Question

Find EyNo and Amplitude A required to give Pb = 10-5 for the following coherent digital modulation schemes if No: 10% and time is 0.5msec 2. a. i. On-Off keying (ASK) ii BPSK, i BFSK and iv. BPSK with a phase error of 5 deg. (Each carry 4 Marks)

Answer 1

(i) For on-off keying (ASK),

Pb

Given P_b = 10^-5

Q(周一10-5

= 18.19

or
12.6dB Лу

Given, N_o = 10^-5 and T = 0.5 msec = 0.5 x 10^-3 sec.

so,

= 18.19

  
18.19 × 10-5 E,

18.19 × 10-5 b =

18.19 × 10-5 × 2 -= 0.7276 0.5 ×10

(ii) For BPSK,

2Eb

Given P_b = 10^-5

2

No = 9.1

or  $\Rightarrow \frac{E_{b}}{N_{o}}=9.59 dB$

Given, N_o = 10^-5 and T = 0.5 msec = 0.5 x 10^-3 sec.

so,

No = 9.1

E, 9.1 × 10-

$\Rightarrow E_{b}=\frac{A^{2}T}{2}=9.1\times 10^{-5}$

$\Rightarrow A=\frac{9.1\times 10^{-5}\times 2}{0.5\times 10^{-3}}=0.364$

(iii) Binary FSK (BFSK) is same as ASK.

so,

= 18.19

or
12.6dB Лу

18.19 × 10-5 × 2 -= 0.7276 0.5 ×10

(iv) The degradation of BPSK with a phase error of 5 degree is-

$D_{const}=-20log_{10}[cos(5^{\circ})]=0.033dB$

So the required SNR to give a bit error probability of 10^-5 is 9.59+0.033 = 9.623 dB.