL KAGAN, “ECONOMICS OF LOCATION-BASED SERVICES,” CITED IN PRESS RELEASE, OCT. 21, 2010)