Method for offloading traffic by means of wireless LAN in mobile communications system and apparatus therefor

The present invention relates to a method for offloading traffic by means of wireless LAN in a mobile communications system and apparatus therefor, and more particularly to a method for a terminal to offload traffic at a bearer level, and to a base station communicating with the terminal. The method for a terminal to offload traffic according to the present invention includes the steps of: while performing a data communication with a base station through a bearer of a first communications network, receiving from the base station an offloading command for offloading a part of traffic to a second communications network; transmitting a report of the offloading to the base station in response to the offloading command; and performing a data communication of the partial traffic with an accessible AP through a bearer of the second communications network without releasing the bearer of the first communications network.

TECHNICAL FIELD

The present invention relates to a method and an apparatus for offloading traffic by using a Wireless Local Area Network (WLAN) in a mobile communication system and, more particularly, to a method for offloading traffic at a bearer level.

BACKGROUND ART

Recently, wireless communication technology has achieved rapid progress, and accordingly, communication system technology has also repeatedly evolved. As a result, there is a Universal Mobile Telecommunications System (UMTS) system as the third generation (3G) mobile communication technology, and it is a Long-Term Evolution (LTE) system that is spotlighted as the fourth generation (4G) mobile communication technology.

Particularly, in today's wireless communication system, data usage amount of users has exploded according to the spread of smart phones, and an attempt is made to distribute the data usage amount by additionally interworking a WLAN network with an existing mobile communication network (i.e., a 3G cellular network and a 4G cellular network) in order to deal with the exploding data usage amount.

However, the current technology cannot deal with closely interworking the cellular network with the WLAN network. Specifically, currently, the cellular network and the WLAN network independently operate except for some limited functions (e.g., authentication).

Accordingly, when a user equipment, which does not know a location at which a WLAN network is located, desires to use the WLAN network, the user equipment needs to continuously search for a neighboring WLAN network, which results in the power consumption of the user equipment. Also, a problem arises in that WLAN power of the user equipment needs to be always turned on in order to search for a neighboring WLAN network.

Even when the user equipment has found an available WLAN network and accesses the available WLAN network, the user equipment needs to release the connection with the current cellular network and needs to transmit/receive all traffics of the user equipment to/from the available WLAN network, and thus service quality, that a user of the user equipment actually feels, may be degraded. Also, when user data, such as Voice over Internet Protocol (VoIP) in which a real-time property is important, a Radio Resource Control (RRC) message, or the like is transmitted/received through the WLAN, the WLAN may not provide service quality that the relevant service requires.

Further, due to a limitation on the coverage of the WLAN network, a case may occur in which the user equipment that has used the WLAN network needs to come back to the wireless cellular network (e.g., an LTE network). Service quality, that the user actually feels, may be seriously degraded when the user equipment has released the connection with the LTE network and re-accesses the LTE network in a process during which the user equipment sets up access to the WLAN network and releases the access thereto.

DISCLOSURE OF INVENTION

Technical Problem

The present invention provides a method and an apparatus for offloading traffic at a bearer level by using a WLAN in a bearer mobile communication system.

Solution to Problem

In order to solve the above-mentioned technical problems, in accordance with an aspect of the present invention, a method for offloading traffic by a user equipment is provided. The method includes: receiving, from a base station, an offload command for offloading partial traffic to a second communication network while performing data communication with the base station through a bearer of a first communication network; transmitting an offload report to the base station in response to the offload command; and performing, by the user equipment, data communication related to the partial traffic with an accessible Access Point (AP) through a bearer of the second communication network without releasing the bearer of the first communication network.

Also, in accordance with another aspect of the present invention, a method for offloading traffic by a base station is provided. The method includes: transmitting, to a user equipment, an offload command for offloading partial traffic to a second communication network while performing data communication with the user equipment through a bearer of a first communication network; receiving an offload report from the user equipment in response to the offload command; and forwarding data related to the partial traffic to an Access Point (AP), with which the user equipment is capable of communicating, without releasing the bearer of the first communication network.

Also, in accordance with still another aspect of the present invention, there is provided a user equipment which includes: a transmission/reception unit for performing data communication with a base station or an Access Point (AP); and a control unit for controlling the transmission/reception unit to transmit an offload report to the base station in response to the offload command, in such a manner that the user equipment performs data communication related to the partial traffic with an accessible Access Point (AP) through a bearer of a second communication network without releasing a bearer of a first communication network, when the transmission/reception unit receives, from the base station, an offload command for offloading partial traffic to the second communication network while the transmission/reception unit performs data communication with the base station through the bearer of the first communication network.

Further, in accordance with yet another aspect of the present invention, there is provided a base station which includes: a transmission/reception unit for performing data communication with a user equipment; and

a control unit for controlling the transmission/reception unit to transmit, to a user equipment, an offload command for offloading partial traffic to a second communication network while the transmission/reception unit performs data communication with the user equipment through a bearer of a first communication network, to receive an offload report from the user equipment in response to the offload command, and to forward data related to the partial traffic to an Access Point (AP), with which the user equipment is capable of communicating, without releasing the bearer of the first communication network.

Advantageous Effects of Invention

The present invention can effectively support the offload of user traffic by using a WLAN in a mobile communication system, and can minimize a service interruption phenomenon occurring during the offload.

MODE FOR THE INVENTION

In the following description of the present disclosure, a detailed description of known configurations or functions incorporated herein will be omitted when it is determined that the detailed description may make the subject matter of the present disclosure unclear. Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings.

The present invention relates to a method and an apparatus in which a user equipment capable of accessing a wireless cellular network and a WLAN network transmits/receives a part of data through the WLAN network. Hereinafter, before the description of the present invention, an LTE system will be briefly described.

In the present invention, for convenience of description, the description will focus on an LTE system as an example of a cellular network, but the present invention can all be applied to other cellular networks (e.g., a UMTS).

FIG. 1is a view illustrating a configuration of an LTE system, to which the present invention is applied.

Referring toFIG. 1, a radio access network of the LTE system includes one or more ENBs (next-generation base stations, Evolved Node Bs, Node Bs, or base stations)105,110,115and120, a Mobility Management Entity (MME)125, a Serving-Gateway (S-GW)130, and a User Equipment (hereinafter a “UE” or a “terminal”)135.

The UE135accesses an external network through the ENB105,110,115, or120and the S-GW130.

The ENBs105,110,115and120each correspond to a Node B of the existing UMTS system. The ENB105,110,115, or120is connected to the UE135through a wireless channel, and plays a more complex role than the existing Node B.

In the LTE system, since all user traffic including real-time services, such as VoIP, is serviced through a shared channel, there is a need for a device for collecting status information, such as a buffer status of the UEs135s, an available transmission power status thereof, a channel status thereof, etc., and performing scheduling depending thereon, and the ENBs105,110,115and120serve as the device.

One ENB105,110,115, or120typically controls multiple cells. For example, in order to achieve a transmission speed of 100 Mbps, the LTE system uses Orthogonal Frequency Division Multiplexing (OFDM) in a bandwidth of 20 MHz as radio access technology. Also, the LTE system applies an Adaptive Modulation & Coding (AMC) scheme which determines a modulation scheme and a channel coding rate according to a channel status of the UE135.

The MME125is a device in charge of various control functions as well as a mobility management function for the UE, and is connected to multiple ENBs.

The S-GW130is a device for providing a data bearer, and generates or removes a data bearer under the control of the MME125.

FIG. 2is a view illustrating a structure of a wireless protocol in an LTE system, to which the present invention is applied.

Referring toFIG. 2, the wireless protocol of the LTE system includes Packet Data Convergence Protocol (PDCP)205and240, Radio Link Control (RLC)210and235, Medium Access Control (MAC)215and230, and Physical Layer (PHY)220and225in each of the UE and the ENB.

The PDCP205and240is in charge of operations, such as IP header compression/decompression and the like.

The RLC210and235reconfigures a PDCP Packet Data Unit (PDU) into a suitable size.

The MAC215and230is connected to multiple RLC layer entities configured in one UE. Also, the MAC215and230performs an operation of multiplexing RLC PDUs into a MAC PDU and demultiplexing RLC PDUs from a MAC PDU.

The PHY220and225channel-codes and modulates higher layer data into OFDM symbols, and transmits the OFDM symbols through a wireless channel. Also, the PHY220and225demodulates and channel-decodes OFDM symbols received through a wireless channel and transfers the decoded OFDM symbols to a higher layer.

The PHY220and225may use Hybrid Automatic Retransmit reQuest (HARQ) for additional error correction. A reception side transmits 1-bit information, which indicates whether the reception side receives a packet transmitted by a transmission side, to the transmission side. The 1-bit information is referred to as “HARQ ACKnowledgement/Negative ACKnowledgement (ACK/NACK) information.” The downlink HARQ ACK/NACK information corresponding to uplink transmission may be transmitted through a Physical Hybrid-ARQ Indicator CHannel (PHICH) physical channel, and the uplink HARQ ACK/NACK information corresponding to downlink transmission may be transmitted through a Physical Uplink Control CHannel (PUCCH) physical channel or Physical Uplink Shared CHannel (PUSCH) physical channel.

Hereinafter, offload using the existing WLAN in the LTE system will be described.

FIG. 3is a view explaining typical WLAN offload.

Today's LTE system provides offload using a WLAN network in order to meet an exploding wireless data demand. Particularly, it emerges as a powerful service model that an operator independently builds a WLAN network and provides WLAN services to only subscribers of the operator.

Referring toFIG. 3, multiple WLAN Access Points (APs)310and315are deployed within the coverage of an LTE ENB305, and the APs310and315and the LTE ENB305are connected to an operator's wired network (OPERATOR managed NW)320.

When the UE is located in an area that only an LTE radio signal reaches (hereinafter “LTE coverage”) as indicated by reference numeral325, all user traffic is transmitted/received through an LTE network. In contrast, when the UE has moved toward the APs310and315and is located in an area that an LTE radio signal and a WIFI radio signal both reach (hereinafter “WIFI coverage”) as indicated by reference numeral330, the operator may release the LTE connection of the UE and may set the UE in such a manner that user traffic is transmitted/received through the APs310and315.

Thereafter, when the UE has left the WIFI coverage and is located again in the LTE coverage as indicated by reference numeral335, the LTE ENB305newly establishes a connection with the UE and again transmits/receives user traffic through the LTE wireless network.

The operator may be provided with a WIFI server340in order to provide the UE with WIFI offload-related information. The UE may acquire the WIFI offload-related information (e.g., an offload policy, etc.) from the WIFI server340.

When, as described above, the UE releases the RRC connection and resets up an RRC connection whenever the UE performs WIFI offload, in the LTE network, there arises a problem such that the number of RRC connection-related control messages rapidly increases and the transmission/reception of user traffic is stopped, and the like.

These problems can be solved by maintaining the RRC connection without releasing the RRC connection even when the UE enters the WIFI coverage. Alternatively, these problems may be solved in such a manner that, according to the type of service, only some services, for example, non-real-time services such as a File Transfer Protocol (FTP) and the like which cause a large amount of data traffic, are serviced through WIFI, and that a voice service and the like, which have strong requirements for service quality, are serviced through LTE.

Accordingly, the present invention proposes a method in which the UE maintains the RRC connection even when the UE enters the WIFI coverage while, according to the type of service, only some services are serviced through WIFI and the remaining services are serviced through the LTE wireless network. The offload method proposed by the present invention is hereinafter referred to as “bearer level offload.”

First Embodiment

FIG. 4is a flow diagram illustrating an example of bearer level WIFI offload according to an embodiment of the present invention.

First, in step415, an ENB410transmits system information to a UE405located in the coverage of the ENB410. At this time, when a WIFI network accessible to the coverage of the ENB410exists, the ENB410provides WIFI-related information to the UE405through the system information. When the WIFI-related information is referred to as “common WIFI information,” the common WIFI information may include the elements below.

[Common WIFI Information]Whether there exists an accessible WIFI AP within an area of a serving cellWIFI channel informationWIFI AP location information (e.g., location information or Global Positioning System (GPS) coordinate information with an LTE radio signal received signal strength as a reference)A list of neighboring frequencies at which an accessible WIFI network exists (or Service Set IDentifier (SSID) information of a WIFI network for each neighboring frequency)

The reason why the information is referred to as “common WIFI information” is because the information is commonly provided to multiple unspecified UEs.

The UE405may support a WIFI offload function, and may currently receive a WIFI service from an operator. The UE405stores the WIFI-related information, namely, the common WIFI information, which has been received from ENB410.

In step420, when a need occurs to transmit/receive data for a certain reason, the UE405performs an RRC connection setup process and an RRC connection reconfiguration process with the ENB410. The UE405and the ENB410establish a Signaling Radio Bearer (SRB) through the RRC connection setup process, and establish a Data Radio Bearer (DRB) through the RRC connection reconfiguration process. The SRB is a radio bearer for transmitting/receiving an RRC message and a higher layer control message, and the DRB is a radio bearer for transmitting/receiving user data. A radio bearer provides a predetermined service quality according to the establishment of the radio bearer. A DRB may be established for each service in order to be able to meet a Quality of Service (QoS) requirement of a service. When services having similar required service qualities exist, the services may be serviced through one DRB. After the RRC connection reconfiguration process is completed, the UE405may report WIFI offload support-related UE information to the network. The WIFI offload support-related UE information may be the elements below.

[UE Information on WIFI Offload Support]Information on the WIFI network that the UE can access. For example, there may be SSID information of an AP that the UE can access.Bearer-related information to which the UE may apply offload. For example, there may be information, such as QoS Class Identifier (QCI) information or Evolved Packet System (EPS) bearer identifier information to which WIFI offload is applied.

The UE405may previously receive the WIFI offload support-related UE information from a WIFI server.

Next, in step425, the UE405transmits/receives downlink data and uplink data to/from the ENB410through the established radio bearer.

In step430, the ENB410determines that the ENB410performs bearer level offload on a part of traffic of the UE405for a certain reason at a certain time point. Specifically, the ENB410determines that the ENB410offloads a part of traffic to WIFI on the basis of whether offload is required and whether a state of data transmission/reception meets an offload condition. Hereinafter, for convenience of description, a bearer to which WIFI offload is applied is named a “WIFI offload bearer.” A WIFI offload bearer may be mapped to a WIFI offload IP flow, a WIFI offload EPS bearer, and a WIFI offload DRB, and hereinafter, these terms are used together.

The ENB410may determine that the ENB410offloads, for example, an IP flow, which generates massive non-real-time data, to WIFI. Specifically, the ENB410offloads an EPS bearer or a DRB, which is mapped to the IP flow, to WIFI.

When a UE exists which is determined to increase the generation amount of non-real-time data and to be located near an accessible WIFI network among UEs supporting WIFI offload, the ENB410may determine that the ENB410offloads a part of traffic of the UE to WIFI.

In step430, when the bear level offload has been determined, the ENB410transmits an offload command control message including the following information to the UE405.

Offload Bearer Identifier

As described above, it is desirable to offload only some DRBs all having a low service requirement to WIFI, and the ENB410notifies the UE405of an identifier of a DRB (or an identifier of an EPS bearer) to be offloaded.

Also, in another method, the UE may directly select an offload bearer on the basis of an offload policy.

LTE Comeback Condition

An LTE comeback condition is information on a condition for stopping WIFI offload and coming back to LTE. Details will be described below.

An offload policy is provided from the WIFI server to the UE, and may be the elements below.

[Offload Policy]WIFI offload-related operator information (e.g., a Public Land Mobile Network (PLMN) id)WIFI offload-related SSID; SSID information to which the UE may apply WIFI offload. The UE determines that a WIFI network, through which the SSID is broadcasted, is an accessible WIFI network.WIFI offload-related QoS information; WIFI offload is applied to only traffic of indicated QoS. The QoS may be expressed by information called QCI, and a QCI is assigned for each bearer. Accordingly, the policy may be such that traffic is processed through WIFI with respect to data of a bearer, for which a QCI x is set, when accessible WIFI exists, and traffic is not processed through WIFI with respect to data of a bearer, for which a QCI y is set, even when accessible WIFI exists.A WIFI offload-related EPS bearer identifier. Offload is applied to only an EPS bearer having the indicated identifier

In step435, the UE405, which has received the offload command control message, scans for an accessible WIFI AP existing around the UE405by using common WIFI information.

When the accessible WIFI AP is found in step440, the UE405proceeds to the next step. When the accessible WIFI AP is not found in step440, the UE405continuously performs the WIFI scan. At this time, in order to reduce the battery consumption of the UE405, the UE405may periodically perform WIFI scan, and a cycle of the WIFI scan may be adjusted according to the current speed or an LTE channel situation of the UE405. For example, as the UE405has a higher operation speed and the LTE channel situation becomes worse, the UE405may adjust the WIFI scan cycle to be shorter. Alternatively, the UE405may adjust the WIFI scan cycle on the basis of the WIFI scan cycle that the ENB410has indicated through the offload command control message.

Next, in step445, in order to report that the accessible WIFI AP has been found, the UE405generates an offload report control message and transmits the generated offload report control message to the ENB410. The offload report control message includes, for example, the pieces of information below.The channel status/signal quality of the found AP (or WLAN)An SSID of the found AP (or WLAN)Load information of the found AP (or WLAN)An offload DRB list

The UE405acquires the SSID and the load information of the AP through a beacon signal that the AP periodically transmits.

Also, in order to notify the ENB410of a buffer status change of the DRB to be offloaded, the UE405triggers a regular Buffer Status Report (BSR), and transmits the regular BSR and the control message together to the ENB410.

The BSR is a control message through which the UE405reports the amount of data to be transmitted to the ENB410, and is triggered when a predetermined condition is satisfied. According to the related art, the periodic expiration of a timer, the generation of data having a high priority, and the like are defined as trigger conditions of the BSR. In the present invention, the following trigger conditions of the BSR are added thereto.

[WIFI Offload-Related BSR Generation Conditions]An AP (or a WLAN network) in which bearer level WIFI offload is to be executed is found or an accessible AP (or a WLAN network) is found after an offload command control message is received from the ENB; andA buffer status of an offload DRB has previously been reported to the current serving ENB (or a buffer status of an offload DRB has ever been reported in a current serving cell),A value, which is most recently reported as the data amount of the offload DRB, is greater than zero.

When the condition is satisfied, the UE405triggers a regular BSR to the ENB410. At this time, the UE405reports only the amount of type C data to the ENB410instead of reporting the amount of all data. The type C data of a certain DRB refers to data which needs to be retransmitted among data stored in a transmission buffer of the DRB, and will be described in more detail below with reference toFIG. 6.

Alternatively, in order to reduce the complexity of the UE405, the UE405may report a predetermined value (e.g., 0 byte), in which the actual data amount is not reflected, to the ENB410as a buffer status of the offload DRB. Specifically, when the WIFI offload-related BSR generation condition is satisfied, the UE405may simplify an operation by triggering a regular BSR, which represents the buffer status of the offload DRB as 0 byte, to the ENB410.

When the regular BSR is triggered, the UE405sends a request for transmission resources to the ENB410in order to transmit the BSR. In contrast, even when another BSR (e.g., a periodic BSR) is triggered, the UE405does not send a request for transmission resources to the ENB410in order to only transmit the BSR.

The ENB410, which has received the offload report control message and the BSR, recognizes that predetermined DRBs are no longer used in LTE and related traffic is to be transmitted/received through WIFI. Also, even when data to be transmitted/received is subsequently no longer generated from the offload DRB, the ENB410maintains the DRB without initiating a process for releasing a DRB. This is for reusing the DRB by the UE405when the UE405subsequently comes back to LTE coverage from LTE/WIFI coverage. Also, the ENB410forwards data, of which transmission is not yet initiated among downlink data of the DRB to be offloaded, to a related AP.

When preparation for offload is completed, the UE405locally forwards type D data from among uplink data of the offload DRB to a transmission buffer of a WLAN module. Then, the UE405maintains the DRB as it is even when the DRB to be offloaded no longer includes data to be transmitted.

Alternatively, it may be considered that the current data of the DRB is processed through the LTE network, and subsequently, only new data is processed through WIFI. In this case, the UE405transmits/receives data of the offload EPS bearer to/from the ENB410through both WIFI and LTE during a considerable time period after the WIFI load is initiated.

A forwarding operation, an operation of maintaining a DRB, and the like of the UE405will be described in more detail below with reference toFIG. 7.

Next, in step455, the UE405transmits/receives data related to the offload DRB by using an accessible AP450.

The accessible AP450(or the accessible WLAN network) signifies an AP (or a WLAN network) that satisfies the conditions below.

[Accessible WLAN Network]A WLAN signal strength is greater than or equal to a predetermined reference,A user's subscription allows access to the AP (or an SSID of the WLAN network allows access to the SSID by the UE according to an offload policy).

While the UE405transmits/receives data to/from the AP450, the UE405continuously monitors whether an LTE comeback condition is satisfied. The LTE comeback condition may be the elements below.

[LTE Comeback Condition]Return is achieved when a state, in which WIFI channel quality is lower than or equal to a predetermined reference, continues during a predetermined time period. The reference channel quality and the reference time period may be indicated through the offload command control message indicated by reference numeral430.Return is achieved when a state, in which the QoS of WIFI is lower than or equal to a predetermined reference, continues during a predetermined time period. More specifically;

A state, in which capability (throughput) or transmission speed (data rate) is less than or equal to a predetermined reference, continues during a predetermined time period or longer. The throughput may be defined as the amount of data transmitted/received successfully through the WLAN network during a given time period. The transmission throughput (or data rate) of the UE and the reception throughput (or reception speed) thereof may be considered together, or may be independently considered. For example, whether the comeback condition is valid may be determined by comparing the sum of transmission throughput and reception throughput with a reference throughput, by comparing the transmission throughput with another reference throughput, or by comparing the reception throughput with still another reference throughput. The reference throughput and the reference time period may be indicated through the offload command control message indicated by reference numeral430.

A state, in which a transmission Packet Error Rate (PER) or a transmission Bit Error Rate (BER) is lower than or equal to a predetermined reference, during a predetermined time period or longer. A PER may be defined as a ratio of data, for which a positive acknowledgement is not received among data transmitted through the WLAN network during a predetermined time period, against the data transmitted through the WLAN network. The reference PER/BER and the reference time period may be indicated through the offload command control message indicated by reference numeral430.

A state, in which a buffering delay is longer than or equal to a predetermined reference, continues during a predetermined time period or longer. A transmission delay signifies a difference between a time point when data arrives at a transmission buffer and a time point when data is transmitted through WIFI. The reference buffering delay and the reference time period may be indicated through the offload command control message indicated by reference numeral430.Data transmission/reception does not occur to an offload EPS bearer during a predetermined time period. The offload EPS bearer is an EPS bearer connected to an offload DRB and an offload IP flow. The EPS bearer is a bearer providing particular QoS, and is a superordinate concept of a DRB. When a DRB includes a PDCP entity and an RLC entity on a protocol stack, the EPS bearer connects between a higher layer of the PDCP and an IP flow (or an IP 5-tuple). One EPS bearer is connected to one DRB. The IP 5-tuple is a collective name for a source IP address, a destination IP address, a source port number, a destination port number, and a protocol ID (or an IP flow id, or a QoS id), and is information specifying one IP flow. The reference time period may be indicated through the offload command control message indicated by reference numeral430.A need arises to release the offload EPS bearer. For example, when an application connected to an EPS bearer is terminated, the relevant EPS bearer also needs to be released.

When the LTE comeback condition is satisfied, the UE405may scan for another accessible WLAN network. When another accessible WLAN network does not exist, the UE405releases the WLAN connection, and comes back to the LTE network. When data, that the UE405has never transmitted, is stored in a WLAN transmission buffer, the UE405locally forwards the data to the offload DRB. The comeback to the LTE network corresponds to a viewpoint from the DRB which has been offloaded. From the standpoint of the UE405, the UE405continuously stays in the LTE network, and thus the expression “comeback” may not be appropriate.

Next, in step465, the UE405checks whether there exists data to be transmitted to the offload DRB. When data has been forwarded from the WLAN transmission buffer to the offload DRB, data to be transmitted exists. In this case, the UE405triggers a regular BSR to the ENB410. When data to be transmitted no longer exists and thus the UE405comes back to the LTE network, data to be transmitted to the offload DRB does not exist. In this case, in step470, in order to prevent the DRB from being unnecessarily maintained, the UE405transmits COMEBACK INDICATION, which represents an offload comeback control message, to the ENB410. The offload comeback control message may include the pieces of information below.

[Offload Comeback Control Message]A comeback reason: may represent one of a reason why QoS is lower than or equal to a reference, a reason why channel quality is lower than or equal to a reference, a reason why data to be transmitted no longer exists, and the like.A WLAN usage log: an SSID of a WLAN AP, a Base Service Set Identifier (BSSID) thereof, a channel number thereof, and the like. The amount of data transmitted/received through a WLAN. Average transmission/reception throughput in the WLAN, an average transmission delay in the WLAN, an average transmission error rate in the WLAN, and the like.An average value (or a representative value) of pieces of WLAN load information, an average value (or a representative value) of channel statuses of the WLAN

The ENB, which has received the offload comeback control message, performs a necessary operation (e.g., an operation of releasing the DRB of the UE, etc.), and delivers a WLAN usage log, WLAN load information, and the like to a WLAN management server and a billing server.

FIG. 5is a flow diagram illustrating another example of bearer level WIFI offload according to an embodiment of the present invention.

In step522, an ENB510determines that it is necessary to apply WIFI offload to a UE505. For example, the determination is made in a case where the conditions below are valid.A WIFI network that the UE can access exists around the UEIt is expected that a large amount of data to be transmitted/received will exist or be generated in a bearer to which offload is to be appliedThere is a need for offload to WIFI when the current load of an LTE network is considered

In step523, the ENB510generates a control message (e.g., a control message including measurement control information), which instructs the UE505to scan for WIFI, and transmits the generated control message to the UE505. The measurement control information usually includes Measurement Object representing measurement object information, report configuration representing measurement report configuration information, and the like. Conventional measurement objects are defined as objects in which a cellular network specializes, for example, an LTE frequency, a UMTS frequency and a cell identifier, and the like. In the present invention, WIFI is added thereto as a measurement object. The ENB510delivers, to the UE505, information (e.g., SSID information, WIFI channel information, etc.) for identifying a WIFI network as the measurement object information. The measurement report configuration information is defined in the form of an event. For example, event A1 implies that the channel quality of a serving LTE cell becomes better than a predetermined reference value, whereas event A2 implies that the channel quality of the serving LTE cell becomes worse than the predetermined reference value. In the present invention, a new event is defined in relation to WIFI measurement.Event C1: the channel quality of the accessible WIFI network becomes better than the predetermined reference value.Event C2: the channel quality of the WIFI network, of which the channel quality has been reported to be better than the predetermined reference value, becomes worse than another predetermined reference value.

The ENB510may indicate a cycle, in which WIFI measurement is performed, to the UE505through the control message. Also, the ENB510may indicate a condition for initiating the WIFI measurement to the UE505through the control message. For example, the ENB510provides the UE505with Radio Frequency (RF) fingerprint representing an RF map corresponding to the location of a WIFI network, or GPS coordinates of a WIFI AP and area information (e.g., radius information of AP coverage) of the AP, and thereby causes the UE505to initiate the WIFI measurement only when the UE505approaches the WIFI network.

WIFI-related information provided through the measurement control information as described above is referred to as “dedicated WIFI information.”

Next, in step524, the UE505scans for whether an accessible WIFI network exists, by using the dedicated WIFI information provided in step523. When the dedicated WIFI information is not provided or only a part of the dedicated WIFI information is provided, the UE505may combine common WIFI information with the dedicated WIFI information, and may use the common WIFI information combined with the dedicated WIFI information.

When the accessible WIFI AP has been found in step525, in step526, the UE505proceeds to the next step, and generates a measurement report control message and reports the generated measurement report control message to the ENB510. The measurement report control message may include the pieces of information below.An SSID and a BSSID of the found WIFI network (or AP)The channel quality of the found WIFI network (or AP)Load information recognized from a beacon signal of the AP

In step527, the ENB510, which has received the control message, determines that the ENB510offloads some bearers of the UE505, and transmits an offload indication message to the UE505, in step530.

InFIGS. 4 and 5, when a predetermined condition is satisfied, the UE transmits a BSR to the ENB. The BSR is divided into a long BSR and a short BSR. The long BSR reports a buffer status of four Logical Channel Groups (LCGs), and the short BSR reports a buffer status of only one LCG. The LCG is a set of logical channels which are formed as a group by control performed by the ENB, and the logical channels usually have similar logical channel priorities. A buffer status of an LCG is the sum of buffer statuses of logical channels included in the LCG. A logical channel is one-to-one mapped to a radio bearer, and is a path between an RLC entity and a MAC entity. A buffer status of a LCG that the BSR reports is related to the amount of transmissible data stored in logical channels (or radio bearers) belonging to the LCG.

Referring toFIG. 6, data stored in a radio bearer may be largely divided into four types.Type A data605: data which has already been transmitted, of which successful reception has been confirmed by a reception side, and for which a discard timer does not expire. The confirmation of successful reception signifies the reception of a positive acknowledgement of the RLC layer. Typically, it is not necessary to store the type A data, but the type A data is not discarded but is stored in view of a need for retransmission and the like in a target cell during a handover in the LTE system. When the discard timer expires, the UE discards the relevant data. The discard timer is a timer that is driven when a PDCP Service Data Unit (SDU) arrives at a PDCP transmission buffer, and is used not to transmit but to discard data which is delayed during an excessively long time period and is not valid.Type B data610,620and630: data which has already been transmitted, but of which successful reception has not yet been confirmed by a reception side, and for which a discard timer does not expire. This type of data is data which needs subsequent retransmission thereof, or which needs to be stored until the discard timer expires although the data is not required.Type C data615and625: data which has already been transmitted, but of which retransmission is requested by a reception side and the retransmission is required, and for which a discard timer does not expire.Type D data630: data which has not yet been transmitted, and for which a discard timer does not expire.

For convenience of description, a situation is considered in which WIFI offload is applied to an EPS bearer x, the EPS bearer x is connected to a DRB x′, and a certain LCG x″ includes only the DRB x′.

At this time, the amount of type C data and that of type D data are reported for the LCG x″ by the BSR transmitted before WIFI offload is applied, namely, before step445or step545.

However, only the amount of type C data is reported for the LCG x″ by a BSR triggered immediately before the WIFI offload is initiated, or immediately after the WIFI offload is determined to be applied. This is for transmitting type D data through the WIFI network and transmitting type C data through the LTE network after the offload. It may be considered that the type C data is also transmitted/received through the WIFI network. However, in that case, a problem arises in that type B data620and630, which has a buffer arrival time point later than that of type C data, needs to be retransmitted through the WIFI network.

The UE triggers and transmits a BSR in which only the amount of the type C data is reflected, and thereby can prevent the ENB from allocating transmission resources to data which has already been offloaded.

When the UE comes back to LTE from WIFI, the UE delivers data, which is not yet transmitted through the WIFI network, to a transmission buffer of the DRB x′. When new data is generated in the transmission buffer of the DRB x′ as a result of the operation, the UE triggers and transmits a BSR to the ENB. At this time, the UE also reflects the amount of type D data in the BSR, and generates the BSR in which the amount of type D data is also reflected.

FIG. 7is a view explaining data delivery in a WLAN offload process.

When the UE offloads the EPS bearer x to WIFI, the UE may release or maintain a DRB to which the EPS bearer x is mapped. When the UE releases the DRB, if the UE subsequently comes back to the LTE network, the UE needs to newly establish a DRB, and it is desirable to maintain the DRB since the establishment of the new DRB signifies an additional exchange of control messages and a service interruption.

In order to maintain the DRB of the EPS bearer which has already been offloaded to WIFI as described above, the UE needs to request the ENB not to release the DRB although data is not transmitted/received through the relevant DRB. To this end, the UE transmits a predetermined control message to the ENB in step445and step545.

When WIFI offload is initiated, the UE establishes a MAC layer and a physical layer of WIFI. The UE stops an operation of a DRB720connected to the EPS bearer to be offloaded, and locally forwards type D data of the DRB to a transmission buffer of a WIFI bearer730. The UE also reestablishes a Traffic Flow Template (TFT)710, and thereby does not deliver data of the EPS bearer x to the DRB x′ but to WIFI. The TFT is a device that connects an IP flow to an appropriate DRB by using information, such as an IP 5-tuple. The UE establishes the TFT so as to deliver traffic of the offload EPS bearer (or traffic of an offload IP flow) to an appropriate DRB until the WIFI offload is initiated, and adjusts the TFT so as to deliver traffic of the offload EPS bearer to the WIFI bearer when the WIFI offload is initiated. Next, when the WIFI offload is terminated, the UE readjusts the TFT so as to again deliver traffic of the EPS bearer x to the DRB x′. When the WIFI offload is terminated, the UE locally forwards data in the WIFI bearer, which is not yet delivered, to the DRB x′.

FIG. 8is a flowchart illustrating a method for measuring a WLAN by a UE according to an embodiment of the present invention.

In step805, the UE reports WIFI-related capability of the UE to the ENB or the network.

A WIFI UE capability report may be initiated by a request from the ENB. For example, when the UE receives a UE capability enquiry control message indicating a WIFI-related capability report, the UE generates a UE capability information control message including UE information on WIFI offload support, and transmits the UE capability information control message to the ENB.

In step810, the UE receives a control message indicating WIFI measurement. In the control message, an SSID, channel information, and the like of WIFI are specified as measurement object information, and event C1 or event C2 are specified as measurement report configuration information. The control message may also include information related to a WIFI measurement initiation condition.

In step815, the UE performs WIFI measurement according to the control message. In performing the WIFI measurement, the UE may consider only dedicated WIFI information, or may consider the dedicated WIFI information and common WIFI information together.

When a predetermined event (e.g., event C1 or event C2) occurs in step820, the UE proceeds to step825, and generates a measurement result report message and transmits the measurement result report message to the ENB. The measurement report control message may include an SSID and a BSSID of an accessible WIFI network, of which channel quality is higher than or equal to a predetermined reference, channel quality information of the WIFI network, load information thereof, and the like. The ENB determines whether WIFI offload is performed, by using the measurement result report message. When it is determined that the WIFI offload is performed, the ENB delivers type D data of an offload bearer to a relevant AP. The ENB specifies the AP by using the SSID and the BSSID that the UE has reported.

FIG. 9is a flowchart illustrating a WLAN offload method of a user equipment according to an embodiment of the present invention.

In step910, the UE recognizes WIFI-related information and an LTE comeback condition. The information may be acquired through system information of a serving cell, may be acquired through a unicast RRC control message or a dedicate RRC control message which represents a one-to-one RRC control message, or may be acquired through a combination of the system information and the one-to-one RRC control message.

In step915, the UE determines whether a WIFI offload condition is satisfied while the UE transmits/receives data in the current serving cell. When the WIFI offload condition is satisfied, the UE proceeds to step920. The WIFI offload condition is satisfied when the ENB indicates offload to the UE or the UE finds an accessible WIFI network in a state where an offload bearer is established for the UE and the amount of data stored in the offload bearer is larger than or equal to a predetermined reference.

In step920, the UE determines a bearer to be offloaded. The UE may independently determine the bearer to be offloaded with reference to an offload policy acquired from a WIFI server. Alternatively, the ENB may determine the bearer to be offloaded, and may indicate the determined bearer to the UE.

In step925, the UE generates an RRC control message, which reports offload, and reports the generated RRC control message to the ENB. When a WIFI offload-related BSR generation condition is satisfied, the UE also generates a BSR, and transmits the BSR and the RRC control message together to the ENB.

In step930, in order to transmit/receive data through WIFI, the UE appropriately establishes a MAC layer entity and a PHY layer entity of WIFI. Then, the UE locally forwards a predetermined data (e.g., type D data) from among data stored in a transmission buffer of the offload bearer, to a transmission buffer of WIFI. The UE also establishes a TFT in order to change a delivery path of data of the offload bearer from LTE to WIFI. Specifically, the UE establishes the TFT so that the offload bearer may not be delivered to a relevant DRB of LTE but to a related transmission buffer of WIFI.

In step935, the UE transmits/receives data of the offload bearer through WIFI. At this time, the UE may transmit/receive data through both LTE and WIFI during a predetermined time period (e.g., until the transmission/reception of type C data is completed), and may transmit/receive type C data through LTE and may transmit/receive type D data through WIFI. Alternatively, the UE may transmit/receive both type C data and type D data through LTE, and may transmit/receive only new data through WIFI.

As a method for reducing the complexity of the UE, it may be considered that both type C data and type D data are transmitted/received through WIFI. When the offload is determined, the UE locally forwards, to the transmission buffer of WIFI, the type C data, the type D data, and type B data (e.g., as indicated by reference numerals620and630inFIG. 6) which lags in time behind the type C data, and discards type A data and type B data (e.g., as indicated by reference numerals610inFIG. 6), which precedes the type C data in time, in a transmission buffer. Next, when the transmission of the offload report control message is completed, the UE stops an operation of the offload DRB. The stop of an operation of a certain offload DRB implies that uplink data is not transmitted through the DRB and downlink data of the DRB is quietly discarded in the MAC layer and is not delivered through the relevant DRB even when the downlink data of the DRB is received.

In step940, the UE checks whether an LTE comeback condition is satisfied. When the LTE comeback condition is satisfied, the UE proceeds to step945, and releases the MAC entity and the PHY entity of WIFI and locally forwards type D data from among data stored in the transmission buffer of WIFI, to a transmission buffer of the offload DRB. At this time, the UE may deliver the type D data and type C data together. Then, the UE resumes an operation of the offload DRB.

In step950, the UE generates an offload comeback control message, and transmits the offload comeback control message to the ENB. When a WIFI offload-related BSR generation condition 2 is satisfied, the UE triggers/generates a regular BSR, and transmits the regular BSR to the ENB.

The WIFI offload-related BSR generation condition 2 is as follows.

[WIFI Offload-Related BSR Generation Condition 2]Comeback to an LTE network from a WLAN network; andData is stored in a buffer of an offload DRB.

Hereinafter, as another embodiment of the WLAN offload method according to the present invention, a method and an apparatus are proposed for performing a Discontinuous Reception (DRX) operation in order to reduce the battery consumption of the UE.

Second Embodiment

FIG. 10is a view explaining a DRX operation of a UE.

The DRX operation corresponds to a scheme in which the UE periodically turns on a receiver at predetermined time points and checks whether a scheduling is performed, thereby minimizing the power consumption of the UE. The operation in which the UE turns on the receiver and checks whether a scheduling is performed is expressed as “the UE is in an active time,” and the UE monitors a downlink control channel in the active time. A downlink control channel is referred to as a “Physical Downlink Control CHannel (PDCCH),” through which a downlink scheduling command, which is for allocating a downlink transmission resource and includes other pieces of control information necessary to receive downlink data, or an uplink scheduling command, which is for allocating an uplink transmission resource and includes other pieces of control information necessary to transmit uplink data, is transmitted. In the standards, the downlink scheduling command is referred to as a “downlink assignment” and the uplink scheduling command is referred to as an “uplink grant.” Hereinafter, the expression “reception of a downlink scheduling command or an uplink scheduling command by a UE” has an identical meaning to that of the reception of a downlink assignment or an uplink grant by the UE, and is used together with the expression “reception of a PDCCH by the UE.”

The downlink scheduling command or the uplink scheduling command is divided into a command for HARQ initial transmission and a command for HARQ retransmission. Hereinafter, a downlink or an uplink scheduling command for HARQ initial transmission is expressed as a downlink or an uplink initial transmission scheduling command, and a downlink or an uplink scheduling command for HARQ retransmission is expressed as a downlink or an uplink retransmission scheduling command.

The DRX operation is specified by defining a time point when the UE shifts to an active time and monitors a PDCCH and a time point when the UE shifts to a non-active time, stops monitoring the PDCCH, and turns off the receiver.

The UE includes an on-duration timer, an inactivity timer, a HARQ retransmission timer, and the like, and operates in an active time when any one of the timers is being driven.

The on-duration timer is driven during a predetermined time interval1205or1210at every DRX cycle1215.

The inactivity timer is driven whenever the UE receives a scheduling command indicating an initial transmission. For example, the inactivity timer is driven when the UE receives a downlink scheduling command indicating an initial transmission as indicated by reference numeral1220while the on-duration timer is driven. The inactivity timer is not re-driven even when a downlink scheduling command indicating a retransmission is received while the inactivity timer is driven.

Since a downlink data reception and an uplink data transmission are performed according to an HARQ scheme, the UE needs to receive a scheduling command for HARQ retransmission when an error remains in the data after the UE receives initial HARQ transmission or receives HARQ retransmission. To this end, the HARQ retransmission timer is defined in the UE. Whenever receiving downlink data, the HARQ retransmission timer is driven after the passage of a predefined time period1230and1235at a time point when the downlink data is received. The predefined time period is defined by a timer which is called a HARQ Round Trip Time (RTT) timer and has a predetermined length. When receiving a scheduling command indicating a retransmission as indicated by reference numeral1260, the HARQ retransmission timer is stopped.

Hereinafter, a problem will be described which arises due to an early stop of the HARQ retransmission timer during the DRX operation of the UE.

FIG. 11is a view explaining a problem caused by an early stop of the HARQ retransmission timer.

It is problematic that one HARQ retransmission timer is included per HARQ process and thus the HARQ retransmission timer inefficiently operates in a Multiple-Input Multiple-Output (MIMO) in which two Transport Blocks (TBs) are transmitted through one transmission wherein a TB is obtained by appending a Cyclic Redundancy Check (CRC) to a MAC PDU.

For example, TB1 and TB2 are transmitted/received in a certain HARQ process at a certain time point as indicated by reference numeral1305. When the two TBs both fail to be transmitted, the UE transmits a Negative Acknowledgement (NAK) for each of TB1 and TB2 as indicated by reference numeral1310.

When the HARQ retransmission timer is driven at a certain time point and the UE receives one of the two TBs, the UE stops driving the retransmission timer as indicated by reference numeral1315. At this time, the retransmission of the remaining TB is delayed until the HARQ retransmission timer is re-driven as indicated by reference numeral1320.

Hereinafter, an operation of the UE for solving the above-described problems according to an embodiment of the present invention will be described.

FIG. 12is a view explaining an operation for controlling a HARQ retransmission timer according to an embodiment of the present invention.

In order to solve the above-described problems, in an embodiment of the present invention, when the MIMO is driven, the HARQ retransmission timer is stopped after all TBs, which are not yet successfully received among TBs of a relevant HARQ process, are received.

For example, referring toFIG. 12, when TB1 and TB2 are simultaneously transmitted/received in a certain HARQ processor at a certain time point as indicated by reference numeral1405and the two TBs both fail to be transmitted, the UE transmits a NAK for each TB as indicated by reference numeral1410. Both TB1 and TB2 are stored in a buffer of the HARQ process.

In step1415, although the retransmission of TB1 is received, since the retransmission of TB2 is not yet received, namely, since another TB necessary to be retransmitted is stored in the relevant HARQ process, the UE does not stop the HARQ retransmission timer. At this time, the HARQ RTT timer is normally driven.

In step1420, when the retransmission of TB2 is received, retransmissions of TBs necessary to be retransmitted are all received while the HARQ retransmission timer is driven, and thus the UE stops the HARQ retransmission timer. At this time, the UE re-drives the HARQ RTT timer, which is already being driven, as indicated by reference numeral1425. This is for preventing the HARQ RTT timer from expiring when the HARQ retransmission timer is being driven. This is because when the above-described situation occurs, the UE cannot determine whether the UE needs to re-drive the HARQ retransmission timer or needs to maintain the HARQ retransmission timer as it is.

Hereinafter, the operation of the UE for controlling the HARQ retransmission timer, which has been described in detail, will be described in more detail.

FIG. 13is a flowchart illustrating an operation of a UE according to an embodiment of the present invention.

In step1505, the UE acquires DRX setting information. The DRX setting information may be received through a control message, such as a RRC connection reconfiguration. Also, the DRX setting information may include information on an onDurationTimer, a drx-InactivityTimer, a HARQ retransmission timer, a DRX cycle length, a drxStartOffset, and the like. In step1510, the UE starts a DRX operation. Specifically, the UE specifies a start subframe of the onDurationTimer by applying the DRX cycle length and the drxStartOffset to Equation 1 below.
[(SFN×10)+subframe number]modulo(DRX−Cycle)=(drxStartOffset)modulo(DRX−Cycle)  Equation 1

In Equation 1, a System Frame Number (SFN) is an integer between 0 and 1023, and is increased by 1 at every time interval of 10 ms.

Also, the UE maintains an active time while the onDurationTimer is at least driven, from the subframe. When a downlink assignment or an uplink grant indicating a new transmission is received during the time period, the active time is extended by the drx-InactivityTimer.

When receiving a downlink assignment for a certain HARQ process in step1515, the UE proceeds to step1520, and checks whether a HARQ RTT timer of the HARQ process is already being driven.

When the HARQ RTT timer of the HARQ process is already being driven, the UE proceeds to step1530, and re-drives the HARQ RTT timer in such a manner as to apply an initial value of the HARQ RTT timer. When the HARQ RTT timer of the HARQ process is not being driven, the UE proceeds to step1525, and drives the HARQ RTT timer.

When a HARQ retransmission timer of the relevant HARQ process is being driven, the UE proceeds to step1535, and determines whether the HARQ retransmission timer is stopped.

When the HARQ retransmission timer is not being driven, the UE stands by until a new downlink assignment is received, and returns to step1515.

In step1535, the UE checks whether all TBs, which are stored in the relevant HARQ process, namely, are not yet successfully decoded in the relevant HARQ process, are received while the timer is driven. When all of the TBs, which are stored in the relevant HARQ process, namely, are not yet successfully decoded in the relevant HARQ process, are received while the timer is driven, the UE proceeds to step1545, and stops the HARQ retransmission timer. In contrast, when any of the TBs, which are stored in the relevant HARQ process, namely, are not yet successfully decoded in the relevant HARQ process, is not received while the timer is driven, the UE proceeds to step1540, and does not stop the HARQ retransmission timer but continuously drives the HARQ retransmission timer.

The condition of step1535may be changed as described below.

When all of the TBs, which have not yet been successfully decoded when the timer is started, are received while the timer is driven, the UE proceeds to step1545. When a TB from among the TBs, which have not yet been successfully decoded when the timer is started, is not received while the timer is driven, the UE proceeds to step1540.

Third Embodiment

A Carrier Aggregation (CA) technique, in which multiple serving cells are aggregated for one UE in order to increase the transmission speed (data rate) of a UE, has been introduced.

Referring toFIG. 16, one ENB typically transmits and receives multiple carriers in different frequency bands. For example, when an ENB1605transmits a carrier1615having a downlink center frequency f1and a carrier having a downlink center frequency f31610, one UE transmits/receives data through one of the two carriers according to the related art. However, a UE1630having carrier aggregation capability may transmit/receive data by simultaneously using multiple carriers. The ENB1605may allocate more carriers to the UE1630, which has carrier aggregation capability, according to the situation, and thereby may increase the transmission speed of the UE1630. The aggregation of downlink carriers and uplink carriers, that one ENB transmits and receives as described above, is referred to as “CA.”

Terms to be frequently used in embodiments of the present invention will be described below.

When one cell includes one downlink carrier and one uplink carrier transmitted and received by one ENB in the conventional sense, the CA can be understood as a simultaneous transmission and reception of data through multiple cells by a UE. Through the CA, the maximum transmission speed increases in proportion to the number of aggregated carriers.

Hereinafter, in describing embodiments of the present invention, the reception of data through a certain downlink carrier or the transmission of data through a certain uplink carrier by a UE refers to the transmission/reception of data by the UE through a control channel and a data channel which are provided by a cell corresponding to a central frequency and a frequency band characterizing the carriers. In the present invention, particularly, the aggregation of carriers will be expressed as “setting of multiple serving cells,” and use is made of terms, such as a primary serving cell (hereinafter a “PCell”), a secondary serving cell (hereinafter an “SCell”), an activated serving cell, and the like. The terms have meanings used in an LTE mobile communication system as they are, and details of the terms can be found in TS 36.331, TS 36.321, and the like. In the present invention, also, use is made of terms, such as timeAlignmentTimer, Activation/Deactivation MAC Control Element (CE), C-RNTI MAC CE, and the like, and a more detailed description of the terms can be found in TS 36.321.

When an SCell is set or activated for the UE or the SCell is released or deactivated, the UE may reconfigure a radio frequency frontend. This includes a procedure of reconfiguring an RF filter bandwidth according to a situation in which the SCell is set or activated newly or released or deactivated, and the transmission/reception of data is stopped while the UE reconfigures the RF filter bandwidth. The RF bandwidth reconfiguration is characterized as follows.

When an SCell having a frequency band identical to that of a PCell is set, activated, released, or deactivated, the transmission/reception of data is stopped through the PCell during a predetermined time period, and the stop of the transmission/reception of data is expressed as “PCell interruption.”

Whether PCell interruption has occurred and the length of a period of the PCell interruption may be changed according to the processing capability of the UE and hardware performance.When the PCell and the SCell are set in different frequency bands, ### the RF bandwidth reconfiguration is not required, and the PCell interruption does not occur.When the PCell and the SCell are set in an identical frequency band, if the UE includes one or more RF apparatuses, and if the one or more RF apparatuses are used in the frequency band, the RF bandwidth reconfiguration is not required, and the PCell interruption does not occur.When the PCell and the SCell are set in the identical frequency band, and if only one RF apparatus is used in the frequency band, the RF bandwidth reconfiguration is required, and the PCell interruption occurs.

When the SCell is activated or deactivated, when the measurement of the SCell needs to be performed, when the SCell is activated or deactivated during the execution of the RF bandwidth reconfiguration, and before and after the UE performs the measurement of the SCell in an inactive state, the PCell interruption occurs. When the RF apparatus is reconfigured to include both the PCell and SCell in setting the SCell and when the RF apparatus is reconfigured to include only the PCell in releasing the SCell, the PCell interruption does not occur while the SCell is set.

The present invention proposes a method and an apparatus in which the UE reports to the ENB whether the PCell interruption is required and the ENB schedules the UE in view of whether the PCell interruption has occurred, a time point of the occurrence of the PCell interruption, and the like.

FIG. 17is a flowchart illustrating a method for scheduling a user equipment based on PCell interruption according to an embodiment of the present invention.

Referring toFIG. 17, in a mobile communication system including a UE1705, an ENB1710, and an MME1715, the UE1705is powered in step1720. In step1725, the UE1705searches for a cell, of which a radio signal is received, and a corresponding PLMN through a cell search process and the like, and determines a cell of a PLMN, through which the UE1705is to perform a registration process, on the basis of a result of the search.

In step1730, the UE1705performs an RRC connection setup process through the selected cell, and then transmits, to the MME1715, ATTACH REQUEST representing a control message requesting for registration. This message includes information, such as identifier of the UE1705.

Upon receipt of the ATTACH REQUEST message, the MME1715determines whether to accept the registration of the UE1705and, when it is determined to accept the registration of the UE1705, transmits Initial Context Setup Request representing a control message to the serving ENB1710of the UE1705, in step1735. When the MME1715has capability information of the UE1705, the MME1715includes the capability-related information of the UE1705in the control message, and transmits the control message including the capability-related information of the UE1705; however, the MME1715does not have the capability information of the UE1705in the initial registration process, and thus the control message does not include the capability-related information of the UE1705.

When the ENB1710receives the Initial Context Setup Request message which does not include the capability information of the UE1705, the ENB1710transmits, to the UE1705, a control message called UE CAPABILITY ENQUIRY, in step1740. This message instructs the UE1705to report the capability, and requires capability information on particular Radio Access Technology (RAT) of the UE1705by using a parameter called RAT type. When the UE1705is performing the process in the LTE network, the RAT type is set to Evolved Universal Terrestrial Radio Access (EUTRA). When there is another wireless network (e.g., a UMTS network) around the ENB1710, the ENB1710may require the UMTS-related capability information of the UE1705by adding UTRA to the RAT type in preparation for a subsequent handover and the like.

When receiving the UE CAPABILITY ENQUIRY control message, the UE1705generates UE CAPABILITY INFORMATION including its capability information on the wireless technology indicated by the RAT type. This control message includes one or more pieces of band combination information for each band combination that the UE1705supports. The band combination information indicates a CA combination supported by the UE1705, and the ENB1710sets appropriate CA for the UE1705by using the band combination information. The control message also includes the information (PCell interruption information) indicating whether the UE1705needs the PCell interruption for a predetermined band combination. The UE1705transmits a UE CAPABILITY INFORMATION message to the ENB1710in step1745.

The ENB1710transmits a UE CAPABILITY INFO INDICATION message to the MME1715in order to report the capability information of the UE1705included in the UE CAPABILITY INFORMATION message to the MME1715, in step1750. The ENB1710also appropriately reconfigures the UE1705with reference to a traffic status, a channel status, and the like of the UE1705on the basis of the capability information reported by the UE1705. For example, the ENB1710sets an additional SCell for the UE1705or configures a measurement gap in such a manner as to instruct the UE1705to measure another frequency, in step1755.

The ENB1710performs scheduling of the PCell in view of the PCell interruption, and the UE1705performs RF bandwidth reconfiguration so as to cause PCell interruption to occur during a predetermined time period, in step1760.

FIG. 18is a flowchart illustrating a first embodiment of an operation of a user equipment in a method for scheduling the user equipment based on PCell interruption according to an embodiment of the present invention.

Referring toFIG. 18, in step1805, the UE reports its capability to the ENB. At this time, the UE reports frequency bands, that the UE supports, and a frequency band combination supporting carrier aggregation. When the frequency band combination is an intra-band combination, the UE reports a need for RF bandwidth reconfiguration.

FIG. 19illustrates information on a band combination and a measurement capability parameter which are included in capability information of a UE.

Hereinafter, a case is considered in which the UE supports a frequency band x and a frequency band y and supports CA as described below. Table 1 below shows a frequency band and the number of serving cells for each frequency band combination.

TABLE 1Band combinationFrequency band combination 1 1910One serving cell in band xFrequency band combination 2 1915Two serving cells in band xFrequency band combination 3 1920One serving cell in band yFrequency band combination 4 1925One serving cell in band x and Oneserving cell in band y

The UE capability report message includes 1-bit information, which indicates whether the PCell interruption has occurred, in frequency band combination information satisfying the condition below.A band combination in which at least two serving cells are set in one band.

According to the above-described embodiment of the present invention, two serving cells are set for the UE in the band x of the frequency band combination21915, and thus the UE includes PCell interruption information1930in the capability information. When the UE applies one or more RF apparatuses to the band x, the UE sets the PCell interruption information to “no.” In contrast, when the UE applies only one RF apparatus to the band x, the UE sets the PCell interruption information to “yes.” In an embodiment of the present invention, the UE may report whether the PCell interruption is required, by using other pieces of information, which already exist, instead of explicitly including the PCell interruption information. For example, if the UE sets an interFreqNeedForGaps bit, which satisfies a predetermined condition, to “no,” it implies that the PCell interruption does not occur in a predetermined band.

As described above, the capability information of the UE includes SupportedBandCombination (hereinafter “SBC”)1905, which represents information on a band combination supported by the UE, and MeasParameters1935representing a measurement capability parameter of the UE.

The SBC1905includes BandCombinationParameters (hereinafter “BCP”)1910,1915,1920and1925representing one or more band combination parameters. The BCP1910,1915,1920and1925is information on the respective band combinations supported by the UE.

The BCP1910,1915,1920and1925includes BandParameters (hereinafter “BP”) representing one or more band parameters. A BP includes FreqBandIndicator representing information indicating a band, bandParametersDL (hereinafter “BPDL”) representing a downlink band parameter, and bandParametersUL (hereinafter “BPUL”) representing an uplink band parameter. A BPDL again includes bandwidthClass representing a bandwidth class indicating the number of serving cells supported by a relevant band, and antenna capability information. Bandwidth class A represents capability which corresponds to an entire bandwidth going up to a maximum of 20 MHz and can be used to set one serving cell. Bandwidth class B represents capability which can be used to set two serving cells and corresponds to an entire bandwidth going up to a maximum of 20 MHz. Bandwidth class C represents capability which can be used to set two serving cells and corresponds to an entire bandwidth going up to a maximum of 40 MHz.

Measurement capability information of the UE includes BandInfoEUTRA (hereinafter “BI”)1940and1950representing pieces of band information, the number of which is identical to that of BCP1910,1915,1920and1925. One BI1940and1950one-to-one corresponds to one BCP1910,1915,1920, and1925in order of including the relevant pieces of information. Specifically, the first BI1940corresponds to the first BCP1910, and the second BI1945corresponds to the second BCP1915. The BI1940and1950includes interFreqBAndList (hereinafter “IFBL”), which is information indicating whether a measurement gap is required during inter-frequency measurement for EUTRA frequency bands, and interRAT-BandList which is information indicating whether a measurement gap is required during the measurement of frequency bands of different RATs, such as UTRA.

The IFBL includes interFreqNeedForGaps (hereinafter “IFNG”)1950and1955representing as many measurement gap need indicators as the number of EUTRA frequency bands supported by the UE. The IFNG1950and1955indicates whether a measurement gap is required in order for EUTRA frequency bands included in bandListEUTRA representing an EUTRA frequency band list supported by the IFNG1950and1955. For example, when the UE has included a band X and a band Y in the bandListEUTRA, the first IFNG1950indicates a need for a measurement gap for the band X, and the second IFNG1955indicates a need for a measurement gap for the band Y. Specifically, when the first IFNG1950is set for the related BCP1910, the first IFNG1950indicates whether a measurement gap is required in performing, by the UE, inter-frequency measurement for the band X. The second IFNG1955indicates whether a measurement gap is required in performing inter-frequency measurement for the band Y.

Hereinafter, a description will be made of a method in which the UE implicitly reports PCell interruption information on the predetermined BCP1910,1915,1920and1925.

When the UE is set to use one or more RF apparatuses in a predetermined frequency band, the UE reports that PCell interruption is not required for the frequency band. At this time, the UE reports that the PCell interruption is not required by setting an IFNG, which corresponds to the frequency band among IFNGs of a BI corresponding to a BCP (BCP which is not CA) in which only one serving cell is set for the frequency band, not to need a measurement gap. For example, when an SCell of the same frequency band as a frequency band x is set, released, activated, deactivated, or measured for the UE for which a PCell is set in the frequency band x, the UE represents that the PCell interruption is not required, by determining that the IFNG1950for the frequency band x is “no” at the BI1940corresponding to the BCP1910, in which only one serving cell is being set in the frequency band x, in order to represent that the PCell interruption does not occur.

In other words, when the SCell is set, released, activated, deactivated, or measured in the frequency band in which the PCell is set, if the UE reports its capability as in Table 2 below, the UE uses a separate RF apparatus in the PCell and the SCell, and the PCell interruption does not occur.

TABLE 2When only one serving cell is set for the UE and the serving cell is setin the frequency band, a measurement gap is not required in performinginter-frequency measurement for the frequency band.

In step1810, the UE receives a control message which sets at least one SCell. In step1815, the UE checks whether a frequency band of the SCell belongs to and is adjacent to a frequency band identical to that of the serving cell (e.g., a PCell), which is already set.

When the condition is not satisfied, the UE proceeds to step1820, and does not perform RF bandwidth reconfiguration but determines that the PCell interruption is not allowed and performs an operation. An operation of the UE in a case where it is determined that the PCell interruption is not allowed is described in Table 3 below, and an operation of the UE in a case where it is determined that the PCell interruption is allowed is described in Table 4 below.

TABLE 3The ENB may schedule the transmission/reception of data for the UEduring a time period which may be specified by the PCell interruptionand, since the ENB expects the UE to perform uplink transmission, theUE monitors a PDCCH during the time period, and performs thescheduled uplink transmission.

TABLE 4The ENB may not schedule the transmission/reception of data for the UEduring a time period which may be specified by the PCell interruptionand, since the ENB expects the UE not to perform uplink transmission,the UE performs RF bandwidth reconfiguration during the time periodwhich may be specified by the PCell interruption. After completing theRF bandwidth reconfiguration, the UE resumes PDCCH monitoring andthe execution of scheduled uplink transmission.

The time period which may be specified by the PCell interruption is, for example, a time period between n+m1 and n+m1+k1 when a time point of receiving a control message, which sets an SCell, is a subframe n. k1 needs to be defined so that all types of UEs may reconfigure a radio frequency frontend, and may be equal to, for example, 5. m1 needs to be defined so that all types of UEs may receive and interpret the control message and may recognize the fact that it is necessary to reconfigure the radio frequency frontend, and may be equal to, for example, 20.

When a newly-set SCell is set in a frequency band identical to that of the PCell and frequency bands of the two serving cells are adjacent to each other, the UE proceeds to step1825, and checks whether the condition shown in Table 5 below is satisfied.

TABLE 5When only one serving cell is set in a frequency band in which thePCell and the SCell are set, it is reported that a measurement gapis not required to perform inter-frequency measurement for theidentical frequency band. Alternatively, it is reported that ameasurement gap is not required, when inter-frequency measurementis performed for an adjacent cell of the frequency band inBandInfoEUTRA corresponding to the setting of non-CA for thefrequency band in which the PCell and the SCell are set.

When the condition shown in Table 5 is satisfied, the UE proceeds to step1830. When the condition shown in Table 5 is not satisfied, the UE proceeds to step1835. Proceeding to step1830signifies that the ENB determines that the PCell interruption does not occur, and the UE causes an RF apparatus of the PCell not to be reconfigured by configuring a separate RF apparatus for the SCell. Then, the UE performs the operation shown in Table 3.

Proceeding to step1835signifies that the ENB determines that the PCell interruption occurs, and the UE reconfigures an RF bandwidth during a predetermined time period, and causes the PCell interruption to occur within the predetermined time period.

FIG. 20is a flowchart illustrating a second embodiment of an operation of a UE in a method for scheduling the user equipment based on a PCell interruption according to an embodiment of the present invention.

Details of step2005illustrated inFIG. 20are the same as described in step1805illustrated inFIG. 18.

In step2010, the UE receives an Activation/Deactivation MAC CE (hereinafter “A/D MAC CE”) in which a bit for at least one SCell is set to 1.

The A/D MAC CE is a MAC layer control message activating or deactivating SCells which are set for the UE, and includes a MAC sub-header and a payload.

The MAC sub-header includes a Logical Channel ID (LCID) representing the type of a payload, an E bit representing whether another MAC sub-header exists, and the like.

FIG. 21is a view illustrating a configuration of a bitmap in a payload.

Referring toFIG. 21, the payload is a 1-byte bitmap, wherein a C7 bit2105represents a state of a serving cell having an SCell index of 7 (hereinafter a serving cell having an SCell index of x is expressed as an SCell x), a C4 bit2110represents a state of an SCell 4, and a C1 bit2115represents a state of an SCell 1. When the bit is set to 1, if the relevant SCell is already in an active state, the UE maintains the active state. If the relevant SCell is in an inactive state, the UE transitions to the active state. When the bit is set to zero, if the relevant SCell is in the active state, the UE transitions to the inactive state. If the relevant SCell is already in the inactive state, the UE maintain the inactive state.

In step2015, the UE checks whether an SCell having a bit set to 1 is an already-activated SCell. When the SCell is an already-activated SCell, the UE proceeds to step2050. When the SCell is an SCell which is not yet activated, the UE proceeds to step2020.

In step2020, the UE checks whether a frequency band of the SCell belongs to a frequency band identical to that of an already-set serving cell (e.g., a PCell) and is adjacent to the frequency band of the PCell.

When the frequency band of the SCell is not the already-set serving cell, the UE proceeds to step2025. When the frequency band of the SCell is the already-set serving cell, the UE proceeds to step2030.

In step2025, the UE starts the transmission of a CQI to the activated SCell from n+x1.

In step2030, the UE determines whether the condition shown in Table 5 is satisfied. When the condition is satisfied, the UE does not need RF bandwidth reconfiguration, and proceeds to step2025. When the condition is not satisfied, the UE needs the RF bandwidth reconfiguration, and proceeds to step2035.

In step2035, the UE determines that PCell interruption is allowed during a predetermined time period, for example, between a subframe n+m2 and a subframe n+m2+k2, and performs RF reconfiguration during the predetermined time period. m2 is a value defined to enable the HARQ feedback transmission of an A/D MAC CE, and is equal to, for example, 5. k2 may have a value identical to that of k1.

In step2040, the UE starts the transmission of a CQI to the SCell from a predetermined subframe (e.g., a subframe n+m2+k2+1), and resumes the transmission of a CQI to the PCell.

In step2045, the UE determines whether the condition shown in Table 6 below is satisfied. The condition shown in Table 6 below is used for the UE to specify an activation operation completion final time point for the SCell. When a certain SCell is activated, the UE performs an operation, such as PDCCH-monitoring of the SCell, Sounding Reference Signal (SRS) transmission, and the like. In order to start the operation, an additional reconfiguration operation is required to transmit/receive an SCell signal after RF bandwidth reconfiguration. A time period required for the additional reconfiguration operation may be changed according to the capability of the UE. The standards define a minimum requirement (i.e., a final time point) with which the UE needs to comply. When the condition shown in Table 6 below is satisfied, the UE may more quickly complete the reconfiguration and a maximum activation delay applied at this time is referred to as “activation delay 1 (ad1).” When the condition shown in Table 6 below is not satisfied, a longer time period may be required to complete the reconfiguration, and a maximum activation delay applied at this time is referred to as “activation delay 2 (ad2).”

TABLE 6When an A/D MAC CE which activates an SCell is received in a subframen, a measurement result report control message including a result ofmeasuring an SCell is transmitted within a previous predeterminedtime period with the subframe n as a reference. Specifically, thetransmission of a MAC PDU including a measurement result reportcontrol message is started between a subframe n-y and the subframe n.y may be defined as a time period during which a result of measurementis valid when the UE performs the measurement of an SCell in theinactive state. Valid measurement results can be produced when therenormally exist measurement samples obtained by performing measurementfive times, and since the UE performs measurement once at every DRXcycle or at every time period called measCycleSCell, y may be definedas a larger value among the DRX cycle multiplied by 5 andmeasCycleSCell multiplied by 5.

When the condition shown in Table 6 is satisfied, the UE proceeds to step2055, and drives an sCellDeactivationTimer at n+x1 and triggers a Power Headroom Report (PHR) at n+w1. w1 is an integer which specifies a subframe related to a time point of completing the activation of the SCell, and has a maximum value of ad1. In other words, the UE triggers the PHR at the time point of completing the activation of the SCell, and the activation completion needs to be completed until n+ad1 at the latest.

When the condition shown in Table 6 is not satisfied, the UE proceeds to step2060, and drives the sCellDeactivationTimer at n+x1 and triggers a PHR at n+w2. w2 is an integer which specifies a subframe related to a time point of completing the activation of the SCell, and has a maximum value of ad2. In other words, the UE triggers the PHR at the time point of completing the activation of the SCell, and the activation completion needs to be completed until n+ad2 at the latest.

In step2050, the UE re-drives the sCellDeactivationTimer at n+x1 and triggers the PHR.

The sCellDeactivationTimer deactivates an SCell through which data is not transmitted/received during a predetermined time period, and one sCellDeactivationTimer is configured for each SCell. When an SCell is activated, the UE drives the timer, and re-drives the timer whenever a downlink assignment or an uplink grant for an SCell is received, or whenever the SCell is re-activated.

A PHR is control information that the UE reports the current available transmission output to the ENB. When an SCell is activated, the UE reports a PHR to the ENB, and reports a transmission output situation of the an SCell to the ENB.

SCell activation types may be divided into three types as follows.SCell activation 1: when an A/D MAC CE indicating activation to an already-activated SCell is receivedSCell activation 2: when an A/D MAC CE indicating activation to an deactivated SCell is received and the condition shown in Table 6 is satisfiedSCell activation 3: when an A/D MAC CE indicating activation to an deactivated SCell is received and the condition shown in Table 6 is not satisfied

An A/D MAC CE may include activation commands for activating multiple SCells, and thus one A/D MAC CE may cause the multiple types of activations to simultaneously occur.

At this time, the UE triggers a PHR only once, and a trigger time point is a time point when the activation of an SCell is completed, wherein the activation of the SCell is completed latest. For example, when an A/D MAC CE has been received in a subframe n and only SCell activation 1 occurs with respect to the A/D MAC CE, the UE triggers a PHR at n+x1. When the A/D MAC CE causes SCell activation 1 to occur in a predetermined SCell and causes SCell activation 2 to occur in another SCell, the UE triggers a PHR after activations of all the SCells are completed, and triggers the PHR until at least n+ad1. When the A/D MAC CE causes SCell activation 3 to occur, the UE triggers a PHR after activations of all the SCells are completed, and triggers the PHR until at least n+ad2.

FIG. 14is a block diagram illustrating a configuration of a UE according to an embodiment of the present invention.

Referring toFIG. 14, the UE according to an embodiment of the present invention includes a transmission/reception unit1005, a control unit1010, a multiplexing/demultiplexing unit1020, a control message processing unit1035, a radio bearer apparatus1025,1030and1033, an offload control unit1040, a WLAN apparatus1045, a TFT1050, an IP layer1055, and the like.

The transmission/reception unit1005receives data and predetermined control signals through a downlink channel of a serving cell and transmits data and predetermined control signals through an uplink channel. When multiple serving cells are set, the transmission/reception unit1005transmits and receives data and control signals through the multiple serving cells.

The multiplexing/demultiplexing unit1020multiplexes data of the radio bearer apparatus1025,1030and1033, or demultiplexes data received from the transmission/reception unit1005and delivers the demultiplexed data to an appropriate radio bearer apparatus.

The radio bearer apparatus1025,1030and1033includes a PDCP entity and an RLC entity, and processes a packet delivered from the TFT1050.

The control message processing unit1035is an RRC layer entity, and processes a control message received from the ENB and performs a necessary operation. For example, the control message processing unit1035receives a RRC control message, and delivers WIFI-related information to the control unit and the offload control unit1010.

The control unit1010controls the transmission/reception unit1005and the multiplexing/demultiplexing unit1015to identify the scheduling command (e.g., uplink grants) received by the transmission/reception unit1005and to perform uplink transmission by using appropriate transmission resource at an appropriate time point, and controls a DRX.

The offload control unit1040performs a control operation related to all procedures for offload. More particularly, the offload control unit1040performs a required control operation related to a UE operation illustrated inFIG. 4,FIG. 5,FIG. 7,FIG. 8,FIG. 9, and the like. Although not illustrated in the drawings for convenience, the offload control unit1045may be connected to the control unit1010, the control message processing unit1035, the radio bearer apparatus1025,1030and1033, the TFT1050, and the like.

According to predetermined criteria, the TFT1050delivers IP packets delivered by the IP layer to an appropriate radio bearer apparatus, or to the WLAN apparatus.

FIG. 15is a block diagram illustrating a configuration of an ENB device according to an embodiment of the present invention.

Referring toFIG. 15, the ENB device according to an embodiment of the present invention includes a transmission/reception unit1105, a control unit1110, a multiplexing/demultiplexing unit1120, a control message processing unit1135, a radio bearer apparatus1125,1130and1133, a scheduler1115, a downlink traffic handler1140, and an offload control unit1145.

The transmission/reception unit1105transmits data and predetermined control signals through a downlink carrier, and receives data and predetermined control signals through an uplink carrier.

The multiplexing/demultiplexing unit1120multiplexes data of the radio bearer apparatus1125,1130and1133, or demultiplexes data received by the transmission/reception unit1105and delivers the demultiplexed data to the appropriate higher layer processing unit1125and1130or control unit1110.

The control message processing unit1135processes a control message transmitted by the UE and performs a necessary operation, or generates a control message to be transmitted to the UE and delivers the generated control message to the lower layer.

The radio bearer apparatus1125,1130and1133configures data delivered by an S-GW or another ENB into an RLC PDU, and delivers the RLC PDU to the multiplexing/demultiplexing unit1120, or configures an RLC PDU delivered by the multiplexing/demultiplexing unit1120into a PDCP SDU, and delivers the PDCP SDU to an S-GW or another ENB.

The scheduler1115allocates transmission resource to the UE at an appropriate time point in view of a buffer status, a channel status, and the like of the UE, and allows the transmission/reception unit1105to process a signal received from the UE, or to transmit a signal to the UE.

The control unit1110performs all control operations for transmitting/receiving data in the LTE network and a DRX-related control operation.

The offload control unit1145performs a control operation related to all procedures for offload. More particularly, the offload control unit1145performs an operation that the ENB needs to perform in relation to a UE operation illustrated inFIG. 4,FIG. 5,FIG. 7,FIG. 8,FIG. 9, and the like, and performs a control operation required for an ENB operation illustrated inFIGS. 4 to 9.

According to the control of the offload control unit1145, the downlink traffic handler1140delivers a downlink PDCP SDU to the appropriate the radio bearer apparatus1125,1130and1133, or to a WLAN AP.