FM/FDM VIDEO SIGNAL TRANSMISSION

- SHEWETA RANI

What is VIDEO SIGNAL TRANSMISSION? Method of sending video signal from one place to another.

3 Stages of sending the signal :-

The Video signal is electronically changed into pulse light.

The Light is then injected to the Opt.Fibre for transmission.

At the receivers end, This Pulse light is changedback into an electronic signal

Why only Optical Fibre used? Fiber Optics Cable is not affected by electrical interference &

has no problem even in contact with high voltage power.

Video Signal can be sent over long distance with very MINIMUM DEGRADATION in its quality.

Fiber optics cable transmits video signal with extremely high efficiency.

Much lower levels of signal attenuation.

Much Larger BANDWIDTH More Data to be delivered

Much lighter than the coaxial cables.

What is FM?FM means Frequency Modulation

It is a type of modulation in which the frequency of the carrier wave is varied in accordance with the modulating

signal keeping the amplitude constant.

FDM means Frequency Division Multiplexing

This method combined many modulated signal (through FM) which allow the transmission medium to be shared by

multiple independent signals.

It is a method /way in which multiple signals are combined at one point for transmission using a transmission medium

(ie. Optical fiber)

“THE VIDEO SIGNAL NEEDS TO BE TRANSMITTED THROUGH AN ORTICAL FIBRE ARE FIRST FREQUENCY

MODULATED & THEN FREQUENCY-DIVISION MULTIPLEXED”

Examples of FDMRADIO

Multiple Radio signals at different frequencies (93.5, 91.1 etc) pass through the air at the same time

DISH /CABLE TVMultiple TV Channel are carried

on a single cable at the same time.

BLOCK DIAGRAM OPTICAL-FIBRE VIDEO SIGNAL

TRANSMISSION USING FM/FDM METHOD

BLOCK DIAGRAM

There are 3 Video signals to be sent. Channel #1 () Channel #2 (DD News) Channel #3 ()

The 1st stage is LPF (Low pass filter)

It removes the unwanted components of frequencies of the video signals feeded to it. Hence reduces background noise.

The 2nd stage is the Frequency Modulator

At this stage, each video signal is modulated by a CARRIER SIGNAL which provided by a local oscillator which is not been shown in the diagram.

3rd stage is FDM

These frequency modulated Video signal are then frequency-division multiplexed.

This combined signal is fed as an input of the optical transmitter

4th Stage is OPTICAL TRANSMITTER

Filtering of modulated video signal such BANDWIDTH RESTRICTIONS can be maintained.

It adjust the signal level to be maintained COMPATIBILITY with the optical source.

It converts the FDM o/p VOLTAGE INTO CURRENT in order to drive the optical source.

5th stage is OPTICAL SOURCE

Converts the electronic signal pulse into light signal so as to send it to the optical fiber.

1) LED DEVICES

- Low noise - High degree of reliability

- Cheaper in cost

2) LASER DEVICES It is exactly opposite to LED characteristics :

- High noise - Low degree of reliability

- Expensive

6th stage is the OPTICAL FIBRE

- It is a communication/transmission medium between sender and receive station.

- It carries light signals.

7th stage is OPTICAL DETECTOR

- It converts the optical power/ LIGHT SIGNAL back into electrical signal.

8th stage is OPTICAL RECEIVER

- It amplifies the received electrical signal to the level required by the Demultiplexer.

9th stage is FREQUENCY ‘DE’MULTIPLEXER - It performs the reverse function of FREQ.MULTIPLEXER.- It decomposes the combined FDM signal into each individual video signals at various places.

10th stage is FREQUENCY ‘DE’MODULATION-It performs reverse function of FREQ.MODULATER.-Each freq. modulator extracts its original video signal from the output signal of demultiplexer(DEMUX) received by it.-It ‘DE’Modulates each signal into 2 components :- -Video signal + -Carrier wave

PARAMETERSSNR : Sound-to-Noise Ratio

-It is a ratio that compares the signal strength relative to background Noise Incoming signal strength Noise level strength

SNR= --------------------------------------------------Level of Desired SignalLevel of Background Noise

CNR : Carrier-to-Noise - It is the ratio of Carrier power to Noise power.

CNR= ----------------------------------------------------Power of Received Modulated Signal (Pc)Power of Received Noise

RECIEVER SENSITIVITY :

Minimum acceptable value of optical power that a receiver needs to operate reliably with a proper BER is called Receiver sensitivity.

HARMONIC DISTORTIONS :

Harmonic Irregularities/ Distortions arises in the transmitted signal due to Non-Linearity of the Optical source.

LINK DISTANCE :

It is a distance covered by an optical fiber during transmission of signal.

ADVANTAGES OF FM/FDM MODE

- Larger link Distance

- Substantial Improvement in SNR

DISADVANTAGES

- Limited no of Video Signal can be processed Harmonic DistortionNo of Video signals

Link Distance

searchnetworking.techtarget.com

https://en.wikipedia.org/wiki/Optical_fiber

www.optiwave.com

www.ece.arizona.edu/~ece487/det2.pdf

ieeexplore.ieee.org

REFERENCES

www.webopedia.com