QUESTION BANK IN MOBILE

COMMUNICATION ENGINEERING

BE (ETC) SEM VII – ELECTIVE II

MODULE I

1) What are the applications of Cellular Mobile Communications?2) Mention the frequency bands utilized for Cellular communications, for different cellular systems

such as : (i) AMPS, (ii) NMT Network, (iii) TACS, (iv) GSM, (v) DECT (vi) AURORA, (vii) IMTS, (viii) TETRA , (ix) PCS (8)

3) What are the advantages of the cellular approach of achieving mobile communications as (4)(iii) compared to the earlier conventional approach?

4) Draw the block diagram of a Cellular Mobile Communication system and explain. (7)5) Explain the various steps involved in placing a call from : (i) Mobile to a Landline phone, (ii)

(ii) Landline Phone to a Mobile Phone.6) Explain the following performance criteria used to evaluate performance of mobile systems : (i)

Voice Quality, (ii) Service Quality. (8)7) Why is the mobile radio environment unique as compared to other forms of wireless

communication and what are the major difficulties experienced in providing mobile service? (8)8) Explain why a hexagon has been chosen to represent a cell in Cellular layouts, even though most

of the cells are not hexagonal in shape ? (3)9) Explain the concept of “FREQUENCY REUSE” as applied to Cellular Communications. What are

the advantages of this approach ? (6)10) What are the different frequency reuse schemes? (4)11) Define and explain the importance of the following term : Frequency reuse Distance. (3)12) Why is the frequency reuse distance never violated, when allotting frequency channels to various

cells? What are the consequences of violating this distance? (6)13) What are the consequences of choosing : (i) A large Cell Reuse Pattern (Cluster Size) and 14) (ii) Small Cell Reuse Pattern (Cluster) on the following parameters : (a) Spectrum Utilization

(iii) Efficieny, (b) Carrier to Interference Ratio, (iii) No. of calls per cell, (iv) No. of channels

(iv) available per cell. (8)

15) Derive an expression relating the Co-channel interference Reduction Factor with the Carrier16) to Interference Ratio for a cellular system? (5)17) Derive an expression for the Carrier to Interference Ratio for an omnidirectional system? (5)18) What are the different types of Handoff’s encountered in Mobile Communications? (7)19) Explain how Handoff is achieved in Cellular Mobile Communication Systems. (6)20) What are the disadvantages associated with Handoff’s taking place at a very high rate? (5)21) Explain the following terms : (i) 1G Telephone Systems, (ii) 2 G Phone Systems, (iii) 2.5 G Systems, (iv) 3 G Systems. (7)22) What is Cell Splitting? (3)23) When is Cell Splitting to be resorted to? (4)24) Explain Permanent And Dynamic Splitting of Cell Sites. (6)25) Explain with the help of suitable example/s how Cell Splitting helps in increasing the traffic

handled. (6)26) What are the merits and demerits of Cell Splitting? (8)27) Explain the following terms : (i) Pico Cells, (ii) Micro Cells, (iii) Macro Cells. (7)28) Explain the importance of the following terms : (2 marks each)

i. Paging channel

ii. Mobile Identification numberiii. System identificationiv. Supervisory Audio Tone

29) What are the factors to be considered while splitting a cell? What are its disadvantages? (5)30) What are the pros and cons of having cells of different sizes? (5)31) What does a small delay spread indicate about the characteristics of the fading channel? If the

delay spread is 1 s, will two different frequencies that are 5 MHz apart, experience correlated Fading? (7)

32) What are the causes of Fast and Slow Fading. Distinguish between them. (6)33) In what way is radio propagation on land different from that in free space? (5)34) A Base station has a 900 MHz transmitter and a vehicle is moving at the speed of 50 kmph.

Compute the received carrier frequency if the vehicle is moving : (i)Directly towards the BS, (ii) Directly away from the BS, (iii) In a direction that is 60 to the direction of arrival of the transmitted signal? (8)

35) Explain the following types of reflection : (i) Specular Reflection, (ii) Diffuse Reflection (iii) Diffraction. (8)

36) A cellular system uses a 12 cell repeating pattern. There are 120 cells in the system and 37) 20,000 subscribers. Each subscriber uses the phone on an average of 30 minutes per day but38) on an average 10 of these minutes are during the peak hour. Calculate :

i. Average and Peak Traffic in Earlangs for the whole system,ii. Average and Peak Traffic in Earlangs for one cell,

iii. Assume the callers are evenly distributed.39) A vehicle travels through a cellular system at 100 kmph. How often will Handoffs occur if the cell

radius is (i) 10 km, (ii) 5 km, (iii) 500 m. (5)40) Explain the following effects encountered in Cellular Mobile Communication : (10)

i. Long Term Fading,ii. Short Term Fading,

iii. Delay Spread,iv. Coherence Bandwidth.

41) A base and a mobile are separated by 5 km. What is the propagation time for a signal Traveling between them? (1)

42) Write the full form of the following abbreviations : (7) AMPS,IMTS, TETRA,TACS,PCS,GSM,PDC

43) The traffic carried by for a 7 cell cellular system located in a busy metropolitan area is as follows.The total no. of available channels is 395. (14)

Cell Number Traffic in Erlangs

1 30.82 66.7

3 48.64 33.25 38.26 37.77 32.6

44) Assuming that (i) Each subscriber in the system generates 0.04 E of Traffic with an average call holding time of 180 seconds, (ii) System covers an area of 1200 Square km, (iii) Cells are designed for 2 % Blocking Probability. Calculate the following :

1. Number of Channels needed in Each cell,

2. Number of subscribers in each cell,3. Total Number of subscribers in the system,4. Number of calls per cell,5. Average no. of Subscribers per channel,6. Number of Calls supported by the System,7. Subscriber Density per square km,8. Call Density per Square km,9. Cell Radius in Kms assuming the area of each cell is 2.6R2

10. Channel Reuse Factor.45) During a Busy Hour, the number of calls per hour for each of the 12 cells of a cellular cluster is 2200, 1900, 4000, 1100, 1000, 1200, 1800, 2100, 2000, 1580, 1800 & 900.

Assuming that 75 % of the mobile phones in this cluster are used and during this period one call is made per phone. (7)

1. Calculate the following :2. Number of Customers in the system,3. Assuming an average holding time of 60 seconds, what is the traffic in the

cluster in Erlangs?4. Find the reuse distance if R= 5 Kms.

46) Draw a cell structure that has a frequency allocation such that there is a separation of at least 4 cells between cells that reuse the same frequency. Ensure that the total number of frequencies used are minimum. (3)47) If a total of 33 MHz of bandwidth is allocated to a particular Cellular telephone system

which uses two 25 KHz simplex channels to provide full Duplex voice and control channels calculate the number of channels available per cell if s system uses a (i) 4 cell cluster, (ii) 7 cell cluster, (iii) 12 cell cluster. If 1 MHz of the allocated spectrum is dedicated to control channels, determine how control and voice channels can be distributed for each of the three systems. (9)48) If a Signal to Interference ratio of 15 dB is required for satisfactory forward channel performance of a Cellular system, what is the frequency reuse factor and Cluster Size that should be used for maximum capacity if the path loss exponent is (i) 3 , (ii) 4. Assume that there are six co-channel cells in the first tier and all of them are there at the same distance from the mobile. (8)49) How many users can be supported for 0.5 % Blocking Probability for the following number of trunked channels in a blocked calls cleared system? (i) 1, (ii) 5, (iii) 10, (iv) 20, (v) 100. Assume that each user generated 0.1 E of traffic. (5)50) A urban area has a population of 2 million residents. Three competing mobile networks (System A, B & C) provide Cellular service in the area. System A has 394 cells with 19 channels each, system B has 98 cells with 57 channels each and system C has 49 cells each with 100 channels. Find the number of users that can be supported at 2 % Blocking rate if each user averages 2 calls per hour at an average call duration of 3 minutes. Assuming that all three trunked radio systems are operated at maximum capacity, compute the percentage

market penetration of each cellular provider. (9) 51) A certain city has an average area of 1300 km2 and is covered by a cellular system using a 7 cell reuse pattern. Each cell has a radius of 4 kms. And the city is allocated 40 MHz of spectrum with a full duplex channel bandwidth of 60 KHz. Assume a GOS of 2 % is specified and the offered traffic per user is 0.03 E, calculate : (i) No. of cells in the service area, (ii) No. of channels per cell, (iii) Traffic intensity of each channel, (iv) Maximum Carried Traffic, (v) Total No. of users that can be served for 2 % GOS, (vi) No. of mobiles per unique channel, (vii) Maximum no. of users that can be served at one time by the system.

(10)

52) A hexagonal cell with 4 cell cluster has a radius of 1.387 km. A total of 60 channels are used within the entire system. If the load per user is 0.029 E and rate of arrival of calls is 1 per hour, calculate the number of users per square kilometer this system will support if GOS is 5 %. (4)53) Consider a Cellular system with a total of 395 allocated voice channel frequencies. If the traffic is uniform with an average call holding time of 120 seconds and call blocking during Busy hour is 3 %, Calculate the following for Cell Reuse Factors equal to 4,7, 12 & 19.

1. No. of calls per cell site per hour,2. Mean Carrier to Interference Ratio.

Assume omnidirectional antennas with 6 interferers in the first tier and slope for path loss equal to 40 dB/decade.54) Define and explain the following terms :

1. Home Mobile Station (1)2. Land Station (1)3. Control Channel (2)4. Setup Channel (2)5. Forward Control Channel (1)6. Reverse Control Channel (1)7. Forward Voice Channel (1)8. Reverse Voice Channel (1)9. Access Channels (1)10. Paging Channels (1)11. Digital Colour Code (1)12. Flash Request (1)13. Signaling Tone (1)14. Paging (1)15. Paging Channel (1)16. Registration (2)17. Roamer (1)18. SAT (1)19. SID (1)20. ESN (1)21. Group Identification (2)22. Channel Spacing (1)

55) Explain the following specifications of the Mobile station. (i) Power, (ii)Modulation, (iii) Limitation on Emission, (iv) Security & Identification, (v) Supervision, (vi) Call

Processing, (vii) Various Mobile station controls on the voice channels, (viii) Signaling Format. (18)

56) Explain the following specifications of a Land Station : a. Power, (3)b. Limit on Emission, (3) c. Call Processing, (4)d. Land station support of system access, (4) e. Mobile station Control on voice channels, (4)f. Signaling Formats. (6)

57) Consider a cellular system with a one way spectrum of 12.5 MHz and channel separation of 200 KHz. There are three control channels per cell and the reuse factor is 4. Assuming an omnidirectional antenna with six interferers in the first tier and path loss slope equal to 40 dB/decade. Calculate the number of call per cell site per hour with 2 % Blocking Probability during Busy hour and an average holding time of 120 seconds. What is the Carrier to

Interference Ratio. (7) 58) Consider a cellular system with a one way spectrum of 12.5 MHz and channel seperation of 200 KHz. There are three control channels per cell and the reuse factor is 4. Assuming an omnidirectional antenna with six interferers in the first tier and path loss slope equal to 45 dB/decade. Calculate the number of call per cell site per hour with 2 % Blocking Probability during Busy hour and an average holding time of 120 seconds. What is the Carrier to Interference Ratio. (7)

59) Consider a cellular system with 395 allocated voice channels of 30 KHz each. The total available bandwidth in each direction is 12.5 MHz. The traffic is uniform with average

call holding time of 120 seconds and call blocking probability during the system Busy Hour of 2 %. Calculate : (i) Calls per cell site per hour,

(ii) Mean Carrier to Interference Ratio, For a Cell reuse factor of 4, 7 & 12 and for omnidirectional 120 and 60 systems, calculate the Call Capacity. Assume that there are 10 Mobile stations per km2 with each MS generating 0.02 E of traffic. Assume path loss slope is 40 dB/decade. (12)60) Assume that a cell named “Radio Knob” (RB) has 57 channels , each with EIRP of 32 W and cell radius of 10 km. The path loss is 40 dB per decade. The Blocking Probability is 5 %, the average call length is 2 minutes and each user averages two calls per hour. Assume that the cell has reached its maximum capacity and must be split into four new microcells to provide four times the earlier capacity in the same area. Assume 57 channels are used at the base station and the split cells. Calculate the following :

(i) What is the current capacity of RB cell? (ii) What is the radius and transmit power of the new cells? (iii) How many channels are needed in each of the new cells to maintain frequency reuse

stability in the system? (iv) If the traffic is uniformly distributed, what is the new traffic carried by each new cell?(v) Will the probability of Blocking in the new cells be below 0.1 % after the split?

MODULE II61) Explain how Area to Area prediction curves can be obtained can be obtained? What role do the 1 Km intercept and the path loss slope play in obtaining the Area to area prediction curves? (6)62) Explain why Propagation Path Loss is one of the major parameters of interest in analysis of radio wave propagation for mobile communication? (6)63) Explain what role the following factors play in while attempting to predict the propagation path loss for a particular mobile radio environment?

(i) Radio Horizon, (2)(ii) Sky Reflections (2)(iii) Signal Averaging, (2)(iv) Terminal in Motion, (2)(v) Mobile Antenna Height, (2)(vi) Effect of Surface Waves. (3)

64) Explain how propagation Loss is affected by (i) Smooth Terrain, (ii) Rough Terrain. (8) 65) Explain the use of two wave Model to explain Mobile Radio Path Loss and Antenna Height Effects? Show that the power received is given by (8) Pr = [h1 h2 / d ]2 , where h1 and h2 are the heights of the transmitting antenna and mobile antenna respectively and ‘d’ is the distance between them.

66) Explain the general classifications of areas depending on the presence of buildings and structures along the propagation path, along with terrain contours. (8) 67) How is the service areas classified , depending on the following two criteria : (i) Human made structures along the propagation path , (ii) Natural terrain. (8) 68) Explain the free space propagation Model and derive an expression for the received power. Make suitable assumptions as necessary. (8)

69) Derive an expression for the phase difference between direct path and the ground reflected path. (5)70) Derive an expression for the received power and the phase difference between between two fixed stations over flat open land. Assume that the height of the transmitting and receiving antenna are h1 and h2 respectively and are located at a height H1 and H2 above the ground level. (8)71) Derive an expression for the received power and the phase difference between between two fixed stations over water . Assume that the height of the transmitting and receiving antenna are h1 and h2 respectively and are located at a height H1 and H2 above the ground level. (7)72)What is the effect of foliage on Cellular signal transmission? 73)Explain what role does Duct propagation play in reception of the mobile signal over large distances. What are its causes? (5)74) With the help of suitable examples, explain the procedure for obtaining the effective height of an antenna. Explain how path loss can be obtained from a point to pint prediction Model. (10) 75) What are the merits of the Point to Point Model? (4)76) Derive an expression for the transfer function of a Propagation Model for Mobile to Mobile

Propagation? Obtain the statistical model for mobile to mobile channel. (8) 77) What are the different ways in which a signal can propagate over long distances? (5) 78) Explain what is the effect of diffraction loss in an obstructive environment on path loss? (6)

79) Explain the Lee Point to Point Model and mention the general formula for the following Conditions : (i) Direct wave case, (ii) Shadow Case, (iii) Over the water condition. Form the model for obstructive path, non-obstructive path and land to mobile over water. (8)

80) What is the effect of change of (i) cell site antenna height, (ii) Change in location of antenna height, (iii) Change of effective antenna height with change of location of mobile unit, when the mobile is driven up a positive slope (up to a high spot) or driven down a hill. (8)81) Explain how “HOLES” in cell signal coverage area are tackled? (6)82) Derive an expression for the following : (i) Spatial Time Co-relation function for Mobile to Mobile Model, (ii) Power Spectrum of the complex envelope for Mobile to Mobile Propagation . (7)83) What are the factors to be considered in choosing location of cell site antenna ? (6)84) What are the different types of cell site and mobile antennas? (8)85) Explain what is meant by Diversity Reception? What are the different types? What are its advantages in Cellular communication? (8) 86) What is the minimum separation needed for cell site receiving antenna and the explain the necessity of the separation. (5)87) Mention and explain the different Sum and Difference radiation Patterns for antennas used in mobile communication. (8) 88) Why is the antenna pattern different in free space and in an mobile environment? (5)89) Distinguish between horizontally and vertically oriented space diversity antennas? (4)90) Explain the advantages and disadvantages of the two ray ground reflection model in analysis of path loss? (8)

91) In the following cases, indicate if the two ray ground reflection model can be applied or not applied, with suitable justification.

(i) ht = 35 m, hr = 3 m, d = 250 m,(ii) ht = 30 m, hr = 1.5 m, d = 450 m (4)

92) What insight does the two ray model provide about large scale path loss that was disregarded for macro cells (very large cells) ? (3) 93) Explain “Antenna Pattern Ripple Effect” (8)

94) An improvement in signal gain can be obtained by raising the height of the base station antenna. Assuming that the received radio signal is – 110 dB and height of the base station antenna is 30 m, calculate how much higher should the base station antenna be raised to obtain an increase from –110 to 100 dBm in received power? (8)95) Consider a mobile communication link where reception over a distance of 10 km is satisfactory

with a base station antenna height of 50 m and mobile antenna height of 2 m. If the base station antenna height is lowered to 10 m, what will be the effect of reception in terms of distance? If the distance is the same i.e 10 km, how high must the mobile antenna height be raised to ensure satisfactory reception? (8)

96) The antenna height at the cell site is 30 m and at the mobile unit is 3 m and the distance between them is 8 km. Calculate the phase difference between direct and reflected wave at the mobile terminal. (3)

97) In a mobile radio environment, the average cell site antenna height is 50 m, the mobile antenna height is 3 m, and the communication path length is 5 km. Calculate the following :

a. Incident angle,b. The elevation angle at the antenna of the mobile unit,c. The elevation angle at the location of the mobile unit. (6)

97) If a transmitter produces 50 W of power, express the transmit power in units of dBm and dBW. If 50 W is applied to unity gain antenna with a 900 MHz carrier, find the received power in dBm and dBW at a free space distance of 100 m and 10 km from the antenna. Assume unity gain for the receiver antenna. (6)

98) A mobile is located 5 km away from from a base station and uses vertical /4 monopole antenna with a gain of 2.55 dB to receive cellular radio signals. The E field at a distance of 1 km from the transmitter is measured to be 10–3 W V/m. The carrier frequency used is 900 MHz. Calculate the following : (a) Length and effective aperture of the receiving antenna, (b) received power at the mobile unit using the two ray Ground Reflection Model, assuming that the height of the transmitting antenna is 50 m and receiving antenna is 1.5 m above the ground. (8)99) Let the distance between two fixed station be 30 Kms. The effective antenna height at one end

Is 150 m above sea level. Find the effective height above the seal level at the other end so that the received power always meets the condition Pr < Po at 850 MHz. If Pr > Po is the condition to be satisfied, find the effective antenna height. (8)

100) In a two ray ground reflected model, assume that must be kept below 6.261 radians for phase cancellation reasons. Assuming a receiver height of 2 m, given a requirement that incident angle should be less than 5, what are the minimum allowed values for Transmitter Receiver transmit separation distance and the height of the transmitter antenna if the carrier frequency is 900 MHz.

MODULE III 101) Explain what is meant by Diversity Reception? What are the different types? What are its advantages in Cellular communication? (8) 102) What role does “SECTORIZATION” of a cell area have on the performance of a Cellular

system? Explain what is Sectorization? (4) 103) What are the causes of C0-channel Interference in Cellular Mobile communication? Why is this effect the most pre-dominant in Cellular communication? What are the limitations caused by this interference in cellular communications? (9)

104) Explain how Co-channel Interference can be measured at (i) Mobile Unit & (ii) Cell site. (10)105) What is the effect of reduction of cell site antenna height on the antenna gain when the antenna

is located in : (i) High Hill or a high spot, (ii) In a valley, (iii) In a forested area. 106) Explain how Co-channel Interference can be reduced by means of notch in the Tilted antenna

pattern. (8)107)What is the effect of down tilting the antenna on the coverage area? When is this resorted to?

What are the different methods of downtilting the antenna? (9)108) Explain how the use of Sectorization helps in reducing the Co-channel Interference problem. (6)109) Explain the difference types of Interference encountered in Cellular Communication. (10)110) Explain how downtilting the antenna helps in reducing Cochannel Interference. (8)111)What are the precautions to be taken while down tilting the antennas? (4)112) Explain how Interference at the cell site can be reduced by the use of parasitic Elements,

so as to create a pattern in the desired direction.113) What is the Umbrella pattern Effect? What are its benefits? (8)114) Macroscopic Diversity techniques can be used successfully when two transmitting antennas are

cited at two different locations. What is the rationale for using microscopic diversity techniques for two transmitting antennas located at the same site and separated between proper spacing between antenna elements. (8)

115) Consider the case where a base station is simultaneously serving two mobile units. One mobile unit is 0.1 km away from the base station and the other is 15 km distant. Calculate the near end to far end interference ratio. If the required Signal to Interference ratio is 15 dB, how much is the adjacent channel frequency separation ? (5)

116) Explain the cause of the following : Near End Far End Interference with suitable sketches in

i. One Cell, ii. Two system cells.

117)What are the method/s used to avoid Near-End-far-End Interference? Derive an expression for the minimum Frequency Band separation needed to overcome the above effect. (8)

118) Explain the following Interference encountered in Cellular Mobile Communication: (i) Cochannel Interference, (ii) Adjacent Channel Interference, (iii) Intermodulation Interference, (iv) Intersymbol Interference. (18)

119)Explain how the effects of Signal Coverage and Interference can be tackled by : (i) Decreasing Power, (ii) Decreasing antenna Height, (iii) Beam Tilting, (iv) Proper Cell site location (12)

120) What is the interference contributed by Channel combiner? What is a frequency agile and a ring channel combiner? (9)

121) What are the major functions of a SAT tone? (4)122) What are the characteristics of a SAT tone? (3)123) Assuming that a SAT tone is a sine signal, derive an expression for the modulated carrier. Draw

the FM phasor diagram. (5)124) What are the characteristics of a SAT Tone Generator? (4)125) Consider a situation where the base station receiver is capable of providing 100 dB of isolation

between channels is receiving a signal from a mobile 1 km away. What is the maximum distance that a second mobile can transmit its signal without causing interference without causing interference with the signal from the near end mobile unit. (6)

126)Why is it essential for the MTSO to control the transmitted power level at both the cell site and the mobile units? (4)

127)What is Cross-Talk? What are its causes in Mobile Communication? Explain the following types of Cross-Talk :

1. Near End Mobile Unit Cross Talk,2. Close in Mobile Unit Cross Talk3. Co-channel Cross Talk,4. Channel Combiner Cross Talk,5. Telephone Line Cross Talk.

128)Explain what effect does reducing the height of the antenna have on various types of interference encountered in Cellular Communication ? (6)

129)Explain how interference between two systems (Duopoly Market) on account of IM products be avoided? Explain what are the causes and effects of interference due to Intermodulation

Products. (5)130) What are the coordinating measures that have to be taken by two cellular service providers operating it the same frequency band between two adjacent cities or areas to prevent interference between each other? What are the different methods used ? (6)131) What are the two types of Interference that can occur between UHF television and 850 MHz cellular mobile phone. Explain the two effects. What result does third order intermodulating give in the two cases of interfering UHF TV Receivers. (12)130) When can TV channels in the UHF region interference with Mobile Communication ? (6)131) Explain the interference encountered by by cellular mobile receivers UHF TV transmitters. (7)132) Explain UHF TV Interference with respect to the following cases :

(i) When the mobile transmitter is located near a TV receiver,(ii) When the cell site transmitter is located near a TV receiver. (5)

133)What is the necessity of Channel Allocation/Assignment in Cellular Mobile Communication? (3)134) Explain the Long Distance Interference encountered due to duct propagation overwater path

and overland path? (6)135) What are the causes of Duct Propagation? (5)136) Why is Duct propagation predominant near water bodies? (3)137) Mention and explain the following channel allocation schemes used :

(i) Fixed Channel Allocation Schemes, (ii) Dynamic Channel Allocation Schemes, (iii) Hybrid Channel Allocation Schemes. (16)

138) What are the borrowing schemes used in Fixed Channel Allocation? (8)139) What is Dynamic Channel allocation? What are the different types?140)What are advantages and disadvantages of Dynamic Channel allocation over Fixed

Channel allocation? (12)141) Explain and distinguish between fixed and Dynamic Channel allocation. (8)142) Explain what is meant by Hybrid Channel Allocation? What are its merits and demerits? (8)143) Explain what is meant by Flexible Channel Allocation. (4)144) What precautions have to be taken to prevent cochannel interference between cells, when

borrowing channels from other cells. (9)145)Mention any two distinguishing points between Setup channels and Voice Channels. (3)146)Explain the different channel borrowing schemes used in Cellular Communication. (6) 147) Distinguish between Fixed and Dynamic Channel Allocation. (6 points) (6) 148)Explain the following channel allocation strategies in specialized systems: (16)

i. Reuse Partitioning Based Channel Allocation, ii. Underlay Overlay Arrangement.

iii. Channel allocation in one dimensional system (like a highway),iv. Overlapped Cells based Channel Allocation Schemes.

149) Draw the block diagram of a Analog system for cellular communication and explain. (6)

150) A cellular system with omni directional antennas employs a cluster of size 7. The cell at the center of the cluster has a lot more traffic than others and needs to borrow some channels from adjacent cells. Explain the strategy to be used to determine the donor cell within the cluster and outside the cluster. (6)

151) A cellular system with 7 cell cluster has the following average no. of calls at a given time as shown in the table given below. If the system is assigned 49 channels, how would you distribute the channels if (i) Static Channel Allocation is used, (ii) Simple Borrowing scheme is used, (iii) A Dynamic Channel Allocation scheme is used

Cell Number Avg. no of calls/unit time1 9002 20003 25004 11005 12006 18007 1000

152) Explain how different channel allocation strategies maintain the frequency reuse distance, while burrowing channels from other cells. Illustrate with the aid of suitable examples and diagrams. (12)

153) Explain Forcible Borrowing Channel Assignment. (6) 154) Explain the following specialized features incorporated to handle Cellular Traffic (12)

i. Underlay Overlay arrangement, ii. Directed Call Retry,

iii. Hybrid systems using High & Low Cell sites, iv. Intersystem Handoffs.

155)Explain the different MTSO Interconnections to wire line networks and Cell site. (5)156) Explain the use of Enhancers to cover HOLES in the cellular coverage areas? 157) Mention and explain the different types of Enhancers used. (8)158) What are the different switching techniques used in mobile communication? (6)159) Draw the block diagram of Analog switching system for Cellular Mobile Communication

and explain the function of the various blocks. (7)160) Draw the block diagram of a Cellular Digital Switching system showing the interconnection

between MTSO, Mobile and Cell site. (9)161) With the help of suitable diagram, explain the four basic types of Intersystem Handoff’s. (8)162) Explain the MTSO Clearing House Concept. (4)163) Explain how MTSO is interconnected to (i) Wire line networks & (ii) Cell site. (8)164) Explain the following type of MTSO Interconnections : (i) Type 1, (ii) Type 2A, (iii) Type 2B,

(iv) Interconnection to a cell site .165) How are MTSO’s interconnected? (6)166) Consider a cellular system with 100 sites, a frequency reuse factor of 7, and 500 overall two way

Channels : Calculate the following :(i) Number of channels per cell,(ii) Total no. of channels available to the service provider,(iii) Minimum C/I Ratio of the system in dB.(iv) To expand the network, we create an underlay – overlay system, where the new system

uses a frequency factor of K=3. Calculate the number of cells assigned to the inner and outer cells to keep a uniform traffic density over the entire coverage area. (9)

MODULE IV167) How are Multiple Access Radio Protocols classified? (5)168)What are the drawbacks of CSMA-CD in Wireless communication? (4)169) Explain the following effects : (i) Hidden & Exposed terminals, (ii) Near & far Terminals (8)170)Explain how the following methods are used in Wireless Communication :

(i) SDMA, (3)(ii) FDMA (4)(iii) TDMA, (4)(iv) Fixed TDM. (3)

171) Explain what is ALOHA? Compare Classical & Slotted ALOHA. (8)172) How does Slotted ALOHA improve throughput as compared with pure ALOHA? (6)173) Explain CSMA. How is CSMA classified? (6)174) Explain the Collision mechanism in CSMA. (4)175) Distinguish between Persistent & Non-persistent CSMA. (6) 176) Explain the following types of CSMA Protocols: (7)

(ii) 1 persistent CSMA, (iii) p persistent CSMA,

177) Explain CSMA/CA. (4) 178) What are the merits and demerits of contention based protocols? (6) 179) What are the merits and demerits of non contention based protocols? (6) 180) Explain the following methods :

(i) DAMA, (4)(ii) PRMA, (4)(iii) Reservation TDMA, (3)(iv) MACA, (5)(v) Polling, (4)(vi) ISMA, (5)(vii) SAMA. (5)

181) What are the advantages of CDMA over other methods? (6) 182) What is the main physical reason for the failure of many MAC schemes used successfully in wired networks in wireless networks? (6) 183) Considering the problem of Hidden and exposed terminals, what happens in the case of such terminals if ALOHA, Slotted ALOHA, reservation ALOHA or MACA is used? (10) 184) How does the near far effect influence TDMA systems? What are the countermeasures in TDMA systems? (7) 185) How does the near far effect influence CDMA systems? What are the countermeasures in CDMA systems? (7) 186) What is the basic pre-requisite for applying FDMA? How does this factor increase complexity compared to TDMA systems? (8) 187) What are the advantages of Fixed TDMA pattern as compared to random demand driven TDMA? Compare the efficiency in the case of several connections with fixed data rates or in the case of varying data rates. (7) 188) Explain Interference in space, time, frequency and code domain. What are the countermeasures in SDMA, TDMA, FDMA & CDMA systems respectively. (8) 189) What are the merits and demerits of Reservation schemes? (6) 190) What are the advantages of CDMA as compared to other Multiple Access strategies in Cellular Communication? (4) 191) Compare TDMA, FDMA & CDMA. (8) 192) Ina ALOHA network, how does the terminal learn that its packet has collided? (4)

193) What is the difficulty of implementing CSMA/CD in a wireless environment? (4) 194) Explain CDMA. What are its limitations? (8) 195) Explain the difference between carrier sensing mechanism between wireless and wired channels. (6) 196) What is the Capture Effect and how does it impact the performance of random access method? (6) 197) Mention the frequency band in which a GSM-900 & DCS-1800 system operates. (6) 198) Explain what is meant by GSM Public Land Mobile Network (PLMN). What are its objectives? What are its subsystems? (10) 199) Explain the following GSM subsystem Entities : (

(i) Mobile Station showing the GSM Reference Model, Classification of MS based on power, Types of MS’s and explain International Mobile Equipment identity (IMEI), Temporary Mobile Subscriber identity (TMSI), International Mobile Subscriber identity (IMSI), SIM (Subscriber Identity Module) (10)

(ii) Base Station Subsystem, (8)(iii) Operation & Maintenance Subsystem (OMSS). (6)

200) Explain the following GSM Radio Interfaces : (12)(i) Mobile Station (MS) to Base transceiver Interface (BTS),(ii) BTS to BSC,(iii) BSC to MSC,(iv) Interfaces between other GSM Entities.

201) What are the different types of services offered by GSM ? (6) 202) Name some of the key features of GSM, DECT & TETRA systems. Which features do the systems have in commaon? What are the advantages and disadvantages of each system? (12) 203) Name the main elements of GSM system architecture and describe their functions. What are the advantages of specifying not only the radio interface but also all internal interfaces of the GSM system? (12) 204) Describe the functions of MS and SIM. Why does the GSM separate MS and SIM? How and where is user related data represented/stored in the GSM system? How is the user data protected from unauthorized access, especially at the air interface? (12) 205) How can the position of MS be localized? (6) 206) Explain the VLR/HLR database approach used in GSM. How does this approach limit the scalability among users, especially moving users? (8) 207) What are the limitations of GSM cell in terms of diameter and capacity for traditional GSM? How can the capacity be increased? (8) 208) What are the multiplexing schemes used in GSM? (6) 209) How is synchronization achieved in GSM? Who is responsible for Synchronization? Why is it very important? (8) 210) How is localization, location update, roaming, etc done in GSM and reflected in the databases? What are the typical roaming scenarios? (10) 211) Why are so many different identifiers/addresses needed in GSM? Distinguish between user related and system related identifiers. (8) 212) Explain Traffic Channels (TCH) & Control Channels (CCH) in GSM. What are the different types of CCH in GSM? (10) 213) Explain the following Control Channels in GSM : (i) BCCH, (ii) CCCH, (iii) DCCH. (9) 214) What are different protocols used in GSM? Explain the protocol architecture in GSM (12) 215) Explain how Handover takes place in GSM. What are the problems associated with Handover in GSM? (9) 216) Explain the different types of Handover encountered in GSM. (10) 217) What are the functions of authentication and encryption used in GSM? How is system security maintained? (10)

218) Explain the three algorithms used for providing security in GSM I.e A3, A5 & A8. (4) 219) How is subscriber authentication and data Encryption done in GSM? (8) 220) Explain what is DECT? What is the frequency of operation of DECT? (5) 221) Explain the DECT system architecture and reference model, with the help of a suitable diagram. (8) 222) Explain the DECT protocol architecture. (10) 223) What is TERTA? 224) Who are the typical users of TETRA? Why is TETRA cheaper as compared to other systems. (5) 225) Distinguish between TETRA and other systems. (8) 226) What are typical data rated in DECT? How are they achieved considering the TDMA frames? (6) 227) What are the multiplexing schemes used in DECT. (6) 228) Compare the complexity of DECT with GSM. (8)