CHAPTER 1 Basic Elements in Communication System Chapter

CHAPTER 1 Basic Elements in Communication System

Chapter 1 (cont…) Part 1 Introduction to Communication System n Part 2 Noise n Part 3 Transmission Media and EM Propagation n Part 4 Filter n

Part 1 Introduction to Communication System

Objectives n n n n To understand the principles of basic communication systems To define information, message and signals To differentiate between analog and digital signals To explain the elements of communication system To explain the terms modulation and why they are needed in communication system To explain the limitations in communication system To define frequency and wavelength

Lecture overview n n n n n Definition of communications Information, message and signals Analog and digital signals Basic requirements of communication system Elements of communication system Modulation Noise, interference and distortion Limitations in communication system Frequency and wavelength d. B in communications

Signals and Systems Defined n n n A signal is any physical phenomenon which conveys information Systems respond to signals and produce new signals Excitation signals are applied at system inputs and response signals are produced at system outputs

A Communication System as a System Example n n A communication system has an information signal plus noise signals This is an example of a system that consists of an interconnection of smaller systems

Signal Types

Conversions Between Signal Types Sampling Quantizing Encoding

COMMUNICATION SYSTEM Definitions n Communications: Ø Ø n Transfer of Information from one place to another. Should be efficient, reliable, and secured. Communication system: Ø components/subsystems act together to accomplish information transfer/exchange

Definitions (Cont’d) n Electronic communication system Ø transmission, reception and processing of information between two or more locations using electronic circuits. n Information source Ø analog/digital form

Think! n Have you ever pictured yourself living in a world without any communication system?

Need For Communication n Importance of communication: exchange of information between two parties separated in distances in a more faster and reliable way.

Information, message and signals n Information Ø The commodity produced by the source for transfer to some user at the destination. n Message Ø The physical manifestation of information as produced by the information source. n Signals ØA physical embodiment of information – voltage signal or current signal

Brief History in Communication Year 1844 1876 1904 1923 1936 1962 1966 1972 1989 Events Telegraph Telephone AM Radio Television FM Radio Satellite Optical links using laser and fiber optics Cellular Telephone Internet

Development and progress n Communications between human beings Ø Form of hand gestures and facial expressions Ø Verbal grunts and groans n Long distance communications Ø Smoke signals Ø Telegraph Ø Telephone

Cont’d… n Wireless radio signals Ø Triode vacuum tube Ø Commercial radio broadcasting

Analog vs. Digital n Analog Ø Continuous Variation Ø Assume the total range of frequencies/time Ø All information is transmitted n Digital Ø Takes § samples: non continuous stream of on/off pulses Ø Translates to 1’s and 0’s

Analog vs. Digital CS Advantages: -Inexpensive -Privacy preserved(data encrypted) -Can merge different data -error correction Analog Cs Disadvantages: -expensive -No privacy preserved -Cannot merge different data -No error correction capability n n Disadvantages: -Larger bandwidth -synchronization problem is relatively difficult Advantages: -smaller bandwidth -synchronization problem is relatively easier.

Basic Requirements of Communication System n Rate of information transfer: Ø how n fast the information can be transferred Purity of signal received: Ø whether the signal received is the same as the signal being transmit n Simplicity of the system Ø the n simpler the system, the better Reliability

Elements of Communication System(CS)

Elements of CS (cont’d) n Information Ø The communication system exists to convey a message. Ø Message comes from information source Ø Information forms - audio, video, text or data

cont’d… n Transmitter: Ø Processes input signal to produce a transmitted signal that suited the characteristic of transmission channel. Ø E. g. modulation, coding, mixing, translate Ø Other functions performed - Amplification, filtering, antenna Ø Message converted to into electrical signals by transducers Ø E. g. speech waves are converted to voltage variation by a microphone

Elements of CS (cont’d) n Channel (transmission media): Øa medium that bridges the distance from source to destination. Eg: Atmosphere (free space), coaxial cable, fiber optics, waveguide Ø signals undergoes degradation from noise , interference and distortion

Elements of CS (cont’d) n Receiver: Ø to recover the message signal contained in the received signal from the output of the channel, and convert it to a form suitable for the output transducer. Ø E. g. mixing, demodulation, decoding Ø Other functions performed: Amplification, filtering. Ø Transducer converts the electrical signal at its input into a form desired by the system used

Modulation n What is modulation? Øa process of changing one or more properties of the analog carrier in proportion to the information signal. Ø One of the characteristics of the carrier signal is changed according to the variations of the modulating signal. § § § AM – amplitude, E FM – frequency , ω PM - phase , θ

Modulation (cont’d) n Why modulation is needed? Ø To generate a modulated signal suited and compatible to the characteristics of the transmission channel. Ø For ease radiation and reduction of antenna size Ø Reduction of noise and interference Ø Channel assignment Ø Increase transmission speed

Noise, interference and distortion n Noise Ø Ø n Internal noise Ø n unwanted signals that coincide with the desired signals. Two type of noise: internal and external noise. Caused by internal devices/components in the circuits. External noise Ø Ø noise that is generated outside the circuit. E. g. atmospheric noise, solar noise, cosmic noise, man made noise.

Noise, interference and distortion (Cont’d) n Interference Ø Contamination by extraneous signals from human sources. Ø E. g. from other transmitters, power lines and machineries. Ø Occurs most often in radio systems whose receiving antennas usually intercept several signals at the same time Ø One type of noise.

Noise, interference and distortion (Cont’d) n Distortion Ø Signals or waves perturbation caused by imperfect response of the system to the desired signal itself. Ø May be corrected or reduced with the help of equalizers.

Limitations in communication system n Technological problems Ø Includes equipment availability, economic factors, federal regulations and interaction with existing systems. Ø Problem solved in theory but perfect solutions may not be practical.

Limitations in communication system (cont’d) n Physicals limitations Ø Bandwidth Ø Measure limitation of speed Ø The system ability to follow signal variations depends on the transmission bandwidth. Ø Available bandwidth determines the maximum signal speed.

Limitations in communication system (cont’d) Ø Noise limitation Ø Unavoidable. Ø The kinetic theory. Ø Noise relative to an information signal is measured in terms of signal to noise ratio (SNR).

Communication system design n Compromise within: Ø Transmission time and power Ø SNR performance Ø Cost of equipments Ø Channel capacity Ø Bandwidth

FREQUENCY AND WAVELENGTH n n Cycle - One complete occurrence of a repeating wave (periodic signal) such as one positive and one negative alternation of a sine wave. Frequency - the number of cycles of a signal that occur in one second. Period - the time distance between two similar points on a periodic wave. Wavelength - the distance traveled by an electromagnetic (radio) wave during one period.

PERIOD AND FREQUENCY COMPARED T = One period time One cycle Frequency = f = 1/T

Frequency and wavelength compared + T 0 time f = 1/T distance

CALCULATING WAVELENGTH AND FREQUENCY = 300/f f = 300/ = wavelength in meters f = frequency in MHz

(f = 300/ ) Frequency 300 GHz 30 GHz VHF UHF SHF EHF Millimeter waves 10 -4 m 10 -3 m 10 -2 m 10 -1 m 1 m 102 m 103 m 104 m 105 m 106 m 107 m Wavelength 3 GHz HF 300 MHz MF 30 MHz LF 3 MHz VLF 300 k. Hz VF 30 k. Hz ELF 3 k. Hz 300 Hz 30 Hz THE ELECTROMAGNETIC SPECTRUM FROM 30 HZ TO 300 GHZ ( = 300/f)

LOW AND MEDIUM FREQUENCIES n Extremely Low Frequencies - 30 to 300 Hz n Voice Frequencies - 300 to 3000 Hz n Very Low Frequencies - 3 k. Hz to 30 k. Hz n Low Frequencies - 30 k. Hz to 300 k. Hz n Medium Frequencies - 300 k. Hz to 3

HIGH FREQUENCIES n High Frequencies - 3 MHz to 30 MHz n Very High Frequencies - 30 MHz to 300 MHz n Ultra High Frequencies - 300 MHz to 3 GHz (1 GHz and above = microwaves) n Super High Frequencies - 3 GHz to 30 GHz n Extremely High Frequencies

300 GHz Cosmic rays Gamma rays X-rays Ultraviolet Visible Infrared Millimeter waves 0. 4 x 10 -6 m 0. 8 x 10 -6 m 10 -5 m 10 -4 m 10 -3 m THE ELECTROMAGNETIC SPECTRUM ABOVE 300 GHZ Wavelength

OPTICAL FREQUENCIES n Infrared - 0. 7 to 10 micron n Visible light - 0. 4 to 0. 8 micron n Ultraviolet - Shorter than 0. 4 micron Note: A micron is one millionth of a meter. Light waves are measured and expressed in wavelength rather than frequency.

TYPES OF COMMUNICATIONS TX Channel TX RX RX Channel(s) RX TX Simplex: One-way Duplex: Two-way Half duplex: Alternate TX/RX Full duplex: Simultaneous TX/RX

COMMUNICATIONS SIGNAL VARIATIONS n Baseband - The original information signal such as audio, video, or computer data. Can be analog or digital. n Broadband - The baseband signal modulates or modifies a carrier signal, which is usually a sine wave at a frequency much higher than the baseband signal.

Various forms of communication system Broadcast: radio and television n Mobile communications n Fixed communication system- land line n Data communication-internet n

Frequency Spectrum & Bandwidth The frequency spectrum of a waveform consists of all frequencies contained in the waveform and their amplitudes plotted in the frequency domain. n The bandwidth of a frequency spectrum is the range of frequencies contained in the spectrum. It is calculated by subtracting the lowest frequency from the highest. n

Power gain

Power gain It is the ratio of output power, Pout over input power, Pin. n Absolute power ratio (unitless), Power ratio, Ap = Pout/Pin n where, Pout =output power levels (watts) Pin =input power levels (watts) n Absolute power ratio can be converted to a power gain in d. B value, Power gain (d. B), Ap(d. B) = 10 log (Ap) n A positive (+) d. B value indicates a power gain or amplification. A negative (-) d. B value indicates a power loss or n

Voltage Gain in Communication n In communication, due to known characteristic impedance of the channel, the power and voltage gains become explicit. Voltage gain in d. B = 20 log (Vout/Vin) d. B.

Alternatively: Power gain = 10 (gain in d. B/10) Voltage gain = 10 (gain in d. B/20) Example: A 64 d. B gain means 10(64/10) = 2. 5212 x 106 An attenuation by 0. 01= 10 log(0. 01) = -20 d. B

Example: Let there be two amplifiers in cascade. Their gains are 13 d. B and 10 d. B respectively. n The overall gain is 13+10 = 23 d. B. Sum n In terms of ratio: n 23 d. B = 10(23/10)= 200 same OR n 13 d. B = 10(13/10)= 20 n 10 d. B = 10(10/10)= 10 n Overall gain in terms of ratio 20 x 10 = n

Relative d. B It is convenient to express signals with some reference such as 1 m. W power or, 1 V voltage level. n This permits input- and output- signals to be expressed in terms of relative d. B. n When referenced to 1 m. W, it is written d. Bm n When referenced to 1 V, it is written as d. B V n

n The d. Bm unit is expressed mathematically as: Where P is any power in watts and 1 m. W is the reference power n Relative d. B is not a gain but is termed as gain with respect to a reference n

Example 1 n Convert a power level of 5 watts signal to d. Bm, In relative d. B; d. Bm = 10 log(5 W/1 m. W) = 36. 99 d. Bm n Convert a power level of 200 m. W signal to d. Bm: In relative d. B; d. Bm = 10 log(200 m. W /1 m. W ) = 23 d. Bm

Example 2 Convert 10 d. Bm to watts n Solution: n 10 d. Bm = 10 log (P / 1 m. W) antilog (10 d. Bm/10) = P / 1 m. W P = 0. 01 W @ 1 m. W

Power levels, gains and losses n When power levels are given in watts and power gains are given in absolute values, the output power is determined by multiplying the input power times the power gains.

Example 3 Given: A three-stage system comprised of two amplifiers and one filter. The input power Pin = 0. 1 m. W. The absolute power gains are Ap 1 = 100, Ap 2 = 40 and Ap 3 = 0. 25. Determine: (a) The input power in d. Bm. (b) Output power (Pout) in watts and d. Bm (c) The d. B gain of each of the three stages (d) The overall gain in d. B

Example 4 For a three-stage system with an input power Pin= -20 d. Bm and power gains of the three stages as Ap 1 = 13 d. B, Ap 2 = 16 d. B and Ap 3 = -6 d. B, determine the output power (Pout) in d. Bm and watts.

End of Chapter 1 Part 1