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This set of Software Defined Radio online test focuses on “Antenna Tradeoffs – 2”.

1. Which of the following option cannot be employed to overcome fading?
a) Reduced channel symbol rates
b) Diversity transmission and reception
c) Decreased bandwidth
d) Structured data

Explanation: Increased instantaneous bandwidth for multipath resolution and equalization can mitigate the effect of fading. The reduction of channel symbol rate can reduce intersymbol interference. Diversity transmission and reception, and structuring of data provide resilience against fading.

2. Which of the following can reduce the probability of non-recoverable fade depth?
a) Diversity
b) FEC
c) Interleaving
d) FEC and Interleaving

Explanation: Diversity transmission and reception can reduce the probability of non-recoverable fade depth. It tends to choose the signal with maximum strength, improving the error floor. FEC and interleaving are useful for compensating the erasure caused by fading.

3. Doppler spread is given by _______
a) carrier frequency times the ratio of maximum velocity of a transmitter divided by propagation velocity
b) carrier frequency times the ratio of minimum velocity of a transmitter divided by propagation velocity
c) carrier frequency times the ratio of propagation velocity divided by maximum velocity of a transmitter
d) carrier frequency times the ratio of propagation velocity divided by minimum velocity of a transmitter

Explanation: Doppler spread is given by carrier frequency times the ratio of maximum velocity of a transmitter divided by propagation velocity. Doppler spread is observed in the study of spatial coherence.

4. The rule of thumb for antenna diversity states that for an antenna separation of 10 wavelengths or more, there is a considerable probability for the diversity signal to be substantially decorrelated from the primary signal.
a) True
b) False

Explanation: Doppler spread introduces decorrelation as a function of antenna separation.The rule of thumb for antenna diversity states that for an antenna separation of 10 wavelengths or more, there is a considerable probability for the diversity signal to be substantially decorrelated from the primary signal.

5. Cellular systems employ ____ sectorization.
a) two way
b) four way
c) eight way
d) three way

Explanation: The three way sectors are functionally distinct. Each sector is assigned with separate RF channels to satisfy high subscriber densities.
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6. _____ offers fade resistance for slow-moving mobiles.
a) FEC
b) Diversity
c) Frequency hopping
d) Interleaving

Explanation: Frequency hopping can provide fade resistance for slow-moving mobiles. GSM’s frequency hopping plan improves SNR by averaging deep fades.

7. Which stage carries out diversity combining?
a) RF access stage
b) IF stage
c) Bit stream processing stage
d) Development

Explanation: Diversity combining is performed in the IF stage. Diversity antennas require parallel RF/IF converters and ADC channels.

8. ______ combiner picks the diversity channel with maximum received signal strength.
a) Baseband diversity
b) Carrier diversity
c) Digital diversity
d) Analog diversity

Explanation: Analog diversity combiner selects the diversity channel with maximum signal strength whereas digital diversity combiner uses time delay and addition of signal to yield signal of better strength and coherence.

9. The increase in demand for DSP resources due to the introduction of diversity can be controlled by _______
a) dynamically-pooled DSP resources
b) increasing DSP resources
c) fixing the number of users
d) combining diversity with frequency hopping

Explanation: All subscribers do not require diversity simultaneously. Dynamically pooled DSP resources can be used to enhance channels with low carrier to interference ratio.

10. The physical location of the antennas may cause _____
a) site interference
b) co-site interference
c) diversity interference
d) diversity combining interference

Explanation: The impact of physical location of the antennas on self-generated EMI is called as co-site interference.It occurs when two or more closely located RF systems affect each other negatively.

11. Military applications resort to channelized architectures due to _____
a) excess of bandwidth
b) lack of bandwidth
c) excessive programmability
d) excess of bandwidth and programmability

Explanation: Military application resort to channelized architectures due to excess of bandwidth and programmability. The channelized architectures have dedicated antenna and RF conversion subsystem for each subbandof resonant antenna.

12. Which of the following is not influenced by antenna characteristics?
a) Gain
c) Number of DAC’s
d) Diversity

Explanation: Gain, number of antenna channels required to support multiband multimode operation, number of ADC’s and number of DAC’s are parameters influenced by antenna characteristics.

13. Which of the following is not observed due to co-site interference?
a) Eddy currents
b) Near field effects
c) Multicarrier active intermodulation
d) Multicarrier passive intermodulation

Explanation: Co-site interference may result in multimode, multiband antenna interaction, eddy currents, near field effects, electrical isolation and multicarrier active intermodulation.

14. Which of the following is not a challenge posed by antenna?
a) Multiband antenna
b) RF MEMS
c) Co-site interference
d) Programmability

Explanation: RF MEMS can improve the performance of the antenna by introducing re-configurability. Multiband antenna, co-site interference, and programmability are challenges posed by antenna.

15. Cost of production electronics is an exponential function of parts count, number of antennas, and related RF/IF paths.
a) True
b) False

Explanation: Cost of production electronics is a linear function of parts count, number of antennas and related RF/IF paths.Antenna and RF system accounts for nearly 60% of the total cost of a radio node.

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