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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64 views

Capacity and channel estimation algorithms: explanation of results

I study a spectral efficiency of a system with a precoding scheme with different channel schemes. Algorithm A for channel estimation gives a smaller estimation error instead of Algorithm B. I have ...
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29 views

For an LTI system, the zeos and poles are defined in the z plane. How to add additional poles and zeroes so LTI system is real valued?

The question already has a zero and a pole in the complex plane. It is asking to add additional zero and pole so LTI becomes zero valued. zeros=-1/2 + 1/2 i , poles = -1/3 -1/3 i . What I understand ...
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What causes this type of distortion in a constellation I/Q plot?

I'm transmitting QPSK through a digital pulse shaping filter (RRC, 35% excess BW, 2 samples per symbol, 64 taps) at a rate of 56Msym/sec. Receiving it on standard lab equipment (Vector signal ...
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46 views

Spectral Inversion in Zero IF Receivers

Is spectral inversion possible in zero IF receivers? If yes, then can somebody explain with an example how that happens and what can be done to correct it. The following problem can be taken as ...
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1answer
28 views

Filters used in FBMC

On page 137, chapter 5 in the book titled 5G Physical Layer: Principles, Models and Technology, the author says: An important attribute of the FBMC waveforms is that they typically do not employ any ...
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1answer
36 views

Why is it that the input to an IFFT is first reordered in an OFDM Modulator

I am back with my questions! I recently came across a paper titled "Low Latency IFFT Design for OFDM Systems Supporting Full-Duplex FDD" where they claim a new method of IFFT input mapping ...
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27 views

burst qpsk timing recovery

I am working on the burst qpsk transmit receive with data rate varying from 100 kbps to 1 mbps. My modem works fine for continuous tx & rx with costas loop for carrier recovery and Gardner for ...
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3answers
74 views

Meaning of sampling frequency?

Say there is a communication system, which can manage sampling frequency up to 4 MHz (given by software). Can the system be able to process signals with maximum frequency more than 2 MHz? Because ...
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1answer
79 views

Sample rates, Samples per Symbol, and Digital Pulse Shaping

Having some confusion about digital pulse shaping for complex baseband (passband) signals. The complex baseband linear modulation equation is $$s(t)=\sum_{m=-\infty}^{\infty}\text{Re}\{a_m\}h(t-mT)+j\...
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1answer
30 views

what is the relationship between the reliability of a monte carlo test and the length of the samples tested and the number of errors found?

Considering this setup, single tone transmission over a channel impaired by AWGN, doppler spread, and inter symbols interference. We are to compute the BER as a function of the SNR. We want to find ...
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How are the constellation point coordinates determined in digital modulation

I need to understand where the concept of the distance comes from. What I mean is, how do we know what coordinates are to assign to points in the constellation. For example here for QPSK the points ...
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Threshold Estimation from a Linear FM Pulse Position Modulated signal

I have a signal chain to detect multi channel LFM (Linear Fm - Hann window being applied as shaping filter for the pulses) pulses as shown in picture below. (Numbers in the picture is in Hz., for ...
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1answer
32 views

How to Tx CDMA signal physically using an existing point-to-point modem? [closed]

I am working in acoustic communication, I want to test CDMA network capabilities in acoustic environment. I had an acoustic modem that has serial interface, a WHOI micromodem. How can i serialized ...
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1answer
48 views

What the disadvantages of up-sampling

Let's say we have a signal $x[n]$ upsampled at the transmitter by $4$ and then downsampled at the receiver by $4$ too. As known, the performance will be much better compared with transmitting the ...
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1answer
35 views

channel estimation based on time-domain pillots

I am confused if it's possible to estimate the channel based on the time-domain pilots. I mean I have such signal $x$ with length $N$ after taking its $iFFT$ we get $X = ifft(x)$. I have perfect ...
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1answer
25 views

Trying to find an intuitive understanding of OQAM/FBMC

I am trying to understand, possibly in an intuitive way, why would OQAM/FBMC when used with a Phydyas filter lead to a signal that does not need any cyclic prefix just like in any OFDM signal also ...
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1answer
52 views

Symbol synchronization with unknown symbol rate

I'm learning about the early late gate symbol synchronization and understand that it needs to be given the symbol rate ahead of time. How could a multi-symbol rate system use an early late gate? It is ...
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1answer
30 views

How to filter OFDM Signal with an analog filter

I am using OFDM system in Matlab, I want to use an analog filter after the DAC. Because we don't a simulation for the DAC, the generated OFDM analog signal does not have a specific frequency (they ...
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1answer
58 views

Analog Square Root Raised Cosine Filter

I am wondering if it is possible to realize an analog square root raised cosine filter. Any idea about how to do that with Matlab?
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1answer
29 views

Calculating the bit period

I want to calculate the bit period in my RF packets that I transmit them with 50Kbaud (Symbol rate=bit rate in my case) , how can I calculate the bit period?
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1answer
44 views

Should we upsample the channel when upsample the signal

I have an OFDM system with Number of sub-carriers $N= 1024$, modulated data using $QAM$ modulation is transmitted via those subcarriers as follows: ...
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1answer
20 views

What is the phase response of SRRC/NRZ/RZ pulse shapping filters and does it matter?

So I would like to know if filters usually used for pulse shaping (like SRRC) have a linear phase response, and if not, what this response looks like and does it matters in any circumstances?
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1answer
28 views

Sample and Hold Circuit at Digital to Analog Converters

Does DACs contain sample-and-hold circuits? I am a bit confused thanks
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27 views

Confusion about the impact of flat fading and frequency selective fading on OFDM

OFDM divides the signal in frequency domain into orthogonal and relatively narrow subcarriers where fading can be considered to be flat Flat fading is not associated with delay spread and is corrected ...
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1answer
27 views

Aperture Jitter in Digital to Analog Converters

I have noticed in the literature that there is an internally induced timing jitter inside Analog to digital converters called (aperture jitter). It is caused by the sample-and-hold circuit of the ADC. ...
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1answer
81 views

How to compand an OFDM signal?

Im trying to run a simulation of an OFDM system with convolutional coding and u-law compander on MATLAB. The problem is I dont know how to compand the OFDM signal. Do I need to do something to the ...
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Question regarding match filter implementation in receiver [closed]

For example, if you have a QAM 16, which mean there are 16 symbols. Each symbol will have different level of the QAM constellation. Each symbol will have a corresponding match filter. At the ...
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1answer
27 views

Cross-correlation with SDPSK modulation

I'm trying to detect a sync word in a signal using Symmetrical Differential PSK (bit 0 = +90° phase, bit 1 = -90° phase). Given the signal is encoded in the phase difference between two symbols, the ...
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11 views

what do we mean by frequency flat block fading channel model?

I need to understood from MATLAB point of view about frequency-flat and block-fading channel model, where the channel hold unchanged within the channel coherence time but may vary in different ...
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1answer
38 views

Difference between slow, medium, fast AGC

In digital receivers, at the RF level (not audio), I often read about "slow AGC" and "fast AGC", and sometimes even "medium AGC" (but I think the latter is for audio). From my understanding, the slow ...
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1answer
26 views

Most reliable way to decode PAM2 signal with unknown signal levels?

I assume this is pretty much a standard problem. I have a PAM2 signal that comes from a complex envelope (i.e., it is not zero-centered) and is heavily imposed by noise. This shows 20 different ...
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32 views

DETECTION the start of my packets

I'm spending some time in understanding L1 PHY development and have some questions on the start of packet detection in an IQ capture Let's say I have a WiFi IQ capture which consists of 600 packets ...
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28 views

How to make noise power estimation on a single tone transmission?

Suppose we have a single tone transmission over a Single Input, Single Output (SISO) channel impaired by Inter-symbol Interference and Additive White Gaussian Noise (AWGN). How to compute the noise ...
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1answer
51 views

AGC noise level

Typically AGC is used to increase the noise level. If my receiver sensitivity is -100 dBm with 60 gain After AGC it becomes -40 dBm. If the noise figure of AGC is less. So the noise also increased by ...
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7 views

For single tone transmission impaired by IES, how Doppler Spread is translated in Channel impulse response computation?

If we are to transmit in single tone transmission in a Single Input Single Output configuration. And the channel is impaired by awgn and inter symbol interference with the following characteristics: ...
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1answer
61 views

Carrier and timing not properly locking?

I have designed a simple BPSK system which is operating in UHF band. My transmit data rate is chosen to be 500 kbps. My receiver has AGC, timing recovery and carrier recovery bocks. I am using ...
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1answer
22 views

Cross corelation understanding -Digital Signal Communications (searching for specific vector inside the other vector)

I have two vectors , one called v1 and the other v2 , the size of v1 is 10k , and the other v2's size is 32 , I want to search inside the vector v1 if there's v2 , this means when I find that the ...
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1answer
52 views

Variations in MATLAB plot each time the program is executed

Every time I run the program my PLOT in MATLAB gets changed to some extent (some times to larger extent too). I understood that the channel is random and this might happen due to random distributions ...
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1answer
30 views

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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2answers
28 views

Understanding of wireless communication system from MATLAB point of view

I am dealing with a communication model described as $$\overrightarrow{y(n)}=\pmb{H(n)}\overrightarrow{x(n)}+\overrightarrow{w(n)}$$ where $\pmb{H(n)}$ is the $M\times M$ fading coefficient matrix ...
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1answer
40 views

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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1answer
20 views

Correlated fading channel: transmit and receive antenna correlation matrices

I am trying to create a non-i.i.d channel: correlated Rayleigh fading channel. $$ H= R_H \cdot H_o,$$ where $H_o$ is i.i.d. channel ( uncorrelated) and $ R_H$ is a channel correlation matrix, is ...
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2answers
31 views

About length of the signal

In my research work i have the equation y(n) = hx(n)+w(n). My understanding about this equation from MATLAB point of view are: h has to be a single number. (for e.g., rayleigh generated). x(n) , w(n) ...
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40 views

Need assistance from MATLAB point of view [closed]

In my work there are three entities i.e, Tag , reader and RF source. In which for a single bit (0 or 1) from tag towards reader there are 40 consecutive complex gaussian signals at reader . How to ...
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40 views

From symbol rate to sample rate fractional ratio

My design has symbol rate and sample rate to DAC fixed but the ratio is not an integer. For example assume my symbol rate is 3 Mbps but the sample rate to DAC is 20 Mbps. So i am having 3 MHZ and ...
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1answer
38 views

Simulation of wireless communication system [closed]

In monte carlo simulation of the wireless communications system why we multiply noise by SNRlin( Signal to Noise Ratio in linear). What is the logic behind doing this. Any help in this basic doubt is ...
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1answer
30 views

My preamble bits not enough for locking the timing recovery for a gaussian channel

I have chosen the preamble to be 48 bits (16 bits for carrier recovery+16 bits for timing recovery+ 16 bits for AGC of 30dB + 16 bits for phase ambiguity) As channel is gaussian and there is no much ...
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1answer
33 views

Complex gaussian random variable [closed]

In my work i need to generate circularly symmetric complex gaussian random variables with non zero mean and certain variance in matlab. I know the command for generating in case of zero mean , but ...
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0answers
35 views

Degrees of freedom in coding (for a communication channel)

I was reading on my lecture slides about how to achieve diversity (i.e. transmit more copies of the same message in order to avoid its corruption; this technique may be realized by repeating the ...
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2answers
42 views

Can two modulations be used in the same frame

Can two modulations be used in the same frame? For qam/qpsk/psk/ modulation scheme for the data bits can i have a fixed preamble with psk modulation? does this help in achieving faster carrier freq ...

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