Method and apparatus for triggering power headroom report for multiple pathloss reference in a wireless communication system

Abstract

A method and apparatus are disclosed from the perspective of an User Equipment (UE). In one embodiment, the method includes the UE deriving a first pathloss value from a first pathloss reference of a serving cell, wherein the first pathloss value is used for deriving a power headroom value included in a first power headroom report. The method also includes the UE deriving a second pathloss value from a second pathloss reference of the serving cell after deriving the first pathloss value, wherein the second pathloss reference is used for power control for a first Physical Uplink Shared Channel (PUSCH) transmission on the serving cell. The method further includes the UE deriving the pathloss change based on the first pathloss value and the second pathloss value. In addition, the method includes the UE determining whether a second power headroom report is triggered based on whether the pathloss change is more than a threshold.

What is claimed is: 
     
         1 . A method for deriving a pathloss change, comprising:
 deriving, at a User Equipment (UE), a first pathloss value from a first pathloss reference of a serving cell;   deriving, at the UE, a second pathloss value from a second pathloss reference of the serving cell after deriving the first pathloss value, wherein the second pathloss reference is separate from the first pathloss reference; and   deriving, at the UE, the pathloss change based on the first pathloss value and the second pathloss value.   
     
     
         2 . The method of  claim 1 , wherein the first pathloss value is used for deriving a power headroom value. 
     
     
         3 . The method of  claim 2 , wherein the power headroom value is included in a first power headroom report. 
     
     
         4 . The method of  claim 1 , further including determining, at the UE, whether a second power headroom report is triggered. 
     
     
         5 . The method of  claim 4 , wherein the second power headroom report is triggered when the pathloss change is more than a threshold. 
     
     
         6 . The method of  claim 5 , wherein the second power headroom report is transmitted via a first Physical Uplink Shared Channel (PUSCH) transmission when the second power headroom report is triggered. 
     
     
         7 . The method of  claim 1 , wherein the second pathloss reference is further used for power control for a first PUSCH transmission on the serving cell. 
     
     
         8 . The method of  claim 1 , wherein the first pathloss value is used for power control for a second PUSCH transmission on the serving cell, and a first power headroom report is transmitted via the second PUSCH transmission. 
     
     
         9 . The method of  claim 8 , wherein a second downlink control information (DCI) scheduling the second PUSCH transmission indicates the first pathloss reference. 
     
     
         10 . The method of  claim 8 , wherein the second PUSCH transmission is configured by a parameter ConfiguredGrantConfig indicating the first pathloss reference. 
     
     
         11 . The method of  claim 1 , wherein a first DCI scheduling transmission indicates the second pathloss reference. 
     
     
         12 . The method of  claim 1 , wherein a first PUSCH transmission is configured by a parameter ConfiguredGrantConfig indicating the second pathloss reference. 
     
     
         13 . The method of  claim 1 , wherein the first pathloss reference is a pathloss reference with the smallest entry of a pathloss reference configuration of the serving cell when the UE does not transmit any PUSCH transmission on the serving cell when transmitting a first power headroom report. 
     
     
         14 . The method of  claim 13 , wherein the pathloss reference configuration is PUSCH-PathlossReferenceRS. 
     
     
         15 . A User Equipment (UE) for deriving a pathloss change, comprising:
 a processor; and   a memory operatively coupled to the processor, wherein the processor is configured to execute a program code to:
 derive, at the UE, a first pathloss value from a first pathloss reference of a serving cell, wherein the first pathloss value is used for deriving a power headroom value included in a first power headroom report; 
 derive, at the UE, a second pathloss value from a second pathloss reference of the serving cell after deriving the first pathloss value, wherein the second pathloss reference is separate from the first pathloss reference; and 
 derive, at the UE, the pathloss change based on the first pathloss value and the second pathloss value. 
   
     
     
         16 . The UE of  claim 15 , further including determining whether a second power headroom report is triggered based on whether the pathloss change is more than a threshold. 
     
     
         17 . The UE of  claim 16 , wherein the second power headroom report is transmitted via a first Physical Uplink Shared Channel (PUSCH) transmission when the second power headroom report is triggered. 
     
     
         18 . The UE of  claim 15 , wherein the second pathloss reference is used for power control for a first PUSCH transmission. 
     
     
         19 . The UE of  claim 15 , wherein the first pathloss value is used for power control for a second PUSCH transmission, wherein the first power headroom report is transmitted via the second PUSCH transmission. 
     
     
         20 . The UE of  claim 15 , wherein the first pathloss reference is a pathloss reference with the smallest entry of a pathloss reference configuration of the serving cell when the UE does not transmit any PUSCH transmission on the serving cell when transmitting the first power headroom report.