Signal encoding techniques 1

DEPARTMENT OF TECHNOLOGYFAISAL QADEER

DATA COMMUNICATION

TEACHER NAME

UMAIR RASHID

THE UNIVERSITY OF LAHORE2

Topic Name

Data Communication- Signal Encoding Techniques

Encoding Techniques

Encoding is a process of converting data into a form that is capable of being transported Data en over digital medium such as carrier waves. This conversion process is usually performed by a converter mechanism such as a modem.

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BackgroundAnalog signals is low frequency signals and

data lost in it Digital signal is high speed and efficient

signals most of our devices now support digital signal

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New Approach DiscussA new approach of

parallel data transmission through optical waveguide with SOA based frequency encoding/decoding technique

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Topic Discuss1. Digital data, digital signal2. Analog data, digital signal3. Digital data, analog signal4. Analog data, analog signal

Digital Data, Digital SignalIn general, the equipment for encoding

digital data into a digital signal is less complex and less expensive than digital-to-analog modulation equipment.

Digital signalDiscrete, discontinuous voltage pulsesEach pulse is a signal elementBinary data encoded into signal elements

Types of Digital to Digital Encoding

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Digital Data, Analog Signal Some transmission media, such as optical

fiber and unguided media, will only propagate analog signals.

Public telephone system 300Hz to 3400Hz (voice frequency range) Use modem (modulator-demodulator)

Three basic encoding (modulation techniques) for transforming digital data into analog signals: Amplitude shift keying (ASK) Frequency shift keying (FSK) Phase shift keying (PSK)

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Modulation Techniques

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Analog Data, Digital SignalAnalog data, such as voice and video, are often

digitized to be able to use digital transmission facilities.

DigitizationConversion of analog data into digital dataDigital data can then be transmitted using NRZ-L

(coding scheme)Digital data can then be transmitted using code other

than NRZ-LDigital data can then be converted to analog signalAnalog to digital conversion done using a codecTwo principal techniques used in codec:

Pulse code modulation (PCM) Delta modulation (DM) 12

Digitizing Analog Data

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Analog Data, Analog Signals Analog data are modulated by a carrier

frequency to produce an analog signal in a different frequency band, which can be utilized on an analog transmission system.

Why modulate analog signals? Higher frequency can give more efficient

transmission Permits frequency division multiplexing

Types of modulation Amplitude (AM) Frequency (FM) Phase (PM)

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Analog Modulation

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STARTING

AdvantagesFewer transcription errors There is less chance of an error if the data entry clerk has

to key in only one or two letters.

Less time spent on data entry It does not take as long to key in shortened codes.

Greater data consistency If data conforms to pre-established codes, it is more likely

to be consistent and therefore easier to interrogate.

Less memory neededAlthough the saving might seem to be a small one.

Databases holding significant numbers of data items need to be as economical as possible. [1]

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DisadvantageEncoding can coarsen dataEncoding requires data to fit into pre-established categories.

However, some data does not easily fit into one category. To use the example above ’long term cohabetee’ is not the same as ‘just moved in with boyfriend’ but the two entries would end up with the same category. This loss of precision is an inevitable effect of encoding and must be weighed against its advantages.

Subjective judgement There is a particular difficulty when the data being encoded

relates to valued judgement. For instance someone may be asked “was your hotel: ‘Excellent’, ‘Very Good’, ‘Good’, or ‘Poor’? Apart from the problem of having to fit the data into a category, there is the additional problem of ‘subjectivity’. One persons ‘Excellent’ hotel is another person’s ‘Good’. Such problems can have an effect on the value of the resulting information.(http://www.kgv.ac.uk/intranet/it/pmc/as_ict_MAF/Theory/1_1_Knowledge_Information_and_Data/What_Is_Encoding.doc)

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