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The goal of symbol-timing recovery is to sample message signals at the receiver for best performance. After the in-phase and quadrature signals pass through a matched filter, a delay-locked loop attempts to find the peaks in the output waveforms.

Introduction

This receiver exercise introduces the primary components of a QPSK receiver with specific focus on symbol-timing recovery.In a receiver, the received signal is first coherently demodulated and low-pass filtered (see Digital Receivers: Carrier Recovery for QPSK ) to recover the message signals (in-phase and quadrature channels). The next step for the receiver is tosample the message signals at the symbol rate and decide which symbols were sent. Although the symbol rate is typicallyknown to the receiver, the receiver does not know when to sample the signal for the best noise performance. Theobjective of the symbol-timing recovery loop is to find the best time to sample the received signal.

illustrates the digital receiver system. The transmitted signal coherently demodulated with both a sineand cosine, then low-pass filtered to remove the double-frequency terms, yielding the recovered in-phase andquadrature signals, s I n and s Q n . These operations are explained in Digital Receivers: Carrier Recovery for QPSK . The remaining operations are explained in this module. Both branches are fed through a matched filter and re-sampled at the symbol rate. The matched filter is simply an FIR filter with an impulse responsematched to the transmitted pulse. It aids in timing recovery and helps suppress the effects of noise.

Digital receiver system

If we consider the square wave shown in as a potential recovered in-phase (or quadrature) signal ( i.e. , we sent the data

    +1 -1 +1 -1
) then sampling at any point other than the symbol transitions will result in the correct data.

Clean BPSK waveform.
Noisy BPSK waveform.

However, in the presence of noise, the received waveform may look like that shown in . In this case, sampling at any point other than the symboltransitions does not guarantee a correct data decision. By averaging over the symbol duration we can obtain a betterestimate of the true data bit being sent ( +1 or -1 ). The best averaging filter is the matched filter, which has the impulse response u n u n T symb , where u n is the unit step function, for the simple rectangular pulse shape used in Digital Transmitter: Introduction to Quadrature Phase-ShiftKeying .

For digital communications schemes involving different pulse shapes, theform of the matched filter will be different. Refer to the listed references for more information on symbol timing andmatched filters for different symbol waveforms.
and show the result of passing both the clean and noisy signal through the matchedfilter.

Averaging filter output for clean input.
Averaging filter output for noisy input.

Note that in both cases the output of the matched filter has peaks where the matched filter exactly lines up with thesymbol, and a positive peak indicates a +1 was sent; likewise, a negative peak indicates a -1 was sent. Although there is still some noise in second figure, the peaks are relatively easy to distinguishand yield considerably more accurate estimation of the data ( +1 or -1 ) than we could get by sampling the original noisy signal in .

Questions & Answers

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
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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.
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absolutely yes
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it is a goid question and i want to know the answer as well
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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
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On having this app for quite a bit time, Haven't realised there's a chat room in it.
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what is biological synthesis of nanoparticles
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how did you get the value of 2000N.What calculations are needed to arrive at it
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