When And Why Did The Cell Phone Occur? What Changes Have Been Made To The Cell Phone In The Last 30 Years?


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The thing that made the cell phone concept unique was the idea of "frequency re-use". In the days before cellular radio, there were only a very few radio channels for mobile telephone use, and the usual system installed a transceiver on a high tower or mountain to cover a very large region. The scarcity of channels caused the service to be very expensive, and over-demanded. You could wait a very long time to get a dial-tone to make a phone call.
Cellular phone at the beginning used an idea known as the Frequency Modulation (FM) "capture effect", where if two FM radio signals were being received, the stronger one dominated the reception, excluding the weaker one. This realization made the idea of frequency re-use feasible, and experiments were performed to determine how far away another phone user had to be to allow a radio channel to be re-used. The results of the analysis and experimentation showed frequency re-use to be possible, and even that cells could be sub-divided in regions of higher population density. The early practical experiments were run in the late 1970s.
Early cellphones were about the size and weight of a brick, which made them very difficult to clip onto your belt or tuck into a pocket. Even the early FM phones eventually became smaller.
The advent of digital transmission techniques (like Code-Division-Multiple-Access a.k.a CDMA, and Time-Division-Multiple-Access a.k.a. TDMA, etc.) improved capacity, but took some time to implement because advances in digital signal processing were needed to make them feasible. Eventually these techniques lead to lower power, smaller phones, and higher capacity (more callers on the same amount of frequency space or spectrum). The technological transition was aided by the rapid decrease in the size of the integrated circuits that are used to build cell phones.
The changes in mobile telephony over the past 30 years are amazing. Something that was an expensive luxury, has turned into a commonplace experience, something that even grade-school kids carry around.
There is an old story about a highly respected technical organization (BTL?) and telephone carrier (AT&T?) that hired a consultant to estimate the market for the cellphone, and the conclusion was something like "maybe a few million maximum". Whoops... That was perhaps the biggest marketing mistake of the century!

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