Patent Description:
With the rapid development of wireless communication technology, communication systems are also evolving, employing it. One of the examples is a long term evolution (LTE) system, which has been developed as the <NUM>th generation LTE system. LTE systems employ a variety of technologies to meet the rapid increase in traffic demand, one of which is carrier aggregation. Carrier aggregation refers to a technology that increases the number of carriers in communication between user equipment (UE) and an evolved Node B (ENB) to employ from one carrier in conventional art to a primary carrier and one or more secondary carriers, thereby increasing the amount of transmission by the number of secondary carriers. In LTE technology, a cell where a primary carrier is served is called a Primary Cell (PCell) and a cell where a secondary carrier is served is called a Secondary Cell (SCell).

In order to comply with the rapid increase in traffic, service providers have installed Pico ENBs with narrow service coverage as well as Macro ENBs with wide service coverage. This causes overlaps between the service coverages of Pico ENB and Macro ENB. In order to increase data transmission rate of UE in a state where the service coverage overlap occurs, a technology has been discussed where UE are simultaneously connected to a macro ENB and a pico ENB and also uses the carriers of the Macro ENB and carriers of the Pico ENB.

In the scenario described above, a macro ENB has three carriers (since a primary ENB doesn't have to be a macro ENB, it is hereinafter called a serving ENB). UE uses one of the three carriers as a PCell and the two carriers as SCell <NUM> and SCell <NUM> respectively. In addition, a pico ENB has two carriers (since the other ENBs except for the primary ENB don't have to be pico ENBs, they are hereinafter called drift ENBs). UE uses one of the three carriers as a PCell and the two carriers as SCell <NUM> and SCell <NUM> respectively. UE uses the two carriers as SCell <NUM> and SCell <NUM>. Carriers (PCell, SCell <NUM> and SCell <NUM>) of the serving ENB are called a Primary Set. Carriers (SCell <NUM> and SCell <NUM>) of the drift ENB are called a Non-primary Set.

UE transmits a Buffer Status Report (BSR) on the uplink via a cell in order to report an amount of data to be transmitted. Since the UE is connected with a number of ENBs, there arises the problem of how many resources each ENB must allocate to the UE. <CIT> discloses a method for reporting buffer status in carrier aggregation. It proposes to use different logical channel group assignments for different carriers, each reporting its one BSR. The main objective of the disclosure of D2 is to avoid padding, which is a waste of resources, in case of pre-configured periodic allocations. Therefore, instead of padding a BSR for the next lower LCG priority group can be transmitted or data for that group.

<CIT> Document D1 discloses a method in which new data arrival in a buffer triggers a BSR. The BSR per LCG is reported in unused bits of the MAC sub-header. For aggregated PDUs the multiple sub-headers, one is used per LCG.

The present invention has been made in view of the above problems, and provides a method for transmitting a Buffer Status Report (BSR) from UE to ENB, using an inter-ENB carrier aggregation technology, in a wireless mobile communication system, and a method and apparatus for processing BSR in ENB.

In accordance with an exemplary embodiment of the present invention, the present invention provides a method for processing a buffer status report (BSR) in user equipment (UE) of a wireless communication system, according to independent claim <NUM>.

In accordance with another exemplary embodiment of the present invention, the present invention provides an apparatus for receiving a buffer status report (BSR) in an ENB of a wireless communication system, according to independent claim <NUM>.

The features and advantages of the invention will become more apparent from the following detailed description in conjunction with the accompanying drawings, in which:.

Hereinafter, exemplary embodiments of the present invention are described in detail with reference to the accompanying drawings. Detailed descriptions of well-known functions and structures incorporated herein may be omitted to avoid obscuring the subject matter of the invention.

In the following description, embodiments of the present invention are described with reference to the accompanying drawings explaining mobile devices.

<FIG> illustrates a view that describes the configuration of an LTE system according to an embodiment of the invention.

Referring to <FIG>, the LTE system configures the wireless access network, including Evolved Node Bs (ENBs) <NUM>, <NUM>, <NUM>, and <NUM>, a mobility management entity (MME) <NUM>, and a serving-gateway (S-GW) <NUM>. User equipment (UE) <NUM> is connected to an external network via the ENB <NUM>, <NUM>, <NUM>, or <NUM> and the S-GW <NUM>.

ENBs <NUM> to <NUM> correspond to conventional Node B of the UMTS system. ENBs <NUM> to <NUM> are connected to UE <NUM> via wireless channels, performing more complicated functions than conventional Node B. Since real-time Voice over IP (VoIP) services and all user traffic are served via shared channels in LTE system, devices are required to collect information regarding states, such as buffer states of UE, available transmission power states, channel states, etc., and to make schedules. This job can be performed via ENBs <NUM> to <NUM>.

One ENB controls a number of cells. For example, in order to implement a transmission rate of <NUM> Mbps, an LTE system employs orthogonal frequency division multiplexing (OFDM) at a bandwidth of <NUM>. The LTE system also employs adaptive modulation & coding (AMC) to determine modulation scheme and channel coding rate, meeting with the channel state of UE. S-GW <NUM> is a device that establishes data bearers. S-GW <NUM> can create or remove data bearers according to the control of MME <NUM>. MME <NUM> manages the mobility of UE and controls a variety of functions. MME <NUM> connects to a number of ENBs.

<FIG> illustrates a view that describes the wireless protocol stack of an LTE system according to an embodiment of the invention.

Referring to <FIG>, UE and ENB have packet data convergence protocols (PDCP) <NUM> and <NUM>, radio link control (RLC) <NUM> and <NUM>, and medium access controls (MAC) <NUM> and <NUM>, respectively. PDCP <NUM> and <NUM> compress/decompress the IP header. RLC <NUM> and <NUM> reconfigure PDCP packet data unit (PDU) in proper size. MAC <NUM> and <NUM> connect to a number of RLC layer devices configured in one UE device. MAC <NUM> and <NUM> multiplex RLC PUDs to MAC PDU, and de-multiplex RLC PDUs from MAC PDU. Physical layers (PHY) <NUM> and <NUM> in UE and ENB channel-code and modulate data from the upper layers, create OFDM symbols, and transmit them via a wireless channel. In addition, PHY <NUM> and <NUM> demodulate and channel-decode OFDM symbols received via a wireless channel, and transfer them to the upper layers.

PHY <NUM> and <NUM> also employ Hybrid ARQ to perform addition error correction, where the receiving end determines whether a packet from a transmitting end has been received by transmitting <NUM> bit to the transmitting end, which is called HARQ ACK/NACK information. Downlink HARQ ACK/NACK information with respect to uplink transmission is transmitted via physical hybrid-ARQ indicator channel (PHICH). Likewise, uplink HARQ ACK/NACK information with respect to downlink transmission is transmitted via physical uplink control channel (PUCCH) or physical uplink shared channel (PUSCH).

<FIG> illustrates a view that describes carrier aggregation in user equipment UE.

Referring to <FIG>, one ENB broadcasts/receives multi-carriers over frequency bands. For example, when an ENB <NUM> broadcasts a carrier <NUM> of center frequency f1 and a carrier <NUM> of center frequency f3, one conventional UE device transmits/receives data via one of the carriers <NUM> and <NUM>. However, according to the invention, UE that performs carrier aggregation can simultaneously transmit/receive data using a number of carriers. In that case, ENB <NUM> can allocate more carriers to UE <NUM> that can perform carrier aggregation, so that the UE <NUM> can increase the data transmission rate.

If it is assumed that a cell is formed by one forward carrier and one reverse carrier that are each transmitted/received from/by one ENB, carrier aggregation may be understood as UE simultaneously transmits/receives data via a number of cells. In that case, the maximum transmission rate may increase in proportion to the number of aggregated carriers.

In the following description, receiving data by UE via a forward carrier or transmitting data by UE via a reverse carrier means that data is received/transmitted via a control channel and a data channel provided by a cell corresponding to a frequency band and a center frequency characterizing the carrier. For the sake of convenience, the following embodiment will be described based on LTE systems. However, it should be understood that the invention is not limited to the embodiment. For example, the invention can be applied to all types of wireless communication systems that can support carrier aggregation.

In the following description, it is assumed that UE uses carriers by aggregating cells covering a number of ENBs, which is inter-ENB carrier aggregation.

<FIG> illustrates a signal flow chart that describes a message flow in a method for reporting a buffer status according to a first embodiment of the present invention.

It is assumed that UE <NUM> aggregates one or more cells of a serving ENB <NUM> and one or more cells of a drift ENB <NUM>. UE <NUM> is triggered to report the buffer status when it has data to be transmitted or when a periodic timer for reporting a buffer status has expired (<NUM>).

Details regarding the BSR to be triggered are as follows:.

When UE <NUM> is allocated with uplink resources from the serving ENB <NUM> (<NUM>), it transmits the triggered BSR to the serving ENB <NUM> (<NUM>). The triggered BSR is the same BSR of the conventional LTE system and includes the amount of packets stacked in buffers according to LCGs. Therefore ENB sets an amount of uplink resources to be allocated to the UE and makes a schedule. An LTE system classifies packets by logical channel identifiers according to the characteristics of traffic and transmits them. When reporting a buffer status, the LTE system groups logic channels classified by the logical channel identifiers and reports buffer statuses according to the groups.

After receiving the BSR, the serving ENB <NUM> transmits, when UE <NUM> is simultaneously communicating with other ENB (the drift ENB <NUM> in an embodiment of the present invention), the received information to other ENB (the drift ENB <NUM> in an embodiment of the present invention) (<NUM>). According to reception times of the BSR, the information regarding the received BSR may not be effective. Therefore, the information regarding the received BSR may further include timestamp as information regarding a reception time point of BSR. In addition, the serving ENB <NUM> may further transmit a data transmission rate and an amount of resources, which will be allocated to the UE <NUM>, while receiving the BSR.

Likewise, UE <NUM> is triggered to report a buffer status to the drift ENB <NUM> when it has data to be transmitted or a periodic timer for reporting a buffer status has expired (<NUM>). When UE <NUM> is allocated with uplink resources from the drift ENB <NUM> (<NUM>), it transmits the BSR to the drift ENB <NUM> (<NUM>). After receiving the BSR, the drift ENB <NUM> transmits it to other ENB (the serving ENB <NUM> in an embodiment of the present invention). In addition, the drift ENB <NUM> may further transmit Timestamp and a data transmission rate and an amount of resources, which will be allocated to the UE <NUM>.

<FIG> illustrates a flow chart that describes a method for receiving a buffer status report (SBR) in an ENB according to a first embodiment of the present invention.

ENB receives a BSR from UE (<NUM>). ENB determines whether the UE is connected to other ENB (or ENBs) for carrier aggregation (<NUM>). When ENB ascertains that the UE is connected to another ENB (or ENBs) for carrier aggregation at operation <NUM>, it transmits the BSR to another ENB (or ENBs) (<NUM>). The ENB may also transmit Timestamp and a data transmission rate and the amount of resources that will be allocated to the UE to the other ENB (or ENBs).

After that, the ENB allocates resources to the UE based on the BSR (<NUM>). When the ENB transmits a data transmission rate and the amount of resources that will be allocated to the UE to the other ENB (or ENBs) at operation <NUM>, it allocates resources to the UE based on the transmitted information.

On the contrary, when ENB ascertains that the UE isn't connected to another ENB (or ENBs) for carrier aggregation at operation <NUM>, it allocates resources to the UE based on the BSR at operation <NUM>.

<FIG> illustrates a signal flow chart that describes a message flow in a method for reporting a buffer status according to an embodiment of the present invention.

When UE <NUM> is allocated with uplink resources from the serving ENB <NUM> (<NUM>), it transmits the triggered BSR to the serving ENB <NUM> (<NUM>). After that, UE <NUM> is allocated with uplink resources from the serving ENB <NUM> (<NUM> and <NUM>), it transmits corresponding uplink data via the allocated resources to the serving ENB <NUM>, respectively (<NUM> and <NUM>).

After that, when UE <NUM> is allocated with an uplink resource from another ENB (e.g., a drift ENB <NUM> in an embodiment of the present invention) (<NUM>), it concludes that the last BSR was not transmitted to the drift ENB <NUM> (<NUM>). After that, when UE <NUM> is triggered to make a transmission of a regular or periodic BSR (<NUM>), it transmits the BSR to the drift ENB <NUM> (<NUM>).

In that case, a problem as described in the embodiment of <FIG> may occur. That is, the BSR reported at operation <NUM> and the BSR reported at operation <NUM> are duplicated, so a larger amount of information regarding the BSR may be reported than the real amount. To resolve the problem, when UE <NUM> is allocated with uplink resources from other ENB <NUM> at operation <NUM>, it concludes that the last BSR was not transmitted to the ENB <NUM> at operation <NUM> and determines whether the amount of data stacked in the buffer whose status is reported at operation <NUM> is less than or equal to a threshold value (<NUM>). Only if the amount of data stacked in the buffer whose status was reported at operation <NUM> is less than or equal to a threshold value at operation <NUM> and a trigger is made to transmit a regular or periodic BSR at operation <NUM>, UE <NUM> transmit the BSR to the drift ENB <NUM> at operation <NUM>.

The threshold value may be set to a dynamic value by using a message of Radio Resource Control (RRC) layer or to a fixed value set by the standard or according to the implementation.

<FIG> illustrates a flow chart that describes a method for reporting a buffer status in UE according to an embodiment of the present invention. That is, <FIG> is a flow chart that describes in detail operations <NUM> to <NUM> shown in <FIG>.

UE is allocated with an uplink resource from an ENB (<NUM>). UE determines whether the ENB allocating the uplink resource is the ENB to which it transmitted the last BSR, i.e., the uplink resource is allocated by another ENB to which it didn't transmit the last BSR (<NUM>). When UE ascertains that the uplink resource is allocated by another ENB at operation <NUM>, it determines whether the amount of buffer is less than a threshold value (<NUM>).

When UE ascertains that the amount of buffer is less than a threshold value at operation <NUM>, it is triggered to transmit a regular or periodic BSR (<NUM>). After that, UE transmits the triggered BSR via the uplink resource (<NUM>). Meanwhile, the method may be modified in such a way to include operation <NUM> as an option. To express this, the symbol of operation <NUM> is illustrated in the dashed line.

On the contrary, when UE ascertains that the uplink resource isn't allocated by other ENB at operation <NUM>, it ends the BSR reporting procedure. In addition, when UE ascertains that the amount of buffer is greater than a threshold value at operation <NUM>, it ends the BSR reporting procedure.

<FIG> illustrates a signal flow chart that describes a message flow in a method for reporting a buffer status according to a third embodiment of the present invention.

It is assumed that UE <NUM> aggregates one or more cells of a serving ENB <NUM> and one or more cells of a drift ENB <NUM>. It is also assumed that logical channels according to ENBs (e.g., serving ENB <NUM> and drift ENB <NUM> shown in <FIG>) differ from each other. For example, UE has five logical channels for data, Channel Nos. <NUM>, <NUM>, <NUM>, <NUM> and <NUM>. Channel Nos. <NUM>, <NUM>, and <NUM> form a logic channel group (LCG) LCG <NUM>. Channel Nos. <NUM> and <NUM> form a logic channel group (LCG) LCG <NUM>. LCG <NUM> is processed by the serving ENB <NUM> and LCG <NUM> is processed by the drift ENB <NUM>.

UE <NUM> receives a command for associating with cells of the drift ENB <NUM> and information regarding LCGs transmissible to the drift ENB <NUM> from the serving ENB <NUM> (<NUM>). LCGs that UE <NUM> will transmit to the serving ENB <NUM> and drift ENB <NUM> according to the information regarding LCGs are determined. In an embodiment of the present invention, in order to transmit the command for associating with cells of the drift ENB <NUM> to the UE <NUM>, the serving ENB <NUM> may use messages, such as RRCConnectionReconfiguration, etc..

When receiving the command and information at operation <NUM>, UE <NUM> transmits an acknowledgement message, e.g., RRCConnectionReconfigurationComplete, etc., to the serving ENB <NUM> (<NUM>).

After that, UE <NUM> manages a set of buffers available for transmission by the serving ENB <NUM> and a set of buffers available for transmission by the drift ENB <NUM>, independently.

UE <NUM> is triggered to transmit a regular or periodic BSR for the buffers that can perform transmission (i.e., a set of primary carriers) to the serving ENB <NUM> (<NUM>). When UE <NUM> is allocated with an uplink resource from the serving ENB <NUM> (<NUM>), it transmits the BSR including the buffer status of transmissible LCGs in a set of primary carriers to the serving ENB <NUM> (<NUM>).

In addition, UE <NUM> is triggered to transmit a regular or periodic BSR for the buffers that can perform transmission (i.e., a set of non-primary carriers) to the drift ENB <NUM> (<NUM>).

When UE <NUM> is allocated with an uplink resource from the drift ENB <NUM> (<NUM>), it transmits the BSR including the buffer status of transmissible LCGs in a set of non-primary carriers to the drift ENB <NUM> (<NUM>).

The BSR triggered at operation <NUM> or <NUM> may have different information according to types of BSR, i.e., regular, periodic, etc..

In particular, a regular BSR may be independently used according to sets. A periodic BSR may be independently or unitedly used according to sets.

For example, if a periodic BSR is independently used, a retxBSR-Timer and a periodicBSR-Timer may be separately configured according to sets, which means that BSR transmitted via the periodic BSR includes only the BSR of the corresponding LCG. If a periodic BSR is unitedly used, a retxBSR-Timer and a periodicBSR-Timer are operated by only one value. In addition, the periodic BSR can be transmitted to any cell and can include values of any LCGs.

<FIG> illustrates a flow chart that describes a method for reporting a buffer status in UE according to a third embodiment of the present invention.

UE receives a configuration message for associating with cells of a serving ENB or drift ENB from an ENB (<NUM>). The message also includes information regarding LCGs transmissible according to ENBs. An example of the message is RRCConnectionReconfiguration.

When receiving the configuration message at operation <NUM>, UE transmits an acknowledgement message, e.g., RRCConnectionReconfigurationComplete, etc., to the ENB (<NUM>). After that, UE determines whether BSR is triggered (<NUM>). When UE ascertains that a regular or a periodic BSR is triggered at operation <NUM>, it determines to which LCG the triggered BSR corresponds (<NUM>). UE creates a BSR of the corresponding LCG and transmits it to the ENB that can perform transmission (<NUM>).

<FIG> illustrates a signal flow chart that describes a message flow in a method for reporting a buffer status according to a fourth embodiment of the present invention.

UE <NUM> receives a command for associating with cells of the drift ENB <NUM> from the serving ENB <NUM> (<NUM>). After receiving the command, UE <NUM> transmits the acknowledgement message to the serving ENB <NUM> (<NUM>).

In order to activate the associated cells of the drift ENB <NUM> at <NUM>, UE <NUM> receives an activation message from the serving ENB <NUM> (<NUM>). In order to align uplink timings of the associated cells, UE <NUM> receives a command message for transmitting preambles to the cells from the serving ENB <NUM> (<NUM>).

UE <NUM> transmits a corresponding Random Access preamble to the drift ENB <NUM> (<NUM>), and receives the Random Access Response (RAR) message from the drift ENB <NUM> (<NUM>). The RAR message includes Timing Advance information regarding uplink timing alignment and information regarding additionally allocated uplink resources. UE <NUM> triggers the BSR according to the allocated uplink resources (<NUM>). UE <NUM> transmits the BSR via the resources (<NUM>).

<FIG> illustrates a flow chart that describes a method for reporting a buffer status in UE according to a fourth embodiment of the present invention.

UE receives a command for associating with cells of the drift ENB from an ENB (<NUM>). After receiving the command, UE transmits the acknowledgement message to the ENB (<NUM>).

In order to activate the associated cells of the drift ENB, UE receives an activation message (<NUM>). In order to align uplink timings of the associated cells, UE receives a command message for transmitting preambles to the cells (<NUM>).

UE transmits a corresponding Random Access preamble to the drift ENB according to the command (<NUM>) and receives the Random Access Response (RAR) message from the drift ENB (<NUM>). The RAR message includes Timing Advance information regarding uplink timing alignment and information regarding additionally allocated uplink resources.

UE triggers the BSR according to the allocated uplink resources (<NUM>). UE transmits the BSR via the resources (<NUM>).

<FIG> illustrates a schematic block diagram of user equipment (UE) according to an embodiment of the invention.

UE transmits/receives, to/from the other systems, data via the upper layer processing unit <NUM> and control messages via the control message processor <NUM>. In transmission, the controller <NUM> controls the multiplexer-demultiplexer <NUM> to multiplex data and the transceiver <NUM> to transmit the multiplexed data. In reception, the controller <NUM> controls the transceiver <NUM> to receive physical symbols and the multiplexer-demultiplexer <NUM> to de-multiplex the symbols, and transfers the de-multiplexed data to the upper layer unit <NUM> or the control message processor <NUM> according to the control message.

<FIG> illustrates a schematic block diagram of an ENB according to an embodiment of the invention.

The ENB includes a transceiver <NUM>, a controller <NUM>, a multiplexer-demultiplexer <NUM>, a control message processor <NUM>, an upper layer processing unit <NUM>, and a scheduler <NUM>.

The transceiver <NUM> transmits data and control signals via a forward carrier and also receives data and control signals via a reverse carrier. If multi-carriers are configured, the transceiver <NUM> receives/transmits data and controls signals via the multi-carriers.

The multiplexer-demultiplexer <NUM> multiplexes data from the upper layer processing unit <NUM> or the control message processor <NUM>. The multiplexer-demultiplexer <NUM> also de-multiplexes data received via the transceiver <NUM> and transfers it to the upper layer processing unit <NUM>, the control message processor <NUM>, or the controller <NUM>.

The control message processor <NUM> processes control messages transmitted from UE and performs corresponding operations. The control message processing unit <NUM> also creates control messages to be transmitted to UE and transfers them to the lower layers.

The upper layer processing unit <NUM> can be configured according to UE devices and services. The upper layer processing unit <NUM> processes data, created by user services such as FTP, VoIP, etc., and transfers them to the multiplexer-demultiplexer <NUM>. The upper layer processing unit <NUM> processes data from the multiplexer-demultiplexer <NUM> and transmits them to service applications in the upper layer.

The controller <NUM> detects a time of CSI/SRS transmission by UE and controls the transceiver <NUM>.

The scheduler <NUM> assigns transmission resources to UE at a time point according to buffer status of UE, channel state, active time of UE, etc. The scheduler <NUM> allows the transceiver <NUM> to process signals transmitted from UE or to transmit signals to UE.

According to the embodiments of the present invention, when aggregating inter-ENB carriers, UE can transmit corresponding uplink data values to ENBs and be evenly allocated with uplink resources from the ENBs.

Claim 1:
A method performed by a user equipment, UE, (<NUM>) that aggregates a cell of a first base station (<NUM>) and a cell of a second base station (<NUM>) in a communication system, the method comprising:
receiving, from the first base station (<NUM>), a radio resource control, RRC, message including information on a threshold value (<NUM>); identifying (<NUM>, <NUM>) that a buffer status report, BSR, corresponding to a buffer, is triggered; and
transmitting (<NUM>, <NUM>) the triggered BSR to the first base station (<NUM>), characterised by,
in case that the UE (<NUM>) is, after transmitting the triggered BSR to the first base station, allocated (<NUM>) with uplink resources from the second base station (<NUM>) and an amount of data volume for the UE (<NUM>) in the buffer is <NUM> smaller than the threshold value (<NUM>), a further BSR is transmitted to the second base station (<NUM>).