Dear Emre,
1+1 is a hot standby or protected system,with a single IDU(One unit)with two Baseband Modems.
1+1 can be used as X-PIC but in that case it will be used as 2+0 system,with the same single IDU(One unit)with two Baseband Modems.
X-pic solution is generally used for SDH solution while 1+1 is used for both PDH & SDH.