Chapter 1 & 2 : Elec 2: Important Questions

 Q1. Draw the block diagram of communication system.

Answer: 

 Q2. What do you mean by data rate?

Answer: The data rate of a communication system is defined as the amount of data that it transfers per second. The unit of data rate is bits/sec.

For Tb= duration of one bit, data rate is 

Data rate = 1 / Tb

Q3. Define hamming code

Answer: Hamming code is a set of error correction codes that can be used to detect and correct bit errors that can occur when digital data is transmitted or received.

Q4. What is the need of modulation ?

Answer: When we want to transmit information over long distances we convert data frequencies into electrical signals. But these signals cannot be practically transmitted directly since they are weak in strength and can get mixed with other signals easily. Hence, modulation is done to increase the strength of signals which allows better and faster transmission of information.

Q5. Define Modulation.

Answer: Modulation is the process of modifying one or more characteristics of a high frequency wave (carrier signal) in accordance with a seperate signal which typically contains the information to be transmitted. 

The information that we want to transmit is called the modulating signal and signal which is being modulated is called carrier signal.

Q6. Define demodulation.

Answer: The process of recovering the original signal from the modulated wave is known as demodulation.

Q7. Explain pulse code modulation.

Answer: When a signal undergoes pulse code modulation, it is converted into binary codes sequence (0s and 1s). It is a type of pulse modulation system, where the analog signal is converted into digital signal. The information is transmitted in form of code words.

- Transmitter : It converts (encodes) message signal into a series of coded pulses.

- Communcation channel: The PCM signal travel through the channel.

-Receiver: It receives the coded pulses which is decoded back into analog form.

Q7. Give advantages and disadvantages of PCM.

Answer: Advantages of PCM:

1) It has high noise immunity.

2) Suitable for long distance communication.

Disadvantages:

1) The encoder, decoder and quantization circuitry is required.

2) It requires comparatively higher bandwidth.

Q8. Explain FSK.

Answer: FSK or Frequency-shift keying the frequency of a sinusoidal carrier is shifted between two discrete values in accordance with digital input signal (0 or 1). One of the frequencies (f1) represents binary 1 and another frequency (f0) represents binary 0.

FSK Generation : The voltage controlled oscillator (VCO) produces sine waves at frequency f1 and f2 according to binary input.

FSK receiver : It consists of two BPF, with corresponding envelop detecters which rectify and filter their inputs and generate dc output.

Q9. Draw waveform of FSK for data 110011.

Answer: 

Chapter 3: Modulation and Demodulation

1 mark

Q. Give any two examples of half-duplex communication systems:

a. Walkie-talkies: Users can either transmit or receive signals but not simultaneously.

b. Push-to-Talk (PTT) communication systems: Users can take turns transmitting and receiving, but cannot do both simultaneously.

Q. Define simplex communication system and give one example:

-Simplex communication system is a one-way communication method where data flows in only one direction, from the transmitter to the receiver. The receiver cannot send data back to the transmitter. An example of a simplex communication system is broadcast radio, where radio stations transmit signals to listeners who cannot send signals back to the station.

Q. Draw waveform of FSK for 10101100, 110011:

- 

Q. Draw waveform of ASK for data 101010, 11010110:

- 

Q. Draw frequency spectrum of AM:

- 

Q. What is a broadband signal?

a. A broadband signal refers to a signal that contains a wide range of frequencies, typically spanning a broad frequency spectrum. It carries multiple signals or data simultaneously over different frequency channels. Broadband signals are commonly used in telecommunications and internet connections to transmit large amounts of data at high speeds.

Q. What is a baseband signal?

b. A baseband signal refers to a signal that contains the original or unmodulated form of information. It typically represents the information as a direct electrical or digital representation without any modulation or frequency shifting. Baseband signals usually have a frequency range starting from zero or near-zero frequency up to the highest frequency component in the signal.

Q. Give any two advantages of FM over AM:

a. Better noise immunity: Frequency Modulation (FM) is less susceptible to noise interference compared to Amplitude Modulation (AM). This is because FM signals encode information in the frequency variations, and noise affects the amplitude more than the frequency, making FM more resilient to noise.

b. Higher audio fidelity: FM provides higher audio quality and fidelity compared to AM. FM signals have a wider bandwidth, allowing for a broader range of audio frequencies to be transmitted, resulting in clearer and more accurate reproduction of sound.

Q. Draw a constellation diagram of QPSK:-

-

5 mark

-Q. Differentiate between AM and FM with respect to any five points.

-

AM	FM
a. Modulation Technique	a. Modulation Technique
Modulates the amplitude of the carrier signal.	Modulates the frequency of the carrier signal.
b. Noise Immunity	b. Noise Immunity
More susceptible to noise interference, resulting in lower signal quality.	More immune to noise interference, resulting in better signal quality.
c. Bandwidth	c. Bandwidth
Requires a narrower bandwidth for transmitting the same information.	Requires a wider bandwidth for transmitting the same information.
d. Power Efficiency	d. Power Efficiency
Less power-efficient compared to FM for transmitting the same information.	More power-efficient compared to AM for transmitting the same information.
e. Application	e. Application
Commonly used for broadcasting audio signals.	Used for high-fidelity music transmission, two-way radio communications, and broadcasting in higher frequency bands.

-Q. Explain FSK modem with help of block diagram.

-

Q. With neat block diagram explain PAM

Q. With help of diagram, explain PCM modulator and demodulator.

Q. Explaub QPSK with respect to the following points:

-1. Concept

-2. Truth table

-3. Phasor Diagram

-Q. Explain steps involved in PCM and give any two applications of it.Demerits of it.

- 

Chapter 4: Multiplexing and spread spectrum 

5 mark

-Q. Describe basic concept of TDM with help of block diagram.

-

In the block diagram:

The individual users (User 1, User 2, User 3) represent different data sources or signals.

Each user has their own data stream to transmit.

The users' data streams are divided into discrete time slots (Time Slot 1, Time Slot 2, Time Slot 3) using a time division multiplexer (Muxer).

The time slots are combined or multiplexed to create a composite signal.

The composite signal is then transmitted through a shared channel (Channel Output).

At the receiving end, the composite signal can be demultiplexed, and the original individual data streams can be extracted based on the time slots.

Q. Differentiate between TDM and FDM.

-

TDM (Time Division Multiplexing)	FDM (Frequency Division Multiplexing)
Divides channel into time slots.	Divides channel into frequency bands.
Assigns each user a dedicated time slot.	Allocates each user a specific frequency band.
Sequential transmission of data.	Simultaneous transmission of data.
Requires strict synchronization.	Does not require strict synchronization.
Commonly used in digital communication.	Commonly used in analog communication.

Q. Explain FDM transmitter with neat block diagram.

-a. Multiple Input Sources: FDM transmitter receives multiple input signals representing different users or data streams.

b. Bandpass Filters: Each input signal is filtered to isolate specific frequency bands.

c. Modulators: Filtered signals are modulated onto carrier signals to transmit them at desired frequencies.

d. Adders: Modulated signals from different users are combined or added together.

e. Amplifier: The combined signal is amplified to ensure sufficient strength for transmission.

f. Transmission Medium: Amplified signal is transmitted through the chosen medium (e.g., cable, fiber, or wireless) for further propagation.

-Q. Write any five features of TDMA.

-Features of TDMA (Time Division Multiple Access):

a. Time Slot Allocation for users.

b. Efficient utilization of time through slot division.

c. Increased capacity of the communication system.

d. Reduced interference and improved signal quality.

e. Flexibility in resource allocation based on bandwidth requirements.

Chapter 5: Media Access Control

Q. What do you mean by multiple access.

-

Multiple access refers to a communication technique that allows multiple users or devices to share a common communication channel or medium simultaneously. It enables multiple users to access and transmit information over the same channel or medium without significant interference or data collisions.

5 mark

-Q. Write any five features of CDMA.

- 

CDMA:

a. Increased capacity with unique codes.

b. Improved call quality and resistance to interference.

c. Enhanced security with individual codes.

d. Flexible resource allocation.

e. Smooth handoff between base stations.

--Q. Write any five featrues of FDMA.

-

FDMA:

a. Efficient frequency reuse.

b. Simple implementation.

c. Predictable performance and reduced interference.

d. Compatibility with legacy systems.

e. Control over resource allocation.

Q. Comment on “Guard band is essential in FDMA”.

-

Guard band in FDMA:

a. Prevents interference and maintains signal separation.

b. Facilitates tuning and filtering.

c. Ensures spectral efficiency.

d. Mitigates frequency drift and non-linearities.

e. Simplifies design and implementation.