Friday, Jan 07, 2005 at 10:31
From:
http://www.voiceanddata.com.au/vd/feature_article/item_072001.asp
(Looks like telstra is using the simpler network-based version rather than the more accurate TDOA - read on for an explaination)
Lost on LBS?
The location of wireless devices is a fundamental element of wireless networks and an asset that has huge potential. Location based
services (LBS) in the US were pushed by the Federal Communications Commission's mandatory rule for operators to locate wireless emergency callers or e-911
services. Now the market potential for location-based
services is rich with commercial
services for global markets.
Location-based
services are destined to be successful, because they serve both consumers and wireless network operators. For consumers, LBS promises more personalised
services and better communication capabilities. For network operators, location-based
services help differentiate their
services, increase network efficiency and create pricing flexibility.
The technology behind LBS can basically be divided into three components:
The Position or Location Determining Technology;
The Middleware or the Mobile Location
Services Engine, which provides a platform on which applications can be launched and accessed by end-users and can also collect and maintain information (see Figure 1);
The applications and content development platforms, which are responsible for the generation of the location relevant content to be delivered to the end-user.
Position determining technology
Two fundamentally different system architectures allow mobile systems to pinpoint the location of subscribers - network-based systems and handset-based systems. There are also technologies that are a hybrid of the two.
Network-based
In a network-based solution, the network computes the position. No hardware or software computation takes place in the end-device. These techniques thus, work with legacy phones. Cell-ID is the only location determinant technology already commercially deployed. The technique basically determines the location according to the strongest base station signal the end-device receives and thus the approximate position of the user. The accuracy of this technique depends on how closely the cells are located. This is the technique NTT-DoCoMo and J-phone in Japan have been using to provide some sort of LBS applications since 1999 and it works
well there because the base stations are relatively close together.
TDOA or time difference of arrival technique basically uses geometry or triangulation using the angle-of-arrival to determine the location. The location measurement units, collocated with the carrier's base stations derive the angle of arrival and time difference of arrival of a mobile unit's signal. Then the mobile's position is determined, using inputs from multiple LBS subsystems, which supplies the position to external users. Despite multipath problems which cause potential for overlap that can result in reduced accuracy, TDOA is touted as the choice for analogue telephones and is preferred for its relatively low installation cost.
Handset-based systems
Handset-based systems are those that use hardware or software changes in the handset to locate its position. The most common of the handset-based technologies is GPS.
Global positioning system (GPS) consists of 24 operational satellites in six circular orbits that lie in non-synchronous orbits at inclinations of 55 degrees, 20,200 km above the earth. There are currently two 'public' GPS systems. The NAVSTAR system is owned by the
United States and is managed by the Department of Defence. The Russian Federation owns the GLONASS system.
The GPS satellites are used to calculate the position of a GPS receiver on or above the surface of the earth by applying simple geometry, together with computing algorithms that assist the receiver in determining which satellites to use, thereby resolving any ambiguity related to location. The major drawbacks of GPS are that it is expensive and also that its performance can be compromised indoors or in high-density urban areas.
Hybrid systems
Hybrid systems are those that incorporate a combination of network- and handset-based technology.
Enhanced observed time difference (EOTD) is a time difference of arrival technology solution that measures the apparent time differences and received time of signals transmitted from the network to the handset. A fair amount of calculation happens in the handset that needs to detect and measure the time of arrival data from three sites. This technology is fairly accurate and for digital GSM operators, the network
infrastructure as
well as handset upgrade cost is minimal.
Assisted GPS (AGPS) GPS requires a host of complex calculations before determining the latitude and longitude of the user. In AGPS solution, the network provides the handset with additional bits of data that allow the handset to lock onto satellites with greater alacrity, meaning that it is presumed to be the most accurate of all PDTs.
Each technological approach - network-based, handset-based and hybrid - sacrifices desired qualities to gain an advantage in another. Network-based solutions such as TDOA do not require changes in handsets, making it easier and cheaper to implement. The hybrid techniques are far more accurate and have been widely adopted, however the up-front investment is greater. Handset-based techniques have a major advantage in that they help to overcome privacy issues and concerns because the location information is computed and stored in the end device.
Ultimately whichever location positioning determining technology the operator chooses to use depends on what best meets business objectives, cost constraints, and desired accuracy level.
The success of location-based service offerings will depend on how
well these three players, in conjunction with the network operator, bundle the
services and juggle initial growing pains to meet user expectations.
For further information contact EdgeMatrix Pty Ltd
AnswerID:
91743