Communication Systems
NEC Electrical and Electronic Engineering · 713 practice MCQs
The 'Communication Systems' chapter in the Electrical and Electronic Engineering discipline covers essential concepts such as Pulse Code Modulation (PCM), Block Codes, and Quadrature Amplitude Modulation (QAM). With 713 practice MCQs, this chapter prepares you for the NEC licensing exam by reinforcing critical knowledge and problem-solving skills.
Understanding communication systems is vital for any aspiring engineer, as it forms the backbone of modern telecommunications. To excel, focus on mastering the key principles and practicing with the provided MCQs to enhance your readiness for the exam.
Sample questions with answers
1.How can PCM SNR be improved?
- A.By lowering the carrier
- B.By cutting down message frequency
- C.By using less bandwidth
- D.By increasing quantization levels
Why: Increasing quantization levels in PCM improves the signal-to-noise ratio (SNR) by allowing for more distinct signal representations, reducing the error between the actual signal and its quantized version.
2.What does BER stand for?
- A.Binary Encoding Rate
- B.Bandwidth Efficiency Ratio
- C.Baseband Energy Rate
- D.Bit Error Rate
Why: Bit Error Rate (BER) is a measure of the number of bit errors divided by the total number of transferred bits, making it a crucial metric for assessing the performance of a communication system.
3.How can you reduce the granularity in delta modulation?
- A.Adjusting phase
- B.Lowering sampling rate
- C.Decreasing pulse amplitude
- D.Increasing step size
Why: Increasing step size in delta modulation reduces granularity by allowing larger changes in signal levels per sample, which simplifies the representation of the signal and improves its tracking.
4.In linear block codes, the parity-check matrix H must meet:
- A.H = G
- B.G·Hᵀ = I
- C.H·Gᵀ = 0
- D.H·cᵀ = 0
Why: The condition H·cᵀ = 0 ensures that the codeword c is orthogonal to the rows of the parity-check matrix H, which is essential for detecting errors in linear block codes.
5.Reed-Solomon codes operate over which type of alphabet?
- A.Real numbers
- B.Complex numbers
- C.Symbols in GF(q)
- D.Only binary symbols
Why: Reed-Solomon codes operate over symbols in Galois Field GF(q), which allows them to correct multiple symbol errors, making them suitable for applications like CDs and QR codes.
6.How does the traceback length in Viterbi influence the system?
- A.Symbol alphabet
- B.Generator polynomial
- C.Only CRC detection
- D.Delay and error propagation
Why: The traceback length in Viterbi decoding affects delay and error propagation because a longer traceback can help in accurately determining the most likely transmitted sequence, but it also introduces more delay in the decoding process.
7.For cyclic codes, a zero syndrome indicates:
- A.The generator polynomial is wrong
- B.A one-bit error has occurred
- C.The received polynomial is divisible by g(x)
- D.The codeword weight is even
Why: A zero syndrome indicates that the received polynomial is divisible by the generator polynomial g(x), meaning that no errors were detected in the transmission.
8.How does QAM symbol spacing influence?
- A.Probability of error
- B.Ambiguity in phase
- C.Frequency of the carrier
- D.Only bandwidth
Why: QAM symbol spacing influences the probability of error because closer spacing can lead to increased confusion between symbols, especially in noisy environments.
9.How does soft-decision Viterbi decoding compare to hard-decision?
- A.About 2 dB better
- B.No improvement
- C.10 dB worse
- D.Always the same performance
Why: Soft-decision Viterbi decoding is about 2 dB better than hard-decision decoding because it takes into account the reliability of each bit, leading to improved error correction performance.
10.What does PCM quantization create?
- A.Carrier drift
- B.Quantization noise
- C.Sideband suppression
- D.Only phase error
Why: PCM quantization creates quantization noise as it introduces errors when mapping continuous signal levels to discrete values, which can affect the overall signal quality.
11.What ensures integrity of serial data?
- A.Clock recovery
- B.Multiple wires
- C.Ring token
- D.Parallel alignment
Why: Clock recovery ensures the integrity of serial data by synchronizing the timing of data transmission and reception, preventing data loss or misalignment.
12.What does the instantaneous frequency of FM depend on?
- A.Amplitude of the message signal
- B.Only the modulation index
- C.Only noise
- D.Amplitude of the carrier
Why: The instantaneous frequency of FM depends on the amplitude of the message signal because variations in the message signal's amplitude directly affect the frequency deviation in frequency modulation.
Practice all 713 Communication Systems questions
Adaptive mock tests, AI explanations on every question, and a personalized study plan.
Frequently asked questions
- How can PCM SNR be improved?
- PCM SNR can be improved by increasing the quantization levels or using better filtering techniques.
- What does BER stand for?
- BER stands for Bit Error Rate, a measure of the number of bit errors in a transmission.
- How can you reduce the granularity in delta modulation?
- Granularity in delta modulation can be reduced by increasing the step size and sampling rate.
- In linear block codes, the parity-check matrix H must meet:
- The parity-check matrix H must satisfy the condition that H * G^T = 0, where G is the generator matrix.
- Reed-Solomon codes operate over which type of alphabet?
- Reed-Solomon codes operate over finite fields, specifically GF(q), where q is a power of a prime.