WO2009107221A1

WO2009107221A1 - Radio base station, scheduling method and radio communication system

Info

Publication number: WO2009107221A1
Application number: PCT/JP2008/053553
Authority: WO
Inventors: 秀和佐藤
Original assignee: 富士通株式会社
Priority date: 2008-02-28
Filing date: 2008-02-28
Publication date: 2009-09-03

Abstract

Data units constituting respective data on logical channels associated with transport channels of a radio link are held for each of the logical channels, the transmission timing of each of the data units is scheduled according to the priority set for each of the logical channels, and any of the data units is selected according to the scheduled transmission timing and transmitted to a communication path which leads to a radio terminal.

Description

Radio base station, scheduling method, and radio communication system

The present invention relates to a radio base station, a scheduling method, and a radio communication system. The present invention can also be used, for example, in a technique for scheduling data addressed to a wireless terminal in a wireless communication system or the like.

In a mobile communication system that performs packet data communication between a wireless terminal and a wireless base station, there is packet scheduling for managing transmission timing of packet data to the wireless terminal.
As an existing technique related to this packet scheduling, for example, in Patent Document 1 below, when a plurality of mobile terminals are assigned to a common channel and the priority of transmission opportunities is set for each terminal, the radio base station In accordance with the weighted round robin method, one priority is selected from the plurality of priorities in which transmission standby data exists, and a radio terminal having a high radio link quality is selected from a set of mobile terminals having the selected priority. A packet scheduling method for providing a transmission opportunity is described.
JP 2004-260261 A

However, since the above-described conventional technique cannot be said to have a scheduling unit optimized from the viewpoint of data arrival time at the wireless terminal, until data transmission to the mobile terminal given a transmission opportunity is completed, It may not be possible to start another data transmission. As a result, there may be a delay in the time for data to reach the wireless terminal.
One of the purposes of this case is to shorten the data arrival time to the wireless terminal.

It should be noted that the present invention is not limited to the above-described object, and can be positioned as one of other objects that is an effect obtained by each configuration shown in the embodiments to be described later and that cannot be obtained by conventional techniques. .

For example, the following means are used.
(1) A wireless base station that communicates with a wireless terminal via a wireless link, wherein a plurality of data units constituting individual data of a plurality of logical channels associated with a transport channel of the wireless link Based on the buffer unit held for each channel, the scheduler for scheduling the transmission timing of each data unit in the buffer unit based on the priority set for each logical channel, and the transmission timing scheduled by the scheduler, It is possible to use a radio base station including a transmission processing unit that selects any one of the data units from the buffer unit and transmits the selected data unit to a communication path that reaches the radio terminal.

(2) Here, the communication path is the communication path between the wireless link or the destination wireless base station of the wireless terminal and between the destination wireless base station and the wireless terminal after the movement. A wireless link may be included.
(3) Further, the scheduler may perform the scheduling so that a data unit of a logical channel having a higher priority is preferentially transmitted to the communication path.

(4) Further, the scheduler may perform the scheduling so that the number of selections of data units of individual logical channels is adjusted according to the priority of the logical channels.
(5) Here, the scheduler may perform the scheduling so that the number of selections of the data unit of each logical channel is adjusted based on the buffer amount for each logical channel in the buffer unit. Good.

(6) The scheduler may temporarily set a priority of the data unit of the logical channel to be transmitted to the movement-destination radio base station higher than others.
(7) Further, when the data unit of the logical channel is a data unit received from the source wireless base station of the wireless terminal, the scheduler temporarily sets the priority of the data unit higher than others. You may do it.

(8) A scheduling method in a radio base station that communicates with a radio terminal via a radio link, and a plurality of data constituting individual data of a plurality of logical channels associated with a transport channel of the radio link A unit is held for each logical channel, and the transmission timing of each data unit is scheduled based on the priority set for each logical channel, and according to the scheduled transmission timing, any one of the data units is scheduled. It is possible to use a scheduling method that selects these and transmits them to the communication path leading to the wireless terminal.

(9) Furthermore, at least one wireless terminal, a wireless base station communicating with the wireless terminal via a wireless link, and individual data of a plurality of logical channels associated with the transport channel of the wireless link are configured. A buffer unit that holds a plurality of data units for each logical channel; a scheduler that schedules the transmission timing of each data unit in the buffer unit based on a priority set for each logical channel; and the scheduler A wireless communication system including a transmission processing unit that selects one of the data units from the buffer unit and transmits the selected data unit to a communication path that reaches the wireless terminal according to the transmission timing scheduled in (1) can be used.

It becomes possible to shorten the data arrival time to the wireless terminal.

It is a block diagram which shows the structure of the communication system which concerns on one Embodiment. It is a figure which shows the data format of a layer 2. It is a figure which shows the data processing of a layer 2. It is a figure which shows the conventional packet scheduling between eNB-UE. It is a figure which shows the processing flow at the time of a hand-over. It is a figure which shows the conventional packet scheduling between eNBs. It is a block diagram which shows the structure of eNB which concerns on one Embodiment. It is a figure which shows the example of data storage in eNB shown in FIG. It is a figure which shows an example of a priority information table. It is a figure explaining operation | movement of eNB which concerns on one Embodiment. It is a figure which shows an example of a priority information table. It is a figure explaining operation | movement of eNB which concerns on a 1st modification. It is a figure explaining operation | movement of eNB which concerns on a 2nd modification.

Explanation of symbols

1 Radio base station (eNB)
1-1 Handover source radio base station (HO source eNB)
1-2 Handover destination radio base station (HO destination eNB)
2 Radio terminal (UE)
3 Core network equipment (MME / UPE)
4 IP network 5 IP packet termination processing unit 6 Downstream RLC layer processing unit 7 Storage buffer 8 Data selection unit 9 Scheduler

Hereinafter, embodiments will be described with reference to the drawings. However, the embodiment described below is merely an example, and there is no intention to exclude various modifications and technical applications that are not clearly shown in the embodiment described below. That is, the present embodiment can be implemented with various modifications (combining the embodiments) without departing from the spirit of the present embodiment.
[1] Outline The outline of this example will be described with reference to the example shown in FIG.

The communication system illustrated in FIG. 1 includes two radio base stations (evolved Node-B, eNB for short) 1, two radio terminals (UE: User Equipment) 2, and a core network system device (MME / UPE: Mobile Management Entity / User Plane Entity) 3. Of course, the number of eNBs and the number of UEs are not limited to the numbers shown in FIG. Any one or more of them can exist. In the following, a packet communication system based on 3GPP LTE (3rd Generation Partnership Project Long Service Term Evolution) standard will be described as an example of a communication system, but of course, the communication system is not limited to such a communication system. For example, the radio base station 1 is not limited to the eNB, but may be a radio base station (BS: Base Station) of a generation earlier than LTE / SAE (Long Term Evolution / System Architecture Evolution).

Here, eNB1 has the function of the radio base station (Node-B) of the generation before LTE / SAE and the function of a radio base station controller (RNC: Radio Network Controller).
ENB1 is connected to MME / UPE3 using a communication interface called S1 (S1 interface), and connected to other eNB1 using a communication interface called X1 (X1 interface).

Furthermore, the eNB 1 of this example has a function of communicating with the UE 2 via a radio link. The radio link includes a downlink (DL) that is a direction from eNB1 to UE2, and an uplink (UL) that is the opposite direction.
The UE 2 has a function of performing radio communication with the eNB 1 via the radio link, and can communicate with another UE 2 or an external packet network via the eNB 1.

MME / UPE3 is an entity corresponding to a higher-level device of eNB1, and has a function of managing and controlling eNB1, a function of managing location registration of UE2, a function of transmitting and receiving messages between UE2 and the external packet network, etc. It has.
(1.1) Packet scheduling between eNB1 and UE2, for example, eNB1 receives information on QoS (Quality of Services) of packet data, packet data type (whether initial transmission or retransmission, etc.), and radio propagation path status reported from UE2 RLC (Radio Link Control) that constitutes a protocol data unit (PDU: Protocol Data Unit) in the MAC (Media Access Control) sub-layer addressed to UE 2 based on priority information corresponding to any one or a combination of two or more Scheduling (assignment of transmission timing) of DL data addressed to the UE 2 is performed using a service data unit (SDU) in the sublayer as a basic unit. Note that a part or all of the priority information can be notified (set) to the eNB 1 (scheduler) by a higher-level device (MME / UPE 3 or the like).

Here, the data format in layer 2 (data link layer) will be described with reference to FIG.
As shown in FIG. 2, a PDU in the MAC sublayer (hereinafter referred to as MAC_PDU) includes a MAC header and a MAC payload, and the MAC payload includes a plurality of PDUs in the RLC sublayer (hereinafter referred to as RLC_PDU). Can be stored. The RLC_PDU includes an RLC header and an RLC payload that can store a plurality of RLC_SDUs. A part or all of the RLC_SDU is stored in the RLC payload by division (segmentation) and combination processing described later. That is, the RLC_PDU is also a service data unit (hereinafter referred to as MAC_SDU) in the MAC sublayer.

An example of data processing in each sublayer of layer 2 in this example will be described with reference to FIG.
First, for example, a radio bearer as a service access point (SAP) providing inter-layer communication is defined between a PDCP (Packet Data Convergence Protocol) sublayer and an RLC sublayer, and user data addressed to the UE 2 Is subjected to header compression processing by RoHC (Robust Header Compression), which is one of the parameters defining the radio bearer, and becomes RLC_SDU which is variable length data.

In the RLC sublayer, the RLC_SDU is divided (segmented) into units suitable for processing such as ARQ (Automatic Repeat Request) control and order control, combined to generate an RLC payload, and a unit in which an RLC header is added ( RLC_PDU (MAC_SDU)) can be delivered to the MAC sublayer. Control data can also be delivered to the MAC sublayer in units corresponding to RLC_PDUs.

Here, delivery of user data between the RLC sublayer and the MAC sublayer can be performed via a logical channel (SAP) of communication between layers (protocols) called a logical channel (LCH). Control data can be transmitted through a logical channel (SAP) called a control channel (CCH).
Only one LCH may be assigned to one UE 2 or a plurality of LCHs may be assigned. In the example shown in FIG. 3, LCH # 1 to LCH # l (l is a natural number) are assigned to UE # 1, and LCH # m (m is a natural number) is assigned to UE # n (n is a natural number). Is assigned. The priority information is set in the LCH by, for example, the MME / UPE3.

In the MAC sublayer of this example, the RLC_PDU (MAC_SDU) delivered from the RLC sublayer via the LCH is divided (segmented) into the storage buffer for each LCH, and distributed and held in units of RLC_SDUs before being combined. On the basis of the priority information set in the above, scheduling is performed not in units of RLC_PDU (MAC_SDU) but in units based on RLC_SDU. Therefore, in some cases, it is preferable that the data transfer from the RLC sublayer to the MAC sublayer via the LCH is performed by adding an RLC header in units of variable length RLC_SDU before the segmentation and combination are performed.

By this scheduling, packet data addressed to UE2 is selected and combined in units based on RLC_SDU based on priority information for each LCH, and is converted into RLC_PDU (MAC_SDU) with an RLC header added.
Further, the MAC_SDU is added to a MAC header including control information (sequence number, etc.) for HARQ (Hybrid Automatic Repeat Request), etc., and converted into MAC_PDU, together with CCH control data generated in the RLC layer Then, it is multiplexed (mapped) to a transmission channel (Transport Channel) and transmitted to UE2.

That is, RLC_SDU corresponds to one of a plurality of data units constituting individual data (RLC_PDU) of a plurality of logical channels (LCH) associated with a transport channel of a radio link between eNB1 and UE2. The eNB 1 of this example can perform buffering and scheduling for each LCH in units of the data unit.

Here, as illustrated in FIG. 4, when scheduling is performed in units of MAC_SDUs for each UE 2 based on the priority information set in the LCH, the eNB 1 has the MAC_SDU of the LCH # 1 with the priority “high”, The transmission timing is scheduled in the order of MAC_SDU of LCH # 2 having a medium priority, MAC_SDU of LCH # 3 having a medium priority, and MAC_SDU of LCH # m having a high priority.

Therefore, the transmission of the MAC_PDU addressed to UE # 1 is completed even though the MAC_PDU addressed to UE # n has the same priority ("high") as the LCH # m priority of LCH # m. Otherwise, transmission will not start. This leads to a delay in data arrival time to UE # n.
That is, in this scheduling method, it cannot be said that the unit of scheduling is optimized from the viewpoint of the data arrival time to UE2, so if data transmission to a certain UE2 is not completed, data transmission to another UE2 is not performed. May not start.

On the other hand, as described above, based on the priority information set for each LCH, the data of each LCH is scheduled in smaller RLC_SDU units, and is transmitted to the radio link addressed to UE 2 based on the scheduling result. If this is the case, it is possible to evenly provide DL data transmission opportunities of the same priority to a plurality of UEs 2, and to shorten the data arrival time to each UE 2.

(1.2) Packet scheduling between handover source eNB and handover destination eNB Next, packet scheduling between the handover source eNB and the handover destination eNB will be described.
For example, when the UE 2 moves from an area (cell) covered by the handover source eNB (HO source eNB) 1-1 to an area (cell) covered by the handover destination eNB (HO destination eNB) 1-2, FIG. The handover process is performed according to the flow shown.

That is, first, when the UE 2 measures and reports the radio quality of the transmission path in communication to the HO source eNB 1-1, the HO source eNB 1-1 determines whether to perform handover based on the result of the measurement report. If it is determined and it is determined that the handover is to be performed, the handover is requested to the HO destination eNB 1-2.
When the HO destination eNB 1-2 permits the handover request, the HO source eNB 1-1 transfers (forwards) the packet data addressed to the UE 2 remaining in the local station 1-1 to the HO destination eNB 1-2.

In an existing communication system, there is a case where only control data is transferred without transferring packet data addressed to the UE from the HO source radio base station to the HO destination radio base station at the time of handover. Then, at the time of handover, the packet data addressed to UE2 remaining in the HO source eNB1-1 is transferred to the HO destination eNB1-2 together with the control data.
For the data transfer at that time, it is preferable to apply the packet scheduling in units of RLC_SDU as described above in (1.1).

For example, the HO source eNB 1-1 in this example performs scheduling in units of RLC_SDU at the time of data transfer between eNBs 1, and based on the scheduling result, packet data addressed to UE 2 in units based on RLC_SDU. Transfer to HO destination eNB1-2.
At that time, for example, the HO source eNB 1-1 may temporarily set the priority of the RLC_SDU transferred to the HO destination eNB 1-2 to be higher than the others, and perform scheduling in units of the RLC_SDU.

In the HO destination eNB 1-2, for example, the priority of the RLC_SDU transferred from the HO source eNB 1-1 may be temporarily set higher than the others, and the scheduling in units of the RLC_SDU may be performed.
As illustrated in FIG. 6, when scheduling is performed in units of RLC_PDU (MAC_SDU) at the time of data transfer between eNBs 1, RLC_PDU of LCH # 1 with priority “Large”, RLC_PDU of LCH # m with priority “Large” The transmission timing is scheduled in the order of RLC_PDU of LCH # 2 having a medium priority and RLC_PDU of LCH # 3 having a medium priority.

Therefore, transmission of data addressed to UE # n is not started unless data transmission of LCH # 1 is completed, even though LCH # m has the same priority as LCH # 1 of UE # 1.
That is, when there are a plurality of LCHs having the same priority, a time difference occurs at the start of the transfer process, and the variation in arrival time of each transfer data to the HO destination eNB 1-2 becomes large. As a result, even when the transfer data is transmitted from the HO destination eNB1-2 to the UE2, the data arrival time to the UE2 varies.

On the other hand, the eNB 1 of the present example, for example, in the data transfer between the HO source eNB 1-1 and the HO destination eNB 1-2, for example, in the same manner as the scheduling method described in (1.1), 1 performs scheduling in units of RLC_SDUs, and transfers RLC_SDUs to the HO destination eNB 1-2 based on the scheduling result, so that it is possible to shorten the data arrival time to each UE2.

In addition, since the transfer unit at this time is the RLC_SDU unit, it is possible to efficiently perform ARQ retransmission processing, concealment processing, and the like.
In the above (1.1) and (1.2), the scheduling in the downlink (downlink) data transmission from the eNB1 to the UE2 has been described as an example, but the uplink from the UE2 to the eNB1 (uplink) The same scheduling may be applied to the above.

In this case, data processing in each sublayer of layer 2 is performed in the opposite direction to the example shown in FIG.
[2] Configuration and Operation of eNB 1 (2.1) One Embodiment FIG. 7 is a block diagram illustrating a configuration of eNB 1 according to one embodiment. The HO source eNB 1-1 and the HO destination eNB 1-2 shown in FIG. 7 include, for example, an IP packet termination processing unit 5, a downlink RLC layer processing unit 6, a storage buffer 7, a data selection unit 8, and a scheduler, respectively. 9 is provided.

In the following, when the HO source eNB 1-1 and the HO destination 1-2 are not distinguished from each other, they are simply expressed as eNB1. Also, the number of eNBs 1 provided in the communication system is, of course, not limited to the number shown in FIG. 7 indicates the flow of packet data transferred between eNBs.
Here, the IP packet termination processing unit 5 of this example receives packet data (RLC_SDU) as control plane (C-Plane) information and user plane (U-Plane) data from the MME / UPE 3 via the IP network 4. And a function of performing a predetermined termination process.

In addition, the IP packet termination processing unit 5 of this example has a function of transferring packet data from the HO source eNB 1-1 to the HO destination eNB 1-2 via the IP network 4 when the UE 2 is handed over, for example.
The downlink RLC layer processing unit 6 has a function of distributing the RLC_SDU received by the IP packet termination processing unit 5 to the storage buffer 7 for each LCH.

Further, the downlink RLC layer processing unit 6 of the present example has a function of performing predetermined protocol processing (header addition, etc.) on transfer data from the HO source eNB 1-1 to the HO destination eNB 1-2 at the time of handover of the UE 2. To do.
Furthermore, the downlink RLC layer processing unit 6 of this example has a function of notifying the scheduler 9 of the priority of each LCH set by the MME / UPE 3, for example.

The storage buffer (buffer unit) 7 stores, for each LCH, a plurality of RLC_SDUs constituting individual packet data of a plurality of logical channels (LCH) associated with the transport channel of the radio link between eNB1 and UE2. It has the function to hold.
The storage buffer 7 of this example, for example, as in the example shown in FIG. 8, RLC_SDUs indicated by codes “# 1” to “# 4” for LCH # 1, and codes “#” for LCH # 2. RLC_SDUs indicated by 5 ”to“ # 8 ”, RLC_SDUs indicated by“ # 9 ”to“ # 13 ”for LCH # 3, and“ # 100 ”to“ # 100 ”for LCH # m The RLC_SDU indicated by “# 103” is stored.

The data selection unit (transmission processing unit) 8 selects and extracts packet data stored in the storage buffer 7 in units of RLC_SDUs based on the transmission timing scheduled by the scheduler 9, performs predetermined radio processing, It has a function to transmit to a wireless link.
Further, the data selection unit 8 of the present example has a function of transferring the selected / extracted data addressed to the UE 2 to the HO destination eNB 1-2 based on the transmission timing scheduled by the scheduler 9 when the UE 2 is handed over. To do.

Here, the scheduler 9 of this example has a function of scheduling the transmission timing of the RLC_SDU stored in the storage buffer 7 based on the priority information of each LCH set by the MME / UPE 3, for example, The scheduler 9 of this example has a function of controlling the data selection unit 8 so that RLC_SDU to be transmitted to the UE 2 is preferentially selected and extracted.

For this purpose, the scheduler 9 of this example has a priority information table that holds, for example, the priority information set by the MME / UPE 3 and each LCH in association with each other. This priority information table holds (stores) a user (UE) number, an LCH, and a priority, for example, as in the example shown in FIG.
Here, the priority set by the MME / UPE 3 is given by numerical data “1” to “20”, for example. The scheduler 9 of this example uses “high” as priority information based on the numerical data. ”,“ Medium ”, and“ small ”may be defined.

For example, the scheduler 9 of this example defines a priority “Large” for LCHs having a priority (numerical data) of “20” to “15”, and a priority (numerical data) of “14” to “10”. “L” can be defined for LCHs with priority (numerical data) “9” to “1”. Thereby, the scheduler 9 of this example performs scheduling control so that the RLC_SDU is selected and extracted by the data selection unit 8 in the order of LCH having the priorities of “large”, “medium”, and “small”, for example.

According to this, in the example shown in FIGS. 8 and 9, the priority of LCH # 1 and LCH # m is “high”, and the priority of LCH # 2 and LCH # 3 is “medium”. The priority definition method described above is merely an example, and the present invention is not limited to this.
Each information held in the priority information table may be updated after the data selection unit 8 selects / extracts data or when a new setting is notified by the MME / UPE 3. .

In the eNB 1 of this example configured as described above, the scheduler 9 schedules the data of each LCH in smaller RLC_SDU units based on the priority information set for each LCH, and the data selection unit 8 Based on the scheduling result, RLC_SDU is selected and extracted from the storage buffer, predetermined radio processing is performed, and it is transmitted to the radio link addressed to UE2.

For example, as in the example illustrated in FIG. 10, the eNB 1 schedules to transmit the RLC_SDU of the LCH # 1 having the priority “Large” (see the code “# 1”) first, and then performs the priority “ Scheduling to transmit RLC_SDU (see code “# 100”) of “large” LCH # m.
That is, the RLC_SDU of LCH # 1 with the priority “Large” (refer to code “# 1” to code “# 4”) and the RLC_SDU of LCH # m (refer to code “# 100” to code “# 103”) , Scheduled in turn (alternately) in units of RLC_SDU and transmitted to UE2.

Then, RLC_SDU of LCH # 2 having a medium priority (refer to code “# 5” to code “# 7”) and RLC_SDU of LCH # 3 (refer to code “# 9” to code “# 11”) Similarly, scheduling is performed in units of RLC_SDU and transmitted to UE2.
Thereby, since the transmission timing of RLC_SDU can be evenly distributed for a plurality of LCHs having the same priority, it is possible to suppress the occurrence of transmission delay.

In addition, the HO source eNB 1-1 of the present example can apply the same scheduling as described above to data transfer with the HO destination eNB 1-2.
For example, the scheduler 9 performs scheduling for each RLC_SDU, and the data selection unit 8 transfers the RLC_SDU to the HO destination eNB 1-2 based on the scheduling result.

Thereby, even in the data transfer between the HO source eNB 1-1 and the HO destination eNB 1-2 at the time of the handover of the UE 2, the transmission timing of the RLC_SDU can be evenly distributed for a plurality of LCHs having the same priority. It is possible to suppress the occurrence of transmission delay.
Note that the scheduler 9 may temporarily set the LCH priority of the RLC_SDU to be transferred to the HO destination eNB 1-2 to be higher than the others, thereby improving the degree of freedom of scheduling. Therefore, it is possible to further optimize the data transmission time.

Next, the operation of the HO destination eNB 1-2 will be described.
As shown in FIG. 7, the HO destination eNB 1-2 has the same configuration as that of the HO source eNB 1-1. For example, the above-described scheduling may be performed for the RLC_SDU transferred from the HO source eNB 1-1. Good.
For example, the HO destination eNB 1-2 receives the priority information table together with the transfer data from the HO source eNB 1-1.

As a result, the scheduler 9 and the data selection unit 8 of the HO destination eNB 1-2 schedule the RLC_SDU transferred from the HO source eNB 1-1 based on the priority information set in each LCH and address it to a plurality of UEs 2. Send.
Also, the scheduler 9 of the HO source eNB 1-1 temporarily sets the priority information for the LCH of the UE 2 that performs the handover out of the priorities held in the priority information table, for example, so that the UE 2 You may make it transmit addressed data preferentially over others.

For example, when the UE # 1 performs a handover, the HO source eNB 1-1 and / or the HO destination eNB 1-2 are configured so that the priority of the LCH of the UE # 1 becomes higher as in the example illustrated in FIG. By updating (changing) the priority information, it is possible to transmit the transfer data addressed to the UE # 1 with higher priority than others. As another method, the priority information corresponding to UE 2 that does not perform handover may be set low, or both of them may be performed.

Further, the scheduler 9 and the data selection unit 8 of the HO destination eNB 1-2 detect that there is no data addressed to the UE 2 that has performed the handover in the storage buffer 7, and the transfer data transmission to the UE 2 addressed after the handover is completed You may make it detect that it did.
When the completion of transmission of the transfer data is detected, the transfer process is stopped, the priority information in the priority information table is returned to the value before the update (setting), and preferential scheduling for the transfer data is performed. You may make it cancel. As another method, the priority information of the LCH set by the MME / UPE 3 may be received to create a new priority information table and perform the above-described scheduling.

As a result, the HO destination eNB 1-2 can obtain the same effect as that of the HO source eNB 1-1 described above, and can temporarily transmit data addressed to the UE 2 that has performed the handover preferentially over others. it can.
Note that when transmitting transfer data from the HO destination eNB 1-2 to the UE 2, the transport block size (TBS) may be changed according to the data length.

As described above, the eNB 1 can reduce the data arrival time to each UE 2 by suppressing the transmission delay of the transfer data during the handover.
The scheduler 9 and the data selection unit 8 may change the scheduling unit according to, for example, the transmission destination of the RLC_SDU. For example, when the transmission destination of RLC_SDU is another eNB1, scheduling may be performed in units of a plurality of RLC_SDUs, and when the transmission destination of RLC_SDU is UE2, scheduling may be performed in units of RLC_SDUs.

Also, for example, the scheduling unit of RLC_SDU may be changed according to the stage of handover (“HO preparation”, “HO execution”, “HO completion”, etc. shown in FIG. 5).
In this way, since the degree of freedom (flexibility) of the scheduling can be improved, the data transmission time can be optimized.

(2.2) First Modification In the above-described embodiment, an example in which all RLC_SDUs are the targets of the scheduling has been described. However, based on the LCH priority, the RLC_SDU is selected and the scheduling is applied. Also good.
For example, the scheduler 9 of this example performs the scheduling so that the RLC_SDU of the LCH having a higher priority is preferentially transmitted.

Here, the operation of this modification will be described with reference to FIG.
For example, when the priority “medium” is set as the priority threshold, the eNB 1 in this example has the priority “Large” LCH # 1 and the RLC_SDU of the LCH # m having a higher priority than the threshold ( In the same manner as described above in 2.1), that is, scheduling in units of RLC_SDU and transmitting to each UE2.

On the other hand, RLC_SDUs of LCH # 2 and LCH # 3 having a priority equal to or lower than the threshold are stored in the RLC_PDU (MAC_SDU) unit or in the order stored in the storage buffer 7, that is, codes “# 5” to Scheduling is performed in the order of code “# 13” and transmitted to UE 2.
In this way, in this modified example, RLC_SDU of LCH with higher priority can be preferentially transmitted, so that it is possible to improve the degree of freedom of scheduling and further optimize the data transmission time. Become.

The scheduler 9 and the data selection unit 8 may change the unit of RLC_SDU scheduling according to, for example, the transmission destination of the RLC_SDU. For example, when the destination of RLC_SDU is another eNB1, scheduling may be performed in a unit in which a plurality of RLC_SDUs are combined, and when the destination of RLC_SDU is UE2, scheduling may be performed in units of RLC_SDU.

Also, for example, the scheduling unit of RLC_SDU may be changed according to the stage of handover (“HO preparation”, “HO execution”, “HO completion”, etc. shown in FIG. 5).
In this way, it is possible to improve the degree of freedom of scheduling, so that it is possible to further optimize the data transmission time.

(2.3) Second Modification In the above-described embodiment, RLC_SDU is selected and scheduled based on the LCH priority. However, based on the buffer amount for each LCH in the storage buffer 7, each LCH is selected. Scheduling may be performed so that the number of RLC_SDU selections is adjusted. That is, the scheduling unit may be changed based on the amount of LCH remaining (waiting to be transmitted).

For example, the scheduler 9 and the data selection unit 8 of this example monitor the data remaining amount of RLC_SDU for each LCH stored in the storage buffer 7 regularly or irregularly, and the data remaining amount is equal to or greater than a predetermined threshold value. For LCH, scheduling is performed in units of a plurality of RLC_SDUs of the LCH.
Here, the operation of this modification will be described with reference to FIG.

For example, the scheduler 9 and the data selection unit 8 try to transmit the RLC_SDU of the LCH # 1 having the priority “Large” (see the code “# 1”) first, but the remaining data amount of the LCH # 1 is predetermined. RLC_SDUs indicated by code “# 1” and code “# 2” are collectively (continuously) transmitted after being determined to be equal to or greater than the threshold.
Next, when transmitting RLC_SDU of LCH # m with priority “L”, it is determined that the remaining data amount of LCH # m is less than the predetermined threshold, and only RLC_SDU indicated by code “# 100” is transmitted. To do.

Also, for the RLC_SDU of LCH # 1 having the priority “L” (see symbol “# 3”), it is determined that the remaining data amount of LCH # 1 is less than the predetermined threshold, and the symbol “# 3”. Only the RLC_SDU indicated by is transmitted.
Then, the RLC_SDU of the LCH # m having the priority “Large” (see the code “# 101”) is to be transmitted, but it is determined that the remaining data amount of the LCH # m is equal to or greater than a predetermined threshold. RLC_SDUs indicated by “# 101” to “# 103” are transmitted together.

In this way, the subsequent RLC_SDU is also transmitted in the same manner. Note that the data amount may be updated every time RLC_SDU is transmitted from each LCH.
In addition, the scheduler 9 and the data selection unit 8 of the present modification, for example, set a plurality of threshold values for the LCH data remaining amount, and based on the relationship between the remaining data amount and the plurality of threshold values, RLC_SDU You may make it change a transmission unit in steps.

As described above, in this modification, the transmission unit of RLC_SDU is changed according to the remaining amount of data in the storage buffer 7, so that the degree of freedom in scheduling can be improved and the data transmission time can be further optimized. It becomes possible.
Note that the scheduler 9 in this example may perform scheduling so that the number of RLC_SDU selections for each LCH is adjusted according to the priority of the LCH, or the remaining data amount of the LCH and the priority of the LCH. In accordance with both, scheduling may be performed so that the number of selections of RLC_SDUs of individual LCHs is adjusted. In this way, it is possible to further improve the degree of freedom of scheduling, and it is possible to further optimize the data transmission time.

[3] Others In the example described above, the HO source eNB 1-1 transfers data to the HO destination eNB 1-2 via the IP network 4, but instead of using the IP network 4, the HO source eNB 1-1 transfers data using a high-speed dedicated line or the like. You may make it perform.
Further, in the above-described example, the eNB 1 has been described with respect to an example of scheduling and transmitting in units of RLC_SDU. However, if the data size is smaller than RLC_PDU (MAC_SDU), the same processing is performed in units of data other than RLC_SDU. It may be.

Furthermore, in the above-described example, the example in which the scheduling is applied to the data transfer at the time of handover between different eNBs 1 has been described. However, the same processing is also performed for the data transfer at the time of handover between sectors in the same eNB 1. May be.
Further, the functions of the HO source eNB 1-1 and the HO destination eNB 1-2 described above may be selected as necessary.

Furthermore, the functions provided in the above-described HO source eNB 1-1 and HO destination eNB 1-2 may be provided in another entity as necessary.

Claims

A wireless base station that communicates with a wireless terminal via a wireless link,
A buffer unit that holds, for each logical channel, a plurality of data units constituting individual data of a plurality of logical channels associated with the transport channel of the radio link;
A scheduler that schedules the transmission timing of each data unit in the buffer unit based on the priority set for each logical channel;
According to the transmission timing scheduled by the scheduler, a transmission processing unit that selects any of the data units from the buffer unit and transmits the selected data unit to a communication path that reaches the wireless terminal;
A radio base station characterized by having
The communication path includes the wireless link, or a communication path between the wireless terminal and a destination wireless base station, and a wireless link between the destination wireless base station and the moved wireless terminal. The radio base station according to claim 1, wherein:
The scheduler
The radio base station according to claim 1, wherein the scheduling is performed so that data units of logical channels with higher priority are transmitted to the communication path with higher priority.
The scheduler
The radio base station according to claim 1, wherein the scheduling is performed so that the number of selections of data units of individual logical channels is adjusted according to the priority of the logical channels.
The scheduler
2. The radio base station according to claim 1, wherein the scheduling is performed so that the number of times of selecting a data unit of each logical channel is adjusted based on a buffer amount for each logical channel in the buffer unit. .
The scheduler
The radio base station according to claim 2, wherein the priority of the data unit of the logical channel transmitted to the destination radio base station is temporarily set higher than others.
The scheduler
The data unit of the logical channel is temporarily set higher than others when the data unit received from the source radio base station of the radio terminal is a data unit. 1. A radio base station according to 1.
A scheduling method in a radio base station that communicates with a radio terminal via a radio link,
A plurality of data units constituting individual data of a plurality of logical channels associated with a transport channel of the radio link are held for each logical channel,
Scheduling the transmission timing of each data unit based on the priority set for each logical channel;
According to the scheduled transmission timing, select one of the data units and transmit to the communication path to the wireless terminal,
The scheduling method characterized by the above-mentioned.
At least one wireless terminal;
A radio base station communicating with the radio terminal via a radio link;
A buffer unit that holds, for each logical channel, a plurality of data units constituting individual data of a plurality of logical channels associated with the transport channel of the radio link;
A scheduler that schedules the transmission timing of each data unit in the buffer unit based on the priority set for each logical channel;
According to the transmission timing scheduled by the scheduler, a transmission processing unit that selects any of the data units from the buffer unit and transmits the selected data unit to a communication path that reaches the wireless terminal;
A wireless communication system, characterized by comprising: