The Evolution in Telecommunication: From Wire to Wireless
Wires
1) Twisted-Pair Wire
Twisted-pair wire, also known as twisted-wire pairs or cable, is by far the least expensive transmission media. It consists of two insulated wires twisted around each other so that each wire faces the same amount of interference (noise) from the environment (see figure 1). Unfortunately, this noise becomes part of the signal being transmitted. Twisting the wires together reduces but does not eliminate the noise.
Twisted pair cable is good for transferring balanced differential signals. The practice of transmitting signals differentially dates back to the early days of telegraph and radio. The advantages of improved signal-to-noise ratio, crosstalk, and ground bounce that balanced signal transmissions bring are particularly valuable in wide bandwidth and high fidelity systems. By transmitting signals along with a 180 degree out-of-phase complement, emissions and ground currents are theoretically canceled. This eases the requirements on the ground and shield compared to single ended transmission and results in improved EMI performance.
The most commonly used form of twisted pair is unshielded twisted pair (UTP). It has pairs of insulated copper wires twisted round each other to cancel out electromagnetic interference. Any data communication cables and normal telephone cables are this type. Shielded twisted pair (STP) differs from UTP in that it has a foil jacket or a metal sheath encasing the twisted pairs, shielding them further from outside electromagnetic interference that helps prevent crosstalk and noise from outside source. In data communications there is a cable type called FTP (foil shielded pairs) which consists of four twisted pair inside one common shield (made of aluminium foil). Twisted pair comes with each pair uniquely colour coded when it is packaged in multiple pairs. Different uses such as analog, digital and Ethernet require different pair multiples.
The advantages of using telephone wires are their relative low cost than other type local-area network (LAN) cable, thin, flexible cable that is easy to string between walls and their availability. Their disadvantages include susceptibility signal distortion errors and the relatively low transmission rates they provide over long distances. Twisted wire can handle a data flow of up to approximately one megabit per second (Mbps) over several hundred feet. For a small local-area network with a limited number of users, twisted-pair is an ideal choice because it is both inexpensive and easy to install.
Twisted-wire pairs used in data communications are either private or public lines. Private lines are those provided by the user. Public lines are those provided by a common carrier such as American Telephone and Telegraph (AT&T). Generally, public lines are used whenever distances are great or the terrain or other environmental factors prohibit the use of private lines. Public lines may be either switched lines or leased lines.
Switched lines are used whenever the amount of data to be transmitted is short in duration or when many locations must be contacted for relatively short periods of time. There is a drawback. The telephone company cannot guarantee you exactly which path or switching equipment such a connection will use. Therefore, the speed and quality of the switched connection are questionable.
Leased lines come into play when the connection time between locations A and B is long enough to cover the cost of leasing, or if higher speeds than those available with switched lines must be attained. Leased lines can also be conditioned by the telephone company to lower the error rate and increase transmission speeds. Conditioned leased lines typically operate at speeds of up to 64,000 bits per second (bps). Very-high-speed connections are also available from the common carrier. These are designated T1, T2, T3, and T4, and offer transmission rates of 1.5, 6.3, 46, and 281 million bits per second (Mbps), respectively.
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2) Coaxial Cables
RG-59 flexible coaxial cable.
A: outer plastic sheath
B: woven copper shield
C: inner dielectric insulator
D: copper core
← Coaxial cable cutaway
Coaxial cable, or coax, the medium used by most cable television companies, was developed primarily because of the crosstalk in twisted-wire pairs when transmission occurs at a high rate of speed. While coax is more expensive than twisted-pair, it can transmit data significantly faster, over much longer distances, and with less electrical interference. Coaxial cable is made up of one or two central data transmission wires composed of copper surrounded by a dielectric insulator, which is in turn surrounded by the other, outer conductor, producing an electrically shielded transmission circuit. The whole cable is wrapped in a protective plastic sheathing. The signal propagates within the dielectric insulator, while the associated current flow is restricted to adjacent surfaces of the inner and outer conductors. Many of these cables or pairs of coaxial tubes can be placed in a single outer sheathing and, with repeaters, can carry information for a great distance.
A coaxial cable is one that consists of two conductors that share a common axis. The inner conductor is typically a straight wire, either solid or stranded and the outer conductor is typically a shield that might be braided or a foil.
Coaxial cable is a cable type used to carry radio signals, video signals, measurement signals and data signals. Coaxial cables existed because we can't run open-wire line near metallic objects (such as ducting) or bury it. We trade signal loss for convenience and flexibility. Coaxial cable consists of an insulated ceter conductor which is covered with a shield. The signal is carried between the cable shield and the centre conductor. This arrangement give quite good shielding against noise from outside cable, keeps the signal well inside the cable and keeps cable characteristics stable.
Coaxial cables and systems connected to them are not ideal. There is always some signal radiating from coaxial cable. Hence, the outer conductor also functions as a shield to reduce coupling of the signal into adjacent wiring. More shield coverage means less radiation of energy (but it does not necessarily mean less signal attenuation).
Coaxial cables are typically characterized with the impedance and cable loss. The length has nothing to do with coaxial cable impedance. Characteristic impedance is determined by the size and spacing of the conductors and the type of dielectric used between them. For ordinary coaxial cable used at reasonable frequency, the characteristic impedance depends on the dimensions of the inner and outer conductors. The characteristic impedance of a cable (Zo) is determined by the formula 138 log b/a, where b represents the inside diameter of the outer conductor (read: shield or braid), and a represents the outside diameter of the inner conductor.
Most common coaxial cable impedances in use in various applications are 50 ohms and 75 ohms. 50 ohms cable is used in radio transmitter antenna connections, many measurement devices and in data communications (Ethernet). 75 ohms coaxial cable is used to carry video signals, TV antenna signals and digital audio signals. There are also other impedances in use in some special applications (for example 93 ohms). It is possible to build cables at other impedances, but those mentioned earlier are the standard ones that are easy to get. It is usually no point in trying to get something very little different for some marginal benefit, because standard cables are easy to get, cheap and generally very good. Different impedances have different characteristics. For maximum power handling, somewhere between 30 and 44 Ohms is the optimum. Impedance somewhere around 77 Ohms gives the lowest loss in a dielectric filled line. 93 Ohms cable gives low capacitance per foot. It is practically very hard to find any coaxial cables with impedance much higher than that.
Coaxial cable is the kind of copper cable used by cable TV companies between the community antenna and user homes and businesses. Coaxial cable is sometimes used by telephone companies from their central office to the telephone poles near users. It is also widely installed for use in business and corporation Ethernet and other types of local area network.
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3) Fiber-Optics
Fiber optics is an glass or plastic fiber that carries light along the length. Fiber optical fibers are widely used in the fiber-optic communications, which allow the transmission over longer distances and at higher bandwidths (data rates) in the form of communications. Fibers are normally used to compare the metal wires because the signals travel along with them less loss, and it also immune to the electromagnetic interference. The fiber is normally functions to illumination, and it is wrapped in the bundles so that it can used to carry images, thus it allows viewing in the tight spaces. Besides that, it is specially designed for the used of variety application such as sensors and also as fiber lasers.
The light is kept in the core of optical fiber are done by total internal reflection. This may cause the fiber to act as a waveguide. The fiber that support many propagation path or transverse modes are normally called as multi-mode fiber.(MMF) Meanwhile the fiber that support only a single mode are called as single mode fibers(SMF).
i. Multi-mode fibers(MMF)
Generally have a larger core diameter. That are used for short-distance communication links and for applications where high power must be transmitted.
ii. Single-mode fibers(SMF)
It is normally used for most communication links longer than 550 meters (1,800 ft).
The optical fiber joining lengths are more complex than joining electrical wire or cable. Therefore, the ends of the fibers must be carefully cleaved, after that then spliced it together either mechanically or by fusing them together with an electric arc.
Wireless
Wireless is a term used to describe telecommunications in which electromagnetic waves carry the signal over part or the entire communication path. Sometimes, some monitoring devices, such as intrusions alarms, employ acoustic waves at frequencies above the range of human hearing also classified as wireless.
In the early 20th century, the first wireless transmitters went on the air by using radiotelegraphy. Later, the medium called “radio” made it possible to transmit voice and music via wireless. With the advent of television, fax, data communication, and the effective use of a larger portion of the spectrum, the term “wireless” has been resurrected.
Wireless technology is rapidly growing and is playing an increasing role in the lives of people throughout the world. Besides, ever-large numbers of people are relying on the technology directly or indirectly. More specialized and exotic examples of wireless communications and control include Global System for Mobile Communication (GSM), General Packet Radio Service (GPRS), Enhanced Data GSM Environment (EDGE), Universal Mobile Telecommunications System (UMTS), Wireless Application Protocol (WAP) and i-Mode.
Wireless can be divided into Fixed Wireless (the operation of wireless devices or systems infixed location such as home and offices), portable wireless (the operation of autonomous, battery-powered wireless devices or systems outside the office, home, or vehicle; example included the handheld cell phones and PCS units) and IR wireless (the use of devices that convey data via IR radiation; employed in certain limited- range communication and control systems.
Wireless technologies include terrestrial microwave, communications satellites, cellular and PCS telephone and pager systems, mobile data radio, wireless LANs, and various Internet technologies. Each technology utilizes specific ranges within the electromagnetic spectrum (in megahertz) of electromagnetic frequencies that are specified by national regulatory agencies to minimizes interference and encourage efficient telecommunication.
1) Wireless LAN
Wireless LAN (wireless local area network) is one in which user can connect to a local area network through a wireless (radio) connection. The use of wireless LANs is growing rapidly as new high-speed technologies are implemented. A prime example is a new open-standard wireless radio-wave technology technically known as IEEE 802.11b or more popularly as Wi-Fi (for wireless fidelity). Wi-Fi is faster (11 Mbps) and less expensive than Standard Ethernet and other common wire-based LAN technologies. Thus, Wi-Fi enable lap-top PCs, PDAs and other devices with Wi-Fi modems to connect internet easily in a rapidly increasing number of business, public, and home environment.
2) Terrestrial Microwave
Terrestrial microwave communication is an Earth-based transmitters and receivers. The frequencies of the used are in the low-gigahertz range, which will limit all communications to line in the sight. The terrestrial microwave equipment are usually in the form of telephone relay towers, which are placed every few miles to relay telephone signals cross country.
Microwave transmissions typically use a parabolic antenna that produces a narrow, highly directional signal. The similar antenna at the receiving site is very sensitive to signals only within a narrow focus. This is probably because of the transmitter and receiver is highly focused. Therefore, they must be adjusted carefully so that the transmitted signal is aligned with the receiver. The microwave antenna were usually placed on the top of the building, towers, hills, and mountain peaks, and they are familiar sight in many section of the country.
3) Communication Satellites
A communications satellite (COMSAT) is an artificial satellite stationed in space for the purpose of telecommunications. Its also use microwave radio as their telecommunications medium Modern communications satellites are place in the stationary .It normally use a variety of orbits including geostationary orbits(approximately 22,000 miles above the equator), Molniya orbits, other elliptical orbits and low (polar and non-polar) Earth orbits.
Communication satellites used the initially voice and video transmission, they also use for high –speed transmission of a large volumes of data. While, satellites is the most powerful solar panel because it can transmit the microwave signal at a high rate(hundred million bits per second).they serve and always relay on the station for the communication signal transmitted from earth stations. Satellites are used for a large number of purposes. Common types include military (spy) and civilian Earth observation satellites, communication satellites, navigation satellites, weather satellites, and research satellites.
4) Bluetooth
Bluetooth is a proprietary of open wireless protocol that function as exchanging the data over a short distance from a fixed and mobile devices by using the short length radio wave. This Bluetooth will therefore create a personal area networks (PANs).
Bluetooth is also call as standard communications protocol. That is designed for low power consumption, with a short range (power-class-dependent: 100m, 10m and 1- see the table below) depend on the low-cost. of the transceiver microchips in each device. For your information, the devices use a radio (broadcast) communications system, actually do not have to be in line of sight of each other.
Bluetooth is a standard for a small, cheap radio chip to be plugged into computers, printers, and mobile phone. A bluetooth chip designed to replace cables by taking the information normally, carried by taking the information which normally carried by the cable and transmitting it at a special frequency to the receiver of the bluetooth chip. Bluetooth chip will give the information to the receiver like computer, or mobile phone.
