A central objective in designing Long Term Evolution networks (LTE) is to provide a better quality of experience for the end user. One of the implemented enhancements is a direct connection between neighbouring base stations through $X_2$ interface. This interface enables mobility management and the transfer of the user's data in case of a handover. The aim of this paper is to study the impact of user mobility on capacity planning and to provide an analytical model to dimension the $X_2$ bandwidth under certain performance objectives.