Hi Steve,
Congratulations on a really first-rate piece of work!!
I hope to find some time next week (or possibly the week after) to do
some independent tests -- presumably, to confirm your results.
I believe your test used simulated data on an AWGN channel. It might be
useful to try also
- simulated, near threshold signals with Rayleigh fading
- real EME signals
- a standard set of files each containing many on-the-air JT65 signals
Yes, we certainly should do a parallelized version for multi-core
machines. As Bill already pointed out, there's no need for this
processing step to remain a separate, stand-alone program; it should
simply be called as a C (or possibly C++) function.
-- Joe, K1JT
On 9/20/2015 11:11 AM, Steven Franke wrote:
> Joe -
> For the record, here are the results of analyzing 1000 SimJT JT65A
> files with sync level set to 0 (a setting of -1 gave the same
> results) and with Rx frequency set equal to the simulated signal’s frequency:
>
> kvasd (this result should be for the high-effort “on frequency” setting):
> 198/1000 (20%)
> sfrsd 5000 trials, p1 metric, erasure probabilities 0.5, 0.6, 0.6, 0.6, 0.8:
> 157/1000 (16%)
> sfrsd 10000 trials, p1 metric, erasure probabilities 0.5, 0.6, 0.6, 0.6, 0.8:
> 182/1000 (18%)
> sfrsd 20000 trials, p1 metric, erasure probabilities 0.5, 0.6, 0.6, 0.6, 0.8:
> 201/1000 (20%)
>
> - Overall yield roughly doubled when the sync threshold was lowered from the
> wideband setting to the on-frequency setting.
>
> - The results confirm that sfrsd is capable of achieving the same decode
> probability as kvasd on weak simulated signals.
>
> You have probably already noticed the fact that the sfrsd should be easy to
> parallelize. It should be possible to test a bunch of candidate vectors at
> once. Perhaps that is something worth investigating for sfrsd. In an earlier
> thread, Bill had suggested that using Qt’s threading facility is the way to
> go, in general, for WSJT-X — but it’s not clear to me if that applies for
> this stand-alone C program.
>
> Steve k9an
>
>> On Sep 19, 2015, at 5:03 PM, Steven Franke<[email protected]> wrote:
>>
>> I have just now realized that the sync threshold is higher for “off
>> frequency” signals. Since I had set Rx freq to 3000, the results reported
>> below were obtained using the higher wideband sync threshold. That probably
>> explains the lower than expected yield. I’m re-running with Rx frequency set
>> equal to the simulated signal’s frequency…
>> Steve k9an
>>
>>> On Sep 19, 2015, at 2:57 PM, Steven Franke<[email protected]> wrote:
>>>
>>> Thanks Joe! This has been a fun project, and I’m learning a lot from it.
>>>
>>> I used your SimJT program to generate 1000 JT65A files at -24 dB SNR.
>>> Here’s what I get:
>>>
>>> kvasd (with Rx frequency set to 3000, so this should be the low-effort
>>> setting): 106 decodes out of 1000 (10.6%)
>>> sfrsd 5000 trials: 94 decodes (9.4%)
>>> sfrsd with 10000 trials: 112 decodes (11.2%)
>>>
>>> I expected higher percentages overall at this SNR but, in any case, the
>>> results seem to confirm that sfrsd is a viable decoder. I noticed that only
>>> a fraction of the files result in a vector being submitted to the decoder -
>>> maybe around 50% - I didn’t count carefully. Maybe this is another reason
>>> to take a look at the upstream processing. I think that your earlier
>>> results showed something closer to 40% at this SNR.
>>>
>>> Also, I am surprised at how little guidance the soft information is
>>> providing with the settings that we are using. Almost none, as it turns
>>> out. Note that if I change just the two probabilities that I use to set the
>>> erasure frequency of the “best” and “worst” symbols, such that all of the
>>> probabilities are the same, then we wouldn’t even need to sort the data
>>> according to probability (for the stochastic patterns), i.e. we would be
>>> using no soft information whatsoever! The results would change - but we’d
>>> be in the same ballpark. This makes me feel like one or both of the
>>> following might be true:
>>>
>>> 1. it may be possible to achieve the same results with fewer trials if the
>>> soft-symbol information was utilized in a smarter way
>>>
>>> and/or
>>>
>>> 2. the quality of the presently used soft-symbol information is so bad that
>>> it’s not worth using.
>>>
>>> In 2, I do not mean to say that there is something wrong with the signal
>>> processing. Instead, I’m wondering if information only on 2 of 63 symbols
>>> is just too watered down to be useful.
>>>
>>> Steve k9an
>>>
>>>
>>>> On Sep 19, 2015, at 2:11 PM, Joe Taylor<[email protected]> wrote:
>>>>
>>>> Hi Steve,
>>>>
>>>> I've looked again at the innards of sfrsd. I'm *much* impressed by what
>>>> you have done.
>>>>
>>>> Soon, it may be time to look again at the upstream decisions made in the
>>>> JT65 decoding chain -- decisions that determine what symbol vectors are
>>>> passed on to the actual decoder. Among other things to consider:
>>>> various parameters affecting those decisions were optimized (a long time
>>>> ago) for the EME situation with very weak signals, little if any QRM,
>>>> and only one or two signals in the Rx passband at a time. For HF use we
>>>> might want to change some of these parameters.
>>>>
>>>> -- Joe, K1JT
>>>>
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