Digital Communication and Switching Class Lecture 2
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Questions and Answers

What is the name of the course lecturer?

Lenin Joseph (LJ)

What are the two outcomes discussed in this lecture?

Outcome 2 and 3, Design of Digital Communication Systems

Which of the following can be transmitted in digital transmission?

  • A digital message originating from a data source, for example a computer or keyboard.
  • An analog signal such as a phone call or video signal, digitized into a bit stream using PCM or advanced source coding.
  • Both A and B (correct)
  • None of the above

    • The term "digital-over-digital" transmission refers to the method where analog signals are converted into digital signals and then transmitted.

    <p>False (B)</p> Signup and view all the answers

    Baseband Transmission requires modulation.

    <p>False (B)</p> Signup and view all the answers

    Which of the following are examples of line coding schemes used in baseband transmission?

    <p>All of the above (D)</p> Signup and view all the answers

    Passband transmission involves modulation.

    <p>True (A)</p> Signup and view all the answers

    What is the purpose of using a modem in passband transmission?

    <p>The modem is used to perform modulation and demodulation in passband transmission.</p> Signup and view all the answers

    Parallel transmission is the simultaneous transmission of signal elements of a character or other entity of data, regardless of the type of transmission (digital or analog).

    <p>True (A)</p> Signup and view all the answers

    What is the main advantage of parallel transmission compared to serial transmission?

    <p>Parallel transmission allows for higher data transfer rates than serial transmission.</p> Signup and view all the answers

    What is the main disadvantage of parallel transmission?

    <p>Skewing occurs due to different properties of wires in parallel transmission, leading to bits arriving at different times and potentially corrupting the message.</p> Signup and view all the answers

    Serial transmission transmits data sequentially over a single path, such as a wire, frequency, or optical path.

    <p>True (A)</p> Signup and view all the answers

    Serial transmission is ideal for long distances compared to parallel transmission, particularly when using electrical wires.

    <p>True (A)</p> Signup and view all the answers

    Asynchronous transmission is sometimes called start-stop transmission because it uses start-stop characters to define the beginning and end of a data block.

    <p>True (A)</p> Signup and view all the answers

    Which of the following statements is NOT true about asynchronous transmission?

    <p>Data blocks are sent, typically hundreds or thousands of characters, marked by start and stop bits. (D)</p> Signup and view all the answers

    Synchronous transmission uses start and stop bits to define the beginning and end of each character.

    <p>False (B)</p> Signup and view all the answers

    What is the purpose of sync bytes in synchronous transmission?

    <p>Sync bytes synchronize the internal clocks of the transmitting and receiving devices, ensuring proper data transmission and interpretation.</p> Signup and view all the answers

    Synchronous transmission requires the use of SYN characters.

    <p>True (A)</p> Signup and view all the answers

    What is the main advantage of synchronous transmission over asynchronous transmission?

    <p>Synchronous transmission offers quicker data transfer rates compared to asynchronous transmission.</p> Signup and view all the answers

    What is the formula to calculate the bandwidth (B) in Hertz?

    <p>B = fH - fL</p> Signup and view all the answers

    What is the bandwidth of a periodic signal consisting of five sine waves with frequencies of 100, 300, 500, 700, and 900 Hz?

    <p>800 Hz</p> Signup and view all the answers

    If a periodic signal has a bandwidth of 20 Hz and a highest frequency of 60 Hz, what is the lowest frequency?

    <p>40 Hz</p> Signup and view all the answers

    What is the meaning of information capacity in the context of digital transmission?

    <p>Information capacity refers to the amount of information that can be transmitted through a communication system in a given time.</p> Signup and view all the answers

    What is the most basic digital symbol used to represent information?

    <p>Binary digit (bit)</p> Signup and view all the answers

    Information capacity is directly proportional to bandwidth and transmission time.

    <p>True (A)</p> Signup and view all the answers

    The formula for Hartley's Law is I ______ B x t.

    <p>∝</p> Signup and view all the answers

    Who developed the relationship between bandwidth, transmission time, and information capacity known as Hartley's Law?

    <p>R. Harley of Bell Telephone Laboratories</p> Signup and view all the answers

    What is the Shannon Limit, and what does it relate to?

    <p>The Shannon Limit is the maximum theoretical data rate achievable for a given noise level and bandwidth.</p> Signup and view all the answers

    The Shannon Limit is also known as the Shannon-Hartley Theorem.

    <p>True (A)</p> Signup and view all the answers

    A higher signal-to-noise ratio results in higher information capacity.

    <p>True (A)</p> Signup and view all the answers

    What is the mathematical formula for the Shannon Limit for information capacity?

    <p>I = B * log2(1 + S/N)</p> Signup and view all the answers

    The Shannon-Hartley Theorem is applicable only for binary information.

    <p>False (B)</p> Signup and view all the answers

    What is the formula for the information capacity (I) in the Shannon-Hartley Theorem when considering multiple coding levels (M) and ignoring noise?

    <p>I = 2 * B * log2(M)</p> Signup and view all the answers

    For binary information with two possible levels (0 and 1), the information capacity is determined by I = 2 * B * log (2) * M.

    <p>True (A)</p> Signup and view all the answers

    What is the purpose of M-ary encoding?

    <p>M-ary encoding represents a method to represent information using multiple levels, reducing the number of bits needed to represent a specific condition.</p> Signup and view all the answers

    What is the mathematical formula to calculate the number of bits (N) required to generate M levels in M-ary encoding?

    <p>N = log2(M)</p> Signup and view all the answers

    How can you represent the number of conditions possible with N bits in M-ary encoding?

    <p>2^N = M</p> Signup and view all the answers

    What is the bit rate in a system where each bit is represented by a pulse of width Tb = 0.1 ms?

    <p>10 kHz</p> Signup and view all the answers

    What is the alternative name for baud rate?

    <p>Symbol rate</p> Signup and view all the answers

    Baud rate is directly proportional to the bit rate.

    <p>False (B)</p> Signup and view all the answers

    What is the baud rate for a system that transmits binary data with a bit duration of 1 μsec and each symbol is represented by four bits?

    <p>250 Kbaud</p> Signup and view all the answers

    What is the bit rate for a modulator that transmits symbols with 64 possible states at a rate of 10,000 symbols per second?

    <p>60 Kbps</p> Signup and view all the answers

    What is the minimum allowable bandwidth to transmit a 2-bit binary signal with a bit rate of 3 Mbps?

    <p>1.5 MHz</p> Signup and view all the answers

    The error probability (Pb) is calculated as the number of errors divided by the total number of bits received.

    <p>True (A)</p> Signup and view all the answers

    What is the typical range for acceptable error probability in communication systems?

    <p>From around 10^-5 to 10^-12</p> Signup and view all the answers

    How is the average number of errors calculated in a transmission with m bits and error probability Pb?

    <p>Average number of errors = m * Pb</p> Signup and view all the answers

    What does BER stand for?

    <p>Bit Error Rate</p> Signup and view all the answers

    BER is an exact measure of the bit error probability.

    <p>False (B)</p> Signup and view all the answers

    Study Notes

    Digital Communication and Switching Course Notes

    • Course title: Digital Communication and Switching
    • Semester: I AY 2024-25
    • Class lecture: 2
    • Outcome: #2&#3-Design of Digital Communication Systems
    • Lecturer: Lenin Joseph (LJ)
    • Date: Dec 24, 2024

    Outcome #2 & #3

    • Explain general constraints and limitations in designing communication systems.
    • Understand problems and techniques involved in baseband data transmission (ISI, Pulse Shaping, Eye diagram).

    Digital Transmission

    • Transmission of digital signals between two or more points in a communication system.
    • Physical transfer of digital bit stream over a point-to-point or multipoint communication channel.
    • Information transmitted can be:
      • Digital messages originating from a data source (e.g., computer, keyboard).
      • Analog signals (e.g., phone calls, video signals) digitized into a bit stream using PCM or advanced source coding (Analog-to-Digital Conversion and data compression).

    Transmission Schemes for Analog and Digital Signals

    • Diagrams illustrating different transmission schemes for analog and digital signals.
      • Analog signal with no modulation
      • Standard analog modulation system
      • Digital transmission on digital scheme
      • Digital transmission on analog scheme
      • Analog transmission on digital channel
      • Digitized analog signal transmission on analog scheme

    Types of Digital Data Transmission

    • Baseband Transmission:
      • "Digital-over-digital" transmission (direct transmission of information signal without modulation).
      • Transmission of electrical or light pulses using line coding schemes (RZ, NRZ, Manchester coding).
      • Used in serial cables, wired LANs (e.g., Ethernet), and optical communication.
    • Passband Transmission:
      • "Digital-over-analog" transmission (transmission of a modulated sine wave representing a digital bit stream).
      • Utilizes digital modulation schemes (PSK, FSK, QAM).
      • Demodulation carried out by modem equipment.
      • Used in wireless communication and over telephone network local loop and cable-TV networks.

    Digital Transmission Mode - Parallel Transmission

    • Simultaneous transmission of signal elements of a character or entity of data.
    • Signal elements of related data transmitted over multiple separate paths.
    • Uses multiple electrical wires for higher data transfer rates than serial transmission.
    • Used internally within computers (e.g., internal buses) and sometimes externally (e.g., printers).
    • Disadvantage: Skewing (bits arriving before others) can corrupt the message. Electrical wire parallel data transmission less reliable for long distances.
    • Error check bit (parity bit) can help reduce the error.

    Digital Transmission Mode - Serial Transmission

    • Sequential transmission of signal elements of a group representing a character or entity of data.
    • Bits sent over a single wire, frequency, or optical path sequentially.
    • Requires eight clock pulses to transmit eight bits of data.
    • Less signal processing and fewer error chances compared to parallel transmission.
    • Faster transfer rate for individual paths.
    • Usable over longer distances with error check bit or parity bit.

    Two Types of Serial Transmission

    • Asynchronous Transmission:
      • One character transmitted at a time.
      • Each character (or 8-bit series) marked by a start bit and a stop bit.
    • Synchronous Transmission:
      • Data sent in blocks (frames or packets) containing hundreds or thousands of characters.
      • Frames started and ended by one or more sync bytes.
      • Sync bytes synchronize internal clocks in transmitting and receiving devices.

    Transmission Bandwidth

    • Band of frequencies allowed for signal transmission.
    • Set of frequencies for transmitting data.
    • Example calculations and illustrations (Example 3, 4 on specific signals).

    Parameters in Digital Transmission

    • Information Capacity: A measure of how much information can be propagated through a communication system; function of bandwidth and transmission time.
    • Hartley's Law: The amount of information transmitted in a given time is directly proportional to bandwidth and transmission time (I = B * t).
    • Shannon Limit for Information Capacity: Mathematically expressed, relating the information capacity of a communication channel to bandwidth and signal-to-noise ratio. (I=B * log2(1+S/N)).
    • Shannon-Hartley Theorem: Maximum theoretical data rate for a given noise level.
    • M-ary Encoding: M represents the number of conditions, levels, or combinations possible for a given number of binary variables. The number of bits necessary is expressed as N=log2M.

    Probability of Error (Pb), Bit Error Rate (BER) and Energy per Bit (Eb)

    • Errors in digital communication systems result from noise.
    • Error probability (Pb) is the number of errors per total number of bits received.
    • Acceptable error probability in communication systems.
    • Average number of errors = m * Pb.
    • BER (Bit Error Rate) is the number of bit errors for a given number of bits transmitted.
    • Example calculations.

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    Digital Communication and Switching Lecture Notes PDF

    Description

    Dive into the complexities of designing digital communication systems with this quiz. It covers general constraints, limitations, and techniques in baseband data transmission, including ISI and pulse shaping. Perfect for students looking to understand the intricacies of digital transmission and communication methods.

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