Data Communication Analog Transmition Behrouz A. Forouzan 1Data Communication - Analog Transmition

Index DIGITAL-TO-ANALOG CONVERSION – Amplitude Shift Keying – Frequency Shift Keying – Phase Shift Keying – Quadrature Amplitude Modulation ANALOG-TO-ANALOG CONVERSION – Amplitude Modulation – Frequency Modulation – Phase Modulation 2Data Communication - Analog Transmition

Analog Transmission digital transmission is desirable, low-pass channel needed. analog transmission is the only choice if we have a bandpass channel. Converting digital data to a bandpass analog signal is called digital-to-analog conversion. Converting low-pass analog signal to bandpass analog signal called analog-to-analog conversion Data Communication - Analog Transmition3

Digital-to-analog conversion Data Communication - Analog Transmition4

Digital-to-analog conversion QAM is the mechanism commonly used today Data Communication - Analog Transmition5

Aspects of Digital-to-Analog Conversion Data Element Versus Signal Element – data element smallest piece of information to be exchanged, bit – signal element smallest unit of a signal that is constant a little bit different in analog transmission compare to digital transmission Data Rate Versus Signal Rate Data Communication - Analog Transmition6

Aspects of Digital-to-Analog Conversion Data Element Versus Signal Element Data Rate Versus Signal Rate – L is the type of signal element, not the level. – In analog transmission of digital data, baud rate is less than or equal to bit rate Data Communication - Analog Transmition7

Aspects of Digital-to-Analog Conversion Example: An analog signal has a bit rate of 8000 bps and a baud rate of 1000 baud. How many data elements are carried by each signal element? How many signal elements do we need? Data Communication - Analog Transmition8

Aspects of Digital-to-Analog Conversion Carrier Signal – sending device produces a high-frequency signal that acts as a base for the information signal Bandwidth – The required bandwidth for analog transmission of digital data is proportional to the signal rate except for FSK Data Communication - Analog Transmition9

Amplitude Shift Keying amplitude of carrier signal is varied to create signal element Binary ASK (BASK) Multilevel ASK Data Communication - Analog Transmition10

Amplitude Shift Keying Binary ASK (BASK) Also called on-off keying (OOK) Although can have several levels of signal, each with a different Binary 0: signal level is 0 Binary 1: same as amplitude of carrier frequency Data Communication - Analog Transmition11

Amplitude Shift Keying Binary ASK (BASK) Data Communication - Analog Transmition12

Amplitude Shift Keying Binary ASK (BASK) Bandwidth? Point is, the location of bandwidth which The middle of the bandwidth is where center of the carrier frequency, is located d, depends on modulation and filtering process – value of d is between 0 and 1 Data Communication - Analog Transmition13

Amplitude Shift Keying Binary ASK (BASK) Implementation? Multiplying NRZ digital signal by carrier signal Data Communication - Analog Transmition14

Amplitude Shift Keying Binary ASK (BASK) Example: available bandwidth of 100 kHz, which spans from 200 to 300 kHz. What are the carrier Frequency? bit rate using ASK with d =1 and r=1? Data Communication - Analog Transmition15

Amplitude Shift Keying Multilevel ASK there are more than two levels. use 4,8, 16, or more different amplitudes using 2, 3, 4, or more bits at a time (r = 2, r = 3, r =4, and so on ) it is implemented with QAM Data Communication - Analog Transmition16

Frequency Shift Keying requency of carrier signal is varied to represent data Binary FSK (BFSK) Multilevel FSK Data Communication - Analog Transmition17

Frequency Shift Keying Binary FSK (BFSK) new carrier frequencies (f c is carrier frequency ) – f1 = f c + ∆f – f2 = f c - ∆f Binary 0: use first carrier Binary 1: use second carrier Data Communication - Analog Transmition18

Frequency Shift Keying Binary FSK (BFSK) Data Communication - Analog Transmition19

Frequency Shift Keying Binary FSK (BFSK) Bandwidth? Data Communication - Analog Transmition20

Frequency Shift Keying Binary FSK (BFSK) minimum value of 2∆f? at least S for proper operation of modulation and demodulation Data Communication - Analog Transmition21

Frequency Shift Keying Binary FSK (BFSK) Example: available bandwidth of 100 kHz, which spans from 200 to 300 kHz. What are the carrier Frequency? bit rate using ASK with d =1 and r=1? Data Communication - Analog Transmition22

Frequency Shift Keying comparing BASK and BFSK Example: available bandwidth of 100 kHz, which spans from 200 to 300 kHz. What are the carrier Frequency? bit rate using ASK with d =1 and r=1? BASK BFSK Data Communication - Analog Transmition23

Frequency Shift Keying Binary FSK (BFSK) Implementation? Noncoherent BFSK – two ASK modulations, using two carrier frequencies may be discontinuity in the phase, when one signal element ends and the next begins coherent BFSK – voltage-controlled oscillator, that changes its frequency according to input voltage phase continues through the boundary of two signal elements Data Communication - Analog Transmition24

Frequency Shift Keying Multilevel FSK MFSK is not uncommon (use more than two frequencies) use four frequencies fI,f2,f3, f4 to send 2 bits at a time or use 8 frequencies to send 3 bit. remember that frequencies need to be 2∆f apart. – minimum value of 2∆f needs to be S Data Communication - Analog Transmition25

Frequency Shift Keying Multilevel FSK Bandwidth? If d=0 Data Communication - Analog Transmition26

Frequency Shift Keying Multilevel FSK Example: send data 3 bits at a time at bit rate of 3 Mbps, carrier frequency is 10 MHz number of levels (different frequencies), the baud rate, and the bandwidth? (d=0) Data Communication - Analog Transmition27

Phase Shift Keying phase of the carrier is varied to represent two or more different signal elements PSK is more common than ASK or FSK Binary PSK (BPSK) Quadrature PSK (QPSK) Data Communication - Analog Transmition28

Phase Shift Keying Binary PSK (BPSK) Binary 0: phase of 0° Binary 1: phase of 180° Binary PSK is as simple as binary ASK with one big advantage-it is less susceptible to noise Data Communication - Analog Transmition29

Phase Shift Keying Binary PSK (BPSK) Bandwidth? The same as that for binary ASK, but less than that for BFSK No bandwidth is wasted for separating two carrier signals. Data Communication - Analog Transmition30

Phase Shift Keying Binary PSK (BPSK) Implementation? polar NRZ signal instead of unipolar NRZ signal polar NRZ signal is multiplied by carrier frequency Data Communication - Analog Transmition31

Phase Shift Keying Quadrature PSK (QPSK) use 2 bits at a time in each signal element Binary 00: 45° Binary 01: -45° Binary 10: 135° Binary 11: -135° Data Communication - Analog Transmition32

Phase Shift Keying Quadrature PSK (QPSK) use 2 bits at a time in each signal element Implementation? uses two separate BPSK modulations 1.The incoming bits are first passed through a serial-to- parallel conversion that sends one bit to one modulator and the next bit to the other modulator. 2.Send each bit to a BPSK modulator 3.When they are added, result is sine wave, with four possible phases: 45°, -45°, 135°, and -135°. Data Communication - Analog Transmition33

Phase Shift Keying Quadrature PSK (QPSK) Data Communication - Analog Transmition34

Phase Shift Keying Quadrature PSK (QPSK) Example: Find the bandwidth? signal transmitting at 12 Mbps for QPSK. The value of d =O Data Communication - Analog Transmition35

Constellation Diagram four pieces of Information – X axis defines the peak amplitude of the in-phase component; – Y axis defines the peak amplitude of the quadrature component. – The length of the vector, that connects the point to the origin is the peak amplitude of the signal element – angle the line makes with the X axis is, phase of signal element –. Data Communication - Analog Transmition36

Constellation Diagram Data Communication - Analog Transmition37

Quadrature Amplitude Modulation (QAM) PSK has limited bit rate, because of the ability of equipments to distinguish small differences in phase. QAM is combination of ASK and PSK Data Communication - Analog Transmition38

QAM possible variations of QAM Data Communication - Analog Transmition39

QAM Bandwidth? minimum bandwidth required is the same as that required for ASK and PSK transmission. Data Communication - Analog Transmition40

ANALOG-TO-ANALOG CONVERSION Modulation is needed if only a bandpass channel is available example: radio. – government assigns a narrow bandwidth to each radio station. – analog signal produced by each station is a low- pass signal, all in the same range Data Communication - Analog Transmition41

ANALOG-TO-ANALOG CONVERSION Data Communication - Analog Transmition42

Amplitude Modulation carrier signal is modulated so that its amplitude varies with the changing amplitudes of the modulating signal Data Communication - Analog Transmition43

Amplitude Modulation Implementation: – simple multiplier, because amplitude of carrier signal needs to be changed according to amplitude of modulating signal. Data Communication - Analog Transmition44

Amplitude Modulation Bandwidth – twice the bandwidth of the modulating signal – covers a range centered on the carrier frequency – However, the signal components above and below the carrier frequency carry exactly the same information – some implementations discard one-half of the signals and cut the bandwidth in half. Data Communication - Analog Transmition45

Bandwidth Allocation of AM radio bandwidth of an audio signal (speech and music) is usually 5 kHz. AM radio station needs a bandwidth of 10kHz. AM stations are allowed carrier frequencies anywhere between 530 and 1700 kHz (1.7 MHz) Data Communication - Analog Transmition46

Frequency Modulation frequency of carrier signal is modulated to follow the changing voltage level (amplitude) of the modulating signal (as amplitude of information signal changes, frequency of carrier changes correspondingly). Data Communication - Analog Transmition47

Frequency Modulation Implementation using a voltage-controlled oscillator as with FSK. The frequency of the oscillator changes according to the input voltage which is the amplitude of the modulating signal Data Communication - Analog Transmition48

Frequency Modulation Bandwidth The actual bandwidth is difficult to determine shown empirically: ß is a factor depends on modulation technique with a common value of 4. Data Communication - Analog Transmition49

Bandwidth Allocation of FM radio bandwidth of an audio signal (speech and music) broadcast in stereo is almost 15 kHz 200 kHz (0.2 MHz) for each station. ß = 4 with some extra guard band allowed carrier frequencies anywhere between 88 and 108 MHz FCC requires that in a given area, only alternate bandwidth allocations may be used. The others remain unused to prevent any possibility of two stations interfering with each other. there are 100 potential PM bandwidths in an area, of which 50 can operate at anyone time Data Communication - Analog Transmition50

Phase Modulation phase of carrier signal is modulated to follow changing voltage level (amplitude) of modulating signal proved mathematically, PM is same as FM with one difference. – In FM, instantaneous change in carrier frequency is proportional to amplitude of modulating signal; – in PM instantaneous change in carrier frequency is proportional to derivative of amplitude of the modulating signal Data Communication - Analog Transmition51

Phase Modulation Data Communication - Analog Transmition52

Phase Modulation Implementation using a voltage-controlled oscillator along with a derivative frequency of the oscillator changes according to the derivative of input voltage (amplitude) Data Communication - Analog Transmition53

Phase Modulation Bandwidth ß is around 1 for narrowband and 3 for wideband Data Communication - Analog Transmition54