MOBILE COMPUTING ,Wireless Communication Fundamentals
1.What are the 3 fundamental propagation behaviors depending on their frequency?
Ground Wave, Sky Wave and Line of Sight.
2.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.
3.What is guard space? Guard spaces are needed to avoid frequency band overlapping is also called channel interference.
4.What are the 3 different basic schemes analog modulation? Amplitude modulation, Frequency modulation and Phase modulation.
5.What is the use of Phase Lock Loop(PLL)? To receive the signal correctly, the receiver must synchronize in frequency and phase with the transmitter.
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 is dwell time? The time spend on a channel with a certain frequency is called the dwell time. 8. What are the advantages of cellular systems? Higher capacity, Less transmission power, Local interface only and Robustness.
9. What is browsing channel allocation and fixed channel allocation? Cells with more traffic are dynamically allotted more frequencies. This scheme is known as browsing channel allocation, while the first fixed scheme is called fixed channel allocation.
10. What are the disadvantages of cellular systems? Infrastructure needed, Handover needed and Frequency planning.
11. What is digital sense multiple access? The scheme which is used for the packet data transmission service Cellular Digital Packet Data in the AMPS mobile phone system is also known as digital sense multiple access (DSMA).
12. What is Network and Switching subsystem? The heart of the GSM is formed by the Network and Switching System (NSS). NSS consists of the following switches and databases: • Mobile Services switching center(MSC) • Home Location register (HLR) • Visitor Location Register (VLR)
13. What is authentication centre? As the radio interface and mobile stations are particularly vulnerable a separate AuC has been defined to protect user identity and data transmission. The AuC contains the algorithms for authentication as well as the keys for encryption and generates the values needed for user authentication in the HLR. The AuC may, in fact, be situated in a special protected part of the HLR.
14. What is called burst and normal burst? Data is transmitted in small portions called bursts, normal burst are used for data transmission inside a slot (user and signaling data).
15. What are the basic groups of logical channels? GSM specifies 2 basic groups: Traffic channels and Control channels.
16. Define traffic multi frame and control multi frame? The periodic pattern of 26 slots occurs in all TDMA frames with a TCH. The combination of these frames is called traffic multi frame TDMA frames containing data for the other logical channels are combined to a control multi frame.
17. What is OVSF? Using orthogonal codes separates the different data streams of a sender UMTS uses so-called Orthogonal Variable Spreading factor codes (OVSF).
18. Specify the steps perform during the search for a cell after power on? • Primary synchronization • Secondary synchronization • Identification of the scrambling code
19. Explain about transparent mode? It simply forwards MAC data without any further processing. The system then has to rely on the FEC which is always used in the radio layer.
20. What are the basic classes of handovers? UMTS has 2 basic classes of handovers: Hard handover and Soft handover.
21. What limits the number of user in TDM and FDM compared to CDM? The code space is huge compared to the frequency space and time space. Beacuse of the limited time space and frequency space, the number of user in TDM and FDM are limited. 22. How does near and far effect influence CDMA? What are counter measurements? The near and far effect is a server problem of wireless networks using CDM. All signals should arrive at the receiver with more or less the same strength. Precise power control is needed to receive all senders with the same strength at a receiver.
23. Name one wired MAC scheme that fails for wireless. The wired MAC scheme CSMA/CD fails for wireless because of the hidden and exposed terminal problem.
24.What are the main benefits of a spread spectrum? The main benefit of spread spectrum is the resistance to narrow band interference. The spread spectrum converts the narrow band into broad band signal. The energy needed to transmit the signal is the same, but it is now spread over a large frequency range. Thus the power level of the signal can be much lower than that of the original narrowband signal.
25.What is BCA? In the case of a heavy load in one cell and a light load in a neighboring cell, for instance it could make sense to borrow frequencies. Cells with more traffic are dynamically allotted more frequencies. This scheme is know as Borrowing channel Allocation (BCA).
26.Define FCA and DCA. Allocating a fixed frequencies for a channel is called as Fixed channel Allocation (FCA). In Dynamic Channel Allocation (DCA) scheme frequencies can only be borrowed, but it is also possible to freely allocate frequencies to cells. With dynamic assignment of frequencies to cells, the danger of the interference with cells with same frequency exists. Thus the borrowed frequencies in the surroundings cells can be blocked.
2.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.
3.What is guard space? Guard spaces are needed to avoid frequency band overlapping is also called channel interference.
4.What are the 3 different basic schemes analog modulation? Amplitude modulation, Frequency modulation and Phase modulation.
5.What is the use of Phase Lock Loop(PLL)? To receive the signal correctly, the receiver must synchronize in frequency and phase with the transmitter.
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 is dwell time? The time spend on a channel with a certain frequency is called the dwell time. 8. What are the advantages of cellular systems? Higher capacity, Less transmission power, Local interface only and Robustness.
9. What is browsing channel allocation and fixed channel allocation? Cells with more traffic are dynamically allotted more frequencies. This scheme is known as browsing channel allocation, while the first fixed scheme is called fixed channel allocation.
10. What are the disadvantages of cellular systems? Infrastructure needed, Handover needed and Frequency planning.
11. What is digital sense multiple access? The scheme which is used for the packet data transmission service Cellular Digital Packet Data in the AMPS mobile phone system is also known as digital sense multiple access (DSMA).
12. What is Network and Switching subsystem? The heart of the GSM is formed by the Network and Switching System (NSS). NSS consists of the following switches and databases: • Mobile Services switching center(MSC) • Home Location register (HLR) • Visitor Location Register (VLR)
13. What is authentication centre? As the radio interface and mobile stations are particularly vulnerable a separate AuC has been defined to protect user identity and data transmission. The AuC contains the algorithms for authentication as well as the keys for encryption and generates the values needed for user authentication in the HLR. The AuC may, in fact, be situated in a special protected part of the HLR.
14. What is called burst and normal burst? Data is transmitted in small portions called bursts, normal burst are used for data transmission inside a slot (user and signaling data).
15. What are the basic groups of logical channels? GSM specifies 2 basic groups: Traffic channels and Control channels.
16. Define traffic multi frame and control multi frame? The periodic pattern of 26 slots occurs in all TDMA frames with a TCH. The combination of these frames is called traffic multi frame TDMA frames containing data for the other logical channels are combined to a control multi frame.
17. What is OVSF? Using orthogonal codes separates the different data streams of a sender UMTS uses so-called Orthogonal Variable Spreading factor codes (OVSF).
18. Specify the steps perform during the search for a cell after power on? • Primary synchronization • Secondary synchronization • Identification of the scrambling code
19. Explain about transparent mode? It simply forwards MAC data without any further processing. The system then has to rely on the FEC which is always used in the radio layer.
20. What are the basic classes of handovers? UMTS has 2 basic classes of handovers: Hard handover and Soft handover.
21. What limits the number of user in TDM and FDM compared to CDM? The code space is huge compared to the frequency space and time space. Beacuse of the limited time space and frequency space, the number of user in TDM and FDM are limited. 22. How does near and far effect influence CDMA? What are counter measurements? The near and far effect is a server problem of wireless networks using CDM. All signals should arrive at the receiver with more or less the same strength. Precise power control is needed to receive all senders with the same strength at a receiver.
23. Name one wired MAC scheme that fails for wireless. The wired MAC scheme CSMA/CD fails for wireless because of the hidden and exposed terminal problem.
24.What are the main benefits of a spread spectrum? The main benefit of spread spectrum is the resistance to narrow band interference. The spread spectrum converts the narrow band into broad band signal. The energy needed to transmit the signal is the same, but it is now spread over a large frequency range. Thus the power level of the signal can be much lower than that of the original narrowband signal.
25.What is BCA? In the case of a heavy load in one cell and a light load in a neighboring cell, for instance it could make sense to borrow frequencies. Cells with more traffic are dynamically allotted more frequencies. This scheme is know as Borrowing channel Allocation (BCA).
26.Define FCA and DCA. Allocating a fixed frequencies for a channel is called as Fixed channel Allocation (FCA). In Dynamic Channel Allocation (DCA) scheme frequencies can only be borrowed, but it is also possible to freely allocate frequencies to cells. With dynamic assignment of frequencies to cells, the danger of the interference with cells with same frequency exists. Thus the borrowed frequencies in the surroundings cells can be blocked.
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