KR100392765B1 - Handover method for USTS in next generation asynchronous mobile telecommunication - Google Patents

Abstract

The present invention provides a next generation asynchronous mobile communication system for improving a handover process occurring in an inter-cell overlapping area when a mobile subscriber station operating in a USTS mode is used in an asynchronous mobile communication system employing a reverse synchronous transmission method (USTS). The present invention relates to a handover method for USTS in a system, wherein a radio link with a plurality of base stations (21, 22, 23) is connected in a handover region of an asynchronous next generation mobile communication system (USTS). The radio link with one of the base stations 21 performs handover with respect to the mobile terminal 10 communicating in the USTS mode, from the mobile terminal 10 for each forward signal of the plurality of radio links. The distance information between the mobile terminal 10 and each of the base stations 21, 22, and 23 is obtained, while acquiring the measured received radio wave strength information. Obtain (S401, S402); After determining whether the received radio wave strength information of the radio link communicating in the current USTS mode among the plurality of radio links is equal to or less than a preset threshold, and if it is below, based on the obtained radio wave strength information and distance information, the plurality of radio links By selecting one of the radio links to be set to the USTS mode (S403), and then the USTS communication to the selected radio link, and to delete the radio link that was communicating in the previous USTS mode (S404-S412), continuous during handover The effect of achieving the USTS and removing the load on the system due to frequent exchange of signal information is created.

Description

Handover method for backward synchronous transmission in next generation asynchronous mobile communication system {Handover method for USTS in next generation asynchronous mobile telecommunication}

The present invention relates to a handover method for uplink synchronous transmission in a next generation asynchronous mobile communication system. Next-generation asynchronous mobile communication in asynchronous next-generation mobile communication system, such as a system or asynchronous IMT-2000 system, to improve the handover process occurring in the inter-cell overlapping area when a mobile subscriber station operating in USTS mode is moved. The present invention relates to a handover method for backward synchronous transmission in a system.

Currently, USTS is a technology under consideration in the standardization work for the 3rd generation mobile communication system of asynchronous type, and is used in a base station receiver for a reverse link for transmitting data from a mobile station (UE) having a low mobility to a base station (Node B). Is a technique for adjusting a transmission time point for a reverse link in a mobile terminal based on a reception timing of.

That is, the mobile terminal irregularly located in the cell has a different distance with respect to each base station, so the propagation delay of the signal is also different. In the CDMA system, if the orthogonal characteristic of the code can be used to the maximum, it is possible to increase the transmission capacity, and the technique applied to the reverse link is USTS. Further adjustment of the data transmission time at each mobile terminal by the propagation delay with respect to the reverse link enables synchronization of the timing at which the signal is received at the base station receiver and maximizes the orthogonality of the code. In addition, since the initial propagation delay is changed due to the continuous movement of the mobile terminal, the timing can be continuously adjusted.

USTS has the following three modes. The first mode is Normal mode, which does not control the timing in this mode, and the mobile terminal is classified by the scrambling code. The second is USTS mode, where timing control is performed and the mobile terminal is divided into the scrambling code and the channel code. . Third is non-USTS mode. In this non-USTS mode, timing control is not performed and the mobile terminal is classified into a scrambling code and a channel code.

As a handover procedure for the USTS that has been proposed so far, there are two methods as follows, which will be described with reference to FIG. 1.

First, the proposed first handover method will be described.

In the first step S1, the mobile terminal UE0 10 has a single radio link at the base station B1 21, and the radio link is in USTS mode. In the next second process (S2), when the mobile terminal 10 moves to the base station B2 (Node B2) 22, the radio link of the base station B2 22 is added, wherein the added radio link is non- USTS mode.

In the next third step (S3), when the mobile terminal 10 moves to an area where three cells overlap, a non-USTS mode radio link of a base station B3 (Node B3) 23 is added to the mobile terminal ( 10) communicates via one USTS mode and two non-USTS mode radio links. In the next fourth step (S4), if the mobile terminal 10 is out of the service area of the base station B1 21, the radio link of the corresponding USTS mode is disconnected, and communication with the other two non-USTS mode radio links. do.

Finally, in the fifth step S5, if the mobile terminal 10 is out of the service area of the base station B2 22 and only one non-USTS mode radio link with the base station B3 23 is connected, mode conversion is performed. The procedure goes to USTS mode.

However, the first handover method described above is connected to the radio links of the two base stations 22 and 23 when the mobile terminal 10 enters the area of the fourth process S4. Because they operate in non-USTS mode, the synchronization is not performed on the reverse link, and thus the performance improvement by USTS is not obtained. In particular, since the USTS is applied to low-speed mobility, it takes time for the mobile terminal 10 to exit the corresponding handover area of the fourth process S4 and connect to the USTS mode link, which causes the USTS to connect to the USTS. There was a problem that the performance improvement due to the limited.

Next, the proposed second handover method will be described.

According to the proposed second handover method, the mobile terminal 10 overlaps the performing region of the second process S2, the third process S3, or the fourth process S4 (that is, between base stations). In the case of moving to a handover area, the radio wave strength of each base station (21, 22, 23) is measured to perform a handover to a base station having a large radio wave strength. However, in this method, the main link operates in USTS mode regardless of the handover region, so that the USTS performance can be continuously obtained. However, in the handover region, the radio wave strength of the base station varies from time to time depending on the direction of the mobile terminal or the surrounding environment. As such, the main link associated with the mobile terminal changes from time to time. For handover, the mobile terminal and the base station communicate with each other to exchange information. In a situation where the main link connected to the mobile terminal changes from time to time, the corresponding information needs to be transmitted and received each time, which causes a large load on the system, causing performance degradation. There was a problem.

In conclusion, in the two handover methods proposed above, handover to the USTS mode is limited according to the handover region, and the load due to the frequent exchange of signal information due to the ping-pong phenomenon between the mobile station and the base station is provided. Because of the transfer to the user, only the limited performance effect of the USTS is seen, and the increase in the amount of signal information causes a problem that a greater burden is placed on the system rather than the performance effect by the USTS.

The present invention has been made to solve the above problems, and its object is to provide continuous USTS during handover in an asynchronous mobile communication system such as a W-CDMA system and / or an asynchronous IMT-2000 system. To achieve the maximum performance by the USTS and to eliminate the load on the system due to the frequent exchange of signal information, to provide a handover method for the reverse synchronous transmission in the next generation asynchronous mobile communication system will be.

1 is a diagram illustrating a conventional handover method for reverse synchronization transmission, and shows a radio link connection state between a subscriber station and a base station for each belonging region according to a movement procedure of the corresponding mobile terminal.

2 and 3A-3E are diagrams for explaining a handover method for reverse synchronous transmission according to an embodiment of the present invention.

2 is a diagram illustrating a radio link connection state between a mobile station of a subscriber station and a base station for each belonging area according to a mobile process of the mobile station;

3A and 3E are signal flows in a corresponding process of each region of FIG. 2.

※ Explanation of code for main part of drawing

10: mobile terminal 21, 22, 23: base station

21a, 22a, 23a: service area of each base station

21b, 22b, 23b: radio link of each base station

30: wireless network control station

In order to achieve the above object, a handover method for reverse synchronous transmission in a next generation asynchronous mobile communication system according to the present invention includes a plurality of handover regions in an asynchronous next generation mobile communication system to which a reverse synchronous transmission (USTS) is applied. In performing a handover to a mobile terminal in which a radio link with a base station is connected and one of the radio links communicates in a USTS mode, the reception measured from the mobile terminal for each forward signal of the plurality of radio links is performed. A first step of obtaining propagation strength information; A second step of obtaining distance information between the mobile terminal and each base station; A third step of determining whether received radio wave intensity information of the radio link communicating in the current USTS mode among the plurality of radio links is less than or equal to a preset threshold; A fourth step of selecting one radio link to be set to a USTS mode among the plurality of radio links based on the obtained radio wave strength information and distance information as a result of the determination; And a fifth step of allowing the selected wireless link to communicate with the USTS and deleting the wireless link communicating with the previous USTS mode.

The distance information is calculated based on round trip time (RTT) information of a signal obtained based on a transmission time of the forward signal and a reception time of a reverse signal corresponding thereto, and the fourth step includes: For the received radio wave, the greater the intensity of the radio wave and the shorter the distance to the mobile terminal is set to have a larger value within a range of values, to select a radio link of the base station having the largest value among the plurality of base stations It is characterized by.

Hereinafter, a handover method for reverse synchronous transmission in a next generation asynchronous mobile communication system according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

2 and 3A-3E are diagrams for explaining a handover method for reverse synchronous transmission according to an embodiment of the present invention, and FIG. 2 is a view illustrating a wireless link connection state between a subscriber station and a base station of the mobile station. 3A and 3E are signal flows in a corresponding process of each region of FIG. 2.

The present invention will be described with reference to FIG. 2.

In a first step (S100), the mobile terminal UE0 10 belongs to a service area 21a of the base station B1 21 and is connected to a single radio link 21b connected only to the base station B1 21. , Operates in USTS mode.

Subsequently, in the second process (S200), the mobile terminal 10 is a handover area that overlaps the service area 21a of the base station B1 21 and the service area 22a of the neighboring base station B2 22. Upon entering the area, a new link 22b is established with the base station B2 22, where the mobile terminal 10 is still operating in the USTS mode with the base station B1 21 and the base station B2 22. And operate in non-USTS mode.

Subsequently, in the third process S300, the mobile terminal 10 neighbors the service area 21a of the base station B1 21, the service area 22a of the base station B2 22, and their neighbors 21 and 22. When the base station B3 23 moves to a three overlapping area with the service area 23a, a new link 23b is created with the base station B3 23, and the mobile terminal 10 is the base station B2, B3. (22, 23) operates in the non-USTS mode and the base station B1 (21) continues to operate in the USTS mode.

Subsequently, when the mobile terminal 10 moves to an overlapping area between the service area 22a of the base station B2 22 and the service area 23a of the base station B3 23 in the fourth process (S400), In the first step (S100), the link 21b with the base station B1 21, which is set to the USTS mode, is disconnected, and the link 22b with the base station B2 22 and the link with the base station B3 23 are disconnected. Only 23b remains connected. In this case, in the present invention, either the link 22b with the base station B2 22 and the link 23b with the base station B3 23 before the link 21b with the base station B1 21 is disconnected. Selecting whether to communicate 22b or 23b in the USTS mode, the selection of which is the reception strength of radio waves for each of the base stations B1, B2, B3 (21, 22, 23) and the location of the mobile terminal 10; It is determined by the distance to each base station according to.

That is, each base station (21, 22, 23) is a round trip time of the signal obtained by the position of the mobile terminal 10 based on the transmission time of the corresponding forward signal and the reception time of the corresponding reverse signal (Round Trip Time: It is calculated based on the RTT) information. In general, the W-CDMA system acquires the data at 100 ms intervals.

In addition, the mobile terminal 10 with respect to the base station B1 21 at the boundary of the mobile terminal 10 from the performing area of the third process (S300) to the performing area of the fourth process (S400). The received radio wave strength of the signal is lowered below the threshold. At this time, the mobile terminal 10 measures the radio wave strength of the base stations B2 22 and B3 23 that are connected to the base station, and reports the radio wave strength to the radio network controller (RNC). The base stations B2 22 and B3 23 also report the obtained location information (or distance information) to the mobile terminal 10 to the radio network control station (RNC).

The radio network controller (RNC) is based on the reported radio wave strength information and location information, which link 22b of the link 22b with the base station B2 22 and the link 23b with the base station B3 23. Or 23b) selects whether to communicate in USTS mode and delivers information for USTS mode to the mobile terminal 10. Specific criteria for the selection is, for each of the base stations 21, 22, 23, the reception; The larger the intensity of the radio wave and the shorter the distance from the mobile terminal 10, the larger the value within a range of values, so that the base station having the largest value among the plurality of base stations (21, 22, 23) Select the radio link to operate in USTS mode. In the present embodiment, it is assumed that the radio link 23b with the base station B3 23 is selected. In this case, the mobile path of the mobile terminal 10 becomes the service area 23a side of the base station B3 23. It can be expected that the primary target cell (primary target cell) is the service area (23a) of the base station B3 (23).

Finally, in the fifth process S500, if the mobile terminal 10 moves and belongs only to the service area 23a of the base station B3 23, only the USTS with the link 23b with the base station B3 23 is used. In addition to communicating in the mode, the link 22b with the base station B2 22 is deleted to complete the handover process.

The signal flow of each process of FIG. 2 will be described in detail with reference to FIGS. 3A to 3E.

First, FIG. 3A is a signal flowchart of the first process S100.

Referring to FIG. 3A, when the mobile terminal 10 requests a radio link connection to the radio network controller (RNC) 30 via the base station B1 21 (RRC Connection) in step S100. Request (S101), the radio network control station 30 requests the radio link setup request from the base station B1 21 (Radio Link Setup Request) (S102), and the base station B1 21 wirelessly responds to the request. Perform a link setup response (Radio Link Setup Response) (S103). Accordingly, the wireless network control station 30 establishes a link in the USTS mode with the base station B1 21 (S104), and then in response to the request of step S101, the base station B1 21 and the base station B1 (21). A radio link setup message is provided to the mobile terminal 10 via a RRC connection setup (S105), and the mobile terminal 10 communicates with the wireless network control station through the base station B1 (21). Informs 30 that the radio link setup has been completed (RRC Connection Setup Complete) (S106). In this way, the wireless link 21b between the mobile terminal 10 and the base station B1 21 is connected through the steps S101-S106, and is in a USTS mode communication state.

3B is a signal flowchart of the second process (S200).

Referring to FIG. 3B, in the second process (S200), the wireless network control station 30 sends a measurement control message to the mobile terminal 10 (S201) and based on this, the mobile terminal ( 10) measures and reports the reception propagation strength of the forward signal from the base stations B1 and B2 (21, 22) (Measurement Report) (S202). The radio network controller 30 requests a radio link setup request from the base station B2 22 based on the reported radio wave strength information (Radio Link Setup Request) (S203), and the base station B2 22 responds to the request. ) Is a radio link setup response (Radio Link Setup Response) (S204). Accordingly, the wireless network control station 30 establishes a link with the base station B2 22 in a non-USTS mode (S205), and then sends an active set update message to the base station B2 22 and the base station B2 ( 2) the mobile terminal 10 is provided to the mobile terminal 10 to update an active set (Active Set Update) (S206), and correspondingly, the mobile terminal 10 transmits the wireless network through the base station B2 (22). The control station 30 is notified that the active set update has been completed (Active Set Update Complete) (S106).

3C is a signal flowchart of the third process (S300).

In the third process (S300) of FIG. 3C, the wireless network control station 30 sends a measurement control message to the mobile terminal 10 (Measurement Control) S301, and based on this, the mobile terminal 10. ) Measures and reports the received radio wave strength of the forward signals from the base stations B1, B2, and B3 (21, 22, 23) (Measurement Report) (S302). The radio network control station 30 requests a radio link setup request from the base station B3 23 based on the reported radio wave strength information (Radio Link Setup Request) (S303), and the base station B3 (23) responds to the request. ) Is a radio link setup response (Radio Link Setup Response) (S304). Accordingly, the wireless network control station 30 establishes a link with the base station B3 23 in a non-USTS mode (S205), and then sends an active set update message to the base station B2 22 and the base station B2 ( 2) the mobile terminal 10 is provided to the mobile terminal 10 to update an active set (Active Set Update) (S306), and correspondingly, the mobile terminal 10 transmits the wireless network through the base station B2 (22). The control station 30 is notified that the active set update has been completed (Active Set Update Complete) (S306).

3D is a signal flowchart of the fourth process (S400).

In the fourth process (S400) of FIG. 3D, the wireless network control station 30 sends a measurement control message to the mobile terminal 10 (S401), and based on this, the mobile terminal 10. ) Measures and reports received radio wave strengths of the forward signals from the base stations B1, B2, and B3 (21, 22, and 23) (Measurement Report) (S402). When the radio wave strength of the base station B1 21 is less than or equal to a preset threshold for handover based on the reported radio wave strength information, the radio network control station 30 excludes the base station B2 except for the base station B1 21. (22) and the base station B3 (23) to determine which base station to operate in the USTS mode with the mobile terminal 10, the determination method is the same as described above with reference to FIG. 2, it is assumed that the base station B3 23 is selected as the USTS mode base station (S403).

The wireless network control station 30 selects the base station B3 23 as a USTS mode base station in step S403, and then provides an active set update message to the mobile terminal 10 to update the active set. (Active Set Update) (S404) In response, the mobile terminal 10 notifies the radio network control station 30 that the active set update is completed (Active Set Update Complete) (S405).

The radio network control station 30 requests the base station B1 21 to delete the radio link 21b (Radio Link Delection Request) (S406), and correspondingly, the base station B1 21 determines the radio link ( 21b) is deleted and responds (S407). The radio network controller 30 transmits a radio link reconfiguration prepare message to the selected base station B3 23 as information for the USTS mode (Radio Link Reconfiguration Prepare) (S408), and the base station B3 23 In response to the radio link reconfiguration preparation is completed (Radio Link Reconfiguration Ready) (S409), the radio network control station 30 to relocate the radio link to the base station B3 (23) (Radio Link Reconfiguration Commit) (S410). Subsequently, the wireless network control station 30 transmits a physical channel reconfiguration message to the mobile terminal 10 as information for the USTS mode (Physical Channel Reconfiguration) (S411), and correspondingly, the mobile terminal 10 Complete physical channel relocation and respond to it (Physical Channel Reconfiguration Complete) (S412).

3E is a signal flowchart of the fifth process S500.

3E, in the fifth process S500, the wireless network control station 30 sends a measurement control message to the mobile terminal 10 (Measurement Control) S501, and based on this, the mobile terminal ( 10) measures and reports received radio wave strengths of the forward signals from the base stations B2 and B3 (22 and 23) (Measurement Report) (S502). The wireless network control station 30 provides the mobile terminal 10 with an active set update message for the received radio wave strength of the base station B2 22 when the received radio wave strength is lower than or equal to a threshold based on the reported radio wave strength information. Active Set Update (S503), and correspondingly, the mobile terminal 10 notifies the radio network controller 30 that the active set update is completed (Active Set Update Complete) (S504). . Subsequently, the radio network control station 30 requests the base station B2 22 to delete the radio link 22b (Radio Link Delection Request) (S505), and correspondingly, the base station B2 22 transmits the radio link. The link 22b is deleted and responded (S506).

As described in detail above, according to the handover method for backward synchronous transmission in the next-generation asynchronous mobile communication system according to the present invention, it is possible to obtain the maximum performance by the USTS by achieving continuous USTS during handover. The effect of eliminating the load on the system due to frequent exchange of signal information due to the ping-pong phenomenon that occurs is created.

Claims (3)

In the handover area of an asynchronous next generation mobile communication system employing a backward synchronous transmission method (USTS), a radio link with a plurality of base stations is connected, and one of the radio links performs handover to a mobile terminal communicating in USTS mode. In carrying out, A first step of obtaining received radio wave strength information measured from the mobile terminal for each forward signal of the plurality of radio links; A second step of obtaining distance information between the mobile terminal and each base station; A third step of determining whether received radio wave intensity information of the radio link communicating in the current USTS mode among the plurality of radio links is less than or equal to a preset threshold; A fourth step of selecting one radio link to be set to a USTS mode among the plurality of radio links based on the obtained radio wave strength information and distance information as a result of the determination; And And a fifth step of deleting the wireless link communicating in the previous USTS mode as well as allowing USTS communication to the selected radio link. The method of claim 1, The distance information is calculated based on round trip time (RTT) information of a signal obtained based on a transmission time of the forward signal and a reception time of the corresponding reverse signal. A Handover Method for Reverse Synchronous Transmission in BCH. The method of claim 1, In the fourth step, for each base station, the larger the received radio wave strength and the shorter the distance to the mobile terminal is set to have a larger value within a range of values, the largest of the plurality of base stations. A handover method for reverse synchronous transmission in a next generation asynchronous mobile communication system, characterized by selecting a radio link of a base station having a value.