What is "e-cellid"

Enhanced Cell ID, E-CellID, or E-CID is a positioning feature introduced in rel9 E-UTRA ( LTE radio). The UE reports to the network ( ESMLC) the serving cell ID, the timing advance (difference between its transmit and receive time) and the IDs, estimated timing and power of the detected neighbor cells. The enodeB may report extra information to the ESMLC like the angle of arrival. The ESMLC estimates the UE position based on this information and its knowledge of the cells positions.

Cell ID based methods were already possible before rel9. Enhanced cell ID aggregates together some already available measurements, some of them with increased accuracy requirements to improve the positioning accuracy capabilities.