10
votes
Accepted
Flat fading criterion of OFDM subcarrier spacing
Your mathematical derivation is correct, your $H[k]$ is the single-tap equalizer (i.e. one tap for each subcarrier, and the subcarriers do not mix with each other. That's the orthogonal in OFDM).
...
- 6,208
8
votes
Practicality of the assumption of i.i.d. for Rayleigh channels
I am a little late but I post my answer anyway so that someone having the same question will find it interesting and discuss.
The discrete baseband multipath channel can be modeled as a FIR, i.e.
$$...
- 6,080
7
votes
OFDM intra-block multipath interference
By using cyclic prefix and its associated demodulation techniques, LTE OFDM (nearly) eliminates the inter-symbol inteference (ISI).
The intra-block inteference, if I understand well your question, ...
- 6,080
7
votes
Accepted
Educational purpose - What is the correct way to simulate a multipath fading channel which has ISI
Lets say we want to transmit a sequence of discrete data $\left\lbrace x[n] \right\rbrace$. But because we are living in analog world, the sequence must be modulated.
Call $T_s$ is symbol duration ...
- 6,080
5
votes
Rayleigh Fading Simulation
Rephrasing OP's Post for Clarity
It wasn't stated, but I assume the OP is attempting to create a one-tap channel filter with:
...
- 48.9k
5
votes
Accepted
Correct way to simulate Rayleigh fading for indoor environments
A discrete-time baseband model of a multi-propagation channel can be written as
$$y[m] = \sum_l h_l[m] x[m-l] + w[m]$$
where $l$ is the index of channel taps if the channel is modeled as a FIR $\{...
- 6,080
4
votes
Accepted
Transmitting over Unknown Fading Channel
The strategy depends heavily your "realistic scenario", e.g. which estimator, which equalizer, which estimation error, etc.
In general scenario, you cannot trust the estimate of $h$, it means that ...
- 6,080
4
votes
Why do we express complex noise as Gaussian distributed while the channel is Rayleigh distributed?
There are too many things named after Rayleigh floating around in this problem.
Consider first additive white Gaussian noise with two-sided power spectral density $\frac{N_0}{2}$. This is generally ...
- 20.2k
4
votes
Accepted
Matlab: Difference between flat fading and Rayleigh multipath fading, terminologies and concept
The fundamental idea to keep in mind is that in a wireless channels with reflections, if you transmit $s(t),$ you'll receive $$r(t)=\sum_{i=1}^Na_is(t-\tau_i).$$
Another important idea is that ...
- 14.9k
4
votes
Why exponential decay power delay profiles are used to model fading?
While it is correct that discrete-time channel tap is usually modeled as circularly symmetric Gaussian, having power being exponentially distributed (see this answer and the cited book therein for the ...
- 6,080
3
votes
Accepted
Question about path loss exponent estimation from measurment
The path loss exponent does not depend on the reference distance. There are two mistakes in your path loss formula. First, path loss does not include the gains of transmit or receive antennas. Second, ...
- 88.9k
3
votes
Accepted
Matlab: Correct method of generating Rayleigh fading channel
Question 1:
Yes, it is a multipath Rayleigh Channel with $ 1000 $ taps. You need to know that when you generate complex coefficients, and the real part and the imaginary part of this coefficients ...
- 677
3
votes
Accepted
what does mean quasi-static channel
Quasi-static is almost-static. In other words, for a block (or window) period of time, you could assume that your channel is static. Below, i attach a figure that depicts this scenario. As you can see ...
- 730
3
votes
Accepted
Rayleigh fading with frequency selective fading channel
First it is useful to understand what a Rayleigh and Ricean distribution is, and then we can more easily see how that statistic can be used to describe certain fading channels.
A zero-mean complex ...
- 48.9k
3
votes
How to compute the channel gain from the path loss model of a wireless channel
To answer the literal questions you asked:
yes
see above
To Frame Challenge your question and give you what you were probably looking for:
The path loss equation you cited:
$$
128+37\log_{10}(d) ,...
- 2,212
3
votes
Accepted
What's the effect of spread spectrum on frequency- selective channel
In brief, we consider the channel as frequency-selective channel if
the frequency of the signal is larger than then frequency of channel
No offense, but that ought to win the prize for the least-...
- 2,413
3
votes
Accepted
What is the meaning of the channel gain is normalized
Normalizing $h$ means defining it so that the expected value of $|h|$ is equal to 1. The implication is that multi-path is (on average) neither taking energy from $x$ nor adding energy to it.
In an ...
- 14.9k
2
votes
Flat fading criterion of OFDM subcarrier spacing
There's a lot of very valid aspects that you touch, but from what I've learned (and experienced having fun with OFDM SDR transceivers), the main reasoning to do OFDM is having a narrow-channel ...
- 29.6k
2
votes
Accepted
Matlab: Help in applying equalizer and proper calculation of symbol error rate for QAM modulation in Rayleigh channel
Let's take a look at the cost function of CMA:
$ J(\mathbf{w}) = E[|y_{k}^{2} - 1|^{2}] $,
onde $ y_{k} = \mathbf{w}^{H} \mathbf{x}_{k} $ and $ \mathbf{x}_{k} $ is the filter input.
It says that ...
- 677
2
votes
Channel modelling for wireless body area network
IEEE 802.15.4a defines multiple bands from 2.4 to 10 GHz for operation. You should focus on one. Not sure you're actually looking for diffraction and not more for backscatter from surrounding objects ...
- 29.6k
2
votes
Accepted
Brief introduction to wireless communication and communication terminologies
Well, these are very fundamental questions, and I think they are written in any good book. But maybe it's hard to extract the exact information from them, which you ask for. So, let me briefly answer:
...
- 6,208
2
votes
Accepted
MIMO System Model in Matlab
In a wireless system, most of the noise is added by the receiver itself. The received signal is very weak (-100 dB or less is typical), and its power is comparable to the thermal noise of the receiver'...
- 14.9k
2
votes
Accepted
why did convolution coding achieve BER less than Reed-Solomon?
Reed-Solomon codes are good for correcting bursts of errors (such as those that often occur in computer memory systems such as RAM, or on less volatile media such as CDs and DVDs) or at the output of ...
- 20.2k
2
votes
Correct way to simulate Rayleigh fading for indoor environments
Your question is quite unclear, but it seems like you're trying to simulate the continuous-time radio channel. In this model, you do not multiply by complex coefficients; rather, you add delayed and ...
- 14.9k
2
votes
Cyclic prefix length in baseband OFDM with ZF equalizer
The channel which you have created is having 4-Taps and all taps are one after the other, meaning roughly there are 4 multi-paths and they are very close to each other. How close depends on what is ...
- 2,591
2
votes
what does mean quasi-static channel
Quasi-static channels are a "block-wise" time (in)variant. For example, your channel has no variations over time (not in the delay domain) for some time period(e.g., 1 ms), but the channel ...
- 39
2
votes
Intersymbol interference due to limited channel bandwidth
Here is a graphic I have that demonstrates ISI due to multipath propogation:
Notice the eye diagram in the upper right hand corner showing what we should receive if there was no ISI, or other noise ...
- 48.9k
2
votes
Accepted
Is the Channel shortening similar to Time domain Equalizer (TEQ)
Most likely people use different words to describe the same concept. This happens quite often. The TEQ is the more general term and also used to equalize other methods that OFDM, while CS is related ...
- 1,056
2
votes
Accepted
How can I generate time-variant Rayleigh channel in MATLAB
Yes, you can have time variant channel in MATLAB either by using comm.RayleighChannel() , you can read about it in help of matlab.
or the other way you use the ...
- 1,056
2
votes
Digital communication BER performance
OK, let me explain that in easier way,
As you know, in a communication system, to transmit information from transmitter to receiver, we use the binary information system. which means, for example, ...
- 1,056
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