Signal Encoding Techniques Chapter 6 Digital Vs Analog
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Signal Encoding Techniques Chapter 6
Digital Vs Analog
Reasons for Choosing Encoding Techniques n Digital data, digital signal n n Equipment less complex and expensive than digital-to-analog modulation equipment Analog data, digital signal n Permits use of modern digital transmission and switching equipment
Reasons for Choosing Encoding Techniques n Digital data, analog signal n n n Some transmission media will only propagate analog signals E. g. , optical fiber and unguided media Analog data, analog signal n n Analog data in electrical form can be transmitted easily and cheaply Done with voice transmission over voice-grade lines
Terms n n Data element, bits, a signal binary 0 or 1 Data rate, bits per second, the rate at which data elements are transmitted. Signal elements, Signal rate or modulation rate, signal elements per second (baud), the rate at which signal elements are transmitted.
Signal Encoding Criteria n What determines how successful a receiver will be in interpreting an incoming signal? n n n Signal-to-noise ratio Data rate Bandwidth An increase in data rate increases bit error rate An increase in SNR decreases bit error rate An increase in bandwidth allows an increase in data rate
Factors Used to Compare Encoding Schemes n Signal spectrum n n With lack of high-frequency components, less bandwidth required With no dc component, ac coupling via transformer possible Transfer function of a channel is worse near band edges Clocking n Ease of determining beginning and end of each bit position
Factors Used to Compare Encoding Schemes n Signal interference and noise immunity n n Performance in the presence of noise Cost and complexity n The higher the signal rate to achieve a given data rate, the greater the cost
Basic Encoding Techniques n Digital data to analog signal n Amplitude-shift keying (ASK) n n Frequency-shift keying (FSK) n n Amplitude difference of carrier frequency Frequency difference near carrier frequency Phase-shift keying (PSK) n Phase of carrier signal shifted
Basic Encoding Techniques
Amplitude-Shift Keying n n One binary digit represented by presence of carrier, at constant amplitude Other binary digit represented by absence of carrier n where the carrier signal is Acos(2πfct)
Amplitude-Shift Keying n n Susceptible to sudden gain changes Inefficient modulation technique On voice-grade lines, used up to 1200 bps Used to transmit digital data over optical fiber
Binary Frequency-Shift Keying (BFSK) n Two binary digits represented by two different frequencies near the carrier frequency n where f 1 and f 2 are offset from carrier frequency fc by equal but opposite amounts
Binary Frequency-Shift Keying (BFSK) n n Less susceptible to error than ASK On voice-grade lines, used up to 1200 bps Used for high-frequency (3 to 30 MHz) radio transmission Can be used at even higher frequencies on LANs that use coaxial cable
Multiple Frequency-Shift Keying (MFSK) n n More than two frequencies are used More bandwidth efficient but more susceptible to error n n n f i = f c + (2 i – 1 – M)f d f c = the carrier frequency f d = the difference frequency M = number of different signal elements = 2 L L = number of bits per signal element
Multiple Frequency-Shift Keying (MFSK) n Total bandwidth required 2 Mfd Minimum frequency separation required 2 fd=1/Ts Therefore, modulator requires a bandwidth of n n Wd=2 L/LT=M/Ts
Multiple Frequency-Shift Keying (MFSK) n To match data rate of input bit stream, each output signal element is held for: Ts=LT seconds n n where T is the bit period (data rate = 1/T) So, one signal element encodes L bits
Multiple Frequency-Shift Keying (MFSK)
Phase-Shift Keying (PSK) n Two-level PSK (BPSK) n Uses two phases to represent binary digits
Phase-Shift Keying (PSK) n Differential PSK (DPSK) n Phase shift with reference to previous bit n n Binary 0 – signal burst of same phase as previous signal burst Binary 1 – signal burst of opposite phase to previous signal burst
Phase-Shift Keying (PSK) n Four-level PSK (QPSK) n Each element represents more than one bit
Phase-Shift Keying (PSK) n Multilevel PSK n Using multiple phase angles with each angle having more than one amplitude, multiple signals elements can be achieved n n D = modulation rate, baud R = data rate, bps M = number of different signal elements = 2 L L = number of bits per signal element
Performance n Bandwidth of modulated signal (BT) n n ASK, PSK FSK n n n BT=(1+r)R BT=2 DF+(1+r)R R = bit rate 0 < r < 1; related to how signal is filtered DF = f 2 -fc=fc-f 1
Performance n Bandwidth of modulated signal (BT) n MPSK n MFSK n n L = number of bits encoded per signal element M = number of different signal elements
Performance n n n Bandwidth efficiency ― The ratio of data rate to transmission bandwidth (R/BT) For MFSK, with the increase of M, the bandwidth efficiency is decreased. For MPSK, with the increase of M, the bandwidth efficiency is increased.
Performance
Performance
Performance n Tradeoff between bandwidth efficiency and error performances: an increase in bandwidth efficiency results in an increase in error probability.
Minimum shift keying Where Eb is the transmitted signal energy per bit, and Tb is the bit duration, the phase (0) denotes the value of the phase at time t=0.
Quadrature Amplitude Modulation n QAM is a combination of ASK and PSK n Two different signals sent simultaneously on the same carrier frequency
Quadrature Amplitude Modulation
Reasons for Analog Modulation n Modulation of digital signals n n When only analog transmission facilities are available, digital to analog conversion required Modulation of analog signals n n A higher frequency may be needed for effective transmission Modulation permits frequency division multiplexing
Basic Encoding Techniques n Analog data to analog signal n n Amplitude modulation (AM) Angle modulation n n Frequency modulation (FM) Phase modulation (PM)
Amplitude Modulation n n n cos 2 fct = carrier x(t) = input signal na = modulation index n n Ratio of amplitude of input signal to carrier a. k. a double sideband transmitted carrier (DSBTC)
Amplitude modulation
Spectrum of AM signal
Amplitude Modulation n Transmitted power n n Pt = total transmitted power in s(t) Pc = transmitted power in carrier
Single Sideband (SSB) n Variant of AM is single sideband (SSB) n n n Advantages n n n Sends only one sideband Eliminates other sideband carrier Only half the bandwidth is required Less power is required Disadvantages n Suppressed carrier can’t be used for synchronization purposes
Other variants n n Double sideband suppressed carrier (DSBSC): filters out the carrier frequency and sends both sidebands. Vestigial sideband (VSB), uses one sideband reduced-power carrier.
Angle Modulation n Angle modulation n Phase is proportional to modulating signal n np = phase modulation index
Angle Modulation n Frequency modulation n Derivative of the phase is proportional to modulating signal n nf = frequency modulation index
Angle Modulation n Compared to AM, FM and PM result in a signal whose bandwidth: n n is also centered at fc but has a magnitude that is much different n n Angle modulation includes cos( (t)) which produces a wide range of frequencies Thus, FM and PM require greater bandwidth than AM
Angle Modulation n Carson’s rule where n The formula for FM becomes
Basic Encoding Techniques n Analog data to digital signal n n Pulse code modulation (PCM) Delta modulation (DM)
Analog Data to Digital Signal n Once analog data have been converted to digital signals, the digital data: n n n can be transmitted using NRZ-L can be encoded as a digital signal using a code other than NRZ-L can be converted to an analog signal, using previously discussed techniques
Pulse Code Modulation n n Based on the sampling theorem Each analog sample is assigned a binary code n n Analog samples are referred to as pulse amplitude modulation (PAM) samples The digital signal consists of block of n bits, where each n-bit number is the amplitude of a PCM pulse
Pulse Code Modulation
Pulse Code Modulation n n By quantizing the PAM pulse, original signal is only approximated Leads to quantizing noise Signal-to-noise ratio for quantizing noise Thus, each additional bit increases SNR by 6 d. B, or a factor of 4
Delta Modulation n Analog input is approximated by staircase function n n Moves up or down by one quantization level ( ) at each sampling interval The bit stream approximates derivative of analog signal (rather than amplitude) n n 1 is generated if function goes up 0 otherwise
Delta Modulation
Delta Modulation n Two important parameters n n n Accuracy improved by increasing sampling rate n n Size of step assigned to each binary digit ( ) Sampling rate However, this increases the data rate Advantage of DM over PCM is the simplicity of its implementation
Reasons for Growth of Digital Techniques n Growth in popularity of digital techniques for sending analog data n Repeaters are used instead of amplifiers n n TDM is used instead of FDM n n No additive noise No intermodulation noise Conversion to digital signaling allows use of more efficient digital switching techniques
- Digital signal as a composite analog signal
- Data encoding techniques in computer networks
- Digital to analog encoding
- Analog and digital system difference
- Hardware or software encoding
- Disadvantages of fsk
- Analog mixed signal verification
- Dpcm advantages and disadvantages
- Precision analog signal processing
- Encoding storage and retrieval
- Coding principles
- Data encoding techniques
- Encoding in digital communication
- Compare and contrast weather
- Pengertian teknologi digital dan analog
- Analog digital transmission
- Analog vs digital
- Modulation digital to analog
- Analog and digital video in multimedia
- Amw huebsch
- Advantages and disadvantages of flash adc
- Single slope adc
- Kepanjangan adc
- Contoh soal sinyal analog
- Rtv 332
- Analog vs digital communication systems
- Analog vs digital chips
- Analog image and digital image
- Sebutkan kelemahan modulasi digital
- Digital to analog converter
- Analog and digital signals in computer networking
- Digital to analog converters basic concepts
- Analog vs digital video
- Digital to analog conversion in data communication
- Digital and analog quantities
- Filter lpf hpf bpf brf
- Advantages of digital computers
- Analog signla
- Analog vs digital
- Alat-alat yang menggunakan konsep elektronika analog
- Impulse invariant method formula
- Digital image acquisition for analog sem
- Digital control
- Analog and digital difference
- Compare and contrast analog and digital forecasting
- Modulasi analog dan digital
- Baseband signal and bandpass signal
- Baseband signal and bandpass signal
- Classification of signal
- Digital signal 3
- For digital
- Sysc
- Lattice ladder structure of fir filter