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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Circuit synthesis example [migrated]
What will look like combinational logic circuit using any basic gates having the output=1 when the input=110 ad 101.
Thanks much
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1answer
35 views
Laser diode bitrate datasheet
I'm a student studying communications engineering. I'm trying to understand why this particular laser diode is made for 155 Mbps and 622 Mbps. I'm thinking that the bitrate is entirely dependent ...
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2answers
64 views
Bandpass filter BPSK
I have a question concerning BPSK and the bandpass filter that seems to be sometimes placed before the receiver circuit (the receiver is a mixer and lowpass filter).
Basically, from what I've ...
2
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2answers
93 views
Understanding matched filter
I have a question about matched filtering. Does the matched filter maximise the SNR at the moment of decision only? As far as I understand, if you put, say, NRZ through a matched filter, the SNR ...
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1answer
49 views
What are the options for turning a bit stream into a byte stream?
I am creating a system (modulator and demodulator) for broadcasting binary data through an analog signal. I'm using BPSK with great success – at least, I'm generating great graphs.
Green is input ...
2
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1answer
54 views
OFDM training symbol format
For OFDM synchronisation, we are using two training symbols according to the Schmidl and Cox method of frequency synchronization and timing synchronization. The paper says:
The first OFDM training ...
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47 views
Appropriate sampling frequency for bpsk modulated signal
I'm modulating a message with particular baudrate, say 2MHz using BPSK , Carrier frequency(Fc) is 8MHz, What should be appropriate Sampling Frequency(Fs) following Nyquist criteria, Should it be ...
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1answer
54 views
Need for Oversampling in OFDM and symbol time determination
I am trying to implement OFDM on gnuradio. I have two questions.
The sampling frequency which is slightly higher than available bandwidth satisfies Nyqvist criterion for complex baseband signals. ...
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3answers
89 views
OFDM coarse freq estimation
I am trying to read OFDM synchronization paper by Schmidl and Cox. The math is slightly overwhelming.
What is the formula that they use in implementation that distinguishes between coarse estimation ...
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1answer
65 views
Determining sampling rate in OFDM demodulation
I have seen that in OFDM, the sampling rate is much lesser than twice the bandwidth of signal. why is it so? How is sampling rate calculated in OFDM? Does it depend on the modulation type used inside ...
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1answer
65 views
Find the time lag for a wave
suppose that we have a wave which has some peaks in some indexes like 2,12,25,... and otherwise zero.
I want to extract the time lag or lags between peaks of a signal. could anyone help me ?
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2answers
70 views
Fixed point channel model for OFDM system
I'm testing an OFDM system implemented in fixed point. The data format is Q11. My system work's fine but I need to test it under some channel for evaluation of the design before field testing. The ...
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1answer
132 views
Remove spurious peaks of Hilbert transform
I want to eliminate spurious peaks of Hilbert transform for finding Glottal closure in LP residual. I have the following 4 steps:
1-down-sample.
2-Hilbert Transform.
3-Identify Peaks in Hilbert ...
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1answer
135 views
Apply AWGN noise to QPSK-OFDM symbol
I'm working on an OFDM-QPSK based system and I'm having some trouble to match the BER of my system with the theoretical curve. My OFDM implementation fills all the subcarriers and have t_symbol s ...
2
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2answers
70 views
How to normalize the power of a QAM signal?
If I have, for example a 16-QAM signal, and the constellation points are (3,3),(3,1),(1,3),(1,1),...(-3,-3).
Now I have a simulated in coming signal with arbitrary ...
2
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0answers
34 views
How to find the group delay of IIR filters in Python/SciPy
I sent a square wave signal (red) through a IIR filter (butterworth in this case), to make it more "realistic". Then there's a slight group delay in my output signal (blue). Is there a way to find out ...
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1answer
197 views
How to perform carrier phase recovery in software?
What are the options for recovering the phase of a BPSK signal in software? The only resources I can find online contain circuit diagrams – there seems to be no one willing to explain this to people ...
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1answer
51 views
Does any error correction code still work in such situation?
I'm looking for a kind of error correction code or solution that can correct my codeword in this case:
My message holds k bits, and 2*k bits codeword (rate is 1/2) is produced by the generator ...
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1answer
76 views
Determine the optimum receiver and the corresponding $P_{eM}$ for an AWGN channel
I have a source that emits $M$ equiprobable messages, which are assigned signals $s_1, \dots,s_M,$ that are equidistant by $a$. That is, if we plot the $s_k$ signals in a horizontal axis they are dots ...
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32 views
How to encode a byte array to sound file and then convert back?
This question is moved from Stack Overflow.
Sorry about this noob question, because I never work with matlab and signal processing before. Here is what I want to do: I have a fixed length of byte ...
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1answer
145 views
Why does OFDM use cyclic-prefix while QPSK uses root-raised cosine filters?
My understanding is that BPSK/QPSK/... are often implemented with root-raised cosine (RRC) filters to reduce ISI and bandwidth.
OFDM can be understood to be BPSK/QPSK/... implemented on multiple ...
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4answers
271 views
How is symbol synchronization with OFDM done?
I'm trying to understand how symbol synchronization is done in OFDM using pilot tones, cyclic prefixes, or any other technique.
I've read the following answers which provide some explanation, but I ...
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1answer
72 views
Meaning of Q and I in all-software QPSK communication systems?
Q and I seem to come up a lot in discussions of digital communications, such as the comprehensive answer provided to this question:
FFT window phase syncronising
It seems like the Q and I channels ...
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1answer
68 views
Intersymbol Interference — Root raised cosine filter redundant if doing impulse response equalization?
I'm implementing DBPSK (differential binary phase-shift keying) over audio (44.1kHz sample-rate) using software. Eventually I'll use multiple audio frequencies at once, so I'm using FFTs and inverse ...
5
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1answer
83 views
How to send / receive a short impulse in an extremely noisy signal with high timing accuracy?
I am pretty new to DSP. I need a computer to transmit data to a receiver through audio signals in a loud outdoor environment. (I am writing the software for both sender and receiver so I can design ...
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2answers
209 views
Why do you get instantaneous phase by calculating correlation with a carrier signal?
I am somewhat new to DSP. I'm trying to implement BPSK by following this Python QAM tutorial.
My code seems to work, but I really just ported the tutorial's Python code to C++, and do not understand ...
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3answers
242 views
Common methods of transmitting digital data through an extremely noisy audio signal?
I am developing software for transmitting data from a computer to a mobile device using audio. Specifically, from the computer's speaker to the device's microphone. (I am developing both the sender ...
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3answers
92 views
Optimal DC-free line encoding
I have a block of n bits that I'd like to encode into m bits that have an equal number of zeros and ones.
I looked at protocols like 8b/10b but it wastes 25% of the data to achieve balance.
As an ...
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1answer
106 views
increase of encoding rate increases bandwidth?
I came across this paragraph in an article about signal processing.
Addition of redundant bits for improving the error probability leads to bandwidth expansion of the
transmitted signal by an amount ...
5
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1answer
136 views
Which digital modulation scheme would be suitable for transmitting digital data through the output of a PC soundcard
I need to output a data stream at 40 kbit/s or faster out of a computer system whose only accessible output peripheral is the audio interface. This interface has reasonable specs, 96 kHz sample rate, ...
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1answer
194 views
formula to calculate ber in wireless 802.11 according to distance from tx and rx
I'm looking for a formula to calculate the bit error rate of a wifi communication 802.11a/b/g according to the distance between transmitter and receiver.
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2answers
169 views
Is it possible to transmit and/or receive multiple types of signals at the same time?
Using an inexpensive SDR (such as the USRP or Per Vices Phi), I want to process two or more communication protocols at the same time (e.g. WiFi and GSM). Is it possible to Tx (or Rx) both at the same ...
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1answer
128 views
Help with dB calculation in power transmission
why if I lose 80% power in the output of a system, it is equivalent to 10×log10(0.2) = -7dB ?
why it is not ...
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1answer
473 views
Information Theory - units of channel capacity
In a first course in Information Theory, when the operational interpretation of channel capacity is introduced, it is said to be the highest data rate (in bits/channel-use) of reliable communication. ...
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506 views
Why does my simulation of the binary symmetric channel disagree with theory?
Could someone please answer me why the simulated performance (using matlab) of a Hamming code over a binary symmetric channel does not fit exacly with the theoretical?
Here is my code:
...
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1answer
209 views
Why the error probability is given by this expression?
I have seen this equation:
$$
\Pr({\epsilon}) = Q({\sqrt{2E_b/N_0}}) \,.
$$
where these definitions hold:
$$N_0/2 - the \ spectral \ density \ of \ white \ noise$$
$$E_b = PT_b - the \ energy ...
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1answer
124 views
How to apply the CA-CFAR methods in practice?
Applying constant false alarm rate is a critical step for estimation of performance of all detectors. Has anybody experience on practical implementation of this estimator for energy detector? Can ...
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1answer
144 views
Why is privacy scrambling a standalone block in a communications transmitter?
In some telecommunication systems, scrambling of transmitted data is applied to provide some level of security. For example, the communication system might look like:
Data -> Scrambling -> ...
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2answers
2k views
Extracting Binary Magnetic-Strip Card Data from raw WAV
I am faced with a tricky challenge: To extract binary data from an iPhone magnetic strip card reader. This is what the magnetisation on the card looks like:
Source
Here is the .WAV the iPhone ...
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2answers
107 views
What input to use for an AR model of a vowel sound?
I've recorded a 2-sec pronunciation of a vowel sound. The first 0.12 or so seconds of the signal are shown below.
Now, I've constructed an auto-regressive (AR) 8th-order model to compress this ...
6
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1answer
230 views
What are thoughts on best modulation to use for underwater acoustic communications at low frequencies?
I wanted to ping the DSP hivemind for general thoughts on what would be the best modulation type to use for low frequency underwater communications. I have chosen this project since I can learn a lot ...
6
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1answer
537 views
How to estimate and compensate for doppler shift in wireless signals?
I was wondering what good method(s) exist for the estimation (and subsequent compensation) of doppler shift for transmitted signals, be they acoustic or RF, in the context of comms.
The question: ...
9
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1answer
966 views
Optimum matched filter without ISI
Given a filter used to shape the digital signal, $p(x)$, and given that we do not want the filter combination to cause any ISI, what "matched" filter, $q(x)$ will maximise the SNR?
Matched filters ...
