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Cellular Communications ExplainedFrom Basics to 3G
By Ian Poole
NewnesCopyright © 2006 Ian Poole
All right reserved.
Chapter OneIntroduction to cellular telecommunications
Mobile phone technology is now a major aspect of today's life, both business and personal. Instant access to people, wherever they are, is now an accepted part of today's culture. Business requires that people, whether at home or abroad, remain in constant touch, and this is now possible through the development of the mobile phone. In their private lives people have also come to depend on mobile phones, initially using them sparingly and only in cases of emergency, but they have now become an accepted part of everyday life. Many people do not have a traditional landline, and rely only on the mobile for their telecommunications requirements.
Before work started on developing the mobile phone itself, there were many technologies that needed to be in place. Obviously the work of the early pioneers, including Volta, Ampère, Galvani and many more who established the foundations of electricity, was paramount. However, electricity was not used as a means of communication for a number of years. Long-distance communication was generally by written message carried by a courier. Other systems were also used, but these were either mechanical or crude in nature – for example, a network of bonfires was set up along the South of England to warn of the invasion by the Spanish Armada, and in 1792 Claude Chappe devised and installed some semaphore towers in France, for which the word telegraph was coined. However, it took the discovery of electromagnetism by Hans Christian Oersted before viable electrical systems could be developed. One of the first schemes to be tested was developed by Wheatsone and Cooke. This used a variety of needles to point to the relevant letter. Although a trial system was installed between Paddington Station in London and Slough to the west of London, its use was never widespread because it required five wires – and insulated wire was very expensive at the time. Nevertheless, the imagination of the public was fired when a murderer was arrested as a result of this telegraph. A man named John Tawell had escaped from the scene of the crime in Slough, travelling on the train to London. A description of Tawell was sent ahead to Paddington Station by telegraph, and he was arrested on his arrival there.
It took an inventive American named Samuel Morse to devise a viable system. An unlikely inventor, Morse was an artist – one of the finest that America has ever produced. On a return ship journey from Europe he heard about the discovery of the electromagnet, and started to think of ways it could be used in an electrical communication system. On his return to the USA, his painting and teaching activities took precedence and the idea lay dormant. However, he enlisted the help of some others to speed the development, and the system for opening and closing a circuit to send a series of coded characters started to come together. Realizing that they would need backing from large organizations if they were to be able to install the system, they took the idea around several organizations but there was little interest and the group split. Morse persevered, and eventually managed to secure a grant from the US Congress to install a trial system from Washington to Baltimore. On 24 May 1844, he sent the famous message 'What hath God wrought'. This started one of the largest communications revolutions ever, and the Morse system (see Figure 1.1), with its accompanying Morse code, entered the history books. The idea quickly spread, not only through the USA, but also worldwide. In Britain, for example, the telegraph enabled the government in London to communicate with people in the colonies around the world.
The next major event was the development of the telephone. After the invention of the telegraph, a number of people worked on transmitting sound over wires. In 1857 an Italian-American named Antonio Meucci developed a primitive telephone system but, coming from a poor background, he was unable to obtain any financial backing. The traditionally acknowledged inventor of the telephone was a Scot named Alexander Graham Bell.
Bell conceived his idea in the summer of 1874, which was to generate a 'speech shaped electric current'. To achieve this, in June 1875 Bell tried a system whereby a stretched parchment membrane, with one end of a ferro-metallic reed attached to the centre, was placed over the pole of an electromagnet. Sounds caused the reed to vibrate over the electromagnet and generate a 'speech shaped electric current'. However, the results were a little disappointing, as the sounds it produced were very muffled. The following year Bell tried a new system. This consisted of a damped reed receiver and a new type of transmitter or microphone – an idea that had previously been tried by Elisha Gray in his telephony work. The device consisted of a diaphragm, attached to which was a metal wire which hung into a dilute acid solution; the sounds from the diaphragm would move the wire up and down in the acid, thereby changing the resistance of the circuit. The first telephone message took place on 10 March 1876 when Bell spoke to his assistant, saying 'Mr Watson, come here, I want you'. Bell had spilled some acid over his clothes and wanted some assistance. With this success the telephone system was born, and it soon started to make a large impact.
Although originally Bell was credited with the invention of the telephone, in recent years the American Congress has given that honour to Antonio Meucci. Meucci had filed a law suit against Bell, but did not have the means to support it and died before it came to court.
With the telephone system established, the next major development was that of wireless (or radio) technology. James Clerk Maxwell was the first to deduce mathematically the existence of electromagnetic waves. It then fell to Hertz to prove their existence, relating them to Maxwell's equations, although a number of other people before him had undoubtedly seen effects of radio waves.
Initially Hertzian waves (as they were first known) were seen as little more than a scientific novelty. However, a young Italian named Marconi did much to exploit them and apply them to practical uses for communication. Seeing their potential for enabling communication between ships, he first approached the Italian navy; when he was turned down, he came to Britain with his mother (who was of Irish stock) and started to develop his ideas here. He successfully demonstrated communications over increasing distances, finally, in 1901, transmitting a signal across the Atlantic.
Marconi concentrated on the marine market, as did many others. Here, wireless was the only means of communication over long distances, and it was especially valuable in sending distress messages. A station was set up in the South Goodwin Lightship, not far from Dover in the UK, and a link between the lightship and the South Foreland lighthouse enabled a number of emergencies to be reported – including one where a ship named the S.S. R.F. Matthews collided with the lightship.
Radio technology continued to develop, especially with the introduction of the thermionic valve (Figure 1.2). This enabled signals to be amplified and processed more effectively. Until this point receivers had been severely limited by a lack of sensitivity. Also, transmitters were often spark transmitters that spread their energy over a wide range of frequencies. The introduction of the valve enabled oscillators using a single frequency to be built.
The two world wars gave impetus to radio technology development, but the next major step forward took place after the Second World War. A research programme had been organized in the USA, by Bell Laboratories, to investigate the possible use of semiconductors in electronics. Teams were set up to work on different areas of semiconductor-related research. One team, headed up by Shockley and including Bardeen and Brattain, started to investigate a three-terminal field-effect device. Initially unable to make it operate, they switched their efforts to other areas. Eventually they managed to develop a device consisting of two back-to-back diodes, which was the first transistor – a point-contact device that provided gain. After having the idea, they tried it and it worked first time. A week later, on the day before Christmas Eve 1947, they demonstrated it to executives at Bell.
While the transistor was being developed, others at Bell Laboratories were looking ahead to other ideas. In 1947, D. H. Ring put forward a proposal for a radio system that would use a number of lower power transmitters in 'cells' to enable the re-use of frequencies – a critical element if a large number of people were to be allowed access to a system. The proposal even mentioned the need for a method of 'handing over' the mobile station from one cell to the next as it moved along. However, Ring's document does not state how this might be achieved. Moreover, radio and electronics technology had not advanced sufficiently for the idea to be implemented and, as a result, it lay dormant for several years.
Meanwhile, transistor technology started to advance. The original point-contact transistor was not reliable and, only a few weeks after the invention of the first transistor, Shockley proposed the junction transistor. With further developments in semiconductor technology, improved methods of processing the materials and of manufacturing were developed. As a result, transistors became cheaper to produce, their performance improved and they became more reliable, leading to an increase in their use. The field-effect transistor that Bardeen, Brattain and Shockley had tried to develop also came to fruition, and was to play an important part in one of the next major developments – that of the integrated circuit.
There had been a number of projects set up to investigate how electronic circuits could be made smaller and more reliable. However, the development of the integrated circuit has been attributed to two individuals. The first was Jack Kilby, then a young engineer working for Texas Instruments. Having insufficient leave, he had to work during the company shutdown. As there was little call on his time from others, and all the equipment he needed was available, he started work on developing a small oscillator on a single chip of silicon. Working on his own, he made the first circuits work successfully on 12 September 1958. The second, Robert Noyce, working for Fairchild, reasoned that it was nonsensical to make a large number of individual transistors on a wafer, cut them up to make separate transistors and then reassemble them when equipment was constructed. Noyce applied this concept, and set down many of the foundations on which today's integrated circuit industry is founded.
With many of the enabling technologies in place, the scene was set for mobile phone technology to start to become a reality. There had been a number of intermediate steps along the way. Mobile radio was already in use. The first walkie-talkies had been made in the USA by Motorola in 1940, and were still very heavy (35 lb, or about 16 kg), but they enabled the military to have radio communications on the move. After the war, mobile car telephones were introduced – the first from AT&T in St Louis, Missouri, USA, in 1946. The service was very successful, and soon spread to twenty-four other cities. However, these telephones were effectively two-way radios linked to the ordinary phone network. The services used a transmitter–receiver station located in the centre of the relevant city and, accordingly, had limited range. Also, owing to the limited number of frequencies available, there was a waiting list many times longer than the number of people who were connected. Services were also set up in other countries around the world, with the same problems of waiting lists longer than the number of users.
Seeing the popularity of these services, and realizing their potential, the idea of a cellular system like that previously suggested by Ring resurfaced. AT&T lobbied the FCC (Federal Communications System) in the USA repeatedly between 1958 and 1968, and finally the FCC agreed to set aside some frequencies for an experimental system. As a result, a radio telephone system employing frequency re-use was set up aboard a train in 1969. A total of six channels in several zones were used along the route, which spanned over 200 miles, with the system under computer control.
Meanwhile, in the late 1960s and early 1970s a number of countries started to consider seriously the possibility of a cellular telecommunications system. In Japan, for example, the Nippon Telegraph and Telephone Company proposed a nationwide cellular system at 800 MHz. Ideas also started to move forward in Finland. Then, in December 1970, in the USA, the Bell Telephone Laboratories submitted a patent proposal.
Excerpted from Cellular Communications Explained by Ian Poole Copyright © 2006 by Ian Poole. Excerpted by permission of Newnes. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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