001 dalal psn chapter_1.pdf

7/24/2019 001 Dalal PSN Chapter_1.pdf

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Oxford University Press 2014. All rights reserved.

Upena Dalal

Wireless

Communication

and Networks


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Chapter 1

Fundamentals and

present scenario


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Key Topics

Fundamental terms of communication

Wireless communication link model Bandwidth and Signal-to-Noise Ratio

Types of signals

Types of communication systems

Wired vs Wireless Communication

Types of wireless systems

Existing technologies and requirements

Evolution of wireless systems

First-to-fourth generation wireless systems

Licensed and unlicensed band communication Spectrum policies


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Interdisciplinary learning model for wireless

communication


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Fundamental terms of communication

Information---It is analog/digital form messages or meaningful

data to be received

Modulation---It is Process by which a signal is transformed into

waveforms that are compatible with the channel requirements

Carrier---It is the frequency over which actual communication is

done

Transmitter---It is system that prepares the signal to transmit

over the channel

Channel---It is media through which signal propagates Receiver---It is system that receives the signal and interpret the

messages


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Types of Channel

Simplex---one way communicationHalf duplex---bidirectional but on switching basis,

one way at a time

Full duplex---bidirectional and simulteneous


7/13 Oxford University Press 2014. All rights reserved.

Noise addition in the signal over the

channel



Basic model of wireless digital

communication link



About the blocks

Source Encoder-Decoder---Encoder does the job of digitization

and compression as per the information theory. Decoder doesthe reverse tasks

Encryption and decryption are for secure presentation of the

message

Channel Coder-Decoder---Coder adds structured redundancy tomitigate channel errors. Decoder tries to remove the error

Other peer stages are modulator-demodulator, IF to RF

frequency up converter at the transmitting end and RF to IF

down converter at receiving end



Additional tasks at transmitter

Sending training sequences for channel estimation and

equalization and also for synchronization

Filtering for allowing certain frequencies, pulse shaping to

reduce the bandwidth and windowing to reduce out of band

components are few actions at the transmitter end.



Additional tasks at the receiver

The peer and reverse tasks of that of transmitter mentioned in

the previous slide are performed at the receiver.

Apart from that estimation and equalization process for

channel corrections and phase corrections respectively.

Following are the desirable receiver characteristics:

Sensitivity

Selectivity

Fidelity

Noise Figure



Bandwidth

No universally satisfying definition of bandwidth

Spectrum of a signal is the collective representation of all thefrequency contents along with their amplitude weights. It is used

to characterize a signal, which can be the input signal as well as

baseband or broadband to be transmitted. Correspondingly, this is

called the signal or transmission bandwidth. Channel allocated to the user or application is identified as channel

bandwidth.

While designing the transceiver hardware, certain frequency

components are allowed, is called system bandwidth. Transmission or system bandwidths must be less than or equal to

channel bandwidth.



Bit rate, symbol rate and baud rate

Bit is the smallest unit representing a binary level of the digital

signal. Digital data transfer is normally measured in bits persecond unit. Group of bits in general is called symbols or words.

When the number of bits are processed together at modulator

front end for amplitude and phase mapping, they are called

symbols and rate of transfer is measured into symbol rate andmeasured in symbols per second unit.

Symbol rate =

Each symbol represents M finite states. Each symbol represents k

bits of information, where, k = log2M

Baud rate is the rate of change of signalling or electrical (or

voltage level) transitions per second.

symboleachwithedtransmittbitsofnumberthe

ratebit

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