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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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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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37 views

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 ...
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Representing data in combination of QAM and BPSK

I have a question regarding the data representation in different modulations. Assuming we are using MIMO system whith $4$ $T_x$ x $4$ $R_x$ which means four transmission antennas by four receiving ...
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125 views

How to generate IQ component for transmitting 2FSK

I am trying to generate IQ components for 2FSK modulation. I have started off from this thread FSK and IQ modulation , but I don't quite understand the IQ TX components plotted in the example there by ...
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Input and Output SNR Calculation in AM receiver input and output

For the FOM calculation of an AM receiver, the input and output signal powers are respectively, $$P_{in} = \frac{A_c^2(1 + k_a^2P_m)}{2}$$ $$P_{out} = k_a^2A_c^2P_m$$ These are obtained from the input ...
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About combination between QAM and PAM

I have confused question regarding the possibility of combination between QAM modulation and PAM in order to improve the spectral efficiency. Is that possible? As you see in the below Figure, it's ...
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How to calculate $E_b/N_0$ for a 8-PSK?

How to calculate $E_b/N_0$ for a 8PSK? My BER is given. But I don't understand how to calculate $E_b/N_0$ as it is inside a Q function.
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Characterization of the amount of modulation in a signal

We have used the ICRA babble noise to generate an 8-talker babble. As a background - babble noise is used as a substitute for competing talkers as babble noise lacks lexical content, but contains the ...
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What is the index modulation in OFDM and Subcarrier Index modulation?

I'm new here, I'd like to ask about the OFDM-IM (OFDM - Index modulation), what is it and how it works? Is it the same as SIM-OFDM? I checked white papers, I see it's using the index of sub-...
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Advantage of using DFT and IDFT hardware for modulation

I am doing a course in communications and while discussing multicaruer modulation to break down a signal into smaller bandwidths (for BW to be less than coherence bandwidth), there was mention of ...
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What is the mixed numerology in OFDM

In order to meet the user requirements in the next generation radio access technology, the ongoing standardization within 3rd Generation Partnership Project (3GPP) offers flexibility in terms of ...
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upconverting a kHz/MHz signal to GHz

I want to know how in practice we can take a kHz/MHz signal to a GHz band? Suppose we have an FSK modulated signal at around 300 kHz (or 20 MHz). I want to take it to 3.5 GHz, so about 3499700 kHz ...
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Why would we simulate baseband rather than passband

My question is, Why do we usually use baseband in simulation rather than passband? however, if we want to test our simulated idea in real environment, it must be sometimes in passband !! So, should ...
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How to convert sampled real audio signal to it's IQ components for IQ modulation?

So my question is this: How to convert sampled real audio signal to it's IQ components for IQ modulation? For instance: WHen I have my DSP or FPGA receive a audio signal through a ADC, which is just ...
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How to calculate the accurate BER expression of circular 8-QAM constellation modulation?

It is easy to understand the BER derivation of square QAM, but the circular 8-QAM? I'm quite confused. The decision region is not in a rectangular shape anymore, meaning regular way does not work here....
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Contradiction between complex baseband and real-valued baseband

Suppose a direct-conversion transmitter+receiver (ideal transmitter) along with its filters. In complex baseband, the filters in the signal chain can be modeled as a complex-valued FIR filter ($y$, $c$...
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How to test I/Q modulation with only one branch (I or Q)?

Given is a direct-conversion I/Q up- and downconverter system. Receiver and transmitter share the same (10MHz) reference and hence the LO frequency is identical and there is an (unknown) phase ...
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Modulation and allocation in GSM900

I want to do one project and I just want to make sure that I've understood correctly. Human's voice frequency is around 85-255Hz. When we talk on phone, carrier is modulated with voice signal in ...
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How range of the signal increases when modulation is done? [closed]

I am very confused because we know by increasing frequency we decrease the wavelength hence the distance covered will be very less but when we modulate a signal we are basically increasing the signal ...
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Bandlimiting and OFDM spectrum - what is considered “bandlimited”?

I have been reading about OFDM modulation, it's not clear to me how you can have band-limited OFDM but given its prevalence in wireless communication there must be some designation of approximately ...
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443 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 ...
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What is the relationship between FFT size and demodulation in OFDM

As I mentioned in the title of the question, how can we demodulate the data in order to get the same number of subcarriers with different FFT size. For example, 10 MHz LTE can be sampled with 15.36 ...
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88 views

How can I do QPSK in MATLAB [closed]

Could you please explain the step below, what is the benefit of it and how does it work. . I do qpsk demodulation, do I started doing the meshgrid, ...
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135 views

Inter Symbol Interference (ISI) / Equalization in Digital Signal Processing

I am studying the OFDM system and before to start I have decided to study the main concepts of modulation. And I have spent yet a lot of time to understand the concept of an equalization to reduce ISI....
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125 views

IQ modulation: baseband to bandpass transformation

can someone explain me these doubts? it is a baseband signal representation. A- complex signal, R- real. If I multiply baseband signal with FT( cos) then the signal will look like this ( on the ...
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Modulation of real-valued signal

I have one doubt according to modulation of a real signal. there are so many examples where the real signal was modulated with frequency bigger then 0. Why the signal could not be putted in f=0? is ...
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Calculating SNR from Frequency Domain

As I am newbie to signals, I have collected an appliance signal in frequency domain as follows: (PSD- Power Spectral Density). So, I need to calculate the SNR (Signal to Noise Ratio) and BER (Bit ...
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224 views

The code explanation about QPSK modulation

This is the code about the QPSK modulation, and I don't understand the real part and the imaginary part code. Can anyone explain it to me if you know? Why is ...
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47 views

Homodyne concept of receiver

I would like to understand a concept of homodyne architecture of I-Q demodulator and how the wave looks like at each step. It is a bandpass Signal: Step 1: multiplication with cos and sin wave. I ...
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Don't understand the relation about the wireless communication flow chart and TDMA illustration diagram

The first picture is the wireless communication flow chart,and the second is the TDMA illustration diagram,Which part of first picture is TDMA ? or if first picture is the standard process for TDMA,...
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Modulation to achieve Shannon capacity in AWGN channels

If my understanding is correct, to achieve the Shannon capacity in AWGN channels, we need a modulation that codewords follow Normal distribution, or uniform on surface of a sphere (sphere hardening ...
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271 views

Why does my OFDM demod in GNU Radio not return anything?

This is the flowgraph I used: Output after mod: Output after demod: I've read that it might be a synchronization problem but since I'm not actually transmitting anything over a medium, that shouldn'...
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What are the pros and cons of common modulation techniques? [closed]

What are the pros and cons of commonly used modulation techniques? Why is one preferred over another in a given situation? Why do so many exist? Are some better at resisting noise, travelling long ...
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50 views

IQ modulation principle

I am new in the signal processing. I hope I can get help. I want to ask a question regarding IQ modulation work . Why can’t I simply multiply a complex base-band signal with a cosine to modulate it?
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45 views

Synchronization with a specified sequence

I'm currently creating a project in Matlab where I'm simulating a communication, based on the SSB modulation, between a transmitter and a receiver. I've added a Barker sequence in the trasmitted ...
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126 views

Audio Steganography: Inaudible Audio Watermarking for Source Identification

What is a relatively inaudible audio watermarking technique to overlay a broadband audio signal on top of playing music without analysing the music for low-bitrate source identification? Ideally ...
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481 views

GNU Radio QPSK 4 Symbols

I'd like to generate a simple QPSK signal in GNU radio, but so far I haven't been able to get it to perform the way I'd like and I'm not sure if this has to do with some misunderstanding I have about ...
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Is Oversampling a Signal Same as Discretizing the Signal?

I am confused about the new terminology 'oversampling' I have encountered very recently. To explain it better, I am going to use numerical examples. Now let's assume I am using a BPSK modulator and my ...
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102 views

modulate/demodulate audio file as FSK signal mixed with music signal

What I want to do: I want to encode an audio message inside a regular music file; this shall be decoded by an audio analyzer running on another machine (by listening to the audio playback from the ...