Mobile station handoff between different CDMA frequencies

Abstract

A method and system for mobile assisted handoff between base stations using different carrier frequencies in a Code Division Multiple Access (CDMA) cellular system. In the method and apparatus, a mobile station performs handoff measurements on forward link transmissions of handoff candidate CDMA base stations, where the forward link transmissions are transmitted on a carrier frequency that differs from the forward link carrier frequency of the current base station. The handoff measurements are performed during selected transmission frames that define transmission periods on the reverse link by the mobile station. During the measurement time in the selected transmission frame, the mobile station does not receive (punctures) data sent to it on the forward link and does not transmit data on the reverse link.

1. A method for handoff of a mobile station from a first base station to a second base station in a telecommunications system, and wherein a plurality of transmission frames are transmitted from the first base station to the mobile station on a first frequency, said method comprising the steps of:
 transmitting a plurality of transmission frames from the first base station to the mobile station on a first frequency; 
 receiving a first at least one data  transmission frame of said plurality of transmission frames at the mobile station; and  
 performing measurements on transmissions received from the second base station on a second frequency, wherein said measurements are performed during a time period, said time period including a time when a second at least one transmission frame of said plurality of transmission frames is transmitted to the mobile station and at least a portion of said second at least one transmission frame of said plurality of transmission frames is punctured and not received at the mobile station.  
 
     
     
       2. The method of  claim 1 , wherein said plurality of transmission frames comprises a first plurality of transmission frames, and wherein said method further comprises the step of  generating a second plurality of transmission frames at the mobile station, said second plurality of transmission frames for transmission to the first base station, and wherein said time period during which said measurements are performed in said step of  performing further includes a time when at least one transmission frame of said second plurality of transmission frames is to be transmitted from the mobile station to the first base station, and at least a portion of said at least one transmission frame of said second plurality of transmission frames is punctured and not transmitted from the mobile station to the first base station. 
     
     
       3. The method of  claim 2 , wherein said measurements performed in said step of  performing are performed according to timing information transmitted to the mobile station from the telecommunications system. 
     
     
       4. The method of  claim 2 , wherein said method further includes the step of  selecting said time period during which said measurements are performed based on the data rate of said at least one transmission frame of said second plurality of transmission frames. 
     
     
       5. The method of  claim 4 , wherein said time period is selected based on a determination that the data rate of said at least one transmission frame of said second plurality of transmission frames is less than a predetermined data rate. 
     
     
       6. A method for handoff of a mobile station from a first base station to a second base station in a telecommunications system, said method comprising the steps of :
 generating a plurality of transmission frames in the mobile station, said plurality of transmission frames for transmission to the first base station on a first frequency;  
 determining a selected at least one transmission frame from said plurality of transmission frames; and  
 performing measurements on a transmission from said second base station on a second frequency during a time period when at least a portion of said selected at least one transmission frame is to be transmitted to the first base station, wherein said at least a portion of said selected at least one transmission frame is punctured and not transmitted to the first base station.  
 
     
     
       7. The method of  claim 6 , wherein said step of  determining a selected at least one transmission frame comprises determining a selected at least one transmission frame having a data rate less than a predetermined data rate. 
     
     
       8. The method of  claim 6 , wherein said step of selecting is performed  determining further includes determining said selected at least one transmission frame according to timing information transmitted to the mobile station from the telecommunications system. 
     
     
       9. A system for performing Mobile Assisted Hard Handoff (MAHHO) comprising:
 a first base station comprising a transmitter for transmitting a plurality of transmission frames on a first frequency;  
 a second base station comprising a transmitter for transmitting transmissions on a second frequency;  
 a mobile station, including a receiver for receiving a first at least one transmission frame of said plurality of transmission frames from said first base station, said mobile station further including a MAHHO apparatus for performing measurements on said transmissions from said second base station, wherein said measurements are performed during a time period, said time period including a time when a second at least one transmission frame of said plurality of data frames is transmitted from said first base station to said mobile station, and at least a portion of said second at least one transmission frame of said plurality of data frames is punctured and not received at said mobile station.  
 
     
     
       10. The system of  claim 9 , wherein said plurality of transmission frames comprises a first plurality of transmission frames and said mobile station further comprises a processor for generating a second plurality of transmission frames, said second plurality of transmission frames for transmission to the base station, and wherein said time period during which said MAHHO apparatus performs said measurements on said transmissions from the second base station further includes a time when at least one transmission frame of said second plurality of transmission frames is to be transmitted from the mobile station to the first base station, and at least a portion of said at least one transmission frame of said second plurality of transmission frames is punctured and not transmitted from the mobile station to the first base station. 
     
     
       11. The system of  claim 10 , wherein said MAHHO apparatus performs said measurements performed in said step of performing are performed  according to timing information transmitted to the mobile station from the first base station. 
     
     
       12. The system of  claim 10 , wherein said MAHHO apparatus selects said time period during which said measurements are performed based on the data rate of said at least one transmission frame of said second plurality of transmission frames. 
     
     
       13. A mobile station for providing handoff from a first base station to a second base station, said mobile station comprising:
 a processor for generating a plurality of transmission frames, said plurality of transmission frames for transmission to the first base station on a first frequency; and  
 a MAHHO apparatus for selecting at least one transmission frame from said plurality of transmission frames, and performing measurements on a transmission from said second base station on a second frequency during a time period when at least a portion of said at least one transmission frame is to be transmitted to the first base station, wherein said at least a portion of said at least one transmission frame is punctured and not transmitted to the first base station.  
 
     
     
       14. The apparatus  mobile station of  claim 13 , wherein said MAHHO apparatus selects said at least one transmission frame based on the data rate of said at least one transmission frame. 
     
     
       15. The apparatus  mobile station of  claim 14 , wherein said MAHHO apparatus selects said at least one transmission frame based on a determination that the data rate of said at least one transmission frame is less than a predetermined rate. 
     
     
       16. The apparatus  mobile station of  claim 13 , wherein said MAHHO apparatus performs said measurements according to timing information transmitted to the mobile station from the first base station. 
     
     
       17. A method for handoff of a mobile station from a first frequency over which a plurality of transmission frames are transmitted to said mobile station in a communications system, said method comprising:
   receiving at least one transmission frame of a plurality of transmission frames at said mobile station on said first frequency; and        performing measurements on transmissions received on a second frequency, wherein said measurements are performed during a time period, said time period including a time when at least a portion of a second transmission frame of said plurality of transmission frames is punctured at said mobile station.     
     
     
       18. A device comprising:
   a receiver to receive on a first frequency a first at least one transmission frame of a plurality of transmission frames; and        an apparatus to perform measurements on transmissions on a second frequency from a second base station, wherein said measurements are performed during a time period, said time period including a time when a second at least one transmission frame of said plurality of transmission frames is transmitted, and at least a portion of said second at least one transmission frame of said plurality of transmission frames is punctured at said device.