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Correct choice is (b) Probability of detection and probability of false alarm

Best explanation: Probability of detection and probability of false alarm are factors of significance in energy detection TECHNIQUE. They depend on the SIGNAL to noise ratio, time-bandwidth PRODUCT, COMPLETE and incomplete gamma functions, and GENERALIZED Marcum Q-function.

The CORRECT option is (a) Matched filter detection

For explanation I would say: The matched filter detection method REQUIRES prior knowledge of the signal to be transmitted by the PRIMARY user such as the pulse shape, the packet format, and the order and MODULATION type. If the information is available, then the matched filter is the most compatible detection method. Matched filter can MAXIMIZE the signal to noise ratio.

Correct option is (a) Latency

Explanation: Network parameters namely packet ordering, packet checksums, packet loss, congestion, LINK capacity, link FAILURE, latency, and strength of a signal on the link are essential to validate a new protocol. High end sensors can be employed to calculate hysteresis and damping algorithms to mitigate NOISE that PROVOKES UNWANTED response.

Right option is (c) Burst

For explanation: LORAN SYSTEM sends a known burst signal with fixed periodicity from multiple TRANSMITTERS. The receivers construct time DIFFERENCE of arrival HYPERBOLOID curve to determine the location of the TRANSMITTER. LORAN provides published charts corresponding to hyperboloid curves, to find the intersection of two-time difference pairs.

The correct answer is (d) Limit sensing when a single RADIO is deployed

The best I can explain: Radio cannot sense the entire available spectrum CONTINUOUSLY. An UPPER limit is established on energy consumption for a period of time. Thus ACCURATE spectrum knowledge is unavailable at all times. Cross-layer interaction is required for switching between transmissions and sensing operations during in-band sensing OPERATION.

Right answer is (a) Bits PER unit area

The explanation is: Spectrum usage in the COGNITIVE radio includes the area of PROPAGATION along with the amount of spectrum used. HENCE the number of bits per unit area is an appropriate unit for spectrum usage in cognitive radio. This necessitates the inclusion of propagation in the Shannon limit.

Right option is (d) Federal Communication Commission

Best explanation: Federal Communication Commission OVERLOOKS the communication CARRIED out over radio, television, wire, satellite, and cable. The FCC consists of jurisdiction over the areas of broadband access, fair competition, radio FREQUENCY USE, and public safety.

Right option is (d) Access delay

The best I can EXPLAIN: Transmission Control Protocol is a connection oriented, reliable, END to end protocol of the transport layer. TCP generally exhibits performance degradation in wireless networks due to a high packet loss rate. COGNITIVE radio introduces NEW challenges such as interruption due to loss of availability of a channel.

Correct ANSWER is (a) Contiguous licensed spectrum band

For EXPLANATION: The spectrum pool comprises of a COLLECTION of contiguous licensed spectrum bands. Each spectrum band contains several channels. A spectrum band is considered as a preliminary bandwidth unit for operating any wireless ACCESS TECHNOLOGY.

Correct choice is (a) True

The explanation is: XG networks allow usage of SPECTRUM band without a fixed infrastructure by MAINTAINING COMMUNICATION PRIORITY and response time. It is also capable of adding a temporary or permanent spectrum to infrastructure links that are used for relaying traffic.

The correct answer is (b) PROTOCOL standardization

Easiest explanation: Cognitive radio can utilize a large network of services to complete user requests. Network based reasoning can collect information localized to a location such as finding restaurants, detecting traffic, detecting weather, etc. It introduces flexibility in the radio and reduces the amount of resources USED. HOWEVER, it exhibits poor LATENCY and requires protocol standardization.

The CORRECT CHOICE is (c) Text dependency

To explain I would say: Speaker recognition consists of TWO errors namely false recognition and recognition failure (failure to identify enrolled user). The systems are characterized by WHETHER the speech is dependent on text involving phrase prompts or INDEPENDENT of text such as a conversational speech.

Correct answer is (a) Time tag the transmitted SIGNAL

The best explanation: The hyperboloid curve of time difference of arrival approach is DRAWN by considering the speed of propagation and difference between the arrival times of the same signal at two RECEIVERS. To expand the curve to include three receivers, the results are CONVERTED to a common coordinate system. Finally, the curve equations are solved to identify the POSITION of the source.

The correct ANSWER is (a) High bit ERROR rate

Explanation: The effect of primary user interference in the physical layer is a high bit error rate. It can be mitigated by ADJUSTING the CODING DYNAMICALLY. It also can be resolved by allowing higher layers to tackle interference for a period of time.

Correct choice is (B) Determination of the LOCATION of the FIXED receiver

To explain I would say: Radio astronomy studies the celestial phenomena by measuring the radio waves characteristics emitted by the physical processes occurring in space. The location of the fixed receiver is a policy challenge as the receiver has to be located at a spot with minimum INTERFERENCE from commercial SYSTEMS.

Correct choice is (b) False

To elaborate: The calculation of relative values of CONSUMER services compared with scientific investigation and Earth exploration is a challenge imposed on policymakers by the MOBILE transmitter, fixed receiver configuration. This INFORMATION helps in assigning the usefulness of creating a mechanism to access an unused spectrum in a location.

Right answer is (a) Spectrum Sharing INNOVATION Test BED sets aside a portion of the spectrum for testing

For explanation I would SAY: Spectrum Sharing Innovation TestBed sets aside a portion of the spectrum for testing and evaluating the developing spectrum sharing methods. The Spectrum Policy INITIATIVE predicted a likely surge in spectrum usage and developing spectrum sharing methods have to be tested accordingly.

Right option is (a) TOPOLOGY configuration

The best explanation: SPECTRUM sensing is capable of DETECTING interference only at the transmitters. Interference measurements should be shared to identify the amount of interference at other users and receivers. This is carried out by cooperative sensing. However cooperative sensing generates large communication overhead that leads to reduced PERFORMANCE in terms of channel capacity and energy consumption.

Correct choice is (c) CENTRAL cross-layer plane

Best explanation: The Central cross-layer plane is the most popularly used IMPLEMENTATION of cross-layer design concept. It can be implemented as a SHARED database. Otherwise, each protocol layer CREATES separate interfaces for its internal protocol parameters and functions.

Right answer is (c) Round TRIP time

Explanation: HIGH spectrum handoff latency leads to increased round trip time. This in turn leads to retransmission time out. Existing PROTOCOLS deduce the cause as packet loss and invoke the congestion AVOIDANCE mechanism resulting in the decrease of throughput. Cognitive radio NETWORK requires transport protocols that support spectrum mobility.

The correct option is (d) BEST path selection

For 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.

The CORRECT option is (d) Clustering

The explanation: In a local group, each node shares several channels with its NEIGHBOURS. Each group may employ a clustering algorithm to select a COMMON CHANNEL for communication. Distributed SENSING and spectrum sharing is also carried out in the common channel.

The CORRECT ANSWER is (a) True

Best explanation: Hybrid handoff is a combination of proactive handoff and REACTIVE handoff. An ALTERNATE channel is proactively sensed before or during transmission. However handoff is performed only after the TRIGGERING event.

Correct ANSWER is (C) RECOVERY TIME

To explain: Spectrum switching time depends on hardware as well as the algorithms used for spectrum sensing, spectrum decision, link layer, and routing. The spectrum switching time caused by spectrum mobility increases the recovery time.

Correct answer is (b) XG user performs sensing and sensing is performed after TRIGGERING event

The EXPLANATION: In the REACTIVE handoff, the xG user begins to sense for available spectrum bands for handoff only after the triggering event. The advantage of this method is that the best available spectrum BAND is selected. However this method exhibits longer handoff latency.

Correct choice is (a) Combining MULTIPLE characterization parameters

The explanation: Spectrum decision models can be built for various characterization parameters such as signal to noise, date rate, error rate, and other parameters that affect the quality of service. HOWEVER a decision model combining SEVERAL spectrum parameters is not available. Spectrum decision models SUPPORT OFDM networks that have multiple spectrum bands operating simultaneously for TRANSMISSION.

Right ANSWER is (C) Management of interference at the receiver

For explanation: The interference detection METHOD requires information such as type of unlicensed signal modulation, power control, and the activity level of licensed and unlicensed users. It does not consider the EFFECT of multiple xG users. It requires the location of nearby primary users.

Right answer is (b) CEPSTRUM coefficients are OBTAINED by taking Fourier transform of DECIBEL spectrum

Easy explanation: Cepstrum coefficients are features employed in speech SIGNAL processing. It is obtained from the spectrum of a speech signal. Cepstrum coefficients are obtained by taking the Laplace transform of the decibel spectrum. Shifted delta cepstrum coefficients measure the changes in the speech spectrum over multiple frames of spectrum to model language CHARACTERISTICS.

Correct choice is (B) DARPA Policy-Based Survivable communication program

For explanation: DARPA Policy-Based Survivable communication program preceded the development of DARPA NeXt Generation radio communication program. It PROVIDED high survivability in the military ENVIRONMENT and better performance gain could be achieved by downloading DYNAMIC mission POLICIES to supervise the radio networks automatically.

Correct option is (d) Transport layer

The explanation is: The effect of primary user interference in the transport layer is the failure to ROUTE a packet. It can be mitigated by identifying missing packets USING the sequence NUMBER and REQUESTING of the retransmission of the packets.

Right answer is (b) Mobile transmitter, mobile receiver

Explanation: Mobile transmitter, mobile receiver configuration includes a variety of mobile services. The private land mobile radio services allow GOVERNMENTS, COMMERCIAL organizations, and non-profit organizations to use mobile and fixed communication systems to GUARANTEE safety, increase productivity and EFFICIENCY.

The correct choice is (d) Operational area is UNKNOWN

To explain I would say: Mobile transmitter, fixed RECEIVER CONFIGURATION INCLUDES active and passive meteorological and Earth exploration system. In passive sensing configuration, the operational area is unknown. In the active sensing configuration, the transmitter LOCATION is unknown.

The CORRECT OPTION is (a) Establishment of Spectrum Policy Task Force

To elaborate: FCC stated that establishing the Spectrum Policy Task Force led to a thorough review of the spectrum policy of the FCC. The Spectrum Policy Task Force identified that a COGNITIVE RADIO demanded changes in the spectrum policy. It ALSO required different approaches to implement the spectrum policy.

Right choice is (c) Radio astronomy

For explanation: Broadcasting primarily includes consumer communication applications such as AM, FM, etc. Radio positioning includes SERVICES such as GPS and radio NAVIGATION. The long-wave standard time signal PRODUCED by The NATIONAL Institute of Standards and Technology (NIST) which continuously BROADCASTS time and frequency signals at 60 kHz is an example of standard time signal services.

Correct answer is (d) Cross-layer design makes channel CONNECTIONS unpredictable

The explanation: Cross-layer design CREATES diverse waveforms to ESTABLISH predictable connections under the existing channel conditions and medium access control parameters. High quality of service can be provided by exchanging information among all layers of the protocol STACK. Cross-layer design also helps to ACHIEVE higher throughput.

The correct option is (a) Transmission coordination

Best EXPLANATION: The COMMON control channel is used to exchange spectrum information among xG USERS and ALSO support transmission coordination. The common control channel is mainly classified as an in-band channel or as an out-of-band channel.

Right answer is (d) Spectrum management

Explanation: Spectrum sharing process is INTEGRATED with spectrum sensing, spectrum ALLOCATION, spectrum access, handshake mechanism, and spectrum mobility. THUS the selection of best AVAILABLE spectrum, prevention of collision due to the overlapping portion of the spectrum, and seamless connection for communication regardless of the LOCATION of the user involves spectrum sharing.

The correct choice is (a) XG user

The explanation: ROUTE breaking is likely to occur during spectrum handoff. The xG user has to recover the routing table in case of a route break. One approach is to BUILD a new routing table for handoff and the other method is to CREATE a routing table for the redundant channel before beginning data transmission.

Right answer is (a) Wavelet bases

To elaborate: In multi-carrier wavelet packet modulation, wavelet bases replace the static sine/cosine pulses of OFDM. This TECHNIQUE provides HIGHER sideband SUPPRESSION. It also reduces inter-channel INTERFERENCE and inter-symbol interference.

Correct CHOICE is (b) Periodicity

To elaborate: MODULATED signals are coupled with sine WAVE carriers, hopping sequences, or cyclic PREFIXES to attain periodicity. The signals are regarded as cyclostationary due to periodic mean and AUTOCORRELATION.

Right CHOICE is (a) Rapid increase in processing gain

For explanation: Matched filter DETECTION ACHIEVES HIGH processing gain rapidly due to coherency. However when accurate information is not available about the signal transmitted by the primary user, then the matched filter detection method exhibits poor PERFORMANCE.