Fundamentals of Telecommunication

Eng. Mohammed Eldaw

https://twitter.com/Mo7ammedEldaw

Brief Contents

• Telecommunication definition• Modulation and demodulation .Analog modulation . Digital modulation • Transmission Media• Signaling • Switching• Multiple access

what is Telecommunication ?

• Telecommunication has been defined as a technology with communication from a distance .

• The simplest form of telecommunications takes place between two stations. However, it is common for multiple transmitting and receiving stations to exchange data among themselves.

Frequency

 Frequency is the number of complete cycles per second in alternating current direction.

The standard unit of frequency is the hertz, abbreviated Hz.

One (1) Hz is the frequency at which the current complete one cycles.

• Kilohertz (kHz) thousand of cycles• Megahertz (MHz)�������� million

of cycles• Gigahertz

(GHz)���������� billion of cycles• Terahertz

(THz)����������� zillion of cycles

•  

Wavelength

• Wavelength is the distance between identical points in the adjacent cycles of a waveform.

• � In Radio Frequency (RF), the wavelength length is usually in meters, centimeters, or millimeters ranges.

Bandwidth

• Bandwidth is a broad term defined as the bit-rate measure of the transmission capacity over a network communication system .

• Bandwidth also refers to a range of  frequncies used to transmit a signal.

• bandwidth is measured in hertz and is often referenced in signal processing applications.

Bandwidth Diagram

Modulation

• What is Modulation ?• Modulation is the process by which a

carrier wave is altered in such a way that it is able to carry information on it.

• There are tow types of modulation:1.analog modulation includes: FM,PM,AM2.Digital modulation includes: ASK,PSK,FSK

Modulation process

Analog Modulation

• In this chapter we will discuss about the types of analog modulation and you will be able to know the difference between them .

Amplitude Modulation AM

• When an amplitude modulated signal is created, the amplitude of the signal is varied in line with the variations in intensity of the sound wave. In this way the overall amplitude or envelope of the carrier is modulated to carry the audio signal. Here the envelope of the carrier can be seen to change in line with the modulating signal.

• ts most basic form as a function of time (t) is:

•A, the amplitude, is the peak deviation of the function from zero.

• f, the ordinary frequency, is the number of oscillations (cycles) that occur each second of time.

•ω = 2πf, the angular frequency, is the rate of change of the function argument in units of radians per second

• , the phase, specifies (in radians) where in its cycle the oscillation is at t = 0.

Amplitude Modulation advantages & disadvantages

• ADVANTAGES:• It is simple to implement• It can be demodulated using a circuit

consisting of very few components• AM receivers are very cheap as no

specialised components are needed.

• DISADVANTAGES :• An amplitude modulation signal is

not efficient in terms of its power usage.

• It is not efficient in terms of its use of bandwidth.

• An amplitude modulation signal is prone to high levels of noise because most noise is amplitude based and obviously AM detectors are sensitive to it.

Frequency Modulation FM

• Frequency modulation uses the information signal, Vm(t) to vary the carrier frequency within some small range about its original value. Here are the three signals in mathematical form:

• Here are the three signals in mathematical form:

• • Information: Vm(t) • Carrier: Vc(t) = Vco sin ( 2 p fc t + f ) • FM: VFM (t) = Vco sin (2 p [fc +

(Df/Vmo) Vm (t) ] t + f)

Advantages and disadvantages of FM

•Advantages :• Resilient to signal strength variations• Resilient to noise• Does not require linear amplifiers in

the transmitter• Enables greater efficiency than many

other modes

disadvantages • Requires more complicated

demodulator• Some other modes have higher data

spectral efficiency.• Sidebands extend to infinity either

side

pm

• PM changes the phase angle of the complex envelope in direct proportion to the message signal.

• Suppose that the signal to be sent (called the modulating or message signal) is and the carrier onto which the signal is to be modulated is

Advantages and disadvantages of PM

• Advantages :

• 1. Phase modulation is easy matched against Frequency modulation.

• • 2. Phase modulator makes it easy in

finding velocity of acting target by pulling out Doppler info.

• .

• 3. Doppler info needs unchanging carrier which will be fairly easy in phase modulation but not really in frequency modulation

• Disadvantages :

• 1. Phase ambiguity comes up if we surpass its transition index pi rad (180 degree).

• 2. We require frequency multiplier to maximize phase modulation index.