Questions tagged [qpsk]

Quadrature Phase Shift Keying

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votes
1answer
3k 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. ...
1
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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 ...
6
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2answers
2k 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. ...
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 ...
0
votes
3answers
995 views

Processing OBPSK as OQPSK

I'm trying to create and process an OBPSK signal, which, as I understand it, transmits even bits on one axis and the odd bits on the opposite axis, resulting in a constellation with 4 unique points. ...
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 ...
0
votes
3answers
1k 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 ...
10
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3answers
68k views

the relationship between bandwidth and the datarate

One Question of my note is like this. ...
2
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1answer
189 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 ...
3
votes
1answer
548 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\...
1
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2answers
888 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 ...
0
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2answers
357 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 ...
0
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1answer
265 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 ...
5
votes
2answers
9k 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 ...
2
votes
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
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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
4k 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 ...
0
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1answer
138 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 ...
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 ...
2
votes
1answer
305 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
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 ...
1
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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 ...
0
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0answers
37 views

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 (...
0
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1answer
85 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 ...
0
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1answer
85 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 ...