Quadrature amplitude modulation (QAM) is the name of a family of digital modulation methods .. Since the carriers are independent, the overall bit error rate is the same as the per-carrier error rate, just like BPSK and QPSK: P b = P b c. Modulación por corrimiento de fase QPSK ¿En que consiste? Se transmite un tren de datos el cual se divide en pares de bits consecutivos. INTEGRANTES: CRISTOFER MIRANDA TORRES. - JOSE FABRICIO PAREDES FRANCO. - DAVID.


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Ultimately, the goal is shown in the figure below where the multipath channel is creating some distortion in the signal as shown in the frequency modulacion qpsk.


The task of the equalizer is to invert modulacion qpsk channel. Basically, we want to modulacion qpsk the distortion that's caused by the channel such that the output of the equalizer is flat.

But, instead of adjusting the taps by hand, we have algorithms that update these taps for us.


modulacion qpsk Our job is to use the modulacion qpsk equalizer algorithm and set up the parameters. One important parameter here is the number of taps in the equalizer. As we can see in our simulation, five taps gives fairly coarse control over the frequency response.

Alternatively, the more taps, the more time it takes to both compute modulacion qpsk taps as well as run the equalizer against the signal. Equalizers GNU Radio comes with two easily usable equalizers.

The CMA, or Constant Modulus Algorithm, is a blind equalizerbut it only works on signals that have a constant amplitude, or modulus. This means that digital signals like MPSK are good candidates since they have points only on the unit circle think back to the experiment we did where we locked the signal timing but had a frequency offset; what we were seeing was the unit circle.

The CMA algorithm accepts the number of taps to use in the equalizer, which will be based on some combination of an educated guess, known best practices, and maybe some actual knowledge of the channel itself.

We want to keep this number small to reduce the overhead of the algorithm while making sure there are modulacion qpsk degrees of freedom to correct for our channel. This is a simulation, and that number has worked well in the past.

Quadrature amplitude modulation

Play around with it and see how it affects performance, both from a computational and signal standpoint. We can watch the CMA algorithm converge.

Note, too, that since we have both a clock sync and equalizer block, they are converging independently, but the one stage will affect the next stage. So there is modulacion qpsk interaction going on here while both are locking on to the signal.

modulacion qpsk

Quadrature amplitude modulation - Wikipedia

In the end, though, we can see the effect of the time-locked multipath signal before modulacion qpsk after the equalizer. Before the equalizer, we have a very ugly signal, even without noise. The equalizer nicely figures out how to invert and cancel out this channel so that we have a nice, clean signal again.


We can also see modulacion qpsk channel itself and how it flattens out nicely after the modulacion qpsk. Play with the taps provided to the channel model block to change the multipath. The current taps were simply randomly generated to provide a multipath profile with no real mathematical basis for them.

There is a lot of overlap between the parameters, except for one major feature. Instead of a blind equalizer like the CMA, this equalizer requires knowledge of the received signal. The equalizer needs to know the constellation points in order to correct, and it uses decisions about the samples to inform how to update the taps for the equalizer.

This equalizer is great for signals that don't fit the constant modulus requirement of the CMA algorithm, so it can work with things like QAM-type modulations.

Guided Tutorial PSK Demodulation

On the other hand, modulacion qpsk the SNR is bad enough, the decisions being made are incorrect, which can ruin the receiver's performance. The block is also more computationally complex in its modulacion qpsk. When the signal is of good quality, though, this equalizer can produce better quality signals because it has direct knowledge of the signal.

A common model is to use a blind equalizer for initial acquisition to get the signal good enough for a directed equalizer to take over.

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