KR20030048694A - Handover Method in CDMA system - Google Patents

Abstract

PURPOSE: A handover method in a CDMA(Code Division Multiple Access) mobile communication system is provided to enable hard handover between FAs(Frequency Assignments) without a beacon, when an MS(Mobile Station) under a call state passes two BTSs(Base Transceiver Subsystems) to which FAs are discontinuously performed. CONSTITUTION: One sector of FAs by BTSs is sectioned to a subcell as a unit service area(S111) and subcell types are divided into an NC(Normal Cell) and a BC(Border Cell)(S112), wherein an FA sector not included in more than one second BTS adjacent to the first BTS, for the FA included in the first BTS, is set as the BC and other FA sectors are set as the NC. Types of subcells in which a speech path with an MS is formed are decided(S121). If the NC and the BC coexist in the subcell types(S123), information on signal strength for signals from the BC and the NC measured by the MS and reported to a CDMA system is collected(S131), to decide whether to provide an FA list to the MS(S132). If provision of the FA list is decided and the subscell types are all BCs, FA list information is provided to the MS(S140). The MS forms a speech path for the provided FA, and the CDMA system performs handover(S150).

Description

Handover Method in Code Division Multiple Access Mobile Communication System

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a handover method in a code division multiple access mobile communication system. More particularly, in a code division multiple access (CDMA) mobile communication system, a mobile station in a call state is a frequency (FA). The present invention relates to a method for enabling a hard handover between FAs without a beacon when two stations are allocated discontinuously.

In a CDMA mobile communication system, a handover method is used to guarantee a continuous communication channel to a mobile station moving a communication area between adjacent base stations. Handover is divided into soft handover and hard handover, and soft handover is a state in which a mobile station does not release radio resources of a serving base station when a sector is moved between sectors within the same base station or between base stations. This refers to a procedure of releasing radio resources of the serving base station when the radio resources of the target base station are shared and the wireless environment satisfies a predetermined condition. In contrast, the hard handover proceeds to a procedure in which the mobile station first releases radio resources of the serving base station and then allocates radio resources of the target base station. Soft handovers are classified into handovers between base stations (Inter BTS), base station control period (Inter BSC), and switching period (Inter MSC) according to the call processing procedure. It is classified as an Inter Frame Offset handover and can occur between BTS, BSC, and MSC mutuals, similar to soft handover. In particular, hard handover between FAs is used to ensure continuous communication of mobile stations in areas where frequency allocation information between neighboring base stations is different. Currently, pilot beacons, flash beacons, and intra-cell hard handoffs are used. Algorithms such as Intra Cell Hard HandOff) are used.

Basically, (hard) handover in a call state is possible for handover of the mobile station only if the same FA signal of the serving base station to which the mobile station is tuned is serviced at the target base station to which the mobile station is to be handed over.

On the other hand, the distribution of mobile stations is large and small depending on the type of distribution of subscribers, such as downtown and suburban areas.In the CDMA system, the number of subscribers that can be serviced by one FA is limited, and the capacity of subscribers that FA can accommodate If the limit is exceeded, FA will be added to accommodate the mobile station. In this case, the number of FAs serviced by the base station is determined in consideration of the regional distribution of subscribers. When the distribution of subscribers differs locally, the number of FAs is adjusted between adjacent base stations. If the number of FAs that are adjacent to each other is different, FAs serving or serving by a target base station may be different from each other. In addition, there may be a case in which the serving and the FA of the target base station are operated differently instead of the distribution of subscribers.

As described above, in a communication environment in which different FAs are operated between neighboring base stations, a pilot beacon (Pilot Becon) as described above is used to guarantee a continuous call channel to a mobile station moving a call area between neighboring base stations. Or an inter-FA hard handover method using an algorithm such as Flash Beacon has been proposed and is currently in use.

However, in order to implement the above existing inter-FA hard handover method, a base station configured as a beacon may generate a beacon signal for a FA resource of a neighboring base station separately from the FA as a radio resource to be actually serviced. Cards and radio frequency (RF) resources are required, which requires a large investment in materials for the construction of nationwide telecommunications networks, and the success rate of handovers is lower than that of soft handovers.

The present invention was created to solve the above problems, and the object is that the target base station does not have the FA served by the serving base station (that is, does not radiate the pilot signal of the corresponding FA) in the target base station. In the case of service without a beacon, a handover method in a CDMA mobile communication system that guarantees continuous communication to a mobile station by allowing a mobile station to be allocated to any FA serviced and held by a target base station without a beacon. It is to provide.

1 is a flowchart illustrating a handover method for each sequential process in a CDMA mobile communication system according to an embodiment of the present invention;

2A and 2B are diagrams for describing the first process S110 of FIG. 1. FIG. 2A is a diagram for describing a method of setting a subcell type into normal cells and border cells. FIG. 2A is a view for explaining an example of a method of dividing and setting a subcell type into a normal cell and a border cell in consideration of a specific geographical condition in FIG. 2A;

FIG. 3 is a flowchart illustrating a first example of a determination condition at step S132 of the third process S130 of FIG. 1.

FIG. 4 is a flowchart illustrating a second example of a determination condition at step S132 of the third process S130 of FIG. 1;

5 is a flowchart illustrating a third example of the determination condition at step S132 of the third process S130 of FIG. 1;

FIG. 6 is a flowchart illustrating a fourth example of the determination condition at step S132 of the third process S130 of FIG. 1.

※ Explanation of code for main part of drawing

20: road

210,220,230: base station BC: border cell

NC: Normal Cell

In order to achieve the above object, a handover method in a CDMA mobile communication system according to the present invention is characterized in that, in a code division multiple access (CDMA) mobile communication system, a mobile station in a call state is connected to two base stations to which FAs are discontinuously assigned. In the method for performing a hard handover between FAs without a beacon when passing through, a sector of a FA for each base station is divided into subcells as a unit service area, and the subcell type is divided into normal cells. For the FA held by one serving base station, a sector of the FA not held in one or more expected target base stations adjacent to the serving base station is set as the border cell. A first step of setting a sector of FA to the normal cell; If any mobile station is receiving service from the border cell of the serving base station, providing the corresponding mobile station with FA list information held by the expected target base station and instructing the search for the provided FA; And a third step of performing a handover on the FA signal of the serving border cell and the searched FA signal based on the reception strength at the corresponding mobile station.

In the second step, when at least one border cell and at least one normal cell are simultaneously configured as active_set paths to the corresponding mobile station, reception from border cells and / or normal cells measured at the corresponding mobile station is performed. Based on the information on the signal strength, it is determined whether to provide the FA list information, and the determination condition is set as follows.

As an example of the determination condition, if the received signal strength from the normal cell is less than or equal to a preset value, the FA list information is provided from the system to the mobile station.

As another example of the determination condition, when the absolute value of the difference between the received signal strength from the border cell and the received signal strength from the normal cell is greater than or equal to a preset value, the FA list information is provided from the system to the mobile station. do.

As another example of the determination condition, if the largest of the received signal strengths from the normal cell (s) is less than (or less than) the smallest of the received signal strengths from the border cell (s), The FA list information is provided to the mobile station.

As another example of the determination condition, if the largest of the received signal strengths from the normal cell (s) is less than (or less than) the largest of the received signal strengths from the border cell (s), The FA list information is provided to the mobile station.

In addition, for message communication without disconnection between the mobile station and the system, a base station capable of creating an optimal communication condition for the mobile terminal should be set as a reference base station to allow message communication. If one or more subcells are configured as an active_set path, the corresponding base station of the subcell having the best signal strength among the subcells is set as the reference base station, and the parameters for handover of the reference base station are provided to the mobile station. To allow the corresponding mobile station to perform communication for handover or the like based on the provided parameters, or as another example, based on information on the received signal strength from the subcell measured by the mobile station. Based on the base station with the largest pilot strength among the base stations in The base station is set as a base station, and parameters for handover possessed by the reference base station are provided to the mobile station so that the mobile station can perform communication for handover or the like based on the received parameters.

In addition, as an example of a design method for setting a border cell and a normal cell in the first step, in a specific region, the relationship between the serving base station and the expected target base station is such that the relationship between base stations adjacent to each other on a specific road is established. In general, it is desirable to consider the case where the mobile station's movement path is frequently along the road.

Hereinafter, a handover method in a CDMA mobile communication system according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings, wherein the mobile station searches for one or more other FA frequencies in addition to the FA it has tuned to. It is assumed that it has a built-in function.

1 is a flowchart illustrating a handover method for each CDMA mobile communication system according to an embodiment of the present invention.

First, in a first step (S110), a sector of a base station FA is divided into subcells as unit service areas, and the subcells are divided into normal cells (NCs) and border cells (Border Cells). BC), the division principle divides one sector of FA by base station into a subcell as a unit service area (S111), and forms the subcell into a normal cell (NC) and a border. For the FA held by any first base station, a sector of the FA not held in one or more second base stations adjacent to the first base station is set as the border cell (BC). A sector of FA is set to the normal cell (S112). According to this principle, an example of dividing a subcell into a normal cell and a border cell will be described with reference to FIGS. 2A and 2B.

FIG. 2A is a diagram illustrating an example of a FA allocation retention state of adjacent base stations, and illustrates a method of dividing a sub cell type into a normal cell and a border cell. (210,220,230) are adjacent to each other, the first base station 210 has FA1, FA2, FA3, FA4 and FA5, the second base station 220 has FA1, FA2, and the third base station 230 ) Shows FA1, FA2 and FA3, so that FA is discontinuously allocated between adjacent base stations. In FIG. 2A, for FA1, FA2, FA3, FA4 and FA5 held by the first base station 210, FA4 not held by the second and third base stations 220 and 230 adjacent to the first base station 210. And sectors of FA5 are set to the basic border cell BC, as well as sectors of FA3 not held by the second base station 220 as border cells BC, and other FA1 and FA2 are normal. Set to cell NC. Similarly, since FA1 and FA2 held by the second base station 220 are both held by the adjacent base stations 210 and 230, the FA1 and FA2 held by the third base station 230 are set to normal cells NC. And for FA3, set each sector of FA3 not held in the second base station 220 adjacent to the third base station 230 as a border cell BC, and the remaining FA1 and FA2 are all in adjacent base stations 210 and 220. Since it is reserved, it is designated as a normal cell (NC).

FIG. 2B is a view for explaining an example of a method of dividing and setting a subcell type into a normal cell and a border cell in consideration of a specific geographical condition in the communication environment of FIG. 2A. As shown in FIG. The base station 210 and the third base station 230 are adjacent to each other on a specific road 20, but the second base station 220 is not on the road 20. Therefore, when setting the cell shape in consideration of the road 20 condition, for example, the FA of the second base station 220 is not considered with respect to the FA of the first base station 210 and the specific road is not considered. It is set in consideration of the FA of the third base station 230 adjacent on the (20), as a result, the first base station 210 is not retained by the third base station 230 adjacent on the road (20) Set FA4 and FA5 to the border cell (BC) and set other FA1, FA2 and FA3 to the normal cell (NC). Similarly, since the FA of the third base station 230 is all retained in the first base station 210, the FA is set to a normal cell NC. The FA of the second base station 230 is independent of the road 20 with respect to the FA of the second base station 230. Therefore, as shown in FIG. 2A, the normal cell NC is set in consideration of FAs of the adjacent first and third base stations 210 and 230.

Next, as described above, the subcell is divided into a normal cell and a sidewalk cell, and then enters the second process (S120).

After entering the second process (S120), the system including the base stations (210, 220, 230) determines the shape of the sub-cell in which the communication path is formed with a specific mobile station (not shown) (S121). That is, the mobile station cannot know whether the FA served by the serving base station exists in the target base station, and in the IMT-2000 system, the mobile station can basically set up a call path simultaneously with up to six subcells. Is determined whether all of the forms of one or more subcells in which a mobile station and a communication path are formed are border cells (S122), whether normal cells and border cells coexist (S123) or all normal cells (S124). It will be determined whether to perform the following process of the present invention to be described.

Next, when it is determined in step S123 of the second step (S120) that the form of the subcell in which the mobile station and the call path are established is a state in which the normal cell and the border cell coexist, the process enters the third step (S130). Collects information on the (received) signal strength from the border cell and the normal cell measured by the mobile station and reported to the CDMA system (S131), and compares the collected information in the form of subcells and compares them with each other. Based on the determination of whether or not to provide a list of FA of the expected target base station adjacent to the serving base station to the mobile station (S132).

That is, a mobile station can basically set up a call path with up to six subcells simultaneously, and the CDMA system forms a call path with a specific mobile station in one or more subcell units (defined as an Active_Set path). When the signals from the normal cell and the border cell are all formed in the call path as in step S123, the shape of the subcell determined in the second process S120 as well as the third cell determined in the third process S130 are determined. The handover should be indicated by considering the signal strength. The reason for this is that in the present invention, the condition that the CDMA system instructs the handover basically requires that all the subcells in the Active_Set path are set to the border cell as in step S122. Since the border cell and the normal cell are frequently set to the active_set path at the same time according to the radio environment in which the mobile station is located, the process instruction for handover (especially step S140) is not provided in the CDMA system of the present invention. This can cause arc cutting of the mobile station.

Next, in step S132 of the third step S130, it is determined that the FA list of the expected target base station as the base station adjacent to the serving base station should be provided to the corresponding mobile station, or the step S121 of the second step S120. If it is determined that all of the subcells set up with the mobile station and the call path are the border cells, the mobile station enters the fourth process (S140) and provides the corresponding mobile station with the FA list information held by the expected target base station. For example, the FA list information may be sent in a format included in a general neighbor list message (GNLM) defined in the IS-2000 standard.

Finally, entering the fifth process (S150), the mobile station searches for the provided FA according to the command to form a call path, and accordingly, the system generates an FA signal of the serving border cell and the searched FA. The received strength measured and reported by the corresponding mobile station for the signal is compared with a preset reference value for handover, and then terminated after performing a hard handover between FAs based on the comparison result.

FIG. 3 is a flowchart illustrating a first example of the determination condition in the step S132 of the third process of FIG. 1. The normal cell measured in the mobile station in the step S132 based on the collection information in the step S131. (S132a), the CDMA system performs the step S140. Otherwise, the CDMA system leaves the information collecting state of the step S131 without performing the step S140.

4 is a flowchart illustrating a second example of the determination condition in the step S132 of the third process of FIG. 1, and based on the collection information in the step S131, the signal strength NP of the normal cell in the step S132. And the signal strength (BP) of the border cell are compared and the comparison result determines that the absolute value of the quantum difference is greater than or equal to the preset value P2 (S132b), the CDMA system performs the step S140, otherwise the step S140 It is to be in the information collecting state of the step S131 without performing.

FIG. 5 is a flowchart showing a third example of the determination condition in the step S132 of the third process of FIG. 1, based on the collection information in the step S131, from the normal cell (s) in the step S132. If it is determined that the largest of the received signal strength (NP _max ) is less than the smallest of the received signal strength from the border cell (s) (BP _min ) (S132b), the CDMA system performs the step S140. Otherwise, the information collection state of step S131 is left without performing step S140.

FIG. 6 is a flowchart showing a fourth example of the determination condition in the step S132 of the third process of FIG. 1, based on the collection information in the step S131, from the normal cell (s) in the step S132. If it is determined that the largest of the received signal strengths (NP _max ) is less than the largest of the received signal strengths from the border cell (s) (BP _max ) (S132b), the CDMA system performs the step S140. Otherwise, the information collection state of step S131 is left without performing step S140.

The above four determination conditions described above with reference to FIGS. 3 to 6 may be applied as individual conditions, or two or more conditions may be applied in combination according to a communication environment as logical products or logical sum conditions.

On the other hand, in the present invention for a mobile assisted inter-frequency hard handover (MAHO) function, that is, the inter-FA hard handover method based on the received signal strength information of the sub-cell measured by the mobile station, defined in the IS-2000 protocol for each sub-cell If the mobile station has moved in the path of border cell 1 → border cell 2 → border cell 3, it is necessary to determine which border cell should be transmitted to the mobile station.

Basically, a mobile station and a CDMA system manage a reference PN, so that all signal processing is processed through a corresponding subcell of a reference PN base station. Therefore, there is a need to define an algorithm for updating the reference PN so that the relevant parameter corresponding to the subcell having the best signal strength in closest proximity to the mobile station can be transmitted to the mobile station.

If the mobile station having the best signal strength farther away from cell 1 is far from its location, the signal FA of the base station PN to receive the MAHO-related parameters of the border cell 2 having the worst signal strength and handover it. If you search for and handover, the call may be dropped because the radio environment was not considered at all.

Therefore, there is a need for a method of updating the reference PN as follows.

First, when a handover of the mobile station occurs, the CDMA system sets the subcell having the best signal strength among the suscells in the active_set path as the reference PN. Second, the mobile station measures the signal strength of the subcell and reports it to the CDMA system, ie, a pilot strength measurement message (PSMM), a power measurement report message (PMRM), and a periodic signal (PPSMM). Among the PNs in the active_set path among the Pilot Strength Measurement Message (PSM) and the Pilot Strength Measurement Mini Message (PSMMM), the pilot strength (Pilot Strength) is set as the reference PN.

As described in detail above, the handover method in the code division multiple access mobile communication system according to the present invention can replace the existing inter-FA hard handover method using beacons without beacons, and install beacon FA and RF related hardware. Because it is not necessary, the system can be simply implemented, and the success rate of hard handover is improved to the level similar to that of soft handover. In the region where the frequency allocation information between neighboring base stations is different, providing a list of information of neighboring base stations may ensure smooth handover between FAs of the mobile station. Therefore, when constructing a new next-generation communication network, it is possible to drastically reduce the beacon material investment cost and to reduce the existing beacon material transfer equipment, and to improve the communication quality during hard headover.

Claims (10)

In a code division multiple access (CDMA) mobile communication system, a method in which a mobile station in a call state can perform a hard handover between FAs without a beacon when the FA passes through two discontinuously allocated base stations. A sector of FA for each base station is divided into subcells as a unit service area, and the subcell type is divided into a normal cell and a border cell, but an arbitrary serving base station. A step of setting a sector of the FA that is not held in at least one expected target base station adjacent to the serving base station as the border cell, and a sector of the other FA as the normal cell, for the FA held by the; If any mobile station is receiving service from the border cell of the serving base station, providing the corresponding mobile station with FA list information held by the expected target base station and instructing the search for the provided FA; And And a third step of performing a handover on the FA signal of the serving border cell and the searched FA signal based on the reception strength at the corresponding mobile station. Handover method in the system. The method of claim 1 The FA list information of the second step is included in a General Neighbor List Message (GNLM) defined in the IS-2000 standard. The method according to claim 1 or 2 In the second step, when one or more of the border cells and one or more of the normal cells are simultaneously set to an Active_Set path with respect to the corresponding mobile station, from the border cells and / or normal cells measured at the corresponding mobile station. The handover method in a code division multiple access mobile communication system, characterized in that it is determined whether the FA list information is provided based on the information on the received signal strength. The method of claim 3 And in the determination, if the received signal strength from the normal cell is equal to or less than a preset value, the FA list information is provided. The method of claim 3 In the determination, if the absolute value of the difference between the received signal strength from the border cell and the received signal strength from the normal cell is greater than or equal to a preset value, the FA list information is provided. Handover method in the system. The method of claim 3 In the determination, if the largest of received signal strengths from the normal cell (s) is less than the smallest of the received signal strengths from the border cell (s), the code division is provided. Handover Method in a Multiple Access Mobile Communication System. The method of claim 3 In the determination, if the largest of the received signal strengths from the normal cell (s) is less than the largest of the received signal strengths from the border cell (s), the FA list information is provided. Handover Method in a Multiple Access Mobile Communication System. The method of claim 1 When one or more subcells are set as an active_set path for the corresponding mobile station, the base station of a subcell having the best signal strength among the subcells is set as a reference base station, and message communication is performed through the reference base station. A handover method in a code division multiple access mobile communication system. The method of claim 1 Based on the information on the received signal strength from the subcell measured by the mobile station, the base station having the largest pilot strength among the base stations in the active_set path is set as the reference base station, and message communication is performed through the reference base station. A handover method in a code division multiple access mobile communication system characterized by the above-mentioned. The method of claim 1 The serving base station and the target base station is a handover method in a code division multiple access mobile communication system, characterized in that adjacent to each other on a particular road.