Inter Node B Handover

Inter Node B (intra RNS). A mobile terminal moves across the areas covered by two different nodes B. Both nodes B involved in the handover session are connected to the same RNC. In the case of a dual mode RNC, intra RNS handover may include a change of mode (TDD-FDD).
Inter Node B (inter RNS, with Iur). In this scenario, the handover still occurs within the UTRAN, but is now between cells under the control of different RNCs
The scenario can be split into two phases: handover and SRNS relocation. For a particular UE, the SRNS Relocation phase is optional. It may be executed at any time by UTRAN (SRNC) in the case of a UE moving to a cell that belongs to a different RNC from the current SRNC. Inter RNS hard handover may include a change of mode (FDD-TDD). This scenario will be supported by the UTRAN as both soft and hard handover. Step a and b show the UE entering in macrodiversity state. In step c the UE is connected to the DRNC only. The core network either during step b or c can start the SRNC relocation.
the Iur interface is available between the SRNC and the DRNC. However, in some cases UTRA can be deployed without necessarily having all RNC connected through an Iur interface. In these cases only hard handover procedures can be used.
Inter URAN (different URAN types) 3GPP specifications include handover between different types of radio access, e.g., between UMTS and BRAN. Although Release ‘99 does not support this scenario, it is very promising for CELLO studies.

Handover in 3G networks

Handover in 3G systems may be initiated by the network based on RF quality (signal level, connection quality, power level propagation delay) or traffic criteria (current traffic loading per cell, interference levels and maintenance requests). MS continuously gathers measurements from neighboring cells and reports such measurements to the serving cell on an event driven or regular basis. When a network determines a need for executing a handover the procedures given in 3GPP TS 08.08, 3GPP TS 25.303, 3GPP TS 25.331 are followed.

3G systems support both soft and hard handover. Soft handover is the preferred mode of operation since it exploits macrodiversity functionality essential for CDMA efficiency. In this mode of operation the mobile terminal is connected to a variety of nodes B and signals are combined at the RNC level.

The RNC responsible for handling the recombining function is called Serving RNC (SRNC) while the supporting controller is named Drift RNC (DRNC). The Iur interface between two adjacent RNCs is essential to support macrodiversity and therefore soft-handover.
The mobile terminal holds a list of nodes B it is connected with. This list, namely the active list, is continuously updated following the user’s movements. As soon as a node B signal decrease below a pre-defined threshold, this is removed from the active list. Conversely, as soon as the MT receives a new node B over a given threshold, this is added in the active list.