# Wireless & Mobile Communications Questions & Answers – Quantization Techniques

This set of Wireless & Mobile Communications Multiple Choice Questions & Answers (MCQs) focuses on “Quantization Techniques”.

1. Quantization is a process of mapping a ________ range of amplitude of a signal into a finite set of __________ amplitudes.
a) Continuous, discrete
b) Discrete, continuous
c) Discrete, discrete
d) Continuous, continuous

Explanation: Quantization is a process of mapping a continuous range of amplitude of a signal into a finite set of discrete amplitudes. Quantizers are the devices that remove the irrelevancies in the signal.

2. For a n bit quantizer, number of levels is equal to __________
a) n
b) 2n
c) n2
d) 2n

Explanation: A quantizer that uses n bits can have M = 2n discrete amplitude levels. Amplitude quantization is an important step in any speech coding process, and it determines to a great extent the overall distortion as well as bit rate necessary to represent each waveform.

3. Distortion produced by quantization is directly proportion to ________ and inversely proportional to ______
a) Number of levels, step size
b) Amplitude of the signal, step size
c) Square of step size, number of levels
d) Amplitude of the signal, number of levels

Explanation: The distortion introduced by any quantization operation is directly proportional to the square of the step size. It is inversely proportional to the number of levels for a given amplitude range.

4. Signal to quantization noise ratio of a PCM encoder is given by _________
a) 6.02n + α
b) 3n + 6.02α
c) n + 6.02α
d) 6.02n + α

Explanation: Signal to quantization noise (SQNR) ratio of a PCM encoder is related to the number of bits, n used for encoding. It follows the following relation, SQNR= 6.02n + α. Here, α = 4.77 dB for peak SQNR and α = 0 dB for average SQNR.

5. Companding technique used in the US is called ____________
a) μ law
b) A law
c) Hybrid companding
d) Direct companding

Explanation: Companding technique known as μ law is used in US. In Europe, A law companding technique is used.
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6. An adaptive quantizer varies its ___________ in accordance to input speech signal power.
a) Level
b) Step size
c) Amplitude
d) Frequency

Explanation: An adaptive quantizer varies its step size in accordance to the input speech signal power. Its characteristics shrink and expand in time like an accordion.

7. Shannon predicted that better performance can be achieved by coding one sample at a time.
a) True
b) False

Explanation: Shannon predicted that better performance can be achieved by coding many samples at a time instead of one sample at a time.

8. ________ is a delayed decision coding technique.
b) Uniform quantization
c) Vector quantization
d) Non-uniform quantization

Explanation: Vector (VQ) quantization is a delayed decision coding technique. It maps a group of input samples called a vector to a code book index. A code book is set up consisting of a finite set of vectors covering the entire anticipated range of values.

9. The characteristics of compressor in μ-law companding are _________
a) Continuous in nature
b) Logarithmic in nature
c) Linear in nature
d) Discrete in nature

Explanation: In the μ law companding, the compressor characteristic is continuous. It approximates the linear dependence on x for low input signals and a logarithmic one for high input signals.

10. What is the sequence of operations in PCM?
a) Sampling, quantizing, encoding
b) Quantizing, encoding, sampling
c) Quantizing, sampling, encoding
d) None of the mentioned

Explanation: Sequence of operation in PCM is sampling, quantization and encoding. Sampling and quantizing operations transform an analogue signal to a digital signal. The quantizing and encoding operations are usually performed in the same circuit at the transmitter, which is called an Analogue to Digital Converter (ADC). At the receiver end the decoding operation converts the pulse back into an analogue voltage in a Digital to Analogue Converter (DAC).

11. In Adaptive Delta Modulation, the slope error reduces and ___________
a) Quantization error decreases
b) Quantization error increases
c) Quantization error remains same
d) None of the mentioned

Explanation: ADM reduces slope error, at the expense of increasing quantizing error. This error can be reduced by using a low-pass filter.

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