Patent Publication Number: US-2012039223-A1

Title: Method of Handling Power Headroom Reporting and Communication Device Thereof

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/372,872, filed on Aug. 12, 2010 and entitled “PHR MAC format”, the contents of which are incorporated herein in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The application relates to a method utilized in a wireless communication system and a communication device thereof, and more particularly, to a method of handling power headroom reporting in a wireless communication system and a 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, such as in Node B (NB) alone rather than in NB and RNC (Radio Network Controller) respectively, so that the system structure becomes simple. 
     The power headroom report (PHR) is generated by a power headroom reporting procedure, and is used to provide the serving eNB with information about the difference between the maximum UE transmission (TX) power and an estimated TX power for Uplink Share Channel (UL-SCH). With the PHR information sent by the UE, the network can allocate radio resource to the UE and make schedule decision more efficiently. In the power headroom reporting procedure, the UE uses a MAC control element of a MAC protocol data unit (PDU) to carry PHR information. 
     Toward advanced high-speed wireless communication system, such as transmitting data in a higher peak data rate, LTE-Advanced system is standardized by the 3rd Generation Partnership Project (3GPP) as an enhancement of LTE system. LTE-Advanced system 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), etc. 
     For bandwidth extension, carrier aggregation (CA) is introduced to the LTE-Advanced system for extension to wider bandwidth, where two or more component carriers are aggregated, for supporting wider transmission bandwidths (for example up to 100 MHz) and for spectrum aggregation. According to carrier aggregation capability, multiple component carriers are aggregated into overall wider bandwidth, where the UE can establish multiple links corresponding to the multiple (downlink and uplink) component carriers for simultaneously receiving and transmitting. On the other hand, the UE may not need to use all of the configured component carriers, and thereby only some of the multiple component carriers are activated. Please note that, when a downlink and uplink component carrier is activated, the UE shall receive PDSCH and PDCCH, and transmit PUSCH and PUCCH, and is expected to be able to perform CQI measurement. 
     In carrier aggregation, the UE only has one RRC connection with the network. At RRC connection establishment/re-establishment/handover, one serving cell provides the NAS mobility information, and at RRC connection re-establishment/handover, one serving cell provides the security input. This cell is referred to as a Primary serving cell (PCell). In the downlink, the carrier corresponding to the PCell is the Downlink Primary Component Carrier (DL PCC) while in the uplink it is the Uplink Primary Component Carrier (UL PCC). In addition, cells other than the PCell are named secondary serving cell (SCell). Generally, a UE configured with CA can be equipped one PCell and at most four SCells. 
     It is possible to configure a UE to aggregate a different number of CCs originating from the same eNB and of possibly different bandwidths in the UL and the DL. Note that, the number of DL CCs that can be configured depends on the DL aggregation capability of the UE, the number of UL CCs that can be configured depends on the UL aggregation capability of the UE, it is not possible to configure a UE with more UL CCs than DL CCs, and in typical TDD deployments, the number of CCs and the bandwidth of each CC in UL and DL is the same. In addition, the PCell is always configured with DL PCC and UL PCC, and the SCell can be configured only with DL SCC. 
     To enable reasonable UE battery consumption when CA is configured, an activation/deactivation mechanism of SCells is supported (i.e. activation/deactivation does not apply to PCell). On the other hand, the PCell is always activated. The activation/deactivation mechanism is based on the combination of a MAC control element and deactivation timers. The MAC control element carries a bitmap for the activation and deactivation of SCells. With the bitmap, SCells can be activated and deactivated individually, and a single activation/deactivation command can activate/deactivate a subset of the SCells. In addition, When the SCell is activated, the DL CC and UL CC (if configured) on the SCell is (are) activated. 
     In LTE-A system (e.g. Rel-10), it&#39;s been agreed that simultaneously PUCCH and PUSCH transmission. Consequently, eNB should take into account PUCCH and PUSCH transmission power contributing to the UE current transmission power, so as to assist eNB to schedule PUSCH and PUCCH. Note that, for uplink resource, the PCell has PUSCH and PUCCH, but SCell only has PUSCH. 
     For a UE supporting a single uplink component carrier in the LTE system, the UE reports a PHR only for the one uplink component carrier. For a UE supporting multiple uplink component carriers in the LTE-Advanced system, the UE has to report PHRs for multiple uplink component carriers (e.g. configured uplink component carriers). However, how to report the PHRs for the configured uplink component carrier is not clearly specified in LTE-Advanced system. More specifically, a format of a MAC control element for the PHRs is never concerned. Thus, the eNB may not know the power status of each uplink component carrier of the UE and thus incorrectly schedule radio resources to the UE. 
     SUMMARY OF THE INVENTION 
     The application discloses a method of handling PHR reporting in a wireless communication system and a related communication device in order to solve the abovementioned problem. 
     A method of handling power headroom report, hereafter called PHR, reporting for a mobile device configured with a plurality of uplink component carriers in a wireless communication system is disclosed. The method comprises generating PHRs for at least one uplink component carrier of the plurality of uplink component carriers, determining a format of a MAC control element of a MAC PDU generated by the mobile device according to a number of the at least one uplink component carrier, and reporting the PHRs with the predetermined format of the MAC control element. 
     A method of handling power headroom report, hereafter called PHR, reporting for a mobile device configured with a plurality of uplink component carriers in a wireless communication system is disclosed. The method comprises generating PHRs for at least one uplink component carrier of the plurality of uplink component carriers, and reporting the PHRs with a dynamic format of a MAC control element of a MAC PDU generated by the mobile device, wherein a length of the dynamic format of the MAC control element is associated with a number of the at least one uplink component carrier. 
     A communication device of a wireless communication system for handling power headroom report, hereafter called PHR, reporting is disclosed. The communication device is configured with a plurality of uplink component carriers in the wireless communication system and comprises means for generating PHRs for at least one uplink component carrier of the plurality of uplink component carriers, means for determining a format of a MAC control element of a MAC PDU generated by the communication device according to a number of the at least one uplink component carrier, and means for reporting the PHRs with the predetermined format of the MAC control element. 
     A communication device of a wireless communication system for handling power headroom report, hereafter called PHR, reporting, is disclosed. The communication device is configured with a plurality of uplink component carriers in the wireless communication system and comprises means for generating PHRs for at least one uplink component carrier of the plurality of uplink component carriers, and means for reporting the PHRs with a dynamic format of a MAC control element of a MAC PDU generated by the communication device, wherein a length of the dynamic format of the MAC control element is associated with a number of the at least one uplink 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  illustrates a schematic diagram of an exemplary wireless communication system. 
         FIG. 2  is a schematic diagram of a user equipment and multiple cells under an eNB in a wireless communication system in  FIG. 1 . 
         FIG. 3  illustrates a schematic diagram of an exemplary communication device. 
         FIG. 4  illustrates a schematic diagram of communication protocol layers for an exemplary communication system. 
         FIG. 5  is a flowchart of an exemplary process. 
         FIG. 6  illustrates a schematic diagram of a short format of the MAC control element. 
         FIG. 7  illustrates a schematic diagram of a long format of the MAC control element. 
         FIG. 8  is a flowchart of an exemplary process. 
         FIG. 9  illustrates a schematic diagram of a dynamic format of the MAC control element. 
     
    
    
     DETAILED DESCRIPTION 
     Please refer to  FIG. 1 , which is a schematic diagram of a wireless communication system  10 . The wireless communication system  10  is a Long-Term Evolution advanced (LTE-A) system or other mobile communication systems, 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 communication system  10 . Practically, the network may be an evolved universal terrestrial radio access network (E-UTRAN) comprising a plurality of evolved base stations (eNBs). The UEs can be devices such as mobile phones, computer systems, etc. Besides, the network and the UE can be seen as a transmitter or receiver according to transmission direction, e.g., for uplink (UL), the UE is the transmitter and the network is the receiver, and for downlink (DL), the network is the transmitter and the UE is the receiver. 
     Please refer to  FIG. 2 , which is a schematic diagram of a UE and multiple cells under an eNB in the wireless communication system  10 . The UE communicates with one primary serving cell (PCell) and several secondary serving cells (SCells), as SCell 1 -SCellN shown in  FIG. 2 , In the downlink, the component carrier corresponding to the PCell is the Downlink Primary Component Carrier (DL PCC) while in the uplink it is the Uplink Primary Component Carrier (UL PCC). Depending on UE capabilities, SCells can be configured to form together with the PCell a set of serving cells. In the downlink, the component carrier corresponding to an SCell is a Downlink Secondary Component Carrier (DL SCC) while in the uplink it is an Uplink Secondary Component Carrier (UL SCC). 
       FIG. 3  illustrates a schematic diagram of an exemplary communication device  20 . The communication device  20  can be the UE shown in  FIG. 1 , but is not limited herein. The communication device  20  may include a processing means  200  such as a microprocessor or Application Specific Integrated Circuit (ASIC), a storage unit  210  and a communication interfacing unit  220 . The storage unit  210  may be any data storage device that can store program code  214 , for access by the processing means  200 . Examples of the storage unit  210  include but are not limited to a subscriber identity module (SIM), read-only memory (ROM), flash memory, random-access memory (RAM), CD-ROMs, magnetic tape, hard disk, and optical data storage device. The communication interfacing unit  220  is preferably a radio transceiver and can exchange wireless signals with the network according to processing results of the processing means  200 . 
     Please refer to  FIG. 4 , which illustrates a schematic diagram of communication protocol layers for the LTE system. The behaviors of some of the protocol layers may be defined in the program code  214  and executed by the processing means  200 . The protocol layers from top to bottom are a radio resource control (RRC) layer  300 , a packet data convergence protocol (PDCP) layer  310 , a radio link control (RLC) layer  320 , a medium access control (MAC) layer  330  and a physical (PHY) layer  340 . The MAC layer  330  is responsible for generating a MAC PDU (Protocol Data Unit), and the MAC PDU includes a MAC control element for power headroom reporting, and includes a MAC subheader corresponding to the MAC control element for indicating that the MAC control element is a PHR MAC control element. 
     Please refer to  FIG. 5 , which illustrates a flowchart of an exemplary process  50 . The process  50  is utilized in a UE configured with a plurality of uplink component carriers, for PHR reporting. The process  50  can be compiled into the program code  214  and includes the following steps: 
     Step  500 : Start. 
     Step  510 : Generate PHRs for at least one uplink component carrier of the plurality of uplink component carriers. 
     Step  520 : Determine a format of a MAC control element of a MAC PDU generated by the UE according to a number of the at least one uplink component carrier. 
     Step  530 : Report the PHRs with the predetermined format of the MAC control element. 
     Step  540 : End. 
     According to the process  50 , the UE reports the PHRs for all of the configured uplink component carriers or for ones of the configured uplink component carriers (e.g. the activated uplink component carrier) with one MAC control element. In a word, all PHRs are included in the same MAC control element. The format of the MAC control element utilized for the PHRs is fixed and is determined according to the number of the uplink configured component carriers or the activated uplink component carriers. 
     Take an example based on the process  50 . Assume that the UE is configured with one PCell and two SCells (i.e. SCell 1  and SCell 2  in  FIG. 2 ) which all are configured with uplink component carrier. The UE shall report PHRs for PCell, SCell 1 , and SCell 2  in a MAC control element. Please refer to  FIG. 6 , which illustrates a short format of a MAC control element according to an embodiment. Note that, the PCell has PUSCH and PUCCH resource, which can be referred from the prior art, so within the MAC control element, the UE reports a PHR for PUSCH (called type  1  PHR) and a PHR for PUCCH (called type  2  PHR) on the PCell. Besides, the UE reports two PHRs for the SCell 1  and SCell 2  respectively. In addition, a MAC subheader corresponding to the MAC control element is necessary, wherein the MAC subheader includes a logic channel identity (LCID) field to indicate that the MAC control element is in a short format. 
     On the other hand, the UE may report the PHRs with a long format MAC control element. Assume that the UE is configured with one PCell and four SCells which all are configured with uplink component carrier (i.e. i.e. SCell 1 -SCell 4  in  FIG. 2 ). Please refer to  FIG. 7 , which illustrates a long format of a MAC control element according to an embodiment. Within the MAC control element, the UE reports a type  1  PHR and a type  2 PHR for the PCell. Besides, the UE reports four PHRs for the SCell 1 -SCell 4  respectively. Moreover, a MAC subheader corresponding to the MAC CE includes a LCID field to indicate that the MAC control element is in a long format. 
     Briefly, a short MAC control element format is utilized if a number of the SCell which is configured with uplink component carrier configured to the UE is no more than a particular number (e.g. the number is 2); otherwise, a long format MAC control element is utilized. 
     Please refer to  FIG. 8 , which illustrates a flowchart of an exemplary process  80 . The process  80  is utilized in a UE configured with a plurality of uplink component carriers, for PHR reporting. The process  80  can be compiled into the program code  214  and includes the following steps: 
     Step  800 : Start. 
     Step  810 : Generate PHRs for at least one uplink component carrier of the plurality of uplink component carriers. 
     Step  820 : Report the PHRs with a dynamic format of a MAC control element of a MAC PDU generated by the UE, wherein a length of the dynamic format of the MAC control element is associated with a number of the at least one uplink component carrier. 
     Step  830 : End. 
     According to the process  80 , the UE reports the PHRs for all of the configured uplink component carriers or for ones of the configured uplink component carriers (e.g. the activated uplink component carriers) with one MAC control element. Note that, the length of the MAC control element is dynamic and is determined according to the number of the configured uplink component carriers or activated uplink component carriers. 
     Take an example based on the process  80 . Assume that the UE is configured with one PCell and N SCells which are configured with uplink component carrier (i.e. SCell 1 -SCellN in  FIG. 2 ). The UE shall report PHRs for PCell and SCell 1 -SCellN in a MAC control element. Please refer to  FIG. 9 , which illustrates a dynamic format of a MAC control element according to an embodiment. Within the MAC control element, the UE reports a type  1  PHR and a type  2  PHR for the PCell. Besides, the UE reports N PHRs for the SCell 1 -SCellN respectively. In order to achieve byte-alignment, some reserved bits (represented as “R”) may be included in the tail of the MAC control element. In addition, a MAC subheader corresponding to the MAC control element is necessary, and includes a LCID field to indicate that the MAC control element is in a dynamic format. 
     Please note that, in addition to report the PHRs for all of the configured uplink component carriers, the examples of  FIGS. 6 ,  7 , and  9  are also applied for the activated uplink component carriers. 
     Please note that, the abovementioned steps of the processes 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 present invention provides methods and apparatus for handling PHRs in multiple uplink component carrier system, to clearly define the MAC control element format for reporting the PHRs. 
     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.