# 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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### Spreading sequence in DSSS [closed]

In DSSS, the spreading sequence is known only to the receiver and the transmitter. But for example, if we consider a spreading sequence built around a certain signal known only to the receiver and not ...
1 vote
81 views

### Basics of interpolation: is filter or upsample first?

I am studying interpolation filter. I have thought if we speak about interpolation, we filter and then upsample a signal. BUT In an article, Interpolation (Digital Filter Design Toolkit, is given a ...
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### Upsampling after S/P convertor in MSK modulation

I have found this post "implementation a S/P conversion: different length / in Matlab" In the given implementation, Tsym = 2*ovs. ...
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### Order statistics: always applicable tool in wireless communication?

I have seen few papers where generalized order statistics is used to obtain statistics of the instantaneous SNR. "Performance analysis of monostatic multi-tag backscatter systems with general ...
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1 vote
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### Understanding Pathloss and latency

In my class on wireless communication, I came across the following sentence: The round trip path-loss can be defined to include aspects such as attenuation and/or latency etc Hence I am looking for ...
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### How to proprely rescale measured channel statistics

I’ve got a vector of measured instantaneous power at the receiver side. The vector is normalized in a way that the average is 1W. Now I would like to apply this vector to my channel model to check if ...
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33 views

### Related to wireless channel variance?

I am reading wireless research papers and found that mostly the wireless channel is considered to be Zero mean circularly symmetric Complex Gaussian (ZMCSCG) with variance 1 or 2 or 5 or 10 etc. My ...
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1 vote
30 views

### Power of noise signal through a matched filter (Digital Receiver)

I am studying matched filters and the sense of signal to noise ratio. In a question I was given, stated that: Show that a matched filter of a signal $s(t)$ maximizes the SNR of the output on a ...
55 views

### convert from binary to hexadecimal according to the algorithm "keeloq"

Good afternoon. I have the key to my gate. I received its recording in the form of a PWM pulse train. Instead, I converted the impulses into binary code. Now I should get the hex numbers but it doesn'...
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### Why should costas loop be done after clock recovery, as opposed to before?

In GNURadio's PSK tutorial they place the costas loop after clock sync and linear equalizer. This seems odd to me. I'm thinking that it's easier to lock onto a carrier frequency at the higher RF ...
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### GNURadio 3.8 QPSK : Hard time to recover the right symbols/data

Cheers, I am demodulating a QPSK signal on GNURadio, the data transmitted is a known HEX file with the "1ACFFC1D" foreword every 124 bytes, to check if the demodulation is a success, it ...
49 views

### Understanding mathematical representation of SINR

I am getting confused in SINR for the following received signal expression. $$y(n) = (h+fg)s(n) + w(n) \tag{1}$$ Where $h,f,g$ are zero mean circularly symmetric Complex Gaussian (ZMCSCG) channels. ...
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### High error when adding small value of SFO into the OFDM signal

I am trying to emulate the SFO effect for OFDM system, I did it using linear interpolation as shown HERE . That can be explained as if I have the time domain signal $s_n$ representing the output of ...
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### How to efficiently shape the input payload matrix for cdma?

Is there a better way to shape the input payload metric for cdma ? currently modulating a matrix defined as Users x time matrix. I define user per column which is ...
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### GMSK Transmitter Implementation based on AMP representation ( laurent decomposition)

Implementation of a linear approximated GMSK block scheme based on Laurent decomposition. My goal is the Implementation of the following block scheme: I think $v_k$ is an NRZ element ( 1 or -1). <...
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### Sampling frequency offset vs carrier frequency offset effects

I am reading about the sampling frequency offset (SFO) of OFDM system. According to my understanding and all sources I read, it can be defined in similar way to the carrier frequency effect (CFO). I ...
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### implementation a S/P conversion: different length / in Matlab

I want to compare a linear and a nonlinear implementation gmsk transmitter. A reference of the linear transmitter is chapter 2 , p 77, a reference for the nonlinear design is on p 63, Fig. 2-31 In the ...
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46 views

### How to choose correctly oversampling ratio?

As many of us have noticed, last two months I am working on GMSK modulation and demodulation design. Before continuing my research, I want to be sure I chose the correct oversampling ratio ( how many ...
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### Question on Signal to noise ratio (SNR)

I am trying to form the SNR expression for the system model but I am getting stucked due to presence of multiple antennas at receiver. System model: It consists of one single antenna Transmitter, $L$ ...
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1 vote
39 views

### Relationship between the BER and the data rate?

I want compute data rate I can reach with my design of a nonlinear modulator. Matlab generates a modulated baseband signal (output of the modulator) and I can add a random signal as a noise to create ...
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1 vote
83 views

### A question regarding using analog PLL circuit with QAM modulation for phase sync

I was wondering if you can implement analog PLL circuits for phase synchronization in communication systems that transmit MQAM modulation signals? I heard that you can't use analog PLL because QAM ...
17 views

### data rate for mc-cdma

I would like to know how to calculate the data rate of MC-CDMA (combination of OFDM and CDMA and the spread is in frequency.) with $K$ the number of subcarriers, $T_g$ the guard time, $log_2(M)$ the ...
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### Why the transpose of wireless channel vector is taken in SIMO system?

I am getting confused about the received signal expression in case of SIMO wireless channel. SIMO system=> Here we will have one antenna at Tx and multiple ($N$) antenna at Rx. Therefore received ...
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1 vote
83 views

### Why distance index between 2 frequencies in M-FSK has to be odd?

I'm learning about M-FSK modulation from A. Bruce Carlson book, Communication systems. I've seen that ak, an index to select the frequency of each symbol, has to take odd values, spaced by 2 fd (...
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1 vote
37 views

### localization based on TDOA

To locate a transmitter, I use a localization based on TDOA(Chan's method) with 3 receivers. The results obtained are not effective. What is a possible solution to improve the localization accuracy ...
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### Related to SNR when the channel is in the form of vector and matrix

In my system model there is a sensor (transmitter) with $M$ antennas and receiver with $Q$ antennas. The received signal expression is $y_q(n) = (h_q+\textbf{f}_q\textbf{G}$)$s(n)$+$w_q(n)$----(1) ...
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### GMSK modulation: Simulation in Matlab for BT <0.3

My previous questions gmsk: suppression of higher-frequency spectral components Gaussian filter: The best parameters for an implementation I study gmsk modulation last 2 month and tested my ...
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### dsss and correlation

Generally, a DSSS (Direct Sequence Spread Spectrum) communication is used to secure a communication. However, because of the repetition of the spreading sequence, a cyclostationary analysis makes it ...
24 views

### gmsk: suppression of higher-frequency spectral components

I study gmsk modulation and worked with gmsk implementation, BT = 0.5. I have decided to test with BT = 0.25, which is used for near Earth communicaiton. Spectrum of output signal with BT = 0.5, ...
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1 vote
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### Frequency-domain vs Time-domain OFDM oversampling

I sometimes read some references where the oversampling of OFDM signal is performed in frequency domain, for example, $(N-1)L \times 1$ zeros are inserted in the middle of the modulated signal $s$ ...
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1 vote
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### How to eliminate a cyclic spectrum estimation window artifact?

I am using an implementation of the averaged cyclic periodogram (section 3.2.4 in Antoni, Jérôme. "Cyclic spectral analysis in practice." Mechanical Systems and Signal Processing 21.2 (2007):...
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### Oversampling ratio ( factor) calculation

I study GMSK modulator. In its simulation we use an oversampling ratio if we implement gaussian filter or oversample the input signal. In my simulation I can test different value of the oversampling ...
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### how to tune and demo

How does one go about tunning your fm demod algorithm to a given carrier frequency. Consider the following algorithms that are present in this website: DSP Tricks: Frequency demodulation algorithms ...
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### A question on communication system without modulation

I know that these sort of platforms are strict and you need to have an idea of what you are doing before asking a question. I am not really that knowledgeable about signal processing though I have an ...
52 views

### Understanding $E_b/N_0$ under different coding rates

I'm trying to understand the $\\E_b/N_o$ concept and how different coding rates affect it. I've read a bunch of topics, specifically this and this, but I'm still missing something to have a clear ...
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### Adding Fractional STO to an OFDM Signal using Frequency Domain Zero Padding

I have an OFDM system. I would like to introduce a fractional delay of (0.25 samples). Therefore: I increase the sampling rate of the OFDM signal by a factor of 4 (via frequency domain zero padding (...
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1 vote
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### GMSK: NRZ pulse train

Fig from "Digital Modulations Using Matlab", p 95 (pdf) but it is also described here : Bandwidth-Efficient Digital Modulation with Application to Deep-Space Communications My question is ...
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1 vote
55 views

### understanding a spectrum of a modulated signal

I plot a spectrum of a modulated signal. It is a GMSK modulated signal. My goal to find the best parameter for a realisation it. My first spectrum with oversampling ration M = 4 and BT (the product of ...
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### the meaning of management of bandwidth and energy resources

I have read in this paper, Single-Carrier Frequency Domain Equalization, second page, first paragraph, that Single Carriers (SC) cannot offer the same flexibility as OFDM in the management of ...
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### Real parameters design and computation for a filter, modulator

I design in Gaussian filter for a modulator in MATLAB, which should be later implemented in FPGA. I have an implemented design of the filter and the modulator as well and now I have to determine some ...
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### Subquestion: From IQ signal to FM modulated carrier, how its done?

The following post I have gotten as suggestion: From IQ signal to FM modulated carrier, how its done? 1. Mr Andy Walls gave an Octave simulation in his answer. For his phase computation he used ...
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### Realisation GMSK modulation in Matlab

I implement a GMSK modulation scheme presented here (p 64 in pdf and copied below) As gaussian density function I use the standard Maltab function gaussfir and ...
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### How to generate eye diagram in Matlab ( without communication toolbox)

I want to plot an eye dagram of output of modulator. In Maltab I tried plot( I, Q), but it doesnt give me the diagram. In Matlab there is a function ...
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58 views

### Calculate the probability of error of two vectors

I am trying to calculate the probability of error of two vectors, for example the first one is transmitting a modulated data $x$ with modulation order $M$ as following $y_1 = [x \ \ 0]^T$ while the ...
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### Phase computation in Matlab

I want t o compute a phase ( angle) of my signal, which is an array of complex numbers. My code: ...
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### Variant of cryptography

Let $$S_1=\{(s_1(t),s_2(t)),(s_3(t),s_4(t))\}$$ and $$S_2=\{(s'_1(t),s'_2(t)),(s'_3(t),s'_4(t))\},$$ with $s_i(t)$ different waveforms. We have $s_1(t)$ is orthogonal to $s_3(t)$ and $s_2(t)$ is ...