12
votes
Isn't Gardner's algorithm and Early-Late gate the same thing?
The Gardner Timing Error Detector is diagrammed in the graphic below, where two samples per symbol are used, and the error is determined using Prompt*(Late-Early), and when synchronized the center ...
- 55k
3
votes
Accepted
Symbol Sync blocks in GNU Radio seem to use PID (well, PI) for their clock sync feedback loops. Why not IIR/FIR?
Keep in mind that we are talking about a clock synchronization loop, so you need to think of the behavior from a control-systems perspective.
FIR
Just discard that notion right out. There are good ...
- 13.3k
3
votes
Accepted
How do I Correlation Estimate both for a pattern and its inverse in GNU Radio?
Map 0 to 1 and 1 to -1 on both the reference sequence and the received bit sequence, and then correlate; an inversion will also just invert the sign.
If that mapping is hard to do on the received ...
- 32.5k
3
votes
Symbol Synchronization for GFSK/FSK signals in GNU Radio
The Symbol Synchronizer block is a PLL-based synchronizer that is trying to estimate the symbol clock period and symbol clock phase (aka timing offset) based on the samples coming in that represent ...
- 2,710
2
votes
Accepted
Symbol Timing recovery for modulation producing ISI
In general the ISI is never severe enough for the symbol timing recovery algorithm not to work, but it does degrade its achievable performance on the $P_{be}$ vs. $\dfrac{E_b}{N_0}$ curve. In other ...
- 2,710
2
votes
Confussion on roll-off factor, sampling time and Raised Cosine pulses.
An easy way to see what's going on is by plotting the signal's eye diagram.
With low roll-off factors, the eye diagram will show you that deviating a small amount from the optimum sampling time will ...
- 15.4k
2
votes
How does the Meyr-Oerder Timing Algorithm work?
For PAM signals, the squaring creates a spectral component at $\dfrac{1}{T}$. Consider the following trigonometric identity to understand why this is the case:
$$\cos^2\left(2\pi \dfrac{1}{2T}\right)...
- 2,710
2
votes
How to determine the symbol rate of a 2-FSK signal?
One approach could be to perform an FM-detection step (e.g. an atan2() operation followed by a first-order difference) to transform the waveform to measurements of ...
- 24.8k
2
votes
Fractional spaced equalizer + timing (clock) recovery
The answer is to NOT down-select to one sample per symbol until after using the Gardner Timing recovery since the TED requires 2 samples per symbol. If the equalizer is running at 2 samples per symbol,...
- 55k
2
votes
Symbol time offset simulation
If you postulate that receiever's clock is perfect, then you want to make the transmitter send symbols every $T_s \pm \varepsilon$ seconds, where $T_s$ is the symbol period according to the receiver.
...
- 15.4k
2
votes
Accepted
Time recovery algorithm and a symbol with samples
Preamble: This answer is about timing recovery in a sense of symbol synchronization, i.e. finding the proper sampling phase of a baseband signal.
Based on the stated requirement of only 8 samples per ...
- 406
2
votes
Why should costas loop be done after clock recovery, as opposed to before?
The job of the costas loop is to "derotate" the constellation points.
But for that you first need to look at the constellation points at the symbol instants. If you look at the signal ...
- 32.5k
2
votes
Accepted
Symbol Timing Recovery with Fractional Sample per Second
Since ultimately the recovered time must be symbol synchronous (in the end we need one sample per symbol and that sample should be at the correct sampling location to minimize error), it would make ...
- 55k
1
vote
Accepted
Effect of high SPS under low SNR
Let me simplify the question as there can be many secondary effects based on implementation details between the two approaches suggested.
If we ask if there is any difference in sampling four samples ...
- 55k
1
vote
GRC implementation for IQ data acquisition of 2-GFSK Radio
Yes, understood. This non-linearity is not an issue in GMSK as i understand but a problem in GFSK, how does one equalize a GFSK signal then anyway?
Not at all, usually. GFSK use cases are systems ...
- 32.5k
1
vote
Accepted
How to choose sample offset values in timing synchronization for a QPSK demodulator?
The target offset is 0. This corresponds to zero timing error, and also has the highest slope (sensitivity) to a timing offset which is the ideal location to lock a loop.
The Gardner using three ...
- 55k
1
vote
Accepted
oQPSK symbol synchronization
I was finally able to resolve the synchronization issue by increasing the number of samples per symbol. The system was working at 2 sps. Increasing it higher (e.g. 2.1) solved the problem completely ...
1
vote
Accepted
Can an OFDM signal be demodulated at a sample offset over the cyclic prefix?
Yes it can, for time advances relative to the ideal selection but not for time delays. Since the Cyclic Prefix (CP) is taken from the end of the exact same OFDM symbol, it is circularly invariant, up ...
- 55k
1
vote
Accepted
MSK receiver for ultra-low SNR
I don't think you actually need to worry about clock recovery; just oversample by a factor $o$ (>> 4; at this chip rate, maybe a factor of 128?), correlate with the spreading sequence, and pick ...
- 32.5k
1
vote
Design a timing recovery algorithm with predefined samples with max amplitude
I would recommend the Gardner Timing Error Detector vs the CORDIC for determining timing error for use in a timing recovery loop. (The CORDIC is an algorithm of choice when we desire to trade ...
- 55k
1
vote
What is a correct approach to baud-rate digital timing recovery for self-equalized line code
A good option for timing function for such signal happens to be the canonical $(a_k x_{k-1} - a_{k-1} x_k )$ with additional condition to calculate its value only when $a_k$ equals $a_{k-1}$ (i.e. ...
- 406
1
vote
Accepted
Symbol synchronization with M-QAM. M < 16
Are there any superior ways of doing symbol sync?
Yes! As you've noticed, your initial estimation of timing isn't "valid" forever.
This might be caused by clock jitter, or simply remaining sampling ...
- 32.5k
1
vote
Accepted
What is symbol in signal processing?
A symbol is a symbolic representation of a baseband signal in digital communication. Imagine you have 2 bits with equal probability 0 and 1. For 0 you transmit $s_0(t)=+A$ for $0 \le t \le T$. For 1 ...
- 2,303
1
vote
What is symbol in signal processing?
Below is the constellation diagram of 8 QPSK, The circles you see below are modulation symbols. The alphabet A here is the set of all these 8 possible symbols that are equally likely to be transmitted....
- 2,655
1
vote
Accepted
Loop Bandwidth for Carrier Demodulation loop
Your results are not showing that the data is being "filtered out" necessarily but that you are using a non-linear phase filter resulting in group delay variation over your passband, as evidenced by ...
- 55k
1
vote
Isn't Gardner's algorithm and Early-Late gate the same thing?
There has been a longstanding confusion between the two expressions. For the matched filter output denoted by $z[m]$ and symbol time by $T_M$, an early-late TED has an expression
$$
\begin{align}
...
- 809
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