Wireless telecommunication began only a little later than the wired variety. Morse’s telegraph (1837) and Bell’s telephone (1876) were soon followed by Hertz’s first experiments with radio (1887). Hertz’s system was a laboratory curiosity, but Marconi communicated across the English Channel in 1899 and across the Atlantic Ocean in 1901. These successes led to the widespread use of radio for ship-to-ship and ship-to-shore communication using Morse code.

Early wireless systems used crude, though often quite powerful, sparkgap transmitters, and were suitable only for radiotelegraphy. The invention of the triode vacuum tube by De Forest in 1906 allowed for the modulation of a continuous-wave signal and made voice transmission practical.

There is some dispute about exactly who did what first, but it appears likely that Reginald Fessenden made the first public broadcast of voice and music in late 1906. Commercial radio broadcasting in both the United States and Canada began in 1920.

Early radio transmitters were too cumbersome to be installed in vehicles. In fact, the first mobile radio systems, for police departments, were one-way, with only a receiver in the police car. The first such system to be considered practical was installed in Detroit in 1928. Two-way police radio, with the equipment occupying most of the car trunk, began in the mid-1930s. Amplitude modulation (AM) was used until the late 1930s, when frequency modulation (FM) began to displace it.

World War II provided a major incentive for the development of mobile and portable radio systems, including two-way systems known as “walkietalkies” that could be carried in the field and might be considered the distant ancestors of today’s cell phones. FM proved its advantages over AM
in the war.

Postwar Expansion
Soon after the end of World War II, two systems were developed that presaged modern wireless communication. AT&T introduced its Improved Mobile Telephone Service (IMTS) in 1946, featuring automatic connection of mobile subscribers to the public switched telephone network (PSTN).

This was an expensive service with limited capacity, but it did allow true mobile telephone service. This system is still in use in some remote areas, where, for instance, it allows access to the PSTN from summer cottages.

The next year, in 1947, the American government set up the Citizens’ Band (CB) radio service. Initially it used frequencies near 460 MHz, but in that respect it was ahead of its time, since equipment for the UHF range was prohibitively expensive.

Frequencies in the 27-MHz band were allocated in 1958, and CB radio immediately became very popular. The service was shortrange, had no connection to the PSTN, and offered users no privacy, but it was (and still is) cheap and easy to set up. The popularity of CB radio has declined in recent years but it is still useful in applications where its short range and lack of connectivity to the rest of the world are not disadvantages.

For example, it serves very well to disseminate information about traffic problems on the highway.
Meanwhile another rather humble-appearing appliance has become ubiquitous: the cordless phone. Usually intended for very short-range communication within a dwelling and its grounds, the system certainly lacks range and drama, but it does have connectivity with the PSTN. Most cordless phones use analog FM in the 46- and 49-MHz bands, but some of the latest models are digital and operate at either 900 MHz or 2.4 GHz. Cordless phones are cheap and simple to use, but their range is limited and, except for the digital models, they offer little privacy.

Pagers were introduced in 1962. The first models merely signaled the user to find a telephone and call a prearranged number. More recent models can deliver an alphanumeric message and even carry a reply. Though relatively limited in function, pagers remain very popular due to their low cost
and small size.

The Cellular Revolution
The world’s first cellular radio service was installed in Japan in 1979, followed in 1983 by North American services. Cellular systems are quite different from previous radiotelephone services such as IMTS in that, instead of using a single powerful transmitter located on a tall tower for wide coverage, the power of each transmitter is deliberately kept relatively small so that the coverage area, called a cell, will also be small.

Many small cells are used so that frequencies can be reused at short distances. Of course, a portable or mobile telephone may move from one cell to another cell during the course of a conversation. In fact, this handoff may occur several times during a conversation. Practical cellular systems had to await the development of computers fast enough and cheap enough to keep track of all this activity.

Theoretically at least, the number of users in a cellular system can be increased indefinitely, simply by making the cells smaller. The first cellular systems used analog FM transmission, but digital modulation schemes, which provide greater privacy and can use bandwidth more efficiently, are used in all the new systems.

These personal communication systems (PCS) usually operate in a higher frequency range (about 1.9 GHz compared with 800 MHz for North American cellular service). Current cellular systems are optimized for voice but can also transmit data. In the near future, high-speed data transmission using PCS is expected to become a reality. 

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