Uplink Power Control for Power Limited Terminals

Abstract

Transmit power control methods and apparatus are disclosed. In several embodiments, a mobile terminal is configured to effectively ignore “UP” transmit power control commands in the event that the mobile terminal is operating in a power-limited state. In an exemplary method for controlling transmit power at a mobile terminal, a plurality of transmit power control commands are received. An accumulated power control value is adjusted in response to each transmit power control command that directs a negative adjustment in transmit power. However, the accumulated power control value is adjusted in response to a transmit power control command that directs a positive adjustment in transmit power only if the mobile terminal is not in a power-limited state. Transmit power settings for each transmission are calculated based on the accumulated power control value and the one or more radio link parameters.

What is claimed is: 
     
         1 . A method for controlling transmit power at a mobile terminal in a wireless communication system, the method comprising:
 receiving a plurality of transmit power control commands, each transmit power control command directing an adjustment in transmit power relative to a prior transmission by the mobile terminal;   adjusting an accumulated power control value in response to each transmit power control command that directs a positive adjustment in transmit power only if a provisional power setting calculated from one or more radio link parameters and the unadjusted accumulated power control value indicates that the mobile terminal is not in a power-limited state;   calculating transmit power settings for each transmission by the mobile terminal based on the accumulated power control value and the one or more radio link parameters;   monitoring for the occurrence of one or more predetermined transmit power control reset criteria; and   resetting the accumulated power control value to a pre-determined value in response to each occurrence.   
     
     
         2 . The method of  claim 1  wherein the mobile terminal is in the power-limited state when transmissions by the mobile terminal are performed at a transmission bandwidth and/or radio propagation conditions that require the mobile terminal to transmit at the maximum transmit power. 
     
     
         3 . The method of  claim 1  wherein adjusting an accumulated power control value in response to each transmit power control command that directs a positive adjustment in transmit power only if a provisional power setting calculated from one or more radio link parameters and the unadjusted accumulated power control value indicates that the mobile terminal is not in a power-limited state reduces a time until the mobile terminal exits the power-limited state when the transmission bandwidth and/or the radio propagation conditions changes so that the maximum transmit power is no longer required for transmissions by the mobile terminal. 
     
     
         4 . The method of  claim 1  wherein receiving a plurality of transmit power control commands comprises:
 receiving a control channel from a serving base station; and 
 extracting the transmit power control commands from the control channel. 
 
     
     
         5 . The method of  claim 4  wherein extracting the transmit power control commands from the control channel comprises extracting the transmit power control commands according to a scheduling assignment format or a power control command format. 
     
     
         6 . The method of  claim 1  wherein calculating transmit power settings for each transmission by the mobile terminal based on the accumulated power control value and the one or more radio link parameters further comprises calculating the transmit power settings as a function of at least one of a transmission path loss estimate and a modulation and coding scheme. 
     
     
         7 . The method of  claim 1  further comprising receiving one or more offset values from a serving base station, and wherein calculating the transmit power settings for each transmission by the mobile terminal further comprises calculating the transmit power settings based on the one or more offset values. 
     
     
         8 . The method of  claim 7  wherein the one or more offset values include one or both of a cell-specific transmit power offset and a mobile terminal specific transmit power offset. 
     
     
         9 . The method of  claim 1  wherein the predetermined transmit power control reset criteria include one or more of:
 a change in serving cell for the mobile terminal; 
 a loss of uplink synchronization; 
 elapse of a pre-determined period with no transmissions by the mobile terminal; 
 receipt of a changed power control parameter from the serving cell; and 
 receipt of a transmit power control command specifying an absolute power offset instead of a relative power adjustment. 
 
     
     
         10 . A mobile terminal configured for use in a wireless communication network where a transmission bandwidth allocated for transmissions by the mobile terminal is variable per transmission, the mobile terminal comprising:
 a radio transceiver; and   a control circuit configured to:
 receive a plurality of transmit power control commands, each transmit power control command directing an adjustment in transmit power relative to a prior transmission by the mobile terminal; 
 adjust an accumulated power control value in response to each transmit power control command that directs a positive adjustment in transmit power only if a provisional power setting calculated from one or more radio link parameters and the unadjusted accumulated power control value indicates that the mobile terminal is not in a power-limited state; 
 calculate transmit power settings for each transmission by the mobile terminal based on the accumulated power control value and the one or more radio link parameters; 
 monitor for the occurrence of one or more predetermined transmit power control reset criteria; and 
 reset the accumulated power control value to a pre-determined value in response to each occurrence. 
   
     
     
         11 . The mobile terminal of  claim 10  wherein the mobile terminal is in the power-limited state when transmissions by the mobile terminal are performed at a transmission bandwidth and/or radio propagation conditions that require the mobile terminal to transmit at the maximum transmit power. 
     
     
         12 . The mobile terminal of  claim 10  wherein the control circuit, by being configured to adjust an accumulated power control value in response to each transmit power control command that directs a positive adjustment in transmit power only if a provisional power setting calculated from one or more radio link parameters and the unadjusted accumulated power control value indicates that the mobile terminal is not in a power-limited state, is configured to reduce a time until the mobile terminal exits the power-limited state when the transmission bandwidth and/or the radio propagation conditions changes so that the maximum transmit power is no longer required for transmissions by the mobile terminal. 
     
     
         13 . The mobile terminal of  claim 10  wherein the radio transceiver is further configured to:
 receive a control channel from a serving base station; and 
 extract the transmit power control commands from the control channel. 
 
     
     
         14 . The mobile terminal of  claim 13  wherein the radio transceiver is further configured to extract the transmit power control commands from the control channel according to a scheduling assignment format or a power control command format. 
     
     
         15 . The mobile terminal of  claim 10  wherein the control circuit is further configured to calculate the transmit power settings as a function of at least one of a transmission path loss estimate and a modulation and coding scheme. 
     
     
         16 . The mobile terminal of  claim 10  wherein the radio transceiver is further configured to receive one or more offset values from a serving base station, and wherein the control circuit is further configured to calculate the transmit power settings based on the one or more offset values. 
     
     
         17 . The mobile terminal of  claim 16  wherein the one or more offset values include one or both of a cell-specific transmit power offset and a mobile terminal specific transmit power offset. 
     
     
         18 . The mobile terminal of  claim 10  wherein the predetermined transmit power control reset criteria include one or more of:
 a change in serving cell for the mobile terminal; 
 a loss of uplink synchronization; 
 elapse of a pre-determined period with no transmissions by the mobile terminal; 
 receipt of a changed power control parameter from the serving cell; and 
 receipt of a transmit power control command specifying an absolute power offset instead of a relative power adjustment.