The future of communication will fascinate your imagination, from wireless Internet connection to video, voice and data transfer. But before we get into the technical and functional purpose of our project, we would like to thoroughly discuss what exactly has brought us to this point in time. It is important to understand the basis and background of this technology along with the speed with which this technology is
changing. Understanding those concepts will enable you to understand the future applications of our project. A future, with no boundaries, that also offers seamless access to information.
The history of wireless communication dates back to as early as the 1800s, when Scottish physicist James Maxwell discovered the electromagnetic spectrum and Italian born Gugliemlmo Marconi invented the wireless telegraph. These discoveries prompted much exploration into the field of mobile and wireless communications devices, and sparked ideas for many new inventions.
Between 1928 and 1950 leaps were made in the advancement of radio technology, from the introduction of the first mobile radio system to the first crude voice pager. These pagers were actually analog AM radio receivers that used extensive antenna systems, and therefore had very small ranges. They were initially used only for in-building communication. Motorola introduced its first modern-type pager, the Handy – Talkie Pocket Receiver, in 1955. The format was decidedly different than that of today in that voice messages were broadcast to all carriers of the pagers instead of one specific user, and then all recipients would call in to the system to see if any messages were for them. This system continued, and spread to citywide use in 1960, until the same company unveiled the single person pager in 1965. In this format, the user would receive a tone only beep and then call in to an operator to obtain the message. Although the retail price of the pager, named the Pageboy, premiered at around $245, pager sales began to climb. By 1969, Motorola offered 16 different pager models including tone plus voice models in addition to the old tone only model. And in the mid-1970s the first alphanumeric pagers were introduced, and by 1980 there were over one million paging subscribers.
PART I
First Mobile Systems
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 were never truly committed to mobile telephone systems. Their wireless engineers were keen and ardent but the System itself held them back. Federal regulations also hindered many projects but in Europe, where state-run telephone companies controlled their own research and development, wireless came no sooner, and in many cases, later.
In 1921 United States mobile radios began operating at 2 MHz, just above the present AM radio band. These were chiefly experimental police department radios, with practical systems not implemented until the 1940s. 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. Radiotelephone used large frequency allocations to serve a few people. No radio telephone channels were designated until after World War II.
On June 17th 1946 in St. Louis MO, AT&T and Southwestern Bell introduced the first American commercial mobile radiotelephone 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 60 kHz channel spacing. Bad cross channel interference, something like cross talk in a landline phone, soon forced Bell to use only three channels.
Installed high above Southwestern Bell’s headquarters, a centrally located antenna transmitting 250 watts paged mobiles and provided radio telephone traffic on the downlink. Operation was straightforward.
Telephone customer dials Long Distance and asks to be connected with the mobile service operator, to whom they give the telephone number of the vehicle he wants to call. The operator sends out a signal from the radio control terminal, which causes a lamp to light and a bell to ring in the mobile unit. The occupant answers his telephone, his voice traveling by radio to the nearest receiver and then by the 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.
The 20-watt mobile sets did not transmit back to the central tower but to one of five receivers placed across the city. Once a mobile went off hook all five receivers opened. The Mobile Telephone Service (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.
In 1947 AT&T asked the FCC for more frequencies. The FCC finally allocated a few more channels in 1949, but gave half to other companies wanting to sell mobile telephone services.
On March 1st 1948 a fully automatic radiotelephone service began operating in Richmond IN, eliminating the operator to place most calls. The Richmond RadioTelephone Company out did 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 telephone systems.
In 1956 the Bell System began providing manual radiotelephone service at 450 MHz, a new frequency band assigned to relieve overcrowded. They did not automate the service until 1969.
In 1964 AT&T introduced a second generation of mobile telephones, known as improved mobile telephone service (IMTS). This provided full duplex operation, automatic dialing, and automatic channel searching. Initially 11 channels were provided in the 152 – 158 MHz band, but in 1969 an additional 12 channels were added in the 454 – 459 MHz band. Since only 11 or 12 channels were available for all users of the system within a given geographic area and since each frequency was used only once in that geographic area, the IMTS system faced a high demand for a very limited channel resource.
During this time the American cellular radio system, known as the advanced mobile phone system, or AMPS, was developed primarily by AT&T and Motorola. In 1978 AMPS started operating and North American. In that year, AT&T labs rolled out an analog based cellular telephone service. Ten cells covering 21,000 square miles made up the Chicago system. It operated in the newly allocated 800 MHz band. This early network, using large-scale integrated circuits throughout, a dedicated computer and switching system, custom-made mobile telephones and antennas, proved cellular could work.
Worldwide AMPS deployment followed quickly. A two-cell system started operating in Bahrain, Saudi Arabia in May 1978, and an 88-cell system in Tokyo in December 1979. United States cellular development didn’t keep up. The Bell Systems impending breakup and a new FCC competition requirement delayed its rollout. The Federal Communication Commission’s 1981 regulations required the Bell System or a regional operating company, such as Bell Atlantic, to have competition in every cellular market.
Ameritech provided the first United States commercial service in Chicago on Oct. 12 1983. Europe saw cellular service introduced in 1981, when the Nordic Mobile Telephone System began operating in Denmark, Sweden, Finland, and Norway in the 450 MHz range. Plans were started during the early 1980s, to create a single European wide digital mobile service with advanced features and easy roaming. While North American groups concentrated on building out their robust but increasingly fraud plagued and featureless analog network, Europe planned for a digital future.
The United States did not suffer from incompatible systems. Roaming from one city or state to another wasn’t difficult like in Europe. Your mobile usually worked as long as there was coverage. Little desire existed to design an all-digital system when the present one was working well and proving popular. To illustrate that point, the American cellular phone industry grew from less than 214,000 subscribers in 1985 to 1,600,000 in 1988. And with each analog based phones sold, chances dimmed for an all-digital future.
Europeans saw things differently. No new telephone system could accommodate their existing services on so many frequencies. They decided instead to start a new technology in a new radio band. Cellular structured but fully digital, the new service would incorporate the best thinking of the time. They patterned their new wireless standard after landline requirements, hoping to make a wireless counterpart to it. The new service was called GSM.
GSM stands for Global System for Mobile Communications. GSM development began in 1982 by a group of 26 European national phone companies. In 1989 the European Telecommunication Standards Institute or ETSI took responsibility for further developing GSM. In 1990 the first recommendations were published. Pre-dating American PCS, the United Kingdom asked for and got a GSM plan for higher frequencies.
The late 1980s saw North American cellular becoming standardized as network growth and complexity accelerated. In 1988 the analog networking cellular standard called TIA- IS-41 was published. This Interim Standard is still evolving. IS-41 seeks to unify how network elements operate; the way various databases and mobile switches communicate with each other and with the regular landline telephone network.
In March 1990 the American cellular network added a new feature. Voice traffic went digital. IS–54B or Digital AMPS became the first North American dual mode digital cellular standard. It separated calls by time, placing parts of conversations on the same frequency, one after the next. It thus tripled call capacity by sampling, digitizing and then multiplexing conversations, and technique called TDMA or time division multiple access. But IS-54 kept analog routines to the first setup calls.
It should be noted, that no radio service can be judged on whether it is all-digital or not. PCS 1900, for example, the American GSM equivalent, operates a higher frequency than it does in most of Europe. Nearly twice as many base stations are required in Europe, leaving gaps and holes in coverage that do not exist with lower frequency, conventional cellular.
In Europe, commercial GSM networks started operating in mid-1991. As of October 1998, GSM’s popularity remains unrivaled. Consider these points:
100 million subscribers 5 million new users each month 120 countries served 300 GSM system operators worldwide 60% of all digital mobiles produced are GSM
GSM developed later than conventional cellular and in many respects was better designed. Its North American counterpart is PCS, sometimes called PCS 1900, operating at higher frequency then the original European GSM.
By 1993 American cellular was again running out of capacity, despite a wide movement to IS 54. The American cellular business continued booming. Subscribers grew from 1,000,000 customers in 1988, to more than 13,000,000 subscribers in 1993, and over 50,000,000 subscribers today. Many carriers were at their system capacity in densely populated cities. More room and more carriers were needed. After much study the FCC began auctioning space in the newly designated PCS band, from December 5th, 1994 to January 14th, 1997.
B. Detailed Outline of the Components in A Cellular System
A cellular mobile communications system uses a large number of low-power wireless transmitters to create “cells”, the basic geographic service area of a wireless communications system. Variable power levels allow cells to be sized according to the subscriber density and demand within a particular region. As mobile users travel from cell to cell, their conversations are “handed off” between cells in order to maintain seamless service. Channels or frequencies used in one cell can be reused in another cell some distance away. Cells can be added to accommodate growth, creating the cells in unserved areas or overlaying cells in existing areas.
Each mobile uses a separate, temporary radio channel to talk to the cell site. The cell site talks to many mobiles at once, using one channel per mobile. Channels use a pair of frequencies for communication, one frequency, the forward link, for transmitting from the cell site, and one frequency, the reverse link, for the cell site to receive calls from the users. Radio energy dissipates over distance, so mobiles must stay near the base station to maintain communications. The basic structure of mobile networks includes telephone systems and radio services. Where mobile radio service operates in a closed network and has no access to the telephone system, mobile telephone service allows interconnection to the telephone network.
Traditional mobile service was structured similar to television broadcasting: one very powerful transmitter located at the highest spot in an area would broadcast in a radius of up to 50 kilometers. The cellular concept structured the mobile telephone network in a different way. Instead of using one powerful transmitter, many low-power transmitters were placed throughout a coverage area. For example, by dividing a metropolitan region into 100 different areas or cells, with low-power transmitters using 12 conversations or channels each, the system capacity theoretically could be increased from 12 conversations, or voice channels using one powerful transmitter, to 1200 conversations or channels, using 100 low-power transmitters.
Interference problems caused by mobile units using the same channel in adjacent areas proved that all channels could not be reused in every cell. Areas had to be skipped before the same channel could be reused. Even though this affected the efficiency of the original concept, frequency reuse was still a viable solution to the problems of mobile telephone systems.
Engineers discovered that the interference effects were not due to the distance between areas, but to the ratio of the distance between areas to the transmitter power of the areas. By reducing the radius of an area by 50 percent, service providers could increase the number of potential customers in an area fourfold. Systems based in areas with a one-kilometer radius would have 100 times more channels than systems with areas ten kilometers in radius. Speculation led to the conclusion that by reducing the radius of areas to a few hundred meters, millions of calls could be served.
The cellular concept employs variable low-power levels, which allows cells to be sized according to the subscriber density and demand of a given area. As the population grows, cells can be added to accommodate that growth. Frequencies used in one-cell clusters can be reused in other cells. Conversations can be handed off from cell to cell to maintain constant phone service as the user moves between cells.
The cellular radio equipment or base station can communicate with mobiles as long as they are within range. Radio energy dissipates over distance, so the mobiles must be within the operating range of the base station. Like the early mobile radio system, the base station communicates with mobiles via a channel. The channel is made up of two frequencies, one for transmitting to the base station in one to receive information from the base station.
Increases in demand and the poor quality of existing service led mobile service providers to research ways to improve the quality of service and to support more users in their systems. Because the amount of frequency spectrum available for mobile cellular use was limited, efficient use of the required frequencies was needed for mobile cellular coverage. In modern cellular telephones, rural and urban regions are divided into areas according to specific provision guidelines. Engineers experienced in cellular system architecture determine deployment parameters, such as amount of cell splitting and cell sizes. Provisioning for each region is planned according to an engineering plan that includes cells, clusters, frequency reuse, and handovers.
A cell is the basic geographic unit of a cellular system. The term cellular comes from the honeycomb shape of the areas into which a coverage region is divided. Cells are base stations transmitting over small geographic areas that are represented as hexagons. Each cell size varies depending on the landscape. Because of constraints imposed by natural terrain and man-made structures, the true shape of cells is not a perfect hexagon.
A cluster is a group of cells. No channels are reused within the cluster.
Because only a small number of radio channel frequencies were available for mobile systems, engineers had to find a way to reuse radio channels in order to carry more than one conversation at a time. The solution the industry adopted was called frequency planning or frequency reuse. Frequency reuse was implemented by restructuring the mobile telephone system architecture into the cellular concept.
The concept of frequency reuse is based on assigning to each cell a group of radio channels used within a small geographic area. Cells are signed a group of channels that is completely different from neighboring cells. The coverage area of cells is called the footprint. This footprint is limited by a boundary so that the same group of channels can be reused in different cells that are far enough away from each other so that their frequencies do not interfere. Cells with the same number have the same set of frequencies.
Unfortunately, economic considerations made the concept of creating full systems with many small areas impractical. To overcome this difficulty, system operators developed the idea of cell splitting. As a service area becomes full of users, this approach is used to split a single area into smaller ones. In this way, urban centers can be split into as many areas as necessary in order to provide acceptable service levels in heavy traffic regions, while larger, less expensive cells can be used to cover remote rural regions.
The final obstacle in the development of the cellular network involved the problem created when a mobile subscriber traveled from one cell to another during a call. Since adjacent areas do not use the same radio channels, a call must either be dropped or transferred from one radio channel to another when a user crosses the line between adjacent cells. Because dropping the call is unacceptable, the process of handoff was created. Handoff occurs when the mobile telephone network automatically transfers a call from radio channel to radio channel as mobile crosses adjacent cells. During a call, two parties are on one voice channel. When the mobile unit moves out of the coverage area of a given cell site, the reception becomes weak. At this point, the cell site in use requests a handoff. The system switches the call to a stronger frequency channel in a new site without interrupting the call or alerting the user. The call continues as long as the user is talking, and the user does not notice the handoff at all.
Originally devised in the late 1970s to early 1980s, analog systems have been revised somewhat since that time and operate in the 800 MHz range. A group of government, telecommunications and equipment manufacturers worked together as a committee to develop a set of rules that govern how cellular subscriber units communicate with the cellular system. System development takes into consideration many different, and often opposing, requirements for the system, and often a compromise between conflicting requirements results. Cellular development involves some basic points:
1. frequency and channel assignments
2. type of radio modulation
3. maximum power levels
4. modulation parameters
5. messaging protocols
6. call processing sequences
AMPS was released in 1983 using the 800 MHz to 900 MHz frequency band and the 30 kHz bandwidth for each channel as a fully automated mobile telephone service. It was the first standardized cellular service in the world and is currently the most widely used standard for cellular communications. Designed for use in cities, AMPS later expanded to rural area. It maximized the cellular concept of frequency reuse by reducing radio power output. The AMPS telephones have the familiar telephone style user interface and are compatible with any AMPS base station. This makes mobility between service providers simpler for subscribers. There does happen to be some limitations with AMPS. The limitations associated with AMPS include:
1. low call capacity
2. limited spectrum
3. no room for spectrum growth
4. poor data communications
5. minimal privacy
6. inadequate fraud protection
AMPS is used throughout the world and is particularly popular in the United States, South America, China, and Australia. AMPS uses frequency modulation (FM) for radio transmission. In the United States, transmissions from mobile to cell site use separate frequencies from the base station to the mobile subscriber.
Since analog cellular was developed, systems have been implemented extensively throughout the world as a first generation cellular technology. In the second generation of analog cellular systems, NAMPS was designed to solve the problem of low calling capacity. NAMPS is now operational and 35 U.S. and overseas markets and NAMPS was introduced as an interim solution to capacity problems. NAMPS is a U.S. cellular radio station that combines existing voice processing with digital signaling, tripling the capacity of today’s AMPS systems. The NAMPS concept uses frequency division to get three channels in the AMPS 30 kHz single channel bandwidth. NAMPS provides three users in an AMPS channel by dividing the 30 kHz AMPS bandwidth into three 10 kHz channels. This increases the possibility of interference because channel bandwidth is reduced.
The cellular system offers mobile and portable telephone stations the same service provided fixed stations over conventional wired loops. It has the capacity to serve tens of thousands of subscribers in a major metropolitan area. The cellular communications system consists of the following four major components that work together to provide mobile service to subscribers:
1. public switched telephone network
2. mobile telephone switching office
3. cell site with antenna system
4. mobile subscriber unit
The Public Switched Telephone Network (PSTN) is made up of local networks, the exchange area networks, and the long-haul network that interconnect telephones and other communication devices on a worldwide basis. The Mobile Telephone Switching Office (MTSO) is the central office for mobile switching. It houses the mobile switching center, field monitoring and relay stations for switching calls from cell sites to wireline central offices. In analog cellular networks, the MSC controls the system operation. The Mobile services Switching Center (MSC) control calls, tracks billing information, and locates cellular subscribers.
The term cell site is used to refer to the physical location of radio equipment that provides coverage within a cell. A list of hardware located at a cell site includes power sources, interference equipment, radio frequency transmitters and receivers, and antenna systems. The mobile subscriber unit consists of a control unit and a transceiver that transmits and receives radio transmissions to and from a cell site. Three types of mobile subscriber units are available:
1. the mobile telephone
2. the portable
3. the transportable
The mobile telephone is installed in the trunk of a car, and the handset is installed in a convenient location to the driver. Portable and transportable telephones are hand-held and can be used anywhere. The use of portable and transportable telephones is limited to the charge life of the internal battery.
As demand for mobile telephone service has increased, service providers found that basic engineering assumptions borrowed from wireline (landline) networks did not hold true in mobile systems. While the average landline phone call lasts at least 10 minutes, mobile calls usually run 90 seconds. Engineers who expected to assign 50 or more mobile phones to the same radio channel found that by doing so they increased the probability that a user would not get dial tone, this is known as call blocking probability. As a consequence, the early systems quickly became saturated, and quality of service decreased rapidly. The critical problem was capacity. The general characteristics of TDMA, GSM, PCS 1900, and CDMA promise to significantly increase the efficiency of cellular telephones systems to allow a greater number of simultaneous conversations.
The advantages of digital cellular technologies over analog cellular networks include increased capacity and security. Technology options such as TDMA and CDMA offer more channels in the same analog cellular bandwidth and encrypted voice and data. Because of the enormous amount of money that service providers have invested in AMPS hardware and software, providers look for a migration from AMPS to DAMPS by overlaying their existing networks with TDMA architectures.
North American digital cellular is called DAMPS and TDMA. Because AMPS preceded digital cellular systems, DAMPS uses the same setup protocols as analog AMPS. TDMA has the following characteristics:
1. IS-54 standard specifies traffic on digital voice channels
2. Initial implementation triples the calling capacity of AMPS systems
3. Capacity improvements of 6 to 15 times that of AMPS are possible
4. Uses many blocks of spectrum in 800 MHz and 1900 MHz
5. All transmissions are digital
6. TDMA/FDMA application 7.3 caller’s per radio carrier, providing three times the AMPS capacity
TDMA is one of several technologies used in wireless communications.
It provides each call with time slots so that several calls can occupy one bandwidth. Each caller is assigned a specific time slot. In some cellular systems, digital packets of information are sent during each time slot and reassembled by the receiving equipment into the original voice components. TDMA uses the same frequency band and channel allocations as AMPS. Like NAMPS, TDMA provides three to six time channels in the same bandwidth as a single AMPS channel. Unlike NAMPS, digital systems have the means to compress the spectrum used to transmit voice information by compressing idle time and redundancy of normal speech. TDMA is the digital standard and has 30 kHz bandwidth. Using digital voice encoders, TDMA is able to use up to six channels in the same bandwidth where AMPS uses one channel.
The extended TDMA (E-TDMA) standard claims to capacity of 15 times that of analog cellular systems. This capacity is achieved by compressing quiet time during conversations. E-TDMA divides the finite number of cellular frequencies into more time slots than TDMA. This allows the system to support more simultaneous cellular calls.
Fixed wireless access is a radio based local exchange service in which telephone service is provided by common carriers. It is primarily a rural application, that is, it reduces the cost of conventional wireline. Fixed wireless access extends telephone service to rural areas by replacing a wireline local loop with radio communications. Other labels for wireless access include fixed loop, fixed radio access, wireless telephone, radio loop, fixed wireless, radio access, and Ionica. FWA systems employ TDMA or CDMA access technologies.
The future of telecommunications includes personal communications services. PCS at 1900 MHz is the North American implementation of DCS 1800 (GSM). Trial networks were operational in the United States by 1993, and in 1994 the FCC began spectrum auctions. As of 1995, the FCC auctioned commercial licenses. In the PCS frequency spectrum the operators authorized frequency block contains a definite number of channels. The frequency plan assigns specific channels to specific cells, following a reuse pattern, which restarts with each nth cell. The uplink and downlink bands are paired mirror images. As with AMPS, a channel number implies one uplink and one downlink frequency.
Code division of multiple access (CDMA) is a digital air interface standard, claiming 8 to 15 times the capacity of analog. It employs a commercial adaptation of military spread spectrum single sideband technology. Based on spread spectrum theory, it is essentially the same as a wireline service, the primary difference is that access to the local exchange carrier is provided via wireless phone. Because users are isolated by code, they can share the same carrier frequency, eliminating the frequency reuse problem encountered in AMPS and DAMPS. Every CDMA cell site to use the same 1.25 MHz band, so with respect clusters, n=1. This greatly simplifies frequency planning in a fully CDMA environment.
CDMA is an interference-limited system. Unlike AMPS/TDMA, CDMA has a soft capacity limit; however, each user is a noise source or the shared channel and the noise contributed by users accumulates. This creates a practical limit to how many users a system will sustain. Mobiles that transmit excessive power increase interference to other mobiles. For CDMA, precise power control of mobiles is critical in maximizing the systems capacity and increasing battery life of the mobiles. The goal is to keep each mobile at the absolute minimum power level that is necessary to ensure acceptable service quality. Ideally, the power received at the base station from each mobile should be the same.
This has shown the rapid and fast changing environment that our industry is facing. Here are some of the facts, thats show the dramatic expansion of the Wireless Industry.
Direct Employment by the Wireless Service Providers has increased from 3556 people in 1986 to over 113,111 people today. Revenues in the Wireless Industry has grow from $354,316,000 in 1985 to over $29,637,742,000 today. Wireless Subscribership has grown from 203,600 people in 1985 to over 60,831,431 people today.
