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ISRO (VSSC) Technical Assistant Electronics 2019 Official Paper

Option 2 : Twice

NIC Scientist B 2020: Full Mock Test

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120 Questions
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180 Mins

__Concept__**:**

For the same symbol rate (R_{s}), the data rate for different modulation techniques is as shown:

__BPSK__:

\({\left( {Data\;rate} \right)_{BPSK}} = \frac{1}{{{T_s}}} = 1\;{R_s}\;bps\)

Since in BPSK, only one bit per symbol is transmitted.

__QPSK__**:**

\({\left( {Data\;rate} \right)_{QPSK}} = \frac{2}{{{T_s}}} = 2{R_s}\;bps\)

∴ (Data rate)_{QPSK} = 2 × (Data rate)_{BPSK}

Since in QPSK, only two bits per symbol are transmitted.

Therefore, we can say that the data rate of QPSK is twice as that of BPSK for the same symbol rate.

__Important Points__:

- Bit rate or Data rate (R
_{b}) is the transmission of the number of bits per second. - Symbol rate or Band rate (R
_{s}) is the transmission of the number of symbols per second. - Bit rate = (symbol rate) × (number of bits per symbol)
- Bandwidth of BPSK = 2R
_{b}and Bandwidth of QPSK = R_{b}

So, we can say that the Bandwidth of QPSK is half of the bandwidth of BPSK.