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Easy to manipulate Flexible Compatibility with other digital systems Only digitized information can be transported through a noisy channel without degradation Integrated networks Disadvantages of Digital - Sampling Error Digital communications require greater bandwidth than analogue to transmit the same information. The detection of digital signals requires the communications system to be synchronized, whereas generally speaking this is not the case with analogue systems. Some more explanation of advantages and disadvantages of analog vs digital communication. 1.The first advantage of digital communication against analog is it’s noise immunity. In any transmission path some unwanted voltage or noise is always present which cannot be eliminated fully. When signal is transmitted this noise gets added to the original signal causing the distortion of the signal. However in a digital communication at the receiving end this additive noise can be eliminated to great extent easily resulting in better recovery of actual signal. In case of analog communication it’s difficult to remove the noise once added to the signal. 2.Security is another priority of messaging services in modern days. Digital communication provides better security to messages than the analog communication. It can be achieved through various coding techniques available in digital communication. 3. In a digital communication the signal is digitized to a stream of 0s and 1s. So at the receiver side a simple decision has to me made whether received signal is a 0 or a 1.Accordingly the receiver circuit becomes simpler as compared to the analog receiver circuit. 4. Signal when travelling through it’s transmission path gets faded gradually. So on it’s path it needs to be reconstructed to it’s actual form and re-transmitted many times. For that reason AMPLIFIERS are used for analog communication and REPEATERS are used in digital communication. Amplifiers are needed every 2 to 3 Kms apart where as repeaters are needed every 5 to 6 Kms apart. So definitely digital communication is cheaper. Amplifiers also often add non-linearity that distort the actual signal.
5. Bandwidth is another scarce resource. Various Digital communication techniques are available that use the available bandwidth much efficiently than analog communication techniques. 6. When audio and video signals are transmitted digitally an AD (Analog to Digital) converter is needed at transmitting side and a DA (Digital to Analog) converter is again needed at receiver side. While transmitted in analog communication these devices are not needed. 7. Digital signals are often an approximation of the analog data (like voice or video) that is obtained through a process called quantization. The digital representation is never the exact signal but it’s most closely approximated digital form. So it’s accuracy depends on the degree of approximation taken in quantization process. Sampling Theorem: There are 3 cases of sampling:
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 and 18: 14.Detailed Notes UNIT 1 : Elements
Page 19 and 20: A communication system may transmit
Page 21: the wavelength is extremely long, m
Page 25 and 26: asic elements of digital communicat
Page 27: 4. Channel introduced many types of
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
Page 67 and 68: Generation and Detection of Coheren
Page 69 and 70: Figure 6.29 Signal-space diagram fo
Page 72 and 73: UNIT 3 Base Band Transmission And O
Page 74 and 75: • The tails of hI(t) decay as 1/|
Page 76 and 77: • 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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