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.

2. Quantization

• Assigns integer values to sampled instances.

3. Binary Encoding

• Translating quantized samples into binary.

4. 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.

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.