Chapter V Fundamentals of telecommunications

Transcription

1 Chapter V Fundamentals of telecommunications Wired Wireless And beyond 1

2 Chapter objectives Evolution from electricity to electronics Understand telecommunication and its different technologies From Telegraphy to telephony Understand and recognize different telecommunication media. From wired to wireless to T lines. Understand frequency, wave, signal propagation and antennas. Understand role of towers and satellites Understand GPS technology and GPS applications. Understand cellphone technology and applications. Understand RADAR, infra-red and LASER and their applications 2

3 Electricity and electronics Amber as source of ancient electricity: Greek and Arabs 1000 BC 1600: William Gilbert (father of electricity) discovered electrification of many substances. He coined the word electricity referring to ELECTROCUS (Greek word for amber ) Maxwell discovered that waves travel at speed of light and Hertz confirmed that and established the Hz as frequency unit Marconi came up with the first radio and in 1904 John Flemmings invented the diode and Lee De Forest developed the triode and Electronics technology was born (Atalla & Khang) invented the first silicon transistor a t Bell labs (MOS-transistor) 3

4 Transistor characteristics Very little power consumption Very small size. Easiness of mass production Availability of raw material at cheap cost. Vacuum tube MOS semiconductor 4

5 Telegraphy 1825W. Sturgeon invented electromagnet 1838 SAM Morse invented the telegraph by sending electrical pulses to magnet and pull key to strike a code on a tape US post started the service 1913: Western Union started multiplexing (8 different messages sent simultaneously over same wire) 1943 Western union merged with US post and used it in business and introduced Fac-simile service 1938 and the telex 1959 With Telex businesses could subscribe and dial each other Congress funded first 40 miles telegraph linking Washington D.C and Baltimore. Morse code comprises 2 symbols : a point and a dash (3points) that were like the binary enough to represent characters and symbols Trained operators could handle 300 wpm Light, wistles and mirrors can be used to send and receive Morse code. Still used in many areas. 5

6 Telephone Alexander Graham Bell was the first to patent the telephone as apparatus for transmitting vocal or other sounds telegraphically in His granted patent number (#174,465). Elisha Grey used liquid microphone to design a telephone in 1876 (five days after the patent application of Alexander Bell). Many people believe that Bell had stolen Grey s invention and credit Grey for the invention of the telephone as a complete device. Bell won the legal battle in the court. Thomas Edison invented the carbon microphone in This Microphone used the carbon particles as variable electronic resistance that amplifies electrical signal and produces high quality voice and sounds. His invention was also disputed by Emile Berliner who filed patent application in June But the patent rights were awarded to Edison by a US court and later by a British court. 6

7 Microphone TELEPHONE STRUCTURE CARBON PARTICULES Cable Membrane (Speaker) Magnet 7

8 How it works Transmitter converts audio signal into electrical signal and send electrical signal carrying speech modulation. The microphone does the job by changing the resistance when you speak that result in changing the current function of your vocal audio waves Receiver is needed to capture the electrical signals and convert them back into Audio signals and a speaker to amplify audio signal so that they will be heard by human. The speaker on the other side using electromagnet that is magnetized by the received signal causes a thin membrane to resonate so that it reproduces the audio signals. A transmission medium able to provide a safe pathway between sender and receiver. Amplifiers interposed on the way to compensate the loss in decibel of the signal due to resistance encountered on the way. 8

9 Telephone evolution High business demand in the early telephone market and the mounting pressure to develop the new technology to allow someone to speak with many other people resulted in inventing the telephone central exchange. No direct communication was possible with the first manual exchange; instead operators answer calls and connect them to parties they ask to be connected with. Modern automatic exchange enables everyone to directly connect to everyone else in dialing a number (automatic electronic switching work to accommodate the links all along the itinerary). Automatic switching had deep impact on the job market; it resulted in the loss of millions of telephone operator jobs worldwide. Because of these technological advances under business pressure, telephone technology found itself evolving toward networking technology very naturally. 9

10 Pros and Cons of telephone The pros: Stable and reliable communication with no restraints of signal loss or influence of weather conditions Very well suitable to the military and business campuses. High level of security (no wave interception to worry about especially in local and in-campus networks. Cost is very reasonable. No power connection required (very reliable during communication in case of prolo9nged power outage during natural disasters. Easy networking Easy control and updating High voice quality No special skills, no expertise and no training required to use it. Telephone network extends all over the planet so you can reach anyone you want anytime you want. The cons: Very limited mobility (fixed structure) Difficult lay down of ground cable with digging required sometimes Difficulties of maintenance and troubleshooting Installation cost is high and sometimes prohibitive. 10

11 Wired media This technology requires the transmitter and receiver to be connected to a pair of wires that form a closed electrical circuit. Telegraphy and telephony were both wired technologies until recently telephone technology started using combined wired/wireless connection Wired technology uses many different types of cables: Twisted pairs cable: Consists of many pairs of twisted insulated wires protected by a hard insolation shield. In order to make it possible to recognize the reference of subscriber, inner wires insolation is colored (each twisted pair has different color than the other). This technology is subject to significant loss of signal strength if used in long distance communication. It is widely used for local short distance wired communication Coaxial cable: Consists of an inner copper conductor insulated from surrounding metal braiding shield and both insulated from the outside with strong hard insulation. Inner and outer conductors travel parallel to each other that result in minimal decibel loss. This technology is used when high quality connection is needed especially in connecting antennas, dishes, network connections, etc This cable is relatively very expensive. It is only used for special short distance connections. 11

12 Fiber-optic technology Fiber optic cable: This technology is more and more used to replace copper wire technology for wired connections. It consists of up to 800 fibers in one shielded cable. A fiber is 1/8 mm diameter coated with an insulator its size will be doubled to.25mm. They are widely used in campuses, buildings, subdivisions, industrial plants, etc Used by cable TV and Internet providers to lay out their networks and distribute the bulk of their services to community, subdivisions and big campuses Provides the backbone for most business networks Businesses usually lay much more than they need because difference in cost is not really meaningful. May be laid underwater in oceans to form transcontinental links. 12

13 How fiber-optic works? Imagine a very thin very long (60 miles) pipe whose interior surface is coated with a mirror. If you flash a light at one end of the pipe it will travel amplified by successive reflections and shine at the other end of the pipe (similar to the LASAR principle). If you install transmitter of signals at one end and a receiver to capture the signal at the other end then each fiber will form a separate circuit to accommodate one communication circuit or one subscriber. Signal transmitted over the fibers are all transformed into digital (light or no light) and that is how the transmission works. 13

14 Pros and cons of Fiber-optic Pros: Operates at very high speed and large capacity Not affected by surrounding electromagnetic noise generated by motors, radio, other cables, etc Easier and cheaper maintenance. Signals travel long distance without any need for amplifying and strengthening. Cons: They are very fragile and need to be protected from bending and passing over by transportation means, people and animals. Need to be protected from water contamination. Any wear or degradation in the fiber insulation will cause signal flare to affect other fibers causing quality deterioration. High cost. 14

15 High capacity cables T1 line: Reserved circuit that uses copper or fiber optic cables to operate over various networking distances. T1 data rate is 1.54 Mbps similar to symmetric DSL Monthly Cost is about $1000 and more and mostly used by hotels, apartment buildings and subdivision and some business and college campuses where the cost can be justified. T3 line: Use copper and fiber optic cables to operate as a reserved circuit equivalent to an aggregation of 28 T1 lines. Data rate is about 44.7 Mbps (1.54 x 28 = 44.7). Monthly cost is about $3000 or more that s why it is used as a backbone of large business network or the headquarters of big businesses and large size campuses and military bases. Cables in general have some advantages over wireless: Compatibility with industry standards are very flexible to be tailored so that industry standards are satisfied. Capacity is usually higher Reliability 15

16 Radio frequency (wave) 1- Introduction: a. Radio telecommunications use waves propagating from antennas or dishes while carrying the signals we need to transmit. b. Radio signal travels at the speed of light in the vacuum (300,000 kilometers/second or 300,000,000 meters/second), that is a little more than one billion kilometers/hour. 2- Signal characteristics: Frequency and wavelength a. Frequency = number of cycles/second or Hz/second b. Wavelength is the distance covered by 1 cycle = 300/frequency in MHz (when the frequency increases the wavelength decreases and when the frequency decreases the wavelength increases accordingly). 3- Examples: a. The wavelength of 3 MHz frequency = 300/3 = 100 meters b. The wavelength of 30 MHz frequency = 300/30 = 10 meters + Analog digital 16

17 Radio frequency (wave) 30 GHz 300 GHz Microwave EHF Extremely High Frequency 3 GHz - 30 GHz Microwave SHF Super High Frequency medium 330 MHz 3 GHz Microwave UHF Ultra High Frequency long oven 30 MHz 330 MHz VHF Very High Frequency 3 MHz 30 MHz HF High Frequency 300KHz 3 MHz MF Medium Frequency 30 KHz 300 KHz LF Low Frequency 10 KHz 30 KHz VLF Very Low Frequency 17

18 NASA classification Radio waves : 30 KHz- 3 GHz Height of Statue of liberty diameter Microwaves: 300 MHz- 300 GHz Baseball diameter Infrared waves: 300 GHz- 400,000 GHz Human hair diameter Visible light waves 400,000 GHz 500,000 GHZ Red frequency Visible light waves 500,000 GHz 600,000 GHz yellow & green Visible light waves 600,000 GHz 750, 000 GHz Blue and Violet Ultraviolet waves 750,000 GHz 3,000,000 GHz Ultraviolet X-Rays 100 million GHz 1 billion GHz Gamma rays Shortest wave with a frequency higher than X-Rays; produced on earth by lightening, nuclear explosion and radiation and produced in the space by the most energetic objects of the universe. 18

19 Signal propagation While wired telecommunication uses cables to carry signals, wireless telecommunication is based on the ability of electro-magnetic waves then known as (Hertz waves) to travel in the air at the speed of light by means of propagation from antennas. Although German physicist Heinrich Hertz ( ) is credited with building the first antenna in , the word Antenna (frequently known as aerial) is an Italian word that means pole in English was first used by Italian radio pioneer Guglielmo Marconi ( ) who developed radio telecommunication into commercial and military success. Marconi developed transmission and reception stations and antennas between 1895 and 1900 and his first antenna was a wire attached to the top of a 2.5 meters pole and running down the pole. His invention was credited by the United Kingdom with saving people who survived the Titanic disaster. The first transatlantic transmission achieved by Marconi in 1901 used 500 feet (152.4 meters) wire as reception antenna. 19

20 How it works? Sender (Transmitter): Signal charges cause the antenna to radiate electromagnetic waves that travel at the speed of light in the vacuum (the speed is slightly less in the open air due to the atmospheric conditions) Receiver antenna intercepts radio waves (weakened by trip resistance), sends them to electronic circuitry to get amplified and further converted into their original type of signal at the output (audio, picture, etc ) 20

21 Types of antennas Omnidirectional: propagate in all directions and used when there is no determined direction in sending and/or receiving signals and for medium and low frequency signal transmission. Whip antenna: like car antenna Turnstile antenna: high pole function as antenna, Directional antennas: When the sending and receiving direction matter then the antenna should be directed following a given angle: Dipole antenna first invented by Heinrich Hertz and consist of 2 rods like rabbit ears connected by a central wire. The rods are adjusted to be aligned with the signal angle. Yagi antenna: consists of several bars fixed in parallel on an axis with a folded one reflector in the middle: this is a directional antenna used mainly in television receivers. Parabolic or Dish antenna: a parabola like curved surface is an extremely directional antenna used mainly in microwave transmission because of its high directional selectivity. 21

22 Wireless line of sight Goethe, ( ) evoking wave propagation, said: why is it possible to hear around corners, but not see around them? Although all radio signals travel at the speed of light, the frequency of the signal controls the way it is influenced by obstacles on the way. Higher frequency are highly absorbed by obstacles and lower frequencies are more refracted, diffracted or reflected by obstacles or thru openings of buildings, cities and nature geographical landscape. Compare the frequency to the drill bit: The faster it turns the sharper it perforates things. It can also be compared to the bullet s velocity that enables bullet to travel a distance and hit a target. Does that mean lower frequencies are better than higher frequencies for telecommunication purposes? The answer is NO because communication over long distance will add a lot of conflicting refraction, reflection and diffraction that weakens the signal and make the telecommunication impossible. 22

23 Relay Towers Towers as relays: To satisfy the line of sight condition necessary for radio telecommunication, service providers use high towers to install the antennas. Towers may be installed as free standing or on top of high rise building roofs in cities: Since its inauguration in 1931 the Empire state building had a mast installed on its roof where (National Broadcasting Company (NBC) and several broadcasting stations installed their TV and FM broadcasting antennas Today the Empire State building is the hub of most radio FM and television stations and wireless Internet channels that operate in the New York area. Satellites as relays: A telecommunication satellite works as a 300 miles high tower. The round shape of the earth pose a natural obstacle between 2 distant locations Telecommunication satellite orbits the earth at miles altitude while covering a specific area. When you look at the satellite from Earth you cannot see that it is traveling because it is matching the Earth movement for a complete cycle every 24 hours. 23

24 Other roles of relay Radio signals traveling encounter resistance and lose a lot of their strength. The loss is measured in decibels. Relays intercept and retransmit signals Relays are equipped with repeaters and transponders that amplify signals before being retransmitted or redirected to their destinations. Satellites broadcast the coordinates of their location in orbit (very important information that makes the GPS technology possible. 24

25 25 Communication topology Simplex topology: This technology is based on the use of only one frequency channel to accommodate the communication. Only one station can transmit or broadcast Examples are radio AM stations, radio FM stations, Television stations. Half duplex technology also known as (HDX) technology Use only one frequency channel to accommodate both transmitting and receiving of communicating devices. All stations can transmit and receive but not simultaneously (only one station can transmit at a time) Must push a button or a switch in order to switch from receiving to transmitting and vice versa. Examples are: Citizens band (CB) radio, walkie-talkies and a lot of military radio equipment. Walkie-talkie has low transmission power can reach a range up to one mile. CB radios have more transmission power they can be used for a range up to 5 miles by citizens, businesses, police and other agencies This radio telecommunication system is not controlled by an technology protocol that enforces transmission priorities Transmitting station should end its transmission message by the word over or any other signal that invites other stations to transmit if they wanted to.

26 Microwave Communications High-frequency radio signals sent up to 30 miles through the air.

27 Microwave Communications Line-of-sight communications

28 Microwave Communications Satellite Transmission Line-of-sight required

29 Networking Software 29

30 Full duplex Full duplex technology also known as (FDX) technology: The full duplex technology basically uses 2 different frequency channels to send and receive in each station. Unlike half duplex that need switch from receive to send full duplex technology allows each station to simultaneously transmit while listening or receiving data without any switching need. New time and frequency multiplexing technologies allow Full duplex to use only one frequency that results in doubling the communication power without any need for adding new towers and equipment. Examples of FDX includes but not limited to: Wired telephone networks. Wireless phones known as cordless phones. Internet telephony Cellphone technology 30

31 GPS The actual GPS we are using is a utility owned by the US government and operated by the government s specialized agencies. A Department of Defense project that started in 1973 and became fully operational for both military and civilian use in The first satellite navigation system in the US was used in 1960 and consists of a constellation of 5 satellites. The system in use now is the GPSIII. It is composed of 3 parts: The satellite constellation comprises 24 satellites each of them broadcasts the coordinates of its own location in orbit. GPS service receiving and computing devices: intercept satellite signals and compute their own location on earth by interpolation. Since we may have 24 points the center will indicate the actual location with great precision. Control and correction service: The computing accuracy is highly affected by the strength and accuracy of satellite signals To maintain signal quality and correct any errors there are ground stations around the world (US, Europe, Japan, etc ) specialized in receiving signals, correcting them and retransmitting them to users 31

32 Other GPS systems Russian GLONASS (Global Navigation Satellite System) started in 2007, also consists of 24 satellites able to provide full global coverage used by smart phones technology 4G and 5G (Sony and other phones). China has its own GPS (Chinese satellite navigation system) known as the BeiDou system that consists now of 4 satellites with 6 more scheduled to be launched soon and the complete constellation of 35 satellites by 2020 will cover the globe. Europe has its GPS known as the Galileo system which is advertised as a civilian-controlled alternative to the American GPS it consists of 4 satellites that will be tuned and joined by 22 other satellites by

33 How GPS work? Each satellite continually send messages that have information about: Coordinates of their location in orbit. The time they sent the message GPS receivers use that information in space navigation formula that enables them to compute their own position on earth with high accuracy. More than 3 satellites must be visible in order to get accurate results. GPS basic areas of use can be summarized by the abbreviation PNT Positioning Navigation Timing 33

34 Cell Phone Technologies A cellular network is a radio network in which a geographic area is divided into cells, with a transmission tower and station at the center of each cell, to support mobile communications.

35 Operational cellphone data Transmitter basically have to be operational with low transmission power (between.5 watt and 3 watts) Each cellular provider gets from FCC (Federal Communication Committee) 832 different radio frequencies for a specific area of served by that provider. 42 frequencies are used for control purposes. Each communication call uses 2 frequencies; Transmitting frequency Receiving frequency For an area of 7 cells, cellphone provider can accommodate up to 56 possible user communications simultaneously in each cell (56x7 = 392). The low transmission powers it possible for non-adjacent cells to use the same frequencies without any fear from interference between conflicting calls using same frequencies.

36 Cellphone operational technology Transmitter basically have to be operational with low transmission power (between.5 watt and 3 watts) Each cellular provider gets from FCC (Federal Communication Committee) 832 different radio frequencies for a specific area of served by that provider. 42 frequencies are used for control purposes. Each communication call uses 2 frequencies; Transmitting frequency Receiving frequency For an area of 7 cells, cellphone provider can accommodate up to 56 possible user communications simultaneously in each cell (56x7 = 392). The low transmission powers it possible for non-adjacent cells to use the same frequencies without any fear from interference between conflicting calls using same frequencies.

37 Operational technology There are two incompatible technologies to operate cellphone networks; Code Division multiple Access (CDMA): Used in the USA, JAPAN and some companies in ASIA and South America. Phones use the same frequencies but are separated and recognized by a different code used by the network to encode each call. Compare it to your possibility to recognize the guitar sound from the drum sound from the piano sound in a music concert. GSM/TDMA (Global System for Mobile communications/time Division Multiple Access). European system used everywhere in the world even in the USA and JAPAN. GSM is universal system. The network assigns frequencies and time slots within each second to each individual call (it tells your phone what frequencies to use and what time to broadcast). Has SIM (Subscriber Information Module) card or chip to record information of each subscriber authorized to use to network.

38 CDMA/GSM GSM is global (when you travel you need only to buy a new SIM and fit it into your cellphone and you are ready to go. GSM/TDMA has a limited number of communication calls that may go simultaneously. This ceiling is much higher or inexistent in CDMA. Although CDMA is the initial cellular technology, GSM is taking over because it is much more user friendly. One disadvantage of GSM is when you are moving into neighboring cells where in TDMA/GSM you cannot use the same frequencies which may create a problem that would jeopardize efficient use of frequency spectrum. With smartphones extensively using the web. TDMA/GSM has proven to be fit to handle data transmission and internet services better than CDMA.

39 RADAR Principle: Radar technology is based on the principle of wave reflection when they hit metal target. It was developed by the German before WWII and adoption accelerated by Great Britain who thought that the Germans were developing (Death rays). Radar system consists of Transmitter equipped with directed dish or antenna that sends radar pulses in predefined direction Receiver that gets weakened reflected signals, amplify them and display them on a monitor. Signals captured help calculate: The range or distance of the target The altitude of the target The speed of the target if it is moving The direction of movement Some applications allow to analyze and make a judgment about the shape and behavior of the shape

40 Principle: LASER Simulated emission as theorized by Einstein in 1917 can be defined as the laser foundation. Amplification and concentration of light emission power Laser development requires the following necessary components: Flash tube or flash lamp to provide Gain medium that amplifies the light A unit that supply energy to the gain medium Feedback provided by a couple of mirrors installed on either end of the gain medium. Topology of lasers: There are many different types of laser that use different material and therefore, different technologies: Crystal Laser: also called solid state laser generate lot of heat that was overcome by adding a diode with thin disk may produce a Laser power up to one Kw. Gas Laser: Gases were proven to amplify light and many gas Lasers were built widely used in optical research and training labs. Helium-neon Laser Carbon dioxide Laser and Argon Laser Semiconductor Laser: use electrically pumped diodes. Widely used in business equipment applications: Laser printers Pointers of different uses. CD and DVD players and burners Cutting industry Chemical Laser: Very powerful Laser of high interest in military applications and combat Weaponry. Hydrogen fluoride Laser Deuterium fluoride laser Fiber Laser: is a specific type of semiconductor laser with reduced thermal effect

41 Laser business apps Military: Many applications using powerful laser in weaponry guiding and missile defense. Industry: many laser equipment sold for billions of dollars that include and not limited to: Cutting and welding applications, components measurement and marking. Products like printers, CD and DVD players, barcode scanners, pointing devices and thermometers holograms Light shows. Medicine Laser Surgery and healing Eye treatment and eye laser surgery Cosmetics hair and skin treatment. Many other activities use Lase applications mainly in forensics and many research areas

42 Infrared Infrared light waves are also used for short range communication of information between computer devices. IrDA (Infrared Data Association) is a group of computer device manufacturers that developed, implemented and still maintaining the standard. The wave spectrum used is below the visible light waves (red waves are is the lowest visible frequencies). Absolute line of site is needed because these waves cannot penetrate obstacles or overcome them. Used for short distance (about 10 meters 30 feet) in communicating and networking computer devices Most modern computer equipment and computer devices are equipped with IrDA ports so they can communicate and exchange files without any need of connecting IrDA special accommodations. Wireless mouse, wireless keyboard, wireless printer, wireless scanner and generally any wireless peripheral device is equipped with an infrared port and infrared transmitter and receiver. Remote control devices use IrDA standard to transmit command to electronic equipment and electronically operated gates and other industrial features.

43 Light travel distance & time from space to earth Planet Distance (Km) Time Sun 150,000, Mars 92,500, Moon 384,000 ( 01.3) Sirius (Brightest star) 80,000,000,000, years