Patent Publication Number: US-2011055387-A1

Title: Method and Apparatus for Performing Buffer Status Reporting

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/239,069, filed on Sep. 2, 2009 and entitled “Interaction between BSR and SR”, the contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method and apparatus for performing buffer status reporting, and more particularly, to a method and apparatus for performing buffer status reporting in an user equipment of a wireless communication system, so as to prevent a new trigged buffer status report from being transmitted immediately. 
     2. Description of the Prior Art 
     Long Term Evolution wireless communication system (LTE system), an advanced high-speed wireless communication system established upon the 3G mobile telecommunication system, supports only packet-switched transmission, and tends to implement both Medium Access Control (MAC) layer and Radio Link Control (RLC) layer in one single communication site, such as in base stations (Node Bs) alone rather than in Node Bs and RNC (Radio Network Controller) respectively, so that the system structure becomes simple. 
     In LTE system, the 3rd Generation Partnership Project, 3GPP, introduces a Buffer Status Reporting (BSR) procedure, which is used to provide the serving NB (or enhanced NB) with information about the amount of data in UL buffers of the UE. In the BSR procedure, the UE uses a MAC PDU (Protocol Data Unit) to carry a BSR MAC control element with information about the amount of data in the UL buffers to the network. Accordingly, the network can determine the total amount of data available across one or all logical channel groups. 
     There are three types of BSR for different triggering events, a regular BSR, a periodic BSR and a padding BSR. The regular BSR is triggered when UL data arrives at the UE transmission buffer and the UL data belongs to a logical channel with higher priority than those for which data already existed in the UE transmission buffer, or is triggered when a serving cell change occurs. The periodic BSR is triggered when a periodic BSR timer “PERIODIC BSR TIMER” expires. The padding BSR is triggered when UL resources are allocated and an amount of padding bits is equal to or greater than the size of the BSR MAC control element. 
     According to the current specification (3GPP TS36.321 V8.6.0), the Buffer Status reporting procedure shall determine that at least one BSR has been triggered since the last transmission of a BSR or if this is the first time that at least one BSR is triggered. After at least one BSR is determined triggered, if the UE has UL resources allocated for a new transmission for a current Transmission Time Interval (TTI), the UE shall generate a BSR MAC control element to report information about the amount of data in the UL buffers. Else, if the UE does not have UL resources allocated for a new transmission for this TTI and the triggered BSR is a Regular BSR, a Scheduling Request (SR) shall be triggered, for requesting the network to allocate an uplink grant for the UE, such that the triggered BSR can be transmitted. 
     In addition, all triggered BSRs shall be cancelled in the following two cases: (1) when the UL grant can accommodate all pending data available for transmission but is not sufficient to additionally accommodate the BSR MAC control element plus its sub-header; (2) when a BSR is included in a MAC PDU for transmission. 
     However, in some cases, the above BSR operations may cause a later triggered BSR cannot be transmitted immediately, resulting in that higher priority data of the UE may be delayed. 
     For example, please refer to  FIG. 1 , which shows an operational diagram of a conventional BSR procedure. At the beginning, the UE triggers a first BSR BSR 1  at a timing point T 1 . Since the UE has no UL resources allocated for a new transmission for this TTI, an SR is then triggered to request the network to allocate an uplink grant for the UE. Then, the allocated UL grant is received on a Physical Downlink Control Channel (PDCCH) at a timing point T 2 . In this case, the UE generates a BSR MAC control element corresponding to the first BSR BSR 1 , and includes it into a MAC PDU at a timing point T 3 . Such that the BSR MAC control element can be transmitted at a timing point T 4  along with other uplink data. In general, the time interval between reception of the UL grant and transmission of the first BSR BSR 1  is about 4 milliseconds, i.e. T 4 =T 2 +4. In addition, since the BSR MAC control element is generated at the timing point T 3 , all triggered BSRs are cancelled at the same time. 
     Assuming that the UE triggers a second BSR BSR 2  at a timing point T 5  before the first BSR BSR 1  is sent due to higher priority data coming, since the UL grant is already used by the first BSR BSR 1 , the UE has to trigger another SR to request UL grants for the second BSR BSR 2 . However, when the UL grant is received by the UE at a timing point T 6 , the UE cannot determine whether any BSR has been trigged based on the above method, i.e. no BSR is triggered after the last transmission of a BSR. As a result, the UE shall not generate a BSR MAC control element corresponding to the second BSR BSR 2  at a timing point  7 . 
     In this case, the second BSR BSR 2  is not included in the MAC PDU using the lately allocated UL grant, such that the higher priority data in the UE UL buffer cannot be sent immediately, resulting in data delay of the UE. 
     In addition, please refer to  FIG. 2 , which shows another operational diagram of the conventional BSR procedure. At the beginning, the UE triggers a first BSR BSR 1  at a timing point T 1 . Then, the first BSR BSR 1  is cancelled at a timing point T 2  since the allocated UL grant can only accommodate all pending data available for transmission but is not sufficient to additionally accommodate the BSR MAC control element plus its sub-header. That means the first BSR BSR 1  is not included in the uplink transmission. Afterwards, the UE triggers a second BSR BSR 2  and an SR due to UL data arrival at a timing point T 3 . In this case, when an UL grant is received by the UE at a timing point T 4 , the second BSR BSR 2  is supposed to be included in a MAC PDU. However, since the first BSR BSR 1  is cancelled, the UE cannot determine whether there is triggered BSR based on the above method. 
     Assuming that the first BSR BSR 1  is the first time a BSR is triggered, since the first BSR BSR 1  is cancelled, the UE has no triggered BSRs. The second BSR BSR 2  is either not a first-time triggered BSR. Thus, the UE cannot determine whether any BSR has been triggered based on the above-mentioned method. In this case, the UE shall not generate a BSR MAC control element corresponding to the second BSR BSR 2 , such that the higher priority data in the UE UL buffer cannot be sent immediately. 
     In brief, if the new BSR is triggered before transmission of the old BSR which is triggered earlier than the new BSR, and the UL grant is received later than the transmission of the old BSR, the way to determine whether any BSR has been triggered may cause incorrect execution of the BSR procedure, such as the BSR MAC control element corresponding to the new BSR cannot be generated, and result in occurrence of UE data delay. 
     SUMMARY OF THE INVENTION 
     It is therefore an objective of the present invention to provide a method and apparatus for performing buffer status reporting in an user equipment of a wireless communication system. 
     According to the present invention, a method for performing Buffer Status Reporting (BSR) in an user equipment (UE) of a wireless communication system is disclosed. The method includes steps of determining any BSR has been triggered since last cancellation of a triggered BSR to a current Transmission Time Interval (TTI); and performing a BSR procedure when at least one BSR is determined triggered; wherein the triggered BSR is cancelled because a first uplink grant received by the UE can only accommodate all pending data available for transmission but is not sufficient to additionally accommodate a first BSR MAC control element corresponding to the triggered BSR plus its sub-header, or when the first BSR MAC control element is included in a first MAC PDU for transmission. 
     According to the present invention, a communications device for performing Buffer Status Reporting in an user equipment (UE) of a wireless communication system is disclosed. The communications device includes a processor for executing a program, and a memory, coupled to the processor, for storing the program. The program includes steps of determining any BSR has been triggered since last cancellation of a triggered BSR to a current Transmission Time Interval (TTI); and performing a BSR procedure when at least one BSR is determined triggered; wherein the triggered BSR is cancelled because a first uplink grant received by the UE can only accommodate all pending data available for transmission but is not sufficient to additionally accommodate a first BSR MAC control element corresponding to the triggered BSR plus its sub-header, or when the first BSR MAC control element is included in a first MAC PDU for transmission. 
     According to the present invention, a method for performing Buffer Status Reporting (BSR) in an user equipment (UE) of a wireless communication system is disclosed. The method includes steps of determining any triggered BSR has not been cancelled till a current Transmission Time Interval (TTI); and performing a BSR procedure when at least one BSR has not been cancelled; wherein the triggered BSR is cancelled because a uplink grant received by the UE can only accommodate all pending data available for transmission but is not sufficient to additionally accommodate a BSR MAC control element corresponding to the triggered BSR plus its sub-header, or when the BSR MAC control element is included in a MAC PDU for transmission. 
     According to the present invention, a communications device for performing Buffer Status Reporting in an user equipment (UE) of a wireless communication system is disclosed. The communications device includes a processor for executing a program, and a memory, coupled to the processor, for storing the program. The program includes steps of determining any triggered BSR has not been cancelled till a current Transmission Time Interval (TTI); and performing a BSR procedure when at least one BSR has not been cancelled; wherein the triggered BSR is cancelled because a uplink grant received by the UE can only accommodate all pending data available for transmission but is not sufficient to additionally accommodate a BSR MAC control element corresponding to the triggered BSR plus its sub-header, or when the BSR MAC control element is included in a MAC PDU for transmission. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an operational diagram of a conventional BSR procedure. 
         FIG. 2  shows another operational diagram of a conventional BSR procedure. 
         FIG. 3  is a schematic diagram of a wireless communications system. 
         FIG. 4  is a function block diagram of a wireless communications device. 
         FIG. 5  is a diagram of program code of  FIG. 4 . 
         FIG. 6  is a flowchart of a process according to an embodiment of the present invention. 
         FIG. 7  shows an operational diagram of the process in  FIG. 6 . 
         FIG. 8  shows another operational diagram of the process in  FIG. 6 . 
         FIG. 9  is a flowchart of a process according to another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Please refer to  FIG. 3 , which illustrates a schematic diagram of a wireless communications system  10 . The wireless communications system  10  is preferred to be a Long Term Evolution (LTE) system, and is briefly composed of a network and a plurality of user equipments (UEs). In  FIG. 1 , the network and the UEs are simply utilized for illustrating the structure of the wireless communications system  10 . Practically, the network may comprise a plurality of base stations (Node Bs), radio network controllers and so on according to actual demands, and the UEs can be devices such as mobile phones, computer systems, etc. 
     Please refer to  FIG. 4 , which is a functional block diagram of a communications device  100  in a wireless communications system. The communications device  100  can be utilized for realizing the UEs or the network in  FIG. 3 . For the sake of brevity,  FIG. 4  only shows an input device  102 , an output device  104 , a control circuit  106 , a central processing unit (CPU)  108 , a memory  110 , a program  112 , and a transceiver unit  114  of the communications device  100 . In the communications device  100 , the control circuit  106  executes the program code  112  in the memory  110  through the CPU  108 , thereby controlling an operation of the communications device  100 . The communications device  100  can receive signals input by a user through the input device  102 , such as a keyboard, and can output images and sounds through the output device  104 , such as a monitor or speakers. The transceiver unit  114  is used to receive and transmit wireless signals, delivering received signals to the control circuit  106 , and outputting signals generated by the control circuit  106  wirelessly. From a perspective of a communications protocol framework, the transceiver unit  114  can be seen as a portion of Layer 1, and the control circuit  106  can be utilized to realize functions of Layer 2 and Layer 3. 
     Please continue to refer to  FIG. 5 .  FIG. 5  is a diagram of the program  112  shown in  FIG. 4 . The program  112  includes an application layer  200 , a Layer 3  202 , and a Layer 2  206 , and is coupled to a Layer 1  218 . The Layer 3  202  performs radio resource control. The Layer 2  206  comprises a Radio Link Control (RLC) layer and a Medium Access Control (MAC) layer, and performs link control. The Layer 1  218  performs physical connections. 
     In the LTE system, the MAC layer in the Layer 2  206  can execute a Buffer Status Reporting (BSR) procedure, which uses a MAC Protocol Data Unit (PDU) to carry a BSR MAC control element with information about the amount of data in the UE UL buffers to the network. Accordingly, the network can determine the total amount of data available across one or all logical channel groups. In this case, the embodiment of the present invention provides a buffer status reporting program  220  for correctly handling all triggered BSRs in the UE, so as to avoid occurrence of data delay. 
     Please refer to  FIG. 6 , which illustrates a schematic diagram of a process  40 . The process  40  is utilized for Buffer Status Reporting (BSR) in an user equipment (UE) of the wireless communications system  10 , and can be compiled into the buffer status reporting program  220 . The process  40  includes the following steps: 
     Step  400 : Start. 
     Step  402 : Determine any BSR has been triggered since last cancellation of a triggered BSR to a current Transmission Time Interval (TTI). 
     Step  404 : Perform a BSR procedure when at least one BSR is determined triggered. 
     Step  406 : End. 
     According to the process  40 , the UE first determine any BSR has been triggered since last cancellation of a triggered BSR to the current TTI. When at least one BSR is determined triggered, the UE then performs the BSR procedure. That is to say, if the UE has an uplink grant allocated for a new transmission for the current TTI, a BSR MAC control element corresponding to the at least one BSR is generated. Otherwise, if the UE does not have an uplink grant allocated for a new transmission for the current TTI and the at least one BSR is a Regular BSR, the UE shall trigger a Scheduling Request (SR). 
     In addition, all triggered BSRs shall be cancelled in the following two cases: (1) when the UL grant can accommodate all pending data available for transmission but is not sufficient to additionally accommodate the BSR MAC control element plus its sub-header; (2) when the BSR MAC control element is included in a MAC PDU for transmission. 
     Therefore, in the embodiment of the present invention, the time interval for determining any BSRs has been triggered is between the last cancellation of a BSR and the current TTI. Compared to the prior art that the determination begins at the last transmission of BSR, the embodiment of the present invention advances the start timing of the determination to the last cancellation of BSR. As a result, the new BSR can be transmitted immediately. 
     For example, please refer to  FIG. 7 , which shows an operational diagram of the process  40 . The scenario in  FIG. 7  is similar to that in  FIG. 1 , and thus the same descriptions are not given herein. Assume that the UE triggers a second BSR BSR 2  at a timing point T 5  before a first BSR BSR 1  is sent due to higher priority data coming. Since the timing of determining any BSRs has been triggered is advanced to the last cancellation of a BSR (i.e. when the first BSR BSR 1  is included in the MAC PDU), the UE can then successfully determine that there is new triggered BSR at the TTI the UL grant is received (i.e. at a timing point T 6 ), and generate a BSR MAC control element corresponding to the second BSR BSR 2  at a timing point T 7 . As a result, the second BSR BSR 2  can be transmitted at a timing point T 8  along with the other uplink data. 
     Similarly, the problem in  FIG. 2  can also be solved by the process  40 . Please refer to  FIG. 8 , which shows another operational diagram of the process  40 . The scenario in  FIG. 8  is similar to that in  FIG. 2 , and thus the same descriptions are not given herein. As shown in  FIG. 8 , since the timing of determining any BSRs has been triggered is advanced to the last cancellation of a BSR, i.e. the timing point T 2  that the first BSR BSR 1  is cancelled, the UE can then successfully determine that there is new triggered BSR at the TTI the UL grant is received (i.e. at a timing point T 4 ), and generate a BSR MAC control element corresponding to the second BSR BSR 2  at a timing point T 5 . 
     Please note that the above determination method is not for the scenario that the new BSR is the first-time triggered BSR. If the new BSR is the first-time triggered BSR, the UE shall directly perform the BSR procedure, i.e. generating a BSR MAC control element or triggering a SR according to whether the UE has an uplink grant at this TTI. 
     In addition, the spirit of the invention can be realized in like manners as long as the BSRs triggered after the last BSR cancellation can be determined. For example, please refer to  FIG. 9 , which illustrates a schematic diagram of a process  70 . The process  70  is also utilized for Buffer Status Reporting (BSR) in an user equipment (UE) of the wireless communications system  10 , and can be compiled into the buffer status reporting program  220 . The process  70  includes the following steps: 
     Step  700 : Start. 
     Step  702 : Determine any triggered BSR has not been cancelled till a current Transmission Time Interval (TTI). 
     Step  704 : Perform a BSR procedure when at least one BSR has not been cancelled. 
     Step  706 : End. 
     According to the process  70 , the UE first determine any triggered BSR has not been cancelled till the current TTI. If at least one BSR is triggered and has not been cancelled, the UE shall perform the BSR procedure, i.e. generating a BSR MAC control element or triggering a SR according to whether the UE has an uplink grant at this TTI. Compared to the process  40 , this embodiment does not need to separately consider the first-time triggered BSR. If the UE has triggered BSRs that has not been cancelled before the current TTI, the UE shall perform the BSR procedure in any case. 
     In brief, the process  70  also advances the timing of determining any BSR has been triggered to the last BSR cancellation, to solve the problem that the new triggered BSR cannot be transmitted immediately. 
     As mentioned above, the embodiment of the present invention provides a method and apparatus for performing buffer status reporting, for correctly handling all triggered BSRs in the UE, so as to avoid occurrence of UE data delay. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.