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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The error probability of 16QAM
The signal constellation for a communication system with 16 equiprobable symbols is shown as below. The channel is AWGN with noise power spectral density of $N_ 0/2.$Using the union bound, find a bound ...
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High error when adding small value of SFO into the OFDM signal
I am trying to emulate the SFO effect for OFDM system, I did it using linear interpolation as shown HERE . That can be explained as if I have the time domain signal $s_n$ representing the output of ...
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Symbol timing recovery in Python
My objective is to demodulate QPSK signal. At the receiver I apply RRC filter and interpolate the signal to get the values of the signal (approximately) at the sampling instances. Then I am concerned ...
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Matlab code for Simulating of Phase Noise for OFDM systems [closed]
I am trying to simulate phase noise for OFDM systems.
I have been reading about phase noise, some literature suggests that phase noise is cumulative as follows:
$\phi(n)=\phi(n-1)+\omega(n)$
where $\...
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Exact formula for 8-PSK BER
Is there an exact formula for the probability of bit error (or bit error rate, BER) for 8-PSK (in the literature, course slides, etc.)? I am not referring to SEP (Symbol Error Probability) but BER.
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Using MIMO with DS-CDMA and spread spectrum
I have a question about using MIMO with DS-CDMA. suppose we are using 4 TX antennas, and 4 RX antennas, then the Reyleigh ...
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Recursive Least Square Adaptive Linear Equalizer
For the adaptive filter to work properly, a desired signal d(n) needs to be provided. The output from the equalizer y(n) is subtracted from d(n) to produce an error signal, which is used to adjust the ...
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Optimum matched filter without ISI
Given a filter used to shape the digital signal, $p(x)$, and given that we do not want the filter combination to cause any ISI, what "matched" filter, $q(x)$ will maximise the SNR?
Matched filters ...
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Information Theory - units of channel capacity
In a first course in Information Theory, when the operational interpretation of channel capacity is introduced, it is said to be the highest data rate (in bits/channel-use) of reliable communication. ...
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Capacity of AWGN channel
I am confused understanding basic concepts of communication over AWGN channels. I know the capacity of a discrete time AWGN channel is:
$$C=\frac{1}{2}\log_2\left(1+\frac{S}{N}\right)$$
and it is ...
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How to send / receive a short impulse in an extremely noisy signal with high timing accuracy?
I am pretty new to DSP. I need a computer to transmit data to a receiver through audio signals in a loud outdoor environment. (I am writing the software for both sender and receiver so I can design ...
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Which digital modulation scheme would be suitable for transmitting digital data through the output of a PC soundcard
I need to output a data stream at $40\textrm{ kbit/s}$ or faster out of a computer system whose only accessible output peripheral is the audio interface. This interface has reasonable specs, $96\...
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Alternative to Orthogonal Matching Pursuit (OMP) Algorithm
In the Compressed Sensing context, assume there is a signal $ x \in {\mathbb{R}}^{n} $ which is $ k $ sparse. Namely its Pseudo $ {\ell}_{0} $ Norm is $ {\left\| x \right\|}_{0} = k $ (The signal has ...
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BPSK vs $\pi/2$ BPSK, what the benefits?
I have come across modulation techniques that have $\pi/2$ phase shifts from the regular constellations.
For example $\pi/2 $ BPSK vs constellation the regular BPSK.
Other examples include $\pi/2 $ ...
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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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orthogonal family and pulse shaping filter
I am a beginner in digital communications and I have a question on the pulse shaping filter.
For example, I have an orthogonal family $ \{s_1,...,s_N \}$. Can we preserve the orthogonality with a ...
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ADC quantization +thermal noise
ADC noise can affect the overall noise performance of a receiver. The noise is partially quantization noise and partially thermal noise and as a general rule it extends up to the Nyquist frequency = ...
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OFDM training symbol format
For OFDM synchronisation, we are using two training symbols according to the Schmidl and Cox method of frequency synchronization and timing synchronization. The paper says:
The first OFDM training ...
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What does the one-tap equalizer used with OFDM accomplish?
I've read that OFDM normally uses a one-tap equalizer. It seems that a one-tap equalizer could only scale and delay a signal. Why is this useful?
I thought multipath was handled through the cyclic-...
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BT value in GMSK signal equations
I am studying MSK/GMSK modulation technique. Before I posted 2 questions:
subquestion: original Q "Difference between MSK and GMSK?"
subquestion 2 : original Q "Difference between MSK ...
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Value of power spectral density $N_0$ or effect of scaling bandwidth to SNR
I want to compare performance over AWGN channel of two systems that are exactly identical but their bandwidth. I will talk only about baseband system for sake of simplicity. For more details about ...
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Orthogonal Codes for Band Limited Channel
In this question orthogonal family and pulse shaping filter the user asked about possible loss of orthogonality of orthogonal codes due to the use of raised cosine pulse shaping and I showed as an ...
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Power Spectral Density of Digital Modulations
I want to simulate the power spectral densities of different modulations in MATLAB (without Simulink). Unfortunately I have only very basic understanding of signal processing, hence I struggle with ...
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What is the theoretical upperbound of information that could be transmitted by a device per second?
Suppose I would like to stream data from a device in a single second. What would be the theoretical upperbound of the amount of information (in bits, bytes, pixels...) that could be sent during this ...
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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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Computing the decimation ratio between two m-sequences
Let's suppose I have an LFSR that generates an m-sequence $y_1[k]$ --- in other words, the LFSR has $N$ bits and $y_1[k]$ has period $m=2^N - 1$.
Now suppose I know someone has decimated this and ...
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Time recovery algorithm and a symbol with samples
I am working on my graduation thesis. The topic is a receiver implementation in FPGA. I am doing an implementation of symbol timing recovery. For this part I have decided to choose the Gardner ...
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Why Isn't the ML Estimator (MLE) in MIMO Spatial Multiplexing Obtained by the Least Squares Solution?
In the simplest scenario of MIMO spatial multiplexing: $$\mathbf{y} = H\mathbf{s} + \mathbf{n}$$
where: $\mathbf{s}=[s_0,s_1,...s_{M-1}] \\\mathbf{y}=[y_0,y_1,...y_{N-1}]$
$\mathbf{n}=[n_0,n_1,......
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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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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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Average Power Spectral Density of PAM signals
I am reading through the PAM transmission scheme and about the power spectral density of the signals. Given that the Average Power Spectral Density of PAM Signals is:
$$
\Phi_{ss}(f)=\Phi_{aa}\left(e^...
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Offset QPSK detection in GNU Radio - Sample delay
An OQPSK detector is being tested in GNU Radio. The architecture was obtained from Michael Rice's Digital Communications - A discrete-time approach. The flowgraph is shown below.
The modulator ...
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Purpose of interleaving in OFDM systems
Interleaving is often encountered in digital communication systems. I have seen interleaving between codewords in a single OFDM symbols as follows
Assume the bits are denoted by
$$\{c_o,c_1,c_2,\...
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GNU Radio | Transceiver loopback adapted | Transmission stops unexpectedly
(This is a follow up question to a previous question: link)
I have implemented a flowgraph of a transceiver loopback inspired by the examples found at ...
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SNR in analog and digital domain
In the digital domain a higher sampling will have a better SNR.
Similarly does a narrow filter give a better SNR in analog domain?
Once analog signal is converted into digital signal can SNR be ...
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Calculating Data Rate using Bandwidth, Transmission Power, Noise Power Spectrum Density and Channel Gain
I'm a Software Engineering student researching on Load Balancing in IoT and I need to calculate data rate. However, I don't know how to use these values to attain data rate despite searching on the ...
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Low pass equivalent of bandpass white noise
Let
$$n(t) = Re\{z(t)e^{j2\pi f_ct}\},\ $$ where $z(t)$ is the low pass equivalent of white noise $n(t)$. We know the autocorrelation of $n(t)$ is
$$R_n(\tau) = \frac{N_0}{2} \delta(\tau),\ $$
$\delta(...
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upsampling in the frequency domain
I have the Fourier transform $S(\nu)$. If I oversample by a factor $R$ in the frequency domain. Does the duration of the signal $s(t)=IFFT(S(\nu))$ change?
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OQPSK vs QPSK envelope query
We use OQPSK because of envelope of signal but my question is
"In Phase Shift Keying(or QPSK) the amplitude of the transmitted signal is constant then how the envelope will change in OQPSK"??
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Use of equalizers in communication systems for Intersymbol Interference
In communication systems with high data rates, Intersymbol Interference (ISI) is a major problem (ISI).
I have read in books that one way to combat this problem is to use time domain equalizers (ZF, ...
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Understanding time delay estimation for GPS?
I really need help to understand these questions which is highlight, for the GPS situation, I hope anyone who has been working in this situation before, please help me to have a clear understanding ...
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Subquestion: From IQ signal to FM modulated carrier, how its done?
The following post I have gotten as suggestion: From IQ signal to FM modulated carrier, how its done?
1. Mr Andy Walls gave an Octave simulation in his answer. For his phase computation he used ...
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SFBC Alamouti Scheme LTE
A sentence I copied from book.
That a 2$\times$1 Alamouti SFBC is referred to as a rate 1 code, two symbols are sent over two adjacent subcarriers.
This question is regarding this SFBC encoder (...
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General questions regarding OFDM modulation
In Orthogonal frequency division multiplexing (OFDM), data symbols are modulated using an N pt-IFFT operation to produce ONE output OFDM
Assume we have total of $N$ QAM symbols which are input to ...
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Sequence Length for a Linear Feedback Shift Register
What is the total length for the sequence for a linear feedback shift register generated with a maximum length sequence, before repeating?
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subquestion 2 : original Q "Difference between MSK and GMSK?"
if we talk about a modulation, we mention a linear and nonlinear modulation.
GMSK is nonlinear modulation, but it can be derived from a linear modulation as MSK, PAM and we talk about a linear ...
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Why do we do oversampling in raised cosine?
I would like to do know why do we need to do oversampling in a raise cosine filter. There is already a question like this but the answer is very confusing and not sufficient.
I need to know what this ...
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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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What are the advantages of barker sequence over marker sequnce?
I read that barker sequence is used for synchronization among other uses. Barker sequences are rare and they have special properties - this part I understood. I am missing some thing when I think ...
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Apply AWGN noise to QPSK-OFDM symbol
I'm working on an OFDM-QPSK based system and I'm having some trouble to match the BER of my system with the theoretical curve. My OFDM implementation fills all the subcarriers and have t_symbol s ...
