Specialized Mobile Radio—Originally Voice, Later Data
Initially, the 800 to 900 MHz range of specialized mobile radio spectrum was used for voice applications. Examples of customers who use these services are contractors and concrete companies. They push a microphone button to talk. Conversations between the mobile units and from mobile units to a central site are private. These systems have no interconnection with the public switched telephone network. This spectrum was later used for analog data-only service by ARDIS, now merged with AMSC (American Mobile Satellite Company) and RAM, now part of Cingular Wireless. Eventually, companies such as Nextel Communications used the spectrum for digital services to sell voice, data, paging and short messaging services.
Organizations that provide delivery services, field service and installation and transportation services use these services for mobile employees. Consider companies that send out telephone repair people to fix phone systems. The hours that a technician is on-site are entered into a portable computer by the technician so that the customer is billed accurately. Giving technicians the capability of entering hours at customer locations translates to more accurate time and material billing.
Private Networks over Mobile Radio Frequencies
In the late 1970s, companies started using radio frequency networks to transmit data from mobile workers. A prime example of an organization using wireless for private data communications is FedEx. FedEx's early implementation of its private data communications network gave it a major edge over competitors. The service is used to track the location of packages. Each package has a bar code; when the package is picked up or dropped off for delivery, its bar code is scanned into FedEx's computer system at the drop-off site or by a driver's hand-held device. The hand-held device transmits the bar code to FedEx's computers. The scanning is repeated at each strategic point in the delivery system and transmitted to FedEx's computers over the radio frequency network; thus, FedEx knows where each package is in each step of its journey.
A complementary technology that helped spur the use of radio networks for mobile workers is the availability of portable computers and hand-held devices and scanners for data entry. Improvements in flash memory, developed by Intel, allow computers to hold information in memory while computers are turned off. In addition, lighter batteries and micro-circuitry make portable computers and scanners lighter and smaller so that technicians and delivery people can easily carry them.
Specialized Mobile Radio—Packetized Data Networks for Two-Way Email and Field Services
Specialized mobile radio networks cover the major urban centers in the United States. These data-only packet radio systems have been available since 1984. Other than Nextel, they do not connect to the public switched telephone network. They operate at a top throughput speed of 14.4 Kbps. Hand-held devices such as the Palm, Blackberry and Handspring use these networks for wireless access to email. The Blackberry wireless device is used with the Motient DataTAC networks in the United States and Canada as well as the Bell Mobility data network in Canada.
Rather than develop their own private radio networks, companies often lease specialized mobile radio networks from companies such as Cingular Interactive (formerly BellSouth Mobile Data) and Motient Corporation (formerly American Mobile Satellite Company, which purchased ARDIS). They were originally used mainly for trucking, field service and dispatch services and communications from mobile workers. Cingular Interactive is part of Cingular Wireless.
The underlying packet technology used in the Motient network is called DataTAC® (Total Access Communications). SMR (specialized mobile radio) uses FCC-allocated spectrum in the 800 to 900 MHz range, close to the spectrum set aside for cellular telephone service. SMR was initially analog, but carriers have upgraded to digital facilities. Nextel Communications, located in Reston, Virginia, is an interesting example of a specialized mobile radio carrier upgrading its facilities to digital and expanding its reach of services from data communications over analog facilities to digital voice communications.
Mobitex—Packet Access Method for Personal Digital Assistants (PDAs) and Blackberry Devices
Hand-held devices such as Palm and Blackberry access and send email over Mobitex packet networks. Mobitex is a packet data network technology based on a cellular structure. It was originally developed and put into trials in 1983 by Swedish Telecom Radio and developed further by Eritel, then jointly owned by Swedish Telecom and Ericsson. Eritel later relinquished all rights to Ericsson. Mobitex is the packet technology used in the Cingular Interactive packet data network. There are 30 Mobitex networks in 23 countries worldwide. Because European Mobitex networks operate at 400 MHz and the North American and South American networks operate at 900 MHz, devices that operate on U.S. Mobitex networks in the United States can't be used on other Mobitex networks.
In the late 1990s, Research in Motion developed a radio modem for a pager to support two-way electronic mail and Internet access. Manufacturers also developed integrated internal radio modems for personal digital assistants like Palm and Handspring. The Research in Motion (RIM) hand-held device weighs less than 5 ounces and the smallest one is only 2.5 inches long by 3.5 inches wide with a 6- or 8-line display and keyboard. The ones sold by AOL and EarthLink are preconfigured with email from these ISPs. The Blackberry devices sold to enterprises can receive email from enterprise email systems such as Lotus Domino and Microsoft Exchange. The Blackberry two-way email pager is also available from UK cellular provider BT Cellnet and Canadian Mobitex operator Rogers™ AT&T® Wireless. Unlike the Palm where the user must manually check for messages, the RIM is an “always on” device. Email is automatically sent when there are messages.