Method of handling soft buffer for carrier aggregation and related communication device

A method of handling a soft buffer of a mobile device in a wireless communication system is disclosed. The mobile device is configured a plurality of component carriers (CCs) by a network of the wireless communication system. The plurality of CCs comprise a primary CC (PCC) and at least one secondary CC (SCC). The method comprises determining a plurality of weightings corresponding to the plurality of CCs according to an indication; determining a plurality of sizes of a plurality of sub-blocks according to the plurality of weightings; and dividing the soft buffer into the plurality of sub-blocks according to the plurality of sizes of the plurality of sub-blocks, to arrange a plurality of hybrid automatic repeat request (HARQ) processes of the plurality of CCs in the plurality of sub-blocks.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method used in a wireless communication system and related communication device, and more particularly, to a method of handling a soft buffer for carrier aggregation in a wireless communication system and related communication device.

2. Description of the Prior Art

A long-term evolution (LTE) system supporting the 3GPP Rel-8 standard and/or the 3GPP Rel-9 standard are developed by the 3rd Generation Partnership Project (3GPP) as a successor of a universal mobile telecommunications system (UMTS), for further enhancing performance of the UMTS to satisfy increasing needs of users. The LTE system includes a new radio interface and a radio network architecture that provides a high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, a radio access network known as an evolved UTRAN (E-UTRAN) includes multiple evolved Node-Bs (eNBs) for communicating with multiple user equipments (UEs), and communicates with a core network including a mobility management entity (MME), a serving gateway, etc., for Non Access Stratum (NAS) control.

A LTE-advanced (LTE-A) system, as its name implies, is an evolution of the LTE system. The LTE-A system targets faster switching between power states, improves performance at coverage edge of an eNB. Besides, the LTE-A system includes advanced techniques, such as carrier aggregation (CA), coordinated multipoint transmission/reception (COMP), UL multiple-input multiple-output (MIMO), etc. For a UE and an eNB to communicate with each other in the LTE-A system, the UE and the eNB must support standards developed for the LTE-A system, such as the 3GPP Rel-10 standard or later versions.

The CA is introduced to the LTE-A system by which more than one component carriers (CCs) are aggregated to achieve a wider-band transmission. Accordingly, the LTE-A system can support a wider bandwidth up to 100 MHz by aggregating a maximum number of 5 CCs, where a maximum bandwidth of each CC is 20 MHz and is backward compatible with the 3GPP Rel-8 standard. The LTE-A system supports the CA for both contiguous and non-contiguous CCs, wherein each CC limited to a maximum of 110 resource blocks. The CA increases bandwidth flexibility by aggregating the CCs.

When a UE is configured with the CA, the UE has the ability to receive and/or transmit packets on one or multiple CCs to increase throughput. In the LTE-A system, it is possible that an eNB configures the UE different numbers of uplink (UL) and downlink (DL) CCs. Moreover, the CCs configured to the UE necessarily consists of one DL primary CC (PCC) and one UL PCC. The most important feature of the DL PCC and the UL PCC is exchanging control information between the UE and the eNB. CCs other than the PCCs are named UL or DL secondary CCs (SCCs). Numbers of the UL and DL SCCs are arbitrary, and are related to UL and DL aggregation capabilities of the UE and available radio resources.

A hybrid automatic repeat request (HARQ) process is used in the LTE system to provide both efficient and reliable communications. Different from an ARQ process, a forward correcting code (FEC) is used for the HARQ process. For example, a receiver feeds back an acknowledgment (ACK) to inform a transmitter that a packet has been received correctly if the receiver decodes the packet correctly. Oppositely, the receiver feeds back a negative acknowledgment (NACK) to the transmitter if the receiver cannot decode the packet correctly. In this situation, the UE stores part or the whole of the packet in a soft buffer of the UE. After the UE receives a retransmitted packet from the transmitter, soft values of the retransmitted packet and the stored packet are combined. The receiver decodes the packet by using the combined soft values. Furthermore, the combination of the previously erroneously received packet (s) and the currently received packet increases a probability of successful decoding. The UE continues the HARQ process until the packet is decoded correctly, or until a maximum number of retransmissions have been sent, at which time the HARQ process declares a failure and leaves it up to the ARQ process in radio link control (RLC) for trying again. In other words, space of the soft buffer should be reserved for the HARQ process such that the UE can store the HARQ process which has not been decoded correctly. Otherwise, the UE blocks the HARQ process if the soft buffer is fully occupied. When multiple packets are transmitted to the UE, the UE may need to store multiple HARQ processes due to unsuccessful decoding of the packets.

In detail, the UE can store up to 8 HARQ processes in the soft buffer in the LTE system (i.e., single CC system). A transport block (TB) is a physical interface between an eNB and a UE, and corresponds to the data carried in a LTE radio subframe. Further, each LTE radio subframe is 1 millisecond (ms), and each LTE radio frame is 10 ms, which consists of 10 LTE radio subframes. When using the MIMO (e.g. spatial multiplexing), more than one transport blocks can be transmitted per transmission time interval (TTI) for the UE.

A soft buffer partition rule in the LTE system (i.e., single CC system) is introduced as follows. The total number of soft channel bits, Nsoft, depends on UE category of the UE, as shown in a table10ofFIG. 1, wherein various values of Nsoftare listed according to an example of the prior art. Nsoftcan be divided into multiple partitions according to the following equation:

NIR=⌊NsoftKMIMO·min⁡(MDL_HARQ,Mlimit)⌋,(Eq.⁢1)
wherein NIRis a size of a partition which is used for storing a transport block. Nsoftis the total number of soft channel bits of the UE. KMIMOis a number of transport blocks that may be transmitted to the UE in a TTI, and is related to the MIMO used by the UE and the network. In general, if the spatial multiplexing with n spatial streams is configured to the UE, KMIMOis set to n. Mlimitis a positive value which equals to 8. MDL—HARQis a maximum number of DL HARQ processes per serving cell, and corresponds to a duplex mode and its configuration. For example, MDL—HARQis set to 8 for frequency-division duplexing (FDD). Values 4, 7, 10, 9, 12, 15 and 6 are used for time-division duplexing (TDD) UL/DL configuration 0, 1, 2, 3, 4, 5 and 6, respectively, as shown in a table20ofFIG. 2, wherein various values of MDL—HARQare listed according to an example of the prior art. min(x,y) returns the smaller one of x and y.

As shown in the equation Eq.1, up to min (MDL—HARQ, Mlimit) HARQ processes can be stored in the soft buffer. If the spatial multiplexing with KMIMOspatial streams is configured to the UE, each HARQ process consists of KMIMOtransport blocks. Therefore, the entire soft buffer is divided into KMIMOmin (MDL—HARQ,Mlimit) partitions. Each partition consists of NIRsoft channel bits which can be used for storing one transport block.

Please refer toFIG. 3, which is a schematic diagram of a soft buffer SBp according to the prior art. In this example, the spatial multiplexing is not configured to the UE (i.e., KMIMO=1), the soft buffer SBp is divided into 8 partitions P301-P308for storing 8 HARQ processes while MDL—HARQis equal to or larger than 8. Nsoftis a size (e.g. number of bits) of the soft buffer SBp, and depends on UE category of the UE. NIRis a number of bits of a partition of the soft buffer SBp. Therefore, a transport block with a maximum size NIRcan be stored in a corresponding partition, and at most 8 HARQ processes can be stored in the soft buffer SBp.

However, the UE may need to store more than 8 HARQ processes in the soft buffer in the LTE-A system when multiple CCs are configured to the UE. For example, when the UE is configured with 5 DL CCs and operates in FDD duplex mode, the UE may need to store up to 40 HARQ processes due to unsuccessful decoding of the packets. There are two possible solutions in the LTE-A system with multiple CCs, which are introduced as follows. In the first solution, the soft buffer partition rule is the same as that for the LTE system (i.e., the single CC system). In other words, up to 8 HARQ processes can be stored in the soft buffer. All the erroneous HARQ processes can share the soft buffer statistically. Thus, a blocking probability of a HARQ process increases, and the system throughput is diminished. In the second solution, the soft buffer can be simply divided into 40 partitions for storing up to 40 HARQ processes, a size of each partition of the soft buffer is reduced. For each erroneous HARQ process, the number of soft channel bits that UE can store is reduced according to the size reduction of a corresponding partition. As a result, the coding performance is reduced and more retransmissions are required, and the system throughput is diminished. Obviously, neither the first nor the second solution can achieve optimal system throughput. Therefore, when the CA is configured to the UE, how to handle a soft buffer of a UE for storing HARQ processes is a topic to be discussed and addressed.

SUMMARY OF THE INVENTION

The present invention therefore provides a method and related communication device for handling a soft buffer for carrier aggregation in a wireless communication system to solve the abovementioned problems.

A method of handling a soft buffer of a mobile device in a wireless communication system is disclosed. The mobile device is configured a plurality of component carriers (CCs) by a network of the wireless communication system. The plurality of CCs comprise a primary CC (PCC) and at least one secondary CC (SCC). The method comprises determining a plurality of weightings corresponding to the plurality of CCs according to an indication; determining a plurality of sizes of a plurality of sub-blocks according to the plurality of weightings; and dividing the soft buffer into the plurality of sub-blocks according to the plurality of sizes of the plurality of sub-blocks, to arrange a plurality of hybrid automatic repeat request (HARQ) processes of the plurality of CCs in the plurality of sub-blocks.

A method of handling a soft buffer of a mobile device in a wireless communication system is disclosed. The mobile device is configured a plurality of component carriers (CCs) by a network of the wireless communication system. The method comprises dividing at least one sub-block of the soft buffer into a plurality of partitions, wherein a number of the plurality of partitions is determined according to an indication; and arranging a plurality of hybrid automatic repeat request (HARQ) processes of the plurality of CCs in the plurality of partitions.

A method of handling a soft buffer of a mobile device in a wireless communication system for a network of the wireless communication system is disclosed. The mobile device is configured a plurality of component carriers (CCs) by the network. The plurality of CCs comprise a primary CC (PCC) and at least one secondary CC (SCC). The method comprises determining a plurality of weightings corresponding to the plurality of CCs according to an indication; and determining a plurality of sizes of a plurality of sub-blocks according to the plurality of weightings, for dividing the soft buffer into the plurality of sub-blocks according to the plurality of sizes.

A method of handling a soft buffer of a mobile device in a wireless communication system for a network of the wireless communication system is disclosed. The mobile device is configured a plurality of component carriers (CCs) by the network. The method comprises determining a number of a plurality of partitions according to an indication; and dividing at least one sub-block of the soft buffer into the plurality of partitions according to the number of the plurality of partitions.

A mobile device of a wireless communication system for handling a soft buffer of the mobile device is disclosed. The mobile device is configured a plurality of component carriers (CCs) by a network of the wireless communication system. The plurality of CCs comprise a primary CC (PCC) and at least one secondary CC (SCC). The method comprises means for determining a plurality of weightings corresponding to the plurality of CCs according to an indication; means for determining a plurality of sizes of a plurality of sub-blocks according to the plurality of weightings; and means for dividing the soft buffer into the plurality of sub-blocks according to the plurality of sizes of the plurality of sub-blocks, to arrange a plurality of hybrid automatic repeat request (HARQ) processes of the plurality of CCs in the plurality of sub-blocks.

A mobile device of a wireless communication system for handling a soft buffer of the mobile device is disclosed. The mobile device is configured a plurality of component carriers (CCs) by a network of the wireless communication system. The method comprises means for dividing at least one sub-block of the soft buffer into a plurality of partitions, wherein a number of the plurality of partitions is determined according to an indication; and means for arranging a plurality of hybrid automatic repeat request (HARQ) processes of the plurality of CCs in the plurality of partitions.

A network of a wireless communication system for handling a soft buffer of a mobile device in the wireless communication system is disclosed. The mobile device is configured a plurality of component carriers (CCs) by the network. The plurality of CCs comprise a primary CC (PCC) and at least one secondary CC (SCC). The method comprises means for determining a plurality of weightings corresponding to the plurality of CCs according to an indication; and means for determining a plurality of sizes of a plurality of sub-blocks according to the plurality of weightings, for dividing the soft buffer into the plurality of sub-blocks according to the plurality of sizes.

A network of a wireless communication system for handling a soft buffer of a mobile device in the wireless communication system is disclosed. The mobile device is configured a plurality of component carriers (CCs) by the network. The method comprises means for determining a number of a plurality of partitions according to an indication; and means for dividing at least one sub-block of the soft buffer into the plurality of partitions according to the number of the plurality of partitions.

DETAILED DESCRIPTION

Please refer toFIG. 4, which is a schematic diagram of a wireless communication system40according to an example of the present invention. The wireless communication system40, such as a long term evolution-advanced (LTE-A) system or other mobile communication systems supporting carrier aggregation (CA) (e.g. multiple component carriers (CCs)), is briefly composed of a network and a plurality of user equipments (UEs). InFIG. 4, the network and the UEs are simply utilized for illustrating the structure of the wireless communication system40. Practically, the network can be referred to as an evolved universal terrestrial radio access network (E-UTRAN) comprising a plurality of evolved Node-Bs (eNBs) and relays in the LTE-A system. The UEs can be mobile devices such as mobile phones, laptops, tablet computers, electronic books, and portable computer systems. Besides, the network and a UE can be seen as a transmitter or a receiver according to transmission direction, e.g., for an uplink (UL), the UE is the transmitter and the network is the receiver, and for a downlink (DL), the network is the transmitter and the UE is the receiver.

Please refer toFIG. 5, which is a schematic diagram of a communication device50according to an example of the present invention. The communication device50can be a UE or the network shown inFIG. 4, but is not limited herein. The communication device50may include a processor500such as a microprocessor or an Application Specific Integrated Circuit (ASIC), a storage unit510and a communication interfacing unit520. The storage unit510may be any data storage device that can store a program code514, accessed by the processor500. Examples of the storage unit510include but are not limited to a subscriber identity module (SIM), read-only memory (ROM), flash memory, random-access memory (RAM), CD-ROM/DVD-ROM, magnetic tape, hard disk and optical data storage device. The communication interfacing unit520is preferably a radio transceiver and can exchange wireless signals with the network according to processing results of the processor500.

Please refer toFIG. 6, which illustrates a schematic diagram of communication protocol layers for the wireless communication system40. Behaviors of some of the communication protocol layers may be defined in the program code514and executed by the processor500. The communication protocol layers from top to bottom are a radio resource control (RRC) layer600, a packet data convergence protocol (PDCP) layer602, a radio link control (RLC) layer604, a media access control (MAC) layer606and a physical (PHY) layer608. The RRC layer600is used for performing broadcast, paging, RRC connection management, measurement reporting and control and radio bearer control generating or releasing radio bearers. The PDCP layer602is used for ciphering and integrity protection of transmissions, and maintaining delivery order during a handover. The RLC layer604is used for segmentation/concatenation of packets and maintaining delivery sequence when packet loses. The MAC layer606is responsible for a hybrid automatic repeat request (HARQ) process, multiplexing logical channels, a random access procedure and maintaining a UL timing alignment. In each HARQ process, an acknowledgement (ACK) is reported if the MAC data/control packet is received and decoded successfully. Otherwise, a negative acknowledgement (NACK) is reported. The PHY layer608is used to provide physical channels to the UEs and the network (e.g. eNB and/or relay).FIG. 6simply illustrates the behaviors of the communication protocol layers conceptually, and detail of the behaviors may be different for the LTE-A system and other communication systems.

Please refer toFIG. 7, which is a flowchart of a process70according to an example of the present invention. The process70is utilized in a UE and the network shown inFIG. 4, for handling a soft buffer of the UE. The UE is configured a plurality of CCs by the network, and the plurality of CCs includes a primary CC (PCC) and at least one secondary CC (SCC). The process70maybe compiled into the program code514and includes the following steps:

Step702: Determine a plurality of weightings corresponding to the plurality of CCs for the soft buffer according to an indication.

Step704: Determine a plurality of sizes of a plurality of sub-blocks according to the plurality of weightings.

Step706: Divide the soft buffer into the plurality of sub-blocks according to the plurality of sizes of the plurality of sub-blocks, to arrange a plurality of HARQ processes of the plurality of CCs in the plurality of sub-blocks.

According to the process70, the UE determines the plurality of weightings corresponding to the plurality of CCs for the soft buffer according to the indication. Then, the UE determines the plurality of sizes of the plurality of sub-blocks according to the plurality of weightings. Thus, the UE can divide the soft buffer into the plurality of sub-blocks according to the plurality of sizes of the plurality of sub-blocks, to arrange the plurality of HARQ processes of the plurality of CCs in the plurality of sub-blocks. In other words, the UE arranges (e.g. stores) the plurality of HARQ processes of the PCC and the at least one SCC in sub-blocks with various sizes (and thus in partitions with various sizes). For example, the HARQ processes of the PCC can be arranged in sub-blocks with larger sizes (e.g. by using a large weighting) since packets transmitted on the PCC are more important (e.g. including control information) and a number of the packets (i.e., traffic load) is large. The HARQ processes of the at least one SCC can be arranged in sub-blocks with smaller sizes (e.g. by using at least one small weighting) since packets transmitted on the SCC are less important and a number of the packets is small. That is, the soft buffer is utilized efficiently and flexibly. As a result, blocking probabilities of the HARQ processes of both the PCC and the at least one SCC are reduced, and data transmitted on the PCC can be recovered and executed rapidly. Therefore, system throughput is increased, and the UE can operate regularly without an interrupt or a delay.

Please note that, a spirit of the process70is that the UE arranges the HARQ processes of the PCC and the at least one SCC in sub-blocks with various sizes (and thus in partitions with various sizes) in the soft buffer such that the soft buffer is utilized efficiently and flexibly. Factors according to which the UE determines the plurality of weightings are not limited. Methods based on which the UE divides the soft buffer and arranges the HARQ processes are also not limited.

In general, a soft buffer partition rule for the wireless communication system40configured with CA is introduced as follows. First, the total number of soft channel bits (i.e., a size of the soft buffer) of a UE, Nsoft, is divided into NCsub-blocks for NCconfigured CCs according to an arbitrary partition rule (e.g. Nsoftis equally divided for all the configured CCs). A tentative size of a sub-block in terms of soft channel bits for the nc-th CC is defined as N′soft(nc), wherein 1≦nc≦Ncand

∑nc=1Nc⁢⁢Nsoft′⁡(nc)=Nsoft.
Then, the UE determines a plurality of weightings corresponding to the plurality of CCs according to an indication, and divides the soft buffer into a plurality of sub-blocks according to the plurality of weightings, as follows

Nsoft⁡(nc)=⌊w⁡(nc)·Nsoft′⁡(nc)⌋,⁢wherein⁢⁢∑nc=1Nc⁢⁢Nsoft⁡(nc)=Nsoft.(Eq.⁢2)
w(nc) is the weighting for the nc-th CC according to the indication, and is a positive value larger than zero. Note that the weighting of the PCC can be set equal to or greater than the weightings of SCCs. Nsoft(nc) is the size of the sub-block in terms of soft channel bits for the nc-th CC, and is determined according to the weighting w(nc) and the tentative size N′soft(nc). After the UE determines the size of the soft buffer for each configured CC, a size of a partition for a transport block of each configured CC can be determined as follows:

NIR⁡(nc)=⌊Nsoft⁡(nc)KMIMO·min⁡(MDL_HARQ⁡(nc),Mlimit)⌋,(Eq.⁢3)
wherein NIR(nc) is the size of the partition for the transport block of the nc-th CC. Nsoft(nc) is the size of sub-block in terms of soft channel bits for the nc-th CC. KMIMOis a number of transport blocks that may be transmitted to the UE in one TTI per CC, and is related to the MIMO used by the UE and the network. Mlimitis a positive value. MDL—HARQ(nc) is a maximum number of DL HARQ processes of the nc-th CC, and corresponds to a duplex mode and its configuration.

For example, please refer toFIG. 8, which is a schematic diagram of a soft buffer SB according an example of the present invention. The UE is configured 2 CCs by the network and operates in a FDD mode, wherein one of the two CCs is a PCC and the other one is a SCC. Since only one transport block may be transmitted to the UE in one TTI (i.e., the spatial multiplexing is not enabled), the UE divides the soft buffer SB into two sub-blocks SB_1and SB_2for the configured CCs, respectively, according to the present invention, such that at most 8 HARQ processes can be stored in each sub-block. Thus, the UE can arrange HARQ processes of the two CCs in the sub-blocks SB_1and SB_2, wherein each HARQ process is arranged to a corresponding partition. In detail, a size (e.g. number of soft channel bits) of the soft buffer SB is Nsoft. Sizes of the sub-blocks SB_1and SB_2which are Nsoft(1) and Nsoft(2), respectively, are the same, i.e., N′soft(1)=N′soft(2)=Nsoft/2. The sub-blocks SB_1and SB_2are used for the HARQ processes of the PCC and the SCC, respectively. Then, the sizes of the sub-blocks SB_1and SB_2are modified by using weightings w(1)=wPCCand w(2)=(2−wPCC), respectively, as follows: Nsoft(1)=N′soft(1)·w(1) and Nsoft(2)=N′soft(2)·w(2), wherein 1≦wPCC≦2, such that Nsoft(1) is equal or larger than Nsoft(2).

Further, as shown inFIG. 8, the sub-block SB_1is divided into 8 partitions P801-P808, and the sub-block SB_2is divided into 8 partitions P809-P816. The UE can determine partition sizes NIR(1) and NIR(2) for the transport blocks of the configured CCs, respectively, according to the equation Eq.3. That is, a size of each of the partitions P801-P808is NIR(1), and a size of each of the partitions P809-P816is NIR(2). Therefore, the HARQ processes of the PCC which are more important can be arranged in the 8 partitions with a large size NIR(1). At the same time, the HARQ processes of the SCC which are less important can also be arranged in the 8 partitions with a small size NIR(2). Please note that, the above example illustrates a case wherein the soft buffer is first equally divided into sub-blocks with the same size (i.e., N′soft(n1)=N′soft(n2), wherein n1≠n2are indices of CCs) before applying weightings to the sub-blocks. However, the soft buffer can also be first divided into sub-blocks with various sizes, i.e., N′soft(nc) for the nc-th CC is arbitrary. Then, a weighting w(nc) is applied to the sub-block corresponding to the nc-th CC to obtain a size Nsoft(nc) by using Nsoft(nc)=N′soft(nc)·w(nc). As a result, blocking probabilities of the HARQ processes of both the PCC and the SCC are not increased. Control information and data transmitted on the PCC are recovered rapidly, since the HARQ processes with the large size (i.e., better coding performance) can be stored in the soft buffer. System throughput is increased efficiently by using the CA without being affected by inefficient use of the soft buffer.

Please note that, factors according to which a weighting for a PCC is determined are not limited. For example, please refer toFIG. 9, which is a table90of weightings wPCCaccording to an example of the present invention. The table90is preferably is stored in the UE. In the table90, a weighting wPCCis determined according to a parameter RatioPCCand a number of CCs NC, wherein └x┘ is the largest integer not greater than x. In other words, the weighting wPCCis indicated by the parameter Ratio and the number of CCs NC. In detail, an indication is generated by the UE according to the parameter RatioPCCand the number of CCs NC. Alternatively, the indication is generated by the network according to the parameter RatioPCCand the number of CCs NC, and the indication is then transmitted by the network to the UE. Further, the indication can also be generated by both the UE and the network according to the parameter RatioPCCand the number of CCs Nc(i.e., the same rule). The parameter RatioPCCis represented as follows:

RatioPCC=⌊BW⁡(PCC)∑nc=1Nc⁢BW⁡(nc)⌋,0<RatioPCC≤1,(Eq.⁢4)
wherein BW(PCC) and BW(nc) are bandwidths of the PCC and the nc-th CC, respectively, and rij, 1≦i≦5, 1≦j≦4 are positive values. After the weighting wPCCfor the PCC is determined, a weighting for the n-th SCC w(nc) can be determined as follows w(nc)=(NC−wPCC)/(NC−1), wherein ncε indices of the SCCs. Therefore, sizes of the partitions for each CC can be modified or adjusted accordingly.

Please note that, an indication (and thus weightings) can be generated according to various factors, such as design considerations or system requirements. For example, the indication (and thus the weightings) can be determined according to a combination of priorities of CCs configured to the UE, UE category of the UE, a number of NACKs transmitted by the UE, an average number of HARQ processes of the UE, traffic load of the UE, a number of the CCs configured to the UE, bandwidths of the CCs configured to the UE and a maximum number of layers supported by the UE, and is not limited herein. That is, the indication (and thus the weighting Moverbooking) is generated (e.g. by the UE or the network) according to the combination of the abovementioned parameters and variables. Besides, the indication (and thus the weightings) mentioned above can be generated by the UE itself. Alternatively, the indication is generated by a network, and is transmitted by the network to the UE via a signaling (e.g. radio resource control (RRC) signaling). Furthermore, the indication can be generated by both the UE and the network according to the same rule, to reducing overhead of the signaling. On the other hand, a time at which a soft buffer is divided into multiple partitions for multiple CCs is not limited. For example, the soft buffer can be divided after a PCC of the CCs is reconfigured, i.e., an indication capable of determining the weightings is generated after the PCC is reconfigured. Alternatively, the soft buffer can be divided after a number of the CCs is changed, i.e., an indication capable of determining the weightings is generated after the number of the CCs is changed. Further, the CCs mentioned in the above examples are preferably referred to as DL CCs, since HARQ processes stored in the UE are corresponding to packets transmitted on DL.

Besides, the process70and examples mentioned above can be realized in the network. For example, the network can determine weightings according to an indication, and transmit the weightings to a UE such that the UE can determine sizes of sub-blocks according to the weightings. Alternatively, the network may further determine the sizes of the sub-blocks according to the weightings, and transmits the sizes to the UE such that the UE can divide the soft buffer into the sub-blocks according to the sizes of the sub-blocks. Furthermore, the network may not need to transmit the weightings nor the sizes of the sub-blocks to the UE since the same indication is also generated by the UE according to the same rule. Thus, the UE can determine the weightings, and determine the sizes of the sub-blocks according to the weightings, for dividing the soft buffer into the sub-blocks according to the sizes of the sub-blocks.

Please refer toFIG. 10, which is a flowchart of a process100according to an example of the present invention. The process100is utilized in a UE and the network shown inFIG. 4, for handling a soft buffer of the UE. The UE is configured a plurality of CCs by the network, and the plurality of CCs includes a primary CC (PCC) and at least one secondary CC (SCC). The process100may be compiled into the program code514and includes the following steps:

Step1002: Divide at least one sub-block of the soft buffer into a plurality of partitions, wherein a number of the plurality of partitions is determined according to an indication.

Step1004: Arrange a plurality of HARQ processes of the plurality of CCs in the plurality of partitions.

According to the process100, the UE divides the at least one sub-block of the soft buffer into the plurality of partitions, wherein the number of the plurality of partitions is determined according to the indication. Then, the UE arranges the plurality of HARQ processes of the plurality of CCs in the plurality of partitions. In other words, the UE divides one or more sub-blocks of the soft buffer into various numbers of partitions, to arrange (e.g. stores) the plurality of HARQ processes of the plurality of CCs in the partitions. For example, the UE can divide the soft buffer into more partitions for arranging more HARQ processes with a small size in the partitions, to reduce blocking probabilities of the HARQ processes. Alternatively, the UE can divide the soft buffer into less partitions for arranging less HARQ processes with a large size in the partitions, to improve coding performance of the HARQ processes. That is, the soft buffer is utilized efficiently and flexibly. As a result, a better tradeoff between the blocking probabilities and the coding performance can be achieved. Therefore, system throughput is increased, and the UE can operate regularly without an interrupt or a delay.

Please note that, a spirit of the process100is that the UE divides one or more sub-blocks of the soft buffer into various numbers of partitions, to arrange (e.g. stores) the plurality of HARQ processes of the plurality of CCs in the partitions such that the soft buffer is utilized efficiently and flexibly. Factors according to which the UE determines a number of partitions are not limited. Methods based on which the UE divides the soft buffer and arranges the HARQ processes are also not limited.

For example, a soft buffer of a UE can be directly divided into more partitions such that more HARQ processes can be stored in the soft buffer. In other words, the soft buffer is not divided into multiple sub-blocks, i.e., the soft buffer is divided into only one sub-block. Please refer toFIG. 11, which is a schematic diagram of a soft buffer SBa according an example of the present invention. The soft buffer SBa can be divided into various numbers of partitions as shown inFIG. 11. A number of CCs configured to the UE is not limited. In detail, the soft buffer SBa with a size Nsoftis divided into multiple partitions wherein a size of each partition is NIR, according to the following equations:

NIR=⌊NsoftKMIMO·Moverbooking·min⁡(MDL_HARQ′,Mlimit)⌋,(Eq.⁢5)
wherein KMIMOa number of transport blocks that may be transmitted to the UE in one TTI per CC, and is related to the MIMO used by the UE and the network.

In general, if spatial multiplexing with n spatial streams is configured to the UE, KMIMOis set to n. Moverbookingis a weighting comprised in the indication for controlling a number of the partitions, and is a positive value. Mlimitis a positive value, e.g. Mlimit=8. M′DL—HARQis the maximum number of DL HARQ processes per serving cell if the configured CCs are configured the same duplex mode and configurations. On the other hand, if the UE operates in a TDD mode, M′DL—HARQis the maximum number of DL HARQ processes of the PCC if at least one configured SCC are configured with different UL-DL configurations. Thus, when the UE operates in a FDD mode and does not support spatial multiplexing, the soft buffer SBa is divided into 8·Moverbookingpartitions, wherein sizes of the partitions are the same when using a fixed Moverbooking. That is, when the weighting Moverbookingis set to 1, 2, 3, 4 and 5, the soft buffer SBa is divided into 8, 16, 24, 32 and 40 partitions, respectively, if the spatial multiplexing is not supported by the UE. In this case, the size of each partition is set to

NIR=⌊Nsoft8·Moverbooking⌋.
As shown inFIG. 11, the DL HARQ processes of all the CCs share all the partitions in the soft buffer SBa for a fixed Moverbooking. That is, sizes of partitions used for a PCC and a SCC are the same (i.e., NIR). A tradeoff between blocking probabilities and coding performance of the DL HARQ processes can be made when determining the weighting Moverbooking. That is, more partitions result lower blocking probabilities at cost of worse coding performance, and less partitions result better coding performance at cost of higher blocking probabilities.

Please note that, an indication (and thus the weighting Moverbooking) can be generated according to various factors, such as design considerations or system requirements. For example, the weighting Moverbookingcan be determined according to a combination of priorities of CCs configured to the UE, UE category of the UE, a number of NACKs transmitted by the UE, an average number of HARQ processes of the UE, traffic load of the UE, a number of the CCs configured to the UE, bandwidths of the CCs configured to the UE and a maximum number of layers supported by the UE, and is not limited herein. That is, the indication (and thus the weighting Moverbooking) is generated (e.g. by the UE or the network) according to the combination of the abovementioned parameters and variables. Please refer toFIG. 12A, which is a table120of the weightings Moverbookingrelating to the number of the CCs according to an example of the present invention, and fi, 1≦i≦5, are positive values. As shown in the table120, the weighting Moverbookingis determined according to the number of the CCs. For example, if 4 CCs are configured to the UE, the weighting Moverbookingis set to f4. On the other hand, the weighting Moverbookingcan also be determined according to both the UE category of the UE and the number of the CCs. Please refer toFIG. 12B, which is a table122of the weightings Moverbookingrelating to the UE category and the number of the CCs according to an example of the present invention, and fi,j, 1≦i≦8, 1≦j≦5 are positive values. For example, if the UE category is 5 and 3 CCs are configured to the UE, the weighting Moverbookingis set to f5,3. Furthermore, the weighting Moverbookingcan be determined according to both the UE category of the UE and the maximum number of layers supported by the UE. Please refer toFIG. 12C, which is a table124of the weightings Moverbookingrelating to the UE category and the maximum number of layers supported by the UE according to an example of the present invention, and fi,j, 1≦i≦8, 1≦j≦8 are positive values. For example, if the UE category is 7 and the maximum number of layers supported by the UE is 4, the weighting Moverbookingis set to f7,4.

In the abovementioned examples, the present invention is applied to all CCs configured to a UE. However, the present invention can also be applied to a subset of the CCs configured to the UE. Please refer toFIG. 13, which is a schematic diagram of a soft buffer SBb according an example of the present invention. In the present example, 5 CCs including a PCC C1and SCCs C2-C5are configured to a UE. In detail, a weighting Moverbookingcorresponding to the PCC C1is set to 1, and weightings Moverbookingcorresponding to the SCCs C2-C5are set to 3. That is, 8 partitions P1301-P1308which are unchanged are seen by the PCC C1as shown by a soft buffer SBb_1inFIG. 13, wherein a size of each partition is NIR(1). Besides, 24 partitions P1301a-P1324aare seen by the SCCs C2-C5as shown by a soft buffer SBb_2inFIG. 13, wherein a size of each partition is NIR(2), i.e., NIR(1)=3NIR(2). Then, HARQ processes of the PCC C1and the SCCs C2-C5can be arranged in the soft buffer SBb according to the corresponding partitions shown by the soft buffers SBb_1and SBb_2. An example of arranging the HARQ processes of the CCs is illustrated as follows. At time t1, the UE needs to arrange (e.g. store) a HARQ process of the PCC C1. Since the soft buffer SBb is empty, the UE arranges the HARQ process of the PCC C1in the partition P1301(i.e., the partitions P1301a-P1303a). At time t2, the UE needs to arrange a HARQ process of the SCC C5, and the UE continues to arrange the HARQ process of the SCC C5in the partition P1304a. At time t3, the UE needs to arrange another HARQ process of the PCC C1again. Since the size of the partition seen by the PCC C1is NIR(1) as shown by the soft buffer SBb_1, the UE arrange the another HARQ process of the PCC C1in the partition P1303(i.e., the partitions P1307a-P1309a). Further, the UE needs to arrange HARQ processes of the SCC C3and the SCC C4at times t4and t5, respectively. The UE arranges the HARQ processes of the SCC C3and the SCC C4in the partitions P1305aand P1306a, respectively. Therefore, except low blocking probability and better coding performance, the present invention further utilizes the soft buffer flexibly by dividing the soft buffer into smaller partitions for only part of CCs configured to the UE.

On the other hand, the present invention can also be applied to part of a soft buffer of a UE. That is, only the part of the soft buffer is divided into partitions with various sizes and amounts according to weightings, and the other part of the soft buffer is divided into 8 partitions according to the prior art. For example, please refer toFIG. 14, which is a schematic diagram of a soft buffer SBc according to an example of the present invention. The soft buffer SBc is used for HARQ processes of CCs C1-C5, and is first divided into two sub-blocks SBc_1and SBc_2. The sub-block SBc_1is used for the CCs C1and C2, and the sub-block SBc_2is used for the CCs C3-C5. Sizes of the sub-blocks SBc_1and SBc_2which are Nsoft,sb(1) and Nsoft,sb(2), respectively, can be determined according to different design considerations or system requirements (e.g. the indication), and is not limited. Then, the sub-block SBc_1is further divided into various number of partitions. In other words, methods based on which the sub-block SBc_1is further divided are not limited. Realizations and methods which have been illustrated above can be directly applied. For example, the method illustrated byFIG. 8can be applied to the sub-block SBc_1as shown inFIG. 14by replacing NsoftinFIG. 8with Nsoft,sb(1) inFIG. 14. Similarly, the sub-block SBc_1is further divided into two sub-blocks SBc_11and SBc_12with sizes of Nsoft(1) and Nsoft(2), respectively. The sub-blocks SBc_11and SBc_12are divided into partitions P1401-P14016, wherein a size of each of the partitions P1401-1408is NIR(1), and a size of each of the partitions P1409-1416is NIR(2). The sub-block SBc_2is divided into 8 partitions according to the prior art, and is not narrated herein for simplicity. In short, those skilled in the art should readily make combinations, modifications or alterations on the process70, the process100and examples mentioned above. Therefore, except low blocking probability and better coding performance, the present invention further utilizes the soft buffer flexibly by dividing only part of the soft buffer into smaller partitions.

Besides, the indication (and hence the weighting) mentioned above can be generated by the UE itself. Alternatively, the indication is generated by a network, and is transmitted by the network to the UE via a signaling (e.g. radio resource control (RRC) signaling). Furthermore, the indication can be generated by both the UE and the network according to the same rule, to reducing overhead of the signaling. On the other hand, a time at which a soft buffer is divided into multiple partitions for multiple CCs is not limited. For example, the soft buffer can be divided after a PCC of the CCs is reconfigured, i.e., an indication capable of determining the weightings is generated after the PCC is reconfigured. Alternatively, the soft buffer can be divided after a number of the CCs is changed, i.e., an indication capable of determining the weightings is generated after the number of the CCs is changed. Further, the CCs mentioned in the above examples are preferably referred to as DL CCs, since HARQ processes stored in the UE are corresponding to packets transmitted on DL.

Besides, the process100and examples mentioned above can also be realized in the network. For example, the network can determine a number of partitions according to an indication, and transmit information (e.g. the number) of the partitions to a UE such that the UE can divide the soft buffer into the partitions according to the information. Besides, the network may not need to transmit the information to the UE since the same indication is also generated by the UE according to the same rule. Thus, the UE can determine the number and divide the soft buffer into the sub-blocks according to the number.

Please note that, the abovementioned steps of the processes including suggested steps can be realized by means that could be a hardware, a 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 a system on chip (SOC), system in package (SiP), a computer on module (COM), and the communication device30.

To sum up, the present invention provides methods for handling a soft buffer of a UE configured with multiple CCs in a wireless communication system. Blocking probabilities of HARQ processes of the CCs are reduced. Further, data transmitted on a PCC can be recovered and executed rapidly. Therefore, system throughput is increased, and the UE can operate regularly without an interrupt or a delay.