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Modulation and Demodulation. Introduction. A communication system that sends information between two locations consists of a transmitter, channel, and receiver as illustrated in Figure 1. The channel refers to the physical medium carrying the information signal (voice, video, data etc.) from one location to another.
This textbook presents the fundamental concepts underlying the design of modern digital communication systems, which include the wireline, wire-less, and storage systems that pervade our everyday lives.
- 171KB
- 17
One important reason why high-frequency transmission is attractive is that the size of the antenna required for efficient transmission is roughly one-quarter the wavelength of the propagating wave, as discussed in Chapter 10.
- Binary Bits to Input signals
- Signal decoder �
- 6.2.2 Channel imperfections: a preliminary view
- k uk p(t
- 6.3.3 Relation between PAM and analog source coding
- 6.6.1 Distance and orthogonality
- k vkp(t
- 6.7 Carrier and phase recovery in QAM systems
- 6.7.1 Tracking phase in the presence of noise
Signals to � waveform Baseband to � passband sequence of signals baseband waveform � passband Channel waveform
Waveform to signals � Passband to baseband � Figure 6.1: The layers of a modulator (channel encoder) and demodulator (channel decoder). ARQ has always been an active area of communication and information theoretic research, but it will not be discussed here for the following reasons: It is important to understand communication in a single direction...
Physical waveform channels are always subject to propagation delay, attenuation, and noise. Many wireline channels can be reasonably modeled using only these degradations, whereas wireless channels are subject to other degrations discussed in Chapter 9. This subsection provides a preliminary look at delay, then attenuation, and finally noise. The t...
modulator is determined by the signal constellation , the signal interval A kT ), for a PAM − T and the real L2 modulation pulse p(t). It may be helpful to visualize p(t) as the impulse response of a linear time-invariant filter. Then u(t) is the response of that filter to a sequence of T -spaced impulses ukδ(t kT ) . The problem { − } of choosing ...
The main emphasis in PAM modulation has been that of converting a sequence of T -spaced signals into a waveform. Similarly, the first part of analog source coding is often to convert a waveform into a T -spaced sequence of samples. The major difference is that with PAM modulation, we have control over the PAM pulse p(t) and thus some control over t...
Previous sections have shown how to modulate a complex QAM baseband waveform u(t) up to a real passband waveform x(t) and how to retrieve u(t) from x(t) at the receiver. They have also discussed signal constellations that minimize energy for given minimum distance. Finally, the use of a modulation waveform p(t) with orthonormal shifts, has connecte...
− and the energy difference in the signal points by
Consider a QAM receiver and visualize the passband-to-baseband conversion as multiplying the positive frequency passband by the complex sinusoid e− 2πifct . If the receiver has a phase error φ(t) in its estimate of the phase of the transmitted carrier, then it will instead multiply the incoming waveform by e− 2πifct+iφ(t). We assume in this analysi...
The problem of deciding on or detecting the signals uk} from the received samples r(kT ) { { } in the presence of noise is a major topic of Chapter 8. Here, however, we have the added complication of both detecting the transmitted signals and also tracking and eliminating the phase error. Fortunately, the problem of decision making and that of phas...
Modulation is a technique that changes the characteristics of the carrier frequency in accordance with the input signal. Figure 1.1 shows the conceptual block diagram of a modern wireless communication system, where the modulation block is shown in the inset of the dotted block. As shown in the figure, modulation is performed at the
- Saleh Faruque
- 2017
This application note introduces the concepts of digital modulation used in many communications systems today. Emphasis is placed on explaining the tradeoffs that are made to optimize efficiencies in system design.
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Typically the objective of a digital communication system is to transport digital data between two or more nodes. In radio communications this is usually achieved by adjusting a physical characteristic of a sinusoidal carrier, either the frequency, phase, amplitude or a combination thereof.
