History of Cellular Phones

The basic concept of cellular phones began in 1947 when researchers looked at crude mobile (car) phones and realized that by using small cells (range of service area) with frequency reuse could increase the traffic capacity of mobile phones substantially, however, the technology to do it was nonexistent.

Anything to do with broadcasting and sending a radio or television message out over the airwaves comes under a Federal Communications Commission (FCC) regulation that a cellular phone is actually a type of two-way radio. In 1947, AT&T proposed that the FCC allocate a large number of radio spectrum frequencies so that wide-spread mobile phone service could become feasible and AT&T would have a incentive to research the new technology. We can partially blame the FCC for the gap between the concept of cellular phone service and it's availability to the public. Because of the FCC decision to limit the cellular phone frequencies in 1947, only twenty three cellular phone conversations could occur simultaneously in the same service area - not a market incentive for research.

The FCC reconsidered it's position in 1968, and stated "if the technology to build a better mobile phone service works, we will increase the cellular phone frequencies allocation, freeing the airwaves for more mobile phones." AT&T - Bell Labs proposed a cellular phone system to the FCC of many small, low-powered broadcast towers, each covering a 'cell' a few miles in radius, collectively covering a larger area. Each tower would use only a few of the total frequencies allocated to the cellular phone system, and as cars moved across the area their cellular phone calls would be passed from tower to tower.

Individual Inventors & Mobile Phone Patents

Dr. Martin Cooper for Motorola. US03906166 09/16/1975 Radio telephone system Martin Cooper, Richard W. Dronsuth, ; Albert J. Mikulski, Charles N. Lynk Jr., James J. Mikulski, John F. Mitchell, Roy A. Richardson, John H. Sangster

Related Class Patents Related to cellular phone patents and cordless phones, 64 patents listed.

By 1977, AT&T Bell Labs constructed and operated a prototype cellular phone system. A year later, public trials of the new cellular phone system were started in Chicago, IL with over 2000 trial cellular phone customers. In 1979, the first commercial cellular phone system began operation in Tokyo. In 1981, Motorola and American Radio phone started a second U.S. cellular radio-phone system test in the Washington/Baltimore area. By 1982, the slow moving FCC finally authorized commercial cellular phone service for the USA. A year later, the first American commercial for analog cellular phone service or AMPS (Advanced Mobile Phone Service) was offered in Chicago, IL by Ameritech. Despite the incredible demand, it took cellular phone service 37 years to become commercially available in the United States.

Consumer demand quickly outstripped the cellular phone system's 1982 standards, by 1987, cellular phone subscribers exceeded one million, and the airways were crowded. Three ways of improving services existed:

• one - increase cellular phone frequencies allocation
• two - split existing cellular phone cells
• three - improve the cellular phone technology
  

The FCC did not want to handout any more bandwidth and building/splitting cells would have been expensive and add bulk to the cellular phone network. To stimulate the growth of new cellular phone technology, the FCC declared in 1987 that cellular phone licensees may employ alternative cellular phone technologies in the 800 MHz band. The cellular phone industry began to research new transmission technology as an alternative.

For more information on Cellular Phone Technology, read Cellular Telephony by Brian Oblivion.

How Mobile Telephone Calls Are Handled

Telephone customer (1) dials 'Long Distance' and asks to be connected with the mobile services operator, to whom he gives the telephone number of the vehicle he wants to call. The operator sends out a signal from the radio control terminal (2) which causes a lamp to light and a bell to ring in the mobile unit (3). Occupant answers his telephone, his voice traveling by radio to the nearest receiver (4) and thence by telephone wire.

To place a call from a vehicle, the occupant merely lifts his telephone and presses a 'talk' button. This sends out a radio signal which is picked up by the nearest receiver and transmitted to the operator.[BLR1]

(The above accompanies a Bell Laboratories Record illustration, from the 1946 article first describing the system. It's a 346k download.)

The 20 watt mobile sets did not transmit back to the central tower but to one of five receivers placed across the city.[BLR2] Once a mobile went off hook all five receivers opened. The Mobile Telephone Service or MTS system combined signals from one or more receivers into a unified signal, amplifying it and sending it on to the toll switchboard. This allowed roaming from one city neighborhood to another. Can't visualize how this worked? Imagine someone walking through a house with several telephones off hook. A party on the other end of the line would hear the person moving from one room to another, as each telephone gathered a part of the sound.

One party talked at a time with MTS. You pushed a handset button to talk, then released the button to listen. (This eliminated echo problems which took years to solve before natural, full duplex communications were possible.) Mobile telephone service was not simplex operation as many writers describe, but half duplex operation. Simplex uses only one frequency to both transmit and receive. In MTS the base station frequency and mobile frequency were offset by five kHz. Privacy is one reason to do this; eavesdroppers could hear only one side of a conversation. Like a citizen's band radio, a caller searched manually for an unused frequency before placing a call. But since there were so few channels this wasn't much of a problem. This does point out radio-telephones' greatest problem of the time: too few channels.

This system presaged many cellular developments, indeed, Bell Laboratories' D.H. Ring articulated the cellular concept one year later in an unpublished paper. Young states all the elements were known then: a network of small geographical areas called cells, a low powered transmitter in each, the cell traffic controlled by a central switch, frequencies reused by different cells and so on. Young states that from 1947 Bell teams "had faith that the means for administering and connecting to many small cells would evolve by the time they were needed." [Young] While recognizing the Laboratories' prescience, more mobile telephones were always needed. In every city where mobile telephone service was introduced waiting lists developed, growing every year. By 1976 only 545 customers in New York City had Bell System mobiles, with 3,700 customers on the waiting list. Around the country 44,000 Bell subscribers had AT&T mobiles but 20,000 people sat on five to ten year waiting lists. [Gibson] Despite this incredible demand it took cellular 37 years to go commercial from the mobile phone's introduction. But the FCC's regulatory foot dragging slowed cellular as well. Until the 1980s they never made enough channels available; as late as 1978 the Bell System, the Independents, and the non-wireline carriers divided just 54 channels nationwide. [O'Brien] That compares to the 666 channels the first AMPS systems needed to work.

In mobile telephony a channel is a pair of frequencies. One frequency to transmit on and one to receive. It makes up a circuit or a complete communication path. Sounds simple enough to accommodate. Yet the radio spectrum is extremely crowded. In the late 1940s little space existed at the lower frequencies most equipment used. Inefficient radios contributed to the crowding, using 60 kHz to send an signal that can now be done with 10kHz or less. But what could you do with just six channels, no matter what the technology? Users by the scores vied for an open frequency. You had, in effect, a wireless party line, with perhaps forty subscribers fighting to place calls on each channel. Most mobile telephone systems couldn't accommodate more than 250 people. There were other problems.

Radio waves at lower frequencies travel great distances, sometimes hundreds of miles when they skip across the atmosphere. High powered transmitters gave mobiles a wide operating range but added to the dilemma. Telephone companies couldn't reuse their precious channels in nearby cities, lest they interfere with their own systems. They needed at least seventy five miles between systems before they could use them again. While better frequency reuse techniques might have helped, something doubtful with the technology of the times, the FCC held the key to opening more channels for wireless.

In 1947 AT&T began operating a "highway service", a radio-telephone offering that provided service between New York and Boston. It operated in the 35 to 44MHz band and caused interference from to time with other distant services. Even AT&T thought the system unsuccessful.

In that same year the Bell System asked the FCC for more frequencies. The FCC allocated a few more channels in 1949, but gave half to other companies wanting to sell mobile telephone service.

Berresford says "these radio common carriers or RCCs, were the first FCC-created competition for the Bell System" He elaborates on the radio common carriers, a group of market driven businessmen who pushed mobile telephony in the early years further and faster than the Bell System:

The telephone companies and the RCCs evolved differently in the early mobile telephone business. The telephone companies were primarily interested in providing ordinary, 'basic' telephone service to the masses and, therefore, gave scant attention to mobile services throughout the 1950s and 1960s. The RCCs were generally small entrepreneurs that were involved in several related businesses-- telephone answering services, private radio systems for taxicab and delivery companies, maritime and air-to-ground services, and 'beeper' paging services. As a class, the RCCs were more sales-oriented than the telephone companies and won many more customers; a few became rich in the paging business. The RCCs were also highly independent of each other; aside from sales, their specialty was litigation, often tying telephone companies (and each other) up in regulatory proceedings for years.

As proof of their competitiveness, the RCCs serviced 80,000 mobile units by 1978, twice as many as Bell. This growth built on a strong start, the introduction of automatic dialing in 1948. On March 1, 1948 the first fully automatic radiotelephone service began operating in Richmond, Indiana, eliminating the operator to place most calls. [McDonald] The Richmond Radiotelephone Company bested the Bell System by 16 years. AT&T didn't provide automated dialing for most mobiles until 1964, lagging behind automatic switching for wireless as they had done with landline telephony. (As an aside, the Bell System did not retire their last cord switchboard until 1978.) Most systems, though, RCCs included, still operated manually until the 1960s. Interestingly, some claim the Swedish Telecommunications Administration's S. Lauhrén designed the world's first automatic mobile telephone system, with a Stockholm trial starting in 1951.

I've found no literature to support a claim they were the first, before the 1948 Richmond Telephone Company service. For completeness, I should mention the following.

Anders Lindeberg of the Swedish Museum of Science and Technology does point out the link I provide in the preceding paragraph is "a summary from an article in the yearbook "Daedalus" (1991) for the Swedish Museum of Science and Technology http://www.tekmu.se/

The Swedish original article is much more extensive than the summary." He adds that "The Mobile Phone Book" by John Meurling and Richard Jeans, ISBN 0-9524031-02 published by Communications Week International, London in 1994 does briefly describe the "MTL" from 1951.

Speaking of Sweden, let's go to Europe to read about a typical radio-telephone unit, something similar to American installations:

It was in the mid-1950's that the first phone-equipped cars took to the road. This was in Stockholm - home of Ericsson's corporate headquarters - and the first users were a doctor-on-call and a bank-on-wheels. The apparatus consisted of receiver, transmitter and logic unit mounted in the boot of the car, with the dial and handset fixed to a board hanging over the back of the front seat. It was like driving around with a complete telephone station in the car. With all the functions of an ordinary telephone, the telephone was powered by the car battery. Rumor has it that the equipment devoured so much power that you were only able to make two calls - the second one to ask the garage to send a breakdown truck to tow away you, your car and your flat battery. . . These first car phones were just too heavy and cumbersome - and too expensive to use - for more than a handful of subscribers. It was not until the mid-1960's that new equipment using transistors were brought onto the market. Weighing a lot less and drawing not nearly so much power, mobile phones now left plenty of room in the boot - but you still needed a car to be able to move them around.

In 1956 the Bell System began providing manual radio-telephone service at 450 MHz, a new frequency band assigned to overcrowding. AT&T did not automate this service until 1969. In 1958 the innovative Richmond Radiotelephone Company improved their automatic dialing system. They added new features to it, including direct mobile to mobile communications.

Other independent telephone companies and the Radio Common Carriers made similar advances to mobile-telephony throughout the 1950s and 1960s. If this subject interests you, The Independent Radio Engineer Transactions on Vehicle Communications, later renamed the IEEE Transactions on Vehicle Communications, is the publication to read during those years.

In that same year the Bell System petitioned the FCC to grant 75 MHz worth of spectrum to radio-telephones in the 800 MHz band. The FCC had not yet allowed any channels below 500MHz, where there was not enough continuous spectrum to develop an efficient radio system. Despite the Bell System's forward thinking, the FCC sat on this proposal for ten years and only considered it in 1968 when requests for more frequencies became so backlogged that they could not ignore them.

In 1964 the Bell System introduced Improved Mobile Telephone Service or IMTS, a replacement to the badly aging Mobile Telephone System. It worked in full-duplex so people didn't have to press a button to talk. Talk went back and forth just like a regular telephone. It finally permitted direct dialing, automatic channel selection and reduced bandwidth to 25-30 kHz.

Before leaving conventional radio telephony I should mention fraud. As telephone folks were well acquainted with landline toll fraud, begun in earnest in the late 1960s, so they were aware of wireless fraud. Here's a summary from a 1985 article in Personal Communications Technology Magazine: "The earliest form of mobile telephony, unsquelched manual Mobile Telephone Service (MTS), was vulnerable to interception and eavesdropping. To place a call, the user listened for a free channel. When he found one, he would key his microphone to for service: 'Operator, this is Mobile 1234; may I please have 555-7890.' The operator knew to submit a billing ticket for account number 1234 to pay for the call. So did anybody else listening to the channel--hence the potential for spoofing and fraud.

Squelched channel MTS hid the problem only slightly because users ordinarily didn't overhear channels being used by other parties. Fraud was still easy for those who turned off the squelch long enough to overhear account numbers.

Direct-dial mobile telephone services such as Improved Mobile Telephone Service (IMTS) obscured the problem a bit more because subscriber identification was made automatically rather than by spoken exchange between caller and operator. Each time a user originated a call, the mobile telephone transmitted its identification number to the serving base station using some form of Audio Frequency Shift Keying (AFSK), which was not so easy for eavesdroppers to understand.

Committing fraud under IMTS required modification of the mobile--restrapping of jumpers in the radio unit, or operating magic keyboard combinations in later units--to reprogram the unit to transmit an unauthorized identification number. Some mobile control heads even had convenient thumb wheel switches installed on them to facilitate easy and frequent ANI (Automatic Number Identification) changes."

Mobile Phone History

Digital wireless and cellular roots go back to the1940s when commercial mobile telephony began. Compared to today's furious pace of development, it may seem odd that wireless didn't come along sooner. There are many reasons for that. Technology, disinterest, and to some extent regulation limited early United States radio-telephone development. As the vacuum tube and the transistor made possible the early telephone network, the wireless revolution began only after low cost microprocessors and digital switching became available. And while the Bell System built the finest landline telephone system in the world, they never seemed truly committed to mobile telephony. Their wireless engineers were brilliant and keen but the System itself held them back. Federal regulations also hindered many projects but in Europe, where state run telephone companies controlled their own telecom development, although, admittedly, without competition, wireless came no sooner, and in most cases, later. Starting in 1921 in the United States mobile radios began operating at 2 MHz, just above the present A.M. radio broadcast band. [Young] These were chiefly experimental police department radios, with practical systems not implemented until the 1940s. [FCC] Police and emergency services drove mobile radio pioneering, with little thought given to private telephone use.

In 1934 the United States Congress created the Federal Communications Commission. In addition to regulating landline interstate telephone business, they also began managing the radio spectrum. It decided who would get what frequencies. It gave priority to emergency services, government agencies, utility companies, and services it thought helped the most people. Radio users like a taxi service or a tow truck dispatch company required little spectrum to conduct their business. Radio telephone used large frequency allocations to serve a few people. The FCC designated no radio-telephone channels until after World War II.

On June 17, 1946 in Saint Louis, Missouri, AT&T and Southwestern Bell introduced the first American commercial mobile radio-telephone service. Mobiles used newly issued vehicle radio-telephone licenses granted to Southwestern Bell by the FCC. They operated on six channels in the 150 MHz band with a 60 kHz channel spacing. [Peterson] Bad cross channel interference, something like cross talk in a landline phone, soon forced Bell to use only three channels. In a rare exception to Bell System practice, subscribers could buy their own radio sets and not AT&T's equipment. Installed high above Southwestern Bell's headquarters at 1010 Pine Street, a centrally located antenna transmitting 250 watts paged mobiles and provided radio-telephone traffic on the downlink. Operation was straightforward, as the following describes:

Mobile phone networks

The most common example of a cellular network is a mobile phone (cell phone) network. A mobile phone is a portable telephone which receives or makes calls through a cell site (base station), or transmitting tower. Radio waves are used to transfer signals to and from the cell phone. Large geographic areas (representing the coverage range of a service provider) may be split into smaller cells to avoid line-of-sight signal loss and the large number of active phones in an area. In cities, each cell site has a range of up to approximately ½ mile, while in rural areas, the range is approximately 5 miles. Many times in clear open areas, a user may receive signals from a cellsite 25 miles away. All of the cell sites are connected to cellular telephone exchanges "switches", which connect to a public telephone network or to another switch of the cellular company.

As the phone user moves from one cell area to another cell, the switch automatically commands the handset and a cell site with a stronger signal (reported by each handset) to switch to a new radio channel (frequency). When the handset responds through the new cell site, the exchange switches the connection to the new cell site.

With CDMA, multiple CDMA handsets share a specific radio channel. The signals are separated by using a pseudonoise code (PN code) specific to each phone. As the user moves from one cell to another, the handset sets up radio links with multiple cell sites (or sectors of the same site) simultaneously. This is known as "soft handoff" because, unlike with traditional cellular technology, there is no one defined point where the phone switches to the new cell.

Modern mobile phone networks use cells because radio frequencies are a limited, shared resource. Cell-sites and handsets change frequency under computer control and use low power transmitters so that a limited number of radio frequencies can be simultaneously used by many callers with less interference.

Since almost all mobile phones use cellular technology, including GSM, CDMA, and AMPS (analog), the term "cell phone" is used interchangeably with "mobile phone". However, satellite phones are mobile phones that do not communicate directly with a ground-based cellular tower, but may do so indirectly by way of a satellite.

Old systems predating the cellular principle may still be in use in places. The most notable real hold-out is used by many amateur radio operators who maintain phone patches in their clubs' VHF repeaters.

There are a number of different digital cellular technologies, including: Global System for Mobile Communications (GSM), General Packet Radio Service (GPRS), Code Division Multiple Access (CDMA), Evolution-Data Optimized (EV-DO), Enhanced Data Rates for GSM Evolution (EDGE), 3GSM, Digital Enhanced Cordless Telecommunications (DECT), Digital AMPS (IS-136/TDMA), and Integrated Digital Enhanced Network (iDEN).

Coverage comparison

Following table shows the dependency of frequency on coverage area of one cell of a CDMA2000 network:^[3]

Frequency (MHz)	Cell radius (km)	Cell area (km2)	Relative Cell Count
450	48.9	7521	1
950	26.9	2269	3.3
1800	14.0	618	12.2
2100	12.0	449	16.2

Frequency choice

The effect of frequency on cell coverage means that different frequencies serve better for different uses. Low frequencies, such as 450 MHz NMT, serve very well for countryside coverage. GSM 900 (900 MHz) is a suitable solution for light urban coverage. GSM 1800 (1.8 GHz) starts to be limited by structural walls. This is a disadvantage when it comes to coverage, but it is a decided advantage when it comes to capacity. Pico cells, covering e.g. one floor of a building, become possible, and the same frequency can be used for cells which are practically neighbours. UMTS, at 2.1 GHz is quite similar in coverage to GSM 1800. At 5 GHz, 802.11a Wireless LANs already have very limited ability to penetrate walls and may be limited to a single room in some buildings. At the same time, 5 GHz can easily penetrate windows and goes through thin walls so corporate WLAN systems often give coverage to areas well beyond that which is intended.

Moving beyond these ranges, network capacity generally increases (more bandwidth is available) but the coverage becomes limited to line of sight. Infra-red links have been considered for cellular network usage, but as of 2004^[update] they remain restricted to limited point-to-point applications.

Cell service area may also vary due to interference from transmitting systems, both within and around that cell. This is true especially in CDMA based systems. The receiver requires a certain signal-to-noise ratio. As the receiver moves away from the transmitter, the power transmitted is reduced. As the interference (noise) rises above the received power from the transmitter, and the power of the transmitter cannot be increased any more, the signal becomes corrupted and eventually unusable. In CDMA-based systems, the effect of interference from other mobile transmitters in the same cell on coverage area is very marked and has a special name, cell breathing.

Old fashioned taxi radio systems generally use low frequencies and high sited transmitters, probably based where the local radio station has its mast. This gives a very wide area coverage in a roughly circular area surrounding each mast. Since only one user can talk at any given time, coverage area doesn't change with number of users. The reduced signal to noise ratio at the edge of the cell is heard by the user as crackling and hissing on the radio.

One can see examples of cell coverage by studying some of the coverage maps provided by real operators on their web sites. In certain cases they may mark the site of the transmitter, in others it can be calculated by working out the point of strongest coverage.

Frequency reuse

The increased capacity in a cellular network, compared with a network with a single transmitter, comes from the fact that the same radio frequency can be reused in a different area for a completely different transmission. If there is a single plain transmitter, only one transmission can be used on any given frequency. Unfortunately, there is inevitably some level of interference from the signal from the other cells which use the same frequency. This means that, in a standard FDMA system, there must be at least a one cell gap between cells which reuse the same frequency.

The frequency reuse factor is the rate at which the same frequency can be used in the network. It is 1/K (or K according to some books) where K is the number of cells which cannot use the same frequencies for transmission. Common values for the frequency reuse factor are 1/3, 1/4, 1/7, 1/9 and 1/12 (or 3, 4, 7, 9 and 12 depending on notation).

In case of N sector antennas on the same base station site, each with different direction, the base station site can serve N different sectors. N is typically 3. A reuse pattern of N/K denotes a further division in frequency among N sector antennas per site. Some current and historical reuse patterns are 3/7 (North American AMPS), 6/4 (Motorola NAMPS), and 3/4 (GSM).

If the total available bandwidth is B, each cell can only utilize a number of frequency channels corresponding to a bandwidth of B/K, and each sector can use a bandwidth of B/NK.

Code division multiple access-based systems use a wider frequency band to achieve the same rate of transmission as FDMA, but this is compensated for by the ability to use a frequency reuse factor of 1, for example using a reuse pattern of 1/1. In other words, adjacent base station sites use the same frequencies, and the different base stations and users are separated by codes rather than frequencies. While N is shown as 1 in this example, that does not mean the CDMA cell has only one sector, but rather that the entire cell bandwidth is also available to each sector individually.

Depending on the size of the city, a taxi system may not have any frequency-reuse in its own city, but certainly in other nearby cities, the same frequency can be used. In a big city, on the other hand, frequency-reuse could certainly be in use.

Cellular telephone frequency reuse pattern. See U.S. Patent 4,144,411

Although the original 2-way-radio cell towers were at the centers of the cells and were omni-directional, a cellular map can be redrawn with the cellular telephone towers located at the corners of the hexagons where three cells converge.^[1] Each tower has three sets of directional antennas aimed in three different directions and receiving/transmitting into three different cells at different frequencies. This provides a minimum of three channels for each cell. The numbers in the illustration are channel numbers, which repeat every 3 cells. Large cells can be subdivided into smaller cells for high volume areas.^[2]

[edit] Movement from cell to cell and handover

In a primitive taxi system, when the taxi moved away from a first tower and closer to a second tower, the taxi driver manually switched from one frequency to another as needed. If a communication was interrupted due to a loss of a signal, the taxi driver asked the base station operator to repeat the message on a different frequency.

In a cellular system, as the distributed mobile transceivers move from cell to cell during an ongoing continuous communication, switching from one cell frequency to a different cell frequency is done electronically without interruption and without a base station operator or manual switching. This is called the handover or handoff. Typically, a new channel is reserved for the mobile unit on the new base station which will serve it. The mobile unit then automatically switches from the current channel to the new channel and communication continues.

The exact details of the mobile system's move from one base station to the other varies considerably from system to system. For example, in all GSM handovers and W-CDMA inter-frequency handovers the mobile station will test the reserved channel before changing channels. Once the channel is confirmed okay, the network will command the mobile unit to switch to the new channel and at the same time start bi-directional communication on the new channel. In CDMA2000 and W-CDMA same-frequency handovers, both channels will actually be in use at the same time (this is called a soft handover or soft handoff). In IS-95 inter-frequency handovers and older analog systems such as NMT it will typically be impossible to test the target channel directly while communicating. In this case other techniques have to be used such as pilot beacons in IS-95. This means that there is almost always a brief break in the communication while searching for the new channel followed by the risk of an unexpected return to the old channel.

If there is no ongoing communication or the communication can be interrupted, it is possible for the mobile unit to spontaneously move from one cell to another and then notify the base station with the strongest signal.