Explore topic-wise InterviewSolutions in .

The CORRECT choice is (b) Constant Envelope Orthogonal FREQUENCY DIVISION Multiplexing

Explanation: In Constant Envelope Orthogonal Frequency Division Multiplexing, the complex modulated signals are positioned in a complex conjugated arrangement to obtain a REAL value inverse fast Fourier transform output. ALSO, phase modulation is applied in the real value time domain. This technique reduces the high peak to average power ratio of OFDM.

Correct option is (d) Selection of duration for transmission

Easy EXPLANATION: In-band sensing is MAINLY concerned with interference avoidance. Sensing time and transmission time are the major factors computed by in-band sensing. The duration and the frequency at which sensing should be CARRIED out to ACHIEVE satisfying sensing accuracy is DETERMINED by in-band sensing.

Right choice is (C) Correlator

Easiest EXPLANATION: Energy detection consists of three operational units namely squaring device, integrator, and THRESHOLD device. The received signal energy is measured by squaring and integrating the received signal over an interval T. The output of the integrator is then EVALUATED by the threshold device to determine the existence of the primary user in the LICENSED spectrum.

Correct CHOICE is (a) Large spectrum

Explanation: Cognitive MESH NETWORKS require high capacity to support applications that require high throughput. xG networks are capable of accessing large portions of the spectrum and can support the demand generally present in dense urban AREAS. Cognitive mesh networks are used for providing BROADBAND connectivity.

Correct option is (a) Transcript generation

The explanation is: Text to SPEECH conversion voices textual information. The source of the information COULD be text based communication or display readouts. The regions of interest are associating news with PARTICULAR voice and tone, producing human SOUNDING voice, pronunciation of named ENTITIES, quality of voice synthesis, and conveyance of expression.

The correct choice is (d) Enrollment

Explanation: VOICE samples are OBTAINED from users to generate a model or a template. The verification phase involves the comparison of a SIGNAL taken from the application with that of a template for matching. The result of verification may be POSITIVE or NEGATIVE identification.

Right choice is (c) Priority assignment

The best I can EXPLAIN: Policy language allows assignment of priorities and preference. Priority assignment aids in the RESOLUTION of conflicts as the sequence of execution is CLEARLY defined. It allows the prioritization of RULES to reflect local MANAGEMENT priorities. For example, a rule can ensure that efficiency is given more importance than reliability.

The correct answer is (d) Eliminates multiple path

Explanation: Multiple input, multiple OUTPUT is a technique that introduces multiple antennas at the transmitter and the receiver generating several paths for TRANSMISSION. MIMO introduces channel AWARENESS on an ARCHITECTURAL level and is employed in the generation of links and topology. It utilizes multipath and converts multiple paths into multiple channels.

Right option is (a) Federal Communication Commission

For explanation I WOULD SAY: Federal Communication Commission introduced interference temperature as a metric for modeling interference at the primary user produced by the SECONDARY user. It is a measure of RF power GENERATED by undesired transmitters and noise sources that are present in the receiver system per unit of BANDWIDTH.

The CORRECT ANSWER is (d) Exploit spectrum holes

Explanation: The OBJECTIVES of the cognitive radio are to minimize the radio presence in a network while gathering data about the spectrum from the spectrum environment and to ADAPT to the available spectrum determined from the gathered data. The dynamic characteristics of the cognitive radio rely on its ability to SENSE the propagation conditions.

Right option is (b) Processing EFFICIENCY

The explanation is: Processing efficiency ACCOUNTS for the additional routing costs applicable for cross-layer information processing. It especially affects the high SPEED links where only the time to live field of a packet is decreased to ensure fast processing of packets.

Right option is (b) DISTRIBUTED QUALITY of Service Dynamic Reservation scheme

Explanation: In Distributed Quality of Service Dynamic Reservation scheme, a base-station COMPETES with an interfering base-station to allocate a spectrum band that satisfies the quality of service requirements of the user APPLICATION.

Correct option is (a) LOCAL bargaining group is a set of USERS with a threshold limit guaranteed to provide MINIMUM SPECTRUM allocation to each user

The EXPLANATION is: Local bargaining scheme is a cooperative intra-network sharing technique. It improves spectrum utilization and ensures fairness in the allocation of spectrum. It involves creating a local bargaining group with a threshold limit that ensures minimum allocation of spectrum to each user of the group.

Correct ANSWER is (b) False

To explain I would say: The TRANSMITTER-receiver handshake conveys the selected spectrum for communication to the receiver. This protocol is not LIMITED between a transmitter and a receiver and may also include external ENTITIES such as a primary base-station especially in methods such as cooperative spectrum SHARING.

The correct answer is (a) Expected interference at primary user

To explain I would say: The expected amount of interference on the primary user due to an xG user is the interference of INTEREST in xG ARCHITECTURE. Interference at the primary transmitter can be CONTROLLED through the radiated power, the out-of-band EMISSIONS, and the location at the transmitters.

Right answer is (d) Automatic detection of input modality

The EXPLANATION: Services can be provided by automatic detection or by explicit request. Cognitive RADIO employs hybrid request handling techniques with RESPECT to the applications. The service requires interfaces to represent the user state, predict the OUTCOME of a task, and to duplicate the human INTERFACE.

The correct choice is (a) Promote manual control of networks

The best I can explain: Network policy MANAGEMENT INVOLVES the creation of policy ENABLED devices that are capable of enforcing policies. The administrators use policy languages to represent network objectives. Policy SERVERS configure the device to accomplish the objectives. Security, optimization of the performance of network applications, AUTOMATING the control of networks, and the development of machine-readable policies are the primary objectives.

Correct answer is (c) Domain MANAGER

Easiest explanation: KAoS is a semantic web language and is USED to enforce policies in terms of SOFTWARE context. The domain manager operates as the policy DECISION point and INTERPRETS policies to control the behaviour of the network. It administers policies ranging over all domains.

The CORRECT OPTION is (c) Resolve conflicts in policy rules

For explanation I would say: The spectrum policy management solves the conflicts in policy RULE by identifying INCONSISTENCIES. It depends on the network administrators to DETERMINE the applicable spectrum policy for the spectrum environment, spectrum sharing mechanism, and other issues that arise due to cross layer design.

The correct option is (a) Conflict between the required amount of frequency by the radio system and frequency used

Explanation: The policy challenge of the mobile transmitter, FIXED RECEIVER configuration is that the frequency usage is extremely small but it demands a LARGE amount of frequency. The OPERATIONAL frequencies also tend to be PARTICULAR to the physical characteristics of the chemicals that are to be sensed.

Right option is (d) Construction of channel models to estimate the propagation of a SIGNAL in the channel environment

The BEST I can explain: Cross-layer design requires the characteristic parameters of each layer to be made available to other layers of the protocol STACK during run time. In order to achieve this, DIFFERENT degree of abstraction is required. This requires the development of new data structures such as constructing squares for storing information.

Correct option is (b) JAMMING attack

The explanation is: 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.

The correct answer is (a) Hidden terminal problem

Explanation: SENSING in a limited geographic area with a fixed bandwidth limit on secondary users is a challenge for HARDWARE constrained MAC protocol.Thus hidden terminal problem is observed in the hardware constrained MAC protocol. The demand for SYNCHRONIZATION among xG users is a problem of concern for cognitive MAC protocol.

The correct choice is (b) Link capacity is a route metric used to represent link failure

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.

The correct option is (b) Back up channel list

To elaborate: The most preferred approach for mitigating performance DEGRADATION, DUE to poor channel characteristics, is building a backup channel list. The potential target channels are added to a list. The list is maintained by sharing information between users in the area. It is INTEGRATED in the IEEE 802.22 Wireless REGIONAL Area Network.

Correct option is (d) Spectrum handoff and connection management

Easy EXPLANATION: Spectrum handoff is the process of transferring current data communication from ONE channel to another channel. Connection management adjusts the protocols associated with each layer of the OSI model to sustain the quality of service REQUIREMENTS of SECONDARY USER communication.

Right answer is (a) Interference

The explanation: Following the characterization of the spectrum, the spectrum band for transmission is selected by weighing the spectrum characteristics and the quality of service requirements. Spectrum manager FIXES the data rate, tolerable error rate, transmission MODE, the bandwidth of transmission, and the delay bound according to the USER requirements.

Right choice is (b) Amount of INTERFERENCE at the PRIMARY receiver

The explanation: Channel capacity can be estimated by determining the permissible POWER of an xG USER. The permissible power is computed by determining the amount of interference at the primary receiver. The amount of interference sometimes DEPENDS on the number of users in the spectrum.

Right choice is (d) 300

For explanation I would SAY: The ALLOWABLE one way delay for normal CONVERSATION is less than 300 millisecond seconds. Speech CODING PROVIDES intelligible and quality speech, stress detection, language independence, error free transmission, and tone communication.

The correct choice is (a) True

For EXPLANATION: Effective spectrum USAGE considers both the amount of spectrum used and the area of propagation.Under GOOD propagation conditions, increasing the transmission energy is a poor TECHNIQUE to increase spectrum efficiency. By increasing the efficiency of a single radio, the spectrum cannot provide proper communication conditions for other users of the spectrum.

Correct option is (d) High delay

Easy explanation: FFT operation demands WIDEBAND ADC and extensive digital signal PROCESSING. The ADC imposes restrictions on the instantaneous BANDWIDTH. The energy usage is increased due to the high amount of digital signal processing.

The correct choice is (d) CENTRAL entity

Easiest explanation: Cooperative spectrum sharing involves sharing spectrum USAGE and noise information to other nodes of the spectrum. This mode considers the operation of other spectrum users thus raising the overall spectrum EFFICIENCY of the network. It requires non-corrupt neighbouring radios, KNOWLEDGE of spectrum environment, understanding of limits IMPOSED on transmission parameters, and transparent sharing of spectrum information by transmitters.

Correct choice is (a) NUMBER of bits per Hertz of bandwidth

Explanation: MODULATION designers describe spectrum efficiency in terms of the number of bits per Hertz of bandwidth. It is used as a METRIC for measuring the performance of modulation techniques.

Correct option is (a) Spectrum handoff latency is the time TAKEN to switch to a new FREQUENCY during handoff

For explanation I WOULD say: Depending on the AVAILABLE spectrum, the OPERATIONAL frequency of the radio changes with time. When the radio changes its frequency of operation, the time taken for the new frequency to become operational is called spectrum handoff.

The correct answer is (a) Central entity is used to lease the SPECTRUM

For EXPLANATION I would say: The dynamic spectrum access protocol (DSAP) is a centralized protocol where a central entity is used for leasing spectrum to users in a limited geographical area. DSAP consists of CLIENTS, DSAP server, and RELAY for relaying information between the server and the clients that are not in the direct RANGE of the server.

The CORRECT option is (b) Spread spectrum techniques

Easiest explanation: UNDERLAY spectrum SHARING technique employs spread spectrum techniques while transmitting in the LICENSED portion of the spectrum band. Spread spectrum involves stretching a signal over a bandwidth which is wider than its original bandwidth. Therefore bandwidth utilization and interference towards the PRIMARY user is increased.

The correct answer is (d) Different SPECTRUM pool and same base-station

Easy explanation: When an xG user SWITCHES from ONE spectrum pool to another spectrum pool within a single cell coverage area, it is TERMED as intra-cell/inter-pool handoff. The is no transfer from serving base-station to the neighbour base-station. A Cell is a unit of coverage area. Spectrum pool is a set of contiguous licensed spectrum bands.

The correct option is (b) Link maintenance probability is the measure of sustenance of transmission during handoff

Explanation: Link maintenance probability is the measure of sustenance of the COMMUNICATION of secondary user, when the secondary user vacates a channel. Link maintenance probability INCREASES with the number of handoffs. Link maintenance probability is one of the PERFORMANCE measuring parameters of spectrum MOBILITY.

The correct option is (a) Complex COMPUTATION is necessary

The best explanation: OFDM requires only the computation of fast Fourier transform and INVERSE fast Fourier transform of the signal to be transmitted. However it requires the subcarriers to remain orthogonal and exhibits a LARGE peak to average POWER ratio due to the PRESENCE of complex sinusoids in time domain OFDM signals.

The correct CHOICE is (d) Repair

The best I can explain: The major functions of spectrum management are spectrum sensing, spectrum ANALYSIS, and spectrum decision-making. Spectrum sharing and spectrum mobility are also included in the management framework. Every function operates over all LAYERS of the OSI model except sensing which is IMPLEMENTED only in the physical layer.

Right answer is (a) Interference avoidance

The explanation is: Spectrum sensing identifies UNUSED spectrum HOLES that are available for TRANSMISSION for COGNITIVE radio users. During transmission, the cognitive radio users continue to monitor the spectrum band. They also sense other users of the primary network in ORDER to avoid interference. Spectrum sensing carried out during transmission is called in-band sensing.

The CORRECT answer is (b) SOURCE extraction

For explanation I would SAY: Computation auditory scene analysis applies heuristic grouping rules developed using psychological OBSERVATIONS to separate a source from a single channel of audio. It separates the sound into music, voice, noise, etc.

Right option is (c) PROTOCOL element KNOWLEDGE and application information

Easy explanation: Protocol element knowledge is RESPONSIBLE for adapting to network CONDITIONS. Protocol element knowledge and application knowledge are combined to select and define protocol elements.