Sasken Papers: Sample Questions 28 - 29 of 35

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Question number: 28

» Aptitude

Short Answer Question▾

Write in Short

When asked what the time is, a person answered that the amount of time left is 1/5

of the time already completed. What is the time?

Explanation

  • Whole day is of 24 hours.
  • Let, the completed time is x and remaining time is 24 – x.
  • When a person is asked for time, he answered that the amount of time left is 1/5 of the time already completed.
  • Writing the statement into equation form,

  • So, current time is 20 hrs or 8: 00 p. m.

Question number: 29

» Aptitude

Short Answer Question▾

Write in Short

What is the difference between PSK and QPSK?

Explanation

  • Phase shift keying (PSK) is a digital modulation scheme that conveys data by changing, or modulating, the phase of a reference singnal (the carrier wave). Various types of PSK are, BPSK (Binary Phase Shift Keying), QPSK (Quadrature Phase Shift Keying), OQPSK (Offset Quadrature Phase Shift Keying), / 4 QPSK (Π/ 4 – Quadrature Phase Shift Keying) and DPSK (Differential Phase Shift Keying).
  • In PSK or BPSK we use only one single type of phase shift for a bit transition, whereas in QPSK we use four types of phase shift for a bit transition.
    Constellation Diagram

    Constellation Diagram

    Constellation diagram for BPSK Constellation diagram for QPSK

     Constellation Diagram

    Constellation Diagram

    Constellation diagram of BPSK shows that only two symbols are transmitted (0 and 1), which requires only one bit. In case of QPSK, four symbols are transmitted (00,01,10,11), which requires two bit. The phase shift between two BPSK symbols is 180 degrees while 90 degree in case of QPSK.