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Tuesday, August 14, 2012

Approaches to Inter-Technology Mobility that will enable Ubiquitous 4G

Inter-radio access technology is the ability to support the mobility of a user device between differing radio access network types, also known as vertical handovers. Inter-radio access between heterogeneous networks is important to be executed properly for seamless communication with minimum delay and packet loss to disassociate from the current serving BS to associate to the new BS. 

Inter-technology access can be supported using different techniques. The most primitive one is the mobility from one technology to another without the intervention of the network. In this case the device is equipped with different technology interfaces. The user or the device selects which technology to access and associate to the corresponding network. Once this network becomes unavailable, the user or the device selects another technology and associate with. This type of inter-technology handover is acceptable for delay-tolerant and low QoS requirementapplications such as http and e-mail. However, delay-intolerant or session based applications cannot tolerate the service interruption and may require reinitiation of the session including the re-authentication process. A more efficient inter-technology mobility for session based applications is one that supports the data session continuity across multiple technologies. In this type of mobility, session continuity is preserved while the user moves across different technologies. Association to a new technology and disassociation from a serving one is accomplished with no user actions and it is transparent to the applications. Hence, re-authentication by users or data interruption has no impact in this type of mobility.

Different approaches are used to provide inter-technology mobility with session continuity and these include;

Single Transmit Device..........................:

Mobile IP (MIP) is standardized by the IETF to support for the session continuity at the IP layer. Hence, cannot support user authentication and login while moving across the different technologies. Single transmit device- MIP based approach makes use of the MIP service and hence it is a single transmit device, the device is only capable to associate with one technology at a time. In other words, it needs to disassociate from the serving technology before associating to the target technology. Despite the simplicity of this type, it suffers from a large delay associated with the signaling needed to associate and authenticate with the target technology. The type of inter-technology handover is known as non-optimized inter-technology handover. 3GPP standard use this approach to support inter technology mobility between WiMAX and LTE and between EVDO and LTE. Optimized inter technology handover is defined in LTE as the inter-technology handover which allows/requires the serving technology exchanging control data and signaling messages with the target technology as described in the following approach. The optimized handover is expected to support delay-stringent applications such as VoIP.

Access Network Interconnect:.................................

This approach is used mainly in networks managed by single operator and employ technology with different generations but similar origin (newer technology that supports backward compatibility with older generations) such as CDMA2000 and EVDO or UMTS and GSM. The access network interconnect requires the serving and the target networks to be physically connected to facilitate the handover process and exchange the signaling messages (optimized handover). Access network interconnect is limited to the technologies produced by the same standardization body, however, 3GPP with collaboration with 3GPP2 defined procedures to extend this approach to EVDO. 3GPP and IEEE 802.16 working group are in the process of investigating optimized handover between LTE and WiMAX.

Dual-Transmit Devices (DTD) based inter-technology handover:...........

This type of mobility does not require the serving technology to be connected to the target technology, since the user device is involved in the initiation and termination of the connection to the technology. It is realized by two types of services, Mobile IP (MIP) and Session Initiation Protocol (SIP).

·      MIP: In this type, since the device is equipped with dual transmitters, the device during handover employs make-before-brake handover. The device while it is connected to its serving technology uses its second transmitter to connect to the target technology, hence maintaining its data session and preventing data loss. Once the association process is completed with the target technology, the device uses the MIP service to move the data session to the target network. Examples are the inter-technology handover between LTE and WiFi and EVDO and WiMAX.

·             SIP: This solution is suitable for inter-device inter-technology mobility where a data session is required to be moved not only between technologies but also between devices. This is the only solution to support inter-device mobility. However, it is only applicable for SIP based applications. An example of this type of mobility is the standardization of LTE-Advanced which is expected to support inter-device and inter-technology mobility based on SIP and IMS.

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