OsmoTRX / BER, RSSI and Link Quality

Tom Tsou tom at tsou.cc
Thu Jul 7 20:24:38 UTC 2016


On Wed, Jul 6, 2016 at 10:19 PM, Alexander Chemeris
<alexander.chemeris at gmail.com> wrote:
> On Jul 7, 2016 7:58 AM, "Tom Tsou" <tom at tsou.cc> wrote:
>> The full BER calculation takes the re-coded and re-punctured sequence
>> (performed after decoding and CRC verification)
>
> Why after CRC?

Assume that we lower the detection threshold in the TRX and allow the
OsmoBTS to perform most of the burst gating based on the CRC. If we
calculate BER before the CRC, then the BER will be computed mostly on
garbage data.

>> A close and simple approximation to the full BER calculation treats
>> all zero valued soft bits as punctured bits and removes them from the
>> calculation.
>>
>> I think this is a reasonable approach to make the current BER measurement
>> sane.
>
> Why do you think re-puncturing is not a good approach - because of the added
> CPU load?

Yes, there is overhead. But, more simply, re-puncturing doesn't gain
very much. If we increase the accuracy of our BER calculation by some
fraction of a percent, will that really improve UE performance?

  -TT


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