Uplink Time Difference of Arrival (U-TDOA)

This is sometimes referred to simply as Time Difference of Arrival (TDOA). Time Difference of Arrival relies on the fact that each cell site is generally a different distance from the caller and that signals travel with constant velocity. Therefore, each signal arrives at the cell site at slightly different times. Using these properties, a signal defines a locus of points on a circle around a base station on which a mobile could be located. Then, using synchronized receivers, the times can be compared and a latitude and longitude can be computed and sent to the PSAP. At least three different receivers are needed for TDOA to work. TDOA works with any handset – digital, analog, TDMA, GSM, CDMA, etc.

Source: http://www.iwi.uni-hannover.de/lv/ucc_ws04_05/riemer/pic/tdoa.gif

Location Technologies (Angle of Arrival)

Location Technologies (Angle of Arrival): Known as AOA, Angle of Arrival technology measures the direction of arrival of the caller’s signal (generally at least three measurements are needed) at different cell sites. Each cell site receiver sends this direction information to the mobile switch where the angles are compared and the latitude and longitude of the caller is computed and sent to the Public Safety Answering Point (PSAP).

PSAP: Public Safety Access Points are customarily segmented as “primary”, “secondary”, and so on. The primary PSAP is the first contact a 911 caller will get. Here, the PSAP operator verifies or obtains the caller’s whereabouts (called locational information), determines the nature of the emergency and decides which emergency response teams should be notified. Automatic Location Information (ALI) contained in a database, provides supplemental information for purposes of locating the caller, determining if hazardous materials are located at the subject, and so on. In some instances, the primary PSAP may dispatch aid. In most cases, the caller is then conference or transferred to a secondary PSAP from which help will be dispatched. Secondary PSAPs might be located at fire dispatch areas, municipal police force headquarters or ambulance dispatch centers. Often the primary PSAP will answer for an entire region.

Source: http://www.911dispatch.com/911/aoa.gif

Location Services

Cellphone carriers will soon be able to figure out, within 100 meters where you, a cellphone user, are. The first application of this technology is called Emergency Location Services (or E911). What this means is that if you dial 911 in the United States on your cellphone, the operator will know where you are and be able to send help. There are two basic technologies currently being adopted; E-OTD (Enhanced Observed Time Difference) uses a software-enabled cellphone handset and cell sites to calculate your location. GPS (Global Positioning Systems) relies on a chip being installed in the cellular phone and orbiting satellites to determine position. From October 1, 2001, the FCC mandated 50% of all the new cellphone activations in the United States should be equipped with location services.

Within the two broad categories of cellphone location technology, there are a number of technologies available for determining a caller’s location after initiating a 911 call from a mobile handset, but the state of their development differs. We will explore a partial list of these in the next few days. Stay tuned!

Location Tracking

Vehicle Location Tracking Devices (VLD) are products targeted at the mobile fleet/vehicle management space. Weighing less than eight ounces, they can be installed in almost any vehicle including: automobiles; construction equipment; trucks; buses; motorcycles or even boats. When used with a carrier-grade server, it allows users to track the locations of specific vehicles equipped with these devices, via the Internet. A company called Paradigm Advanced Technologies, Inc. has licensing rights to a wireless location patent covering apparatus and method of transmitting position information from satellite navigational signals (like GPS) over cellular systems to a base unit, and displaying the location of a person object so equipped. Paradigm owns PowerLOC Technologies, Inc. which anticipates providing a comprehensive range of L-Commerce and L-Business products and services including a family of proprietary wireless-location devices for this industry and for location-based service providers (LSPs) in particular.

Location Based Services (LBS)

Location Based Services enable personalized (customized) services to be offered based on a person’s (or item’s) location. Services include areas of security, fleet and resource management, location based information, vehicle tracking, person-to-person location and messaging applications. To enable these services, there are a number of different technology layers that need to be coordinated on a network. These technologies include Applications, Middleware, Determination technologies and associated Silicon and Intellectual Property (IP).

Some examples of location-based services are:

• Requesting the nearest business or service, such as an ATM or restaurant
  
• Turn by turn navigation to any address
  
• Locating people on a map displayed on the mobile phone
  
• Receiving alerts, such as notification of a sale on gas or warning of a traffic jam
  
• Location-based mobile advertising
  
• Asset recovery combined with active RF to find, for example, stolen assets in containers where GPS wouldn't work
  

Source: http://en.wikipedia.org/wiki/Location-based_service

Source: http://www.watblog.com/wp-content/uploads/2008/04/a-gps-944.jpg

Radio Common Carrier (RCC)

Parallel to IMTS in the U.S. until the rollout of cellular AMPS was a competing mobile telephone technology called RCC. An RCC was a common carrier engaged in Public Mobile Service, which also was not the business of providing land line local exchange telephone service. The service from RCC’s was provided from the 1960s until the 1980s when cellular AMPS made RCC equipment obsolete. These systems operated in a regulated environment in competition with the Bell System’s MTS and IMTS. RCC’s handled telephone calls and were operated by private companies and individuals. One impediment of the service was that RCCs were not governed by any single interoperable technical standard. If you had RCC in Omaha, for instance, your phone would not be likely to work in Phoenix. Thus, the concept of “roaming” did not apply which made interstate traveling with RCC extremely difficult. The fact that there was no centralized industry billing database for RCCs contributed to this as well.

Improved Mobile Telephone Service (IMTS)

In the beginning, there was dispatch mobile service. The base operator broadcasted a message to you. Everyone could hear it. You responded. Then they had mobile telephone service. You picked up the phone in your car, the operator responded. You asked for the number you wanted and she/he dialed it and connected you. You had the channel to yourself but others could still tune in. Then came Improved Mobile Telephone Service (IMTS). Now you could dial from your car without using an operator with some assurance of privacy. IMTS was the pre-cellular mobile telephone service enhancement introduced in 1965, which permitted full duplex mobile radio communications, as well as other enhancements. The original Mobile Telephone Service was introduced in 1946.

IMTS can be considered “0 G” (zero G) as it is a pre-cellular VHF/UHF radio system that links directly to the Pubic Switch Telephone Network (PSTN). The original US mobile telephone system included 3 frequency bands, VHF Low (35-44 MHz, 9 channels), VHF High (152-158 MHz, 11 channels), and UHF (454-460 MHz, 12 channels). The low band was prone to network congestion and interference. Cellular networks remedied this problem by decreasing the area covered by one tower and increasing the number of cells in that area.

IMTS technology severely limited the number of subscribers able to use the service. In the 70s and 80s, there were “waiting lists” of up to 3 years for those wishing to have mobile telephone service. This limited the sales of IMTS devices driving the prices up to $2000 - $3000. The limit of customer numbers on MTS and IMTS was the driver for investment in cellular networks. In remote regions, this is not the case. In remote regions, obsolescence is the driver, but the lack of a suitable and affordable alternative has resulted in regulatory obstacles: customers do not want the MTS/IMTS service to be withdrawn. Increasing affordability of satellite service, and government investment in cellular expansion is slowly allowing MTS and IMTS to be removed.