Unguided Media

In this tutorial, you will learn about the concept of Unguided Media. You will also learn what are the types, features, applications, advantages and disadvantages of unguided media, and how unguided media is used in computer networks.

Contents:

  1. What is Unguided Media?
  2. Types of Unguided Media
  3. Radio Waves Transmission
  4. Microwaves Transmission
  5. Infrared Waves Transmission
  6. Propagation in Unguided Media
  7. Comparison of Unguided Media Types
  8. Limitations of Unguided Media

What is Unguided Media?

The medium which transmits signals in the form of electromagnetic waves without using any physical conductor is known as unguided media.

  • Unguided media is the second type of transmission media after guided media. It is used to connect devices to the network without using cables.
  • When unguided media is used to connect the end device to the network, the end device’s wireless NIC is used. Because, wired NIC is used in wired or guided media and wireless NIC is used in wireless or unguided media.
  • Unguided media transmits signals that represent bits of data. Typically, unguided media represent bits of data using radio waves, microwaves, or infrared waves.
  • IEEE and the telecommunications industry specify standards for wireless communications such as Wi-Fi, Bluetooth, and Wi-Max.

Types of Unguided Media

Unguided media uses three types of waveforms to transmit signals representing bits of data. They are as follows:

  1. Radio waves
  2. Microwaves
  3. Infrared waves
  • Radio waves: Electromagnetic waves with a frequency of 3 kHz to 1 GHz are called radio waves.
  • Microwaves: Electromagnetic waves with a frequency of 1 GHz to 300 GHz are called microwaves.
  • Infrared waves: Electromagnetic waves with a frequency of 300 GHz to 400 THz are called infrared waves.

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Radio Waves Transmission

Unguided media transmit bits as electromagnetic waves having a range of 3 kHz to 1 GHz frequency, known as radio waves.

  • Radio waves are omnidirectional in nature, so when radio waves are transmitted through an antenna, they propagate in all directions. In simple words, sender and receiver antennas do not have to be aligned.
  • The main problem with radio waves here is that radio waves transmit signals in all directions, which can be interrupted by another antenna that uses the same frequency.
  • Radio waves can travel long distances, so it is used in broadcasting. It can also penetrate through a wall because of its low frequency.
  • The frequency of radio waves varies according to the wavelength, power, and purpose of transmission.

The figure below shows the transmission of radio waves.

transmission of radio waves

As you can see in the figure above, radio waves are omnidirectional, propagating in all directions. It also shows that the signal coming from antenna-1 is interrupted by antenna-2 because antenna-2 uses the same frequency as antenna-1. In addition, radio waves can penetrate the wall, as shown in the figure.

Microwaves Transmission

Unguided media transmit bits as electromagnetic waves having a frequency range of 1 GHz to 300 GHz, known as microwaves.

  • Microwaves are unidirectional, which means that when antennas transmit signals, they transmit along a narrow-focused path. Due to the narrow path, the sender and receiver antenna have to be aligned.
  • Microwaves are unidirectional, so the signal is transmitted without interfering with other antennas signals.
  • When microwaves are of higher frequencies, they cannot penetrate walls like radio waves. For example, the sender sends a high-frequency microwave signal to the receiver, but the receiver is indoors, the signal will not be able to penetrate the wall, causing signal loss.

The figure below shows the transmission of microwaves.

transmission of microwaves

As you can see in the diagram above, a parabolic dish antenna has a focus point where all incoming signals intersect. You can see that it acts as a funnel that captures multiple waves and directs them towards the focus point. The diagram above also shows that microwaves cannot penetrate a wall, like radio waves.

Infrared Waves Transmission

Unguided media transmit bits as electromagnetic waves having a frequency range of 300 GHz to 400 THz, known as infrared waves. Generally, infrared waves are used for short-distance communication.

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  • Infrared waves block interference with other system waves. For example, when a user is communicating using infrared waves in a room, such as controlling a TV with a remote, it does not affect neighboring TVs.
  • Infrared waves are not used for long-distance communication. Also, we cannot use infrared waves in the sun’s rays outside because the sun’s rays also contain infrared waves, which can interfere with other infrared waves and result in data loss.
  • Infrared waves have very high bandwidth, such as 400 terahertz. Therefore infrared waves can transmit signals at a very high data rate.
  • The Infrared Data Association (IRDA) has defined a data rate of 75 kbps, which can cover a distance of up to 8 meters. They have also defined another data rate which is 4 Mbps.

The below diagram describes the transmission of Infrared waves.

transmission of Infrared waves

The diagram above shows that infrared waves are used for short distances, such as controlling a TV with a remote. It also shows that TV-1 is controlled by remote-1, and TV-2 is controlled by remote-2, and both remote-1 and remote-2 do not interfere with each other’s signals.

Propagation in Unguided Media

When a signal travels from sender to receiver, it can travel in different ways as follows:

  1. Ground Propagation
  2. Sky Propagation
  3. Line of sight Propagation
  • Ground Propagation: It follows the curvature of the Earth, which means that radio waves travel very closely through the lowest part of the Earth’s atmosphere. It can measure the distance according to the signal strength. The higher the signal strength, the greater the distance the signal can travel.
    • Ground Propagation is used in long-range radio navigation.
  • Sky Propagation: In this propagation, the waves traveling upward into the ionosphere are reflected. The ionosphere is one of the layers of the atmosphere that consists of particles in the form of ions. In this transmission, the signals can travel long distances with minimum output power.
    • Sky propagation is used in AM and FM radio, Very High-Frequency Television, and Citizen Band, etc.
  • Line of sight Propagation: Signals of very high frequencies are transmitted from antenna to antenna in a straight line. Here the antennas used for transmission are facing each other and are directional.
    • Line of sight propagation is used in cellular phones, satellite signals, and radars, etc.

In ground propagation, the transmitted signal frequency is less than 2 MHz. In sky propagation, the transmitted signal frequency is between 2 MHz and 30 MHz. And in line of sight propagation, the transmitted signal frequency is greater than 30 MHz.

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The below diagram describes the propagation of unguided media.

propagation of unguided media

The above diagram shows that there are 3 types of propagation in Unguided Media. It also shows that ground propagation, sky propagation, and line of sight propagation are used when the signal frequency is less than 2 MHz, between 2 MHz and 30 MHz, and greater than 30 MHz, respectively.

Comparison of Unguided Media Types

The table below shows a comparison between the types of unguided media.

Key Radio Waves Microwaves Infrared Waves
Definition Unguided media transmit bits as electromagnetic waves having a range of 3 kHz to 1 GHz, known as microwaves. Unguided media transmit bits as electromagnetic waves having a range of 1 GHz to 300 GHz, known as microwaves. Unguided media transmit bits as electromagnetic waves having a range of 300 GHz to 400 THz, known as microwaves.
Frequency 3 kHz to 1 GHz 1 GHz to 300 GHz 300 GHz to 400 THz
Nature Omnidirectional Unidirectional Short-range waves
Data Loss Moderate Low Very Low
Advantage Penetrate through the wall. One microwave does not interfere with another microwave. One infrared wave does not interfere with another infrared wave.
Use Used for long-distance transmission such as broadcasting. Used for unicast communication, such as military and radar. Used for short-distance communication such as controlling a TV with a remote.

Limitations of Unguided Media

However, Unguided Media saves cost, as it does not use any cables to connect the devices. But still, it has some limitations, which are as follows:

  • Unguided media limits effective coverage due to the materials used in buildings and local area networks. For example, if you are using microwaves for communication, then they cannot penetrate through the wall.
  • Radio waves are interrupted by radio waves from other antennas because they are omnidirectional, increasing the likelihood of one radio wave colliding with other radio waves.
  • Microwaves are unidirectional, but they cannot penetrate through a wall, which can cause an error in the signal.
  • Wireless or unguided media do not have a physical shield, like guided media. Therefore, unauthorized access and loss of data increased, and the network administrator has to check media and network regularly.
  • Wireless LAN uses a half-duplex mode for communication which means that one device can send or receive at a time, and wireless media is shared with all communication devices, which reduces the bandwidth of the network. This is because multiple users try to access the WLAN simultaneously.

Key Points to Remember

Here is the list of key points we need to remember about the “Unguided Media”.

  • The medium which transmits signals in the form of electromagnetic waves without using any physical conductor is known as unguided media.
  • Wireless NICs are used when unguided media is used to connect devices to the network.
  • Radio Waves, Microwaves, and Infrared waves are the types of unguided media.
  • Radio waves, microwaves, and infrared waves range from 3 kHz to 1 GHz, 1 GHz to 300 GHz, and 300 GHz to 400 THz, respectively.
  • Radio waves are used for long-distance communications such as broadcasting, microwaves are used for unicasting purposes such as voice communication, and infrared waves are used for short-distance communications such as controlling a TV with a remote.
  • Radio waves can penetrate the wall, while microwaves and infrared waves cannot penetrate the wall.
  • Ground propagation, sky propagation, and line-of-sight propagation are types of propagation used when the signal is traveling from sender to receiver.
  • Unguided media have no physical shield, like guided media, so there is a possibility of unauthorized access to the communication channel, due to which network administrators have to check the network regularly.

If you find any mistake above, kindly email to [email protected]

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Manish Bhojasia - Founder & CTO at Sanfoundry
Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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