Electrical Engineering Stack Exchange
Electrical Engineering Stack Exchange

Questions tagged [qpsk]

24 questions
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Designing an optimal BPSK and/or QPSK transciever in SDR

I'm currently working on writing firmware for the modem on a cube satellite for my university's satellite team. My primary goal is to implement the data uplink & downlink. The RF system, completed before I arrived, receives on the 2m band and…
Synchrondyne
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Gray code usage in modulation constellations

When mapping symbols of various modulation constellations, Gray code is used such that - each adjacent symbol only differs by one bit. Why do we want small physical changes in the signal to correspond to small changes in the symbol ? Why not use…
shaiko
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Difference between O-QPSK with half-sine shaping and MSK?

The IEEE 802.15.4 standard specifies that O-QPSK modulation with half-sine pulse shape (HSS) should be used at the 2.4 GHz band. But according to Wikipedia, O-QPSK modulation uses square pulses, and O-QPSK that encodes each bit as a half sine is…
kfx
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Offset QPSK Frame sync markers

What actual protocols exist out there that employ Offset Quadrature Phase-Shift Keying (OQPSK)? What do they use for the frame synchronization marker (or "preamble" or "sync word" or "flag")? Do they use a unique word, a unique pattern of bits? If…
robert bristow-johnson
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How to interpret transitions in a QPSK constellation diagram?

I have one doubt regarding how to analyze a constellation diagram. It is from a QPSK transmitter. The constellation diagram looks typically as books (as a square as you can see in Figure 1), but for shorts periods it changes as you can see in Figure…
Gabriel
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Phase rotation for QPSK

I have two SDRs and I want to do a simple test: I want to send data values using QPSK modulation with coordinates: (1,1), (-1, 1), (1, -1), (-1, -1), but on Rx site I got all possible values on the circle created by rotation of the square. Why…
sluge
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QPSK Transmitter/Modulator Question

So I was curious, from the image below showing a QPSK Modulator What would happen if the phase shift applied to the reference carrier signal going to the modulator for the Q channel is changed from +90 degrees to -90 degrees? What would happen if…
hihihii
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QPSK/QAM, digital quadrature modulation: square wave as local oscillator possible?

Goal is to build a lab exercise for students to illustrate digital IQ-modulation (QPSK, M-QAM). The bit stream for I and Q are generated by e.g. an Arduino. Is it possible to use a square wave as local oscillator (original and 90-phase shifted) or…
kgmuzu
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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 QPSK constellation points after frequency and phase…
SAM
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Is there a method to get the carrier from the recieved QPSK signal?

If we have given a signal and we know that is a modulated QPSK signal, can we recover the carrier if we know the carrier frequency fc. Edit: A clarification, I do not have to do it in hardware, a matlab code is fine.
Creator
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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 sampls from the received signal. So what is the minimum sampling rate we must have? Cosider that somehow we have…
Creator
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Need some help in bit error rate calculation for QPSK when using Gray coding

Why is Probability of Bit Error = 2 times the Probability of Symbol Error in QPSK with Gray Coding. Is it because one bit error has the potential to cause two symbol errors (2 symbols where they differ by 1 bit from the original symbol being sent) ?…
user3656142
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what relationships exists between the BER vs SNR graphs of QPSK and QAM modulation schemes on data throughput. which scheme does better?

Using QAM and QPSK modulation schemes, RF field measurements like received signal power and pathloss were obtained from where the SNR values were estimated. Their BER values were also calculated and Matlab was used to plot the BER vs SNR graphs for…
ceo
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Newbie: From bitstream to QPSK

I'm a complete newbie. I don't want to bother this fantastic resource with my ignorance, but I'm starting to have strange thoughts. How do I go from a bitstream (say, the output of an USB port) to a RF signal (say, to a QPSK chip like the AD8346)? A…
cedivad
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Relation between AWGN and bit rate

I want to get the value of the maximum rate of digital information to be transmitted by carrier modulation through an AWGN channel with a bandwidth of \$ 100\ \mathrm{kHz} \$ and \$ N_o = 10^{-10}\ \mathrm{W/Hz}\$. That is transmitted through the…
user8836128
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