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=V m /V c 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.
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UNIT I –ANALOG MODULATION SYSTEMS
1. Definemodulation
Modulation is aprocessbywhich some characteristics of a high frequencycarrier signal is
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?