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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Loop bandwidth for symbol timing recovery

I am trying to design the Symbol timing recovery (STR) block of DVBS Receiver. How should I chose the loop bandwidth and damping ratio for determining the loop filter coefficients $k_1$ and $k_2$? ...
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28 views

How to derive the transmitted signal from a constellation diagram

Let us assume we have $16$ symbols to transmit. We can represent these $16$ symbols by $16$ unique signals and transmit. If at the receiver we can identify these $16$ signals correctly, we have ...
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Method of reconstructing a band-limited signal from discrete samples

I understand current cell phones use digital communications. Given that this industry brings in billions of dollars each year, there is much incentive to get the best performance possible. So what ...
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15 views

Exponential power delay/decay channel

If I want my channel gain to resemble an exponential power delay profile is it enough to define h= [1 0.66] if I have two channel taps (i.e memory length of ...
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14 views

Why SEs (symbol error) are not same?

I simulated 16 QAM in MATLAB using binary and Gray coding. In both cases SE should be same even though bit error (BE) will be less in case of Gray coding. I wrote the following MATLAB program to ...
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2answers
46 views

How does BER performance depend on gray or natural binary?

I read that BER performance would be improved if Gray code is used in 16 QAM rather than natural binary coding. I think that it should not depend on the coding used. 16 QAM simply assigns to each of ...
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26 views

Fractional spaced equalizer + timing (clock) recovery

I am trying to figure out how timing recovery is used after equalization (or, being more correct, when the equalizer is in the timing recovery loop), having a T/2 fractional spaced equalizer and using ...
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49 views

Proving DFT equation

How can I prove the equation $(3)$? I can't understand why there is a $2/N$ in $(3)$. Why he just get the second term in DFT? Consider a sinusoidal input signal of frequency $\omega$ given by ...
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Frequency autocorrelation function - Communication channel

If we have two discrete stochastic spectra and each spectra has $N$ points. We want to calculate the autocorrelation of these spectra, what should be the number of points in the resulting ...
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24 views

Loop Filter Coefficients in Timing Recovery loop in Baseband Receiver

I am trying to design the Symbol timing recovery(#STR) block of #DVBS Receiver. For reference, I am using the following matlab simulink design (NDA timing recovery part within Digital Baseband ...
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1answer
36 views

Digital Filters deal only with samples, right?

I'm new to digital filters. So I'm trying to get things right and I can't find an explicit answer to my question on the internet. Question: Digital filters only accept samples as input? I mean the ...
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2answers
34 views

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

Generating LDPC codes of arbitrary sizes in MATLAB

I am having problems generating LDPC codes of arbitrary sizes in MATLAB primarily because MATLAB insists on the parity check matrix that is input into its ldpcenc ...
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26 views

Methods for calculating signal quality metric

i'm sure this is a fairly large topic area, but I'm not quite sure where to start. I have a signal in which I can change several parameters, such as the frequency, gain, etc. The modulation is a ...
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18 views

Entropy of a dynamical system and source code length

The entropy of a source $H(S)$, gives you the average codeword length to encode a given source alphabet. i.e. it is the average number of bits per symbol required to encode the information in the ...
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1answer
31 views

Cyclic prefix vs. guard interval. Why use one over the other?

I'm currently studying some OFDM techniques, and have found that in order to avoid Inter-Symbol Interference (ISI), there needs to be some space in between symbols. Lets assume this length to be ...
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45 views

Practical diversity combining at receivers (Maximal Ratio Combining & Equal Gain Combining)

I am trying to perform practical diversity combining implemented in GNU Radio by using Ettus N210 USRPs, one as a transmitter and two as receivers. To compare Equal Gain Combining (EGC) and Maximal ...
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16 views

What is the difference between multipath channel and fading channel? [duplicate]

what is the formula of channel reponse of multipath fading? is it h = 1/sqrt(2)[randn(1,N) + irandn(1,N)]; % with N: length of signal or 1/sqrt(2)1/sqrt(Ntap)[r andn(1,Ntap) + ...
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106 views

How to calculate transmission capacity?

My textbook doesn't explain how they got the answer to this question: "If a transmission channel uses an analog carrier wave that is modulated by eight amplitudes and sixteen frequencies per bit ...
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2answers
42 views

M-Array DPSK decoding and encoding

So i'm trying to figure how how to do the encoding and decoding of an M-array Differential Phase Shift Keying (DPSK) signal. I understand how to do it for binary DPSK, but on higher ordered signals ...
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47 views

Resources on Non-Gaussian Channels

I understand why most of the classic textbooks only consider Additive White Gaussian Noise channels in digital data transmission. Unfortunately in my case noise is not Gaussian and it might even be ...
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1answer
25 views

Reasoning Behind Additional Phase Shift in DPSK

In MATLAB's Comm System Toolbox there is an option for 'Phase Rotation', defined as the phase difference between previous and current modulated symbols when the input is zero. This is the first time ...
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19 views

Is adding zeros part of the Hermitian Symmetry process?

I have been reading about DMT/OFDM and every source I find defines their system differently. I simply want to know if zero insertion is part of the Hermitian symmetry process that produces real OFDM ...
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Help using an example how to calculate the word length for words formed using sliding window

I have a binary sequence of length N as $10110110111...$ I want to segment the above series into equal blocks of a window of length $L$. One way of determining the block length is using the ...
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30 views

Maximum Likelihood for colored noise

I have the following question about the maximum likelihood (ML) in presence of inter-symbol interference and colored noise. Assume the communication system is as follows. Information source, ...
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1answer
41 views

What is the cost of Hamming coding?

We know that (7,4) hamming code has 4 message bits and 7 code bits and can detect any single bit error. The (12,4) repetition code has 4 message bits and 12 code bits and can detect any single bit ...
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30 views

Maximum Likelihood question

I have a basic question about maximum likelihood (ML) estimator and its implementation. I am trying to simulate a communication system affected by ISI and noise, while using ML at the receiver side ...
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5 views

small HID tag for 50cm range (like glass HID) interference issues

i was looking at different rfid tags , passive ones to be exact and found that there is a very small and very nice injectable rfid tag, i was wondering if those tags can be bunched one next to the ...
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22 views

How to generate Golay sequence?

I am trying to follow the 25.213 3GPP spec point 5.2.3.1 to generate Golay sequence for the P-SCH channel. I was able to do it recursively for Hadamard sequences, but I am unsure of what golay ...
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1answer
40 views

How can I shift this signal to it's midpoint in order to decode it

I'm wondering if there's a simple way to decode this pulse signal as I'm reading it in. I'm thinking the simplest way to decode this is if i can shift the whole signal down so that it's centered ...
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46 views

Optimal time for sampling symbol in digital receivers

I'm studying various publications about symbol timing recovery algorithms, Early-late, Mueller and Muller & Gardner. All documents I've read tells that, to minimize ISI : The optimal time for ...
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2answers
35 views

systematic way to determine best bit mapping policy

So in class, we've been asked to find the best bit mapping policy for QAM modulation schemes (4-QAM, 8-QAM, 128-QAM, etc). Best meaning the one that will provide the lowest bit error Probability ...
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3answers
61 views

What is bit rate? How is it related to bandwidth? [closed]

I am very confused about when to use bandwidth as bit rate and where not. Are these terms one and the same?
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1answer
82 views

Calculating energy spectral density function of half-cosine function

I have the following function: $$ g(t) = A\cdot \textrm{rect}\left(\frac{t}{T}\right)\cos\left(\frac{\pi t}{T}\right)$$ How do I find the energy spectral density function? I think? it is defined as ...
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How to write cyclic codes?

I am studying cyclic codes. From what I understood of it, a cyclic code is a special kind of linear code with the property that any codeword cyclic shift is also a codeword. Generally, we start with ...
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34 views

Coherence bandwidth/delay spread in OFDM

Say we want to design an OFDM system and we have some parameters given to us, i.e. the coherence time $T_c$ and the max delay spread $T_m$. It's clear to me why we need to ensure $T_s(N+N_{cp}) \ll ...
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How often do a LTE eNodeB scheduler schedule?

Scheduler schedules the resource for each UE. How often do a LTE eNodeB scheduler schedule? Is the time between each scheduling fixed? any idea/reference will be great help on this regard. Thanks.
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1answer
52 views

Derive chernoff bound for $\mathrm{erfc}(x)$

I'm trying to derive the Chernoff bound $\mathrm{erfc}(x) \le \exp(-x^2)$, by first showing: $$\mathrm{erfc}(x) = ...
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1answer
36 views

Fully random PN sequence

Can a CDMA PN sequence be fully random, as in encryption-grade randomness, or must it be deterministic? I have tried the first bytes of SHA-256 hashes as PN sequences, but somehow they don't coexist ...
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2answers
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suppose if we send AM modulated message signal through space how the receiver will be knowing that we applied AM modulation?

suppose if we send AM modulated message signal through space how the receiver will be knowing that we applied AM modulation basically how it will be knowing that which modulation is applied for our ...
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1answer
98 views

Bit Error Probability for 8PSK

I'm trying to understand how to derive the BEP for 8PSK by geometrically looking at the decision regions. Say I have this 8PSK signal set and the corresponding decision boundaries. I assume that ...
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Inconsistency in LTE UE-Specific Reference Signal for Special Subframe Configurations 9

Refer 3GPP 36.311 (Release 11 or higher) section 6.10.3.2 or Figure 6.10.3.2-3 shown below, Here UE-RS is defined for Special Subframe configuration# 9 as seen in the middle row of sub figures in ...
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39 views

How to achieve Shannon's capacity if coding introduces a spectral efficiency loss?

I am a little bit confused concerning different Shannon's notions : Over an AWGN channel Shannon's capacity is in my knowledge : $R_b<C=B.\log(1+SNR)$. Is Shannon's "limit" a different notion than ...
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1answer
67 views

Question about ASK, correlation, and frequency domain

So I'm currently studying ASK (amplitude shift keying) and how it is modulated and demodulated. The modulation take out data signal, $M(t)$, and multiplies it with our carrier frequency, lets say ...
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71 views

How to measure/estimate symbol rate of a signal with unknown ( but probably QAM ) modulation?

Is it possible to estimate the symbol rate of a signal whose modulation is not know exactly but it can only be guessed that it is probably some kind of QAM (probably 64 or 256). What is the best way ...
4
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1answer
73 views

Why do we really split pulse shaping between the transmitter and the receiver?

EDIT: There was a small error in my code when plotting the Squared RC. Below is the correct frequency response, and clearly RCĀ² doesn't fulfill Nyquist's criterion. ...
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10 views

Repeater based pathing

I'm having trouble finding information on the topic I'm interested in, and maybe my problem is just how I'm wording things. So, let's say I have a repeater-based communication system, where one node ...
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1answer
85 views

What benefits can we get from the use of GFDM?

Existing literatures say that the generalized frequency division multiplexing (GFDM) has lower out-of-band emission (OOBE) levels compared to orthogonal frequency division multiplexing (OFDM). ...
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Level crossing rate, Rayleigh

So I'm solving an exercise and I'm wondering if I'm being tricked or not. The problem is to calculate the level crossing rate for a Rayleigh fading channel with threshold $15$ dB below the average ...
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Why is CDMA so complicated, wouldn't this simpler solution work?

I am now reading about Code Division Multiple Access method (CDMA), which is used for multiple hosts to send data at the same time. The main idea behind it is to use orthogonal vector basis to ...