History of mobile phones

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A man talks on his mobile phone while standing near a conventional telephone box, which stands empty. Enabling technology for mobile phones was first developed in the 1940s but it was not until the mid 1980s that they became widely available. By 2011, it was estimated in the United Kingdom that more calls were made using mobile phones than wired devices.[1]

This history focuses on communication devices which connect wirelessly to the public switched telephone network. The transmission of speech by radio has a long and varied history going back to Reginald Fessenden's invention and shore-to-ship demonstration of radio telephony. The first mobile telephones were barely portable compared to today's compact hand-held devices. Along with the process of developing more portable technology, drastic changes have taken place in the networking of wireless communication and the prevalence of its use.

Predecessors

Before the devices that are now referred to as mobile phones existed, there were some precursors. In 1908 a Professor Albert Jahnke and the Oakland Transcontinental Aerial Telephone and Power Company claimed to have developed a wireless telephone. They were accused of fraud and the charge was then dropped, but they do not seem to have proceeded with production.[2] Beginning in 1918 the German railroad system tested wireless telephony on military trains between Berlin and Zossen.[3] In 1924, public trials started with telephone connection on trains between Berlin and Hamburg. In 1925, the company Zugtelephonie A. G. was founded to supply train telephony equipment and in 1926 telephone service in trains of the Deutsche Reichsbahn and the German mail service on the route between Hamburg and Berlin was approved and offered to 1st class travelers.[4]

File:Simplicissimus Karl Arnold Mobile Telephony.jpg
Karl Arnold drawing of public use of mobile telephones

In 1907, the English caricaturist Lewis Baumer published a cartoon in Punch magazine entitled "Predictions for 1907" in which he showed a man and a woman in London's Hyde Park each separately engaged in gambling and dating on wireless telephony equipment. Then in 1926 the artist Karl Arnold created a visionary cartoon about the use of mobile phones in the street, in the picture "wireless telephony", published in the German satirical magazine Simplicissimus.[5]

The portrayal of a utopia of mobile phone in literature dates back to the year 1931. It is found in Erich Kästner's children's book The 35th of May, or Conrad's Ride to the South Seas:

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A gentleman who rode along the sidewalk in front of them, suddenly stepped off the conveyor belt, pulled a phone from his coat pocket, spoke a number into it and shouted: "Gertrude, listen, I'll be an hour late for lunch because I want to go to the laboratory. Goodbye, sweetheart!" Then he put his pocket phone away again, stepped back on the conveyor belt, started reading a book...

— Erich Kästner

The Second World War made military use of radio telephony links. Hand-held radio transceivers have been available since the 1940s. Mobile telephones for automobiles became available from some telephone companies in the 1940s. Early devices were bulky and consumed high power and the network supported only a few simultaneous conversations. Modern cellular networks allow automatic and pervasive use of mobile phones for voice and data communications.

In the United States, engineers from Bell Labs began work on a system to allow mobile users to place and receive telephone calls from automobiles, leading to the inauguration of mobile service on 17 June 1946 in St. Louis, Missouri. Shortly after, AT&T offered Mobile Telephone Service. A wide range of mostly incompatible mobile telephone services offered limited coverage area and only a few available channels in urban areas. The introduction of cellular technology, which allowed re-use of frequencies many times in small adjacent areas covered by relatively low powered transmitters, made widespread adoption of mobile telephones economically feasible.

One of the earliest fictional descriptions of a mobile phone can be found in the 1948 science fiction novel Space Cadet by Robert Heinlein. The protagonist, who has just traveled to Colorado from his home in Des Moines, receives a call from his father on a pocket telephone. Before going to space he decides to ship the telephone home “since it was limited by its short range to the neighborhood of an earth-side [i.e. terrestrial] relay office.” Ten years later, an essay by Arthur C. Clarke envisioned a "personal transceiver, so small and compact that every man carries one." He wrote: "the time will come when we will be able to call a person anywhere on Earth merely by dialing a number." Such a device would also, in Clarke's vision, include means for global positioning so that "no one need ever again be lost." Later, in Profiles of the Future, he predicted the advent of such a device taking place in the mid-1980s.[6] US TV series Get Smart (1965-1970) depicted spy gadgets with mobile telephones concealed in random objects, including shoes.

In the USSR, Leonid Kupriyanovich, an engineer from Moscow, in 1957-1961 developed and presented a number of experimental models of handheld mobile phones. The weight of one model, presented in 1961, was only 70 g and could fit on a palm.[7][8] However, in the USSR the decision at first to develop the system of the automobile "Altai" phone was made. [9]

In 1965, Bulgarian company "Radioelektronika" presented on the Inforga-65 international exhibition in Moscow the mobile automatic phone combined with a base station. Solutions of this phone were based on a system developed by Leonid Kupriyanovich. One base station, connected to one telephone wire line, could serve up to 15 customers. [10]

The advances in mobile telephony can be traced in successive generations from the early "0G" services like MTS and its successor Improved Mobile Telephone Service, to first generation (1G) analog cellular network, second generation (2G) digital cellular networks, third generation (3G) broadband data services to the current state of the art, fourth generation (4G) native-IP networks.

Early services

MTS

In 1949 AT&T commercialized Mobile Telephone Service. From its start in St. Louis in 1946, AT&T then introduced Mobile Telephone Service to one hundred towns and highway corridors by 1948. Mobile Telephone Service was a rarity with only 5,000 customers placing about 30 000 calls each week. Calls were set up manually by an operator and the user had to depress a button on the handset to talk and release the button to listen. The call subscriber equipment weighed about 36 kg.[11]

Subscriber growth and revenue generation were hampered by the constraints of the technology. Because only three radio channels were available, only three customers in any given city could make mobile telephone calls at one time.[12] Mobile Telephone Service was expensive, costing 15 USD per month, plus 0.30 to 0.40 USD per local call, equivalent to about 176 USD per month and 3.50 to 4.75 per call in 2012 USD.[11]

In the UK there was also a vehicle based system called "Post Office Radiophone Service"[13] it was launched around the city of Manchester in 1959, and although it required callers to speak to an operator, it was possible to be put through to any subscriber in Great Britain. The service was extended to London in 1965 and other major cities in 1972.

IMTS

AT&T introduced the first major improvement to mobile telephony in 1965, giving the improved service the obvious name of Improved Mobile Telephone Service. IMTS used additional radio channels, allowing more simultaneous calls in a given geographic area, introduced customer dialing, eliminating manual call setup by an operator, and reduced the size and weight of the subscriber equipment.[11]

Despite the capacity improvement offered by IMTS, demand outstripped capacity. In agreement with state regulatory agencies, AT&T limited the service to just 40,000 customers system wide. In New York City, for example, 2,000 customers shared just 12 radio channels and typically had to wait 30 minutes to place a call.[11]

Radio Common Carrier

A mobile radio telephone

Radio Common Carrier [14] or RCC was a service introduced in the 1960s by independent telephone companies to compete against AT&T's IMTS. RCC systems used paired UHF 454/459 MHz and VHF 152/158 MHz frequencies near those used by IMTS. RCC based services were provided until the 1980s when cellular AMPS systems made RCC equipment obsolete.

Some RCC systems were designed to allow customers of adjacent carriers to use their facilities, but equipment used by RCCs did not allow the equivalent of modern "roaming" because technical standards were not uniform. For example, the phone of an Omaha, Nebraska–based RCC service would not be likely to work in Phoenix, Arizona. Roaming was not encouraged, in part, because there was no centralized industry billing database for RCCs. Signaling formats were not standardized. For example, some systems used two-tone sequential paging to alert a mobile of an incoming call. Other systems used DTMF. Some used Secode 2805, which transmitted an interrupted 2805 Hz tone (similar to IMTS signaling) to alert mobiles of an offered call. Some radio equipment used with RCC systems was half-duplex, push-to-talk LOMO equipment such as Motorola hand-helds or RCA 700-series conventional two-way radios. Other vehicular equipment had telephone handsets and rotary dials or pushbutton pads, and operated full duplex like a conventional wired telephone. A few users had full-duplex briefcase telephones (radically advanced for their day)

At the end of RCC's existence, industry associations were working on a technical standard that would have allowed roaming, and some mobile users had multiple decoders to enable operation with more than one of the common signaling formats (600/1500, 2805, and Reach). Manual operation was often a fallback for RCC roamers.

Other services

In 1969 Penn Central Railroad equipped commuter trains along the 360 km New York-Washington route with special pay phones that allowed passengers to place telephone calls while the train was moving. The system re-used six frequencies in the 450 MHz band in nine sites.[12]

European mobile radio networks

In Europe, several mutually incompatible mobile radio services were developed. West Germany had a network called A-Netz launched in 1952 as the country's first public commercial mobile phone network. In 1972 this was displaced by B-Netz which connected calls automatically. In 1966 Norway had a system called OLT which was manually controlled.

Cellular concepts

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See also: Cellular network
File:Transmitting tower top us.jpg
A multi-directional, cellular network antenna array ("cell tower")

In December 1947, Douglas H. Ring and W. Rae Young, Bell Labs engineers, proposed hexagonal cells for mobile phones in vehicles.[15] At this stage, the technology to implement these ideas did not exist, nor had the frequencies been allocated. Two decades would pass before Richard H. Frenkiel, Joel S. Engel and Philip T. Porter of Bell Labs expanded the early proposals into a much more detailed system plan. It was Porter who first proposed that the cell towers use the now-familiar directional antennas to reduce interference and increase channel reuse (see picture at right) [16] Porter also invented the dial-then-send method used by all cell phones to reduce wasted channel time.

In all these early examples, a mobile phone had to stay within the coverage area serviced by one base station throughout the phone call, i.e. there was no continuity of service as the phones moved through several cell areas. The concepts of frequency reuse and handoff, as well as a number of other concepts that formed the basis of modern cell phone technology, were described in the late 1960s, in papers by Frenkiel and Porter. In 1970 Amos E. Joel, Jr., a Bell Labs engineer,[17] invented a "three-sided trunk circuit" to aid in the "call handoff" process from one cell to another. His patent contained an early description of the Bell Labs cellular concept, but as switching systems became faster, such a circuit became unnecessary and was never implemented in a system.

A cellular telephone switching plan was described by Fluhr and Nussbaum in 1973,[18] and a cellular telephone data signaling system was described in 1977 by Hachenburg et al.[19]

Emergence of automated services

The first fully automated mobile phone system for vehicles was launched in Sweden in 1956. Named MTA (Mobiltelefonisystem A), it allowed calls to be made and received in the car using a rotary dial. The car phone could also be paged. Calls from the car were direct dial, whereas incoming calls required an operator to locate the nearest base station to the car. It was developed by Sture Laurén and other engineers at Televerket network operator. Ericsson provided the switchboard while Svenska Radioaktiebolaget (SRA) and Marconi provided the telephones and base station equipment. MTA phones consisted of vacuum tubes and relays, and weighed 40 kg. In 1962, an upgraded version called Mobile System B (MTB) was introduced. This was a push-button telephone, and used transistors and DTMF signaling to improve its operational reliability. In 1971 the MTD version was launched, opening for several different brands of equipment and gaining commercial success.[20][21] The network remained open until 1983 and still had 600 customers when it closed.

In 1958 development began on a similar system for motorists in the USSR.[22] The "Altay" national civil mobile phone service was based on Soviet MRT-1327 standard. The main developers of the Altay system were the Voronezh Science Research Institute of Communications (VNIIS) and the State Specialized Project Institute (GSPI). In 1963 the service started in Moscow, and by 1970 was deployed in 30 cities across the USSR. Versions of the Altay system are still in use today as a trunking system in some parts of Russia.

In 1959 a private telephone company located in Brewster, Kansas, USA, the S&T Telephone Company, (still in business today) with the use of Motorola Radio Telephone equipment and a private tower facility, offered to the public mobile telephone services in that local area of NW Kansas. This system was a direct dial up service through their local switchboard, and was installed in many private vehicles including grain combines, trucks, and automobiles. For some as yet unknown reason, the system, after being placed online and operated for a very brief time period, was shut down. The management of the company was immediately changed, and the fully operable system and related equipment was immediately dismantled in early 1960, not to be seen again.[citation needed]

In 1966, Bulgaria presented the pocket mobile automatic phone RAT-0,5 combined with a base station RATZ-10 (RATC-10) on Interorgtechnika-66 international exhibition. One base station, connected to one telephone wire line, could serve up to six customers ("Radio" magazine, 2, 1967; "Novosti dnya" newsreel, 37, 1966).

One of the first successful public commercial mobile phone networks was the ARP network in Finland, launched in 1971. Posthumously, ARP is sometimes viewed as a zero generation (0G) cellular network, being slightly above previous proprietary and limited coverage networks.[citation needed]

Handheld mobile phone

Martin Cooper photographed in 2007 with his 1973 handheld mobile phone prototype

Prior to 1973, mobile telephony was limited to phones installed in cars and other vehicles.[17] Motorola was the first company to produce a handheld mobile phone. On 3 April 1973 when Martin Cooper, a Motorola researcher and executive, made the first mobile telephone call from handheld subscriber equipment, placing a call to Dr. Joel S. Engel of Bell Labs.[23][24] The prototype handheld phone used by Dr. Cooper weighed 1.1 kg and measured 23 cm long, 13 cm deep and 4.45 cm wide. The prototype offered a talk time of just 30 minutes and took 10 hours to re-charge.[25]

John F. Mitchell,[26][27][28] Motorola's chief of portable communication products and Cooper's boss in 1973, played a key role in advancing the development of handheld mobile telephone equipment. Mitchell successfully pushed Motorola to develop wireless communication products that would be small enough to use anywhere and participated in the design of the cellular phone.[29][30]

Analog cellular networks – 1G

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Main article: 1G

First automatic analog cellular systems deployed were NTT's system first used in Tokyo in 1979, later spreading to the whole of Japan, and NMT in the Nordic countries in 1981.

The first analog cellular system widely deployed in North America was the Advanced Mobile Phone System (AMPS).[31] It was commercially introduced in the Americas in October 13, 1983, Israel in 1986, and Australia in 1987. AMPS was a pioneering technology that helped drive mass market usage of cellular technology, but it had several serious issues by modern standards. It was unencrypted and easily vulnerable to eavesdropping via a scanner; it was susceptible to cell phone "cloning;" and it used a Frequency-division multiple access (FDMA) scheme and required significant amounts of wireless spectrum to support.

On 6 March 1983, the DynaTAC mobile phone launched on the first US 1G network by Ameritech. It cost $100m to develop, and took over a decade to reach the market.[32] The phone had a talk time of just thirty-five minutes and took ten hours to charge. Consumer demand was strong despite the battery life, weight, and low talk time, and waiting lists were in the thousands.[33][34]

Many of the iconic early commercial cell phones such as the Motorola DynaTAC Analog AMPS were eventually superseded by Digital AMPS (D-AMPS) in 1990, and AMPS service was shut down by most North American carriers by 2008.

Digital cellular networks – 2G

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Main articles: 2G, 2.5G, and 2.75G
Two 1991 GSM mobile phones with several AC adapters

In the 1990s, the 'second generation' mobile phone systems emerged. Two systems competed for supremacy in the global market: the European developed GSM standard and the U.S. developed CDMA standard. These differed from the previous generation by using digital instead of analog transmission, and also fast out-of-band phone-to-network signaling. The rise in mobile phone usage as a result of 2G was explosive and this era also saw the advent of prepaid mobile phones.

In 1991 the first GSM network (Radiolinja) launched in Finland. In general the frequencies used by 2G systems in Europe were higher than those in America, though with some overlap. For example, the 900 MHz frequency range was used for both 1G and 2G systems in Europe, so the 1G systems were rapidly closed down to make space for the 2G systems. In America the IS-54 standard was deployed in the same band as AMPS and displaced some of the existing analog channels.

In 1993, IBM Simon was introduced. This was possibly the world's first smartphone. It was a mobile phone, pager, fax machine, and PDA all rolled into one. It included a calendar, address book, clock, calculator, notepad, email, and a touchscreen with a QWERTY keyboard.[35] The IBM Simon had a stylus you used to tap the touch screen with. It featured predictive typing that would guess the next characters as you tapped. It had applications, or at least a way to deliver more features by plugging a PCMCIA 1.8 MB memory card into the phone.[36] Coinciding with the introduction of 2G systems was a trend away from the larger "brick" phones toward tiny 100 – 200 gram hand-held devices. This change was possible not only through technological improvements such as more advanced batteries and more energy-efficient electronics, but also because of the higher density of cell sites to accommodate increasing usage. The latter meant that the average distance transmission from phone to the base station shortened, leading to increased battery life while on the move.

Personal Handy-phone System mobiles and modems used in Japan around 1997–2003

The second generation introduced a new variant of communication called SMS or text messaging. It was initially available only on GSM networks but spread eventually on all digital networks. The first machine-generated SMS message was sent in the UK on 3 December 1992 followed in 1993 by the first person-to-person SMS sent in Finland. The advent of prepaid services in the late 1990s soon made SMS the communication method of choice among the young, a trend which spread across all ages.

2G also introduced the ability to access media content on mobile phones. In 1998 the first downloadable content sold to mobile phones was the ring tone, launched by Finland's Radiolinja (now Elisa). Advertising on the mobile phone first appeared in Finland when a free daily SMS news headline service was launched in 2000, sponsored by advertising.

Mobile payments were trialed in 1998 in Finland and Sweden where a mobile phone was used to pay for a Coca Cola vending machine and car parking. Commercial launches followed in 1999 in Norway. The first commercial payment system to mimic banks and credit cards was launched in the Philippines in 1999 simultaneously by mobile operators Globe and Smart.

The first full internet service on mobile phones was introduced by NTT DoCoMo in Japan in 1999.

Mobile broadband data - 3G

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Main article: 3G

As the use of 2G phones became more widespread and people began to utilize mobile phones in their daily lives, it became clear that demand for data (such as access to browse the internet) was growing. Further, experience from fixed broadband services showed there would also be an ever increasing demand for greater data speeds. The 2G technology was nowhere near up to the job, so the industry began to work on the next generation of technology known as 3G. The main technological difference that distinguishes 3G technology from 2G technology is the use of packet switching rather than circuit switching for data transmission.[37] In addition, the standardization process focused on requirements more than technology (2 Mbit/s maximum data rate indoors, 384 kbit/s outdoors, for example).

Inevitably this led to many competing standards with different contenders pushing their own technologies, and the vision of a single unified worldwide standard looked far from reality. The standard 2G CDMA networks became 3G compliant with the adoption of Revision A to EV-DO, which made several additions to the protocol while retaining backwards compatibility:

  • Introduction of several new forward link data rates that increase the maximum burst rate from 2.45 Mbit/s to 3.1 Mbit/s
  • Protocols that would decrease connection establishment time
  • Ability for more than one mobile to share the same time slot
  • Introduction of QoS flags

All these were put in place to allow for low latency, low bit rate communications such as VoIP.[38]

The first pre-commercial trial network with 3G was launched by NTT DoCoMo in Japan in the Tokyo region in May 2001. NTT DoCoMo launched the first commercial 3G network on 1 October 2001, using the WCDMA technology. In 2002 the first 3G networks on the rival CDMA2000 1xEV-DO technology were launched by SK Telecom and KTF in South Korea, and Monet in the USA. Monet has since gone bankrupt. By the end of 2002, the second WCDMA network was launched in Japan by Vodafone KK (now Softbank). European launches of 3G were in Italy and the UK by the Three/Hutchison group, on WCDMA. 2003 saw a further 8 commercial launches of 3G, six more on WCDMA and two more on the EV-DO standard.

During the development of 3G systems, 2.5G systems such as CDMA2000 1x and GPRS were developed as extensions to existing 2G networks. These provide some of the features of 3G without fulfilling the promised high data rates or full range of multimedia services. CDMA2000-1X delivers theoretical maximum data speeds of up to 307 kbit/s. Just beyond these is the EDGE system which in theory covers the requirements for 3G system, but is so narrowly above these that any practical system would be sure to fall short.

The high connection speeds of 3G technology enabled a transformation in the industry: for the first time, media streaming of radio (and even television) content to 3G handsets became possible,[39] with companies such as RealNetworks[40] and Disney[41] among the early pioneers in this type of offering.

In the mid-2000s (decade), an evolution of 3G technology began to be implemented, namely High-Speed Downlink Packet Access (HSDPA). It is an enhanced 3G (third generation) mobile telephony communications protocol in the High-Speed Packet Access (HSPA) family, also coined 3.5G, 3G+ or turbo 3G, which allows networks based on Universal Mobile Telecommunications System (UMTS) to have higher data transfer speeds and capacity. Current HSDPA deployments support down-link speeds of 1.8, 3.6, 7.2 and 14.0 Mbit/s.

By the end of 2007, there were 295 million subscribers on 3G networks worldwide, which reflected 9% of the total worldwide subscriber base. About two thirds of these were on the WCDMA standard and one third on the EV-DO standard. The 3G telecoms services generated over 120 Billion dollars of revenues during 2007 and at many markets the majority of new phones activated were 3G phones. In Japan and South Korea the market no longer supplies phones of the second generation.

Although mobile phones had long had the ability to access data networks such as the Internet, it was not until the widespread availability of good quality 3G coverage in the mid-2000s (decade) that specialized devices appeared to access the mobile internet. The first such devices, known as "dongles", plugged directly into a computer through the USB port. Another new class of device appeared subsequently, the so-called "compact wireless router" such as the Novatel MiFi, which makes 3G internet connectivity available to multiple computers simultaneously over Wi-Fi, rather than just to a single computer via a USB plug-in.

Such devices became especially popular for use with laptop computers due to the added portability they bestow. Consequently, some computer manufacturers started to embed the mobile data function directly into the laptop so a dongle or MiFi wasn't needed. Instead, the SIM card could be inserted directly into the device itself to access the mobile data services. Such 3G-capable laptops became commonly known as "netbooks". Other types of data-aware devices followed in the netbook's footsteps. By the beginning of 2010, E-readers, such as the Amazon Kindle and the Nook from Barnes & Noble, had already become available with embedded wireless internet, and Apple Computer had announced plans for embedded wireless internet on its iPad tablet devices beginning that Fall.

Native IP networks – 4G

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Main article: 4G

By 2009, it had become clear that, at some point, 3G networks would be overwhelmed by the growth of bandwidth-intensive applications like streaming media.[42] Consequently, the industry began looking to data-optimized 4th-generation technologies, with the promise of speed improvements up to 10-fold over existing 3G technologies. The first two commercially available technologies billed as 4G were the WiMAX standard (offered in the U.S. by Sprint) and the LTE standard, first offered in Scandinavia by TeliaSonera.

One of the main ways in which 4G differed technologically from 3G was in its elimination of circuit switching, instead employing an all-IP network. Thus, 4G ushered in a treatment of voice calls just like any other type of streaming audio media, utilizing packet switching over internet, LAN or WAN networks via VoIP.[43]

Thefts

According to the Federal Communications Commission, one out of three robberies involved the theft of a cellular phone. Police data in San Francisco showed that one-half of all robberies in 2012 were thefts of cellular phones. An online petition on Change.org called Secure our Smartphones urged smartphone manuacturers to install kill switches in their devices to make them unusable in case of theft. The petition is part of a joint effort by New York Attorney General Eric Schneiderman and San Francisco District Attorney George Gascon and was directed to the CEOs of the major smartphone manufacturers and telecommunication carriers. [45] On Monday, 10 June 2013, Apple announced it would install a kill switch on its next iPhone operating system, due to debut in October 2013.[46]

Satellite mobile

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Main article: Satellite phone

Earth-orbiting satellites can cover remote areas out of reach of wired networks or where construction of a cellular network is uneconomic. The Inmarsat satellite telephone system, originally developed in 1979 for safety of life at sea, is now also useful for areas out of reach of landline, conventional cellular, or marine VHF radio stations. In 1998 the Iridium satellite system was set up, and although the initial operating company went bankrupt due to high initial expenses, the service is available today.

See also

References

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  6. ↑ Arthur C. Clarke: Profiles of the Future (1962, rev. eds. 1973, 1983, and 1999, Millennium edition with a new preface)
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  8. ↑ Мартин Купер был не первым. Олег Измеров (in Russian).
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  12. ↑ 12.0 12.1 Gordon A. Gow, Richard K. Smith Mobile and wireless communications: an introduction, McGraw-Hill International, 2006 ISBN 0-335-21761-3 page 23
  13. ↑ http://www.btplc.com/today/art91356.html
  14. ↑ https://books.google.ca/books?id=hsA8AAAAIAAJ&pg=PA94&dq=%22radio+common+carrier%22&hl=en&sa=X&ei=caK2VL2xG5PVasaPgsgK&redir_esc=y#v=onepage&q=%22radio%20common%20carrier%22&f=false The Code of Federal Regulations of the United States of America, 47 CFR1 22.2, 10-1-92 Edition, retrieved 2015 Jan 14
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  16. ↑ article by Tom Farley "Cellular Telephone Basics". Privateline.com. Retrieved on 2012-12-30.
  17. ↑ 17.0 17.1 See Amos Joel patent 3,663,762.
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  26. ↑ John F. Mitchell Biography. Brophy.net (2012-08-07). Retrieved on 2012-12-30.
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  28. ↑ Who invented the cell phone?. Brophy.net (2012-08-07). Retrieved on 2012-12-30.
  29. ↑ "Motorola Executive Helped spur Cellphone Revolution, Oversaw Ill-fated Iridium Project". The Wall Street Journal, 20–21 June 2009,
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  38. ↑ Lua error in package.lua at line 80: module 'strict' not found.
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Further reading

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External links

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