Modulation Types and Amplitude Modulation PDF

UNIT 7 Modulation Types and Amplitude Modulation PROF. THUSHARA WEERAWARDANE Outcomes  Define Types of Communication  Differentiate Modulation Techniques  Discuss Amplitude Modulation and Applications  Study Transmitter and Receiver Techniques  Analyze Different Amplitude mo...

UNIT 7 Modulation Types and Amplitude Modulation PROF. THUSHARA WEERAWARDANE Outcomes  Define Types of Communication  Differentiate Modulation Techniques  Discuss Amplitude Modulation and Applications  Study Transmitter and Receiver Techniques  Analyze Different Amplitude modulation schemes and Their Usage Type of Communication Baseband Communication Carrier Communication Baseband Communication Frequency Domain P2P Transmission Ethernet coaxial twisted-pair fiber-optic (broadband) Carrier Communication High power transmission Modulation? Modulation is a process of modification of carrier signal with respect to modulating (message) signal 𝐴𝑠𝑖𝑛(𝜔𝑡 + 𝜙) or 𝐴𝑐𝑜𝑠(𝜔𝑡 + 𝜙)  We send the information by changing some fundamental characteristics of the carrier wave  Amplitude  Frequency and  Phase  The faster we can change the carrier, the more information we can transmit  Plank constant Why Modulation is needed Energy 𝐸 = ℎ𝜈  Height of the Antenna frequency  Compare antenna height for 3kHz signal and 3 GHz Signal (𝐶 = 𝑓𝛌, 𝐴𝑛𝑡𝑒𝑛𝑛𝑎 𝐻𝑒𝑖𝑔ℎ𝑡 𝛌/4)  Radiated power by Antenna  Power transmitted 𝜶 (1Τ𝛌2 )  Reduce Interference  Same frequency bands are overlapping  Different carrier frequency can be used for multiplexing  High Bandwidth  High frequency results in High Bandwidth  Type of Modulation Analog Modulation Digital Modulation Continuous Wave Modulation AM – Amplitude Modulation ASK – Amplitude Shift Keying FM – Frequency Modulation FSK – Frequency Shift Keying PM – Phase Modulation PSK – Phase Shift Keying Carrier signal Pulse Modulation PAM – Pulse Amplitude Modulation PCM – Pulse Code Modulation PWM – Pulse Width Modulation (Delta Modulation and Adaptive Carrier signal PPM – Pulse Position Modulation delta Modulation) 𝐴𝑐𝑜𝑠(𝜔𝑡 + 𝜙) Example of Amplitude Modulation Example of Frequency Modulation Example of Phase Modulation Pulse Modulations (PAM, PWM, PPM and PCM) PWM – Pulse Width Modulation PAM – Pulse Amplitude Modulation PPM – Pulse Position Modulation PCM – Pulse Code Modulation Digital Modulation Schemes ASK FSK PSK Example of ASK, FSK and PSK ASK FSK PSK AMPLITUDE MODULATION Amplitude Modulation  In amplitude modulation, the amplitude of the carrier wave is varied in proportion to that of the message signal, such as an audio signal.  AM is used in broadcasting transmission (Radio and television) over the short, medium and long wavebands.  AM is used in the VHF transmissions for many airborne applications such as ground-to-air radio communications or two-way radio links for ground staff personnel.  Since AM is easy to demodulate, radio receivers for amplitude modulation are therefore easier and cheaper to manufacture.  However, amplitude modulation is sensitive to noise and electromagnetic interference. Modulating Index, 𝜇 = 𝐴𝑚 𝐴𝑐 Double Sides Full Carrier (DSBFC) System X(𝜔) - Fourier transform of x(t)  Important Aspects AM  Information is located in sidebands  Carrier is only operating frequency C(𝜔) - Fourier transform of c(t)  Bandwidth of AM signal is twice of the maximum frequency of modulating signal (2𝜔m ) Power transmitted 𝑃𝑡𝑜𝑡𝑎𝑙 = 𝑃𝑐 + 𝑃𝑈𝑆𝐵 + 𝑃𝐿𝑆𝐵 S(𝜔) - Fourier transform of s(t) 𝜇2 𝜇2 𝑃𝑡𝑜𝑡𝑎𝑙 = 𝑃𝑐 + 𝑃𝑐 + 𝑃𝑐 4 4 𝜇2 𝑃𝑡𝑜𝑡𝑎𝑙 = 𝑃𝑐 + 𝑃𝑐 2 𝜔c- 𝜔m 𝜔c+ 𝜔m Amplitude Modulation Cont. Under Modulated 𝜇1 mathematical convenience only. Hence, we can say that the modulating signal contains Over Modulated frequencies from 0 to fm or simply the bandwidth of modulating signal is fm.  AM Radio Transmitter (Simplified) The crystal oscillator generates the high frequency carrier The modulator is the place where the wave which is sent to the buffer which isolates the RF power superposition of the carrier wave and the signal amplifier keeping the frequency of the crystal-controlled generated takes place. oscillator constant. Further the modulator mixes the carrier wave and the AF signal, which is fed to the antenna for transmission. Signal is generated through the microphone. The magnitude of energy of the signal is very poor and hence, it is fed to the AF amplifier. This signal is further powered up by the AF power amplifier and sent to the modulator. AM Radio Transmitter (Simplified)  The AM radio transmitter consists of two sections.  Audio Frequency (AF) section and  Radio Frequency section.  The signal basically gets generated in the AF section and modulated in the RF section.  Main components  Preamplifier  RF Oscillator  AM modulator  Power Amplifier  Antenna AM Radio Receiver ✓ Receiving antenna - converts the received signal into electrical form. ✓ Amplifier is used to amplify the signal before processing. ✓ This is passed through an IF stage where the frequency band is translated down from the carrier frequency to the intermediate frequency. ✓ Detector translates the frequency down to the original frequency and demodulation occurs. ✓ A standard envelope detector used for demodulation. ✓ It consists of a parallel RC circuit which captures the envelope of the AM signal and hence demodulates the AM signal. ✓ Value of RC should neither be too large, nor too small for efficient demodulation. ✓ Finally, the demodulated signal is passed through an amplifier for large amplification.  Double sideband with full carrier modulation (AM) Types of Double sideband-suppressed carrier modulation (DSB-SC) Amplitude Modulation Single Sideband Modulation (SSB) Vestigial Sideband Modulation (VSB) Double sideband-suppressed carrier modulation (DSB-SC)  DSB-SC is the analog modulation techniques in which carrier is suppressed to save power (66% of power saved compared to AM) and only the sidebands are transmitted  Coherent detection is needed to maintain the local oscillator in perfect synchronisation for DSB-SC: obtaining the carrier phase is biggest challenges in all demodulators. Coherent detection increases the complexity of the receiver and increased the cost. This is in fact the price one has to pay for suppressing the carrier at wave to save transmit power Single sideband-suppressed carrier modulation (SSB-SC) In radio communications, single- sideband modulation (SSB) or single- sideband suppressed-carrier modulation (SSB-SC) is a type of modulation used to transmit information, such as an audio signal, by radio waves. A refinement of amplitude modulation, SSB uses less transmitter power, therefore power efficient SSB is transmitted only single Band which has the information, therefore bandwidth efficient. Vestigial Sideband Modulation (VSB) Vestigial Sideband Modulation (VSB) refers to the process where the “vestige” part of a signal is modulated alongside one sideband. A guard band of very small width is laid on either side of VSB in order to avoid the interferences. BW = fm + fv It is a highly efficient modulation technique used for wave transmission. This VSB modulation is mostly used in television transmissions. It reduces the bandwidth utilization. The filter characteristics do not need to be highly accurate thus making its design simple. It easily transmits low-frequency components and possesses good phase characteristics. Application is transmission of TV signal Comparison of DSB-SC, SSB-SC and VSB-SC DSB-SC SSB-SC VSB-SC Advantages Lower power consumption Better management of It is compromise between DSB Modulation system is frequency spectrum and SSB. Therefore, it is easier simple Low power consumption to generate than VSB-SC Disadvantages Complex detection Complex detection, Generation Demodulation system is still (coherent receiver with of exact SSB is rather difficult complex synchronization) (exact filter design and coherent Its bandwidth is about 25% receiver) greater than SSB-SC Applications Analog TV systems: to two-way radio (audio) Std for Analog TV broadcast transmission of color transmission – Prefer long system and wideband data information distance transmission of voice transmission signal ANY QUESTION?? THANK YOU!! Double sideband-suppressed carrier modulation (DSB-SC) DSB-SC is the analog modulation techniques in which carrier is suppressed to save power (66% of power saved compared to AM) and only the sidebands are transmitted Coherent detection is needed to maintain the local oscillator in perfect synchronisation for DSB-SC: obtaining the carrier phase is biggest challenges in all demodulators. This increases the complexity of the receiver and increased the cost. This is in fact the price one has to pay for suppressing the carrier at wave to save transmit power