Outer Loop Link Adaptation for Device Resumption

Abstract

Outer loop link adaptation for device resumption. A user equipment (UE) and base station (BS) may be in communication in a first network (e.g., an LTE network). Communication between the UE and the BS may be interrupted, e.g., due to a long fading environment, the UE tuning away to a second network (e.g., a CDMA network). Accordingly, the measured error rate may increase dramatically. After resumption from the interruption, a negative offset may be applied to a reported SINR value from the UE due to the previous increase in error rate. Upon improvement in the error rate, a larger, positive offset adjustment may be added to the negative offset, allowing the estimated SINR to return to reported SINR more quickly. Additionally, the error rate estimation may be adjusted to converge to a more recently measured more quickly by decreasing a feedback filter coefficient.

What is claimed is: 
     
         1 . A user equipment (UE), comprising a radio configured to:
 communicate with a base station (BS) in a wireless communication network according to a first modulation and coding scheme (MCS) during a first period of time, wherein the BS selects the first MCS based on a first historical error rate estimated using a smoothing factor at a first level;   communicate with the BS according to a second MCS during a second period of time that is after the first period of time, wherein the BS selects the second MCS based on a second historical error rate estimated using the smoothing factor, and wherein the second historical error rate is higher than the first historical error rate; and   communicate with the BS according to the first MCS during a third period of time that is after the second period of time, wherein the BS reduces the smoothing factor to a second level that is lower than the first level in response to the second historical error rate being higher than the first historical error rate, and wherein the BS selects the first MCS based on a third historical error rate estimated using the smoothing factor at the second level;   wherein each historical error rate is estimated using the smoothing factor applied to a current error rate and a previous error rate, wherein a window averaged error rate is used as the current error rate.   
     
     
         2 . The UE of  claim 1 , wherein the second historical error rate is higher than the first historical error rate at least partially because the radio did not communicate with the BS during a fourth period of time that was after the first period of time and before the second period of time. 
     
     
         3 . The UE of  claim 1 , wherein the reducing the smoothing factor to a second level is further in response to the current error rate being substantially lower than the second historical error rate. 
     
     
         4 . The UE of  claim 1 , wherein in the communicating with the base station, the radio is further configured to transmit to the BS at least one of acknowledge messages or no-acknowledge messages in response to receiving transmissions from the BS, wherein the window averaged error rate is based at least in part on the at least one of acknowledge messages or no-acknowledge messages. 
     
     
         5 . The UE of  claim 4 , wherein the BS interprets the absence of an acknowledge message in response to a transmission to the UE as a no-acknowledge message, and wherein the BS calculates the window averaged error rate by:
 generating a first sum by summing the number of no-acknowledge messages occurring within a specified window;   generating a second sum by summing the number of acknowledge messages and no-acknowledge messages occurring within the specified window; and   dividing the first sum by the second sum.   
     
     
         6 . A method performed by a base station (BS) in a wireless communication system, the method comprising:
 the BS communicating with a user equipment (UE);   during the BS communicating with the UE, the BS estimating historical error rates using a smoothing factor at a first level;   the BS losing communication with the UE after said communicating;   during a time when the BS has lost communication with the UE, the BS estimating historical error rates that are substantially higher than when the BS is communicating with the UE;   the BS resuming communication with the UE after said losing communication; and   after the BS resuming communication with the UE, the BS estimating historical error rates using the smoothing factor at a second level;   wherein each of the historical error rates is estimated using the smoothing factor applied to a current error rate and a previous error rate, wherein a window averaged error rate is used as the current error rate.   
     
     
         7 . The method of  claim 6 , wherein, in communicating with the UE, the BS uses a modulation and coding scheme (MCS) selected based on the historical error rates. 
     
     
         8 . The method of  claim 7 , wherein, after the BS resuming communication with the UE, the BS estimating the historical error rates using the smoothing factor at the second level operates to more quickly improve the MCS. 
     
     
         9 . The method of  claim 6 , further comprising:
 during the BS communicating with the UE, the BS receiving at least one of acknowledge messages or no-acknowledge messages in response to transmissions to the UE;   during the time when the BS has lost communication with the UE, the BS not receiving acknowledge messages or no-acknowledge messages in response to transmissions to the UE, wherein the BS interprets receiving neither an acknowledge message nor a no-acknowledge message in response to a transmission to the UE as a no-acknowledge message; and   the BS estimating the window averaged error rate based at least in part on the at least one of acknowledge messages or no-acknowledge messages.   
     
     
         10 . The method of  claim 9 , wherein the BS calculates the window averaged error rate by:
 generating a first sum by summing the number of no-acknowledge messages occurring within a specified window;   generating a second sum by summing the number of acknowledge messages and no-acknowledge messages occurring within the specified window; and   dividing the first sum by the second sum.   
     
     
         11 . The method of  claim 6 , wherein the BS estimating historical error rates using the smoothing factor at a second level is further in response to the current error rate being substantially lower than the previous error rate. 
     
     
         12 . The method of  claim 6 , wherein the historical error rates are historical block error rates (BLER). 
     
     
         13 . A method performed by a base station (BS) in a wireless communication system, the method comprising:
 the BS communicating with a user equipment (UE);   during the BS communicating with the UE, the BS estimating a first historical error rate using a smoothing factor at a first level;   the BS losing communication with the UE after said communicating;   during a time when the BS has lost communication with the UE, the BS estimating a second historical error rate, wherein the second historical error rate is substantially higher than the first historical error rate;   the BS resuming communication with the UE after said losing communication; and   after the BS resuming communication with the UE,
 the BS estimating a third historical error rate; and 
 the BS decreasing the smoothing factor to a second level based on the third historical error rate estimated after the BS resumes communications with the UE; 
 wherein a plurality of historical error rates estimated after the BS decreases the smoothing factor to a second level are calculated using the smoothing factor at the second level; 
   wherein each of the historical error rates is estimated using the smoothing factor applied to a current error rate and a previous error rate, wherein a window averaged error rate is used as the current error rate.   
     
     
         14 . The method of  claim 13 , further comprising:
 during the BS communicating with the UE, the BS receiving at least one of acknowledge messages or no-acknowledge messages in response to transmissions to the UE;   during the time when the BS has lost communication with the UE, the BS not receiving acknowledge messages or no-acknowledge messages in response to transmissions to the UE, wherein the BS interprets receiving neither an acknowledge message nor a no-acknowledge message in response to a transmission to the U E as a no-acknowledge message; and   the BS estimating the window averaged error rate based at least in part on the at least one of acknowledge messages or no-acknowledge messages.   
     
     
         15 . The method of  claim 13 , wherein the BS calculates the window averaged error rate by:
 generating a first sum by summing the number of no-acknowledge messages occurring within a specified window;   generating a second sum by summing the number of acknowledge messages and no-acknowledge messages occurring within the specified window; and   dividing the first sum by the second sum.   
     
     
         16 . The method of  claim 13 , wherein the decreasing the smoothing factor to a second level is further based on the current error rate being substantially lower than the third historical error rate. 
     
     
         17 . A method for estimating error rate, comprising:
 during a first period of time, a base station (BS) communicating with a user equipment (UE) over a network;   during the first period of time, the BS estimating a first error rate using a smoothing factor at a first level;   during a second period of time, the BS losing communication with the UE;   during the second period of time, the BS estimating a second error rate, wherein the second error rate is substantially higher than the first error rate;   during a third period of time, the BS communicating with the UE;   during the third period of time, the BS decreasing the smoothing factor to a second level based on the second error rate being substantially higher than the first error rate;   during the third period of time, the BS estimating a third error rate using the smoothing factor at the second level;   during a fourth period of time, increasing the smoothing factor back to the first level;   during the fourth period of time, the BS estimating a fourth error rate using the smoothing factor at the first level, wherein the fourth error rate is substantially less than the second and third error rates;   wherein each error rate is estimated using the smoothing factor applied to a current error rate and a previous error rate, wherein a window averaged error rate is used as the current error rate.   
     
     
         18 . A method performed by a base station (BS) in a wireless communication system, the method comprising:
 the BS estimating a first historical error rate using a smoothing factor at a first level;   after the BS estimating the first historical error rate, the BS estimating a second historical error rate;   the BS determining that the second historical error rate is different than the first historical error rate;   in response to the determining, the BS changing the smoothing factor to a second level;   after the BS changing the smoothing factor to the second level, the BS estimating a third historical error rate using the smoothing factor at the second level;   wherein each historical error rate is estimated using the smoothing factor applied to a current error rate and a previous error rate, wherein a window averaged error rate is used as the current error rate.   
     
     
         19 . The method of  claim 18 , wherein the changing the smoothing factor to a second level comprises scaling the smoothing factor in a manner inversely proportional to the difference between the first historical error rate and the second historical error rate. 
     
     
         20 . The method of  claim 18 , wherein:
 the determining that the second historical error rate is different than the first historical error rate comprises determining that the second historical error rate is substantially higher than the first historical error rate; and   the changing the smoothing factor to a second level comprises decreasing the smoothing factor.   
     
     
         21 . The method of  claim 18 , wherein the changing the smoothing factor to a second level is further in response to determining that a current error rate is substantially lower than the second historical error rate.