04 Signal measurement

• Signal Measurement in Data Transmission
• 1. Throughput
  • [[#1. Throughput#Definition|Definition]]
  • [[#1. Throughput#Factors Affecting Throughput|Factors Affecting Throughput]]
  • [[#1. Throughput#Example|Example]]
• 2. Propagation Speed and Time
  • [[#2. Propagation Speed and Time#A. Propagation Speed|A. Propagation Speed]]
  • [[#2. Propagation Speed and Time#B. Propagation Time|B. Propagation Time]]
• 3. Wavelength
  • [[#3. Wavelength#Definition|Definition]]
  • [[#3. Wavelength#Examples|Examples]]
• 4. Frequency
  • [[#4. Frequency#Definition|Definition]]
  • [[#4. Frequency#Common Frequency Ranges|Common Frequency Ranges]]
  • [[#4. Frequency#Example|Example]]
• 5. Bandwidth and Spectrum
  • [[#5. Bandwidth and Spectrum#A. Bandwidth|A. Bandwidth]]
  • [[#5. Bandwidth and Spectrum#B. Spectrum|B. Spectrum]]
  • [[#5. Bandwidth and Spectrum#Comparison: Bandwidth vs. Throughput|Comparison: Bandwidth vs. Throughput]]

Signal Measurement in Data Transmission

Signal measurement involves various parameters that define how efficiently and accurately data is transmitted through a network. These parameters include throughput, propagation speed and time, wavelength, frequency, bandwidth, and spectrum.

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1. Throughput

Definition

• Throughput refers to the actual amount of data successfully transmitted over a network per second.
• It is measured in bits per second (bps), kilobits per second (Kbps), megabits per second (Mbps), or gigabits per second (Gbps).

Factors Affecting Throughput

• Network congestion – More users = slower throughput.
• Hardware limitations – Older routers or cables can reduce speed.
• Signal interference – Wireless signals may be affected by obstacles and noise.

Example

• A 100 Mbps internet connection does not always achieve full speed due to network congestion; actual throughput might be 85 Mbps.

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2. Propagation Speed and Time

A. Propagation Speed

• The speed at which a signal travels through a medium.
• Depends on the medium type (copper wire, fiber optics, air, etc.).
• Examples:
  • Electrical signals (copper cable): ~2 × 10⁸ m/s (slower than light).
  • Optical fiber (light signals): ~3 × 10⁸ m/s (speed of light in vacuum).
  • Wireless (radio waves): ~3 × 10⁸ m/s.

B. Propagation Time

• The time taken by a signal to travel from sender to receiver.
• Formula: Propagation Time=DistancePropagation Speed\text{Propagation Time} = \frac{\text{Distance}}{\text{Propagation Speed}}
• Example:
  • If a signal travels 1,000 km (1,000,000 meters) through fiber optic cable (2 × 10⁸ m/s), Propagation Time=1,000,0002×108=5 milliseconds\text{Propagation Time} = \frac{1,000,000}{2 \times 10^8} = 5 \text{ milliseconds}

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3. Wavelength

Definition

• The distance between two consecutive peaks or troughs of a wave.
• Measured in meters (m), centimeters (cm), or nanometers (nm).
• Formula: Wavelength(λ)=Speed of Light(c)Frequency(f)\text{Wavelength} (\lambda) = \frac{\text{Speed of Light} (c)}{\text{Frequency} (f)}

Examples

• Radio waves (AM/FM radio): Long wavelength (~100m).
• Microwaves (Wi-Fi, mobile networks): Shorter (~12 cm for 2.4 GHz Wi-Fi).
• Visible light (fiber optics): Extremely short (~500 nm).

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4. Frequency

Definition

• Number of wave cycles per second, measured in Hertz (Hz).
• Higher frequency = shorter wavelength and higher energy.

Common Frequency Ranges

Frequency Range	Type of Signal	Example Applications
3 kHz – 300 kHz	Low-frequency (LF)	AM radio, navigation signals
300 kHz – 3 MHz	Medium-frequency (MF)	AM radio, marine communication
3 MHz – 30 MHz	High-frequency (HF)	Shortwave radio, aircraft communication
30 MHz – 300 MHz	Very high-frequency (VHF)	FM radio, TV signals
300 MHz – 3 GHz	Ultra high-frequency (UHF)	Wi-Fi, mobile networks, GPS
3 GHz – 300 GHz	Super high-frequency (SHF)	5G networks, satellite communication

Example

• Wi-Fi operates at 2.4 GHz and 5 GHz.
• Higher frequencies (5 GHz) provide faster data rates but shorter range.

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5. Bandwidth and Spectrum

A. Bandwidth

• The maximum data transfer rate a network can handle.
• Measured in Hertz (Hz) for signals and bps for data transfer.
• Higher bandwidth = higher data transmission speed.

B. Spectrum

• Range of all possible frequencies used for communication.
• Includes radio, microwave, infrared, visible light, etc..
• Example:
  • FM radio operates in the 88 MHz – 108 MHz range.
  • 5G networks use 600 MHz – 39 GHz frequency bands.

Comparison: Bandwidth vs. Throughput

Feature	Bandwidth	Throughput
Definition	Maximum data capacity	Actual data transmitted
Measured In	Hz (signal) or Mbps (network)	Mbps or Gbps
Affected By	Medium limitations	Congestion, interference
Example	Fiber optic has 1 Gbps bandwidth	Actual throughput may be 900 Mbps

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• Throughput: Actual data transmitted per second, affected by congestion and interference.
• Propagation Speed and Time: Determines signal travel time; fiber optics are fastest.
• Wavelength: Inversely proportional to frequency; used in different communication types.
• Frequency: Higher frequency means more data capacity but shorter range.
• Bandwidth and Spectrum: Bandwidth defines network capacity; spectrum covers all frequencies used for communication.