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There are two basic approaches to an AGC. The traditional approach uses analog circuitry to adjust the gain before the sampling. The more modern approach uses the output of the sampler to adjust thegain. The advantage of the analog method is that the two blocks (the gain and the sampling) are separate and do not interact.The advantage of the digital adjustment is that less additional hardware is required since the DSP processing is already presentfor other tasks.

The goal of the AGC is to maintain the dynamic range of the signal by attenuating it when it is too large (as in (a)) and by increasing it when it is too small (as in (b)).
The goal of the AGC is to maintain the dynamic range of the signal by attenuating it when it is too large (as in (a))and by increasing it when it is too small (as in (b)).

A simple digital system for AGC gain adjustment is shown in [link] . The input r ( t ) is multiplied by the gain a to give the normalized signal s ( t ) . This is then sampled to give the output s [ k ] . The assessment block measures s [ k ] and determines whether a must be increased or decreased.

An automatic gain control adjusts the gain parameter a so that the average energy at the output remains (roughly) fixed, despite fluctuations in the average received energy.
An automatic gain control adjusts the gain parameter a so that the average energy at the output remains (roughly) fixed, despitefluctuations in the average received energy.

The goal is to choose a so that the power (or average energy) of s ( t ) is approximately equal to some specified s 2 . Since

a 2 avg { r 2 ( t ) } t = k T avg { s 2 ( k T ) } avg { s 2 [ k ] } ,

it would be ideal to choose

a 2 s 2 avg { r 2 ( k T ) } ,

because this would imply that avg { s 2 ( k T ) } s 2 . The averaging operation (in this case a movingaverage over a block of data of size N ) is defined by

avg { x [ k ] } = 1 N i = k - N + 1 k x [ i ]

Unfortunately, neither the analog input r ( t ) nor its power are directly available to the assessment blockin the DSP portion of the receiver, so it is not possible to directly implement [link] .

Is there an adaptive element that can accomplish this task? As suggested in the beginning of "Iteration and Optimization" , there are three steps to the creation of a viableoptimization approach: setting a goal, choosing a solution method, and testing. As in any real life engineering task, a propermathematical statement of the goal can be tricky, and this section proposes two (slightly different) possibilitiesfor the AGC. By comparing the resulting algorithms (essentially, alternativeforms for the AGC design), it may be possible to trade off among various design considerations.

One sensible goal is to try to minimize a simple function of the difference between the power of the sampled signal s [ k ] and the desired power s 2 . For instance, the averaged squared error in the powers of s and s ,

J L S ( a ) = avg 1 4 ( s 2 [ k ] - s 2 ) 2 = 1 4 avg { ( a 2 r 2 ( k T ) - s 2 ) 2 } ,

penalizes values of a which cause s 2 [ k ] to deviate from s 2 . This formally mimics the parabolic form of the objective [link] in the polynomial minimization example of the previous section.Applying the steepest descent strategy yields

a [ k + 1 ] = a [ k ] - μ d J L S ( a ) d a a = a [ k ] ,

which is the same as [link] , except that the name of the parameter has changed from x to a . To find the exact form of [link] requires the derivative of J L S ( a ) with respect to the unknown parameter a . This can be approximated by swapping the derivative and the averaging operations to give

d J L S ( a ) d a = 1 4 d avg { ( a 2 r 2 ( k T ) - s 2 ) 2 } d a 1 4 avg d ( a 2 r 2 ( k T ) - s 2 ) 2 d a = avg { ( a 2 r 2 ( k T ) - s 2 ) a r 2 ( k T ) } .

Questions & Answers

find the 15th term of the geometric sequince whose first is 18 and last term of 387
Jerwin Reply
The given of f(x=x-2. then what is the value of this f(3) 5f(x+1)
virgelyn Reply
hmm well what is the answer
Abhi
how do they get the third part x = (32)5/4
kinnecy Reply
can someone help me with some logarithmic and exponential equations.
Jeffrey Reply
sure. what is your question?
ninjadapaul
20/(×-6^2)
Salomon
okay, so you have 6 raised to the power of 2. what is that part of your answer
ninjadapaul
I don't understand what the A with approx sign and the boxed x mean
ninjadapaul
it think it's written 20/(X-6)^2 so it's 20 divided by X-6 squared
Salomon
I'm not sure why it wrote it the other way
Salomon
I got X =-6
Salomon
ok. so take the square root of both sides, now you have plus or minus the square root of 20= x-6
ninjadapaul
oops. ignore that.
ninjadapaul
so you not have an equal sign anywhere in the original equation?
ninjadapaul
hmm
Abhi
is it a question of log
Abhi
🤔.
Abhi
Commplementary angles
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Uday
what is a good calculator for all algebra; would a Casio fx 260 work with all algebra equations? please name the cheapest, thanks.
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a perfect square v²+2v+_
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or infinite solutions?
Kim
The answer is neither. The function, 2 = 0 cannot exist. Hence, the function is undefined.
Al
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Kristine 2*2*2=8
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Differences Between Laspeyres and Paasche Indices
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No. 7x -4y is simplified from 4x + (3y + 3x) -7y
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. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
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Cied
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I start with an easy one. carbon nanotubes woven into a long filament like a string
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Porter
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what is system testing?
AMJAD
preparation of nanomaterial
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Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
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AMJAD
what is system testing
AMJAD
what is the application of nanotechnology?
Stotaw
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
Azam
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Prasenjit
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
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Azam
Hello
Uday
I'm interested in Nanotube
Uday
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Prasenjit
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Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
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the Beer law works very well for dilute solutions but fails for very high concentrations. why?
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how did you get the value of 2000N.What calculations are needed to arrive at it
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Source:  OpenStax, Software receiver design. OpenStax CNX. Aug 13, 2013 Download for free at http://cnx.org/content/col11510/1.3
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