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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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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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DSSS — Why does bandwidth increase when modulating with a chipping sequence?

Here is an example image: Why does the bandwidth increase when modulating the carrier with a chipping sequence. All it's doing is phase shifting the carrier sinusoid with -1 and 1 more frequently. ...
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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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Phase Modulation

a phase modulator produces a maximum phase shift of 45 degrees. The modulating frequency range is 300 to 4000hz. What is the maximum frequeny deviation possible. How and what formula do I use to ...
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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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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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78 views

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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48 views

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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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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56 views

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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103 views

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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40 views

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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107 views

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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37 views

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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293 views

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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107 views

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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4answers
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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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2answers
637 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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138 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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2answers
156 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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2answers
159 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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1answer
36 views

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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897 views

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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452 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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49 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 ...