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11 votes

Envelope behavior dIfference between QPSK, OQPSK and $\pi/4$-QPSK

Let's look at each in turn: Standard QPSK: With standard QPSK, each of the signal points are in quadrature (Note that the signal points in the constellation can be at any arbitrary phase really; ...
Dan Boschen's user avatar
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9 votes
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What is a constant envelope modulation?

You've pointed out a very important distinction between theory and practice. In theory, as suggested by your book and in Fat32's answer, modulation schemes where all information resides in the phase ...
Matt L.'s user avatar
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6 votes
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Gardner Timing Recovery for Repeated Symbols

Your Gardner Loop would properly "Flywheel" in the absence of symbol transitions. So it would slowly drift off of synchronization, but would not spiral out of control as you describe. This is ideal ...
Dan Boschen's user avatar
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5 votes
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Recommendation for good ressources on digital processing and D-QPSK

Wow, I'm honored by Matt L. doing what I'm often doing: Referring people to GNU Radio. The project actually has a list of recommended literature, but I don't know how well that'd fit you. It's ...
Marcus Müller's user avatar
5 votes

Recovering signal for psk

To add to the excellent information given by Cassman in his response, here is a block diagram of a carrier recover loop for QPSK and QAM modems using a decision directed approach. I have detailed the ...
Dan Boschen's user avatar
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5 votes
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Sample rates, Samples per Symbol, and Digital Pulse Shaping

Yes the OP is correct in that you can implement pulse shaping in less than 2 samples per symbol for exactly the reasons that was outlined. However importantly we must also keep in mind having excess ...
Dan Boschen's user avatar
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4 votes
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Noise variance calculation for 16APSK Demodulator

This is to take into account the oversampling operation. Symbol time = sample time implies no oversampling. See AWGN model for more details about the conversion among EbN0, EsN0 and SNR. For ...
AlexTP's user avatar
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4 votes

What is the theoretical bit error rate for QPSK Matlab simulation when constellation points are transmitted (no symbol duration)?

TL;DR The theoretical BER of an ideal QPSK system is $\displaystyle Q\left(\sqrt{\frac{2E_b}{N_0}}\right)$ where $E_b$ is the energy per bit and $\frac{N_0}{2}$ is the two-sided power spectral density ...
Dilip Sarwate's user avatar
4 votes

The difference between MSK as CPFSK and OQPSK

The answer to your question is yes, these two representations are equivalent. The first important thing to note is that in your formula, $d_k$ must be either $1$ or $-1$, because the frequency ...
Matt L.'s user avatar
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4 votes
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When I double bit rate I do not see a difference in I_spectrum and Q_spectrum, but why?

Do you know how ADS is plotting the spectrum? Plotting the spectrum without doing some kind of normalization will give you a higher magnitude. Once you determine the size of the FFT, normalizing by ...
Envidia's user avatar
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4 votes
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Block diagram of M-PSK modulation and demodulation

So this seems to be a general block diagram for these types of modulations. No, this is a block diagram of a IQ upconverter with some unspecified digital data modulator on the input. You need to ...
Marcus Müller's user avatar
3 votes
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How to correct the phase offset for QPSK I-Q data

Assuming we have timing recovery resolved (meaning our system knows the correct time locations for our symbol decisions), then we can use the decided symbols along with our pre-decision values in a ...
Dan Boschen's user avatar
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3 votes
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Recovering signal for psk

So not only do you need to do timing synchronization to recover the baud clock, you need to do some form of turn on detection. You could start your PSK synchronization at the first sample, but the ...
cassman's user avatar
  • 90
3 votes
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Adding AWGN noise with a correct noise power to the signal

The kind of AWGN channel you're simulating is sometimes called a "discrete time" channel. That means that you're going to simulate the bit error rate at the output of a decision device, the input to ...
MBaz's user avatar
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3 votes
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Constellation diagram for QPSK modulation

I think you may be missing some fundamental understanding of QPSK modulation, which was likely the point of the homework exercise so let me hopefully fill in some blanks, from which you can figure out ...
Dan Boschen's user avatar
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3 votes
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Relation between constellation SNR and baseband SNR

I think that the question by OP xvan has several misconceptions in it and these propagate into the answer that he has provided for his own question. Define \begin{align}\phi_1(t) &= \sqrt{\frac ...
Dilip Sarwate's user avatar
3 votes
Accepted

Carrier Tracking Loop: Tracking noise vs Phase Noise Trade-off

The question is specific to optimizing loop bandwidth for the decision directed carrier tracking loop with one sample per symbol. In other posts such as this one PLL for Phase Demodulation and Carrier ...
Dan Boschen's user avatar
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3 votes
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Phase Noise in Constellation Plot

The spread in the plot is the peak to peak phase, while the integrated phase noise is an rms quantity- The OP in his comment below this answer reported a measurement of 35° in the constellation and a ...
Dan Boschen's user avatar
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3 votes
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Use of pulse shaping in digital modulation

QPSK in its raw form would appear just as the OP has shown, where the information is encoded into four symbols given by the four phase states alone. The problem is this has a very wide transmit ...
Dan Boschen's user avatar
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3 votes

Spectral properties of QPSK modulation

The spectrum is that of the base pulse used in the modulation, so in this case a rectangular pulse. A single rectangular pulse in time, as given by the Fourier Transform, is a Sinc in Frequency with ...
Dan Boschen's user avatar
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3 votes

Do BPSK vs QPSK have the same performance?

BPSK and QPSK have the same BER performance under additive white Gaussian noise only if the symbols are appropriately mapped to bits (such as Gray coding) since they can be viewed / treated as two ...
Dan Boschen's user avatar
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3 votes
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QPSK implementation with 2 BPSK

Your constellation points are the sum of {+1, -1} and {+1j, -1j}, so you get the points {+1+1j, +1-1j, -1+1j, -1-1j}, which have these odd multiples of 45° as angles. That's one way to look at it. The ...
Marcus Müller's user avatar
3 votes

Which is the correct equation for union bounds for non-standard QPSK?

You are assuming $\textrm{Pr}\{s_2|s_0\} \ll \textrm{Pr}\{s_1|s_0\}$. However, it could be possible that $\textrm{Pr}\{s_2|s_0\} \approx \textrm{Pr}\{s_1|s_0\}$ when $0 < \beta \ll \alpha$. The ...
AlexTP's user avatar
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3 votes

Which is the correct equation for union bounds for non-standard QPSK?

It is important not to confuse the union bound with further assumptions and simplifications made to our calculation of the probability of error. The analysis starts with a constellation of only two ...
MBaz's user avatar
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2 votes
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Sphere decoding for non-binary modulation

This channel model is known as a multiplicative channel, and it differs from the AWGN channel in that the signal amplitude is scaled by a gain factor. If the gain factor is real (that is, if the ...
MBaz's user avatar
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2 votes
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what is the difference between QPSK and 4QAM?

There are different types of QPSK: Offset (staggerd) QPSK, $\pi/4$-QPSK, etc. In its most known form, QPSK is identical to $4$-QAM or $4$-PSK. That is, the same constellation can be referred to by ...
msm's user avatar
  • 4,295
2 votes

Which window function to use for QPSK signal?

For purpose of recovering the clock, no window function is needed. Also to clarify, your signal is downsampled to 10GS/s which is samples per second, not "Symbols per second" as you specified the ...
Dan Boschen's user avatar
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2 votes

Envelope behavior dIfference between QPSK, OQPSK and $\pi/4$-QPSK

The main purpose of OQPSK, $\pi/4$-QPSK and other variants is to prevent the signal frequently transition through zero. When a digitally modulated signal stream input to a power amplifier passes from ...
QMC's user avatar
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2 votes
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QPSK on baseband question

Yes, you are correct, though your formula puts the constellation points at 0, 90, 180, and 270 degrees, where usually the constellation points are represented as being at 45, 135, 225, and 315 degrees....
Jim Clay's user avatar
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2 votes
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Question on the definition of one-sided PSD in AWGN channel

The relation between one-sided and two-sided noise PSD is correct. But note that the power of a complex random variable $n$ is given by $E\{|n|^2\}$, and not by $E\{n^2\}$. So in your case you obtain $...
Matt L.'s user avatar
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