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Note for Mobile Computing - MC By Ramyaa Shenbagaraman

  • Mobile Computing - MC
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DEPARTMENT OF MCA MC7503 MOBILE COMPUTING III YEAR UNIT I 1. List out the characteristics of communication devices? (Nov/Dec -2011) Fixed and wired Mobile and wired Fixed and wireless Mobile and wireless 2. What is Line-of-sight? (Nov/Dec -2011) A straight line exists between a sender and a receiver it is called line-of-sight. 3. What is guard space? Guard spaces are needed to avoid frequency band overlapping is also called channel interference. 4. What is the 3 different basic schemes analog modulation? Amplitude modulation Frequency modulation Phase modulation 5. What is multipath propagation? Multipath propagation is the direct from a sender to a receiver the propagation effects mentioned in the previous section lead to one of the most severe radio channel impairments 6. What is hopping sequence? Transmitter and receiver stay on one of these channels FDM and TDM. The pattern of channel usage is called the hopping sequence, 7. What are the advantages of cellular systems? The advantages of cellular systems are, Higher capacity Less transmission power Local interface only Robustness 8. What is borrowing channel allocation and fixed channel allocation? Cells with more traffic care dynamically allotted more frequencies. This scheme is known as borrowing channel allocation, while the first fixed scheme is called fixed Channel allocation. 9. What is modulation? Modulation is the process of varying one or more properties of a high-frequency periodic wave form, called the carrier signal, with respect to a modulating signal (which typically contains information to be transmitted). 10. What is multiplexing? Multiplexing is a fundamental mechanism in communication system. Multiplexing describes how several users can share a medium with minimum or no interference. 11. What are the 3 fundamental propagation behaviors depending on their frequency? Ground Wave Sky Wave Line of Sight. 12. What are the disadvantages of cellular systems? The advantages of cellular systems are, Infrastructure needed Handover needed Frequency planning

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13. What is digital sense multiple access? The scheme which is used for the packet data transmission service Cellular Digital Packet Domain the AMPS mobile phone system is also known as digital sense multiple access (DSMA). 14. What is OVSF? Using orthogonal codes separates the different data streams of a sender UMT Successor called Orthogonal Variable Spreading factor codes (OVSF). 15. Specify the steps perform during the search for a cell after power on? Primary synchronization Secondary synchronization Identification of the scrambling code 16. Why baseband signals cannot be directly transmitted in a wireless system? Antennas must be the order of magnitude of the signal’s wavelength. Medium Characteristics. 17. Define beacon? Beacon frame is used to convey timing information within a BSS. It contains a time stamp and other management information used for power management and roaming. The timestamp is used by the node to adjust its local clock. 18. What are the handovers in hiperLAN? The handovers in hiperLAN are Sector handover Radio handover Network handover 19. Distinguish infrastructure and adhocnet works? Infrastructure networks Adhoc networks Communication takes place only between a wireless node and an access point Communication takes place only between two wireless nodes The wireless node is simple as The wireless node is complex Functionality is based on the access point Can forward messages across Networks Can forward messages only with in the specified range 20. Why is physical layer in IEEE802.11 subdivided? What are its sub layers? The physical layer in IEEE802.11 is subdivided because a sub layer has to be dependent on the upper layers (architecture dependent) and the other has to be medium dependent. The two sublayers are namely, Physical layer convergence protocol Physical medium dependent sub layer 21. Define MSDU lifetime? MSDU lifetime is used to provide time bounded service which specifies the maximum time that can elapse between sending and receiving a MSDU. It has arrange of 0-16000 ms. 22. What are the elements in core protocols in Bluetooth? The elements in core protocols in Bluetooth are, Radio Baseband Link Manager Protocol

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Logical Link control and adaptation protocol Service discovery protocol. 23. What are the advantages and disadvantages of FHSS? (Dec 2009) Advantages • frequency selective fading and interference limited to short period • simple implementation • uses only small portion of spectrum at any time Disadvantages  not as robust as DSSS   simpler to detect  24) What are the categories of Mobile services? • Bearer services • Tele services • Supplementary services 25) What are the services provided by supplementary services? • User identification • Call redirection • Call forwarding • Closed user groups • Multiparty Communication 26) What are the four types of handover available in GSM? 1. Intracell Handover 2. Intercell Intra BSC Handover 3. Inter BSC Intra MSC handover 4. Inter MSC Handover 27). What is meant by GPRS? The General Packet Radio Service provides packet mode transfer for applications that exhibit traffic patterns such as frequent transmission of small volumes. 28) What are subsystems in GSM system? • Radio subsystem(RSS) • Network & Switching subsystem(NSS) • Operation subsystem(OSS) 29) What are the information in SIM? • card type, serial no, list of subscribed services • Personal Identity Number(PIN) • Pin Unlocking Key(PUK) • An Authentication Key (KI) 30) Define Normal Burst? The frame used for normal data transmission with in a time slot is called Normal Burst. 31) What are the logical channels in GSM? • Traffic channel (TCH) • Control channel (CCH) 32) what is meant by beacon? A beacon contains a timestamp and other management information used for power management and roaming. e.g., identification of the base station subsystem(BSS) 33).What are the reasons for delays in GSM for packet data traffic. 1. Different data rates provided by traffic channels are low.

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2. Authentication and encryption also makes the packet data transmission low. 3. Various interferences and noises from the channel also causes delay. 34).List out disadvantages of cellular system. 1. Self–jamming 2. Near–far problem 3. Soft Handoff 35).How much of the original GSM network does GPRS need. Which elements of the network perform the data transfer. GPRS is an enhancement of SM. It uses same physical channel as GSM and only new logical GPRS radio channels are defined. Elements needed for data transfer: 1. GPRS support nodes(GSN) 2. Gateway GPRS Support Node(GGSN) 3. Servicing GPRS Support Node(SGSN) 4. GPRS Register(GR) 36).Explain the various entities available in radio subsystem 1. BSS: It performs all function necessary to maintain radio connections to a MS. 2. BTS: It comprises all radio equipments 3. BSC: It basically manages BTSs. 4. MS: It comprises all user equipment and software needed for communication with in a GSM network. 37). Explain the various entities available in NSS. NSS consist of following switches and databases. 1. MSC: They setup connection to other MSCs and to BSCs via A interface. 2. HLR: It is the most important database which stores all user relevant information. 3. VLR: It is a dynamic database which stores all important information needed for MS Users currently in the that is associated to MSC. 38). Explain the various systems available in Operation Subsystem. Operating sub system: It contains necessary functions for network operation and maintenance. 1. OMC: It manages traffic monitoring, accounting and billing 2. AuC : It is used to protect user identity and data transmission. 3. EIR : Its to res all device identifications registered for this network. 39). Explain the various control channels available in GSM. 1. BCCH: ABTS uses this channel to signal information to all MSs with in a cell. 2. CCCH: All information regarding connection setup between MS and BS are exchanged via CCCH. 3. DCCH: It is used to exchange large amounts of data in less time. 40). What is mobile routing? Even if the location of a term in alis known to the system, its till has to route the traffic through the network to the access point currently responsible for the wireless terminal. 41). What are the functions which support service and connection control? Access point control function Call control and connection Control function Network security agent Service control function Mobility management function

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