LTE, LTE-Advanced and WiMAX: Towards IMT-Advanced Networks

Inter-Technology Handovers

Advances in supporting IP mobility, coupled with the convergence to an All-IP wireless infrastructure, have made possible the interworking of different access technologies. A key advantage in this viability is the possibility of multi-modal devices to maintain sessions while traversing different access technologies, for example, cellular to WiFi, or LTE-to-WiMAX. Both standardization bodies, in addition to 3GPP2, have defined extensive signaling mechanisms to support both interworking and inter-technology handovers at both the radio interface and the core level. There is also the IEEE 802.21 working group, the purpose of which is to define extensible media access mechanisms that facilitate handovers between IEEE 802 based networks and cellular systems and to optimize handovers between heterogeneous media. It aims at providing link layer intelligence and other related network information to upper layers, or the mobility management entity responsible for handover decision making. The scope of IEEE 802.21 is to cover handover initiation and handover preparation where functionalities include network discovery, selection, and handover negotiation in the former and layer 2 and 3 connectivity in the latter. On the other hand, remaining functionalities such as handover signaling, context transfer, and packet reception, fall into handover execution and thus are out of the scope of 802.21.