# 6.1 Interpolation, decimation, and rate changing by integer fractions

 Page 1 / 1

## Interpolation: by an integer factor l

Interpolation means increasing the sampling rate, or filling in in-between samples. Equivalent to sampling abandlimited analog signal $L$ times faster. For the ideal interpolator,

${X}_{1}(\omega )=\begin{cases}{X}_{0}(L\omega ) & \text{if \left|\omega \right|< \frac{\pi }{L}}\\ 0 & \text{if \frac{\pi }{L}\le \left|\omega \right|\le \pi }\end{cases}$
$y(m)=\begin{cases}{X}_{0}(\frac{m}{L}) & \text{if m=\{0, ±(L), ±(2L), \dots \}}\\ 0 & \text{otherwise}\end{cases}$
The DTFT of $y(m)$ is
$Y(\omega )=\sum_{m=-\omega }$ y m ω m n x 0 n ω L n n x n ω L n X 0 ω L
Since ${X}_{0}({\omega }^{\prime })$ is periodic with a period of $2\pi$ , ${X}_{0}(L\omega )=Y(\omega )$ is periodic with a period of $\frac{2\pi }{L}$ (see [link] ). By inserting zero samples between the samples of ${x}_{0}(n)$ , we obtain a signal with a scaled frequency response that simply replicates ${X}_{0}({\omega }^{\prime })$ $L$ times over a $2\pi$ interval!

Obviously, the desired ${x}_{1}(m)$ can be obtained simply by lowpass filtering $y(m)$ to remove the replicas.

${x}_{1}(m)=(y(m), {h}_{L}(m))$
Given ${H}_{L}(m)=\begin{cases}1 & \text{if \left|\omega \right|< \frac{\pi }{L}}\\ 0 & \text{if \frac{\pi }{L}\le \left|\omega \right|\le \pi }\end{cases}$ In practice, a finite-length lowpass filter is designed using any of the methods studied so far ( [link] ).

## Decimation: sampling rate reduction (by an integer factor m)

Let $y(m)={x}_{0}(Lm)$ ( [link] )

That is, keep only every $L$ th sample ( [link] ) In frequency (DTFT):
$Y(\omega )=\sum_{m=()}$ y m ω m m x 0 M m ω m n M m n x 0 n k δ n M k ω n M ω ω M n x 0 n k δ n M k ω n DTFT x 0 n DTFT δ n M k
Now $\mathrm{DTFT}(\sum \delta (n-Mk))=2\pi \sum_{k=0}^{M-1} X(k)\delta ({\omega }_{\prime }-\frac{2\pi k}{M})$ for $\left|\omega \right|< \pi$ as shown in homework #1, where $X(k)$ is the DFT of one period of the periodic sequence. In this case, $X(k)=1$ for $k\in \{0, 1, \dots , M-1\}$ and $\mathrm{DTFT}(\sum \delta (n-Mk))=2\pi \sum_{k=0}^{M-1} \delta ({\omega }_{\prime }-\frac{2\pi k}{M})$ .
$(\mathrm{DTFT}({x}_{0}(n)), \mathrm{DTFT}(\sum \delta (n-Mk)))=({X}_{0}({\omega }^{\prime }), 2\pi \sum_{k=0}^{M-1} \delta ({\omega }_{\prime }-\frac{2\pi k}{M}))=\frac{1}{2\pi }\int_{-\pi }^{\pi } {X}_{0}({\mu }^{\prime })2\pi \sum_{k=0}^{M-1} \delta ({\omega }_{\prime }-{\mu }_{\prime }-\frac{2\pi k}{M})\,d {\mu }^{\prime }=\sum_{k=0}^{M-1} {X}_{0}({\omega }_{\prime }-\frac{2\pi k}{M})$
so $Y(\omega )=\sum_{k=0}^{M-1} {X}_{0}(\frac{\omega }{M}-\frac{2\pi k}{M})$ i.e. , we get digital aliasing .( [link] ) Usually, we prefer not to have aliasing, so the downsampler is preceded by a lowpass filter to remove all frequencycomponents above $\left|\omega \right|< \frac{\pi }{M}$ ( [link] ).

## Rate-changing by a rational fraction l/m

This is easily accomplished by interpolating by a factor of $L$ , then decimating by a factor of $M$ ( [link] ).

The two lowpass filters can be combined into one LP filterwith the lower cutoff, $H(\omega )=\begin{cases}1 & \text{if \left|\omega \right|< \frac{\pi }{\max\{L , M\}}}\\ 0 & \text{if \frac{\pi }{\max\{L , M\}}\le \left|\omega \right|\le \pi }\end{cases}$ Obviously, the computational complexity and simplicity of implementation will depend on $\frac{L}{M}$ : $2/3$ will be easier to implement than $1061/1060$ !

Is there any normative that regulates the use of silver nanoparticles?
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
why we need to study biomolecules, molecular biology in nanotechnology?
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
why?
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?
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
what does nano mean?
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?
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
it is a goid question and i want to know the answer as well
Maciej
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
there is no specific books for beginners but there is book called principle of nanotechnology
NANO
what is fullerene does it is used to make bukky balls
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
so some one know about replacing silicon atom with phosphorous in semiconductors device?
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
for screen printed electrodes ?
SUYASH
What is lattice structure?
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
Got questions? Join the online conversation and get instant answers!