10. Timeline for Wireless Communication RADAR Spark Vacuum tubes Discrete Transistors MSI LSI VLSI, ASICS Devices Modulation CW AM FM FSK PM PSK QAM DQPSK GMSK Radio Communication Systems Mobile Telephony 30-50MHz 150MHz 450MHz 800MHz 1900MHz AM Bcst FM Bcst VHF-TV Bcst UHF-TV Bcst HF Amateur Marine Military VHF Land Mobile Microwave Point-to-Point Microwave Satellite 1920 1930 1940 1950 1950 1960 1970 1980 1990 Time
11. Timeline for Wireless Communication RADAR Spark Vacuum Tubes Discrete Transistors MSI LSI VLSI, ASICS Devices Modulation CW AM FM FSK PM PSK QAM DQPSK GMSK Radio Communication Systems Mobile Telephony 30-50MHz 150MHz 450MHz 800MHz 1900MHz AM Bcst FM Bcst VHF-TV Bcst UHF-TV Bcst HF Amateur Marine Military VHF Land Mobile Microwave Point-to-Point Microwave Satellite 1920 1930 1940 1950 1950 1960 1970 1980 1990 Time
12. Timeline for Wireless Communication RADAR Spark Vacuum Tubes Discrete Transistors MSI LSI VLSI, ASICS Devices Modulation CW AM FM FSK PM PSK QAM DQPSK GMSK Radio Communication Systems Mobile Telephony 30-50MHz 150MHz 450MHz 800MHz 1900MHz AM Bcst FM Bcst VHF-TV Bcst UHF-TV Bcst HF Amateur Marine Military VHF Land Mobile Microwave Point-to-Point Microwave Satellite 1920 1930 1940 1950 1950 1960 1970 1980 1990 Time
13. Timeline for Wireless Communication RADAR Spark Vacuum Tubes Discrete Transistors MSI LSI VLSI, ASICS Devices Modulation CW AM FM FSK PM PSK QAM DQPSK GMSK Radio Communication Systems Mobile Telephony 30-50MHz 150MHz 450MHz 800MHz 1900MHz AM Bcst FM Bcst VHF-TV Bcst UHF-TV Bcst HF Amateur Marine Military VHF Land Mobile Microwave Point-to-Point Microwave Satellite 1920 1930 1940 1950 1950 1960 1970 1980 1990 Time
14. Evolution of Public Mobile Telephony 1960 1990 Standards Evolution MTS 150MHz IMTS 150MHz 450MHz AMPS 800MHz N_AMPS D-AMPS CDMA PCS 1900MHz GSM CDMA AMPS, etc... ESMR 800MHz System Capacity Evolution - Users Dozens Hundreds 100,000’s 1,000,000’s Technology Evolution Analog AM, FM Digital Modulation DQPSK, GMSK Access Strategies FDMA, TDMA, CDMA Vacuum Tubes Discrete Transistors MSI LSI VLSI, ASICs
Page Student Notes Global Wireless Education Consortium Partial support for this curriculum material was provided by the National Science Foundation's Course, Curriculum, and Laboratory Improvement Program under grant DUE-9972380 and Advanced Technological Education Program under grant DUE‑9950039. GWEC EDUCATION PARTNERS: This material is subject to the legal License Agreement signed by your institution. Please refer to this License Agreement for restrictions of use.
Page Student Notes Global Wireless Education Consortium
The following topics will be discussed during this module. The history and evolution of wireless communications, as viewed from three different perspectives: Type of system (e.g., HF, broadcast, TV, microwave, etc.). Type of signal used to carry the information (e.g., AM, FM, CW, etc.). Device and technology used to produce the signal (e.g., vacuum tubes, transistors, etc.). Allocation of the wireless spectrum for cellular and personal communications system (PCS) bands. PCS licensing including the licensed narrowband, licensed broadband, and unlicensed.
After completing this module, you will be able to: Describe the physical channel deployment and allocation within the cellular and PCS industry.
In order to understand the evolution of cellular and PCS, it is important to look at the history of wireless communication. It is this evolution that determined the frequency and channel allocations.
What we would recognize as “radio” has only been around about 100 years: The first communication by radio with any serious purpose or consequences was in the merchant marine and the military as World War I (WWI) began. Soon after WWI, the 1920s saw the birth of amplitude modulated (AM) radio broadcasting and for the first time, the public had a reason to be interested. AM broadcasting grew to be a big business in the 1930s. In 1922, the first mobile use of radio was a simplex (one way only) broadcast to police cars in Detroit, Michigan. This was short lived for three reasons: Base station did not know if the call was received. Radios were large and bulky and took up the entire trunk of the car. Early radios were all tubes, resistors, capacitors and wires. This made them very susceptible to breaking by being jarred around. In 1929, the first two-way mobile voice took place. This is now known as half duplex communication . Simply put, it used a single frequency that each end took turns using. This meant that while one end was talking, the other end had to wait. When the first end would finish, then the second end could talk. Walky-talkies and CB radios are an outgrowth of this technology. In the 1940s, war again intruded (WWII), forcing rapid development of radio techniques. Equipment was built in smaller and more reliable packages, and for the first time, radio links were built with enough power output and gain to be able to hear their delayed signal echoes from passive objects. Radar was born and barely saw its first practical use, giving about 50-minutes’ warning of incoming enemy aircraft during the Battle of Britain.
Television was a lab curiosity during the late 1930s, but the war prevented its successful commercial introduction until the early 1950s. Even though color television was first broadcast in the late 1940s, it was not introduced commercially until the early 1960s. First attempts at public mobile telephony also began in the late 1940s and early 1950s. The mobile telephone service required a trunk full of vacuum tube equipment, and that an operator manually dialed and place calls for the few dozen users on a single radio channel. A significant advancement was the introduction of full duplex communication . This meant that users could now talk on a mobile phone just like it was a landline phone. This was accomplished by providing two frequencies for each radio channel. One was used for transmit, the other for receive. However, this limited the number of channels that could be used in the spectrum.
The history of radio communication can be viewed from three different perspectives: The type of communication system (HF, broadcast, TV, microwave, etc.) The type of signals used to carry the information (continuous wave, amplitude modulated, etc.) The devices and technology used to produce the signals (vacuum tubes, transistors, etc.) Each of these will be discussed individually on the following pages.
In the 1920s, crude spark transmitters were used that could only be turned on and off. This limited capability was exploited by sending the dots and dashes of Morse code. Morse code, developed by Samuel Morse in 1836 for telegraph, became the worldwide code and is still in use in many places throughout the world today. Morse code uses continuous wave (CW) modulation . The frequencies used for CW were mostly in the range of what is now called high frequency , or simply, HF . Later, higher frequencies would prove to be more suitable for the kind of transmissions needed in cellular and PCS. For more information on CW modulation, refer to Radio Frequency Principles and Applications , by A. A. Smith.
With Lee de Forest’s invention of the vacuum tube, it became possible to produce steady, pure radio signals and to modulate them with voice and other information signals. This made possible amplitude modulated (AM) broadcasting, frequency modulated (FM) broadcasting, and later television and radar. New types of modulation were experimented with that were variations of the basic AM and FM formats: Frequency shift keying (FSK) was an early attempt to digitize a signal and it is still used today in many parts of the telephony industry. The signal shifts between two specific frequencies with a series of shift patterns representing a letter or number. Phase modulation (PM) shifts the phase of a signal to encode a message. The shift is measured in degrees and series of shifts represents a letter or number. Phase shift keying (PSK ) is similar in principle to FSK, but shifts the phase of a signal via the frequency. PSK is the basis for the modulation methods used by time division multiple access (TDMA) and global system for mobile communications (GSM). (For more information on modulation, refer to the GWEC module AI-Modulation .)
Development of the transistor in the 1950s spawned development of more portable equipment and the development of integrated circuits, which led to medium-scale integration (MSI) , large-scale integration (LSI) , very large-scale integration (VLSI) , and application specific integrated circuits (ASICs) such as the chip sets inside today’s cellular phones. The terms, MSI, LSI, VLSI, and ASIC refer to the level of integration that a circuit employs. The term discrete transistor means each transistor is an individual component, must be isolated in troubleshooting, and be replaced individually. The term discreet applies to any component that is handled separately from the other components in its circuit. ASICs are fully integrated, meaning that they are complete circuits unto themselves. They perform the same functions that it used to take to make resistors, capacitors, wires, inductors, and either tubes or transistors perform. Because of reduced size of circuit components, the door to the world of communications has been opened and is limited only by our imagination.
Acronyms used in slide above : AMPS: Advanced mobile phone service PCS-1900: GSM systems on 1900 MHz N-AMPS: Narrowband AMPS (Motorola) FDMA: Frequency division multiple access D-AMPS: Digital AMPS (IS-54, IS-136 TDMA) TDMA: Time division multiple access ESMR: Enhanced specialized mobile radio CDMA: Code division multiple access GSM: Global system for mobile communication _________________________________________________________________________________________ When first introduced, mobile telephones were a scarce commodity and priced accordingly. They have evolved and become much more readily available, and at more reasonable prices. Mobile telephone service (MTS ) systems that were demonstrated in the late 1940s and 1950s at 50 MHz and 150 MHz could serve only dozens of users within a single market. By the early 1960s, the improved mobile telephone service (IMTS) offered automatic dialing of the called party by the mobile user. Because these systems did not reuse channels in individual markets, their capacity was limited, handling a few hundred users on half-a-dozen channels in each of the largest cities. Cellular telephony was theorized in published papers but awaited the development of low-cost, fast-locking frequency synthesizers to become practically deployable. Instead of the “Voice of America” syndrome that high-powered IMTS stations used, which blanked out the channel throughout the whole metropolitan area, cellular was able to reuse channels over and over again, multiplying their capacity. By 1985, the first commercial cellular systems were beginning operation.
Acronyms used in slide above : MSA: Metropolitan statistical area RSA: Rural statistical area NOTE : Some books and periodicals may refer to MSAs and RSAs as service areas versus statistical areas. _________________________________________________________________________________________ In the 1970’s, Bell Labs proposed the basic concept of cellular to the Federal Communications Commission (FCC). Bell Labs promised that if the FCC would allocate 70 MHz for a cellular system, the Bell System could deliver essentially unlimited capacity by exploiting frequency reuse in one nationwide system. The FCC authorized cellular, but gave only 40 MHz and decided to approve two competing operating companies in each of 306 cities and 428 rural areas. Cellular was born! After rapid public acceptance of cellular in the late 1980s, it became obvious that additional capacity was required in most markets. The FCC allocated an additional 10 MHz (the so-called expanded spectrum ) for cellular use. Analog was the first technology used and allowed for one user per 30 kHz channel. It was sufficient initially, but soon proved inadequate to handle the ever increasing demand for service. In the 1990s, more efficient multiple-access technologies such as TDMA and CDMA were developed. They are now competing for commercial availability and acceptance in the marketplace. GSM uses the TDMA technology. (For more information on CDMA, TDMA, and GSM, refer to the GWEC modules AI-CDMA , AI-TDMA and AI-GSM .)
Because the first cellular phones operated in the analog mode, rules governing frequency allocation were designed around analog. Advanced Mobile Phone System (AMPS) is the set of rules developed to cover North American cellular. (For more information on AMPS, refer to the GWEC modules AI-AMPS and FRP-Cellular Coverage Concepts .) The AMPS rules state that: Each channel must have a pair of frequencies, one for the uplink and one for the downlink. The uplink (also called the reverse channel or reverse frequency) is the frequency that is transmitted by the mobile and received by the cell. The downlink (also called the forward channel or forward frequency) is the frequency that is transmitted by the cell and received by the mobile. The use of two frequencies allows true duplex operation, that is, it accurately emulates a landline phone conversation where both parties can talk at the same time. In the 800 MHz system, the uplink and downlink are always separated by 45 MHz. In the diagram above, note that there are two bands of frequencies, often referred to as a paired band. This is because every frequency in the lower band is “paired” with a frequency in the upper band, 45 MHz apart. Each channel must have a bandwidth of 30 kHz.
The North American AMPS cellular band includes two ranges of frequencies in the 800 MHz region. This pairing of frequencies allows for full duplex operation, that is, both parties can speak at the same time. This made the cellular telephone a true emulation of the landline telephone: The lower range of frequencies is used for transmission by the users (e.g., mobiles, transportables, hand-helds). The upper range of frequencies is used for transmission by the base stations (cell sites). To foster competition, the FCC divided the available spectrum for use into two competing operators in each market: The “B” or “wireline” operator was originally required to be a wireline telephone company already serving the market. The “A” or “non-wireline” operator could be any other business entity except a wireline company. Today, these restrictions no longer apply in the United States, although Canada still abides by them. Any operator can buy and operate an A or a B system. The only restriction is that the same operating company cannot operate in both the A and B system in the same market area.
Trial personal communication services (PCS) designs have been widely tested in U.S., Canada and Europe. PCS use has been stimulated in the U.S. by FCC allocation of narrowband and broadband spectrum at 900 MHz and 1.9 GHz. The FCC has made available an abundance of spectrum. FCC narrowband auctions generated over $1 billion in revenue for the federal government. Broadband auctions raised over $20 billion.
The chart above provides an overview of the entire radio spectrum, including general locations of various radio services from the medium wave to the super high frequency bands. Note the location of the cellular and PCS bands in the UHF spectrum. (For more information on the electromagnetic spectrum, refer to the GWEC module RT-RF Propagation .) The “cellular” and “PCS” bands are located where they are in the spectrum for a number of reasons: Available frequencies are located here. Higher frequencies require less transmit power, thus smaller components. Ideal length of an antenna is ½ wavelength (1/4 and 5/8 wavelength are also commonly used). .
Cellular and PCS bands are located where they are in the spectrum because that is where available frequencies are located. This is self explanatory. You cannot use what is not there. Frequencies were found in the Ultra-High Frequency (UHF) 800 MHz range that were not in use, so the Federal Communication Commission (FCC) gave these frequencies to the cellular community. When more frequencies were needed for 800 MHz networks, the FCC “stole” the high end of the UHF television range and gave it to the cellular companies. UHF television lost these upper frequencies because they failed to make use of them. Later, frequencies in the 1900 MHz range were also allocated for PCS use. Recently, frequencies in much higher ranges have also been allocated to mobile use. On a very limited basis, there are frequencies in the microwave band that are being used for both mobile and satellite telephones. Line-of-sight (LOS) and satellite mobile phones can be found up in the microwave frequency band. All cellular and PCS phones operating in the 800 MHz and 1900 MHz bands are LOS mobiles while only some in the microwave bands are LOS. This simply means that the transmission range of the phones is limited by both power and the ability of the cell tower to “see” the mobile and vice-versa. For more information on this topic, refer to Essentials of Wireless Communications , by W.C.Y. Lee.
Cellular and PCS bands are located in the spectrum where they are because higher frequencies require less transmit power. Transmitted radio frequency (RF) signals are composed of two fields of energy, E and H fields: The E field (electrical field) and H field (magnetic field) contain the information that is being transmitted. Variations in atmospheric density cause lower frequencies to be reflected, normally through a process of refraction, along the earth’s surface, therefore, lower frequency broadcasts can be “heard” further away on the earth’s surface than higher frequencies. High frequencies are not as affected by the atmospheric density, so satellite signals, laser, and optical light signals travel in a straight line. Radio waves in the Cellular and PCS bands are refracted too little and are considered line of sight signals. The wavelength of a signal is a function of its frequency and the speed of light. Wavelength = C/F where C is the speed of light and F is the transmitted frequency. Because the speed of light is a constant (i.e., it does not change), when the frequency goes up, the wavelength decreases; and when the frequency goes down, the wavelength increases. One wavelength is the distance one 360 degree sine wave travels in one second. For more information on Radio Wave Propagation, see Radio-frequency Electronics , chapter 29, by Jon B. Hagen.
Cellular and PCS bands are located where they are in the spectrum because the ideal length of an antenna is ½ wavelength. One wavelength is 360 degrees of sine wave and it has an equal amount of positive and negative signals in both the E and H fields. Full wave antennas are not used in cellular. ½ wavelength provides the greatest amount of transfer of energy with the least amount of loss. ¼ wavelength is also common due to its more compact size, however, it is not as efficient as the ½ wave length. In many cellular phones, the antenna is a two-position antenna: All the way out = ½ wavelength All the way in = ¼ wavelength Using the formula for wavelength, the ideal size of an antenna for the 800 MHz range can be determined. Using 870 MHz as the basis (middle of the 800 MHz allotted spectrum), and plugging it into the wavelength formula ( = C/F), the ideal antennas size would be approximately 6.5 inches for a half wavelength. If the HF range (2MHz to 32MHz) was used, the ½ wavelength antenna would be approximately 20 to 24 feet long. (How would you like to hold a 24 foot antenna while trying to use your phone?) As you can see, there are many practical reasons for staying in the higher ranges. For more information on this topic, refer to Electronics The Easy Way, chapter 13, by Miller & Miller.
Directly or otherwise, all of us are affected by activity concerning the new PCS systems. Originally, PCS was only GSM systems in the 1900 GHz band. Today, PCS encompasses a wide variety of mobile, portable and ancillary communications services to individuals and businesses using multiple technologies such as TDMA, CDMA, and GSM. The spectrum is divided into three broad categories: Licensed narrowband Licensed broadband Unlicensed
Virtually all the cellular licenses have been issued. The original cellular licenses in the 800 MHz range were distributed free-of-charge through a lottery system. Anyone (e.g., doctors, plumbers, private residents, etc.) could put their name in the “hat” and have an equal chance at getting a license. In order to keep their license, the selected parties had to submit a “build out” plan for approval and implement it, or they would be required to sell their license. Many sold their license at great financial gain. Enterprising individuals and companies designing a piece of wireless market led the drive for a new band. Today, attention is focused on PCS. The FCC learned its lesson from cellular and decided to auction off the PCS licenses.
The FCC allocated a total of three MHz of the spectrum for narrowband PCS , which is used for advanced messaging and paging. This is a licensed spectrum that must be purchased and follow defined implementation plans. No one but the licensee can operate in this band of this particular market. Some systems are already providing service, but because narrowband PCS is in its initial stage, many facets of its operation are still unknown. There is a spectrum cap limiting each carrier to no more than three licenses in a market. The FCC allocated a total of 120 MHz of the spectrum to broadband PCS , which offers primarily mobile telephone service. There is a spectrum cap in this band, which means that the amount of spectrum that any one entity may control in the same area is limited. This is a licensed spectrum that must be purchased and follow defined implementation plans. No one but the licensee can operate in this band in this particular market. The first commercially available PCS service began operations in Washington, D.C. and Baltimore in November 1995. The FCC allocated a total of 20 MHz of the spectrum for unlicensed PCS , which is used for short-range communications such as local area networks in offices. There are no defined implementation plans for unlicensed PCS. Because there is no license involved, there is no restriction as to who can operate in this band of frequencies. This also means the potential for interference is very high. These systems can operate with very low power and will have a limit on duration of transmissions.
Narrowband personal communications services (Narrowband PCS) is broadly defined by the FCC as a family of mobile or portable radio services that may be used to provide wireless telephony, data, advanced paging, and other services to individuals and businesses, and which may be integrated with a variety of competing networks. For example, narrowband PCS could be used to develop advanced paging systems. Pagers may become equipped with a small keyboard allowing the subscriber to both retrieve and send complete messages through microwave signals (e.g., wireless e-mail). Narrowband PCS uses a smaller portion of the spectrum than broadband PCS. Narrowband PCS licenses will most likely be used to provide such new services as voice message paging, two-way acknowledgement paging, and other text-based services. Narrowband PCS is in the 900 MHz band of the electromagnetic spectrum. Three MHz has been allocated to narrowband PCS in the 901-902, 930-931, and 940-941 MHz bands.
Acronyms used in slide above : MTA: Major trading area BTA: Basic trading area _________________________________________________________________________________________ The FCC approved a plan that called for the PCS spectrum to be divided into six bands: A and B are for larger cities called major trading areas (MTAs). C through F are for large rural regions called basic trading areas (BTAs). In the PCS spectrum, the operator’s authorized frequency block contains a definite number of channels. As with AMPS, a channel number implies one uplink and one downlink frequency: Channel 512 = 1850.2 MHz uplink paired with 1930.2 MHz downlink. The down or forward link is the higher of the two frequencies, however, in PCS, the separation is 80 MHz versus 45 MHz. (For additional information on uplink and downlink, refer to the GWEC module RFT-Cellular Coverage Concepts .)
Broadband personal communications services (broadband PCS) is defined by the FCC as radio communications that encompass mobile and ancillary fixed communication services, provide services to individuals and businesses, and can be integrated with a variety of competing networks. Broadband PCS is in the 2 GHz band of the electromagnetic spectrum, from 1850 to 1990 MHz. The spectrum allocated for broadband PCS totals 140 MHz; 20 MHz in the block that is reserved for unlicensed applications that could include both data and voice services. Various business interests, both within and outside the cellular industry, convinced the FCC in the early 1990s that the two existing cellular carriers per market were insufficient to service customers’ mobility needs. Broadband PCS was originally conceived to be “something more” than cellular. One frequently touted design principle was to allow people to be reached at the same number, anytime and anywhere. Because of the strong North American interest, the FCC allocated 140 MHz of the spectrum to PCS. In 1994 and 1995, frequencies between 1850 MHz and 1900 MHz were licensed. Standards for PCS in the U.S. are under development by subcommittees of the Alliance for Telecommunications Industry Solutions (ATIS) Committee T1 , Telecommunications Industry Association (TIA) Committee TR46 , and Institute of Electronic and Electrical Engineering (IEEE) Committee 802. From here forward, mention of “PCS” refers to broadband PCS.
In 1989, the British Department of Trade and Industry created the personal communication network (PCN ), a new mobile telephony concept, to encourage competition between existing mobile and landline service providers. Three PCN licenses were granted to service providers in the United Kingdom. These licenses specified that the providers would agree to implement this new service using GSM standards modified to function in the 1.7 to 2.3 GHz band. The European Telecommunications Standards Institute (ESTI) provided extensions to GSM standards to support PCN. As a result, PCN is currently defined as GSM at 1800 MHz and is known by the ESTI GSM body as DCS1800 for digital cellular system at 1800 MHz.
A market division concept, similar to the “MSA/RSA” idea of cellular, was adopted for PCS licenses. The auctions for the C blocks were even more hotly contested than the A and B blocks, bringing in over $10 billion!
PCS ventures seeking to be “first to market” chose to implement GSM systems since the GSM technology was well-proven and easily adaptable to 1900 MHz. The choice of GSM, however, has some disadvantages. Since GSM systems do not exist domestically on 800 MHz, it is not possible to roam between 1900 MHz systems and 800 MHz systems. The 800 MHz “fallback” roaming has to be done under analog, with different feature set support than on the home system. Dual-band, dual-mode phones will support this capability. CDMA systems came on the air by late 1996, and TDMA in 1997. This offered alternatives to using GSM. TDMA was directly compatible with analog and CDMA could be overlaid on an analog network with no degradation to service. TDMA (IS-136) proponents claim their technology choice is the easiest to implement for integration and ease of roaming on both 800 and 1900 MHz, since it follows the same channelization structure as analog. AT&T’s nationwide combined 800 MHz and 1900 MHz footprint demonstrates the flexibility of this choice. With dual-band phones, the subscriber need not be concerned on which band he’s operating--just the market that has “AT&T Digital PCS” service. (“Dual-band” refers to 800 MHz and 1900 MHz; dual or tri-mode refers to the access technologies such as analog, TDMA, CDMA, or GSM.). Some companies, e.g., Verizon Wireless, offer tri-mode phones that operate in either analog, TDMA or CDMA, and can change dynamically during a call. GSM is not at this level of compatibility at this time.
Since the initial PCS systems are simply “me-too” cellular systems, PCS success depends on how well potential subscribers perceive PCS “beats” cellular for their particular needs. Thus, a PCS choice will be made based on: Price Marketing innovation New features Service quality Already, the cellular carriers are having to cut rates in order to compete with advertised PCS rate plans. Perhaps more important to subscribers are innovative PCS subscription policies: lessening of onerous “lock-in” contracts, easier credit checks, and “turn it on and talk” activation. New features initially deployed include “first incoming minute free” and caller ID, although these features are also becoming available on the existing cellular systems and are not likely to “differentiate” service for long.
Page Student Notes Global Wireless Education Consortium
Page Student Notes Global Wireless Education Consortium
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