Questions tagged [qpsk]

Quadrature Phase Shift Keying

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13
votes
1answer
11k views

How to perform carrier phase recovery in software?

What are the options for recovering the phase of a BPSK signal in software? The only resources I can find online contain circuit diagrams – there seems to be no one willing to explain this to people ...
9
votes
3answers
62k views

the relationship between bandwidth and the datarate

One Question of my note is like this. ...
9
votes
1answer
13k views

Matlab plot of QPSK system doesn't agree perfectly with theoretical BER curves

Does anyone know if there is a simple explanation on the fact that the theoretical bit-error rate (BER) curves of a Quadrature phase-shift keying (QPSK) system are approximately 1 dB shifted from the ...
9
votes
2answers
4k views

How to soft decode DQPSK?

I'm successfully soft-decoding D-BPSK by taking the dot-product of the constellation-position of the symbol and of the previous symbol. If the result is >= 1, then the symbol phase hasn't changed and ...
6
votes
2answers
1k views

Recovering signal for psk

I am currently working on a product(cant disclose too much details of the actual project) in which some data is being sent via audible(but on the higher freq) sound that is encoded with dqpsk. ...
5
votes
2answers
8k 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 ...
5
votes
1answer
11k views

QPSK Modulation/Demodulation in C++

I'm trying to implement a QPSK Mod/DeMod system in C++. So far i have a bit generator that generates N bits and stores it into an array: ...
4
votes
4answers
6k views

Why does OFDM use cyclic-prefix while QPSK uses root-raised cosine filters?

My understanding is that BPSK/QPSK/... are often implemented with root-raised cosine (RRC) filters to reduce ISI and bandwidth. OFDM can be understood to be BPSK/QPSK/... implemented on multiple ...
4
votes
3answers
129 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 ...
4
votes
1answer
3k views

QPSK soft decoding

I'm trying to decode a Hamming Block Code transmitted using a QPSK modulation. For the moment I can sucessfully decode it using hard decision but in order to improve performance I'd like to use soft ...
4
votes
1answer
699 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 ...
4
votes
1answer
272 views

QPSK Phase Recovery : Maximum-likelihood Vs Costa's Loop

I have implemented a QPSK Costa's loop in GNU Radio and run some BER benchmarking. All is going well. Out of curiosity, I'm trying to implement the Maximum Likelihood phase recovery shown below. For ...
3
votes
1answer
2k 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 ...
3
votes
1answer
78 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 ...
3
votes
1answer
152 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\...
3
votes
1answer
2k 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 ...
3
votes
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 ...
2
votes
1answer
235 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 ...
2
votes
1answer
2k 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. ...
2
votes
1answer
969 views

Frequency detection

What I have: A digital signal sampled at Fs composed of a QPSK modulation at Fmod plus some additive white gaussian noise. ...
2
votes
3answers
180 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 ...
2
votes
1answer
16k 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.
2
votes
1answer
3k views

Rectangular 8 QAM bit error rate calculation

I am simulating an 8-QAM communication system over an AWGN channel for various signal to noise ratios, in order to plot the average bit error. However I have not been able to derive an equation for ...
2
votes
1answer
999 views

QPSK, from Square Root Raised Cosine to Rectangular Impulse Shaping

I have implemented a QPSK modulator and demodulator using classic text-book examples: Square Root Raised Cosine Impulse shaping and Matched Filtering. The problem is that I've been told that I could ...
2
votes
1answer
4k views

Apply AWGN noise to QPSK-OFDM symbol

I'm working on an OFDM-QPSK based system and I'm having some trouble to match the BER of my system with the theoretical curve. My OFDM implementation fills all the subcarriers and have t_symbol s ...
2
votes
2answers
131 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 ...
2
votes
1answer
218 views

OQPSK vs QPSK envelope query

We use OQPSK because of envelope of signal but my question is "In Phase Shift Keying(or QPSK) the amplitude of the transmitted signal is constant then how the envelope will change in OQPSK"??
2
votes
1answer
105 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 ...
2
votes
2answers
2k 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 ...
2
votes
1answer
275 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 ...
2
votes
1answer
1k views

QPSK Data Rate vs Bandwidth at Passband: Why can it only transmit 1 bit per Hz and not 2 bits per Hz?

1) This is a follow up question to the most up-voted answer to this question. 2) The accepted answer is that "QPSK transmits 1 bit per Hz at passband". 3) The theory found in books seems to agree ...
2
votes
1answer
1k 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:...
2
votes
0answers
437 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....
2
votes
1answer
1k views

I/Q Sampling and Demodulation

A bit stream is mapped to symbols during baseband modulation, each symbol (say for QPSK) represents two bits. Each symbol has a corresponding I & Q value, which in QPSK, are used as the amplitude ...
1
vote
2answers
3k views

QPSK and OQPSK Modulation

In QPSK, after splitting the odd and even bits into the I and Q channels, and then multiplying them with the sine and cosine function, what next am I suppose to do? Do I rearrange them back into ...
1
vote
2answers
3k 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 ...
1
vote
1answer
4k 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 ...
1
vote
2answers
850 views

Why is a precoder necessary for DQPSK and what does it accomplish?

I've implemented a soft-decoder for DQPSK using the wonderful answers I received here: How to soft decode DQPSK? To get the soft-decoder working properly I needed to precode the data I was sending ...
1
vote
2answers
96 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: ...
1
vote
1answer
96 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 ...
1
vote
1answer
804 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 ...
1
vote
1answer
3k views

Why oversample data before using raised cosine filter?

In the process of creating a baseband signal, the complex symbols are filtered using a raised cosine filter to perform pulse shaping (I'm following some literature as a guide). The pulse shaping is ...
1
vote
2answers
3k views

Why do you get instantaneous phase by calculating correlation with a carrier signal?

I am somewhat new to DSP. I'm trying to implement BPSK by following this Python QAM tutorial. My code seems to work, but I really just ported the tutorial's Python code to C++, and do not understand ...
1
vote
1answer
84 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 ...
1
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1answer
30 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 ...
1
vote
1answer
27 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 ...
1
vote
1answer
397 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 ...
1
vote
1answer
2k 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 ...
1
vote
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 ...
1
vote
1answer
2k views

Practical Gardner timing error implementation

I'm trying to demodulate a QPSK communication. For the moment I do: Signal detection by computing the ratio between the power of the carrier wave compared to the signal power. Initial clock ...