Satellite Communication
- A satellite is a physical object that
revolves around the earth at a known height.
- Satellite communication is more reliable
nowadays as it offers more flexibility than cable and fibre optic systems.
- We can communicate with any point on the
globe by using satellite communication.
How Does Satellite
work?
The satellite accepts the signal that is transmitted
from the earth station, and it amplifies the signal. The amplified signal is
retransmitted to another earth station.
Advantages Of
Satellite Microwave Communication:
- The coverage area of a satellite
microwave is more than the terrestrial microwave.
- The transmission cost of the satellite is
independent of the distance from the centre of the coverage area.
- Satellite communication is used in mobile
and wireless communication applications.
- It is easy to install.
- It is used in a wide variety of
applications such as weather forecasting, radio/TV signal broadcasting,
mobile communication, etc.
Disadvantages Of
Satellite Microwave Communication:
- Satellite designing and development
requires more time and higher cost.
- The Satellite needs to be monitored and
controlled on regular periods so that it remains in orbit.
- The life of the satellite is about 12-15
years. Due to this reason, another launch of the satellite has to be
planned before it becomes non-functional.
Infrared
- An
infrared transmission is a wireless technology used for communication over
short ranges.
- The
frequency of the infrared in the range from 300 GHz to 400 THz.
- It
is used for short-range communication such as data transfer between two
cell phones, TV remote operation, data transfer between a computer and
cell phone resides in the same closed area.
Characteristics Of Infrared:
- It
supports high bandwidth, and hence the data rate will be very high.
- Infrared
waves cannot penetrate the walls. Therefore, the infrared communication in
one room cannot be interrupted by the nearby rooms.
- An
infrared communication provides better security with minimum interference.
- Infrared
communication is unreliable outside the building because the sun rays will
interfere with the infrared waves
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Simplex
In simplex
transmission mode, the communication between sender and receiver occurs in only
one direction. The sender can only send the data, and the receiver can
only receive the data. The receiver cannot reply to the sender.
Simplex transmission
can be thought of as a one-way road in which the traffic travels only in one
direction—no vehicle coming from the opposite direction is allowed to drive
through.
To take a keyboard /
monitor relationship as an example, the keyboard can only send the input to the
monitor, and the monitor can only receive the input and display it on the
screen. The monitor cannot reply, or send any feedback, to the keyboard.
Half Duplex
The communication
between sender and receiver occurs in both directions in half duplex
transmission, but only one at a time. The sender and receiver can both
send and receive the information, but only one is allowed to send at any given
time. Half duplex is still considered a one-way road, in which a vehicle
traveling in the opposite direction of the traffic has to wait till the road is
empty before it can pass through.
For example, in
walkie-talkies, the speakers at both ends can speak, but they have to speak one
by one. They cannot speak simultaneously.
Full Duplex
In full duplex
transmission mode, the communication between sender and receiver can occur
simultaneously. The sender and receiver can both transmit and receive at
the same time. Full duplex transmission mode is like a two-way road, in which
traffic can flow in both directions at the same time.
For example, in a
telephone conversation, two people communicate, and both are free to speak and
listen at the same time.
Differences of the Three Transmission
Modes
- In simplex mode, the signal is
sent in one direction. In half duplex mode, the signal is sent in both
directions, but one at a time. In full duplex mode, the signal is
sent in both directions at the same time.
- In simplex mode, only one device
can transmit the signal. In half duplex mode, both devices can transmit
the signal, but one at a time. In full duplex mode, both devices can
transmit the signal at the same time.
- Full duplex performs better than
half duplex, and half duplex in turn performs better than simplex.
- Simplex: The keyboard sends the
command to the monitor. The monitor cannot reply to the keyboard.
- Half duplex: Using a
walkie-talkie, both speakers can communicate, but they have to take turns.
- Full duplex: Using a telephone, both
speakers can communicate at the same time.
·
The
full duplex transmission mode offers the best performance among the three, on
account of the fact that it maximises the amount of bandwidth available.
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