Questions and Answers of Introduction Wireless Mobile Systems

What is the operational difference between standard ACKs used in conventional TCP and SACKs used in wireless TCP? What improvement in performance does it provide for wireless networks?
When is the reliable link layer useful in enhancing TCP performance?
What makes the fast-retransmission approach desirable in improving TCP performance over wireless networks?
What are the problems faced by designers of wireless TCP stacks when using link layer protocols?
What are the inherent characteristics of wireless networks that require changes in existing TCP?
Explain the significance of initial sequence number in TCP.
What are the disadvantages of using wireline TCP over wireless networks?
With suitable examples, explain the differences between connection-oriented and connectionless protocols.
What is DHCP? How does DHCP support dynamic address allocation?
What are the differences between path-vector routing and shortest-path routing? Explain clearly.
“Basic RIP supports single subnet masking for each IP network.” Give a practical example where this becomes a critical issue.
Look at your favorite Web site and find the difference between interior and exterior routing protocols.
What are the differences between OSI and TCP/IP protocol models? Explain clearly.
Describe the OSI model. In which layer(s) does CDPD operate?
Why are wireless mesh networks yet to become popular in spite of some very useful characteristics? Explain clearly.
What are the limitations of Femto cells? Can you conceive of them as a wireless heterogeneous network? Explain clearly.
What are potential uses of wireless multicasting in a realistic set up?
How is UWB different from a conventional frequency hopping? Explain.
What are specific disadvantages of using UWB technology?
How can you use UWB signals for location-determination? Explain clearly.
What is meant by bidirectional tunneling? Why do you need HA–FA in addition to the HLR–VLR pair? Explain clearly.
In a wireless network, the radio signal is broadcast through the air. Therefore, what is the significance of multicasting in this context? Explain in detail.
What is the use of “attachment points” from one network to another network? Explain their significance in wireless network routing?
In the backbone network, it is desirable to find the shortest path from the source to the destination. How do you do this in a wireless network environment, where the subscribers have finite
Assume that you just got out of an airplane and you switched on your cell phone.If the closest BS is located at a distance of 5 km, what are the minimum and the maximum delay before a contact is
What is the bandwidth and the power level used by the “beacon signals” in your area?
You have temporarily moved to a new area and you would like to use your cell phone. What alternatives do you have if(a) There is no service provider in that area?(b) There is no agreement between
What kind of technique(s) you could possibly use to serve a new call if all the channels in the current cell have been occupied and no channel can be borrowed from neighboring cells.
Which cell(s) may borrow channels and which could be an appropriate donor(s) in Problem 5.11?
From a local wireless service provider, find out what kind of EIR information is retained for each subscriber.
What is the impact on the answer for Problem P8.20 if the number of reserved channels is changed toProblem P8.20In a cellular system, the total number of channels per cell, is given as 6 and 2
In a cellular system, the total number of channels per cell, is given as 6 and 2 channels are reserved exclusively for hand off calls. What are the blocking probabilities for originating and if
Repeat Problem P8.18 for the case that the number of channels is increased to ten.Repeat ProblemIn a cellular system with 4 channels, one channel is reserved for handoff calls.(a) What is the value
In a cellular system with 4 channels, one channel is reserved for handoff calls.(a) What is the value of BO and BH , given λO = λH = 0.001 and μ = 0.0003?(b) What are the values of probabilities
Providing cellular service along a freeway is a tough job and such a scenario is illustrated in the following. A typical road-width varies from 200 m to 400 m. If you select 1000 m as the radius of
A service provider decided to split each hexagonal cell of 20 km radius to 7 microcell of appropriate size.(a) What is the size of each microcell?(b) How is the signal strength influenced by such a
For a wireless network with integrated services, e.g., including both voice and data applications, there are two basic channel allocation schemes: Complete Sharing (CS) and Complete Partitioning
How do you compare hybrid with flexible channel allocation? Which one would you prefer and why?
A service provider decided to restructure allocation of channels by selecting a cluster with 4-cell format as its basic building block. What will be impact of channel borrowing if each cell
In a cellular system, a cluster of 7-cell, is assigned 48 traffic channels. Show the assignment of channels to each cell if(a) Omni-directional antennas are used.(b) 3-sector directional antennas are
Each cell of a wireless system, is partitioned in 6-sector as shown in Figure 8.13.(a) What will be the impact of channel-borrowing and co-channel interference if sectoring scheme of (i) is used?(b)
What will be the impact of such sectoring on channel borrowing and what will be its effect on co-channel interference? Explain carefully.What will be the impact of such sectoring on channel borrowing
In a cellular system, with 7-cell clusters, has the following average number pf calls at a given time:Cell number Average number
What are the advantages of cell sectoring? How do you compare this with SDMA?
In a cellular system, with omni-directional antennas, employs a cluster of size 7. The cell at the center of the cluster has much more traffic than the others and need to borrow some channels from
If you do not sector the cells, can you still borrow channels from adjacent cells? Explain clearly.
What are the differences in channel allocation problem in FDMA/TDMA-based system versus CDMA-based system? Explain clearly.
Are there collisions present in traffic or information channels in a cellular system?
What are the specific advantages of static channel allocation over dynamic channel allocation strategies? Explain clearly.
Increasing the number of amplitude level and phase shift, we can gain higher level xQAM, such as 64QAM and 256QAM. It seems the transmission rate can be as high as we want by using this kind of
Use 16QAM to transmit a binary sequence, if the baud rate is 1200 Hz, how many bits can be transmitted in one second?
Besides BPSK and QPSK, 8PSK is another kind of phase shift keying. Try to give the constellation for 8PSK.
The message signal is given byand the carrier is given byUsing frequency modulation with modulation index is 5,(a) Write an expression for the modulated signal(b) What is the maximum frequency
A signal shown in Figure 7.33 amplitude modulates a carrier c(t) = cos (50t).Precisely plot the resulting modulated signal as a function of time. c(t)=cos(50t). CoS
The message signal x(t) = sin(100t) modulates the carrier signal c(t) = A cos (2πfct). Using amplitude modulation. Find the frequency content of the modulated signal. x(t) = sin (100t)
How do you decide the range of a guard channel? Is it a function of the carrier frequency? Explain clearly.
Why does the power control become one of the main issues for the efficient operation of CDMA?
What is FSK/QPSK?
What frequency band is used in biomedical devices surgical applications? How does that limit the use of wireless devices?
What are the non-military applications of frequency hopping? Why is it selected Bluetooth used in home devices and wireless computer mouse?
The number of Walsh codes determines the maximum number of MSs that can be serviced simultaneously. Why not use a large Walsh code? What are the limitations or disadvantages? Explain clearly (Range
To address the service to be increased in the number of MSs in a CDMA system, it was decided to use TDMA as well. Is it possible to do so? If yes, how; and if no, why not?
Is it possible to jam CDMA? Explain clearly.
Is it possible to jam CDMA? Explain clearly.
Find the Walsh functions for 16-bit code.
Repeat Problem P7.3 if the difference in path length is 4 km.Repeat ProblemRadio signal travels from the BS to an MS along different paths-some direct, some reflected and some deflected. If the worst
Repeat Problem P7.2 if only four users per frame can be supported.
Radio signal travels from the BS to an MS along different paths-some direct, some reflected and some deflected. If the worst case difference in the path length traversed by a signal is 2 km, what is
A TDMA system uses 270.833 kbps data rate to support 8 users per frame.(a) What is the raw data rate provided for each user?(b) If guard time and synchronization occupy 10.1 kbps, determine the
What is the difference between the “guard band” and the “guard time”, and why are they important in a cellular system? Explain clearly.
Go to your favorite Web site and find out, what is meant by the hidden terminal problem and the exposed terminal problems? Explain clearly, how can you address them?
The IEEE 802.11x is the popular CSMA/CA protocol employed for wireless LANs and ad hoc networks. Briefly describe all the current 802.11 standards and explain clearly how each is distinct from the
Under the CSMA/CA protocol, suppose there are n users and the contention window for each user is W; then what is the collision probability?
In an experiment, the persistent value p is varied as a function of load G, from 1 to 0.5 to 0.1 to 0.01. For what value of G, would you have such a transmission? Is there any specific advantage of
Suppose the propagation delay is α, SIFS is α, DIFS is 3α, and RTS and CTS are 5α, respectively, for CSMA/CA with RTS/CTS.(a) What is the earliest time for the receiver to send the CTS
In CSMA/CA, why do you need a contention window, even after DIFS? What is the typical size of the contention window?
Why does contention window need to be changed sometimes? Explain clearly.
In a CSMA/CA scheme, a random delay is allowed whenever a collision occurs. What is the guarantee that future collision between previously collided terminals will not occur? Explain the rationale
What in your opinion should be the criteria to select the value of the contention window? Also explain how you will decide the value of the time slot for CSMA/CA.
What are the relative advantages and disadvantages of basic CSMA/CA and CSMA/CA with RTS/CTS protocols? What makes you select one over the other?
What are the purposes to use RTS/CTS in CSMA/CA?
What is the difference between collision detection and collision avoidance?
What are the major factors affecting the throughput of CSMA/CA?
Can we use CSMA/CD in cellular wireless networks? Explain your answer with solid reasoning.
Describe the advantages and disadvantages of 1-persistent CSMA and p-persistent CSMA respectively.
What are relative advantages and disadvantages of persistent and non-persistent CSMA protocols? What makes you select one over the other? Explain clearly.
In a given system with shared access, the probability of €œn€ terminals communicating at the same time is given by
What is meant by a collision in data transfer and why is it not possible to decipher information from collided data? Explain clearly.
Is it impractical to use ALOHA or slotted ALOHA for MSs to access control channel associated with the BS? Explain clearly.
How does slotted ALOHA improve throughput as compared to pure ALOHA?
What is the key issue for contention-based access protocols? How is it solved? Give an example to explain your answer.
What are the advantages of cell-sectoring? Explain with suitable diagrams.
What are the differences between adjacent channel interference and co-channel interference? Explain with suitable diagrams.
What is meant by handoff interval and handoff region? Explain their usefulness with appropriate diagrams.
Calculate the co-channel interference ratio in the worst case for the forward channel, given N = 7, R = 3 km, and γ = 2.
Prove the following for a hexagonal cellular system with radius R, reuse distance D and given the value of N(a) N = 3, prove D = 3R.(b) N = 4, prove D = √12 R.(c) N = 7, prove D = √21 R.
The figure shows the cell structure of a metro area. Can you explain why this might have been designed so? 4 12 8. 12 12 12 12 12 12 12 20 4. 4 12 12 12 12 8. 4.
The following figure shows a cellular architecture. Is there some specific reason why it could have been designed this way? (4 5 3
If a wireless service provider has 20 cells to cover the whole service area, with each cell having 40 channels, how many users can the provider support if a blocking probability p of 2 % is required?
Given a bandwidth of 25 MHz and a frequency reuse factor of 1 and RF channel size of 1.25 MHz and 38 calls per RF channel, find:(a) The number of RF channels for CDMA.(b) The number of permissible

Showing 200 - 300 of 394