Microprocessors
In 1971 Intel introduced their first microprocessor, the 4004. (4004B pictured here, courtesy of Intel: http://www.intel.com (external link) ) Designed originally for a desktop calculator, the microprocessor was soon improved on and quickly put into all fields of electronics, including cell phones. The original did 4,000 operations a second. According to the June, 2001 issue of Wired magazine, Gordon Moore described the microprocessor as "one of the most revolutionary products in the history of mankind." At the time Intel's chairman Andrew Grove was not so impressed. He reflected that "I was running an assembly line to build memory chips. I saw the microprocessor as a bloody nuisance." Motorola also did much to pioneer the microprocessor and semiconductor field, indeed, in their advertisements of the time, they rightly noted that Motorola circuits were on board each NASA mission since the American space program begain.
In a manuscript submitted to the IEEE Transactions On Communications on September 8, 1971, NTT's Fumio Ikegami explained that his company began studying a nationwide cellular radio system for Japan in 1967. Radio propagation experiments, measuring signal strength and reception in urban areas from mobiles, were ongoing throughout this time, first at 400Mhz and then at 900Mhz. [Ikegami] A successful system trial may have happened in 1975 but I am unable to confirm this. What I can confirm is that Ito and Matsuzaka wrote in late 1977 that "Field tests have been carried out in the Tokyo metropolitan area since 1975 and have now been brought to a successful completion." The two authors wrote this in a major article describing how the first Japanese cellular system would work. [Ito]
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Resources:
Ikegami, Fumio, "Mobile Radio Communications in Japan." IEEE Transactions On Communications Vol. Com-20 No. 4, August 1972: 744
Ito , Sadao and Yasushi Matsuzaka. "800 MHz Band Land Mobile Telephone System -- Overall View." IEEE Transactions on Vehicular Technology, Volume VT-27, No. 4, November 1978, p.205, as reprinted from Nippon Telegraph and Telephone's The Review of the Electrical Communication Laboratories, vol. 25, nos 11-12, November-December, 1977 (English and Japanese)