GATE 2024 EC – Question 57
Let $X(t)=A\cos(2\pi f_0t+\theta)$ be a random process, where amplitude $A$ and phase $\theta$ are independent of each other, and are uniformly distributed in the intervals $[-2,2]$ and $[0,2\pi]$, respectively. $X(t)$ is fed to an 8-bit uniform mid-rise type quantizer. Given that the autocorrelation of $X(t)$ is $R_X(\tau)=\dfrac23\cos(2\pi f_0\tau)$, the signal to quantization noise ratio (in dB, rounded off to two decimal places) at the output of the quantizer is ________.
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Correct answer: 44.92 to 45.38
Explanation
The signal power is $R_X(0)=\frac23$. The input range is $[-2,2]$, so with 8 bits the step is $\Delta=4/2^8=1/64$ and the quantization noise power is $\Delta^2/12=\dfrac{1}{4096\times12}=2.035\times10^{-5}$. SQNR $=\dfrac{2/3}{1/(4096\cdot12)}=32768$, i.e. $10\log_{10}32768=45.15$ dB.