Patent Publication Number: US-9888474-B2

Title: Method and device for activating secondary carrier in wireless communication system for using carrier aggregation technique

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a continuation application of prior application Ser. No. 14/721,519, filed on May 26, 2015 and of prior application Ser. No. 13/877,552, filed on Apr. 3, 2013, which has issued as U.S. Pat. No. 9,055,565 on Jun. 9, 2015 and which claimed the benefit under 35 U.S.C. § 371 of an International application filed on Nov. 7, 2011 and assigned application number PCT/KR2011/008428, which claimed the benefit of a U.S. provisional patent application filed on Nov. 5, 2010 in the United States Patent and Trademark Office and assigned Ser. No. 61/410,493, and of a U.S. provisional patent application filed on Jan. 11, 2011 in the United States Patent and Trademark Office and assigned Ser. No. 61/431,635, the entire disclosure of each of which is hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a wireless communication system and, in particular, to a method for activating a secondary carrier in addition to the primary carrier in a Long Term Evolution (LTE) system supporting Carrier Aggregation. 
     Description of the Related Art 
     With the rapid advance of wireless communication technology, the communication system has evolved to the 4th Generation mobile communication systems such as Long Term Evolution (LTE) system. The LTE system adopts various techniques to meet the increased traffic requirements and, Carrier Aggregation is one of these techniques. The carrier aggregation is a technique capable of increasing the data rate in proportion to the number of aggregated carriers including plural secondary carrier as well as the primary carrier between a User Equipment (UE) and an evolved Node B (eNB) as compared to the conventional system using a single carrier. In LTE, the primary cell is referred to as PCell and the secondary cell is referred to as SCell. 
     In order to use the carrier aggregation technique, it is inevitable that the complexity increases to control the PCell and the SCells. That is, there is a need of control to determine the SCell(s) to be configured for use along the PCell and to be activated for actual use. 
     There is therefore a need of a detailed procedure for activating an SCell. That is, it is necessary to specify the operation of the UE when an S Cell activation command is received from the eNB. 
     DISCLOSURE OF INVENTION 
     Technical Problem 
     The present invention has been made in an effort to solve the above problem, and it is an object of the present invention to provide a method for activating secondary carriers in the mobile communication system supporting carrier aggregation. 
     Solution to Problem 
     In the present invention, the operations for performing secondary carrier (SCell) activation are sorted into two groups that are executed at different timings. 
     In order to accomplish this, a secondary carrier activation method of a terminal in a wireless communication system supporting carrier aggregation includes receiving secondary carrier aggregation activation information instructing activation of secondary carriers configured to the terminal; checking a first timing in configuring the activation of the secondary carriers and performing first operations at the first timing; and checking a second timing and performing second operations before the second timing. 
     A terminal for activating secondary carriers under the control of a base station in a wireless communication system supporting carrier aggregation includes a transceiver which transmits and receives control signals or data to and from the base station; and a controller which controls receiving secondary carrier aggregation activation information instructing activation of secondary carriers configured to the terminal from the base station, checking a first timing in configuring the activation of the secondary carriers and performing first operations at the first timing, and checking a second timing and performing second operations before the second timing. 
     Advantageous Effects 
     With the proposed method, it is possible to execute all the operations for activating cells such that the UE is capable of performing the secondary carrier activation without error. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating the architecture of an LTE system to which the present invention is applied; 
         FIG. 2  is a diagram illustrating a protocol stack of the LTE system to which the present invention is applied; 
         FIG. 3  is a diagram illustrating an exemplary situation of carrier aggregation in the LTE system to which the present invention is applied; 
         FIG. 4  is a signaling diagram illustrating message flows between the eNB and the UE in the secondary carrier activation method according to an embodiment of the present invention; 
         FIG. 5  is a diagram illustrating operation timings in unit of subframe for secondary carrier activation method according to an embodiment of the present invention; 
         FIG. 6  is a flowchart illustrating the UE procedure of the SCell activation method according to an embodiment of the present invention; 
         FIG. 7  is a flowchart illustrating the eNB procedure of the SCell activation method according to an embodiment of the present invention; and 
         FIG. 8  is a block diagram illustrating the configuration of the UE according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     In the following, detailed description of well-known functions and structures incorporated herein may be omitted to avoid obscuring the subject matter of the present invention. Exemplary embodiments of the present invention are described with reference to the accompanying drawings in detail. 
     The present invention relates to a secondary carrier activation method and apparatus of a UE capable of carrier aggregation. 
       FIG. 1  is a diagram illustrating the architecture of an LTE system to which the present invention is applied. 
     Referring to  FIG. 1 , the radio access network of the mobile communication system includes evolved Node Bs (eNBs)  105 ,  110 ,  115 , and  120 , a Mobility Management Entity (MME)  125 , and a Serving-Gateway (S-GW)  130 . The User Equipment (hereinafter, referred to as UE)  135  connects to an external network via eNBs  105 ,  110 ,  115 , and  120  and the S-GW  130 . 
     In  FIG. 1 , the eNBs  105 ,  110 ,  115 , and  120  correspond to legacy node Bs of Universal Mobile Communications System (UMTS). The eNBs  105 ,  110 ,  115 , and  120  allow the UE to establish a radio link and are responsible for complicated functions as compared to the legacy node B. In the LTE system, all the user traffic including real time services such as Voice over Internet Protocol (VoIP) are provided through a shared channel and thus there is a need of a device which is located in the eNB to schedule data based on the state information such as UE buffer conditions, power headroom state, and channel state. Typically, one eNB controls a plurality of cells. In order to secure the data rate of up to 100 Mbps, the LTE system adopts Orthogonal Frequency Division Multiplexing (OFDM) as a radio access technology. Also, the LTE system adopts Adaptive Modulation and Coding (AMC) to determine the modulation scheme and channel coding rate in adaptation to the channel condition of the UE. The S-GW  130  is an entity to provide data bearers so as to establish and release data bearers under the control of the MME  125 . MME  125  is responsible for various control functions and connected to a plurality of eNBs  105 ,  110 ,  115 , and  120 . 
       FIG. 2  is a diagram illustrating a protocol stack of the LTE system to which the present invention is applied. 
     Referring to  FIG. 2 , the protocol stack of the LTE system includes Packet Data Convergence Protocol (PDCP)  205  and  240 , Radio Link Control (RLC)  210  and  235 , Medium Access Control (MAC)  215  and  230 , and Physical (PHY)  220  and  225 . The PDCP  205  and  240  is responsible for IP header compression/decompression, and the RLC  210  and  235  is responsible for segmenting the PDCP Protocol Data Unit (PDU) into segments in appropriate size for Automatic Repeat Request (ARQ) operation. ARQ is the technique for checking whether the packet transmitted by the transmitted is received by the received successfully and retransmitting the packets received erroneously. The MAC  215  and  230  is responsible for establishing connection to a plurality of RLC entities so as to multiplex the RLC PDUs into MAC PDUs and demultiplex the MAC PDUs into RLC PDUs. The PHY  220  and  225  performs channel coding on the MAC PDU and modulates the MAC PDU into OFDM symbols to transmit over radio channel or performs demodulating and channel-decoding on the received OFDM symbols and delivers the decoded data to the higher layer. 
       FIG. 3  is a diagram illustrating an exemplary situation of carrier aggregation in the LTE system to which the present invention is applied. 
     Referring to  FIG. 3 , typically an eNB can use multiple carriers transmitted and receive in different frequency bands. For example, the eNB  305  can be configured to use the carrier  315  with center frequency f 1  and the carrier  310  with center frequency f 3 . If carrier aggregation is not supported, the UE  330  has to transmit/receive data unit one of the carriers  310  and  315 . However, the UE  330  having the carrier aggregation capability can transmit/receive data using both the carriers  310  and  315 . The eNB can increase the amount of the resource to be allocated to the UE capable of carrier aggregation in adaptation to the channel condition of the UE so as to improve the data rate of the UE. 
     In case that a cell is configured with one downlink carrier and one uplink carrier as a conventional concept, the carrier aggregation can be understood as if the UE communicates data via multiple cells. With the use of carrier aggregation, the maximum data rate increases in proportion to the number of aggregated carriers. 
     In the following description, the phrase “the UE receives data through a certain downlink carrier or transmits data through a certain uplink carrier” means to transmit or receive data through control and data channels provided in a cell corresponding to center frequencies and frequency bands of the downlink and uplink carriers. Although the description is directed to an LTE mobile communication system for explanation convenience, the present invention can be applied to other types of wireless communication systems supporting carrier aggregation. 
     An embodiment of the present invention proposes a UE operation when a secondary carrier (SCell) activation command is received from the eNB. In an embodiment of the present invention, the UE operations upon receipt the secondary carrier activation command are sorted into two sets which are applied at different timings. This is because if the operations requiring different operation time durations are executed at the same timing determined based on the operation requiring longer time duration this increases the activation delay. 
     For example, the UE cannot use the secondary carrier (SCell) for data transmission upon receipt of the command from the eNB. This is because it takes addition time to activate devices for use of the secondary carrier (SCell). Furthermore, once the devices have been activated, there may be other operations requiring more time. 
       FIG. 4  is a signaling diagram illustrating message flows between the eNB and the UE in the secondary carrier activation method according to an embodiment of the present invention. 
     The eNB  403  determines the SCells to be activated or deactivated among the SCells configured to the UE  401 . The eNB generates a SCell activation information (or Activation/Deactivation MAC Control Element (CE) including an indicator indicating activation or deactivation of the SCell and sends the UE  401  the Activation/Deactivation MAC CE at Nth subframe at step  405 . The Activation/Deactivation MAC CE is 8-bit fixed size MAC CE including 7 C fields and one R field. Here, R denotes a reserved field, and 7 C fields are expressed as C7, C6, C5, C4, C3, C2, and C1 (i.e. Ci). If Ci corresponding to SCell i is set to 1, this indicates activation and, otherwise if Ci is set to 0, this indicates deactivation. 
     If the Activation/Deactivation MAC CE is received, the UE checks the SCells to be activated or deactivated at step  407  and checks the first timing at step  409 . The first timing is (N+m)th subframe where m is a integer equal to or greater than 1 (e.g. 8). The first timing is of performing the operations that can be executed immediately among the UE&#39;s SCell activation operations. The parameter m is preferably set to a value large enough by taking notice of the UE having low processing capability in consideration of the time necessary for the UE to receive and decode the Activation/Deactivation MAC CE and recognize the meaning 
     At the first timing of (N+m)th subframe, the UE  401  performs the predetermined first operations at step  411 . The first operations are as follows.
         scheduling channel monitoring   CQI measurement   PUSCH transmission/PDSCH reception   CQI reporting   SRS transmission       

     Afterward, the UE  401  checks the second timing at step  413 . The second timing (N+z+4)th subframe where z is an integer equal to or greater than m, (N+z)th subframe is the downlink subframe available for channel quality (Channel Quality Information (CQI) or Channel Status Information (CSI)) measurement which arrives first, and 4 is a constant value given for measurement before 4 subframes. That is, the CQI measurement is performed at (N+z)th subframe, and the measured CQI is reported at the (N+z+4)th subframe or later. The valid downlink subframe is defined as the time fulfilling the following conditions:
         DL subframe is configured for corresponding UE,   transmission mode 9 is ruled out and no MBSFN subframe,   not include DwPTS field when the length of DwPTS is equal to or less than 7680*TS   the subframe is not positioned in measurement gap for the UE   For periodic CSI report, CSI subframe set is configured to the UE, component of CSI subframe associated with periodic CSI report.       

     After checking the second timing, the UE  401  performs the predetermined second operations before the second timing. Here, the predetermined second operations include the operations related to CQI report as follows.
         If valid CQI measurement is performed, report CQI actually.   At the CQI reporting timing, the UE reports a CQI index value selected in the range from 1 to 15 by referencing table 1 according to the actual measurement.       

     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 CQI index  
                 modulation 
                 code rate × 1024 
                 efficiency 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 0 
                 out of range 
               
            
           
           
               
               
               
               
               
            
               
                   
                 1 
                 QPSK 
                  78 
                 0.1523 
               
               
                   
                 2 
                 QPSK 
                 120 
                 0.2344 
               
               
                   
                 3 
                 QPSK 
                 193 
                 0.3770 
               
               
                   
                 4 
                 QPSK 
                 308 
                 0.6016 
               
               
                   
                 5 
                 QPSK 
                 449 
                 0.8770 
               
               
                   
                 6 
                 QPSK 
                 602 
                 1.1758 
               
               
                   
                 7 
                 16QAM 
                 378 
                 1.4766 
               
               
                   
                 8 
                 16QAM 
                 490 
                 1.9141 
               
               
                   
                 9 
                 16QAM 
                 616 
                 2.4063 
               
               
                   
                 10  
                 64QAM 
                 466 
                 2.7305 
               
               
                   
                 11  
                 64QAM 
                 567 
                 3.3223 
               
               
                   
                 12  
                 64QAM 
                 666 
                 3.9023 
               
               
                   
                 13  
                 64QAM 
                 772 
                 4.5234 
               
               
                   
                 14  
                 64QAM 
                 873 
                 5.1152 
               
               
                   
                 15 
                 64QAM 
                 948  
                 5.5547 
               
               
                   
                   
               
            
           
         
       
         
         
           
             if there is no valid CQI, report CQI set to 0 (refer to table 1). 
           
         
       
    
     Next, the UE reports the CQI before the second timing at step  417  such that all the operations are performed correctly since the second timing. 
       FIG. 5  is a diagram illustrating operation timings in unit of subframe for secondary carrier activation method according to an embodiment of the present invention. 
     In  FIG. 5 , the CQI report resource for SCell is allocated at an interval of 5 ms (a subframe has a length of 1 ms) and indicated by arrows (at [n−7], [n−2], [n+3], [n+8], . . . ). 
     First, the UE receives the Activation/Deactivation MAC CE at (n−5)th subframe. At this time, the UE interprets the MAC CE to determine the SCells to be activated or deactivated for a certain time. Assuming that it takes 6 msec for activation/deactivation of the synchronized SCells, the value m is 6 at the first timing in  FIG. 4 . At [n+1] of  FIG. 5 , the UE performs the first operations scheduled to be performed at the first timing, and this is identical with the description of step  411  of  FIG. 4 . 
     Here, the first timing is the last time point when the operations scheduled to be performed at the first timing are initiated, and if the UE is capable of interpreting the MAC CE as soon as possible, the operations can be performed in advance. In this case, the next CQI report can be performed with the average of more values so as to report more accurate value. 
     Afterward, the UE calculates the second timing of  FIG. 4  (after 4 subframes in  FIG. 5 ) and starts the second operations scheduled to be performed at the second timing. The CQI report is performed as described with reference to  FIG. 4 , and the UE starts CQI report for the SCell based on the second timing. That is, although the resource for CQI report is allocated at [n−7], [n−2], and [n+3] timings in  FIG. 5 , the CQI report is not performed at these timings but at [n+8] timing as the first resource allocated since the subframe [n+5]. Here, comparing the [n+5] timing of  FIG. 5  to (N+z+4) defined as the second timing in  FIG. 4 , z equal to m, i.e. 6. If the UE has the capability of reporting CQI before the second timing, it is possible to report the CQI before the second timing. 
       FIG. 6  is a flowchart illustrating the UE procedure of the S Cell activation method according to an embodiment of the present invention. 
     First, the UE receives the Activation/Deactivation MAC CE including an 8-bit bitmap at the Nth subframe at step  601 . Each bit of the bitmap carried in the MAC CE indicates whether to activate/deactivate the corresponding SCell. 
     If the Activation/Deactivation MAC CE is received, the UE determines whether there is any SCell to be newly activated and, if so, checks the SCell to be activated at step  603 . In more detail, the UE checks the deactivated SCells before the receipt of the MAC CE and, when the MAC CE is received, determines whether any of the deactivated SCells is indicated to be indicated to be activated by the corresponding bit of the bitmap in the MAC CE. 
     If any SCell to be activated newly is checked, the UE checks the first timing and performs the operations scheduled to be performed at the first timing at step  605 . The first timing corresponds to (N+m)th subframe, i.e. the subframe arriving after m subframes since the receipt of the Activation/Deactivation MAC CE at Nth subframe. The UE performs the first operation scheduled to be performed at the first timing based on the (N+m)th subframe. As described with reference to  FIG. 4 , these operations include at least one of the following operations that have been described with reference to  FIG. 4 .
         scheduling channel monitoring   CQI measurement   PUS CH transmission/PDS CH reception   CQI reporting   SRS transmission       

     Also, m is the fixed value known to all UEs and eNBs (e.g. m=8). 
     Afterward, the UE checks the second timing and performs the second operations scheduled to be performed at the second timing at step  607 . The second timing is the (N+z+4)th subframe equal to the second timing of  FIG. 4 , and z is an integer value equal to or greater than m. The second operations scheduled to be performed at the second timing includes CQI report as described with reference to  FIG. 4 . In more detail, the UE reports the CQI for the activated SCell through the allocated CQI report resource arriving first since the second timing. The UE also reports the CQI for the S Cell continuously through the CQI report resource allocated for the activated SCell. Although the CQI report is not transmitted between the first and second timings, if the valid CQI measurement result becomes available before the arrival of the second timing, it is possible to perform CQI report for the SCell. If there is no valid CQI measurement result between the first and second timings, the UE reports a predetermined value (e.g. CQI=0). However, if valid CQI measurement result is achieved before the second timing, the UE stops reporting the predetermined value and reports the report value reflecting the actual CQI measurement result to the eNB. 
       FIG. 7  is a flowchart illustrating the eNB procedure of the S Cell activation method according to an embodiment of the present invention. 
     The eNB determines whether to activate SCell x of the UE at step  701 . This may be the case when the traffic load of the cell increases due to the increase of the number of UEs served by the eNB. 
     Afterward, the eNB generates and transmits Activation/Deactivation MAC CE message for activating the SCell x at step  703 . 
     Afterward, the eNB performs the first operations scheduled to be performed at the first timing at step  405 . The first operations include allocating resource to the UE in the SCell x and receiving signals such as SRS message. 
     Finally, the eNB performs the operations scheduled to be performed at the second timing at step  407 . These operations include receiving the CQI report at the subframe designated to carry the CQI report of the SCell. 
       FIG. 8  is a block diagram illustrating the configuration of the UE according to an embodiment of the present invention. 
     The UE communicates data with higher layer processor  805  and transmits/receives control messages via the control message processor  807 . When transmitting control signal or data to the eNB, the UE multiplexes the control signals or data by means of the multiplexer/demultiplexer  803  and transmits the multiplexed signals to by means of the transceiver  801  under the control of the controller  809 . The UE also receives the physical signal by means of the transceiver  801 , demultiplexes the received signal by means of the multiplexer/demultiplexer  803 , and delivers the demultiplexed information to the higher layer processor  805  or control message processor  807  under the control of the controller  809 . 
     In an embodiment of the present invention, if the Activation/Deactivation MAC CE is received, the control message processor  807  notifies the SCell activation processor  811  of the receipt of the Activation/Deactivation MAC CE. The S Cell deactivation processor  811  checks the first timing and instructs the controller  809  and the control message processor  807  to perform the first operations at the first timing or even before the arrival of the first timing. Afterward, the SCell activation processor  811  checks the second timing and performs the second operations at the second timing or even before the arrival of the second timing. The second operations include reporting CQI for the second cell, and the CQI report for the SCell is performed using the CQI report resource allocated for the SCell. 
     Although  FIG. 8  is directed to the case where the UE is configured with plural function blocks in charge of different roles, the present invention is no limited thereto. For example, the functions of the SCell activation processor  811  can be performed by the controller  809 . 
     As described above, the SCell activation method of the present invention is capable of facilitating execution of the operations scheduled to be performed at predetermined timings in activating an SCell, resulting in improvement operation reliability. 
     Although exemplary embodiments of the present invention have been described in detail hereinabove with specific terminology, this is for the purpose of describing particular embodiments only and not intended to be limiting of the invention. While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention.