Method for maintaining a group call

A method for maintaining a group call in a mobile radio system, said method comprising:

• dividing a geographical area covered by said mobile radio system into radio cells so that adjacent cells overlap;
• providing each radio cell with a base station provided with an identity;
• each base station having at least one control channel and at least one traffic channel for being in radio communication with mobile radio stations located in said radio cell;
• establishing and maintaining a group call marked with an identity between said mobile stations belonging to a group call group and residing within the areas of said radio cells forming a limited group call area;
• sending from said base stations of said limited group call area during an ongoing group call on said traffic channel, one or a plurality of group call maintenance messages to said mobile stations participating in said group call;
• said group call maintenance messages containing at least said identities of said base stations located within the areas of said radio cells forming said group call area, and said group call group identity;
• said mobile station receiving on said traffic channel, said base station identities and said respective group call group identity;
• maintaining in a memory of said mobile station, a memory table capable of storing said identities of said base stations located within said group call area and said respective group call group identity;
• said mobile station storing said identities of said base stations located within said group call area and said group call group identity in said memory;
• on transferring to an area of another radio cell, said mobile station receiving said base station identity sent by said base station of said other radio cell;
• said mobile station comparing said base station identity with the received identities of said base stations located within said group call area that are already stored in said memory table;
• in response to said comparing step, in case said base station identity received by said mobile station is identical to any of said identities of said base stations stored in said memory of said mobile station, connecting said mobile station to said group call by sending a request message to re-enter said group call from said mobile station to said base station of said other redio cill, said request message containing said group call group identity and said identity of said mobile station;
• receiving said message to re-enter said group call by said base station;
• in response to said request message to re-enter said group call, said base station checking whether said group call is still going on;
• in case said group call is still ongoing, sending a go-to-channel message from said base station to said mobile satation;
• and
• in response to said go-to-channel message, switching said mobile station to listen to said respective traffic channel of said base station and to participate in said group call.

A method for maintaining a group call in a mobile radio system, said method comprising:

• dividing a geographical area covered by said mobile radio system into radio cells so that adjacent cells overlap;
• providing each radio cell with a base station provided with an identity;
• each base station having at least one control channel and at least one traffic channel for being in radio communication with mobile radio stations located in said radio cell;
• establishing and maintaining a group call marked with an identity between said mobile stations belonging to a group call group and residing within the areas of said radio cells forming a limited group call area;
• sending from said base stations of said limited group call area during an ongoing group call on said traffic channel, one or a plurality of group call maintenance messages to said mobile stations participating in said group call;
• said group call maintenance messages containing at least said identities of said base stations located within the areas of said radio cells forming said group call area, identities of said control channels of said base stations located within the areas of said radio cells, and said group call group identity;
• maintaining in a memory of said mobile station, a memory table capable of storing said identities of said base stations located within said group call area, said identities of said control channels of said base stations, and said respective group call group identity;
• said mobile station receiving said identities of said base stations located within said group call area, said identities of said control channels of said base stations, and said respective group call group identity;
• said mobile station storing said identities of said base stations located within forming said group call area, said identities of said control channels of said base stations, and said respective group call group identity in said memory table;
• on transferring to an area of another radio cell, said mobile station tuning successively to each one of said control channels whose identity said mobile station has received;
• searching on each control channel for the base station identity of said respective base station and comparing said received base station identity to said identities of said base stations stored in said memory;
• when said mobile station finds said control channel on which said base station identity sent by said base station to said base station identity stored in said memory of said mobile station, connecting said mobile station to said group call by sending a request message to re-enter said group call from said mobile station to said base station of said other radio cell, said request message containing said group call group identity and said identity of said mobile station;
• receiving said request message to re-enter said group call message by said base station;
• in response to said request message to re-enter said group call, said base station checking whether said group call is still going on;
• in case said group call is still ongoing, sending a go-to-channel message from said base station to said mobile station;
• and
• in response to said go-to-channel message switching said mobile station to listen to said respective traffic channel of said base station and to participate in said group call.

A method for maintaining a group call in a mobile radio system, said method comprising:

• dividing a geographical area covered by said mobile radio system into radio cells so that adjacent cells overlap;
• providing each radio cell with a base station provided with an identity;
• each base station having at least one control channel and at least one traffic channel for being in radio communication with mobile radio stations located in said radio cell;
• establishing and maintaining a group call marked with an identity between said mobile stations belonging to a group call group and residing within the areas of said radio cells forming a limited group call area;
• sending from said base stations of said limited group call area during an ongoing group call on said traffic channel, one or a plurality of group call maintenance messages to said mobile stations participating in said group call;
• said group call maintenance message containing at least said identities of said base stations located within said group call area, said identities of said traffic channels used as group call traffic channels at said base stations, and said respective group call group identity;
• maintaining in a memory of the mobile station, a memory table capable of storing said identities of said base stations located within said group call area, said identities of said traffic channels used as group call traffic channels at said base stations, and said respective group call group identity;
• said mobile station receiving said identities of said base stations located within said group call area, said identities of said traffic channels of said base stations used as group call traffic channels, and said respective group call group identity;
• said mobile station storing said identities of said base stations located within said group call area, said identities of said traffic channels of said base stations used as group call traffic channels, and said respective group call group identity in said memory;
• on transferring to an area of another radio cell, said mobile station tuning successively to each one of said traffic channels whose identity said mobile station has received;
• searching for the base station identity of said respective base station, successively on each traffic channel;
• comparing said received base station identity to said identities of said base stations stored in said memory;
• when said mobile station finds a traffic channel on which the received field strength is sufficient, said mobile station checking that said traffic channel is actually used by said group call by waiting for the next group call maintenance message sent by said base station on said traffic channel and comparing said group call group identity contained in said message with the group call identity of the group call in which said mobile station was originally involved;
• and
• when said mobile station finds a traffic channel on which said group call identity contained in said group call maintenance message sent on said traffic channel by said base station is equal to said group call group identity of said group call in which said mobile station was originally participating, said mobile station opening a communication connection to said group call.

A mobile station in a mobile radio system, said mobile station comprising:

• a transceiver for maintaining a group call on a traffic channel;
• receiving means for receiving on the traffic channel of a first base station, one or a plurality of group call maintenance messages containing information concerning base stations located within the area of radio cells forming a group call area, and a group call group identity;
• a memory arranged to store the identities of base stations maintaining the same group call, said identities being contained in said group call maintenance messages;
• measuring means for measuring the signal strength of signals received from said first base station and from other base stations of said mobile radio system;
• and
• a controller for controlling operation of said mobile station, said controller being arranged to select a base station, whose identity is stored in said memory, when said measuring means indicates that the field strength of signals received from said selected base station is higher than the field strength of signals received from said first base station.

A mobile station in a mobile radio system, said mobile station comprising:

• a transceiver for maintaining a group call on a traffic channel;
• receiving means for receiving on the traffic channel of a first base station one or a plurality of group call maintenance messages containing information concerning base stations located within the area of radio cells forming a group call area, and a group call group identity;
• a memory arranged to store identities of base stations maintaining the same group call and control channel identities of base stations maintaining the same group call, said identities and said control channel identities being contained in said group call maintenance messages received on said traffic channel;
• measuring means for measuring the signal strength of signals received from said first base station and from other base stations of said mobile radio system;
• and
• a controller for controlling operation of said mobile station, said controller being arranged to select a base station, whose identity is stored in said memory, when said measuring means indicates that the field strength of signals received from said selected base station is higher than the field strength of signals received from said first base station.

A mobile station in a mobile radio system, said mobile station comprising:

• a transceiver for maintaining a group call on a traffic channel;
• receiving means for receiving on the traffic channel of a first base station, one or a plurality of group call maintenance messages containing information concerning base stations located within the area of radio cells forming a group call area, and a group call group identity;
• a memory arranged to store identities of base stations maintaining the same group call and identities of traffic channels used by the same call at base stations maintaining the same group call, said identities and said traffic channel identities being contained in said group call maintenance messages received on said traffic channel;
• measuring means for measuring the signal strength of signals received from said first base station and from other base stations of said mobile radio system;
• and
• a controller for controlling operation of said mobile station, said controller being arranged to select a base station, whose identity is stored in said memory, when said measuring means indicates that the field strength of signals received from said selected base station is higher than the field strength of signals received from said first base station.

A mobile station in a mobile radio system, said mobile station comprising:

• a transceiver for maintaining a group call on a traffic channel;
• receiving means for receiving on the traffic channel of a first base station, one or a plurality of group call maintenance messages containing information concerning base stations located within the area of radio cells forming a group call area, and a group call group identity;
• a memory arranged to store identities of base stations maintaining the same group call, control channel identities of base stations maintaining the same group call, and identities of traffic channels used by the same call at base stations maintaining the same group call, said identities, said control channel identities, and said traffic channel identities being contained in said group call maintenance messages received on said traffic channel;
• measuring means for measuring the signal strength of signals received form said first base station and from other base stations of said mobile radio system;
• and
• a controller for controlling operation of said mobile station, said controller being arranged to select a base station, whose identity is stored in said memory, when said measuring means indicates that the field strength of signals received from said selected base station is higher than the field strength of signals received from said first base station.