Question

Answer only 7 questions out of the following 10 questions.

+ Describe the impulse noise?

+ Define the cross-talk noise

+ Define an Antenna and give 3 of its characteristics

+ What is the Modulation and why it is needed to modulate a signal?

+ What is the primary cause of a signal loss in satellite communications?

+ Describe the Propagation Modes

+ What is the difference between fast and slow fading?

+ Which Modulation is better BPSK or 256-QAM? justify your answer

+ Describe briefly the differences between the two Spread Spectrum techniques: FHSS and DSSS techniques

+ What is the principle of frequency reuse in a cellular network

Answer 1

1>> impulse noise consisting of single bursts with duration of less than 1 second with a peak levels 15 dB higher than background noise. impulse noise includes unwanted instant sharp sound. impulse noise caused by electromegnetic interference, recording disks scratches, explosions or weak synchronization.

2>> cross-talk noise is unwanted coupling between two or more signal paths. it can occur in audio equipment network circuits and computer microcircuits.

3>> an antenna is a device made by conductive metal work as a sender or reciever of electromegnetic radio waves.

characteristics of antenna--

a. effective length

b. gain and directivity

c. bandwidth

d. radiation efficiency

e. power gain

f. radiation intensity

g. polarization of antenna

h. input impedance.

4>> modulation is a process of imposing an input signal onto a carrier wave. modualtion chage carrier wave to somehow encode data that we want it to carrying.

modulation allows to send a signal over a bandpass frequency range. modulation translates baseband signal to higher frequency. modulation of signal allow to use a smaller antenna.

5. Primary cause of a signal loss in satellite >>

propagation losses ( free space losses, pointing losses, atmospheric losses)

local losses ( equipment losses, environmental losses)

free space loss is the major component in the loss of the strength of signal as it travel through free space.

pointing loss depend antennas alignment.  

reason of misalignment 1. off axis loss at GS, 2. off axis loss at satellite.

6. propagation modes

1. ground wave- ground wave propagation follows the counter of the earth.

2. line-of-sight-- in line of sight propagation waves travel in a direct path from the source to the reciever.

3. sky wave- sky wave propagation uses reflection by both earth and ionosphere.

7. fast and slow fading>>

slow fading occur when changes in signal strength between a transmitter and receiver as the distance between the two chages by a large distance.

fast fading occur when changes in signal strength between a transmitter and reciever as the distance between the two changes by a small distance.