This set of Cognitive Radio Multiple Choice Questions & Answers (MCQs) focuses on “Next Generation Wireless Network – Upper Layers Issue – 1”.
1. Which among the following is not an upper layer issue?
a) Channel sensing
d) Congestion control
Explanation: Upper layer issues are the challenges in the application layer, the transport layer, and the network layer in the implementation of cognitive radio networks. Route selection and maintenance is a challenge of the network layer. Prevention of intrusion is a challenge of the transport layer.
2. Which among the following is a not route metric?
a) Power efficiency
d) Data size
Explanation: Route metrics are parameters whose values are evaluated to assign a cost to a link in the path between the source and the destination. Routing algorithms rely on route metrics to select the optimum path for forwarding the packets.
3. Which among the following is an issue for routing in cognitive radio networks?
a) Spectrum sensing
b) Power allocation
c) Spectrum knowledge
d) Spectrum characterization
Explanation: The routing layer requires information about the spectrum for determining the path of communication. The consolidation of information obtained by sensing and by characterization operations of the physical layer is a challenge as it is difficult to decide which information should be stored. The user requires local as well as global knowledge of the spectrum.
4. What is the term used to define the additional data that has to be transferred other than the message during communication?
a) Encoded bits
c) Support bits
Explanation: Overhead refers to the additional transmissions that exceed the allowable number of transmissions resulting in a decrease of efficiency and throughput of the entire network. For example, in cooperative sensing, before transmission of information, the sensing information collected by a user has to be forwarded to other secondary users in the network.
5. Which among the following is false about the routing issue link failure?
a) Interference is a route metric used to represent link failure
b) Link capacity is a route metric used to represent link failure
c) Link failure is caused by the displacement of an intermediary node
d) Link failure is caused by the arrival of the primary user
Explanation: Link failure arises due to the arrival of a primary user or due to the lack of replacement of a displaced intermediary node. Link failure, depending on the triggering event, may be recovered by employing an extra power signal.
6. Which among the following is not a route metric of the routing issue mobility handling?
d) Link stability
Explanation: Mobility handling is required when a secondary user moves from one place to another due to the arrival of a primary user or due to variation in the spectrum environment. It is also required when an intermediary node leaves the path of communication. Mobility handling is responsible for finding an alternate node and re-establishing communication.
7. Which among the following issues consider cost as a route metric?
a) Spectrum knowledge
c) Link failure
d) Best path selection
Explanation: Best path selection considers the following route metrics namely delay, power efficiency, interference, throughput, and cost. The path that closely meets the quality of service requirements of the application is chosen as the best path. The cognitive radio network calculates several paths considering the possibility of the arrival of a primary user, the robustness of a path, etc.
8. Why common channel control is required for routing?
a) Transmission coordination
b) Time of arrival synchronization
d) Spectrum analysis
Explanation: The existing routing protocols for functionalities such as neighbour discovery, route discovery, and route establishment need to broadcast messages either globally or locally. The lack of a common control channel makes it difficult to send broadcast messages in xG networks.
9. Which among the following issues require channel-based models for analysis?
a) Common control channel
b) Spectrum knowledge
c) Queue management
d) Intermittent connectivity
Explanation: Intermittent connectivity is caused due to the time-changing nature of the spectrum and loss of channel due to the arrival of the primary user. It is also due to the fact that when the user chooses a channel for communication, the node cannot be reached through other channels. Thus channel-based models are required for developing time-based solutions.
10. Why is queue management required?
a) Form a queue of xG users which require access for a particular channel in the licensed band
b) Handle multiple interfaces
c) Form a queue of xG users which require access for a particular channel in the unlicensed band
d) Form a queue of xG users to forward information to spectrum broker
Explanation: An xG terminal uses multiple interfaces to interact with multiple nodes. Queue management is responsible for finding an interface best suited for the traffic in the spectrum environment. Queues are generated after evaluating each interface with each traffic type.
11. What is the best path from N1 to N3 in dynamic source routing?
a) N1 – N4 – N2 – N3
b) N1 – N4 – N5 – N4 – N1 – N2 – N3
c) N1 – N4 – N5 – N3
d) N1 – N2 – N3
Explanation: Dynamic source routing initiates by broadcasting a packet to nodes N2 and N4. N2 broadcasts request packets to N3 and N5. N3 identifies itself as the target. N5 forwards the packets to N4 and N3. The nodes which received the request packet for a second time discard the request packets. N3 identifies two routes N1-N2-N3 and N1-N4-N5-N3. N3 returns the path N1-N2-N3 in reverse order since it is the shorter route.
12. Which among the following is not a network layer attack?
a) Network endo parasite attack
b) Jamming attack
c) Channel ecto parasite attack
d) Low cost ripple effect attack
Explanation: Network endo parasite attack increases the amount of interference. Channel ecto parasite attack switches its interference to a channel occupied by a high priority user. Low cost ripple effect attack shares false channel assignment information.
13. Cross layer approach is the combination of route selection and spectrum management.
Explanation: Cross layer approach jointly considers route and spectrum selection in xG networks. Typically, route selection is carried out centrally with a global view of the network. On constructing a route, each hop is associated with a time slot and a channel.
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