Handover method for mobile radio system

Abstract

The invention relates to a method in mobile radio systems in which the responsibility for transmitting message information to a mobile station is handed over from a first base station transmitter to a second base station transmitter. In this method, the same radio channel is used, if possible, before and after the handover for transmitting message information to the mobile station. If the same radio channel can be utilized, the handover takes place without the mobile station being informed beforehand of the handover by a special signal or order or the like. In digital mobile ratio systems with digital transmission of message information by digital modulation of the radio signals, the transmission is preferably started from a second base station transmitter before the transmission is terminated from a first base station transmitter. During a certain transmission time substantially the same message information is transmitted to the mobile station from both the first and second base station transmitters.

I claim: 
     
       1. In a mobile radio communication system comprising base stations and mobile stations and a plurality of radio channels for transmitting control information and message information between base stations and mobile stations, said base stations and mobile stations including radio transmitters and radio receivers for a plurality of radio channels, a method for handing over the responsibility for transmitting message information to a mobile station from at least one first base station transmitter to at least one second base station transmitter, comprising the steps of: before handing over the responsibility carrying out a test in the stationary part of the system to see whether after the handover the second base station transmitter can use the same radio channel for transmitting message information to the mobile as the radio channel used by the first base station transmitter before handover; and   if the test result is positive then using the same radio channel after the handover as before for transmitting message information to the mobile.   
     
     
       2. A method according to claim 1 comprising the further step of: executing handover without first informing the mobile of the handover.   
     
     
       3. A method according to claim 1 comprising the further steps of: starting the transmission of message information to the mobile station from the second base station transmitter before terminating the transmission of message information to the mobile station from the first base station transmitter; and   transmitting substantially the same message information during a transition period from both the first base station transmitter and the second base station transmitter.   
     
     
       4. In a mobile radio communication system comprising base stations and mobile stations having radio transmitters and radio receivers for transmitting control information and message information therebetween, a method for handing over the responsibility for transmitting message information to a mobile station from at least one first base station transmitter to at least one second base station transmitter comprising the steps of: starting the transmission of message information to the mobile station from the second base station transmitter before terminating the transmission of message information to the mobile station from the first base station transmitter; . .and.!.   transmitting substantially the same message information during a transition period from both the first base station transmitter and the second base station transmitter.Iadd.; and   combining, in said mobile station, information transmitted by said first base station transmitter and information transmitted by said second base station transmitter to reconstruct said message information.Iaddend..   
     
     
       5. A method according to claim 4 comprising the further steps of: before handing over the responsibility, carrying out a test in the stationary part of the system to see whether after the handover the second base station transmitter can use the same radio channel for transmitting message information to the mobile as the radio channel used by the first base station transmitter before handover; and   when the radio transmission conditions and remaining radio communication in the system permit, then using the same radio channel after the handover as before for transmitting message information to the mobile.   
     
     
       6. A method according to claim 5 comprising the further steps of: executing the handover without first informing the mobile station of the handover. .Iadd.7. The method according to claim 4, further comprising the step of:   receiving, at said mobile station signals transmitted by said first base station transmitter and signals transmitted by said second base station   
     
     
        transmitter with a time shift therebetween. .Iaddend.8. .Iadd.The method according to claim 7, further comprising the step of: introducing a delay in transmission of either said signals transmitted by said first base station transmitter or said signals transmitted by said second base station transmitter, said delay at least in part causing said time shift. .Iaddend..Iadd.9. The method according to claim 7, wherein said step of combining further comprises the step of:   combining said information received within a reception time interval, said reception time interval being greater than said time shift. .Iaddend..Iadd.10. The method according to claim 4, further comprising the step of:   selecting said second base station transmitter based on a position of said mobile station. .Iaddend..Iadd.11. The method according to claim 4, wherein said first and second base station transmitters are co-located and share transmitting circuitry. .Iaddend..Iadd.12. In a mobile radio communication system comprising base stations and mobile stations having radio transmitters and radio receivers for transmitting control information and message information therebetween, a method for handing over the responsibility for transmitting message information to a mobile station from at least one first base station transmitter to at least one second base station transmitter comprising the steps of:   starting the transmission of message information to the mobile station from the second base station transmitter before terminating the transmission of message information to the mobile station from the first base station transmitter;   transmitting substantially the same message information during a transition period from both the first base station transmitter and the second base station transmitter, wherein a fixed delay is introduced between said transmission of a symbol of said message information from said first base station transmitter and said transmission of said same symbol of said message information from said second base station transmitter; and   combining, in said mobile station, information transmitted by said first base station transmitter and information transmitted by said second base station transmitter, to reconstruct said message information.   
     
     
        .Iaddend..Iadd.13.  The method according to claim 12, further comprising the step of: receiving, at said mobile station, signals transmitted by said first base station transmitter and signals transmitted by said second base station transmitter with a time shift therebetween. .Iaddend..Iadd.14. The method according to claim 13, wherein said step of combining further comprises:   combining said information received within a reception time interval said reception time interval being greater than said time shift. .Iaddend..Iadd.15. The method according to claim 12, further comprising the step of:   selecting said second base station transmitter based on a position of said mobile station. .Iaddend..Iadd.16. The method according to claim 12, wherein said first and second base station transmitters are co-located and share transmitting circuitry. .Iaddend..Iadd.17. In a mobile radio communication system comprising base stations and mobile stations having radio transmitters and radio receivers for transmitting control information and message information therebetween, said base stations and said mobile stations operating within a geographic area divided into a plurality of communication cells, a method for handing over the responsibility for transmitting message information to a mobile station from at least one first base station transmitter to at least one second base station transmitter when said mobile station moves from a first one of said plurality of cells serviced by said at least one first base station transmitter to a second one of said plurality of cells serviced by said at least one second base station transmitter, comprising the steps of:   starting the transmission of message information to the mobile station from the second base station transmitter before terminating the transmission of message information to the mobile station from the first base station transmitter;   transmitting substantially the same message information during a transition period from both the first base station transmitter and the second base station transmitter, said transition period being that time required for the mobile station to move from said first cell to said second cell;   combining, in said mobile station, information transmitted by said first base station transmitter and information transmitted by said second base station transmitter to reconstruct said message information; and   terminating the transmission of message information to the mobile station from said first base station transmitter when the mobile station has moved   
     
     
        from said first to said second cell. .Iaddend..Iadd.18.  The method according to claim 17, further comprising the step of: receiving, at said mobile station, signals transmitted by said first base station transmitter and signals transmitted by said second base station transmitter with a time shift therebetween. .Iaddend..Iadd.19. The method according to claim 18, further comprising the step of:   introducing a delay in transmission of either said signals transmitted by said first base station transmitter or said signals transmitted by said second base station transmitter, said delay at least in part causing said time shift. .Iaddend..Iadd.20. The method according to claim 18, wherein said step of combining further comprises the step of:   combining said information received within a reception time interval, said reception time interval being greater than said time shift. .Iaddend..Iadd.21. The method according to claim 17, further comprising the step of:   selecting said second base station transmitter based on a position of said   
     
     
        mobile station. .Iaddend..Iadd.22.  The method according to claim 17, wherein said first and second base station transmitters are co-located and share transmitting circuitry. .Iaddend.