Wireless Media | Unguided Media

Ø Unbound transmission media are the ways of transmitting data without using any cables.

Ø These media are not bounded by physical geography.

Ø This type of transmission is called Wireless communication.

Ø Nowadays wireless communication is becoming popular. Wireless LANs are being installed in office and college campuses. This transmission uses Microwave, Radio wave, Infra-red are some of popular unbound transmission media.

Ø Wireless communication involves no physical link established between two or more devices, communicating wirelessly.

Ø Electro-magnetic signals are spread over in the air and are received and interpreted by appropriate antennas.

Note: Electro-magnetic waves are special type of wave that can travel without medium.

Ø When an antenna is attached to electrical circuit of a computer or wireless device, it converts the digital data into electromagnetic signals and spread all over within its frequency range.

Ø The receptor on the other end receives these signals and converts them back to digital data.

Ø A little part of electromagnetic spectrum can be used for wireless transmission.

1) Radio Transmission

Ø Radio frequency is easier to generate and because of its large wavelength & it can travel long distance.

Ø Radio waves can have wavelength from 1 mm – 100,000 km and have frequency ranging from 3 Hz to 300 GHz.

Ø Radio waves are generated by Radio transmitters and received by Radio receivers.

Ø Radio stations transmit radio waves using transmitter, which are received by the receiver installed in your device. Both transmitter and receiver use antennas to radiate radio signals.

Ø It can penetrate walls easily, so these waves are widely used for communication both indoors and outdoors.

Ø Radio waves are omni-directional in nature.

Ø Radio waves at lower frequencies can travel through walls whereas higher RF can travel in straight line and bounce back.

Ø The power of low frequency waves decreases sharply as they cover long distance. High frequency radio waves have more power.

Ø Lower frequencies such as VLF, LF, MF bands can travel on the ground up to 1000 kilometres, over the earth’s surface.

Ø Radio waves of high frequencies are prone to be absorbed by rain and other obstacles. They use Ionosphere of earth atmosphere. High frequency radio waves such as HF and VHF,UHF bands are spread upwards. When they reach Ionosphere, they are refracted back to the earth.

Ø Types of Radio Waves:

1. Short Wave-Used in AM radio

2. VHF(Very High Frequency)-Used in FM radio (TV)

3. UHF(Ultra High Frequency)-Used in TV

Advantages

· Offers mobility

· Cheaper than cables

· Freedom from Land Acquisition

· Ease of Communication in difficult terrains

Disadvantages

· Insecure communication(Eavesdropping)

· Susceptible to weather condition

2) Microwave Transmission

Ø They are used to transmit data without use of cables.

Ø Microwaves are a type of radio waves with high frequency.

Ø In this parabolic antennas are mounted on the towers to send the beam to another antenna KMs away.

Ø Higher is the tower à Greater is the range

Ø Microwaves are in unidirectional in nature.

Ø It is example of Line-of-Sight transmission

LOS:-Type of propagation that can transmit and receive data only where transmit and receive stations are in view of each other without any sort of an obstacle between them. Example Radio, microwave and satellite transmissions are examples of Line-of-Sight

Ø Microwaves can have wavelength ranging from 1 mm – 1 meter and frequency ranging from 300 MHz to 300 GHz.

Ø It will support bandwidth upto 1 to 10 Mbps

Ø Attenuation: (Reduction in the strength of a signal. Sometimes called Loss of signal)-Affected by environmental conditions, antenna size and strength of signal(Frequency it using)

Ø Microwaves have higher frequencies and do not penetrate wall like obstacles.

Ø It is used for satellite communication,navigation,radar,remote sensing and other short distance communication

Ø They will be encountered by Eavesdropping(Person sitting in between two antennas and wants to access the signals by using his own antenna),jamming

Advantages

· Cheaper than using cable

· Freedom from Land Acquisition rights

· Ease of communication in difficult terrains

· Ability to communicate over oceans

Disadvantages

· Insecure communication(Eavesdropping)

· Out of phase signals

· Susceptible to weather condition

· Bandwidth is limited

· Cost of design, implementation and maintenance is high

3) Infrared Transmission

Ø Infrared wave lies in between visible light spectrum and microwaves.

Ø It has wavelength of 700-nm to 1-mm and frequency ranges from 300-GHz to 430-THz.

Ø Infrared wave is used for very short-range communication purposes such as television and it’s remote, wireless speakers, automatic doors, hand held devices etc

Ø Infrared travels in a straight line hence it is directional by nature. Because of high frequency range, Infrared cannot cross wall-like obstacles.

Ø We cannot use infra-red waves outside a building because sun’s ray contain infrared waves that can interfere with communication.

Light Transmission

Ø Highest most electromagnetic spectrum which can be used for data transmission is light or optical signalling. This is achieved by means of LASER.

Ø Because of frequency light uses, it tends to travel strictly in straight line.Hence the sender and receiver must be in the line-of-sight.

Ø Because laser transmission is unidirectional, at both ends of communication the laser and the photo-detector needs to be installed.

Ø Laser beam is generally 1mm wide hence it is a work of precision to align two far receptors each pointing to lasers source.

Ø Laser works as Tx (transmitter) and photo-detectors works as Rx (receiver).

Ø Lasers cannot penetrate obstacles such as walls, rain, and thick fog. Additionally, laser beam is distorted by wind, atmosphere temperature, or variation in temperature in the path.