Syed Usama Hasan. NUST-135.Docx

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Syed Usama Hassan

VI-EE-803

2011-NUST-PNEC-BE-EE-135

Assignment:

Communication System.



Question # 02:

1-Bit Error Rate:

Bit error rate is usually a parameter that is used to check and certify quality of

performance of digital communication systems. Mathematically it is taken as ratio of number of

bit errors and total number of bit received during certain under consideration period of time.

We have an instrument to detect BER; it is called bit error tester.

2-Quality factor:

The better performance in a communication system can be known by a factor known as

Quality factor denoted by Q.

The equation to show the relation between BER and Quality factor is:

As it has been illustrated by the equation above, BER is indirect proportion to Q-factor.

3-Constellation Diagram:

Constellation diagram is way to demonstrate the modulated signal with respect to relative

peaks of phasor. By this we can we understand the behavior of modulated signal e.g. in QAM

and PSK.



Example is as shown below.

4-Eye Diagram:

It is a way of demonstrating the overlap of incoming 0’s and 1’s in digital

communication.

To find out the quality factor from the eye diagram we use the formula.

µ= 0’s mean.

σ= S. deviation of zeroes

EYE Diagram:

The perpendicular feed of oscilloscope is done through customary beat stream and

activate response by symbol clock. Sweep rate is set equal to symbol data rate



Perfect established heft is shown by upright appearances, whereas ideal result

period shown by horizontal ranks.

Spectrum Analyzer:

Question # 03

Pulse Code Modulation

Pulse code modulation is the fundamental sort of pulse modulation. In this type the signal is

expressed through pulses of signal. Operation is pulse code modulation has following procedures

in it.

Sampling

Quantizing

Encoding

LPF is used to avert aliasing, A to D converter executes processes at transmitter.

TYPES:

DELTA MODULATION

ADAPTIVE DELTA MODULATION

DIFFERENTIAL MODULATION

SIGMA DELTA MODULATION

Quantizing:



We sample the received signal by using a stream of rectangular pulses. These trains of pulses are

sufficiently narrow to nearly estimate the sudden sampling procedure.

An example of 2 sampling levels 5,-5 is given below.

Encoding:

Encoding is done to make a signal more appropriate and apt. so we have a code which is used in

this process. In Pulse Scheme Modulation signal sets itself just in accordance with the given or

mentioned code. Another important phenomenon noted is this that the transmitter side does a bit

of compression with the signal and the receiver is utilized in order to perform expansion.

Noise Effect:

In working systems, there must be a noise due to quantization procedure. This noise can’t

be completely removed and finished into system. This noise only carries out its function when

system is working otherwise it’ll not be there to be observed.

Bandwidth:

We have already studied in Nyquist episode that PCM is half of BW.

Practical applications of PCM:

When we come across analogue modulation, we realize that it is very difficult as well as

very costly. So it becomes hard for us to manage, understand and accommodate. So we go to

PCM, the digital modulation scheme.



This scheme is cheaper and easier. Because of its easiness to understand, we always try to

prefer its option. PCM scheme being utilized in the telephony is also a good application to

mention. Moreover, Computing also includes this scheme.

Question # 04

Generation and detection of Frequency Modulation and Pulse Modulation signals

Frequency Modulation:

In the generation of FM-signal, we vary the frequency of carrier signal according to themessage signal. In FM modulation the frequency of the carrier is changed just in accordance

with baseband signal. A baseband signal is frequency bands.

Phase Modulation:

In phase modulation, we simply change the phase of carrier with respect to concernedsignal. We generate it by first differentiating the m(t) signal. Modulator can by utilized in series

as well parallel operation. Series is shown below.



Single tone, narrow Band and wide Band FM signals

The equation for narrow band FM is:

π

From this, we can conclude that the modulator can handle carrier in two ways; direct path with

90 degree phase shift & way of doing it with product modulator.

Wide band:

Where, h is Modulation index. So in the case of h>>1 BW will be .

This is known as wide band FM.

The primarily most remarkable thing about this is, it can accommodate more bandwidth

than the narrow band.So we can use it where we are supposed to handle more part of bandwidth.

Narrow bandwidth is where we have h<<1.

Single tone Signal.

It is actually a signal with a const. frequency. It undergoes no variation with respect to its

amplitude.

Transmission Bandwidth of Angle modulated signals:

Phase modulated signal possesses infinite side frequencies. Therefore, the bandwidth

being used also goes infinite. As we see a limited sidebands and pre-determined distortion.

Transmission BW is actually a sign of distinction of couple of frequencies. However, we find

that signal has a limited number of sidebands with a defined amount of distortions. We take BW

2nf, F show mod. frequency. whereas n is the integrator largest number. Bessel function:



So PM is:

Pre emphasis and De-emphasis in FM:

Pre emphasis is actually the area of transmitter. On this we can perform the amplification

of higher frequencies. Then we have another part used for compensation procedure called

De-emphasis. We here get boosted frequencies decreased.

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Syed Usama Hasan. NUST-135.Docx