Abstract:
A method of managing TA functionality for a communication device of a wireless communication system which supports carrier aggregation that multiple component carriers are aggregated to support wider transmission bandwidth is disclosed. The method comprises receiving a RRC message indicating a usage of a timing advance command for each of a plurality of component carriers configured to the communication device, from a cell in a network of the wireless communication system, when the timing advance command has been received from the cell for each of the plurality of component carriers, applying the timing advance functionality corresponding to each of the plurality of component carriers, for updating a timing advance value for each of the plurality of component carriers, and when updating the timing advance value for each of the plurality of component carriers, starting or restarting a time alignment timer for each of the plurality of component carriers.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application of U.S. application Ser. No. 12/721,515, filed on Mar. 10, 2010 and entitled “Method of Managing Timing Alignment Functionality for Multiple Component Carriers and Related Communication Device”, which claims the benefit of U.S. Provisional Application No. 61/160,715, filed on Mar. 17, 2009 and entitled “Method for handling TA update in multiple connections in a wireless communication system and related apparatus”, the contents of which are incorporated herein in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     A method utilized in a wireless communication system and communication device thereof are provided, and more particularly, to a method of managing timing alignment functionality for multiple component carriers in a wireless communication system and related communication device. 
     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, so that the system structure becomes simple. 
     According to structure of the LTE system, timing alignment (TA) functionality allows a user equipment (UE) with a component carrier to be synchronized with a serving base station on uplink timing for preventing signals transmitted from the UE from colliding with those sent from other UEs under the coverage of the base station. In the TA functionality, the UE has to maintain a time alignment timer whose running state indicates that uplink transmission is still synchronized. The network can control the TA functionality of the UE with a timing advance command. Detailed operation of the TA functionality can be referred in related specifications, and is not given herein. 
     Toward advanced high-speed wireless communication system, such as transmitting data in a higher peak data rate, LTE-Advanced is standardized by the 3rd Generation Partnership Project (3GPP) as an enhancement of LTE system. LTE-Advanced targets faster switching between power states, improves performance at the cell edge, and includes subjects, such as bandwidth extension, coordinated multipoint transmission/reception (COMP), uplink multiple input multiple output (MIMO) extension up to 4×4, downlink MIMO extension up to 4×4, relaying, and etc. 
     Based on a concept of bandwidth extension, carrier aggregation is introduced to the LTE-Advanced for extension to wider bandwidth, where two or more component carriers are aggregated, for supporting wider transmission bandwidths e.g. up to 100 MHz and for spectrum aggregation. According to carrier aggregation capability, multiple component carriers are aggregated into overall wider bandwidth, wherein a UE can establish multiple links corresponding to the multiple component carriers for simultaneously receiving and/or transmitting on each component carrier. Each component carrier includes a hybrid automatic repeat request (HARQ) entity and a transport block. 
     However, in the LTE system, each UE is only allowed to use a single component carrier, so the UE maintains synchronization with a base station during TA functionality performance only on the single component carrier. Furthermore, the UE is allowed to connect to multiple component carriers according to the LTE Advancement. However, the LTE Advancement does not clearly specify how the TA functionality is applied in the UE with multiple component carriers. The management of TA functionality for the multiple component carriers is never concerned. Improper configuration on TA functionality with multiple component carriers causes failure of UE synchronization and uplink transmission. 
     The applicant provides an uplink transmission problem as below based on a direct image on a basis of a combination of the prior art LTE and LTE-Advanced system. Consider a scenario that a UE in a RRC (Radio Resource Control) connected mode is configured with two component carriers for uplink transmission from two cells and the UE maintains a time alignment timer for uplink synchronization as specified in the LTE system. The two cells have different timing advance values for the UE. According to the prior art, the UE updates the timing advance according to a received timing advance command. When the UE applies the timing advance to the uplink transmission for both component carriers, the uplink transmission in one component carrier will be successful, but the uplink transmission in the other component carrier will be failed because the timing advance value is correct in the component carrier, but is not correct in the other component carrier. 
     SUMMARY OF THE INVENTION 
     A method of managing timing alignment, TA, functionality for a communication device of a wireless communication system which supports carrier aggregation that multiple component carriers are aggregated to support wider transmission bandwidth, is disclosed. The method comprises receiving a radio resource control, RRC, message indicating a usage of a timing advance command for each of a plurality of component carriers configured to the communication device, from a cell in a network of the wireless communication system, when the timing advance command has been received from the cell in the network for each of the plurality of component carriers, applying the timing advance functionality corresponding to each of the plurality of component carriers, for updating a timing advance value for each of the plurality of component carriers, and when updating the timing advance value for each of the plurality of component carriers, starting or restarting a time alignment timer for each of the plurality of component carriers. 
     A method of managing timing alignment, TA, functionality for a cell in a network of a wireless communication system which supports carrier aggregation that multiple component carriers are aggregated to support wider transmission bandwidth, is disclosed. The method comprises transmitting, by a cell of the network, a radio resource control, RRC, message indicating a usage of a timing advance command for each of a plurality of component carriers configured to a communication device of the wireless communication system, to the communication device, and transmitting, by the cell of the network, the timing advance command for each of the plurality of component carriers to the communication device, for updating a timing advance value for each of the plurality of component carriers. 
     A communication device of a wireless communication system which supports carrier aggregation that multiple component carriers are aggregated to support wider transmission bandwidth, for managing timing alignment, TA, functionality, is disclosed. The communication device comprises a non-transitory computer-readable medium for storing program code corresponding to a process, and a processor coupled to the non-transitory computer-readable medium, for processing the program code to execute the process, wherein the process comprises: receiving a radio resource control, RRC, message indicating a usage of a timing advance command for each of a plurality of component carriers configured to the communication device, from a cell in a network of the wireless communication system, when the timing advance command has been received from the cell in the network for each of the plurality of component carriers, applying the timing advance functionality for each of the plurality component carriers, for updating a timing advance value for each of the plurality of component carriers, and when updating the timing advance value for each of the plurality of component carriers, starting or restarting a time alignment timer for all of the indicated at least one component carrier. 
     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  is a schematic diagram of a wireless communication system with multiple component carriers. 
         FIG. 2  is a schematic diagram of an exemplary communication device. 
         FIG. 3  is a flowchart of an exemplary process. 
         FIG. 4  is a schematic diagram of an exemplary communication device according to  FIG. 3 . 
         FIG. 5  is a flowchart of an exemplary process. 
         FIG. 6  is a schematic diagram of an exemplary communication device according to  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION 
     Please refer to  FIG. 1 , which illustrates a schematic diagram of connections between a UE and cells C 1 -Cn in a wireless communication system. In  FIG. 1 , the cells C 1 -Cn and the UE are communicated through links L 1 -Lm each corresponding to a component carrier configured in the UE, and each supports a LTE-Advanced radio access technology (RAT) or an E-UTRAN (Evolved Universal Terrestrial Radio Access Network) RAT supporting the function of multiple component carriers on one UE. For example, the UE is communicated with the cell C 1  through the link L 1 , communicated with the cell C 2  through the links L 2 -L 4 , and so on. The component carriers of the links can be the same component carrier frequency band if the component carriers are associated to different cells. For example, the component carrier of any of the links L 2 -L 4  can use the same frequency band as the component carrier of the link L 1 . 
     Please refer to  FIG. 2 , which illustrates a schematic diagram of an exemplary communication device  20 . The communication device  20  can be the UE shown in  FIG. 1  and includes a processor  200  such as a microprocessor or ASIC, a computer readable recording medium  210 , and a communication interfacing unit  220 . The computer readable recording medium  210  is any data storage device that stores storage data  212 , including program code  214 , thereafter read and processed by the processor  200 . Examples of the computer readable recording medium  210  include a subscriber identity module (SIM), read-only memory (ROM), random-access memory (RAM), CD-ROMs, magnetic tapes, hard disks, optical data storage devices, and carrier waves (such as data transmission through the Internet). The communication interfacing unit  220  is preferably a radio transceiver and accordingly exchanges wireless signals with a network (i.e. the cells C 1 -Cn) according to processing results of the processor  200 . 
     The program code  214  includes program code of a Medium Access Control (MAC) layer which can manage timing alignment (TA) functionality for multiple component carriers. Please refer to  FIG. 3 , which illustrates a flowchart of an exemplary process  30 . The process  30  is utilized in the UE for managing TA functionality with multiple component carriers in a wireless communication system. The process  30  can be compiled into the program code  214  and includes the following steps: 
     Step  300 : Start. 
     Step  302 : Separately manage TA functionality of a plurality of component carriers. 
     Step  304 : End. 
     According to the process  30 , the UE manages TA functionality of each of the plurality of component carriers with independent TA configuration sets can be configured by timing advance command sent by the network. That is, when a timing advance command is received from a link belonging to a component carrier, the UE applies the TA functionality for the component carrier only. In one example, no limitation on carrier-to-cell allocation is introduced. The component carriers belonging to the same or different cells are depended on network resource allocation. 
     Take an example associated with  FIG. 1 . If a UE has a first link (i.e. link L 1 ) belonging to a first component carrier and a second link (i.e. link L 2 ) belonging to a second component carrier for uplink transmission, the UE applies the TA functionality for the first component carrier when a first timing advance command is received in the first component carrier, applies the TA functionality for the second component carrier when a second timing advance command is received in the second component carrier, and so on. 
     For TA functionality operation, when the TA functionality is applied in a component carrier for updating a timing advance value corresponding to a cell, the UE starts or restarts a time alignment timer for the component carrier. For example, as abovementioned, when the TA functionality is applied in the first component carrier for updating a first timing advance value corresponding to a cell (i.e. cell C 1 ), the UE starts or restarts a first time alignment timer for the first component carrier according to the first timing advance command. Please note that, the abovementioned time alignment timer of the UE is utilized for indicating whether the UE is synchronized with the cell on uplink timing. When the time alignment timer is running, uplink timing is considered synchronized. If the time alignment timer expires, then this indicates that the UE no longer has uplink synchronization with the cell. Therefore, when the first time alignment timer expires, the UE releases resources of Channel Quality Indication (CQI) report, Sounding Reference Signal (SRS), scheduling request (SR), and Physical Uplink Control Channel (PUCCH) for the first component carrier. Similarly, when the TA functionality is applied in the second component carrier, the UE starts or restarts a second time alignment timer for the second component carrier according to the second timing advance command, and releases resources of CQI report, SRS, SR, and PUCCH for the second component carrier when the second time alignment timer expires. In the LTE-Advanced system, the released CQI-report, SRS, SR, and PUCCH resources can be CQI-ReportConfig, soundingRS-UL-Config, schedulingRequestConfig and pucch-Config configurations, respectively. 
     In addition, for network configuration flexibility and reduction of a signaling quantity, a Radio Resource Control (RRC) message can be used to indicate the usage of the following timing advance command(s). When a RRC message indicating one component carrier is received, the UE applies TA functionality for the indicated component carrier when a timing advance command is received in the indicated component carrier. 
     Alternatively, when the RRC message indicating more than one component carrier is received, the UE applies the TA functionality for each of the indicated component carriers when the timing advance command is received in any one of the indicated component carriers. Take an example associated with  FIG. 1 . If the RRC message indicates component carriers corresponding to the links L 2 -L 4 , the UE applies the TA functionality for each of the TA configuration sets corresponding to the links L 2 -L 4  when the timing advance command is received in any one of the links L 2 -L 4 . Please note that the abovementioned TA functionality applying is not against with the separate management concept of the process  30 . The UE still sets the TA functionality of the component carriers one by one although the configuration source, namely timing advance command, is come from one link. 
     Please refer to  FIG. 4  which is a schematic diagram of an exemplary communication device  40 . The communication device  40  is used for realizing the process  30  and includes TA executing units TA 1 -TA n  and a management unit  401 . The TA executing units TA 1 -TA n  are used for executing TA functionality (e.g resource releasing or time advance applying) of component carriers of the communication device  40  and each of the TA executing units TA 1 -TA n  is responsible for one component carrier. The management unit  401  is used for separately managing the TA functionality of the component carriers. The management unit  401  includes a reception unit  402  for receiving a timing advance command, and a configuration applying unit  403 . In an example, when the reception unit  402  receives a timing advance command from one of the component carriers. The configuration applying unit  403  then applies the TA functionality for the component carriers received the timing advance command, and starts or restarts a time alignment timer for this component carrier according to the received timing advance command. In addition, the reception unit  402  is further used for receiving a RRC message for indicating at least one of the component carriers. The configuration applying unit  403  applies the TA functionality for the indicated component carriers when the timing advance command is received in one of the indicated component carriers, and starts or restarts a time alignment timer for all of the indicated component carriers. The related description can be realized by referring to the above, so a detailed description is omitted herein. 
     On the other hand, for reducing a configuration signaling quantity or complexity of TA functionality operation, please refer to  FIG. 5  which is a flowchart of an exemplary process  50 . The process  50  is utilized in the UE for managing the TA functionality with multiple component carriers in a wireless communication system. The process  50  can be compiled into the program code  214  and includes the following steps: 
     Step  500 : Start. 
     Step  502 : Jointly manage TA functionality of a plurality of component carriers belonging to a cell. 
     Step  504 : End. 
     According to the process  50 , the UE manages the TA functionality in the plurality of component carriers belonging to the same cell with a common timing advance command. That is, when a timing advance command is received in one of the component carriers belonging to a cell, the UE jointly applies the TA functionality for the component carriers belonging to the cell. 
     Take an example according to  FIG. 1 . When a timing advance command is received in any one of the links L 2 -L 4  belonging to the cell C 2 , the UE applies the TA functionality for the links L 2 -L 4  according to the timing advance command. In this situation, the network does not need to generate and send timing advance command duplications for the links L 2 -L 4 , and on the other hand, the UE does not need to handle the TA functionality for each component carrier belonging to the same cell. As a result, the signaling quantity is reduced and furthermore complexity problem of separately configuring each component carrier is avoided. 
     For TA functionality operation, when the TA functionality is applied in the plurality of component carriers belonging to the same cell for updating a timing advance value corresponding to the cell, the UE starts or restarts a time alignment timer for those component carriers according to the timing advance command. Therefore, when the time alignment timer expires, the UE releases resources of CQI report, sounding RS, scheduling request, and PUCCH for all component carriers belonging to the cell. As a result, according to the abovementioned example, the UE starts or restarts a time alignment timer for the links L 2 -L 4 , and releases resources of the links L 2 -L 4  when the time alignment timer expires. 
     Based on the process  50 , the UE applies the TA functionality and maintains one time alignment timer for certain component carriers belonging to the same cell through a single timing advance command, so as to reduce the number of times for the timing advance command reception and related signalling quantity. 
     Please refer to  FIG. 6  which is a schematic diagram of an exemplary communication device  60 . The communication device  60  can be used for realizing the process  40 , which includes a plurality of TA executing unit TA 1 -TA n  for executing TA functionality of component carriers belonging to a cell, and a management unit  601  for jointly managing the TA functionality of the component carriers. The management unit  601  includes a reception unit  602  for receiving a timing advance command, and a configuration applying unit  603 . When the reception unit  602  receives a timing advance command in one of the component carriers belonging to a cell, the configuration applying unit  603  applies the TA functionality for at least a component carriers belonging to the cell. In addition, the configuration applying unit  603  starts or restarts a time alignment timer for the component carriers belonging to the cell according to the timing advance command. Detailed description can be referred from above, so the detailed description is omitted herein. 
     Please note that the abovementioned steps of the processes  30  and  50  including suggested steps can be realized by means that could be hardware, firmware known as a combination of a hardware device and computer instructions and data that reside as read-only software on the hardware device, or an electronic system. Examples of hardware can include analog, digital and mixed circuits known as microcircuit, microchip, or silicon chip. Examples of the electronic system can include system on chip (SOC), system in package (Sip), computer on module (COM), and the communication device  20 . 
     In conclusion, the above-mentioned examples provide a separately managing way to manage the TA functionality for multiple component carriers to avoid an erroneous situation where one component carrier belonging to a cell is successful in uplink synchronization while other component carriers belonging to other cells are failed. Furthermore, the other examples provide a jointly managing way for component carriers belonging to the same cell in order to reduce a signaling quantity or complexity of TA functionality operation. 
     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.