Chap4

Transcript

Chapter 4: Practical Communication Systems 18/09/2016 Nurul/DEE 3413/Practical Com System 1 Outline Fibre Optic Communication System  Telephone System  Radio Communication System  Satellite Communication System  Telecommunication Networks  18/09/2016 Nurul/DEE 3413/Practical Com System 2 Outline:  Fibre Optic Communication System Introduction  Elements in an optical fiber communication link  Propagation mode  Advantages fiber optic cables over conventional electrical cables  Attenuation in fiber optic link  Application of fiber optic system  18/09/2016 Nurul/DEE 3413/Practical Com System 3 Outline:  Telephone system Introduction  Public telephone network  Telephone connection signalling  Mobile telephone system  Cellular concept  Frequency re-use in cellular communication  18/09/2016 Nurul/DEE 3413/Practical Com System 4 Outline:  Radio communication System Introduction  Radio wave propagation  Microwave radio system (analog and digital microwaves radio transmitters and receiver)  Radio services  18/09/2016 Nurul/DEE 3413/Practical Com System 5 Outline:  Satellite communication system           18/09/2016 Introduction Satellite transponder Satellite system links Earth stations Frequency allocations Satellite orbit System performance Applications of satellite communications Advantages of satellite system Disadvantages of satellite system Nurul/DEE 3413/Practical Com System 6 Outline:  Telecommunication Networks Introduction  LAN, MAN and WAN  Network Topology  18/09/2016 Nurul/DEE 3413/Practical Com System 7 Fibre Optic Communication System  Introduction    18/09/2016 Fiber optic system is a communication system that carries information through a guided fiber optic cable Light frequencies used in fiber optic systems are between 1014 and 4x1014 Hz Thus, the higher the carrier the carrier frequency, the wider the bandwidth and consequently, the greater the information carrying capacity Nurul/DEE 3413/Practical Com System 8 Fibre Optic Communication System  Elements in an optical fiber communication link 18/09/2016 Nurul/DEE 3413/Practical Com System 9 Fibre optic - Basic elements The main elements are:  Driving circuitry:   Light source    LED / LASER Convert electrical energy to optical energy, where the amount of light emitted is proportional to the amount of drive current Light source-to-fiber coupler   Serves as an electrical interface between the input circuitry and light source and to drive the light source An interface to couple the light emitted by the source into the optical fiber cable Fiber optics  18/09/2016 Long thin strand of glass or plastic fiber used to signal in a form of light from a point to another point Nurul/DEE 3413/Practical Com System 10 Fibre optic - Basic elements  Fiber optics   Fiber-to-detector coupler   Long thin strand of glass or plastic fiber used to signal in a form of light from a point to another point Interface between fiber and light detector to couple as much light as possible from the fiber cable into the light detector Light detector  18/09/2016 PIN (p-type-intrinsic-n-type) diode / an APD (avalance photodiode) Nurul/DEE 3413/Practical Com System 11 Propagation Mode  Monomode fiber (core 8 ~ 12 um)   Only one path for the light to propagate along fiber All light rays follow the same path down the cable and take the same time to travel the length of the cable Monomode step-index fiber 18/09/2016 Nurul/DEE 3413/Practical Com System 12 Propagation Mode  Multimode step index fiber (50 ~200 um)   More than one path for light propagate along fiber Light ways are propagated down the cable in a zig-zag pattern and all the light rays do not follow the same path with different propagation time slowest mode input pulse fastest mode output pulse Multimode step-index fiber 18/09/2016 Nurul/DEE 3413/Practical Com System 13 Propagation Mode  Multimode graded index fiber   Light is propagated down the fiber by refraction which result a continuous bending at the light rays, Then the rays traveling near the center, so that all the rays arrive at the end point at the same time input pulse output pulse Multimode graded-index 18/09/2016 Nurul/DEE 3413/Practical Com System 14 Fiber optic - Advantages       Wider bandwidth: have higher information to carry Lower loss/attenuation: there is less signal attenuation over long distance Light weight: higher than copper cable and offer good benefit where weight is critical (plane) Small size: smaller diameter than electrical cable Strength: as it has cladding, they offer more strength Security: cannot be ‘tapped’ easily as electrical cable 18/09/2016 Nurul/DEE 3413/Practical Com System 15 Attenuation The attenuation in fiber optics are due mainly to:  Scattering losses (kehilangan serakan)  Absorption losses (kehilangan penyerapan)  Bending losses (kehilangan pembengkokan /lenturan)  Splicing loss  Coupling losses (kehilangan gandingan) 18/09/2016 Nurul/DEE 3413/Practical Com System 16 Attenuation – standard fiber 1st window 2nd window 3rd window 18/09/2016 wavelength :0.85 um The lowest minimum loss: 5 to 10 db/km 1.30 um 0.5 to 2 dB/km 1.55Nurul/DEE um 01. to 0.5 dB/km 3413/Practical Com System 17 Application of fiber optic cable Some of the applications of fiber optic   Long haul, backbone public and private networks Local loop networks  Fiber backbone networks (LAN connectivity)  High resolution image and digital video  Computer networks, wide area and local area  Shipboard communications  Aircraft communications and controls  Interconnection of measuring and monitoring instruments in plants and laboratories 18/09/2016 Nurul/DEE 3413/Practical Com System 18 Satellite communication system Satellite communications utilizes radio frequencies in the microwave range as the communications medium and uses satellites to 'bounce' an earth-bound station's uplink signal back down to a receiving earth station. A satellite system consist of:    A transponder (a radio repeater in the sky) A ground-based station to control this operation A user network of earth stations that provide the facilities for transmission and reception of communication traffics through the satellite station 18/09/2016 Nurul/DEE 3413/Practical Com System 19 Satellite communication system The uplink and downlink use different carrier frequencies to avoid interference, and the frequency translation is done in the transponder. 18/09/2016 Nurul/DEE 3413/Practical Com System 20 Satellite transponder  Satellite transponder acts like a repeater, consists of a receiver and a transmitter. The main functions of a satellite transponder are:     18/09/2016 To pick up the transmitted signal from the transmission on the earth To amplify the signal To translate the carrier frequency to another frequency To retransmit the amplified signal to the receiver on the earth Nurul/DEE 3413/Practical Com System 21 Satellite transponder Band pass filter Low noise Amplifier (LNA) Mixer Band pass filter (BPF) Low power Amplifier Local oscillator Frequency translator Earth station Earth station A satellite transponder BPF – limits the total noise LNA amplifiers – receive signal and fed it to the frequency translator Freq. translator – convert the high-band uplink frequency to the low-band downlink frequency 18/09/2016 Nurul/DEE 3413/Practical Com System 22 Satellite system link  Uplink     Path of the satellite signal from the earth transmitter to the receiver of the satellite. The freq. signal being transmitted from the earth station to the satellite is called uplink frequency eg: uplink freq. for C-band is 6 Ghz Downlink    18/09/2016 Path of the satellite signal from the satellite transmitter to the receiver on the earth The retransmitted signal from the satellite to the receiving stations is called the down-link eg: downlink freq. for C-band is 4 GHz Nurul/DEE 3413/Practical Com System 23 Earth station Tel Data Video Baseband in FDM or PCM/TDM Modulator (FM, PSK or QAM) Mixer Band pass filter (BPF) Generator High Power Amplifier To (HPA) Satellite transponder Up-Converter AN EARTH STATION TRANSMITTER From satellite transponder Low noise Amplifier (LNA) Mixer Band pass filter (BPF) Demodulator (FM, PSK or QAM Baseband out (FDM or PCM/TDM) Data Video Tel Generator 18/09/2016 Down-Converter Nurul/DEE 3413/Practical Com System AN EARTH STATION RECEIVER 24 Earth station Tel Data Video Baseband in FDM or PCM/TDM Modulator (FM, PSK or QAM) Mixer Band pass filter (BPF) Generator High Power Amplifier To (HPA) Satellite transponder Up-Converter AN EARTH STATION TRANSMITTER - Intermediate freq (IF) modulator converts the input baseband signals to either an FM, a PSK or a QAM modulated intermediate frequency. - The up converter converts the IF to an appropriate RF carrier freq. - The High Power Amplifier (HPA) provides the adequate input sensitivity and output power to propagate the signal to the satellite transponder. 18/09/2016 Nurul/DEE 3413/Practical Com System 25 Earth station From satellite transponder Low noise Amplifier (LNA) AN EARTH STATION RECEIVER Mixer Band pass filter (BPF) Demodulator (FM, PSK or QAM Baseband out (FDM or PCM/TDM) Data Video Tel Generator Down-Converter - LNA which is highly sensitive and low-noise device amplifiers the received signal. - The RF to IF down-converter is a mixer and bans pass filter combination, which converts the received RF signal to an intermediate frequency (IF) 18/09/2016 Nurul/DEE 3413/Practical Com System 26 Frequency Allocation 18/09/2016 Nurul/DEE 3413/Practical Com System 27 Satellite Orbit  Sattellite Orbits  18/09/2016 Satellites are launched into orbit, which is to say that they are shot up into the sky on rockets to get them up above the atmosphere where there is no friction. The idea is to get them flying so fast, that when they fall back to earth, they fall towards earth at the same rate as the earth's surface falls away from them. When an object's path around the earth "trajectory" matches the earth's curvature, the object is said to be "in orbit". Nurul/DEE 3413/Practical Com System 28 Satellite Orbit Three basic types of orbits are: 1. Polar orbit  North-south orbit  Used for navigation, weather satellite, meteorological etc  Not used for telecommunication purposes 2. Elliptically inclined orbit  Used for Russian domestic systems, with inclination of 63 degrees and a 12 hour orbit period, but visible for 8 hours only  So 3 satellites are needed for continuous coverage Basic Orbits 18/09/2016 Nurul/DEE 3413/Practical Com System 29 Satellite Orbit 3) Circular equatorial orbit  It is called geosynchronous orbit  At a height of about 35800 km, has 24 hour orbit period, and its angular speed is equal to the rotational speed of the earth.  So it appears stationary or motionless over a fixed point on the earth’s surface.  The satellite is visible from 1/3 of the earth’s surface, so 3 satellite are needed for full coverage of the earth Basic orbits 18/09/2016 Nurul/DEE 3413/Practical Com System 30 Satellite Orbit Polar orbit Elliptically inclined Equatorial orbit 18/09/2016 Nurul/DEE 3413/Practical Com System 31 System performance Gr Uplink Transponder Gain, Gsat Gt Lp Lp Gt HPA Po Pt Lf Pr Pin LNA Earth station transmitter Earth station receiver HPA – high power amplifier Po - HPA output power Lf - feeder loss Gt - transmit antenna gain Lp - path loss Gr - receive antenna gain 18/09/2016 Downlink Gr LNA – low noise amplifier Pt - total radiated power, Pt = Po - Lf EIRP - Effective Isotropic Radiated Power EIRP = Pt * Gt Nurul/DEE 3413/Practical Com System 32 Uplink And Downlink Chains  The term uplink chain is used to refer to the series of pieces of equipment that are used to produce a radio frequency signal for sending out data. The description provided here is imprecise as the exact configuration can vary widely.  The downlink chain is built using nearly the same equipment in reverse order. 18/09/2016 Nurul/DEE 3413/Practical Com System 33 18/09/2016 Nurul/DEE 3413/Practical Com System 34 Uplink Chains  Digital data - modulator ( Intermediate Frequency range (70140 Mhz)). The modulators use standards such as Digital Video Broadcast to organize communication over the microwave link.  The Intermediate Frequency - "up converter" - a higher frequency  Noise removed - a band pass filter - then amplified.  Signal - transmitted - wave guide to the dish.  The feed horn at the focal point of the dish emits the high frequency radio transmission, which the dish focuses into a directional transmission at the satellite. 18/09/2016 Nurul/DEE 3413/Practical Com System 35 Downlink Chains  The signal is received at the sattellite dish  The signal is amplified and fed to the Down Converter  The Down Converter down mixers the signal to create an intermediate frequency  The intermediate frequency is fed to the demodulator and converted into a data signal  The datastream is forwarded into the network via a router. 18/09/2016 Nurul/DEE 3413/Practical Com System 36 Application of satellite communication Some of the application s of satellite communications are:  Digital audio broadcasting  Television distribution  Serving remote areas  Point-to-multipoint communications  Remote monitoring and control  Vehicle tracking  Mobile communications  Maritime and air navigation  Video teleconferencing 18/09/2016 Nurul/DEE 3413/Practical Com System 37 Advantages/disadvantages of satellite system Advantages of a satellite system include:  It can access to wide geographical area  Wide bandwidth  High reliability  Distance sensitive cost  Independent of terrestrial infrastructure Disadvantages of satellite system  High initial cost  It has propagation delay 18/09/2016 Nurul/DEE 3413/Practical Com System 38 Telecommunication Networks “A network is a communication system that interconnects many users and is designed to let any user send messages to any and/or all other users on a common set of communication links” The word network is used generally to mean a set of computers that are connected together in such a way as to permit them to communicate and share information.  Network applications:    18/09/2016 Offices Linking various personal computers Interconnecting larger computers located in different buildings or cities etc. Nurul/DEE 3413/Practical Com System 39 LAN, MAN and WAN  Three categories of networking depends on the application: LAN, MAN and WAN  LAN (Local Area Networks) MAN (Metropolitan Area Networks) WAN (Wide Area Networks)   18/09/2016 Nurul/DEE 3413/Practical Com System 40 LAN    Is a data communication network across a limited area, at most 5 km Permit the users (normally 10 – 100 users) to share information and computers sources include data storage, software, printer, etc Is used to connect several offices within the same building, or in a working group or as a campus backbone 18/09/2016 Nurul/DEE 3413/Practical Com System 41 MAN  Medium- sized network  Cover an area between 5 – 50 km  Typically MAN may use coaxial cables or optical fiber as the medium  Provide services such as audio, data and video  High capacity backbone (1.544 Mbps or 45 Mbps) 18/09/2016 Nurul/DEE 3413/Practical Com System 42 WAN  Cover a large area, more than 50 km  Typically, WAN is a packet switching network  Used in internet, electronic mail, airline reservation system  In some cases, WAN is built of smaller LANs that are closely linked, or made of mixed combinations of LANs and special longer distance links  Connect computers located over large geographical areas through some combination of telephone lines, satellite, radio transmission and optical fiber over public switched telephone network (PSTN) or private network facilities 18/09/2016 Nurul/DEE 3413/Practical Com System 43 Network Topology  Network topology is a physical schematic for the different configuration or arrangements, to show the interconnection of the users  The logical topology concerns signal flow in the network or how data actually travels There are 3 basic topologies:    18/09/2016 Star network topology Ring network topology Bus network topology Nurul/DEE 3413/Practical Com System 44 Ring network topology  users - connected in closed path token-passing ring protocol predictable access time to the network  Ring scheme    node accepts the message- processes - extracts data -modifies message - passes it on to the next node A drawback of the ring  18/09/2016 The failure of any node - cause breakdown over come by :  Dual or redundant path as a standby path  Watchdog circuitry: When it detect a problem with the node, it sets a switch which electrically by-passes that node Nurul/DEE 3413/Practical Com System 45 Bus network topology   all user nodes - connected by a bus - a coaxial cable or parallel-wire line The signals can move in both directions along the bus 18/09/2016  Advantage - use a single path - saves cost  Drawback – rewiring difficulty - complicated protocols – CSMA/CD (carrier sense multiple access/collision detect) Nurul/DEE 3413/Practical Com System 46 Star network topology   all user nodes - connected to a central hub The signals are sent to central point 18/09/2016  Advantage – expanding flexibility  Drawback – slow – need to go through central hub Nurul/DEE 3413/Practical Com System 47 18/09/2016 Nurul/DEE 3413/Practical Com System 48 Local Area Network Topologies  Local Area Networks (LANs) use one of the following designs. These designs are referred to as 'topologies'. 18/09/2016 Nurul/DEE 3413/Practical Com System 49 18/09/2016 Nurul/DEE 3413/Practical Com System 50 Example: 1. A satellite transponder has a gain of 50 dB. Its receiving and transmitting antenna have equal gain of 20 dB. If the receiving antenna receives a signal power of 10 uW from the earth transmitter, determine the signal power at the output of the satellite transmitting antenna. 18/09/2016 Nurul/DEE 3413/Practical Com System 51 Telephone  Telephone system  Public telephone network - Local loop or local network - Junction network - Trunk network or toll network - # international gateway  Telephone connection signalling - Speech signal/information signal (in analogue form) - Control signal (in analogue or digital form) - Dialling tone - Ringing tone - Busy tone 18/09/2016 Nurul/DEE 3413/Practical Com System 52 Telephone   18/09/2016 Mobile telephone system  Mobile set (handset)  Radio base station (RBS)  Mobile switching centre (MSC) Cellular concept  Frequency re-use in cellular communication Nurul/DEE 3413/Practical Com System 53 Mobile Telephone System Basic elements of a mobile telephone system are:  Mobile set (handset)   Radio base station (RBS)    Act as a small radio station equipment with transmitter and receiver which has an antenna and push button set to enable users to make or receive call through public network Handle the exchange between user and respected area (serves as a centre node for all users) Receive signal and rebroadcast it at higher power Mobile switching centre (MSC)  18/09/2016 Handles the exchange from RBS to PSTN Nurul/DEE 3413/Practical Com System 54 Mobile Telephone System 18/09/2016 Nurul/DEE 3413/Practical Com System 55 Radio Communication System  Radio communication System  Introduction - Is a wireless communication system by using the propagation of electromagnetic signals through free-space - Two categories of radio systems: - Conventional AM or FM radio - Digital radio system - In digital radio system, the modulating and demodulated signals are digital pulses. - Three digital modulation techniques that are commonly used in digital radio systems: - FSK, PSK and QAM  Radio wave propagation - - 18/09/2016 Ground wave : low freq (LF) and medium freq (MF) bands Space wave: VHF, UHF and higher freq bands Sky wave: MF and HF bands Nurul/DEE 3413/Practical Com System 56 Radio Communication System  Microwave radio system (analogue and digital microwaves radio transmitters and receiver) The main difference is the modulation technique used and the multiplexing technique 18/09/2016 Nurul/DEE 3413/Practical Com System 57 Radio Communication System  18/09/2016 Radio services Nurul/DEE 3413/Practical Com System 58