RF COMMUNICATION

RF COMMUNICATION

What is RF Communication?

RF -Radio Frequency communication. It is a wireless communication.
It makes use of Electromagnetic waves that is available in the free space for its communication.
The biggest advantage of RF communication is that it does not have Line of Sight. (No need of Transmitter and Receiver to be in straight line)
Like all other communication it also has source, medium and destination.
The Radio Transmitter is the source, Radio Receiver is the destination and the Free Space is the medium through which the electromagnetic wave travels.
In free space, there is more probability of message signal to get mixed with noise.
In order to avoid the mixing up of noise the message signal is modulated with a carrier signal in the transmitter end.
Again in the receiver end the reverse process takes place i.e. the original message signal is recovered by demodulation.

MODULATION: 

 

The message signal is normally low frequency signal it cannot travel longer distance also have high chance of mixing up with noise.
To make the message signal travel longer distance without interruption it is modulated with high frequency signal called carrier signal.
The process of changing the characteristics of carrier signal with respect to the message signal is called modulation.
It is done in the transmitter.

DEMODULATION:

The process of recovering the message signal from the modulated signal is called demodulation.
It is done in the receiver.

TYPES OF MODULATION:

Amplitude Modulation: The process of changing the amplitude of the carrier signal with respect to the amplitude of the message signal is called Amplitude Modulation.
Frequency Modulation: The process of changing the frequency of the carrier signal with respect to the frequency of the message signal is called Frequency Modulation.
Phase Modulation: The process of changing the phase of the carrier signal with respect to the phase of the message signal is called Phase Modulation.

Radio Transmitter:

Before transmitting data it is encoded for safety transmission by encoder.
The transmitter contains modulator, amplifier and antenna.
The message that has to be transmitted is modulated and transmitted by means of the antenna.
The modulated signal is amplified to make it travel for long distance.

Radio Receiver:

The receiver contains antenna, amplifier and demodulator.
The transmitted signal is received by the antenna.
Even though the message signal is amplified and then transmitted the signal received in the receiver side is very low hence it is amplified once again.
The amplified signal is demodulated by the demodulator.
The encoded data is decoded here in the decoder unit.
NOTE: The modulator and demodulator should have same carrier for getting correct message signal.

GPRS

GPRS

GPRS stands for General Packet Radio Service.
GPRS is a mobile data service that provides e-mail and Internet access for 2G and 3G mobiles.
It is also called as 2.5G technology, that is, a technology between 2G and 3G.
GPRS is usually charged based on amount of data transferred whereas circuit-switched data is billed per min of connection time.
GPRS is a best service that has variable throughput and latency that depends on number of users sharing the service at the same time.

CHARACTERISTICS:

Data rate - 115kbps
Speed - 40 to 50kbps
Latency is very high.
Roundtrip time - 600 to 700ms and often 1s is achieved.

SERVICES OFFERED:

GPRS offers services like SMS, MMS, P2P service, P2M service, Push to Talk, Instant Messaging, etc..
In GPRS, an SMS transmission speed of about 30 SMS per minute can be achieved and it is fast enough technology for MMS and browsing.

PROTOCOLS SUPPORTED:

Internet Protocol (IP) - It is built in mobile browsers and it uses IPv4.
Point to point protocol (PPP) – It is not supported by mobile phones but it is used to provide IP to the phone when it is used as modem to the computer.

HARDWARE SUPPORTED:

CLASS A – It can be connected to GPRS and GSM service using both at a time.
CLASS B – It can be connected to GPRS and GSM service using only one at a time. Most of the GPRS mobile services are Class B.
CLASS C – It can be connected to either GPRS or GSM service.

ACCESSING METHOD:

Multiple Access method used in GSM with GPRS is based on Frequency Division Duplex(FDD) and Time Division Multiple Access(TDMA).
Hence it is possible that the several users can share the same frequency channel.

IR COMMUNICATION

IR COMMUNICATION

IR-Infrared Communication. It uses infrared light to transfer data.
Infrared light is a wavelength of energy that is invisible to the human eye.
It is a point-to-point communication i.e. it has line of sight.
The most popular application of IR is the TV Remote Control.

Why it is called Infrared?

IR is a part of the electromagnetic spectrum.
Infrared waves lie between microwaves and visible light waves in the electromagnetic spectrum.
The prefix infra means "below", the infrared means "below red". This indicates its position in the electromagnetic spectrum.

Won’t the IR Rays affect human?

 

Yes probably the IR rays affect the humans if it is used in higher wavelength.
But most of the electronic devices make use of IR at lower wavelength or near infrared wavelength.
So it won't affect the human.

Advantages of using Infrared Communication:

SECURITY: Infrared communication has high directionality and can identify the person whom you are communicating with.
COMMUNICATION SPEED: Infrared communication has a maximum speed of about 1Gbps.

WIRELESS TECHNOLOGY

 

WIRELESS TECHNOLOGY

From the word Wireless we can understand, this communication doesn't require any wire.
Electromagnetic waves are used to carry the information from one point to other in this communication.

What is the need for Wireless Communication?

 

For communicating with people from one end to other end of the world we need wired connection.
But the cost for connecting entire world by cables will be high. Also it is impossible.
If there causes any damage in the wire we cannot identify the place of the fault.
Due such a kind of problems we go for wireless communication which is of low cost.

Advantages of Wireless communication:

Flexibility: Flexibility is one of the biggest advantages.
Ease of use: wireless networks are easy to setup and handle.
Place devices: These devices won't occupy much place as that of wired devices.
Durability: It has long lasting capability.
Prices: The prices of wireless networks are very low.

Various wireless communications:
Read the following posts to know more about wireless communication:

Wi-Fi - http://digitalnativeengg.blogspot.in/2013/06/wifi.html
GSM - http://digitalnativeengg.blogspot.in/2013/10/gsm.html
GPRS - http://digitalnativeengg.blogspot.in/2013/10/gprs.html
IR - http://digitalnativeengg.blogspot.in/2013/10/ir-communication.html
RF - http://digitalnativeengg.blogspot.in/2013/10/rf-communication.html
Bluetooth - http://digitalnativeengg.blogspot.in/2013/06/bluetooth.html

Zigbee - http://digitalnativeengg.blogspot.in/2013/10/zigbee.html

GPS

 GPS

GPS - Global Positioning System. 

GPS is a space based satellite system that provides the information about exact position on the Earth, anywhere and anytime in all weather conditions.
It is maintained by the US government and is freely accessible by anyone having a GPS receiver.
GPS was developed by the Department of Defense (DoD) and it consists of 24 satellites.       

BASIC CONCEPT:

A GPS receiver calculates its position by timing the signals sent by the GPS satellites above the Earth. Each satellite message contains

• Time of the transmitted message
• Satellite position at the time of message transmission.

Using this message, the receiver determines the transit time of each message and computes the distance of each satellite in the speed of light.
From this information, the location of the receiver was determined.
Then the location is displayed using a moving map display or latitude and longitude.
Elevation, altitude, direction and speed information may also be included.

STRUCTURE:

GPS consists of 3 segments:

• Space segment
• Control segment
• User segment

SPACE SEGMENT:

 

Space segment composed of orbiting GPS satellite or Space Vehicles (SVs) which is 24 in number having six orbital planes with 4 satellites each.
The orbital planes are inclined at 55°. Orbital period is one half a sidereal days i.e., 11 hours & 58 minutes.
Hence each SV makes 2 complete orbits each sidereal day.
There are about 32 satellites in GPS constellation by Dec 2012.
The additional satellites are used to improve the accuracy of the GPS receiver.

CONTROL SEGMENT:

 

The control segment is composed of

• a master control station (MCS),
• an alternate master control station,                   
• four dedicated ground antennas and
• Six dedicated monitor stations.

GPS control segment consists of monitor stations located around the world.
The monitor station receives the signal from the SV and computes the orbital data and clock correction for each satellite sends it to SVs within a nano seconds.

USER SEGMENT:

 

User segment composed of receiver that are now available in variety of formats which can be integrated into cars, phones, watches, etc.
It consists of an antenna that can be tuned to the transmitting frequency of satellite, receiver processor and highly stable clock.
It consists of displays for giving speed and location information to the user.
Receiver is usually described by its number of channels which indicates the number of satellites that it can monitor simultaneously.

APPLICATIONS:

Civilian:
Many civilian applications use one or more GPS components.
Some of the civil applications are astronomy, automated vehicle, cartography, cellular telephony, clock synchronization, disaster relief, GPS for mining, navigation, Robotics, Surveying, Tectonics, Telematics, etc.
Military:
It is used for navigation, Target tracking, Missile & Projectile guidance, Search & Rescue, Reconnaissance.