Bug #4508
Viterbi Conv decoder performance
0%
Description
There seems to be some evidence that the viterbi decoder might not be performing as well as it should (vis-as-vis its ability to correct errors).
The tested code was a very short packet encoded with this code in tail-biting mode :
code = conv_gen.ConvolutionalCode(20,
[
( conv_gen.poly(0,2,3,5,6), 1 ),
( conv_gen.poly(0,1,2,3,6), 1 ),
( conv_gen.poly(0,1,2,4,6), 1 ),
],
name='lte'
)
Decoding results with each time # of bit erasure, % failed packet, % of bit errors.
libosmocore: 0 0.00 0.00 5 0.00 0.00 10 0.00 0.00 15 1.33 0.13 20 1.33 0.13 25 3.33 0.37 30 14.00 1.83 35 40.00 8.10 40 89.33 40.30 HW decoder: 0 0.00 0.00 5 0.00 0.00 10 0.00 0.00 15 0.00 0.00 20 0.00 0.00 25 0.00 0.00 30 0.00 0.00 35 2.67 1.43 40 56.67 24.90
History
#1 Updated by laforge 3 months ago
- Category set to libosmocoding
- Assignee set to Hoernchen
- Priority changed from Normal to High
Let's increae priority of this issue and actually assign it to someone with related area of expertise.
tnt: You compared the results of some FPGA hardware implementation with those of our software implementation? Do we know if this also happens in the convolutional decoding for GSM/GPRS/EGPRS? In the latter case, we should definitely investigate this ASAP.
Might also be a good idea to have unit tests that verify the error recovery matches the expected performance.
tnt if you have time/interest to work on this, sysmocom is happy to pay for it - but I somehow fear you have other priorities at the moment, hence I'm assigning it to Hoernchen for now.
#2 Updated by tnt 3 months ago
Yeah, I can look at it in ~ 1 month if Hoerchen hasn't gotten around to it by then.
I had a look back when I first reported the issue and spent about half a day and couldn't really see anything. Behavior was the same both with the "normal" and the "sse" version of the code despite them sharing almost nothing.
I don't know if the same thing is true for the normal GSM codes. Unfortunately trying a different code, using another termination mode and using different packet length isn't something trivial to change for the hardware decoder so it would take a good few hours to implement that to try.
