Soft handover between cdma systems of the second and third generation

摘要

In a CDMA cellular radiotelephone system, a soft handoff (SHO) is performed when a mobile station communicates with a new inter-generation base station, without interrupting communications with the old base station. Currently, a SHO can only be used between CDMA channels having identical frequency assignments and within the same system generation (i.e., 2G ⇔ 2G, or 3G ⇔ 3G, where 2G is a second generation system, and 3G is a third generation system). The proposed IS-2000 standard for a 2G ⇔ 3G handoff is a hard handoff or "Break-Before-Make" procedure, which greatly reduces the quality of service (QOS). The present invention allows for SHO between second and third generation CDMA systems (2G ⇔ 3G and 3G ⇔ 2G), by modifying the proposed messaging structure (40, 50, 70). This provides a smooth service transition when a mobile station travels from one service area (i.e., 2G), to another service area (i.e., 3G), using the SHO or "Make-Before-Break" approach.