Cross-Layer Design of the Inter-RAT Handover between UMTS and WiMAX

In future mobile networks, different radio access technologies will have to coexist. IEEE 802.21 MIH (Media-Independent Handover) provides primitive mechanisms that ease the implementation of a seamless vertical handover (inter-RAT handover) between different radio access technologies. However, it does not specify any handover execution mechanism. The first objective of this paper is to propose a novel MIHF (Media-Independent Handover Function) variant, which is renamed interworking (IW) sublayer. IW sublayer provides a seamless inter-RAT handover procedure between UMTS and WiMAX systems. It relies on a new intersystem retransmission mechanism with cross-layer interaction ability providing lossless handover while keeping acceptable delays. The second objective of this paper is to design a new TCP snoop agent (TCP Snoop), which interacts with the IW layer in order to mitigate BDP (Bandwidth Delay Product) mismatch and to solve spurious RTO (Retransmission TimeOut) problems. The cross-layer effects on the handover performance are evaluated by simulations. Our results show that cross-layer interaction between IW layer and TCP Snoop smoothes the handover procedure for TCP traffics. Additionally, this novel inter-RAT cross-layer scheme has the merit of keeping existing TCP protocol stacks unchanged.