Computer Networks
The Physical Layer
Wireless Transmission
• Radio Transmission
Presented By:- Ravi Ranjan (MCA-II yr),Reg.No. :- 13352223

Radio Transmission
• Radio is the transmission of signals through free
space by modulation of electromagnetic waves with
frequencies below those of visible light
• In telecommunication, transmission is the process of
sending and propagating an analogue or digital
information signal over a physical p-to-p or p-to-multipoint
transmission medium.

Characteristics of Radio
Transmission
• Radio frequency (RF) waves are easy to generate.
• It can travel long distances, and can penetrate
building easily.
• It is widely used for communication, both indoors
and outdoors .
• Radio waves also are omnidirectional, meaning
that they travel in all directions from the source,
so the transmitter and receiver do not have to be
carefully aligned physically.

Characteristics of Radio
Transmission
• The properties of radio waves are frequency
dependent.
• At low frequencies, radio waves pass through
obstacles well.
• The power falls sharply with distance from the source
at least as fast as 1/r2 in air –as the signal energy is
spread more thinly over a larger surface. This
attenuation is called path loss.
• At high frequency, radio waves tend to travel in
straight lines and bounce off obstacles.
• At all frequencies, radio waves are subject to
interface from motors and other electrical
equipment.

Characteristics of Radio
Transmission
• In the VLF, LF and MF bands, radio waves follow the
ground
• These waves can be detected for perhaps 1000km at
the lower frequencies, less at higher ones.
• In the HF, and VHF band, the ground waves tend to
be absorbed by the earth.
• It is use to way for broadcasting through the air
medium with the help of ionosphere.

Types of transmission..
• Amplitude Modulation (AM)
• Frequency Modulation (FM)
• Phase Modulation (PM)
• Pulse Code Modulation (PCM)

Amplitude Modulation (AM)
• Amplitude modulation (AM) is a modulation technique used
in electronic communication, most commonly for transmitting
information via a radio carrier wave
• Signals of AM band (450-1650 KHz)

Frequency Modulation (FM)
• FM is a system by which the modulating audio to change the
instantaneous frequency of the carrier.
• Frequency modulation (FM) is the standard technique for
high-fidelity communications as is evident in the received.
• Signals of the FM band (88-108 MHz)

Phase Modulation (PM)
• Phase modulation is widely used for transmitting
radio waves and is an integral part of many digital
transmission coding schemes that underlay a wide
range of technologies like WiFi, GSM and satellite
television

Pulse Code Modulation(PCM)
• PCM Transmitters send a digital signal embedded in
the FM radio wave. A digital processor in the
transmitter encodes the signals and sends it out
through a regular FM radio wave.

Propagation
• Radio waves travels by means of oscillating
electromagnetic fields that pass through the air and
the vacuum of space
• Information is carried by systematically changing
(modulating) some property of the radiated waves,
such as amplitude, frequency, phase, or pulse width

Uses
• Audio
• Telephony
• Video
• Navigation
• Radar
• Data (Digital Radio)
• Radio control

Advantages
• Simple Circuit
• Cheap
• No Licenses Needed
• High Speed/Bandwidth
• Covers Large Areas (Penetrates through walls)

Disadvantages
• Limited number of free frequency bands
• Shielding is difficult
• Interference with other electrical devices
• Greater Power Consumption
• Limited Spectrum of Frequency

Examples
• FM Channels
• Walkie Talkies

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