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Questions tagged [qpsk]

Quadrature Phase Shift Keying

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0answers
39 views

SOQPSK-TG pulse shaping

I'm trying to build an SOQPSK-TG signal in MATLAB/Octave. I am following this paper for formulas. I'm trying to generate a waveform for the phase, equation 2.4: Where q(t) is the phase pulse, ...
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29 views

QPSK demodulation problem due to apparent transmitter clock frequency drift

I am using FPGA to generate 10Mbaud QPSK signal in two channels corresponding to two quadratures. Upsampling to 1GSample/s (using raised cos filter for interpolation) and complex upconversion (f_up=...
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1answer
42 views

“Revolving” QPSK Constellation

I am trying to code a QPSK transmitter in VHDL but first I want to create one out of Simulink blocks and translate it into VHDL code. I am using an example project for the PlutoSDR as a guide. This ...
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1answer
93 views

QPSK constellation from baseband signal

My IQ sampler is measuring a QPSK carrier at a set frequency/bandwidth (40MSamp/s), but shifts the signal spectrum to baseband. My signal is 1.5Msym/s, but sampling at 1.5Msym/s gives me a ...
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1answer
57 views

Phase versus time graph of QPSK

In wikipedia, there was an example on QPSK modulation where the main signal was 11000110 and I contained 1001 and Q contained <...
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2answers
546 views

What is a constant envelope modulation?

The Book "Digital Modulation Techniques" by Fuqin Xiong groups digital modulation schemes into two classes: "constant envelope" and "nonconstant envelope." However, I was surprised by the inclusion ...
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1answer
337 views

The code explanation about QPSK modulation

This is the code about the QPSK modulation, and I don't understand the real part and the imaginary part code. Can anyone explain it to me if you know? Why is ...
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1answer
143 views

Understanding the over sampling factor effects before a Matched Filter?

I am trying to design a matched filter at the receiver side to a half sine pulse shaping function sent by the transmitter of an OQPSK transceiver. I am not sure I understand the effect of varying the ...
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2answers
565 views

GNU Radio QPSK 4 Symbols

I'd like to generate a simple QPSK signal in GNU radio, but so far I haven't been able to get it to perform the way I'd like and I'm not sure if this has to do with some misunderstanding I have about ...
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1answer
265 views

What techniques are available for correcting constellation rotation due to phase ambiguity?

In order for a receiver to recover a baseband signal, it needs a carrier signal equivalent to that used by the transmitter for upconverting the original baseband signal. Unless pilot tones are used, a ...
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0answers
254 views

QPSK modulation validation

I tried to replicate a Matlab code in python (for testing reasons) to do a QPSK modulation. So this is the original code(source Gaussian waves website): ...
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0answers
521 views

Help with OQPSK Demodulation with GNU Radio

I am working on demodulating/decoding the GOES-15 satellite EMWIN signal @1692.7MHz, BW: 50KHz Mod: OQPSK. I have minimal experience in signal processing and some experience in using GNU Radio. I have ...
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44 views

BER Graph for a PSK Modulation through a linear channel model

This is the graph that occurs when M-PSK symbols pass through a linear channel with impulse response given in a vector h. The simulation is done in Matlab and I am unsure about the result because of ...
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1answer
74 views

QPSK fundamental

I am trying to understand the QPSK fundamental and when I read that the phase shifts are 45°, 135°, 225°, and 315° in QPSK, I can not figure it out how. In other word, I do not understand how the ...
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1answer
265 views

QPSK on baseband question

Given a signal you are asked to perform baseband QPSK (not on a carrier). Does this mean the following? In baseband QPSK the (possible) constellation points are $$\sqrt {E_s} e^{jn \pi / 2} \...
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1answer
357 views

Question on the definition of one-sided PSD in AWGN channel

I am currently simulating the following in a telecommunications exercise in Python: Consider a binary sequence $m[n]$ that is being modulated with QPSK (Gray-mapped) that is being transmitted via ...
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1answer
1k views

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

I'm simulating a QPSK system in Matlab and I'm trying to calculate the theoretical bit error rate to compare it with the simulated ber. The formula that I'm aware of involves the term Eb/N0, but how ...
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2answers
101 views

mpsk demodulation using digital sample

I am trying to receive and demodulate a 8PSK modulated sinusoidal waveform (real not complex) which is constant envelop and changing only in phase of the continuous sinusoid carrier every Symbol ...
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3answers
490 views

How can I generate offset QPSK symbols from QPSK symbols

I am trying to generate Offset-QPSK modulated symbols. But I am facing some difficulties. I know how to make QPSK symbols but I am unable to figure out at what stage I have to bring in changes to make ...
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1answer
179 views

Noise variance calculation for 16APSK Demodulator

I need to use approximate LLR algorithm for 16APSK demodulation. For that, I need to calculate noise variance which is given as $Noise\;variance = \frac {Signal\;power\;\times\;Symbol\;time}{Sample\;...
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1answer
487 views

Calculating bit-error-rate of QPSK data

I am working on a simulation of QPSK data using the code below (Matlab): ...
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1answer
444 views

Scatter Plot of OQPSK

Below is my MATLAB code for OQPSK communication: ...
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2answers
1k views

Creating an Eye Diagram for QPSK Simulation

I am trying to implement an eye diagram for an application, where the input signal is QPSK. However, I feel that there is some fundamental concept concerning these plots that I am missing. Several ...
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0answers
229 views

How to calculate the doppler shift?

I am writing a QPSK receiver in MATLAB. In the transmitter part, I have generated random data using randi, QPSK modulated and pulse shaped using a RRC filter. The ...
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2answers
5k views

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

I am trying to analyze whats the major difference between these three variants of 4PSK. I know that QPSK - signal points are at 0,90,180,270 OQPSK - The bit period of Quadrature component is ...
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1answer
2k views

Constellation diagram for QPSK modulation

I need to plot (in MATLAB R2011a) constellation diagram of a QPSK modulated signal after AWGN was added to the signal. My current MATLAB code looks like this: ...
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1answer
117 views

Which window function to use for QPSK signal?

I am trying to Receive a QPSK signal and for Sampling I need to recover clock. Now QPSK Signal is generated at 2.4GBaud. It is than sampled at 80GHz.Than further it is downsampled to 10GS/s (Symbols ...
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1answer
147 views

Frequency-ratio at baseband IQ-mixing

I was wondering by what logic or mathematics the frequency-ration $$ \frac{f_{lo}}{f_s} $$ in the sine-functions comes into existence? Source
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0answers
155 views

Eye opening calculation

I wrote a MATLAB code for RRC filtered QPSK modulated signal. The eye diagram is plotted using object commscope.eyediagram. The analysis of the eye object gives a ...
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1answer
331 views

Eye Diagram of QPSK Modulated Signal

I need to plot eye diagram for RRC filtered QPSK modulated signal. The specifications are given as follows Sampling frequency : $1.024$ MHz Symbol Rate : $256$ Kbps (Hence, Upsampling rate = $4$) ...
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2answers
500 views

How to scale measured QPSK points to determine magnitude error?

I am trying to determine the magnitude error between demodulated I,Q values and reference values on a constellation plot for a QPSK signal. The reference points are at (1,0),(0,1),(0,-1), and (-1,0). ...
3
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1answer
176 views

Recommendation for good ressources on digital processing and D-QPSK

I've been a C++ developer for 10 years. Quite high level. And I am completely new to Digital Signal Processing. I am trying to implement a Software Defined Radio. Specifically I am trying to receive ...
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2answers
64 views

Sphere decoding for non-binary modulation

I have a simple question on how to implement SD for non-binary modulation, let say QPSK. Assume we transmit a complex symbol $\overline{a}$ drawn from a QPSK constellation. On a vector form, we can ...
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1answer
9k views

what is the difference between QPSK and 4QAM? [duplicate]

i need to know the main difference between QPSK and 4QAM, i have searched over the internet and still i have not found a good explenation.
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1answer
871 views

QPSK using Root Raised Cosine Filter

The implementation of QPSK requires 2 orthogonal basis. So when using root raise cosine filter to implement QPSK, what is the 2 orthogonal signals?
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0answers
163 views

Unable to stabilize 8-PSK signal with self designed costas loop

I am trying to make a signal processing block which implements the costas loop to stabilize an 8-PSK signal. Here is the flowgraph with "costas_loop" being my block. My workflow is the following - <...
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1answer
1k views

The difference between MSK as CPFSK and OQPSK

I am working on MSK simulation. I have read the Chapter 5 of book entitled Digital Modulation Techniques by Fuqin Xiong. It is said that MSK can be viewed as a Sinusoidal Weighted OQPSK or CPFSK. If ...
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1answer
820 views

Adding AWGN noise with a correct noise power to the signal

I would like to add AWGN noise to my BPSK and QPSK signal. So assume the BPSK signal is x1 and QPSK signal is x2. The ...
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1answer
187 views

How should I isolate a single QPSK signal from a noisy band?

I've worked through a number of PSK demodulation tutorials, but they all start with a single PSK signal that fills the entire sample rate. But what if the signal is in the real world? What kind of ...
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434 views

Compute probability of error to each QPSK symbol

I'm trying to compute the probability error function of a QPSK modulation. I have a single user, who send a determined symbol $x = \frac{1}{\sqrt 2} \left(1+1j\right)$. Then I estimate at the ...
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1answer
1k views

Gardner Timing Recovery for Repeated Symbols

I am implementing the Gardner Timing Error Detection algorithm for a QPSK signal. I understand the concepts behind it but I am curious as to what effect repeated signals can have on the phase lock. ...
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1answer
3k views

How to correct the phase offset for QPSK I-Q data

I have an I-Q data of QPSK modulation, the data is is smeared and I have to correct the phase offset that causes the smearing problem, how can I apply the Phased-locked loop or the Costas loop on this ...
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0answers
439 views

Sampling rate versus number of sample of I and Q

I am acquiring data of an O-QPSK signal (chip rate : 2Mchip/s) with a SDR. I am undersampling the signal at 20 Mhz (carrier is at 2.8 GHz) so I respect the Shannon-Nyquist criterion that you need to ...
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1answer
732 views

O-QPSK constellation interpretation - GNU Radio

I am currently trying to recover the I&Q of a O-QPSK signal generate from the standard XBEE arduino module using a B200. I can get somehow get a "look-like" of a constellation. Here an screenshoot:...
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0answers
380 views

Problem in constellation diagram

In a waveform designing i am getting this type of constellation(image_attached). Can anyone please tell me why i am getting this type of constellation? this constellation is after frequency correction....
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2answers
2k views

High Transmission Power : BPSK or QPSK?

In BPSK, the constellation consists of 2 points (equiprobable) spaced at distance of $\sqrt{E_b}$ each from the origin. So the average power from the constellation can be obtained by: For BPSK, $P = ...
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1answer
3k views

GNU Radio - PSK Mod block - unexpected constellation diagram

I am simulating a QPSK modulation in GNU radio. Here is the flowgraph: . The source is a binary stream coming from the Random Source block. There are 4 PSK Mod blocks configured identically (4 ...
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1answer
140 views

Why does DPSK constellation shrink when noise is added?

I am generating a DQPSK waveform at complex base band with constellation points on the unit circle and when I add AWG noise the constellation shrinks. The noisy constellation "blob" migrate inside ...
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1answer
2k views

Sampling frequency and oversampling factor

A quite naïve question. I need some clarification regarding choosing the sampling frequency and oversampling factor. The scenario is as follows: I have an OQPSK modulated sequence with symbol rate 2 ...
3
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1answer
1k views

Gardner timing recovery and constellation diagram

I would like to ask for some guidance regarding 2 issues mainly QPSK and Gardner algorithm for timing recovery. I am having as input a set of IQ samples (10 samples per symbol) to which I need to ...