Reference Manual

Diversity Supervision
Signal Strength Imbalance The SSI (Signal Strength Imbalance) is
defined here as the mean difference (in
decibels) between the receiver’s two
diversity channels. The SSI is calculated
per observation period
Disturbance Threshold The Disturbance Threshold defines the
limit for the signal strength imbalance, at
which it is classified as abnormal and is
regarded as a disturbance
30.3 Function
The signal strengths of the two diversity channels are measured and
compared after the signals have passed through radio receiver
equipment. The diversity supervision is applied to dedicated channels
only.
The following actions are carried out separately for each TS:
•
The signal strengths are measured separately for the two diversity
channels during all measurement periods for all dedicated channel
connections which qualify for the channel utilisation threshold
criterion
In order to avoid degradation from possible DTX (Discontinuous
Transmission) employed by MS, the signal strength measurements on
TCH are restricted to the subset of 4 SACCH frames and 8 SID
(Silence Descriptor) TDMA frames as defined in /GSM 05.08/.
•
The CUR
i
is calculated for the TS during each observation period
• The SSI
i
value is calculated for the TS during each observation
period
The CURi and the SSI
i
values from all TSs are then evaluated together.
The corresponding transceiver gross measures are calculated for each
observation period:
SSI = i
6
(SSIi * CURi) / i
6 CURi ; i = 0..7
CUR = i
6 CURi / i
6 1 ; i = 0..7
A disturbance is assumed to exist when both of the following criteria
are fulfilled:
• The gross CUR exceeds the minimum channel utilisation ratio
• The value of the gross SSI exceeds the disturbance threshold
A fault is reported after filtering of the detected disturbances. The fault
condition ceases only after a leaky bucket filter is emptied by a number
of valid observation periods without disturbances.
Only those observation periods where the gross CUR exceeds the
minimum channel utilisation ratio are taken into account in the filtering
process. This means that a fault condition is only raised or ceased
during valid observation periods.
244 (421)
EN/LZT 720 0008 R1A
2001-06-26
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