JP5561499B2 - Wireless communication system and communication method thereof - Google Patents

Description

  The present invention relates to a radio communication system including a base station and a mobile station, and more particularly to a communication method thereof, a base station, and a mobile station.

  Currently, various wireless transmission systems such as the third generation mobile phone system (3G), the standard for fixed wireless communication (WiMAX), the standard for wireless LAN (WiFi) have been proposed and put into practical use. Transmission speeds and coverage vary. In general, since the transmission rate and the coverage are in a trade-off relationship, it is not possible to obtain a high transmission rate and a wide coverage at the same time with a single wireless transmission system. Therefore, cells of different radio transmission schemes may be adjacent to each other by setting an appropriate radio transmission scheme (RAT: Radio Access Technology) according to various situations. In this way, in a radio communication system in which a plurality of radio transmission schemes coexist, a handover technique when a radio terminal operable in each radio transmission scheme moves from one radio transmission scheme cell to another radio transmission scheme cell Several have been proposed.

  For example, in the mobile communication system disclosed in Patent Document 1, radio signals of all communication systems (wireless transmission schemes) that can be used by a mobile terminal are received, the type of each communication system is specified from the frequency, and communication quality is determined. The QoS is obtained and reported to the communicating base station (source base station). In response to this, when the switching-destination base station (target base station) is notified from the network side, the mobile terminal secures a radio line between both the source base station and the target base station, and the target-side radio Switch to the transmission method (paragraph 0042, FIG. 3, FIG. 4).

  Further, in the Inter RAT handover described in Non-Patent Document 1, information on the radio transmission scheme (including radio resource configuration and target cell system information) is provided from the target system to the mobile terminal through the source system in communication, It is possible to switch the wireless transmission method at the mobile terminal (see 10.2.2 Handover).

JP 2001-54168 A

3GPP TS36.300 V8.3.0 (2007-12)

  However, in the method of identifying the type of the radio transmission scheme of the transmission source based on the frequency of the downlink radio signal received by the mobile station, a cognitive radio system in which a plurality of radio transmission schemes may use vacant frequencies. In such a case, the wireless transmission method cannot be specified from the frequency being used.

  In a single wireless communication system such as a wireless LAN (IEEE802.11), a plurality of IEEE802.11a and IEEE802.11g using multicarrier OFDM (Orthogonal Frequency Division Multiplexing) and IEEE802.11b using a single carrier. When the wireless access method of IEEE802.11g and IEEE802.11b use the same frequency, the wireless access method cannot be identified from the used frequency band.

  As another method for identifying the radio access scheme, it is also possible to receive a common control signal transmitted by the base station at regular intervals and identify the radio transmission scheme based on the demodulation result. However, since the wireless transmission scheme of the target base station is identified after waiting for reception of the common control signal, a delay of about twice or more than the transmission interval of the common control signal occurs, for example, a delay in handover processing Cause.

  Accordingly, an object of the present invention is to provide a radio communication system and a communication method capable of reducing the delay time at the time of initial connection.

A wireless communication system according to the present invention includes: a first base station that can communicate with a first wireless access scheme; a second base station that can communicate with a second wireless access scheme; and at least one mobile station. And when the mobile station is handed over from the first base station to the second base station, the mobile station uses the RACH (Random Access Channel) signal commonly used by the first and second base stations. The first wireless access method is used for initial connection, and the second base station performs communication after the handover using the second wireless access method.

  According to the present invention, the delay time at the initial connection can be shortened.

1 is a system configuration diagram for explaining handover in a wireless communication system according to an embodiment of the present invention. FIG. FIG. 5 is a sequence diagram for explaining handover between base stations in a wireless communication system according to an embodiment of the present invention. It is a block diagram which shows the functional structure of the mobile station in the radio | wireless communications system by a present Example. It is a block diagram which shows the functional structure of the base station in the radio | wireless communications system by a present Example. FIG. 3 is a sequence diagram showing a specific example of handover within the MME / S-Gateway in the first embodiment shown in FIG. 2.

1. Embodiments In a wireless communication system according to an embodiment of the present invention, at least one of a plurality of different wireless access methods is supported in each cell, and a mobile station can communicate with at least one of the plurality of wireless access methods. It shall have a possible radio transceiver. Hereinafter, in order to describe the radio access scheme identification method according to the present invention, a handover process in which a mobile station in communication moves between cells having different radio access schemes will be described as an example. According to the present invention, by using the common radio access scheme, it is not necessary for the mobile station to identify the radio access scheme of the handover destination base station before the start of the handover process, so that high-speed handover is possible. In addition, even when it is common within a certain range (for example, the area used by the carrier frequency band and the network for location management of the terminal), the radio access method of the handover destination base station can be identified before the start of the handover process. Again, high-speed handover is possible. Note that the present invention can be applied not only in the case of handover processing, but also in the case where a mobile station located in a certain cell is initially connected to the cell.

  FIG. 1 is a system configuration diagram for explaining handover in a wireless communication system according to an embodiment of the present invention. However, to simplify the description, a wireless communication system that supports two different wireless access methods A and B in the same wireless transmission method is assumed.

  As a radio communication system having the same radio transmission scheme and different radio access schemes, for example, a system in which two types of base stations of a single carrier scheme and a multicarrier scheme are mixed, or as described above, a wireless LAN (IEEE802. In a system such as 11), there are cases where the wireless access schemes of IEEE802.11a / 802.11g using multi-carrier OFDM and IEEE802.11b using single carrier are mixed.

  Here, it is assumed that the base station 20a supports the radio access scheme A, the base station 20b supports the radio access schemes A and B, and the radio access scheme A is used as a common radio access scheme for initial connection. However, the present invention is not limited to this, and each base station may support two or more types of radio access schemes, and a specific one may be determined as a common radio access scheme.

  It is assumed that the base station 20a and the base station 20b are connected to the same mobility management entity / main gateway (MME / S-GW) 30. Furthermore, it is assumed that the mobile station 10 can wirelessly communicate with both the wireless access methods A and B. If the mobile station 10 moves and switches the connection from the base station 20a to the base station 20b, the base station 20a becomes the handover source source base station, and the base station 20b becomes the handover destination target base station.

  In the radio communication system according to the present embodiment, all base stations in the same radio transmission system, base stations located in a predetermined area in the same radio transmission system, or bases using the same frequency band in the same radio transmission system Since a common radio access scheme is determined in advance by the station, the mobile station 10 can access the target base station 20b by the common radio access scheme before the handover, and set the uplink radio access scheme of the target base station 20b. I can know. As the predetermined area, for example, Tracking Area (TA) or Public Land Mobile Network (PLMN) can be considered. As an example of the same frequency band, the same wireless transmission system supports frequency band A (for example, 800 MHz band), frequency band B (for example, 1.5 GHz band), and frequency band Z (for example, 2.1 GHz band) at the same time. In this case, it is conceivable that the radio access method is common in each frequency band.

  In this embodiment, the radio access method when the mobile station initially accesses the target base station is a common radio access method determined in advance by all base stations in the same radio communication system, and the area and frequency An example in which the bandwidth does not change is shown. For example, when an area or a frequency band changes in the same wireless communication system, the mobile station specifies an area or a frequency band, thereby determining a radio access method for initial access determined in advance for each area or frequency band. Identify.

  Hereinafter, an embodiment in which a radio access scheme identification method according to the present invention is applied to handover processing will be described in detail by taking a radio communication system proposed in 3GPP LTE (Long Term Evolution) as an example. In this case, the base station may be indicated as eNB, and the mobile station may be indicated as UE. Handover, uplink, and downlink are abbreviated as HO, UL, and DL, respectively, as appropriate.

2. 2. Embodiment 2.1) Handover Procedure FIG. 2 is a sequence diagram for explaining handover between base stations in a wireless communication system according to an embodiment of the present invention. According to the present embodiment, the mobile station 10 receives the uplink radio access information (UL Access Info) of the target base station 20b by transmitting the RACH to the target base station 20b by a predetermined common radio access method. And the uplink (UL) radio access scheme of the target base station 20b can be determined before the handover. The RACH transmission by the common radio access method is possible from the time when the presence of the target base station 20b is identified and the handover instruction (HO Command) can be received. It is not necessary to identify a radio access method, and high-speed handover is possible. This will be described in detail below.

  First, in step 1, the target base station 20b transmits a reference signal (DL RS) for downlink (DL) propagation path estimation, and the mobile station 10 receives it. In this reference signal, a unique sequence (for example, a scrambling code) assigned to each base station is multiplexed.

  In step 2, the source base station 20a transmits source base station scheduling information (UL allocation or Source UL Grant) indicating uplink resources respectively allocated to the mobile stations 10 and 11 in the source base station 20a to the mobile station 10. .

  In Step 3, the mobile station 10 transmits a measurement report (Measurement Report) related to the neighboring cells of the staying source cell to the source base station 20a when performing handover between base stations.

  In Step 4, the source base station 20a transfers the QoS (Quality of Service), Profile, etc. of the mobile station 10 as a HANDOVER REQUEST message (Context Data) to the target base station 20b.

  In step 5, the target base station 20b determines whether or not handover acceptance is possible for the mobile station 10, and uses a HANDOVER REQUEST ACKNOWLEDGE message (Context Confirm), which is handover acceptance information indicating the result, as transfer information. And transfer to the source base station 20a. The transfer information includes radio resource information of time and frequency allocated for random access to the target base station 20b.

  In Step 6, the source base station 20a gives the mobile station 10 a handover start command (HANDOVER COMMAND or HO Command) which is a control signal including handover acceptance information and transfer information including radio resource information for random access. Send.

  In Step 7, after receiving the control signal (HO Command) from the source base station 20b, the mobile station 10 uses the random access signal (UL Synchronization) using the RACH (Random Access Channel) that is the uplink channel to execute the target base station. 20b is accessed. At this time, the mobile station 10 generates a random access signal (UL Synchronization) and transmits it to the target base station 20b by a common radio access method predetermined in some or all of the base stations.

  In Step 8, in addition to the transmission timing adjustment value (Timing Advance: TA) and uplink scheduling information (Target UL Grant), uplink radio access information (UL Access Info) in the target base station 20b is transmitted from the target base station 20b. Is done. Thereby, the mobile station 10 can identify the uplink radio access scheme of the target base station 20b.

  In step 9, the mobile station 10 adjusts the transmission timing according to each transmission timing adjustment value (TA), transmits control information (HO Confirm) to the target base station 20b using the uplink resource allocated to each, and performs handover. Notify that you have come.

  In step 10, the target base station 20b transmits a control signal (RELEASE RESOURCE or HO Completed) to the source base station 20a. In step 11, the target base station 20b transmits the mobile station to the connected MME / Serving-GW 30. 10 notifies that it has moved to the cell managed by the inter-base station handover (UE updated to MME / S-GW), thereby completing the inter-base station handover operation.

  As described above, a radio access method common to the base stations is determined in advance, and RACH transmission is performed using this method, whereby the radio access method of the handover destination can be identified at high speed, and the handover delay can be shortened. it can.

2.2) Mobile Station FIG. 3 is a block diagram showing a functional configuration of the mobile station in the wireless communication system according to the present embodiment. However, only functions related to the sequence shown in FIG. 2 are shown here.

When the receiving unit 101 of the mobile station 10 receives the downlink signal from the base station (here, 20a, 20b), calculates the autocorrelation value using the guard interval or the like, and establishes the downlink synchronization, the received signal S _RX is output to RS separation section 102, TA separation section 106 and handover start command (HOcommand) separation section 107. Note that the reception operation of the receiving unit 101 can be performed according to the radio access scheme of the connected base station or the radio access scheme of the target base station described later.

The RS separation unit 102 receives the received signal S _RX , separates the reference signal S _RS , and outputs it to the ID identification unit 103 and the SNR measurement unit 104. The ID identifying unit 103 identifies the ID (base station identifier) of the base station that is the transmission source of the reference signal from the downlink reference signal S _RS , and the base station identification signal S _ID is a measurement report generating unit 105. Output to. However, when the base station forms a plurality of sectors, one of IDs indicating the sectors is used as the base station identifier. A sector is also called a cell, and in this case, a cell ID (Physical Cell Identity) is used as an identifier. The SNR measurement unit 104 measures a received SNR (Signal-to-Noise Ratio) from the downlink reference signal _SRS, and outputs the SNR measurement signal _SSN to the measurement report generation unit 105.

Measurement Report generation section 105, a base station identification signal S _ID and measurement reports from SNR measurement signal S _SN (Measurement Report) to generate the S _MR. In this example, the Measurement Report generating unit 105 creates a measurement report related to the neighboring cells of the base station 20a in which the mobile station 10 is located (the target cell candidate, but here the cell of the base station 20b). Thus, _the Measurement Report S _MR on the target base station 20b is output to a transmission section 109, and transmitted to the source base station 20a (see Step 3 in FIG. 2).

TA demultiplexing section 106 separates the TA signal S _TA and UL radio access received signal S _WA from the received signal S _RX (see Step 8 in FIG. 2), a TA signal S _TA to the transmission section 109, uplink radio The access reception signal _SWA is output to the transmission unit 109. The TA signal S _TA is an uplink transmission timing adjustment value designated by the base station, and thereby, uplink synchronization is established between the mobile station 10 and the base station, thereby enabling data communication.

The HO Command separation unit 107 separates the HO Command signal from the received signal S _RX , further extracts a RACH resource signal S _RR included as transfer information from the HO Command signal, and outputs it to the RACH generation unit 108. The RACH resource signal S _RR includes information indicating time and frequency resources allocated for random access to the target base station 20b.

The RACH generation unit 108 generates a random access signal S _RH using a resource indicated by the RACH resource signal S _RR by a predetermined common radio access scheme.

Transmitting section 109 transmits to the source base station 20a at the timing indicated by the modulating TA signal S _TA to Measurement Report S _MR described above in the radio access scheme of the source base station 20a. The transmission unit 109 modulates a random access signal S _RH in common radio access scheme, and transmits to the target base station 20b at the timing and frequency according to the RACH resource signal S _RR. Furthermore, the transmission unit 109 can transmit a control signal and data to the target base station 20b according to the radio access scheme of the uplink radio access reception signal _SWA .

  Note that the above-described functions related to handover of a mobile station can also be realized by executing a program on a program control processor such as a CPU.

2.3) Base Station FIG. 4 is a block diagram showing a functional configuration of the base station in the wireless communication system according to the present embodiment. However, since the base stations 20a and 20b in the present embodiment have the same configuration, the base station 20 will be described below. 4 also shows only functions related to the sequence shown in FIG.

The base station 20 includes an uplink radio access information generation unit 200, a base station ID generation unit 201, and an RS generation unit 202. In this embodiment, the uplink radio access information generation unit 200 Information _SWAB indicating the radio access method assigned in advance to the station 20 is output to the TA generation unit 205 described later. Note that when a plurality of predetermined radio access methods are stored in the uplink radio access information generation unit 200, one radio access method may be selected and output to the TA generation unit 205. Furthermore, when a plurality of cells are configured in one base station, the radio access method can be changed for each cell.

The base station ID generation unit 201 generates an ID signal S _IDB indicating the base station identifier and outputs the ID signal S _IDB to the RS generation unit 202. The RS generation unit 202 generates the reference signal S _RSB in a signal sequence corresponding to the base station ID signal S _IDB. Generate and output to the transmission unit 217. Therefore, each mobile station can identify the base station of the neighboring cell by receiving this reference signal S _RSB .

The receiving unit 203 of the base station 20 receives the uplink signal S _TX from the mobile station, and outputs the received signal S _RXB to the RACH separating unit 204, the handover acceptance information (HO confirm) separating unit 206, and the Measurement Report separating unit 208, respectively. . The receiving unit 203 can communicate with one or a plurality of radio access schemes, and a specific one of them is used as a common radio access scheme for random access from a mobile station. For example, in LTE, when the receiving unit 203 can communicate with only one radio access scheme, it seems preferable to use a single carrier scheme.

The RACH separation unit 204 separates the random access signal S _RHB from the received signal S _RXB and outputs it to the TA generation unit 205.

The TA generation unit 205 adjusts the transmission timing of the mobile station so that uplink synchronization is established between the mobile station and the base station 20 based on the reception timing of the random access signal _SRHB received from the mobile station. The TA transmission signal S _TCB is generated and output to the transmission unit 217 as the TA transmission signal S _TCB together with the information _SWAB indicating the radio access scheme input from the uplink radio access information generation unit 200 (see step 8 in FIG. 2). ).

The HOconfirm separation unit 206 separates the HOconfirm signal S _HCB indicating that synchronization between the mobile station and the target base station has been established from the received signal S _RXB and outputs it to the handover preparation completion information (HO Completed) generation unit 207. When receiving the HO confirm signal S _HCB , the HO Completed generation unit 207 generates an HO Completed signal S _HOCB indicating that the preparation for handover is completed, and outputs the generated signal to the inter-base station signal transmission unit 216. The HO Completed signal S _HOCB is a signal notified from the target base station 20b to the source base station 20a.

The measurement report separation unit 208 separates the measurement report transmitted from the mobile station 10 from the reception signal S _RXB and outputs the measurement report to the context data generation unit 215 as the reception measurement report signal S _MRB .

The inter-base station signal receiving unit 209 receives a signal S _RIB from another base station, and converts the inter-base station control signal S _INB into a context acceptance information (Context Confirm) separation unit 210, a Context Data separation unit 211, and an HO Completed separation unit. The output to 212 respectively.

The Context Confirm separation unit 210 separates the Context Confirm signal S _HRB from the inter-base station control signal S _INB and outputs it to the HO Command generation unit 213.

The Context Data separation unit 211 separates the Context Data signal _SHQB from the inter-base station control signal S _INB received from the source base station 20a, and outputs it to the Context Confirm generation unit 214. The Context Data signal S _HQB is a signal indicating a mobile station handover request from the source base station 20a to the target base station 20b.

The HO Command generator 213 generates a HO Command signal S _HOB from the Context Confirm signal S _HRB and outputs it to the transmitter 217. The HO Command signal _SHOB is a signal transmitted from the source base station 20a to the mobile station.

The Context Confirm generating unit 214 determines whether or not to permit handover of the mobile station for reception of the Context Data signal S _HQB , and includes the determination result and radio resource information for random access to the base station 20 A Context Confirm signal S _HPB including the transfer information as a part is generated and output to the inter-base station signal transmission unit 216.

In this example, if the base station 20 is the target base station 20b, a Context Confirm signal S _HPB including handover acceptance permission information and the like is transmitted to the source base station 20a through the inter-base station signal transmission unit 216 (FIG. 2). Step 5).

If the base station 20 is the source base station 20a, the Context Confirm separation unit 210 separates the Context Confirm signal S _HRB from the inter-base station control signal S _INB , and the HO Command generation unit 213 receives the Context Confirm signal S _HRB. The HO Command signal _SHOB is generated and transmitted to the mobile station through the transmitter 217 (step 6 in FIG. 2).

The Context Data generating unit 215 receives the received Measurement Report signal S _MRB, and generates information requesting that the mobile station performs handover from the source base station 20a to the target base station 20b as a Context Data signal S _HTB . If the base station 20 is the source base station 20a, the Context Data signal S _HTB is notified to the target base station 20b (step 4 in FIG. 2).

As described above, when one of the HO Completed signal S _HTB , the Context Confirm signal S _HPB and the Context Data signal S _HTB is input, the inter-base station signal transmission unit 216 transmits the signal to another base station.

When any one of the downlink RS signal S _RSB , the TA transmission signal S _TCB , and the HO Command signal S _HOB is input, the transmission unit 217 transmits these signals as a downlink signal S _TXB to the mobile station.

The HO Completed separation unit 212 separates the HO Completed signal from the inter-base station control signal S _INB, and when the HO Completed signal indicates that the mobile station 10 is ready for handover, the handover process is completed.

  Note that the above-described functions related to handover of the base station can also be realized by executing a program on a program control processor such as a CPU.

2.4) Effect According to the embodiment of the present invention described above, even when the radio access scheme differs between base stations of one radio communication system, the common radio access scheme is used without receiving the common control information. By transmitting the initial connection signal, the radio access scheme of the base station can be known. As a result, handover between base stations can be executed at high speed without increasing the handover delay.

3. Specific Example FIG. 5 is a sequence diagram showing a specific example of handover within the MME / S-Gateway in the embodiment shown in FIG. Hereinafter, MBSFN represents MBMS over a Single Frequency Network, and MBMS represents Multimedia Broadcast and Multicast Service.

3.1) Multiple access The multiple access scheme for LTE physical layer is based on OFDM with cyclic prefix (CP) in the downlink and based on OFDM with CP and / or SC-FDMA with CP. . In the uplink, the multiple access scheme can be configured as cell specific or user specific. To support transmission in the paired or unpaired spectrum, two duplex modes, FDD (Frequency Division Duplex) and TDD (Time Division Duplex) that support full-duplex and half-duplex operation, are available. Supported.

  In order to support smooth handover, the multiple access scheme used for random access is the same in a cell located within a given area or in all cells of the same system, ie either OFDMA or SC-FDMA. It is.

3.2) Control Plane Processing The handover (HO) procedure is executed without intervention of EPC (Evolved Packet Core) by exchanging a preparation message directly between base stations (eNBs), for example. The resource release at the source type in the HO completion phase is triggered by the eNB. In FIG. 5, the basic handover procedure is shown, and neither the MME nor the Serving Gateway is changed. Hereinafter, a handover procedure in the MME / S-Gateway will be described in detail with reference to FIG. The numbers S0 to S18 shown below correspond to the numbers 0 to 18 labeled in the steps shown in FIG.

  S0: The UE context in the source eNB includes information on roaming restrictions provided either at connection establishment or at the last TA update.

  S1: The source eNB sets a UE measurement (measurement) procedure according to the area restriction information. The measurement provided by the source eNB may assist the function of controlling the UE's connection mobility.

  S2: The UE is triggered to send a MEASUREMENT REPORT according to a predetermined rule (for example, system information, specifications, etc.). During the measurement procedure, the UE recognizes the uplink multiple access scheme of the target cell from the sequence included in the downlink reference signal. The sequence included in the downlink reference signal corresponds to one of two uplink multiple access schemes, that is, OFDM or SC-FDMA.

  S3: The source eNB determines UE handoff based on MEASUREMENT REPORT and RRM information.

S4: The source eNB issues a HANDOVER REQUEST message to the target eNB and passes information necessary for handover preparation on the target side (UE X2 signaling context reference at the source eNB, UE S1 EPC signaling context reference, target cell ID, K _{eNB *} , RRC context including UE C-RNT1 at source eNB, AS-configuration (excluding physical layer configuration), EPC bearer context and source cell physical layer ID + for expected RLF recovery MAC). The UE X2 / UE S1 signaling reference enables the source eNB and EPC resolution by the target eNB. The EPC bearer context includes necessary RNL (Radio Network Layer) and TNL (Transport Network Layer) addressing information and an EPS bearer QoS profile.

  S5: Admission control can be performed by the target eNB so that the probability of a successful handover is increased according to the received EPS bearer QoS information if the resource is permitted by the target eNB. The target eNB sets necessary resources according to the received EPS bearer QoS information, and reserves the C-RNTI and optionally the RACH preamble. The AS-configuration to be used in the target cell can be specified independently (eg, establishment) or can be specified as a difference from the AS-configuration used in the source cell (eg, reconfiguration).

  S6: The target eNB prepares for handover at L1 / L2, and transmits HANDOVER REQUEST ACKNOWLEDGE to the source eNB. The HANDOVER REQUEST ACKNOWLEDGE message includes a transparent container to be sent to the UE as part of the Handover Command. This container may contain a new C-RNTI, a target eNB security algorithm identifier for the selected security algorithm, and some other parameters such as access parameters, SIBs, and so on. The HANDOVER REQUEST ACKNOWLEDGE message can also include RNL / TNL information for the forwarding tunnel, if necessary.

  Note that data transfer may be started as soon as the source eNB receives HANDOVER REQUEST ACKNOWLEDGE or as soon as transmission of a handover command is started in the downlink.

  Steps 7-16 described below provide a means to avoid data loss during handover.

  S7: The source eNB generates a HANDOVER COMMAND (RRC message) for the UE. The HANDOVER COMMAND includes a transparent container received from the target eNB. The source eNB performs the necessary integrity protection and message encryption. The UE receives a HANDOVER COMMAND with the necessary parameters (eg, new C-RNTI, target eNB security algorithm identifier, and optional dedicated RACH preamble, expiration date of the dedicated RACH preamble, target eNB SIB, etc.) Handover is executed by an instruction from the eNB. The UE need not delay handover execution in order to deliver the HARQ / ARQ response to the source eNB.

  S8: The source eNB sends an SN STATUS TRANSFER message to the target eNB, and the uplink PDCP SN reception status of the SAE (System Architecture Evolution) bearer to which PDCP (Packet Data Convergence Protocol) status preservation is applied And conveys the downlink PDCP SN transmission status. The uplink PDCP SN reception status includes at least the PDCP SN of the uplink service data unit UL SDU (upper window edge) of the next expected number, and further includes the PDCP SN list of the UL SDU that is considered to have been lost due to collapse of the serial number. May be included. The lost UL SDU needs to be retransmitted by the UE if the SDU exists in the target cell. The downlink PDCP SN transmission status indicates the next PDCP SN to be assigned to a target eNB that is a new SDU and does not yet have a PDCP SN. Note that the source eNB may omit sending this message if none of the UE's SAE bearers should be processed with PDCP status preservation.

  S9: After receiving the HANDOVER COMMAND, the UE synchronizes with the target eNB and accesses the target cell using an uplink radio access scheme configured in advance for random access. Access to the target cell is performed by RACH, but if a dedicated RACH preamble is assigned to the HANDOVER COMMAND, follow the contention-free procedure, and if no dedicated preamble is assigned, the contention-based procedure Follow. The UE derives the target eNB specific key and sets the selected security algorithm used in the target cell.

  S10: The network responds with UL allocation and timing advance TA and UL Access Info.

  S11: When the UE successfully accesses the target cell, the UE transmits a HANDOVER CONFIRM message (C-RNTI) to the target eNB together with an uplink buffer status report (Buffer Status Report) if necessary, and the handover process for the UE is completed. It shows that. The target eNB verifies the C-RNTI transmitted in the HANDOVER CONFIRM message. In this way, the target eNB can start data transmission to the UE. Based on further optimization, it is also possible to start downlink data transmission at a stage after step S8.

  S12: The target eNB transmits a PATH SWITCH message to the MME, notifying that the UE has changed the cell.

  S13: The MME transmits a USER PLANE UPDATE REQUEST message to the serving gateway.

  S14: The serving gateway can switch the downlink data path to the target side and release the U-Plane / TNL resource to the source eNB.

  S15: The serving gateway sends a USER PLANE UPDATE RESPONSE message to the MME.

  S16: The MME responds to the PATH SWITCH message with a PATH SWTICH ACK message.

  S17: By transmitting RELEASE RESOURCE, the target eNB notifies the source eNB of the success of the handover and triggers the release of resources. The timing at which the target eNB between steps S10 and S15 transmits this message is for further study.

  S18: Upon receiving the RELEASE RESOURCE message, the source eNB can release radio and C-plane related resources related to the UE context.

  The present invention is applicable when, for example, the radio access scheme differs between base stations in a 3GPP LTE system. Needless to say, radio access schemes to which the present invention can be applied are not limited to OFDM and SC-FDMA.

10 mobile station 20 base station 20a source base station 20b target base station 30 MME / S-GW
DESCRIPTION OF SYMBOLS 101 Reception part 102 RS separation part 103 ID identification part 104 SNR measurement part 105 Measurement Report generation part 106 TA separation part 107 HO Command separation part 108 RACH generation part 109 Transmission part 200 Uplink radio | wireless access information generation part 201 Base station ID generation part 202 RS generator 203 Receiver 204 RACH separator 205 TA generator 206 HO Confirm generator 207 HO Completed generator 208 Measurement Report generator 209 Inter-base station signal receiver 210 Context Confirm separator 211 Context Data separator 212 HO Completed Separation unit 213 HO Command generation unit 214 Context Confirm generation unit 215 Context Data generation unit 216 Inter-base station signal transmission unit 217 transmission unit

Claims (5)

A first base station capable of communicating by a first wireless access method;
A second base station capable of communicating by the second radio access method;
And at least one mobile station,
When the mobile station is handed over from the first base station to the second base station, the first mobile station uses the first RACH (random access channel) signal commonly used by the first and second base stations. Make an initial connection with the wireless access method,
By the second radio access method, communication with the second base station after handover is performed.
A communication system characterized by the above. A mobile station that can communicate with a first base station that can communicate with a first radio access scheme or a second base station that can communicate with a second radio access scheme;
When handing over from the first base station to the second base station, the initial radio access scheme using the RACH (random access channel) signal commonly used by the first and second base stations connection,
By the second radio access method, communication with the second base station after handover is performed.
A mobile station characterized by that. A base station capable of communicating with a plurality of wireless access methods,
A mobile station that is handed over from another base station, and an initial connection in a first radio access scheme using a RACH (random access channel) signal that is commonly used by the other base station and the base station;
The mobile station communicates with the base station after the handover by a second radio access method.
A base station characterized by that. A communication method in a mobile station that can communicate with a first base station that can communicate with a first radio access scheme or a second base station that can communicate with a second radio access scheme,
When handing over from the first base station to the second base station, the initial radio access scheme using the RACH (random access channel) signal commonly used by the first and second base stations connection,
By the second radio access method, communication with the second base station after handover is performed.
A communication method characterized by the above. A communication method in a base station capable of communicating with a plurality of wireless access methods,
A mobile station that is handed over from another base station, and an initial connection in a first radio access scheme using a RACH (random access channel) signal that is commonly used by the other base station and the base station;
The mobile station communicates with the base station after the handover by a second radio access method.
A communication method characterized by the above.

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