i won’t be able to help on your exact parameters, because i’ve never worked with ZTE before, but i can give you a strategy :
– MS favour camping on 1800 cells (Cell reselect offset of 1800 cells should be between +4dB and +10dB, compared to 900 cells)
– MS that sets up a call in 900 cells should perform a HO towards 1800 cells if possible (using a “push” handover), as soon as a 1800 cells is above a certain “capture” threshold (usually between -75dBm and -80dBm)
– Better cell HO between 1800 cells and 900 cells (and vice versa) should be disabled (to avoid ping pong)
– MS in a 1800 cells shall be able to exit safely to a 900 cells, by using an emergency HO as a “exit HO”. Therefore you need to use the DL HO on low RxLev with a value between -85dBm and -90dBm. You should have a difference of about 10 dB between the capture threshold 900–>1800 (i.e. -75dBm) and the exit threshold 1800–>900 (i.e. -85dBm).
Hope that helps,