Question

QUESTION 1

1. Explain the term “Propagation” and state three propagation phenomenon.
2. Explain the term Ionosphere.                                                          
3. Explain the Ionospheric layers.   

QUESTION 2

1. Draw the block diagram of a GSM network, showing clearly the various interfaces and explain the functions of the following units:

1.         BSS
2. NSS                                                                                                   

2. Define the following:

1. Forward Control Channel (FCC)                                                                
2. Reverse Control Channel (RCC)                                                         
3. Forward Voice Channel (FVC)   
4. Reverse Voice Channel (RVC)                                                            

QUESTION 3

1. Explain the term “mobile computing”.                                                        
2. With the aid of a simple diagram, explain the spectrum of mobility from the network perspective.                                                                                                  
3. Define the following:

1. Home Agent.                                                                                
2. Foreign Agent.                                                                              
3. Home Network.                                                                           
4. Correspondent.

4. List five mobile computing hardware devices                                            

QUESTION 4.

1. What is the main objective of Multiple Access Scheme?   
2. With the aid of diagrams, explain the following CDMA Multiple Access Schemes:

1. DSSS                                                                                                 
2. FHSS                                                                                                  

3. Explain how the combination of FDMA and TDMA can increase capacity.

1. Explain the term “Grade of Service”.   
2. A cell consisting of 100 mobile stations (MSs) generates an average of 60 request(λ) during an hour (3600 seconds), with an average holding time, t=360 seconds.

Calculate the Offered Load, A_O.   

3. A mobile network operator is allocated 25 MHz bandwidth in the 900 MHz band by the National Communication Authority (NCA). The network planning engineer for this operator decided to use a frequency separation of 200 kHz.

1. Find the number of Radio Frequency (RF) channels for this network operator
2. If in the design, i = 2, and, j = 2, find the cluster size N.   

4. Explain the term “Frequency Reuse”.                                                               

QUESTION 6.

1. What is Satellite?   
2. Explain the uses of communications satellites.   
3. Explain the following as applied to Satellite Communication.   

(i) LEO

(ii)MEO

(iii) GEO

Answer 1

I'll try to answer the most number of questions possible according to our guidelines.

Question 1) :-

a). The basic meaning of propagation is to spread something far and wide to make its reach to new regions and new people. Now we have to deal with the propagation of electromagnetic waves. These are the waves tht carry information necessary for establishing communication between two parties. Propagation is the process or phenomenon of movement of wave from one location to another. Electromagnetic waves can propagate through any medium as well as vaccum. With respect to direction of oscillation there are two types of waves

- Longitudinal Waves

- Traverse Waves

The phenomenon of propogation of waves are stated and discussed below:-

They are diffraction, reflection, refraction and scattering also

Diffraction is the phenomenon in which light bends around the obstacles

Reflection is the pheomena in which light changes its direction of propagation on striking a smoothand polished surface.

Refraction is the phenomena of in which light waves bends from their direction of propagation due to change in the medium of propagation.

Scattering of waves by a tenuous distribution of obstacles, such as light off air molecules. This is the reason why the sky we see is blue in color.

b). To understand the ionosphere, let us first understand the atmosphere that covers our earth. The atmosphere is the layer of different gases that covers our planet as well as different heavenly bodies. The Ionosphere is the layer of the eatrh's atmosphere that lies from 75-1000 kms above the surface of the earth. It is the most important layer becasue it reflects and modifies radio waves used for communication and navigation, that we need on a daily basis. The ionosphere influences the radio waves propagation to distant places on the Earth, and between satellites and Earth.

c). The Ionosphere which extends from around 75-1000 kms over the surface of the earth is mainly divided into three regions/layers . They are F-Region, D-Layer and E-Layer. These layers do not have a sharp boundary to distinguish them and the altitude also in which they occur also varies with the changing seasons.

Let's start with the D-Layer which is present at the lowest altitude ranging from 65-100 kms in the atmosphere. This layer is responsible for ionization for mostly in the day. In the nights the ionization becaomes significantly low in the region. Medium frequency radio waves and lower high frequency radio waves are quite weakened within the D region, as the passing radio waves cause electrons to move, which then collide with the neutral molecules, giving up their energy.

Now comes the E-Region which entends from about 90-95 to 150-155 kms above the surface of the earth.In the layer ionization mainly occurs due to due to soft X-rays and far ultraviolet solar radiation ionization of molecular oxygen. This layer is also responsible for reflection and absorption of radio waves. This layer becomes significantly weak because the primary source of ionization is no longer present in the layer in the night time.

Now the last and the important region which is F-Layer which starts from about 150 kms from above the surface of the earth and extends to about 500 kms above the surface of the earth. The signals that penetrate into this layer escapes into the space due to the presence of high electron density of this layer. This layer is responsible for most skywave propagation of radio waves and long distance high frequency radio communications. This wave is mostly responsible for ionization of inos after the sunset. When the E-layer and D-Layer doesn't play a significant role, the F-region begins its work.

I've answered the maximum number of questions according to my guidelines. Hope this helps you. Please give a positive rating if the answer helps you. Feel free to ask for any doubts in the comments section.