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Interim Specification 95 (IS-95) describes a Direct-Sequence Spread-Spectrum (DS/SS) cellular system that uses a Rake receiver to provide path diversity for mitigating the effects of frequency-selective fading. The Rake receiver searches through the different multipath delays for code correlation and thus recovers delayed signals that are then optimally combined with the output of other independent correlators.

Figure 1 show the power profiles associated with the five chip transmissions of the code sequence 1 0 1 1 1. Each abscissa shows three components arriving with delays τ 1 size 12{τ rSub { size 8{1} } } {} , τ 2 size 12{τ rSub { size 8{2} } } {} , and τ 3 size 12{τ rSub { size 8{3} } } {} . Assume that the intervals between the transmission times t i size 12{t rSub { size 8{i} } } {} and the intervals between the delay times τ i size 12{τ rSub { size 8{i} } } {} are each one chip in duration. The component arriving at the receiver at time t 4 size 12{t rSub { size 8{ - 4} } } {} , with delay τ 3 size 12{τ rSub { size 8{3} } } {} , is time-coincident with two others, namely the components arriving at times t 3 size 12{t rSub { size 8{ - 3} } } {} and t 2 size 12{t rSub { size 8{ - 2} } } {} with delays τ 2 size 12{τ rSub { size 8{2} } } {} and τ 1 size 12{τ rSub { size 8{1} } } {} respectively. Since in this example the delayed components are separated by at least one chip time, they can be resolved.

At the receiver, there must be a sounding device dedicated to estimating the τ i size 12{τ rSub { size 8{i} } } {} delay times. Note that the fading rate in mobile radio system is relatively slow (in the order of milliseconds) or the channel coherence time large compared to the chip time duration ( T 0 > T ch size 12{T rSub { size 8{0} }>T rSub { size 8{ ital "ch"} } } {} ). Hence, the changes in τ i size 12{τ rSub { size 8{i} } } {} occur slowly enough that the receiver can readily adapt to them.

Once the τ i size 12{τ rSub { size 8{i} } } {} delays are estimated, a separate correlator is dedicated to recovering each resolvable multipath component. In this example, there would be three such dedicated correlators, each one processing a delayed version of the same chip sequence 1 0 1 1 1. Each correlator receives chips with power profiles represented by the sequence of components shown along a diagonal line. For simplicity, the chips are all shown as positive signaling elements. In reality, these chips form a pseudonoise (PN) sequence, which of course contains both positive and negative pulses. Each correlator attempts to correlate these arriving chips with the same appropriately synchronized PN code. At the end of a symbol interval (typically there may be hundreds or thousands of chips per symbol), the outputs of the correlators are coherently combined, and a symbol detection is made.

The interference-suppression capability of DS/SS systems stems from the fact that a code sequence arriving at the receiver time-shifted by merely one chip will have very low correlation to the particular PN code with which the sequence is correlated. Therefore, any code chips that are delayed by one or more chip times will be suppressed by the correlator. The delayed chips only contribute to raising the interference level (correlation sidelobes).

The mitigation provided by the Rake receiver can be termed path diversity, since it allows the energy of a chip that arrives via multiple paths to be combined coherently. Without the Rake receiver, this energy would be transparent and therefore lost to the DS/SS receiver.

Questions & Answers

anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
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 to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
Maciej
characteristics of micro business
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
s. Reply
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
Devang Reply
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
Abhijith Reply
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?
s. Reply
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 ?
SUYASH Reply
for screen printed electrodes ?
SUYASH
What is lattice structure?
s. Reply
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
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
China
Cied
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Principles of digital communications. OpenStax CNX. Jul 29, 2009 Download for free at http://cnx.org/content/col10805/1.1
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