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– Poor performance at very low BER. – Because turbo codes operate at very low SNR, channel estimation and tracking is a critical issue. • The principle of iterative or “turbo” processing can be applied to other problems. – Turbo-multiuser detection can improve performance of coded multiple-access systems. UNIT 5 : Spread Spectrum Modulation ‣ Use of spread spectrum, ‣ direct sequence spread spectrum(DSSS), ‣ Code division multiple access, ‣ Ranging using DSSS Frequency Hopping spread spectrum, ‣ PN sequences: generation and characteristics, ‣ Synchronization in spread spectrum system, ‣ Advancements in the digital communication SPREAD SPECTRUM MODULATION • Spread data over wide bandwidth • Makes jamming and interception harder • Frequency hoping – Signal broa<strong>dc</strong>ast over seemingly random series of frequencies • Direct Sequence – Each bit is represented by multiple bits in transmitted signal – Chipping code Spread Spectrum Concept: • Input fed into channel encoder – Produces narrow bandwidth analog signal around central frequency • Signal modulated using sequence of digits – Spreading code/sequence – Typically generated by pseudonoise/pseudorandom number generator • Increases bandwidth significantly – Spreads spectrum • Receiver uses same sequence to demodulate signal • Demodulated signal fed into channel decoder
General Model of Spread Spectrum System: Gains: • Immunity from various noise and multipath distortion – Including jamming • Can hide/encrypt signals – Only receiver who knows spreading code can retrieve signal • Several users can share same higher bandwidth with little interference – Cellular telephones – Code division multiplexing (CDM) – Code division multiple access (CDMA) Pseudorandom Numbers: • Generated by algorithm using initial seed • Deterministic algorithm – Not actually random – If algorithm good, results pass reasonable tests of randomness • Need to know algorithm and seed to predict sequence Frequency Hopping Spread Spectrum (FHSS): • Signal broa<strong>dc</strong>ast over seemingly random series of frequencies • Receiver hops between frequencies in sync with transmitter • Eavesdroppers hear unintelligible blips • Jamming on one frequency affects only a few bits Basic Operation: • Typically 2k carriers frequencies forming 2k channels • Channel spacing corresponds with bandwidth of input • Each channel used for fixed interval
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DC COURSE FILE
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GEETHANJALI COLLEGE OF ENGINEERING
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Convolution Codes: Encoding, decodi
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III. To inculcate positive attitude
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7. Importance of the course and how
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DC 12: Compute the power and bandwi
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10. Course mapping with PEO’s and
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13.Micro plan : Sl. no Unit No. Tot
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14.Detailed Notes UNIT 1 : Elements
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A communication system may transmit
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the wavelength is extremely long, m
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asic elements of digital communicat
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4. Channel introduced many types of
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5. Bandwidth is another scarce reso
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Pulse Code Modulation ‣ PCM gener
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77777333333333333333333333333333333
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• The most common technique for s
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Pulse Code Modulation (PCM) : • P
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Figure 3.11 Illustration of the qua
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Quantization (nonuniform quantizer)
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Time-Division Multiplexing(TDM):
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Let m n where T The error signal is
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3. Simplify receiver design Because
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Figure 3.27 Block diagram illustrat
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Adaptive Differential Pulse-Code Mo
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ASK, OOK, MASK: • The amplitude (
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Frequency Shift Keying: • One fre
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s t Acos 2f ct 3 Acos 2f
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QAM and QPR: • QAM is a combinati
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Generation and Detection of Coheren
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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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Page 78 and 79: h( t) N 1 n w n sin c t T b
Page 80 and 81: • Equalization : to compensate fo
Page 82 and 83: e n y n 2E en 2E en 2Eenxnk
Page 84 and 85: - Flexibility - Same H/W may be tim
Page 86 and 87: Interpretation of Eye Diagram:
Page 88 and 89: The set of source symbols is called
Page 90 and 91: We will usually neglect to mention
Page 92 and 93: Note that if Condition1 is satisfie
Page 94 and 95: where dmin is the minimum Hamming d
Page 96 and 97: Linear Block Codes - example 1: •
Page 98 and 99: • S null can be represented by it
Page 100 and 101: G 1 0 I | P 0 0 0 1 0 0 0 0
Page 102 and 103: • Compared with the systematic co
Page 104 and 105: Convolutional Codes ◊ The encoder
Page 106 and 107: Convolution Codes ‣ Encoding, ‣
Page 108 and 109: x m m ''' j j 2 j Here each messa
Page 110: Representing convolutional codes: C
Page 113 and 114: - encoder state diagram for (n,k,L)
Page 115 and 116: • For this reason the non-survive
Page 117 and 118: sequence is 1 1 0 0 0 0 0 (why?). N
Page 119 and 120: Error Correction: • If there is n
Page 121 and 122: correct:1+1+2+2+2=8;8 ( 0.11) 0.88
Page 123 and 124: Motivation: Performance of Turbo Co
Page 125: Performance as a Function of Number
Page 129 and 130: Slow and Fast FHSS: • Frequency s
Page 131 and 132: - 10 bit spreading code spreads sig
Page 133 and 134: Direct Sequence Spread Spectrum Usi
Page 135 and 136: 15.Additional Topics: Voice coders
Page 137 and 138: 'Toll Quality' voice coders, such a
Page 139 and 140: The well-known Shannon-Hartley law
Page 141 and 142: its for a known permutation of the
Page 143 and 144: 16. Question papers: B. Tech III Ye
Page 145 and 146: e received code word 110110. Commen
Page 147 and 148: 17. Question Bank 1. (a) State and
Page 149 and 150: 21. A Discrete Memory less Source (
Page 151 and 152: 19. Unit wise Bits CHOOSE THE CORRE
Page 153 and 154: (d) 5 Answers 1.C 2.D 3.B 4.A 5.C 6
Page 155 and 156: (b) its capacity gets doubled (c) i
Page 157 and 158: (d) 6 5. The cascade of two binary
Page 159 and 160: CHOOSE THE CORRECT ANSWER 1. The mi
Page 161 and 162: 2.C 3.C 4.A 5.D 6.C 7.B 8.B 9.B 10.
Page 163 and 164: (b) H(X/Y)=1bit/message (c) H(X,Y)=
Page 165 and 166: (d) log m bits/symbol 6. Theencoder
Page 167 and 168: 3. .Under error free reception, the
Page 169 and 170: 10.B Code No: 56026 Set No. 1 JAWAH
Page 171 and 172: code No: 56026 Set No. 2 JAWAHARLAL
Page 173 and 174: B) (Power required)/( Minimum Band
Page 175 and 176: 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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