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Location Services (LCS) may be the next ‘killer app’ for wireless. Locating emergency callers is the best known application, but the wireless industry is hoping that commercial applications will soon dwarf it in popularity. Carriers are still investigating a variety of techniques for obtaining location, and trying to determine which position-enabled services their business and consumer customers will benefit from. Carriers must also have protections in place to prevent location information getting into the wrong hands.
Obtaining location information for a mobile phone is the biggest challenge, transporting it and manipulating it are secondary. Techniques for obtaining location vary from merely providing cell/sector information (quick and cheap, but very inaccurate) to building GPS capabilities into phones.
Location information must be transported through the wireless signaling network when it has been obtained. A number of standards are being developed for GSM, CDMA, TDMA and even analog systems to traverse radio and network interfaces. Capacity is not a big issue because location information does not take much bandwidth (unlike high-speed data services, another possible killer app for 3G wireless). Most standards are using a concept known as Calling Geodetic Location or Geographic Area Description (e.g. ANSI standards T1.113 (ISUP), T1.628 (Wireline Emergency Calling), J-STD-036 (Wireless Emergency Calling), PN-4747 (LCS for cdma2000) and 3GPP 23.032 for UMTS). This encodes latitude and longitude and, optionally, altitude and uncertainty in a space smaller than 20 bytes, next to nothing, even for the 10-20 kbps data speeds provided by 1G and 2G systems.
Once location information has been delivered to its destination there are many possibilities for dealing with it, as techniques for handling it have been evolving for hundreds of years, and computerized systems (such as GIS – Geographic Information Systems) are quite mature.
The simplest and quickest way to obtain location information, satisfactory for some services, is to simply use the location of the cell or sector serving a mobile. With cells being several kilometers in width, this obviously cannot compare with GPS systems that might pin location down to 10 meters, but it is available in all wireless systems, so the only cost is that of delivering it to the application. This is currently the commonest solution being used in Europe.
The first techniques proposed for obtaining more accurate location were network based, using either Angle of Arrival (AOA) or Time Difference of Arrival (TDOA or TOA) techniques. These solutions do not require any modifications to mobile phones.
AOA systems can detect the angle at which signals from a target mobile hit a monitoring antenna. In a perfect world only two measurements would be required but, cellular signals often have bounced off a building before being picked up, so even with several measurements there may be a considerable degree of inaccuracy.
TDOA systems monitor the minute differences in time at which signals from a target mobile arrive at different monitoring stations. In theory, three measurements are required but, for similar reasons as with AOA, signals often taken longer to arrive than they should, because of detours they have taken.
Most current network-based location systems, including those from SigmaOne and TruePosition include both AOA and TDOA. Calgary-based Cell-Loc, on the other hand, relies on TDOA, not considering the AOA technique to be of much value. All equipment vendors have proprietary enhancements beyond the basic techniques.
The impetus for developing location services was the US emergency services mandate (FCC 94-102). This required that US wireless carriers provide the location of wireless callers within about 100 meters for most emergency calls. This mandate got the location pot boiling, but there is now danger it will burn dry on the stove. Problems with this mandate include:
US PSAPs have stated that they believe that wireless carriers are going to make buckets of money on commercial wireless services, and therefore the costs of the location equipment should not be subsidized by funds allocated to 911 services. This has resulted in US wireless carriers lining up for waivers to avoid compliance with the mandate, proposing to install network-based systems providing a level of accuracy significantly worse than the mandate, while agreeing to encourage the use of position-enabled phones as the long term, higher accuracy solution.
Canada has taken a voluntary approach to emergency services, but carriers are similarly constrained. If they commit to a technology that stalls in the US, they may end up with an unsupportable, unexpandable location network. Consequently, they are also waiting and watching.
These interminable delays are what caused Cell-Loc to install location networks in Calgary and Austin, independent of wireless carriers, so that they can provide commercial services direct to businesses without having to wait for wireless carriers to choose a technology direction.
GPS-based positioning, which requires handset support, was not at first considered for the US emergency services mandate which was originally supposed to apply to all phones. However, the FCC eventually relaxed that restriction, allowing carriers to consider GPS-based location systems, although carriers using this method have to meet tighter constrains on positioning accuracy, and have to eventually ensure that all new phones are GPS-capable.
GPS satellites, originally placed in space for the use of the US military, have obtained worldwide use for civilian positioning. A GPS system analyzes the signals from multiple satellites to determine its location. They can provide a high degree of accuracy under ideal conditions – outdoors with few obstructions such as buildings and trees in the immediate vicinity. The worst situation for this technology is inside buildings, under thick foliage or inside vehicles.
The first GPS-based system was an add-on device from Tendler Cellular. It uses the voice capability of the phone to announce the location of the emergency caller. The greatest potential of this type of system is in retrofitting existing phones.
The second generation of systems have integrated a low-cost GPS receiver into new phones. These systems, from design companies such as Sirf and Qualcomm (SnapTrack division) are not intended, in most configurations, to allow a phone to determine its own location. To reduce the size and complexity of the device within the phone assistance is given to the mobile to help it acquire enough satellites without a painfully slow search, with the network converting the ‘pseudorange’ information returned by the phone into latitude and longitude. For services where the phone itself needs to know its location, it will have to be provided from the network.
The coordination between the network and the mobile means that changes are required in radio interfaces. Standards providing the appropriate modifications are being made for all major technologies used in Canada – analog (TIA/EIA/IS-817), CDMA (IS-801), TDMA (TIA/EIA-136-740) and GSM (04.31 Radio Resource Location Protocol).
The wireless industry is divided on the long-term solution to positioning, whether network based or GPS-based (mobile-assisted). However, some carriers are considering interim solutions until they have determined that technology is mature enough to make a major investment.
These solutions are generally based on handset triangulation. For example, most digital cellular phones have the ability to measure the signal strength of nearby cells to assist with handoff. These techniques are applicable to TDMA, GSM and CDMA digital systems. They can be implemented with minimal handset software changes (and no hardware changes) or even no handset changes. The results are nowhere near as accurate as GPS-based or network-based location systems, but can be obtained more cheaply.
The best known location application is still locating emergency callers, so that assistance can be delivered more accurately. Another government application is surreptitious surveillance of suspected criminals. Governments, however, are not going to be the biggest users. One hopes that the majority of cellular phone users are neither regularly placing emergency calls, nor under law enforcement surveillance.
According to Jack Hwang of Signal Soft, the services that they first implemented were designed to provide consumers with geographically intelligent information, such as directions to nearby ski resorts, restaurants or banks. By determining the location of the caller, information can be filtered and sorted before being presented. When a caller asks for Japanese restaurants, one that is across the street should be provided first, and one that is 20km away may not be provided at all.
The nice thing about consumer-initiated services is that there is one position fix required for each service invocation, and there is a ready revenue source from the companies that participate in the systems.
Another major class of applications is based on tracking equipment that contains a cellular phone module. This could be applied to trucks, taxis, containers or virtually any asset that is both mobile and expensive enough that the cost of wirelessly enabling it is not prohibitive. The downside with these services, according to Hwang, is that the amount of network traffic is more difficult to control. Minimizing the location reports, so that they are only transmitted through the network when necessary is difficult.
Tracking applications are likely to be successful where manual location reports are currently used. For example, dispatching taxis can be performed automatically, without drivers having to do anything more than press a button indicating that they are available for a trip. More sophisticated systems could estimate the time that a driver will complete their current trip, automatically booking them for the next trip that is closest to their destination before they have even delivered their current passenger.
Future, and more speculative services may be more peer-to-peer in nature. For example, a group of friends or business colleagues may decide to share their location with each other. To consumers this may be merely a fun application (imagine an alert on your phone saying “John Doe is 100 meters away and closing fast”) that may integrate with instant message. To businesses that currently do not have a central dispatcher, however, there may be ways to increase revenue by grabbing opportunities more efficiently, and cost reductions by sending the closest worker. For example, a real-estate agent who is unexpectedly tied up with one client, while an appointment looms to show a house to another, may be able to contact a colleague who happens to be nearby and have them fill in, avoiding the loss of another potential sale.
Location information is very sensitive. A lot can be learned about someone from tracking them over time. Industrial espionage could flourish if competitors had an easy way to obtain information about the movements of the top salespeople of their competition, for example. Luckily, safeguards are being built into systems, so that access to location information can be tightly controlled. A trucking company may contract to obtain the location of its own trucks, but will be denied access to information about its competitors.
There are still some grey areas in the field of location privacy. Can parents track their children without their knowledge? Until what age? Carriers may contract to deliver advertisements within a geographical area. This uses location information, but does not disclose it. Can consumers object to this? New legal precedents must evolve to better define the boundary between acceptable and unacceptable uses.
Law enforcement is very interested in obtaining location information. They are likely to prefer network-based systems, which can track surreptitiously. GPS systems need to request information from the phone. Sophisticated criminals could either have software modified to alert them when the GPS receiver is activated or find a way to disable it entirely. These agencies may eventually decide that installing equipment is good for their needs should be a requirement for wireless carriers.
The increasing availability of location information is stimulating the creative juices of a wireless industry that is looking for new sources of revenue. Location information is compact, globally standardized, easily integrated into existing applications and has a panoply of different uses. Carriers are faced with several choices for location technology, and are afraid of committing to one that may not prove to be the best. They need to balance the cost, speed and accuracy of the information they obtain against the needs of their customers and meet applicable government mandates. They must perform careful trials to establish the characteristics of the candidate technologies in a variety of realistic situations. Those who do nothing may end up being known as the ‘carrier in the dark,’ left behind when their competitors have a commercially viable location system running tomorrow’s killer app.
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Technology |
Accuracy |
Speed |
Network |
Handset |
|
Cell/Sector |
Low |
Fast |
Low |
None |
|
Handset triangulation |
Low to medium |
Medium to slow |
Medium |
None |
|
Network-based AOA or TDOA |
Medium |
Medium |
High |
None |
|
GPS |
High (as |
Medium |
Medium |
Medium to High |
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