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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

what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
sciencedirect big data base
Ernesto
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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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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