ED

Lecture_8_Signals_part_3

IT 219 Physics for IT Lecture 8: Physics Signals - Part 3 Analog & Digital Transmission

Data Transmission Overview

  • General Definition: Transmission of data can be accomplished through digital or analog signals.

  • Types of Data:

    • Digital Data

    • Analog Data

  • Possibilities:

    • Digital Transmission (Encoding)

    • Analog Data (A/D Conversion)

    • Analog Transmission (Analog Modulation)

    • Digital Data (Digital Modulation)

Digital Transmission

Digital-to-Digital Conversion

  • Definition: Involves the transformation of digital data into a digital signal.

  • Benefits: Equipment is less complex and expensive compared to digital-to-analog conversion.

  • Techniques:

    • Line Coding: Converts a string of 1's and 0's into signals.

    • Block Coding: Adds redundant bits for error detection/synchronization.

Line Coding

Process

  • Converts digital data into a digital signal using voltage levels:

    • High voltage (+V) = "1"

    • Low voltage (0 or -V) = "0"

  • Efficient encoding schemes are necessary to convert data into digital signals.

Line Coding and Decoding

  • Example:

    • Digital Data: 0101

    • Encoded Signal: 101

Digital-to-Digital Conversion: Block Coding

  • Purpose: Enhances line coding efficiency with extra bits.

  • Steps:

    1. Division

    2. Substitution

    3. Combination

  • Note: Line coding is a prerequisite for block coding.

Digital Transmission Modes

  • General Modes:

    • Parallel Mode: Multiple bits transmitted simultaneously with each clock tick.

    • Serial Mode: 1 bit sent per clock tick.

  • Types:

    • Synchronous: No gaps & controlled by clock.

    • Asynchronous: Start and stop bits with variable gaps.

Parallel vs Serial Transmission

Parallel Transmission

  • Method: All 8 bits are sent together, requiring multiple lines.

Serial Transmission

  • Method: 8 bits sent one after the other, requiring one line.

Asynchronous Transmission

  • Definition: Involves sending a start bit and one or more stop bits for each byte.

Synchronous Transmission

  • Definition: Bits are sent continuously without start or stop bits; the receiver groups bits.

Analog-to-Digital Conversion (A/D)

Overview

  • Digital signals are less prone to noise and distortion than analog signals.

  • Techniques Used:

    • Pulse Code Modulation (PCM)

Steps in PCM

  1. Sampling and Hold (PAM)

  • Sampling at equal intervals.

  1. Quantization

  • Assigns integer values to sampled instances.

  1. Binary Encoding

  • Translating quantized samples into binary.

  1. Line/Block Encoding

Sampling Techniques

Nyquist Theorem

  • Requirement: Sampling rate must be at least twice the highest frequency.

Examples of Sampling Rate Calculations

  1. Low-pass Signal: Bandwidth of 200 kHz requires a sampling rate of at least 400,000 samples/second.

  2. Bandpass Signal: Minimum sampling cannot be determined without knowing bandwidth endpoints.

Quantization

General Concept

  • Definition: Assigning integer values to sampled signal values.

  • Quantization Error: Affects signal-to-noise ratio; the smaller the quantization levels, the higher the error.

Example Calculation of Bits Required for Sampling

  • Given: 11 levels of precision needed.

  • Solution: 4 bits required (3 for value + 1 sign).

Digital Encoding Process

Steps

  • Each quantized sample is converted to a 7-bit binary equivalent; the eighth bit indicates the sign.

Components of PCM Encoder

  • Elements:

    • Quantized Signal

    • PCM Encoder

    • Sampling, Quantizing, Encoding steps.

Bit Rate Calculation for Human Voice

  • Assumption: 8000 samples/second, 8 bits/sample yields 64 Kbps.

Analog Transmission Overview

Modulation

  • Definition: Transformation of information into a format suitable for transmission via sine waves (modulation affects amplitude, frequency, and phase).

Types of Modulation

  1. Digital Modulation: Converts digital signals to analog for transmission over analog channels.

  2. Analog Modulation: Converts low-frequency analog signals to higher-frequency signals if necessary.

Types of Digital-to-Analog Conversion

  • Key Features: Modulates a carrier signal based on digital data characteristics (amplitude, frequency, phase).

Digital Modulation Types

  1. Amplitude Shift Keying (ASK): Binary data represented by varying amplitude.

  2. Frequency Shift Keying (FSK): Binary data represented by varying frequency.

  3. Phase Shift Keying (PSK): Binary data represented by varying phase.

Summary of Digital Modulation Types

  • ASK: Simple, low bandwidth, high susceptibility to interference.

  • FSK: More bandwidth needed, more resilience.

  • PSK: More complex, robust against interference.

Analog Modulation Types

  • Basic schemes include Amplitude Modulation (AM), Frequency Modulation (FM), and Phase Modulation (PM).

Conclusion

  • Digital transmission generally superior to analog; however, analog remains necessary for specific mediums (e.g. wireless).

  • Essential to perform A/D conversion to transmit analog data digitally and apply both types of modulation for data transmission.

IT 219 Physics for IT Lecture 8: Physics Signals - Part 3 Analog & Digital Transmission

1. Data Transmission Overview

  • Definition: Transmission of data can occur through digital or analog signals, facilitating communication in various technological applications.

1.1 Types of Data

  • Digital Data: Information represented in discrete values (0s and 1s).

  • Analog Data: Continuous data that represents fluctuating signals over time.

1.2 Possibilities for Data Transmission

  • Digital Transmission (Encoding): Encoding digital data for transmission.

  • Analog Data (A/D Conversion): Converting analog data into digital format.

  • Analog Transmission (Analog Modulation): Sending analog signals.

  • Digital Data (Digital Modulation): Modulating digital signals for transmission.

2. Digital Transmission

2.1 Digital-to-Digital Conversion

  • Definition: Transformation of digital data directly into a digital signal.

  • Benefits: Simpler equipment and lower costs compared to digital-to-analog conversion.

  • Techniques:

    • Line Coding: Converts binary strings into signals.

    • Block Coding: Introduces redundant bits for error detection/synchronization.

2.1.1 Line Coding

  • Process: Assigns voltage levels to digital data:

    • High Voltage (+V) = "1"

    • Low Voltage (0 or -V) = "0"

  • Example: Digital Data: 0101 → Encoded Signal: 101

2.2 Digital-to-Digital Conversion: Block Coding

  • Purpose: Enhance line coding efficiency.

  • Steps:

    1. Division: Breaking down data.

    2. Substitution: Modifying bits for error detection.

    3. Combination: Merging bits.

Note: Line coding must precede block coding.

2.3 Digital Transmission Modes

  • Modes:

    • Parallel Mode: Multiple bits transmitted simultaneously.

    • Serial Mode: One bit sent at a time.

2.3.1 Types of Transmission

  • Synchronous: Continuous data without gaps.

  • Asynchronous: Start and stop bits; variable intervals.

2.4 Parallel vs Serial Transmission

  • Parallel Transmission: Sends all bits simultaneously using multiple lines.

  • Serial Transmission: Sends bits sequentially using one line.

2.5 Asynchronous Transmission

  • Definition: Starts with a start bit followed by stop bits, suitable for intermittent flows.

2.6 Synchronous Transmission

  • Definition: Continuous data without initiation signals; bits grouped by the receiver.

3. Analog-to-Digital Conversion (A/D)

3.1 Overview

  • Digital signals are less susceptible to noise and distortion.

3.2 Techniques Used

  1. Pulse Code Modulation (PCM):

    • Steps in PCM:

    1. Sampling and Hold (PAM): Sample the analog signal.

    2. Quantization: Assign integer values.

    3. Binary Encoding: Convert quantized values into binary.

    4. Line/Block Encoding: Optimize signal transmission.

3.3 Sampling Techniques

  • Nyquist Theorem: Sampling rate must be at least twice the highest frequency.

  • Examples:

    • Low-pass signal, 200 kHz bandwidth → 400,000 samples/second needed.

    • Bandpass signals require specific bandwidth information.

3.4 Quantization

  • Definition: Assigns integer values, impacting signal-to-noise ratio.

  • Example Calculation: For 11 levels of precision → 4 bits needed (3 for value + 1 sign).

3.5 Digital Encoding Process

  • Steps: Convert quantized samples to 7-bit binary equivalents; the eighth bit indicates the sign.

3.6 Components of PCM Encoder

  • Elements:

    • Quantized Signal

    • PCM Encoder implementing sampling, quantizing, encoding.

3.7 Bit Rate Calculation for Human Voice

  • Assumptions: 8000 samples/second, 8 bits/sample → 64 Kbps.

4. Analog Transmission Overview

4.1 Modulation

  • Definition: Modifying information for transmission via sine waves.

4.2 Types of Modulation

  • Digital Modulation: Converts digital signals to analog for transmission.

  • Analog Modulation: Adjusts low-frequency analog signals for higher frequencies.

4.3 Types of Digital-to-Analog Conversion

  • Key Features: Modulates carrier signal based on digital data characteristics.

4.3.1 Digital Modulation Types

  1. Amplitude Shift Keying (ASK): Varies amplitude for binary data representation.

  2. Frequency Shift Keying (FSK): Varies frequency for binary data representation.

  3. Phase Shift Keying (PSK): Varies phase for data encoding.

4.4 Summary of Digital Modulation Types

  • ASK: Simple, low bandwidth, high interference susceptibility.

  • FSK: More bandwidth needed, higher resilience.

  • PSK: Complex, robust against interference.

4.5 Analog Modulation Types

  • Basic schemes: Amplitude Modulation (AM), Frequency Modulation (FM), Phase Modulation (PM).

5. Conclusion

  • Generally, digital transmission is superior due to resilience and clarity.

  • Analog techniques remain necessary for specific applications (e.g., wireless communication).

  • A/D conversion is vital for digitizing analog data and modulating signals for effective transmission.