KR19980036283A - Connection Rerouting Method Using Handoff Algorithm with Multistage Threshold - Google Patents

Abstract

The present invention relates to a connection rerouting method in a wired section of a mobile communication system in which a lower part is composed of ATM switches. A hand having a multi-step threshold in order to reduce handoff delay time and unnecessary pre-connections, which is a problem of the conventional rerouting method. Applying off-off algorithm to configure cells in multiple sub-areas and three directions to identify paths that require pre-connections and paths that require pre-disconnections. The connection rerouting method used is presented.

Description

Connection Rerouting Method Using Handoff Algorithm with Multistage Threshold

The present invention relates to a connection rerouting in a wired section when a handoff occurs due to terminal movement in a mobile communication system in which an infrastructure is composed of asynchronous transfer mode (ATM) switches. routing method, and more particularly, a connection rerouting method using a handoff algorithm having a multi-step threshold.

In the conventional wired section, connection rerouting methods can be classified into three main categories: (1) anchor rerouting, (2) dynamic rerouting, and (3) pre-established tree. ) Rerouting. (1) Origin rerouting is easy to guarantee ATM cell sequence and effective in the local area because the connection is continuously made through the same path, but the signal traffic is increased because communication is required in multiple exchange periods. There is a disadvantage that causes. (2) Dynamic rerouting has the advantage of using network resources efficiently because it establishes a connection by finding a path to hand off whenever a handoff occurs, but has the disadvantage of a very long handoff delay time. (3) The default tree rerouting is advantageous in a large area and has a small handoff delay time, but has a disadvantage in that network resources are wasted by requiring a plurality of pre-connections.

The present invention devises a rerouting method that can reduce the handoff delay time, which is an advantage of the default tree rerouting, while reducing the number of pre-connections, which is an advantage of the dynamic rerouting. First, to reduce the handoff delay time, if the terminal can know in advance the target base station (target base station) to be handed off in the network, the pre-connection to the corresponding target base station is established when the actual handoff occurs Changing the path to pre-connection only reduces handoff latency. However, accurately predicting the target base station to be handed off is a difficult problem in reality. Therefore, a method for predicting a target base station to be handed off should be primarily devised. Secondly, in view of the number of pre-connections, it is necessary to reduce unnecessary pre-connections in order to reduce them, which can be solved if the target base station to be handed off is predictable. In other words, if it is not connected to the target base station, it may be regarded as unnecessary pre-connection and released. To this end, an algorithm capable of dynamically determining whether to pre-connect with candidate base stations with a possibility of handoff is required.

Accordingly, the present invention can reduce the number of handoff delays in connection rerouting caused by handoff in a mobile communication system composed of ATM switches, and efficiently use network resources by reducing the number of pre-connections for handoff. The purpose is to present a connection rerouting method.

According to an aspect of the present invention, a terminal measures a pilot signal strength at a current position to identify a sub region to which the terminal belongs, and compares a sub region of the identified current terminal with a previous sub region. Determining the movement direction of the terminal, and when the terminal moves from the buffer region to the region where no pre-connection is necessary, the base station prepares a list of pre-connected paths designated as a rear set and transmits the service to the service base station. And releasing and ending the pre-connection with the corresponding base station at the network side based on the pre-connection path list, and when the terminal stays in the buffer area but changes its position based on the direction as a result of the determination of the movement direction. The base station creates a list of pre-connected paths designated as candidate sets Transmitting to a serving base station, releasing and terminating the pre-connection with the base station at the network side based on the pre-connection path list, and terminating the pre-connection in the buffer area as a result of the determination of the movement direction In the case of moving to, determining the neighboring cell area by measuring the pilot signal strength of the neighboring base stations, and if the terminal stays in the region where pre-connection is necessary as a result of the movement direction, but changes the position based on the direction Generating, by the base station, a list of pre-connected paths designated as candidate sets, and transmitting the same to the service base station; preparing a pre-connected path list and transmitting the same to the service base station; The identified neighboring base station is adjacent to the terminal Determining, by the base station, creating a list of pre-connected paths designated as active regions and transmitting them to a service base station if the determination result is two neighboring states; Establishing and terminating the connection; if the determination result is three neighboring states, creating and transmitting a list of pre-connected paths designated as active sets to the serving base station; and at the network side based on the pre-connected path list. And terminating the connection after establishing the pre-connection with the corresponding base station.

1 is a structural diagram showing an example of a divided cell according to the present invention.

2 is a handoff algorithm with a multistep threshold in accordance with the present invention.

3 is a flowchart of operation according to the present invention.

4 is a block diagram of pre-connection when the terminal is located in the first area according to an embodiment of the present invention.

5 is a block diagram of pre-connection establishment according to terminal movement on a divided cell according to an embodiment of the present invention.

FIG. 6 is a block diagram of pre-connection release according to terminal movement on a divided cell according to an embodiment of the present invention. FIG.

Explanation of symbols on the main parts of the drawings

1: an area that does not require pre-connection to the first area

2: buffer area to the second area

3: area requiring pre-connection to the third area

The present invention relates to a partitioned cell structure, (2) a handoff algorithm having a multi-step threshold for partitioning a cell and identifying the partitioned cell, and (3) a partition based on pilot signal strength received from neighboring base stations. An algorithm for identifying a cell and a direction of movement and determining pre-connection establishment / release, and (4) a method of dynamically performing pre-connection establishment / deletion of a wired section on the network side. In this configuration, (1) is completed through (2), and the algorithms of (2) and (3) must be added as part of the terminal function. (4) is a simple and manual pre-connection establishment / release function, so it is assumed that a specific functional entity in the network performs it.

The wireless interface of the mobile communication system in the background of the present invention is Code Division Multiple Access (hereinafter referred to as CDMA), and the wired section interface composed of ATM switches is ATM. The method of performing the handoff of the present invention may use a Mobile Assited HandOff (MAHO) form and a Mobile Controlled HandOff (MCHO). It is done.

The type of handoff described in the present invention is an inter-cell handoff, and a subject that manages pre-connection establishment / release is an upper switch that controls two base stations. However, the present invention basically applies equally to inter-switch handoff as well as inter-cell handoff.

In general, in CDMA, one connection is used by default while a call is in progress (hereinafter referred to as a basic connection). However, in the present invention, a new connection, a pre-established connection, is required in addition to the basic connection. A pre-connection is a connection in the same form as a basic connection, but is prepared in advance for a quick connection setup at handoff. The pre-connection is dynamically set and released according to the movement of the terminal. The determination is made at the terminal and the direct pre-connection is set and released at the network side. The purpose of the pre-connection is that when a handoff request is received, it is necessary to immediately change the path to the previously-established pre-connection without establishing a new connection at the network side, and thus a fast handoff can be achieved.

The pre-establishment path list described in the text is a list prepared by the terminal and transmitted to the base station. The pre-establishment path list is composed of an active set and a candidate set. The active set is a set of candidate stations that need to be pre-connected, and the candidate set is a set of base stations which need to be pre-linked. That is, if it is determined that pre-connection to a specific neighboring base station is necessary, the base station is designated as an active set, and if it is determined that the pre-connection is determined, the base station is designated as a candidate set. This list is transmitted to the base station whenever the terminal determines that pre-connection establishment / release is necessary.

Hereinafter, with reference to the accompanying drawings will be described in detail the present invention.

(1) partitioned cell structure

1 is a structural diagram showing an example of a divided cell according to the present invention. The divided cell structure is obtained by dividing an existing cell into several sub-regions from the center of the base station to the boundary region of the cell. In the present invention, it is assumed that the number of sub-regions is three, and in this case, it is divided into a first region (Zone) 1, a second region (2), and a third region (3). The entire cell is divided into three directions, namely, a first direction, a second direction, and a third direction, and has three directions regardless of the number of subregions. The reason for devising a cell structure having several sub-areas and three directions as described above is to identify a sub-region and a moving direction in which a terminal is currently located in a divided cell area when the terminal moves. If the subregion and the direction of the cell can be identified, it is possible to know a path that needs to be pre-connected and a path that needs to be disconnected.

The first area 1 is a location where the terminal is close to the base station, and is an area where all pre-connections are released. The second area 2 is a buffer area, which is a middle point between the center of the base station and the cell boundary point. Pre-connections are set and released based on the boundary points of this area. The third area 3 is basically an area where handoff is expected, and it is necessary to establish a pre-connection. Range (hereinafter referred to as R for convenience) R1, R2, and R3 are distances from the base station center to the first area 1, the second area 2, and the third area 3, and R3 is the boundary point of the entire cell. to be. R1, R2 and R3 are determined by thresholds, that is, the threshold of the first region, the threshold of the second region, and the threshold of the third region, and these three boundary points are determined in advance in the cell plan. . In order to have a divided cell as shown, a handoff algorithm having a multi-level threshold is used, and a method of distinguishing a moving direction of a terminal is determined based on pilot signal strengths of neighboring base stations.

(2) handoff algorithm with multi-level threshold

2 is a multilevel threshold handoff algorithm in accordance with the present invention. In general, the pilot signal strength is used as a variable to determine handoff and has a threshold. However, in the present invention, in order to have a divided cell, the deviation between the pilot signal strength and the time reference is subdivided to set a plurality of thresholds, that is, the threshold of the first region, the threshold of the second region, and the threshold of the third region. In the above-described cell structure of FIG. 1, the boundary point for dividing the first area becomes a threshold of the first area having the largest signal strength, the boundary point of the second area is the threshold of the second area, and the boundary point of the third area is the third area. Is the threshold of. These thresholds are fixed values and are determined in advance in network design. In addition, each area is divided based on these thresholds. The first region has a high pilot strength around the reference base station. The second region has a pilot strength relatively lower than that of the first region, and the third region has a pilot strength relatively lower than the first and second regions at the boundary point between the reference base station and the first and second base stations. On this basis a graph as shown is formed. Additional factors that may be considered when determining these threshold values may include areas where the terminal is densely packed or traffic load.

(3) the overall algorithm of the present invention

3 is an operational flowchart of the overall algorithm according to the present invention. This algorithm is based on a state in which a handoff algorithm having a multi-level threshold on a partitioned cell structure is embedded in the terminal. In general description of the overall algorithm, the terminal measures the pilot signal strength at the current location to identify the subregion to which it belongs. Then, these values are compared with the values collected immediately before to find out the direction of movement of the terminal and determine whether to perform the pre-connection establishment / release. If pre-connection establishment / release is determined, a pre-connection path list consisting of an active set and a candidate set is prepared and transmitted to the service base station. The service base station receives this list, and the network side performs pre-connection establishment / release of the wired section based on this list. The algorithm is explained in detail for each step as follows.

When the restricted algorithm starts, the internal timer starts the algorithm every predetermined time (301). That is, the entire algorithm is periodically performed at a predetermined time in the terminal. The start interval of the internal timer can be set in advance or can also be specified dynamically. The terminal collects the pilot signal strength, radio link quality, etc. for the base station to which the terminal belongs (302). The information about the collected base station is applied to a handoff algorithm having a multi-level threshold to identify which area of the divided cell the current terminal location belongs to (303). This step designates the current-position, which is a variable representing the divided region, as one of the first region, the second region, and the third region.

If the current terminal is located in the first area as a result of the divided cell area identification, the terminal updates the location information (304), and updates the location information of the terminal when the current terminal is located in the second area as a result of the divided cell area identification. (305). In addition, if the current terminal is located in the third region as a result of the divided cell region identification, location information of the terminal is updated (306). This step 304 to step 306 is completed through the following detailed procedure. Read the previous position (variable name: old-position) variable value of the terminal and copy the previous position variable value to temporary variable (variable name: tmp), and copy the current position (variable name: current-position) variable value to the previous position variable Copy After this procedure, the current terminal location is stored in the previous location variable, and the previous location is stored in the temporary variable. The previous position variable is used to know the moving area of the terminal by comparing the current position with the previous position of the terminal.

In a state 304 in which it is determined that the current terminal is located in the first area, it is determined whether the terminal has previously been located in the second area and has moved to the first area or within the first area, that is, in its own area. (307). At this time, if it has not moved from the second area, it can be regarded as having moved within the first area, and thus ends without taking any action. However, if the terminal has moved from the second area, it is determined that the terminal has moved from the second area to the first area, and thus the pre-connection of the terminal, which has been maintained until now, is released, and the base station is designated as a candidate set of the pre-connected path list. The list is transmitted to a serving base station, and the network side terminates after disconnecting the pre-connection with the corresponding base station previously maintained based on the list (308). The reason why the pre-connection should be released at step 308 is because the terminal is located close to the serving base station, so it is determined that there is little probability of handing off to another cell. The reason why the pre-disconnect time is not moved from the third area to the second area, and the reason for determining the second area to the first area is to set a new pre-connection when the probability of handoff is high and the move back to the third area. Because of the loss. However, in the latter case, even if the terminal moves back to the second area, the probability of handoff is relatively low. In a state 305 in which it is determined that the terminal is currently located in the second area, it is determined whether the terminal has moved in the same second area but the position has been changed based on the direction in the sub-area (309). That is, it is checked whether or not the previous direction and the current direction are different in the same second area. If the direction is the same as before, exit without action. However, if the direction is changed, the terminal moves in the second area, but since the direction is changed, the previously maintained pre-connection is released, the corresponding base station is designated as a candidate set of the pre-connection path list, and the list is transmitted to the serving base station. The network side terminates after disconnecting the pre-connection with the corresponding base station previously maintained based on this list (310). In a state 306 where it is determined that the current terminal is located in the third area, it is determined whether the terminal has previously moved from the second area to the current third area (311). If the terminal has moved from the second area, it is determined that the pre-connection setting is necessary once, so the pre-connection is established through the steps 314 to 317 or the steps 314 to 318. If the terminal has not moved from the second area, go to step 312. In a state in which it is determined that the terminal has moved within the same area, that is, the third area, it is determined whether the position has been changed based on the direction (312). If no direction reference position has been changed, exit without action. If the location change in the direction in the sub-area to the pre-connection with the base station that has been maintained until now to designate the base station as a candidate set of the pre-connection path list and transmits this list to the service base station. The network side releases the pre-connection with the corresponding base station previously maintained based on the pre-connection list (313). And steps 314 through 317 or 314 through 318 to perform pre-connection with the new base station. In order to establish a new pre-connection in the state where the current terminal is located in the third area, the pilot signal strength, radio link quality, etc. of neighboring base stations are collected (314). The neighbor base station is identified based on the collected information (315). It is a preliminary work to establish a new pre-connection between neighboring base stations through the identified information. In operation 316, it is determined whether the terminal is adjacent to the neighboring base station or in the three neighboring state at the current location of the terminal. Basically, in case of two adjacent cells, one pre-connection is required in addition to the basic connection. If it is determined that the terminal is adjacent to the neighboring base station at the current location of the terminal, pre-connection with one neighboring base station except for the service base station is required, so that the base station is designated as an active set of the pre-connected path list in order to set up the pre-connection. Send this list to the serving base station. The network side sets the pre-connection of the corresponding base station based on the pre-connection list (317). If it is determined that 3 neighbors are determined, the base stations are designated as an active set of the pre-connected path list in order to establish pre-connections with two adjacent base stations, and the list is transmitted to the serving base station. The network side newly establishes a pre-connection with the base stations based on this list and terminates (318).

When the entire algorithm described above is applied, the number of necessary pre-connections may be one of three types. First, no pre-connection is required when the terminal is located in the first area as in the example of step 308. Secondly, in the second area, when the terminal moves in the third area, the previously completed pre-connection is maintained, and when the terminal moves from the first area to the second area, the pre-connection is not established and pre-connection is required. none. Thirdly, in the third region, as in step 317, if the terminal is located in the third region and the neighboring base stations are two neighbors, one pre-connection is required. As in step 318, if the terminal is located in the third area and the neighbor base stations are three neighbors, two pre-connections are required.

In view of the number of pre-connections in the present invention, as described above, the number of pre-connections may vary according to the movement of the terminal. That is, when there is no pre-connection, when there is one pre-connection, the case of two pre-connections occurs, which is dynamically determined according to the movement of the terminal. And in terms of handoff latency, the use of pre-completed connections (pre-connections) makes handoffs fairly fast.

4, 5 and 6 show examples of pre-connection establishment / release based on the overall algorithm of FIG. 3.

4 is a diagram illustrating a cell structure that does not require prior connection according to an embodiment of the present invention. Since the terminal is located in the vicinity of the serving base station, that is, in the first area, the pre-connection with the neighbor base station is not necessary. Each base station shown in this example assumes that one Mobile Switching Center (MSC) is in charge.

5 is a diagram illustrating a cell structure in which pre-connection setting is performed according to an embodiment of the present invention. In this example, the terminal starts from the first area of the serving base station and moves to the third area. The time point at which the pre-connection establishment starts is when the terminal passes the boundary point of the second area and the third area. In this case, the neighboring base station moves to the first base station and the second base station to the second base station or the first base station, so that the pre-connection with the first base station is established.

6 is a diagram illustrating a cell structure in which a pre-connection is performed according to an embodiment of the present invention. In this example, the terminal starts from the third area of the serving base station and moves to the first area. The time point at which the pre-connection is started is when the terminal passes the boundary point between the second area and the first area. In this case, the previously connected pre-connection with the fourth base station is released while moving to the first area of the serving base station. However, until the terminal starts in the third area and is located in the second area, the previously established pre-connection is maintained.

As described above, according to the present invention, when a handoff occurs, the path is immediately switched through a previously completed connection, thereby minimizing handoff delay time, and at the same time, the establishment or release of a pre-connection is performed dynamically according to the movement of the actual terminal. Since it can be used to reduce unnecessary pre-connections, the number of pre-connections can be reduced, so that network resources can be used efficiently.

Claims (3)

Identifying, by the terminal, a pilot signal strength at a current position to identify a subregion to which the terminal belongs; Determining a moving direction of the terminal by comparing the identified subregion of the current terminal with a previous subregion; When the terminal determines that the terminal moves from a buffered area to an area where pre-connection is not necessary, the base station prepares a list of pre-connected paths designated as candidate sets and transmits them to a service base station; Releasing and terminating the pre-connection with the corresponding base station at the network side based on the pre-connection path list; When the terminal stays in the buffer region as a result of the determination of the moving direction but changes its position based on the direction, the base station prepares a list of pre-connected paths designated as candidate sets and transmits them to the service base station; Releasing and terminating the pre-connection with the corresponding base station at the network side based on the pre-connection path list; Determining, by the terminal, a neighboring cell area by measuring pilot signal strengths of neighboring base stations when the terminal moves from a buffered area to a region where pre-connection is necessary; When the terminal stays in an area where pre-connection is necessary as a result of the determination of the moving direction, but the location is changed based on the direction, the base station prepares a list of pre-connected paths designated as candidate sets and transmits them to the service base station; Generating a list of pre-connected paths and transmitting the same to a serving base station, and then measuring pilot signal strengths to identify adjacent cell regions; Determining whether the identified neighbor cell region is in two or three neighboring states with the terminal; When the determination result is two neighboring states, the base station prepares a list of pre-connected paths designated as active areas and transmits them to the service base station; Setting and terminating one pre-connection of a corresponding base station at the network side based on the pre-connection path list; When the determination result is three neighboring states, the base stations prepares a list of pre-connected paths designated as active sets and transmits them to the service base station; And setting up two pre-connections with the corresponding base station on the network side and terminating based on the pre-connection path list. The method of claim 1, wherein the subregion is configured by dividing a cell into a plurality of cells. 3. The method of claim 2, wherein the cell divided into the plurality of sub-regions has three directions.