Questions tagged [qpsk]

Quadrature Phase Shift Keying

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Why do I see a frequency shift from center when transmitting a QPSK via USRP with GNU Radio?

I am transmitting a QPSK signal via GRC and when I look at it on the spectrum analyzer, the signal is shifted away from my center frequency. This shift increases the higher the center frequency (i.e. ...
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understanding FIR SRRC filter with memory implementation in C

I translated the Matlab QPSK receiver/transmitter into real-time C code that I have running on a PlutoSDR platform. QPSK receiver/transmitter I wrote the square root raised cosine filter for the TX ...
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60 views

QPSK sync sequence detection problem

I have IQ data collected This is the beginning of the packet that includes preamble and sync sequence. Red is real part, blue is imaginary. Also constellation diagram for this data I don't have ...
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47 views

Error probability for 8-PSK

How can I calculate bit error rate for 8-PSK modulation when I have $E_b/N_0$ given? I know that for QPSK/BPSK the matter is quite simple, but I cannot cope with 8-PSK. Let's say that my $E_b/N_0$ = ...
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90 views

QPSK demodulator on GNURadio continuously loses phase lock

I am designing a QPSK demodulator to be used for receiving Meteor M2 (LEO satellite) signals (QPSK at 72Kbaud). However, I am finding a lot of problems in my way. First of all, this is the flowchart I ...
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Correcting large frequency offsets at very low data rates

Consider a typical BPSK system running at a baud rate of 1 kbaud/sec - the receiver needs to deal with severe frequency offsets, let's say up to +/- 1 MHz offset and that the frequency offset can ...
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173 views

Block diagram of M-PSK modulation and demodulation

I have come across this quadrature modulator block diagram in many books and websites: I've read that the quadrature modulator allows to realize many different digital modulations, including ...
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20 views

Spectral properties of QPSK modulation

From what I've read, the spectral properties of the modulation largely depend on the rate of change of the signal phase - "a signal in which the phase changes stepwise has a broad spectrum, well ...
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What does this mean? The elliptical constellation in the QPSK constellation diagram?

Can you explain what kind of signal is this or what can you characterize when you see QPSK constellation like this? to get a better signal it needs to be near 1 and be a round circular constellation. ...
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Questionable Eb/N0 results for different modulations - measurements for 8-PSK do not match the theory

I would like to warn you that this post will be long, so thank you in advance to everyone who reads it and is able to help. I am running a certain simulation. I created a measurement environment (...
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74 views

Why is the bandwidth for this QPSK system larger than expected?

Below is my gnuradio-companion graph. As you can see the sample rate is 100k, I am modulating with QPSK, and am filtering the waveform (RRC) with the "Excess BW" parameter, at 0.35. The ...
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86 views

Why 8-PSK modulation has higher Eb/N0 than QPSK or BPSK?

I run a transmitter/receiver simulation using QPSK, BPSK, and 8-PSK modulations. As far as I have noticed, the best SNR per bit results are obtained when simulating with 8-PSK modulation (and also at ...
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Simulating Rayleigh channel - Problem with adding channel coefficents

I am currently trying to simulate a Rayleigh channel using python (numpy). Full Jupyter Notebook on GitHub: Jupyter Notebook I assume that the channel changes with each new symbol. So I create myself ...
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78 views

Offset QPSK Demodulation using GnuRadio

I am currently trying to demodulate an Offset QPSK signal coming from a satellite using GNURadio. If I understood correctly, an OQPSK is a QPSK with one of the two bits per symbol delayed by half a ...
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Trade-off in sample-rate & FFT-size & Doppler

I've got a stream of digital IQ samples let's say at $F_s = 1 MSPS$ that consist of a narrowband signal, in awgn. Let's say the signal BW is ~ 100Hz. The narrowband signal's center (or base) frequency ...
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73 views

Transferring data over sound with QAM / QPSK

Been working on a FSK Modem in the last few weeks and have gotten it to work with 400bps, very reliable, atleast over a virtual audio cable, but it also works when playing a sound directly into a ...
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QPSK transmission simulation

I am trying to simulate a QPSK transmission using GNU Radio following mpsk_stage6.grc example in Gnuradio tutorials. Currently I have no idea where is the problem and everytime I execute the flow ...
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Packet Encoder GNU QPSK Transmission

Hello everyone!. This is a template to QPSK transmission but Packet Encoder block is no longer available in new GNURadio versions, what do I need to replace this block in order to do a QPSK ...
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1answer
78 views

How to separate Even and odd part (in-phase bit streams I and quadrature-bit streams Q) of the signal?

I am working on communication system in simulink and wondering, how can i separate the Even and odd part of the signal. In my Transmitter block, I have : $$ \boxed{\text{Binary Data signal}}{\...
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364 views

Use of pulse shaping in digital modulation

Sorry, I am a little bit confused here cause I thought when we say QPSK, the signal looks like the following. I thought the bits to send/receive depends on the phase shift of the carrier, or is the ...
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88 views

When I double bit rate I do not see a difference in I_spectrum and Q_spectrum, but why?

I wanted to compare two different I-Q spectrum plots of a basic transmitter, one in which I doubled the bit rate. I expected a different result, that of possibly a higher/faster graph. It looks sort ...
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65 views

Modulation upsampling method

I try to implement a qpsk modulator in Octave. The chain is the state of the art I guess: $$\text{Symbol mapper} \rightarrow \text{Upsample 4} \rightarrow \text{Root raised cosine filter} $$ My main ...
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135 views

Differential Encoding for M-PSK

Confused about a few topics w.r.t. differential encoding/decoding. First, consider the below BER curve taken from wikipedia ( https://en.wikipedia.org/wiki/Phase-shift_keying ) comparing BPSK/QPSK and ...
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33 views

How to deal with modulator jitter?

I have a question regarding an implementation of a modulator. I guess some people here have an FPGA background. I would like to implement a QPSK modulator of  31 Mbit bitrate using a 125 MHz clock. I ...
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144 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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341 views

Sample rates, Samples per Symbol, and Digital Pulse Shaping

Having some confusion about digital pulse shaping for complex baseband (passband) signals. The complex baseband linear modulation equation is $$s(t)=\sum_{m=-\infty}^{\infty}\text{Re}\{a_m\}h(t-mT)+j\...
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47 views

How to Tx CDMA signal physically using an existing point-to-point modem? [closed]

I am working in acoustic communication, I want to test CDMA network capabilities in acoustic environment. I had an acoustic modem that has serial interface, a WHOI micromodem. How can i serialized ...
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1k views

Python code for QPSK modulator [closed]

Have any of you done anything like QPSK Modulation in python? I am in the middle of it and having problems in setting up bits? like odd and even bits. Have you got any idea? Regards, Sam
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How are pulse trains generated in a radio transmitter?

When simulating a PSK signal in MATLAB or Python, I often create an impulse train where each impulse is modulated with a symbol. This modulated impulse train then passes through a pulse shape filter ...
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1answer
66 views

How to plot BER Vs SNR of a received signal

I am using USRP to transmit and received MIMO frames similar to Wi-Fi standard that I created on my own. After receiving the signal, it is processed as described in the standard. While I plot the ...
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2answers
144 views

MATLAB: Issue with passing data through AWGN Channel [closed]

I am trying to send QAM data through AWGN channel and I have 256 samples/symbol, I have the following code: ...
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55 views

Phase Noise in Constellation Plot

I have the following phase noise plot (-100dBc/Hz @ 1MHz offset and -130dBc/Hz noise floor): The integrated phase jitter for this phase noise is around $4.6^\circ$. According to my understanding the ...
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187 views

IQ Mismatch and Image

I was reading the following paper about direct conversion receivers from TI: link. In this paper they compare the performance of direct conversion and heterodyne receiver with IQ mismatch. The ...
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1answer
144 views

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

I would like to compare two different implementations of carrier tracking loop which differ in the way phase detection happens in the PLL. I am using PSK modulation for the data. In the first ...
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105 views

Signal Timing Recovery, Loop Bandwidth and SNR

As explained in the answer here, for the symbol timing recovery loop we need to keep loop bandwidth sufficiently below the modulation bandwidth of the signal so as to avoid the filtering of the signal ...
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91 views

MATLAB: Generating a random bit stream in a frequency Band for PSK Modulation

I want to generate a pseudo-random bit stream in MATLAB in a given frequency band for PSK Modulation. I am using the idinput function to generate the bit stream: <...
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74 views

Loop Bandwidth for Carrier Demodulation loop

I am trying to implement a simple MATLAB model for the demodulators for phase modulated signals (PSK) used in communication systems. For the detection of the phase modulated output (PM out in the ...
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1answer
29 views

Modulation classification via demodulation confidence?

I'm not sure if this is the right place to post this question, but will try anyway :-) I recently started reading up on the field of automated modulation classification (AMC) where an algorithm ...
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72 views

Digital Tanlock carrier recovery loop

I’m currently trying to understand a digital tanlock carrier recovery loop for QPSK (for example) I cannot understand how it works. For example we an ideal QPSK constellation. phi = atan2(Q/I) = pi/...
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106 views

ADC sampling rate implications Matlab/Simulink M-PSK modulation

I am trying to find a way to evaluate what would be the minimum sampling rate used in a modulated waveform using matlab / Simulink. The real scenario would be let say a M-PSK waveform of Y bandwidth ...
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1answer
96 views

Burst QPSK demodulator

I am working in burst QPSK demodulator. I just want to double check if what I am doing is right. Large frequency feedforward recovery by FFT Carrier recovery Costas with 4 samples/symbol Timing ...
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83 views

Nyquist sampling theorem / Nyquist - Shannon theorem evaluation over M-PSK

I am trying to simulate an M-PSK Tx-Rx System on Simulink and analyse what the effect of sampling rate reduction would have on it. More, particular I am trying to prove what Nyquist sampling theorem ...
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229 views

Understanding Matlab's Automatic Gain Control function

I am trying to understand the automatic gain control block provided by the communications toolbox. The documentation is here: Documentation My questions are in regards to two of the configurable ...
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Learning PSK Modulation and Demodulation - Good Text to Read?

Title sums it up. I am curious to see what you all suggest. I'm a newbie and just need some beginner/intermediate material. Thanks!
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276 views

GNU Radio - Bandwidth and Band Reject Filter

I am currently trying to generate a psk modulated carrier with gnu radio. Attach is an image of my flow graph. As can be seen I am generating a bit stream using the Random Source module and ...
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59 views

Mapping soft symbols in DQPSK

I'm trying to soft decode DQPSK. According to this paper the bits are: $b_1 = \mathrm{Re}\{s_n s^*_{n-1}\}, b_2 = \mathrm{Im}\{s_n s^*_{n-1}\}$ If I put 0.707 as a 100% probability of 0: $\begin{...
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lte matlab baseband IQ recovery

I am a beginner again to signal processing, I did my degree over ten years ago, and I am relearning all my signal processing stuff. I am a software developer by trade but now I am looking at some LTE ...
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133 views

Phase shifts of QPSK

I'm honestly lost on creating timing diagrams for bit sequences. I understand for QPSK there are symbols 00, 01, 10, 11 with phase shifts of 45,135,225 and 315. I'm just not understanding how you ...
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533 views

What is the minimum sampling rate for QPSK or what is the bandwidth of QPSK signal?

Consider we have created a QPSK signal with a carrier frequency 100kHz. Before applying matched filter or demodulation we need to take samples from the received signal. So what is the minimum ...
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30 views

BER performance of a space-time code over Rayleigh channel model

For a given space-time code, and in general terms, how would one proceed in the evaluation of the BER performance of this code ? In order to be more clear, say i have 16 code matrices(who's elements ...