Mobile and Wireless Networks Course Instructor: Dr. Safdar Ali

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1 Mobile and Wireless Networks Course Instructor: Dr. Safdar Ali

2 BOOKS Text Book: William Stallings, Wireless Communications and Networks, Pearson Hall, 2002.

3 BOOKS Reference Books: Sumit Kasera, Nishit Narang, 3G Networks Architecture, Protocols, and Procedures,Tata McGraw-Hill Education, 2004.

4 COURSE EVALUATION Quiz: 10% Assignments: 20% Mid Term: 20% Final Exam: 50%

5 Communication Networks

6 TYPES OF COMMUNICATION NETWORKS Local area network (LAN) Wide area network (WAN)

7 SWITCHING NETWORK For transmission of data beyond a local area, communication is typically achieved by transmitting data from source to destination through a network of intermediate switching nodes. The switching nodes are not concerned with the content of the data; rather their purpose is to provide a switching facility that will move the data from node to node until they reach their destination.

8 SWITCHING NETWORK Information from station A intended for station F. Data is sent to node 4.

9 SWITCHING NETWORK It may then be routed via nodes 5 and 6 or nodes 7 and 6 to the destination.

10 SWITCHING NETWORK Some nodes connect only to other nodes (e.g., 5 and 7). Their sole task is the internal (to the network) switching of information.

11 SWITCHING NETWORK Other nodes have one or more stations attached as well; in addition to their switching functions, such nodes accept information from and deliver information to the attached stations.

12 SWITCHING NETWORK Node-station links are generally dedicated point-topoint links.

13 SWITCHING NETWORK Usually, the network is not fully connected; that is, there is not a direct link between every possible pair of nodes. However, it is always desirable to have more than one possible path through the network for each pair of stations. This enhances the reliability of the network.

14 SWITCHING NETWORK Two quite different technologies are used in wide area switched networks: Circuit switching and Packet switching. These two technologies differ in the way the nodes switch information from one link to another on the way from source to destination.

15 Circuit and Packet switching??

16 SWITCHING TECHNIQUES Circuit switching Dedicated communications path between two stations The most common example of circuit switching is the telephone network. Packet switching Each node determines next leg of transmission for each packet

17 CIRCUIT SWITCHING Station A wants to send data to station E.

18 PHASES OF CIRCUIT SWITCHING Circuit establishment An end to end circuit is established through switching nodes Information Transfer Information transmitted through the network Data may be analog voice, digitized voice, or binary data Circuit disconnect Circuit is terminated Each node deallocates dedicated resources

19 CONNECTION OVER A PUBLIC CIRCUIT- SWITCHING NETWORK

20 Disadvantages?

21 CIRCUIT SWITCHING Can be inefficient Channel capacity dedicated for duration of connection even no data is being transferred. Utilization not 100%

22 PACKET SWITCHING Data is transmitted in blocks, called packets A typical upper bound on packet length is 1000 octets (bytes). If a source has a longer message to send, the message is broken up into a series of packets

23 PACKET SWITCHING The control information, includes the information that the network requires in order to be able to route the packet through the network and deliver it to the intended destination.

25 PACKET SWITCHING

26 Advantages?

27 PACKET SWITCHING ADVANTAGES Line efficiency is greater Many packets over time can dynamically share the same node to node link Unlike circuit-switching networks that block calls when traffic is heavy, packet-switching still accepts packets, but with increased delivery delay

28 Disadvantages?

29 PACKET SWITCHING DISADVANTAGES Overall packet delay can vary substantially This is referred to as jitter Caused by differing packet sizes, routes taken and varying delay in the switches Each packet requires overhead information Includes destination and sequencing information Reduces communication capacity More processing required at each node

30 Antennas and Propagation

31 What is Antenna???

32 INTRODUCTION An antenna is an electrical conductor or system of conductors Transmission - radiates electromagnetic energy into space Reception - collects electromagnetic energy from space In two-way communication, the same antenna can be used for transmission and reception

33 What is Radiation Pattern??

34 RADIATION PATTERNS An antenna may radiates power in all directions but, typically, does not perform equally well in all directions. A common way to characterize the performance of an antenna is the radiation pattern, which is a graphical representation of the radiation properties of an antenna as a function of space coordinates.

35 RADIATION PATTERNS The simplest pattern is produced by an idealized antenna known as the isotropic antenna. An isotropic antenna is a point in space that radiates power in all directions equally. The actual radiation pattern for the isotropic antenna is a sphere with the antenna at the center.

36 RADIATION PATTERNS Figure (b) shows the radiation pattern of another idealized antenna. This is a directional antenna in which there is a preferred direction of radiation.

37 RADIATION PATTERNS The isotropic antenna produces an omni-directional radiation pattern of equal strength in all directions, so the A and B vectors are of equal length.

38 RADIATION PATTERNS For the antenna pattern of Figure (b), the B vector is longer than the A vector, indicating that more power is radiated in the B direction than in the A direction.

39 Any Example of omni-directional and directional antennas??

40 TYPES OF ANTENNAS Isotropic antenna (idealized) Radiates power equally in all directions Dipole antennas Half-wave dipole antenna (or Hertz antenna) Quarter-wave vertical antenna (or Marconi antenna) Parabolic Reflective Antenna

41 DIPOLE ANTENNA

42 PARABOLIC REFLECTIVE ANTENNA An important type of antenna is the parabolic reflective antenna. Used in terrestrial microwave and satellite applications.

43 PARABOLIC REFLECTIVE ANTENNA If a source of electromagnetic energy is placed at the focus of the paraboloid, and if the paraboloid is a reflecting surface, then the wave will bounce back in lines parallel to the axis of the paraboloid.

45 Antenna Gain??

46 ANTENNA GAIN Antenna gain is a measure of the directionality of an antenna. Antenna gain is defined as the power output, in a particular direction, compared to that produced in any direction by a perfect omni-directional antenna (isotropic antenna). Increased power is radiated in one direction by reducing the power radiated in other directions.

47 Effective Aperture???

48 EFFECTIVE APERTURE A practical antenna with a physical aperture area A will not deliver the total power to the receiver. Some of the energy incident on the aperture is reflected away from the antenna, and some is absorbed by lossy components. The reduction in efficiency is described by the effective aperture.

49 ANTENNA GAIN Relationship between antenna gain and effective area G G = antenna gain A e = effective area f = carrier frequency c = speed of light (3 x10 8 m/s) = carrier wavelength 4 A e 2 4 f c 2 2 A e

50 NUMERICAL For a parabolic reflective antenna with a diameter of 2 m, operating frequency at 12 GHz, what is the effective area of and the antenna gain??

51 HINTS A = л r square

52 SOLUTION

53 PROPAGATION MODES A signal radiated from an antenna travels along one of three routes: Ground-wave propagation Sky-wave propagation Line-of-sight propagation

54 GROUND WAVE PROPAGATION

55 GROUND WAVE PROPAGATION Ground wave propagation more or less follows the contour of the earth. It can propagate considerable distances, well over the visual horizon. This effect is found in frequencies up to about 2 MHz. Example AM radio

56 SKY WAVE PROPAGATION

57 SKY WAVE PROPAGATION

58 SKY WAVE PROPAGATION Sky wave propagation is used for international broadcasts such as BBC and Voice of America. Signal reflected from ionized layer of atmosphere back down to earth. Signal can travel a number of hops, back and forth between ionosphere and earth s surface. With this propagation mode, a signal can be picked up thousands of kilometers from the transmitter.

59 LINE-OF-SIGHT PROPAGATION

60 LINE-OF-SIGHT PROPAGATION Above 30 MHz, neither ground wave nor sky wave propagation modes operate. Transmitting and receiving antennas must be within line of sight Satellite communication signal above 30 MHz not reflected by ionosphere

61 OPTICAL AND RADIO HORIZON

62 LINE-OF-SIGHT EQUATIONS Optical line of sight d h Effective, or radio, line of sight d = distance between antenna and horizon (km) h = antenna height (m) d h K = adjustment factor to account for refraction, rule of thumb K = 4/3

63 LINE-OF-SIGHT PROPAGATION Maximum distance between two antennas for LOS propagation: d h 1 = height of antenna one h 2 = height of antenna two 3.57 h h 1 2

64 NUMERICAL What will be the maximum distance between two antennas for LOS transmission if one antenna is 100 m high and other is at ground level. Ans = 41 km Now suppose that the receiving antenna is 10 m high. To achieve the same distance, how high must the transmitting antenna be? Ans = 46.2m

65 SOLUTION

66 LOS WIRELESS TRANSMISSION IMPAIRMENTS With any communications system, the signal that is received will differ from the signal that is transmitted, due to various transmission impairments. For digital data, bit errors are introduced: A binary 1 is transformed into a binary 0, and vice versa.

67 LOS WIRELESS TRANSMISSION IMPAIRMENTS Attenuation and attenuation distortion Free space loss Noise Atmospheric absorption Multipath Refraction Thermal noise

68 ATTENUATION The strength of a signal falls off with distance over any transmission medium.

69 ATTENUATION Attenuation factors for unguided media: Received signal must have sufficient strength so that circuitry in the receiver can interpret the signal Signal must maintain a level sufficiently higher than noise to be received without error Attenuation is greater at higher frequencies, causing distortion

70 ATTENUATION The first and second factors are dealt with by attention to signal strength and the use of amplifiers or repeaters. For a point-to-point transmission (one transmitter and one receiver), the signal strength of the transmitter must be strong enough to be received intelligibly, but not so strong as to overload the circuitry of the transmitter or receiver, which would cause distortion.

71 ATTENUATION Beyond a certain distance, the attenuation becomes unacceptably great, and repeaters or amplifiers are used to boost the signal at regular intervals.

72 FREE SPACE LOSS Free space loss can be express in terms of the ratio of the radiated power Pt to the power Pr, received by the antenna.

73 FREE SPACE LOSS Free space loss, ideal isotropic antenna P t P r 2 4 d 4 fd P t = signal power at transmitting antenna P r = signal power at receiving antenna = carrier wavelength d = propagation distance between antennas c = speed of light (3 x10 8 m/s) where d and are in the same units (e.g., meters) 2 c 2 2

74 FREE SPACE LOSS Free space loss equation can be recast: L db 10log Pt P r 20log 4 d 20log d db 20log 4 fd 20log 20log c f 20log d db

76 FREE SPACE LOSS Free space loss accounting for gain of other antennas P t P r d d cd G G r G t = gain of transmitting antenna G r = gain of receiving antenna A t = effective area of transmitting antenna A r = effective area of receiving antenna t 2 A r A t f 2 A r 2 A t

77 FREE SPACE LOSS

78 FREE SPACE LOSS Free space loss accounting for gain of other antennas can be recast as L db 20log d 10log A A 20log f 20log d 10log A A t dB 20log t r r

79 NOISE For any data transmission event, the received signal will consist of the: transmitted signal, modified by the various distortions imposed by the transmission system, plus additional unwanted signals that are inserted somewhere between transmission and reception. These unwanted signals are referred to as noise.

80 CATEGORIES OF NOISE Thermal Noise Crosstalk Impulse Noise

81 THERMAL NOISE Thermal noise is due to thermal agitation of electrons. It is present in all electronic devices and transmission media and is a function of temperature.

82 THERMAL NOISE Amount of thermal noise to be found in a bandwidth of 1Hz in any device or conductor is: N kt 0 W/Hz N 0 = noise power density in watts per 1 Hz of bandwidth k = Boltzmann's constant = x10-23 J/K T = temperature, in kelvins (absolute temperature)

83 THERMAL NOISE Noise is assumed to be independent of frequency Thermal noise present in a bandwidth of B Hertz (in watts): or, in decibel-watts N ktb N 10log k 10 log T 10log B dbw 10 log T 10log B

84 NUMERICAL

85 CROSSTALK Crosstalk has been experienced by anyone who, while using the telephone, has been able to hear another conversation. It is an unwanted coupling between signal paths. Crosstalk can also occur when unwanted signals are picked up by microwave antennas.

86 IMPULSE NOISE Impulse noise is consist of irregular pulses or noise spikes of short duration and of relatively high amplitude. It is generated from a variety of causes, including external electromagnetic disturbances, such as lightning, and faults and flaws in the communications system.

87 THE EXPRESSION EB/NO There is a parameter related to SNR that is more convenient for determining digital data rates and error rates and that is the standard quality measure for digital communication system performance. The parameter is the ratio of signal energy per bit to noise power density per Hertz, (Eb / No) The energy per bit in a signal is given by Eb = STb,

88 THE EXPRESSION EB/NO E b N 0 S / R N 0 S ktr where S is the signal power and Tb is the time required to send one bit. The data rate R is just R = 1/Tb.

89 THE EXPRESSION EB/NO In several instances, the noise is sufficient to alter the value of a bit. If the data rate were doubled, the bits would be more tightly packed together, and the same passage of noise might destroy two bits. Thus, for constant signal and noise strength, an increase in data rate increases the error rate.

90 NUMERICAL

91 MULTIPATH In mobile telephony, there are obstacles in abundance.

92 MULTIPATH The signal can be reflected by obstacles so that multiple copies of the signal with varying delays can be received. In fact, in extreme cases, the receiver may capture only reflected signals and not the direct signal.

93 ATMOSPHERIC ABSORPTION An additional loss between the transmitting and receiving antennas is atmospheric absorption. Water vapor and oxygen contribute most to attenuation. A peak attenuation occurs in the vicinity of 22 GHz due to water vapor. The presence of oxygen results in an absorption peak in the vicinity of 60 GHz

94 ATMOSPHERIC ABSORPTION Rain and fog cause scattering of radio waves that results in attenuation.

95 ATMOSPHERIC ABSORPTION

96 MULTIPATH Reinforcement and cancellation of the signal resulting from the signal following multiple paths can be controlled for communication between fixed, well-sited antennas, and between satellites and fixed ground stations. One exception is when the path goes across water, where the wind keeps the reflective surface of the water in motion.

97 MULTIPATH For mobile telephony and communication to antennas that are not well sited, multipath considerations can be paramount.

98 MULTIPATH PROPAGATION

99 MULTIPATH PROPAGATION Reflection - occurs when signal encounters a surface that is large relative to the wavelength of the signal. Diffraction - occurs at the edge of an impenetrable body that is large compared to wavelength of radio wave.

100 MULTIPATH PROPAGATION Scattering occurs when incoming signal hits an object whose size in the order of the wavelength of the signal or less.

Antennas and Propagation. Chapter 5

Antennas and Propagation. Chapter 5 Antennas and Propagation Chapter 5 Introduction An antenna is an electrical conductor or system of conductors Transmission - radiates electromagnetic energy into space Reception - collects electromagnetic