Aptitude [Sasken Placement]: Sample Questions 33 - 34 of 35

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Question 33

Aptitude
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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 for BPSK Constellation Diagram for QPSK
    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

Question 34

Aptitude
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What is error control in OSI Model?

Explanation

Error control is the process of detecting and correcting both the bit level and packet level errors.

Error Detection

Error detection is the process of detecting the error during the transmission between the sender and the receiver.

Error Correction

This type of error control allows a receiver to reconstruct the original information when it has been corrupted during transmission.

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