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ISRO Scientist EC 2016 Official Paper

Option 2 : 800

ISRO Scientist ECE: 2020 Official Paper

349

80 Questions
240 Marks
90 Mins

**Concept:**

QPSK is a modulation scheme that allows one symbol to transfer two bits of data. There are four possible two-bit numbers (00, 01, 10, 11).

\(Bandwidth = \frac{{2{R_b}}}{{{{\log }_2}M}}\)

**Analysis:**

Transmission bandwidth

\(= \frac{{2{R_b}}}{{{{\log }_2}4}} = {R_b}\)

Maximum required bandwidth

\(= \frac{{{R_b}}}{2}\)

40% of \(\frac{{{R_b}}}{2} = 0.2\;{R_b}\)

Total = (0.2 + 0.5) R_{b} = 0.7 R_{b}

No. of channels required

\( = \frac{{36 \times {{10}^6}}}{{0.7 \times 64 \times {{10}^3}}} \approx 800\)