Basics Of Software Defined Radio Architectures And Building Blocks Of Sdr Waveform Development For Sdr

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Girish Chandra
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Quizzes Created: 1 | Total Attempts: 145
Questions: 25 | Attempts: 145

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Questions and Answers
  • 1. 

    What is the major drawback of Superheterodyne transceivers with respect to homodyne receivers?

    • A.

      I/Q imbalance

    • B.

      LO leakage

    • C.

      DC Offset

    • D.

      Difficult to integrate on-chip

    Correct Answer
    D. Difficult to integrate on-chip
    Explanation
    The major drawback of Superheterodyne transceivers with respect to homodyne receivers is that they are difficult to integrate on-chip. This means that it is challenging to incorporate all the necessary components and circuitry of a Superheterodyne transceiver onto a single integrated circuit chip. On the other hand, homodyne receivers are generally easier to integrate on-chip, making them more suitable for compact and integrated systems.

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  • 2. 

    The transmit frequency is kept higher to

    • A.

      Be able to use smaller antenna size

    • B.

      To send more information

    • C.

      Both of above

    • D.

      None of above

    Correct Answer
    A. Be able to use smaller antenna size
    Explanation
    The transmit frequency is kept higher in order to be able to use smaller antenna size. Higher frequencies have shorter wavelengths, which allows for the use of smaller antennas. Smaller antennas are desirable for various reasons, such as reducing the overall size and weight of the equipment, improving portability, and minimizing interference with other devices. By using higher frequencies, the transmission can still be effective while utilizing smaller antennas.

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  • 3. 

    Which of the following is a drawback of Homodyne transceivers:

    • A.

      I/Q imbalance component can be avoided by filtering.

    • B.

           Large size as compared to other architectures.

    • C.

      Difficult to integrate on-chip

    • D.

      DC offset errors interefere with signal of interest.

    Correct Answer
    D. DC offset errors interefere with signal of interest.
    Explanation
    DC offset errors interfere with the signal of interest in homodyne transceivers. This means that the presence of DC offset errors can disrupt the accuracy and quality of the received signal, causing interference and potentially impacting the overall performance of the transceiver.

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  • 4. 

    Without using an IF frequncy, the desired signal is directly frequency downconverted to baseband / frequency up-converted to RF in

    • A.

      Superheterodyne transmitter/ Superheterodyne receiver

    • B.

      Superheterodyne receiver/ Superheterodyne transmitter

    • C.

      Homodyne receiver/ Homodyne transmitter

    • D.

      Homodyne transmitter/ Homodyne receiver

    Correct Answer
    C. Homodyne receiver/ Homodyne transmitter
    Explanation
    In a homodyne receiver/transmitter, the desired signal is directly frequency downconverted to baseband/frequency up-converted to RF without using an IF frequency. This means that the signal is directly converted to a lower frequency (downconversion) or higher frequency (up-conversion) without the need for an intermediate frequency stage. This approach simplifies the overall design and reduces complexity, making it a suitable choice for certain applications. In contrast, a superheterodyne receiver/transmitter uses an intermediate frequency stage to convert the desired signal to a fixed intermediate frequency before further processing.

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  • 5. 

    If measure SNR is around 98 dB in an ADC. What is bit-resolution of ADC ?

    • A.

      16-bit

    • B.

      10-bit

    • C.

      12-bit

    • D.

      8-bit

    Correct Answer
    A. 16-bit
    Explanation
    The signal-to-noise ratio (SNR) is a measure of the quality of a signal compared to the level of background noise. A higher SNR indicates a better quality signal. In this case, with an SNR of 98 dB, it suggests that the signal is very strong compared to the noise. The bit-resolution of an ADC refers to the number of bits used to represent the analog signal digitally. A higher bit-resolution allows for more precise representation of the signal. Therefore, a 16-bit ADC would be able to accurately capture and represent the strong signal with a high SNR of 98 dB.

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  • 6. 

    Which of the following is merit of out-of-band error

    • A.

      NMSE

    • B.

      ACPR

    • C.

      EVM

    • D.

      BER

    Correct Answer
    B. ACPR
    Explanation
    ACPR stands for Adjacent Channel Power Ratio. It is a measure of the power leakage from a signal into adjacent frequency channels. A lower ACPR value indicates better performance, as it means that there is less interference with neighboring channels. Therefore, ACPR is considered a merit or advantage of out-of-band error, as it helps to ensure that the signal is contained within its assigned frequency range and does not cause interference with other signals.

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  • 7. 

    Numerically Controlled Oscillators is used in

    • A.

      Superheterodyne architecture

    • B.

      Digital-IF based Homodyne architecture

    • C.

      Homodyne architecture

    • D.

      Dual-conversion superheterodyne architecture

    Correct Answer
    B. Digital-IF based Homodyne architecture
    Explanation
    Numerically Controlled Oscillators (NCOs) are used in the Digital-IF based Homodyne architecture. In this architecture, the incoming radio frequency (RF) signal is directly converted to a baseband frequency using a mixer and a local oscillator (LO). The NCO is then used to generate a digitally controlled LO signal, which allows for precise control and adjustment of the frequency. This architecture is commonly used in modern communication systems, as it offers improved flexibility, reduced power consumption, and simplified integration with digital signal processing algorithms.

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  • 8. 

    Increase in fIF (IF frequency) in Superheterodyne transceivers is not related to

    • A.

      Capability of filtering the image signal.

    • B.

      Increase in constraint on DAC and ADC.

    • C.

      Increase in clock jitter.

    • D.

      Increase in I/Q imbalance component power

    Correct Answer
    D. Increase in I/Q imbalance component power
    Explanation
    Increasing the I/Q imbalance component power in Superheterodyne transceivers does not affect the increase in fIF (IF frequency). The increase in fIF is primarily determined by the capability of filtering the image signal, the constraint on DAC and ADC, and the clock jitter. Therefore, the correct answer is that the increase in I/Q imbalance component power is not related to the increase in fIF.

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  • 9. 

    Digital-IF based Homodyne transmitter require

    • A.

      Numerically Controlled Oscillators

    • B.

      Two LOs

    • C.

      Two bandpass filters.

    • D.

      More than two LOs and Oscillators.

    Correct Answer
    A. Numerically Controlled Oscillators
    Explanation
    A Digital-IF based Homodyne transmitter requires Numerically Controlled Oscillators (NCOs) because NCOs are used to generate the local oscillator (LO) signals in a digital form. These LO signals are then mixed with the baseband signals to produce the desired RF signals. By using NCOs, the frequency and phase of the LO signals can be easily controlled and adjusted digitally, allowing for greater flexibility and accuracy in the transmitter's operation. This is why NCOs are required in a Digital-IF based Homodyne transmitter.

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  • 10. 

    In an analog quadrature modulator, frequency of input data is 30 MHz and LO frequency is1.8 GHz. What would be frequency of output RF?

    • A.

      1.8 GHz

    • B.

      1.86 GHz

    • C.

      1.83 GHz

    • D.

      None of the above

    Correct Answer
    C. 1.83 GHz
    Explanation
    In an analog quadrature modulator, the frequency of the output RF signal is determined by the sum of the input data frequency and the LO frequency. In this case, the input data frequency is 30 MHz and the LO frequency is 1.8 GHz. Adding these two frequencies together gives us a total frequency of 1.83 GHz, which is the frequency of the output RF signal.

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  • 11. 

    This is not a benefit of oversampling:

    • A.

      Improved bit-resolution of ADC

    • B.

      Increase in SNR.

    • C.

      Avoid aliasing

    • D.

      Decrease in I/Q imbalance signal power.

    Correct Answer
    D. Decrease in I/Q imbalance signal power.
    Explanation
    Oversampling is a technique used to improve the performance of analog-to-digital converters (ADCs). It involves sampling the input signal at a rate higher than the Nyquist rate. Oversampling can improve the bit-resolution of the ADC, increase the signal-to-noise ratio (SNR), and avoid aliasing. However, it does not directly address the issue of I/Q imbalance signal power. I/Q imbalance refers to the mismatch between the in-phase (I) and quadrature (Q) components of a signal. Oversampling may indirectly help mitigate I/Q imbalance, but it is not a direct benefit of oversampling.

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  • 12. 

    Which of the following is not true regarding software-defined-radios

    • A.

      Functions are digitally defined

    • B.

      Reconfigurable

    • C.

      No hardware is required at all

    • D.

      Algorithms should be updated according to the digital platform

    Correct Answer
    C. No hardware is required at all
    Explanation
    Software-defined radios (SDRs) are radios in which the functions are digitally defined and can be reconfigured. They rely on algorithms that can be updated according to the digital platform. However, it is not true that no hardware is required at all for SDRs. While SDRs do rely heavily on software, they still require hardware components such as antennas, amplifiers, and converters to transmit and receive radio signals. Therefore, the statement "No hardware is required at all" is not true regarding software-defined radios.

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  • 13. 

    Pulse shaping is applied on the digitally modulated signal to

    • A.

            Enhance signal quality

    • B.

            Be able to send more information

    • C.

      Contain the signal information in smaller bandwidth

    • D.

      Remove the need for power amplifier

    Correct Answer
    C. Contain the signal information in smaller bandwidth
    Explanation
    Pulse shaping is applied on the digitally modulated signal to contain the signal information in smaller bandwidth. This is achieved by shaping the pulses of the signal in such a way that they occupy less frequency spectrum. By reducing the bandwidth required for transmission, more signals can be accommodated within a given frequency range, allowing for efficient use of the available bandwidth.

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  • 14. 

    Which of the following are the limitations in achieving (completely digital) ideal software define radios

    • A.

      Baseband Processing

    • B.

      Local Oscillators, due to phase noise

    • C.

      Sampling speed of A/D and D/A, which is sufficient to cover transmission frequency

    • D.

      Data encoding which consumes digital resources

    Correct Answer
    C. Sampling speed of A/D and D/A, which is sufficient to cover transmission frequency
    Explanation
    The correct answer is the sampling speed of A/D and D/A, which is sufficient to cover the transmission frequency. This limitation refers to the need for the analog-to-digital (A/D) and digital-to-analog (D/A) converters to have a sampling speed that can adequately capture and reproduce the frequency range of the transmitted signal. If the sampling speed is not sufficient, it can result in distortion or loss of information in the signal, affecting the performance of the software-defined radio system.

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  • 15. 

    Please consider following sentences (i) Rectangular signal in time domain corresponds to a SINC signal in frequency domain. (ii) Rectangular signal in frequency domain corresponds to a SINC signal in time domain.

    • A.

      Only (i) is true

    • B.

      Only (ii) is true

    • C.

      Both (i) and (ii) are wrong

    • D.

       Both (i) and (ii) are correct

    Correct Answer
    D.  Both (i) and (ii) are correct
    Explanation
    The correct answer is that both (i) and (ii) are correct. This means that a rectangular signal in the time domain corresponds to a SINC signal in the frequency domain, and vice versa. This is because the Fourier Transform of a rectangular signal is a SINC function, and the inverse Fourier Transform of a SINC function is a rectangular signal. Therefore, both statements are true.

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  • 16. 

    Select the correct statement

    • A.

      SNR is lower than the SNDR

    • B.

                  SINAD is lower than the SNDR

    • C.

      SINAD is lower than the SNR

    • D.

                 SNR is lower than the SINAD

    Correct Answer
    C. SINAD is lower than the SNR
    Explanation
    SINAD (Signal-to-Noise and Distortion Ratio) represents the ratio of the signal power to the sum of noise and distortion power. SNR (Signal-to-Noise Ratio) represents the ratio of the signal power to the noise power. Since SINAD includes both noise and distortion in its calculation, it will always be lower than SNR, which only considers the noise. Therefore, the statement "SINAD is lower than the SNR" is correct.

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  • 17. 

    Which of the following are most suitable for computation heavy applications

    • A.

      Digital signal processor

    • B.

      Graphics processing units

    • C.

      General-purpose microprocessors

    • D.

      Field programmable gate arrays

    Correct Answer
    B. Graphics processing units
    Explanation
    Graphics processing units (GPUs) are most suitable for computation heavy applications because they are specifically designed to handle complex mathematical calculations and parallel processing tasks. GPUs have a large number of cores that can perform multiple calculations simultaneously, making them highly efficient for tasks such as rendering graphics, running simulations, and performing scientific computations. Additionally, GPUs have high memory bandwidth and can handle large amounts of data, further enhancing their suitability for computation heavy applications.

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  • 18. 

    Highest frequency in the discrete domain is given by

    • A.

      Angular frequency π, frequency 0.5.

    • B.

      Angular frequency π, frequency 0.75.

    • C.

      Angular frequency 4π, frequency 0.5.

    • D.

      Angular frequency π, frequency 1.

    Correct Answer
    A. Angular frequency π, frequency 0.5.
    Explanation
    The highest frequency in the discrete domain is given by the combination of angular frequency π and frequency 0.5. This means that the function oscillates at a rate of π radians per sample, and each oscillation completes 0.5 cycles within that sample. This combination of angular frequency and frequency results in the highest frequency in the discrete domain.

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  • 19. 

    We need to apply N- point DFT for 16382 samples, which of the following is the most suitable value of N to be implemented in a DSP

    • A.

      16384

    • B.

      10000

    • C.

      15000

    • D.

      16380

    Correct Answer
    A. 16384
    Explanation
    The most suitable value of N to be implemented in a DSP for applying N-point DFT for 16382 samples is 16384. This is because the N-point DFT requires the number of samples to be a power of 2. Therefore, the closest power of 2 to 16382 is 16384, making it the most suitable value of N.

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  • 20. 

    Applying windowing techniques in time domain waveform results in

    • A.

      Broader main lobe

    • B.

      Better attenuation of side lobes

    • C.

      Less spectrum leakage

    • D.

      All of the above

    Correct Answer
    D. All of the above
    Explanation
    Applying windowing techniques in time domain waveform results in all of the above. Windowing broadens the main lobe of the waveform, which can help improve the accuracy of frequency analysis. It also helps attenuate the side lobes, reducing the impact of unwanted frequencies or noise. Additionally, windowing can help minimize spectrum leakage, which occurs when spectral components from outside the main lobe leak into the desired frequency range. Therefore, all of these benefits are achieved by applying windowing techniques.

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  • 21. 

    Under-sampling methods allow utilizing lower sampling rates than the highest frequency of the incoming signal for

    • A.

      Pass-band signal

    • B.

      Base-band signal

    • C.

      Both of above

    • D.

      None of above

    Correct Answer
    A. Pass-band signal
    Explanation
    Under-sampling methods allow utilizing lower sampling rates than the highest frequency of the incoming signal for pass-band signals. This means that the sampling rate can be reduced without losing important information in the frequency range of interest. Base-band signals, on the other hand, require a sampling rate at least twice the highest frequency component to avoid aliasing. Therefore, under-sampling is not applicable for base-band signals.

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  • 22. 

    For band-pass sampling

    • A.

      Lower ADC bandwidth is required as compared to baseband sampling technique.

    • B.

      The sampling rate of ADC is always higher than the baseband sampling technique.

    • C.

      Both of above

    • D.

      None of above

    Correct Answer
    D. None of above
    Explanation
    The correct answer is "None of above" because band-pass sampling and baseband sampling are two different techniques used for different types of signals. In band-pass sampling, the signal of interest is a band-limited signal, and the ADC needs to have a higher bandwidth to accurately capture the signal. In baseband sampling, the signal of interest is a low-frequency signal, and the ADC can have a lower bandwidth. Therefore, the statement that a lower ADC bandwidth is required for band-pass sampling compared to baseband sampling is incorrect. Additionally, the statement that the sampling rate of the ADC is always higher than the baseband sampling technique is also incorrect as it depends on the specific application and signal requirements.

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  • 23. 

    For measuring time domain performance and frequency domain performance respectively, we require

    • A.

      Oscilloscope and Spectrum analyzer respectively.

    • B.

      Spectrum analyzer and Oscilloscope respectively.

    • C.

      Oscilloscope only.

    • D.

      Spectrum analyzer only.

    Correct Answer
    A. Oscilloscope and Spectrum analyzer respectively.
    Explanation
    In order to measure time domain performance, an oscilloscope is required as it is used to display and analyze the waveform of a signal over time. On the other hand, for measuring frequency domain performance, a spectrum analyzer is needed as it is used to analyze the frequency spectrum of a signal and identify the different frequencies present in it. Therefore, the correct answer is Oscilloscope and Spectrum analyzer respectively.

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  • 24. 

    If the IF frequency in a transmitter is equal to 0 then the architecture of the transmitter is called

    • A.

      Superheterodyne / Digital-IF

    • B.

      Homodyne / Direct Conversion.

    • C.

      Superheterodyne / Direct Conversion

    • D.

      Homodyne / Digital-IF

    Correct Answer
    B. Homodyne / Direct Conversion.
    Explanation
    If the IF frequency in a transmitter is equal to 0, then the architecture of the transmitter is called Homodyne / Direct Conversion. In this architecture, the incoming signal is directly mixed with a local oscillator signal to produce the desired frequency without the need for intermediate frequency (IF) stages. This eliminates the need for frequency conversion and simplifies the transmitter design.

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  • 25. 

    What to do you understand by Digital IF

    • A.

      IF Shift using analog component

    • B.

      IF Shift in baseband 

    • C.

      Both a and b

    • D.

      None of the above.

    Correct Answer
    B. IF Shift in baseband 
    Explanation
    Digital IF refers to the use of digital signal processing techniques in the intermediate frequency (IF) stage of a communication system. It involves shifting the IF signal to the baseband frequency range for further processing. This allows for more efficient and flexible signal manipulation, as digital processing offers advantages such as programmability and the ability to implement complex algorithms. Analog IF shift, on the other hand, involves using analog components to shift the IF signal. Therefore, the correct answer is "IF Shift in baseband".

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