KR20000022926A - Soft-handoff method and mobile communication system based on the same - Google Patents

Abstract

PURPOSE: A soft hand-off in cellular mobile communication network is provided to prevent an excessive control load in a mobile switching center during inter-BS(Base station system) soft-hand off and the waste of resources such as communication lines between a base station controller and the mobile switching center as well as to avoid a high-priced and complicated control method by performing the inter-BS soft-hand off. CONSTITUTION: Soft hand off between base stations under the control of adjacent base station controllers(441,442) is performed by using a hand off control unit provided in the base station controllers. In the configuration, the excessive cost increase is prevented because there is no need to provide the hand off controller in a mobile switching center(40), and also the excessive control load imposed on the mobile switching center is decreased by performing inter-BSC soft hand off without the meditation of the mobile switching center, and the lack of communication lines, caused by the excessive use between base station controllers and mobile switching centers can also prevented based upon the soft hand-off.

Description

SOFT-HANDOFF METHOD AND MOBILE COMMUNICATION SYSTEM BASED ON THE SAME}

The present invention relates to a soft-handoff method and a mobile communication system using the soft-handoff method, and more particularly, to a soft-handoff method for performing a seamless handoff, and to using the soft-handoff method. A mobile communication system.

"Handoff" is a term used to describe the operation of a mobile station that moves while the mobile station switches its connection from one base station to another in a mobile communication system. In the CDMA (code division multiple access) scheme, unlike the FDMA (frequency division multiple access) scheme, the mobile station communicates with multiple base stations using the same frequency. In this manner, therefore, the mobile station initiates communication with the new base station (target) while maintaining communication with the existing base station (source), and maintains soft diversity while maintaining connection with both base stations. Perform. In this way, the mobile station is performing any interruption-free soft-handoff, i.e., seamless handoff.

1 and 2 are block diagrams illustrating an example of a CDMA mobile communication system performing a conventional soft handoff. In FIG. 1, a mobile communication system includes a mobile switching center (MSC) 10 and a base station system (BS). The base station system (BS) comprises a base station controller (BSC) 14 ₁ , 14 ₂ and a mobile station (MS) 18.

The mobile switching center 10 includes a BSC-interface switch (BSCI / FSW) 20, a handoff control unit (HCU) 22, and a switch 24. The BSC-interface switch 20 connects the handoff control unit 22 to the public switched telephone network (PSTN) 26. The handoff control unit 22 includes an FER detector / selector 28 which detects the error rate of the communication link connected with the mobile station and then selects the communication link having the minimum error rate. The handoff control unit 22 also includes a vocoder 30 for performing speech coding and decoding, and a downlink duplicater 32 for copying downstream data (datalink).

In FIG. 2, the base station controllers 15 ₁ , 15 ₂ include a handoff control unit (HCU) provided in place of the base station controllers 14 ₁ , 14 ₂ of FIG. 1.

In the conventional system of FIG. 1, when soft handoff is performed between base stations 16 ₁ , 16 ₂ , 16 ₃ under the control of adjacent base station controllers 14 ₁ , 14 ₂ [these later, such soft handoff is performed]. Inter-BS (referred to as soft handoff)], the handoff control unit 22 in the mobile switching center 10 monitors the base station controllers 14 ₁ and 14 ₂ to control the handoff. However, considering this handoff frequency, intra-BS soft handoff occurs much less frequently than soft handoff between base stations 16 ₂ , 16 ₃ performed under the control of the same base station controller 14 [after, This handoff is called intra-BS (soft handoff). Despite these statistics, the handoff control unit 22 of the mobile switching center 10 must control all handoffs. This imposes a heavy load on the mobile switching center 10 due to this control operation. In addition, since it is necessary to connect all the communication lines between the base station controllers 14 ₁ and 14 ₂ and the BSC-interface switch 20 of the mobile switching center 10, the resources of the available communication lines are consequently Is reduced.

The vocoder 30 of the handoff control unit 22 includes Q-Code Excited Linear Predictive cording (QCELP) voice data on one side of the BSC-interface switch 20 and pulse code modulation (PCM) on one side of the switch 24. Code modulation) performs data conversion between voice data. However, the handoff control unit 34 shown in FIG. 2 is the handoff control unit 22 via the BSC-interface switch 20 without conversion of QCELP voice data at the base stations 16 ₁ , 16 ₂ , 16 ₃ . Establish a communication link with). Therefore, when converting QCELP voice data of the base stations 16 ₁ , 16 ₂ , 16 ₃ into PCM voice data, a communication link with the switch 24 is established through the BSC-interface switch 20 as necessary. The control dynamics become complicated. In addition, a handoff control unit 22 and a handoff control unit 34 are provided to the mobile switching center 10 and the base station controllers 15 ₁ and 15 ₂ , respectively. The handoff control units 22, 34 each comprise a FER detector / selector 28, a vocoder 30 and a downlink duplicater 32, resulting in an expensive system.

It is an object of the present invention to prevent excessive control load at an inter-BS soft-handoff design mobile switching center and to prevent wasting of resources such as communication lines between the base station controller and the mobile switching center. To provide an off method and a mobile communication system.

Another object of the present invention is to provide a soft-handoff method and a communication system that can avoid expensive redundant control methods by performing inter-BS soft-handoff.

These and other objects are performed in accordance with the present invention regarding a method of performing soft-handoff between base stations under the control of adjacent base station controllers by using a handoff control unit provided within the base station controllers.

In this method, a handoff control unit is provided for performing soft handoff between base stations under the control of adjacent base station controllers in the base station controller. Since the handoff control unit is not required in the mobile switching center, excessive costs can be prevented. Inter-BS soft handoff can be performed without using a mobile switching center as an intermediary, reducing the control load imposed on the mobile switching center. In addition, it is possible to prevent the lack of a communication line between the base station controller and the mobile switching center due to excessive use.

The method also includes a method of performing soft handoff between base stations under control of adjacent base station controllers by using a handoff control unit provided to one of the base station controllers, which was used when the communication was initiated. In this method, soft handoff between base stations under control of adjacent base station controllers is performed by a handoff control unit provided to one of the base station controllers that were used when the communication was initiated. Because of this, inter-BS soft handoff and intra-BS sort handoff can be performed without any interruption between them.

The method also includes establishing a data route between base stations under control of adjacent base station controllers. In this method, a route for data transmission between adjacent base station controllers is set up so that a handoff between base stations can be performed under the control of adjacent base station controllers by a handoff control unit provided to the base station controller.

The method of the present invention also establishes a route for data exchange between adjacent base station controllers via a mobile switching center. In this method, a route for data exchange between adjacent base station controllers is established via the mobile switching center so that the circuit existing between the base station controller and the mobile switching center can be used. This eliminates the need for a dedicated communication line.

In the method of the present invention also the route for data exchange between adjacent base station controllers is based on a dedicated line. In this method, the route for data exchange between adjacent base station controllers is based on a dedicated circuit so that a minimum delay can be achieved with a short path. In addition, timing alignment in the handoff control unit becomes easier.

The present invention also discloses a mobile communication system that seamlessly performs a soft handoff exchange from one base station to another when the mobile station moves. The system includes a handoff control unit that controls soft handoff between base stations under the control of adjacent base station controllers. The handoff control unit is embedded in the base station controllers. In this method, the handoff control unit is embedded in the base station controller to perform soft handoff between base stations under the control of adjacent base station controllers. Since there is no need to provide a handoff control unit in the mobile switching center, excessive costs can be prevented. In addition, since inter-BS soft handoff can be performed without using a mobile switching center as an intermediary, it is possible to reduce the control load imposed on the mobile switching center. In addition, the lack of a communication line due to excessive use of the communication line between the base station controller and the mobile switching center can be prevented.

The mobile communication center of the present invention also includes a handoff control unit that performs soft handoff between base stations under the control of adjacent base station controllers, which is embedded in one of the base station controllers that were used when the communication was initiated. do.

In this method, soft handoff between base stations under control of adjacent base station controllers is performed by handoff control means built into one of the base station controllers used when communication is initiated.

The mobile communication system of the present invention also includes a route set up for data exchange between adjacent base station controllers when performing soft handoff between base stations under the control of adjacent base station controllers. In this method, a route is established for data transmission between adjacent base station controllers so that soft handoff can be performed by the handoff control means built in the base station controller under the control of the adjacent base station controllers.

The mobile communication system of the present invention also includes a route for data exchange between adjacent base station controllers, which route is established via a mobile switching center. In this method, a route for data exchange between adjacent base station controllers is established via the mobile switching center to make use of the existing circuit between the base station controller and the mobile switching sensor. Therefore, there is no need to provide a dedicated communication line.

The mobile communication system of the present invention also includes a route for exchanging data between adjacent controllers, which route is based on a leased line. In this method, the route for exchanging data between adjacent base station controllers is based on a dedicated circuit so as to realize a minimum delay with a short path. In addition, timing alignment in the handoff control unit is facilitated.

In the mobile communication system of the present invention, the base station controllers also perform ATM data transmission from the route to the handoff control unit. In this method, ATM data transfer from the root to the handoff control unit inside the base station controllers can be done, thereby reducing the load on the switching operation.

The mobile communication system of the present invention also provides a user access via a route between adjacent base station controllers by using base station controllers with ATM cells of either AAL (ATM adaptation layer) type 2 or AAL type 0 (not using AAL). Data is transmitted and control data is transmitted by using AAL type 5 ATM cells. In this method, transmission of user data via a route between adjacent base station controllers is performed by using ATM cells of either AAL type 0 or AAL type 2, and the transmission of control data uses AAL type 5 ATM cells. Is performed. In this configuration, data transmission between adjacent base station controllers is performed in the same format as the data transmission format in the base station controller, thereby performing a simpler data transmission operation along the route.

1 is a block diagram illustrating a CDMA mobile communication system that performs a conventional soft-handoff.

2 is a block diagram illustrating a CDMA mobile communication system performing a conventional soft-handoff.

3 is a block diagram illustrating a first embodiment of a CDMA mobile communication system for performing soft-handoff in accordance with the present invention.

4 is a block diagram illustrating a second embodiment of a CDMA mobile communication system for performing soft-handoff in accordance with the present invention.

Fig. 5 is a block diagram showing a first embodiment of a handoff control unit provided in a base station controller according to the present invention.

Figure 6 is a block diagram illustrating a second embodiment of a handoff control unit provided in a base station controller in accordance with the present invention.

7 is a block diagram illustrating an embodiment of a base station controller used in a mobile communication system in accordance with the present invention.

8 is a sequence diagram illustrating an embodiment of a BSC soft handoff unit in accordance with the present invention.

9 is a block diagram illustrating an embodiment of an intra-BS handoff control unit in accordance with the present invention.

10 is a block diagram illustrating an embodiment of an inter-BS handoff control unit in accordance with the present invention.

<Explanation of symbols for main parts of the drawings>

40: mobile exchange center

44 ₁ , 44 ₂ : base station controller

46 ₁ , 46 ₂ ,: base station

3 is a block diagram of a first embodiment of a CDMA mobile communication system for performing soft handoff in accordance with the present invention. In FIG. 3, the mobile communication system includes a mobile switching center (MSC) 40 and a base station system (BS). Base station system, base station controllers _{(BSC) (44 1, 44} 2), base station controllers (BSC) base station is controlled by a _{(44 1, 44 2) (} BTS) (46 1, 46 2, 46 3) and the mobile station (MS) 48.

The mobile switching center 40 includes a switch 52 that connects the public switched telephone network (PSTN) and the MSC interface of the base station controllers 44 ₁ , 44 ₂ . Each of the base station controller (44 _1, 44 ₂₎ comprises a switch 54, the handoff control unit (HCU) (56 ₁ -56 _i) and MSC interface (MSC I / F) (58). Switch 56 is connected to the base stations (46 _1, 46 _2, 46 ₃₎ in one or the MSC interface 58 of the hand-off control unit (56 ₁ -56 _i). The handoff control unit performs control of the soft handoff. MSC interface 58 is connected to the switch 52 of the switch 54 or the hand-off control units (56 ₁ -56 _i) moving one of the switching center (40).

In this embodiment, the handoff-control unit is provided only to the base station controller and not to the mobile switching center. For both inter-BS soft-handoff and intra-BS soft-handoff, the selection or synchronization of ongoing upstream user data from the mobile station to the mobile switching center, and the copying of downstream data, controls handoff until the end of the communication. Supported by the unit. This handoff control unit was selected when the mobile station initiated communication. When inter-BS softhand is performed, a route through the mobile switching center is established between the handoff control unit of the base station controller responsible for the handoff and the adjacent base station controller. This route exchanges upstream user data and downstream data.

In FIG. 3, soft diversity is performed between base stations 46 ₁ , 46 ₂ , 46 ₃ and mobile stations 48 controlled by base station controllers 44 ₁ , 44 ₂ adjacent to each other while communication is maintained. Can be. In this case, the base station (46 ₁₎ is connected to the switch 52 of the switch 54 and base station controller (44 _1), the mobile switching center 40 via the MSC interface 58 of the. The switch 52 is also connected to the handoff control unit 56 ₁ via the MSC interface 58 and the switch 54 of the base station controller 44 ₂ to connect between the base stations 46 ₁ , 46 ₂ , 46 ₃ . Performs an inter-BS soft handoff. This connection is established by generating a connection request to the mobile switching center 40 from the base station controller (44 _1). In addition, the base stations 46 ₂ , 46 ₃ are connected to the handoff control unit 56 ₁ via a switch 54 of the base station controller 44 ₂ .

A communication link for connecting to the embodiment, a base station controller (44 _1), the mobile switching center 40, the base station controller (44 ₁₎ in order to connect the switch 54 to the switch 54 of the base station controller (44 ₂₎ of the example Use

In this method, the soft handoff between base stations is performed by a handoff control unit provided from one of the base station controllers under the control of different base station control stations adjacent to each other, whereby it is necessary to use the handoff control unit in the mobile switching center. Can be prevented from incurring excessive costs. Since inter-BS soft handoff is performed without the need of a mobile switching center, no excessive control load is imposed on the mobile switching center. In addition, waste of communication line resources between the base station controller and the mobile switching center can be avoided. Since soft handoff between base stations under the control of different base station controllers adjacent to each other is performed by a handoff control unit provided to one of the base station controllers used at the beginning of the initial communication, inter-BS soft handoff and intra-BA Soft handoff is done without any interruption.

4 is a block diagram of a second embodiment of a CDMA mobile communication system for performing soft handoff in accordance with the present invention. In FIG. 4, the mobile communication system includes a switching center (MSC) 40 and a base station system (BS). The base station system includes a base station controller (BSC) 44 ₁ , 44 ₂ , base stations (BTS) 46 ₁ , 46 ₂ , 46 ₃ , and mobile station (MS) under the control of the base station controller 44 ₁ , 44 ₂ . (48).

The mobile switching center 40 includes a switch 52 connected to the MSC interface 58 of the base station controller 44 ₁ , 44 ₂ , using a public switched telephone network (PSTN) 50. Each base station controller (44 _1, 44 ₂₎ comprises a switch 54, the handoff control unit (HCU) (56 ₁ -56 _i), and MSC interface (MSC I / F) (58). Switch 54 is by using one or the MSC interface 58 of the hand-off control unit (56 ₁ -56 _i), is connected to the base stations (46 _1, 46 _2, 46 _3). Hand-off control unit (56 ₁ -56 _i) is carried out a control of the soft hand-off. MSC interface 58 using a switch 52 of the mobile switching center 40 is connected to any one of the switch 54 or the hand-off control unit (56 ₁ -56 _i). In addition, the dedicated line 59 will be connected to the switch 54 of the base station controller (44 ₁₎ to the switch 54 of the base station controller (44 _2).

In this embodiment, the handoff unit is provided only to the base station controller and not to the mobile switching center. For both inter-BS soft handoff and intra-BS soft handoff, the selection or synthesis of upstream user data from the mobile station to the mobile switching center and the copying of downstream data to the handoff control unit until the communication is terminated. Supported by At this time, the handoff control unit is selected when the mobile station initiates communication. When inter-BS soft handoff is performed, a route through the dedicated line 59 is established between the handoff control unit of the base station controller responsible for the handoff and the adjacent base station controller. Through this route, upstream user data and downstream data are exchanged.

In FIG. 4, while the communication is maintained, soft diversity is established between the base stations 46 ₁ , 46 ₂ , 46 ₃ and the mobile station 48 controlled by base station controllers 44 ₁ , 44 ₂ adjacent to each other. Can be performed. In this case, the base station (46 ₁₎ is a hand-off of a base station controller (44 ₁₎ of the switch 54, private line (59), and a base station controller (44 _2), a base station controller (44 ₂₎ through a switch 55 of the It is connected to the control unit 56 ₁ to perform inter-BS soft handoff between the base stations 46 ₁ , 46 ₂ , 46 ₃ . In addition, the base station (46 _2, 46 ₃₎ is connected to the hand-off control unit (56 ₁₎ through a switch 55 of the base station controller (44 _2).

In the present embodiment, the dedicated line 59 is provided between the switch 54 of the base station controller 44 ₁ and the switch 55 of the base station controller 44 ₂ . However, the route from the base station (46 ₁₎ to a base station controller (44 ₂₎ of the hand-off control unit (56 ₁₎ are shorter than that. Thus, it is easier to align the timing of the upstream user data in the handoff control unit 56 ₁ between base stations 46 ₁ , 46 ₂ , 46 ₃ . In addition, when using the ATM for data transmission in the switch 54, it is possible to set the switch 55 of the base station controllers 44 ₁ and 44 ₂ very conveniently at an initial stage.

5 is a block diagram of a first embodiment of a handoff control unit provided to a base station according to the present invention. In the figure, vocoder 60 is connected to a mobile switching center to convert PCM voice data provided as downstream data from the mobile switching center into QCELP voice data. QCELP voice data is then provided to the downlink duplicater 62. Vocoder 60 also converts QCELP voice data provided as upstream user data from selector 64 into PCM voice data and provides it to the mobile switching center.

The downstream duplicater 62 stores the data provided from the vocoder 60 in the buffer 65. In addition, the downlink duplicater 62 latches the data in a flip-flop (F.F.) 66-68 that operates under the control of the controller 70 when the data is read from the buffer 65. The downlink duplicater 62 also supplies data to the switch 54 (or 55) as downstream data to the mobile station.

The FER detectors 71-73 receive upstream user data from the mobile station via the switch 54 (or 55) to detect the error rate of the wireless communication link with the mobile station under the operation of the controller 70. Then, the detected error rate is reported to the controller 70. Next, data from the mobile station is provided from the FER detectors 71 to 73 to the selector 64, and the controller 70 selects the communication link with the minimum error rate. Then, the data is supplied to the vocoder 60. In addition, a synthesis circuit may be provided instead of the selector 64 to synthesize data after weighting the data from the mobile station according to the error rate.

6 is a block diagram of a second embodiment of a handoff control unit provided to a base station according to the present invention. In FIG. 6, the same constituent elements as in FIG. 5 are referred to by the same reference numerals.

In FIG. 6, the vocoder 60 is connected to a mobile switching center to convert PCM voice data supplied as downstream data from the mobile switching center into QCELP voice data, which is then provided to the downlink duplicater 74. FIG. . Vocoder 60 also converts QCELP voice data provided as upstream user data from selector 64 into PCM voice data and then provides this PCM voice data to the mobile communication center.

Downlink duplicater 74 provides data provided from vocoder 60 to buffer 75. The downlink duplicater 74 also reads data from the buffer 75 and writes this data to the dual-port RAM 76. The controller 70 reads data from the dual-port RAM 76 and writes this data into the dual-port RAM 77 as many times as the number of mobile stations. Then, data continuously read from the dual-port RAM 77 is provided to the switch 54 (or 55) as downstream data proceeding from the mobile station. This embodiment is only used when using ATM for data transmission on switch 55.

FER detectors 71-73 receive upstream user data from the mobile station via switches 54 and 55 to detect the error rate of the wireless communication link with the mobile station under operational control from the controller 70. The detected error rate is reported to the controller 70. Next, data from the mobile station is provided from the FER detectors 71-73 to the selector 64, so that the communication link with the minimum error rate is selected by the controller 70. The data is then fed to the vocoder 60. In addition, a synthesis circuit is provided instead of the selector 64 so that data from the mobile stations can be synthesized after being weighted according to the error rate.

7 is a block diagram of an embodiment of a base station controller used in a mobile communication system according to the present invention. In Figure 7, EI- interface card (EIT) (102) is E1 link (transmission speed and is embedded in each of the vocoder / handoff function unit _{(VHP) (100 1 -100 N} ), the mobile switch center: 2M bit / sec) interface. EI interface card (102), provided in each of the soft hand-off / vocoder unit _{(SVC) (104 1 -104 N} ), are connected to the vocoder _{(VC) (106 1 -106 N} ). The vocoder (106 ₁ -106 _N) converts the QCELP audio data supplied from the upstream user data to the PCM audio data. The vocoder (106 ₁ -106 _N) also converts the PCM audio data supplied from the downstream data to the QCELP audio data.

Each of the soft hand-off / vocoder unit (104 ₁ -104 _N) are connected to a CLAD (108). The CLAD 108 performs assembly / decomposition of ATM cells for QCELP voice data in a multiplex / demultiplex control scheme of the CPU 110. CLAD (108) is connected to one of the multiplexing / demultiplexing unit via VHP control card (VHC) (112) by an optical communication line _{(MXP) (114 1 -114 2} ). Each of the multiplexing / demultiplexing unit (114 ₁ -114 ₂₎ is multiplexed ATM cells supplied from the vocoder / hand-off the functional units using the MUX / DMUX (116-118) (100 1 -100 N) , and then, These multiplexed cells are provided to the ATM-switch unit 120. In addition, each of the multiplexing / demultiplexing unit (114 ₁ -114 ₂₎ ATM- divided ATM cells supplied from the switch unit 120, and then, the divided cells of the vocoder / handoff function unit (100 ₁ -100 _N ). The multiplexing / demultiplexing unit (114 ₁ -114 ₂₎ of the MUX / DMUX (118) is connected to the ATM- switch unit 120. ATM-switch unit (ASP) 120 includes a number of optical interface (ASI) 122 and ATM-switch unit (ATM-SW) 124, and facilitates the exchange of ATM cells. ATM- switch unit 120 is connected to a BTS interface _{(BDP) (124 1 -124 4} ) and a BSC in soft handoff unit (BSU) (126).

Each BTS interface (124 ₁ -124 _4), BDP control unit (BDC) (130) The optical interface 122 to divide the ATM cells thereof BTS interface terminal unit (BT1-BE1) provided by the (132 ₁ -132 _K ). Also, BDP control unit 130 provides interface to the BTS terminal units (132 ₁ -132 _K) optical interface 122 and multiplexes the received ATM cell to receive the ATM cells from the. Each of the BTS interface terminal unit (132 ₁ -132 _K) divides the ATM cell received from the BDP control unit 130 and provides the divided cells in multiple base stations via a communication line E1 or T1 communication line. E1 communication line (transmission rate: 2 Mbit / sec) or T1 communication line (transmission rate: 1.5 Mbit / sec) of the ATM when it receives from each BTS interface terminal unit (132 ₁ -132 _K) is the ATM cell Multiplex and provide these multiplexed ATM cells to BDP control unit 130.

The BTS interface (124 ₁ -124 _4), having the error correction capabilities of the mid-level, AAL (ATM Adaptation Layer) type -ATM cells (in this specification, a number of user data items are included in one ATM cell) for Transmit user data with the base stations. BTS interfaces 124 ₁ -124 ₄ also convey BTS-control / maintenance data by using AAL type-5 ATM cells with strong error correction. In the base station controller of Fig. 7, an AAL type-0 ATM cell is used for data transmission. This is a simplfied and streamlined format that does not have an error correction code or the like in the information field. In the BTS interface (124 ₁ -124 _4), no conversion is performed with respect to the AAL type ATM cells.

8 is a block diagram of an embodiment of a BSC soft handoff unit 126. In the figure, the BSU control unit (BUC) 136 has a dual function. When ATM cells are provided from the ATM switch unit (ASP) (120), ATM cells are transmitted to the BSU interface card (138 ₁ -138 _8). And it provides the multiplexed ATM cell supplied from the BSU interface card (138 ₁ -138 _8). During this operation, the BSU control unit 136 may also perform a broadcasting function.

In each BSU interface card (138 ₁ -138 _8), a selector (SEL) (140) may select one of the functions of the two BSU control unit 136, and also, if necessary, selecting a broadcasting ATM cells . ATM cells selected by the selector 140 are supplied to the AAL conversion unit 144 via the dual port RAM 142, which operates under the control of the CPU 146. In contrast, ATM cells are provided from the AAL conversion unit 144 to the BSU control unit 136 via the dual port RAM 142 and the selector 140.

The AAL conversion unit 144 converts ATM cells to AAL type 2 if the ATM cell received from the BSU control unit 136 is an AAL type 0 ATM cell (also, these ATM cells can pass through as is without type conversion). has exist). If the received ATM cells are AAL type 5 cells, these cells pass through as is without any type conversion and are provided to the optical interface 148. From an optical interface (148), ATM cells are transferred to another base station controller (44 ₂₎ through the optical communication public lines.Okay. Also, if the received ATM cells are ATM cells of AAL type 2, the ATM cells received from other base station controllers are converted to ATM cells of AAL type 0. On the other hand, if the received ATM cells are ATM cells of AAL type 0 or AAL type 5, these cells pass through without conversion and are provided to the dual port RAM 142.

Referring back to FIG. 7, the control unit 150 includes a CPU card (MPC), a global memory (GDM), a global common memory (GCM), a device control unit (DVC), a hard drive unit (HD), and a magneto-optical disk unit. (MO), and input / output bus terminal control unit (IOB). These control units 150 perform overall control of the base station controller and also manage protocol conversion, handoff control, and the like. The ATCs 153 and 154 of the interface terminal unit exchange AAL type 5 ATM cells with the ATM switch unit 120 via the optical interface (AT1) 155. TIC 156 is an Ethernet interface for a maintenance terminal. SSC (157 ₁ -157 ₃₎ is subjected to the protocol, terminated between the mobile switching center and base station controller. CTP (158) supplies a clock signal for the vocoder to the vocoder / handoff function unit (100 ₁ -100 _N).

The BSU interface from the base station (124 ₁ -124 _4), signaling ATM cells (AAL type 5) transmitted to one of, for example, an ATM switch unit (ASP) (120) and a multiplexing / demultiplexing unit (MUX) (114 ₁₎ Is provided to the vocoder (VC) 106 ₁ of the soft handoff / vocoder (SVC) 104. The vocoder 106 ₁ determines that the received ATM cells are signaling cells, and then controls the cells 150 via the multiplexing / demultiplexing unit 114, the ATM switch unit 120, and the optical interface 148. Signaling control is performed by supplying

In this way, the base station controller is sorted using the ATM cells from the interface with the base station or base station controller program handoff / vocoder units (104 ₁ -104 _M) in accordance with the route transmits the data, and proceeding to this switching operation by Reduce the load In addition, user data is transmitted between adjacent base station controllers using ALL type 0 or ALL type ATM cells, and control data is also transmitted using ALL type 5 ATM cells. In this configuration, data transmission between adjacent base station controllers is performed in the same format as the data transmission format in the base station controller, thereby simplifying the data transmission operation.

9 shows a sequence of an embodiment of intra-BS soft handoff. In the drawings, the same elements as those shown in FIG. 4 are referred to by the same reference numerals. In Figure 9, when the stronger the received power from a target base station (46 _3), the mobile station 48, at step S1 sends a message about the received power in the base station controller (44 _2). In this step, the base station (46 ₃₎ is shared with the base station controller (44 ₂₎ the base station (46 ₂₎ (source).

Accordingly, it transmits to the base station controller (44 ₂₎ is a base station, a request for the soft hand-off in step S2 (46 _3). In step S3, the base station (46 ₃₎ returns a response. In step S4, the base station controller (44 ₂₎ sends a message to the base station (46 ₃₎ to initiate a downlink transmission. If in step S5 the base station (46 ₃₎ is returned a response, the base station controller (44 ₂₎ sends a message to in response to a radio wave to perform a soft handoff to the mobile station (48). Next, in step S7, the mobile station 48 returns a response to the base station controller 44 ₂ . If a handoff is performed to exchange from the source base station 46 ₂ to the target base station 46 ₃ , a message indicating that the handoff is complete is sent via the base station controllers 46 ₂ and 46 ₃ in step S8 to the base station controller 44. ₂ ) is sent.

10 shows a sequence of an embodiment of inter-BS soft handoff. In this figure, the same constituent elements as in FIG. 4 are referred to by the same reference numerals. In Figure 10, when the stronger the received power from the base station (46 _1), in step S10 the mobile station 48 sends a message on the power to the base station controller (44 _2). In this embodiment, the base station 46 ₁ is controlled by a base station controller different from the base station controller of the base station 46 ₂ .

In response, in step S11, the base station controller (44 ₂₎ transmits a request of inter -BS soft hand-off to the base station controller (44 ₁₎ for controlling the target base station (46 _1). In step S12, the base station controller 44 ₁ sends a request for soft handoff to the base station 46 ₁ . In step S13, the base station 46 ₁ returns a response. In step S14, the base station controller (44 ₁₎ then returns a response to the base station controller (44 _2).

In step S15, the base station controller (44 ₂₎ sends a message to the target base station (46 ₁₎ to initiate a downlink transmission via a dedicated line (59). When the base station 46 ₁ returns to the response in step S16, the base station controller 44 ₂ sends a message to the mobile station 48 to perform soft handoff in response to the reception of the radio wave. In step S18, the mobile station 48 returns a response to the base station controller 44 ₂ . When the handoff makes the exchange from the source base station 46 ₂ to the target base station 46 ₁ , a message indicating completion of the handoff is received via the base station controllers 4 ₂ through the base stations 46 ₂ and 46 ₁ in step S19. Is sent).

The above embodiments have been described by way of example only when applied to the CDMA scheme. However, if the mobile station can receive multiple frequencies, the present invention is not limited by the above embodiments and is applicable to other schemes including the CDMA scheme.

The present invention provides a soft handoff method and a mobile communication system using the same, thereby preventing heavy control loads from being applied to the mobile switching center during inter-BSC soft handoff, and providing communication line resources between the base station controller and the mobile switching center. To prevent waste, and to avoid excessive cost increase.

Claims (23)

A mobile communication system for performing soft handoff between base stations, Mobile switching center; A base station controller coupled between the base station and the mobile switching center to control the base station; And A handoff control unit associated with each of the base station controllers to control inter-BSC soft handoff and intra-BSC soft handoff between the base stations; Mobile communication system comprising a. The mobile communication system of claim 1, wherein the mobile switching center includes a switch for establishing a route between the base station controllers for transmitting data during the inter-BSC soft handoff. 3. A mobile communication system according to claim 2, wherein the transmitted data is ATM data. 3. The mobile communication of claim 2, wherein the transmitted data includes both user data consisting of ATM cells of either AAL type 2 or AAL type 0 and transmission control data consisting of AAL type 5 ATM cells. system. 2. The mobile communication system of claim 1, further comprising a dedicated line between the base station controllers to directly transmit data between the base station controllers during the inter-BSC soft handoff. 6. The mobile communication system according to claim 5, wherein the transmitted data is ATM data. 6. The movement of claim 5, wherein the transmitted data includes both user data consisting of ATM cells of either AAL type 2 or AAL type 0 and transmission control data consisting of AAL type 5 ATM cells. Communication system. The mobile communication system of claim 1, wherein the inter-BSC soft handoff is controlled by a single handoff control unit. 9. The mobile communication system of claim 8, wherein prior to performing the inter-BSC soft handoff, the single handoff control unit is associated with the base station controller used first. The method of claim 8, wherein each of the hand off control unit, A buffer for receiving first downstream data; A first memory for storing the first downstream data received by the buffer; And Second memory for storing second downstream data destined for the mobile station It includes a downlink duplicator comprising a, The second downstream data includes first downstream data duplicated a number of times corresponding to the number of mobile stations in the downlink. Mobile communication system, characterized in that. In a mobile communication system, a method for performing soft handoff between base stations, each associated with a base station controller, Associating a handoff control unit with each of said base station controllers only Soft handoff between the base station, characterized in that it comprises a. A mobile communication system for performing soft handoff between base stations, Base station controllers associated with each of the base stations; And A handoff control unit associated only with each base station controller to control soft handoff between the base stations Mobile communication system comprising a. 13. The mobile communication system of claim 12, further comprising a switch for establishing a route between the base station controllers for transmitting data during inter-BSC soft handoff. The mobile communication system of claim 13, wherein the transmitted data is ATM data. The mobile station of claim 13, wherein the transmitted data includes both user data consisting of AAL type 2 or AAL type 0 ATM cells and transmission control data consisting of AAL type 5 ATM cells. Communication system. 13. The mobile communication system of claim 12, further comprising a dedicated line between the base station controllers to directly transmit data between the base station controllers during the inter-BSC soft handoff. 17. The mobile communication system according to claim 16, wherein said transmitted data is ATM data. 17. The method of claim 16, wherein the transmitted data includes both user data consisting of AAL type 2 or AAL type 0 ATM cells and transmission control data consisting of AAL type 5 ATM cells. Communication system. A handoff control unit for a mobile communication system, A buffer for receiving first downstream data; A first memory for storing the first downstream data received by the buffer; And Second memory for storing second downstream data destined for the mobile station Including a downlink duplicater comprising a, And said second downstream data includes first downstream data duplicated a number of times corresponding to the number of mobile stations in said downlink. 20. The handoff of claim 19 further comprising a controller for reading the first downstream data from the first memory and writing the second downstream data to the second memory. Control unit. A method for performing soft handoff between a first base station associated with a first base station controller and a second base station associated with a second base station controller, the method comprising: Sending a handoff request from the first base station controller to the second base station controller; Sending the handoff request to the second base station; Sending a response to the handoff request to the first base station controller; And Transmitting a forward traffic initiation message to the second base station Soft handoff performing method comprising a. 21. The method of claim 20, wherein the response to the handoff request is sent to the first base station controller through the second base station controller. 21. The method of claim 20, wherein the forward traffic initiation message is sent from the first base station controller.