Definition[edit | edit source]
Mobile radio is
|“||radio services that are dedicated to mobile usage on handhelds or mobile telephones for instance. This definition encompasses services which use mobile broadband as well as services using mobile broadcast standards (or both).||”|
Overview[edit | edit source]
The early development of mobile radio was driven by public safety needs. In 1921 Detroit became the first city to experiment with radio-dispatched police cars. However, transmission from vehicles was limited by the difficulty of producing small, low-power transmitters suitable for use in automobiles. Two-way systems were first deployed in Bayonne, New Jersey, in the 1930s. The system operated in "push-to-talk" (i.e., half-duplex) mode; simultaneous transmission and reception, or full-duplex mode, was not possible at the time.
Frequency modulation (FM), invented in 1935, virtually eliminated background static while reducing the need for high transmission power, thus enabling the development of low-power transmitters and receivers for use in vehicles. World War II stimulated commercial FM manufacturing capacity and the rapid development of mobile radio technology. The need for thousands of portable communicators accelerated advances in system packaging and reliability and reduced costs. In 1946 public mobile telephone service was introduced in 25 cities across the United States. The initial systems used a central transmitter to cover a metropolitan area.
The inefficient use of spectrum and the coarseness of the electronic filters severely limited capacity: Thirty years after the introduction of mobile telephone service the New York system could support only 543 users.
A solution to this problem emerged in the 1970s when researchers at Bell Labs developed the concept of the cellular telephone system, in which a geographical area is divided into adjacent, non-overlapping, hexagonal-shaped "cells." Each cell has its own transmitter and receiver (called a base station) to communicate with the mobile units in that cell; a mobile switching station coordinates the handoff of mobile units crossing cell boundaries. Throughout the geographical area, portions of the radio spectrum are reused, greatly expanding system capacity but also increasing infrastructure complexity and cost.
In the years following the establishment of the mobile telephone service, AT&T submitted numerous proposals to the Federal Communications Commission (FCC) for a dedicated block of spectrum for mobile communications. Other than allowing experimental systems in Chicago and Washington, D.C., the FCC made no allocations for mobile systems until 1983, when the first commercial cellular system — the Advanced Mobile Phone System (AMPS) — was established in Chicago.
References[edit | edit source]
Sources[edit | edit source]
- Overview section: The Evolution of Untethered Communications, at 17-18.