Questions tagged [constellation-diagram]

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Complex Filter (Modelling a Channel ) convolved with complex baseband modulation gives error *Plots inside -Updated*

I have a complex filter that is modelling the channel response, its not symmetrical on 0. The complex filter is convolved with a complex baseband modulation of QPSK. Plot 1 Zoom in on impulse response ...
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1answer
81 views

Frequency Error/CFO effect on Constellation for OFDM

Very often in literature we see that effect of carrier frequency offset is seen as rotating of a constellation points. And explanation is generally that after down converting and sampling the time ...
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70 views

Software implementation of Gardner Loop

My objective is to create a Gardner loop to remove the timing offset present in my signal. To achieve best timing SNR, I downsample my signal to 2 samples per symbol. It is depicted below: where blue ...
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0answers
49 views

The timing offset remains after Gardner loop

I would like to use Gardner loop to remove the timing offset in order to demodulate the signal. My signal contains the frequency offset, however I know that the Gardner loop can handle substantial ...
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1answer
244 views

Clock recovery using Mueller and Muller adds noise affecting EVM or SNR (Two cases - GNU Radio & Python code)

The implementation of the Mueller and Muller clock recovery that I am seeing adds a large amount of 'noise' or degradation to the Error Vector Magnitude (EVM) to the symbols on the constellation. This ...
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0answers
37 views

Matlab: Could anyone suggest why Iam getting a different geometry for QPSK constellation diagram

I'm developing a Multi-user MIMO communication model in MATLAB where a base station communicates with 2 users. The model uses OFDM (QPSK) modulation. Channel model, precoding and covolutional encoder ...
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2answers
2k views

How exactly do I plot a constellation Diagram?

I am relatively new to signal processing and I would like to correctly draw a constellation diagram to check the results of a study. I need my signal processing to be as close as them to make sure I ...
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0answers
66 views

Why does carrier frequency offset (CFO) cause carrier phase error (CPE)?

I've already asked 2 questions on this but there is one discrepancy I cannot reconcile and is the crux of the problem: \begin{align} \newcommand{\prefix}{\frac1N\sum\limits_{n=0}^{N-1}} R_l &= \...
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1answer
119 views

Why does fine CFO cause rotation of the constellation?

Just thinking about it, why does fine CFO cause rotation only? I only see diagrams that show rotation of the constellation. We assume this is a complex magnitude frequency domain plot In order for ...
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3answers
215 views

What causes this type of distortion in a constellation I/Q plot?

I'm transmitting QPSK through a digital pulse shaping filter (RRC, 35% excess BW, 2 samples per symbol, 64 taps) at a rate of 56Msym/sec. Receiving it on standard lab equipment (Vector signal ...
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2answers
38 views

How to distinguish between received quadratures

How can you distinguish between two quadratures in QAM when the phase is not known at the receiver? For example, if the quadratures are sin and cos, how can the receiver tell which one is which, since ...
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104 views

Matlab Plotting custom constellation along with decision regions

How do I create a custom constellation along with decision regions in Matlab, any help is greatly appreciated
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159 views

Having trouble transmitting/receiving a BPSK signal using two USRPs

I am relatively new to working with SDRs and GNURadio and I am attempting to generate a BPSK signal and transmit it through one USRP and receive and demodulate it on another USRP. I am using GNURadio ...
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1answer
3k views

Average Energy of modified QAM Constellation

How to compute the average energy for the modified 16-QAM constellation below? I know that for regular/rectangular 16-QAM we can utilize the 4-PAM along each axes but I'm not sure how can we find $E_{...
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1answer
284 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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3answers
1k views

Carrier Frequency Offset, Rotating Constellation and Correlator

I have been further reading up on carrier recovery methods and something is not clear to me: It's written that a carrier frequency offset results in a rotating constellation diagram but if you are ...
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1answer
141 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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1answer
340 views

Why is Error Vector Magnitude (EVM) measured as an RMS value?

I do understand Voltage/Current measurement of a Sine Wave is in RMS, as average yields a zero, and RMS gives a true 'DC equivalent' value. But I do not understand why an EVM measurement could be in ...
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1answer
996 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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1answer
227 views

Understanding unexpected i/q calculation on a downsampled signal

I am reading samples with an RTL-SDR, centered on an FM broadcast station: ...
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0answers
65 views

Constructing Contour for Star QAM Equalization

I am trying to equalize the 16 Star QAM using known blind channel algorithms such as CMA,MMA,SCA,RCA,IRCA,CXA,SCXA.I now need to contruct a new contour for equalizing the 16 Star QAM.As it is in ...
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0answers
665 views

How to generate amplitude and Phase values (I,Q) for 8 QAM?

I am trying to simulate 8QAM with (4,4) amplitude levels. I want to get a constellation like this: What are the amplitude levels should I select for I and Q?
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1answer
595 views

Aliasing in digital communication system

In a digital communication system, is it possible to counteract the aliasing problem by properly tuning the constellation order $M$ and/or the carrier frequency? Here is my train of thought, please ...
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3answers
266 views

Zeros inserted in QAM Constellation

I need to ask about insertion of Zero Symbols after QAM modulation in a OFDM system. Such that the 4 QAM has a constellation with 4 corner and 1 center symbol indicating zero. What advantages or ...
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2answers
782 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). ...
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1answer
3k views

Matlab : How to plot the constellation diagram for this method?

I am trying to generate symbols +1,-1 using a function by partitioning the interval of the function into two levels. The function is the Tent Map. This in a way achieves bpsk modulation. I want to ...
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1answer
234 views

P2 symbol constellation in DVB-T2

DVB-T2, 32K SISO, not extended. I've acquired P2 symbol, PRBS bits have matched with bits recovered from pilots. Then equalization was applied to all subcarriers. The constellation I've got looks ...
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1answer
2k views

Generating QPSK Constellation Diagram

I was wondering how a diagram like this is generated. I am generating a QPSK signal using MATLAB by taking a cos and sin wave, multiplying each one by either 1 or -1 and adding them together to form ...
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2answers
3k views

OFDM symbol acquisition block in GNU Radio gives rotating constellation even if there is no carrier offset. How is this possible?

Why does the constellation rotate when using OFDM Symbol Acquisition block in this flow graph below ? The only explanation I could think of would be carrier frequency offset but in this flowgraph ...
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1answer
1k views

How does carrier frequency offset effect the constellation diagram in OFDM?

In the case of OFDM modulation, if the carrier frequency is slightly off then how does that effect the constellation diagram ? Is there some general rule how it will change (such as rotate) ? Or ...
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0answers
472 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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1answer
4k 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 ...