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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

can someone help me with some logarithmic and exponential equations.
Jeffrey Reply
sure. what is your question?
ninjadapaul
20/(×-6^2)
Salomon
okay, so you have 6 raised to the power of 2. what is that part of your answer
ninjadapaul
I don't understand what the A with approx sign and the boxed x mean
ninjadapaul
it think it's written 20/(X-6)^2 so it's 20 divided by X-6 squared
Salomon
I'm not sure why it wrote it the other way
Salomon
I got X =-6
Salomon
ok. so take the square root of both sides, now you have plus or minus the square root of 20= x-6
ninjadapaul
oops. ignore that.
ninjadapaul
so you not have an equal sign anywhere in the original equation?
ninjadapaul
Commplementary angles
Idrissa Reply
hello
Sherica
im all ears I need to learn
Sherica
right! what he said ⤴⤴⤴
Tamia
what is a good calculator for all algebra; would a Casio fx 260 work with all algebra equations? please name the cheapest, thanks.
Kevin Reply
a perfect square v²+2v+_
Dearan Reply
kkk nice
Abdirahman Reply
algebra 2 Inequalities:If equation 2 = 0 it is an open set?
Kim Reply
or infinite solutions?
Kim
The answer is neither. The function, 2 = 0 cannot exist. Hence, the function is undefined.
Al
y=10×
Embra Reply
if |A| not equal to 0 and order of A is n prove that adj (adj A = |A|
Nancy Reply
rolling four fair dice and getting an even number an all four dice
ramon Reply
Kristine 2*2*2=8
Bridget Reply
Differences Between Laspeyres and Paasche Indices
Emedobi Reply
No. 7x -4y is simplified from 4x + (3y + 3x) -7y
Mary Reply
is it 3×y ?
Joan Reply
J, combine like terms 7x-4y
Bridget Reply
im not good at math so would this help me
Rachael Reply
yes
Asali
I'm not good at math so would you help me
Samantha
what is the problem that i will help you to self with?
Asali
how do you translate this in Algebraic Expressions
linda Reply
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
Crystal Reply
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
Chris 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
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
AMJAD
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
AMJAD
what is system testing
AMJAD
what is the application of nanotechnology?
Stotaw
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
Azam
anybody can imagine what will be happen after 100 years from now in nano tech world
Prasenjit
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
not now but maybe in future only AgNP maybe any other nanomaterials
Azam
can nanotechnology change the direction of the face of the world
Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
bamidele 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, Dsp laboratory with ti tms320c54x. OpenStax CNX. Jan 22, 2004 Download for free at http://cnx.org/content/col10078/1.2
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