 Area Update if the new cell has a different tracking area code. In case of inter-RAT cell reselection, a short message service/circuit switched fall back (SMS/CSFB) capable UE will always initiate a Location Area Update procedure in the 2G/3G target cell, regardless of the location area code of the new cell. These procedures may fail which, in turn, causes the UE to initiate new cell search and reselection attempt to another cell. For example, if reading of SIB1 and SIB2 of the target LTE cell fails due to downlink interference the UE may internally bar the cell for a certain period [4]. This has been noticed to cause problems in high-interference areas, such as high buildings without indoor base stations. 15.3 Inter-layer Connected Mode Measurements In this section inter-layer measurements in connected mode are briefly summarized. An expo- sition of basic concepts can be found in [5] and [6]. Throughout this section it is assumed that the UE needs measurement gaps to perform inter-frequency or inter-RAT measure- ments. A UE supporting carrier aggregation may be able to do inter-frequency measurements without gaps. The inter-layer connected mode measurement and handover process consists of the following phases: 1. Measurement gap activation: If the UE does not support simultaneous reception on multiple carrier frequencies, measurement gaps must be configured before inter-layer measurements can be performed. The eNodeB configures the frequencies and RATs to be measured either at RRC connection setup or at the time of measurement gap activation. In case of GSM and UTRA FDD, a list of scrambling codes and BCCH carriers is also specified at this stage. 4 For GSM/UTRA RATs, the UE is only required to measure the scrambling codes and BCCH frequencies provided in the neighbour list. The measurement configuration 4 For LTE, there is no need to specify PCIs unless specific cell-specific measurement offsets are to be used. Inter-layer Mobility Optimization also lists the measurement quantity, the events that trigger a mea