With 16-QAM, how many bits are carried per symbol?
A 3 bits
B 8 bits
C 4 bits
D 2 bits
Answer: C. 4 bits. Sixteen constellation points represent log₂16 = 4 bits per symbol.
At 3000 symbols/s, what raw rate does 16-QAM provide?
A 24 kb/s
B 3 kb/s
C 12 kb/s
D 6 kb/s
Answer: C. 12 kb/s. The rate is 3,000 symbols/s × 4 bits/symbol.
What PCM rate results from 8 ksamples/s and 7 bits/sample?
A 56 kb/s
B 32 kb/s
C 8 kb/s
D 64 kb/s
Answer: A. 56 kb/s. Multiplying the sample rate by bits per sample gives 56 kb/s.
How many quantization levels does an 8-bit PCM word select?
A 512 levels
B 128 levels
C 64 levels
D 256 levels
Answer: D. 256 levels. An 8-bit word represents 2⁸ = 256 levels.
Sampling a 6 kHz bandlimited input at 13 kHz is how far above Nyquist?
A 7 kHz
B 1 kHz
C 0.5 kHz
D 2 kHz
Answer: B. 1 kHz. Twice 6 kHz is 12 kHz; 13 kHz is 1 kHz higher.
What symbol rate carries 12 kb/s using QPSK?
A 24 kbaud
B 6 kbaud
C 3 kbaud
D 12 kbaud
Answer: B. 6 kbaud. QPSK carries two bits per symbol, so 12 kb/s needs 6 kbaud.
Binary signaling at 2400 baud yields what bit rate?
A 2400 b/s
B 1200 b/s
C 9600 b/s
D 4800 b/s
Answer: A. 2400 b/s. Binary signaling carries one bit per symbol.
How many bits per symbol does 32-PSK carry?
A 3 bits
B 5 bits
C 4 bits
D 6 bits
Answer: B. 5 bits. Thirty-two phase states represent log₂32 = 5 bits.
Neighboring Gray-coded constellation points differ by how many bits?
A 4 bits
B 3 bits
C 2 bits
D 1 bit
Answer: D. 1 bit. Gray labels assign adjacent points codewords differing in one bit.
QPSK’s I and Q carriers are separated by what phase?
A 90 degrees
B 60 degrees
C 180 degrees
D 45 degrees
Answer: A. 90 degrees. The in-phase and quadrature carriers are orthogonal, with a 90-degree phase offset.
Five bit errors occur in 1000 bits. What is BER?
A 0.05
B 0.0005
C 0.005
D 0.5
Answer: C. 0.005. BER is 5 divided by 1,000, or 0.005.
Even parity requires what total count of ones?
A Odd count
B Zero count
C Even count
D Prime count
Answer: C. Even count. The parity bit is chosen so the complete word has an even number of ones.
In a (7,4) block code, how many data bits are carried?
A 4 bits
B 3 bits
C 7 bits
D 11 bits
Answer: A. 4 bits. The notation (7,4) specifies four information bits in each seven-bit codeword.
Each input bit produces how many coded bits with a rate-1/2 encoder?
A 1 bit
B 4 bits
C 2 bits
D 3 bits
Answer: C. 2 bits. A rate-1/2 code uses two coded bits for each information bit.
What is the noiseless binary Nyquist limit for a 3 kHz channel?
A 3 kb/s
B 6 kb/s
C 12 kb/s
D 1.5 kb/s
Answer: B. 6 kb/s. The maximum binary signaling rate is 2B, or 6,000 symbols/s and bits/s.
For B=3 kHz and S/N=3, find Shannon capacity.
A 9 kb/s
B 6 kb/s
C 3 kb/s
D 12 kb/s
Answer: B. 6 kb/s. C = B log₂(1+S/N) = 3 kHz × log₂4 = 6 kb/s.
Eight-PSK adjacent phases are separated by what angle?
A 22.5 degrees
B 60 degrees
C 90 degrees
D 45 degrees
Answer: D. 45 degrees. Eight equally spaced phases divide 360° into 45° intervals.
Convert 0 dB SNR to a linear power ratio.
A 2
B 0
C 10
D 1
Answer: D. 1. A 0 dB power ratio corresponds to a linear ratio of one.
At equal bit rate, 16-QAM needs what fraction of BPSK’s symbol rate?
A One-quarter
B The same
C Four times
D One-half
Answer: A. One-quarter. Sixteen-QAM carries four bits per symbol; BPSK carries one.
Which receiver chooses the most likely transmitted symbol?
A Envelope detector
B Slope detector
C Parity checker
D Maximum-likelihood detector
Answer: D. Maximum-likelihood detector. Maximum-likelihood detection selects the symbol with the greatest likelihood.
Coherent QPSK detection requires which synchronized reference?
A Quantizer step
B Parity bit
C Carrier phase
D Symbol alphabet
Answer: C. Carrier phase. Coherent detection needs a phase-aligned carrier reference.
The binary Hamming distance between 1010 and 1000 is what?
A 2 bits
B 1 bit
C 0 bits
D 3 bits
Answer: B. 1 bit. The words differ in one bit position.
When a symbol lasts 0.25 ms, what is its symbol rate?
A 40 kbaud
B 0.25 kbaud
C 2 kbaud
D 4 kbaud
Answer: D. 4 kbaud. The symbol rate is 1/0.00025 s = 4,000 symbols/s.
Baseband pulse generation from data bits is performed by which process?
A Line coding
B Quantization
C Sampling
D Carrier recovery
Answer: A. Line coding. Line coding maps bits to a baseband signal waveform.
Forward error correction enables what at the receiver?
A Correct errors without retransmission
B Remove sampling
C Raise carrier frequency
D Avoid all noise
Answer: A. Correct errors without retransmission. FEC adds structured redundancy so the receiver can correct some errors locally.