<< Chapter < Page Chapter >> Page >

Two problem formulations

As mentioned in [link] , one can address problem [link] in two ways depending on how one views the role of the transition band in a CLS problem. The original problem posed by Adams in [link] can be written as follows,

min h D ( ω ) - H ( ω ; h ) 2 subject to | D ( ω ) - H ( ω ; h ) | τ ω [ 0 , ω p b ] [ ω s b , π ]

where 0 < ω p b < ω s b < π . From a traditional standpoint this formulation feels familiar. It assigns fixed frequencies to the transition band edges as a number of filter design techniques do. As it turns out, however, one might not want to do this in CLS design.

An alternate formulation to [link] could implicitly introduce a transition frequency ω t b (where ω p b < ω t b < ω s b ); the user only specifies ω t b . Consider

min h D ( ω ) - H ( ω ; h ) 2 ω [ 0 , π ] subject to | D ( ω ) - H ( ω ; h ) | τ ω [ 0 , ω p b ] [ ω s b , π ]

The algorithm at each iteration generates an induced transition band in order to satisfy the constraints in [link] . Therefore { ω p b , ω s b } vary at each iteration.

Two graphs showing two formulations for Constrained Least Squares Problems.
Two formulations for Constrained Least Squares problems.

It is critical to point out the differences between [link] and [link] . [link] .a explains Adams' CLS formulation, where the desired filter response is only specified at the fixed pass and stop bands. At any iteration, Adams' method attempts to minimize the least squares error ( ε 2 ) at both bands while trying to satisfy the constraint τ . Note that one could think of the constraint requirements in terms of the Chebishev error ε by writing [link] as follows,

min h D ( ω ) - H ( ω ; h ) 2 subject to D ( ω ) - H ( ω ; h ) τ ω [ 0 , ω p b ] [ ω s b , π ]

In contrast, [link] .b illustrates our proposed problem [link] . The idea is to minimize the least squared error ε 2 across all frequencies while ensuring that constraints are met in an intelligent manner. At this point one can think of the interval ( ω p b , ω s b ) as an induced transition band, useful for the purposes of constraining the filter. [link] presents the actual algorithms that solve [link] , including the process of finding { ω p b , ω s b } .

It is important to note an interesting behavior of transition bands and extrema points in l 2 and l filters. [link] shows l 2 and l length-15 linear phase filters (designed using Matlab's firls and firpm functions); the transition band was specified at { ω p b = 0 . 4 / π , ω s b = 0 . 5 / π } . The dotted l 2 filter illustrates an important behavior of least squares filters: typically the maximum error of an l 2 filter is located at the transition band. The solid l filter shows why minimax filters are important: despite their larger error across most of the bands, the filter shows the same maximum error at all extrema points, including the transition band edge frequencies. In a CLS problem then, typically an algorithm will attempt to reduce iteratively the maximum error (usually located around the transition band) of a series of least squares filters.

A graph consisting of two waveforms one is identified by a solid line and labeled L_∞. The other is identified by a dotted line and labeled L_2. The x-axis is labeled ω/π and the y-axis is labeled |H(ω)|. Both waveforms follow the same general path starting on the left high on the y-axis and dropping drastically to 0 on the y axis and bouncing along the x axis to the end of the graph.
Comparison of l 2 and l filters.

Another important fact results from the relationship between the transition band width and the resulting error amplitude in l filters. [link] shows two l designs; the transition bands were set at { 0 . 4 / π , 0 . 5 / π } for the solid line design, and at { 0 . 4 / π , 0 . 6 / π } for the dotted line one. One can see that by widening the transition band a decrease in error ripple amplitude is induced.

Questions & Answers

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
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
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
Daniel
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
Good
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get the best Algebra and trigonometry course in your pocket!





Source:  OpenStax, Iterative design of l_p digital filters. OpenStax CNX. Dec 07, 2011 Download for free at http://cnx.org/content/col11383/1.1
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Iterative design of l_p digital filters' conversation and receive update notifications?

Ask