question:what is Multi path fading Channel?

[raghavenderece]

multipath fading channel

what is Multi path fading Channel?
how it can mathematically represented?
what are the CharacteristiCS?

 

[bulx]

multipath fading

of course, the question is not the kind that can be answered in a sentence.

The physical phenomenon is the reflection of radio waves (that are transmited from an antenna) off structures like buildings, mountains, trees, what not..Thus the recieved signal is a sum of several reflections with different delays, different phase changes and different amplitude attentuations. The typical scenario affected by multiplath is a cell phone reciever.

Mathematical models usually split the channel into 3 components
1. fading of signal through atmosphere.
2. time-independent but geography dependent; so-called "slow fading"
3. time-vaying component; so called "fast fading"

The effects are all multiplicative, ie; the transmitted signal is assumed to be multlplied by transfer functions assosciated with each effect. Note this is quite different from the usual additive gaussion noise model of channels. gaussian noise also, of course does exist, as an additive component here too.

1. is a deterministic component, and usual EM thoery results are used to estimate it. Effect of 3 is modelled as a sum of sines whose peak amplitudes are randomly distributed, and whose phases are randomnly varying. Analysis proceeds assuming some statistical characteristics for these..

Hope this is some sort of a begining..

- b

 

[ivar4ever]

what is multipath fading

there are many mathematical models for fading.
just try the query : mathematical modelling of multipath fading (with or without quotes) in google.
all the links in the first page are useful, but i am giving a couple of them for your reference.

h**p://www.site.uottawa.ca/~chadcha/SimulationSystem/introductionChannelModels.pdf#search=%22mathematical%20modelling%20of%20multipath%20fading%22

**broken link removed**

Try this thesis also. it is very useful for me in doing my Graduation Project.

h**p://www.ensc.sfu.ca/people/faculty/cavers/unpubs/Thesis%20-%20Ali%20Keyvani.pdf#search=%22modelling%20and%20simulation%20of%20a%20fading%20channel%22

hope this helps,

ivar.

 

[leo1988]

path fading

the third link of the reply is very good,it is very clear and had matlab source code in it,hope others enjoy it.

 

[manojshukla]

fading path

Fading
If the signal is reaching to distination i.e. receiver from transmitter through various paths and signal is is faded due to ISI and environmental parametrs, it is called multipath fading.
In AWGN the probability of symbol error depends on the received SNR. In a fading
environment the received signal power varies randomly over distance or time due to shadowing and/or multipath fading. Thus, in fading γs is a random variables with distribution pγs(γ), and therefore Ps(γs) is also random.
The performance metric when γs is random depends on the rate of change of the fading. There are three different performance criteria that can be used to characterize the random variable Ps.

The average probability of symbol error applies when the signal fading is on the order of a symbol time (Ts ≈ Tc), so that the signal fade level is constant over roughly one symbol time. Since many error correction coding techniques can recover from a few bit errors, and end-to-end performance is typically not seriously degraded by a few simultaneous bit errors, the average error probability is a reasonably good figure of merit for the channel
quality under these conditions.
However, if the signal power is changing slowly (Ts << Tc), then a deep fade will affect many simultaneous symbols. Thus, fading may lead to large error bursts, which cannot be corrected for with coding of reasonable complexity. Therefore, these error bursts can seriously degrade end-to-end performance. In this case acceptable performance cannot be guaranteed over all time or, equivalently, throughout a cell, without drastically increasing transmit power. Under these circumstances, an outage probability is specified so that the channel is deemed
unusable for some fraction of time or space. Outage and average error probability are often combined when
the channel is modeled as a combination of fast and slow fading, e.g. log-normal shadowing with fast Rayleigh fading.
Note that when Tc << Ts, the fading will be averaged out by the matched filter in the demodulator. Thus, for very fast fading, performance is the same as in AWGN.

 

[geetha]

fading due to multipath

simple definition
multipath:
transmitted signal gets scattered in various paths.i,e they arrive the destination but through different paths.it includes straight path,space reflected.this occurs due to random nature of the medium.
fading:
degradation in amplitude of the transmitted signal due to multipath.

 

[rostam63]

pdf fading signal)

you can find good information about multipath fading channel in the rappaport book, or Proakis book

 

[silawi]

definition multipath fading signal

this link contains useful book explaining everything about Mobile Fading Channels

 

[armess]

multipath fading

the above link does not work any more

 

[mehboob_iiui]

sfu fading setting

In wireless telecommunications, multipath is the propagation phenomenon that results in radio signals' reaching the receiving antenna by two or more paths. Causes of multipath include atmospheric ducting, ionospheric reflection and refraction, and reflection from terrestrial objects, such as mountains and buildings.

The effects of multipath include constructive and destructive interference, and phase shifting of the signal. This causes Rayleigh fading, named after Lord Rayleigh. The standard statistical model of this gives a distribution known as the Rayleigh distribution.