WIRELESS Tute Sheets All_jan2013

THAPAR UNIVERSITY PATIALADepartment of Electronics and Communication EngineeringSubject Code: - UEC-804

Subject:- WIRELESS AND MOBILE COMMUNICATION SYSTEMS

TUTORIAL SHEET-1

1. Explain briefly different communication generation.

2. Explain current wireless scenario and also specify what kind of improvement

you can do in current system.

3. Write down the future trends in wireless communication system.

4. How Satellite network are useful in communication?


Subject:- WIRELESS AND MOBILE COMMUNICATION SYSTEMS

TUTORIAL SHEET No. 2

1. Differentiate between CDMA & GSM.

2. What are problems in GSM over CDMA?

3. Discuss about 1G, 2G, 2.5G, 3G & 4G.

4. What are advantages of 3G over 2.5G?

5. Write details of services provided by GSM.

6. Differentiate between Bluetooth, IRDA, WiFi & Zybee.

7. Explain block diagram of landline Telephone.

8. How GSM networks were designed from Mobile N/W?


Subject: - WIRELESS AND MOBILE COMMUNICATION SYSTEMS


1. How the boundary of cell should be covered in GSM architecture by an

antenna?

2. Why we use directional antenna instead of omni-directional one in cell?

3. Why HEX structure cell is used in GSM?

4. Calculate bandwidth, data rate and throughput for signalling and speech

channels used in GSM.

5.




1. Discuss the Mobile originating and Mobile terminating call scenario in detail.

2. Explain all the handshake signals required for mobile originating and

terminating calls.

3. Discuss in detail all the signaling and traffic logical channels with their

functions available in GSM.

4. Calculate the data rate provided by GSM for full rate. Also calculate the total

load in GSM channel.

5. What is the ping-pong effect? How to avoid it in GSM?




1. How ciphering is done in GSM system?

2. Discuss challenge and response of A3 algorithm used for GSM.

3. Discuss the working of A3, A5, A8 algorithms with their bits of key

generation.

4. What is handover? Discuss it for intra-BTS, intra-BSC and intra-MSC.

5. What is PING-PONG effect? Explain.

6. Explain how handshaking signals required for set-up call and termination call

for MSC.




1. Calculate the distance of Hex cell from its centre point to its all arms given

size of each arm as ‘a’ units.

2. Why we prefer Hex structure of cell in spite of square, rectangular etc?

3. Calculate capacity of cluster for given value of N. Also define the significance

of S,K,N,M,C,I,j in GSM system planning.

4. Define dwell time. Write advantages and disadvantages of Umbrella cell

approach and how is it made?

5. What do you mean by cell dragging? Explain

6. Discuss the different types of channel strategies available and used in 2G and

2.5G.




1. Prove that for a hexagonal cell geometry, the co-channel reuse ratio is given

by Q=root(3N), where N=i2 +j2 +ij. (hint: Use cosine law and hex cell

geometry).

2. If SIR of 15dB is required for satisfactory forward channel performance of a

system, what is the frequency reuse factor and cluster size that must be used

for maximum capacity if the path loss exponent (n) is 4, (b) n=3 ? Assume

there are 6 co-channel cells in the first tier and all of them are at same distance

from mobile.

3. How many users can be supported for 0.5% blocking probability for the

following number of truncated channels in a blocked call cleared system?

a) 1, (b) 5 (c) 10 (d) 20 (e) 100. Assume each user generates 0.1 A of

traffic.

4. An urban area has a population of 2 million residents. Three competing

trunked mobile networks (System A, B, C) provide cellular services in his

area. System A has 394 cells with 19 channels each, system B has 98 cells

with 57 channels each and C has 49 cells with 100 channels each. Find

number of users that can be supported at 2% blocking if each user averages 2

calls per hour at an average call duration of 3 minutes. Assuming that all three

trunked systems are operated at max capacity. Compute the %age market

penetration at each cellular provider.

5. A certain city has an area of 1300 sq.miles and is covered by a system using 7-

cell reuse pattern. Each cell has a radius of 4 miles and the city is allocated a

40 MHz spectrum with a full duplex channel bandwidth of 60 KHz. Assume a

GOS of 2% for an Erlang b System is specified. If the offered traffic per user

is 0.03A, compute (a) number of cells in the service area, (b) number of

channels per cell, (c) traffic intensity of each cell (d) maximum carried traffic

(e) total number of users that can be served for 2% GOS (f) number of mobiles

per channel (g) Theoretical max number of users that could be served at one

time by the system.

6. A hexagonal cell within a 4-cell system has a radius of 1.387 km. A total of 60

channels are used with in the entire system. If the load per user is 0.029 A and

average call rate is 1 call/hour, compute the following for an Erlang C system

that has a 5% probability of a delayed call:

(a) How many users per sq.km will this system support?

(b) What is the probability that a delayed call will have to wait

for more than 10 seconds?

(c) What is the probability that call will be delayed for more than

10 s?

7. For N=7 system with Pr (Blocking)= 1% and average call length of 2 minutes,

find the traffic capacity loss due to Trunking for 57 channels when going

from omni-directional antennas to 60 degree directional antennas . (Assume

that blocked calls are cleared and average call rate = 1 per hour).

(a) What is the maximum system capacity (total and per channel)

in Erlangs when providing a 2% blocking probability with 4

channels, with 20 channels and with 40 channels?

(b) How many users can be supported with 40 channels at 2%

blocking? Assume H=105 s and average call rate= 1

call/hour.

(c) Using the traffic intensity per channel calculated in part (a) ,

find GOS in a lost call delayed system for the case of delays

being greater than 20 s. Assume that H=105s and determine

GOS for 4 channels , for 20 channels and for 40 channels.

Comparing part(a) and (c) , does a lost call delayed system

with a 20 second queue perform better than a system that

clears blocked calls ?

8. A Rx in an urban cellular radio system detects a 1 mW signal at d=d0 = 1

meter from the transmitter. In order to mitigate co-channel interference effects,

it is required that the signal received at any Base station Rx from another base

station Tx which operates with in the same channel must be below -100 dBm.

A measurement team has determined that n=3. Determine major radius of each

cell if N=7 and also for N=4.

9. A system has N=7. It is operated with 660 channels, 30 of which are

designated as setup (control) channels so that there are about 90 voice

channels available per cell. If there is a potential user density of 9000

users/sq.Km in the system, and each user makes an average call rate of 1 per

hour and each call last for 1 minute during peak hours, determine the

probability that a user will experience a delay greater than 20 s if all calls are

queued.



Tutorial Sheet 8

1. What is friss equation?

2. Derive the relationship between Pt and Pr.

3. How to calculate ERP of antenna?

4. Why antenna gain is measured in dbi?

5. What is fraunhofter’s region?

6. Calculate fraunhofter’s distance?



Tutorial Sheet 9

Q1. If Pt=10W, Gt=0db, Gr=0db and fc=900MHz, find Pr in Watts at a free space

distance of 1 km.

Q2. Assume a receiver is located 10 km from a 50 W transmitter. The carrier

frequency is 6GHz and free space propagation is assumed, Gt=1 and Gr=1.

a) Find the power at receiver.

b) Find the magnitude of the E-field at receiver antenna.

c) Find the rms voltage applied to the receiver input, assuming that the

receiver antenna has a purely real impedance of 50 ohm and is matched to

the receiver.

Q3. Fraunhofer distance: Calculate the gain, half power bandwidth( HPBW), and

fraunhofer distance for a uniformly illuminated horn antenna at 60GHz with

dimensions of 4.6cm*3.5cm. Hint: HPBW for the horn antenna can be

estimated as HPBW=51λ/a, where a is the aperture width.

Q4. Free space propagation: Assume the transmitter power is 1W at 60 GHz fed

into transmitter antenna. Using the horn antenna from Q3 at both transmitter

and receiver:

a) Calculate the free space path loss at 1m, 100m, and 1000m.

b) Calculate the received signal power at these distances.

c) What is the rms voltage received at the antenna if the receiver antenna has

purely real impedance of 50ohm and is matched to the receiver?

Q5. Show that Brewster angle(case where ᴦ=0) is given by θi where



Tutorial Sheet 10

Q1. Prove that in the two ray ground reflected model Δ=d”-d’=2hthr/d. Use the

geometry of the fig given below.

Fig.1

Q2. In the two ray ground reflected model assume that θΔ must be kept below

6.261 radians for phase cancelation reasons. Assuming a receiver height of 2m

and given a requirement that θi be less than 5 degree, what are the minimum

allowable values for the T-R separation distance and the height of the

transmitter antenna? The carrier frequency is 900MHz. Refer to fig.1.

Q3. In the two path loss model with Ґ⊥= -1. Derive an appropriate expression for

the location of signal nulls at the receiver.

Q4. Compare the received power for exact equation and

approximate

expression for the two ray ground reflected model. Assume the

height of the transmitter is 40m and height of the receiver is 3m. The freq. Is

1800MHz, and unity gain antennas are used. Plot the received power for both

models continuously over range of 1 km to 20 km, assuming the ground

reflection coefficient of -1 for horizontal polarization.

THAPAR UNIVERSITY PATIALA

Department of Electronics and Communication EngineeringSubject Code: - UEC-804


Tutorial Sheet 11

1. What is coherent time and coherent bandwidth

2. Derive expression for Doppler shift when a car is travelling at constant

velocity with respect to transmitted antenna.

a. When car is moving towards antenna

b. Away from antenna

c. At a distance d from antenna

3. Write a note on time dispersion parameter and Doppler spread

4. Assume a mobile travelling at velocity of 10m/s receive two multipath

components at fc=1000Mhz. The first component arrives at t=0 with initial

phase of 0o and power of -70 dbm. Second component arrive at t=1 µs with

3db weaker than first component with same initial phase. Compute the average

instantaneous power at interval of 0.1 s from 0s to 0.5 s. Compute the average

narrowband power and compare it with wideband power.



Tutorial Sheet 12

1. What is diversity?

2. Write down the advantages and disadvantages of Diversity?

3. What are the types of diversity? Explain.

4. What do you mean by diversity combining techniques? Explain.

5. On basis of received SNR, which diversity combining technique is better?

Justify with SNR exp. of each type.



Tutorial Sheet - 13

1. Discuss modulators and demodulators of DSSS using BPSK with block

diagram and using data input stream of 10 bits with positive logic. Also

explain with waveforms.

2. Generate a DSSS sequence of 10 bits with negative logic for spreading each

bit on 6 bits using EX-OR logic for implementing DSSS. Also show their

waveforms pattern for NRZ.

3. How to calculate the system capacity in CDMA system?

4. Discuss the trade off between Bandwidth and SNR.

WIRELESS Tute Sheets All_jan2013

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