Fault ID and name 9: EFaultId_DacWordChangeAl Used in products FlexiBTS, LTE
Detecting unit FCM
Source FCM
Meaning The reference frequency that the BTS master clock receives has changed by about 0.2 ppm or more (which equals the change magnitude of 204 DAC steps or more) during the measurement period, compared to the BTS master clock frequency. The cause of the alarm can be: 1. The reference frequency has changed due to a fault in the transmission network synchronization (which in turn is caused by an equipment fault or a setting error. Note that if the network synchronization malfunction lasts for a long time, the alarm is canceled when the BTS frequency reaches the faulty reference synchronization. The alarm can also be activated if the faulty reference synchronization is corrected and there is again the difference of 0.2 ppm or more. The alarm is canceled whenever the difference becomes smaller than 0.2 ppm. 2. The reference frequency fluctu-ates continuously due to a great deal of jitter/wander in the transmission network. The alarm is continuously activated/canceled (however, the alarming state might predominate). There is always some jitter/wander in the transmis-sion network; the limits are defined in ITU-T G.823/824/825. 3. If the BTS inte-grated transport part receives the synchronization information via the 2.048 MHz synchronization input (external clock source), the alarm situation might be caused by a fault of that signal. In that case, the alarm behavior notifications listed with the Iub signal (see above) are also valid in this case. 4. There is an equipment fault in the BTS. The equipment fault is, however, not the most common reason. Normally, the reason is in the Iub/reference signal behavior (see the descriptions above).
State Start / Cancel
Unit status Working
Unit status attributes
Effect This fault does not immediately affect the operations of the BTS, but it is a noti-fication that the BTS master clock frequency deviates from the used reference frequency more than in normal circumstances. The BTS master clock tuning continues in spite of the alarm, but because the BTS master clock adjustment is quite slow to filter the instabilities of the reference clock interface, it takes some time (even several hours) before the BTS operations start to be affected.
Reported alarms 7652 BASE STATION NOTIFICATION
LED display Blinking red
96 Id:0900d80580a300da DN0980455 Instructions Because there are several possibilities for the alarm activation, a BTS Clock
Frequency History feature has been developed. You can access the stored history data via BTS Site Manager. You can use the history data as a tool for finding out the reason for the fault/alarm situation (for further instructions about the history feature, see the online help of BTS Site Manager). Depending on the possible reason, follow the instructions below:
1. In case of a fault in the transmission network synchronization, you must correct the network synchronization. The long-term accuracy of the Iub signal must be 0.015 ppm or better (check the correct Iub accuracy by measuring it).
No actions on the BTS are necessary.
2. If the basic accuracy of the Iub signal is in order but there is too much insta-bility, that is, the jitter/wander is outside the acceptable limits, you must correct the synchronization of the transmission network. The limits for the jitter/wander are defined in the ITU-T G.823/824/825. No actions on the BTS are needed.
3. In case of a BTS equipment fault, the location might be:
Transport part:
- First check the alarms of the TRS with BTS Site Manager and act accordingly.
- If there are no alarms, check the TRS synchronization settings.
FCM unit:
- If the TDM reference signal accuracy and the TRS are in order but the FCM unit is still alarming, run the fast tuning with BTS Site Manager.
- If the alarm is still active after the fast tuning is finished, reset
the site. If the problem does not disappear in a few minutes, reset the site.
- If that does not help, replace the FCM unit.
Note that if the reason is in the transmission network synchronization, replacing the faulty unit does not correct the situation. Furthermore, the alarm activity (frequent alarms/cancels) points to an instability in the transmission
network, not to a fault in the unit.
4. After the fault situation has been cleared, you might need to tune the BTS master clock because the BTS master clock adjustment is quite slow. You can perform the tuning:
- manually by changing the DAC word (during a site visit)
- or with fast tuning, in which the BTS master clock is tuned in a few minutes automatically near the Iub reference (normal tuning takes care of the fine tuning).
Note, however, that you should only use the fast tuning in case the Iub refer-ence signal is known to be a good one. Otherwise the BTS frequency might be tuned into a totally incorrect value, causing serious problems in the network performance.
Background information: The principle is that in the mobile network, the
syn-DN0980455 Id:0900d80580a300da 97 chronization goes from S1 interface. But in reality that chain might be broken somewhere and, for example, when using leased lines, the BTS may take the reference synchronization from the transmission network of another operator.
This does not harm the system if the synchronization of the leased line service provider is also accurate/stabile enough. The BTS uses the incoming synchro-nization signal as a reference for the Air interface, the accuracy requirement of which is set by 3GPP.
Related faults
98 Id:0900d80580a300a0 DN0980455