JP2007104344A - Handover method, base station, and mobile station - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a handover method of properly guaranteeing the sequence of up data when a hard handover is made between a plurality of radio base stations connected to a core network. <P>SOLUTION: In the handover method, a base station as a handover source judges whether a mobile station requires a handover, the base station as the handover source requests a base station at a handover destination to allocate a radio resource for a mobile station; and the base station as the handover source reports a handover message including a transmission wait time of up data to the mobile station, and the mobile station having reached a cell at the handover destination transmits the up data to the base station as the handover destination after the lapse of the transmission wait time. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a handover method, a base station, and a mobile station.

  The Rel-99, Rel-4, Rel-5, and Rel-6 specifications of 3GPP, an international standardization organization for third-generation mobile communication systems, have a radio access network (RAN) configuration as shown in Fig. 1. Is stipulated. In the RAN of FIG. 1, the following procedure is performed.

  (1) A mobile station (UE: User Equipment) performs radio communication with a radio base station (Node B) via a radio interface (Uu).

  (2) A physical service area managed by Node B is called a cell, and one cell may be divided into a plurality of sectors. Here, the unit of the smallest area managed by Node B is collectively referred to as a cell.

  (3) Node B is connected to a radio network controller (RNC) via a wired interface (Iub), and generally a plurality of Node Bs are connected to the RNC. The RNC is further connected to a core network (CN) via a wired interface (Iu).

  (4) In the 3GPP Rel-99, Rel-4, Rel-5, and Rel-6 specifications, UE, Node B, and RNC are included as devices in the RAN.

Furthermore, in 3GPP Rel-99, Rel-4, Rel-5, and Rel-6 specifications, soft handover across Node B is shown in FIG. 2 in the uplink in which user data is transmitted from the UE to Node B. Can support. Soft handover in the uplink is known as one means for improving radio transmission efficiency. In the procedure of Figure 2:
(1) UE transmits uplink data in Uu, and a plurality of Node Bs that perform soft handover receive this signal.

  (2) Each Node B that performs soft handover independently demodulates and decodes this received signal, discards the data if the decoding result is incorrect, and conversely transfers the decoded data to the RNC if the decoding result is correct .

  (3) In the RNC, when the same decoded data is transferred from multiple Node Bs, all but one of them is discarded (selective combining function), and the decoded data is corrected in order and transferred to the CN (order guarantee function). .

  In general, many applications do not assume that data will arrive in a redundant state or that the data order will not be normal. Therefore, when combining soft handover in the uplink, selective combining Functions and order assurance functions play an important role in maintaining quality at the application level.

On the other hand, 3GPP is working on the creation of a new standard to achieve higher capacity and lower delay of RAN. This new standard is called LTE (Long Term Evolution) in 3GPP. In LTE, a RAN configuration that does not apply RNC as shown in FIG. 3 has been proposed with the aim of reducing data transfer delay in the RAN, and call and radio resource control delay.
3GPP standard, Internet <URL: http://www.3gpp.org/>

  When the RAN configuration as shown in FIG. 3 is used, since the CN-Node B is directly connected, the data transfer time is shortened, and the call and radio resource control function previously performed in the RNC Since it is implemented in Node B, it is expected that these control delays will be shortened. On the other hand, since there is no RNC, there is no selective combining node for data in the RAN, and in this RAN configuration, soft handover across Node B in the uplink is not applied.

However, even in the RAN configuration of FIG. 3, when the UE moves between Node Bs, it is necessary to perform a hard handover across Node Bs. This is shown in FIG. In Figure 4:
(1) Since there is no RNC in the RAN configuration of FIG. 3, the order guarantee function before the decoded data is transferred to the CN is implemented in Node B.
(2) When performing a hard handover with the RAN configuration shown in FIG. 3 (a) Until the handover, Node B as the handover source receives uplink transmission of UE and guarantees the order of decoded data to CN. Forward.

  (A) Immediately after the handover, the Node B that is the handover destination receives the uplink transmission of the UE and transfers it to the CN in a state in which the order of the decoded data is guaranteed.

  In this case, the order of data transferred from each Node B to the CN is guaranteed by the order guarantee function in the Node B, but the Iu route (Iu_source) between the handover source Node B and CN and the handover destination Node B- Since the Iu path (Iu_target) between the CNs is different, the transmission delays are different, and if the delay time on Iu_source is greater than the delay time on Iu_target, the upstream node can reach the CN in reverse order There is sex. This is shown in FIG.

  As shown in FIG. 5, in the RAN configuration of FIG. 3, the order of data transferred from each Node B to the CN can be guaranteed. May reverse the data from Node B as the handover source and reach the CN. In this case, since the order is not normal, the service quality deteriorates in many applications. Although it is conceivable to implement an order guarantee function in the core network node, this scheme is not preferable if it is desired to use a general-purpose product with a low cost as much as possible for load distribution and the core network node.

  The present invention has been made in order to address at least one of the above-described problems, and the problem is that the order of uplink data when performing a hard handover between a plurality of radio base stations connected to the core network. It is to provide a handover method, a base station, and a mobile station that appropriately ensure the above.

  In the handover method used in the present invention, the handover source base station determines whether or not the mobile station needs to be handed over, and the handover source base station requests the handover destination base station to allocate radio resources for the mobile station. The handover source base station notifies the mobile station of a handover message including the uplink data transmission standby time, and the mobile station that has transitioned to the handover destination cell transmits to the handover destination base station after the transmission standby time elapses. A method for transmitting data.

  According to the present invention, it is possible to appropriately ensure the order of uplink data when performing a hard handover between a plurality of radio base stations connected to a core network.

  A base station according to an embodiment of the present invention determines whether or not a mobile station needs to be handed over, creates a handover message including an uplink data transmission standby time, and notifies the mobile station of the handover message. The mobile station that has moved to the handover destination cell transmits uplink data to the handover destination base station after the notified transmission standby time has elapsed. The transmission standby time may be determined by the time difference ΔT between the transmission delay time T between the core network and the handover source base station and the transmission delay time T ′ between the core network and the handover destination base station.

  More specifically, when a hard handover is performed in the RAN configuration of FIG. 3, the mobile station does not immediately start uplink data transmission to the handover destination radio base station, but the data from the handover source radio base station Starts after interruption for a certain period of time that can guarantee that the data from the wireless base station of the handover destination reaches the node of the core network. The length of the predetermined time is reported as broadcast information from the handover source radio base station, or the handover source radio base station notifies the mobile station in a command that triggers a hard handover.

  As a result, it is possible to prevent the upstream data from reaching the core network node at the time of handover, and to improve the service quality and to simplify and reduce the cost of the system. Moreover, it is not necessary to provide an intermediate device such as an RNC between the radio base station and the core network node, and the order guarantee function need not be implemented in the core network node.

  The first embodiment of the present invention will be described below. As shown in FIG. 6, in this embodiment, the UE moves toward the service area of the target Node B while performing radio communication with the source Node B in the mobile communication system adopting the RAN configuration as shown in FIG. . Then, hard handover is performed according to the following procedure as shown in FIG.

  (1) After measuring that the radio quality of the target Node B exceeds the radio quality of the source Node B by a certain level, the UE reports this to the target Node B (MEASUREMENT REPORT). Here, the radio quality may be the received power of the common pilot transmitted by Node B in the downlink, and a “certain level” threshold is specified from the source Node B when the radio link is established.

  (2) When receiving MEASUREMENT REPORT from the UE, the source Node B prompts the target Node B to prepare for handover, that is, to prepare for allocation of radio resources (SETUP REQUEST).

  (3) Target Node B informs source Node B that the UE is ready for radio resource allocation (SETUP RESPONSE).

  (4) When receiving SETUP RESPONSE, the source Node B transfers the connection information between the UE and the UE to the target Node B (UE context transfer).

(5) The source node B transmits a hard HO message (Hard handover message) for urging hard handover to the UE. Source Node B notifies the UE of “uplink transmission interruption time after handover” in the Hard handover message. The value of “uplink transmission interruption time after handover” may be a value obtained by the following formula:
“Uplink transmission interruption time after HO” = Iu_source delay time−Iu_target delay time Here, Iu_source indicates a transmission path between source Node B and CN, and Iu_target indicates a transmission path between target Node B and CN. In addition, as the delay time in the above formula, it is conceivable to apply a value such as an instantaneous value, a worst value, or a cumulative distribution value (for example, a 95% value of the cumulative distribution).

  (6) The UE stops transmission to the source Node B when receiving the Hard handover message.

  (7) When the “uplink transmission interruption time after handover” elapses after transmission to the source Node B is stopped, the UE starts uplink data transmission to the target Node B.

  8A and 8B show the configuration and operation flow in the UE required for the hard handover procedure. As shown in FIG. 8A, in the mobile station configuration necessary for realizing the first embodiment, an application unit that is a transmission source of data to be transmitted on the uplink, and uplink transmission data transmitted by the application unit are stored. An uplink transmission data buffer unit that discharges accumulated data to the data transmission unit only when uplink transmission is permitted, a data transmission unit that wirelessly transmits the uplink data to Node B, and a Hard handover message from Node B And a timer storage / management unit for storing an “upstream transmission interruption time after handover” timer included in the hard handover message and managing the timer elapsed time.

  As shown in FIG. 8B, the following procedure is performed in the UE.

  (1) The UE message receiver receives a Hard handover message.

  (2) The message receiving unit notifies the uplink transmission data buffer unit that the Hard handover message has been received, and stops discharging accumulated data to the data transmitting unit. That is, the uplink transmission to the source node B is stopped.

  (3) The message receiving unit simultaneously notifies the timer storage / management unit of the “uplink transmission interruption time after handover” included in the Hard handover message, and the timer storage / management unit starts the timer.

  (4) When the timer elapses, the timer storage / management unit notifies the upstream transmission data buffer unit of the fact.

  (5) When the uplink transmission data buffer unit is notified that the timer has elapsed from the timer storage / management unit, the uplink transmission data unit discharges the accumulated data from the application unit to the data transmission unit. Start data transmission.

  Handover is performed as shown in FIGS. 9A-D.

  (A) The UE transmits data (Data 1 to 3 in the figure) to the source Node B until immediately before the handover.

  (B) Immediately after receiving the Hard handover message, the mobile station stops transmission to the source Node B and weights (waits) transmission to the target Node B.

  (C) When the “uplink transmission interruption time after handover” timer elapses, the UE continues to transmit data to target Node B (from Data 4), and data that has been transmitted to source Node B during this time (Data 1 to 3) Has reached the CN via Iu_source with the order guaranteed.

  (E) Data in the guaranteed state from Target Node B (Data 4 to 6) reaches CN via Iu_target, but since data via Iu_source has already reached CN, Iu_source and Iu_target Data reversal between the two can be avoided, and data arrives at CN in the normal order.

It is a figure which shows the radio | wireless access network (RAN) of 3GPP. It is a figure which shows the operation example of the soft handover in RAN of FIG. 1 is a diagram illustrating an LTE radio access network (RAN). FIG. FIG. 4 is a diagram showing an example of handover operation in the RAN of FIG. 3. It is a figure which shows the problem at the time of a hand-over. It is a figure which shows RAN used by one Example of this invention. It is a figure which shows the operation example of the handover by one Example of this invention. The functional block diagram of a mobile station is shown. It is a figure which shows the operation example of a mobile station. It is a figure (before a hand-over) which shows the mode of a hand-over. It is a figure which shows the mode of a handover (immediately after receiving a handover message). It is a figure (after a fixed time progress) which shows the mode of a hand-over. It is a figure which shows the mode of a hand-over (after a hand-over).

Explanation of symbols

RAN radio access network CN core network RNC radio network controller Node B base station UE mobile station

Claims (4)

The handover source base station determines whether the mobile station needs to be handed over,
The handover source base station requests assignment of radio resources for the mobile station to the handover destination base station,
The handover source base station notifies the mobile station of a handover message including the uplink data transmission waiting time,
A handover method, wherein a mobile station that has moved to a handover destination cell transmits uplink data to the handover destination base station after the transmission standby time has elapsed. Means for determining the necessity of handover of the mobile station;
Means for requesting allocation of radio resources for the mobile station to the base station of the handover destination;
Means for the handover source base station to create a handover message including an uplink data transmission waiting time;
Means for notifying the mobile station of the handover message so that the mobile station that has shifted to the handover destination cell transmits uplink data to the handover destination base station after elapse of the transmission standby time;
A base station characterized by comprising: The transmission waiting time is determined by a transmission delay time between a core network and a handover source base station and a time difference between a transmission delay time between the core network and a handover destination base station. 2. The base station described in 2.   Uplink data transmission to the handover destination base station is not started immediately after the transition, and it is possible to guarantee that the data from the handover source base station reaches the core network node before the data from the handover destination base station. A mobile station characterized by starting uplink data transmission after being interrupted for a certain period of time.

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