Wireless Future - Telenor

Figure 4 OSA architecture
service
capability
features (+)
Service
capabilities
(*) ..standardisedinterfaces
(+)..to be standardised
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HLR CSE
• Offer the possibility to locate mobiles without
or only with software changes, and to implement
a self-positioning system (E-OTD).
In general more investments are needed on the
network side for the network-based positioning.
Network-based is the only architecture that can
locate existing mobiles, because normally no
modification of the mobile phones is needed.
This is a great advantage compared to the other
architectures. In a mobile-based solution the
positioning is part of the functionality of the
mobile terminal. This translates into added complexity
and cost due to added software and hardware
for the terminals. The mobile calculates the
position by use of signals from the network, e.g.
base station(s).
All current network-based mobile location services
exist on today’s 2G mobile data and analogue
cellular networks. No location technology
is at this time commercially available for 3G
digital air interfaces such as TDMA, W-CDMA
and CDMA.
An interesting fact is that most of the systems
described here will improve their accuracy as
terminals are moving. In E-OTD and ToA this
is due to the “de-correlation or whitening” introduced
in the multipath channel by the higher
mobile speed, and for other techniques (signal
strength, direction finding) the average of measurements
over a distance eliminates the problems
caused by multipath fading and shadowing.
ETSI considers all GSM LCS (Location Services)
a network feature, and not a supplementary
service. This means that ETSI specifies LSC
whether the Mobile Station (MS) supports LCS
or not. So far ETSI has specified the following
methods:
Applications/Clients
Application
Interface
GSM/GPRS/UMTS protocos CAP/MAPl (*)
GSM/GPRS/UMTS protocol (*)
MS functionalgy, Standardized Services
MEXE and SAT APIs
Client2 ... Client1
MExE
Network
SAT
server
terminal view
• TOA (Time of Arrival);
• E-OTD (Enhanced Observed Time Difference);
• TA (Timing Advance);
• GPS assisted.
GPS-based positioning location systems are currently
under development and standardization
[7] and should be available for the next mobile
phone and mobile communication generation in
2002. However, power consumption, cost, and
some technical challenges are yet to be considered.
Some of these challenges are met with
Assisted GPS systems. These utilize a GPS reference
network (or a wide-area differential GPS
network) that is connected with the GSM network.
The assistance data from the reference
network can be used by the MS to increase performance
of the GPS sensor and
• Reduce the sensor start-up time;
• Increase the sensor sensitivity; and
• Consume less handset power than conventional
GPS does.
Service Platform and Interfaces
There is currently ongoing work on an OSA lab
at Telenor R&D for testing the OSA architecture
and interfaces.
The work from 3GPP on standardizing an open
architecture for service platforms (OSA) in
UMTS networks is highly relevant, and will
therefore be presented as a reference architecture
for services. The OSA (Open Service Architecture)
describes an architecture that enables service
providers to make use of network functionality
through open standard interfaces [5], i.e.
the OSA API. The network functionality is described
as Service Capability Servers. One of the
addressed Service Capability Features is User
Location (SCF), specified in OMG (CORBA)
IDL-format. The reference system chosen for the
coding of locations is the World Geodetic System
1984 (WGS 84). The architecture is illustrated
in more detail in Figure 4.
The purpose of the OSA API is to shield the
complexity of the network, its protocols and specific
implementation from the applications. This
means that applications do not have to be aware
of the network nodes a Service Capability Server
interacts with, in order to provide the Service
Capability Features to the application. The specific
underlying network and its protocols are
transparent to the application enabling external
service providers’ access to the platform and its
underlying networks by using an open API.
Telektronikk 1.2001