Questions tagged [modulation]

Modulation is the process of varying one or more properties of a high-frequency periodic waveform, called the carrier signal, with the amplitude of low-frequence modulating signal which typically contains information to be transmitted.

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The sound of modulated audio signal

As I was learned in signal processing, modulation took the signal spectrum to higher frequency range, so I made an experiment for audio file. The audio file "handel.ogg" plays a small part of music "...
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Length of CDMA code and message length vs. number of participants

What is the minimum code size for CDMA codes for synchronuous CDMA (not asynchronous CDMA!) with N number of participants? Furthermore, suppose N parties want to uniquely transmit a message of length ...
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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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What is DAB modulation in signal generators?

I am using R&S signal generator and for generating a DAB signal there is an option for mentioning the modulation level in %. For example, we can generate DAB modulation 50% . I can understand that ...
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OQPSK - GNU Radio Companion

I was wondering if anyone has had any success in implementing OQPSK in gnuradio. I have a working theory of expanding on the Constellation Modulator to include a custom OQPSK function. I have ...
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What's wrong with my M-ary ASK modulation demodulation MATLAB code?

My MATLAB code linked below implements ASK modulation of an M-ary signal, impresses it on a carrier, adds AWG noise of various SNRs. Then, for each SNR, demodulates the signal and calculates the ...
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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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Pulse shape estimation

Given a captured noisy BPSK signal, how do I formulate the maximum-likelihood problem so as to estimate the matched filter? The model of interest would be baseband BPSK with AWGN: $$c(t) = \sum_{\ell=...
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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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Modulation with Maximum Likelihood decoder and capacity

My question comes from the high spectrum efficiency claim of OFDM. This seems not correct IMHO, at least theoretically. For me, we lose energy in using cyclic prefix, hence OFDM should be a waste of ...
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Binary and Quadrature Phase Shift Keying [duplicate]

I was learning Modulation Techniques and was on the topic Phase Shift Keying (PSK). As far as I have understood, In Binary PSK we encode a single bit on a one signal element and we differentiate ...
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How to make SL to RF inport in simulink work real time?

I am using qam in the simulink and need to upconvert the complex baseband data and obtain the time domain passband signal. I pass the complex baseband data to SL to RF inport and then do the ...
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Demodulation of OFDM symbol in LTE for multi-user case

I was trying to understand what exactly happens when you try to modulate an ofdm symbol in the downlink in LTE for multi-user case. When we modulate, usually we allocate different sets of RBs for ...
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Explanation for the following code in python [closed]

x=2 *(rand(N) >= 0.5) - 1 Can someone please explain how the above expression corresponds to BPSK signal please?
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Why bit rate is same in a lower frequency spectrum and higher spectrum?

If there is a spectrum between 0 Mhz - 1 Mhz, bandwidth would be 1 Mhz here and for example with baseband we can send 2000 bps. What I can't understand is if spectrum is 5-6 Mhz instead of 0 - 1 Mhz, ...
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Is there any relation between QAM and streaming?

I am trying to determine whether there is any relation between QAM and streaming (e.g., video streaming). I know that QAM can be used for broadcast TV. I'm not sure if QAM is used for WiFi bit ...
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27 views

Diode demodulation for AM

What is the capacitor and resistance at output of LPF meant for in the document it was mentioned that it is DC blocker I don't get it can't message contain DC value.
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Envelope detector for AM signals

How or what are the constraints for deciding factors of envelope detector for AM As far as I know that charging time of capacitor should be below 20T where T is periodic time of carrier and ...
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Channel state information from non-HT packets: is that possible?

I read several papers about CSI data, but one thing is not clear. I would like to extract csi from legacy rate packets. I read some forums related to existing CSI tools and they only state that CSI ...
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How to find index of FM modulation

In text I know that frequency of amplitude signal is 10KHz and carrier frequency is 80 MHz. And I need to write code for FM modulation in matlab, I know how to calculate index but here I do not know ...
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Getting the bitstream of an unknown RF signal

I am trying to get the bitstream of a signal sent over 433MHz. I have installed SDR# (I'm on Windows), connected my NESDR SMART, and I identified the signal here: I can see there is only one peak ...
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Why only odd harmonics after non-linear amplification?

Why do I get only odd harmonics appearing? This not only happens at saturation of the transfer curve, but also in the linear portion of the curve. I make a input signal that has too high power that ...
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What does this spectrogram mean?This is spectrogram of a multitone FM signal

! The spectrogram of FM signal has been generated by using Matlab.Now I want to what does these scratch like lined represent, though I have only two frequency components in my message signal(https://i....
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What determines the maximum/minimum values in I/Q constellation diagram?

I need to do some data analysis on I/Q samples and was trying to know what are the parameters that determine the maximum/minimum values of these samples. In other words, what determines the maximum/...
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Generating a phase modulation frequency spectrum with jitter

I would like to produce a frequency spectrum plot like this: (from All About Circuits) I know that one can take the modulation frequency and multiply it by a given order and scale by the modulation ...
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173 views

Relation between constellation SNR and baseband SNR

Let's say I have an I/Q modulation, ie. QPSK. I can simulate an the effects of an AWGN channel by adding to my QPSK symbols the realizations of a complex normal. $\mathcal{CN}(0,\frac{1}{\mathrm{SNR}...
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How to compare two 802.15.4 O-QPSK modulated digitals signals?

I am working on wireless sensors project and I am trying to simulate a transmission between two nodes. So let's say I have two nodes which transmit the message to each other, i.e. node 1 transmits ...
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Does gray coding bring improvement to SER of QPSK, compared with natural coding?

I understand gray coding contributes to BER of QPSK, yet really don't understand why it brings improvement to SER. According to the relationship of SER and BER, it should be improved. Actually, when ...
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IT++ and Alternatives DSP Libraries

I want to implement some signal processing blocks in C++ so I did a bit of search on the available libraries for signal processing in C++ and I found that IT++ provides comprehensive set of functions, ...
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Differential Pulse Code Modulation (DPCM)

In the following figure we see an encoder and a decoder of a Delta Modulation System, which is a simple DPCM System with a 1-bit quantizer: We assume that signal $x(n)$ is known, that $\hat{x}(-1)=0$ ...
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Continuous Phase Modulation

The wikipedia article on continuous-phase modulation states the following: For instance, with QPSK the carrier instantaneously jumps from a sine to a cosine (i.e. a 90 degree phase shift) whenever ...
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confused in using modulation technique

I am given a question in which I have to draw the spectrum of the signal $m(t)$ and then draw the spectrum of this modulated signal. The signal is $$m(t)=\cos(1000\pi t)$$ Now in solution manual ...
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Synchronization Accuracy Required For Communications

One of the biggest problems in phase modulated communication is discovering when your signal has arrived. High accuracy in this area is important, as even a quarter wavelength error can cause the ...
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Multiply signal $x[k]$ with $\cos(2\pi\nu_0k)$, then given $X(\nu)$ draw resulting function in frequency domain?

Let $$y[k]=x[k]\cdot \cos(2\pi\nu_0k) .\tag{1}$$ Then, given a signal $x[k]$ with the DTFT $X(\nu)$ according to the following figure what will the frequency domain for $Y(\nu)$ look like for a ...
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BER vs Eb/N0 for BPSK signal with depth of modulation 120 degrees (+-60 degrees)

I want to draw graph of function BER vs Eb/N0 for BPSK modulation with depth of modulation is from –60 to 60 degrees (or from 0 to 120 degrees). Can I use for that MatLab's tool 'bertool', or I need ...
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magnitude spectrum of a signal xc(t), where xc(t) = square function * cosine function

im currently learning about signal processing in school. The objective i want to achieve is to modulate the square wave to a certain frequency for transmission and apply a LPF and demodulate at the ...
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Why do IQ Impairements, Quadrature Skew and DC offset have these geometric effects on the constellation?

I'm studying telecommunications, and would like to be sure to understand the maths behind these effects. For IQ Imbalance and DC offset, it seems pretty clear why we observe a rectangle shape or a ...
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169 views

What does the phase discriminator portion of the Costas Receiver do mathematically?

What does the phase discriminator portion of the Costas Receiver do mathematically? The output of the I-channel is $ \frac{1}{2}A_C \cos \phi \, m(t) $. Which means for small deviation of phase $ \...
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How is frequency related to data rate?

How does (if it does) frequency affect/relates to Data Rate. Why for example using the same modulation, LoRa (in the physical layer), you get somewhere around 250kbps at 2.4Ghz and only 20kbps at ...
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16-QAM output waveforms vs. 4-PAM levels

I've found some conflicting information about how the I/Q waveforms look compared to the 4-PAM signals before the modulator. Here it is shown that the 4-PAM digital signals are filtered, so the ...
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Filtering of an AM signal at the reciever

Transfer function of a filter at the input of a receiver (synchronous demodulator of AM signal) is given with equation: $$H(f)=e^\frac{-(f-f_0)^2}{B^2}+e^\frac{-(f+f_0)^2}{B^2}$$ $B=10kHz$ It is ...
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How to correct a QAM time delay

How can you correct the anticlockwise rotation that occurs in the received constellation of a QAM system? My only idea is to compensate the delay with an advance but this is impossible since you ...
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Is there a relationship between Average energy of transmission and power saving

As mentioned in many books, the average energy of transmitted symbol is given by: $E_s = (2/3)(M - 1) $ where $M$ indicated the modulation order. Suppose that we are using in the first scenario $...
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Modulation scheme for a noisy channel with a complicated transfer function

I want to build an audio modem with a speaker in a room and a smartphone. The channel is quite bad: Far field, so there is potentially significant reverb Typical residential background noise phone ...
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Question about QAM

I'm trying to understand QAM transmission and I'm struggling to understand this sentence, 'The advantage of using QAM is that it is a higher order form of modulation and as a result it is able to ...
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Converting complex baseband signal to passband signal

I have to convert baseband signal (BW-20MHz) to passband signal centred at 20MHz. I am implementing this in matlab. so, this is how I tried it. I have already generated LTE Waveform BW- 20MHz , fs =30....
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I have the scatter plots for a Hamm and Tukey(0.25) windowed data. The complex data plotted from Hamm windowed forms a pattern, why?

The Hamm windowed complex data forms some sort of a quantized pattern whereas in the same code if tukeywin(0.25) is applied normal noise is observed. Any idea why ?
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Relationship between Bandwidth and Bit Rate

In one of my classes I have learned that if we look at transmitting a binary signal with ASK, we can get the bandwidth (i.e. the width of the main lobe in the frequency domain) with BW = 2 * Fb, where ...
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Modulation and Noise

I am fairly new to studying communication systems. When it comes to different digital modulation techniques, does the effect of an additive complex noise (a) introduced by the system, and (b) by the ...
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Why is carrier wave affected by percentage modulation?

In amplitude modulation, Power of a carrier wave is represented by : $$P_c = \frac{A_c ^2}{2R}$$ Which is independent of modulation index! Question: At what factor is the power of carrier wave ...