3g topics to prepare for interview

7/28/2019 3G Topics to Prepare for Interview

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Make sure to know about WCDMA and its 4 different services: interactive, streaming, background...How the

RAB bearers are allocated & RAB bearer definitions...Different between PS & CS services...Spread-spectrum

techniques and their characteristics (Power control how it work, soft HO, PSC allocation-remember SC are

used both on UL & DL)...Differences between Channelization codes & SC codes...The Signaling may ask to

describe the call set-up procedures and all the related-parameters....Definition of IRAT & IFHO...What are

the procedure of soft HO (active set, monitored set,,,,)...How is the noise in the system and how it affects

the capacity?? How the system capacity is defined?? Whether it is uplink-limited or downlink limited??

If they are tough, they may ask additional questions about PS-services like differences between HSPA

(HSDPA & HSUPA) and R99 services...HSPA may requires description of the technology...how it works...

General Questions about GSM

1. What are the three services offered by GSM? Explain each of them briefly.

2. Which uplink/downlink spectrum is allocated to GSM-900?

3. Which uplink/downlink spectrum is allocated to DCS-1800?

4. How many carrier frequencies are there in GSM-900/DCS-1800? How much

is the separation between the carrier frequencies?

5. What is Ciphering? Why do we need it? Name the algorithm(s) used in it?

6. What is Authentication? Why do we need it? Name the algorithm(s) used in

it?

7. What is equalisation? Why do we need it?

8. What is Interleaving? Why do we need it?

9. Why do we need digitisation?

10. Explain Speech Coding.

11. What is channel coding?

12. What do you mean by Frequency re-use?

13. What is Cell Splitting?

14. Name the interfaces between a) BTS and MS b) BTS and BSC c) BSS andMSC d) TRAU and BSC e)BSC and PCU

15. What are LAPD and LAPDm?

16. What is WPS?

17. What is MA?

18. What is MAIO?

19. What is the difference between Synthesised Frequency Hopping and Base

Band Frequency Hopping?

20. What is Cycling Frequency Hopping?

21. What is HSN? How do we apply it?

22. What is DTX? Why is it used?

23. What is DRX? Why do we need it?24. What is the gross data rate of GSM?

25. What is Erlangs? What is meant by GoS?

26. We use two different bands for GSM/DCS communications; GSM900 and

DCS-1800. Which one is the better of the two in terms of quality and

coverage?

27. What is TA? Why do we need TA?

28. What is meant by Location Area?


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29. What is location update? Why do we need location update?

30. What is meant by IMSI, TMSI, IMEI and MS-ISDN? Why they are needed?

31. What is ARFCN? Which ARFCNs are allocated to Ufone?

32. Explain Power Control.

33. What is the difference between FDD and TDD?

34. What is an extended cell? How does it impact the system?Channels and TDMA structure

35. Why do we use Multiple Access Schemes? What is the difference between

FDMA, TDMA and CDMA?

36. Which channel(s) is used for SMS?

37. Which channel is used by MS to request access to the network?

38. What is AGCH?

39. Why do we need SDCCH?

40. What is a physical channel? How do we differentiate between physical and

logical channels?

41. What are TDMA frames, multiframes, superframes and hyperframes?

42. Why do we need FCCH, SCH and BCCH?43. Why do we need SACCH?

44. What is the purpose of PCH and CBCH?

45. Do we keep BCCH on a hopping radio? Give the reason to support your

answer.

46. How much delay is present between downlink and uplink frames? Why do

we need this delay?

47. Explain the structure of a Traffic Multiframe. Why do we need SACCH and

Idle bursts in a traffic multiframe?

48. How is a FACCH formed? When is a FACCH used?

49. What are bursts? Explain various types of bursts.

Radio Propagation and Antennas50. What is VSWR? Why do we need it?

51. What do you mean by EIRP?

52. What is Polarisation? What are the types of polarisation?

53. What is fading? What are its different types: a) Based on Multipath time

delay spread b) Based on Doppler Spread?

54. What is Rayleigh Fading?

55. What is multipath fading?

56. How can we minimise multipath fading?

57. What are the different types of diversity?

58. Explain various types of Antenna Diversity?

59. Explain Frequency Diversity.60. Explain Time Diversity.

61. What are the basic mechanisms of propagation?

62. What do you mean by Diffraction?

63. What is knife-edge diffraction?

64. What is Scattering?

65. What is FSPL?

66. What is meant by Fresnel zone and Fraunhofer zone?


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67. What is beamwidth? What is the relation of beamwidth to length of antenna?

68. Define: a) Bandwidth, b) 3dB Bandwidth and c) absolute Bandwidth d)

Coherence Bandwidth e) Modulation Bandwidth f) Null-to-Null Bandwidth?

69. What do we understand from the terms a) SNR b) F/B ratio?

Handovers

70. What are the types of Handovers (intra-bsc, inter-msc, etc)?71. What can be the reasons of Handover Failure?

72. What is the difference between a soft handover and a hard handover?

73. What are SYNC handovers? How are the different from asynchronous

handovers?

74. What are emergency handovers?

75. What are the different types of Handovers? (PBGT, Quality, Level, etc)

76. How do we classify the handovers on the basis of decision making?

77. What are Vertical and Horizontal handovers?

78. What is Multilayer Handoff Strategy? What is Ping pong effect and

take-back?

79. Who makes the handover decisions in GSM?80. What is the role of the MSC in handovers?

81. What is the role of the MS in handovers?

Modulation

82. Which modulation scheme is used in GSM? Explain.

83. What is the difference between PSK, ASK and FSK?

84. What are QPSK and OQPSK?

85. What is MSK? What is its application in GSM?

86. What is QAM? What is its application in GSM?

87. What is meant by PAM and PCM? What is its application in GSM?

88. Explain FDM, TDM and OFDM.

89. Which modulation scheme is used in GPRS? In EDGE? Explain/Compare.Drive Testing

90. What is C/I?

91. What is C/A?

92. What is RxQual? How do we relate it to BER?

93. What is the difference between BER-Full and BER-Sub?

94. What is SQI? Why do we prefer it over RxQual?

95. What is BSIC? Why do we need it?

96. What is AMR?

97. What can be the reasons of a Call drop?

98. What are counters? Why do we need them?

99. When do we need drive test?100. What is cell-reselection?

101. What are C1 & C2?

102. What is call re-establishment?

103. Why do we make short calls and long calls during drive test?

104. What do you mean by CEFR and CSSR?

105. What is RSSI?

106. What is the difference between RxLev and RxQual?


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107. What is the difference between FER and BER?

Procedures

108. What is cell selection? How does MS select a cell?

109. Explain the call flow for MOC and MTC.

110. Handover procedures.

111. How does a MS get registered with the network? (Explain IMSIattach procedure)

GPRS and EDGE

112. What is GPRS?

113. What is the basic difference between GSM and GPRS architecture?

114. What makes GPRS technology different from traditional GSM?

115. What are the functions of GGSN and SGSN?

116. How many coding schemes are used in GPRS? Why are they

important?

117. What is the gross data rate offered by GPRS and EDGE?

118. What is EDGE? How is it different from normal GSM/GPRS?

119. How do we classify GPRS terminals?GSM System Architecture

120. What are the main components of BSS?

121. What are the main components of NSS?

122. Why do we need HLR and VLR?

123. Why do we need EIR and AuC?

124. What is RBS?

125. What are the paging limitations of a BSC?

Ans-125. Paging capacity in the BSC The paging capacity in the BSC is dependent on which type of APZ the

BSCis equipped with.A BSC equipped with APZ 212 25 will at least provide a paging capacity of 8000

Paging Commands per second. If instead an APZ 212 20 is used at least18 000 Paging Commands per

second can be handled by the BSC and for a APZ 212 30 the number of Paging Commands per second

is at least 50 000.This shows that at least for an APZ 212 30 equipped BSC other limitation will be

reached before the paging capacity in the BSC. The following calculation is made for APZ 212 25 and

where 8000 Paging commands will be taken to be the maximum limit of the BSC. The BSC paging capacity is no

bottleneck when doing LA dimensioning as long as:

#Cells/LA * #Paging Commands/cell and sec < 8000 Paging Commands/sec

Example 1: BASI model with one TRX cellsAn LA with 500 one TRX cells, the Paging Command load is calculated:4 Erlang/TRX * 500 TRXs =2000 Erlang traffic2000 E * 0.0043 Paging Commands/(sec*E) =8.6 Paging Commands/sec

8.6 * 500 cells =4300 Paging Commands/secExample 2: High paging load with one TRX cells

An LA with 500 one TRX cells, the Paging Command load is calculated:4 Erlang/TRX * 500 TRXs =2000 Erlang traffic2000 E * 0.0083 Paging Commands/(sec*E) =16.6 Paging Commands/sec

16.6 * 500 cells =8300 Paging Commands/secExample 3: High paging load with 4 TRX cells An LA with 250 four TRX cells, the Paging Command loadis calculated:4 Erlang/TRX * 1000 TRXs =4000 Erlang traffic

4000 E * 0.0083 Paging Commands/(sec*E) =33.2 Paging Commands/sec33.2 * 250 cells =8300 Paging Commands/sec


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These examples can be summarized by two graphs using the high paging load traffic model. The first one (Figure 6)presents the limitations of the traffic for different number of cells in the BSC. Figure 7 show how many

TRXs per cell

126. What is a coupling system?

127. What do we mean by E1 and T1?

Ans-127

E1 carrier

It is a PCM carrier having a data rate of 2.048 Mbps. This carrier has 32 8-bit samples

packed into the basic 125usec frame.

T1 carrier

The T1 carrier consists of 24 voice channels multiplexed at a rate of 1.544 Mbps

Case Study 1

Case Study: 1 km high tower in Karachi. Discuss.

Case Study 2

Case Study: Two cells having same BCCH. Discuss.

Case Study 3

Case Study: LAC size. The whole Karachi being given one LAC VS each cell

having its own LAC.

3g topics to prepare for interview

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