Read and translate Text A using Essential Vocabulary
Text A. Adaptive Processing
Conventional signal processing systems for the extraction of information from an incoming signal such as a matched filter operate in an open-loop fashion. That is, the same processing function is carried out in the present time interval regardless of whether that function produced the correct result in the preceding time interval. In other words, conventional signal processing techniques make the basic assumption that the signal degradation is a known and time-invariant quantity.
Adaptive processors on the other hand, operate with a closed-loop (feedback) arrangement. The incoming signal s(n) is filtered or weighted in a programmable filter to yield an output y(n) which is then compared against a desired, conditioning or training signal, y(n), to yield an error signal, e(n). This error is then used to update the processor weighting parameters (usually in an iterative way) such that the error is progressively minimized (i.e., the processor output more closely approximates to the training signal). Such processors fall into the two broad classes of adaptive filters (Figure 1.) and adaptive antennas.
Adaptive filters, which are the subject of this text, are concerned with the use of a programmable filter whose frequency response or transfer function is altered, or adapted, to pass the desired components of the signal without degradation and to attenuate the undesired or interfering signals, or to reduce any distortion on the input signal. Adaptive antennas employ the spatial processing in an antenna array to steer the main-lobe toward the signal and generate nulls in the beam pattern in the direction of the interfering sources. Thus they use spatial processing techniques for interference reduction.
Fig.1. Schematic of adaptive filter
In an adaptive system an absolute minimum of a priori information about the incoming signal is necessary. The adaptive filter operates by estimating the statistics of the incoming signal and adjusting its own-response in such a way as to minimize some cost function. This cost function may be derived in a number of ways depending on the intended application but normally it is derived by the use of the secondary signal source or conditioning input shown in Figure 1. This secondary signal input y(n) may be defined as the desired output of the filter, in which case the task of the adaptive algorithm is to adjust the weights in the programmable filter device in such a way as to minimize the difference or error e(n) between the filter output y(n) and the y(n) input. These adaptive filters are frequently used to recover signals from channels whose characteristic is time varying.
All the systems considered in this text are sampled-data (discrete-time) systems. For convenience the explicit time index has thus been omitted from all mathematical expressions.
Task 1. Translate and learn the following word combinations from Text A. Compose sentences with them.
Conventional signal processing systems; extraction of information; incoming signal; matched filter; open-loop fashion; preceding time interval; basic assumption; time-invariant quantity; closed-loop arrangement; conditioning signal; processor weighting parameters; antenna array; spatial processing; interference reduction; sampled-data system.
Task 2. Compose microtexts to the logical Scheme 1 and Scheme 2 (A, B). Try to reproduce them both: orally and in written form.
Task 3. Home assignment. Compose a microtext to the logical Scheme 3. Present it in written form.
Scheme 1.
*quantity – величина
Scheme 2A.
Scheme 2B. 
Scheme 3.
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