A pragmatic approach to promoting

M-A. Dru, S. Saada location-based services.

Location-based mobile services: the essentials

Introduction New Services Providing New Revenue

So much has been said and written about location-based There is a wide variety of location-based services, of which
mobile services that many people are unsure whether or not the following four have the greatest potential in terms of
to believe all the hype. However, the uncertainty has now sales.
been resolved. Two years of technical and marketing stud-
ies have identified some potentially very profitable services. Information Services
Furthermore, the difference between technical feasibility and Finding the nearest service, accessing traffic news, get-
market reality has been highlighted. What is certain is that ting help with navigating in an unfamiliar city, obtaining
location-based services offer operators a means to differ- a local street map – these are just a few of the many loca-
entiate themselves in the market, and that these services are tion-based services that offer a new source of revenue for
of crucial importance in a mature, highly competitive mar- operators. The market for information services is con-
ket. For the operators, the difficulty lies in the need to invest sidered to be one of the most promising in terms of global
in the best technological solutions to meet the demands of revenue (operators, developers, providers). By the year
their specific markets. An analysis of market trends and con- 2005, the European market for information services
straints, relating to the services to be offered, shows that the should represent a total revenue of $13.5 billion (source:
operators require simple and flexible solutions. Strategis Group). The type of information sought depends
on the target market and users’ lifestyles:

A Better Lifestyle with the Mobile Phone • Companies make use of this new medium of informa-
tion in “Business to Consumer” relationships. Subscriber
The major figures characterizing our increasingly mobile soci- location information enables companies to target users
ety are: more than 394 million Global System for Mobile Com- who subscribe to this service option by launching local
munication (GSM) subscribers worldwide, 60% of whom are product promotions or advertising campaigns. Accord-
in Europe, with projected growth of more than 43% in West- ing to a Strategis Group study of consumers, the great
ern Europe to the year 2005. majority of subscribers to location-based services are
When individuals find themselves in an environment with prepared to receive advertising if, in return, they are
which they are unfamiliar, their behavior and needs are largely offered lower monthly subscription rates for these ser-
predictable, whether in their own country or abroad, in a vehi- vices. This is especially true for younger subscribers and
cle or on foot. People need to find somewhere to eat, per- high volume users, who both want to reduce their
haps a pharmacy, somewhere to obtain cash, a taxi stand, and monthly phone bills. Of course, these services must
so on. When abroad, there are additional requirements: find- respect an individual subscriber’s right to privacy; the
ing the local tourist attractions, getting around, locating a market will not take off if it does not do so. Indeed, the
hotel and a foreign exchange. When driving, there may be subscriber must retain the right to choose when his or
other requirements, such as help with finding a route her location can be identified for the purpose of
through an unknown city or details of breakdown services. receiving advertising. The various regulatory bodies
Today, an ill-prepared traveler (who does not consult the concerned have already drawn up recommendations.
Internet, buy a guide book, pick up information at the hotel • In “Consumer to Business” relationships, the sub-
or airport check-in, book in advance, etc) wastes a lot of time, scriber actually requests his or her location to be deter-
and will not receive much help from his or her mobile phone. mined in order to gain access to precise information
This is a dissatisfied mobile user, and therefore there is a mar- relating to his or her immediate environment. Users
ket that needs to be met by providing suitable services that might require information about local services (restau-
combine ease of use with efficiency. rants, gas stations, pharmacies, etc) or local traffic infor-

Alcatel Telecommunications Review - 1 st Quarter 2001 71 Location-based mobile services: the essentials
 mation – the two most requested categories of infor- Monitoring Services for Fleets of Vehicles or Individuals
mation. Two types of subscriber will use these services: Monitoring mainly covers Business to Business services,
the well-off tourist and the man or woman with com- operating fleet management applications, and tracking the
bined business and personal requirements, who deals location of external resources to optimize their use and
with his or her daily needs in real-time and for whom control or ensure their safety. Here, external resources
the monthly bill is less important than the ability to include individuals, whether in vehicles or not (truck
obtain the required information quickly and easily. drivers, delivery personnel, maintenance technicians,
These two user profiles are distinguished from each security personnel, etc), and objects (cars, trucks, trail-
other by the nature of the information sought. In gen- ers, containers and other such items). Services of this
eral, the former requires information concerning type offer obvious benefits for companies that hire out
leisure activities and business, while the latter requires vehicles and equipment.
information concerning business and family.
• In “Consumer to Consumer” relationships, the sub- Operator Services
scriber can locate friends, family members, or more gen- User location information can be used to improve the way
erally members of a community to which he or she that services are implemented in areas such as network
belongs (sports, music, cinema, etc). This is the sce- planning, quality of service, optimization of radio
nario for which the Alcatel MobiChat product was cre- resources (handover and channel allocation) and pricing.
ated; its target market is young people between 12 and Location-based pricing, by no means least in importance,
20 years of age who like to share experiences, exchange has been identified by the Strategis Group as one of the
information and get together. As the Wireless Appli- most promising applications in Europe, with revenue
cation Protocol (WAP) based extension of an Internet totaling in the region of $15.9 billion.
chat service, Mobichat allows them to make lists of their
favorite clubs, to create their own club, to communi- What Services are Available Today?
cate with each other and to arrange meetings. Each Table 1 shows the services that are currently available
short message is associated with subscriber location over second-generation mobile networks.
information stored by the cyberchat server. This server These services use two main positioning methods: the Cell
informs members of the same group if they are close IDentifier (Cell-ID) and Global Positioning System (GPS),
to one another. In this way, the location-related service which are covered in greater detail later in this article.
allows subscribers to actually meet one another. This Here it is sufficient to mention that most pricing and
solution, based on the Subscriber Identity Module (SIM) information services use the Cell-ID to determine loca-
application toolkit, locates the subscriber at his or her tion. In contrast, individual and fleet monitoring services
request (see Figure 1). Alcatel was the first company make greater use of GPS.
to implement such a solution, as it was able to supply
mobiles that were compatible with the SIM application
toolkit and WAP and enhanced with other features to Issues Relating to Location-based Services
improve the accuracy
of subscriber location Information and pricing services are mass markets. The
Fig. 1 Location-based
(within 50 m in urban solutions developed by suppliers are aimed at GSM sub-
Alcatel MobiChat pack
areas). Moreover, scribers (in view of the large number of existing GSM ter-
Alcatel offers a com- minals) and future Universal Mobile Telecommunications
prehensive solution System (UMTS) subscribers. The advent of third-gener-
based on the location- ation networks will expand the potential of location-based
finding server devel- services in much the same way that innovations have been
oped by Nextenso, an made possible by improvements in network data trans-
Alcatel subsidiary. mission performance and mobile terminals (large screens,
color, etc).
Emergency Services
This category includes public and private emergency ser- Minimizing Operator Investment
vices for both pedestrians and drivers. Public emergency Location-based services use one of several available
services for calling out firefighters, medical teams, etc, position fixing methods, all of which have their limitations.
are currently being regulated in the United States and Some require the SIM card, or even the mobile terminal
Europe. These services do not require a subscription and itself, to be changed, whereas others require changes at
can be accessed by any mobile subscriber, in accordance the network level. The ways in which the chosen method
with the regulations governing the rights of individuals affects the global telecom network will have a direct
to emergency assistance. They do not generate a profit impact on the operators’ investments. Consequently, the
for the operators. aim is to minimize any such impact.
Emergency roadside assistance for drivers appears to be The three positioning methods are, in increasing order of
one of the most promising of the assistance services in accuracy, as follows:
terms of operator revenue (again based on Strategis
Group research). Such services require the vehicle’s loca- • Cell-ID: Accuracy depends on the density of the cellular
tion to be accurately determined so that emergency assis- network; the smaller the cell, the more accurate the loca-
tance can be provided quickly and efficiently. Despite this tion. To improve accuracy, two network radio mea-
need for accuracy, the location-determining mechanism surements are used in addition to the Cell-ID; this is
is greatly simplified in a vehicle. referred to as Cell-ID++. Network measurement results

Alcatel Telecommunications Review - 1 st Quarter 2001 72 Location-based mobile services: the essentials
 (measuring the power received from neighboring cells) Cellular Concept and Utilizable Information
and timing advance (a mechanism for synchronization
on the radio channel in the mobile-to-base station direc- UMTS radiocommunication networks are called ‘cellular’
tion) are used in GSM. Third generation systems use the because of their radio structure. The transmitter power
Round Trip Time (RTT), which measures the time taken of the base stations (Node B) can only serve a finite num-
by the radio waves to complete a round trip. ber of subscribers, so it is adjusted to limit the surface
• Observed Time Difference (OTD): Two OTD methods are avail- area covered to this number of users. This surface forms
able, depending on the cellular network generation. a ‘cell’, the structure of which is repeated over the entire
GSM uses Enhanced OTD (E-OTD), which offers only area to be covered (see Figure 2). An active mobile is
slightly better accuracy than Cell-ID++. However, linked to one or more cells.
UMTS will use OTD Of Arrival (OTDOA), which offers Several radio synchronization mechanisms exist, at both
an appreciable increase in accuracy. mobile unit and network levels, to ensure that cellular net-
• Assisted GPS (A-GPS): This method, which is based on the works can operate. Positioning is made possible by mea-
GPS satellite constellation and the introduction of a ref- suring and using this synchronization.
erence server into the cellular network, offers the great-
est accuracy.
Basic Principles: Radio Methods
The Cell-ID and Cell-ID++ positioning methods can be
either terminal or network based. Both OTD methods Cell-ID
require a software function to be added to the terminal This is the simplest method for determining the location
(and, therefore, a change of terminal) and other equip- of a mobile. It relies on the hypothesis that the geo-
ment to be added to the radio network. A-GPS requires graphical coverage of a cell corresponds to that predicted
a change of terminal and the deployment of a reference by radio coverage studies. When an active mobile is con-
server in the network. nected to a base station, the mobile is assumed to be
located geographically within the area predicted to be best
Value of Differentiation served by this base station.
In such a competitive market, the accuracy offered to Reliable positioning therefore requires accurate maps of
users will certainly have a role in service differentia- the base station coverage area, which are produced using
tion, but not at any price! How users judge such a dif- cellular planning software (see Figure 3). It is then nec-
ferentiation will depend on the absolute gain in accu- essary to model the maps to transform them into a usable
racy. and easily describable format. This is the task of the Alca-
In the existing GSM market, therefore, we believe that tel 956 RNO (Radio Network Optimization) tool, which
subscribers will not be receptive to a service such as has the ability to determine the geometric contours of
E-OTD, which only offers a slight increase in accuracy. cells by using polygons (referred to as ‘Voronoi’ polygons),
Moreover, there is a risk of the service being unavail- as shown in Figure 4.
able to users inside buildings or in rural areas. A change It is possible to refine positioning using RTT measure-
of terminal will be necessary, and the operator will have ments taken by the base station, which measures the time
to invest heavily to offer the service. between the transmission of a frame (from base station
It is a different story with A-GPS, as the increase in to mobile) and the reception of the corresponding frame
accuracy is considerable. Also, the investment required (from mobile to base station). Using this measurement,
by the operator is not on the same scale as that the base station can work out the distance to the mobile,
required for E-OTD. However, there are still problems with a theoretical accuracy of about 80 m.
with service availability to users inside buildings. This makes it possible to restrict the area of inaccuracy.
After describing the various positioning technologies Although the information is of little use for a cell served
and the degree of accuracy to be expected with each, by an omnidirectional antenna, it can offer improved accu-
we look at which techniques offer the required accu- racy in the case of “sectored” cells served by several
racy for various services. antennas (see Figure 5).
Unlike second generation systems, in which a mobile only
communicates with a single base station, a third gener-
Fig. 2 Cellular network ation mobile terminal can be in communication with sev-
eral base stations in soft handover situations. An addi-
tional difficulty lies in the fact that the base stations for
which the mobile is active can change several times a sec-
ond. A method is therefore needed to identify the cell that
best represents the geographical position of the mobile.
For example, the mobile may be asked which is the best
cell for reception, or statistical processing of the cells used
by the mobile can be carried out. The latter solution would
allow further refinement of the positioning accuracy by
determining in which zone of the cell the mobile is
located.
In conclusion, methods based on cell coverage may turn
out to be effective for services that do not require an accu-
racy better than a few hundred meters. The advantage

Alcatel Telecommunications Review - 1 st Quarter 2001 73 Location-based mobile services: the essentials
Fig. 3 Map showing predicted coverage based on radio is their low cost of deployment and operation, as well as
propagation models - Alcatel 955 Radio the fact that they can be implemented across the whole
Network Planning population of mobile users, since no special development
is required to the mobile itself.
The main difficulty with these methods lies in correctly
predicting the geographical coverage of the cells, as the
“best” base station will not always be the one that is phys-
ically closest. The reliability and accuracy of the posi-
tioning obtained depend on the precision of the radio pre-
dictions.

Triangulation
We can avoid the coverage prediction problem by using
a triangulation method, using measurements of the time
taken by signals coming from several base stations.
If the position of two base stations is known accurately,
and it is possible to measure the difference in time that
the signals transmitted by these stations take to reach the
mobile – the System Frame Number (SFN) observed time
difference, that is, the time difference observed on the
system clock as received from the two base stations – it
is then possible to work out a locus (hyperbola) for which
this time difference is constant and equal to that mea-
sured by the mobile. The estimated position of the
mobile is obtained by repeating this operation and tak-
ing the intersection of the hyperbolas defined in this way.
This method can be combined with the RTT measurement
to further increase positioning accuracy.
Fig. 4 Cell modeling using Voronoi polygons
This triangulation method (see Figure 6) is more accu-
- Alcatel 956 RNO
rate than the method based on cell identification and, in
particular, does not depend on correctly predicting the
coverage. However, its accuracy is related directly to the
time taken for the signals to travel from the base stations,
and can therefore be affected by multiple reflections in
urban areas. In addition, it requires three base stations
to be visible, which may not be the case in a rural area
or inside buildings.
The mobile can only measure observed time differ-
ences. Differences in signal transit times can only be
worked out if the time interval between two base stations
(Relative Time Difference; RTD) during transmission is
known. Several solutions exist for dealing with this sit-
uation:

• Synchronize the base stations’ transmission relative to

a common time reference (GPS type).

Fig. 5 Use of RTT Fig. 6 Observed time difference of arrival

RTT circle

Base Station

Base Station

Cell with omnidirectional Sectored cell OTDOA

antenna locuses Base Station

Alcatel Telecommunications Review - 1 st Quarter 2001 74 Location-based mobile services: the essentials
• Regularly observe and measure the RTD and its drift graphical coordinates plus any potential degree of uncer-
using dedicated Location Measurement Units (LMU). tainty. It is free to choose the positioning method in accor-
dance with the quality of service requested by the GMLC
Both solutions are relatively costly, either because of the and the capability of the mobile. In addition, the SMLC
price of the GPS receivers (equipment, layout of site to give receives information about coverage and cellular planning
a direct view of the sky), or because of the prices of the when a knowledge of the network geography is needed.
LMUs, which are expensive to install (site, monitoring). • Location Measurement Unit for OTDOA only: The role of the LMUs
There are two versions of OTDOA, depending on the role is to help the SMLC take base station synchronization mea-
assigned to the mobile: surements. LMUs are either integrated into Node B
(B type LMU), or distributed over the network (A type
• When the mobile only reports observations of the SFN- LMU). In the latter case, it is considered that one LMU is
SFN observed time difference to the network, with the required for every three or four base stations.
position calculations being carried out by the network,
this is referred to as mobile-station-assisted OTDOA. In addition, the existing network elements have to be modi-
• It is also possible to transmit the RTD information mea- fied. The Mobile Switching Center (MSC) has to be capa-
sured by the LMUs and the positions of the base sta- ble, in particular, of verifying in the Home Location Regis-
tions to the mobile. After measuring the SFN-SFN ter (HLR), that an LCS client is authorized to determine the
observed time difference, the mobile can calculate its location of a user, depending on the identity of the LCS
own position independently. This is referred to as client, among other things, and the subscriber profile and
mobile-station-based OTDOA. options. For positioning methods that require the mobile to
be actively in communication, the MSC must also be capa-
Satellite ble of activating a communication, with or without notify-
Satellite positioning systems, such as GPS or Galileo, can ing the subscriber.
be used to further improve accuracy. The RNC is also affected, since it has to incorporate the
Terrestrial mobile networks offer the possibility of trans- SMLC functions, or even control the SMLC.
mitting support information (e.g. ephemeris, time refer- Lastly, the Node Bs have to incorporate B type LMUs, and
ences or even differential corrections) to these satellite must be able to measure RTTs.
receivers. Using this support data, positioning time Figure 7 illustrates the global architecture of a UMTS net-
(time-to-fix), accuracy and sensitivity are improved work with the elements necessary for positioning as defined
considerably. Accuracies to within several meters can be in the Third Generation Partnership Project (3GPP) standard.
achieved in this way. However, the service is not available
inside buildings, unless the user is close to a window.
Moreover, this method requires a full satellite receiver Choosing an Appropriate Positioning Tech-
(processing + radio) to be integrated into the mobile, nology
which has an adverse impact on the cost.
Each positioning method is characterized by an impor-
tant parameter with respect to positioning: accuracy.
Standard Architecture of a Positioning Table 1 lists each positioning method and shows its accu-
Network racy, impact on the access terminal and impact on the net-
work.
The new network elements required for location fall into Taking these levels of accuracy into account, we can
three categories: establish a correspondence between services and posi-
tioning methods (see Figure 8). Technologies based on
• Gateway Mobile Location Center (GMLC): Responsible for the inter- Cell-Id and Cell-Id++ meet the accuracy requirements for
face with the outside world, the ‘LoCation Services (LCS) pricing and information services, whereas only the A-GPS
clients’, suppliers who are the source
of positioning requests. The center
receives the positioning request, Fig. 7 Architecture of a positioning network in compliance with the 3GPP
authenticates the client, and checks standard
that he or she is authorized to request
a user location. The GMLC is also {LMU
responsible for transmitting the type A}
required service quality (accuracy, Uu HLR
3G
response time, etc) to the network, and Iu SGSN Lg
for converting the positioning results Node B SRNC
Lh
Iu-b
into the desired format, for example, a UE {LMU SMLC 3G External
GMLC
different coordinate system. type B} inside MSC LCS client
• Serving Mobile Location Center (SMLC): Le
Whether integrated into the Radio Node B Iu-r
Network Controller (RNC) which con- Iu-b
{LMU
trols the base stations, or located in a type A}
RNC
separate network element, the SMLC
has the role of determining the posi-
tion of the mobile, that is, its geo- SGSN: Serving GPRS Support Node UE: User Equipment

Alcatel Telecommunications Review - 1 st Quarter 2001 75 Location-based mobile services: the essentials
and OTDOA technologies would be Tab. 1 Choice of positioning methods
suitable for navigation and assistance Positioning Accuracy Terminal-based Network-based
services. OTDOA offers better accu- technology
racy than Cell-ID++, making it a gen-
CELL-ID from 300 m to 10 km SIM Tool Kit OR IN (handset universal)
uine alternative to the latter in a
NMR
future market such as UMTS. CELL-ID++ TA from 100 m to 500 m SIM Tool Kit OR BSS/UTRAN (handset universal)
RTT

E-OTD GSM from 150 m to 500 m Software AND Hardware

Advantages for Operators
A consideration of operator require- OTDOA 3G from 30 m Software AND Hardware
ments confirms the preceding view- A-GPS from 5 m Hardware Hardware
AND
point. Table 2 shows the main opera-
tor requirements, and indicates the NMR: Network Measurement Results TA: Timing Advance
appropriateness of each positioning
method to meet this requirement.
Fig. 8 Services supported by different positioning technologies

Conclusion Information and billing services

Alcatel is actively preparing for the

introduction of positioning services
into its second- and third-genera- Pricing by Zone Traffic & Navigation
tion networks. Based on meticulous C2B
analysis of the needs of users and Information requested by subscriber: Assistance
find a bank, gas station, etc.
operators, Alcatel is optimizing
B2B
investment by carefully selecting the Fleet management, vehicle and equipment
positioning technologies to be imple- monitoring, etc.
mented, and by promoting these B2C
Service supplier initiates the sending of
technologies within the standardiza- information advertisements, discounts, events
tion organizations. ■ C2C
Information requested by subscriber:
find a friend or family member Accuracy

Marie-Anne Dru is Marke- CELL-ID CELL-ID++ OTDOA A-GPS

ting Manager in the Com-
munication Marketing & 2G & 3G 2G 3G 2G & 3G
Network Solution depart-
ment of the Alcatel Mobile
Tab. 2 Operator needs in relation to positioning technologies
Communication Division
(MCD) in Vélizy, France. Operator
positioning Cell-ID Cell-ID++ A-GPS E-OTD OTDOA
requirements 2G 3G

Stéphane Saada is Positio- GSM and UMTS shared

investment 1 Average 1 Medium 3 High 3 Low 0 Low 0
ning and Localization Pro-
duct Manager at Evolium Ease of maintenance
3 High 3 High 3 High 3 Low 0 Low 0
SAS, the Alcatel-Fujitsu and operation
joint venture, in charge of Supply of emergency services
R&D on second- and third- with limited investment 0 Low 0 Low 3 High 3 Low 0 Low 0
generation cellular radio in the mobile network

access systems, in Vélizy, Coverage inside buildings:

France. shopping centers, parking lots, 3 High 3 High 0 Low 3 Medium 0 Medium 1
high rise buildings

Consumer market 3 High 3 High 0 L H 3 Low 0 High 3

Complete end-to-end control 3 High 3 High 1 Medium 1 High 3 High 3

No intellectual property
3 High 3 High 0 Low 0 Medium 1 Medium 1
copyright

Differentiation / competitive
0 Low 1 Medium 3 High 3 Medium 1 High 3
advantage

Mark 16 17 13 16 6 11

Alcatel Telecommunications Review - 1 st Quarter 2001 76 Location-based mobile services: the essentials