This set of Software Defined Radio Multiple Choice Questions & Answers (MCQs) focuses on “Smart Antenna ”.
1. Smart antenna integrates the contributions of _____ antenna elements.
a) band distributed
b) band centralized
c) spatially distributed
d) spatially centralized
Explanation: Smart antenna integrates the contributions of spatially centralized antenna elements. Frequency reuse and co-channel suppression characteristics of smart antenna provide wireless communication systems with large capacity and high quality links.
2. If a multibeam array has ____, it may not be feasible to assign a complete frequency-reuse plan to each beam.
a) a single beam
b) two beams
c) less than five beams
d) more than ten beams
Explanation: If a multibeam array has more than ten beams, it may not be feasible to assign a complete frequency-reuse plan to each beam. This is due to the interference with adjoining sectorized antennas.
3. Interference with adjoining sectorized antennas can be avoided by _____
a) frequency nulling
b) spatial nulling
c) spatial beam-forming
d) frequency beam-forming
Explanation: The interference with adjoining sectorized antenna can be avoided by the introduction of spatial nulls in the direction of nonsubscriber signal components. In high traffic intensity areas, nulls track subscribers that are on the same frequency and cancel their path movements.
4. Spatial nulling subsystem replaces three element sectors of conventional base station with ____ disposed antenna elements.
a) four spherically
b) eight spherically
c) four circularly
d) eight circularly
Explanation: Spatial nulling subsystem replaces three element sectors of conventional base station with eight circularly disposed antenna elements. The signal is then preamplified and converted to digital form using eight wideband ADCs.
5. In the context of smart antenna, SAT stands for _____
a) Scholastic Assessment Test
b) Site Acceptance Test
d) Supervisory Audio Tones
Explanation: The out-of-band Supervisory Audio Tones generated by the basestation is relayed in the mobile. The base station can therefore differentiate its subscribers from cochannel interference based on SAT.
6. _____ process determines delay azimuth parameters.
b) Auto correlation
c) Cross correlation
Explanation: Cross correlation process determines delay azimuth parameters needed for the final beam forming-equalization stage. The resulting signal exhibits enhanced carrier to interference ratio.
7. Which of the following statements is false regarding the spatial distribution of a wavefront?
a) Multipath components are collinear with direct path
b) Multipath components have less signal strength than direct path
c) Multipath components are present
d) Multipath components exhibit time delay
Explanation: Multipath components exhibit delay with respect to main components. They are not collinear with direct path. They have less signal strength than direct path. When interference is present, it tends to mix with multipath components.
8. In space-time adaptive processing, _____ and equalization parameters are calculated _____
a) diversity, jointly
b) diversity, independently
c) beamforming, jointly
d) beamforming, independently
Explanation: Space-time adaptive processing involves two-dimensional filtering technique using a phased array antenna with multiple spatial channels. In space-time adaptive processing, beamforming and equalization parameters are calculated jointly.
9. In ____, the interference has difference placement on the long-code.
Explanation: Cellular systems employ different techniques to differentiate subscriber signal from co-channel interference. In the case of CDMA, the interference has a different placement on the long-code. In the case of GSM, the burst has different header bits.
10. ____ is a method used for calculating beamforming weights.
a) Sample matrix inversion
b) Indirect matrix inversion
Explanation: Sample matrix inversion or direct matrix inversion is a method used for calculating beamforming weights based on a known training sequence of length L. Adaptive algorithms iterate the weights in accordance to the received training sequence. A final estimate is obtained at the end of the training sequence.
11. ____ technique exploits lack of coherence between desired signal and interference.
a) Multibeam arrays
b) Adaptive spatial nulling
d) Space-time adaptive processing
Explanation: Space-time adaptive processing technique exploits lack of coherence between desired signal and interference. It separated the signals in parameter space. It can be employed to reduce collinear interference.
12. In_____, the highest-power signal is demodulated to estimate its bitstream.
a) maximum likelihood
b) sequential interference cancellation
c) least mean square
d) recursive least square
Explanation: In sequential interference cancellation, the highest-power signal is demodulated to estimate its bitstream. By employing this technique, co-channel interference from strongest interferer can be reduced substantially.
13. Decoded Channel Bits Interface is defined between ____ functional block and ____ functional block.
a) antenna, RF/IF
b) RF/IF, modem
c) modem, INFOSEC
d) INFOSEC, bitstream
Explanation: The process of digital to analog conversion, filtering add noise to signals. To mitigate this condition, an interface is introduced between the smart antenna and the core base station. Decoded Channel Bits Interface is defined betweenmodem functional block and INFOSEC functional block.
14. Multibeam antenna technology is more complex than null-forming.
Explanation: Null forming is more complex than mutlibeam antenna technology. Multibeam antenna is used to enhance SNR. Null-forming is used to suppress interference in high density traffic.
15. Maximum likelihood techniques formulate the likelihood ratio for a sequence of channel symbols.
Explanation: Maximum likelihood techniques formulate the likelihood ratio for a sequence of channel symbols. The maximum likelihood ratio determines signal parameter estimate.
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