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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Pulse Shaping in Digital communication

I am new here. I hope I can get help. I want to ask a question regarding digital communication. Does anyone know what are pulse shaping used for? Are they used for ISI mitigation or for something ...
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OFDM modulator in LTE

My understanding of what an OFDM modulator does, is that it takes a parallel sequence of QAM symbols of size M, pads it with zeroes corresponding to the zero subcarriers, then passes them through an ...
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Questions Downlink OFDMA in LTE

I am looking for a clear and precise explanation of how an OFDMA modulator in downlink LTE operates. I have many books that explain it but each has its own way and do not answer my questions ...
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LTE questions (subcarriers and cyclic prefix)

Assume we have transmission bandwidth of 10 MHz, in this case the total number of subcarriers (FFT size) present is 1024. According to LTE standards, 600 out of 1024 subcarriers are data subcarriers. ...
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33 views

Transmission Bandwidth and Sampling frequency

In LTE standards, for a transmission bandwith of 2.5 MHz, the sampling frequency is 3.84 MHz. I was wondering with this choice, are we violating Nyquist theorem? I found the details in the following ...
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General Questions MIMO Communication theory

The following are questions regarding MIMO communication theory. I have come across a MATLAB implementation of MIMO channel. My questions are not regarding the implementation, but rather regarding the ...
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what are the advanatages of using a scrambler

What is the purpose of using a scrambler in communication systems? The link wiki_for_scrambling says that it is used to randomize data. But the data is already random (like speech,audio,video,etc..), ...
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Modulation of data bits into complex symbols in MATLAB

In communication theory, a modulator takes the input sequence and and maps it to some complex numbers. In MATLAB the following commands can do that. ...
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Decoders, Detectors and Demodulators (Digital Communications)

In digital communication systems, we use forward error correction codes such as LDPC, turbo, convolutional codes (to decrease the bit error), then we have to use an appropriate decoder at the receiver ...
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Question regarding 16 QAM digital modulation

Below is an example of a digital modulation system using 16-QAM. I have copied this example from MATLAB communications toolbox, ...
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Where do I ask Wireless Communications Questions [migrated]

Please consider this as a soft question. I am wondering where is the best place to ask questions related to Digital Communications and Wireless Communications. Is there any stack exchange that can ...
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Visualising a Z-transformed Transfer Function?

For designing any analog filter and various other outputs of filter we use laplace transform,I can visualise a laplace transform like for ex. s[X(s)] can be ...
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What is difference between OFDM and GFDM?

I am trying to understand the difference(s) between OFDM (Orthogonal Frequency Division Multiplexing) and GFDM (Generalized Frequency Division Multiplexing) which are used as a multicarrier modulation ...
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Question related to Principle of Communication

Why the frequency of carrier wave is always kept at least $10$ times higher than the highest frequency of base band signal? Can you explain me this with a practical example?
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Basic “filtering” in digital communications

I am completely stuck on solving some problems for my digital communications class. Junior level undergrad class, so fairly basic. I have been searching around all day for related articles etc but ...
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Basic “filtering” in digital communications [duplicate]

I am completely stuck on solving some problems for my digital communications class. Junior level undergrad class, so fairly basic. I have been searching around all day for related articles etc but ...
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20 views

Find the essential bandwidth of rect function? i want the ans by using Energy spectral density and then essential bandwidth… [duplicate]

I am trying to find EBW of rect function but i am unable to solve the integral after finding the fourier transform and then apply parseval's theorem?
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The channel capacity with additive Gaussian noise with changing variance?

As we all know the capacity for a AWGN channel with constant noise variance is just given by $\frac{1}{2}\log(1+SNR)$. What if the variance of the noise changes with the type (assuming the variance ...
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262 views

What is the theoretical upperbound of information that could be transmitted by a device per second?

Suppose I would like to stream data from a device in a single second. What would be the theoretical upperbound of the amount of information (in bits, bytes, pixels...) that could be sent during this ...
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79 views

Simulating BPSK Costas Loop in Matlab

I am trying to implement BPSK demodulator in FPGA. First, I am modeling the system in MATLAB. Now, I am trying to design Costas Loop for carrier synchronization. This is the block diagram I'm trying ...
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Linear Block Codes Digital Communication Problem

How to design a (8,4) linear block code with highest possible error correction and error detection capability? I have studied linear block codes topic but if i do the conventional way ,In case of ...
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Sub-carriers spacing in DVB-T2

Looking at DVB-T2 technical specifications I see that sub-carriers spacing has, in the worst case, a value of few hundred hertz, (something like 279 Hz). 32K sub-carriers are used to reach such a low ...
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48 views

Gaussian, Rayleigh, and Exponential RVs

I am doing some simulations on the performance of OFDM systems in multi-path channels and I am confused about something. It is explained below: Assume that we have a multi-path channel with a number ...
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3answers
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Can OFDM modulate analog signal?

I suppose that OFDM can't modulate analog signal. The basic mathematical description for OFDM is $$ v(t)=\sum_{k=0}^{N-1}X_{k}\exp(j2\pi k t /T),\quad 0<t<T$$ In this equation, $X_k$ is a ...
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92 views

Rectangular 8 QAM bit error rate calculation

I am simulating an 8-QAM communication system over an AWGN channel for various signal to noise ratios, in order to plot the average bit error. However I have not been able to derive an equation for ...
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Interpretation Of 4th-Order Cumulants For Complex Signals

For complex signal $y(n)$, we have the following three 4th-order cumulants: $$ \begin{align} C_{40} & = \operatorname{cum} \left( y(n), y(n), y(n), y(n) \right) \\ C_{41} & = ...
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Must OFDM signal be time-division in a multiple-transmitter and SFN system when the signal is free of spread-spectrum?

The OFDM baseband signal can be demodulated since each subcarrier is orthogonal to another. But In SFN system, i.e., Single Frequency Network, all OFDM signals from several transmitters are in the ...
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How to find orthonormal basis function in the following digital communication problem?

I'm trying to express the following set of signals on orthonormal basis functions. These signals are to be transmitted using a 4-ary modulation scheme.How do i write ψ1(t)and ψ2(t) for the same. Also ...
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89 views

I/Q Sampling and Demodulation

A bit stream is mapped to symbols during baseband modulation, each symbol (say for QPSK) represents two bits. Each symbol has a corresponding I & Q value, which in QPSK, are used as the amplitude ...
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41 views

Processing OBPSK as OQPSK

I'm trying to create and process an OBPSK signal, which, as I understand it, transmits even bits on one axis and the odd bits on the opposite axis, resulting in a constellation with 4 unique points. ...
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Relationship between “received” signal power and “transmitted” energy per bit?

In digital communications textbooks (e.g., Digital Communications by Bernard Sklar), the relationship between the "received" signal power $P_r$ and the "transmitted" energy per bit $E_b$ is given as ...
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83 views

carrier frequency difference

Papers use wireless device-dependent radio-metrics as fingerprints. A radio-metric is a component of radio signal, amplitude, frequency and bandwidth. Each device creates a unique set of radio-metrics ...
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96 views

Is multirate signal processing involved in ADSL?

Telecom companies offer different data rates for home/office purposes depending on the money they pay. How are the telecom people able to control the flow of data of different cables. Say supposing a ...
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27 views

Transmit bitstream from USB over radio

I am extremely new to this and I'm learning by building stuff myself so please let me know if this is too vague and Ill elaborate if I can. Im sure this is something very simple, but cant figure out ...
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OFDM transmitter bandwidth

Theory Suppose an OFDM transmitter with four subcarriers is implemented using the structure shown below. If the serial data input rate is 40 bps, each parallel stream will run at 10 bps. ...
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Simulating noise in OFDM

I'd like to simulate a certain $E_s/N_0$ in a baseband OFDM MATLAB modem to generate SER curves. I randomize 50 QAM symbols with $N$ subcarriers each in frequency domain, add null frequencies (guard ...
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65 views

sampling a signal below nyquist rate

This question is for people working in multi rate signal processing. Using compressive sensing techniques, we can still recover a signal by sampling below nyquist rate(by decimating the signal). How ...
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“Time To Lock” in Bit Timing Synchronisation

In the context of bit timing synchronisation in digital communications, what is meant by the requirement that says the "Time to lock to a sampling point should be no more than X symbols"? There seems ...
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Important differences between BCJR and SOVA algorithms?

BCJR algorithm needs noise variance for Gamma (branch metrices) calculation. So I am wondering does SOVA (soft output Viterbi algorithm) needs noise variance?
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Legal issues when using a paper [closed]

I'm just curious about the copyright issues when publishing a paper on the Internet. Can some simply take the idea I explained in a manuscript and implement it for his own work? (e.g. using some ...
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calculating average PSD of N radio frames

i've written a matlab code for the basic ofdm with bpsk modulation. there is no channel coding or compression used at this point. i just want to see the PSD of the transmitted packet. i am getting a ...
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How to simulate two OFDM Users with low complexity FFT/IFFT?

have two User one of them sending over freq (0-B] and the other transmit over (B-2B]. Both of them are using OFDM and each one has Nc subcarriers. I wanted to simulate the received signal using ...
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Are there any research value in visible light communication?

My advisor wants me to take the area of visible light communication as my MS project, but I don't know whether there are any research value in this area, it seems most of the tenichnical difficulties ...
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spread spectrum communication in airport

Does anyone know , how the spread spectrum sequences are used in airports. I've attended a presentation this morning regarding spread spectrum in my college, the author mentioned that the sequences ...
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digital modulation

Theoretically in BPSK signal generation we will multiply the digital signal with the carrier and this output we will call as BPSK signl which is an analog signal. But in OFDM if the data is ...
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74 views

Relationship between Carrier Frequency Offset and the Constellation Diagram

As part of a project I am doing, I have to investigate how having a carrier frequency offset would affect the constellation pattern of the received signal.This question has got me baffled because to ...
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103 views

OFDM violates sampling theorem

The "textbook" OFDM block diagram is as the below figure. But I wonder if it satisfies the sampling theorem. Here, we have N points $X[k]$ before IFFT, and $$x[n]=\frac{1}{\sqrt{N}}\sum_{k=0}^{N-1} ...
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48 views

What is the maximum data rate a wireless link can support using BPSK for given BER and SNR?

What is maximum data rate a wireless link can support using BPSK for 10^-6 BER, Bandwidth of channel is 200 kHz and SNR ...
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Hooping in Physical uplink shared channel

in 4G/LTE communications, there are terms such as group hopping and sequence hopping, in the uplink shared channel. what is the need to do hopping? what is the physical significance of these hoppings? ...
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causal and ROC and which side the system is on

I want to try to summerize some relationships between z transform, ROC and causality. But I am getting confused between left/right sided sequences, the ROC and causal. If you need stability then ...