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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60 views

frequency/phase offset estimation in satellite DOA beamforming applications

In satellite QPSK demodulation, we first estimate and remove the phase offset introduced by the channel. Then, we demodulate the baseband information bits (I & Q channels). In satellite DOA ...
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15 views

Should the correlation check should happen at the start of the receive chain?

Should the correlation check should happen at the start of the receive chain. does it act like a start of burst data? But does phase and freq offset has any effect on this? or should it happen at bit ...
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Capacity and BER as performance of transmission system

We study the performance of the transmission system by channel capacity or BER/SER. If the system performance is studied as BER/SER, does it make sense to study a channel capacity?
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Do we need Channel estimation prior to (time domain DFE or linear) adaptative equalization in single tone transmission?

If we are to transmit a single tone signal over a channel impaired by inter symbol interference and awgn, and if the equalization is adaptative (LMS/RLS track) and is done in time domain by LE (linear ...
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How to demonstrate the orthogonality of OFDM subcarriers?

Assume if we have $N$ OFDM subcarriers represented by results of the inverse FFT of $N$ data symbols $\mathbf x$. As I know, the subcarriers of OFDM should be orthogonal. It means that $$X(n)X(n+1) = ...
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281 views

QPSK Phase Recovery : Maximum-likelihood Vs Costa's Loop

I have implemented a QPSK Costa's loop in GNU Radio and run some BER benchmarking. All is going well. Out of curiosity, I'm trying to implement the Maximum Likelihood phase recovery shown below. For ...
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1answer
89 views

Use of the harris-Moerder Nyquist Pulse Shaping Filter

I became aware today through fred harris' excellent presentation at the DSP Online Conference (https://www.dsponlineconference.com/) of the harris-Moerder pulse shaping filter which was published 15 ...
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1answer
369 views

Getting hilbert transform of IQ signal

Im new to communications so this may be a stupid question, but I am somewhat confused. I am trying to train an automatic modulation classification (AMC) algorithm on IQ data from the RadioML dataset. ...
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Why is the noise on an eye diagram not in the centre i.e. at 0?

I don't yet completely understand eye diagrams. Why isn't the noise in the centre of this polar BPSK diagram and instead are 2 margins at -4 and 4.. surely that's not where the noise would be in ...
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41 views

Multipath channel estimation in single carrier modulation

I think it’s a basic question, but I couldn’t get it’s clear answer. If we have data symbols $x$ vector of length $N$ x $1$ ; it’s convoluted with a multipath channel $h$ of length $L$ x $1$; the ...
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55 views

Inter Channels interference in MIMO system

If we have MIMO system with $2$ transmit antennas, ($T_1$ and $T_2$) and $2$ receive antennas ($R_1$ and $R_2$). The received signal of the first received antennas can be explained: $r_1$ = $h_{11}$$...
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Decoding packets in Long Mode Range

Im using CC1350 launchpad microprocessor of Texas Instrument that I configure my transmitted packets using SmartRF studio Im trying to decode my packets for verifying if my transmitted packet is valid ...
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Non Coherent BPSK with no Channel State Information at the receiver

Where or what is the proof for the failure of BPSK in fading channel when we have no knowledge of the fading coefficient $h$ at the receiver in the equation $y=hx+w$, where $x$ is BPSK symbol equally ...
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81 views

QAM Amplitude Levels

I'm working on a project to stream video between 2fpgas by using QAM. While mapping symbols with different amplitude pulses(PAM) a question popped up in my mind. In real life how does communicating ...
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2answers
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What are the practical constraints on designing Sensing matrix in compressed Sensing?

In a typical compressed sensing scenario, $y=Ax$, where $x$ is a sparse signal and $A$ is the sensing matrix. To reconstruct the sparse signal $x$ from $y$, $A$ should posses the Restricted Isometry ...
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FSK technique to superpose the digital communication on top of 4–20 mA signals

I start a working with HART devices and I really try to understand how digital data is transferred trough 4-20ma current loop. I start read this article: https://instrumentationtools.com/hart-...
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How to encode binary sequence if the number of bits are odd to e.g. 4-PAM? (Beginner)

I'm new to signal constellation and trying to understand how M-PAM works. If there is a binary sequence that has on odd number of bits and I want to send a 4-PAM signal, there will be one bit left ...
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29 views

Quantization types

Suppose i have input sequence {-1.3,1.2,-0.2,-0.5,0.4,0.89,1.3} Which are uniformly quantized through a quantizer having range (-1.5,1.5) with 4 levels My calculted answers for- First method:mid rise ...
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29 views

μ-law compression technique

In μ-law compression formula i have always seen that the value of Xmax and Ymax is always same but can they be different?
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SNR of μ-law companding

I know the snr after μ-law compression is $\text{SNR}\approx\frac{3L^2}{[\ln(1+ \mu)]^2}$ when $\mu \gg \frac{\max_t m(t)}{\text{rms}(m(t))}$, where $m(t)$ is the message signal, and $L$ the number ...
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37 views

Quantization processs

In a quantization process what happens when the signal range is more than the quantizer range? Suppose i have a sinusoidal signal which ranges from -5 to +5 but the quantizer which has four levels ...
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27 views

Received signal's power under Raleigh fading

I am trying to understand how to calculate the power of a received signal under Raleigh fading. What I gather is that the Rayleigh fading is a complex Gaussian random variable and that the multipath ...
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Self-correlation vs Digital frequency: figure from paper

In the paper, is discussed a MIMO-OFDM system over the frequency self-correlation of i.i.d. Rayleigh channels and subcarrier grouping. in this paper is shown the following figure. it shows the self-...
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How to infer mathematically if the transmission error is correctable after applying Longitudinal and Vertical Redundancy Check LRC,VRC?

I have the following message in binary: Transmitted Message: 1 | 0 | 1 | 1 | 0 | 1 1 | 1 | 0 | 1 | 1 | 0 1 | 1 | 0 | 0 | 1 | 1 1 | 0 | 1 | 0 | 0 | 0 Received Message: 1 | 1 | 1 | 0 | 0 | 1 1 | 0 | 1 | ...
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50 views

BPSK and QPSK demodulation computational complexity

I wanted to ask about the real operations of BPSK and QPSK demodulation. How can we calculate it? I mean for example if I have a received symbol +0.6, then I need to demodulate it to be 0 or 1. what's ...
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Series Sum Operator Properties and Identities

As I was reading my book, I came across the following expression: \begin{equation} \sum _{n=-N}^N\sum _{m=-N}^N \phi \left(n-m\right) \end{equation} Then the book said, if we let $k = n-m$, then: \...
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1answer
34 views

CFO estimation and compensation

I am reading about CFO estimation in OFDM system, assume for example that we estimate it based on CP as mentioned HERE and the estimated CFO for the received signal $r(t)$ is $β$. My question, how now ...
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69 views

Signal bandwidth and channel bandwidth

I have a channel bandwidth $B_c$ and a signal bandwidth $B_s$ with $B_s<<B_c$. What is the problem when the signal bandwidth is smaller than the channel bandwidth? For example, my channel ...
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403 views

BER vs SNR for PAM2

Many sources describe the BER vs Eb/N0 as $$ \mathrm{BER} = 0.5 \operatorname{erfc}\left(\sqrt{\frac{E_b}{N_0}}\right) $$ I can verify this relation with (modified from krishna@dsplog.com): ...
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61 views

Estimation algorithms for Multi-User MIMO

I am interested in a question how to estimate a channel/symbol in a multi-user system. In the case of a single-user, it can used ZF/ pilot estimation/ MS/ LS algorithms. Do we have a difference in ...
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In a communications system does the order of channels is in a cascaded channel affect the overall capacity?

I'm currently looking at capacity for cascaded channels as part of my Communications Systems module and we're looking at a question in which we have four identical channels represented by the ...
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Design RRC filter [closed]

I have designed a RRC filter, as below : ...
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47 views

OFDM time-domain equalization

I am working on OFDM, and recently I have read a new type of OFDM called TDS-OFDM, where they guard interval is not neither zeros nor CP. It's a pseudo-noise inserted between symbols. The structure ...
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32 views

What can be a limit to the maximum possible power of a pilot signal

In practice, what can be a limit to the maximum power of a pilot signal in wireless communication?
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38 views

the best pre emphasis for MMSE equalizer

The system consists of multiple low-pass filter and noise, $h_1$, $h_2$, $h_3$, ..., $n_1$, $n_2$, $n_3$, ... At the transmitter, the power of signal is fixed; and at the receiver, MMSE equalizer is ...
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Doopler spread and delay spread in an equation of channel freq response

Assumed the transmission system with channel impulse response is determined by the matrices $H(\tau_l) \in C^{N_R \times N_T}$ ( $N_R$ and $N_T$ are numbers of received and transmit antennas) By ...
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2answers
25 views

transmitting the real/imaginary parts of pass-band signal

As I know, the transmitted pass-band signal whose carrier frequency is $f_c$ can be written as follow: $s_1(t) = \text{Re}(a(t)e^{j2πf_ct})$ , where $a(t)$ is the complex modulated base-band signal. ...
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BW of a modulated signal

I come across different types of bandwidth. In digital modulation should it be null to null always? when do we use 3 db bandwidth?
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autocorrelation peak

Let $s(t)$ a signal of duration $T_s$ on a bandwidth $B$. The matched filtering of this signal gives: $R=max|s(t) \ast s^{\ast}(-t)|$ and here theoretically I saw that $R=BT_s$. But does anyone know ...
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Relation between ICI and EVM in OFDM System

in an OFDM system with ICI, how can I calculate the ICI power using the error vector magnitude (EVM) constellation? thanks
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differential modulation and reception

I use a differential modulation with a SIMO system. At the reception, I have $2$ antennas.To find my symbol, I use the relation $r^{\ast}_i(n-1)r_i(n)$ to have the phase of the symbol with $r_i(n)=\...
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102 views

Differential Encoding for M-PSK

Confused about a few topics w.r.t. differential encoding/decoding. First, consider the below BER curve taken from wikipedia ( https://en.wikipedia.org/wiki/Phase-shift_keying ) comparing BPSK/QPSK and ...
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22 views

Resource block size in freq-selective channel

I asked about the basic of a frequency selective channel [here][1]. It was discussed Resource block (adjacent subcarriers and time indices together into "chunks") what parameters affect the ...
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“How is the noise floor of RF section is mapped to ADC noise floor for a 10MHz BW?”

My interpretation is if a gain of 40 is used before AGC -40 dBm become 0 dBm and -121dBm (noise level) becomes -81dBm SNR remain same (assuming NF =0 for theretical purposes). Noise floor of ADC is (6....
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Do we have to insert the DC null in OFDM when using RF direct sampling ADC architecture?

Generally, DC Nulls are added in OFDM because zero-IF receivers don't pass the DC component. But what if I use an RF direct sampling architecture? Will there be DC offset? If not, then is it okay not ...
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Legacy LongRange Mode information (mode 1 in the my attached link)

Mode 1- Legacy Long Range Packet Format and Im attaching a photo of ti reference: link for more information about this mode category : TI SWRA642 I want to understand the packet format, what's my ...
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71 views

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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A communication system

I am solving the following problem as an exercise. I have a signal $$z(t) = x(t)\cos(wt) + y(t)\cos(ut)$$ and we assume $x,y$ to be band-limited continuous time signals. In the frequency domain we ...
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2answers
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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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49 views

system bit rate vs channel coding

We are usually asked about the full system bit rate. However, we use channel encoding in practical systems, for example conventional coding with rate $(1/3)$. My question is about the full system bit ...

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