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.  
     
     
       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.  
     
     
       7. 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: 
       
         determining whether the second base station can use a same radio channel as said first base station for transmitting message information;  
       
       
         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.  
       
     
     
       8. The method of  claim 7 , wherein said step of determining further comprises the step of: 
       
         determining whether said second base station already uses said same radio channel resource.  
       
     
     
       9. The method of  claim 7 , wherein said step of determining further comprises the step of: 
       
         evaluating interference associated with usage of said same radio channel by said second base station.  
       
     
     
       10. The method of  claim 7 , wherein if said mobile radio communication system is a TDMA mobile radio system, then said same radio channel is the same radio frequency and same time slot.  
     
     
       11. 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: 
       
         evaluating interference associated with a radio channel over which message information can be transmitted by said second base station;  
       
       
         selectively starting the transmission of message information to the mobile station from the second base station transmitter on said radio channel 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.  
       
     
     
       12. The method of  claim 11 , wherein if said mobile radio communication system is a TDMA mobile radio system, then said radio channel is defined by a radio frequency and a time slot.