Abis trace : retrieve messages on the interface between the serving BTS and BSC, and between the target BTS and the BSC. Filter the messages concerning your mobile phone, and you might isolate all the messages concerning handovers. Compare those messages with the usual Handover protocol (which message comes when, and which message should come after it). That should tell you where the problem is. Software : K12…
QoS counters : if you know enough about them, you can also detect where is the problem occuring, even though it is not as detailed as Abis interface. Software.. it is vendor dependant.
Drive-test : looking at the layer 3 messages, you’ll find interesting messages about HO too. Software : TEMS, Agilent, etc…