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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.

Introduction

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

where we get a research paper on Nano chemistry....?
Maira Reply
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
Google
da
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Bhagvanji
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
revolt
da
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
nanocopper obvius
Alexandre
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
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
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
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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