Presentation on theme: " Analog data to analog signal (AM, FM, PM) Digital data to analog signal (ASK, FSK, BPSK, QAM) Analog data to digital signal (PCM, DM) Digital data."— Presentation transcript:
Analog data to analog signal (AM, FM, PM) Digital data to analog signal (ASK, FSK, BPSK, QAM) Analog data to digital signal (PCM, DM) Digital data to digital signal (line codes) Signal Encoding Techniques (modulation and encoding) 1 DCTC, By Ya Bao
Analog Signals 2 DCTC, By Ya Bao
Digital Signals 3 DCTC, By Ya Bao
Analog and Digital Transmission
AMPLITUDE MODULATION 5 DCTC, By Ya Bao
6 Modulation The process by which some characteristics of a carrier wave is varied in accordance with an information- bearing signal. Continuous-wave modulation Amplitude modulation Frequency modulation AM modulation family Amplitude modulation (AM) Double sideband-suppressed carrier (DSB-SC) Single sideband (SSB) Vestigial sideband (VSB)
DCTC, By Ya Bao 7 AMPLITUDE MODULATION 1. DEFINING AM A carrier wave whose amplitude is varied in proportion to the instantaneous amplitude of a modulating voltage 2. GENERATING THE AM nonlinear device: diode or transistor biased in its nonlinear region Carrier wave: is a waveform (usually sinusoidal) that is modulated (modified) with an input signal for the purpose of conveying information. This carrier wave is usually a much higher frequency than the input signal.
DCTC, By Ya Bao 8
9 3.ANALYSIS OF THE AM WAVE
DCTC, By Ya Bao 10
DCTC, By Ya Bao 11 4. Different Carriers and AM Carriers are spaced at 20 kHz, beginning at 100kHz. Each carrier is modulated by a signal with 5kHz bandwidth. Is there interference from sideband overlap?
DCTC, By Ya Bao 12 5. MODULATION INDEX AND SIGNAL POWER
DCTC, By Ya Bao 13 Moduiation Index and Power
DCTC, By Ya Bao 14 Current Calculations Example A carrier of 1000 W is modulated with a resulting modulation index of 0. 8. What is the total power? What is the carrier power if the total power is 1000 W and the modulation index is 0.95?
DCTC, By Ya Bao 15 6.2 Double Sideband Suppressed Carrier (DSBSC) When the carrier is reduced, this is called double- sideband suppressed-carrier AM, or DSB-SC. If the carrier could somehow be removed or reduced, the transmitted signal would consist of two information- bearing sidebands, and the total transmitted power would be information
DCTC, By Ya Bao 16 6.3 Single-Sideband (SSB) suppressing the carrier and one of the sidebands
DCTC, By Ya Bao 17
DCTC, By Ya Bao 18 6.4 Filtering the SSB LSB or USB Dual Conversion : up-converting the modulating frequency twice and selecting the upper or lower sideband for transmission.
DCTC, By Ya Bao 19 AM: Features and Drawbacks: the AM signal is greatly affected by noise impossible to determine absolutely the original signal level conventional AM is not efficient in the use of transmitter power AM is useful where a simple, low-cost receiver and detector is desired
Angle Modulation 20 DCTC, By Ya Bao
21 ANGLE MODULATION: The intelligence of the modulating signal can be conveyed by varying the frequency or phase of the carrier signal. When this is the case, we have angle modulation, which can be subdivided into two categories: frequency modulation (FM), and phase modulation (PM). DCTC, By Ya Bao
22 Frequency Modulation. The carrier's instantaneous frequency deviation from its unmodulated value varies in proportion to the instantaneous amplitude of the modulating signal. Phase Modulation. The carrier's instantaneous phase deviation from its unmodulated value varies as a function of the instantaneous amplitude of the modulating signal;
23 FIGURE 4-1 The FM and PM waveforms for sine-wave modulation: (a) carrier wave; (b) modulation wave; (c) FM wave; (d) PM wave. ( Note: The derivative of the modulating sine wave is the cosine wave shown by the dotted lines. The PM wave appears to be frequency modulated by the cosine wave.) DCTC, By Ya Bao
24 MODULATION INDEX modulation index for an FM signal δ = maximum frequency deviation of the carrier caused by the amplitude of the modulating signal f m = frequency of the modulating signal
DCTC, By Ya Bao 25 FREQUENCY ANALYSIS OF THE FM WAVE where: e Fm = the instantaneous amplitude of the modulated FM wave Ac = the peak amplitude of the carrier J n = solution to the nth order Bessel function for a modulation index m f. m f = FM modulation index, Δf/f m
26 DCTC, By Ya Bao
27 Spectral components of a carrier of frequency, f c, frequency modulated by a sine wave with frequency f m DCTC, By Ya Bao
28 FM signal characters The FM wave is comprised of an infinite number of sideband components bandwidth of an FM signal must be wider than that of an AM signal As the modulation index increases from m f = 0, the spectral energy shifts from the carrier frequency to an increasing number of significant sidebands. J n (m f ) coefficients, decrease in value with increasing order, n. negative Jn(mf) coefficients imply a 180 0 phase inversion. DCTC, By Ya Bao
29 Carrier Frequency Eigenvalues in some cases the carrier frequency component, J O, and the various sidebands, J n go to zero amplitudes at specific values of m. These values are called eigenvalues.
DCTC, By Ya Bao 30 Bandwidth Requirements for FM The higher the modulation index, the greater the required system bandwidth where n is the highest number of significant ( least 1%, or -40 dB; (20 log 1/100 ), of the voltage of the unmodulated carrier ) sideband components and f m is the highest modulation frequency. Carson's Rule
31 Amplitude versus frequency spectrum for various modulation indices (f m fixed, & varying): (a) m f = 0.25; (b) m f = 1; (c) m f = 2; (d) m f = 5; (e) m f = 10. DCTC, By Ya Bao
33 FIGURE 4-6 Commercial FM broadcast band. DCTC, By Ya Bao
34 Commercial FM broadcast band The maximum permissible carrier deviation, δ, is ±75 kHz Modulating frequencies (voice or music) is ranging from 50 Hz to 15 kHz The modulation index can range from as low as 5 for f m = 15 kHz (75 kHz/15 kHz) to as high as 1500 for f m = 50 Hz (75 kHz/50 Hz). The ±75-kHz carrier deviation results in an FM bandwidth requirement of 150 kHz for the receiver. A 25-kHz guard band above and below the upper and lower FM sidebands. Total bandwidth of one channel is 200Hz.
DCTC, By Ya Bao 35 Narrowband FM (NBFM) NBFM uses low modulation index values, with a much smaller range of modulation index across all values of the modulating signal. An NBFM system restricts the modulating signal to the minimum acceptable value, which is 300 Hz to 3 KHz for intelligible voice. 10 to 15 kHz of spectrum. Used in police, fire, and Taxi radios, GSM, amateur radio, etc.
DCTC, By Ya Bao 36 POWER IN THE FM WAVE power of the unmodulated carrier For a modulated carrier
DCTC, By Ya Bao 37 FM NOISE Increased bandwidth of an FM – to enhance the signal- to-noise ratio (SNR). Advantages of FM over AM. To take this advantage, large m f is necessary– high order sidebands are important – wider bandwidth is required. Phase Analysis of FM Noise where α = the maximum phase deviation of the carrier frequency caused by the noise V N = noise voltage V c = carrier voltage
39 The ratio of carrier voltage to noise voltage, is the SNR (voltage) α represents the equivalent modulation index produced by the noise.
40 The effect of noise on an FM carrier signal is directly proportional to the modulation frequency f m. Increasing f m, degrades the Voice, data, and music contain many frequencies, which are distributed throughout the given modulation passband. Therefore, the SNR is not uniform throughout. To maintain a flat SNR, some techniques are employed. DCTC, By Ya Bao