[Olsr-dev] Maximal LQ less than 1 on Ethernet

Henning Rogge (spam-protected)
Thu Jun 19 10:43:27 CEST 2008

I just did a few experiments to discover the reason why the LQ of perfect 
links (switched ethernet) does not go up to 1.

The reason seems to be a combination of three points:
- we use a exponential moving average in the default LQ calculation
- we save the LQ values directly in the 1 byte network format
- we use a fixed point math system in the default LQ calculation

This two points creates a rounding problem that prevent the LQ value to rise 
above certain values.

The exponential depends on the following formula, with default alpha as 0.05:
    new_LQ = old_LQ * (1 - alpha) + measured_lq * alpha

the second part of this formula seems to get small enough that we cannot store 
it in a 1 byte value.

So we have to stop using the exponential average or change the number formats 
for LQ calculation, but I'm not completely sure about the effects of both 


Diplom-Informatiker Henning Rogge
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Angewandte Naturwissenschaften e. V. (FGAN) 
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