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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20 views

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 ...
3
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1answer
246 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 ...
3
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1answer
49 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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2answers
29 views

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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0answers
15 views

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 ...
2
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1answer
45 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
47 views

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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1answer
58 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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36 views

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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1answer
16 views

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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2answers
55 views

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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1answer
77 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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1answer
30 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. ...
1
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1answer
36 views

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 ...
2
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2answers
78 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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1answer
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 ...
0
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1answer
26 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 ...
3
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2answers
158 views

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. ...
2
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2answers
76 views

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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1answer
60 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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0answers
32 views

“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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1answer
34 views

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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1answer
47 views

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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0answers
16 views

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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0answers
36 views

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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34 views

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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33 views

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 ...
0
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1answer
23 views

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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2answers
71 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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2answers
100 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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2answers
47 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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0answers
10 views

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? ...
0
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1answer
44 views

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 ...
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1answer
41 views

what is the relation between bandwidth and channel taps

I've studied that when the bandwidth increases, the number of taps we consider for channel modelling increases(example in WLAN or LTE). why is that happening. why signals with lower bandwidth (example ...
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1answer
23 views

does scrambling increse the bandwidth

In LTE systems the in the scrambling section, a gold sequence is used. But I've studied that gold sequences are used in spread spectrum communication. This generally increases the bandwidth. So ...
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1answer
50 views

Q and I part in QAM

I have one confusion in QAM about in-phase I and quadrature Q part, i.e. do they transmit identical data or not? For e.g. if i have 11001001 as a byte to be transferred, so will 4-QAM separate it ...
0
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1answer
35 views

what is the significance of pilot carriers in ofdm [duplicate]

in an OFDM system having a radix two FFT (Say N=64) . all of these sub-carriers are not utilized. while some of the carriers are nulls to prevent leakage in to adjacent bands, say a four to five ...
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1answer
27 views

PAPR in the SC-FDMA system

in wireless communication,compared to the OFDM system , why does the SC-FDMA (single carrier FDMA) system has a lower PAPR (peak to average power ratio)? regards, phani tej
0
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1answer
115 views

What is the significance of the DFT in SC-FDMA systems? [closed]

Long term evolution (LTE) systems use single-carrier frequency division multiplex (SC-FDMA) in the uplink. In such a system, there is a DFT block and a sub carrier mapping block before the IFFT block. ...
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2answers
271 views

Sampling rate in Wifi 802.11 -> 20 MHz enough with a BW of 20 MHz?

In a Wifi 802.11n context, I'm looking to find the sampling rate to perform some processing on the signal and I've something I cannot understand : in the book Next Generation Wireless LAN's: 802.11n ...
2
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0answers
90 views

Phase noise estimation and compensation schemes

Brief background There is a known problem that high order modulation schemes suffers from phase noise of reference generator. It's very important issue for e.g. line-of-sight (LOS) modems exploiting ...
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0answers
58 views

DC offset removal from tetra signal

Hey I want to remove DC offset from tetra signal captured as inphase and quadrature phase samples(I and Q samples). I and and Q samples are 16 bit signed values. I tried averaging 2000 I and Q samples ...
3
votes
2answers
162 views

Viterbi equalizer in a GSM system

I'm about to tackle implementing a Viterbi equalizer fo a GSM system in gnuradio. I went through the internet and ieeexplore and I think that this document explains it best: Application of Viterbi ...
0
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1answer
250 views

How to simulate AWGN in communication systems for specific bandwidth

I am trying to generate a AWGN waveform to add it to the signal of my simulated communication system. The operating bandwidth of the communication system is about ...
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2answers
77 views

What is wrong with this method of detecting the presence of a signal?

I am trying to decode Morse code from an audio (wav) file. Here is the technique I am using to detect the presence of the signal: I have a window of size (sampling_freq/tone), where tone is the ...
0
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1answer
28 views

Timing synchronization in limited channel

I need measure timing of an signal that is send through a noise band limited channel (wireless). By measure timing, I mean measure as exactly as possible when the signal has arrived at the receiver. ...
0
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2answers
69 views

Adding encryption to a ham radio

Suppose I want to encrypt the voice data before sending using a ham radio, for example this unit. Assume the encryption is simply AES encryption/decryption using predefined fixed key. I am thinking ...
0
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1answer
62 views

SINR averaging in communication system

Under the simulation of a communication system suffering from noise (AWGN) and co-channel interference, what is the appropriate way of calculating SINR? Could one calculate it at a packet level as: ...
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1answer
34 views

Difference between delayed down-converted signal and a down-converted delayed signal

I am having trouble understand what I think should be a pretty simple concept. Conceptually I can understand that a signal that has been down-converted, and then delayed in time is different than a ...
0
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1answer
131 views

How to find the frequency response of a communication channel from input and output symbols' functions in MATLAB?

I want to find the channel frequency response of a digital communications system. I have the functions of the input symbol (a triangle) and the output symbol - a distorted triangle: $$\dfrac{1}{1 + ...