A Cross-Layer Scheme for Inter-RAT Handover from WiMAX to UMTS

In future mobile networks, different radio access technologies, such as GSM, UMTS, WiMAX, WIFI, will coexist. In order to realize a seamless vertical handover (inter-RAT handover) among these technologies, a variety of interworking architectures and inter-RAT handover mobility managements have been proposed. Based on an integrated coupling architecture, we propose a novel common interworking sublayer (IW sublayer) at layer 2 on RNC and UE to provide a seamless PS inter-RAT handover between UMTS and WiMAX systems. This IW sublayer scheme focuses on eliminating packet loss and reducing handover latency which are common problems for most inter-RAT handover scenarios. In addition, an enhanced TCP proxy, which interacts with the IW sublayer, is also introduced to RNC to resolve other two typical inter-RAT handover problems of TCP traffics: BDP mismatch and spurious RTO. Compared with other vertical handover solutions, our novel inter-RAT scheme has the merits of keeping existing TCP protocol stacks unchanged and is robust to different handover scenarios. The simulation results show our total solution not only achieves a lossless and prompt handover procedure, but also accommodates BDP mismatch and prevents spurious RTO of TCP sender.