Base station, mobile station, communication system, transmission method and reordering method

Abstract

A radio communication system, that includes a source base station; a target base station; and a mobile station for receiving either first sequence number or second sequence number, or both of the first and second sequence numbers from the target base station, whereby the first sequence number is transferred from the source base station to the target base station and the second sequence number is added to PDCP (Packet Data Convergence Protocol) SDU (Service Data Unit) which is transferred from the source base station to the target base station.

Claims

1. A radio communication system, comprising: a source base station; a target base station; and a mobile station for receiving a first sequence number or both the first sequence number and a second sequence number from the target base station, wherein the first sequence number is transferred from the source base station to the target base station without (Packet Data Convergence Protocol) PDCP (Service Data Unit) SDU and the second sequence number is transferred from the source base station to the target base station with PDCP SDU, wherein the target base station comprises: a control circuitry configured to add the first sequence number to a first PDCP SDU which is received from a host station and add the second sequence number to a second PDCP SDU which is received from the source base station; and a transmitter configured to transmit, to the mobile station, the first PDCP SDU with the first sequence number and the second PDCP SDU with the second sequence number.

2. The radio communication system according to claim 1, wherein the source base station comprises: a transmitter configured to transmit the first sequence number via a control plane from the source base station to the target base station; and the PDCP SDU on which the second sequence number is attendant via a user plane from the source base station to the target base station.

3. A mobile station comprising: a receiver configured to receive from a target base station, a first (Packet Data Convergence Protocol) PDCP (Service Data Unit) SDU which is created by adding a first sequence number transferred from a source base station to the target base station without PDCP SDU, to the first PDCP SDU received from a host station or both the first PDCP SDU and a second PDCP SDU which is created by adding a second sequence number transferred from the source base station to the target base station with a PDCP SDU, to the second PDCP SDU received from the source base station; and a reordering circuitry configured to perform reordering of the PDCP SDUs received from the target base station using the first and second PDCP SDUs with the sequence numbers.

4. A base station, comprising: a buffer configured to receive a first sequence number, or both the first sequence number and a second sequence number from a source base station, wherein the first sequence number is transferred without (Packet Data Convergence Protocol) PDCP (Service Data Unit) SDU and the second sequence number is transferred with PDCP SDU; a control circuitry configured to add the first sequence number to a first PDCP SDU received from a host station and add the second sequence number to a second PDCP SDU received from the source base station; and a transmitter configured to transmit, to a mobile station, the first PDCP SDU with the first sequence number or both the first PDCP SDU with the first sequence number and the second PDCP SDU with the second sequence number.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a drawing explaining a first embodiment of the invention.

(2) FIG. 2 shows an example of the format of a PDCP PDU packet.

(3) FIG. 3 is a drawing explaining packet processing in the PDCP layer and RLC layer before a handover sequence.

(4) FIG. 4 is a drawing explaining packet processing in the PDCP layer and RLC layer during a handover sequence.

(5) FIG. 5 is a drawing showing the construction of a base station.

(6) FIG. 6 is a drawing showing the construction of a mobile station.

(7) FIG. 7 is a flowchart of the operation of a target base station in a first embodiment of the invention.

(8) FIG. 8 is a flowchart of the operation of a source base station in a first embodiment of the invention.

(9) FIG. 9 is a flowchart of the operation of a mobile station in a first embodiment of the invention.

(10) FIG. 10 is a flowchart of the reordering process by a mobile station.

(11) FIG. 11 is a drawing explaining a second embodiment of the invention.

(12) FIG. 12 shows an example of the format of a PDCP PDU packet.

(13) FIG. 13 is a drawing explaining packet processing in the PDCP layer and RLC layer during a handover (1/2).

(14) FIG. 14 is a drawing explaining packet processing in the PDCP layer and RLC layer during a handover (2/2).

(15) FIG. 15 is a flowchart of the operation of a target base station in a second embodiment of the invention.

(16) FIG. 16 is a flowchart of the operation of a mobile station in a second embodiment of the invention.

(17) FIG. 17 shows an example of attaching PDCP PDU sequence numbers SN to PDCP SDU data and performing notification via the data plane (U-plane).

(18) FIG. 18 shows an example of attaching PDCP PDU sequence numbers SN to PDCP SDU data and performing notification via the U-plane, as well as performing notification of sequence numbers via the C-plane.

(19) FIG. 19 is a drawing showing the procedure of the handover sequence in FIG. 18.

(20) FIG. 20 shows an example when there is absolutely no PDCP PDU data to forward.

(21) FIG. 21 is a drawing explaining the takeover of communication during a handover.

(22) FIG. 22 is a drawing explaining a handover in a LTE communication system.

(23) FIG. 23 is a drawing explaining the handover procedure that is currently presumed for a LTE communication system.

(24) FIG. 24 is a first drawing explaining the reordering process by a mobile station.

(25) FIG. 25 is a second drawing explaining the reordering process by a mobile station.

(26) FIG. 26 is a third drawing explaining the reordering process by a mobile station.

(27) FIG. 27 is a fourth drawing explaining the reordering process by a mobile station.

(28) FIG. 28 is a drawing explaining the protocol configuration between a mobile station and a network.

(29) FIG. 29 is a flowchart of the operation of a source base station during a handover.

(30) FIG. 30 is a flowchart of the operation of a target base station during a handover.

(31) FIG. 31 is a flowchart of a mobile station during a handover.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(32) (A) Theory of the Present Invention

(33) With the present invention, the problems described above are solved by making it possible for a base station and a mobile station to execute the two following procedures.

(34) Procedure 1: When there is a delay in data forwarding from the source base station after a handover, the target base station sends data that has already been received from the host station without waiting to receive the delayed data (jump transmission) and the mobile station is made to be able to recognize that the data. In other words, discrimination information is included in, attached to or correlated with the data in order to recognize that the data is jump data, and transmitted with the data or transmitted using a control channel.

(35) Procedure 2: When it is detected that jump transmission has occurred, the mobile station decides the jump data is not the object of reordering and holds it in a buffer, and the mobile station waits for the data being forwarded from the source base station to arrive. In other words, the mobile station discriminate data that is forwarded from the source station from data that is transmitted without going through the source base station using the discrimination information and performs reordering of the data that is forwarded from the source station.

(36) In the conventional method, when data forwarding from the source base station to the target base station is delayed, the mobile station must wait transmission of the data that is forwarded from the host station to the target base station. Therefore, by waiting until a specified amount of time (Waiting Time) has elapsed for that data from the source base station to arrive, a problem occurs in that delay in communication increases and the throughput is degraded. However, as described above, by performing jump transmission of data, it is possible to quickly send data that was received from the host station to the mobile station even when data transfer (forwarding) from the source base station is delayed, and in doing so, communication delay is reduced. Therefore, when compared with the conventional method, the present invention is able to maintain high-quality communication immediately before and after a handover.

(37) (B) First Embodiment

(38) FIG. 1 is a drawing explaining a first embodiment of the invention, and in this embodiment, the case of adding order information to each packet is explained, however, it is also possible to use data having a specified size.

(39) Here it is presumed that before a handover, packets n−5 to are stored in the source base station 11a, and of these packets, packets n−5 to n−2 are transmitted to the mobile station 14, however, packets n−1 and are not transmitted to the mobile station 14. For example, the packets n−1 and arrived at the source base station 11a after the radio communication line between the source base station 11a and mobile station 14 was cut, so these packets n−1 and could not be transmitted to the mobile station 14. Also, of the packets that were transmitted to the mobile station 14, it is presumed that the mobile station 14 could not rightly receive the packets n−5 and n−3 (NACK), however was able to rightly receive the packets n−4 and n−2 (ACK). Therefore, the mobile station 14 saves packets n−4 and n−2, but does not save packets n−5 and n−3.

(40) When a handover occurs in this state, the source base station 11a transfers (forwards) the packets n−5 and n−3 that could not be rightly received by the mobile station 14 and the unsent packets n−1 and to the target base station 11b. The forwarding of the packets will be explained below, however, the invention is not limited to this example.

(41) In addition, after the handover, the host station 12 transmits two packets m to m+1 that are destined for the mobile station 14 to the target base station 11b. It is presumed that the transfer (forwarding) of packets n−5 to is delayed.

(42) When that the target base station 11b receives packets m and m+1 from the host station 12 before packets n−5, n−3, and n−1 to are forwarded from the source base station 11b, the target base station 11b adds jump ID code F to the packets m and m+1 that are received from the host station 12 and sends those packets to the mobile station 14 first (jump transmission).

(43) The mobile station 14 saves the packets that were received from the base station and to which jump ID code F is added in a buffer BF2, and excludes those packets as objects of the reordering process. In (A) of FIG. 1, the state is shown in which the mobile station 14 saves packets m and m+1 in the buffer BF2, and saves the packets n−4 and n−2 that were received before the handover in buffer BF1.

(44) Next, the target base station 11b transmits the packets n−5, n−3 and n−1 to that were forwarded from the source base station 11a to the mobile station 14. The mobile station 14 saves the packets n−5, n−3 and n−1 to that were received from the target base station 11b in the buffer BF1, then executes the reordering process for these packets that were received after the handover and the packets n−4 and n−2 that were received before the handover (see (B) of FIG. 1), and delivers the packets to the upper layer in the order of continuous sequence numbers.

(45) In a case where the mobile station 14 do not receive packets having continuous sequence number even when a prescribed time has been elapsed, the mobile station ends reordering process, and rearranges the order of the packets that have been already received and delivers them to the upper layer.

(46) The mobile station 14 then delivers the packets to which the jump ID code F has been added in order to the upper layer.

(47) During forwarding, a source base station can transfer an entire packet to a target base station, or can transfer data of just part of the packet (user data portion). Preferably, order information is added to the forwarded data.

(48) In addition, in FIG. 1, sequence numbers (order information) m, m+1 are assigned to the packet for which jump transmission is performed, however, the target base station 11b can assign arbitrary sequence numbers, can add numbers that overlap the sequence numbers that are added to the forwarded packets, or can add numbers that do not overlap.

(49) Jump ID Code

(50) As an example of jump ID code F that is added to packets, a 3-bit ‘type’ field that is included in the PDCP PDU header is used. In other words, in that type field, a new type number is defined as jump ID code F, and that type number is added to a packet for which jump transmission is performed. FIG. 2 is an example of the PDCP PDU format, where (A) is an example of format when there is no header, (B) is an example of format when the PDCP PDU sequence number is not added, and (C) and (D) are examples of format when the PDCP PDU sequence number is added. In the format of (C) and (D), a type field and PID field are defined in the header HD, where the type field indicates the PDCP PDU type. The PID field is a field that indicates the header compression type that is used for the data included in the data portion. In the type field, ‘type=000’ and ‘type=001’ are already regulated, however, the types ‘type=010 to 111’ are not regulated and are unused. Therefore, ‘type=010’ is used as the type number (jump ID code) for discriminating the PDCP PDU for which jump transmission is performed.

(51) PDCP Layer and RLC Layer Processing Before and after Handover Control

(52) FIG. 3 is a drawing explaining the packet processing of the PDCP layer and RLC layer before a handover. The source base station 11b stores packets n−5 to n−2 of the PDCP layer in a buffer ((A) of FIG. 3), and in the RLC layer the packets are divided into a plurality of data as shown in (B), then RLC layer sequence numbers I, I+1, I+2, . . . , I+6 are added to the divided data, and the data (RLC PDU data) are sent to the mobile station 14. Before a handover, the mobile station performs order control for the PDCP layer using RLC SDU(PDCP PDU) and PLC PDU in the RLC layer. In (C), (D) of FIG. 3, the mobile station 14 did not rightly receive the divided data I, I+4 and I+5, or in other words, packets n−5 and n−3, however, the mobile station 14 did rightly receive packets n−4 and n−2. Before a handover, the mobile station 14 performs order control for the PDCP layer using RLC SDU (PDCP PDU) and PLC PDU in the RLC layer, however, after a handover, the RLC layer is regulated to be initialized. Therefore, processing for order control moves to the PDCP layer, and the mobile station 14 executes the handover sequence in the PDCP layer.

(53) During reordering, the mobile station 14 starts a timer in order to determine when reordering ends.

(54) The arrival of the packets m and m+1 that are received from the host station 2 is early, so jump ID code is attached to those packets m, m+1 and they are sent to the mobile station 14 first (jump transmission). The mobile station 14 saves the packets that are received from the base station and to which jump ID code is attached in a buffer B2 (see FIG. 1), and removes them as objects of the reordering process. After that, the mobile station 14 executes the reordering process for the packets n−5, n−3, and n−1 to that were received from the target base station 11b and the packets n−4 and n−2 that were received before the handover, then delivers the data to the upper layer.

(55) When the specified time TM of the timer has elapsed, the mobile station 14 ends the reordering process and sends the packets that have been received to the upper layer even though there may be missing packets.

(56) Window Control

(57) FIG. 4 is a drawing explaining the packet processing of the PDCP layer and RLC layer after a handover, and shows in detail window control.

(58) In consideration of the fact that more than the allowable amount of data arrives, the mobile station 14 internally generates a buffer size window, and during the reordering process, performs the following window control. In the example shown in FIG. 4, the left end of the window WD is initially the number n−5 of the expected data, and the right end of the window is the number decided according to the amount of allowable data (window buffer size), and is taken to be n−2. The mobile station 14 does not apply the window process to the packets to which jump ID code F has been added.

(59) In the initial state (window state (0)), when the mobile station 14 receives the expected packet (n−5) and executes the reordering process, the window state becomes as shown in (1). Therefore, the mobile station 14 delivers the expected packet (n−5) and the packet (n−4) that continues after the packets(n−5) to the upper layer. Thereafter, the window state becomes as shown in (2), and in this state, when the mobile station 14 receives the expected packet (n−3) and performs the reordering process, the window state becomes as shown in (3). Therefore, the mobile station 14 delivers the expected packet (n−3) and the packet (n−2) that continues after the packet(n−3) to the upper layer. The window state then becomes as shown in (4), and in this state, the mobile station 14 waits to receive the packets (n−1) and n, and when the packets are received within the set period of time T.sub.M, the mobile station 14 then delivers the packets to the upper layer. However, when the mobile station 14 does not receive the packets (n−1) and within the set period of time T.sub.M, the mobile station 14 delivers the packets starting from packet m that are saved in the buffer BF2 to the upper layer, and moves to normal control as before handover. As was explained above, by removing the jump packets from the reordering process and performing window control as described above, it is possible to execute the reordering processing on just packets n−5 to n.

(60) In this window control, when a packet is received that has a sequence number that is smaller than the sequence number on the left end of the window, the mobile station 14 deletes that packet. Also, when a packet is received that has a sequence number that is larger than the sequence number on the right side of the window, the mobile station 14 takes the sequence number of that packet to be the sequence number on the right side of the window and changes the sequence number on the left side of the window according to the window buffer size, while at the same time, delivers the packets that have moved out of the window range and that have been received to the upper layer.

(61) If this window processing is applied to the jump packets as well, at the instant that packet m is received, the window state will be such that the left side of the window is n−2 and the right side of the window is m. In this case, the mobile station 14 gives up on receiving the packets n−5 and n−3 that have not yet been received, and delivers the already received packets n−4 and n−2 to the upper layer. In addition, the mobile station decides the sequence number of the right side of the window to m, and decides the sequence number of the left side of the window to the number n−1 that is determined according to the window size, then after that waits for packet n−1, packet n, packet n+1, . . . , packet m−1 to arrive. However, since packet n+1 to packet m−1 are packets that do not actually exist, the mobile station uselessly waits to receive those packets, and trouble occurs in packet processing.

(62) Construction of a Base Station

(63) FIG. 5 is a drawing that shows the construction of a base station, and shows the buffer unit, scheduler unit, transmission/reception unit and control unit.

(64) The buffer unit 21 is memory for storing packets that come from the host station, and packets that are forwarded from an adjacent base station (source base station). In the FIG. 5, two buffers 21a, 21b are physically provided, however, construction is also possible in which just one memory is physically provided, and that one memory is used by dividing it using software.

(65) The scheduler unit 22 selects a mobile station from among a plurality of communicating mobile stations with which to perform radio transmission, fetches packets for that mobile station that are stored in the buffer unit and sends them to the transmission/reception unit 23. The transmission/reception unit 23 encodes and modulates the packets that are input from the scheduler unit 22, and transmits the actual data using radio communication. In addition, the transmission/reception unit 23 receives and demodulates control signals and various data that are sent from the mobile station.

(66) The control unit 24 comprises a buffer management unit 24a, HO control unit 24b and measurement control unit 24c. The buffer management unit 24a manages the various packets that are stored in the buffer 21. When data is taken over in a handover, the control unit 24 forwards at least the packets that are stored in the buffer unit 21b for which a confirmation (ACK) indicating that the packets were rightly received has not been obtained from the mobile station to the target base station 11b.

(67) On the other hand, when the arrival of packets that are being forwarded from the source base station 11a are delayed due to the take over of data, and jump transmission is performed for the packets that are received from the host station 12, ‘type=010’ is entered into the type field of the headers of the packets that will jump.

(68) The HO control unit 24b executes handover control as explained in FIG. 23, and the measurement control unit 24c gathers various measurement data that is sent from the mobile station, such as the radio communication quality CQI (Channel Quality Information) of the mobile station and the like.

(69) Construction of a Mobile Station

(70) FIG. 6 is a drawing showing the construction of a mobile station, and shows the transmission/reception unit 31, buffer unit 32, reordering unit 33 and control unit 34. The transmission/reception unit 31 transmits packets and control information to or receives packets and control information from a base station. When RLC PDU data could not be created from a lower-layer packet that was received, the buffer unit 32 holds that lower-layer packet until that RLC PDU data can be created, and after the RLC PDU data is created, the buffer unit 32 removes the header and delivers that data to the reordering unit 33 as RLC SDU (PDCP PDU) data. The reordering unit 33 has a function for rearranging the PDCP PDU data in order of sequence numbers and delivers the data to the upper layer. When a missing PDCP PDU sequence number is detected, the reordering unit 33 saves the PDCP PDU data following that PDCP PDU data in internal memory until the PDCP PDU data with the continuing sequence number is received. However, when that PDC PDU data has still not arrived after a set period of time has elapsed, the reordering unit 33 stops the reordering process and delivers all of the stored PDCP PDU data to the upper layer. Moreover, the reordering unit 33 performs window control so that the amount of data being processed does not exceed the allowable amount.

(71) The control unit 34 comprises a measurement unit 34a, reordering management unit 34b and retransmission management unit 34c. The measurement unit 34a measures various kinds of measurement information that are sent to a base station. For example, the measurement unit 34a measures the radio communication quality (Channel Quality Information) of the mobile station. The reordering management unit 34b controls the reordering unit 33, and when there is a missing sequence number in the PDCP PDU data that is held by the reordering unit 33, the reordering management unit 34b instructs the reordering unit 33 to wait for that PDCP PDU data having the continuing sequence number to arrive. Moreover, when a set amount of time for waiting for that packet to arrive has elapsed, the reordering management unit 34b instructs the reordering unit 33 to stop the reordering process, as well as instructs the reordering unit 33 to delete the headers of all of the saved PDCP PDU data and to delivers that data to the upper layer as PDCP SDU data, then sets the reordering unit 33 to a state in which it is able to receive new PDCP PDU data. In addition, the reordering management unit 34b finds the maximum sequence number from among sequence numbers that have been received up to that time as the sequence number on the right end of the window, and determines and sets the sequence number of the left end of the window by taking into considering the window size. Here, in the case where there is a packet that has already been received that has a sequence number that is smaller than the sequence number on the left end of the window, that packet is immediately delivered to the upper layer. When there is retransmission control, the retransmission management unit 34c sends a retransmission request signal to a base station via the transmission/reception unit by a route indicated by the dashed line.

(72) Operation of the Target Base Station

(73) FIG. 7 is a flowchart showing the operation of the target base station in a first embodiment of the invention.

(74) When the handover control unit 24b of the target base station 11b receives a HO request from the source base station 11a (including the mobile station ID, QoS information, and the like) (step S201), the handover control unit 24b determines whether to allow accepting the mobile station (step 202). When accepting the mobile station is not allowed, the handover control unit 24b performs post processing (step 213) and ends handover control.

(75) On the other hand, in a case where the handover control unit 24b allows the acceptance of the mobile station, the handover control unit 24b return a HO request response message to the source base station 11a (step 203). Then the target base station waits the packets that are forwarded from the source base station 11a. When the packets arrivers from the source base station, the buffer 21 stores them (step 204).

(76) When the handover control unit 24b receives a HO complete report from the mobile station 14 (step 205), the handover control unit 24b then sends a HO complete report to the host station 12 (step 206). After receiving the HO complete report, the host station 12 changes the transmission path for packets from the source base station 11a to the target base station 11b, and returns a HO complete response to the target base station 11b. After the handover control unit 24b of the target base station 11b receives the HO complete response from the host station 12 (step 207), the handover control unit 24b sends an instruction to the scheduler unit 22 to start transmitting packets (step 208).

(77) From this, the scheduler unit 22 checks whether jump transmission of packets is necessary (step 209), and when jump transmission is not necessary, the scheduler unit 22 sends the packets that were forwarded from the source base station 11a to the mobile station 14 first (step 210). However, when forwarding of packets from the source base station 11a is delayed, and it is necessary to perform jump transmission of packets, the scheduler unit 22 executes jump transmission of the packets that were received from the host station 12.

(78) In order to execute jump transmission, the scheduler unit 22 sets the type number in the type fields of the packets for which jump transmission will be performed to 010 (type=010) in order that the mobile station 14 will be able to recognize that the packets are jump packets (step 211), then after that, sends the packets to the mobile station 14 (step 210).

(79) At the same time as this, the handover control unit 24b sends a resource release to the source base station 11a (step 212), then performs post processing (step 213) and ends handover control.

(80) Operation of the Source Base Station

(81) FIG. 8 is a flowchart showing the operation of a source base station in a first embodiment of the invention.

(82) In FIG. 8, when the measurement control unit 24c of the source base station 11a receives a Measurement Report which indicates reception state information from the mobile station 14 (step 251), the handover control unit 24a determines whether or not a handover (HO) is necessary based on that reception state information (step 252), and when a handover is not necessary, returns to the start.

(83) However, when the handover control unit 24b determines that a handover HO is necessary, the handover control unit 24b decides a target base station 11b according to the contents of the Measurement Report and sends a handover request to that target base station 11b (step 253).

(84) After that, when a HO response message that is sent from the target base station 11b is received (step 254), the HO control unit 24b sends a HO instruction message to the mobile station 14 (step 255), and instructs the buffer management unit 24a to forward packets that are saved in the buffer 21b to the target base station 11b. Thereby, using the route indicated by the dotted line, the buffer management unit 24a forwards packets that are saved in the buffer 21b and that were not sent to the mobile station 14, or packets that were not received rightly (NACK packets) by the mobile station, to the target base station 11b (step 256). After that, when a resource release message is received from the target base station 11b (step 257), the HO control unit 24a performs a resource release (step 258).

(85) Operation of the Mobile Station

(86) FIG. 9 is a flowchart showing the operation of the mobile station. The measurement unit 34a of the mobile station 14 notifies the source base station 11a of the reception status using a Measurement Report (step 271). The control unit 34 then waits for a HO instruction message to be sent from the source base station 11a, and when a HO instruction message is received (step 272), the control unit 24 establishes synchronization between the mobile station and the target base station 11b using L1/L2 signaling (step 273), and after synchronization is established, sends a handover complete report to the target base station 11b (step 274). After that, the control unit 34 checks whether a received packet is a jump packet, or in other words whether the type number of a packet is type=010 (step 275), and when a packet is a jump packet, the control unit 34 removes that packet as an object of reordering and saves the packet in a buffer 32, then after a set period of time has elapsed, removes the header and delivers the packet to the upper layer as a PDCP SDU packet (step 276). On the other hand, when a packet is not a jump packet, the control unit 24 executes reordering, and rearranges the order according to the sequence number, then removes to header from the reordered packets and delivers them to the upper layer as a PDCP SDU packets (step 277).

(87) FIG. 10 is a flowchart showing the reordering process by the mobile station.

(88) When the transmission/reception unit 31 of the mobile station 31 receives a lower layer packet from the target base station 11b (step 301), the reordering management unit 34b checks whether it is possible to create RLC PDU data (step 302), and when it is not possible to create RLC PDU data, checks whether a set amount of time has elapsed (step 303), and when the set amount of time has not elapsed, saves the lower layer packet in the buffer 32 (step 304), then performs processing again from step 301. When it is not possible to create RLC PDU data even though a set amount of time has elapsed since the lower layer packet was received, that lower layer packet is deleted from the buffer (step 305).

(89) On the other hand, in step 302, when it is possible to create RLC PDU data using the received lower layer packet, that RLC PDU data is delivered to the reordering unit 33 as RLC SDU (PDCP PDU) data (step 306). After receiving the RLC SDU (PDCP PDU) data, the reordering unit 33 checks whether there is a missing sequence number (step 307), and when there is no missing sequence number and the sequence numbers are continuous, the reordering unit 33 removes the header of that RLC SDU (PDCP PDU) data and delivers it to the upper layer as PDCP SDU data (step 311). However, when there is a missing sequence number, the reordering management unit 34b instructs the reordering unit 33 to save the PDCP PDU data (step 308). Thereby, the reordering unit 33 saves the RLC SDU (PDCP PDU) data, and checks whether RLC SDU (PDCP PDU) data with a continuing sequence number is received (step 309). After receiving RLC SDU (PDCP PDU) data with a continuing sequence number, the reordering unit 33 removes the header of the RLC SDU (PDCP PDU) data and delivers it to the upper layer as PDCP SDU data, and then delivers similarly the saved PDCP PDU as PDCP SDU to the upper layer (step 311).

(90) Moreover, in step 309, when RLC SDU (PDCP PDU) data having a continuing sequence number is not received, the reordering unit 33 monitors a preset period of time T.sub.M (step 310), and when the set period of time has not yet elapsed, repeats processing from step 308, however, when the set period of time T.sub.M has elapsed, the reordering unit 33 removes the header of the saved PDCP PDU data and delivers it to the upper layer even though the sequence numbers are not continuous (step 311).

(91) With the first embodiment of the invention as described above, packets that are transmitted from the host station 12 to the target base station 11b can be transmitted to the mobile station 14 as jump packets without waiting, so it is possible to eliminate delay time of the data, and to improve the throughput of the overall system. Moreover, the mobile station 14 removes jump packets as objects of reordering control (sequence order control), and performs sequence order control on packets other than jump packets and delivers those packets to the upper layer in order of sequence numbers. As a result, the mobile station is able to perform sequence order control of packets even when there is only one order control function.

(92) (C) Second Embodiment

(93) In the first embodiment, the mobile station 14 performed the reordering process during a set period of time TM, and ended the reordering process when that set period of time TM elapsed (see step 310 in FIG. 10). In that case, when the set period of time TM has not yet elapsed even though all of the packets that have been forwarded from the source base station 11a to the target base station 11b are received, the mobile station 14 continues the reordering process. Therefore, in a second embodiment of the invention, in order that the mobile station 14 is able to recognize the last packet that is an object of the reordering process, the target base station 11b adds an identifier to a specified packet (last packet) and transmits that packet to the mobile station 14, and after receiving that last packet, the mobile station 14 immediately ends the reordering process even though the set time TM has not elapsed.

(94) FIG. 11 is a drawing explaining a second embodiment of the invention, where it presumed that packets n−5 to are stored at the source base station 11a before a handover, and of these packets, packets n−5 to n−2 were sent to the mobile station 14, however, packets n−1 and were not sent to the mobile station 14. For example, packets n−1 and arrived after the radio communication line between the source base station 11a and the mobile station had been cut, so these packets n−1, were not sent to the mobile station 14. In addition, it is presumed that of the packets that were sent to the mobile station 14, packets n−5 and n−3 were not received rightly by the mobile station 14 (NACK), and that packets n−4 and n−2 were received rightly (ACK). Therefore, the mobile station 14 saves packets n−4 and n−2, and does not save packets n−5 and n−3.

(95) When a handover occurs in this state, the source base station 11a forwards the packets n−5 and n−3 that were not rightly received by the mobile station 14, and the unsent packets n−1 and to the target base station 11b. Also, the host station 12 sends two packets m to m+1 to the target base station 11b after the handover. It is presumed that the forwarding of the packets n−5, n−3 and n−1 to n is delayed.

(96) When the target base station 11b receives the packets m and m+1 from the host station 12 before the packets n−5, n−3 and n−1 to n are forwarded from the source base station 11a, the target base station 11b adds jump ID code F to the packets m and m+1 that were received from the host station and sends them to the mobile station 14 first (jump transmission). The mobile station 14 saves the packets received from the base station with the jump ID code added in the buffer BF2, and removes them as objects of the reordering process. In (A) of FIG. 11, the state is shown in which the mobile station 14 saves packets m and m+1 in the buffer BF2, and saves the packets n−4 and n−2 that were received before the handover in the buffer BF1.

(97) The target base station 11b sends the packets that are forwarded until a preset time T.sub.M (called the Waiting Time) has elapsed to the mobile station 14, and when the Waiting Time has elapsed the target base station 11b discards any packets that may be forwarded. Therefore, the target base station 11b receives the packets n−5, n−3 and n−1 that were forwarded from the source base station 11a before the Waiting Time elapsed and saves them in the buffer BF, then sends the packets one by one to the mobile station 14. In addition, the target base station 11b receives packet from the source base station 11a, however, the Waiting Time was complete before the packet could be sent to the mobile station 14. In this case, the target base station 11b adds an identifier (L) to packet to indicate that it is the last packet forwarded from the source base station, and sends packet n to the mobile station 14.

(98) The mobile station 14 saves the packets n−5, n−3, n−1 and that were received from the target base station 11b in the buffer BF1, and as shown in (B) of FIG. 11, executes the reordering process to rearrange these packets and the packets n−4 and n−2 that were received before handover. Moreover, after detecting packet with the identifier (L) added, the mobile station 14 determines that forwarding has ended, so delivers the packets that have been reordered to the upper layer and ends the reordering process even though the set time period T.sub.M for reordering has not ended.

(99) The case in which the Waiting Time T.sub.w ends before packet is sent is described above, however, the Waiting Time T.sub.w may end after the packet has been sent to the mobile station. In that case, the target base station 11b adds an identifier (L) to a packet m+2 that will be received from the host station 12 indicating that it is the last packet, and sends the packet m+2 to the mobile station 14. After receiving the last packet to which that identifier (L) has been added, the mobile station 14 determines that forwarding has ended, and immediately ends reordering even though the set period of time T.sub.M for reordering has not ended.

(100) Moreover, packets n−5 and n−3 are received by forwarding, however, the Waiting Time T.sub.w may end in the stage before packets n−1 and are received. In that case, the target base station 11b may add an identifier (L) to packet n−3 indicating that it is the last packet, and sends that packet to the mobile station 14. The mobile station 14 detects the Last packet to which that identifier (L) is added and ends the reordering process.

(101) Last Packet ID Code L

(102) To add an identifier (last packet ID code) L to a packet identifying that the packet is the last packet, a 3-bit ‘type’ field that is included in the PDCP PDU header is used. In other words, a new type number is defined in that ‘type’ field as the last packet ID code L, and that type number is assigned to the first packet to be sent after the Waiting Time T.sub.w ends. FIG. 12 shows an example of the PDCP PDU format, where (A) is an example of format without a header, (B) is an example of format in which the PDCP PDU sequence number is not added, and (C) and (D) are examples of format in which the PDCP PDU sequence number is added. In the format shown in (C) and (D), a type field and a PID field are defined in the header HD, where the type field indicates the type of PDCP PDU. For the type field, ‘type=000’ and ‘type=001’ are already regulated, however, the type numbers ‘type=010 to 111’ are not regulated and are unused. Therefore, ‘type=011’ is used as the type number for recognizing the PDCP PDU packet (last packet) that is to be sent first after the Waiting Time T.sub.w has ended.

(103) PDCP Layer and RLC Layer Processing

(104) FIG. 13 and FIG. 14 are drawings explaining packet processing for the PDCP layer and RLC layer after a handover.

(105) FIG. 13 shows the case in which the last packet ID code L is added to the packet that is sent to the mobile station 14. In the first embodiment, during reordering, the mobile station 14 starts a timer in order to determine the end of reordering. Here, when the set time T.sub.M is set to be a large value, the reordering process continues regardless of whether or not packet is the last packet forwarded, and the packets cannot be delivered to the upper layer until the set time T.sub.M ends. However, in this second embodiment, after receiving packet (Last packet) to which the last packet ID code L has been added, the mobile station 14 immediately ends reordering and delivers all of the PDCP PDU packets to the upper layer.

(106) When more than the allowable amount of data arrives at the mobile station 14, the mobile station 14 performs window control during reordering. The left side of the window is n−5, which is the number expected for arrival, and the right side of the window is the value of the upper limit of the allowable amount of data (in the figure, this value is n). However, window processing is not applied to ‘type=010’ packets (jump packets) as in the first embodiment. By performing processing in this way, it is possible to execute reordering from packet n−5 to packet n.

(107) FIG. 14 shows the case in which last packet ID code L is added to packet m+2. At the instant that packet m+2 (Last packet) is received, the mobile station 14 immediately ends reordering even though the set time T.sub.M may not have ended yet, and delivers all of the received PDCP PDU packets to the upper layer. Also, in the case of window control, the mobile station 14 executes window control in the same way as shown in FIG. 13.

(108) Operation of the Target Base Station

(109) FIG. 15 is a flowchart showing the operation of the target base station in the second embodiment of the invention, where the same reference numbers are given to steps that are the same as the steps of the first embodiment shown in FIG. 7. The base stations and mobile station of this second embodiment have the construction shown in FIG. 5 and FIG. 6.

(110) When the handover control unit 24b of the target base station 11b receives a HO request from the source base station 11a (includes the mobile station ID, QoS information, etc.), the handover control unit 24b performs call-receiving control based on that information and determines whether to allow acceptance of the mobile station. When acceptance is not allowed, the handover control unit 24b performs post processing, and ends handover control (steps 201 to 202, and 213).

(111) On the other hand, when the handover control unit 24b allows the acceptance of the mobile station 14, the handover control unit 24b returns a HO request response message to the source base station 11a, and starts measuring the elapsed time. After that, the target base station 11b waits for packets forwarded from the source base station 11a, and stores the packets in the buffer unit 21 (steps 203 and 204).

(112) In this state, after receiving a HO complete report from the mobile station 14, the handover control unit 24b sends a HO complete report to the host station 12 (steps 205 and 206). After the host station 12 receives the handover complete report, the host station 12 then changes the transmission path for the packets from the source base station 11a to the target base station 11b, and returns a HO complete response to the target base station 11b. The handover control unit 24b of the target base station 11b receives the HO complete response from the host station 12, and then instructs the scheduler unit 22 to start transmitting packets to the mobile station(steps 207 and 208).

(113) Next, the scheduler unit 22 monitors whether or not the elapsed time has exceeded a set period of time T.sub.w, that is, whether or not the Waiting Time has ended (step 501), and when the Waiting Time has not ended, checks whether it is necessary to perform jump transmission of packets (step 209), and when it is not necessary, starts sending packets that were forwarded from the source base station 11a (step 210) preferentially to the mobile unit 14 via transmission/reception unit 23. However, when forwarding is delayed and it is necessary to perform jump transmission of packets, the scheduler unit 22 executes jump transmission of packets that are received from the host station 12. In order to execute jump transmission, the scheduler unit 22 sets the type number of the type field in the header of the packets for which jump transmission will be performed to 010 (type=010), thereby the mobile station 14 will be able to identify that the packets are jump packets (step 211). After that, the transmission/reception unit 23 sends the jump packets to the mobile station.

(114) At the same time as this, the handover control unit 24b sends a resource release to the source base station 11a (step 212), then returns to step 501 to check whether the Waiting Time has ended, and when the Waiting Time has not ended, repeats the process from step 209.

(115) On the other hand, in step 501, when the Waiting Time T.sub.w has ended, the scheduler unit 22 sets the type number of the packet that will be transmitted immediately after the Waiting Time has ended to ‘011’. In other words, the scheduler unit 22 adds a last packet ID code L to the packet that will be transmitted immediately after the Waiting Time ends, and transmits that packet (Last packet) to the mobile station 14 (steps 502 and 503), then after that, performs post processing and ends handover control (steps 212 and 213).

(116) In step 502, in order to be able to identify whether the last packet to which the last packet ID code L has been added is a packet that has been forwarded from the source base station 11a, or is a packet that was received from the host station 12, the scheduler unit 22 sets the type number to ‘011’ in the case of the former, and sets the type number to ‘100’ in the case of the latter. By doing this, it becomes easy for the mobile station 14 to perform the reordering process as will be described later.

(117) Operation of the Mobile Station

(118) FIG. 16 is a flowchart showing the operation of the mobile station, where the same reference numbers are used for steps that are the same those in the operation flowchart shown in FIG. 98. The measurement unit 34a of the mobile station 14 uses a Measurement Report to notify the source base station 11a of the reception status. The control unit 34 then waits for a HO instruction message to be sent from the source base station 11a, and after receiving the HO instruction message, establishes synchronization between the mobile station 14 and the target base station 11b using L1/L2 signaling, and after synchronization has been established, sends a handover complete report to the target base station 11b (steps 271 to 274).

(119) After that, the control unit 34 checks whether a received packet is a jump packet, or in other words, a packet having a type number type=010 (step 600), and when the packet is a jump packet, removes that packet from being an object of reordering and saves it in the buffer 32 (step 601).

(120) On the other hand, when the packet is not a jump packet, the control unit 34 checks whether the received packet is the Last packet, or in other words, a packet having a type number type=011 (step 602). In the case where the packet is not the Last packet, the control unit 34 starts the reordering process, and arranges the PDCP PDU packets according to sequence numbers, then creates PDCP SDU data and delivers that data to the upper layer (step 603).

(121) The control unit 34 then checks whether the preset time period T.sub.M has ended (step 604), and when the set time period T.sub.M has not yet ended, the control unit 34 repeats processing from step 600, and when the set time period T.sub.M has ended, the control unit 34 ends the reordering process, then deletes the header from RLC SEU (PDCP PDU) packets that have not yet been delivered to the upper layer, creates PDCP SDU data and delivers that data to the upper layer (step 605). Next, the control unit 34 delivers packets that are not the object of reordering to the upper layer and ends processing (step 606).

(122) However, in step 602, when the received packet is the Last packet, the control unit 34 immediately stops the reordering process (step 607). At that time, in the case where the Last packet is a forwarded packet, the control unit 34 creates a PDCP SDU packet from that Last packet and delivers that packet to the upper layer, then stops reordering. When the Last packet is a packet received from the host station 12, the control unit 34 immediately stops reordering, and connects the Last packet to the last packet that is not an object of reordering and stored in the buffer. After that, the control unit 34 delivers the packets that were not the object of reordering to the upper layer and ends processing (step 606).

(123) As described above, with this second embodiment of the invention, the mobile station detects the end of the forwarded packets by referencing the Last packet ID code, making it possible to quickly stop the reordering process. Therefore, it is possible to eliminate the data delay time, and improve the throughput of the overall system.

(124) (D) Third Embodiment

(125) The order information (sequence numbers n, m) that has been presented up until now has been convenient numbers for simplifying the explanation, however, actually, it is information that is added at the base station.

(126) As was explained above, in a LTE communication system, forwarding is performed in PDCP SDU data units. Therefore, when forwarding occurred, it was not possible to send the Sequence Number field from the source base station 11a to the target base station 11b, and it was necessary to notify the target base station 11b of the sequence numbers using some method.

(127) In this embodiment, the source base station 11a notifies the target base station 11b of the sequence numbers together with the PDCP SDU data, and based on those sequence numbers, the target base station 11b adds a header including the sequence numbers to the forwarded PDCP SDU data (packets) thereby PDCP PDU(RLC SDU) packet is created.

(128) FIG. 17 is an example of sending the PDCP PDU sequence number together with the PDCP SDU data (packets) via the data plane (U-plane). In FIG. 17, only the PDCP SDU data and the sequence numbers that accompany that data are shown, however, in order that the PDCP SDU data is recognized to be a bunch of packets, control information (header information) must be added. Each time the source base station 11a forwards PDCP SDU data, the source base station 11a notifies the target base station 11b of the sequence number that accompanies that PDCP SDU data using the format shown in FIG. 17, and based on that sequence number, the target base station 11b adds the sequence number to the forwarded PDCP SDU data (packet).

(129) In other words, in the condition shown in FIG. 17, the source base station 11a first forwards sequence number n−5 and the first PDCP SDU data via the data plane U-plane. Next, the source base station 11a forwards sequence number n−3 and the next PDCP SDU data via the data plane U-plane. After that, when forwarding following PDCP SDU data that were received from the host station 12, the source base station 11a similarly forwards the PDCP SDU data and the sequence numbers n−1 and thereof to the target base station 11b via the U-plane. At the target base station 11b, by receiving the sequence numbers n−5, n−3, n−1 and that were notified via the U-plane, it is possible for the target base station 11b to recognize the numbers as the sequence numbers for the forwarded data.

(130) FIG. 18 is an example of the source base station 11a notifying the target base station 11b via the U-plane of the PDCP PDU sequence number together with the appropriate PDCP SDU data, and notifying the target base station 11b via the C-plane of the sequence number of PDCP SDU data, for which right reception by the mobile station could not be confirmed, as the Next SN. Notification of the sequence number (Next SN) via this C-plane is shown as taking over of the SN (SN takeover) in the handover sequence shown in FIG. 19. It may possible to perform SN taking over at the same time that the source base station 11a sends a HO request to the target base station 11b.

(131) In the state shown in FIG. 18, the source base station 11a first forwards the sequence number n−5 and the first PDCP SDU data via the U-plane. Also, at the same time, the source base station 11a notifies the target base station via the C-plane of the just the sequence number n−5 of the PDCP SDU data, for which proper reception by the mobile station could not be confirmed, as the Next SN (SN takeover). Next, the source base station 11a forwards the sequence number n−3 and the next PDCP SDU data via the U-plane. After that, when forwarding the PDCP SDU data that was received from the host station 12, the source base station 11a similarly forwards that PDCP SDU data and the sequence number n−1, thereof to the target base station 11b via the U-plane. The target base station 11b receives the sequence number n−5 that was notified via the C-plane, and the sequence numbers n−5, n−3, n−1 and that were notified via the U-plane, however, since the sequence numbers that were notified via the U-plane are larger than the sequence number notified via the C-plane, the target base station 11b adds the sequence numbers that were notified via the U-plane to the following PDCP SDU data received via the U-plane, and transmits the data to the mobile station. In other words, the target base station 11b ignores the sequence number n−5 that was notified via the C-plane.

(132) FIG. 20 is an example of the case in which there is no PDCP SDU data to forward.

(133) The source base station 11a notifies the target base station 11b via the C-plane of the next sequence number n+1, as the Next SN. When the Waiting Time ends without the target base station 11b receiving PDCP SDU data from the source base station 11a, the target base station 11b adds the sequence number to the following PDCP SDU data based on the sequence number n+1 that was notified via the C-plane, and transmits the data to the mobile station. In other words, the source base station 11b sets the sequence number of the packet m that was received from the host station to n+1 and transmits that data to the mobile station.

(134) Advantage of the Present Invention

(135) With the present invention described above, it is possible to quickly send packets that were sent from host station to the target base station to the mobile station as jump packets, thus making it possible to eliminate the delay time of data, and to improve the throughput of the overall system. Moreover, the mobile station removes jump packets from being the object of reordering control (sequence order control), and performs order sequence control only on packets other than jump packets, then delivers the packets to a higher apparatus (upper layer) in order of sequence numbers. As a result, the mobile station is able to properly perform sequence order control of packets that are the object of reordering even when there is only one sequence order function.

(136) Furthermore, with the present invention, the mobile station detects the end of the forwarded packets by referencing last packet ID code, and so is able to quickly stop reordering. Therefore, it is possible to eliminate the delay time of data, and to improve the throughput of the overall system.