JP5781098B2 - Wireless communication system, mobile station and base station - Google Patents

Description

  The present invention relates to a radio communication system, a mobile station, and a base station, and more particularly to a radio communication system, a mobile station, and a base station that are reordered in a mobile station by a sequence number.

Mobile communication systems such as mobile phones are currently being serviced by the CDMA third-generation system, but next-generation mobile communication systems (LTE: Long Term Evolution) that enable higher-speed communication are being studied. It is being promoted by 3GPP (3rd Generation Partnership Project) (Non-Patent Document 1). In this case, in addition to increasing the transmission rate, reducing transmission delay is a major issue.
In order to increase the transmission rate and reduce the transmission delay, the LTE communication system has been devised to improve the handover method compared to the conventional system. In mobile communication, when a mobile station moves during communication, switching (handover) of a base station for communication occurs according to a reception state. Therefore, advanced handover is essential for high-speed / low-delay communication. In the LTE communication system, since the packet switching system is basic, the handover is a hard handover. In hard handover, after the line connection with the base station with which the mobile station was communicating before moving is disconnected, the line between the mobile station and the destination base station is connected. In hard handover, it is possible to perform handover in a short time by obtaining system information of a destination base station immediately before handover, but a user data transmission interruption state occurs during handover.
Therefore, in order to reduce the transmission delay, it is important to shorten the transmission interruption state and to prevent packet loss during the transmission interruption. If a packet loss occurs during transmission interruption, the lost packet is recovered by end-to-end packet retransmission, resulting in an increase in transmission delay.

  Therefore, in handover in the LTE communication system, among the data including control information and packets addressed to the mobile station, packets that are not transmitted from the source base station to the mobile station are transferred from the source base station to the destination base station. The method of taking over is specified (Non-patent Document 2).

Takeover at handover FIG. 21 is an explanatory diagram of takeover at handover. In FIG. 21A, two base stations 1a and 1b are connected to an upper station (for example, MME / SAE gateway) 2. The mobile station 4 exists in the cell 3a of the base station 1a and is currently communicating with the base station 1a. In this state, as shown in FIG. 21B, when the mobile station 4 moves in the direction of the base station 1b and enters the cell 3b, a handover is executed, and the communication base station of the mobile station is changed from the base station 1a to the base station. Switch to 1b. Note that a base station that is communicating before a handover is called a source base station (source base station), and a base station that communicates after a handover is called a destination base station (target base station).
The source base station 1a stores the packet received from the upper station 2 in a built-in buffer, and sequentially transmits the packet stored in the buffer to the mobile station 4. For this reason, when a handover occurs, there are packets that are not transmitted to the mobile station but accumulated in the buffer. In FIG. 21B, packets n−2 to n are stored in the buffer without being received and sent to the mobile station before the handover, and these packets are transmitted from the destination base station 1b to the mobile station 4 after the handover. There is a need to. For this reason, at the time of executing the handover sequence, the source base station 1a transfers the packets n-2 to n to the destination base station 1b (forwarding). By using this forwarding method, the destination base station 1b transmits the packet to the mobile station 4 immediately after the handover, so that the packet is not interrupted. For this reason, packet retransmission does not occur end-to-end, and high-speed handover can be executed. The above n-2 to n are numbers (sequence numbers) indicating the order of packets.

Handover FIG. 22 is an explanatory diagram of handover in the LTE communication system, and FIG. 23 is an explanatory diagram of handover procedures currently assumed in the LTE communication system.
The mobile station 4 notifies the source base station 1 that a handover HO (Hand Over) is necessary by a measurement report (report of reception statuses from the base station 1 and neighboring base stations) (1. measurement control).
The source base station 1 determines the target base station 1b based on the contents of the Measurement Report (2.HO determination), and transmits a handover request to the destination base station 1b (3.HO request). At that time, the source base station 1a also transmits mobile station information (such as mobile station ID and QoS (Quality of Service) information). The movement-destination base station 1b performs call admission control based on the information (4. call admission control).
When the movement-destination base station 1b permits acceptance of the mobile station, a handover response is returned to the movement-source base station (5. HO response). Subsequently, the source base station 1a issues a handover instruction to the mobile station 4 (6. HO instruction), and starts taking over data (packets) before and after that (packet transfer: forwarding).
The mobile station 4 that has received the handover instruction ensures synchronization with the movement-destination base station 1b by L1 / L2 signaling (7. synchronization synchronization), and when synchronization is secured, transmits a handover completion report to the movement-destination base station 1a (8 .HO completed).
Thereby, the movement-destination base station 1b transmits a handover completion report to the upper station 2 (9.HO completion). Upon receiving the handover completion report, the upper station 2 switches the packet transmission path from the source base station 1a to the destination base station 1b (10. path switching), and returns an HO completion response to the destination base station 1b. (11. HO completion response). The movement-destination base station 1b notifies the movement-source base station 1a that the handover HO is completed by an HO completion response (12. resource release). Thereafter, the path between the source base station 1a and the upper station 2 is deleted (13. resource release).

Packet order matching control When packet forwarding (forwarding) occurs during the above handover sequence, the forwarded packet is skipped by the packet flowing in from the upper station 2 at the destination base station 1b, and the sequence number is May be disturbed. If packets are transferred to the mobile station 4 while the sequence number is disturbed from the destination base station 1b, the mobile station cannot receive the packets in the correct order, so the communication quality deteriorates, resulting in high quality communication before and after the handover. It cannot be realized.
Therefore, in the LTE communication system, the packet order consistency is maintained in the base station and the mobile station by the following method. FIG. 24 is an explanatory diagram of the order matching of such packets. The destination base station 1b preferentially transmits the packet transferred from the source base station 1a over the packet received from the higher-order station. Keep order consistency.
In FIG. 24, packets n-5 to n are accumulated in the source base station 1a before the handover, and among these packets, packets n-5 to n-2 are transmitted to the mobile station 4, but packet n −1 and n are not transmitted to the mobile station 4. Of the packets transmitted to the mobile station, the packets n-5 and n-3 are not correctly received by the mobile station 4 (NACK), and the packets n-4 and n-2 are normally received. (ACK). For this reason, the mobile station 4 stores the packets n-4 and n-2 in the buffer BF1, and does not store the packets n-4 and n-2.
In this state, when handover occurs, the source base station 1a moves the packets n-5 and n-3 that have not been normally received by the mobile station 4 and the packets n-1 to n that have not yet been transmitted to the mobile station 4. Transfer (forwarding) to the destination base station 1b, the destination base station 1b stores the packet in the buffer BF. The upper station 2 transmits two packets m to m + 1 addressed to the mobile station 4 after the handover to the destination base station 1b, and the destination base station 1b stores the packets in the buffer BF.
When the destination base station 1b becomes communicable with the mobile station 4, first, packets n-5, n-3, n-1 to n transferred from the source base station 1b are preferentially sent to the mobile station 4. Send. Next, the packets m to m + 1 received from the upper station 2 are transmitted. As shown in FIG. 25, the mobile station 4 receives received packets n-4 and n-2 received before the handover and packets n-5, n-3, n-1 to n, and m to m received after the handover. +1 is rearranged in order of sequence number and passed to the upper layer in order.

The above is a case where all of packets n-5, n-3, n-1 to n are transferred (forwarded) to destination base station 1b by forwarding, but only packets n-5, n-3 are transferred. , N-1 to n may be delayed. FIG. 26 is an explanatory diagram of packet order matching in such a case. The movement-destination base station 1b stores the transferred packets n-5 and n-3 and the packets m to m + 1 that flow in from the upper station in the buffer BF. The received packets n-5 and n-3 are preferentially transmitted to the mobile station. Thereafter, if the transfer of the packets n-1 and n from the source base station 1a is delayed, the movement-destination base station 1b monitors whether the set time (Waiting Time) has passed and the Waiting Time has passed. If the packets n-1 and n are not transferred from the source base station 1a, it is considered that the forwarding is completed, and the packets m and m + 1 received from the upper station are transmitted. Note that the movement-destination base station 1b discards the packet even if it is received from the packets n-1 and n from the movement-source base station 1a after the completion of the forwarding.
The mobile station 4 executes processing (reordering) for rearranging the received packets in order of sequence numbers. As shown in FIG. 27, the mobile station 4 arranges the received packets n-4, n-2 received before the handover and the packet packets n-5, n-3, m, m + 1 received after the handover in the order of sequence numbers. Sort and pass to higher layers in order.

Protocol Configuration As described above, packet transfer (forwarding) and packet reordering processing are essential techniques for handover in an LTE communication system. Here, the relationship between these functions will be described in more detail.
FIG. 28 is an explanatory diagram showing a protocol configuration between a mobile station and a network. Between the mobile station and the base station, at least a PDCP (Packet Data Convergence Layer) layer, an RLC (Radio Link Control) layer, and a lower layer (MAC layer / physical layer MAC / PHY) are installed. The MME / S-GW has a packet routing function.
The main functions of each protocol are as follows.
(1) PDCP: In the PDCP layer, the transmission side compresses the header of the upper protocol and adds a sequence number for transmission. The receiving side checks the sequence number and thereby discards duplicate reception. Retransmission is not performed in the PDCP layer.
(2) RLC: The RLC layer is a layer having a retransmission function, and transmits a sequence number newly added to the RLC layer separately from the sequence number added to the data from the PDCP. For example, if data of sequence number n is received from PDCP, the data is divided into a plurality of pieces, and sequence numbers I (1), I (2), I (3). Add and send. The reception side notifies the transmission side of a delivery confirmation signal (Ack / Nack signal) indicating normal reception / abnormal reception of data using the sequence number I (•). If the Ack signal is returned, the transmission side discards the retained data, and if the Nack signal is returned, the transmitting side resends the retained data.
(3) Lower layer • MAC: The MAC layer is a layer that multiplexes / separates RLC layer data. That is, the transmitting side multiplexes the RLC layer data into transmission data, and the receiving side separates the MAC layer reception data into RLC layer data.
PHY: The PHY layer is a layer that wirelessly transmits and receives data between the user terminal 4 and the base station 1, and converts MAC layer data into wireless data or converts wireless data into MAC layer data.

Data addressed to the mobile station first flows from the upper layer (for example, IP layer) to the PDCP layer to become PDCP SDU (Service Data Unit), and further header information (PDCP layer sequence number, etc.) is added to the PDCP PDU (Protocol Data). Unit).
The PDCP PDU is forwarded to the RLC layer to become an RLC SDU, and further header information (such as an RLC layer sequence number) is added to become an RLC PDU. The RLC PDU arrives at the RLC layer of the mobile station through lower layer processing. In this RLC layer, the header is removed and the RLC SDU is reconstructed, and in the PDCP layer, the PDCP PDU header is removed to form a PDCP SDU, which is forwarded to the upper layer.
In such a protocol configuration, in the LTE communication system, packet transfer is performed in units of PDCP SDUs, and reordering is performed in units of PDCP PDUs. In addition, when forwarding is performed in units of PDCP SDUs, since header information such as sequence numbers is not added to the packets in units of PDCP SDUs, the sequence numbers cannot be forwarded. Therefore, when forwarding is performed in units of PDCP SDU, header information such as a sequence number to be added is also forwarded. Since RLC SDU and PDCP PDU are substantially the same data, in this specification, unless otherwise specified, these are simply referred to as packets, and when the number of the packet is described, the number is the PDCP PDU. The sequence number of

Operation of source base station apparatus FIG. 29 is an operation flowchart of the source base station apparatus during handover.
If the source base station 1a receives the received field strength from the user terminal 4 according to the measurement report (step 101), the source base station 1a determines whether or not the handover HO is necessary (step 102).
However, if it is determined that handover is necessary, the source base station 1a determines the destination base station 1b based on the contents of the Measurement Report, and transmits a handover request to the destination base station 1b (step 103).
Thereafter, a handover response transmitted from the movement-destination base station 1b is received (step 104), and the remaining packets are forwarded (step 107).
Thereafter, a resource release message sent from the movement-destination base station 1b is received (step 108), and resource release is executed (step 109).

Operation of destination base station FIG. 30 is an operation flowchart of the destination base station at the time of handover.
When the destination base station 1b receives an HO request (including the mobile station ID and QoS information) from the source base station 1a (step 121), it performs call admission control based on the information and accepts the mobile station. It is determined whether or not to permit (step 122). If not permitted, post-processing is performed (step 130), and the handover control is terminated.
On the other hand, when the acceptance of the mobile station is permitted, an HO response is returned to the source base station 1a (step 123). Subsequently, the movement-destination base station 1b accumulates the packets transferred from the movement-source base station 1a in the buffer (step 124), and receives a report of HO completion from the mobile station 4 (step 125). If the HO completion report is received, the movement-destination base station 1b transmits the HO completion report to the upper station 2 (step 126). Upon receiving the handover completion report, the upper station 2 switches the packet transmission path from the source base station 1a to the destination base station 1b, and returns an HO completion response to the destination base station 1b. If the destination base station 1b receives an HO completion response from the upper station 2 (step 127), the destination base station 1b starts transmission from the packet forwarded from the destination base station 1b preferentially to the mobile station, and after transmitting the packet The packet received from the upper station 2 is transmitted to the mobile station (scheduling: step 128). In parallel with step 128, the destination base station 1b transmits resource release to the source base station 1a (step 129), performs post-processing (step 130), and ends the handover control. If the packet forwarding from the source base station 1a is delayed in the scheduling process of step 128, the destination base station 1b monitors whether the set time (Waiting Time) has elapsed and the Waiting Time has elapsed. However, if the packet is not transferred, it is regarded as the end of forwarding, and the packet received from the upper station is transmitted. Even if the packet is received from the source base station 1a after the completion of forwarding, the packet is discarded. .

-Operation of mobile station FIG. 31 is an operation flowchart of the mobile station at the time of handover.
The measuring unit of the mobile station 4 notifies the source base station of the received electric field strength and the like by a measurement report (step 151). Thereafter, when the HO instruction is waited from the source base station 1a and the HO instruction is received (step 152), synchronization is ensured with the destination base station 1b by L1 / L2 signaling (step 153), and handover is completed when synchronization is ensured. Is transmitted to the movement-destination base station 1b (step 154). Thereafter, when the mobile station receives a packet from the movement-destination base station 1b, it executes reordering processing (steps 155 to 160).
That is, when the control unit of the mobile station receives the lower layer packet from the movement-destination base station 1b, it constructs an RLC SDU and passes the RLC SDU (PDCP PDU) to the reorder unit (step 155). The reorder unit checks whether there is a missing sequence number (step 156), and if there is no missing sequence number, the RLC SDU (PDCP PDU) is passed to the higher layer as a PDCP SDU (step 160). On the other hand, if there is a missing sequence number, the control unit instructs the reorder unit to hold the PDCP PDU. As a result, the reorder unit holds the PDCP PDU (step 157) and checks whether an RLC SDU (PDCP PDU) having a continuous sequence number is received (step 158). If RLC SDUs (PDCP PDUs) having consecutive sequence numbers are received, the RLC SDUs (PDCP PDUs) are passed to the upper layer as PDCP SDUs, and the held PDCP PDUs are passed to the upper layer (step 160).
In step 158, if an RLC SDU (PDCP PDU) having a continuous sequence number is not received, it is monitored whether a preset time has elapsed (step 159). If not, processing in and after step 157 is performed. If the sequence number is discontinuous, the held PDCP PDU is passed to the upper layer (step 160).

-Problems By the way, when performing packet transfer accompanying handover in an LTE communication system, there are the following problems. That is, when the handover is executed, the LTE communication system takes over the data of the mobile station remaining in the source base station 1a as described above, and packet transfer (forwarding) occurs along with the takeover. However, in the above handover control, if the value of the Waiting Time of the destination base station 1b is small, the destination base station 1b starts transmission of packets received from the host station even though all packets are not forwarded. The problem of discarding unforwarded packets occurs. On the other hand, if the value of Waiting Time is large, the destination base station 1b does not transmit the packet received from the host station until the Waiting Time elapses even though all packets are forwarded, resulting in a transmission delay. There is a problem to do. That is, in the conventional handover control, communication delay increases and throughput deteriorates, and high-quality communication quality cannot be maintained before and after handover.

As a first conventional technique, there is a method of notifying the last packet to be forwarded (Last Packet) from the source base station to the destination base station (see Non-Patent Document 3). When the destination base station notified of the Last Packet is delayed in forwarding, the sequence number of the packet received from the higher-level station can be jumped and transmitted as the Last Packet sequence number +1. Also, the destination base station can forcibly end the waiting timer by comparing the sequence number of the forwarded packet with the sequence number of the last packet, and detects the end of forwarding at the optimal timing. can do. However, if the Last Packet is discarded during forwarding, the destination base station cannot reliably detect the Last Packet.
As a second conventional technique, there is a mobile communication system for realizing high-speed packet data transfer without data loss at the time of handover between base stations during high-speed packet communication (see Patent Document 1). In this mobile communication system, when a handover occurs, the handover source base station transfers packet data to the handover destination base station (forwarding). However, this does not improve communication delay increase or throughput degradation due to reordering in the mobile station.
Further, as a third prior art, there is a method in which a destination base station transmits a packet transmitted from a higher-level station without waiting for arrival of a forwarded packet (see Patent Document 2). In this method, the packet received from the source base station is distinguished from the packet received from the host station, thereby enabling the inter-packet transmission. However, in the mobile station, it is necessary to install two sequential control functions, and the control becomes complicated.

JP 2004-282652 A Japanese Patent Application No. 2006-086537

3GPP, "Requirements for Evolved UTRA (E-UTRA) and Evolved UTRAN (E-UTRAN)," TR25.913 V7.3.0, Release 7, March 2006. 3GPP, "Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN)," TS36.300, Release 8, V8.0.0, April2007. Samsung, "Method to release resources at source ENB during handover," R3-061032, RAN3 # 53, September 2006.

From the above, the object of the present invention is transmitted from the upper station (for example, a device different from the source base station and transmitting data (packets) to the destination base station) to the destination base station. It is to transmit the incoming packet to the mobile station promptly.
Another object of the present invention is to exclude a packet transmitted from the upper station from a target of sequence control even if a packet forwarded from the source base station and a packet transmitted from the upper station are mixed. Even if there is only one order control function, the forwarded packet is correctly reordered.
It should be noted that provision of matters that are described in the examples and the like but not disclosed in the prior art can be positioned as another object of the present invention. Preferably, such matters are necessary to obtain an effect that cannot be obtained by the prior art.

The present invention is a wireless communication system, a mobile station, and a base station.
The wireless communication system of the present invention includes a source base station, a destination base station, and a mobile station, and the destination base station receives a first sequence number from the source base station via a control plane. Receiving means capable of receiving the PDCP SDU and the second sequence number associated with the PDCP SDU from the source base station via the user plane, the first added to the PDCP SDU data transmitted to the mobile station Transmission means for transmitting either one of the sequence number and the second sequence number attached to the PDCP SDU received from the source base station to the mobile station for reordering in the mobile station The mobile station comprises a receiving means for receiving either the first sequence number or the second sequence number from the destination base station, the first sequence number or the second sequence number. And a reordering unit for reordering the data using Nsu number. The PDCP SDU data to which the first sequence number is added in the movement-destination base station is PDCP SDU data received by the movement-destination base station from the upper station.
The mobile station of the present invention is a sequence number that is transferred from the source base station to the destination base station via the control plane and is added to the PDCP SDU data transmitted to the mobile station by the destination base station. A second sequence number that can be received by the source base station and attached to the PDCP SDU that the source base station transfers to the destination base station via a user plane, and the destination base station adds to the PDCP SDU Receiving means capable of receiving from the destination base station, and reordering means for reordering data using the first sequence number or the second sequence number. The PDCP SDU data to which the first sequence number is added in the movement-destination base station is PDCP SDU data received by the movement-destination base station from the upper station.
The base station of the present invention can receive the first sequence number from the source base station via the control plane, and the second sequence associated with the PDCP SDU and the PDCP SDU from the source base station via the user plane. Receiving means capable of receiving a number, the first sequence number added to the PDCP SDU data transmitted to the mobile station, and the second sequence attached to the PDCP SDU attached to the PDCP SDU received from the source base station Transmitting means for transmitting any one of the sequence numbers to the mobile station for reordering in the mobile station. The PDCP SDU data to which the first sequence number is added is PDCP SDU data received by the destination base station from the upper station.

As described above, according to the present invention, packets transmitted from the upper station to the destination base station can be quickly transmitted to the mobile station as interlaced packets, data delay time can be eliminated, and the throughput of the entire system can be improved. In addition, the mobile station excludes the interlaced packet from the target of reordering control (order control), performs the order control of packets other than the interlaced packet, and passes the packet to the higher order apparatus in the order of the sequence number. As a result, the mobile station can correctly perform the order control of the reordering target packets even if the order control function is one.
Further, according to the present invention, the mobile station can detect the end of forwarding with reference to the last packet identification code, and can immediately stop the reordering. Therefore, the data delay time can be eliminated and the throughput of the entire system can be improved. Furthermore, according to the present invention, data order information (sequence number) can be transmitted from the source base station to the destination base station during forwarding. Further, the mobile station can reorder received data using the order information.

It is explanatory drawing of 1st Example. It is a format example of a PDCP PDU packet. It is explanatory drawing of the packet process of the PDCP layer and RLC layer before a hand-over. It is explanatory drawing of the packet processing of the PDCP layer and RLC layer after a hand-over. It is a block diagram of a base station. It is a block diagram of a mobile station. It is an operation | movement flowchart of the movement destination base station in 1st Example. It is a flowchart of the movement origin base station in 1st Example. It is an operation | movement flowchart of the mobile station of 1st Example. It is a reordering process flow of a mobile station. It is explanatory drawing of 2nd Example. It is a format example of a PDCP PDU packet. FIG. 7 is a diagram (part 1) illustrating packet processing of a PDCP layer and an RLC layer after handover. FIG. 11 is a diagram (part 2) illustrating packet processing of the PDCP layer and the RLC layer after handover. It is an operation | movement flowchart of the movement destination base station in 2nd Example. It is an operation | movement flowchart of the mobile station of 2nd Example. In this example, the sequence number of the PDCP PDU is notified through the data plane (U-plane) in association with the corresponding PDCP SDU data. This is an example in which the sequence number SN of the PDCP PDU is attached to the corresponding PDCP SDU data and notified by the U-plane, and the sequence number is notified via the C-plane. 19 is a handover sequence procedure of FIG. This is an example when there is no PDCP SDU data to be forwarded. FIG. 6 is an explanatory diagram of handover at the time of handover. It is a handover explanatory diagram of the LTE communication system. FIG. 10 is an explanatory diagram of a handover procedure currently assumed in the LTE communication system. It is the 1st explanatory view of reordering processing of a mobile station. It is the 2nd explanatory view of reordering processing of a mobile station. It is a 3rd explanatory drawing of the reordering process of a mobile station. It is the 4th explanatory view of reordering processing of a mobile station. It is explanatory drawing which shows the protocol structure between a mobile station and a network. It is an operation | movement flowchart of the movement origin base station apparatus at the time of a hand-over. It is an operation | movement flowchart of the movement destination base station at the time of a hand-over. It is a flowchart of the mobile station at the time of a handover.

(A) Principle of the present invention The present invention solves the problem by enabling the base station and the mobile station to execute the following two procedures.
Procedure 1: Since the data transfer from the source base station is delayed after the handover, when the received data is transmitted (interlaced transmission) from the upper station without waiting for the reception of the data, the mobile station Can be identified as interlaced data, and interlaced transmission is executed. That is, identification information for identifying the interlaced data is included in the data, added to the data, or associated with the data, and transmitted using, for example, a control channel.
Procedure 2: When the mobile station detects that interlaced transmission has occurred, the interlaced data is held in a buffer without being reordered, and waits for arrival of data transferred from the source base station. That is, reordering is performed by discriminating between data transferred from the source base station using identification information and data transmitted without going through the source base station.
In the conventional method, when data transfer (forwarding) from the source base station to the destination base station is delayed, transmission of data transmitted from the upper station to the destination base station is awaited. . For this reason, there is a problem that communication delay increases and throughput deteriorates by waiting for the arrival of a predetermined time (Waiting Time). However, as described above, when interlaced data transmission is performed, even if data transfer (forwarding) is delayed, the data received from the upper station can be quickly transmitted to the mobile station, thereby reducing communication delay. Decrease. Therefore, compared with the conventional method, the communication quality before and after the handover can be kept high.

(B) First Embodiment FIG. 1 is an explanatory diagram of the first embodiment, and it is described that order information is added in units of packets, but data of a predetermined size may be used.
Before the handover, packets n-5 to n are stored in the source base station 11a, and among these packets, packets n-5 to n-2 are transmitted to the mobile station 14, but packets n-1, n Is not transmitted to the mobile station 14. For example, since the packets n−1 and n arrive after the radio link between the source base station 11 a and the mobile station 14 is disconnected, the packets n−1 and n are not transmitted to the mobile station 14. Of the packets transmitted to the mobile station, the packets n-5 and n-3 are not correctly received by the mobile station 14 (NACK), and the packets n-4 and n-2 are normally received. (ACK). For this reason, the mobile station 14 stores packets n-4 and n-2 and does not store packets n-5 and n-3.
In this state, when a handover occurs, the source base station 11a transfers the packets n-5 and n-3 that have not been normally received by the mobile station 14 and the untransmitted packets n-1 and n to the destination base station 11b. (Forwarding). Hereinafter, although it demonstrates as transferring a packet, it is not limited to such an example.
The upper station 2 transmits packets m to m + 1 addressed to the two mobile stations to the movement destination base station 11b after the handover. Note that the transfer (forwarding) of packets n-5 to n is delayed.
If the destination base station 11b receives the packets m, m + 1 from the upper station 2 before the packets n-5, n-3, n-1 to n are forwarded from the source base station 11a, The interlaced identification code F is added to the packets m and m + 1 received from the upper station, and the packet is transmitted to the mobile station 14 (interlaced transmission) first.
The mobile station 14 saves the packet with the interlaced identification code F received from the base station in the buffer BF2, and excludes it from the reordering processing target. FIG. 1A shows a state where the mobile station 14 stores packets m and m + 1 in the buffer BF2, and stores packets n-4 and n-2 received before the handover in the buffer BF1.
Next, the movement-destination base station 11b transmits packets n-5, n-3, n-1 to n forwarded from the movement-source base station 11a to the mobile station. The mobile station 14 stores these packets n-5, n-3, n-1 to n received from the destination base station 11b in the buffer BF1, and these received packets after the handover and those received before the handover. The reordering process with n−4 and n−2 is executed (see FIG. 1B), and the packets are transferred to the upper layer in the order of consecutive numbers. If a packet having a consecutive number is not received even after a predetermined time has elapsed, the reordering process is terminated, and the packets that have been received and rearranged are passed to the upper layer. Next, the mobile station 14 passes the packets to which the interlaced identification code F is added in order to the upper layer.
During forwarding, the entire packet can be transferred from the source base station to the destination base station, or only a part of data (user data part) included in the packet can be transferred. Preferably, order information is added to the transfer data.
In FIG. 1, the sequence numbers (order information) m and m + 1 are assigned to the packets that have been subjected to interlaced transmission. However, the destination base station 11b can assign an arbitrary sequence number and is forwarded. A number that overlaps the sequence number added to the packet can be added, or a number that does not overlap.

Interlaced identification code As an example of adding the interlaced identification code F to the packet, a 3-bit “type” field included in the header of the PDCP PDU is used. That is, a new type number is defined as a skip identification code F in the “type” field, and the type number is added to a packet to be transmitted by skipping. FIG. 2 is a format example of a PDCP PDU, where (A) is a format example without a header, (B) is a format example without a PDCP PDU sequence number added, and (C) and (D) are PDCP PDU formats. It is a format example to which a sequence number is added. In the formats (C) and (D), a type field and a PID field are defined in the header HD, and the type field indicates the type of PDCP PDU. The PID field is a field indicating the type of header compression for data included in the Data portion. In the type field, “type = 000” and “type = 001” are already defined, but “type = 010 to 111” is not defined and unused. Therefore, for example, “type = 010” is used as a type number (interlaced identification code) for identifying a PDCP PDU that has performed interlaced transmission.

Processing of PDCP layer and RLC layer before and after handover control FIG. 3 is an explanatory diagram of packet processing of the PDCP layer and RLC layer before handover. The source base station 11b accumulates the PDCP layer packets n-5 to n-2 in the buffer ((A) in FIG. 3), and the RLC layer divides the packet into a plurality as shown in (B), RLC layer sequence numbers I, I + 1, I + 2,..., I + 6 are added to the respective divided data and transmitted to the mobile station 14. The mobile station 14 performs order control on the PDCP layer at the RLC layer before the handover. In FIG. 3, the mobile station 14 has divided data I, I + 4. It is assumed that I + 5, that is, packets n-5 and n-3 were not normally received, but packets n-4 and n-2 were normally received.
FIG. 4 is an explanatory diagram of the packet processing of the PDCP layer and the RLC layer after the handover, and specifically shows the state of processing of the PDCP layer and the RLC layer. Note that the mobile station 14 performs order control on the PDCP layer in the RLC layer before the handover, but it is specified that the RLC layer is initialized after the handover. For this reason, the order control process moves to the PDCP layer, and the mobile station 14 executes the handover sequence in the PDCP layer.
At the time of reordering, the mobile station 14 starts a timer to determine the end of reordering.
Since the arrival of the packets m and m + 1 received from the upper station 2 is early, the movement-destination base station 11b adds the identification code F to the packets m and m + 1 and transmits the packets m and m + 1 to the mobile station 14 first (jumping transmission). The mobile station 14 saves the packet with the interlaced identification code F received from the base station in the buffer BF2, and excludes it from the reordering processing target. Thereafter, the mobile station 14 reorders the packets n-5, n-3, n-1 to n received from the destination base station 11b and the packets n-4, n-2 received before the handover. And pass it to the upper layer.
The mobile station 14 ends the reordering process when the timer elapses a predetermined time T _M , and forwards the received packet to the upper layer even if there is a missing packet.

Window control The mobile station 14 internally generates a buffer size window in preparation for the arrival of data exceeding the allowable data amount, and performs the following window control during the reordering process. In the example of FIG. 4, the left end of the window is n-5 which is a number expected to arrive at the initial stage, and the right end of the window is a number determined by the allowable data amount (window buffer size), which is n-2. The mobile station does not apply window processing to a packet to which the interlaced identification code F is added.
In the initial state (window state (0)), if the mobile station 14 receives the expected packet (n-5) and performs reordering processing, the window state becomes as shown in (1). For this reason, the mobile station transfers the expected packet (n-5) and the packet (n-4) continuous thereto to the upper layer. Next, the window state becomes as shown in (2). When the mobile station 14 receives the expected packet (n-3) in this state and performs reordering processing, the window state becomes as shown in (3). . For this reason, the mobile station transfers the expected packet (n-3) and the packet (n-2) continuous thereto to the upper layer. Then, the window state becomes as shown in (4), the mobile station 14 is a packet in this state (n-1), waits to receive a n, and transfers it to the upper layer if received within a period of set time T _M . However, if the packets (n−1) and n are not received within the set time T _M , the mobile station 14 transfers the packets after the packet m stored in the buffer BF2 to the upper layer and performs normal handover. Transition to previous control. As described above, reordering for packets n-5 to n can be executed by performing the above-described window control while excluding interlaced packets.
In the window control, when the mobile station 14 receives a packet having a sequence number smaller than the sequence number at the left end of the window, the mobile station 14 discards the packet. When the mobile station 14 receives a packet with a sequence number larger than the sequence number at the right end of the window, the sequence number at the right end of the window is used as the sequence number of the packet, and the sequence number at the left end of the window is changed to a number determined by the window buffer size. At the same time, the received packet popped out of the window range is passed to the upper layer.
If window processing is also applied to the interlaced packet, when the packet m is received, the window state is, for example, n-2 at the left end of the window and m at the right end of the window. In this case, the mobile station gives up the reception of the packets n-5 and n-3 that have not yet been received, and transfers the received packets n-4 and n-2 to the upper layer. Then, the sequence number at the right end of the window is set to m, the sequence number at the left end of the window is set to a number n-1 determined by the window size, and thereafter, packet n-1, packet n, packet n + 1,. Wait for the arrival of packet m-1. However, among these packets, packets n + 1 to m−1 are packets that do not actually exist, so that the reception of these packets is wasted, resulting in a problem in packet processing.

Configuration of base station FIG. 5 is a configuration diagram of a base station, which shows a buffer unit, a scheduler unit, a transmission / reception unit, and a control unit.
The buffer unit 21 is a memory for accumulating packets that flow in from the upper station and packets that are transferred from the adjacent base station (source base station). In this figure, two buffers 21a and 21b are physically installed. However, a device configuration in which one memory is physically installed and divided into software can be used.
The scheduler unit 22 selects a mobile station that performs radio transmission from a plurality of communicating mobile stations, extracts the packet of the corresponding mobile station stored in the buffer unit, and forwards the packet to the transmission / reception unit. The transmission / reception unit 23 performs encoding and modulation processing of packets transmitted from the scheduler, and performs actual data transmission over the air. It also receives and demodulates control signals and various data transmitted from the mobile station.
The control unit 24 includes a buffer management unit 24a, an HO control unit 24b, and a measurement information control unit 24c. The buffer management unit 24a manages various packets stored in the buffer 21. When data takeover is executed at the time of handover, packets stored in the buffer unit 21b for which at least normal reception confirmation (ACK) has not been obtained are transferred to the destination base station 11b. On the other hand, when the arrival of the packet forwarded from the source base station 11a is delayed due to the data takeover and the packet received from the upper station 12 is interlaced, “type = 010” is set in the type field of the interlaced packet header. Fill in.
The HO control unit 24b executes the handover control described in FIG. 23, and the measurement control unit 24c collects various measurement information transmitted from the mobile station, for example, radio quality CQI (Channel Quality Information) of the mobile station.

Configuration of Mobile Station FIG. 6 is a configuration diagram of the mobile station, and shows a transmission / reception unit 31, a buffer unit 32, a scheduler unit 32, a reorder unit 33, and a control unit 34. The transmission / reception unit 31 performs transmission / reception of packets and control information with the transmission / reception unit of the base station. If the RLC PDU cannot be constructed from the received lower layer packet, the buffer unit 32 holds the RLC PDU until the RLC PDU can be constructed. If the RLC PDU can be constructed, the buffer unit 32 removes the header and reorders the RLC SDU (PDCP PDU). Pass to part 33. The reorder unit 33 has a function of rearranging PDCP PDUs in order of sequence numbers and passing them to the upper layer. When the reorder unit 33 detects a missing sequence number of the PDCP PDU, the reorder unit 33 holds subsequent PDCP PDUs in the built-in memory until receiving PDCP PDUs having consecutive sequence numbers. However, if the PDCP PDU does not arrive even after a predetermined time has elapsed, the reorder unit stops the reordering process and passes all the accumulated PDCP PDUs to the upper layer. Further, the reorder unit 33 performs window control so that the amount of data to be processed does not exceed the allowable amount during reordering.
The control unit 34 includes a measurement control unit 34a, a reorder management unit 34b, and a retransmission management unit 34c. The measurement control unit 34a measures various measurement information transmitted to the base station. For example, radio quality CQI (Channel Quality Information) of the mobile station is measured. The reorder management unit 34b controls the reorder unit 33, and instructs to wait for arrival of PDCP PDUs having consecutive numbers when the number of PDCP PDUs held by the reorder unit 33 is lost. When the arrival time of the packet has passed a predetermined time, the reorder unit 33 is instructed to stop reordering, and the headers of all held PDCP PDUs are removed and passed to the upper layer as PDCP SDUs. Instruct to make it possible to receive new PDCP PDUs. Further, the reorder management unit 34b sets the maximum sequence number received so far as the sequence number at the right end of the window, and determines and sets the sequence number at the left end of the window in consideration of the window size. If there is a received packet having a sequence number smaller than the sequence number at the left end of the window, the packet is directly transferred to the upper layer. During retransmission control, the retransmission management unit 34c transmits a retransmission request signal to the base station via the transmission / reception unit via a route indicated by a dotted line.

Operation of destination base station FIG. 7 is an operation flowchart of the destination base station of the first embodiment.
When the handover control unit 24b of the destination base station 11b receives an HO request (including the mobile station ID and QoS information) from the source base station 11a (step 201), it performs call admission control based on the information, It is determined whether or not to accept the mobile station (step 202). If not permitted, post-processing is performed (step 213), and handover control is terminated.
On the other hand, when permitting acceptance of the mobile station, the handover control unit 24b returns an HO request response message to the source base station 11a (step 203). Subsequently, the movement-destination base station 11b waits for a packet transferred from the movement-source base station 11a, and thereafter, the buffer unit 21 stores the packet forwarded from the movement-source base station 11a if received (step 204). .
In this state, when the handover control unit 24b receives the HO completion report from the mobile station 14 (step 205), the handover control unit 24b transmits the HO completion report to the upper station 12 (step 206). Upon receiving the handover completion report, the upper station switches the packet transmission path from the source base station 11a to the destination base station 11b, and returns an HO completion response to the destination base station 11b. If the handover control unit 24b of the movement-destination base station 11b receives an HO completion response from the upper station 12 (step 207), it instructs the scheduler unit 22 to start transmitting packets (step 208).
Thereby, the scheduler unit 22 checks whether it is necessary to perform inter-packet transmission (step 209). If there is no need, the scheduler unit 22 preferentially transmits the packet forwarded from the source base station 11a to the mobile station 14. (Step 210). However, if the forwarding of the packet from the source base station 11a is delayed and it is necessary to perform the inter-packet transmission, the scheduler unit 22 executes the inter-transmission transmission of the packet received from the upper station 12.
To execute interlaced transmission, the type number of the type field of the interlaced packet is set to 010 (type = 010) so that the mobile station 14 can identify the interlaced packet (step 211). The packet is transmitted to the mobile station 14 (step 210).
In parallel with the above, the handover control unit 24b transmits resource release to the source base station 11a (step 212), performs post-processing (step 213), and ends the handover control.

Operation of source base station FIG. 8 is an apparatus operation flowchart of the source base station of the first embodiment.
In FIG. 8, if the measurement control unit 24a of the source base station 11a receives the reception state information from the mobile station 14 using the Measurement Report (step 251), a handover (Hand Over: HO) is required based on the reception state information. Whether or not (step 252). If handover is unnecessary, the process returns to the beginning.
However, if it is determined that the handover HO is necessary, the handover controller 24b determines the destination base station 11b based on the contents of the Measurement Report, and transmits a handover request to the destination base station 11b (step 253).
Thereafter, if the HO response message transmitted from the movement-destination base station 11b is received (step 254), the HO control unit 24b transmits the HO instruction message to the mobile station 14 (step 255), and the buffer management unit 24a stores the buffer. 21 instructs the forwarding (packet transfer) of the remaining packet to the destination base station 11b. As a result, the buffer management unit 24a forwards the packet that has not been transmitted to the mobile station 14 existing in the buffer 21b or the packet (NACK packet) that has not been normally received (NACK packet) to the destination base station 11b by the dotted line route (step 256). ). Thereafter, a resource release message sent from the movement-destination base station 11b is received (step 257), and resource release is executed (step 258).

-Operation of mobile station FIG. 9 is an operation flowchart of the mobile station.
The measurement unit 34a of the mobile station 14 notifies the movement source base station 11a of the reception state and the like by a measurement report (step 271). Thereafter, the control unit 34 waits for the HO instruction message sent from the source base station 11a, and if it receives the HO instruction message (step 272), it ensures synchronization with the destination base station 11b by L1 / L2 signaling ( Step 273) When synchronization is secured, a handover completion report is transmitted to the destination base station 11b (Step 274). Thereafter, the control unit 34 checks whether the received packet is a skipped packet, in other words, a packet of type = 010 (step 275). If it is a skipped packet, it is excluded from the reordering target. The data is stored in the buffer 32, and after the set time has elapsed, the header is removed and the PDCP SDU packet is passed to the upper layer (step 276). On the other hand, if the packet is not an interlaced packet, reordering is performed, rearranged in order, and passed to the upper layer as a PDCP SDU packet (step 277).

FIG. 10 is a reordering process flow of the mobile station.
When the transmitting / receiving unit 31 of the mobile station receives the lower layer packet from the destination base station 11b (step 301), the reorder management unit 34b checks whether the RLC PDU can be constructed (step 302). (Step 303), if the set time has not elapsed, the lower layer packet is stored in the buffer 32 (step 304), and the processing after step 301 is performed. If the RLC PDU cannot be constructed even after the set time has elapsed after receiving the lower layer packet, the lower layer packet is deleted from the buffer (step 305).
On the other hand, if the RLC PDU can be constructed using the lower layer packet received in step 302, the RLC PDU is transferred to the reorder unit 33 as an RLC SDU (PDCP PDU) (step 306). If the reorder unit 33 receives the RLC SDU (PDCP PDU), the reorder unit 33 checks whether there is a missing sequence number (step 307). If there is no missing sequence number and the sequence numbers are consecutive, the RLC SDU (PDCP PDU) The header is deleted and PDCP SDU is passed to the upper layer (step 311). However, if there is a missing sequence number, the reorder management unit 34b instructs the reorder unit 33 to hold the PDCP PDU (step 308). As a result, the reorder unit 33 holds the PDCP PDU and checks whether an RLC SDU (PDCP PDU) having a continuous sequence number has been received (step 309). When RLC SDUs (PDCP PDUs) having consecutive sequence numbers are received, the RLC SDUs (PDCP PDUs) are transferred to the upper layer as PDCP SDUs, and the held PDCP PDUs are transferred to the upper layer (step 311).
In step 309, if RLC SDUs (PDCP PDUs) having consecutive sequence numbers are not received, it is monitored whether a preset time T _M has passed (step 310). When the set time T _M elapses, even if the sequence number is discontinuous, the held PDCP PDU is passed to the upper layer (step 311).
As described above, according to the first embodiment, a packet transmitted from the upper station 12 to the movement-destination base station 11b can be transmitted to the mobile station 14 without waiting as an interlaced packet, and the data delay time can be eliminated. Overall throughput can be improved. Further, the mobile station 14 excludes the interlaced packets from the reordering control (order control) target, performs the order control of the packets other than the interlaced packets, and passes the packets to the host device in the order of the sequence numbers. As a result, the mobile station can control the order of packets even if there is only one order control function.

(C) In the second embodiment the first embodiment, the mobile station 14 performs the time reordering processing time setting T _M, and ends the reordering process when the set time T _M has elapsed (step of FIG. 10 310 ). For this reason, the mobile station 14 continues the reordering process if the set time T _M has not elapsed even after receiving all the forwarded packets from the source base station 11a to the destination base station 11b. Therefore, in the second embodiment, the destination base station 11b adds an identifier to a predetermined packet (Last packet) and transmits it to the mobile station so that the mobile station 14 can identify the last packet to be reordered. If the mobile station 14 receives the Last packet, the mobile station 14 immediately ends the reordering process even if the set time T _M has not elapsed.
FIG. 11 is an explanatory diagram of the second embodiment, in which packets n-5 to n are stored in the source base station 11a before handover, and among these packets, packets n-5 to n-2 are mobile stations. 14, but the packets n−1 and n are not transmitted to the mobile station 14. For example, since the packets n−1 and n arrive after the radio link between the source base station 11 a and the mobile station 14 is disconnected, the packets n−1 and n are not transmitted to the mobile station 14. Of the packets transmitted to the mobile station, the packets n-5 and n-3 are not correctly received by the mobile station 14 (NACK), and the packets n-4 and n-2 are normally received. (ACK). For this reason, the mobile station 14 stores packets n-4 and n-2 and does not store packets n-5 and n-3.
In this state, when a handover occurs, the source base station 11a transfers the packets n-5 and n-3 that have not been normally received by the mobile station 14 and the untransmitted packets n-1 and n to the destination base station 11b. (Forwarding). The upper station 12 transmits two packets m to m + 1 to the movement-destination base station 11b after the handover. Note that the transfer (forwarding) of packets n-5 to n is delayed.
If the destination base station 11b receives the packets m, m + 1 from the upper station 2 before the packets n-5, n-3, n-1 to n are forwarded from the source base station 11a, The interlaced identification code F is added to the packets m and m + 1 received from the upper station, and the packet is transmitted to the mobile station 14 (interlaced transmission) first. The mobile station 14 saves the packet with the interlaced identification code F received from the base station in the buffer BF2, and excludes it from the reordering processing target. FIG. 11A shows a state where the mobile station 14 stores the packets m and m + 1 in the buffer BF2, and stores the packets n-4 and n-2 received before the handover in the buffer BF1.

The movement-destination base station 11b sends the forwarded packet to the mobile station until a preset time T _W (Waiting Time) elapses, but receives the forwarded packet when the Waiting Time elapses. Destroy it. Therefore, the movement-destination base station 11b receives the packets n-5, n-3, n-1 forwarded from the movement-source base station 11a before the waiting time has elapsed, stores them in the buffer BF, and stores them one by one. Transmit to the mobile station. Then, it is assumed that the waiting time has expired when the packet n is received from the source base station 11a and is not yet transmitted to the mobile station. In such a case, the movement-destination base station 11b adds the identifier (L) indicating that it is the last packet forwarded to the packet n and transmits it to the mobile station 14.
The mobile station 14 stores the packets n−5, n−3, n−1, and n received from the destination base station 11b in the buffer BF1, and as shown in FIG. Reordering processing is performed on the packets n-4 and n-2 received at the same time and rearranged. Also, if the identifier (L) added to packet n is detected, it is determined that forwarding has ended, and the reordered packet is passed to the upper layer even if the reordering set time T _M has not expired. Then, the reordering process is terminated.
The above is a case where the Waiting Time expires before transmitting the packet n. However, the Waiting Time may expire when the packet n is transmitted to the mobile station. In this case, the movement-destination base station 11b adds the identifier (L) indicating that it is the last packet to the packet m + 2 received from the higher-level station 12, and transmits the packet m + 2 to the mobile station 14. The mobile station 14 that has received the Last packet with the identifier added determines that the forwarding has ended, and immediately ends the reordering even if the reordering set time T _M has not expired.
In addition, although the packet n-3 is received by forwarding, the waiting timer may expire at the stage where the packets n-1 and n are not received. In such a case, the movement-destination base station 11b adds the identifier (L) indicating that it is the last packet to the packet n-3 and transmits it to the mobile station 14. The mobile station 14 detects the Last packet to which the identifier (L) is added and ends the reordering process.

・ Last packet identification code L
In order to add an identifier (last packet identification code) L indicating a Last packet to the packet, a 3-bit “type” field included in the header of the PDCP PDU is used. That is, a new type number is defined as the last packet identification code L in the “type” field, and the type number is assigned to the first packet to be transmitted after the waiting time expires. FIG. 12 is a format example of a PDCP PDU, where (A) is a format example without a header, (B) is a format example without a PDCP PDU sequence number added, and (C) and (D) are PDCP PDU formats. It is a format example to which a sequence number is added. In the formats (C) and (D), a type field and a PID field are defined in the header HD, and the type field indicates the type of PDCP PDU. In the type field, “type = 000” and “type = 001” are already defined, but “type = 010 to 111” is not defined and unused. Therefore, for example, “type = 011” is used as a type number for identifying the first PDCP PDU packet (Last packet) to be transmitted after the Waiting Time expires.

PDCP Layer and RLC Layer Processing FIGS. 13 and 14 are explanatory diagrams of PDCP layer and RLC layer packet processing after handover.
FIG. 13 shows a case where the last packet identification code L is added to the packet n transmitted to the mobile station. At the time of reordering, the mobile station 14 starts a timer to determine the end of reordering. Here, if the set time T _M is set to a large value, the reordering process is continued even though the packet n is the last packet that has been forwarded, and the packet is not received until the set time T _M expires. Cannot forward to higher layer. However, in the second embodiment, when the mobile station 14 receives the packet n (Last packet) to which the last packet identification code L is added, it immediately terminates the reordering and forwards all PDCP PDU packets to the upper layer. .
In addition, the mobile station 14 performs window control at the time of reordering in preparation for the arrival of data exceeding the allowable data amount. The left end of the window is n-5, which is a number that is expected to arrive, and the right end of the window is a value that is the upper limit of the allowable data amount (in the figure, it is n). However, as in the first embodiment, window processing is not applied to a packet of “type = 010”. By processing in this way, it is possible to execute reordering for packets n-5 to n.
FIG. 14 shows a case where the last packet identification code L is added to the packet m + 2. Even when the set time T _M has not expired when the mobile station 14 receives the packet m + 2 (Last packet), the mobile station 14 immediately ends the reordering and forwards all received PDCP PDU packets to the upper layer. To do. Further, the window control is executed in the same manner as in FIG.

Operation of destination base station FIG. 15 is an operation flowchart of the destination base station of the second embodiment, and the same steps as those in FIG. 7 of the first embodiment are denoted by the same reference numerals. The base station and mobile station of the second embodiment have the configurations shown in FIGS.
When the handover control unit 24b of the destination base station 11b receives an HO request (including the mobile station ID and QoS information) from the source base station 11a, it performs call admission control based on the information and accepts the mobile station. Determine whether to allow. If not permitted, post-processing is performed, and handover control is terminated (steps 201 to 202, 213).
On the other hand, when permitting acceptance of the mobile station 14, the handover control unit 24b returns an HO request response message to the source base station 11a and starts counting elapsed time. Thereafter, the destination base station 11b waits for a packet transferred from the source base station 11a and stores the packet in the buffer unit 21 (steps 203 to 204).
In this state, when receiving the HO completion report from the mobile station 14, the handover control unit 24b transmits the HO completion report to the upper station 12 (steps 205 to 206). Upon receiving the handover completion report, the upper station 12 switches the packet transmission path from the source base station 11a to the destination base station 11b, and returns an HO completion response to the destination base station. When the handover control unit 24b of the movement-destination base station 11b receives the HO completion response from the upper station, the handover control unit 24b instructs the scheduler unit 22 to start packet transmission (steps 207 to 208).
Then, the scheduler unit 22, or elapsed time has exceeded the set time T _W, i.e., monitors whether Waiting Time has expired (step 501), unless and Waiting Time expires, you need to jump transmission of packets If there is no necessity, transmission is preferentially started from the packet forwarded from the source base station 11a to the mobile station 14 (step 210). However, if the forwarding is delayed and it is necessary to perform inter-packet transmission, the scheduler unit 22 performs inter-transmission of the packet received from the upper station 12. In order to execute interlaced transmission, the type number 010 (type = 010) of the type field of the packet header to be interlaced is set so that the mobile station 14 can identify the interlaced packet (step 211). The packet is transmitted to the mobile station (step 210).
In parallel with the above, the handover control unit 24b transmits resource release to the source base station 11a (step 212), returns to step 501, and checks whether the waiting time has expired. Repeat the process.
On the other hand, if the waiting time expires in step 501, the type number of the packet to be transmitted immediately after the expiration of the waiting time is set to “011”. That is, the last packet identification code L is added to the packet to be transmitted immediately after expiration, and the packet (Last packet) is transmitted to the mobile station (steps 502 to 503). Thereafter, post-processing is performed, and handover control is terminated. (212-213).
In step 502, the former packet can be identified so that it can be identified whether the Last packet to which the last packet identification code L is added is a packet forwarded from the source base station 11a or a packet received from the upper station 12. Type number is set to “011” in the case of the packet, and type number is set to “100” in the case of the latter packet. In this way, reordering processing of the mobile station 14 described later becomes easy.

FIG. 16 is a flowchart of the operation of the mobile station. The same steps as those in the operation flow of FIG. The measurement unit 34a of the mobile station notifies the source base station 11a of the reception state and the like using a measurement report. Thereafter, the control unit 34 waits for the HO instruction message sent from the source base station. If the control unit 34 receives the HO instruction message, the control unit 34 ensures synchronization with the destination base station 11b by L1 / L2 signaling. A completion report is transmitted to the movement-destination base station (steps 271 to 274).
Thereafter, the control unit 34 checks whether the received packet is a skipped packet, in other words, a packet of type = 010 (step 600). If it is a skipped packet, it is excluded from reordering targets. The data is stored in the buffer 32 (step 601).
On the other hand, if it is not an interlaced packet, it is checked whether the received packet is a Last packet, in other words, a packet of type = 011 (step 602). If it is not the Last packet, reordering is started, the PDCP PDU packets are rearranged in order, a PDCP SDU is generated and passed to the upper layer (step 603).
Thereafter, it is determined whether the set time T _M has expired in advance (step 604), if there are set time T _M has expired repeat steps 600 and subsequent steps, if the set time T _M has expired, reordering After the process is completed, the header is deleted from the PDCP PDU packet that has not been passed to the upper layer and a PDCP SDU is generated and passed to the upper layer (step 605). Next, the non-reordering target packet is passed to the upper layer, and the process is terminated (step 606).
On the other hand, if the received packet is a Last packet in step 602, the reordering process is immediately stopped (step 607). At this time, if the Last packet is a forwarded packet, a PDCP SDU packet is generated from the Last packet, passed to the upper layer, and reordering is stopped. If the Last packet is a packet received from the upper station 12, the reordering is immediately stopped, and the Last packet is connected to the end of the packet not to be reordered. Thereafter, the non-reordering target packet is passed to the upper layer and the process is terminated (step 606).
As described above, according to the second embodiment, the mobile station can detect the end of forwarding with reference to the last packet identification code, and can immediately stop reordering. Therefore, the data delay time can be eliminated and the throughput of the entire system can be improved.

(D) Third Embodiment The order information (sequence numbers n, m) shown so far is a convenient number for simplifying the explanation, and is actually added at the base station.
As described above, in the LTE communication system, forwarding is performed in units of PDCP SDU data. For this reason, when forwarding occurs, the Sequence Number field cannot be transmitted from the source base station 11a to the destination base station 11b, and it is necessary to notify the sequence number (Sequence Number) by some method.
In this embodiment, the source base station 11a notifies the destination base station 11b of the sequence number together with the PDCP SDU data, and the destination base station is forwarded based on the sequence number PDCP SDU data (packet) Is appended with the sequence number.
FIG. 17 shows an example in which the sequence number of the PDCP PDU is notified through the data plane (U-plane) in association with the data (packet) of the corresponding PDCP SDU. FIG. 17 shows only the PDCP SDU data and the sequence number SN associated with the data, but control information (header information) needs to be added in order to consider the PDCP SDU data as a set of packets. Each time the source base station 11a forwards the PDCP SDU data, the source base station 11a notifies the sequence number SN accompanying the PDCP SDU data in the format of FIG. 17, and the destination base station 11b is forwarded based on the sequence number. The sequence number is added to the PDCP SDU data (packet).
That is, in the situation of FIG. 17, the source base station 11a first forwards the sequence number n-5 and the first PDCP SDU data via the data plane U-plane. Subsequently, the sequence number n-3 and the next PDCP SDU data are forwarded via the U-plane. Thereafter, when PDCP SDU data n−1, n received from the upper station 12 is forwarded, the PDCP SDU data and its sequence number are similarly forwarded to the movement-destination base station 11b via the U-plane. The movement-destination base station 11b can recognize the sequence number of the forwarded data by receiving the sequence numbers n-5, n-3, n-1, and n notified by the U-plane.

FIG. 18 shows a PDCP in which the PDCP PDU sequence number SN is attached to the corresponding PDCP SDU data and notified in U-plane (in band), and the source base station 11a has not confirmed normal reception from the mobile station. In this example, the sequence number of SDU data is notified as Next SN via a control plane (C-plane). The notification of the sequence number (Next SN) via the C-plane is indicated as “SN takeover” in the handover sequence diagram of FIG. SN handover can be performed simultaneously when the source base station 11a makes an HO request to the destination base station 11b.
In the situation of FIG. 18, the source base station 11a first forwards the sequence number n-5 and the first PDCP SDU data via the U-plane. Subsequently, the sequence number n-3 and the next PDCP SDU data are forwarded via the U-plane. In addition, the source base station 11a notifies the destination base station 11b via the C-plane of only the sequence number n-5 of the PDCP SDU that could not be confirmed normally by the mobile station as Next SN (SN takeover). ). Thereafter, when the source base station 11a forwards the PDCP SDU data n−1, n received from the upper station 12, the PDCP SDU data and its sequence number are similarly transmitted to the destination base station 11b via the U-plane. Forward. The movement-destination base station 11b receives the sequence number n-5 notified by the C-plane and the sequence numbers n-5, n-3, n-1, and n notified by the U-plane. Since the sequence number notified by the plane is larger than the sequence number notified by the C-plane, the sequence number is added to the PDCP SDU data based on the sequence number notified by the U-plane and then transmitted to the mobile station. . That is, the movement-destination base station 11b ignores the sequence number n-5 notified by the C-plane.
FIG. 20 shows an example where there is no PDCP SDU data to be forwarded.
The movement-source base station 11a notifies the movement-destination base station 11b of the sequence number n + 1 that has not been confirmed by the mobile station via the C-plane as Next SN. When the Waiting Time expires without receiving the PDCP SDU data from the source base station 11a, the destination base station 11b moves after adding the sequence number to the PDCP SDU data based on the sequence number notified by the C-plane. Transmit to the station. That is, the movement-destination base station 11b transmits the sequence number of the packet m received from the upper station 12 to the mobile station as n + 1.

11a source base station 11b destination base station 12 upper station 14 mobile station

Claims (6)

The source base station,
The destination base station,
A mobile station,
The destination base station is
Receiving means capable of receiving a first sequence number from a source base station via a control plane and receiving a PDCP SDU and a second sequence number associated with the PDCP SDU from a source base station via a user plane;
Either the first sequence number added to the PDCP SDU data transmitted to the mobile station or the second sequence number attached to the PDCP SDU attached to the PDCP SDU received from the source base station is moved. Transmitting means for transmitting to the mobile station for reordering at the station,
The mobile station
Receiving means for receiving either the first sequence number or the second sequence number from the destination base station;
Reordering means for reordering data using the first sequence number or the second sequence number
A wireless communication system. The PDCP SDU data to which the first sequence number is added in the movement-destination base station is PDCP SDU data received by the movement-destination base station from an upper station.
2. The wireless communication system according to claim 1, wherein First sequence number the destination base station to the PDCP SDU data to be transmitted to the mobile station the source base station a sequence number to be transferred to the target base station via the control plane is added can receive, and the the source base station via a user plane associated with PDCP SDU to be transferred to the target base station, the second sequence number which the target base station is added to the PDCP SDU can be received from the movement destination base station Receiving means;
Reordering means for reordering data using the first sequence number or the second sequence number;
A mobile station. The PDCP SDU data to which the first sequence number is added in the movement-destination base station is PDCP SDU data received by the movement-destination base station from an upper station.
The mobile station according to claim 3. Control plane from the source base station to receive a first sequence number via, and a receiving means from the source base station may receive a second sequence number associated with the PDCP SDU and the PDCP SDU via the user plane ,
Associated with PDCP SDU received the first sequence number added to the PDCP SDU data to be transmitted to the mobile station from the source base station, move either one of the added to the PDCP SDU second sequence number Transmitting means for transmitting to the mobile station for reordering at the station;
A base station characterized by comprising: The PDCP SDU data to which the first sequence number is added is PDCP SDU data received by a destination base station from an upper station.
The base station according to claim 5.

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