Cross sector is easy to find,here i explain cross feeder(cross feeder TCH trx only,if it is a Cross feeder BCCH trx, it is believed to be Cross sector although still its cross feeder,you need to rectify it)
for a drive tester to test it(before going to BTS and arranging a cable trace):
the site should have atleast 2 trx each sector without combiner,(combiner bypassed)each trx connected to seperate antenna port.
now go into main beam of the suspected sector,make calls on all the trx it has,
first BCCH trx,note the Rxlevel,disable downlink power control before making the tests if you can.
than TCH trxs of the same sector,distinguish them with their differnt MAIO values,again note Rxlevel of all these trx.it should be same in ideal conditions but if there is cross feeder it would be different,the trx connected to(feeder swapped) different sector antenna will show alot lower Rxlevel then others, being transmitted in different direction as it is connected to some different antenna,now if you lock the call on that feeder swapped trx on which you are getting 20 – 30 dB less level and go around the site,it’ll show better level in some different sector in which it is swapped to.
same way try other sectors and trx too.its somewhat complicated and time consuming but can serve the purpose before going to BTS.
now if there are 2 or 3 trx per sector and combining is used,drive tester cant figure out the cross feeder since the crossed feeder has no transmission assosiated with it.it only serve as RX diversity.till the time anyone get that much experiance to figure it out,he is not a drive tester anymore.
Now for optimisers.
it’ll effect handovers,call establishments,SDCCH assignments.
if you look at sector wise and trx wise reports.
the crossed trx would cause maximum number of call drops HO failures, SD failures if SD is assigned on those Trx.and other services being served by those trx.
the performance of those trx degrade with TA,more the TA worst it would be.
Handovers based on Rxlevel can fail and result in a dropped call if the timeslot is reserved on the crossed trx,although the Rxlevel of BCCH was good enough to trigger a handover but since the trx on which the TCH timeslot for that call is allotted is transmitting in some different direction and the power in too less in the direction where the handover is being performed,either it will fail or drop.
same way while establishing a call when latched to the effected sector,if the call is matured on crossed trx it may drop or sustain after intracell handover.and if SD is assigned on crossed trx,it’ll cause more problems.
Diversity gain is reduced as well.
and much more,find such cells and have detailed study for more information on the system you are working on.
its based on my experiance,correct me if im wrong