Updated: Thu, Apr 04 2013. 11 40 PM IST
Mumbai: Today’s cellphone is nothing like the one which Martin Cooper, a Motorola researcher and executive, developed for use on a cellular network and on which he made his first call on 3 April 1973, to his rival, Joel S. Engel of Bell Labs. The “brick” or “shoe”, as the hand phone was called, weighed over a kilogram and was 10 inches long. In contrast, today’s cellphones are very slim and have chips that rival those in laptops and personal computers (PCs). Of course, some smartphones also cost as much.
A cellphone is actually an extremely sophisticated radio, but a radio nonetheless. The telephone was invented by Alexander Graham Bell in 1876, and wireless communication can trace its roots to the invention of the radio by Nikola Tesla in the 1880s (formally presented in 1894 by a young Italian named Guglielmo Marconi). It was only natural that these two great technologies would eventually be combined
Both walkie-talkies and citizen band, or CB, radios are half-duplex devices. That is, two people communicating on a CB radio use the same frequency, so only one person can talk at a time. A cellphone is a full-duplex device. That means that you use one frequency for talking and a second, separate frequency for listening. The power consumption of the cellphone, which is normally battery-operated, is relatively low. Low power means small batteries and this is what has made handheld cellular phone possible.
GSM feature phones, the most popular variety—as opposed to CDMA (code division multiple access) ones (for instance, the ones used by Reliance Communications Ltd)—require a small microchip called a Subscriber Identity Module or SIM Card, to function. The SIM card is approximately the size of a small postage stamp (today’s micro-SIMs and nano-SIMs, used in some smartphones, are even tinier) and is usually placed underneath the battery in the rear of the unit. The SIM securely stores the service-subscriber key (IMSI) and allows users to change phones by simply removing the SIM card from one mobile phone and inserting it into another. The first SIM card was made in 1991 by Munich smart card maker Giesecke and Devrient for the Finnish wireless network operator Radiolinja. A hybrid mobile phone can hold up to four SIM cards.
SIM and RUIM (Removable User Identity Module) cards may be mixed together to allow both GSM and CDMA networks to be accessed, popular in countries such as India.
Today’s smartphones take advantage of third generation or 3G technology which have potential transfer speeds of up to 3 Mbps (about 15 seconds to download a three-minute MP3 song). Compared with that, the fastest 2G phones can achieve up to 144Kbps (about eight minutes to download a three-minute song). None of this would be possible without towers that carry cellphone signals from phone to phone.
India also has the speedier 4G services in some metros being offered by telecom operators such asBharti Airtel Ltd. In March 2008, the International Telecommunications Union-Radio communications sector (ITU-R) specified a set of requirements for 4G standards, named the International Mobile Telecommunications-Advanced (IMT-Advanced) specification, setting peak speed requirements for 4G service at 100 megabits per second (Mbit/s) for high mobility communication (such as from trains and cars) and 1 gigabit per second (Gbit/s) for low mobility communication (such as pedestrians and stationary users).
Since the first-release versions of Mobile WiMAX (which failed in India) and LTE (long term evolution) support much less than 1 Gbit/s peak bit rate, they are not fully IMT-Advanced compliant, but are often branded 4G by service providers. Reliance Industries Ltd is expected to launch its LTE service by the year end.
Fifth generation, or 5G, is not officially used for any specification or official document yet made public by telecommunication companies or standardization bodies, and standard releases beyond 4G are in progress by standardization bodies, but are at this time not considered as new mobile generations but under the 4G umbrella
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