STARZ COLLEGE OF TECHNOLOGY

Course Title: TENG 310 Mobile & Satellite Communication System

Questions and Answers on Mobile Communication

1.    IMT-2000 is a digital mobile system that functions as

Answer: Pager, Cordless and Low earth orbit satellites

2. The 2G cellular network uses

Answer: TDMA/FDD, CDMA/FDD and Digital modulation formats

3. 2G CDMA standard – cdma one supports up to

Answer: 64 users

4. 2G standards support

Answer: Limited internet browsing and Short Messaging Service

5. The 2G GSM technology uses a carrier separation of

ANSWER: 200 KHz

6. 3G W-CDMA is also known as

ANSWER: UMTS

7. The modulation technique used for mobile communication systems during world

war II was

ANSWER: Frequency modulation

8.  ———– introduced Frequency Modulation for mobile communication systems

in 1935.

ANSWER: Edwin Armstrong

9. The early FM push-to-talk telephone systems were used in

ANSWER: Half duplex mode

10. DECT stands for

Answer: Digital European Cordless Telephone

11. World’s first cellular system was developed by

ANSWER: Nippon Telephone and Telegraph (NTT)

12. Paging systems were based on

ANSWER: Simplex systems

13. In Frequency Selective Fading, the

ANSWER: Coherence Bandwidth of the channel is less than bandwidth of

transmitted channel

14. If coherence time of the channel is smaller than the symbol period of the

transmitted signal, it is

ANSWER: Fast fading

15. The power delay profile helps in determining

Answer: Excess delay, rms delay spread and Excess delay spread

16. Coherence bandwidth is

Answer: Channel that passes all spectral components with equal gain; Channel that

passes all spectral components with linear phase

17.  Small scale multipath propagation is caused due to waves with

Answer: Different propagation delays, Different amplitudes and Different phase

18. The effects of small scale multipath propagation are

Answer: Changes in signal strength; Random frequency modulation and Time

dispersion
19. Impulse response of a multipath channel is determined by the fact that

Answer: Mobile radio channel may be modeled as linear filter; Impulse response is

time varying

20. The received signal from a multipath channel is expressed as

ANSWER: Convolution of transmitted signal and impulse response

21. Direct RF pulse system helps in calculating

ANSWER: Power delay of the channel

22. The techniques used for small scale multipath measurements are

1. Direct RF pulse system

2. Spread spectrum sliding correlator channel sounding

3. Frequency domain channel sounding

23. Paging systems could be used to

Answer: a. Send numeric messages b. Send alphanumeric messages c. Voice

message

24. Garage door opener is a

ANSWER: Transmitter

25. Carrier frequency of a TV remote control is in the range

ANSWER: of Infra red

26. Half duplex system for communication has

ANSWER: Communication in single direction at a time

27. MIN stands for

ANSWER: Mobile Identification Number

28. The process of transferring a mobile station from one base station to another is

ANSWER: Hand off

29.  PCN is
a. Wireless concept of making calls

b. For receiving calls

c. Irrespective of the location of the user

30. IMT-2000 is a digital mobile system that functions as

a. Pager

b. Cordless

c. Low earth orbit satellites

31. The 2G cellular network uses

a. TDMA/FDD

b. CDMA/FDD

c. Digital modulation formats

32.  2G CDMA standard – cdma one supports up to

ANSWER: 64 users

33. 2G standards support

a. Limited internet browsing

b. Short Messaging Service

34. The 2G GSM technology uses a carrier separation of

ANSWER: 200 KHz

35. 3G W-CDMA is also known as

ANSWER: UMTS

36. Commonly used mode for 3G networks is

ANSWER: FDD

37. The minimum spectrum allocation required for W-CDMA is

ANSWER: 5MHz

38. CDMA2000 1xEV provides high speed data access with channel allocation of

ANSWER: 1.25 MHz

39. In TD-SDMA, there is a frame of _____milliseconds and the frame is divided

into _____ time slots.

ANSWER: 5, 7
40. The interference between the neighboring base stations is avoided by

ANSWER: Assigning different group of channels

41. Radio capacity may be increased in cellular concept by

ANSWER: Increasing the number of base stations & reusing the channels

42. The shape of the cellular region for maximum radio coverage is

ANSWER: Hexagon

43. Hexagon shape is used for radio coverage for a cell because

a. It uses the maximum area for coverage

b. Fewer number of cells are required

c. It approximates circular radiation pattern

44. Centre excited hexagonal cells use

ANSWER: Omni directional antennas

45. Spectrum Efficiency of a cellular network is

b. The traffic carried per cell divided by the bandwidth of the system and the area of a

cell

c. Expressed in Erlang /MHz /km2

46. The advantage of using frequency reuse is

a. Increased capacity

b. Limited spectrum is required

c. Same spectrum may be allocated to other network

47. The strategies acquired for channel assignment are

a. Fixed

b. Dynamic

48. In a fixed channel assignment strategy, if all the assigned channels are occupied,

the call

ANSWER: Gets blocked

49. In a fixed channel assignment strategy

a. Each cell is assigned a predetermined set of frequencies

b. The call is served by unused channels of the cell

c. The call gets blocked if all the channels of the cell are occupied

50. In a dynamic channel assignment strategy,

a. Voice channels are not permanently assigned

b. The serving base station requests for a channel from MSC

c. MSC allocates the channel according to the predetermined algorithm

51. Advantage of using Dynamic channel assignment is

a. Blocking is reduced

b. Capacity of the system is increased

52. Disadvantage of using Dynamic channel assignment is

a. More storage required

b. Calculations and analysis is increased

53. In Dynamic channel assignment, any channel which is being used in one cell can be

reassigned simultaneously to another cell in the system at a reasonable distance.

54. In Handoff

a. Process of transferring the call to the new base station

b. Transfers the call

c. New channel allocation is done

55. Delay in handoffs is caused due to

a. Week signal conditions

b. High traffic conditions

c. Unavailability of the channel

56. Inter system Handoffs are done

a. When mobile station moves in two cellular systems with different MSC

b. When mobile station moves between two cellular systems

c. When mobile station receives more power from other base station than the serving

base station

57. When a fraction of assigned channel is reserved for handoffs, it is

ANSWER: Guard channel concept

58. While handoffs, the termination of call may be avoided by

a. Providing Guard channel

b. Queuing of handoffs
59. Dwell time is the time for

ANSWER: A call within the cell

60. Dwell time depends upon

a. Interference

b. Distance between the subscriber and the base station

c. Propagation of call

61. In Mobile Assisted Handoff (MAHO), the handoff takes place when

ANSWER: The power received by the mobile station from other base station is more

than the serving base station

62. Mobile Assisted Handoff (MAHO) provides

a. Faster handoffs

b. Suitability for frequent handoffs

c. MSC need not monitor the signal strength

63. Trunking in a cellular network refers to

ANSWER: Accommodating large number of users in limited spectrum

64. When all of the radio channels are in use in a trunking system

a. The user is blocked

b. The access to the system is denied

c. The queue may be provided

65. Umbrella cell approach

a. Uses large and small cells

b. Uses different antenna heights

c. Is used for high speed users with large coverage area and low speed users with

small coverage area

66. Interference in cellular systems is caused by

a. Two base stations operating in same frequency band

b. Two calls in progress in nearby mobile stations

c. Leakage of energy signals by non-cellular systems into cellular frequency band

67. Interference in frequency bands may lead to

a. Cross talk

b. Missed calls

c. Blocked calls

68. Co-channel reuse ratio depends upon

a. Radius of the cell

b. Distance between the centers of the co channel cells

69. Increase in Co- channel reuse ratio indicates

a. Better transmission quality

b. Low co-channel interference

70. Grade of service refers to

ANSWER: Ability of a user to access trunked system during busy hour

71. Traffic intensity is expressed in

ANSWER: Erlangs

72. The techniques used to improve the capacity of cellular systems are

a. Splitting

b. Sectoring

c. Coverage zone approach

73. Distributed antenna systems are used at

ANSWER: Inputs and outputs of repeaters

74. Antenna down tilting refers to

ANSWER: Focusing radio energy towards ground

75. Diffraction, at high frequencies, depends upon

1. Geometry of the object

2. Polarization of the incident wave

3. Amplitude of the incident wave

76. The rainbow pattern seen on a CD is an example of

ANSWER: Diffraction
77. Fresnel Reflection Coefficient is a factor of

1. Polarization of the wave

2. Properties of the material at which reflection occurs

3. Angle of incidence of wave

78. When a wave falls on a perfect conductor

ANSWER: All incident energy is reflected back without loss of energy

79. Brewster angle is the angle at which

a. No reflection occurs at the first medium

b. Reflection coefficient is zero

80. Fading is caused due to

1. Multi path propagation

2. Obstacles

3. Variation in amplitude and phase at receiver

81. Coherence time refers to

ANSWER: Minimum time for change in magnitude and phase of the channel

82.  Fading due to shadowing is

a. Fading due to large obstructions

b. Large coherence time of the channel as compared to the delay constraints

83.  Deep fade is

1. Strong destructive interference

2. Drop in signal to noise ratio

3. Temporary failure of message transfer

84. Doppler spread refers to

ANSWER: Signal fading due to Doppler shift in the channel

85. Friis free space equation

1. Is a function of transmitting and receiving antenna gain

2. Depends upon the distance between transmitting and receiving antenna

86. The free space model of propagation refers to

1. Unobstructed line of sight between the transmitter and receiver

 2. Satellite communication systems and Microwave line of sight radio links

72)   According to Friis free space equation

1. Received power falls with square of the distance between the transmitter and

receiver

2. Increases with square of the distance between the transmitter and receiver

3. Received power increases with gains of transmitting and receiving antennas

87. EIRP is

1. Effective Isotropic Radiated Power

2. Maximum radiated power available by the transmitter

3. A factor of power and gain of transmitter

88. Spread spectrum modulation involves

1. PN sequence for modulation

2. Large bandwidth

3. Multiple users

89. PN sequence at the decoder acts as a locally generated carrier at the receiver and

decodes the signal using

ANSWER: Correlator

90. In spread spectrum technique, the multiple users are assigned with
ANSWER: Same spectrum and different PN code

91. Advantage of using Spread Spectrum modulation is/are

1. Interference rejection capability

2. Frequency planning is not required

3. Resistance to multipath fading

4. ISI is lesser

92. Fast hopping is

a. More than one frequency hop during each symbol

b. Hopping rate greater than or equal to information symbol rate

93. Slow frequency hopping refers to

ANSWER: One or more symbols transmitted in time interval between frequency

hops

94. Probability of outage refers to

ANSWER: Number of bit errors during transmission

95. The digital modulation technique used in frequency selective channels is

ANSWER: BPSK

96. The diversity schemes are based on

1. Time diversity

2. Frequency diversity

3. Space diversity

4. Polarization diversity

97. In time diversity

ANSWER: Multiple versions of signals are transmitted at different time instants

98. RAKE receiver is

1. Several sub receivers

2. Several correlators

3. Fingers
99. The RAKE receiver involves the steps

ANSWER: Correlator, estimation of transmitted signal, demodulation, bit decision

100. Search window of a RAKE receiver is

ANSWER: Range of the time delays

101. Speech Coders are categorized on the basis of

ANSWER: Signal compression techniques

102. Waveform coders and Vocoders are the types of

ANSWER: Speech coders

103. PCM, DPCM, DM, ADPCM are the types of

ANSWER: Waveform coders

104. Speech coding technique that is independent of the source is

ANSWER: Waveform coders

105. Advantage of using waveform coders is

1. Independent of the signal source

2. Less complexity

3. Suitable for noisy environments

106. The type of frequency domain coding that divides the speech signal into

sub bands is

ANSWER: Sub-band coding

107. The speech coding technique that is dependent on the prior knowledge of

the signal is

ANSWER: Vocoders

108. The steps involved in Channel vocoders for speech transmission are

ANSWER: Envelope detection, sampling, encoding, multiplexing

109. Vocal tract cepstral coefficients and excitation coefficients are separated

by

ANSWER: Linear filters

110. In voice excited vocoders, PCM transmission helps in transmission of

ANSWER: Low frequency bands of speech

111. Linear predictive coders are based on the principle that

1. Current signal sample is obtained from linear combination of past samples

3. These are time domain vocoders

4. They are among low bit rate vocoders

112. Multi pulse excited LPC includes

1. Multiple pulses per period

2. Minimization of weighted mean square error

3. Better speech quality

4. Pitch detection is not required

113. In residual excited LPC,

ANSWER: The residue of subtraction of generated and original signal is quantized at

the transmitter

114. The speech sequence in GSM Codec consists of

ANSWER: Pre emphasis, segmentation, windowing, filtering

115. The windowing technique used for speech coding in GSM Codec is

ANSWER: Hamming window

116. The received signal at the GSM speech decoder is passed through

ANSWER: LTP filter

117. In GSM Codec, the bits encoded for forward error correction are

a. Ia bits

b. Ib bits

118. The speech coders are selected on the basis of

1. Robustness to transmission errors

2. Cell size

3. Type of modulation technique used

119. FDMA is the division of

ANSWER: Spectrum
120. Guard band is

ANSWER: The small unused bandwidth between the frequency channels to avoid

interference

121. Cable television is an example of

ANSWER: FDMA

122. In FDMA,

1. Each user is assigned unique frequency slots

2. Demand assignment is possible

3. Fixed assignment is possible

123. FDMA demand assignment uses

1. Single channel per carrier

2. Multi channel per carrier

124. The advantages of FDMA over TDMA includes

1. Division is simpler

2. Propagation delays are eliminated

125. TDMA is a multiple access technique that has

ANSWER: Different users in different time slots

126. In TDMA, the user occupies the whole bandwidth during transmission

127. TDMA allows the user to have

ANSWER: Use of same frequency channel for different time slot

128. GSM is an example of

ANSWER: TDMA cellular systems

129. TDMA is employed with a TDMA frame that has preamble. The
preamble contains Address of base station and subscribers
1. Synchronization information
2. Frequency allotted

130. CDMA is
1. Spread spectrum technology
2. Using same communication medium
4. Each user has unique PN code

131. Global Positioning System uses

ANSWER: CDMA

132. CDMA is advantageous over other Spread Spectrum techniques for

1. The privacy due to unique codes
2. It rejects narrow band interference
3. Resistance to multi path fading
4. Its ability to frequency reuse
133. The wide band usage in CDMA helps in
1. Increased immunity to interference
2. Increased immunity to jamming
3. Multiple user access
134. The advantages of using a CDMA technique over other spread spectrum
techniques are
1. Increased capacity
2. Easier handoff
3. Better measure of security

135. FHMA is
1. Spread spectrum technology
2. Using same communication medium
3. Every user has assigned unique frequency slot
4. Each user has unique PN code

136. OFDM is a technique of

1. Encoding digital data
2. Multiple carrier frequencies
3. Wide band digital communication
4. 4G mobile communication

137.  Advantages of using OFDM include

1. Avoids complex equalizers
2. Low symbol rate and guard interval
3. Avoids ISI
4. Multiple users at same frequency

138. The troubles that OFDM faces over other spread spectrum techniques are
1. Sensitivity to Doppler shift
2. Frequency synchronization problems
4. Low efficiency due to guard intervals

139. The guard interval is provided in OFDM

a. To eliminate the need of pulse shaping filter
b. To eliminate ISI

140. Packet radio refers to

ANSWER: Multiple users on single channel
141. Disadvantages of packet radio are
a. Induced delays
b. Low spectral efficiency
142. Pure ALOHA is a
ANSWER: Random access protocol
143. The increase in number of users in PURE ALOHA causes
a. Increase in delay
b. Increase in probability of collision
144. SDMA technique employs
a. Smart antenna technology
b. Use of spatial locations of mobile units within the cell
145. The advantage of using SDMA over other spread spectrum technique is
a. Mobile station battery consumption is low
c. Increased spectral efficiency
146. The increased capacity of SDMA is due to
a. Focused signal transmitted into narrow transmission beams
b. Smart antennas pointing towards mobile stations
147. Coherence time is
ANSWER: Directly proportional to Doppler spread
148. Types of small scale fading, based on Doppler spread are
ANSWER: Fast fading
149. Flat fading or frequency nonselective fading is a type of
ANSWER: Multipath delay spread small scale fading
150. In Frequency Selective Fading, the
ANSWER: Coherence Bandwidth of the channel is less than bandwidth of
transmitted channel
151. If coherence time of the channel is smaller than the symbol period of the
transmitted signal, it is
ANSWER: Fast fading
152. The power delay profile helps in determining
a. Excess delay
b. rms delay spread
c. Excess delay spread
153. Coherence bandwidth is
a. Channel that passes all spectral components with equal gain
c. Channel that passes all spectral components with linear phase
154. Small scale multipath propagation is caused due to waves with
1. Different propagation delays
2. Different amplitudes
3. Different phase
155. The effects of small scale multipath propagation are
1. Changes in signal strength
2. Random frequency modulation
3. Time dispersion
156. Impulse response of a multipath channel is determined by the fact that
a. Mobile radio channel may be modeled as linear filter
b. Impulse response is time varying
157. The received signal from a multipath channel is expressed as
ANSWER: Convolution of transmitted signal and impulse response
158. Direct RF pulse system helps in calculating
ANSWER: Power delay of the channel
159. The techniques used for small scale multipath measurements are
1. Direct RF pulse system
2. Spread spectrum sliding correlator channel sounding
3. Frequency domain channel sounding