1 SIGNAL ENCODING TECHNIQUES Networks and Communication Department

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1 SIGNAL ENCODING TECHNIQUES Networks and Communication Department NET 352

1 SIGNAL ENCODING TECHNIQUES Networks and Communication Department NET 352

Lecture Contents 2 Why programming? ? Why Java ? ? From C++ to java

Lecture Contents 2 Why programming? ? Why Java ? ? From C++ to java 4 Key OOP Concepts � Encapsulation � Inheritance � Abstraction � Polymorphism 27 -Dec-21 Networks and Communication Department

3 Analog Data, Analog Signals 27 -Dec-21 Networks and Communication Department

3 Analog Data, Analog Signals 27 -Dec-21 Networks and Communication Department

Analog Data, Analog Signals Ø Ø modulate carrier frequency with analog data why modulate

Analog Data, Analog Signals Ø Ø modulate carrier frequency with analog data why modulate analog signals? l l Ø higher frequency can give more efficient transmission permits frequency division multiplexing (chapter 8) types of modulation l l l Amplitude Frequency Phase

Analog Modulation Techniques Ø Ø Ø Amplitude Modulation Frequency Modulation Phase Modulation

Analog Modulation Techniques Ø Ø Ø Amplitude Modulation Frequency Modulation Phase Modulation

6 Digital Data, Analog Signals 27 -Dec-21 Networks and Communication Department

6 Digital Data, Analog Signals 27 -Dec-21 Networks and Communication Department

Digital Data, Analog Signal Ø main use is public telephone system has freq range

Digital Data, Analog Signal Ø main use is public telephone system has freq range of 300 Hz to 3400 Hz l use modem (modulator-demodulator) l Ø encoding techniques Amplitude shift keying (ASK) l Frequency shift keying (FSK) l Phase shift keying (PSK) l

Modulation Techniques

Modulation Techniques

Amplitude Shift Keying Ø encode 0/1 by different carrier amplitudes l Ø Ø Ø

Amplitude Shift Keying Ø encode 0/1 by different carrier amplitudes l Ø Ø Ø usually have one amplitude zero susceptible to sudden gain changes inefficient used for up to 1200 bps on voice grade lines l very high speeds over optical fiber l

Binary Frequency Shift Keying Ø Ø most common is binary FSK (BFSK) two binary

Binary Frequency Shift Keying Ø Ø most common is binary FSK (BFSK) two binary values represented by two different frequencies (near carrier) less susceptible to error than ASK used for l l l up to 1200 bps on voice grade lines high frequency radio higher frequency on LANs using co-ax

Multiple FSK Ø Ø each signalling element represents more than one bit more than

Multiple FSK Ø Ø each signalling element represents more than one bit more than two frequencies used more bandwidth efficient more prone to error

MFSK

MFSK

Phase Shift Keying Ø Ø phase of carrier signal is shifted to represent data

Phase Shift Keying Ø Ø phase of carrier signal is shifted to represent data binary PSK l Ø two phases represent two binary digits differential PSK l phase shifted relative to previous transmission rather than some constant reference signal

DPSK

DPSK

Quadrature PSK Ø get more efficient use if each signal element represents more than

Quadrature PSK Ø get more efficient use if each signal element represents more than one bit e. g. shifts of /2 or (90 o) l each element represents two bits l split input data stream in two & modulate onto carrier & phase shifted carrier l Ø can use 8 phase angles & more than one amplitude l 9600 bps modem uses 12 angles, four of which have two amplitudes

QPSK and OQPSK Modulators

QPSK and OQPSK Modulators

QPSK

QPSK

Performance of Digital to Analog Modulation Schemes Ø bandwidth ASK/PSK bandwidth directly relates to

Performance of Digital to Analog Modulation Schemes Ø bandwidth ASK/PSK bandwidth directly relates to bit rate l multilevel PSK gives significant improvements l Ø in presence of noise: l bit error rate of PSK and QPSK are about 3 d. B superior to ASK and FSK

19 Analog Data, Digital Signals 27 -Dec-21 Networks and Communication Department

19 Analog Data, Digital Signals 27 -Dec-21 Networks and Communication Department

Analog Data, Digital Signal Ø digitization is conversion of analog data into digital data

Analog Data, Digital Signal Ø digitization is conversion of analog data into digital data which can then: be transmitted using NRZ-L l be transmitted using code other than NRZ-L l be converted to analog signal l Ø analog to digital conversion done using a codec pulse code modulation l delta modulation l

Digitizing Analog Data

Digitizing Analog Data

Pulse Code Modulation (PCM) Ø sampling theorem: “If a signal is sampled at regular

Pulse Code Modulation (PCM) Ø sampling theorem: “If a signal is sampled at regular intervals at a rate higher than twice the highest signal frequency, the samples contain all information in original signal” l e. g. 4000 Hz voice data, requires 8000 sample per sec l Ø Strictly: these are analog samples l Ø Pulse Amplitude Modulation (PAM) so assign each a digital value

PCM Example

PCM Example

PCM Block Diagram

PCM Block Diagram

Non-Linear Coding

Non-Linear Coding

Companding

Companding

Delta Modulation Ø analog input is approximated by a staircase function l Ø can

Delta Modulation Ø analog input is approximated by a staircase function l Ø can move up or down one level ( ) at each sample interval has binary behavior since function only moves up or down at each sample interval l hence can encode each sample as single bit l 1 for up or 0 for down l

Delta Modulation Example

Delta Modulation Example

Delta Modulation Operation

Delta Modulation Operation

PCM verses Delta Modulation Ø Ø Ø DM has simplicity compared to PCM but

PCM verses Delta Modulation Ø Ø Ø DM has simplicity compared to PCM but has worse SNR issue of bandwidth used l e. g. for good voice reproduction with PCM want 128 levels (7 bit) & voice bandwidth 4 khz need 8000 x 7 = 56 kbps Ø Ø data compression can improve on this still growing demand for digital signals l Ø use of repeaters, TDM, efficient switching PCM preferred to DM for analog signals

Problem Ø Q 6. The analog waveform shown in the following figure is to

Problem Ø Q 6. The analog waveform shown in the following figure is to be delta modulated. The sampling period and the step size are indicated by the grid. The first DM output is also shown. Give the DM output for the complete signal.

Problem

Problem

33 Reference 27 -Dec-21 Data and Computer Communications, Ninth Edition by William Stallings, �

33 Reference 27 -Dec-21 Data and Computer Communications, Ninth Edition by William Stallings, � Chapter 5 (5. 2 , 5. 3, 5. 4) Networks and Communication Department