Sample Questions_Test 2_Solutions

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Durham College *

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CYBERSECUR

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Electrical Engineering

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Jan 9, 2024

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1.A continuous time signal is said to be periodic if x(t) = x(t+T) Here T is called … A. Starting period B. Dummy period C. Sampling period D. Fundamental Period A continuous time signal is said to be called a periodic signal if it repeats itself after s specific period of time (T) This time T is known as fundamental time period 2. For a periodic signal x(t) = 30 sin 100t + 10 cos 300t + 6 sin 500t, the fundamental frequency is … 3. What is the period of the following signal: x(t) = cos (pi t)/4 A. 1/8 s B. 8 s C. 4 s D. ¼ s 4. What is the principle of frequency reuse in the context of cellular network? For frequency reuse in a cellular system, the same set of frequencies are used in multiple cells, with these cells separated from one another by enough distance to avoid interference.

5. Consider 4 different cellular systems that share the following characteristics. The frequency bands are 825 to 845 MHZ for mobile unit transmission and 870 to 890 MHZ for Base Station transmission. A duplex circuit consists of one 30 KHZ channel in each direction. The systems are distinguished by reuse factor, which is 4, 7, 12, and 19 respectively. a) Suppose that in each of the systems, the cluster of cells (4, 7, 12, 19) is duplicated 16 times. Find the number of simultaneous communications that can be supported by each system. b) Find number of simultaneous communications that can be supported by a single cell in each system. c) What is the area covered, in cells, by each system? a. We have the number of clusters M = 16; bandwidth assigned to cluster BCL = 40 MHz; bandwidth required for each two-way channel bch = 60 kHz. The total number of simultaneous calls that can be supported by the system is kSYS = MBCL / bch = 10,666 channels b. Total number of channels available is K = BCL / bch = 666. For a frequency reuse factor N , each cell can use kCE = K / N channels. For N = 4, kCE = 166 channels For N = 7, kCE = 95 channels For N = 12, kCE = 55 channels For N = 19, kCE = 35 channels c. For N = 4, area = 64 cells; For N = 7, area = 112 cells; For N = 12, area = 192 cells; For N = 19, area = 304 cells. 6. A cellular system uses FDMA with the spectrum allocation of 12.5 MHZ in each direction, a guard band at the edge of the allocated spectrum of 10 KHZ, and a channel bandwidth of 30 KHZ. What is the number of available channels? (12.5 × 10 6 – 2(10 x 10 3 )/(30 × 10 3 ) = 416 7. … is a type of digital modulation A. Amplitude modulation B. Frequency modulation C. Amplitude Shift Keying D. Phase Modulation 8. The format of the messages exchanged between entities on a network are defined by:

A. the transport layer B. end systems C. a protocol D. sockets 9. Which of the following is not a typical application of Bluetooth wireless communication? A. Hands-free calling by connecting a mobile phone to a car’s stereo system B. Wireless headset for a mobile phone C. Connecting several devices to the wireless internet D. Wireless connection between a computer and peripheral devices ( eg. Mouse, keyboard, camera, printer, …) 10. Which layer of OSI model consists of bit-level data streams and computer network hardware? A. Physical B. Data Link C. Session D. Network 11. Graph the following sine and cosine functions: A. Sin(x) B. cos(x) A.

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B. 12. Determine the period of the following function A. x(t) = cos (t/3)

B. x(t) = 0.5cos (2.5t) C. x(t) = 4 sin (3t) 13. Determine the period and frequency of the following signals: 14. what are issues that have to be taken into consideration when deploying a cellular infrastructure?

1. Authentication: Cellular networks have a large number of subscribers, and each has to be authenticated to ensure the right people are using the network. Since the purpose of 3G is to enable people to communicate from anywhere in the world, the issue of cross region and cross provider authentication becomes an issue. 2. Integrity: With services such as SMS, chat and file transfer it is important that the data arrives without any modifications. 3. Confidentiality: With the increased use of cellular phones in sensitive communication, there is a need for a secure channel in order to transmit information. 4. Access Control: The Cellular device may have files that need to have restricted access to them. The device might access a database where some sort of role based access control is necessary [Fernandez05-1 ]. 5. Operating Systems In Mobile Devices: Cellular Phones have evolved from low processing power, ad-hoc supervisors to high power processors and full fledged operating systems. Some phones may use a Java Based system, others use Microsoft Windows CE and have the same capabilities as a desktop computer. Issues may arise in the OS which might open security holes that can be exploited. 6. Web Services: A Web Service is a component that provides functionality accessible through the web using the standard HTTP Protocol. This opens the cellular device to variety of security issues such as viruses, buffer overflows, denial of service attacks etc. [Fernandez05-2 ] 7. Location Detection: The actual location of a cellular device needs to be kept hidden for reasons of privacy of the user. With the move to IP based networks, the issue arises that a user may be associated with an access point and therefore their location might be compromised. 8. Viruses And Malware: With increased functionality provided in cellular systems, problems prevalent in larger systems such as viruses and malware arise. The first virus that appeared on cellular devices was Liberty. An affected device can also be used to attack the cellular network infrastructure by becoming part of a large scale denial of service attack. 9. Downloaded Contents: Spyware or Adware might be downloaded causing security issues. Another problem is that of digital rights management. Users might download unauthorized copies of music, videos, wallpapers and games. 10. Device Security: If a device is lost or stolen, it needs to be protected from unauthorized use so that potential sensitive information such as emails, documents, phone numbers etc. cannot be accessed.

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