Call drop caused by Forward and Reverse Imbalance and Call drop caused by Forward Interference
Call drop caused by forward and reverse imbalance
Typical case:
MS received power and strongest pilot Ec/Io maintain in good state, such as Rx
Power>-100dBm, Ec/Io>-15dB;
As MS moves, MS reverse Tx power is increasing continuously to 23dBm, until call
drop happen;
As MS moves, MS Tx_Adj is increasing continuously and it is one positive value, until
call drop happen;
After call drops, MS will initialize and stay in previous pilot. There is signal in MS, but
origination call is difficult, even if origination is successful, call drop is very possible.
Analyzing:
In the above case, MS Rx power and pilot Ec/Io are all good, and this means the
forward link is good. But in MS origination procedure MS is increasing transmitting
power until maximum, and this means the reverse link is bad. That is forward and
reverse imbalance. Tx_Adj>0 also means forward is better than reverse.
Because forward is better than reverse, so in the edge of coverage BTS can not receive
the signal from MS correctly and BTS call drop mechanism is triggered, and then call
drop will happen.
Note:
Forward and reverse link imbalance includes two kinds: forward is better than reverse;
reverse is better than forward.
The above case is the former. It popular in practice and effect is large. Because
subscriber can not tolerate that call failure and call drop happen when there is signal in
MS, so this case should be cared for very much.
Optimization method:
Find the rootstock of imbalance:
For the case that forward is better than reverse:
Judge if the cell power configuration is too high;
Judge if the pilot gain is too high;
Judge if there is reverse interference;
For the case that reverses is better than forward:
Judge if the cell power configuration is too low;
Judge if the pilot gain is too low;
Judge if there is forward interference;
Call drop caused by forward interference
Typical case:
As MS moves, its Rx power is increasing;
As MS moves, the strongest pilot Ec/Io is decreasing and is not enough for
demodulation requirement, F-FER increases very fast until call drop;
As MS moves, MS Tx power is normal and will not tend to maximum;
After call drops, MS will initialize and stay in previous pilot, but origination call is
difficult and call drop is very easy to happen. MS may stay in one new pilot and the
signal stabilization is decided by interference source.
Analyzing:
MS Rx power is increasing, but the pilot Ec/Io is decreasing, this means there is
forward interference. When MS moves to interference continuously, the pilot Ec/Io will
decrease continuously, until F-FER increases very fast and MS fading timer expires,
MS will initialize again, that is call drop.
Note:
For the forward interference source, there are two kinds: external interference; internal
interference.
External inherence: the radio signal from other system drops into MS receive
bandwidth, MS will re-initialize after call drop and stay in previous pilot. Call drop is
very easy to happen again, even if origination call is successful.
Internal interference: usually it is handoff which causes call drop. When MS moves to
a new cell, for some reasons (wrong neighbor list setting; too narrow search window)
handoff is failed, and the objective cell pilot will be a strong pilot interference. This
kind of interference belongs to internal interference. The difference from external interference is: MS will re-initialize after call drop and stay in one new pilot (the
objective handoff cell pilot) very well.
Optimization method:
External interference: Inform customer and they connect with government to clear;
Internal interference: Check background configuration and adjust the related
parameters.
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