Hi RBS
This is due to the feature in BTS its also called Dynamic Power Shutdown, it is there so that if the traffic in a cell is very less then the bts will shutdown the trx of the cell thus saving the power consumption of the bts, but the trx should start automatically if traffic increases, if you are facing this problem then get the feature disabled from OMCR. This feature is in the new bts’s in ericsson and huawei too but we usually turn it off in our network due to such problems.
Regards
Tanuj