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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123 views

State-of-art of telecommunications? [closed]

There seems to be a number of different ways for telecommunication. What is the most recent (and maybe standard) technique used today? It seems the simple AM/FM modulations are definitely somewhere in ...
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460 views

WIDELY UNKNOWN?? Wireless Channel Transfer Function or freq response - frequency vs attenuation

We know that the signal attenuates out with distance and according to the channel transfer function or frequency response, the signal frequency components attenuate to different values based on ...
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1answer
284 views

How is GPS used to synchronize oscillators in a distributed system?

I heard that it is important to have all oscillator clocks at different places be synchronized for example in a geographically distributed system such a telecommunication network. Of course to some ...
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193 views

Line coding for a modulation order that is not power of 2

In case a symbol encodes a non-integer number of bits, how is done the bit-symbol pairing? For example, we have a 3-levels FSK with bit rate of 1Mbps and a sequence 01011001. What is the symbol ...
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2answers
747 views

16 psk demodulation

I have to implement a complete receiver in digital communications. The transmitter gives me an output vector which has real and imaginary values. It uses 16psk for modulation. How would I ...
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189 views

PPM Variant - Analytic symbol error probability

I'm trying to calculate symbol error probability of variant of pulse position modulation considering only AWGN channel. The decoder is maximum likelihood so the implementation of the detector is by ...
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1answer
758 views

Using Doppler velocimetry with digital signals such as Bluetooth

I have found several sources describing how to use Doppler velocimetry/anemometry to measure the Doppler shift with analog signals, but i cannot find much about using this method for digital signals ...
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2answers
215 views

Entropy Of A Symbol

Does the entropy of a symbol represent the most optimal average number of bits that can be used to represent a symbol? For example take the example of tossing a coin: $$ H_{source} = -p_{head} ...
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2answers
354 views

Filter design for frequencies in range 0-60Mhz

First of all excuse me for asking a seemingly vague question. But i am going nowhere in the problem i am trying to solve. I am working on a powerline communication system where i need to upconvert ...
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Digital Communication System [closed]

How can we determine whether the receive filter is optimal or not in a digital receiver? For a decision region, how can we choose a noise value zk?
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329 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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What does the one-tap equalizer used with OFDM accomplish?

I've read that OFDM normally uses a one-tap equalizer. It seems that a one-tap equalizer could only scale and delay a signal. Why is this useful? I thought multipath was handled through the cyclic-...
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612 views

Barker Sequence for QPSK

I'm trying to implement a QPSK burst modulation and demodulation through a channel and I'm now considering the synchronization part. I've read that Barker sequence were excellent option for this as ...
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1answer
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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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172 views

Rician factor effect

The Rician factor is the ratio between the mean power of the LOS path to the mean power of all other (non-LOS) paths. Increasing/decreasing this factor means increasing/decreasing the mean power of ...
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2answers
8k views

Is there a closed form for the average energy of a QAM constellation?

I'm trying to come up with a formula for the average energy of the signals in a M-QAM constellation. If $b$ is the number of bits represented by each point in the constellation, such that $M=2^b$. For ...
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1answer
882 views

Bandwidth of a communication system

As a rule of thumb, the bandwidth of a communication system with a complex signal must be equal to the bit-rate or symbol-rate? Besides, after reading this post, it is not clear for me how a band-...
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1answer
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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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1answer
141 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
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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 noticed,...
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1answer
192 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 ...
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3answers
555 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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2answers
440 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
5k 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
4k 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 ...
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2answers
8k 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 ...
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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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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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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
534 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 ...
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1answer
208 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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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
813 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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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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670 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 ...
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598 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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356 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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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 signal....
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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 ...