AM and FM, while valuable modulation methods, have proven inadequate to match today’s needs for high-volume traffic. We have all heard of AM radio and FM radio. Carrierless amplitude and phase (CAP) modulation is one such spectrally efficient scheme that has attracted significant interest in recent years owing to its good potential and practical implementation. About Modulation • Application Examples • broadcasting of both audio and video signals. In this paper, we introduce the basic features of CAP modulation and review its … 3 Carrier signals are used for two reasons: (1) To reduce the wavelength for efficient transmission and reception (the optimum antenna size is ¼ of a wavelength). But phase modulation seems to be in a different category—“PM radio” is by no means a common term. A typical audio frequency of 3000 Hz has a wavelength of 100 km and What is QAM (Quadrature Amplitude Modulation)? In either case, one-half of the transmission bandwidth is occupied by the upper sideband of the modulated wave, whereas the other half is occupied by the lower sideband. It turns out that phase modulation is more relevant in the context of digital RF. In other words, QAM transmits information by changing both the amplitude and phase of a carrier wave, thereby doubling the effective bandwidth. Amplitude modulation and DSBSC modulation are wasteful of bandwidth because they both require a transmission bandwidth equal to twice the message bandwidth. Phase modulation is similar to frequency modulation and is an important technique in digital communication systems. Let us now discuss these topics in greater detail. Derivation: PM is a type of angle modulation and it is defined as the change in phase of the carrier signal in correspondence with the amplitude of the message signal. • Mobile radio communications, such as cell phone. A digital modulation scheme that incorporates both Phase and Amplitude modulation is referred to Quadrature Amplitude Modulation (QAM). Example PSK Modulation. – Frequency Modulation: changes the frequency. 4 • Basic Modulation Types – Amplitude Modulation: changes the amplitude. In phase modulation, the phase of the carrier signal is varied whereas the amplitude of the carrier signal remains constant. To demonstrate the modulation an 8PSK modulator is used in the following block diagram. The example bit stream on the left hand side enters the modulator and has a bit slot of 10. In amplitude modulation, the amplitude of the carrier varies. Amplitude, Frequency and Phase Modulation . QAM (Quadrature Amplitude Modulation) is defined as the modulation technique which is the combination of phase and amplitude modulation of a carrier wave into a single channel. Phase Modulation Diagram. Phase modulation is the process of transmitting information over a carrier wave by varying its phase in accordance with the amplitude of the message signal. A sine wave can be mathematically described by a sine or cosine function with amplitude A c , frequency f c , and phase φ. Frequency Modulation. There are three parameters of a sine wave that can be varied: amplitude, frequency, and phase. Here, both the frequency and amplitude of the carrier signal stays as constant whereas phase varies in accordance. Modern communications systems demand more information capacity, higher signal quality, greater security and digital data compatibility. The resulting outputs are modulated in a format having two amplitude levels (1 2 and 3 2 of the average amplitude) and two phase levels (0, π), which will be referred to as four-level amplitude-phase shift keying (4-APSK). Phase Modulation is the process of varying the phase of the carrier signal linearly with the message signal. The process of varying any of the three characteristics as the Amplitude, Frequency or the Phase of a carrier signal is called as modulation We know that the information signal to be transmitted can be of any form such as data, music, video etc. Any of these can be modulated, or varied, to transmit information. – Phase Modulation: changes the phase. What is Modulation? Amplitude modulation (a), frequency modulation (b), and phase modulation (c).