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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Help on understanding Gardner's original paper for QPSK symbol timing recovery?

I am fairly new to DSP and RF receivers in general, and I was recommended to read Gardner's original paper for symbol timing error recovery for QPSK signals. I have a question regarding an equation ...
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Bandwidth and BER of FM0 encoding

What is the bandwidth (i.e., the lowest possible bandwidth) and BER for FM0 encoding? To be precise, this is my example of an FM0 encoded waveform: There is always a transition between each bit. For ...
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Approximate IIR filter with FIR filter with energy restrictions

Hi I was presented with this problem I would like some guidance to solve: I am given the following DT channel model: $$C(z) = 1-0.3z^{-1}$$ I am first asked to design an IIR linear zero forcing ...
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How can we generate an orthogonal sinusodial signal to any other signal?

I have three signals which are \begin{align} A&=\cos\left(2\pi ft + \frac \pi2\right)\\ B&=\cos\left(2\pi ft\right)\\ C&=\cos\left(2\pi ft + \frac {5\pi}4\right) \end{align} What i need ...
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pulse shaping concept

I'm a little confused about pulse shaping I know that pulse shaping is a filter used to convert a signal that needs to be transmitted from a rectangular pulse signal into a signal that similar to Sinc....
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85 views

The use of LS estimation with Vector OFDM

I work in Vector OFDM, but I had an issue in channel estimation in that scheme. For example, I try to use LS channel estimation but I can't get the performance back. However, in conventional OFDM, I ...
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How can I shape my time channel response, in order to have Gaussian shaped Doppler Spread?

I know how to generate a Rayleigh fading channel but I have no clue how I can shape the Doppler spectrum to be Gaussian. Any help will be really appreciated. ps: I am coding on matlab
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Maximizing sum-rate with constraints

I have an SNR measure, which is a ratio of two linear functions, and I need to maximize the sum rate of a cellular system given by $$R = \sum_{i=1}^{N_{1}}\sum_{j=1}^{N_{2}}\mathrm{log}_{2}\left(1 + \...
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91 views

PLL for Phase Demodulation and Carrier Tracking

I've been playing around with using a PLL for phase demodulation and it's working pretty well. The PLL locks to the carrier and the error term is the demodulated message signal. However, depending on ...
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76 views

Channel estimation and interpolation by vector in OFDM

I have V-OFDM system (Vector OFDM) where every symbol is organized as in below figure: The black cirles are pilots and white circles are data. First, iFFT operation it taken per column, and then ...
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Do we need a transmit and a receive filter in a OFDM transceiver system? [duplicate]

can anyone specify in brief what are the filters that can be used as a transmit and receive filter in OFDM. Any material to start with will be very much appreciated. Thank you!
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How do you determine the power required for a phase shift keying modulation scheme?

This wiki article has a diagram : which shows how the message "11000110" is conveyed as a waveform. I'm trying to understand how the power to transmit this message can be determined. Do I need ...
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how can the channel fading model (Rayleigh, or Rice, or Log normal distribution) infer the way channel estimation is done?

For a dense urban environment with rich scattering and no Line of sight (LoS) path, the Rayleigh distribution can be used to model the fading. Rician fading is a stochastic model for radio propagation ...
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Comparing the performance of a digital communication sim against a reference

I have a complex baseband simulation of binary FSK modulation and demodulation. The modulated signal $s[k]$ is computed as $$ s[k] = e^{-j2\pi f_ik/f_s} , i \in [0,1] $$ where the sampling rate is $...
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34 views

Is there a term called “Fourier Beamforming”?

I understand delay and sum beamforming, where we want to add the signals obtained from different sensors. But adding different time samples from different element of the array depending on the angle ...
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Channel Capacity of OFDM with Index Modulation

I am trying to figure out the channel capacity of OFDM with index modulation (OFDM-IM). One of the article reports that the conditional channel capacity of OFDM-IM is $\mathcal{C}_{\mathrm{OFDM-IM}}(\...
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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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Looking for WiFi Phase and RSSI data

I'm not sure if this is right platform to post . I am researching on WiFi Localization algorithms using Machine learning and was wondering if anyone knows any dataset which is publicly available. ...
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Serial to Parallel Converter

in many texts about modulators I have seen there is a component called "Serial to Parallel Converter". For instance, let's consider this scheme and let's focus on the second block (reference): The ...
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1answer
45 views

Confusion about collection of bits and symbols

I'm taking an intro communications module and I'm quite confused on what the term "symbol" really means? Consider this setup: My understanding is as folllows After the information source, we have ...
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36 views

start of packet detection

With the current lockdown, 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 ...
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What does filtering do to a signal in time domain? Does the signal gets distorted?

When considering a transceiver system, if we do a certain filtering operation on the signal, will the BER of the system be affected? My point is, since filtering in frequency domain filters a portion ...
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Effect of Adding the cyclic prefix on the toeplitz matrix in OFDM

Assuming we have $N$ symbols to transmit encoded in block $k$, Performing $N$−iFFT at the transmitter, we now have The resulted signal $x(k)$ has length of $N$. inserting a cyclic prefix $CP$ ...
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Eye pattern construction and interpretation

I have read some text about the eye pattern (or eye diagram), but I do not understand how should I read it. The wikipedia definition of it is this one: In telecommunication, an eye pattern, also ...
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1answer
49 views

Help in designing filter for DUC (Digital Up-Converter) and DDC (Digital Down-Converter) using the built-in DUC and DDC blocks in MATLAB Simulink

Can anyone please help me in simulating a simple BPSK transceiver system that correctly receives a signal through a DUC and DDC? I have attached the screenshot of my Simulink system along with ...
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bandwidth between the signal and the channel

I have a signal with a bandwidth $B=4$ kHz and the bandwitdh is between $6$ kHz and $10$ kHz. I want to transmit this signal in a channel with bandwidth $B'=4$ kHz but for the channel the bandwidth is ...
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I can't wrap my mind around the concept of filtering and the unit circle ? any help? [closed]

Can someone elaborate this theory where there is a link between the stability of a filter and the zeros or nulls being on the unit circle?
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How to compute the DFE based MMSE equalizer FF and FB coefficients in a non adaptative way?

I seek your assistance, I am reading the Proakis 5th edition and I came across a paragraph explaining the tuning of DFE filters, i.e, how to compute the FF(FeedForward) and FB (Feedback Filter) ...
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46 views

WiFi Channelization for 40, 80 and 160 MHz

I have some questions on WiFi channelization in 802.11n and 802.11ac. Here is the snip of List of WiFi channels (source: WiKi): I am working on the L1 layer for 802.11n and 802.11ac model where I am ...
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1answer
85 views

Timing recovery lock in receiver

I have done my receiver design with QPSK modulation. I am trying to communication between two systems at L band. My data rate is 1 Mbps. As my data rate is high I have allocated 64 bit for timing ...
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111 views

Blind Carrier Synchronization

From my reading, I see that there are two ways people usually do carrier synchronization: Decision directed, where the transmitted symbols are unknown are the receiver, decisions are made, and then ...
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Interference Distribution Assumption in NOMA IoT Scenario

I am assuming a NOMA IoT Uplink scenario, which is interference marred. I have to ascertain the SINR at the Access Point (AP) for the NOMA users. A sub-channel is allocated to various users and ...
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Code implementation of Channel estimation based DFE Equalizer in matlab (or octave) without the the signal processing tool box

I want to implement a DFE in matlab without the signal processing toolbox: I have two filters ( FeedForward and FeedBack) with taps length equal to 15. I know the update equation of the LMS ...
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24 views

Relation between Gaussian and bi-Gaussian distribution

A Gaussian Doppler Spectrum can be seen as a bi-Gaussian Doppler spectrum in wich only one Gaussian function is present ( the second having a zero power gain) ? any help will be really appreciated
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HF ionospheric Channel Model Example in matlab : Watterson model

In the example file in matlab HFIonosphericChannelModelExample.m, the watterson model is simulated. In this model the channel is represented as one tap (for the sake of simplification) delay channel. ...
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1answer
43 views

Can someone explain me how to generatee a doppler spectrum? [duplicate]

I have a signal generated in matlab, with Rayleigh Fading, how can I add a given type of Doppler spectrum ( Gaussian for instance) to that signal ? Any help will be really appreciated
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timing recovery resampler filter

I will explain the system: i am trying to transfer data from tx node to rx at UHF band on 400 MHz. I am trying first only wired transfer then i will try wireless.i am assuming only gaussian noise. My ...
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41 views

MMSE- Channel estimated based - DFE Equalization

For HF ionospheric channels ( frequency range 3 up to 30 MHz), I Want to make channel equalization in time domain, using MMSE criterion. I have to do it using the channel estimation. I have some ...
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1answer
34 views

Why we have to multiply the images with $(-1)^{x+y}$ to center the transform in frequency domain filtering?

To perform the filtering infrequency domain we perform multiplication of $(-1)^{x+y}$ why??
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227 views

why does DFE feedback filter matters?

I recently came across an article on the inventor of adaptative equalizer Robert Lucky, In this article : An Oral History by Robert Lucky (http://www.ieeeghn.org/wiki/index.php/Oral-History:...
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to choose the right preamble in the rx

What is the criteria to choose the preamble in the receiver. Is it good to have many transitions in both I and Q so that i can get faster timing lock? if there are less transitions probably my timing ...
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Two-GSMK channels demodulation: 3dB difference in BER

I am trying to demodulate individually two GSMK channels separeted by 50kHz (one channel = 25kHz). I am working on a limited ressources hardware so I decided to make some optimization on the signal ...
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134 views

Early-Late Symbol Synchronizer on Non-Triangular Pulses

I've been studying the basics of digital communications using the free book at desktopsdr.com. One of the examples is a 4-QAM demodulator which where symbol timing recovery is done with some Early-...
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RRC filter order

I have a question on rrc filter. Hope somebody can answer it. Tx path: My symbol rate is 1 mbps. I am using rrc 8x which becomes 8mpbs. For four symbols the order of the filter becomes 32. Next ...
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72 views

farrow resampler in timing recovery

My receiver contains: AGC,timing recovery,carrier recovey blocks. I am using gardner timing recovery with loop filter and farrow parabolic filter. The input to the farrow filter is the fractional ...
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Designing a PI filter for a Costas Loop

I am currently trying to implement a Costas Loop in order to demodulate a BPSK signal. Here is the reference block diagram I have been using to design the loop:Costas Loop Block Diagram I originally ...
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35 views

Channel impulse response in freqency domain

I have a doubt about DFT matrix and channel impulse response. Let $h$ is a channel impulse response , $F$ is a DFT matrix. IF I take a product. I got: $$ F* h=\tilde{h}$$ $\tilde{h}$ is a frequency ...
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61 views

processing gain in the receiver

I am always confused about the processing gain in the receiver. assume my receiver had LNA-> mixer->filter->ADC. does the filter in the analog section has any role to play with the processing gain? ...
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MIMO multipath delay [duplicate]

How is multi-path delay dealt with in MIMO systems? Most of the theory I have read on MIMO doesn't address multipath delay and assumes the multipath interference is limited to secondary antenna ...
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Rayleigh multipath fading channel in Matlab

I have to calculate eigen values of covariance matrix of Rayleigh multipath fading channel. The exact value should depends on delay spread and subcarrier spacing. I am able to find eigen values but ...

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