A communications apparatus is disclosed. A receiving module receives an observed time difference of arrival (OTDOA) request and a search list of cells provided by a network at a second time point. A comparing module compares the received search list to a stored search list of cells which is received at a first time point and stored in a database. A searching module searches at least one of the cells from the received search list by using different search ranges adjusted according to the comparison result, and stores the at least one of the cells in the database. A measuring module performs OTDOA measurements by detecting positioning reference signals (PRS) from the at least one of the cells.