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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65 views

BPSK based audio digital communication system

As part of my diploma thesis I'm implementing digital communication system based on audio transmission in free space (STMF401RE + analog microphone). I'm using BPSK modulation and I've implemented ...
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Why is there fear of interference between 5G and airline altimeter C-band?

The C-band frequency range to be used for the 5G-advanced rollout is the US is in the 3.7-3.98 GHz range. Whereas altimeters operate in the 4.2-4.4 GHz range. Is there any genuine reasons to worry ...
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62 views

What is the result of taking the real part and imaginary part of a complex signal in the frequency domain?

Suppose that $g(t)$ is a lowpass complex signal with magnitude (solid line) and phase (dashed line) To modulate $g(t)$ into a bandpass equivalent signal $f(t)$ with center frequency $f_c$, we compute ...
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73 views

BPSK consecutive same symbols

I have a question regarding BPSK. If we want to modulate the bit stream $[0, 0]$ with $T_\text{ bit}=0.25 \text{ sec}$ and the carrier frequency of the cosine that carries the BPSK signal is $2\ \rm ...
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1answer
57 views

Impulse response of Time Varying Channel

I have just started studying LTV channels in wireless communication. I know that $y(t) = \int _{-\infty} ^\infty x(t-\tau)h(t,\tau)d\tau$ Is there any way we can calculate the Impulse response $h(t,\...
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time division duplexing (TDD) with USRP B2xx

I am going to implement a real-time TDD link (in the order of one-millisecond burst durations) using two laptops and two USRP B2xx (in either single antenna or dual-antenna ways). I searched a lot on ...
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28 views

GNU Radio and USRP audio source problem

I have a modem which accepts a voice in GNU Radio, digitizes and compresses it (codec2) and transmits it using USRP on one laptop and receives it on another laptop. When I use "Wave File Source&...
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64 views

Scalar vs Vector signal Quantization

I am studying about scalar vs vector quantization, and I have an assignment to implement (in MATLAB) a scalar quantizer , using the Lloyd-Max algorithm, and a vector quantizer via k-means clustering. ...
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2answers
41 views

Confusion In DC power,Average Power,Ac Power and total Power

These are Things I studied. $ E[X]:-$ THis gives us Average value or Dc value $E[X^2]:-$Total power $\sigma^2=E[X^2]-E[X]^2$:-Ac power From Autocorrelation $R_x(0)=E[X^2]$--Total power And $ \lim_{x\...
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1answer
34 views

MAP (BCJR) Algorithm with channel LLRs

I have a question about the decoding of convolutional codes with the MAP (BCJR) algorithm. Let $\mathbf{u}$ denote the uncoded bits and $\mathbf{v}$ is the coded bits. Here is the point! Let $\mathbf{...
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1answer
45 views

How is SNR Calculated in OFDM Reciever? [closed]

Can you please guide me on the information to calculate SNR for OFDM Reciever? Is OFDM Pilots used for it? And do we need to follow channel estimation like steps of interpolation to determine it? I'm ...
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41 views

What's practical interpretation of showing DC Offset in frequency domain?

In homodyne reciever, we read about LO Leakage causing DC Offset. Say my output at downconversion is in analog voltage range +5 and -2, and there is a DC offset of 1 unit So, it can be added right? To ...
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26 views

Find the unit-energy for $\mathrm{rect}(t/T)$?

My book says: The width-1 NRZ pulse is $$ \mathrm{rect} (t) = \begin{cases} 1 , \qquad -1/2 \leq t \leq 1/2\\ 0, \qquad \mathrm{otherwise} \tag 1 \end{cases} $$ The unit-energy width-$T$ NRZ pulse ...
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OFDM Query : Why In Phase and Quadrature Phase RF Conversion is needed? [duplicate]

OFDM Basic Query- x[n] produced at output of IFFT is in discrete time, so we can use DAC and then RF Upconversion (multiply it with LO Frequency say f) and send it, why are we doing RF up conversion ...
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16 views

GNU RadioTagged Stream: How to clip the stream as "packet length" tag long

I am currently trying to develop a GNU Radio block which takes a tagged stream as an input. The tags keeps the length of the packets. But the distance between the tags and the packet length are not ...
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1answer
77 views

Premier Signal Processing conference

I am interested in the following area: Digital Communications and Signal Processing, especially used for VLSI design of communication systems. (Some sub-topics may be MIMO communications, channel ...
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MIMO Noise Power Calculation Using SNR

i'm in the process of simulating a MIMO-OFDM transceiver, in which we have $N_T$ transmit and $N_R$ receive antennas ($N_R \geq N_T$), as shown in the image below for the 2x2 case What i'm having ...
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1answer
51 views

Simulating Es/N0 by adding noise to analog signal

I believe I am familiar with simulating $E_s/N_0$ by adding noise to the output of the matched filter, but what would be the correct way to simulate $E_s/N_0$ starting with the analog signal at the ...
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1answer
40 views

Did Dialup Modem use closed or open loop power/volume control? How did they determine Tx level?

I have been reading about dialup modems, but one thing I cannot seem to find out about is how implementers determined optimal transmit power/volume. Is this part of the echo cancelation framework? The ...
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1answer
37 views

On-Off keying for wireless communication channel estimation

Let us assume I have $k$ (a fixed number) sensors in a wireless sensor network with unknown channel statistics $\{h_1,h_2 \ldots, h_k\}$. In my system model, each of these $k$ sensors has an ...
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1answer
22 views

Find the band pass signal for a given low pass range and cutoff frequency?

We know the fact that a bandpass signal is defined for real values. But for a typical scenario where we have a signal in the lowpass range:say : 𝑥𝐿(𝑡)=𝑗𝑋0 sinc(Bt) and the transformation of the ...
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22 views

what relationships between time sequence and nyquist bin or Dc bin?

I worked on fft recently, and I found kiss_fft code have some comments I do not understand. The sum of tdc.r and tdc.i is the sum of the input time sequence. yielding DC of input time sequence The ...
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45 views

Coherent detection in fading channel

I want to design an optimum receiver for a fading AWGN channel for ML Detection. I know that in the case of non-coherent communication we have to use an energy detector(even when the fading channel is ...
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33 views

Parsing downlink cellular towers signals

I want to parse signals coming from 4G/5G towers to extract only the ID of the tower and the transmission time (on simplex communication: only downlink). Are these packets (or frames) sent on a ...
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3answers
133 views

Do BPSK vs QPSK have the same performance?

I'm trying to re-learn digital communication theory again and am creating a bit error probability simulation for various modulations. So far I've added BPSK, QPSK, and 8PSK and below is a plot that ...
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25 views

BER for DPSK with decision regions

In this response https://dsp.stackexchange.com/a/79258/235, the calculation for the BER of an 8-PSK is performed. Can we use the same method for a differential modulation (DPSK) for example DQPSK? I ...
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34 views

How to calculate BER of M-ary PSK? [duplicate]

I want to find the BER of 8PSK. The way I learned is to divide the 3 bits to 1 bit at a time to find the error rate and then average it. The first bit and second bit were obtained by separating and ...
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1answer
50 views

GNU Radio, Frequency Hopping Spread Spectrum for High Hopping Intervals

I am planning to implement a frequency hopping spread spectrum transmitter and receiver in GNU Radio. In my project, the bandwidth of the message signal is around 200 kHz and the maximum frequency ...
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1answer
50 views

narrow-band and wide-band

My question concerns the definition of a narrow-band signal and a wide-band signal. To determine the nature of the signal, the following relation is used: $\alpha=\frac{B}{f_c}$ where $B$ is the ...
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24 views

How is uplink MU MIMO established

My question is more suitable for communication but im trying here. If you guys think there is a better suitable place please let me know. I understand the concept of DL MU MIMO in the sense that a ...
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6answers
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How can I work on DSP using C/C++?

I have been working on MATLAB for signal processing for a while. Many companies from DSP for a communication background has asked me whether I know C/C++ very well. I am confused as to why the ...
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1answer
75 views

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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28 views

multiuser communication and SNR

The signal received from an uplink communication is given by: $r(t)=\sum_{i=1}^{K}s_i(t) \ast h_i(t,\tau)+n(t)$ where $K$ is the number of users, $s_i(t)$ is the signal for the user $i$, $h_i(t,\tau)$ ...
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1answer
39 views

Requirements on Signal Spectrum for Fractionally Spaced Equalization

I'm constructing an ultrasonic communication system and I am struggling with the correct parameters for my receiver. In baseband, my channel input signal $x(t)$ has infinite bandwidth, since I use a ...
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1answer
22 views

SIMO for the binary message

Normally, the SIMO system sum is applied on reception. For example for a Gaussian channel with $p \in [1,R]$ antennas we have: $$r_p(t)=s(t)+n_p(t)$$ with $n(t)$ the gaussian noise. $$s(t)=\sum_{k=1}^...
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2answers
37 views

OFDM SubCarrier and its relationship with IFFT in context of Real and Complex

In the process of OFDM Signal generation. We take symbols (constellation symbols) and map it to a sub-carrier (real analog time domain) harmonics of 15khz, add different sub-carriers separated by ...
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1answer
52 views

Doesn't use of Duplexer in FDD system limits it's capability?

I read FDD has separate Rx and TX frequency to operate on, so it can work simultaneously and do Receive and Transmission. When I use Duplexer ( I read Duplexer needed if we want a single antenna to do ...
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1answer
25 views

Log Path Loss Model with Directivity Accounted

Suppose that I have the log Path Loss distance model described here https://en.wikipedia.org/wiki/Log-distance_path_loss_model $$PL(d,\gamma) = P_{t}-P_{r}=PL_{0}+10\gamma log_{10}\frac{d}{d_{0}}+X_{g}...
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Derivation of Costas Loop SNR in digital domain

The tracking performance of PLL-based is often expressed in terms of error variance. To take into account the effect of Loop bandwidth, another parameter, called loop SNR is used. Loop SNR for an ...
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1answer
83 views

Efficient Implementation of Digital Upconversion

I have an application where I have a pulse shaped QAM signal, at 2 samples per symbol. I need to take the I/Q samples and perform quadrature upconversion so that they can be output on a DAC that's ...
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1answer
93 views

Find some signal x[n] whose auto-correlation function is R[k] [closed]

I want to write a MATLAB code for generating a random message signal 𝑥[n] where its autocorrelation function is: R[k] = sinc^2 [1/4 k] where k is an integer. (Hint: Generate a process where ...
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1answer
37 views

Relation between SNR and fading channel coefficients?

I am trying to understand the following thing: Does the average signal to noise ratio (SNR) depends on fading channel coefficients ? Any help in this regard will be highly appreciated.
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64 views

Probability of achievable data rate greater than target data rate $\Pr\left[\frac{1}{2}\log_2\left(1+\text{SINR}\right)>R_{\text{target}}\right]$?

I came across this formulation of the probability that the achievable data rate is greater than the target data rate for the NOMA system. $$\Pr\left[\frac{1}{2}\log_2\left(1+\text{SINR}\right)>R_{\...
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1answer
68 views

5G uplink switching from CP OFDM to DFT-s-OFDM

5g NR standards can allow for both CP-OFDM and DFT-s-OFDM in the uplink. Suppose a UE is allocated resources. Can the UE switch from CP-OFDM to DFT-s-OFDM from one slot to the next ? Are these ...
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1answer
107 views

In wireless communications, is it true to say: The more the range, the more the delay spread?

The general idea which can be drawn by reviewing wireless channel models says that the longer the range/distance, the more the delay spread, even in LOS microwave links. But I really wonder why it is ...
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1answer
53 views

How to choose the roots of 4 different Zadoff-Chu sequences? [closed]

I would like to generate 4 Zadoff-Chu sequences. The sequence length is 63. I need to properly choose the roots (r1, r2, r3, and r4) so that: Each root is relatively prime to the sequence length ...
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24 views

How to choose the training sequence for a zero-forcing equalizer?

I am trying to understand how to design N-tap zero forcing equalizer. For the case of 3 taps, I need a training sequence $z[k]$ which I believe can only take the shape of a pulse [0, 1, 0] to ensure ...
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2answers
100 views

Pulse-shaping FIR filter

I understand that pulse-shaping is performed to limit the bandwidth of the transmitted signal, but I would like to know how pulse-shaping can be implemented using an FIR filter.
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1answer
55 views

Increasing Spreading Factor vs reducing FEC rate

This time, I have been reading a lot about how LoRa works and how it is able to achieve such long ranges in non-LOS propagation channels. However, a simple doubt arises regarding the way they ...
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30 views

Related to successive interference cancellation?

I am trying to understand the following query: " Is it necessary to do channel estimation to perform successive interference cancellation at the receiver operating over fading channel" Any ...

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