Several UEs are reported not to attach and not reselect the corresponding geographical cell, in this case cell 2, but the adjacent cell3 causing sliglty higher load and interference on the latter one. The UE type is CPE EA360-135.
No alarm is issued, the abnormality is indicated first by the RSRP measurement at base station. Low percentage in the graph below indicates high PUSCH RSRP:
From the configuration file we find different frequency channel on cells 2 and 3:
eNodeBId=4, CellId=2, DlEarfcn=42715 ---- Band:42, Freq:3458.5MHz
eNodeBId=4, CellId=3, DlEarfcn=43715 ---- Band:42, Freq:3558.5MHz
First recommended check is on the neighboring cell relation, which according to the configuration file, is correct:
Considering that frequency band of the serving cell ( cell3 in this case) is lower that the band of cell 2 it is suggested to look into the cell selection algorithm that is implemented in the CPE and the question that arises is " Does the CPE perform a full frequency scan before connecting to the network or stops after the first suitable cell is found?"
The root cause can be explained better based on the current cell planning antenna parameters ( azimouth and downtilt ) and also on the cell selection mechanism that the CPE is following.
In the picture below is illustrated that between cells 2 and 3 the overlapping between the coverage areas is approximately 90 degrees hence the premise that the UEs (highlighted on the map) are belonging to the cell2 coverage area is partially wrong.
In order to understant why the cell 3 is preferred in the above situation it is recommended to perform drive-tests in the UE position and compare the measured values between the two cells and even the adjacent cell 4.
The mechanism of cell selection described in the 3GPP TS 36.304 explains this behavior for the situations the the cell 3 RSRP doesn't drop below -110dBm (configured threshold - InterFreqHoA2ThdRsrp) therefore cell reselection doesn't occur.
Cell 2 direct selection is not possible due to the "Stored information cell selection feature" (TS 36.304) that allows the UE to connect directly to the last known cell ( if "suitable cell" criteria is fulfilled) without scanning entire bandwidth and saving time in the reconnecting process.
The client was advised to use the "cell lock" feature that the CPE EA360-135 is provided with for initial manual cell selection and eventually deactivate the feature for the situation severe netwwork disturbances occur.
I was suggested to review the planning paameters and adjust the values for less coverage overlap.