3-ANALOG PULSE MODULATION AND MULTIPLEXING

Question 1

what is sampling

Answer 1

The process of converting continuous time signals into equivalent discrete time signals,
can be termed as Sampling. A certain instant of data is continually sampled in the
sampling process.

Question 2

what is sampling theorem

Answer 2

The sampling theorem states that, “a signal can
be exactly reproduced if it is sampled at the rate f_s, which is greater than or equal to
twice the maximum frequency of the given signal W.”

Question 3

what is nyquist rate

Answer 3

If the sampling rate is equal to twice the maximum frequency of the given signal W,
then it is called as Nyquist rate.

Question 4

Nyquist theorem

Answer 4

The sampling theorem, which is also called as Nyquist theorem, delivers the theory of
sufficient sample rate in terms of bandwidth for the class of functions that are
bandlimited.

Question 5

Aliasing effect.

Answer 5

Aliasing can be referred to as “the phenomenon of a high-frequency component in the
spectrum of a signal, taking on the identity of a low-frequency component in the
spectrum of its sampled version.”

Question 6

TYPES OF SAMPLING

Answer 6

There are basically three types of Sampling techniques, namely:
1. Natural Sampling
2. Flat-top Sampling
3. Ideal Sampling

Question 7

Natural Sampling

Answer 7

Natural Sampling is a practical method of sampling in which pulse have finite
width equal to τ. Sampling is done in accordance with the carrier signal which is digital
in nature.

Question 8

Flat Top Sampling:

Answer 8

Flat top sampling is like natural sampling In this sampling techniques,
the top of the samples remains constant and is equal to the instantaneous value of the
message signal x(t) at the start of sampling process.

Question 9

Ideal Sampling

Answer 9

deal Sampling is also known as Instantaneous sampling or Impulse Sampling.
Train of impulse is used as a carrier signal for ideal sampling. In this sampling technique
the sampling function is a train of impulses and the principle used is known as
multiplication principle.

Question 10

pulse modulation

Answer 10

pulse modulation is a type of modulation in which the signal is transmitted in the form of pulses

Question 11

types of pulse modulation

Answer 11

It gives rise to three forms of pulse modulation techniques: Pulse amplitude Modulation (PAM)
Pulse width Modulation (PWM)
Pulse Position Modulation (PPM)

Question 12

PULSE AMPLITUDE MODULATION

Answer 12

is an analog modulating scheme in which the
amplitude of the pulse carrier varies proportional to the instantaneous amplitude of the
message signal.

Question 13

PULSE WIDTH MODULATION

Answer 13

is an analog modulating scheme in which the duration or
width or time of the pulse carrier varies proportional to the instantaneous amplitude of
the message signal.

Question 14

PULSE POSITION MODULATION

Answer 14

is an analog modulating scheme in which the
amplitude and width of the pulses are kept constant, while the position of each pulse,
with reference to the position of a reference pulse varies according to the
instantaneous sampled value of the message signal.

Question 15

COMPARISON BETWEEN PAM, PWM, AND PPM

Answer 15

PAM PWM PPM

1Amplitude is varied/ 2Width is varied/ 3Position is varied

1Bandwidth depends on the
width of the pulse/

2Bandwidth depends on the
rise time of the pulse/

3Bandwidth depends on the
rise time of the pulse/

1Instantaneous transmitter
power varies with the
amplitude of the pulses

2Instantaneous transmitter
power varies with the
amplitude and width of the
pulses

3Instantaneous transmitter
power remains constant with
the width of the pulses

1System complexity is high/2 System complexity is low/ 3 System complexity is low/

1Noise interference is high/ 2Noise interference is low /3Noise interference is low/

1It is similar to amplitude
modulation/

2It is similar to frequency
modulation/

3It is similar to phase
modulation/

Question 16

multiplexing

Answer 16

It is a process of transmitting bar, and receiving ‘n’ number of message signals, simultaneously over a common communication channel, without any cross talk (or) interference.

Question 17

TYPES OF MULTIPLEXERS

Answer 17

Frequency Division Multiplexing (FDM),
Time Division Multiplexing (TDM).
Quadrature carrier multiplexing (QCM)

Question 18

Frequency Division Multiplexing (FDM),

Answer 18

FDM is an analog multiplexing technique that combines different signals by
modulating each analog signal with a different carrier frequency.

Question 19

Time Division Multiplexing (TDM).

Answer 19

TDM is a multiplexing technique in which each signal is assigned a different time
slot for transmission. TDM requires synchronization between the switching unit at
Transmitter and Receiver.

Question 20

Quadrature carrier multiplexing (QCM)

Answer 20

method enables two DSBSC modulated waves to occupy the
same transmission band width and yet the two message signals can be
separated at the receiver.

Question 21

COMPARISON OF MULTIPLEXING TECHNIQUES

Answer 21

FDM
The signals which are to be multiplexed are added in the time domain. But they occupy different slots in the frequency domain.
FDM is usually preferred for the analog signals.
Synchronization is not required.
The FDM requires a complex circuitry at Tx and Rx.
FDM suffers from the problem of crosstalk due to imperfect BPF.
Due to bandwidth fading in the Tx medium, all the FDM channels are affected.
Due to slow narrowband fading taking place in the transmission channel may be affected in FDM

TDM
The signals which are to be multiplexed can occupy the entire bandwidth in the time domain.
TDM is preferred for the digital signals.
Synchronization is required.
TDM circuitry is not very complex.
In TDM the problem of crosstalk is not severe.
Due to fading only a few TDM channels will be affected.
Due to slow narrowband fading all the TDM channels may get wiped out.