KR100970445B1 - Method of resource management for handover in wireless communication system - Google Patents

Abstract

The present invention relates to a resource management method for handover in a mobile communication system, and to minimize system resource waste and handover delay by maximizing resource reuse between sectors in intra handover (inter-sector handover), and further, intra / In the inter handover, an attempt is made to effectively deal with the ping-pong situation by maintaining the resources of the previous cell (sector) for a predetermined time even after the handover is performed.

To this end, the present invention provides a resource management method for handover in a mobile communication system, comprising: a handover request receiving step of receiving a handover request by a second base station from a first base station where a current user terminal resides; And a resource reuse step in which the second base station receiving the handover request reuses resources of the first base station or newly configures resources according to whether resources are reusable.

Mobile communication, 3G LTE, SAE, intra eNB handover, inter eNB handover, resource management, resource reuse, ping pong phenomenon

Description

Resource management method for handover in mobile communication system {METHOD OF RESOURCE MANAGEMENT FOR HANDOVER IN WIRELESS COMMUNICATION SYSTEM}

The present invention relates to a resource management method for handover in a mobile communication system, and more particularly, to minimize system resource waste and handover delay by maximizing resource reuse between sectors in intra handover (inter-sector handover). In addition, in intra / inter handover, resource management for handover in a mobile communication system, which can effectively cope with the ping-pong situation by maintaining the resources of the previous cell (sector) without releasing resources even after the handover is performed. It is about a method.

The present invention is derived from a study conducted as part of the next generation core technology development project of the Ministry of Information and Communication and the Ministry of Information and Communication Research and Development (Task Management Number: 2005-S-404-22, Task Name: 3G Evolution Access Technology Development).

In handover in mobile communication systems, especially 3rd generation future long-term evolution (3G LTE) systems, intra eNB handovers performed between sectors within the same cell and inter eNBs performed between different cells There is a handover.

Conventional Intra eNB handover reconfigures all resources as shown in FIGS. 3A and 3B each time the sector changes, which not only results in waste of system resources but also causes delays in intra eNB handover There is this.

In addition, in the conventional Intra / Inter eNB handover, since the source base station releases the resource as soon as it receives a "HO Request Confirm" message from the target base station, the user terminal with the handover has been performed. Even if the ping-pong situation returns to the original base station area, there is a problem that all resources must be newly configured.

Therefore, there is an urgent need for efficient resource management to increase resource utilization (reuse) and effectively cope with the ping-pong situation in intra / inter eNB handover.

The prior art as described above has a problem in that system resources are wasted and handover delays are caused by reconfiguring all resources whenever a sector is changed in relation to intra handover (inter-sector handover). There is also a problem in that it does not effectively cope with the ping-pong phenomenon, it is an object of the present invention to solve this problem.

Accordingly, the present invention minimizes system resource waste and handover delay by maximizing resource reuse between sectors in intra handover (inter-sector handover), and also maintains a fixed time period after handover is performed in intra / inter handover. An object of the present invention is to provide a resource management method for handover in a mobile communication system, which can effectively cope with a ping-pong situation by maintaining resources of a previous cell (sector) without releasing them.

The objects of the present invention are not limited to the above-mentioned objects, and other objects and advantages of the present invention which are not mentioned can be understood by the following description, and will be more clearly understood by the embodiments of the present invention. Also, it will be readily appreciated that the objects and advantages of the present invention may be realized by the means and combinations thereof indicated in the claims.

The present invention, in order to achieve the above object, in the intra handover (inter-sector handover), in order to minimize the system resource waste and handover delay, to minimize the new resource setting and reuse the existing resources as possible It is characterized by.

In addition, the present invention is characterized in that the intra / inter handover is maintained without releasing the resources of the previous cell (sector) for a certain time even after the handover is performed, so as to effectively cope with the ping-pong situation.

More specifically, the present invention relates to a method for managing resources for handover in a mobile communication system in a mobile communication system, wherein the first base station in which the user terminal currently resides is handed to a second base station determined as a target base station to be handed over to. A handover request step of requesting over; And a resource holding step of maintaining, by the first base station without releasing resources for a predetermined time even after the handover is performed.

In addition, the present invention provides a resource management method for handover in a mobile communication system, comprising: a handover request receiving step of receiving a handover request by a second base station from a first base station where a user terminal currently resides; And a resource reuse step in which the second base station receiving the handover request reuses resources of the first base station or newly configures resources according to whether resources are reusable.

The resource recycling (reuse) technology in the Intra-eNB handover according to the present invention has the effect of significantly reducing handover delay and system resource waste by maximizing resource reuse between sectors in the Intra-eNB handover. have.

That is, the recycling technique in the intra handover according to the present invention has the effect of increasing the speed of handover and minimizing the resource occupancy by preventing new configuration of unnecessary entities and reusing existing entities as much as possible when moving between sectors. .

In addition, the resource maintenance technology according to the present invention has an effect that can effectively cope with special situations such as ping pong.

That is, the resource maintenance technique in the intra / inter handover according to the present invention maintains a resource of a cell which previously resided for a predetermined time, and thus can support relatively fast handover even when returning to a previous cell such as a ping-pong phenomenon. It has an effect.

The present invention relates to a resource reuse technique related to intra eNB handover (ie, intersectoral handover) in a base station of a mobile communication system, especially a 3GPP Long Term Evolution (LTE) system, and a ping pong phenomenon in an intra / inter eNB handover. It is about resource maintenance techniques to cope.

That is, the present invention is a structural change (eg, eNodeB (eNB)) of 3G LTE based on inter-sector handover in existing cellular mobile communication systems, for example, GSM, CDMA, WCDMA, etc. = NodeB + RNC, aGW = S / GGSN) in consideration of the direct interface between the eNodeB and a method for faster intra eNB handover is characterized.

Conventional GC technology predicts calls (calls from neighboring cells to their cells) that an active call in a neighboring cell may handover to its own cell and reserves the resources required by the predicted calls in advance. On the contrary, the present invention, in contrast to the GC technique, is a technique for effectively coping with a special case such as a ping-pong situation by maintaining a certain amount of time for a call leaving from one cell to another cell.

The foregoing and other objects, features and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings, in which: There will be. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

1 is a configuration diagram of a general 3G LTE system. That is, FIG. 1 shows a part of a 3G Long Term Evolution (LTE) system or a System Architecture Evolution (SAE) system.

As shown in FIG. 1, the 3G LTE / SAE system includes a user equipment (UE) 10, an evolved NodeB (eNB) 11, 12, and an access gateway (aGW) (aGW). 13) is made.

Interfaces in the 3G LTE / SAE system are mainly the air interface (uu + or RRC +) of the UE 10 and the eNBs 11 and 12, and the interface (S1 interface (RANAP +) of the aGW 13 and the eNBs 11 and 12). The control unit is IU +, the user-plane is IU-UP +, and the interface between the eNB 11 and the eNB 12 (X2 interface (RNSAP +), the control unit is IUR +, and the user-plane is IUR- There are three such as UP +).

In FIG. 1, two eNBs are assumed, such as eNB1 11 and eNB2 12, and it is assumed that each eNB 11 and 12 is in charge of three sectors (sectors a, b, and c). In addition, an expression such as "sector c of eNB1" and the like referred to as a subject for transmitting and receiving a signal hereinafter indicates 'a logical part that governs sector c in eNB1'.

On the other hand, the mobility of the user terminal (UE) 10 can be divided into four cases as follows. That is, an intra-eNB handover 101 in which the user terminal UE moves from sector c of eNB1 to sector b, and in which the user terminal UE moves from sector c of eNB1 to sector a of eNB2 Inter-eNB Handover 102 and Instant-return1 103 and Instant Return, a ping-pong situation that returns back to the previous sector in each handover (101, 102). 2 (Instant-return 2) 104 and the like.

The present invention relates to a resource recycling technique in an intra eNB handover 101, and an application technique for coping with instant return 1 103 and instant return 2 104. It is about.

2 is a structural diagram of a protocol stack for the 3G LTE system of FIG.

The UE 10 constituting the 3G LTE system, the eNB1 11 corresponding to the base station 1, the eNB2 12 corresponding to the base station 2, and the access gateway (aGW) 13 facilitate access to each other. In order to do so, it has a protocol structure as shown in FIG. 2, which corresponds to a standard specification in a 3G LTE system, and thus a detailed description thereof will be omitted. However, in FIG. 2, the term “undecided” means that it is not yet determined by standardization.

3A to 3C are conceptual diagrams for reuse in intra eNB handover according to the present invention.

Each eNB 11 and 12 illustrated in FIG. 1 has a concept of a source eNB and a target eNB for each sector. For example, when moving from sector c of eNB1 11 to sector b of eNB1 11, as in intra eNB handover 101 of FIG. 1, eNB1 11 is the source for sector c. It has the concept of eNB and the concept of target eNB for sector b.

In general, as shown in FIG. 3A, if a user terminal (UE) receives a service, a resource corresponding to the user terminal (UE) (RRC +, 3GE PHY, 3GE MAC, 3GE RLC in “31”) Occupies in sector c of eNB1 11.

If the UE moves to sector b of eNB1 as in the intra eNB handover 101 of FIG. 1, as shown in FIG. 3B, RRC + ′, 3GE PHY ′, 3GE MAC ′, A resource 32 such as 3GE RLC 'is configured in the user equipment UE and the eNB1 sector b, and the RANAP + and the IU-UP / GTP-U are recycled to connect traffic to the sector b.

The present invention can improve the speed of intra eNB handover by recycling not only RANAP + and IU-UP / GTP-U related to the UE, but also reusable parts provided by the system.

Next, a radio link control (RLC) recycling (reuse) method according to the present invention will be described with reference to FIG. 3C.

Normally, since RLC is initialized during intra eNB handover, RLC packets of sector c that have not been reconfigured and transmitted to RLC + 'should be forwarded to the target (RLC of sector b) and have to be re-ordered. The situation arises. As a result, a time delay for reconfiguring the RLC and a packet reordering occurs.

In order to solve this problem, in the present invention, as shown in FIG. 3C, it is recommended that the user terminal / base station maintains the 3GE RLC '' (RLC 'entity and changes only the logical connection point with the 3GE MAC. 331, and is managed programmatically as RRC + '' (meaning that it has both the RRC + context in sector c and the RRC + 'context in sector b for the user terminal UE). .

By doing so, it is possible to reduce 3GE RLC 'setup time, re-ordering time, system resources (memory) and the like. This recycling is related to the system configuration inside the eNB, it is possible to maximize the recycling depending on the configuration.

4A and 4B are detailed configuration diagrams of the reuse entity of FIG. 3. When the UE receives one service through one sector, how resources of the UE and eNB are specifically configured Indicates whether or not

Basically, all resource configuration information of the user equipment UE arrives at the terminal RRC + 40 through an RRC + message transmitted by the eNB RRC + to the user equipment UE, and the configuration information is controlled under the control of the terminal RRC + 40. UE resources of 3GE PHY, 3GE MAC, and 3GE RLC through L1 / PHY, L2 / MAC (Medium Access Control), and L2 / RLC (Radio Link Control) Control (401 to 403) To control.

Meanwhile, resources of the 3GE PHY, 3GE MAC, and 3GE RLC in the eNB corresponding to the network side may be determined by the eNB RRC + 41 through the L1 / PHY, L2 / MAC, and L2 / RLC Control (411 to 413). To control.

FIG. 5 is an explanatory diagram of backward average signal strength and shows signal strength important for a handover trigger.

When a reference signal transmitted from a sector of the eNB is received for 0.5 seconds in a situation where the UE is far from the sector, the strength of the raw received signal is a square box shape (50). The results of taking Backward Smoothing Averaging on them are as indicated by the circle 51.

In the present invention, as the comparison value of the received signal strength and event used for the handover trigger, the averaged signal strength 51 may be used instead of the raw data. Various techniques can be used to reduce the signal change caused by fading.

The number of sample data to backward averaging may indicate to the network side the measurement / report to the UE through a measurement control message, but in the present invention, the optimized number of samples has already been determined. As shown in FIG. 5, it is assumed that the noise and the tendency of the increase and decrease of the signaling signal can be easily identified.

The user terminal UE measures the average signal strength of the number of samples determined by the indication of a measurement control message or the averaged signal strength of various samples. The messages can be provided to the network.

Event as shown in FIGS. 6A to 6D based on a backward averaging of the optimized number of samples (n) for the reference signal as shown in FIG. 5. As defined, it will be described later. Here, backward averaging is obtained as Σ (i-n to i) signal strength / n. In this case, i represents a current observation time point in the user terminal (UE).

6A and 6B are diagrams illustrating an embodiment of a change in rear average signal strength according to movement of a user equipment (UE) in an intra-eNB HO and an Instant Return 1 situation. to be.

FIG. 6A illustrates backward averaged signal strength measured by a user terminal (UE) at the time of intra eNB handover of FIG. 1. In detail, the signal of sector c of eNB1 11 is illustrated. It can be seen that the strength 601 is decreasing and the signal strength 602 of the sector b of the eNB1 11 is increasing.

In general, in cell planning, a signal strength threshold that can communicate is designed, and a certain margin A is also designed. Therefore, the user terminal (UE) through the RRC + message of the eNB to report in the event 'Event (Event) 1'.

The 'event 1' situation refers to a case in which there are cells whose signal strength exceeds the threshold A plus margin A (hereinafter, referred to as 'baseline 1 _Intra '). Report event 1 to the network through a MR (Measurement Report) message (or measurement control message). In this case, the margin A may be set to "0" (in this case, the threshold value is 1 _{Intra in} this case), or an appropriate margin value is determined by the system in consideration of cell planning. It may be.

In FIG. 6A, only the reference signal 602 of the eNB1 sector b is assumed, but in practice, 'event 1' may occur when a reference signal of another cell exceeds a threshold. If there is a report according to 'event 1' from a plurality of cells, the optimal cell will be found among the cells generating 'event 1' and determined as a cell to be handed over. The Handover Decision method can use various existing methods.

In FIG. 6A, 'event 2' denotes 'reference value 2 _Intra ' which is a value in which a reference value 601 of a cell (eNB1 sector c) in which the user terminal immediately resides is incapable of communication, or a certain margin is added to the threshold value. In this case, the reference value 2 _Intra may be equal to or different from the reference value 1 _Intra ), and in this case, the user terminal may be currently residing in 'Event 2' through a measurement report. Report to cell eNB1 sector b.

In FIG. 6B, 'event 3' indicates that 'event 3' initially resides in eNB1 sector c and is handed over to eNB1 sector b by handover decision by trigger of 'event 1'. The signal strength of sector c is greater than the system margin adjustment value (System Margin A-α + threshold, which is referred to as 'reference value 3 _Intra ', where α satisfies the condition A> α with some adjustment value). Is maintained within a predetermined time (Δt) from the time point at which handover is determined from eNB1 sector c to eNB1 sector b through Measurement Control, and the signal strength of the previous resident cell eNB1 sector c is It refers to a situation that is greater than the signal strength, and when such a situation occurs, the user terminal reports 'event 3' through a measurement report. The predetermined time Δt mentioned here has already been notified to the mobile terminal through measurement control.

Meanwhile, FIGS. 6C and 6D illustrate changes in rear average signal strength according to movement of a user equipment (UE) in an inter-eNB HO and instant return 2 situation. It is explanatory drawing. Hereinafter, an inter-eNB handover (Inter-eNB HO) and related instant return 2 will be described with reference to FIGS. 6C and 6D.

'Event 2' of FIG. 6C refers to a situation in which a reference signal from a cell (eNB1 sector c) that has previously resided falls below a threshold at which communication is impossible (or a value added with a constant margin), in which case the user terminal Report the event 2 to the cell (eNB2 sector a) that currently resides through a measurement report. 6A, margins A and B of 'event 1' may be different from each other or may be the same according to embodiments. 6A to 6D show that the event 2 falls below the threshold without considering the margin, but according to the exemplary embodiment, the event 2 is the same as the event 1. For example, you can apply margins to thresholds (if you apply margins to 'event 2', you can assume A 'for intra handover and B' for inter handover). In this case, the margins A 'and B' may be the same as A and B in 'event 1' or may be other values smaller than A and B.

In Event 3 of FIG. 6D, the signal intensity difference between the cell in which the cell currently resides (eNB2 sector a) and the cell immediately residing is the system Margin B-α + threshold value. _Inter ', where α is a slight adjustment value that satisfies the condition of B> α), the constant given by Measurement Control at the time when handover is initiated from eNB1 sector c to eNB2 sector a. It refers to a situation that is maintained within the time Δt and is greater than the signal strength of the eNB1 sector c than the signal strength of the eNB1 sector a. When this occurs, the user terminal reports 'event 3' through a measurement report. . Compared to FIG. 6B, according to the exemplary embodiment, α values may be different for inter handover and intra handover.

In the situation of FIGS. 6C and 6D, 'Event 2' becomes a trigger point for releasing resource maintenance in the previous cell (eNB1 sector c), and 'Event 3' selects an appropriate cell in a ping-pong situation. It becomes the trigger point.

In summary, 'baseline 1 _Intra ', 'baseline 2 _Intra ' and 'baseline 3 _Intra ' used in 'Event 1', 'Event 2', and 'Event 3' in FIGS. 6A and 6B related to intra eNB handover. The concept of 'can be applied to the inter-eNB handover as it is, the' baseline 1 _Inter ',' baseline 2 _Inter 'in the' event 1 ',' event 2 ', and' event 3 'in FIGS. 6C and 6B And a reference value such as 'reference value 3 _Inter '. Each corresponding reference value may be the same or different from each other.

FIG. 7A is a flowchart of a general Intra-eNB handover method, assuming the intra eNB handover situation 101 of FIGS. 1 and 6A, the same eNB1 11 regards sector c as the source eNB and sector b. Can be regarded as a target eNB.

When 'event 1' of FIG. 6A occurs, the UE transmits a measurement report (“Measurement Report”) (RRC + message, uu +) to eNB1 through sector c (701).

The source eNB (sector c) then makes a handover request (“HO Request”) via the eNB intercommunication (IP) to the target eNB (sector b) (702). At this time, the source eNB (sector c) and the target eNB (sector b) are performed according to internal processing (IP).

The target eNB (sector b) that receives the handover request (“HO Request”) configures the RRC / RLC / MAC / PHY resource in sector b. When the resource configuration in sector b is completed, a handover request confirmation (“HO Request Confirm”) message is transmitted to source eNB1 (sector c) via eNB intercommunication (IP) (703).

The eNB1 (sector c) receiving the handover request confirmation ("HO Request Confirm") transmits a handover command (HO Command) to the user terminal (UE) through the old link (old link) (704). At this time, the traffic transmission to the downlink DL of the eNB1 (sector c) is stopped, and the UE receiving the handover command (“HO Command”) also stops the traffic forwarding to the uplink UL. .

As shown in FIG. 7A, the interruption 71 by the wireless L1 / L2 layer includes frequency synchronization, downlink synchronization, timing advance, and uplink resource request / acceptance. It may be caused by (UL Resource Request / Grant) or the like (705). Here, frequency synchronization can be ignored when the carrier frequency is the same during intra eNB handover, and DL synchronization can be performed by aligning baseband and radio frequency (RF). As the time required for alignment, it may be ignored according to the design method in the intra eNB handover. In addition, timing advance and UL resource request / grant may also be ignored during intra eNB handover.

After the above process of "705" is performed, data forwarding occurs from the source eNB to the target eNB according to internal processing (IP) (706).

The UE receiving the handover command (“HO Command”) reconfigures the RRC +, 3GE PHY, 3GE MAC, and 3GE RLC to enable connection in sector b. When reconfiguration of terminal resources (terminal resources related to connection to sector b) in the user terminal (UE) is completed, a handover complete ("HO Complete") (RRC + message, uu +) message is uploaded to a new cell, sector b. (707).

At this time, the network receiving the handover complete (“HO Complete”) message transmits downlink (DL) traffic that has been suspended and receives an L2 ACK for handover complete (“HO Complete”) (708). ) Will transmit uplink (UL) traffic that was suspended.

In some cases, data forwarding from the source eNB to the target eNB may be continuously performed after the path switch due to handover is performed (709).

Meanwhile, although not shown in the drawing, when a handover request confirmation (“HO Request Confirm”) is transmitted from the target eNB1 sector b to the source eNB1 sector c, a release procedure is additionally performed on the resources in the sector c.

In the conventional general procedure as described above, whenever a sector is changed, all resources shown in FIGS. 3A and 3B are reconfigured, and the reconfiguration time causes a delay for intra eNB handover.

That is, the interruption according to the general Intra-eNB handover as shown in FIG. 7A includes an interruption 71 by the radio L1 / L2 layer, an interruption 72 by the uplink (UL) RRC, There is an interruption 73 due to downlink (DL) RRC, and this interruption causes a delay in handover.

Therefore, in the present invention, the sectors in the eNB are integratedly managed (particularly, in the RRC + perspective, the integrated management is very efficient for programming), and the context of the sector c is transferred to the sector b using the concept of resource reuse (recycling). In this case, the delay caused by the reconfiguration of resources and the delay due to re-ordering in retransmission can be reduced. The context may include configuration information related to RRC +, 3GE RLC, 3GE MAC, 3GE PHY, data context related to undelivered RLC data, and HARQ (Hybrid ARQ). Information, an Automatic Repeat Request (ARQ) status, and the like.

FIG. 7B is a flowchart of a general inter eNB handover method, assuming that the inter eNB handover situation 102 of FIGS. 1 and 6C, sector c in eNB1 may be regarded as a source eNB and sector a of eNB2 is a target. Can be considered an eNB.

When 'event 1' of FIG. 6c occurs, the UE transmits a measurement report (“Measurement Report”) (RRC + message, uu +) to eNB1 via sector c (711).

The source eNB1 (sector c) then sends a handover request (“HO Request”) message to the target eNB2 (sector a) via the inter-eNB interface X2 (712).

The target eNB2 (sector a) receiving the handover request (“HO Request”) message configures the RRC / RLC / MAC / PHY resource in sector c of eNB1. When the base station resource configuration in the eNB2 sector a is completed, a handover request confirmation (“HO Request Confirm”) is transmitted to the source eNB1 (sector c) through the inter-eNB interface X2 (713).

The eNB1 (sector c) receiving the handover request confirmation ("HO Request Confirm") transmits a handover command ("HO Command") to the user terminal (UE) through an existing link (old link) (714). At this time, the downlink (DL) traffic forwarding in the access gateway (aGW) may be stopped by the message design with the aGW, but in FIG. Assume that it is forwarded to sector a of eNB2 and buffered during the handover interruption interval. In addition, the UE receiving the handover command (“HO Command”) also stops traffic transmission on the uplink (UL).

As shown in FIG. 7B, the interruption 74 by the radio L1 / L2 layer may include frequency synchronization, downlink synchronization, timing advance, uplink resource request / acceptance. (UL Resource Request / Grant) or the like (715). Here, Frequency Synchronization takes a small amount of time that can be ignored when Carrier Frequency is different during Inter eNB handover, and DL Synchronization is performed using Baseband and Wireless. A delay of 5-10 msec is expected as the time required to align the frequency RF. In addition, timing advance and UL resource request / grant are expected to be negligible for inter-eNB handover, and more buffering is required than for intra-eNB handover. .

After the process of "715" is performed, data forwarding occurs from the source eNB to the target eNB (716).

The UE receiving the handover command (“HO Command”) reconfigures UE resources such as RRC +, 3GE PHY, 3GE MAC, and 3GE RLC to enable connection in eNB2 sector a. When reconfiguration of terminal resources (terminal resources related to connection to eNB2 sector a) in the user terminal UE is completed, a handover complete (“HO Complete”) message (RRC + message, uu +) is transferred to a new cell eNB2 sector a. Raised.

At this time, when the network side receives the handover complete ("HO Complete") message (717) and requests the access gateway (aGW) to change the traffic transmission path from eNB1 to eNB2, the access gateway (aGW) is downlink. (DL) A traffic packet is switched (switched) from sector c of eNB1 to sector a of eNB2 (718). The user terminal receiving the L2 ACK 719 for handover completion (“HO Complete”) transmits the uplink (UL) traffic that has been suspended.

In some cases, data forwarding from the source eNB to the target eNB may be continuously performed 720 after the path switch 718 is performed by handover.

On the other hand, although not shown in the figure, if a handover request confirmation (“HO Request Confirm”) is transmitted from the target eNB2 sector a to the source eNB1 sector c, the release procedure is additionally performed for the resources in the source eNB1 sector c.

Interruption according to the general Inter-eNB handover as shown in FIG. 7B includes an interruption 74 by the radio L1 / L2 layer, an interruption 75 by the uplink (UL) RRC, and a downlink. (DL) An interruption 76 by RRC, an interruption 77 by a path switch, and the like, a delay occurs in the handover due to the interruption. Therefore, the recycling of resources and the maintenance of resources can be considered in relation to handover.

However, in the 'Intra eNB handover procedure' as shown in FIG. 7A, resource recycling was possible due to system design and speed due to IP. However, 'Inter eNB handover' as shown in FIG. 7B. In the procedure, the node may be completely separated (eNB1 and eNB2 are completely separated) and the X2 interface may be relatively slow, and thus no recycling may be necessary. That is, when the X2 interface is fast enough, Inter eNB handover may use the resource recycling concept of Intra eNB handover, but the present invention will be described under the assumption that inter eNB handover is not recycled.

If resource recycling of intra eNB handover is performed in an inter eNB handover procedure, resource reconstruction may be supported by transferring the context of sector c of eNB1 to sector a of eNB2. Here, the context includes configuration information related to RRC +, 3GE RLC, 3GE MAC, 3GE PHY, data context related to undelivered RLC data, HARQ information, and ARQ status. (status) and the like.

In essence, the inter-eNB handover requires the initialization of the RLC, so if a packet that the RLC did not transmit on the old link is transmitted on a new link, this packet is It must be re-ordered again.

8A and 8B illustrate an embodiment of a definition of an RNTI according to the present invention.

In the present invention, in order to enable the user terminal (UE) and the target eNB1 (sector b) to know the situation of intra eNB handover (Intra-HO), as shown in FIGS. 8A and 8B, Radio Network (RNTI) Define a Temporary Identifier.

In definition 1 of FIG. 8A, RNTI is defined as an S-eNB identity and a serving RNTI identity, and definition 2 of FIG. 8B includes an 'intra-eNB flag', which is an intra-eNB flag. (Intra) Defined to indicate whether or not it is a handover.

The newly defined RNTI is transmitted in a handover command (“HO Command”) (uu +) in FIG. 7A, and thus, the UE is intra by comparing with the RNTI value of the newly moved sector b. It is possible to determine whether or not the eNB handover situation.

That is, when defined as defined in Definition 1 of FIG. 8A, it may be determined whether or not it is an intra eNB handover compared to the 'eNB identity' of the RNTI value previously given to become an ACTIVE situation in sector c. When defined as defined in definition 2 of 8b, since the 'intra-eNB flag' is set, it may be determined whether or not it is an intra eNB handover situation.

If the information defined in FIGS. 8A and 8B is included in a handover request (“HO Request”) (IP or X2) transmitted between the source eNB and the target eNB in FIGS. 7A and 7B, its eNB identity is determined. Compared with or with an Intra-eNB flag, it is possible to determine whether a call currently in its cell is a handover call on an intra eNB side or a handover call on an inter eNB side.

By defining a new RNTI as described above, in case of intra eNB handover, the concept of reuse (recycling) may be applied to process to have a procedure different from that of Inter eNB handover.

9A to 9D are flowcharts illustrating an embodiment of a processing procedure at a 'source eNB' of an intra / inter eNB handover procedure according to the present invention, and FIGS. 10A to 10E are diagrams illustrating an embodiment of the present invention. FIG. 1 is a flowchart illustrating a process performed by a 'target eNB' in an intra / inter eNB handover procedure. Since the handover is performed by the interaction of the 'source eNB' and the 'target eNB', these will be described together. For reference, some eNBs can be both source and target, especially in intra handover.

In the Intra eNB Handover 101 and Instant-Return 1 103 situation of FIG. 1, sector c of eNB1 11 is considered the source eNB and sector b of eNB1 11 is It is considered the target eNB.

Meanwhile, in the Inter eNB handover 102 and Instant-Return 2 104 situation of FIG. 1, sector c of eNB1 11 becomes the source eNB and sector a of eNB2 12. Becomes the target eNB.

<Intra eNB Handover>

9 and 10 from the perspective of the intra eNB handover 101 of FIG. 1, when the UE performs 'event 1' in a service connection with the source eNB1 sector c, A measurement report (MR) is made to the source eNB1 sector c via a uu + interface (900). The measurement report MR should have cell (= sector) information of a reference signal (= sector) that exceeds a threshold (see FIG. 6A).

For example, in the configuration of a 3G LTE system as shown in FIG. 1, sectors that may trigger 'event 1' may be sectors a, b of eNB1 or sectors a, b, c of eNB2. Accordingly, a 'handover decision process' 901 for determining an optimal cell (= sector) in the list of sectors that may trigger such 'event 1' should be performed. An over decision method may be applied, which will not be described further. 'Event 1' used in the present invention in connection with an intra eNB handover is not limited to 'Event 1' in the meaning defined in FIG. 6A, and according to an embodiment, a signal of a serving cell eNB1 sector c An existing handover trigger event, such as a signal strength of a neighbor cell (= sector) (eg, eNB1 sectors a and b) becomes larger than the strength, may be used as 'event 1'.

Once the 'best sector to move' is determined through the handover decision routine 901, the source eNB1 (sector c) is moved from the sector in which the user terminal currently resides to the 'sector (target sector)' decided to move. It is checked whether the movement is 'local mobility' (902).

If the local mobility is confirmed, the source eNB1 sector c will send a handover request message ("HO Request") (IP interface) to the 'target eNB1 sector b' through the internal processing (IP) interface. (903) If it is not local mobility, it will send a handover request message (“HO Request”) (X2 interface) to the 'target eNB2' via the X2 interface (904) (interest with &quot; 904 &quot; (Inter) eNB handover> will be described).

A 'HO Request' (IP interface) including the context information of the source eNB, which is transmitted through internal processing (IP) in “903” of FIG. 9A, is a target as in FIG. 10A. eNB receives (1000).

The target eNB receiving the handover request message ("HO Request") (IP) checks whether the resource is reusable (Reusability) (1001).

As a result of the reusability check, (1) when partial reuse is possible (i.e., when a new partial configuration is needed), the resources of sector c are reused in the intra movement from sector c to source sector b of source eNB1, where reuse Resources related to L1 / PHY, L2 / MAC, and L2 / RLC (RLC may be reused depending on the embodiment, in which case there is no need for new configuration) are newly configured (1004, 1005), (2) If reusability is not possible (i.e. all new configurations are required), then the corresponding L1 / PHY, L2 / MAC, L2 / RLC (RLC may be reused depending on the embodiment, in which case no new configuration is required). Construct resources (1007, 1008). However, if the configuration is already configured during the reusability check, it updates the logical service access point (SAP) of the configured resource and triggers the use of each resource (1002).

As described above, when (1) reuse and partial configuration are completed, (2) complete reconfiguration is completed, and (3) configuration already exists to cope with the ping-pong situation, the target eNB is the source eNB1 sector through IP. c, "HO Request Confirm" ("HO") including the "target context information including the target RNTI" is transmitted (1003, 1006, 1009).

Subsequently, the source eNB1 sector c that has received this handover request confirmation message (“HO Request Confirm”) (IP interface) performs the procedure shown in FIG. 9B (910 to 912).

That is, when the source eNB1 sector c receives the handover request confirmation message ("HO Request Confirm") (IP interface) (910), the target context information including the '' target RNTI to the user terminal (UE) through the sector c Transmits an RRC + message called "Hover Command Message" ("HO Command") (911), and transmits the RLC / MAC / HARQ context and all data arriving at the source eNB via DL (DL). Each time it occurs to the target eNB1 sector b, it transmits (912).

Meanwhile, as shown in FIG. 10D, when the target eNB1 sector b receives the data transmitted from the source eNB1 sector c and the RLC / MAC / HARQ context (1030), the target eNB1 sector b forwards it to the respective configuration entities of the target eNB1 sector b. (1031) Buffer (1032).

Thereafter, as shown in FIG. 10C, when an RRC + message of a handover complete message (“HO Complete”) comes up from the UE side to the target eNB1 sector b (1020), the target eNB1 sector b is selected as the local mobility ( It is checked whether it is Local Mobility (1021), and in case of local movement, data transmission on downlink (DL) is initiated (1022). In this case, the handover complete message ("HO Complete") also includes information for identifying the handover type (intra handover or inter handover) like the handover request message. If it is not a local move, a path switch is made (see 1023, inter handover).

A feature of the present invention is not to release a resource upon receiving a handover request confirmation message (“HO request confirm”) IP from the target eNB1 sector b to the source eNB1 sector c via internal processing (IP), eNB1 sector only after receiving a Measurement Report ('Event 2') that is an RRC + message from eNB1 sector c (because it has already been handed over, eNB1 sector c becomes the target sector of the new handover) (1040). It is to transmit (1041) resource release message ("Resource Release") through the internal processing (IP) from b to eNB 2 sector c.

ENB1 sector c that has received the above resource release message ("Resource Release") (IP) (920), considering the reusability (recyclability) (921), if there is a part to share resources with eNB1 sector b, the resource Resources of the source eNB1 sector c that share and do not share are released (922, 923). That is, in the case of intra eNB handover, recyclable resources are shared.

On the contrary, if recyclability is not considered from the beginning (for example, Inter-eNB handover), a resource release message ("Resource Release") is received and all related resources of sector c of source eNB1 are released (924, 925).

The resource release procedure according to the present invention is continued until the event 2 occurs in the source sector c as well as in the target sector b, even for resources that cannot be reused in the reuse concept in Intra-eNB handover. This is to effectively cope with the ping-pong phenomenon caused by the movement to sector c again.

In addition, if the movement from the eNB1 sector c to the eNB1 sector b is completed by the intra eNB handover situation of FIG. 1 and the measurement report (event 1) as shown in FIG. 6A, the eNB1 sector b corresponds to the source eNB from now on.

As mentioned above, unless the measurement report (MR) ('event 2') comes up to sector b, the resource of eNB1 sector c is not released, and the measurement report corresponding to 'event 3' occurs due to the situation as shown in FIG. If (MR) has risen to eNB 1 sector b (930), the handover decision is determined to be sector c of eNB1 (931) and a handover request message (“HO Request”) (IP) is sent to eNB1 sector b to handover. (932). At this time, eNB1 sector b receives this message as a target eNB and checks reusability as shown in FIG. Therefore, only SAP can be changed to each entity (3GE RLC / MAC / PHY) to easily cope with the ping-pong situation.

<Inter eNB Handover>

Referring to FIGS. 9 and 10 from the inter eNB handover perspective of FIG. 1, if the UE has a service connection with the source eNB1 sector c, 'event 1' occurs, the source eNB1 sector Report the measurement to MR via the uu + interface (900). This measurement report (MR) should have cell (= sector) information of a reference signal (= sector) that exceeds a threshold (see FIG. 6A).

For example, in the configuration of a 3G system as shown in FIG. 1, sectors that may trigger 'event 1' may be sectors a, b of eNB1 or sectors a, b, c of eNB2. Accordingly, a 'handover decision process' 901 for determining an optimal cell (= sector) in a list of sectors that may trigger 'event 1' should be performed. In the present invention, various handovers are performed. Determination methods may be applied and will not be discussed further. However, it is assumed that the optimal sector is determined through the handover decision routine. 'Event 1' used in the present invention in relation to Inter eNB handover is not limited to Event 1 in the meaning defined in FIG. 6C, and in some embodiments, is greater than the signal strength of the serving cell eNB1 sector c. An existing handover trigger event, such as an increase in signal strength of a neighbor cell (= sector) (eg, eNB2 sector a) may be used as 'event 1'.

Once the 'best sector to move' is determined via the handover decision routine 901, the source eNB1 (sector c) moves from the sector in which the user terminal currently resides to the 'sector (target sector) that it has decided to move to'. It is checked whether the movement is 'local mobility' (902).

If the local mobility is confirmed, the source eNB1 sector c will send a handover request message (“HO Request”) (IP interface) to the 'target eNB1 sector b' through the internal processing (IP) interface (903). (As described in this section <Intra eNB Handover>), and if it is not local mobility, the handover request message ("HO Request") (X2 interface) is sent via the X2 interface to the target eNB2. (904).

In FIG. 9A, the "HOHO" (X2 interface) including the context information of the source eNB, which is transmitted through the X2 interface, is the target eNB (eNB2) as shown in FIG. 10B. Sector a) is received (1010).

The target eNB (eNB2 sector a), which has received a handover request message (“HO Request”) X2 (1010), checks whether it is an existing configuration (whether or not a related resource is already configured) (1011). If no, it indicates the resource configuration associated with the L1 / PHY, L2 / MAC, L2 / RLC (1014, 1015). On the contrary, during the checking of the existing configuration, if already configured, the use of the previously configured resource is triggered (1012).

As described above, when utilization 1012 and reconfiguration 1014 and 1015 of the existing resource configuration are completed, the target eNB (eNB2 sector a) receives a handover request confirmation message including 'target context information including the target RNTI' ( "HO Request Confirm") "is transmitted to the source eNB1 sector c via X2 (1013, 1016).

Subsequently, the source eNB1 sector c that receives the handover request confirmation message (“HO Request Confirm”) X2 performs the procedure shown in FIG. 9B (910 to 912). However, the difference from the procedure in <Intra eNB handover> is that it is processed by the X2 interface, not internal processing (IP).

That is, when the source eNB1 sector c receives the handover request confirmation message ("HO Request Confirm") X2 (910), the 'target context information including the target RNTI' is transmitted to the user terminal (UE) through the sector c. Send an RRC + message called an included handover command message (" HO Command " &quot; &quot; (911), and generate an RLC / MAC / HARQ context and all data arriving at the source eNB via the downlink Each time, the data is transmitted to the target eNB2 sector a (912).

Meanwhile, as shown in FIG. 10D, when the target eNB2 sector a receives the data transmitted from the source eNB1 sector c and the RLC / MAC / HARQ context (1030), the target eNB2 sector a delivers the data to each of the configuration entities of the target eNB2 sector a. (1031) Buffer (1032).

Thereafter, as shown in FIG. 10C, when an RRC + message of a handover complete message (“HO Complete”) is raised from the UE side to the target eNB2 sector a (1020), the target eNB2 sector a may be configured as local mobility ( Local Mobility (1021), if not local movement, the access gateway (aGW) to the downlink (DL) to the sector c of the eNB1 through a 'Path Switch message containing the S1 access identifier' (S1) (DL) ) Switch traffic to sector a of eNB2 (1023). Here, the 'S1 access identifier' is a delimiter that is determined when a specific UE is attempted to access a base station, and thus, which eNB and what sector are the S1 access identifiers between the UE and the access gateway aGW? It is the basis for distinguishing which UE.

If it is a local move, "1022" is performed as corresponding to intra handover, which has already been described.

A feature of the present invention is that the eNB1 sector c does not immediately release resources when it receives a handover request confirmation message (“HO request confirm”) from the eNB2 sector a via the X2 interface, but does not immediately release the “eNB1 sector” from the UE. Only after receiving a measurement report ('event 2'), which is an RRC + message from c (1040), does a 1041 deliver a resource release message ("Resource Release") through the X2 from the eNB2 sector a to the eNB 1 sector c (1041). Is the point.

Regarding the resource release, referring to FIG. 9C, when the source eNB1 sector c receives the resource release message (“Resource Release”) X2 (920), the source eNB1 sector c checks whether the resource is reusable (recycled) 921. As a result, in case of inter eNB handover in which resource recycling is not considered from the beginning, all related resources of sector c of eNB1 are released (9245, 925). That is, all resources related to L1 / PHY, L2 / MAC, and RLC are released (924, 925). However, in consideration of resource recyclability, that is, in case of intra eNB handover, only resources related to L1 / PHY and L2 / MAC and RLC not to be reused are released (922 and 923).

In short, the resource release procedure according to the present invention is characterized in that the resource remains in eNB 1 sector c until 'Event 2' occurs in the previous eNB 1 sector c, which moves back to eNB 1 sector c. To cope with the ping pong phenomenon.

Meanwhile, if the movement from eNB1 sector c to eNB2 sector a is completed by the inter eNB handover situation of FIG. 1 and the measurement report (MR) ('event 1') as shown in FIG. Apply the concept of eNB.

As long as the measurement report ('event 2') does not come up to the eNB2 sector a, the resource of the eNB1 sector c is not released, and the measurement report (MR) corresponding to the 'event 3' occurs when the situation as shown in FIG. 6D occurs. If up to sector a (930), the handover decision at this time is determined to be sector c of eNB1 (931) and sends a handover request message (“HO Request) X2 to eNB1 sector c to handover (932). ).

At this time, eNB1 sector c becomes a target eNB. When eNB1 sector c receives the handover request message (“HO Request) X2, as shown in FIG. 10A, the reusability is checked (1001). In a ping-pong situation, since each resource (3GE RLC / MAC / PHY) keeps reusing resources and sector resources that are not being reused, only the SAP needs to be changed (1002). I can cope with it.

On the other hand, the method of the present invention as described above can be written in a computer program. And the code and code segments constituting the program can be easily inferred by a computer programmer in the art. In addition, the written program is stored in a computer-readable recording medium (information storage medium), and read and executed by a computer to implement the method of the present invention. The recording medium may include any type of computer readable recording medium.

The present invention described above is capable of various substitutions, modifications, and changes without departing from the technical spirit of the present invention for those skilled in the art to which the present invention pertains. It is not limited by drawing

1 is a configuration diagram of a general 3G LTE system,

2 is a structural diagram of a protocol stack for the 3G LTE system of FIG.

3A to 3C are conceptual diagrams for reuse in intra eNB handover (Intra-eNB HO) according to the present invention;

4A and 4B are detailed structural diagrams of the reuse entity of FIG. 3 according to the present invention;

5 is an explanatory diagram of a backward averaged signal strength;

6A and 6B are diagrams illustrating an embodiment of a change in rear average signal strength according to movement of a user equipment (UE) in an intra-eNB HO and an Instant Return 1 situation. ,

6C and 6D are diagrams illustrating an embodiment of a change in rear average signal strength according to movement of a user equipment (UE) in an inter-eNB HO and an instant return 2 situation. ,

7a is a flow chart for a general intra eNB handover method,

7b is a flowchart for a general inter eNB handover method;

8A and 8B illustrate an embodiment of a definition of an RNTI according to the present invention;

9A to 9D are flowcharts of an embodiment of a process performed at a 'source eNB' during an intra / inter eNB handover procedure according to the present invention;

FIG. 10A to FIG. 10D are flowcharts illustrating an example of a process performed at a 'target eNB' during an intra / inter eNB handover procedure according to the present invention.

Claims (17)

A resource management method for handover in a mobile communication system, A handover request step of requesting a handover to a second base station determined as a target base station to be handed over by a first base station in which the current user terminal resides; And If the handover is an intra handover after the first base station performs the handover, if the resource release request is received from the second base station, resource retention is maintained while releasing resources that are not reused. step Resource management method for a handover comprising a. The method of claim 1, The handover request step, When the first base station receives a measurement report ('event 1') indicating that the signal strength of the second base station is greater than or equal to a predetermined first reference value from the user terminal, the first base station determines a target base station to which the second base station is to be handed over. Resource management method for handover, characterized in that for transmitting a handover request message. The method of claim 2, The handover request message, The resource management method for handover, characterized in that it comprises any one of identification information or handover type information of the first base station. delete A resource management method for handover in a mobile communication system, A handover request step of requesting a handover to a second base station determined as a target base station to be handed over by a first base station in which the current user terminal resides; And When the handover of the first base station is an inter handover, when the resource release request is received from the second base station, all resources are released. A resource management method for handover in a mobile communication system, A handover request receiving step of receiving a handover request by a second base station from a first base station where the user terminal currently resides; And Resource reuse step of the second base station receiving the handover request to reuse the resource of the first base station or to perform a new resource configuration, depending on whether or not resources are reused Resource management method for a handover comprising a. The method of claim 6, The resource reuse step, The second base station confirms the handover type by comparing the first base station identification information included in the handover request message with its base station identification information or through the handover type information included in the handover request message. The resource management method for handover, characterized in that determining the resource reuse according to the identified handover type. The method of claim 7, wherein The resource reuse step, As a result of checking the handover type, in case of intra handover, the second base station reuses resources that can be reused among the resources of the first base station, and newly configures resources that cannot be reused. Resource management method for handover. The method of claim 7, wherein The resource reuse step, And as a result of the handover type checking, in case of an inter handover, the second base station newly configures a resource. The method of claim 6, After the handover is performed, when the second base station receives a measurement report ('event 2') indicating that the signal strength of the first base station has fallen below a predetermined second reference value from the user terminal, the second base station Requesting resource release from the first base station Resource management method for a handover further comprising. The method of claim 10, After the handover is performed and before the event 2 occurs, if a ping pong situation ('event 3') occurs in which the user terminal returns to the first base station, the second base station sets the first base station as a new target. Determining base station and requesting handover Resource management method for a handover further comprising. The method of claim 11, The ping pong situation, After the handover is performed, a state in which the signal strength of the first base station where the user terminal resides before the handover is greater than or equal to a third reference value larger than the second reference value by a predetermined value is maintained within a predetermined time period, And the signal strength of the first base station is greater than that of the second base station currently inhabiting. The method of claim 11, Each of the event 2 or the event 3, A resource management method for handover, characterized in that it is determined based on the Backward Averaged Signal Strength. The method of claim 6, The resource reuse step, If the resource configured in the previous handover is maintained in preparation for the ping-pong situation, the resource management method for the handover, characterized in that for using the held resource. The method of claim 6, When the second base station receives a handover complete message from the user terminal, confirming handover type information included in the handover complete message; If it is determined that the handover type is an intra handover, the second base station initiating downlink traffic transmission; And If the handover type is determined to be an inter handover, the second base station requesting a path switch for downlink traffic to an access gateway; Resource management method for a handover further comprising. The method according to claim 1 or 6, The first and second base station, In the case of intra handover, the resource management method for handover, characterized in that the base station that manages one cell (Cell) is a logical base station divided by sector. 7. The method according to claim 1 or 6, The first and second base station, In the case of inter handover, the resource management method for handover, characterized in that the base station to manage different cells (Cell).

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