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11 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 ...
Dan Boschen's user avatar
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10 votes
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FSK Demodulation, Bit Timing Recovery

I am currently implementing acoustic FSK modulation and demodulation. I am not a signal processing guy… Since you say you have matched filters, and you mention non-coherent detection, I think you're ...
Marcus Müller's user avatar
3 votes
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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 ...
TimWescott's user avatar
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3 votes
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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 ...
Marcus Müller's user avatar
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 ...
Andy Walls's user avatar
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3 votes
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Loop bandwidth for symbol timing recovery

There is an optimum loop BW that maximizes the SNR, and this applies to both Symbol Timing Recovery as you inquire about as well as Carrier Recovery. The specific answer depends on the characteristics ...
Dan Boschen's user avatar
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2 votes
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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 ...
Andy Walls's user avatar
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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 ...
MBaz's user avatar
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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)...
Andy Walls's user avatar
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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 ...
Jason R's user avatar
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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,...
Dan Boschen's user avatar
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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. ...
MBaz's user avatar
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2 votes
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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 ...
megasplash's user avatar
2 votes
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How to measure/estimate symbol rate of a signal with unknown ( but probably QAM ) modulation?

The nonlinear trick is in fact often used to recover the symbol clock of $\frac \pi {2N}$ phase-shifted signals, e.g. BPSK, QPSK: Squaring samples $x[n]$ (or even taking $x^4$) leads to a removal of ...
Marcus Müller's user avatar
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 ...
Marcus Müller's user avatar
2 votes
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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 ...
Dan Boschen's user avatar
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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 ...
Marcus Müller's user avatar
1 vote
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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 ...
Dan Boschen's user avatar
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1 vote
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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 ...
Moses Browne Mwakyanjala's user avatar
1 vote
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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 ...
Dan Boschen's user avatar
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1 vote
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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 ...
Marcus Müller's user avatar
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 ...
Dan Boschen's user avatar
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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. ...
megasplash's user avatar
1 vote
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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 ...
Marcus Müller's user avatar
1 vote
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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 ...
jithin's user avatar
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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....
Dsp guy sam's user avatar
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1 vote
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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 ...
Dan Boschen's user avatar
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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} ...
QMC's user avatar
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1 vote

Optimal time for sampling symbol in digital receivers

You are mixing up two different notions of sampling. In a digital communications system, the received (analog, continuous-time) signal is passed through an A/D converter so that the needed further ...
Dilip Sarwate's user avatar

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