WIRELESS COMMUNICATION

PART A Marks [10 * 2 =20]

1. Give some of the services available in wireless communication.

2. How to reuse the frequency in regulated spectrum?

3. What is hand off?

4. Define QPSK?

5. Define adaptive equalization?

6. Define cell splitting.

7. Define diversity concept?

8. Mention some merits of MSK.

9. Write the advantages of MSK over QPSK.

10. Write advantages 2G over 1G.

PART B Marks [16 * 5 =80]

11. a) i) what are the noise that disturbs the signal? (8 Marks)

ii) Explain about Interference-Limited Systems. (8 Marks)

(or)

b) The carrier frequency is 950 MHz and the RX sensitivity is (according to GSM

specifications)−102 dBm. The output power of the TX amplifier is 30 W. The antenna

gain of the TX antenna is 10dB and the aggregate attenuation of connectors,

combiners, etc. is 5 dB. The fading margin is 12 dB and the breakpoint dbreak is at a

distance of 100 m. What distance can be covered if n=3.5? (16 Marks)

12. a)Explain in detail the different techniques used to improve coverage &capacity of

cellular system . (16 Marks)

(or)

b) Explain in detail about channel and Narrow band models. (8 Marks)

13. a) Explain in detail the generation & detection of MSK technique? (16 Marks)

(or)

b) Explain in detail the structure of wireless communication link (16 Marks)

14. a) Explain in detail about Linear and Decision feedback equailsers. (16 Marks)

(or)

b) Explain in detail about Diversity, Macrodiversity and Microdiversity. (16 Marks)

15. a) Explain in detail the CDMA technique and give some advantages &

comparison with other techniques (16 Marks)

(or)

b) Explain in detail the 1G,2G,3G generation systems & their standards . (16 marks)

WIRELESS COMMUNICATION

PART A Marks[10 * 2 =20]

Answer Key

1. Give some of the services available in wireless communication.

Body Area Networks

Personal Area Networks

WANs

Cellular systems

Fixed wireless access services

Satellite systems

2. How to reuse the frequency in regulated spectrum?

Since spectrum is limited, the same spectrum has to be used for different wireless

connections in different locations. To simplify, let us consider in the following a cellular

system where different connections (different users) are distinguished by the frequency

channel (band around a certain carrier frequency) that they employ. If an area is served

by a single BS, then the available spectrum can be divided into N frequency channels that

can serve N users simultaneously. If more than N users are to be served, multiple BSs are

required, and frequency channels have to be reused in different locations.

3. What is hand off?

When a mobile moves into a different cell while conversation in progress, the

MSC automatically transfers the call from one cell to other cell without any interference.

This is called as hand off.

4. Define QPSK?

QPSK is a multilevel modulation in which four phase shifts are used for

representing four different symbols.

5. Define adaptive equalization?

To combine Inter Symbol Interference, the equalizer coefficients should change

according to the channel status so as to break channel variations. Such an equalizer is

called an adaptive equalizer since it adapts to the channel variations.

6. Define cell splitting.

Cell splitting is the process of subdividing congested cells into smaller cells each

with its own base stations and a corresponding reduction in antenna height and

transmitter power. It increases the capacity of cellular system.

7. Define diversity concept?

If one radio path undergoes a deep fade, another independent path may have a

strong signal. By having more than one path to select from, both the instantaneous and

average SNRs at the receiver may be improved often by as much as 20dB to 30dB.

8. Mention some merits of MSK.

Constant envelope

Spectral efficiency

Good BER performance

Self-synchronizing capability

MSK is a spectrally efficient modulation scheme and is particularly attractive for use in

mobile radio communication systems.

9. Write the advantages of MSK over QPSK.

1. In QPSKthe phase changes by 90degree or 180 degree .This creates abrupt amplitude

variations in the waveform, Therefore bandwidth requirement of QPSK is more filters of

other methods overcome these problems , but they have other side effects.

2.MSK overcomes those problems. In MSK the output waveform is continuous in phase

hence there are no abrupt changes in amplitude.

10. Write advantages 2G over 1G.

i)Natural integration with the evolving digital wireless network

ii)Higher data rate

iii) Flexibility for capacity expansion

PART B Marks [16 * 5 =80]

11. (a) i..what are the noise that disturbs the signal?(8 marks)

1.Thermal noise:N0 = kB Te(2)

2.Man-made noise: (3)

(a) Spurious emissions:

(b) Other intentional emission sources:

3.Receiver noise: (3)

ii. Explain about Interference-Limited Systems. (8 marks)

Simple Base station explanations with diagram. (4)

Explanation.(4)

11. (b). The carrier frequency is 950 MHz and the RX sensitivity is (according to GSM

specifications)

−102 dBm. The output power of the TX amplifier is 30 W. The antenna gain of the TX

antenna is 10 dB and the aggregate attenuation of connectors, combiners, etc. is 5 dB.

The fading margin is 12 dB and the breakpoint dbreak is at a distance of 100 m. What

distance can be covered if n=3.5?

TX side:

TX power PTX 30 W 45 dBm

Antenna gain GTX 10 10 dB

Losses (combiner, connector, etc.) Lf −5 dB

(4 Marks)

--------------------------------------------------------------------------------------------------------

EIRP (Equivalent Isotropically Radiated Power) 50 dBm

RX side:

RX sensitivity Pmin −102 dBm

Fading margin 12 dB

Minimum RX power (mean) −90 dBm

(4 Marks)

------------------------------------------------------------------------------------------------------ ---

Admissible path loss (difference EIRP and min. RX power) 140 dB

Path loss at dbreak = 100 m [λ/(4πd)]2 72 dB

Path loss beyond breakpoint ∝ d ^−n 68 dB

(4 Marks)

----------------------------------------------------------------------------------------------------------

Depending on the path loss exponent,

n = 1.5 . . . 2.5 (line-of-sight)3

n = 3.5 . . . 4.5 (non-line-of-sight)

we obtain the coverage distance,

dcov = 100 · 1068 /(10n) m

If, n = 3.5, then the coverage distance is 8.8 km. (4 Marks)

12.a)Explain in detail the different techniques used to improve coverage &capacity

of cellular

system .(16 Marks)

Explanation of cell splitting (5)

Explanation of sectoring (5)

Explanation of micro zone coverage (6)

12.b.Explain in detail about channel and Narrow band models.

Stored channel impulse responses explanation (3)

Deterministic channel models explanation (2)

Stochastic channel models explanation(2)

Narrowband Models(3)

Modeling of Small-Scale and Large-Scale Fading Explanation (2)

Path Loss Models explanation (2)

The Motley–Keenan Model explanation (2)

13.a) Explain in detail the generation & detection of MSK technique? (16 Marks)

Principle of MSK (4)

MSK transmitter block diagram &explanation (6)

MSK receiver block diagram &explanation (6)

13.b) Explain in detail the structure of wireless communication link

Principle (4)

Block diagram of a transmitter and receiver (6)

Explanation (6)

14.a) Explain in detail about Linear and Decision feedback equailsers .

Structure of Linear and decision feedback equalizer. (8)

Explanation. (8)

14.b Explain in detail about Diversity, Macrodiversity and Microdiversity.

Principle of Diversity (2)

Definition of the Correlation Coefficient (1)

Explanation(1)

Microdiversity (6)

Spatial diversity

Temporal diversity

Frequency diversity

Angular diversity

Polarization diversity

Macrodiversity (6)

Explanation

15.a) Explain in detail the CDMA multiple access technique and give some

advantages &

comparison with other techniques (16 Marks)

CDMA working principle (8)

Advantages & comparison with other techniques. (8)

15.b.Explain in detail the 1G,2G,3G generation systems & their standards . (16

marks)

Explanation of generation models of 1G,2G,3G (8)

Explanation of their standards (8)