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The phase-locked loop (PLL) is a critical component in coherent communications receivers that is responsible for locking on to the carrier of a received modulated signal. A PLL adjusts the phase of a numerically-controlled oscillator to match that of the received signal. You will simulate a carrier recovery sub-system in MATLAB and then implement the sub-system on the DSP.


After gaining a theoretical understanding of the carrier recovery sub-system of a digital receiver, you will simulate the sub-system in MATLAB and implement it on the DSP. Thesub-system described is specifically tailored to a non-modulated carrier. A complete implementation will requiremodifications to the design presented.

The phase-locked loop ( PLL ) is a critical component in coherent communications receivers thatis responsible for locking on to the carrier of a received modulated signal. Ideally, the transmitted carrier frequencyis known exactly and we need only to know its phase to demodulate correctly. However, due to imperfections at thetransmitter, the actual carrier frequency may be slightly different from the expected frequency. For example, in theQPSK transmitter of Digital Transmitter: Introduction to Quadrature Phase-ShiftKeying , if the digital carrier frequency is 2 and the D/A is operating at 44.1 kHz, then the expected analog carrier frequency is f c 2 2 44.1 11.25 kHz . If there is a slight change to the D/A sample rate (say f c 44.05 kHz ), then there will be a corresponding change in the actual analog carrier frequency( f c 11.0125 kHz ).

This difference between the expected and actual carrier frequencies can be modeled as a time-varying phase. Providedthat the frequency mismatch is small relative to the carrier frequency, the feedback control of an appropriately calibratedPLL can track this time-varying phase, thereby locking on to both the correct frequency and the correct phase.

PLL Block Diagram

Numerically controlled oscillator

In a complete coherent receiver implementation, carrier recovery is required since the receiver typically does notknow the exact phase and frequency of the transmitted carrier. In an analog system this recovery is oftenimplemented with a voltage-controlled oscillator ( VCO ) that allows for precise adjustment of the carrier frequency based on the output of aphase-detecting circuit.

In our digital application, this adjustment is performed with a numerically-controlled oscillator ( NCO ) (see [link] ). A simple scheme for implementing an NCO is based on the followingre-expression of the carrier sinusoid:

ω c n θ c θ n
where θ n ω c n θ c ( ω c and θ c represent the carrier frequency and phase, respectively). Convince yourself that this time-varyingphase term can be expressed as θ n m 0 n ω c θ c and then recursively as
θ n θ n 1 ω c
The NCO can keep track of the phase, θ n , and force a phase offset in the demodulating carrier by incorporating an extra term in this recursiveupdate:
θ n θ n 1 ω c d pd n
where d pd n is the amount of desired phase offset at time n . (What would d pd n look like to generate a frequency offset?)

Questions & Answers

How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
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
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
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.
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
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
characteristics of micro business
for teaching engĺish at school how nano technology help us
How can I make nanorobot?
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
how can I make nanorobot?
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
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.
what is the actual application of fullerenes nowadays?
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.
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.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
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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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