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Digital Communication

Course Title:- Digital Communication

Course Code:- 10B11EC511

Course Credit :- 3+1=4

Contact Hours:- Lecture (3) Tutorial (1)

Course Coordinator : DEEPAK SHARMA

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Course BooksText: 1.Digital Communications: Fundamentals and applications, By “Bernard

Sklar”, Prentice Hall, 2nd ed, 2001.  2.Principles of Communication Systems “Herbert Taub and Donald L.

Schilling” Tata Mcgraw Hill

References:1 Digital Communications, Fourth Edition, J.G. Proakis, McGraw Hill,

2000. 

Introduction: Merits and demerits of digital signals. Review of sampling theorem in frequency domain and time domain.

Waveform coding techniques: PCM generation and detection, quantization, quantization error, non uniform quantization, companding, differential PCM, Delta modulation, Adaptive delta modulation,

Digital modulation techniques: Line codes. Binary & M-ary modulation techniques: FSK, PSK, DPSK, M-ary PSK, Minimum Phase Shift Keying (MSK) and Quadrature Amplitude Modulation.

Course to be cover upto MSE 3

• Performance analysis of Digital systems: Probability of error analysis – Optimum filter, Matched filter. Coherent & Non-Coherent Reception. Probability of error for FSK, PSK, DPSK, M-ary PSK, Minimum Shift Keying (MSK). Introduction to bit Vs symbol error probability & Bandwidth.

• Digital systems and error control: Digital radio. Introduction to error control upto hamming codes. Digital Mutliplexing standards (for telephony). Only introduction and concepts

Course to be cover upto ESE4

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EVALUATION SYSTEM

1. Test – 1 2 hour 30

2. Test – 2 3 hour 45

3. Attendance 5

4. Tutorial & Assignments 10

5. Quiz Test 5+5=10

Total 100

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ATTENDANCEMin Marks = 0Max. Marks = 5Criterion for awarding marks :

75% > -- 180 % > -- 285 % > -- 390 % > -- 495 % > -- 5

Otherwise ‘F’ Grade will be awarded,

Irrespective of your performance in Tests.

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GRADESA+ OutstandingA ExcellentB+ Very GoodB GoodC+ AverageC Below AverageD MarginalF Fail

NOTENOTE : In the final Result, if you get ‘F’ grade, you shall : In the final Result, if you get ‘F’ grade, you shall be permitted to appear in ‘Supplementary Exam’ to get be permitted to appear in ‘Supplementary Exam’ to get better grade.better grade.

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Digital Communication• What is communication ?

• Difference between digital and analog communication

• Why digital ?

• Block diagram of Digital Communication system

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• Main purpose of communication is to transfer information from a source to a recipient via a channel or medium.

Source Transmitter Receiver

Recipient

Channel

Fig. 1 Basic block diagram of a communication system

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• Source: analog or digital

• Transmitter: transducer, amplifier,modulator, oscillator, power amp., antenna

• Channel: e.g. cable, optical fibre, free space

• Receiver: antenna, amplifier, demodulator, oscillator, power amplifier, transducer

• Recipient: e.g. person, (loud) speaker, computer

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• Types of informationVoice, data, video, music, email etc.

• Types of communication systemsPublic Switched Telephone Network (voice, fax, modem)Satellite systems Radio,TV broadcastingCellular phones Computer networks (LANs, WANs, WLANs)

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Information Representation• Communication system converts information into

electrical electromagnetic/optical signals appropriate for the transmission medium.

• Analog systems convert analog message into signals that can propagate through the channel.

• Digital systems convert bits(digits, symbols) into signals

– Computers naturally generate information as characters/bits

– Most information can be converted into bits– Analog signals converted to bits by sampling and

quantizing (A/D conversion)

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Why digital?• Robustness- can reconstruct digital signal from

degraded version

– a big issue in long distance communication

• Digital repeaters reconstruct digital signal at intermediate stages reducing overall error.

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Digital vs. AnalogAdvantages:• Digital signals are much easier to be regenerated.• Digital circuits are less subject to distortion and

interference.• Digital circuits are more reliable and can be produced

at a lower cost than analog circuits.• It is more flexible to implement digital hardware than

analog hardware.• Digital signals are beneficial from digital signal

processing (DSP) techniques.

Disadvantages:

• Heavy signal processing.

• Synchronization is crucial.

• Larger transmission bandwidth.

• Non-graceful degradation.

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• Basic Digital Communication Transformations– Formatting/Source Coding – Transforms source info into digital symbols (digitization) – Selects compatible waveforms (matching function) – Introduces redundancy which facilitates accurate decoding

despite errors

• It is essential for reliable communication – Modulation/Demodulation – Modulation is the process of modifying the info signal to

facilitate transmission – Demodulation reverses the process of modulation. It

involves the detection and retrieval of the info signal • Types • Coherent: Requires a reference info for detection • Noncoherent: Does not require reference phase

information

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– Coding/Decoding Translating info bits to transmitter data symbols Techniques used to enhance info signal so that they are less vulnerable to channel impairment (e.g. noise, fading, jamming, interference)

• Two Categories – Waveform Coding

• Produces new waveforms with better performance – Structured Sequences

• Involves the use of redundant bits to determine the occurrence of error (and sometimes correct it) – Multiplexing/Multiple Access Is synonymous with resource

sharing with other users – Frequency Division Multiplexing/Multiple Access

(FDM/FDMA)

Basic Digital Communication Transformations

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• To maximize transmission rate, R• To maximize system utilization, U

• To minimize bit error rate, Pe• To minimize required systems bandwidth, W

• To minimize system complexity, Cx• To minimize required power, Eb/No

Goals in Communication System Design