Digital communication is distinguished by what symbol-alphabet feature?
A Unbounded phase
B Continuous amplitude
C Finite symbol set
D Fixed carrier frequency
Answer: C. Finite symbol set. A digital link represents information with a finite set of symbols.
Regularly spaced analog measurements are produced by which operation?
A Decoding
B Encoding
C Quantization
D Sampling
Answer: D. Sampling. Sampling records signal values at chosen time instants.
For a signal with highest frequency fmax, what is its Nyquist sampling rate?
A 2fmax
B fmax/2
C fmax
D 4fmax
Answer: A. 2fmax. The theoretical Nyquist rate is twice the highest signal frequency; practical links usually sample faster.
Within PCM, which stage assigns each sample a discrete amplitude level?
A Sampling
B Quantization
C Multiplexing
D Encoding
Answer: B. Quantization. Quantization maps sampled amplitudes to a finite set of levels.
After quantization, which stage turns levels into binary words?
A Reconstruction
B Filtering
C Sampling
D Encoding
Answer: D. Encoding. The encoder represents each quantized level with a binary codeword.
How many bits are required to label eight amplitude levels?
A 3 bits
B 2 bits
C 4 bits
D 8 bits
Answer: A. 3 bits. Three bits represent 2³, or eight, distinct levels.
The sample-to-quantized-level difference is called what?
A Codeword length
B Timing jitter
C Quantization error
D Carrier-frequency offset
Answer: C. Quantization error. Quantization error is the difference between the sample and its assigned level.
At 8 ksamples/s and 8 bits/sample, calculate the PCM bit rate.
A 32 kb/s
B 16 kb/s
C 8 kb/s
D 64 kb/s
Answer: D. 64 kb/s. Bit rate equals 8,000 samples/s × 8 bits/sample.
Instead of full samples, what does DPCM transmit?
A Prediction error
B Quantizer level count
C Sample time
D Carrier phase
Answer: A. Prediction error. DPCM sends the difference between a sample and its predicted value.
Does a one-bit delta modulator report an upward or downward step?
A Carrier phase
B Up/down direction
C Symbol frequency
D Absolute amplitude
Answer: B. Up/down direction. Each bit indicates whether the staircase rises or falls.
Successive marks alternate pulse polarity in which line code?
A Bipolar RZ
B AMI
C Unipolar NRZ
D Manchester
Answer: B. AMI. Alternate mark inversion assigns alternating positive and negative pulses to successive ones.
Name the line code with a guaranteed mid-bit transition.
A AMI
B Unipolar NRZ
C Polar RZ
D Manchester
Answer: D. Manchester. Manchester coding uses a transition in the middle of each bit interval.
Baud rate measures what per second?
A Samples only
B Errors only
C Bits only
D Symbols
Answer: D. Symbols. Baud is the number of transmitted symbols per second.
How many bits does binary signaling carry per symbol?
A One bit
B Two bits
C Three bits
D Four bits
Answer: A. One bit. A binary alphabet has two symbol choices, so each symbol carries one bit.
ASK represents symbols by changing which carrier property?
A Phase
B Frequency
C Amplitude
D Polarization
Answer: C. Amplitude. Amplitude shift keying conveys symbols through carrier-amplitude changes.
In FSK, which carrier property varies between symbols?
A Frequency
B Amplitude
C Phase
D Pulse width
Answer: A. Frequency. Frequency shift keying represents symbols with different carrier frequencies.
BPSK distinguishes its two symbols through which property?
A Amplitude
B Phase
C Sampling rate
D Pulse width
Answer: B. Phase. Binary phase shift keying uses two carrier phases.
How many phase states does BPSK use?
A Four
B Two
C Eight
D One
Answer: B. Two. BPSK uses two distinct phase states.
One QPSK symbol carries how many information bits?
A Three
B One
C Two
D Four
Answer: C. Two. QPSK has four symbols, which represent log₂4 = 2 bits.
Expand the abbreviation AWGN.
A Additive white Gaussian noise
B Average weighted gain noise
C Additive waveform gradient noise
D Alternating wide Gaussian noise
Answer: A. Additive white Gaussian noise. AWGN means additive white Gaussian noise.
Known-pulse detection in white noise uses which filter for maximum output SNR?
A Notch filter
B Differentiator
C Integrator
D Matched filter
Answer: D. Matched filter. The matched filter maximizes output signal-to-noise ratio for a known signal in white noise.
Pulse tails overlapping at decision times produce which interference?
A Quantizer saturation
B Inter-symbol interference (ISI)
C Codeword inversion
D Carrier suppression
Answer: B. Inter-symbol interference (ISI). Pulse tails can interfere at another symbol’s decision time, producing inter-symbol interference.
Nyquist zero-ISI shaping requires what at other symbol-spaced samples?
A No carrier phase
B Constant noise power
C Equal pulse amplitudes
D Zeros at other symbol samples
Answer: D. Zeros at other symbol samples. The pulse response is zero at all other symbol-spaced sampling instants.
Timing and noise margins appear in which display?
A Parity matrix
B Spectrum mask
C Eye diagram
D Constellation table
Answer: C. Eye diagram. An eye diagram shows timing margin and vertical noise margin.
Improved transmission reliability comes from adding what with channel coding?
A Carrier amplitude
B Extra message bandwidth only
C Controlled redundancy
D Sampling jitter
Answer: C. Controlled redundancy. Redundant coded bits help detect or correct transmission errors.