Communication

Q:   Consider the following amplitude modulated signal:
s(t)=cos(2000πt)+4cos(2400πt)+cos(2800πt).
The ratio (accurate to three decimal places) of the power of the message signal to the power of the carrier signal is __________.

Q:   Which one of the following statements about differential pulse code modulation (DPCM) is true?

• A:  The sum of message signal sample with its prediction is quantized
• B:  The message signal sample id directly quantized, and its prediction is not used
• C:  The difference of message signal sample and a random signal is quantized
• D:  The difference of message signal with its prediction is quantized

Q:   Consider the random process X(t)=U+Vt where U is a zero-mean Gaussian random variable and V is a random variable uniformly distributed between 0 and 2. Assume that U and V are statistically independent. The mean value of the random process at t = 2 is________

Q:   Consider binary data transmission at a rate of 56 kbps using baseband binary pulse amplitude modulation (PAM) that is designed to have a raised-cosine spectrum. The transmission bandwidth (in kHz) required for a roll-off factor of 0.25 is ________

Q:   An ideal band-pass channel 500 Hz - 2000 Hz is deployed for communication. A modem is designed to transmit bits at the rate of 4800 bits/s using 16-QAM. The roll-off factor of a pulse with a raised cosine spectrum that utilizes the entire frequency band is ________

Q:   The transmitted signal in a GSM system is of 200 kHz bandwidth and 8 users share a common bandwidth using TDMA. If at a given time 12 users are talking in a cell, the total bandwidth of the signal received by the base station of the cell will be at least (in kHz) _______.

Q:   The modulation scheme commonly used for transmission from GSM mobile terminals is

• A:  4-QAM
• B:  16-PSK
• C:  Walsh-Hadamard orthogonal codes
• D:  Gaussian Minimum Shift Keying (GMSK)

Q:   Consider sinusoidal modulation in an AM system. Assuming no overmodulation, the modulation index (μ) when the maximum and minimum values of the envelope, respectively, are 3 V and 1 V, is ________.

Q:   An analog voltage in the range 0 to 8 V is divided in 16 equal intervals for conversion to 4-bit digital output. The maximum quantization error (in V) is _________

Q:   In a PCM system, the signal m(t)={sin(100πt )+cos(100πt )} V is sampled at the Nyquist rate. The samples are processed by a uniform quantizer with step size 0.75 V. The minimum data rate of the PCM system in bits per second is _____.