Questions tagged [digital-communications]

Digital Communication is the physical transfer of data (a digital bit stream) over a point-to-point or point-to-multipoint communication channel.

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1answer
101 views

How does a Huffman encoded message gets unified before channel encoding?

I aim to understand the signal entire transmission pipeline. Currenlty, I am facing a problem regarding the handling of a Huffman encoded message. Example: Message $X$ contains symbols $a(50\%)$, $...
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24 views

How to decide about length of vectors for estimating correlation matrices

I am optimizing a filter $f$ using mean squared error criterion. $$MSE = f^T*(R_{xx}-R_{yx}^T*R_{yy}^{-1}*R_{yx})*f \tag{1}$$ where $x\in \mathbb{R}^n$ input column vector $y\in \mathbb{R}^m$ ...
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1answer
365 views

i.i.d Raleigh distributed T tap frequency selective channel

A Single-tap 'flat Raleigh fading channel' is implemented as. ...
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1answer
373 views

OFDM Transmitter knowledge

I have some questions regarding some concepts used in designing the OFDM transmitter which i got from different literature reviews but i got mixed up with these concepts. • The N-Ifft points and ...
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2answers
74 views

Why the correct probability for a square M-QAM is equal to the square of correct probability of ($\sqrt M$)-PAM?

The question is why: $P_c (\text{square} $ $M-QAM) = (1 - P_{\sqrt M})^2$ where: $P_{\sqrt M}$ is the error probability for $\sqrt M$-PAM signal. Thanks.
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1k views

QPSK using Root Raised Cosine Filter

The implementation of QPSK requires 2 orthogonal basis. So when using root raise cosine filter to implement QPSK, what is the 2 orthogonal signals?
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3answers
1k views

Bose Chaudhuri Hocquenghem (BCH) vs Reed Solomon (RS) Error correcting codes and sound transmission channel modeling

I've implemented an acoustic based information transmission system using a bandwidth of 2 kHz and the band between 18.5 and 20.5 kHz. I'm trying to find the best error correcting code for it, in the ...
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3answers
1k views

Real-time BPSK demodulation

I am currently studying BPSK demodulation. Most probably my question very basic but i am having difficulties to understand the case of real-time bpsk demodulation. Basically, all the examples (matlab,...
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1answer
551 views

Digital signal and frequency analysis

I am generating a digital signal with software. I have defined the vector $$[0,1,1,1,0,1,0,1,0,1,0,0,0,0,0,0,0,0,0,0] $$ and my sampling rate is 8 million per second. The frequency spectrum is ...
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1answer
283 views

Beginner's guide to OFDM

As the title suggests, I'm a bit of a dummy, and utterly perplexed by the concept of OFDM, overlapping the carriers at the clock nulls and somehow magically not creating an unusable amount of cross ...
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1answer
107 views

How to equalize an ISI channel when the transmitted symbols are unknown?

I am using MATLAB to simulate transmission of binary data sequence, $\mathbf{x}={x_k\in\{+1,-1\}\forall 0\leq k\leq N}$, over an ISI channel whose impulse response $\mathbf{h}=[h_0 h_1 \cdots h_{\mu}]$...
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1answer
141 views

What is 'antenna-chain permutation' and its advantages?

I am working with Wi-Fi channel state information (CSI, a sort of channel matrix with OFDM subcarriers). I am using Intel 5300 Wi-Fi card and this tool provides a way to play around with extracted CSI ...
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1answer
479 views

How to convert the mean and variance of a processed received signal into a SNR or BER?

So I'm trying to eventually get some sort of signal quality metric, and to do that, I'm trying to take the mean and variance of my bit determination signal and use that to come up with a Signal to ...
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2answers
781 views

Difference between diversity gain and coding gain

I am reading about space-time codes. They break down further into 2 sub categories called space-time trellis codes and space-time block codes. It says that trellis codes offer both diversity and ...
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0answers
94 views

Received signal envelope PDF to power PDF [Wireless Communications]

I am deriving the probability density function (pdf) of the received wireless signal envelope in multi-path fading channels. I wish to transform this envelop PDF to the power PDF of that signal. I ...
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1answer
224 views

What are the types of noise (FM,AM, MSK modulated) that I can use for jamming GSM signals?

I need to jam GSM signals in-order to prevent mobiles in near-by vicinity from connecting to the BTS. I am employing a noise based jamming strategy. What type of noise will be most appropriate for ...
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2answers
571 views

MIMO channel capacity being complex?

I'm considering the following simple system model: $$\mathbf{y}=\mathbf{Hx}+\mathbf{n}\quad\textrm{with}\quad \mathbf{n} \sim \mathcal{CN}(\mathbf{0},\mathbf{I})$$ The resulting MIMO channel ...
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0answers
95 views

Blind coarse OFDM frequency estimation

Is it possible to blindly estimate a coarse carrier frequency offset of an OFDM signal where $\lvert f_{\rm off}\rvert > \frac{\Delta f}2$, where $\Delta f$ = subcarrier spacing? Blind is defined ...
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1answer
323 views

How to derive $r(t) = c(t) \circledast \frac{1}{2} h_b(t, \tau)$?

Consider a linear time-variant channel. The transmitted signal is $x(t)$, the channel impulse response is $h(t, \tau)$, and the received signal is $y(t)$. Then $$ y(t) = \int_{-\infty}^\infty x(\tau) ...
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2answers
219 views

Why does AFSK only trasmit in binary?

According to Wikipedia, audio frequency-shift keying (AFSK) is done by using binary FSK, i.e. 2 tones of different frequencies, a tone for the 1 bit and a tone for the 0 bit. But isn't it possible ...
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1answer
8k views

What is difference between the terms bit rate,baud rate and data rate?

Let us consider any video signal. Bit rate of a video signal is the no of bits per frame per second. Also, data rate is the no of bits per second. Baud rate is the number of signal changes per second....
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2answers
397 views

What is the relation between noise (AWGN) variance and number of antennas?

I'm working in two Matlab scripts trying to simulate a MIMO system using OFDM (downlink) and SC-FDE (uplink). My question is: for different numbers of transmit and receive antennas, what is the ...
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1answer
2k views

MFSK vs FSK: Why BER decreases increasing the symbols

My question is related to the performance of 2-FSK modulation scheme against M-FSK (M > 2). From the SNR vs BER curve it seems that as the number of tones (frequencies) increases the BER decrease for ...
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2answers
328 views

Total bandwidth in a network calculation

I have data on the number of devices in a wired network and the data rates on links among these devices. I also know the positions of these devices from which I can compute the distances between the ...
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3answers
6k views

What is the need for prediction filter in PCM and DPCM?

The DPCM works by the difference between actual samples and predicted samples. If we already have the actual samples, we can quantize it and encode it later. But why we use prediction filter? And ...
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1answer
2k views

Energy per bit ($E_b$) in BPSK with non-unity channel gain

I would like to know what is exact and correct definition of $E_b$ (energy per bit) in digital communication. Consider I have a model such as r=a*x+n where <...
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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 ...
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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 ...
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1answer
297 views

Finding $E_b/N_0$ when coding rate is $R_c$

I would like to calculate $E_b/N_0$ when the code rate is $R_c$ for BPSK signal. What I got this $$ E_b/N_0= \frac{1}{2R_mR_c \sigma^2} $$ and that is the case also according to this page. $R_m=1$ ...
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2answers
662 views

Relationship between $E_b/N_0$ and $\rm SNR$ with channel coding

I would like to know what would be the relationship between $E_b/N_0$ and $\rm SNR$ when there is a coding rate of $R_c=K/N$. Normally when there is no channel coding according to this link. $$\...
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2answers
7k views

How to reconstruct RF signal using IQ data

I have a complex IQ signal: $s = X + Yi$. I know my original $f_0$ was $5\textrm{ MHz}$. I can calculate the magnitude/amplitude of $s$: $A = \sqrt{X^2 + Y^2}$ and phase, $\phi = \arctan\left(\frac ...
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1answer
1k views

Properties of root raised cosine filter

In communication systems, the transmitted signal is often passed through a root-raised cosine filter to avoid, in textbook language, intersymbol interference (ISI). An identical filter at the receiver ...
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3answers
2k views

FFT of BPSK signal interpretation

I am plotting spectrum of BPSK signal just series of -1 and 1, and I can see random peaks (looks to me to be random) at various locations but I am really confused if I do not multiply my signal by ...
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1answer
141 views

Adding AWGN noise with certain power

Assume I have a signal(BPSK) and it has a certain amplitude. I would like to add a noise with a certain power to it. Assume I am using coding rate Rc as well. One method I am thinking would be to ...
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1answer
694 views

Does a matched filter give a gain in SNR?

I am trying to know if filtering a sequence with a matched filters gives a gain equal to the sequence length, he are the calculus, is it correct ? In my model $s$ is a deterministic complex sequence (...
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1answer
66 views

Difference between sticky channel Poisson-repeat channel

I don't quite understand the difference between a sticky channel and Poisson-repeat channel. A sticky channel allows duplications of symbols sent over the channel, then the block structure at the ...
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1answer
4k views

Understanding what channel gain is and why it is important side information

I have a two part related question. Channel gain is often being considered the side-information that the Rx and Tx usually know. Why is channel gain such an important side-information? And second, ...
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1answer
4k views

Phase synchronization in BPSK

In BPSK for demodulation at the receiver end we do phase recovery between received wave and carrier wave. We can find the phase difference between the carrier and received waves using : PLL And ...
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0answers
219 views

How to find frequency and phase shift in the recorded wave( .wav file )

I am working on BPSK at frequecies near 20 kHz with a sample rate of 44100 Hz. We can't afford sample rates above than this due to computational complexities. Have found that the frequency of ...
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2answers
900 views

Fast/efficient way to turn real passband samples to complex baseband

I have real-valued samples of a bpsk signal i am receiving (see frequency spectrum in figure A), that I want to turn into complex samples for further processing. However when I just use the received ...
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1answer
223 views

Why does signaling overhead for time synchronization scale up with the number of transmitter nodes in a multiple access system?

I was recently reading about random multiple access methods without time synchronisation (of the pure Aloha type). In this paper it is stated that, The need for transmitter synchronization is a ...
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1answer
188 views

Periodically-varying phase between transmitted sound and received sound

I have a function that can find the phase difference between two signals, this function uses Hilbert transform to do so. Here is the python code for it ...
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1answer
116 views

Advantages of 2-VSB vs BPSK?

Both BPSK and 2-VSB transmit one bit of information per smybol and both modulate the real part of the signal. The difference is, as far as I understand, that BPSK does not modulate the imaginary part ...
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2answers
3k views

Why are QAM Constellations regular and rectangular?

In most IQ graphs of QAM noise, it seems like the constellation ends up with more distortion the farther you get from the center: What causes this non-linear distortion, and why are QAM ...
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1answer
817 views

Problem in understanding DDFS (Direct Digital Frequency Synthesizer.)

I need to generate sine and cosine signals using DDFS (Direct Digital Frequency Synthesizer.) I'm unable to get the idea of the phase increment applied as input which changes the frequency of the ...
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1answer
2k views

Location of Matched Filter

In a digital communication receiver, matched filter(SRRC filter) is used. In different literatures, the location of the matched filter is mentioned in two different places. One is just after the ADC ...
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2answers
414 views

Visible light communication and LED modulation

I work on a VLC system in which 16-PAM symbols with complex pilot symbols are as ifft input. I made the ifft output real and positive. Now how should i use these ofdm symbols to modulate LED? Their ...
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1answer
1k views

Sampling signal after root raised cosine

I am generating series of 1 and 0. then pulse shaped them with root raised cosine and after than deciding to do match filtering and recovering the bits however it turns out that I am not getting the ...
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1answer
268 views

How to find a know signal in another signal which contains other signals along with the signal i need in python

I am working on BPSK with sound waves a carrier waves. Actually I am modulating my data with some known sync bits along with the information I need to send. So the things I will be having at ...
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1answer
104 views

How to find the time instant where my sent signal and received signal can synchronize?

I am having two .wav files, one is modulated wave that is made into a .wav file and another is a recieved .wav file which is recorded from microphone while playing first modulated .wav file. So now ...

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