Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1997-06-23
2001-07-31
Nguyen, Chau (Department: 2663)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S335000, C455S437000
Reexamination Certificate
active
06269087
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a handover type judgement scheme for a CDMA (Code Division Multiple Access) mobile communication system which is capable of carrying out any of multiple types of handover with different handover start conditions at a time of handover in which a mobile station moves from a currently communicating base station to another base station.
2. Description of the Background Art
In the conventional mobile communication system such as PDC (Personal Digital Cellular) system that is currently providing the mobile communication service in Japan, there is only one available type of handover called hard handover.
In contrast, in the CDMA mobile communication system, the soft handover in also available in addition to the hard handover, and this soft handover further includes multiple types of soft handovers such as the same code same frequency soft handover and the different frequency soft handover. Here, these multiple types of handovers are associated with mutually different handover start conditions.
In order for each mobile station to carry out the handover properly, each base station is transmitting the perch channel (or the pilot channel). The mobile station receives the perch channel transmitted from each base station of each nearby cell, compares the receiving level of the perch channel received from each nearby cell with the receiving level of the perch channel of a currently located cell, and judges the start of the handover according to the obtained difference.
Here, as already mentioned above, the available types of handover includes the hard handover, the same code same frequency soft handover, and the different frequency soft handover, and the handover start conditions for these three types of handover are as indicated in FIG.
3
. As can be seen from
FIG. 3
, when an influence on the radio channel capacity is taken into account, the handover start condition is weakest for the same code same frequency soft handover, second weakest for the different frequency soft handover, and strongest for the hard handover.
As already mentioned above, the conventional mobile communication system has been designed to use only one type of handover, so that there has been no means for judging an appropriate type of handover to be executed out of multiple types of handover.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a handover type judgement scheme for a CDMA mobile communication system which is capable of judging an appropriate type of handover from multiple types of handover available.
According to one aspect of the present invention there is provided a handover type judgement method for a CDMA mobile communication system which is capable of carrying out any of multiple types of handover with different handover start conditions, the method comprising the steps of: judging one type of handover for which a handover start condition is weakest among available types of handover at a mobile station; and checking whether the handover start condition for said one type of handover is satisfied or not at the mobile station, and notifying each base station for carrying out said one type of handover when the handover start condition for said one type of handover is satisfied.
According to another aspect of the present invention there is provided a CDMA mobile communication system for carrying out any of multiple types of handover with different handover start conditions, comprising: a plurality of base stations; and at least one mobile station having: a judging unit for judging one type of handover for which a handover start condition is weakest among available types of handover; and a checking unit for checking whether the handover start condition for said one type of handover is satisfied or not, and notifying each base station for carrying out said one type of handover when the handover start condition for said one type of handover is satisfied.
According to another aspect of the present invention there is provided a mobile station apparatus for use as a mobile station in a CDMA mobile communication system for carrying out any of multiple types of handover with different handover start conditions, the apparatus comprising: a judging unit for judging one type of handover for which a handover start condition is weakest among available types of handover; and a checking unit for checking whether the handover start condition for said one type of handover is satisfied or not, and notifying each base station for carrying out said one type of handover when the handover start condition for said one type of handover is satisfied.
According to another aspect of the present invention there is provided a base station apparatus for use as a base station in a CDMA mobile communication system for carrying out any of multiple types of handover with different handover start conditions, the apparatus comprising: a measuring unit for measuring a radio channel state for each cell/sector of the base station; a determining unit for determining each impossible type of handover that cannot be carried out for each cell/sector by the base station according to the radio channel state measured by the measuring unit; and a notifying unit for notifying an information indicating said each impossible type of handover to a mobile station, so that at a time of handover with respect to the base station, the mobile station judges one type of handover for which a handover start condition is weakest among available types of handover which include said multiple types of handover except for said each impossible type of handover according to said information, checks whether the handover start condition for said one type of handover is satisfied or not, and notifies each base station for carrying out said one type of handover when the handover start condition for said one type of handover is satisfied.
According to another aspect of the present invention there is provided a base station apparatus for use as a base station in a CDMA mobile communication system for carrying out any of multiple types of handover with different handover start conditions including a same code same frequency soft handover and a different frequency soft handover, the apparatus comprising: a measuring unit for measuring an interference receiving level or a total receiving level of each frequency bandwidth that is implemented at the base station for each cell/sector of the base station; and a notifying unit for notifying an information indicating that one frequency bandwidth cannot be used for one cell/sector to a mobile station, when a measured value for said one frequency bandwidth and said one cell/sector is greater than a prescribed threshold value, so that at a time of handover with respect to said one cell/sector while the mobile station is currently using said one frequency bandwidth as indicated by said information, the mobile station judges the different frequency soft handover as having a weakest handover start condition among available types of handover, checks whether the handover start condition for the different frequency soft handover is satisfied or not without checking the handover start condition for the same code same frequency soft handover with respect to said one cell/sector, and notifies each base station for carrying out the different frequency soft handover when the handover start condition for the different frequency soft handover is satisfied.
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Nakamura Takehiro
Sato Takaaki
Hyun Soon-Dong
Nguyen Chau
NTT Mobile Communications Network Inc.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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