UNIT I –ANALOG MODULATION SYSTEMS

1. Definemodulation

Modulation is aprocessbywhich some characteristics of a high frequencycarrier signal is

varied inaccordancewith theinstantaneous amplitude ofthemodulatingsignal.

2. Whatarethetypes ofanalogmodulation?

AmplitudeModulation.

AngleModulation

1. Frequencymodulation

2. Phasemodulation.

3. Definedepth ofmodulation or Modulation Index.

It is defined as theratio of amplitude of the message signalto that of carrier signal.

m=Vm/Vc

4. What arethedegrees ofmodulation?

UnderModulation. m<1

Critical Modulation m=1

OverModulation m>1

5. What is theneed formodulation?

Needs formodulation:

Easeoftransmission

Multiplexing

Reduced noise

Narrow bandwidth

Frequencyassignment

Reducetheequipments limitations.

6. Draw the spectrum of AM wave.

7. Define amplitude modulation.

Amplitude modulation is the process in which the amplitude of the carrier signal is varied in

accordance with the instantaneous amplitude of of the message signal.

8. Whatarethetypes ofAM modulators?

Therearetwo types ofAM modulators. Theyare

1. Linearmodulators

2. Non-linearmodulators

Linearmodulators areclassified as follows

1. Transistormodulator.

Therearethreetypes oftransistormodulator.

a) Collectormodulator

b) Emittermodulator

c) Basemodulator

2. Switchingmodulators

Non-linearmodulatorsare classified as follows

1. Squarelaw modulator

2. Product modulator

3. Balanced modulator

9. What is the difference between high level and low level modulation?

In high level modulation, the modulator amplifier operates at high power levels and delivers

power directly to the antenna. In low level modulation, the modulator amplifier performs

modulation at relatively low power levels. The modulated signal is then amplified to high power

level by class B power amplifier. The amplifier feeds power to antenna.

10. Define DSB-SC AM.

After modulation, the process of transmitting the sidebands (USB, LSB) alone and suppressing the

carrier is called as Double Side Band-Suppressed Carrier AM.

11. How will you generating DSBSC-AM?

There are two ways of generating DSBSC-AM

a) Balanced modulator

b) Ring modulators

12. What are the disadvantages of DSB-FC?

(i) Power wastage takes place in DSB-FC

(ii) DSB-FC is bandwidth inefficient system.

13. Define SSB-SC AM. After modulation, the process of transmitting only one sidebands and suppressing the carrier and the

other side band is called as Single Side Band-Suppressed Carrier AM.

14. What is Vestigial Side Band Modulation?

Vestigial Sideband Modulation is defined as a modulation in which one of the sideband is partially

suppressed and the vestige of the other sideband is transmitted to compensate for that suppression.

15. What are advantages of ring modulator?

a).Its output is stable.

b). It requires no external power source to activate the diodes.

c).Virtually no maintenance.

d). Long life.

16. Compare low level and high level modulation.

17. Compare the different SSB generation techniques.

18. What are the advantages of signal sideband transmission?

a) Power consumption

b) Bandwidth conservation c) Noise reduction

19. What are the disadvantages of single side band transmission?

a) Complex receivers: Single side band systems require more complex and expensive receivers than

conventional AM transmission.

b) Tuning difficulties: Single side band receivers require more complex and precise tuning than

conventional AM receivers.

20. Define demodulation.

Detection is the process of extracting modulating signal from the modulated carrier. Different types of

detectors are used for different types of modulations.

21. What is Super Heterodyne Receiver?

The super heterodyne receiver converts all incoming RF frequencies to a fixed lower frequency, called

intermediate frequency (IF). This IF is then amplitude and detected to get the original signal.

22. Define Coherent Detection.

During Demodulation carrier is exactly coherent or synchronized in both the frequency and phase,

with the original carrier wave used to generate the DSB-SC wave. This method of detection is called as

coherent detection or synchronous detection.

23. What are the demerits of coherent detection?

a. It requires an additional system at the receiver to ensure that locally generated carrier is

synchronized with the transmitted carrier.

b. It makes the receiver complex and costly.

24. What are the different types of distortion taking place in envelope detector?

There are two types of distortion occurring in envelope detector.

a. Negative peak clipping

It occurs due to unequal ac and dc load impedances. The modulation index in

demodulated wave is higher than that of modulated output which causes negative peak

clipping.

b. Diagonal Clipping

At high modulating frequencies diode ac load impedance is not purely resistive and it

has reactive components. At high modulation depths, current will be changing so fast that the

time constant of the load may be too slow to follow the change. As a result, the current will

decay exponentially and the output voltage follows the discharge law of the CR circuit.

25. Define envelope detector.

A diode operating in a linear region of its VI characteristics can extract the envelope of a

modulated output. This is known as envelope detector.

26. What is squelch circuit?

The squelch circuit detects the presence of carrier and enables receiver’s output only when

carrier is present, avoiding loud noise. The squelch circuit is also called as muting or quieting

circuit.

1. Define angle modulation.

Angle modulation is the process of varying total phase angle of the carrier wave in accordance

with the instantaneous amplitude of the modulating or message signal.

2. What are the types of angle modulation?

There are two types of angle modulation. They are

a. Frequency modulation b. Phase modulation

3. Define frequency modulation.

Frequency modulation is defined as the process by which the frequency of the carrier wave is

varied in accordance with the instantaneous amplitude of the modulating or message signal.

4. Define phase modulation.

Phase modulation is defined as the process of changing the phase of the carrier signal in

accordance with the instantaneous amplitude of the message signal.

5. Define modulation index of frequency modulation.

It is defined as the ratio of maximum frequency deviation to the modulating signal frequency.

f

m

fm

f

6. What are the types of Frequency Modulation?

Based on the modulation index FM can be divided into two types. They are

Narrow band FM (NBFM)

Wide band FM (WBFM)

If the modulation index is greater than one then it is wide band FM and if the modulation index

is less than one then it is Narrow band FM.

7. Define phase deviation.

The maximum phase deviation of the total angle from the carrier angle ωCt is called phase

deviation.

8. What do you meant by multitone modulation?

Modulation done for the message signal with more than one frequency component is called

multitone modulation.

9. Compare WBFM and NBFM.

10. What is the primary classification of generating FM?

The FM modulator circuits used for generating FM signals can be grouped into two

categories. They are

a. Direct method

The carrier frequency is directly varied in accordance with the instantaneous

amplitude of the baseband signal.

b. Indirect method

The message signal is first integrated and then phase modulated to get frequency

modulated output.

11. How FM is generated using PM?

Frequency modulated signal is obtained by first integrating the message signal or baseband

signal and then it is applied to phase modulator.

12. How PM is generated using FM?

Phase modulated signal is obtained by first differentiating the message signal and then by

applying it to a frequency modulator.

13. State the demerits of direct method of generating FM.

i. Difficult to obtain a higher order stability in carrier frequency

ii. Non linearity produces a frequency variation due to harmonics of the modulating signal

and hence the FM signal is distorted.

14. State Carson’s rule.

The bandwidth of an FM signal is equal to the twice the sum of the frequency deviation and

the highest modulating frequency.

BW=2(Δf+fm)

15. State the disadvantages of FM.

i) Bandwidth requirement of FM is much higher.

ii) FM transmitting and receiving equipment is more complex and costly.

iii) Distance of reception is limited only to line of sight.

16. Draw the spectrum of an FM signal.

17. Compare AM and FM.

18. Compare FM and PM

1. Define FM demodulation and FM detectors.

The process of extracting modulating signal from frequency modulated carrier is called FM demodulation.

Electronic circuit that performs the demodulation process is called FM detectors.

2. Define frequency discriminators and mention their types.

The circuits whose output voltage depends on the input frequency are called frequency discriminators. They

are of two types.

i) Slope detectors

ii) Phase discriminators

3. State the operating principle of slope detectors.

The principle of operation depends on the slope of the frequency response characteristic of a frequency

selective network. Their types are

i) Simple slope detectors.

ii) Balanced slope detectors.

4. What are the demerits of balanced slope detectors?

1. Amplitude limiting cannot be provided

2. Linearity is not sufficient

3. It is difficult to align because of three different frequencies to which various tuned circuits to

be tuned.

4. The tuned circuit is not purely band limited.

5. What are the disadvantages of using foster sealy discriminator?

a. Any variation in the amplitude of FM signal due to noise modifies the characteristics of the discriminators.

b. The undesired frequency components corresponding to amplitude variations are produced in the detected

output and the output gets distorted.

6. State the merits and demerits of ratio detector?

Merit: Variation in amplitude does not modify the characters by connecting a capacitor parallel with the resistor.

Demerit: The ratio detector may not tolerate the long period variation in signal strength.

7. How will you generate message from frequency-modulated signals?

First the frequency-modulated signals are converted into corresponding amplitude- modulated

signal using frequency dependent circuits. Then the original signal is recovered from this AM

signal.

8. What is the purpose of squelch circuit?

The squelch circuit detects the presence of carrier and enables receiver’s output only when

carrier is present, avoiding loud noise. The squelch circuit is also called as muting or quieting

circuit

9. What are the types of FM detectors?

The types of FM detectors are

(i) Slope detector and

(ii) Phase discriminator.

10. What are the types of phase discriminator?

The types of phase discriminator are (i) Foster seeley discriminator and (ii) Ratio detector.

11. What is sensitivity and selectivity of receivers?

Selectivity is the ability of the receiver to select a signal of desired frequency while rejecting all others.

Sensitivity is the ability of the receiver to pick up weak signals.

12. Define Pre-emphasis and De-emphasis.

Pre-emphasis : The premodulation filtering in the transistor, to raise the power spectral density

of the base band signal in its upper-frequency range is called pre-emphasis (or pre distortion)

Pre emphasis is particularly effective in FM systems which are used for transmission of audio

signals.

De-emphasis: The filtering at the receiver to undo the signal pre-emphasis and to suppress

noise is called de-emphasis.

13. What is the purpose of pre emphasis and de emphasis in FM?

The power spectral density of noise at the output of FM receiver usually increases rapidly at high frequencies

but the power spectral density of message signal falls off at higher frequencies. This means the message signal does

not utilize the frequency band in efficient manner. Such more efficient use of frequency band and improved noise

performance can be obtained with the help of pre emphasis and de-emphasis.

14. Define image frequency.

The undesired frequency received by the super heterodyne receiver is called as image frequency.

15. Define intermediate frequency.

Mixer is a non linear device which converts the incoming signal and a local oscillator signal to a difference

frequency. This difference frequency is called intermediate frequency.

16. What is AGC?

Automatic gain control is a system by means of which the overall gain if the radio receiver is varied

automatically varied with the variations in the strength of the receiver signal, to maintain the output substantially

constant.

17. What is the advantage of delayed AGC over simple AGC?

In simple AGC, the unwanted weak signals are also amplified with high gain. To avoid this, in delayed AGC

circuit, AGC bias is not applied to the amplifiers till the signal strength reaches the pre determined level.

18. What is the function of IF amplifier?

IF amplifier amplifies only the tuned frequency signal and reject all others.

19. State the causes for double spotting.

The phenomenon of double spotting occurs at high frequencies due to poor front end selectivity of the receivers. In

this, receiver picks up same short wave station at two nearby points on the receiver dial.

20. What are the factors affecting the choice of intermediate frequency?

a. Very high intermediate frequency will result in poor selectivity and poor adjacent channel rejection.

b. A high value of intermediate frequency increases tracking difficulties.

c. At low value of intermediate frequency, image frequency rejection is poor.

d. At very low values of intermediate frequency, selectivity is too sharp, cutting off the sidebands.

e. At very low IF, frequency stability of the local oscillator must be correspondingly high because any

frequency drift is now a larger proportion of the low IF than a high IF.

UNIT-II

PULSE AND DIGITAL MODULATION SYSTEMS

1. Define pulse code modulation. In pulse code modulation, analog signal is sampled and converted to fix length, serial binary

number for transmission. The binary number varies according to the amplitude of the analog signal

.

2. Define bit rate and baud rate. Bit rate refers to the rate of change of a digital information signal which is

usually binary. Unit is bpsBaud rate is also a rate of change, it refers to the rate of

change of a signal on the transmission medium after encoding and modulation.

Unit is baud 3. Write the advantages of BPSK.

i) BPSK has a Bandwidth which is lower than that of a BFSK signal.

ii) BPSK has the best performance of all the systems in presence

of noise. iii) It gives the minimum possibility of error.

iv) BPSK has very good noise immunity. 4. Compare Bandwidth efficiency of BPSK and QPSK modulated signals.

Bandwidth of BPSK

=fb Bandwidth of

QPSK = fb/2

Where fb is the input data rate 5. What is digital transmission?

Transmission of digital signals between two or more points in a

communication system. The original information can be of analog or digital.

If it is analog then it is converted to digital.

6. List the effects of ‘M’ in M-ary digital modulation technique. M-ary encoding system able to transmit information at a rate that is log 2M

faster than the binary PAM system for a fixed channel bandwidth. M-ary

system requires more transmitted power. 7. What is meant by non-coherent digital modulation technique?

Non-coherent digital modulation technique is the system in which a

synchronous carrier is not used.

8. What is meant by carrier recovery? Carrier is the process of extracting a phase coherent reference carrier from a

received signal.

It is also called as phase referencing.

9. Calculate the capacity of a standard 4 KHz telephone channel with a 30 dBsignal to noise ratio?

Given:

B =4

KHz S/N

=30dB Soln:

I=3.32B log10 (1+S/N) =3.32(4x10 )

log10 (1+1000)

=39.84x10

=39.84Kbps

10 .Comparison of Digital Modulation Systems

Parameter

Binary ASK

Binary FSK

Binary PSK

Variable

Characteristic

s

Amplitude

Frequency

Phase

Noise Immunity

Low

Low

high Performance in

presence of

noise

Poor

Better than ASK

Better than FSK

Complexity

Simple

Moderatel

y Complex

Very Complex

Bit Rate

Suitable upto

100 bps

Upto about

1200 bps

Suitable for high

bit rate

11. Define ASK. In Amplitude Shift Keying the amplitude of the carrier is

varied in proportional with the amplitude of the message signal. Here the

message signal is digital and carrier is analog.

12. Define PAM. The amplitude of a constant width, constant position is varied in

proportion with the instantaneous magnitude of the modulating signal.

3

13. Define PWM.

The width of carrier pulse is made to vary in proportion

with the instantaneous magnitude of the modulating signal.

14. Define PPM. The amplitude and width of the pulse is kept constant but the position of each pulse

is varied in accordance with the amplitudes of the sampled values of the modulating signal.

15. Define PTM. Modulation of the time intervals between successive pulses of constant duration and

amplitude in accordance with a signal; specif : a system of multiplex high-frequency

transmission using this method of modulation.

16. Define PCM. Method used to digitally represent sampled analog signals. It is the standard form of digital

audio in computers, Compact Discs, digital telephony and other digital audio applications. In

a PCM stream, the amplitude of the analog signal is sampled regularly at uniform intervals,

and each sample is quantized to the nearest value within a range of digital steps.

17. Define DM. Delta modulation (DM or -modulation) is an analog-to-digital and digital-to-analog

signal conversion technique used for transmission of voice information where quality is not of

primary importance. DM is the simplest form of differential pulse-code modulation (DPCM)

where the difference between successive samples is encoded into n-bit data streams. 18. Define Nyquist rate.

Let the signal be bandlimited to „W‟ Hz. Then Nyquist rate is given as,

Nyquist rate = 2W samples/sec

Aliasing will not take place if sampling rate is greater than Nyquist rate.

19. What is meant by aliasing effect?

Aliasing .effect .takes .place .when .sampling .frequency .is .less .than .Nyquist .rate.

Under .such .condition, .the .spectrum .of .the .sampled .signal .overlaps .with .itself. Hence higher

frequencies take the form of lower frequencies. This interference of

the frequency components is called as aliasing effect.

20. State Sampling theorem.

A bandlimited signal of finite energy, which has no frequency components higher

than W Hz, may be completely recovered from the knowledge of its samples taken at the rate of 2W

samples per second.

21. What is meant by quantization?

While converting the signal value from analog to digital, quantization is performed.

The .analog value is assigned to nearest digital value. This is called quantization.

The . quantized .value .is .then .converted .into .equivalent .binary .value. .The quantization levels

are fixed depending upon the number of bits.

22. What are the two limitations of delta modulation?

1 Slope of overload distortion.

2. Granular noise

23. How does Granular noise occurs?

It occurs due to large step size and very small amplitude variation in the input

signal.

24. What are the advantages of the Delta modulation?

1 Delta modulation transmits only one bit for one sample. Thus the signaling rate

and transmission channel bandwidth is quite small for delta modulation.

2. .The .transmitter .and .receiver .implementation .is .very .much .simple .for .delta

modulation. There is no analog to digital converter involved in delta modulation.

25.What is matched filter?

The matched filter is a baseband signal receiver, which works in presence of

white Gaussian noise. The impulse response of .the matched response of .the matched filter is

matched to the shape pf the input signal.

26. What is correlator ?

Correlator is the coherent receiver. It correlates the received noisy signal .f(t)

with .the .locally .generated .replica .of .the .unknown .signal .x(t). .It‟ s output .is

denoted as r(t).

UNIT-III

COMMUNICATION TECHNOLOGY

1. Define SNR. Ratio of signal power to the noise power, often expressed in decibels. A ratio higher than

1:1 (greater than 0 dB) indicates more signal than noise.

2. Define NRZ. Non-return-to-zero (NRZ) line code is a binary code in which 1s are represented by one

significant condition (usually a positive voltage) and 0s are represented by some other

significant condition (usually a negative voltage), with no other neutral or rest condition.

3. Define RZ. Return-to-zero (RZ) describes a line code used in telecommunication signals in which the

signal drops (returns) to zero between each pulse. This takes place even if a number of

consecutive 0's or 1's occur in the signal. The signal is self-clocking.

4. Define Error control coding. Error control coding aims at developing methods for coding to check the correctness of the bit

stream transmitted.

The bit stream representation of a symbol is called the codeword of that symbol.

5. Mention the types of error control.

o Linear Block Codes o Repetition Codes

o Convolution Codes

6. Define linear block codes. A code is linear if two codes are added using modulo-2 arithmetic produces a third

codeword in the code. Consider a (n, k) linear block code. Here,

1. n represents the codeword length

2. . k is the number of message bit

3. n − k bits are error control bits or parity check bits generated from message using an

appropriate rule.

7. Define Block Codes. Block codes comprise the large and important family of error-correcting codes that encode

data in blocks. Block Codes are conceptually useful because they allow coding theorists,

mathematicians, and computer scientists to study the limitations of all block codes in a unified

way. Such limitations often take the form of bounds that relate different parameters of the block

code to each other, such as its rate and its ability to detect and correct errors.

8.Define multiplexing.

Multiplexing is defined as the process of transmitting several message signals

simultaneously over a single channel. It can classified as time division multiplexing and frequency

division multiplexing.

9. Define spread spectrum. Spread-spectrum techniques are methods by which a signal (e.g. an electrical,

electromagnetic, or acoustic signal) generated with a particular bandwidth is deliberately

spread in the frequency domain, resulting in a signal with a wider bandwidth. 10. Mention the uses of spread spectrum.

Used for a variety of reasons, including the establishment of secure communications,

increasing resistance to natural interference, noise and jamming, to prevent detection, and to limit

power flux density (e.g. in satellite downlinks). 11. Define multiple access.

Multiple access defined as a means of allowing multiple users to simultaneously share the finite bandwidth with least possible degradation in the performance of the system.

12. Mention the types of multiple access.

1. Frequency Division Multiple Access (FDMA) 2. Time Division Multiple Access

(TDMA)

3. Code Division Multiple Access (CDMA) 4. Space Division Multiple Access (SDMA) 13. Define Frequency Division Multiple Access (FDMA).

In FDMA, each user is allocated a unique frequency band or channel. During the period of the call, no other user can share the same frequency band.

14. Define Time Division Multiple Access (TDMA). TDMA systems divide the channel time into frames. Each frame is further

partitioned into time slots. In each slot only one user is allowed to either transmit or receive.

15. Mention the features of FDMA.

(i)Continuous transmission

(ii)Narrow bandwidth Low ISI (iii)Low overhead

Simple hardware at mobile unit and (iv)BS Use of duplexer

8. Mention the features of TDMA. o Multiple channels per carrier or RF channels.

o Burst transmission since channels are used on a timesharing basis. Transmitter can

be turned off during idle periods.

o Narrow or wide bandwidth – depends on factors such as modulation scheme,

number of voice channels per carrier channel.

o High ISI – Higher transmission symbol rate, hence resulting in high ISI. Adaptive equalizer required.

9. Define CDMA. CDMA is also called DSSS (Direct Sequence Spread Spectrum).

In CDMA, the narrowband message signal is multiplied by a very large bandwidth

signal called spreading signal (code) before modulation and transmission over the air.

This is called spreading.

10. Spreading signal consists of Has Chip period and and hence, chip rate

Spreading signal use a pseudo-noise (PN) sequence (a pseudo-

random sequence)

PN sequence is called a codeword

Each user has its own cordword

Codewords are orthogonal. (low autocorrelation)

Chip rate is oder of magnitude larger than the symbol rate.

11. Mention the advantages of CDMA.

Random access possible Users can start their transmission at any time

Cell capacity is not concerete fixed like in TDMA or FDMA systems. Has soft capacity

Higher capacity than TDMA and FDMA

No frequency management

No equalizers needed

No guard time needed

Enables soft handoff .

UNIT-IV

WIRELESS NETWORKS

1.What is mean by data communication? Data communication is the exchange of data (in the form of 1s and 0s) between two

devices via some form of transmission medium (such as a wire cable).

2.Why are protocols needed? In networks, communication occurs between the entities in different systems. Two

entities cannot just send bit streams to each other and expect to be understood. For communication,

the entities must agree on a protocol. A protocol is a set of rules that govern data communication

3.Distinguish between peer-to-peer relationship and a primary-secondary relationship. Peer-to-peer relationship: All the devices share the link equally.

Primary-secondary relationship: One device controls traffic and the others must transmit

through it.

4.Group the OSI layers by function. The seven layers of the OSI model belonging to three subgroups. Physical, data link and

network layers are the network support layers; they deal with the physical aspects of

moving data from one device to another. Session, presentation and application layers are the user

support layers; they allow interoperability among unrelated software systems. The

transport layer ensures end-to-end reliable data transmission.

5.What are the responsibilities of data link layer?

Specific responsibilities of data link layer include the following.

a) Framing

b) Physical addressing c) Flow control

d) Error control

e) Access control

6.Mention the types of errors.

There are 2 types of errors

a) Single-bit error. b) Burst-bit error.

7.What is redundancy?

It is the error detecting mechanism, which means a shorter group of bits or extra bits may be

appended at the destination of each unit.

8. What are the responsibilities of network layer?

The network layer is responsible for the source-to-destination delivery of packet

across multiple network links. The specific responsibilities of network layer include the following:

Logical addressing.

Routing.

9. Define Routers.

Routers relay packets among multiple interconnected networks. They Route packets

from one network to any of a number of potential destination networks on internet routers operate in

the physical, data link and network layer of OSI model.

10. What is meant by hop count?

The pathway requiring the smallest number of relays, it is called hop-count routing, in

which every link is considered to be of equal length and given the value one.

11. Define IP address.

IP address is the 3-bit number for representing a host or system in the network.

One portion of the IP address indicates a networking and the other represents the host in a network.

12. What is function of transport layer?

The protocol in the transport layer takes care in the delivery of data from one

application program on one device to an application program on another device.

They act as a link between the upper layer protocols and the services provided by the lower layer.

13. What are the duties of the transport layer?

The services provided by the transport layer

End-to- end delivery

Addressing

Reliable delivery Flow control Multiplexing

14. What is frame?

A frame consists of one complete cycle of time slots, including one or more slot

dedicated to each sending device.

15.What is interleaving?

The switch moves from device to device at a constant rate and fixed order. This

process is called interleaving.

16. List the access methods for wireless LAN’s.

LAN is suitable for variations of the CSMA protocol. The packet length is large in LANs.

So, great care is needed in packet collisions. The access methods for wireless LANs are as

follows:

CSMA/CD (Carrier Sense Multiple Access/Collision Detection).

CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance)

17.Define bluetooth.

BLUETOOTH: Bluetooth wireless technology is a short-range radio technology, which is

developed for Personal Area Network (PAN). Bluetooth is a standard developed by a group of

electronics manufacturers that allows any sort of electronic equipment -- from computers and cell

phones to keyboards and headphones -- to make its own connections, without wires, cables or any

direct action from a user

18.What are the types of topology in Bluetooth.

Topology There are two types of topology for Bluetooth – Piconet, Scatternet.

19. Define WiMAX

WiMAX is: Acronym for Worldwide Interoperability for Microwave Access.

Based on Wireless MAN technology.

A wireless technology optimized for the delivery of IP centric services over a

wide area.

A scalable wireless platform for constructing alternative and complementary

broadband networks.

20.Define IEEE 802.11.

IEEE 802.11 IEEE has defined the specifications for a wireless LAN, called IEEE 802.11,

which covers the physical and data link layers.

21.Write the advantages of 3G

high data rates: 144 kbps in all environments and 2 Mbps in low-mobility and indoor

environments

symmetrical and asymmetrical data transmission

circuit-switched and packet-switched-based services

UNIT-V

POWER LINE COMMUNICATION

1.Define power line communication.

Power line communication is the usage of electrical power supply networks for communication

purposes. The main idea behind PLC is the reduction of cost and expenditure in the realization of

in-home PLC networks.

2. Write the Power Supply Networks

High Voltage (110-380kV) networks : Connnect the power stations with large supply regions or

big customers.

Long Distances, power exchange with in a continent

Overhead supply cables.

Medium Voltage(10-30kV) networks : Supplies larger areas, cities and big industrial or commercial

customers

Overhead supply cables and underground networks.

Low-Voltage(230V in Germany) networks: Supply the end users either as individual customers or

ass single users of a bigger customer.

3.Write the types of PLC Architecture.

Narrowband PLC

Broadband PLC

Home PLC Network

4.What are the PLC BASIC NETWORK ELEMENTS

The communication signal has to be converted into a form that allows the transmission via electrical

networks.

• The main task of the basic elements is signal preparation and conversion for its transmision over

power lines as well as signal reception.

• Following two devices exits in every PLC access network: PLC modem, PLC Base Station.

5. Define coupling.

Coupling The coupling has to ensure a safe galvanic separation and act as a high pass filter dividing

the communication signal above 9 kHz from the electrical power(50 or 60Hz).

6 Define PLC Gateways

A gateway is used to divide a PLC access network and an in-home PLC network.

• It can be placed anywhere in a PLC access network to provide both signal generation (repeater

function) and network division on the logical level.

7.Define SMART GRID TECHNOLOGY

Smart Grid objectives include the integration of intermittent renewable energy sources into the

electricity supply chain, securing reliable electricity delivery, and using the existing electrical

infrastructure more efficiently.

8.Write the power line communication

Carrying data on a conductor also used for power transmission

• PLC is a wired communications technology

• But it can compete with wireless technologies with low cost

9.What are the types of PLC Technology?

Three classes of PLC Technologies:

• Broadband (BB):

• Operating at 1.8 – 250 MHz

. • Data Rate: Up to 200 Mbps

• Initial Application: Residential Internet Access

• Short Communication Range (few kilometers)

• Good for AMI/AMR, Not Good for sub-stations

10.Define PLC Base station.

A PLC base station connects a PLC access system to its backbone network. • Provides multiple

network communication interfaces, such as xDSL, Synchronous Digital Hierarchy(SDH) for

connection with a high-speed network, WLL for wireless interconnection and so on.

UNIT I –ANALOG MODULATION SYSTEMS

11 MARKS:

1)Explain the Principle of Amplitude Modulation and how it is represented in Time

domain and Frequency Domain.

2)Explain the method of generating Double Side Band Suppressed Carrier(DSBSC)

with

a.Balanced Modulator using Diode.

b.Balanced Modulator using FET.

3)Explain with necessary block diagram ,the working of vestigial sideband

Modulation(VSB).

4)Draw the block diagram of Armstrong Method and explain its operation for FM

Generation.

5)With a neat sketch explain the operation of round travis detector(Balanced Slope

Detector).

6)With a neat sketch explain the operation of Foster Seeley Discriminator(Phase

Shift Discriminator)

7)Explain with necessary block diagram ,the working of Superhetrodyne Receiver.

8)Explain the working of various AM Modulator Circuits.

9)Explain in detail about AM Transmitters.

10)What is Single Sideband Modulation?Mention various SSB Techniques and

mention its advantages.

11)Explain in detail about AM Detectors.

12)Explain the principle of Frequency Modulation and how it is represented in

Timedomain and Frequency Domain.

13)Compare AM,FM & PM.

14)Explain the working of FM & PM Modulators.

15)Write a notes on Pre-Emphasis & De-Emphasis.

16)Explain the principle of Frequency Modulation and how it is represented in time

domain and Frequency Domain.

17)Derive the Power Relation in AM Signal.

18)Explain the various method of generating SSB.

19)Explain Envelope Detector Circuit used for AM Demodulation.

20)With neat block diagram explain the working principle of Superhetrodyne

Receiver.

21)With neat block diagram explain the working principle of Tuned Radio

Frequency Receiver.

UNIT-II - PULSE AND DIGITAL MODULATION SYSTEMS

11 MARKS:

1)Explain with neat block diagram working principle of PCM?

2)Explain with neat block diagram working principle of Delta Modulation?

3)Explain in detail about working principle of Generation and Detection of

ASK?

4)Explain in detail about working principle of Generation and Detection of

FSK?

5)Explain in detail about working principle of Generation and Detection of

PSK?

6)Write a short notes on Bit Error Rate Calculation?

7)Compare the Performance of BER?

8)With neat block diagram explain Digital-T-Carrier Systems?

9)Compare ASK,FSK & BPSK?

UNIT III: COMMUNICATION TECHNOLOGY

11 MARKS:

1)Explain in detail about model of Spectram Digital Communication Systems?

2)Explain in detail about generation of PN Sequence.

3)Explain in detail about Model of Direct Sequence Spread Spectrum in Digital

Communication Systems.

4)Explain in detail about Direct Sequence Spread Spectrum in Digital

Communication System with coherent BPSK.

5) Explain in detail about Model of Frequency Hopping(FHSS) Spread Spectrum

in Digital Communication Systems.

6)Discuss in detail about various Error Detection & Error Correction

Techniques.

7)Compare FDMA,TDMA,CDMA.

8)Write a Short notes on Hamming Codes.

9)Discuss in detail about TDMA.

10)Discuss in detail about FDMA.

11)Discuss in detail about CDMA.

12)Write a short notes on Linear Block Codes.

13)Explain in detail about ARQ Mechanisum.

UNIT-IV-WIRELESS NETWORKS

11 MARKS:

1)With neat block diagram explain TCP/IP Architecture in detail.

2)Briefly explain about ISO-OSI Reference Model.

3)Briefly explain about IEEE 802.11 Architecture in detail.

4)Mention the Application of BlueTooth in detail.

5)With necessary block diagram explain the Bluetooth protocol Architecture.

6)Explain in detail about requirements of wireless LAN.

7)Discuss in detail about WIMAX Technology.

8)Explain the operation of basic cellular system.

UNIT V: POWER LINE COMMUNICATION

11 MARKS:

1) Explain in detail about power supply networks?

2) With neat block diagram explain Narrowband & Broadband PLC?

3) Write a short notes on PLC Access Networks?

4) Explain in detail about PLC network Elements?

5) Write a short notes on connection to core network?

6) Explain in detail about structure of campus communication network and

performance issues.

7) With neat block diagram explain the architecture of Smart Grid Technology.

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