||Personnel of the Detroit Police Department's radio bureau, began experimentation with a band near 2 MHz for vehicular mobile service. On April 7, 1928 the Department commenced regular one-way radio communication with its patron cars. The system established the practicality of land-mobile radio for police work and led to its adoption throughout the country. Channels in this low-frequency band soon became crowded.|
||The police department in Bayonne, New Jersey initiated regular two-way communications with its patrol cars, a major advance over previous one-way systems. The very high frequency system placed transmitters in patrol cars to enable patrolmen to communicate with headquarters and other cars instead of just receiving calls. Two-way police radio became standard throughout the country following the success of the Bayonne initiative.|
|1940.||New frequencies allocated between 30-40 MHz leads to substantial buildup of police radio systems. A major advance in police radio occurred when the Connecticut State Police began operating a two-way, frequency modulated (FM) system in Hartford. The statewide system developed by Daniel E. Noble of the University of Connecticut and engineers at the Fred M. Line Company greatly reduced static, the main problem of the amplitude modulated (AM) system. FM mobile radio became standard throughout the country following the success of the Connecticut initiative.|
|1940...||FCC allocates some 40 MHz of spectrum in range between 30 and 500 MHz for a host of mobile services for private individuals, companies, and public agencies..|
|Late 1940's||Bell System embarked on a program of supplying "public correspondence systems" (communication among a variety of users provided by a common carrier). FCC classified these services as Domestic Public Land Mobile Radio Service (DPLMRS).|
|1946||First Bell, "urban" DPLMRS inaugurated in St. Louis -- three channels near 150 MHz, manually patched).|
|1947||A 35 to 44 MHz "highway" system between New York and Boston is inaugurated. It was thought that these frequencies would carry further along highways. This was all too true: due to atmospheric skip, unwanted conversations were carried across country.|
|1956||First manually patched 450 MHz service.|
|Note||All of these aforementioned services employed push-to-talk (PTT ) operation -- i.e. radio is half duplex which is unfamiliar and awkward for ordinary phone users -- and required operator intervention to place a call. In fact, most of these services were not directly part of the PSTN at all, and involved a radio channel patched into a phone line.|
|1964||First automatic 150 MHz service (called MJ). Free channel is automatically assigned. System was full duplex and customers could do their own dialing.|
|1969||First automatic 450 MHz service (called MK). Extended MJ to new band. Taken together these two services became the ITMS (Improved Mobile Telephone Service) -- the standard until the develop of AMPS.|
|Late 1970's||In spite of the fact that mobile service was, indeed, a scarce luxury, the demand for service was rising rapidly.|
|1970-77||FCC debates frequency allocation to common carriers. In 1974 it approved the underlying concepts of wireless cellular phone service and allocated for this purpose 666 duplex (two-way) channels in the 800 - 900 MHz frequency range.authorization granted to Illinois Bell in 1978.|
|1978||Field trials: AMPS (Advanced Mobile Phone Service) trials begin (850 MHz) in Chicago and ARTS (American Radio Telephone Service) in Washington DC.|
||World Administrative Radio Conference sets up research group to define a common international standard. Leads to Group Speciale Mobile (GSM) in 1982|
||NMT (Nordic Mobile Telephone System) enters public service in Sweden. Developed by Ericsson using frequencies in the 450 to 470 band.|
||Initial deployment of AMPS cellular system.|
||Responding to a spectacular and unexpected rising demand for wireless services, Congress, in the Omnibus Budget Reconciliation Act of 1993, mandated that the FCC reallocate portions of the electro-magnetic spectrum for "personal communication" and authorized the FCC to employ competitive bidding procedures in awarding licenses for the use of these new spectral resources. The mandate had several objectives, not the least of which was raising revenue to help balance the federal budget. Furthermore, competitive bidding was deemed to be the most effective means to expedite the licensing process and to open up opportunities for beneficial competition|
There were several significant problems in the design and operation of the ITMS which spawned a major reassessment of the architecture of mobile communication.
Characteristics and design goals of AMPS:
- The most significant problem was that a single transmitter was required for all calls. The power of that transmitter had to be quite large (up to 500 W effective radiated power) and located at high elevation. Such a system ensures coverage as far as 20 to 25 miles from the transmitter site. Although the signal level may be poor beyond 25 miles, it is still high enough to interfere significantly with other mobile communications at the same frequency within 60 to 100 miles.
- Further the bandwidth of the single transmitter determined the total number of users -- a number which could not support the service (10 to 20 times the price of normal phone service).
The advent of the cellular concept (1947, D. H. Ring of AT&T Bell Laboratories) was a crucial contribution in the development of mobile communication.As cell size decreases traffic carrier capacity increases. Cell start big and split as system grows.
- Spatial locality: The 800 MHz band is interesting since it provides a compromise between spatial locality and a good degree of propagation into buildings (a problem at microwave frequencies). Choice of this frequency resolves the long range (up to 200 miles) interference problems observed in the 1947 highway system.
- Frequency utilization: The early systems locked each unit to a particular frequency or a small set of frequency and, thus, the sacred switching principle of trunking is violated. Trunking allows any user to use any available channel to avoid blocking and to insure optimal channel utilization.