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Feature #3483

handover decision: if rxlev is ok but rxqual is bad, move from TCH/H to TCH/F

Added by neels 10 months ago. Updated 8 months ago.

Status:
New
Priority:
Normal
Assignee:
Category:
Handover
Target version:
-
Start date:
08/20/2018
Due date:
% Done:

0%

Spec Reference:

Description

Bad quality scenario: rxlev is ok, but rxqual drops below the min_rxqual threshold.

Handover decision 2 contains a switch from TCH/H to TCH/F to improve rxqual. See on_measurement_report() in handover_decision_2.c, by the comment "Bad Quality".
However, that condition seems buggy: "if (... av_rxqual > ho_get_hodec2_min_rxqual(bts->ho))" should probably be the flipped?

To test for this with real equipment, we could manipulate the min_rxqual threshold during a call.
In ttcn3, we could use measurement reports.


Related issues

Related to OsmoBSC - Feature #1608: various handover improvements, meta-issueRejected02/23/2016

History

#1 Updated by neels 10 months ago

  • Related to Feature #1608: various handover improvements, meta-issue added

#2 Updated by laforge 9 months ago

  • Assignee set to neels

#3 Updated by neels 8 months ago

I expect this to already work, just need to make sure by explicit tests.

#4 Updated by neels 8 months ago

  • Category set to Handover

#5 Updated by neels 8 months ago

Another problem: this magic number in on_measurement_report() should rather be ho_get_hodec2_min_rxlev():

if (rxlev2dbm(av_rxlev) > -85)

#6 Updated by neels 8 months ago

to be clarified is the issue of moving between codecs without transcoding support. Some comments are at https://osmocom.org/issues/3503#note-5

#7 Updated by neels 8 months ago

neels wrote:

However, that condition seems buggy: "if (... av_rxqual > ho_get_hodec2_min_rxqual(bts->ho))" should probably be the flipped?

3GPP TS 45.008 8.2.4 Range of parameter RXQUAL:

The BER values used to define a quality band are the estimated error probabilities before channel decoding

and RXQUAL_0 means BER < 0.2%, ... RXQUAL_7 means BER > 12.8%.

i.e. a higher RXQUAL value should indicate a worse signal, and the condition is not flipped.

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