Introduction to communication systems

See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/282023883 Introduction to Communication Systems Book · July 2015 DOI: 10.13140/RG.2.1.4108.8727 CITATIONS READS 0 1,651 1 author: Elmustafa sayed ali ahmed Red Sea University 16 PUBLICATIONS 7 CITATIONS SEE PROFILE Some of the authors of this publication are also working on these related projects: Internet of Things (IoT) Applications View project All content following this page was uploaded by Elmustafa sayed ali ahmed on 22 September 2015. The user has requested enhancement of the downloaded file. Introduction to Communication Systems Communication Model, Transmission Line, and Data Communication Elmustafa Sayed Ali Ahmed Red Sea University, Sudan Introduction to Communication Systems Communication Model, Transmission Line, and Data Communication Elmustafa Sayed Ali Ahmed Red Sea University, Sudan Introduction to Communication Systems Communication Model, Transmission Line, and Data Communication Edited By Elmustafa Sayed Ali Ahmed Red Sea University, Sudan Copyright © 2015 Elmustafa Sayed Ali Ahmed All rights reserved. ISBN-10: 1515246981 ISBN-13: 978-1515246985 DEDICATION To my Family and Students….. I Contents List of Figures List of Tables Preface III III IV Chapter 1 Communication model 1.1-Introduction 1.2-Attenuation 1.3-Distortion 1.3.1- Linear distortion 1.3.2- Nonlinear distortion 1.4-Noise effect 1.5-Summary 1 2 3 3 5 6 7 Chapter 2 Transmission line 2.1-Introduction 2.2-Reflections on transmission line 2.2.1- Open circuit line 2.2.2- Short circuit line 2.3-Practical construction of transmission line for RF & Microwaves 2.3.1- Twisted pairs line 2.3.2- Coaxial cable 2.3.3- Hollow waveguide 2.3.4- Micro strip cables 2.4- Transmission line parameters 2.4.1- Transmission line equations 2.4.2- Lossless line (R = 0 = G) 2.4.3- Distortion less Line (R/L = G/C) 2.5- Input impedance, SWR, and power 2.6- Characteristics of Open circuit and short circuit line 2.7- The Smith Chart 2.8- Summary 8 8 8 9 10 10 10 11 11 12 13 17 17 22 25 28 41 II Chapter 3 Noise in Communication Systems 3.1- Introduction 3.2- Noise in Networks and Noise Factor 3.3- Noise Generated by a lossy Network 3.4- Cascaded Networks 3.5- Summary 42 43 44 46 48 Chapter 4 Attenuator and filters 4.1- Filters 4.1.1- Low-Pass Filter 4.1.2- High-Pass Filter 4.1.3- Band-Pass Filter 4.1.4- Band-Stop Filter 4.1.5- All-Pass Filter 4.2- Attenuator 4.3- Summary 49 51 51 52 52 52 52 54 Chapter 5 Data communication 5.1- History 5.2- Data Communication Concepts 5.3- Data Transmission 5.3.1- Parallel Transmission 5.3.2- Serial Transmission 5.3.2.1- Asynchronous Transmission 5.3.2.2- Synchronous Transmission 5.4-Data Encoding 5.4.1- Non-Return to Zero (NRZ) 5.4.2- Return to Zero (RZ) 5.5- Modem Concept 5.6- Modem Operation 5.7- Summary 55 55 57 57 58 59 59 60 60 60 61 61 63 III List of Figures Figure 1.1: communication system model Figure 1.2: example of communication system Figure 1.3: channel impairments Figure 1.4: attenuation effect Figure 1.5: attenuation example Figure 1.6: amplifiers in communication system Figure 1.7: linear distortion Figure 1.8: example of liner distortion Figure 1.9: Linear distortion Equalizer Figure 1.10: nonlinear distortion Figure 1.11: nonlinear distortion example Figure 1.12: crosstalk noise Figure 1.13: internal noise Figure 1.14: noise and attenuation problem Figure 2.1: Open circuit line Figure 2.2: Short Circuit Line Figure 2.3: Twisted pair cables Figure 2.4: coaxial cables Figure 2.5: micro coaxial cable Figure 2.6: waveguide cable Figure 2.7: micro strip cable Figure 2.8: transmission line circuit Figure 2.9: circle of unit radius Figure 2.10: smith chart Figure 2.11; smith chart parameters Figure 2.12: impedance chart Figure 2.13: admittance chart Figure 3.1: loss cable example 1 1 2 2 3 3 4 4 5 5 5 6 6 7 9 9 10 10 11 11 11 13 29 32 33 34 34 45 List of Tables Table 2.1: transmission Line Parameters Table 2.2: transmission line characteristics 12 19 IV Preface Communication system is a system model describes a communication exchanges between two stations, transmitter and receiver. Signals or information’s passes from source to distention through what is called channel, which represents a way that signal use it to move from source toward destination. To transmit signals in communication system, it must be first processed by several stages, beginning from signal representation, to signal shaping until encoding and modulation. After preparing the transmitted signal, it passed to the transmission line of channel and due signal crossing this media it faces many impairments such noise, attenuation and distortion. This note book gives a brief concepts about transmission line calculation and also provides an idea about communication system impairments with an example for each one. The note book also provides an introduction to data communication with a simple ideas of data processing. This note book is presented to undergraduate student, in communication engineering studies, and dedicated to communication engineering students in fourth semester for electrical and electronics department at faculty of engineering in Red Sea University. The note book chapters were arranged in manner to easy understand and follows, chapter one introduce a concept of communication system models and the impairments that affect it. Chapter two explain all equation calculations that related to transmission line , then chapter three provides a brief concept about noise effecting in communication systems and the methods used to overcome this problem . Chapter four explain filers and attenuator usage in communication system. And finally chapter five introduce the data communication, and gives a simple ideas about data transmission and encoding. Elmutafa Sayed Ali Ahmed 1 Chapter 1 Communication models 1.1- Introduction The Purpose of a communication system is to carry information from one point to another. A typical communication system consists of three main components as shown in figure 1.1, they are:  Source.  Channel.  Destination. Figure 1.1: communication system model An example of communication system shown in figure 1.2 Figure 1.2: example of communication system In telecommunications and computer networking, a communication channel, or channel, refers either to a physical transmission medium such as a wire, or to a logical connection over a multiplexed medium such as a radio channel. A channel is used to convey an information signal, for example a digital bit stream, from one or several senders (or transmitters) to one or several receivers. A channel has a certain capacity for transmitting information, often measured by its bandwidth in Hz or its data rate in bits per second. 2 The channel is a media that information passes through from source to destination and there are many channel impairments affect in channel performance as shown in figure 1.3 .these impairments such as;  Attenuation.  Distortion.  Noise. Figure 1.3: channel impairments 1.2- Attenuation Attenuation can be problematic for long distance communications. This means due to signal propagate through media the initial signal power decreases if the length of the media becomes longer. Figure 1.4: attenuation effect For example if the attenuation level is 0.9 /km, so every length that signal passes the power of the signal becomes lower by 0.9 * Power at every km . As an example, figure 1.5 shows the attenuation effect in the transmission media. 3 Figure 1.5: attenuation example To solve the problem of attenuation, amplifiers used to amplify the signal power, make it able to pass the haul distance between the source and destination. Also use of digital signals are less susceptible to attenuation than analog signals Figure 1.6: amplifiers in communication system 1.3- Distortion Other channel impairment known as distortion, it means that the signal is distorted and may have a bandwidth larger than the channel bandwidth. The distortion causes a variation in signal frequency and maybe a linear or non-linear distortion. 1.3.1- Linear distortion Linear distortion is said to occur if the system has a not flat amplitude transfer function or if the group delay is not zero or constant. Phase- and Amplitude errors cause linear distortions. The linear distortion is shown in figure 1.7 below. 4 Figure 1.7: linear distortion Linear distortion can occur for two reasons. A- The first is a not flat amplitude transfer function. It's called frequency response. It's just a graph of the reproduced amplitude as a function of frequency (as opposed to amplitude as a function of timethe time domain). B- The second is a bit more confusing and has to do with the phase shift that can occur. A signal has amplitude, but it also has a phase characteristic. If the amplitude relationships are reproduced correctly, but the phase relationships are not, this can cause linear distortion. A certain amount of phase shifting between frequencies occurs wherever there is not flat frequency response. But a device can have a flat amplitude transfer function and still have this phase shifting going on between adjacent frequencies. Figure 1.8: example of liner distortion To solve the problem of linear distortion, the message should fit the channel bandwidth by using and equalizer. 5 Figure 1.9: Linear distortion Equalizer 1.3.2- Non-linear distortion Nonlinear distortion is said to occur when the output waveform has any frequency components not present in the original signal. Figure 1.10: nonlinear distortion Means that Non-linear distortion arises when a signal passes through a system element that has a non-linear Vin -Vout transfer characteristic. Figure 1.11 shows a non linear distortion example for two signals that pass through the same media. Figure 1.11: nonlinear distortion example 6 To solve the problem of nonlinear distortion using and equalizer. Equalization compensates for the differences in signal attenuation and delay associated with different frequency components. Around a center frequency, relatively high frequency signals attenuate more than relatively low frequency signals over a distance, so an equalizer may reduce the amplitude of the low frequency signals and increase the amplitude of the high frequency signals in order that the signals at the receiver are in the same relative balance as they were at the transmitter. Adaptive equalizers automatically adjust to levels of distortion that vary as the signal path or its characteristics change over time. 1.4- Noise Effect Noise is the one of channel impairment, causes an interruption in the received signal at the destination. Noise maybe caused by external or internal noise source. External Sources: interference from signals transmitted on nearby channels (crosstalk), interference generated by contact switches, automobile ignition radiation, natural noise from lightning, solar radiation, etc. as an example of external figure 1.12 shows a crosstalk noise. Figure 1.12: crosstalk noise Internal Sources: thermal noise (random motion of electrons in conductors, random diffusion and recombination of charged carriers in electronic devices). As an example figure 1.13 shows an internal noise. Figure 1.13: internal noise 7 Notice that the effects of external noise can be minimized or eliminated. And the effects of internal noise can be minimized but never eliminated. The Solutions for External Noise are;      Shielding or twisting. A different cable design. Proper design of the channel. Use digital transmission Using BPF or LPF at the receiver side. Solutions for Internal Noise are;  Cooling.  Use digital transmission.  Using BPF or LPF at the receiver side. The effect of Impairments ALL Together (Attenuation + Noise) is calculated as shown in figure 1.14. Figure 1.14: noise and attenuation problem 1.5- Summary The chapter reviews a brief introduction to communication system, and communication model components, then explain the channel impairments such as distortion, attenuation and noise with a given simple example of each one. 8 Chapter 2 Transmission line 2.1- Introduction The purpose of the transmission line is to transfer from source over some distance to a remote load. Transmission lines are commonly used in power distribution (at low frequencies) and in communications (at high frequencies). Various kinds of transmission lines such as the twisted-pair and coaxial cables are used in computer networks such as the Ethernet internet. A transmission line basically consists of two or more parallel conductors used to connect a source to a load. The source may be a hydroelectric generator, a transmitter, or an oscillator; the load may be an antenna, or an oscilloscope, respectively. Typical transmission lines include coaxial cable, a two-wire line, a parallel-plate or a wire above the conducting plane, and a micro strip line. 2.2- Reflections on transmission line When signals are travelling down the transmission line, the source does not at first know what the impedance of the load is. If the voltage and the current travelling down the line do not match the impedance, a reflection occurs at the load end. there are two types of example of transmission lines that affected by the reflection they are; 2.2.1- Open circuit line A voltage V with source resistance R is connected by a switch to the transmission line of characteristic impedance Zo at time t =0. To get maximum power from the source into the Transmission Line, R is made equal to Zo. The load is an open circuit. when load is open circuit the current should be zero but the source cannot do that , so initially current starts to flow at t=0 with value V/2Zo (there is a potential divider effect between the source resistance and the Zo of the transmission line , giving 0.5 when R=Zo. When current step arrives at the load it has nowhere to go so it is reflected and a reverse step is created at time t= where is time taken to travel down the line. The value of the reverse step is – V/2Zo the two currents cancel out completely so there is some transient behavior known as the steady state. 9 Figure 2.1: Open circuit line 2.2.2- Short circuit line When the far end is short circuit, the voltage at far end will be zero, but the source does not know what is connected at the end, so initially the voltage step starts to travel down the line when value V/2 When the volage step arrives at the load the step is reflected and a backwardstraveling step is created at the time t= and the value of the reverse step is – V/2 and the two voltages cancel out at the short circuit end. The reflection coefficient is the ratio of the reflected and incident voltage waves. For the short circuit its value is -1 or magnitude 1 phase 180 degrees. Figure 2.2: Short Circuit Line 10 Notes that transient behavior in electricity power transmission con cause huge spikes and destroy the equipment’s. In computer networks the reflections cause data error as bits interface with one another. And in radio systems reflections can also lead to damage to components, inefficient transfer power and data corruption. The way to avoid this problem is to ensure Z source = Z load = Zo of the transmission line, in this case the reflection coefficient of the matched load is zero. For open circuit case the reflection coefficient is 1 angle 0 degrees. 2.3- Practical construction of transmission line for RF & Microwaves 2.3.1- Twisted pairs line Twisted pairs started off life in telephony and were generally regarded as a cheap and simple means of achieving signal for low frequency transmission line. Nowadays they used widespread in computer networking a UTP stands for unshielded twisted pair and this cables are used to supply 100Mb/s. Figure 2.3: Twisted pair cables 2.3.2- Coaxial cables Coaxial cable consists of a centre connector inside a cylindrical outer ground shield, usable to a few hundred MHz. Other types are usable up to GHz. Figure 2.4: coaxial cables There are other types used for computers supports high data rate connections known as Micro – coaxial. 11 Figure 2.5: micro coaxial cable 2.3.3- Hollow waveguide In this waveguide signal propagates as an electromagnetic wave, with a complicated filed pattern, they have low loss and handle high power. Figure 2.6: waveguide cable 2.3.4- Micro strip cables This type consists of signal conductor mounted above ground plane, usually by using dielectric substrate. The micro strip is usable to more than 100 GHz. Figure 2.7: micro strip cable 12 2.4- TRANSMISSION LINE PARAMETERS It’s easy to describe a transmission line in terms of its line parameters, which are its: 1- Resistance per unit length R 2- Inductance per unit length L 3- Conductance per unit length G 4- Capacitance per unit length C. Each of the lines has specific formulas for finding R, L, G, and C For coaxial, two-wire, and planar lines, the formulas for calculating the values of R, L, G, and C are provided in Table below ; Table 2.1: transmission Line Parameters The characteristics of the conductor at each cable are , µ, and other lengths are also used. Normally each of the above line R, L, G and C are given to calculate the transmission line equations. 13 2.4.1- TRANSMISSION LINE EQUATIONS For calculating the equations of the transmission lines assume that we have a line with two conductors they support an electromagnetic wave , the electric and magnetic fields on the line are transverse to the direction of wave propagation , the fields E and H are uniquely related to voltage V and current I, respectively: V = - ∫ E . dI , I =∫ H.dI we will use circuit quantities V and / in solving the transmission line problem instead of solving field quantities E and H , the equivalent circuit for this line shown below . We assume that the wave propagates along the +z-direction, from the generator to the load. Figure 2.8: transmission line circuit  Steps of Equations 1- By applying Kirchhoff's voltage law to the outer loop of the circuit we obtain; V (z, t) =R∆z I (z, t) + L∆ z +V (z + ∆z, t) V (z, t) - V (z + ∆z, t) = R∆z I (z, t) + L∆ z (2.1) (2.2) 14  Divide the equation 2 by ∆z : V (z, t) - V (z + ∆z, t) = R I (z, t) + L ∆z  Taking the limit of ∆z 0 : ∂V (z, t) = R I (z, t) +L ∂ I (z, t) ∂z ∂t (2.3) (2.4) 2- By applying Kirchhoff's current law to the main node of the circuit we obtain; I (z, t) = I (z + ∆z, t) + ∆I (2.5)  From the figure 21 the value of ∆I given by; ∆I = G∆z V (z + ∆z, t) + C ∆z ∂V (z + ∆z, t) (2.6) ∂t  So the equation 5 becomes; I (z, t) = I (z + ∆z, t) + G∆z V (z + ∆z, t) + C ∆z ∂V (z + ∆z, t) (2.7) ∂t I (z, t) - I (z + ∆z, t) = G∆z V (z + ∆z, t) + C ∆z ∂V (z + ∆z, t) (2.8) ∂t  Divide the equation 8 by ∆z : I (z, t) - I (z + ∆z, t) = G V (z + ∆z, t) + C ∂V (z + ∆z, t) ∆z ∂t (2.9)  Taking the limit of ∆z 0 : ∂I (z, t) = G V (z, t) +C ∂ V (z, t) ∂z ∂t (2.10)  If we assume harmonic time dependence so that; V (z, t) = Re [Vs (z) e jωt] (2.11) 15 I (z, t) = Re [Is (z) e jωt] (2.12)  where Vs(z) and Is(z) are the phasor forms of V(z, i) and I(z, t), respectively; equation 4 and 10 become; d Vs = (R + jωL) Is (2.13) dz d Is = (G + jωC) Vs dz (2.14)  Take the second derivative of Vs in equation 13 and apply equation 14 to the equation obtained after second derivative; d2 Vs = (R + jωL) (G + jωC) Vs d z2  or can be written by; d2 Vs – d z2 Where =; =α+ j 2 Vs= 0 = (2.15) (2.16) (2.17)  Take the second derivative of Is in equation 14 and apply equation 13 to the equation obtained after second derivative; d2 Is = (R + jωL) (G + jωC) Is d z2  or can be written by; d2 Is – d z2 2 Is= 0 (2.18) (2.19) 16  for all above equations ; = represents the propagation constant. α= attenuation constant (in nepers per meter or decibels per meter). = phase constant (in radians per meter).  The wavelength λ and wave velocity u are, respectively, given by; λ =βπ u=ω = βπ λ  So; u=fλ  The solutions of the linear homogeneous differential equations 16 and 19 similar to; d2 Vs – d z2 d2 Is – d z2 2 Vs= 0 (2.16) 2 Is= 0 (2.19) Vs (z) = V+o e >+z Is (z) = I+o e >+z z+ z+ V-o e -z< I -o e z -z< z (2.20) (2.21)  Where V+o , V-o , I+o , I-o are wave amplitudes ; wave traveling along +zand -z-directions . 17  The characteristic impedance Zo of the line is the ratio of positively traveling voltage wave to current wave at any point on the line. By applying equation 20 and 21 into 13 and 14 we will obtain; Zo = V+o = - V-o = R+ jωL = I +o I -o ___ G+ jωC (2.22)  So becomes; Where; Ro and Xo are real and imaginary of Zo. 2.4.2- Lossless line (R = 0 = G) A transmission line is said to be a lossless if the conductor of the line are perfect and the dielectric medium separating them is lossless. Means that; R=0=G α=0 ; =j = jω√LC Xo= 0 ; Zo=Ro = √L C 2.4.3- Distortion less Line (R/L = G/C) A signal normally consists of a band of frequencies; wave amplitudes of different frequency components will be attenuated differently in a lossy line as α is frequency dependent. This results in distortion. 18 A distortion less line is one in which the attenuation constant α is frequency independent while the phase constant is linearly dependent on frequency. - For distortion less line, - showing that α does not depend on frequency whereas frequency. Also is a linear function of Or Note that; A- The phase velocity is independent of frequency because the phase constant linearly depends on frequency. We have shape distortion of signals unless α and u are independent of frequency. B- u and Zo remain the same as for lossless lines. C- A lossless line is also a distortion less line, but a distortion less line is not necessarily lossless. Although lossless lines are desirable in power transmission, telephone lines are required to be distortion less. Table below shows the characteristics of transmission line. 19 Table 2.2: transmission line characteristics  Example 1 An air line has characteristic impedance of 70 Ω and phase constant of γ rad/m at 100 MHz Calculate the inductance per meter and the capacitance per meter of the line. Solutions; An air line can be regarded as a lossless line; R=0=G ; α = 0 Zo=Ro = √L C = ω√LC Divide equation 1 by 2; Ro = 1 ωC C= ωRo 20 = γ / (βπ*100*106*70) = 68.2 pF/m L= R2oC = (70)2 (68.2*10-12) = 334.2 nH/m  Example 2 A distortion less line has Zo = 60 fl, α = 20 mNp/m, u = 0.6c, where c is the speed of light in a vacuum. Find R, L, G, C, and λ at 100 MHz. Solution; For a distortion less line, 21  Exercises 1- A transmission line operating at 500 MHz has Zo = 80 Ω, α = 0.04 Np/m, = 1.5 rad/m. Find the line parameters R, L, G, and C. Answer: γ.2 Ω/m, γ8.2 nH/m, 5 * 10-4 S/m, 5.97 pF/m. 2- A telephone line has R = γ0 Ω/km, L = 100 mH/km ; G = 0, and C = 20 µF/km At f = 1 kHz, obtain: (a) The characteristic impedance of the line. (b) The propagation constant. (c) The phase velocity. Answer: (a) 70.75<-1.γ67° Ω, (b) 2.121 * 10-4 + 78.888 * 10-3/m (c) 7.069* 105 m/s. 22 2.5- INPUT IMPEDANCE, SWR, AND POWER Consider a transmission line of length L characterized by and Zo connected to a load ZL as shown in figure below ; the generator sees the line with the load as an input impedance Zin It is our intention in this section to determine the input impedance the standing wave ratio (SWR), and the power flow on the line . - Let the transmission line extend from z = 0 at the generator to z = L at the load; we need the voltage and current waves. Vs (z) = V+o e - z+ V-o e Is (z) = I+o e - z+ I -o e z V-o e Zo z Is (z) = V+o e Zo z+ z (2.20) (2.21) (2.22) - if we are given the conditions at the input, say; Vo = V (Z = 0) ; Io = I (z = 0) V+o= 0.5 (Vo + Zo Io) (2.23) V-o= 0.5 (Vo- Zo Io) (2.24) - If the input impedance at the input terminals is Zin, the input voltage Vo and the input current Io are easily obtained by; 23 Vo = Zin Vg Zin+Zg Io = Vg Zin+Zg - if we are given the conditions at the load, say; VL = V (z = L), IL = I (z = L); substituting this into equations 20 and 22; obtain V+o= 0.5 (VL + Zo IL)e L (2.25) V-o= 0.5 (VL- Zo IL) e- L (2.26) - The input impedance Zin = Vs(z) / Is(z) at any point on the line , at the generator ; Zin = Vs(z) = Zo(V+o + V-o) Is (z) V+o - V-o (2.27) After substitute the equations 25 and 26 into 27 the equation solved by; - We get ; (Lossy) 24 (Lossless) - The voltage reflection coefficient given by гL; гL is the ratio of the voltage reflection wave to the incident wave at the load. гL = V-o e L V+o e- L (2.28) - after Substituting equation 25 and 26 into equation 28 we obtain ; - The voltage reflection coefficient at any point on the line is the ratio of the magnitude of the reflected voltage wave to that of the incident wave. - The current reflection coefficient at any point on the line is negative of the voltage reflection coefficient at that point. - the standing wave ratios denoted by SWR as; - And also the Zin can be at the standing wave ratio; (Max) (Min) 25 - The average input power at a distance € from the load is given by an equation; - The power transmitted through the transmission line given by ; Pi= the incident power. Pr= reflected power. Where Pt is the input or transmitted power. Note: the maximum power is delivered to the load when Y = 0, as expected. 2.6- Characteristics of Open circuit and short circuit line There are special cases when the line is connected to load ZL = 0, ZL = ∞ and ZL = Zo, these special cases can easily be derived from the general case. 1- Shorted Line ZL = 0  From the equation below; when ZL substituted by zero (0)  The result is; 26  From the equation below; when ZL substituted by zero (0)  The result is; 2- Open-Circuited Line ZL = ∞  As the same when you substitutes the ZL = ∞ to the equations below;  The results are;  And  The variation of Zin with t is; 27 3- Matched Line ZL = Zo  This is the most desired case from the practical point of view when substitute the ZL = Zo in the same equations as in the last two cases the results are;  Example 1 Solution: 28  Exercise 2.7- The Smith Chart Prior to the advent of digital computers and calculators, engineers developed all sorts of aids (tables, charts, graphs, etc.) to facilitate their calculations for design and analysis. To reduce the complexity of calculating the characteristics of transmission lines, graphical means have been developed. The Smith chart is the most commonly used of the graphical techniques. It is basically a graphical indication of the impedance of a transmission line as one move along the line. It becomes easy to use after a small amount of experience. The Smith chart is constructed within a circle of unit radius |г| <=1 as shown in figure 2.9 below 29 Figure 2.9: circle of unit radius - The construction of the chart is based on the relation in equation ; Or  Where гr and гi are the real and imaginary parts of the reflection coefficient г. Instead of having separate Smith charts for transmission lines with different characteristic impedances such as Zo = 60,100, and 120 Ω one that can be used for any line. To achieve this , using a normalized chart in which all impedances are normalized with respect to the characteristic impedance Zo of the particular line under consideration For the load impedance ZL for example, the normalized impedance given by;  When substitutes the above equation to the equations below; And  The results are; 30 And  After normalize the obtained equations ;  After Rearranging terms in equations above ;  The results equations similar to;  Which is the general equation of a circle of radius a, centered at (h, k). then equations become; 31 And  Typical r-circles for r = 0,0.5, 1,2, 5 and ∞ for normalized resistance as shown in figure below;  Typical x -circles for x = 0, ± 1/2, ±1, ±2, ±5, ±∞ for x part (L or C ) as shown in figure below; - After superpose the r-circles and x-circles, what we have is the Smith chart shown in Figure below On the chart, we locate a normalized impedance z = 2 + j , for example, as the point of intersection of the r = 2 circle and the x = 1 circle . This is point P1 in the figure. Similarly, z = 1 - 7 0.5 is located at P2 where the r = 1 circle and the x = -0.5 circle intersect. 32 - We can draw the s-circles or constant standing-wave-ratio circles (always not shown on the Smith chart), which are centered at the origin with s varying from 1 to ∞. The value of the standing wave ratio s is determined by locating where an s-circle crosses the гr axis Typical examples of s-circles for s = 1,2, γ, and ∞ are shown also in figure 2.10 below. Figure 2.10: smith cahrt  Important points about smith chart 1- At point Psc on the chart r = 0, x = 0; that is, ZL = 0 + j0 showing that Psc represents a short circuit on the transmission line. At point Poc, r = ∞ and x= ∞, or ZL = =∞+j∞, which implies that Poc corresponds to an open circuit on the line. Also at Poc, r = 0 and x = 0, showing that Poc is another location of a short circuit on the line.see figure 2.10 2- A complete revolution (360°) around the Smith chart represents a distance of λ/2 on the line. Clockwise movement on the chart is regarded as moving toward the generator (or away from the load) as shown by the arrow G in figures below. Counterclockwise movement on the chart corresponds to moving toward the load (or away from the generator) as indicated by the arrow L in. (see figure 2.11). 3- There are three scales around the periphery of the Smith chart as illustrated in Figure B; the three scales are included for the sake of convenience but they are actually meant to serve the same purpose; one scale should be sufficient. The scales are used in determining the distance from the load or generator in degrees or wavelengths. The outermost scale is used to determine the distance on the line from 33 the generator end in terms of wavelengths, and the next scale determines the distance from the load end in terms of wavelengths. The innermost scale is a protractor (in degrees) and is primarily used in determining θr it can also be used to determine the distance from the load or generator. 4- Since a λ/2 distance on the line corresponds to a movement of 360° on the chart, λ distance on the line corresponds to a 720° movement on the chart. 5- Vmax occurs where Zin max is located on the chart and that is on the positive гr axis or on OPOC. Vmin is located at the same point where we have Zin min on the chart that is, on the negative гr axis or on OPsc (see figure 2.11). 6- The Smith chart is used both as impedance chart and admittance chart (Y = 1/Z). Figure 2.11; smith chart parameters - To Calculate the Impedance and admittance by smith chart , calculations of impedance taken in the side of open circuit at the smith chart and the admittance calculations taken from the short circuit side in the smith chart. ( see figures 2.12 and 2.13 below). 34  Impedance chart  Admittance chart Figure 2.12: impedance chart Figure 2.13: admittance cahrt 35  Example Solutions; 36 Note : Locate zL on the Smith chart at point P where the r = 1.2 circle and the x = 0.8 circle meet. To get г at zL, extend OP to meet the r = 0 circle at Q and measure OP and OQ. Since OQ corresponds to г=|1| then at P, 37 Note that OP = 3.2 cm and OQ = 9.1 cm were taken from the Smith chart used by the author; Angle 0r is read directly on the chart as the angle between OS and OP; that is (b) To obtain the standing wave ratio s, draw a circle with radius OP and center at O. This is the constant s or г circle Locate point S where the ^-circle meets the г – axis The value of r at this point is s; that is; 38  Example 2 Solutions: 39 40 41 2.8- Summary This chapter introduces a communication transmission line and the all parameters related to transmission line, explain the effect of each one in the line, in cases of short and open circuits. The chapter also explain the all derivations of transmission line such as propagation constant, the propagation characteristics, input impedance and characteristic line impedance. The chapter ended by explaining how to solve transmission line problems by using smith chart, with simple example of problems solved. 42 Chapter 3 Noise in Communication Systems 3.1- Introduction The term noise refers to unwanted signals over which the designer has little or no control and which tend to disrupt the transmission and reception of signals in a communication system. Noise may enter the system from external sources (eg interference generated by a motor next to the receiver system) or may be generated from fluctuations internal to a circuit. For examples;   flow.   Thermal Noise - Due to the random nature of the movement of electrons. Shot Noise - Arises in electronic devices due to the discrete nature of current 1/f noise - Due to surface leakage in semi-conductors. Partition noise - Due to recombination in the base of a transistor. Usually these types of noise may be considered to be independent of the actual operating frequency (ie have a constant spectral density) and are therefore referred to as White Noise. To model the occurrence of white noise, consider a resistor at temperature T degrees kelvin (°K = 273 + °C). The random movement of charge in the resistor will produce a noise voltage at the resistor terminals. The rms noise voltage is approximately; Where; k is Boltzmann’s constant (1.γ8 × 10-23 J/°K). T is temperature in °K. B is bandwidth in Hz. R is the resistance in Ω. 43 - The maximum power transferred will be ; We can model an arbitrary source of noise (as long as it is White noise) as an equivalent thermal noise power and characterise it with an equivalent noise temperature. An arbitrary source of noise (sin source, amplifier, and antenna) which delivers a noise power Ps to a load resistor R can be replaced by a noisy resistor R at a temperature Te. The temperature Te is calculated so the same noise power is delivered to the load; Note: Components and systems can then be characterized by saying they have an Effective Noise Temperature of Te. 3.2- Noise in Networks and Noise Factor We have already mentioned the effective noise temperature as a measure of a devices noise performance. There is another parameter also commonly used to characterize noise performance, the Noise Factor or Noise Figure. The noise figure is defined as the ratio of the signal to the noise ratio (SNR) at the input of a device to the SNR at the output. 44 In the diagram Si is the input signal power and So is the output signal power. Ni and No are the input and output noise powers. Thus the Noise Figure is defined by; In a practical device, No > G.Ni and so F > 1.0. The closer to 1 is F, the less noise the device introduces and the better its noise performance. In decibels, Fdb = 10 log 10 (F) Since noise figure and effective noise temperature measure the same characteristic they are of course related. Consider a network with gain G, bandwidth B and an equivalent noise temperature Te. 1. The input noise power is Ni = kToB, where To is the surrounding temperature. 2. The output noise power is a sum of the amplified input noise and the internally generated noise; No = kGB(To + Te). The output signal power is So = G Si. - Therefore, Noise Figure F = Thus F = 1 + Te/To and Te = (F-1) To If the network were noiseless, Te = 0, giving F = 1 or 0dB. 3.3- Noise Generated by a Lossy Network Lossy network is one in which the input signal is attenuated at the network output. Some examples are shown below. 45 Figure 3.1: loss cable example What effect does a lossy network have on the noise performance of a system? Consider a lossy network connected to a matched resistor, R. Assume the lossy network is at a temperature To. The gain of the network will be less than one and can be define by a loss factor L = 1/G. Looking back into this network from its output we see a matched resistance R at temperature To. Thus the output noise power will be; No = kToB We can think of this noise as partly coming from the source resistor at the input of the network through the lossy network and the remainder being generated by the lossy network itself. The fraction of the input noise power at the output of the network will be; P1 = GkToB = kToB/L The power added by the network referred to the input is say NN/W and the contribution due to this part at the output will then be; P2 = G. NN/W = NN/W/L The total noise output power is therefore No = P1 + P2. Substituting from above, No = 1/L (kToB + NN/W) 46 Solving for noise generated by the network referred to the input, NN/W; NN/W = (L-1) kToB The Effective temperature Te of the lossy network is; Te = NN/W /(kB) = (L-1) To 3.4- Cascaded Networks We are often required to determine the noise performance of a number of networks in series. Consider the system below involving two noisy networks in cascade and at a temperature, To. The two noisy networks can be considered as 2 noise free networks at which an extra noise term (the effective temperature) is added at the input. That is, The effective temperatures Te1 and Te2 are related to the noise figures and the ambient temperature. Te1 = (F1-1) To and Te2 = (F2-1) To From the diagram then we see that; 47 Ts1 = Te1 + To = F1.To This implies that the input noise at network 1 is N1 = k B Ts1. The output noise power, No1 is this value multiplied by the gain of the “ideal” first stage. No1 = G1.N1 = k B G1 Ts1 = k B G1 F1 To This noise power implies a noise temperature To1 of; To1 = No1/(kB) = G1 F1 To Similarly, Ts2 = To1 + Te2 Therefore, N2 = k B Ts2 = k B To [G1 F1 + (F2-1)] Finally, The total effective noise figure for the two networks taken together (as one device with a gain G1.G2) is; This result may be extended for the cascade of 3 or more networks to get a general expression; 48 We can write a similar expression in terms of effective noise temperatures for the whole system; 3.5- Summary This chapter discuss the effect of the noise in communication systems, providing a brief explanation of noise calculations in communication networks in simple a cascaded networks types. The derivation of the noise effect in communication networks explained in a simple way for quick and deep understanding. 49 Chapter 4 Attenuator and filters 4.1- Filters The function of a filter is to separate different frequency components of the input signal that passes through the filter network. The characteristics of the network are specified by a transfer function H_(jω) or H(s), where s =+jω represents the complex frequency defined for the Laplace transform The transfer function is the ratio of output signal to input signal, voltage, or current: The transfer phase function, φ(ω), is related to the transfer group delay through a differential with respect to frequency as follows: For constant group delay, the phase function must be linear with frequency. In most filters only the magnitude of the transfer function is of interest. However, in modern-day systems using signals with complex modulation schemes, phase and group delay functions are also important. A filter network passes some of the input signal frequencies and stops others, and being a linear circuit, this function is performed without adding or generating new frequency components. The frequency band that passes, ideally without losses (0 dB insertion loss), defines the pass band, and the band that stops the frequencies, ideally with infinite loss, is called the stop band. This loss representation of the ideal low-pass filter. Low pass filter passes all low-frequency signals from dc to some high frequency, ωc and stops all signals above ωc. The frequency, ωc, is called the cutoff frequency of the filter. 50 Similar considerations can be applied in the design of filters using phase linearity and/or group delay flatness. The concept of pass band, stop band, and transition band permits specifications of five major types of filters: (1) low pass, (2) high pass, (3) band pass, (4) band stop, and (5) all pass. The transmission behavior of these filters is shown in figures below; Filters are always used to reduce the effect of the noise to the signals that transmitted through the transmission line. From previous studies the amount of noise in the original signal known as signal to noise ratio SNR. Max signal to noise power ratio, represents a low noise and min signal to noise ratio indicate that the amount of noise is larger than the signal. A matched filter is a linear filter designed to provide the maximum signal to noise power ratio at its output for a given transmitted symbol waveform. consider signal S(t) plus AWGN n(t) is applied to a linear time-invariant receiving filter followed by a sampler as shown in figure below; 51 At t=T, the sampler output. Z (T) =ai+n0  where ai= signal component at the filter output  N0=noise component The variance of the output noise (average noise power) is denoted by o2 4.1.1- Low-Pass Filter Low-pass filter networks are realized by using a cascade of series inductors and shunt capacitors. At low frequencies, series inductances produce low impedance, and shunt capacitors produce high impedance, thus allowing the signal to appear at the output of the filter. Above the cutoff frequency, the series inductors behave as large impedances and shunt capacitors as low impedances, thereby impeding the signal transfer to the load. 4.1.2- High-Pass Filter The high-pass filter allows signal frequencies higher than the cutoff frequency to pass through the filter to the load with a minimum loss and stops all frequencies below the cutoff frequency. This behavior is the reverse of the low-pass filter, and sometimes the high-pass filter is referred to as the complement of the low-pass filter. High-pass filter networks are realized by using a cascade of series capacitors and shunt inductors. Capacitors at high frequencies have low impedance, and inductors have high impedance. Thus the high-frequency signal passes through the filter to the output load with a minimum loss. Just the opposite happens at low frequencies, resulting in a high attenuation of the low frequencies. 52 4.1.3- Band-Pass Filter The band-pass filter allows the signal transfer in the load in a band of frequencies between the lower cutoff frequency, ωc1, and the upper cutoff frequency, ωc2. Between the lower and upper cutoff frequency is the center frequency, ω, defined by the geometric mean of ωc1 and ωc2. 4.1.4- Band-Stop Filter The band-stop filter is a complement of the band-pass filter the signal in a bandstop filter is transferred to the load in two frequency bands, one from a low frequency to a low cutoff frequency, ωc, and the other from the upper cutoff frequency, ωc2, to infinite frequency. The signal experiences high loss between ωc1 to ωc2, hence the name band stop or band rejects. 4.1.5- All-Pass Filter The all-pass filter allows the signal amplitude for all frequencies to pass through the network without any significant loss this network has no frequency selective pass band or stop band. The transmitted signal ideally experiences a linear phase shift or constant group delay with frequency. Unfortunately, minimum phase networks do not have constant group delay: rather there are peaks near the corner frequency. All passive ladder networks, such as filters that have frequency selectivity, are minimum phase. In the design there is a trade-off between flat group delay and filter selectivity. However, a network that is non minimum phase can be cascaded with a minimum phase network to achieve both flat group delay and selectivity. All pass networks with non minimum phase are used as group delay compensation devices. 4.2- Attenuator Attenuators are linear, passive, or active networks or devices that attenuate electrical or microwave signals, such as voltages or currents, in a system by a predetermined ratio. They may be in the form of transmission-line, strip line, or waveguide components. Attenuation is usually expressed as the ratio of input power (Pin) to output power (Pout), in decibels (dB), as; 53 This is derived from the standard definition of attenuation in Nepers (Np), as; Where a is attenuation constant (Np/m) and Dx is the distance between the voltages of interest (E1 and E2). There are many instances when it is necessary to reduce the value, or level, of electrical or microwave signals (such as voltages and currents) by a fixed amount to allow the rest of the system to work properly. Attenuators are used for this purpose. For example, in turning down the volume on a radio, we make use of a variable attenuator to reduce the signal. Almost all electronic instruments use attenuators to allow for the measurement of a wide range of voltage and current values, such as voltmeters, oscilloscopes, and other electronic instruments. Thus, the various applications in which attenuators are used include the following:  To reduce signal levels to prevent overloading.  To match source and load impedances to reduce their interaction.  To measure loss or gain of two-port devices.  To provide isolation between circuit components, or circuits or instruments so as to reduce interaction among them.  To extend the dynamic range of equipment and prevent burnout or overloading equipment. 54 There are various types of attenuators based on the nature of circuit elements used, type of configuration, and kind of adjustment. They are as follows:  Passive and active attenuators.  Absorptive and reflective attenuators.  Fixed and variable attenuators. A fixed attenuator is used when the attenuation is constant. Variable attenuators have varying attenuation, using varying resistances for instance. The variability can be in steps or continuous, obtained either manually or programmable. There are also electronically variable attenuators. They are reversible, except in special cases, such as a high-power attenuator. They are linear, resistive, or reactive, and are normally symmetric in impedance. They include waveguide, coaxial, and strip lines, as well as calibrated and un-calibrated versions. Fixed attenuators, commonly known as ‘‘pads,’’ reduce the input signal power by a fixed amount, such as 3, 10, and 50 dB. A variable attenuator has a range, such as 0–20 dB or 0–100 dB. The variation can be continuous or in steps, obtained manually or programmable. 4.3- Summary This chapter provides a simple ideas about filters and attenuators that used in communication systems. Provides an idea about all filters types such as low , high , band, pass filters .attenuators operation also explained with some example such as passive , active , reflection , fixed and variable atenuators. 55 Chapter 5 Data communication 5.1- History Data communication is an Exchange of digital information between two digital devices is data communication. Data communication history;  1838: Samuel Morse & Alfred Veil Invent Morse code Telegraph System.  1876: Alexander Graham Bell invented Telephone.  1910: Howard Krum developed Start/Stop Synchronization.  1930: Development of ASCII Transmission Code.  1945: Allied Governments develop the First Large Computer.  1950: IBM releases its first computer IBM 710.  1960: IBM releases the First Commercial Computer IBM 360. 5.2- Data Communication Concepts Data communication is most technology widely used nowadays in several proposes. The main contributions of data communication are; 1- Transmission Technology. 2- Packet Switching Technology. 3- Internet. 4- LAN Technology. 5- WAN Technology. There are Various Networks dials with data com;  Personal Area Network (PAN).  Local Area Network (LAN).  Metropolitan Area Network (MAN).  Wide Area Network (WAN).  Global Area Network (GAN). Data communication refers to information’s transfer such data, voice and videos. Each of this information transfers from one device to another through what is called network. 56 Networking is the convenient way of making information accessible to anyone, anytime & anywhere. The Capability of two or more computers of different vendors to transmit & receive data and to carry out processes as expected by the user is called Interoperability. For any data networks there are many requirements that must be available to establish data communication. This requirements are;  At least Two Devices ready to communicate.  A Transmission Medium.  A set of Rules & Procedure for proper communication (Protocol).  Standard Data Representation.  Transmission of bits either Serial or Parallel.  Bit synchronization using Start/stop bits in case of Asynchronous Transmission.  In Synchronous Transmission the agreed pattern of Flag.  Signal encoding rules viz. NRZ or RZ.  And other higher layer protocol. Data represented by using a binary form, A group of bits are used to represent a character/number/ special symbol/Control Characters.  5-bit code can represent 32 symbols (25=32)  7-bit code can represent 128 symbols (27=128)  8-bit code can represent 256 symbols (28=256) A code set is the set of codes representing the symbols. there are many standards of codes that used in data communications such as ASCII , EBCDIC and Baudot Teletype code. 57 ASCII: this is ANSI’s 7-bit American Standard Code for Information Interchange. ASCII code (7-bit) is often used with an 8th bit known as parity bit used for detecting errors during Data Transmission. Parity bit is added to the Most Significant bit (MSB). EBCDIC: this is IBM’s 8-bit Extended Binary Coded Decimal Interchange Code. It is an 8-bit code with 256 Symbols. No parity bit for error checking. Baudot Teletype code is a 5-bit code also known as ITA2 (International Telegraph Alphabet No. 2) used in Telegraphy/Telex. 5.3- Data Transmission Data Transmission means movement of the bits over a transmission medium connecting two devices. Two types of Data Transmission are:  Parallel Transmission.  Serial Transmission. 5.3.1- Parallel Transmission In this all the bits of a byte are transmitted simultaneously on separate wires. Practicable if two devices are close to each other e.g. Computer to Printer, Communication within the Computer using a com port. 58 5.3.2- Serial Transmission Bits are transmitted one after the other .Usually the Least Significant Bit (LSB) has been transmitted first. Serial Transmission requires only one circuit interconnecting two devices and it’s suitable for transmission over long distance. Such serial device is USB. The transmitting speed of each types measured by bit rate. the bit rate is Number of bits that can be transmitted in 1 second If tp is the duration of the bit then the Bit rate R= 1/tp. At receive side; received Signal is never same as transmitted. A clock signal used to samples & regenerates the original bits as it was transmitted. Received Signal should be sampled at right instant. Otherwise it will cause bit error. There are two methods for Timing control for receiving bits. Asynchronous Transmission and Synchronous Transmission. 59 5.3.2.1- Asynchronous Transmission  Sending end commences the Transmission of bits at any instant of time.  No time relation between the consecutive bits.  During idle condition Signal ‘1’ is transmitted.  “Start bit” before the byte and “Stop bit” at the end of the byte for Start/Stop synchronization. 5.3.2.2- Synchronous Transmission  Carried out under the control of the timing source.  No Start/Stop bits.  Continuous block of Data are encapsulated with Header & Trailer along with Flags. 60 5.4- Data Encoding Signal Encoding used to represent the bits as electrical Signals. That because for transmission of bits into electrical signals for two binary states simple +ve and –ve voltages is not sufficient. Sufficient Signal transition should be present to recover the clock properly at the receiving end and the Bandwidth of the signal should match with transmission medium. Two broad classes of encoding are: 5.4.1- Non-Return to Zero (NRZ) 5.4.2- Return to Zero (RZ) 61 A transmission and communication way take place by three possible modes they are;  Transfer in one direction only called simplex, just transmit in one way.  Transfer in two directions but one at a time, known as half duplex, transmission done in two way alternatively.  Transfer in both the direction simultaneously, termed as full duplex, and the transmission take place in two directions simultaneously 5.5- Modem Concept Modem is refers to modulation and demodulation. Modulation is to adapt the signal in transmitter side to be suitable for the media. Then demodulation refers to extracts the original signal after received in receiver side. In order to transmit a signal over a given physical medium we need to adapt the characteristics of the signal to the properties of the medium. In the case of electromagnetic signals, the main object is to fit the spectrum of the signal into a prescribed bandwidth, called the pass band, and this is accomplished by means of a technique called modulation. 5.6- Modem Operation Modulation is performed by multiplying the original signal by a sinusoidal signal called carrier; the mean of the modulation theorem is that, in so doing, we are actually translating the spectrum of the original signal in frequency, over the frequency of the carrier. This frequency is chosen according to the physical medium: copper wires, optical fibers, all require different modulation frequencies since their useful pass bands are located in different portions of the spectrum. The pass band of a communication channel is, roughly speaking, the part of the spectrum which behaves linearly for transmission; there, we can rely on the fact that a properly modulated sinusoidal signal will be received with only phase and amplitude distortions. The pass band of a physical channel is of finite width, so we must make sure that the bandwidth of the original signal prior to modulation is "of the same size as the channel's pass band. In other words, we must build a signal with a finite, prescribed spectral support. 62 A big effort in designing a modem is trying to squeeze as much information as possible over the relatively narrow pass band of the telephone channel for example. The operation of limiting the band-with of a digital communication signal goes under the name of pulse shaping and is basically a linear filtering operation. To illustrate what modulation is all about, take the example of AM radio. The AM band extends from 530 KHz to 1700 KHz and each radio station is allowed by law to transmit over an 8 KHz frequency slot in this range. Assume we want to transmit speech over AM with given slot from Fmin=650 KHz to Fmax=658 KHz, with the bandwidth W=Fmax-Fmin equal to 8 KHz. The speech signal s(t) , obtained with a microphone , has a wideband spectrum which spans several KHz; we can however filter it through a low pass filter with cutoff frequency 4 KHz without losing too much quality and thus reduce its spectral width to 8 KHz. The filtered signal has now a spectrum extending from -4 to 4 KHz; by multiplying it by a sinusoid at frequency Fc=(Fmax+Fmin)/2=654KHz. We can sift it to allotted AM band according to the modulation theorem: For digital communication first the data must flow as a data stream, converts the bit stream to data (baud) stream by mapping the bits into symbols of 2m, this shape not yet suitable for transmission, first there is a need to design its spectral characteristics to fits it into the available bandwidth of the channel, then translate it in frequency to place it right in the pass band of the channel .this functions are performed by a pulse shaper (low pass filter) and by modulator. Demodulation done at receives side by convert modulated signal to original signal. The signal created at the modulator is converted to a continuous time signal c(t) by a D/A converter operating at a sampling frequency fs and sent over the telephone channel. With reasonably good approximation the channel behaves like a 63 linear signal and also introduces a certain amount of additive noise so that the signal appearing at the receiver's input looks like; Where tp is the propagation delay, dependent on the distance between transmitter and receiver, d (t) is the equivalent impulse response of the channel and n (t) is the noise. The first thing the digital receiver does is sampling the incoming signal A fundamental building block of any modem is an adaptive equalizer whose task is to estimate the distortion introduced by the channel in order to eliminate it. A modem is a device consists of modulation and demodulation at each of communication sides. 5.7- summary This chapter provides an introduction to data communication, the chapter introduced the history of data communications and then explain the concept of data transmission using parallel and series mode. An encoding techniques also introduced in this chapter, then chapter ended by a simple ideas about modem operation. ABOUT THE AUTHOR Elmustafa Sayed Ali Ahmed received his M.Sc. degree in electronic engineering, Telecommunication from Sudan University of science and technology in 2012, and B.Sc. (Honor) degree in electrical engineering, Telecommunication from Red Sea University in 2008. He was a wireless networks (Tetra system, Wi-Fi and Wi-Max) engineer in Sudan Sea Port Corporation for 4 years. Now he is a head department of electrical and electronics engineering, faculty of engineering in Red Sea University, Sudan. He is published papers, and chapters in area of MANET routing protocols, and big data clouds. Research interests in field of mobile ad-hoc networks, wireless networks, Vehicular ad-hoc networks and computer networks, and cloud computing. 64 References [1] Upamanyu Madhow;” Introduction to Communication Systems”; anuary 17, 2014;http://www.ece.ucsb.edu/wcsl/Publications/intro_comm_systems_madhow_j an2014b.pdf. [Accessed in 27 July 2015] [2]http://www.ed.gov.nl.ca/edu/k12/curriculum/guides/teched/commtech2104/ct21 04_unit1.pdf. [Accessed in 27 July 2015] [3]Difference between Attenuation and Distortion; http://www.differencebetween .com/difference-between-attenuation-and-vs-distortion/. [Accessed in 27 July 2015] [4]Attenuation, Distortion and Noise (Basics of networking); http://www.bitlanders.com/blogs/attenuation-distortion-and-noise-basics-ofnetworking/282687. [Accessed in 27 July 2015] [5] https://www.st-andrews.ac.uk/~www_pa/Scots_Guide/audio/part7/page1.html. .[Accessed in 27 July 2015] [6] http://www.amanogawa.com/archive/docs/C-tutorial.pdf. [Accessed in 27 July 2015] [7]DR. FARID FARAHMAND;” INTRODUCTION TO TRANSMISSION LINES”;http://122.physics.ucdavis.edu/sites/default/files/files/Electronics/Transmi ssionLinesPart_II.pdf. [Accessed in 27 July 2015] 65 [8]Prof. Tzong-Lin Wu;” Transmission Line Basics”; http://ntuemc.tw/upload/file/20120419205252ec3bb.pdf. [Accessed in 27 July 2015] [9]ROF. A.M.ALLAM;” RANSMISSION LINE THEORY”; http://eee.guc.edu.eg/Courses/Networks/NETW502%20Communication%20Engin eering/LEC/LEC2-%20TRANSMISSION%20LINE%20THEORY.pdf. [Accessed in 27 July 2015] [10] Prof. Ali M. Nikneja;” Lecture 12: Noise in Communication Systems”; University of California, Berkeley; http://rfic.eecs.berkeley.edu/~niknejad/ee142_fa05lects/pdf/lect12.pdf.[Accessed in 27 July 2015] [11] http://www.daenotes.com/electronics/communication-system/noise. [Accessed in 27 July 2015] [12] ATTENUATORS / FILTERS / DC BLOCKS ATTENUATORS; http://jacquesricher.com/EWhdbk/attnfilt.pdf. [Accessed in 27 July 2015] [13] Attenuators, equalizers & filters; http://www.dktcomega.de/Files/Filer/PDF/ Datasheets/att_hpft.pdf. [Accessed in 27 July 2015] [14] K.K.DHUPAR;” DATA COMMUNICATION (Basics of data communication, OSI layers.)”; http://www.di.unipi.it/~bonucce/11-Datacommunication.pdf. [Accessed in 27 July 2015] [15] http://telecom.tbi.net/history1.html. [Accessed in 27 July 2015] [16] http://k-12.pisd.edu/currinst/network/if2_2st.pdf. [Accessed in 27 July 2015] 66 [17]The Difference between Serial & Parallel Data Transfer; http://science.opposingviews.com/difference-between-serial-parallel-data-transfer1608.html. [Accessed in 27 July 2015] [18] http://www.sqa.org.uk/e-learning/NetTechDC01BCD/page_02.htm. [Accessed in 27 July 2015] [19]Dr. Dheeraj Sanghi;” Computer Networks (CS425)”; http://www.cse.iitk.ac.in/users/dheeraj/cs425/lec03.html. [Accessed in 27 July 2015] Communication system is a system model describes a communication exchanges between two stations, transmitter and receiver. Signals or information’s passes from source to distention through what is called channel, which represents a way that signal use it to move from source toward destination. To transmit signals in communication system, it must be first processed by several stages, beginning from signal representation, to signal shaping until encoding and modulation. After preparing the transmitted signal, it passed to the transmission line of channel and due signal crossing this media it faces many impairments such noise, attenuation and distortion. This note book gives a brief concepts about transmission line calculation and also provides an idea about communication system impairments with an example for each one. The note book also provides an introduction to data communication with a simple ideas of data processing. Proof Printed By Createspace View publication stats