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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5
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3answers
225 views

Why are we always interested in mean-squared distortion?

When dealing with quantizers, and in many other communications problems, the interest is usually on the mean-squared distortion or mean-squared error, rather than mean absolute error or anything else. ...
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1answer
37 views

Receiver for low data rate

I am working on satellite receiver burst mode I am trying to build receiver. My data rate is typically 10kpbs. As the data rate is low and carrier frequency offset may also be around 10kbps so i have ...
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1answer
43 views

Damped spring mass system - parameter estimation

I've tried to calculate the parameters of a damped spring mass system of the form $m~ y''(t)+d~y'(t)+c~y(t)=F(t)$ but I have some problems determining the mass m of the system. The damped ...
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1answer
66 views

Carrier frequency offset

Can i track any frequency offset my increasing samples/symbol. For example if my symbol rate is 1Msps. If my sample rate is 10 Msps. Can my receiver correct upto 5 Msps carrier offset using FFT I can ...
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1answer
41 views

Carrier recovery samples

Should carrier recovery be done always 1 sample per symbol? This is ok if carrier recovery is before timing. But Nco inside carrier recovery may work at higher rate If my carrier recovery is first ...
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1answer
41 views

I/Q plane plot understanding?

I am experimenting with some signals. I ma generating a 2.47 Ghz signal from signal generator and receiving it by an SDR (LMS7002m Rf chip) with Rx frequency tuned to 2.47 GHz. Upon plotting the ...
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0answers
25 views

Resampler and PLL reference document

can anybody suggest good documents on resampler for TED and PLL by which i can understand basics because there is lot of confusion for resampler and PLL
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1answer
61 views

Pi/4 dqpsk carrier recovery

I think we don't have to do carrier phase recovery. Do i need to do carrier frequency recovery. My symbol rate is high around 2 MHz so i am thinking carrier freq offset is less compared the symbol ...
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1answer
25 views

Question about a diagram of PWM detection

I have this diagram in a book(taken from Slideshare for clarity) as described in the book PWM is put on the differential to obtain A(as starting of pulse) and B(as the end of pulse) The A is used to ...
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1answer
49 views

burst qpsk demodulator

i am working in burst qpsk demodulator i just want to double check if what i am doing is right large frequency feedforward recovery by fft carrier recovery costas with 4 samples/symbol timing ...
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1answer
52 views

Carrier and timing offset

Assume my reference is 1 ppm so if my transmit frequency is 400 MHz and symbolrate is 100 kHz. Then, my carrier will have +/- 400 Hz offset and then my symbol will have +/-0.001 Hz offset. Similarly,...
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1answer
50 views

matched filter position

I have seen that matched filter should be used in TED (gardner loop) after resampler ...
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1answer
29 views

SNR estimation prior to demodulation?

What are the standard ways to measure SNR, particularly before demodulation/synchronization?
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0answers
10 views

Is the SWIPT technology not the good method to increase the life of using battery?

Is the SWIPT( simultaneous wireless information and power transfer ) technology not the good method to increase the life of using battery? Because I design the Full duplex system with three device,...
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1answer
33 views

How many bps would be required to reproduce the words in speech recognizably?

In Robert Gallager's lecture notes for 6.450 Principles of Digital Communications I, Exercise 2.1 asks an interesting conceptual question: Voice waveforms could be converted to binary data by ...
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0answers
36 views

Block CMA algorithm

The Constant Modulus Algorithm is a common equalization method which adapts at every sample in an attempt to give a filter which produces a fixed power output. Divergence/convergence of the CMA ...
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1answer
30 views

Wireless communications outage

For communication systems, there is usually a target minimum rate $R$ bits per second. An outage occurs if the actual rate ever falls below $R$. Since $\frac{1}{2}\text{log}_2(1+\text{SNR})$, ...
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0answers
22 views

why if I want to create a rayleigh fading channel with $E[|H_{i,j}|^2]$,I should multiply $\sqrt{\frac{1}{N_R \times N_T}}$?

I want to create a rayleigh fading channel,and my classmate told me that I can create an $N_R \times N_T $ channel $\mathbf H$ with $E[|H_{i,j}|^2]$,that is,$\sqrt{\frac{1}{N_R \times N_T}}\times CN(0,...
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1answer
22 views

Example of Entropy and Channel Capacity Computation

Can you help me on verifying if this computation of entropy is correct and on understanding its meaning? I am not sure of the result especially because it is equal to 0: it means that we cannot ...
0
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1answer
55 views

NDA timing estimation for mutli-level QAM(RC pulse)

What non-data0aided techniques are used to estimate the timing for multi-level QAM? For single level QAM(so 4 QAM) you can use variance minimization or power maximization but I'm not sure these ...
0
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1answer
23 views

Can we really use equal gain combining in the receiver in the real world?

Can we really use equal gain combining(EGC) in the receiver in the real world? Because we have to know the phase of elements in the channel matrix first before we do the EGC,however,the channel should ...
2
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0answers
72 views

Lagrange Vs Sinc interpolation

I was wondering what is the practical difference between Lagrange Interpolation using Farrow Structure and Sinc Interpolation? Both require pre-computation of time offset coefficients using a lookup ...
0
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1answer
42 views

Zero Forcing Equalizer in ISI channel

I'm studying on designing 9-tap zero forcing equalizer to remove ISI in the channel. I assumed that the channel response is ht = [0.41 0.815 0.41] and I tried to calculate bit error rate. When I ...
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1answer
38 views

Understanding Asymptotic Equipartition Property

I have some problems in understanding the precise meaning of the Asymptotic Equipartition Property, related to a large number n of independent and identically distributed random variables (X1, X2, ...,...
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0answers
31 views

About the post “How to use “Filter” matlab function to apply channel to signal?”

I would like to add my question to the post How to use “Filter” matlab function to apply channel to signal?, but I don't have permission to do that. The user @Anna Koroleva discussed with @Enginner ...
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2answers
46 views

How are CDMA codes distributed?

I think this question is so trivial that it's nowhere explained (I would not find it) and the answer is probably trivial too. But I still wonder how codes in a typical CDMA system are distributed? ...
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2answers
43 views

Definition of Perfect Code (and example of Hamming Code)

Let's consider the following sentences about coding a message before transmitting it in a communication system (here you find the complete pdf) First question: can you explain me these two ...
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0answers
60 views

Understanding and converting Matlab's coarse frequency compensation function

I am trying to understand and convert to C Matlab's coarse frequency compensator the documentation for which can be found here: Documentation Matlab's design itself is based on this IEEE paper: ...
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1answer
19 views

Small Scale Fading time varying or position varying

I would like to ask how small scale fading can affect a transmission with time. The particular system is an antenna transmitting an ASK modulated signal at 915MHz and with bandwidth between 200KHz to ...
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1answer
39 views

Does any paper use energy harvest to in the baseband?

Most of RF energy harvest system just harvest $\rho$ of the RF signal for charging the battery,and the other part RF energy will be processed to baseband signal by RF Chain to do the information ...
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1answer
52 views

Understanding Matlab's Automatic Gain Control function

I am trying to understand the automatic gain control block provided by the communications toolbox. The documentation is here: Documentation My questions are in regards to two of the configurable ...
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1answer
57 views

How to use “Filter” matlab function to apply channel to signal?

I need to use filter Matlab function to describe the following : H: MR x MT ...
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1answer
32 views

Is my concept of receive diversity right? EGC,MRC and SC

Is my concept of receive diversity right?There are three combining technology belong to receive diversity. 1.Equal gain combining(EGC) $\sum e^{-j\theta_k}(\sqrt{P}|h_k| e^{j\theta_k}x[n]+w[n])$ ...
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0answers
24 views

Can we use beamforming to make sure that the signal will not make interference together in Full duplex?if yes,why?

To avoid signals will make interference to each other in full duplex,there are two methods to solve this problem. Time-division duplexing and Frequency-division duplexing,they just use different ...
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0answers
38 views

Length of CDMA code and message length vs. number of participants

What is the minimum code size for CDMA codes for synchronuous CDMA (not asynchronous CDMA!) with N number of participants? Furthermore, suppose N parties want to uniquely transmit a message of length ...
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1answer
83 views

Why do we need to increase sampling frequency at the transmitter?

I've thinking about this for some time now and I was wondering why do we need to increase smapling rate in the transmitter? I will explain a bit more. From the point of view of a software-defined ...
2
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4answers
117 views

instantaneous frequency for a sum

In the literature, the instantaneous frequency for a signal $s(t)=e^{-j \phi(t)}$ is given by: $$f(t)=\tfrac{1}{2\pi}\frac{d\phi(t)}{dt}$$ This my problem: I have a signal $$u(t)=e^{-j \alpha_1 \phi(...
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0answers
20 views

How to prove that my combiner vector is $\mathbf H \vec f $?

When my received signal is $y=\mathbf H \vec f x+\vec n$,they we need a combiner vector in the receiver,how do i prove that combiner vector $\vec w$ is $\mathbf H \vec f $? After the received signal ...
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1answer
23 views

When i have already found beamforming,do i still need to use MRC?i have some problems for them

I have some problem when i learning MIMO,first thing is that i know designing beamforming and MRC can ensure better receive signals,but they are not the same,so i have some question about them. 1.I ...
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0answers
36 views

Matlab Plotting custom constellation along with decision regions

How do I create a custom constellation along with decision regions in Matlab, any help is greatly appreciated
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1answer
58 views

Isn't Gardner's algorithm and Early-Late gate the same thing?

I'm reading about some symbol synchronization methods and I find these two (ELG and Gardner) very similar. Early-Late gate takes 2 samples, one at $t=T-\delta$ and the other at $t=T+\delta$, then ...
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1answer
32 views

Will the received waves be the same if the transmitter use the beamforming to transmit the same signal?

If there is a transmitter with three transmitted antennas,and a receiver with five antennas,and these five antennas are very close to each others. Now transmitter use beamforming with these three ...
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1answer
19 views

What is the advantage of multiple antenna in receiver in energy harvesting ?harvested more power?

What is the advantage of multiple antenna in receiver in energy harvesting ? Assume there are $3$ transmitted antennas in the A device,and $1$ received antenna in the B device,now assume A device use ...
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0answers
27 views

Doubts about Huffman and Shannon - Fano Coding

I was reading these slides about Source Coding and I have the following questions: 1) Let's consider this part: Can you explain me step by step the reasons of a, b, c? Which is the general rule to ...
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0answers
79 views

To determine the Baud rate (in symbols/s) and throughput (in bits/s) of the system

You need to design a data transmission system where the data symbols come from an alphabet A with cardinality 32; all symbols are equiprobable. The bandwidth constraint is Fmin=250 MHz, Fmax=500 MHz. ...
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1answer
26 views

Assumption of SINR measurement

I am assuming there is an Access Point (AP) and IoT Nodes in NOMA uplink scenario. Following is assumed: the AP does not know the channel gain of IoT Nodes the transmission power of nodes is also ...
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1answer
34 views

Relation between frequency and phase in PLL?

Apparently both frequency and phase are independent properties but what is the relation between frequency and phase in PLL?so that when one is locked ,other is also locked
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1answer
60 views

Output of Zero-forcing equalizer doesn't match theoretical calculations

Let's say I have a sequence $x[n]$ (signal) and perform convolution with another sequence $h[n]$ (channel), so: $$ y[n] = h[n]*x[n] = \sum_{k}{h[k]x[n-k]} \leftrightarrow Y(z) = H(z)X(z) $$ I'm ...
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1answer
25 views

Why can we know the best precoding direction after we do the SVD to the channel?

Why can we know the best precoding direction after we do the SVD to the channel?for example $\mathbf y=\mathbf H\mathbf s+\mathbf n$,now we do the SVD to the $\mathbf H$ If the $\sigma _1$ is the ...
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2answers
62 views

Does zero-forcing equalizer need known channel impulse response?

I'm studying some of the basic equalizing structres and I understand how Zero-forcing works, but it seems to me that a known channel impulse response is needed. Am I right? If so, what's the point? I ...

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