  In recent years several wireless communication standards have been developed
and more are expected, each with different scope in terms of spatial coverage,
radio access capabilities, and mobility support. Heterogeneous networks combine
multiple of these radio interfaces both in network infrastructure and in user
equipment which requires a new multi-radio framework, enabling mobility and
handover management for multiple RATs. The use of heterogeneous networks can
capitalize on the overlapping coverage and allow user devices to take advantage
of the fact that there are multiple radio interfaces. This paper presents the
functional architecture for such a framework and proposes a generic signaling
exchange applicable to a range of different handover management protocols that
enables seamless mobility. The interworking of radio resource management,
access selection and mobility management is defined in a generic and modular
way, which is extensible for future protocols and standards.
