Method, mobile station, basestation and mobile communications system for performing handoff independently for groups of physical direct sequence-code division multiple access channels

DETAILED DESCRIPTION It is an object of the present invention to mitigate one or more disadvantages of the prior art and, in particular, to provide a technique for handing off an active session between a mobile station and at least one basestation with the flexibility of transferring specific channels and/or channel types at the same or different times and using the same or different handoff methods.
The present invention, according to a broad aspect, provides a mobile station that has a number physical channels between itself and a set of basestations.
Groups of one or more physical channels are defined, for example according to channel type.
The mobile station is capable of performing handoffs independently for each of the groups of physical channels.
In an exemplary embodiment, a plurality of groups have associated active sets that when updated allow the handoffs for the groups of channels associated with the particular active sets to be performed independently.
In further aspects, the present invention provides a basestation, a mobile communication system, and a method of performing handoffs.
In each of these aspects, a mobile station is arranged to perform independent handoffs for groups of physical channels between the mobile station and a set of basestations similar to that in the broad aspect described above.
Preferably, the invention is applied in the context of a 3G DS-CDMA system in which the physical channels between the mobile station and the set of basestations consist of a fundamental channel, forward and reverse link supplemental channels, and a dedicated control channel.
In this preferred embodiment, separate active sets are maintained for each of these channels.