Envelope detection

There are a number of ways that envelope detection has been implemented. In purely analog approaches, simple full-wave rectification followed by a low-pass filtering has been shown to work quite well. It is also possible to digitize the RF signals earlier in the processing chain, perform the... 

The DSB+C signal can be demodulated coherently, as described for DSB-SC signals. The real benefit of using DSB+C systems, however, is the ability to receive using envelope detection methods. 

These receivers do not require coherent local oscillators and are much cheaper and easier to built than coherent receivers. Envelope detection is illustrated by the simple systems shown in Fig. 12.19. 

FIGURE 12.19 DSB+C detection using (a) envelope detection, (b) rectifier detection. 

Alternatively, a carrier can be inserted into the SSB signal, which can then be demodulated using simple envelope detection. This SSB-FC approach has the advantages of both low bandwidth and low-complexity receiver design, but is inefficient in power use due to the added carrier and usually performs poorly in the presence of noise. 

As with DSB-SC and SSB-SC, a carrier can be added to the transmitted VSB signal allowing inexpensive envelope detection to be used in the receiver. 

DSB-hC (AM) Easier to generate than DSB-SC, especially at high-power levels. Inexpensive receivers using envelope detection. Poor power efficiency. Poor Spectrum efficiency. Poor low-frequency response. Exhibits threshold effect in noise. Used in commercial AM. 

Envelope detection A demodulation process that senses the shape of the modulated RF envelope. A diode detector is one type of envelope detection device. 

Many researchers have studied the problem of classification from ultrasound images mainly in the area of liver tissue [2]-[10]. Initial attempts to characterize diffuse diseases have utilized different signal processing techniques in order to obtain useful information from the raw radiofrequency signal [2], [3]. In a series of papers, Momenan et al. showed that second order statistical parameters from envelope-detected or intensity echo signals have discriminatory power [4], [5]. Some researchers have treated the task of tissue quantification from the point of description and classification with numerical texture... 

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