Prerequisites Data Communications Networks Communication System Digital Communication

Prerequisites Data Communications & Networks Communication System Digital Communication Tanvir A Niazi Air University 1

Air University Title : n Total Hours : n Instructor : n Wireless Communication 45 Tanvir A Niazi 2

OBJECTIVE n The objective of this course is to familiarize the students about the fundamentals of Mobile and Wireless Communications covering the topics given in the course outline. n The course will also introduce the students with the modern trends in Mobile Communications, WAP Applications, wireless Networks standards, ISDN, GSM architecture, services, cellular principles, functions and protocols. 3

COURSE CONTENTS n n n n Modern Wireless Communication Systems The Cellular Concepts Mobile Radio Propagation Modulation Techniques for mobile radio Multiple Access techniques for wireless Communications Wireless Networking Wireless Systems and Standards 4

Text Book: Rappaport, Theodore S. , “Wireless Communications Principles and Practice” 2/e, Prentice Hall PTR. ¨ Jochen H. Schiller, “Mobile Communications”, 2 nd edition © 2004, Addison. Wesley ¨ Reference Books: Ulysis Black, “Mobile & Wireless", Printice Hall Co. ¨ Bud Bates, "Wireless Network Communication", Mc-Graw Hill. ¨ Asha Melotra, "GSM System Engineering. ", Artech house Inc. London. ¨ Demy stified, "3 G - Wireless ", Mc-Graw Hill. ¨ ¨ Charles Perkins, “Mobile IP” 5

INTRODUCTION TO COMMUNICATION SYSTEMS 6

Communication Systems Introduction Communication systems are found when ever information is to be transmitted from one point to another, e. g. Telephone, radio, and TV are common examples. More complicated examples include the following Comm systems that guide aircrafts, space crafts and automatic trains; other provide live news coverage around the world, often via satellite etc. and the list goes on. Data Communication Concepts includes: ¨Source System ¨Transmission System ¨Destination System 7

n n n Concept of information is central to Communications Message is a physical embodiment of information. Goal of a Communications System is to reproduce at the destination an acceptable replication of the source message. Message may be analog or digital Analog message ¨ n physical quantity that varies with time & distance, usually in a smooth and continuous fashion, e. g. voice, light intensity at some point in a TV message. Digital messages ¨ sequence of symbols from a finite set of discrete elements, e. g. Text printed on a page, keys you press at computer terminal. 8

BASIC TERMINOLOGIES 9

BASIC TERMINOLOGIES Ø CHANNEL The channel is a medium such as wire, coaxial cable, a waveguide, an optical fiber, or a radio link through which the tx o/p is sent. - Ideal channel Ø TRANSDUCER CONVERTS THE ELECTRICAL SIGNAL TO THE ORIGINAL FORM 10

11

BASIC TERMINOLOGIES Ø NOISE: THE SIGNAL IS NOT ONLY DISTORTED BY THE CH, BUT IT IS ALSO CONTAMINATED ALONG THE PATH BY UNDESIRABLE SIGNALS LUMPED UNDER THE BROAD TERM NOISE, WHICH ARE RANDOM & UNPREDICTABLE SIGNALS FROM ANY INTERNAL & EXTERNAL SOURCE THE MOST IMP FACTOR THAT LIMITS ON THE RATE OF COMM & SIGNAL ATTENUATION 12

HOW TO DECREASE NOISE n n n ELECTRONIC FILTERS INCREASING THE STRENGTH OF THE SIGNAL REGNERATION ¨ DIGITAL & ANALOG SIGNALS REQUIRES DIFFERENT SINAL CONDITIONERS. 13

BASIC TERMINOLOGIES Ø SIGNAL TO NOISE RATIO: The (SNR) is the ratio of the signal power to the noise power. The CH distort the signal & noise accumulates along the path, the signal strength decreases while the noise level increases with distance from the TX. Thus the SNR is continuously decreases along the CH. 14

BASIC TERMINOLOGIES AMPLIFICATION OF THE RX SIGNAL TO MAKE UP FOR THE ATTENUATION IS OF NO AVAIL BECAUSE THE NOISE WILL BE AMPLIFIED IN THE SAME PROPORTION, AND THE SNR REMAINS UNCHANGED. FILTERS ARE USED TO EXTRACT NOISE FROM THE ORIGINAL TX SIGNAL. TYPES ARE DIGITAL & ANALOG FILTERS. 15

BASIC TERMINOLOGIES ATTENUATION It is not possible for the original signal level or the quality to be transmitted over the entire length of the media. Copper wire or even fiber optic cable will absorb some of the signal energy as the signal travels, and eventually the signal will be weakened to the point that it can no longer be recognized at the receiving end. Both the original amplitude and the signal quality will be attenuated. Since attenuation occurs rapidly on a copper wire the signal may be amplified or regenerated in order to cover long distances. Fiber optic cable’s much lower attenuation means that the original signal can be transmitted much further before regeneration is required. 16

BASIC TERMINOLOGIES IMPEDANCE This is an electrical characteristic similar to the electrical resistance that restricts the transmission of an electric signal. The higher the impedance, the more energy is required to send an electrical signal. This is measured in ohms. INTERFERENCE This is an undesired second signal that is created by the media and then super imposes itself on the primary signal. It can come from electrical equipment which radiates energy that passes on to the medium. This type of interference is typically referred to as noise. 17

BASIC TERMINOLOGIES Ø DIGITAL MESSAGES: DIGITAL MESSAGES ARE CONTRUCTED WITH A FINITE NUMBER OF SYSMOLS e. g MORSE-CODE THEY ARE TX AS PULSES. VARIOUS METHODS TO REPRESENTS THESE SIGNALS • BINARY SYSTEM • DIFFERENT VOLTAGE LEVELS The duration of a Bit Signal determines the bit rate , the shorter the duration of the bit signal greater the Bps rating of the signal. 18

BIT RATE & BAUD RATE n Baud is the measure of the digital or analog signaling rates in a channel n Bit rate is a measure of the digital bit values the channel conveys with each baud 19

BITS PER SECOND (BPS) Bits per second is a measure of the number of data bits (digital 0's and 1's) transmitted each second in a communications channel. This is sometimes referred to as "bit rate. " Individual characters (letters, numbers, etc. ), also referred to as bytes, are composed of several bits. While a modem's bit rate is tied to its baud rate, the two are not the same. 20

BAUD RATE Baud rate is a measure of the number of times per second a signal in a communications channel varies, or makes a transition between states (states being frequencies, voltage levels, or phase angles). One baud is one such change. Thus, a 300 -baud modem's signal changes state 300 times each second, while a 600 - baud modem's signal changes state 600 times per second. This does not necessarily mean that a 300 -baud and a 600 -baud modem transmit 300 and 600 bits per second. 21

DETERMINING BITS PER SECOND Depending on the modulation technique used, a modem can transmit one bit--or more or less than one bit--with each baud, or change in state. Or, to put it another way, one change of state can transmit one bit--or more or less than one bit. When FSK is used, each baud (which is, a gain, a change in state) transmits one bit; only one change in state is required to send a bit. Thus, the modem's bps rate is also 300: 300 bauds per second X 1 bit per baud = 300 bps 22

Now, consider a hypothetical 300 -baud modem using a modulation technique that requires two changes in state to send one bit, which can also be viewed as 1/2 bit per baud. Such a modem's bps rate would be 150 bps: 300 bauds per second X 1/2 bits per baud = 150 bps To look at it another way, bits per second can also be obtained by dividing the modem's baud rate by the number of changes in state, or bauds, required to send one bit: 300 baud -------- = 150 bps 2 bauds per bit 23

Medium- and high-speed modems use baud rates that are lower than their bps rates. Along with this, however, they use multiplestate modulation to send more than one bit per baud. For example 1200 bps modems that conform to the Bell 212 A standard (which includes most 1200 bps modems used in the U. S. ) operate at 300 baud and use a modulation technique called phase modulation that transmits four bits per baud 300 baud X 4 bits per baud or = 1200 bps 300 baud --------- = 1200 bps 1/4 baud per bit 24

Similarly, 2400 bps modems that conform to the CCITT V. 22 recommendation (virtually all of them) actually use a baud rate of 600 when they operate at 2400 bps. However, they also use a modulation technique that transmits four bits per baud: 600 baud X 4 bits per baud = 2400 bps or 600 baud --------- = 2400 bps 1/4 baud per bit 25

Characters per second (cps) Characters per second is the number of characters (letters, numbers, spaces, and symbols) transmitted over a communications channel in one second. Cps is often the bottom line in rating data transmission speed, and a more convenient way of thinking about data transfer than baud- or bit-rate. Determining the number of characters transmitted per second is easy: simply divide the bps rate by the number of bits per character 26

So, in asynchronous data communication, the number of bits per character is usually 10 (either 7 data bits, plus a parity bit, plus a start bit and a stop bit, or 8 data bits plus a start bit and a stop bit). Thus: 300 bps --------- = 30 characters per/s 10 bits per character 27

Ø ANALOG MESSAGES: Analog messages are x-itised by data whose value varies over a continuous range e. g speech waveform. they are tx as wave form. analog channels are normally broad band Ø ANALOG-TO-DIGITAL CONVERSION SAMPLING QUANTIZATION 28

FREQUENCY The rate of change of the signal is its frequency in cycles per second or hertz (Hz) ¨ Frequency = velocity/wavelength ¨ signal power is more at lower frequency as far as human voice is concerned ¨ 29

BASIC TERMINOLOGIES ØBANDWITH The bandwidth of a CH is the range of frequencies that it can transmit with reasonable fidelity Different media are able to transmit different volumes of information per unit of time. This is usually quoted in bits per second. Bandwidth is effected by inherent noise in the line. Which ultimately determines how small a pulse or signal level change can be transmitted. Coaxial cable has a higher bandwidth as compared to twisted pair cable. Fiber optic cable has a very high bandwidth. 30

BANDWIDTH VERSUS LENGTH B A N D W I D T H DISTANCE 31

BASIC TERMINOLOGIES Ø FACTORS EFFECTING SIGNAL TX BANDWIDTH SIGNAL POWER LARGER SNR Ø BASEBAND SIGNAL If the data is non-electrical (human voice, television picture) it must be converted into an electrical waveform by an i/p transducer. this converted electrical waveform is referred to as the baseband signal or the message signal. 32

33

BASIC TERMINOLOGIES Ø MODULATION BASEBAND SIGNALS TX FROM VARIOUS SOURCES ARE NOT SUITABLE FOR DIRECT TX OVER A CH. MODULATION IS A TECHNIQUE IN WHICH A BASEBAND SIGNAL IS MIXED WITH A CARRIER SIGNAL OF HIGH FREQUENCY FOR TX. EASE OF RADIATION (TX ANTENNA 1/10 , F ) SIMULTANEOUS TX OF SEVERAL SIGNALS TIME DOMAIN & FREQUENCY DOMAIN 34

ANALOG MODULATION & DIGITAL MODULATION CARRIER IN BOTH THE CASES IS ANALOG MOST OF THE TIMES TYPES OF ANALOG MODULATION * AM MODULATION * FM MODULATION * PHASE MODULATION TYPES OF ANALOG MODULATION * ASK * FSK * PSK 35

BASIC TERMINOLOGIES Ø AMPLITUDE MODULATION AM is the oldest form of signal modulation. Tx & Rx equipments are cheap. AM signal ` has a constant frequency but varies in amplitude over time to convey info. INEXPENSIVE DISADVANTAGES Long Distance Comm, Requires Noise shielding Noise Interference (Amplifiers) 36

BASIC TERMINOLOGIES Ø FREQUENCY MODULATION Requires sophisticated HW. A FM signal has a constant amplitude but varies in frequency. Quality is good. DISADVANTAGES Wider bandwidth Line of sight. 37

INTRODUCTION TO NETWORKS 38

Objectives After completing this chapter you will be able to: Under stand networking concept and benefits n Identify basic network components n Recognize different types of network n Describe Local Area Networks (LANs) and Wide Area Networks (WANs) n Understand LAN topologies. n 39

What is a Network n Network consist of computers, printers, scanners, CDROM drivers and other devices connected together over some kind of communication medium. n Each computer connected to the communication medium with a network adapter, called Network Interface Card. 40

What is a Network n Computer networking is a combination of software, hardware and cable that joins computers together to share resource such as data, messages, printer, graphics, fax machines, modems and other devices. 41

Need for Networking Network provides following advantages: n Allows common files to be shared from a central location among multiple users. n Allows sharing of devices such as printer, faxes, modems and scanner etc. n Add to the security of an organization by requiring users to log on. n Allow important files to be managed and backed up from a central location. 42

Tahir Iqbal, Air University 43

LAN Introduction n Serves users in a relatively small area, such as one floor of a large office complex or the offices and warehouse of a small company. n WANs can span cities, countries and continents by incorporated dedicated network devices such as bridges and routers, which connect LANs together using public communication carrier. 44

Tahir Iqbal, Air University 45

LAN Functionality ¨LANs are used to share information and hardware devices. 46

Data Sharing before networks Before network were implemented, people could share data in three basic ways listed below: n n n Voice communication Memos Copying information to a physical medium and passes it on to another user. (affectionately known as sneakernet) 47

Data Sharing - With Networks Offers many benefits to the user community. n n n Reduce computing cost by sharing data and peripherals such as printers. Reduces support cost by establishing corporate standards for applications. Centralizes the installation, management and upgrade of application’s software. Accelerates access to corporate data. Increases security by requiring users to enter a user name and password to access the network. 48

Advantages n n Reducing computing costs by sharing data and peripherals such as printers. Reducing support costs by establishing corporate standards for applications. Increasing communication and scheduling capabilities. Accelerating access to corporate data. 49

LAN THERE ARE THREE ROLES FOR COMPUTERS IN A LOCAL AREA NETWORK Ø CLIENT : WHICH USE BUT DO NOT PROVIDE NETWORK RESOURCES Ø PEER : WHICH BOTH USE & PROVIDE NETWORK RESOURCES Ø SERVERS : WHICH PROVIDES NETWORK RESOURCES 50

Client A client is a stand alone computer that gathers data from a user and prepares it for the server. The client accesses the shared resources provided by a server. 51

52

BASED ON THE ROLE OF THE COMPUTERS ATTACHED, NETWORKS ARE DIVIDED IN TO THREE TYPES n n n SERVER BASED NETWORKS PEER NETWORKS HYBRID NETWORKS 53

Peer to Peer Networking: Features: n n No centralized server Each node can be client or server No centralized security or administration work as workgroup (10 Pc) Operating systems providing peer-to-peer networking are: ¨ Windows 95 ¨ Windows NT ¨ Windows for workgroups 54

Peer to Peer Networking: Features Networking models - Peer-to-peer network n Each client on a network to communicate directly with all other clients. n Each computer performs as both a server with software and devices to share a client the requests network services. n Access to individual resources can be controlled if the user who shared the resources requires a PW to access it. 55

56

Advantages: Peer to peer Easy to install n Inexpensive n Network operating system is not required n Local control is maintained by users n Network support is minimal, no network administrator is required. n No reliance on other computers for their op n 57

Disadvantages: Peer to peer Weak network security n Multiple password may be required n No centralized policy formatting or record keeping n Back up data on multiple computers can be a problem n Lack of central management, which makes large peer Networks hard to work with. n 58

Server Based Network In server based network environment, all communication pass through the server, which is a very powerful computer optimized for sharing resources. Servers are “dedicated” to servicing client requests and ensuring network security for directories and files. 59

Server Based Network Due to the varied requirements imposed on today’s network, specialized servers, which are specifically optimized for certain tasks, have emerged along with operating systems. Note: More than one type of specialized server software can be installed on a server 60

Server Based Network Work stations rely on the services the server provides, such as file storage, printing. Client computers are less powerful than peer or server computers. Domains in win NT (PDC & BDC) 61

62

Advantages : Server based n n Data can be centrally controlled and managed. A good example of central administration is sharing files on Windows NT server through windows explorer. To share a server folder, right click the folder in windows explorer and select sharing. Shared resources and users can be centrally managed. 63

Advantages : Server based n A single user name and password can be used for network wide access. n File access to server-based files is usually quicker. n Security can be applied and managed by one administrator. 64

Advantages: Server Based n n n Data back up can be scheduled and managed more efficiently Thousands of users can be supported. Disk mirroring can be used on the server to provide fault tolerance for user and system data. A duplicate of all data is available online in case the primary data storage area fails to respond to client requests. 65

Disadvantages: Server Based n n n A dedicated NOS must be purchased and installed. Expensive HW. A dedicated network administrator is necessary for larger networks A server failure can result in the entire network becoming unusable. 66

COMBINATION NETWORKING Combination networking represents a combination of a server-based operating systems such as Windows NT server and a peer to peer operating system such as Windows 95 (Domains & workgroup). The NOS handles main application and data storage, while the local operating system provides access to some required personal data on local system. Network users do not have to log on to the Dc to access workgroup resources being shared by peers 67

Combination Networking Combination network incorporates the benefits of both types of network, and it retains the disadvantages of the server-based network. 68

SELECTING THE RIGHT NETWORK TYPE 69

70