Model1 Answer Key

8/9/2019 Model1 Answer Key

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St.JOSEPHS COLLEGE OF ENGINEERING, CHENNAI-119.MODEL EXAMINATION-I

set-1

Subject : Mobile Computing Code : IT1402Branch : IT Semester : VII

Duration : 3Hours Max marks : 100

Part - A (10 * 2 = 20)

1. Define User mobility and Device portability.Two aspects of mobility: user mobility: users communicate (wireless) anytime,anywhere, with anyone device portability: devices can be connected anytime,anywhere to the network.

2. Define Modulation and Demodulation.

modulation is the process of varying one or more properties of a high frequency periodic waveform , called the carrier signal, with respect to a modulating signal. Theinverse of the effect of modulation , or applying a signal to a carrier . A radiotransmitter applies modulation to a carrier wave and the receiver appliesdemodulation to it to recover the message.

3. Define SDM.In this SDM frequency will be divided and it will be allocated for all the channels toavoid interference.

4. What are the main benefits of spread spectrum system?S pread the narrow band signal into a broad band signal using a special code protection against narrow band interference

5. Differentiate Hard and Soft handover.Hard Handover:Hard handover means that all the old radio links in the UE are removed before thenew radio links are established. Hard handover can be seamless or non-seamless.Seamless hard handover means that the handover is not perceptible to the user. In

practice a handover that requires a change of the carrier frequency (inter-frequencyhandover) is always performed as hard handover.

Soft Handover:Soft handover means that the radio links are added and removed in a way that the UEalways keeps at least one radio link to the UTRAN. Soft handover is performed bymeans of macro diversity, which refers to the condition that several radio links areactive at the same time. Normally soft handover can be used when cells operated onthe same frequency are changed.

6. State the objective of UMTS.
http://en.wikipedia.org/wiki/Waveformhttp://en.wiktionary.org/wiki/inversehttp://en.wiktionary.org/wiki/modulationhttp://en.wiktionary.org/wiki/modulationhttp://en.wiktionary.org/wiki/modulationhttp://en.wiktionary.org/wiki/signalhttp://en.wiktionary.org/wiki/signalhttp://en.wiktionary.org/wiki/signalhttp://en.wiktionary.org/wiki/carrierhttp://en.wiktionary.org/wiki/carrierhttp://en.wikipedia.org/wiki/Waveformhttp://en.wiktionary.org/wiki/inversehttp://en.wiktionary.org/wiki/modulationhttp://en.wiktionary.org/wiki/signalhttp://en.wiktionary.org/wiki/carrier


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UTRA (was: UMTS, now: Universal Terrestrial Radio Access)enhancements of GSMEDGE (Enhanced Data rates for GSM Evolution): GSM up to384 kbit/sCAMEL (Customized Application for Mobile Enhanced Logic)VHE(virtual Home Environment) fits into GMM (Global Multimedia Mobility) initiativefrom ETSI.

7. What is dwell time?The time spend on a channel with a certain frequency is called dwell time.

8. Define Inclination angle of satellite.The Inclination angle is defined as the angle between the equatorial plane and the

plane described by the satellite orbit

9. Differentiate symmetrical and asymmetrical communication system.Symmetrical communication systems offers the same transmission capabilities in

both communication directions Asymmetrical communication systems areunidirectional broadcast system where typically a high bandwidth data stream existsfrom one sender to many receivers.

10. Draw the Object structure of MOT.Header core : size of header and body, content type ,Header extension: handlinginformation, e.g., repetition distance, segmentation, Priority information supportscaching mechanisms Body: arbitrary data

7 byte

header core

header extension

body


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Part - B (5 * 16 = 80) 11. a) Explain in detail about FHSS and DSSS. (16)

FHSS (Frequency Hopping Spread Spectrum) I Discrete changes of carrier frequencysequence of frequency changes determined via pseudo random number sequence TwoversionsFast Hopping: several frequencies per user bit Slow Hopping: several user bits per frequency Advantagesfrequency selective fading and interference limited to short periodsimple implementation uses only small portion of spectrum at any time Disadvantagesnot asrobust as DSSS simpler to detectDiagram for FHSS with explanantion and transmitter and receiver diagram with explanationDSSS (Direct Sequence Spread Spectrum) I XOR of the signal with pseudo-random number (chipping sequence)many chips per bit (e.g., 128) result in higher bandwidth of the signalAdvantagesreduces frequency selective fading in cellular networks base stations can use thesame frequency range several base stations can detect and recover the signal soft handover Disadvantagesprecise power control necessary and diagram with explanantion

(OR)b) Compare SDMA,FDMA, TDMA and CDMA (16)

compare by using ideas,terminals ,signal separation,advantages,disadvantages,comments

12. a) Explain the Hidden and Exposed terminal problem and Near/ Far effects (16) Carrier Sense M ultiple Access with C ollision Detection

send as soon as the medium is free, listen into the medium if a collision occurs (legacymethod in IEEE 802.3) Problems in wireless networkssignal strength decreases

proportional to the square of the distance the sender would apply CS and CD, but thecollisions happen at the receiver it might be the case that a sender cannot hear thecollision, i.e., CD does not work furthermore, CS might not work if, e.g., a terminal ishidden example for hidden and exposed terminal problem and also for near /far effects.

(OR)b) Explain in detail about MTC and MOC. (16)

MTC

1: calling a GSM subscriber 2: forwarding call to GMSC3: signal call setup to HLR 4, 5: request MSRN from VLR 6: forward responsible MSC to GMSC7: forward call to current MSC8, 9: get current status of MS10, 11: paging of MS12, 13: MS answers14, 15: security checks16, 17: set up connection explain with diagram

MOC1, 2: connection request3, 4: security check 5-8: check resources (free circuit)9-10: set up call with diagram


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13 a) Explain in detail about GSM system architecture. (16)Architecture refer pg.no 101 schiller Moblie communication

(OR)

b) Explain in detail about UMTS system architecture and radio interface. (16)refer pg.no 142

14. a) Explain in detail about DAB. (16)Digital Video Broadcasting

1991 foundation of the ELG (European Launching Group)goal: development of digital television in Europe

1993 renaming into DVB (Digital Video Broadcasting)goal: introduction of digital television based on

satellite transmissioncable network technologylater also terrestrial transmission

DVB Container DVB transmits MPEG-2 container

high flexibility for the transmission of digital datano restrictions regarding the type of informationDVB Service Information specifies the content of a container NIT (Network Information Table): lists the services of a provider,

contains additional information for set-top boxesSDT (Service Description Table): list of names and parameters for each

service within a MPEG multiplex channelEIT (Event Information Table): status information about the current

transmission, additional information for set-top boxesTDT (Time and Date Table): Update information for set-top boxes

Asymmetric data exchangedownlink: DVB receiver, data rate per user 6-38 Mbit/sreturn channel from user to service provider: e.g., modem with 33

kbit/s, ISDN with 64 kbit/s, DSL with several 100 kbit/s etc. Convergence of broadcasting andmobile comm. Definition of interaction channels Interacting/controlling broadcast via GSM, UMTS, DECT, PSTN, Example: mobile Internet services using IP over GSM/GPRS or UMTS as interaction channel for DAB/DVB

(OR)b) Explain the GPRS architecture with reference model (16)

refer pg.no 12815. a).i. Draw and Explain the UMTS core network together with 3G RNS and2G BSS. (10)

Refer.pg.no 152ii. Explain the basic architecture of the UTRAN network. ( 6)

refer pg.no 149

(OR) b) Compare LEO,GEO and MEO (16)

compare by various parameter


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St.JOSEPHS COLLEGE OF ENGINEERING, CHENNAI-119.MODEL EXAMINATION-I

set-2

Subject : Mobile Computing Code : IT1402Branch : IT Semester : VIIDuration : 3Hours Max marks : 100

Part - A (10 * 2 = 20)

1. Define TDD and FDD.Assigning different slots for uplink and downlink using the same frequency is called timedivision duplex and the two directions mobile station to base station and vice versa arenow separated using different frequencies.This scheme is then called frequency divisionduplex.

2. Define transmission ,detection and interference range.Transmission rangecommunication possible low error rate ,Detection range detection of the signal possible no communication possible ,Interference range signal may not bedetected signal adds to the background noise.

3. What is called DAMA?DAMA also called reservation aloha , aloha scheme can try to reserve future slots.

4. Mention the disadvantages of smaller cells.Coverage, interference

5. What are the contents of GPRS context?

GSN (GPRS Support Nodes): GGSN and SGSNGGSN (Gateway GSN)interworking unit between GPRS and PDN (Packet Data Network)SGSN (Serving GSN)supports the MS (location, billing, security) GR (GPRSRegister)user addresses

6. Mention the types of handover in UMTS. Intra node B, intra RNC Inter node B,intra RNC Inter RNC Inter MSC Inter system

7. Mention the contents of DVB service information. NIT (Network Information Table): lists the services of a provider,contains

additional information for set-top boxes SDT (Service Description Table): list of names and parameters for each service

within a MPEG multiplex channel EIT (Event Information Table): status information about the current transmission,

additional information for set-top boxes


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TDT (Time and Date Table): Update information for set-top boxes8. Define perigee and footprint.

If the satellite does not have a circular orbit, the closest point to the earth is called the perigee. The foot-print can be defined as the area on earth where the signals of thesatellite can be received.

9. List the application of Satellite. Weather forecasting Radio and TV broadcast satellites

Military satellites Satellities for navigation.

10. Define Data streamingStreaming oriented ,asynchronous,synchronized (synchronization with other stream e.gaudio/video possible) or synchronous (data and clock regeneration at receiver possible)end to end delivery of data.

Part - B (5 * 16 = 80)

o11. a) Explain in detail about the spread spectrum techniques. (16)

Spread spectrum technologyProblem of radio transmission: frequency dependent fading can wipe out narrow bandsignals for duration of the interferenceSolution: spread the narrow band signal into a broad band signal using a specialcodeprotection against narrow band interference Side effects:coexistence of severalsignals without dynamic coordination tap-proof Alternatives: Direct Sequence,Frequency Hopping explain FHSS and DSSS

(OR)b) Explain TDMA in detail. (16)

TDD/TDMA -general scheme, Aloha/slotted aloha, DAMA -Demand Assigned MultipleAccess, Access method DAMA: Explicit Reservation, Access method DAMA: PRMAAccess method DAMA: Reservation-TDMA

12. a) Explain in detail about the various modulation schemes. (16)Give the explanation with diagram for ASK,PSK,FSK,MSK,BPSK,QPSK

(OR)b) Explain in detail about the MAC and provide the solutions for

Hidden and Exposed terminal problem. (16)Explain the problem and give the solution by using RTS and CTS

13 a) Explain in detail about GPRS system and protocol reference model. (16)

refer pg.no 128

(OR)b) Explain in detail about DECT system architecture. (16)

refer pg.no 130

14. a) Explain in detail about digital video broadcasting. (16)Answer given in set 1


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(OR)b) Explain in detail about digital audio broadcasting (16)

Introduction, DAB transport mechanism,Transmission frames,sender and receiver diagram with explanantions,goal amd mechanisms,bit rate management,reconfigurationand example,MOT

15. a) Explain in detail about routing and localization in satellite systems. (16)Different links with diagram and SUMR in satellite systems

(OR) b) Explain in detail about the different types handover in satellite systems

and different types of satellite orbits (16)different types of orbits LEO,MEO,GEO,HEO and handovers intersatellite ,intrasatellite,gateway handover and intersystem handover.

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Model1 Answer Key