<< Chapter < Page Chapter >> Page >

This chapter suggests several different ways that the coefficients of the equalizer can be chosen.The first procedure, in "A Matrix Description" , minimizes the square of thesymbol recovery error This is the error between the equalizer output and the transmitted symbol,and is known whenever there is a training sequence. over a block of data, which can be doneusing a matrix pseudoinversion. Minimizing the (square of the)error between the received data values and the transmitted values can also be achieved usingan adaptive element, as detailed in "An Adaptive Approach to Trained Equalization" . When there is no training sequence, other performance functionsare appropriate, and these lead to equalizers such as the decision-directed approach in "Decision-Directed Linear Equalization" and the dispersion minimization method in "Dispersion-Minimizing Linear Equalization" . The adaptive methods considered here are only modestlycomplex to implement, and they can potentially track time variations in the channel model,assuming the changes are sufficiently slow.

Multipath interference

The villains of this chapter are multipath and other additive interferers. Both should be familiar from [link] .

The distortion caused by an analog wireless channel can be thought of as a combination of scaled and delayedreflections of the original transmitted signal. These reflections occur when there are differentpaths from the transmitting antenna to the receiving antenna. Between two microwave towers, for instance, the paths may include one alongthe line-of-sight, reflections from nearby hills, and bounces from a field or lake betweenthe towers. For indoor digital TV reception, there are many (local)time-varying reflectors, including people in the receiving room, and nearby vehicles.The strength of the reflections depends on the physical properties of the reflecting objects, while the delay of thereflections is primarily determined by the length of the transmission path. Let u ( t ) be the transmitted signal. If N delays are represented by Δ 1 , Δ 2 , ... , Δ N , and the strength of the reflections is α 1 , α 2 , ... , α N , then the received signal is

y ( t ) = α 1 u ( t - Δ 1 ) + α 2 u ( t - Δ 2 ) + ... + α N u ( t - Δ N ) + η ( t ) ,

where η ( t ) represents additive interferences. This model of the transmission channelhas the form of a finite impulse response filter, and the total length of time Δ N - Δ 1 over which the impulse response is nonzero is called the delay spread of the physical medium.

This transmission channel is typically modelled digitally assuming a fixed sampling period T s . Thus, [link] is approximated by

y ( k T s ) = a 1 u ( k T s ) + a 2 u ( ( k - 1 ) T s ) + ... + a n u ( ( k - n ) T s ) + η ( k T s ) .

In order for the model [link] to closely represent the system [link] , the total time over which the impulse response is nonzero (the time n T s ) must be at least as large as the maximum delay Δ N . Since the delay is not a function of the symbol period T s , smaller T s require more terms in the filter (i.e., larger n ).

For example, consider a sampling interval of T s 40 nanoseconds (i.e., a transmission rate of 25 MHz).A delay spread of approximately 4 microseconds would correspond to one hundred taps in the model [link] . Thus, at any time instant, the received signalwould be a combination of (up to) one hundred data values.If T s were increased to 0.4 microsecond (i.e., 2.5 MHz), only 10 terms wouldbe needed, and there would be interference with only the 10 nearest data values.If T s were larger than 4 microseconds (i.e., 0.25 MHz), only one term wouldbe needed in the discrete-time impulse response. In this case, adjacent sampled symbols would notinterfere. Such finite duration impulse response models as [link] can also be used to represent the frequency-selective dynamicsthat occur in the wired local end-loop in telephony, and other (approximately) linear, finite-delay-spread channels.

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
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get the best Algebra and trigonometry course in your pocket!





Source:  OpenStax, Software receiver design. OpenStax CNX. Aug 13, 2013 Download for free at http://cnx.org/content/col11510/1.3
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Software receiver design' conversation and receive update notifications?

Ask