data signal

8/8/2019 Data Signal

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Data & Signals


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To be transmitted, data must be

transformed to electromagnetic signals.

Note


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ANALOG AND DIGITALANALOG AND DIGITAL

Data can beData can be analoganalog orordigitaldigital. The term. The term analog dataanalog data refers torefers to

information that is continuous;information that is continuous; digital datadigital data refers torefers to

information that has discrete states. Analog data take oninformation that has discrete states. Analog data take on

continuous values. Digital data take on discrete values.continuous values. Digital data take on discrete values.


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Note

Data can be analog or digital.

Analog data are continuous and take

continuous values.

Digital data have discrete states and take

discrete values.


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Signals can be analog or digital.

Analog signals can have an infinite number

of values in a range; digital signals can

have only a limited

number of values.

Note


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Comparison of analog and digital signals


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Periodic and Non periodic

Aperiodic signalcompletes apatterns within a measurable timeframe, called aperiod.

Repeats the pattern over thesubsequent identical periods.

The completion of one full pattern iscalled a cycle.

A non periodic signalchangeswithout exhibiting a pattern over time.


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PERIODIC ANALOG SIGNALSPERIODIC ANALOG SIGNALS

Periodic analog signals can be classified asPeriodic analog signals can be classified as simplesimple ororcompositecomposite. A simple periodic analog signal, a. A simple periodic analog signal, a sine wavesine wave,,

cannot be decomposed into simpler signals. A compositecannot be decomposed into simpler signals. A composite

periodic analog signal is composed of multiple sine waves.periodic analog signal is composed of multiple sine waves.


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Sine Wave


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Sine wave is represented by 3parameters Peak amplitude: of a signal is the

absolute value of its highestintensity, proportional to the energy

it carries. Frequency: Number of cycles per

second

Phase: describes the position of thewaveform relative to time 0.


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Wave Length

It is the characteristic of the signaltraveling through a transmissionmedium.

The wave length is the distance asimple signal can travel in one period.

The Band width of a composite signalis the difference between the highestand the lowest frequencies containedin that signal


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Amplitude Change


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Frequency Change


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Phase Change


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Band width

The range of frequencies containedin a composite signal is itsbandwidth.

The band width of a composite signalis the difference between the highestand the lowest frequencies contained

in that signal


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l

Bandwidth


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Digital Signals

Bit Rate: is the number of bits sent in 1s Bit length: is the distance of 1 bit occupies

on the transmission medium

Baseband transmission: sending a digitalsignal over a channel without changing toan analog signal.

Broadband transmission: Changing the

digital signal to an analog signal fortransmission.


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TRANSMISSION IMPAIRMENTTRANSMISSION IMPAIRMENT

Signals travel through transmission media, which are notSignals travel through transmission media, which are not perfect. The imperfection causes signal impairment. This perfect. The imperfection causes signal impairment. This

means that the signal at the beginning of the medium is notmeans that the signal at the beginning of the medium is not

the same as the signal at the end of the medium. What isthe same as the signal at the end of the medium. What is

sent is not what is received. Three causes of impairmentsent is not what is received. Three causes of impairmentareare attenuationattenuation,, distortiondistortion, and, and noisenoise..


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Causes of impairment


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Attenuation

Means loss of energy.

When a signal, simple or composite ,travels through a medium, it losessome of its energy in overcoming theresistance of the medium.


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Attenuation


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Decibels for Example 3.28


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Distortion

Means signal changes its form orshape.


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Distortion


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Noise

Noise is another cause of impairment

Several types of noise, such asthermal noise, induced noise, crosstalk, and impulse noise may corruptthe signal.


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Noise


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Signal to noise ratio(SNR)

SNR= Average signal power/average noisepower


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TRANSMISSION MODESTRANSMISSION MODES

The transmission of binary data across a link can beThe transmission of binary data across a link can be

accomplished in either parallel or serial mode. Inaccomplished in either parallel or serial mode. In

parallel mode, multiple bits are sent with each clock parallel mode, multiple bits are sent with each clock

tick. In serial mode, 1 bit is sent with each clock tick.tick. In serial mode, 1 bit is sent with each clock tick.While there is only one way to send parallel data, thereWhile there is only one way to send parallel data, there

are subclasses of serial transmission: asynchronous,are subclasses of serial transmission: asynchronous,

synchronous.synchronous.

Parallel Transmission

Serial Transmission


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Data transmission and modes


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Parallel transmission


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Serial transmission


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In asynchronous transmission, we send 1start bit (0) at the beginning and 1 or more

stop bits (1s) at the end of each byte. There

may be a gap between

each byte.

Note


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Asynchronous here means asynchronousat the byte level,

but the bits are still synchronized;

their durations are the same.

Note


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Asynchronous transmission


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In synchronous transmission, we send bitsone after another without start or stop bits

or gaps. It is the responsibility of the

receiver to group the bits.

Note


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Synchronous transmission

data signal

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