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• Some methods can be used at specific times of the day • Information is not secure. Examples of Today’s Communication Methods All of the following are electric (or electromagnetic) communication systems • Satellite (Telephone, TV, Radio, Internet, … ) • Microwave (Telephone, TV, Data, …) • Optical Fibers (TV, Internet, Telephone, … ) • Copper Cables (telephone lines, coaxial cables, twisted pairs, … etc) Advantages of Today’s Communication Systems • Fast • Easy to use and very cheap • Huge amounts of information can be transmitted • Secure transmission of information can easily be achieved • Can be used 24 hours a day. Basic Construction of Electrical Communication System Sound, picture, ... Electric signal (like audio and video outputs of a video camera Electric Signal (transmitted signal) Electric Signal (received signal) Electric Signal (like the outputs of a satellite receiver) Sound, picture, ... Added Noise Input Input Transducer Transmitter Channel (distorts transmitted signal) Receiver Output Transducer Output Converts the input signal from its original form (sound, picture, … etc) to an electric signal Adapts the electric signal to the channel (changes the signal to a form that is suitable for transmission) Medium though which the information is transmitted Extracts the original electric signal from the received signal Converts the electric signal to its original form (sount, picture, … etc)
A communication system may transmit information in one direction such as TV and radio (simplex), two directions but at different times such as the CB (half-duplex), or two directions simultaneously such as the telephone (full-duplex). Basic Terminology Used in this Communications Course A Signal: A System: Analog Signals: Digital Signals: Noise: is a function that specifies how a specific variable changes versus an independent variable such as time, location, height (examples: the age of people versus their coordinates on Earth, the amount of money in your bank account versus time). operates on an input signal in a predefined way to generate an output signal. are signals with amplitudes that may take any real value out of an infinite number of values in a specific range (examples: the height of mercury in a 10cm–long thermometer over a period of time is a function of time that may take any value between 0 and 10cm, the weight of people setting in a class room is a function of space (x and y coordinates) that may take any real value between 30 kg to 200 kg (typically)). are signals with amplitudes that may take only a specific number of values (number of possible values is less than infinite) (examples: the number of days in a year versus the year is a function that takes one of two values of 365 or 366 days, number of people sitting on a one-person chair at any instant of time is either 0 or 1, the number of students registered in different classes at KFUPM is an integer number between 1 and 100). is an undesired signal that gets added to (or sometimes multiplied with) a desired transmitted signal at the receiver. The source of noise may be external to the communication system (noise resulting from electric machines, other communication systems, and noise from outer space) or internal to the communication system (noise resulting from the collision of electrons with atoms in wires and ICs). Signal to Noise Ratio (SNR):is the ratio of the power of the desired signal to the power of the noise signal. Bandwidth (BW): is the width of the frequency range that the signal occupies. For example the bandwidth of a radio channel in the AM is around 10 kHz and the bandwidth of a radio channel in the FM band is 150 kHz. Rate of Communication: is the speed at which DIGITAL information is transmitted. The maximum rate at which most of today’s modems receive digital
Page 1 and 2: DC COURSE FILE
Page 3 and 4: GEETHANJALI COLLEGE OF ENGINEERING
Page 5 and 6: Convolution Codes: Encoding, decodi
Page 7 and 8: III. To inculcate positive attitude
Page 9 and 10: 7. Importance of the course and how
Page 11 and 12: DC 12: Compute the power and bandwi
Page 13 and 14: 10. Course mapping with PEO’s and
Page 15 and 16: 13.Micro plan : Sl. no Unit No. Tot
Page 17: 14.Detailed Notes UNIT 1 : Elements
Page 21: the wavelength is extremely long, m
Page 25 and 26: asic elements of digital communicat
Page 27 and 28: 4. Channel introduced many types of
Page 29 and 30: 5. Bandwidth is another scarce reso
Page 35 and 36: Pulse Code Modulation ‣ PCM gener
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Page 40 and 41: • The most common technique for s
Page 42 and 43: Pulse Code Modulation (PCM) : • P
Page 44 and 45: Figure 3.11 Illustration of the qua
Page 46 and 47: Quantization (nonuniform quantizer)
Page 48 and 49: Time-Division Multiplexing(TDM):
Page 50 and 51: Let m n where T The error signal is
Page 52 and 53: 3. Simplify receiver design Because
Page 54 and 55: Figure 3.27 Block diagram illustrat
Page 56 and 57: Adaptive Differential Pulse-Code Mo
Page 59 and 60: ASK, OOK, MASK: • The amplitude (
Page 61 and 62: Frequency Shift Keying: • One fre
Page 63 and 64: s t Acos 2f ct 3 Acos 2f
Page 65 and 66: QAM and QPR: • QAM is a combinati
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Figure 6.29 Signal-space diagram fo
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UNIT 3 Base Band Transmission And O
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• The tails of hI(t) decay as 1/|
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• precoding d b d k k k2 symbol 1
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h( t) N 1 n w n sin c t T b
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• Equalization : to compensate fo
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e n y n 2E en 2E en 2Eenxnk
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- Flexibility - Same H/W may be tim
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Interpretation of Eye Diagram:
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The set of source symbols is called
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We will usually neglect to mention
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Note that if Condition1 is satisfie
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where dmin is the minimum Hamming d
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Linear Block Codes - example 1: •
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• S null can be represented by it
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G 1 0 I | P 0 0 0 1 0 0 0 0
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• Compared with the systematic co
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Convolutional Codes ◊ The encoder
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Convolution Codes ‣ Encoding, ‣
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x m m ''' j j 2 j Here each messa
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Representing convolutional codes: C
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- encoder state diagram for (n,k,L)
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• For this reason the non-survive
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sequence is 1 1 0 0 0 0 0 (why?). N
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Error Correction: • If there is n
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correct:1+1+2+2+2=8;8 ( 0.11) 0.88
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Motivation: Performance of Turbo Co
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Performance as a Function of Number
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General Model of Spread Spectrum Sy
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Slow and Fast FHSS: • Frequency s
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- 10 bit spreading code spreads sig
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Direct Sequence Spread Spectrum Usi
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15.Additional Topics: Voice coders
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'Toll Quality' voice coders, such a
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The well-known Shannon-Hartley law
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its for a known permutation of the
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16. Question papers: B. Tech III Ye
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e received code word 110110. Commen
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17. Question Bank 1. (a) State and
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21. A Discrete Memory less Source (
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19. Unit wise Bits CHOOSE THE CORRE
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(d) 5 Answers 1.C 2.D 3.B 4.A 5.C 6
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(b) its capacity gets doubled (c) i
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(d) 6 5. The cascade of two binary
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CHOOSE THE CORRECT ANSWER 1. The mi
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2.C 3.C 4.A 5.D 6.C 7.B 8.B 9.B 10.
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(b) H(X/Y)=1bit/message (c) H(X,Y)=
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(d) log m bits/symbol 6. Theencoder
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3. .Under error free reception, the
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10.B Code No: 56026 Set No. 1 JAWAH
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code No: 56026 Set No. 2 JAWAHARLAL
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B) (Power required)/( Minimum Band
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A) 5 B) 4 C) 2 D) 3 3. Which of the
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Code No: 56026 Set No. 2 JAWAHARLAL
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A) maximum when the source is conti
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Code No: 56026 :2: Set No. 4 II Fil
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Code No: 07A5EC09 Set No. 2 JAWAHAR
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Cont…..2 Code No: 07A5EC09 :2: Se
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8) For the data word 1110 in a (7,
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a) 0 bits b) 1 bit c) 2 bits d) inf
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a) increase with its certainty of o
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Code No: 07A5EC09 :2: Set No.4 10)
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Amplitude of 1v.This speech signal
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. Self Information c. Logarithmic m
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75. What are the advantages and dis
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22. Discussion Topics: Data transmi
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Applications and history Data (main
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o o Mesh network Wireless network A
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25. STUDENTS LIST B.TECH III YEAR I
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48 13R11A04L3 M SAI KUMAR 49 14R18A
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Group 8: 36 13R11A04K1 POLISETTY VE
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Unit 2 Pulse-Amplitude Modulation :
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Unit 3 Differential Pulse-Code Modu
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MISSING TOPICS UNIT 1 Hartley's law
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encoding the desired information an
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• f c denotes center frequency
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An interleaver installed between th
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Subject Contents 1.7. 1. Synopsis p
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