Method and apparatus for selecting carrier in wireless communication system

A method for selecting a carrier in a wireless communication system is provided. A home eNodeB (HeNB) receives a carrier information response message as a response of the carrier information request message, and selects a primary cell (PCell) of the HeNB based on the received information on carriers used by the pico eNB. The carrier information response message includes the information on carriers used by a pico eNB.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to wireless communication, and more particularly, to a method and apparatus for selecting a carrier in a wireless communication system.

2. Related Art

FIG. 1shows network structure of an evolved universal mobile telecommunication system (E-UMTS). The E-UMTS may be also referred to as an LTE system. The communication network is widely deployed to provide a variety of communication services such as voice over internet protocol (VoIP) through IMS and packet data.

As illustrated inFIG. 1, the E-UMTS network includes an evolved UMTS terrestrial radio access network (E-UTRAN), an evolved packet core (EPC) and one or more user equipment. The E-UTRAN may include one or more evolved NodeB (eNB)20, and a plurality of user equipment (UE)10. One or more E-UTRAN mobility management entity (MME)/system architecture evolution (SAE) gateways (S-GW)30may be positioned at the end of the network and connected to an external network.

As used herein, “downlink” refers to communication from eNB20to UE10, and “uplink” refers to communication from the UE to an eNB. UE10refers to communication equipment carried by a user and may be also referred to as a mobile station (MS), a user terminal (UT), a subscriber station (SS) or a wireless device.

An eNB20provides end points of a user plane and a control plane to the UE10. MME/S-GW30provides an end point of a session and mobility management function for UE10. The eNB and MME/S-GW may be connected via an S1 interface.

The eNB20is generally a fixed station that communicates with a UE10, and may also be referred to as a base station (BS) or an access point. One eNB20may be deployed per cell. An interface for transmitting user traffic or control traffic may be used between eNBs20.

The MME provides various functions including non-access stratum (NAS) signaling to eNBs20, NAS signaling security, access stratum (AS) security control, Inter core network (CN) node signaling for mobility between 3GPP access networks, Idle mode UE reachability (including control and execution of paging retransmission), tracking area list management (for UE in idle and active mode), packet data network (PDN) GW and serving GW selection, MME selection for handovers with MME change, serving GPRS support node (SGSN) selection for handovers to 2G or 3G 3GPP access networks, roaming, authentication, bearer management functions including dedicated bearer establishment, support for public warning system (PWS) (which includes earthquake and tsunami warning system (ETWS) and commercial mobile alert system (CMAS)) message transmission. The S-GW host provides assorted functions including per-user based packet filtering (by e.g. deep packet inspection), lawful interception, UE internet protocol (IP) address allocation, transport level packet marking in the downlink, UL and DL service level charging, gating and rate enforcement, DL rate enforcement based on APN-AMBR. For clarity MME/S-GW30will be referred to herein simply as a “gateway,” but it is understood that this entity includes both an MME and an SAE gateway.

A plurality of nodes may be connected between eNB20and gateway30via the S1 interface. The eNBs20may be connected to each other via an X2 interface and neighboring eNBs may have a meshed network structure that has the X2 interface.

FIG. 2shows architecture of a typical E-UTRAN and a typical EPC.

FIG. 3shows a user-plane protocol and a control-plane protocol stack for the E-UMTS.

FIG. 3(a) is block diagram depicting the user-plane protocol, andFIG. 3(b) is block diagram depicting the control-plane protocol. As illustrated, the protocol layers may be divided into a first layer (L1), a second layer (L2) and a third layer (L3) based upon the three lower layers of an open system interconnection (OSI) standard model that is well known in the art of communication systems.

The physical layer, the L1, provides an information transmission service to an upper layer by using a physical channel. The physical layer is connected with a medium access control (MAC) layer located at a higher level through a transport channel, and data between the MAC layer and the physical layer is transferred via the transport channel. Between different physical layers, namely, between physical layers of a transmission side and a reception side, data is transferred via the physical channel.

The MAC layer of the L2 provides services to a radio link control (RLC) layer (which is a higher layer) via a logical channel. The RLC layer of the L2 supports the transmission of data with reliability. It should be noted that the RLC layer illustrated inFIGS. 3(a) and3(b) is depicted because if the RLC functions are implemented in and performed by the MAC layer, the RLC layer itself is not required. A packet data convergence protocol (PDCP) layer of the L2 performs a header compression function that reduces unnecessary control information such that data being transmitted by employing IP packets, such as IPv4 or IPv6, can be efficiently sent over a radio (wireless) interface that has a relatively small bandwidth.

A radio resource control (RRC) layer located at the lowest portion of the L3 is only defined in the control plane and controls logical channels, transport channels and the physical channels in relation to the configuration, reconfiguration, and release of the radio bearers (RBs). Here, the RB signifies a service provided by the L2 for data transmission between the terminal and the UTRAN.

As illustrated inFIG. 3(a), the RLC and MAC layers (terminated in an eNB20on the network side) may perform functions such as scheduling, automatic repeat request (ARQ), and hybrid automatic repeat request (HARQ). The PDCP layer (terminated in eNB20on the network side) may perform the user plane functions such as header compression, integrity protection, and ciphering.

As illustrated inFIG. 3(b), the RLC and MAC layers (terminated in an eNodeB20on the network side) perform the same functions for the control plane. As illustrated, the RRC layer (terminated in an eNB20on the network side) may perform functions such as broadcasting, paging, RRC connection management, RB control, mobility functions, and UE measurement reporting and controlling. The NAS control protocol (terminated in the MME of gateway30on the network side) may perform functions such as a SAE bearer management, authentication, LTE_IDLE mobility handling, paging origination in LTE_IDLE, and security control for the signaling between the gateway and UE10.

The RRC state may be divided into two different states such as a RRC_IDLE and a RRC_CONNECTED. In RRC_IDLE state, the UE10may receive broadcasts of system information and paging information while the UE specifies a discontinuous reception (DRX) configured by NAS, and the UE has been allocated an identification (ID) which uniquely identifies the UE in a tracking area and may perform PLMN selection and cell re-selection. Also, in RRC_IDLE state, no RRC context is stored in the eNB.

In RRC_SONNECTED state, the UE10has an E-UTRAN RRC connection and a context in the E-UTRAN, such that transmitting and/or receiving data to/from the network (eNB) becomes possible. Also, the UE10can report channel quality information and feedback information to the eNB.

In RRC_SONNECTED state, the E-UTRAN knows the cell to which the UE10belongs. Therefore, the network can transmit and/or receive data to/from UE10, the network can control mobility (handover and inter-radio access technologies (RAT) cell change order to GSM EDGE radio access network (GERAN) with network assisted cell change (NACC)) of the UE, and the network can perform cell measurements for a neighboring cell.

In RRC_IDLE state, the UE10specifies the paging DRX cycle. Specifically, the UE10monitors a paging signal at a specific paging occasion of every UE specific paging DRX cycle.

The paging occasion is a time interval during which a paging signal is transmitted. The UE10has its own paging occasion.

A paging message is transmitted over all cells belonging to the same tracking area.

If the UE10moves from one tracking area to another tracking area, the UE will send a tracking area update message to the network to update its location.

FIG. 4shows an example of structure of a physical channel.

The physical channel transfers signaling and data between layer L1 of a UE and eNB. As illustrated inFIG. 4, the physical channel transfers the signaling and data with a radio resource, which consists of one or more sub-carriers in frequency and one more symbols in time.

One sub-frame, which is 1 ms in length, consists of several symbols. The particular symbol(s) of the sub-frame, such as the first symbol of the sub-frame, can be used for downlink control channel (PDCCH). PDCCHs carry dynamic allocated resources, such as PRBs and modulation and coding scheme (MCS).

A transport channel transfers signaling and data between the L1 and MAC layers. A physical channel is mapped to a transport channel.

Downlink transport channel types include a broadcast channel (BCH), a downlink shared channel (DL-SCH), a paging channel (PCH) and a multicast channel (MCH). The BCH is used for transmitting system information. The DL-SCH supports HARQ, dynamic link adaptation by varying the modulation, coding and transmit power, and both dynamic and semi-static resource allocation. The DL-SCH also may enable broadcast in the entire cell and the use of beamforming. The PCH is used for paging a UE. The MCH is used for multicast or broadcast service transmission.

Uplink transport channel types include an uplink shared channel (UL-SCH) and random access channel(s) (RACH). The UL-SCH supports HARQ and dynamic link adaptation by varying the transmit power and potentially modulation and coding. The UL-SCH also may enable the use of beamforming. The RACH is normally used for initial access to a cell.

The MAC sublayer provides data transfer services on logical channels. A set of logical channel types is defined for different data transfer services offered by MAC. Each logical channel type is defined according to the type of information transferred.

Logical channels are generally classified into two groups. The two groups are control channels for the transfer of control plane information and traffic channels for the transfer of user plane information.

Traffic channels are used for the transfer of user plane information only. The traffic channels provided by MAC include a dedicated traffic channel (DTCH) and a multicast traffic channel (MTCH). The DTCH is a point-to-point channel, dedicated to one UE for the transfer of user information and can exist in both uplink and downlink. The MTCH is a point-to-multipoint downlink channel for transmitting traffic data from the network to the UE.

Uplink connections between logical channels and transport channels include a DCCH that can be mapped to UL-SCH, a DTCH that can be mapped to UL-SCH and a CCCH that can be mapped to UL-SCH. Downlink connections between logical channels and transport channels include a BCCH that can be mapped to BCH or DL-SCH, a PCCH that can be mapped to PCH, a DCCH that can be mapped to DL-SCH, and a DTCH that can be mapped to DL-SCH, a MCCH that can be mapped to MCH, and a MTCH that can be mapped to MCH.

The specification of a home eNB (HeNB) is currently ongoing in 3GPP LTE. It may be referred to Paragraph 4.6.1 of 3GPP (3rd generation partnership project) TS 36.300 V 10.2.0 (2010-12). The HeNB is a small base station designed for use in residential or small business environment. The HeNB may be a femto cell. The HeNB is short range about tens of meter, installed by the consumer for better indoor voice and data reception.

Referring toFIG. 5, a HeNB50may be connected with an EPC60through an S1 interface. A HeNB gateway (55, HeNB GW) may be deployed between the HeNB50and the EPC60to allow the S1 interface and to scale to support a large number of HeNBs. The HeNB GW55serves as a concentrator for the C(control)-Plane, specifically the S1-MME interface. The S1-U interface from the HeNB50may be terminated at the HeNB GW55, or a direct logical U(user)-Plane connection between HeNB50and S-GW56may be used. The S1 interface may be defined as the interface between the HeNB GW55and the core network, between the HeNB50and the HeNB GW55, between the HeNB50and the core network, and between the eNB and the core network. Also, the HeNB GW55appears to the MME as an eNB. The HeNB GW55appears to the HeNB as an MME. The S1 interface between the HeNB50and the EPC60is the same whether the HeNB50is connected to the EPC60via a HeNB GW55or not.

Inter-cell interference coordination (ICIC) has the task to manage radio resources such that inter-cell interference is kept under control. The ICIC mechanism includes a frequency domain component and time domain component. The preferred ICIC method may be different in the uplink and downlink.

Meanwhile, the 3GPP LTE rel-8 (hereinafter, rel-8) and the 3GPP LTE rel-10 (hereinafter, rel-10) ICIC mechanisms have been defined for intra-carrier cases. The rel-8 ICIC mechanism is designed for macro cell-only scenario. The Rel-10 ICIC mechanism is designed for scenarios of a macro cell and a femto cell as well as a macro cell and a pico cell. Now for 3GPP LTE rel-11, the method of autonomous interference management in a heterogeneous network (HetNet) with the mixture of different cell types and without tight synchronization requirements is regarded as a next step of further development for the optimal use of available frequency assets.

It is expected that the HetNet deployments in 3GPP LTE rel-11 basically assume that multiple carriers are used and carrier aggregation is supported. On the other hand, 3GPP LTE rel-10 uses single carrier. Therefore, when the ICIC mechanism is applied to the HetNet deployments in 3GPP LTE rel-11, there might be a few of considerations.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for selecting a carrier in a wireless communication system. The present invention provides a method for a home eNodeB (HeNB) selecting a carrier in a heterogeneous network (HetNet).

In an aspect, a method for selecting, by a home eNodeB (HeNB), a carrier in a wireless communication system is provided. The method includes transmitting a carrier information request message including a request of information on carriers used by a pico eNB, receiving a carrier information response message as a response of the carrier information request message, the carrier information response message including the information on carriers used by the pico eNB, the information on carriers indicating information on user equipments (UEs) corresponding to the carriers used by the pico eNB, and selecting a primary cell (PCell) of the HeNB based on the received information on carriers used by the pico eNB.

In another aspect, a method for selecting, by a first home eNodeB (HeNB), a carrier in a wireless communication system is provided. The method includes transmitting a carrier information request message including a request of information on carriers used by a second HeNB, receiving a carrier information response message as a response of the carrier information request message, the carrier information response message including the information on carriers used by the second HeNB, the information on carriers indicating information on user equipments (UEs) corresponding to the carriers used by the second HeNB, and selecting a primary cell (PCell) of the first HeNB based on the received information on carriers used by the second HeNB.

Automatic self carrier selecting mechanism without the need for prior network planning can be provided.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

For clarity, the following description will focus on the LTE-A. However, technical features of the present invention are not limited thereto.

To meet the targets set by 3GPP LTE-A, e.g., bandwidth up to 100 MHz, peak data rates up to 1 Gbps in DL and peak data rates up to 500 Mbps in UL, carrier aggregation (CA) concept is introduced. In the CA, two or more component carriers (CCs) are aggregated in order to support wider transmission bandwidths up to 100 MHz. A UE may simultaneously receive or transmit on one or multiple CCs depending on its capabilities. That is, a rel-10 UE with reception and/or transmission capabilities for the CA can simultaneously receive and/or transmit on multiple CCs corresponding to multiple serving cells. A Rel-8/9 UE can receive on a single CC and transmit on a single CC corresponding to one serving cell only. The CA is supported for both contiguous and non-contiguous CCs. It is possible to configure a UE to aggregate a different number of CCs originating from the same eNB and of possibly different bandwidths in the UL and the DL. That is, the number of DL CCs that can be configured depends on the DL aggregation capability of the UE. The number of UL CCs that can be configured depends on the UL aggregation capability of the UE.

When the CA concept is applied to the scenarios of home eNodeB (HeNB) deployment, the HeNB can operate via a set of allowed carriers configured by operators. The basic principle is that each cell should at least select one active primary carrier. For example, it is assumed that there are two carriers, e.g., carrier A and carrier B. It is also assumed that there are two UEs, e.g., UE C and UE D. For the UE C, the carrier A can be assigned as a primary cell (PCell) and the carrier B can be assigned as a secondary cell (SCell). For the UE D, the carrier B can be assigned as a PCell and the carrier A can be assigned as a SCell. This is an example of CA configuration per UE basis.

On the other hand, in case that a HeNB is switched on, it shall start by selecting one carrier from the available carriers as its primary carrier. In this point, the network configured carriers and the UE-specific carriers shall not be treated equally. This is because the network configured carriers are selected and used prior to UE-specific carriers during the node initialization phase and the CA is configured for the UEs that have radio resource control (RRC) connection with the network. Also, due to the lack of synchronization requirements between a pico eNB (or already deployed HeNB) and a newly deployed HeNB, the interference related problems can happen between the pico eNB (or already deployed HeNB) and the newly deployed HeNB. For example, the newly deployed HeNB may select one carrier which is used by the pico eNB (or already deployed HeNB) as its PCell from the available carriers. Besides, in case that the pico eNB (or already deployed HeNB) and the newly deployed HeNB are already working, the information on which cell is configured for the PCell/SCell(s) of the pico eNB (or already deployed HeNB) can be a clue for newly deployed HeNB to configure its own PCell/SCell(s). This is because, again, due to the lack of synchronization requirements between the pico eNB (or already deployed HeNB) and the newly deployed HeNB, the interference related problems can happen between the pico eNB (or already deployed HeNB) and the newly deployed HeNB which are already working. Thus, some enhancements are needed for the method of carrier selection in a heterogeneous network (HetNet) environment.

There are several ways to resolve the problems mentioned above. Hereinafter, various examples of the proposed method for selecting a carrier in a HetNet according to the present invention are described. Basically, it is assumed that the newly deployed HeNB may measure a reference signal from a macro eNB when it is powered on. Also, in the present invention, it is assumed that all eNBs in the network keeps the information on which physical CCs (primary CC or secondary CC) are used by the UEs as the cells (PCell and/or SCell). As mentioned above, although a cell is assigned and uses a physical primary CC, the cell may be used as a SCell by the UE. By storing this information, the eNB can trace how many UEs are served by its physical primary CC either as a PCell or as a SCell. Similarly, the eNB can trace how many UEs are served by its physical secondary CC either as a PCell or as a SCell. Also, the eNB can trace how many radio resources are used within the corresponding carriers.

FIG. 6shows an example of proposed method of selecting a carrier in a HetNet according to an embodiment of the present invention. This case is for the scenario where the pico eNB and the HeNB cannot setup the direct X2 interface between them.

Referring toFIG. 6, the newly deployed HeNB obtains the information required for carrier selection via the X2 setup procedure between the HeNB and the HeNB GW with the aid of the HeNB GW. Here, the HeNB is ready to first select the PCell.

At step S100, the HeNB transmits an X2 setup request message to the HeNB GW. The X2 setup request message may request the information on carriers used by the pico eNB by triggering the X2 setup procedure. The X2 setup request message may include carrier information request indication IE (information element) to obtain the information on the carriers used by the pico eNB received through the reference signal. The carrier information request indication IE may be added for the total number of carriers detected by the HeNB. Each carrier information request indication IE may include following information:Cell ID related information: physical cell ID (PCI), E-UTRAN cell global ID (ECGI), etcOther possible cell related information to identify the carriers used by the pico eNB received through the reference signal

At step S110, the HeNB GW transmits a carrier information request message to the pico eNB. The carrier information request message may include the carrier information request indication IE included in the X2 setup request message.

At step S120, the pico eNB transmits a carrier information response message to the HeNB GW as a response of the carrier information request message. The carrier information response message may include carrier information response indication IE for the carriers mainly used by the pico eNB. The carrier information response indication IE may be added for the total number of carriers. Each carrier information response indication IE may include following information:Cell ID related information: PCI, ECGI, etcInformation to identify the type of corresponding physical CC: physical primary CC, physical secondary CCOther possible cell related information to identify the carriers used by the pico eNB received through the reference signalUE ratio indication IE: the number of UEs using this carrier as a PCell (primary high density, primary medium density, primary low density)UE ratio indication IE: the number of UEs using this carrier as a SCell (secondary high density, secondary medium density, secondary low density}resource usage status IE: resource usage status of corresponding carrier by UEs (high use, medium use, low use)—The resource usage status may be calculated for the DL/UL/total physical resource block (PRB) as defined in X2.

At step S130, the HeNB GW transmits an X2 setup response message to the HeNB as a response of the X2 setup request message. The X2 setup response message may include the carrier information response indication IE included in the carrier information response message.

When the HeNB receives the X2 setup response message from the HeNB GW, the HeNB may flexibly select its PCell based on the received information for mitigating the interference between itself and the neighbor pico eNB. There may be several possible cases to use the combination of information explained above. For example, if the UE ratio indication IE indicates high density, which means that many UEs use this carrier as a PCell and/or SCell, the HeNB may avoid using this carrier as a PCell. Although the UE ratio indication IE indicates medium density or low density, if the resource usage status IE indicates high use, then the HeNB may avoid using this carrier as a PCell. In this way, the coordinated/uncoordinated deployment of HeNB will benefit from having support of automatic carrier selection method.

FIG. 7shows another example of proposed method of selecting a carrier in a HetNet according to an embodiment of the present invention. This case is also for the scenario where the pico eNB and the HeNB cannot setup the direct X2 interface between them. This example may be performed after the indirect X2 interface is setup between the HeNB and the HeNB GW.

Referring toFIG. 7, the HeNB obtains the information required for carrier selection via a carrier information exchange procedure between the HeNB and the pico eNB with the aid of the HeNB GW. Here, the HeNB is ready to select the PCell.

At step S150, the HeNB transmits a carrier information request message to the HeNB GW. The carrier information request message may request the information on carriers used by the pico eNB by triggering the carrier information exchange procedure. The carrier information request message may include carrier information request indication IE to obtain the information on the carriers used by the pico eNB received through the reference signal. The information on the carriers use by the pico eNB may be also obtained via the X2 setup procedure between the HeNB GW and the HeNB. The carrier information request indication IE may be added for the total number of carriers detected by the HeNB. Each carrier information request indication IE may include following information:Cell ID related information: PCI, ECGI, etcOther possible cell related information to identify the carriers used by the pico eNB received through the reference signal

At step S160, the HeNB GW forwards the carrier information request message to the pico eNB.

At step S170, the pico eNB transmits a carrier information response message to the HeNB GW as a response of the carrier information request message. The carrier information response message may include carrier information response indication IE for the carriers mainly used by the pico eNB. The carrier information response indication IE may be added for the total number of carriers. Each carrier information response indication IE may include following information:Cell ID related information: PCI, ECGI, etcInformation to identify the type of corresponding physical CC: physical primary CC, physical secondary CCOther possible cell related information to identify the carriers used by the pico eNB received through the reference signalUE ratio indication IE: the number of UEs using this carrier as a PCell (primary high density, primary medium density, primary low density)UE ratio indication IE: the number of UEs using this carrier as a SCell (secondary high density, secondary medium density, secondary low density}resource usage status IE: resource usage status of corresponding carrier by UEs (high use, medium use, low use)—The resource usage status may be calculated for the DL/UL/total physical resource block (PRB) as defined in X2.

At step S180, the HeNB GW forwards the carrier information response message to the HeNB.

When the HeNB receives the carrier information response message from the HeNB GW, the HeNB may flexibly select its PCell based on the received information for mitigating the interference between itself and the neighbor pico eNB. There may be several possible cases to use the combination of information explained above. For example, if the UE ratio indication IE indicates high density, which means that many UEs use this carrier as a PCell and/or SCell, the HeNB may avoid using this carrier as a PCell. Although the UE ratio indication IE indicates medium density or low density, if the resource usage status IE indicates high use, then the HeNB may avoid using this carrier as a PCell. In this way, the coordinated/uncoordinated deployment of HeNB will benefit from having support of automatic carrier selection method.

The carrier information request/response messages mentioned above are the simple examples of messages exchanged between the pico eNB and the HeNB to achieve the interference mitigation between them. That is, the carrier information request/response indications described in the above examples may be substituted with the existing X2 messages, e.g., resource status request/response/update message, load information message, etc.

FIG. 8shows another example of proposed method of selecting a carrier in a HetNet according to an embodiment of the present invention. This case is also for the scenario where the pico eNB and the HeNB cannot setup the direct X2 interface between them.

Referring toFIG. 8, the newly deployed HeNB obtains the information required for carrier selection via the S1 setup procedure between the HeNB and the MME with the aid of the MME. Here, the HeNB is ready to first select the PCell.

At step S200, the HeNB transmits an S1 setup request message to the MME. The S1 setup request message may request the information on carriers used by the pico eNB by triggering the S1 setup procedure. The S1 setup request message may include carrier information request indication IE to obtain the information on the carriers used by the pico eNB received through the reference signal. The carrier information request indication IE may be added for the total number of carriers detected by the HeNB. Each carrier information request indication IE may include following information:Cell ID related information: PCI, ECGI, etcOther possible cell related information to identify the carriers used by the pico eNB received through the reference signal

At step S210, the MME transmits a carrier information request message to the pico eNB. The carrier information request message may include the carrier information request indication IE included in the S1 setup request message.

At step S220, the pico eNB transmits a carrier information response message to the MME as a response of the carrier information request message. The carrier information response message may include carrier information response indication IE for the carriers mainly used by the pico eNB. The carrier information response indication IE may be added for the total number of carriers. Each carrier information response indication IE may include following information:Cell ID related information: PCI, ECGI, etcInformation to identify the type of corresponding physical CC: physical primary CC, physical secondary CCOther possible cell related information to identify the carriers used by the pico eNB received through the reference signalUE ratio indication IE: the number of UEs using this carrier as a PCell (primary high density, primary medium density, primary low density)UE ratio indication IE: the number of UEs using this carrier as a SCell (secondary high density, secondary medium density, secondary low density}resource usage status IE: resource usage status of corresponding carrier by UEs (high use, medium use, low use)—The resource usage status may be calculated for the DL/UL/total physical resource block (PRB) as defined in X2.

At step S230, the MME transmits an S1 setup response message to the HeNB as a response of the S1 setup request message. The S1 setup response message may include the carrier information response indication IE included in the carrier information response message.

When the HeNB receives the S1 setup response message from the MME, the HeNB may flexibly select its PCell based on the received information for mitigating the interference between itself and the neighbor pico eNB. There may be several possible cases to use the combination of information explained above. For example, if the UE ratio indication IE indicates high density, which means that many UEs use this carrier as a PCell and/or SCell, the HeNB may avoid using this carrier as a PCell. Although the UE ratio indication IE indicates medium density or low density, if the resource usage status IE indicates high use, then the HeNB may avoid using this carrier as a PCell. In this way, the coordinated/uncoordinated deployment of HeNB will benefit from having support of automatic carrier selection method.

FIG. 9shows another example of proposed method of selecting a carrier in a HetNet according to an embodiment of the present invention. This case is also for the scenario where the pico eNB and the HeNB cannot setup the direct X2 interface between them. This example may be performed after the S1 interface is setup between the HeNB and the MME.

Referring toFIG. 9, the HeNB obtains the information required for carrier selection via a carrier information exchange procedure between the HeNB and the pico eNB with the aid of the MME. Here, the HeNB is ready to select the PCell.

At step S250, the HeNB transmits a carrier information request message to the MME. The carrier information request message may request the information on carriers used by the pico eNB by triggering the carrier information exchange procedure. The carrier information request message may include carrier information request indication IE to obtain the information on the carriers used by the pico eNB received through the reference signal. The information on the carriers use by the pico eNB may be also obtained via the S1 setup procedure between the MME and the HeNB. The carrier information request indication IE may be added for the total number of carriers detected by the HeNB. Each carrier information request indication IE may include following information:Cell ID related information: PCI, ECGI, etcOther possible cell related information to identify the carriers used by the pico eNB received through the reference signal

At step S260, the MME forwards the carrier information request message to the pico eNB.

At step S270, the pico eNB transmits a carrier information response message to the MME as a response of the carrier information request message. The carrier information response message may include carrier information response indication IE for the carriers mainly used by the pico eNB. The carrier information response indication IE may be added for the total number of carriers. Each carrier information response indication IE may include following information:Cell ID related information: PCI, ECGI, etcInformation to identify the type of corresponding physical CC: physical primary CC, physical secondary CCOther possible cell related information to identify the carriers used by the pico eNB received through the reference signalUE ratio indication IE: the number of UEs using this carrier as a PCell (primary high density, primary medium density, primary low density)UE ratio indication IE: the number of UEs using this carrier as a SCell (secondary high density, secondary medium density, secondary low density}resource usage status IE: resource usage status of corresponding carrier by UEs (high use, medium use, low use)—The resource usage status may be calculated for the DL/UL/total physical resource block (PRB) as defined in X2.

At step S280, the MME forwards the carrier information response message to the HeNB.

When the HeNB receives the carrier information response message from the MME, the HeNB may flexibly select its PCell based on the received information for mitigating the interference between itself and the neighbor pico eNB. There may be several possible cases to use the combination of information explained above. For example, if the UE ratio indication IE indicates high density, which means that many UEs use this carrier as a PCell and/or SCell, the HeNB may avoid using this carrier as a PCell. Although the UE ratio indication IE indicates medium density or low density, if the resource usage status IE indicates high use, then the HeNB may avoid using this carrier as a PCell. In this way, the uncoordinated deployment of HeNB will benefit from having support of automatic carrier selection method.

The carrier information request/response messages mentioned above are the simple examples of messages exchanged between the pico eNB and the HeNB to achieve the interference mitigation between them. That is, the carrier information request/response indications described in the above examples may be substituted with the existing X2 messages, e.g., resource status request/response/update message, load information message, etc.

FIG. 10shows another example of proposed method of selecting a carrier in a HetNet according to an embodiment of the present invention. This case is for the scenario where the pico eNB and the HeNB can setup the direct X2 interface between them.

Referring toFIG. 10, the newly deployed HeNB obtains the information required for carrier selection via the X2 setup procedure directly between the HeNB and the pico eNB. Here, the HeNB is ready to first select the PCell.

At step S300, the HeNB transmits an X2 setup request message to the pico eNB. The X2 setup request message may request the information on carriers used by the pico eNB by triggering the X2 setup procedure. The X2 setup request message may include carrier information request indication IE to obtain the information on the carriers used by the pico eNB received through the reference signal. The carrier information request indication IE may be added for the total number of carriers detected by the HeNB. Each carrier information request indication IE may include following information:Cell ID related information: PCI, ECGI, etcOther possible cell related information to identify the carriers used by the pico eNB received through the reference signal

At step S310, the pico eNB transmits an X2 setup response message to the HeNB as a response of the X2 setup request message. The X2 setup response message may include carrier information response indication IE for the carriers mainly used by the pico eNB. The carrier information response indication IE may be added for the total number of carriers. Each carrier information response indication IE may include following information:Cell ID related information: PCI, ECGI, etcInformation to identify the type of corresponding physical CC: physical primary CC, physical secondary CCOther possible cell related information to identify the carriers used by the pico eNB received through the reference signalUE ratio indication IE: the number of UEs using this carrier as a PCell (primary high density, primary medium density, primary low density)UE ratio indication IE: the number of UEs using this carrier as a SCell (secondary high density, secondary medium density, secondary low density}resource usage status IE: resource usage status of corresponding carrier by UEs (high use, medium use, low use)—The resource usage status may be calculated for the DL/UL/total physical resource block (PRB) as defined in X2.

When the HeNB receives the X2 setup response message from the pico eNB, the HeNB may flexibly select its PCell based on the received information for mitigating the interference between itself and the neighbor pico eNB. There may be several possible cases to use the combination of information explained above. For example, if the UE ratio indication IE indicates high density, which means that many UEs use this carrier as a PCell and/or SCell, the HeNB may avoid using this carrier as a PCell. Although the UE ratio indication IE indicates medium density or low density, if the resource usage status IE indicates high use, then the HeNB may avoid using this carrier as a PCell. In this way, the deployment of the HeNB will benefit from having support of automatic carrier selection method.

FIG. 11shows another example of proposed method of selecting a carrier in a HetNet according to an embodiment of the present invention. This case is also for the scenario where the pico eNB and the HeNB can setup the direct X2 interface between them. This example may be performed after the direct X2 interface is setup between the HeNB and the pico eNB.

Referring toFIG. 11, the HeNB obtains the information required for carrier selection via the carrier information exchange procedure directly between the HeNB and the pico eNB. Here, the HeNB is ready to select the PCell.

At step S350, the HeNB transmits a carrier information request message to the pico eNB. The carrier information request message may request the information on carriers used by the pico eNB by triggering the carrier information exchange procedure. The carrier information request message may include carrier information request indication IE to obtain the information on the carriers used by the pico eNB received through the reference signal. The information on the carriers use by the pico eNB may be also obtained via the X2 setup procedure between the pico eNB and the HeNB directly. The carrier information request indication IE may be added for the total number of carriers detected by the HeNB. Each carrier information request indication IE may include following information:Cell ID related information: physical cell ID (PCI), E-UTRAN cell global ID (ECGI), etcOther possible cell related information to identify the carriers used by the pico eNB received through the reference signal

At step S360, the pico eNB transmits a carrier information response message to the HeNB as a response of the carrier information request message. The carrier information response message may include carrier information response indication IE for the carriers mainly used by the pico eNB. The carrier information response indication IE may be added for the total number of carriers. Each carrier information response indication IE may include following information:Cell ID related information: PCI, ECGI, etcInformation to identify the type of corresponding physical CC: physical primary CC, physical secondary CCOther possible cell related information to identify the carriers used by the pico eNB received through the reference signalUE ratio indication IE: the number of UEs using this carrier as a PCell (primary high density, primary medium density, primary low density)UE ratio indication IE: the number of UEs using this carrier as a SCell (secondary high density, secondary medium density, secondary low density}resource usage status IE: resource usage status of corresponding carrier by UEs (high use, medium use, low use)—The resource usage status may be calculated for the DL/UL/total physical resource block (PRB) as defined in X2.

When the HeNB receives the carrier information response message from the pico eNB, the HeNB may flexibly select its PCell based on the received information for mitigating the interference between itself and the neighbor pico eNB. There may be several possible cases to use the combination of information explained above. For example, if the UE ratio indication IE indicates high density, which means that many UEs use this carrier as a PCell and/or SCell, the HeNB may avoid using this carrier as a PCell. Although the UE ratio indication IE indicates medium density or low density, if the resource usage status IE indicates high use, then the HeNB may avoid using this carrier as a PCell. In this way, the deployment of the HeNB will benefit from having support of automatic carrier selection method.

The carrier information request/response messages mentioned above are the simple examples of messages exchanged between the pico eNB and the HeNB to achieve the interference mitigation between them. That is, the carrier information request/response indications described in the above examples may be substituted with the existing X2 messages, e.g., resource status request/response/update message, load information message, etc.

The present invention described above may be applied between HeNBs.

FIG. 12shows another example of proposed method of selecting a carrier in a HetNet according to an embodiment of the present invention. This case is for the scenario where the HeNBs with different closed subscription group (CSG) IDs cannot setup the direct X2 interface between them. Referring toFIG. 12, the newly deployed first HeNB obtains the information required for carrier selection via the X2 setup procedure between the first HeNB and the HeNB GW with the aid of the HeNB GW.

At step S400, the first HeNB transmits an X2 setup request message to the HeNB GW. At step S410, the HeNB GW transmits a carrier information request message to the second HeNB. At step S420, the second HeNB transmits a carrier information response message to the HeNB GW as a response of the carrier information request message. At step S430, the HeNB GW transmits an X2 setup response message to the first HeNB as a response of the X2 setup request message. The detail operation of step S400to step S430may be the same as step S100to step S130ofFIG. 6respectively.

FIG. 13shows another example of proposed method of selecting a carrier in a HetNet according to an embodiment of the present invention. This case is also for the scenario where the HeNBs with different CSG IDs cannot setup the direct X2 interface between them. This example may be performed after the indirect X2 interface is setup between the HeNBs. Referring toFIG. 13, the first HeNB obtains the information required for carrier selection via a carrier information exchange procedure between the first HeNB and the second HeNB with the aid of the HeNB GW.

At step S450, the first HeNB transmits a carrier information request message to the HeNB GW. At step S460, the HeNB GW forwards the carrier information request message to the second HeNB. At step S470, the second HeNB transmits a carrier information response message to the HeNB GW as a response of the carrier information request message. At step S480, the HeNB GW forwards the carrier information response message to the first HeNB. The detail operation of step S450to step S480may be the same as step S150to step S180ofFIG. 7respectively.

FIG. 14shows another example of proposed method of selecting a carrier in a HetNet according to an embodiment of the present invention. This case is also for the scenario where the HeNBs with different CSG IDs cannot setup the direct X2 interface between them. Referring toFIG. 14, the newly deployed first HeNB obtains the information required for carrier selection via the S1 setup procedure between the first HeNB and the MME with the aid of the MME.

At step S500, the first HeNB transmits an S1 setup request message to the MME. At step S510, the MME transmits a carrier information request message to the second HeNB. At step S520, the second HeNB transmits a carrier information response message to the MME as a response of the carrier information request message. At step S530, the MME transmits an S1 setup response message to the first HeNB as a response of the S1 setup request message. The detail operation of step S500to step S530may be the same as step S200to step S230ofFIG. 8respectively.

FIG. 15shows another example of proposed method of selecting a carrier in a HetNet according to an embodiment of the present invention. This case is also for the scenario where the HeNBs with different CSG IDs cannot setup the direct X2 interface between them. This example may be performed after the S1 interface is setup between the HeNB and the MME. Referring toFIG. 15, the first HeNB obtains the information required for carrier selection via a carrier information exchange procedure between the HeNBs with the aid of the MME.

At step S550, the first HeNB transmits a carrier information request message to the MME. At step S560, the MME forwards the carrier information request message to the second HeNB. At step S570, the second HeNB transmits a carrier information response message to the MME as a response of the carrier information request message. At step S580, the MME forwards the carrier information response message to the first HeNB. The detail operation of step S550to step S580may be the same as step S250to step S280ofFIG. 9respectively.

FIG. 16shows another example of proposed method of selecting a carrier in a HetNet according to an embodiment of the present invention. This case is for the scenario where the HeNBs with different CSG IDs can setup the direct X2 interface between them. Referring toFIG. 16, the newly deployed first HeNB obtains the information required for carrier selection via the X2 setup procedure directly between the HeNBs.

At step S600, the first HeNB transmits an X2 setup request message to the second HeNB. At step S610, the second HeNB transmits an X2 setup response message to the first HeNB as a response of the X2 setup request message. The detail operation of step S600to step S610may be the same as step S300to step S310ofFIG. 10respectively.

FIG. 17shows another example of proposed method of selecting a carrier in a HetNet according to an embodiment of the present invention. This case is also for the scenario where the HeNBs with different CSG IDs can setup the direct X2 interface between them. This example may be performed after the direct X2 interface is setup between the HeNBs. Referring toFIG. 17, the first HeNB obtains the information required for carrier selection via the carrier information exchange procedure directly between the HeNBs.

At step S650, the first HeNB transmits a carrier information request message to the second HeNB. At step S660, the second HeNB transmits a carrier information response message to the first HeNB as a response of the carrier information request message. The detail operation of step S650to step S650may be the same as step S350to step S360ofFIG. 11respectively.

FIG. 18is a block diagram showing wireless communication system to implement an embodiment of the present invention.

A pico eNB or HeNB800includes a processor810, a memory820, and an RF (radio frequency) unit830. The processor810may be configured to implement proposed functions, procedures, and/or methods in this description. Layers of the radio interface protocol may be implemented in the processor810. The memory820is operatively coupled with the processor810and stores a variety of information to operate the processor810. The RF unit830is operatively coupled with the processor810, and transmits and/or receives a radio signal.

A HeNB900may include a processor910, a memory920and a RF unit930. The processor910may be configured to implement proposed functions, procedures and/or methods described in this description. Layers of the radio interface protocol may be implemented in the processor910. The memory920is operatively coupled with the processor910and stores a variety of information to operate the processor910. The RF unit930is operatively coupled with the processor910, and transmits and/or receives a radio signal.