6
votes
What's the difference between frequency shift, frequency offset, phase offset, and phase noise?
To complement Dan's answer, this is the way I usually use these terms.
Frequency shift: a change in the frequency of a bandpass signal. It can be intentional, as when downconverting a signal in the ...
- 14.9k
5
votes
What's the difference between frequency shift, frequency offset, phase offset, and phase noise?
Frequency shift and frequency offset could reasonably refer to the same thing, but a shift suggests something that has moved (from one frequency to the next as would occur in a changing Doppler) while ...
- 48.8k
4
votes
Why do we ever use low-order modulation schemes?
As we go for higher modulation order, detection complexity increases by exponentially , Hypothesis grows and detection becomes computationally intensive task.
Also in use cases where channel condition ...
4
votes
Help me understand the concept of IQ signals
The important takeaway is: using a radio, you can transmit two signals "at the same time" (technically: over the same bandwidth). One of the signals is known as I (in-phase), the other as Q (...
- 14.9k
3
votes
Accepted
Mean square error for a quantizer - problem in integral
With
$$y_j=\frac{x_j+x_{j-1}}{2}$$
you obtain
$$\begin{align}\int_{x_{j-1}}^{x_j}(y_j-x)^2dx&=\frac{(y_j-x_{j-1})^3-(y_j-x_{j})^3}{3}\\&=\frac{\left(\frac{x_j+x_{j-1}}{2}-x_{j-1}\right)^3-\...
- 88.9k
3
votes
how to find type of a binary sequence
There are not that many low order Barker Code sequences, so it would be feasible to cross-correlate the sequence against a library of Barker codes to see if there are any direct matches.
As for ...
- 48.8k
3
votes
Learning transceiver algorithms
As Marcus points out, the answer depends on what you mean by "basic". It also depends on whether you already know the math and want to focus on implementations.
If you know how to code, and ...
- 14.9k
3
votes
Accepted
Why Fourier transform can be applied in digital signal processing?
Regardless of block processing with the Fourier Transform, latency in any signal processing cannot be avoided given the laws of causality; any filtering done must have processing delay. For the ...
- 48.8k
3
votes
Accepted
Detection problem with extra noise observation. Does the extra observations help with detection?
$$y=y_1 + \alpha y_2=x+(1+\alpha)n_1+\alpha n_2 \tag{1}$$
As $n_1$ and $n_2$ are iid $\mathcal{N}(0,\sigma^2)$, you have now the new Gausian noise $\mathcal{N}(0,\nu^2)$ where $\nu^2=\left((1+\alpha)^...
- 6,080
2
votes
Accepted
The baseband sampling frequency when the negative spectrum is considered
As Hilmar points out in a comment, the answer depends on whether the baseband signal is real or complex.
Consider a real baseband signal $r(t)$ with bandwidth $B$. It must be sampled at rate $2B$. ...
- 14.9k
2
votes
Choosing the scaling parameters for a modem implementation
The optimum solution for where to set the Automatic Gain Control (AGC) relative to the full scale of the ADC typically allows for some clipping given the goal is to minimize the total noise ...
- 48.8k
2
votes
Accepted
Using Zero-Phase Anti-Causal Filters in Real-Time Embedded Systems
It depends on your definition of "real time" and how you expect the filter to be used.
Can you implement a two-way, offline IIR filtering scheme like Matlab's ...
- 11.8k
2
votes
Accepted
Why do I get the same PAPR effect with all modulation orders in MATLAB
This is because the distribution for OFDM waveforms after the IFFT, prior to using additional crest factor reduction techniques, closely approach a Gaussian, regardless of modulation order. Therefore ...
- 48.8k
2
votes
Difference between cellular modems and modems used in wifi router
I will start my saying that most of my experience in this area is in cellular PHY, not WiFi. So if I get something wrong about the WiFi side of the comparison, I am open to corrections.
I am also ...
- 21
2
votes
Accepted
When can we use real channel coefficient instead of complex one to understand communication scheme?
Well, you can decompose any linear scheme into an imaginary and a real part.
But you'd not be making anything easier: Your channel can lead to any phase rotation, so any complex channel coefficient is ...
- 29.6k
2
votes
How to find sampling frequency in aperiodic signal?
The signal is finite in time and hence it has unlimited bandwidth. You cannot sample it without aliasing. You can only derive a sample rate from the specific requirements of your application, i.e. how ...
- 42.5k
2
votes
Accepted
Is it possible to consider circular convolution in case of appending the guard interval as a suffix instead of a prefix
You raised an interesting question. The purpose of padding prefix in each time-domain OFDM symbol is in order to do frequency-domain equalization (EQ). The reason why EQ is needed is to remove (or ...
- 292
2
votes
how to find type of a binary sequence
Most sequences don't have a "type" of any kind, meaning that they have very little or no linear structure that might allow the sequence to be generated why a relatively short linear feedback ...
- 20.2k
2
votes
What is use of Quadrature Converter in OFDM?
In OFDM, the output of DAC after IFFT is a complex analog signal. In order to transmit this complex signal, two orthogonal RF channels are needed, one to transmit the real part, another one to ...
- 292
2
votes
Spectral power density of thermal noise
“Thermal noise” is synonymous with “Johnson-Nyquist noise”, “Johnson noise”, or “Nyquist noise”: they all refer to the same noise process and is well approximated as a Additive Gaussian White Noise ...
- 48.8k
2
votes
Accepted
How can I simulate a random delay offset between two data streams?
That's definitely a way to go about it!
As you identified, the integer shift $L$ is "easy". The harder part is the $\epsilon$ shift.
By the way, digital communication receivers need to do ...
- 29.6k
2
votes
spectral bandwidth of QPSK signal
Regardless of how $B$ is defined earlier in the Wikipedia article, the equation starting with where the Nyquist rate is introduced is a single-sided bandwidth:
$$f_p < 2B$$
Which state that (single-...
- 48.8k
2
votes
Accepted
How is the normalized power required for unipolar NRZ twice that of polar NRZ?
If the levels of the polar signal were $\pm V$ you would be right, but then it wouldn't be a fair comparison with the unipolar signal with levels $+V$ and zero. A fair comparison would be to have the ...
- 88.9k
2
votes
Help me understand the concept of IQ signals
It might be best to compare an IQ signal with complex numbers, or circle on an XY plane, or phasors.
As the IQ signal is a sum of sine wave with some amplitude and cosine wave with some amplitude, the ...
- 2,268
1
vote
What is use of Quadrature Converter in OFDM?
"Mixing" has a different meaning for RF than it does for audio.
In audio mixing is a linear combination of the two (or more) signals. In RF, it's the modulation that bumps a baseband signal ...
1
vote
Time of arrival
$t_e$ is the absolute time when the signal was transmitted from the transmitter. $\frac{d}{c}$ is the Time of Flight (TOF). The Time of Arrival (TOA) is the absolute time when the signal reaches the ...
- 48.8k
1
vote
How Reducing Dynamic Range by Boosting Signal Improves Burst Detection?
1) How boosting the signal reduces the dynamic range?
I don't think the comment is correctly describing what is happening. Just scaling the entire data set by a constant value, in this case ...
- 1,102
1
vote
Accepted
How correctly choose a channel model?
Different links can have different channel characteristics.
If your (A) is very close to (B) and any scatterers are far away then the LOS component dominates which could be modeled using a Rician ...
- 3,012
1
vote
Why can interleaving make the channel "memoryless"?
[Posted as an answer because it is too long to be left as a comment]
It is not the case that a channel with memory can always be treated as a memoryless channel with sufficiently long interleaving. If ...
- 20.2k
1
vote
Accepted
What is discrete in value/amplitude/magnitude?
A specific example, and common application where this occurs is with an "Analog to Digital Converter" (A/D), which is the boundary between the analog and digital world. Computers store ...
- 48.8k
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