KR20040001077A - Method for Dropping the Reverse Link for Use in Soft Hand-off - Google Patents

Abstract

PURPOSE: A method for releasing a reverse link in a soft hand-off is provided to drive an internal timer without instantly dropping a drop object BTS(Base Station Transceiver Subsystem) when a BTS which is a power control reference and the drop object BTS are identical, count a uniform time, measure radio wave environment again when the counted time of the internal timer expires, and execute the hand-off. CONSTITUTION: A vocoder/selector(154) selects the first BTS(120) in which a transmission state is good, and decides a reverse power control value on the basis of data of the first BTS(120)(S202). The vocoder/selector(154) transmits the power control value to an MS(Mobile Station)(110)(S206). The MS(110) executes a fast reverse power control with respect to the first BTS(120)(S208). The MS(110) transmits a PSMM(Power Strength Measurement Message) to a drop object BTS(130) in which the radio wave strength of a reverse link is less than a reference value(S210). The drop object BTS(130) transmits the PSMM to a CCP(Call Control Processor)(152)(S212-S216). The CCP(152) judges whether the first BTS(120) and the drop object BTS(130) are identical(S218). The CCP(152) transmits a message to the MS(110) for dropping the drop object BTS(130) according as the first BTS(120) and the drop object BTS(130) are identical(S220,S222,S230).

Description

Method for Dropping the Reverse Link for Use in Soft Hand-off}

The present invention relates to a method of releasing a reverse link in a soft hand-off of a code division multiple access (CDMA) system. More particularly, the present invention relates to a method of releasing a reverse link in a wireless channel environment. When the base station that is the power control criterion selected to have a good transmission state and the drop target base station are the same, the internal timer is counted for a predetermined time without propagating the drop target base station immediately and propagated when the timer count expires. A reverse link release method in soft handoff that re-measures an environment to perform a handoff.

1 is a block diagram illustrating some components of a CDMA cellular communication system.

The CDMA cellular communication system has a communication processing control function of a plurality of base station transceiver subsystems (BTSs) 120 to 140 that provide communication services to a mobile station 110 and a plurality of base stations 120 to 140. A base station controller (BSC) 150 for performing the operation, a base station management system (BSM) 160 for operating and managing a plurality of base station controllers, a plurality of base stations via the base station controller 150 ( 120-140, a mobile switching center (MSC) 170 that connects by processing a call request and continues to process a signal until the call ends, and a location registration system 180 that stores and manages information of mobile subscribers. It includes.

The geographic area that each base station can serve is called a cell, which is divided into several sectors. The cells are sequentially expanded to the base station area, the base station controller area, and the service area of the switching center. In the mobile communication network system, systems below the switching center system are commonly referred to as a base station subsystem (BSS). The base station sub-system consists of a base station management system 160, a base station controller 150, and base stations 120 to 140 in a higher order. The base station controller 150 is a call control processor (hereinafter referred to as "CCP") 152 which is a main processor, and processes the actual traffic (voice and data) in the base station controller 150. A vocoder / selector 154 is included, and the main processor of the base stations 120 to 140 is referred to as a base station transmitter control processor (hereinafter referred to as a "BCP").

In the mobile communication network of the above-described configuration, when the mobile station 110 communicates while moving in the area, there should be no interference in communication. When the mobile station 110 is in an idle state, the mobile station 110 maintains a communication state by periodically re-registering with the base station system according to a parameter such as a used power level signal. In this case, the mobile station 110 and the base station (BTS) use the traffic channel element to transmit and receive information.

Under a CDMA communication system, one mobile station 110 may simultaneously receive radio signals from two or more base stations 120-140. In addition, the mobile station 110 may simultaneously establish a channel with two or more base stations 120 to 140 and perform communication. This function can handle handoff from one base station to another, or from one sector to another. In this case, the handoff refers to a process in which the mobile station 110 moves from one base station 120 to a new base station 130 or a new antenna allowable region within one base station, that is, a new traffic channel. During this handoff, it is very important that the quality of the signal and voice information transmitted from the various base stations is not degraded.

Various types of handoffs are provided to ensure call continuity in CDMA communication systems. Depending on the method and the implementation, handoff may have a difference in efficiency in terms of reliability of call continuity and system load. The setting of the channel by handoff is called Add, and the release of the channel by handoff is called Drop.

There are two types of handoff methods: soft hand-off and hard hand-off. Soft hand-off is a make-before-cut method before releasing a call. Hard handoff is a cut-before-make method before making a new call. When handoff is required by the mobile station 110 to move, the CDMA system preferentially handles soft handoff, but inevitable hard handoff guarantees continuity of the call.

Soft hand-off is a method of establishing two or more call paths simultaneously for a single call to ensure continuity of calls. The CDMA system can be configured to simultaneously call by different codes for the same frequency band in the same time zone due to its characteristics, so the soft handoff method can be configured for multiple calls for a single call System-specific handoff technique. Such soft handoffs include inter-cell soft handoffs and base station controller (Inter-BSC) handoffs. On the other hand, soft-sector handoffs are performed for inter-sector handoffs. It is called.

Inter-cell soft handoff refers to a state in which two or more adjacent base stations make a phone call simultaneously with a mobile station for one mobile station. Since two channel elements are required for two channel paths, the efficiency of using hardware resources decreases. In the forward direction (from base station to mobile station), power is transmitted from two base stations, thus increasing the forward interface. As a result, the forward link capacity is reduced.

The base station-controlled period soft handoff is a processing method used when two cells involved in the handoff belong to different base station controllers (BSCs), and the base station controller 150 has two cells involved in the handoff. It is a method of adding a function that can transmit a transmission packet that is not processed by the vocoder / selector 154 to a corresponding base station controller that manages two cells as it is not a control region of the same.

Hard hand-off is provided when two base stations affecting the mobile station 110 are not synchronized or not at the same frequency, and when interruptions occur in voice or data communications. That is, hard handoff refers to a method of guaranteeing continuity of a call by setting a new channel within a short time that is difficult for a caller to recognize after cutting an existing channel.

Soft handoff is described with reference to FIG. 1, the mobile station 110 is moving from the jurisdiction of the second base station 130 to the jurisdiction of the first base station 120, where the mobile station 110 is assigned to each base station ( 120 to 140 measure the strength of the forward signal. Assuming that only the signal strength of the first base station 120 among the signals measured by the mobile station 110 is greater than the soft hand off add (ADD) threshold, the mobile station 110 measures the signal of the measured first base station 120. The signal message about the strength is transmitted to the first base station 120. The first base station 120 reports the received signal message to the CCP 152 of the base station controller 150, and the CCP 152 analyzes the signal message to determine the first base station 120 and the second base station 130. Will be instructed to soft hand off. Accordingly, the first base station 120 and the second base station 130 performs soft handoff in both the forward link and the reverse link. That is, the mobile station 110 measures the pilot strength of the new base station, performs an add procedure for the first base station 120 whose strength is greater than the ad threshold T_ADD, and the strength is the drop threshold T_DROP. A drop procedure is performed for the smaller second base station 130.

However, in the CDMA communication system, the shadowing effect occurs when the mobile station 110 is surrounded by a high building, the corner effect occurs when turning a corner at an intersection, or the scattering effect around the mobile station 110. The communication quality of the link tends to be further deteriorated. In the forward link of the wireless channel environment, both the signals transmitted from the base stations 120 and 130 to the mobile station 110 and the signals transmitted to another mobile station are attenuated, while in the reverse link, the base stations 120 and 130 are transmitted from the mobile station 110. The signal transmitted to the attenuation occurs due to the shading effect, the corner effect, the scattering effect, and the like. As a result, the signal-to-noise ratio is reduced at the receiving end of the base station (120, 130), the call quality of the reverse link is lower than the forward link.

In the reverse link from the mobile station 110 to each of the base stations 120 and 130, the propagation strength (Ec / Io) of the reverse link, the ad threshold (T_ADD), the drop threshold (T_DROP), and the comparison threshold (T_COMP) specified by the operator as parameters. In consideration of the value of), specific base stations / sectors that meet the corresponding criteria are added or dropped.

There is no problem when the coverage is similar between the reverse link and the forward link. However, in an abnormal environment where the difference between the forward link and the reverse link is large, that is, the propagation strength of the forward link of a specific base station is poor but In a good case, there is a problem in that call drop or poor sound quality occurs due to instability of power control when the base station is dropped.

In addition, a handoff error occurs in an area in which a bidirectional link is imbalanced in a cell to which the mobile station 110 is moving. In the early stages of system construction, cells are designed so that the forward and reverse links are balanced, but as the number of subscribers increases, the effective radius of the reverse link cell is often smaller than the effective radius of the forward link cell due to the interference between the cells. Occurs. Therefore, the forward link is good, but the reverse link has an area where communication is poor, so when a handoff occurs, an area with poor call state appears. In particular, if the reverse link cell region does not overlap with the handoff region based on the forward direction, a backward bad frame is generated, which causes a problem that the call is not maintained and is disconnected when the handoff occurs.

In order to solve the above problems, the present invention provides a method of controlling a base station within a wireless channel environment without dropping a drop target base station immediately when a base station serving as a power control criterion selected for good transmission state and a drop target base station are identical. It is an object of the present invention to provide a method for reverse link release in soft handoff, in which a timer is driven to count a predetermined time, and when the timer count expires, the radio wave environment is re-measured to perform a handoff.

1 is a block diagram showing a part of a configuration of a CDMA cellular communication system;

2 is a flowchart illustrating a reverse link release method in soft handoff according to an embodiment of the present invention.

<Description of Symbols for Main Parts of Drawings>

110: mobile station 120 ~ 140: base station

150: base station controller 152: CCP (call control processor)

154: Vocoder / Selector

In order to achieve the above object, the present invention provides a base station transceiver system (BTS) that provides a communication service to a mobile station, and manages the transmission and reception of traffic (voice and data) between the base station and the mobile station. A reverse link release method in soft handoff having a vocoder / selector for selecting a call control and a call control processor (CCP) for performing call control and handoff control, wherein (a) the vocoder / selector is added. Selecting a specific base station having a good transmission state among the added base stations and determining a reverse power control value based on data of the specific base station; (b) transmitting the power control value as data bits to the mobile station at the vocoder / selector; (c) the mobile station executing Fast Reverse Power Control with respect to the base station to which the mobile station is added; (d) the mobile station sending a drop request message (PSMM) to a drop target base station whose propagation strength of a reverse link is below a reference; (e) the drop target base station delivering the drop request message (PSMM) to the CCP via the vocoder / selector; (f) determining whether the specific base station and the drop target base station are the same in the CCP; (g) the CCP transmitting a message for dropping the drop target base station to the mobile station and executing the drop according to whether the specific base station and the drop target base station are the same.

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

2 is a flowchart illustrating a reverse link release method in soft handoff according to an embodiment of the present invention. In FIG. 2, the same parts as in FIG. 1 are denoted by the same reference numerals, and detailed description thereof will be omitted.

In the preferred embodiment of the present invention, when the base station that is the reference for power control and the base station that requests the drop in the mobile station 110 are the same, the base station controller 150 system does not drop the base station immediately. When the timer is expired, the internal timer is driven to re-measure and report the radio wave environment to the mobile station 110 so that the drop target base station is released based on this.

First, the mobile station 110 will be described on the assumption that the mobile station 110 is moving from the area under the control of the second base station 130 to the area under the control of the first base station 120.

When the mobile station 110 adds the first base station 120 with the second base station 130 added in the soft handoff, the propagation strength (Ec / Io) of the forward link and the operator set parameters according to the conventional method. Consider one "T_ADD" or "T_DROP" and "T_COMP".

Accordingly, the mobile station 110, the CCP 152, and the vocoder / selector 154 recognize the first base station 120 and the second base station 130 as active base stations.

In fact, the vocoder / selector 154 that manages the transmission and reception of traffic data is a specific base station having a good transmission state when data of a predetermined frame unit is simultaneously transmitted from the first base station 120 and the second base station 130 added. For example, the second base station 130 is selected and the power control value of the reverse direction is determined based on the data of the second base station 130 (S202). In addition, the vocoder / selector 154 may transmit a power control bit to the first base station 120 and the second base station 130 so as to perform fast reverse power control with respect to the mobile station 110. It transmits to the base station 120 and the second base station 130 (S204). The first base station 120 and the second base station 130 transmit power control bits to the mobile station 110, respectively (S206).

The mobile station 110 performs fast reverse power control according to a power control bit transmitted from the first base station 120 and the second base station 130 (S208).

In addition, the mobile station 110 considers parameters, such as "T_Drop" (drop threshold) and "T_Tdrop" (drop timer threshold), designated by an operator from among the added first base station 120 and the second base station 130. When the propagation strength of the forward link of the second base station 130 falls below a reference value, a PSMM (Pilot Strength Management Message) message requesting a drop is transmitted to the second base station 130 (S210).

The second base station 130 transmits the PSMM message requesting the drop to the vocoder / selector 154 (S212).

The vocoder / selector 154 transmits a Layer 2 Ack message to the mobile station 110 via the second base station 130 in response to the drop request from the mobile station 110 (S214). The vocoder / selector 154 selects the current reverse data among the first base station 120 and the second base station 130 when the drop request is made by the mobile station 110, that is, the second base station list that is the reverse power control reference, that is, the second. A handoff request of the second base station 130 is requested by transmitting a message indicating the base station 130 to the CCP 152 (S216).

The CCP 152 determines whether the second base station 130 requested to drop from the mobile station 110 is the same as the second base station selected and marked with a good transmission state (S218).

When the drop target second base station 130 and the second base station selected to have a good transmission state are the same, the CCP 152 drives an internal timer instead of a command to drop the second base station 130 (S220). When the operation of the internal timer is completed, the CCP 152 sends a pilot strength request order (PSRO) message for re-measuring radio wave strength to the mobile station 110 via the first base station 120 and the second base station 130. It transmits (S222).

When the mobile station 110 requests another handoff because another event occurs in the forward propagation environment while the CCP 152 is processing the handoff requested by the mobile station 110, the CCP 152 rejects the requested handoff message later. (Reject), after completing the handoff that is being processed first, and then sending a PSRO message to the mobile station 110, the mobile station 110 can perform the requested handoff later by measuring and reporting the forward propagation environment again.

The mobile station 110 returns to step S210 to re-measure the radio wave strength with the second base station 130, and then sends a PSMM message requesting handoff to the vocoder / selector 154 via the second base station 130. In operation S212, the vocoder / selector 154 transmits the drop request message to the CCP 152 (S216).

Accordingly, the CCP 152 executes step S218 to determine whether the second base station 130 requested to drop from the mobile station 110 is the same as the second base station selected as having a good transmission state. When the drop target second base station 130 and the second base station selected to have a good transmission state are the same, the CCP 152 drives an internal timer instead of a command to drop the second base station 130. When the operation of the internal timer is completed, the CCP 152 sends a pilot strength request order (PSRO) message for re-measuring radio wave strength to the mobile station 110 via the first base station 120 and the second base station 130. The transmitting steps S218 to S222 are repeated.

On the other hand, in step S218, the CCP 152, if the drop target second base station 130 and the base station selected to have a good transmission state does not match the vocoder / selector 154 to drop a message to drop the second base station 130 And the vocoder / selector 154 transmits it to the second base station 130 so that the second base station 130 drops the mobile station 110 (S230).

In addition, in step S218, the CCP 152 transmits a Reset Report message to the mobile station 110, and the mobile station 110 initializes an internally managed timer and currently drops the second base station. The CCP 152 may determine whether there is a drop by driving the drop timer T_Tdrop Timer again to send the message requesting the drop again to the CCP 152 without dropping the 130.

That is, according to the embodiment, when the base station selected as a good transmission state and the base station for power control and the base station requested to drop from the mobile station are the same, the timer is internally driven in the system without dropping the drop target base station immediately. After maintaining, the radio station re-measures the radio wave environment and parameters to cause the base station to drop when the drop target base station is not the same as the base station selected for good transmission.

In addition, the present invention is not limited to the above-described embodiments, and it will be understood by those skilled in the art that various modifications and changes can be made without departing from the technical gist of the present invention.

As described above, according to the present invention, when performing the soft handoff in consideration of the coverage of the reverse link (Reverse Link), it is conventionally selected as a good transmission state and dropped from the base station and the mobile station serving as a power control criteria. Even if the requested base station is the same, the drop may occur because the reverse link in a specific area is bad.However, if the target base station is the base station to be the power control base, the drop is performed by measuring the propagation environment again after maintaining a certain time. Therefore, the mobile station can maintain a call during soft handoff, and can perform a call drop stably while the mobile station moves, thereby improving the call quality.

Claims (11)

Base Station Transceiver Subsystem (BTS) which provides communication service to Mobile Station, Vocoder / Selector which manages the transmission and reception of traffic (voice and data) between the base station and mobile station and selects data. A reverse link release method in soft handoff having a Call Control Processor (CCP) for performing call control and handoff control, (a) selecting a specific base station having a good transmission state among base stations to which the vocoder / selector is added, and determining a power control value of a reverse direction based on data of the specific base station; (b) transmitting the power control value as data bits to the mobile station at the vocoder / selector; (c) the mobile station executing Fast Reverse Power Control with respect to the base station to which the mobile station is added; (d) the mobile station sending a drop request message (PSMM) to a drop target base station whose propagation strength of a reverse link is below a reference; (e) the drop target base station forwarding the drop request message (PSMM) to the call control processor via the vocoder / selector; (f) determining, by the call control processor, whether the specific base station and the drop target base station are the same; And (g) the call control processor transmitting a message for dropping the drop target base station to the mobile station to execute a drop according to whether the specific base station and the drop target base station are the same; Reverse link release method in soft handoff, comprising the. The method of claim 1, In step (e), when the vocoder / selector forwards the drop request message to the call control processor (CCP), it selects current reverse data in a good transmission state and reverse power control. A method for reverse link release in soft handoff, comprising: transmitting a list of base stations as a reference. The method of claim 1, In step (f), when the call control processor determines the drop of the drop target base station, whether or not the drop target base station requested by the mobile station to drop the base station list in which data is selected for use as a reverse power control criterion is identical or not. The reverse link release method in soft handoff, characterized in that for determining. The method of claim 1, In step (g), if the specific base station and the drop target base station do not match, a message for dropping the drop target base station is transmitted to the mobile station via the vocoder / selector to drop the drop target base station, When the specific base station and the drop target base station match, the call control processor (CCP) internally drives a timer to maintain a predetermined time, and then transmits a handoff message by comparing a forward propagation environment and a parameter in the mobile station. And dropping the drop target base station when the reverse link release is performed. The method of claim 1, In the step (g), the call control processor (CCP) transmits a reset report message to the mobile station, and the drop target base station to which the mobile station is currently dropping by initializing an internally managed timer. The call control processor (CCP) drops the drop target base station by transmitting a message requesting a drop to the call control processor (CCP) by driving the drop timer (T_Tdrop Timer) again. Reverse link release method in soft handoff. A base station transceiver subsystem (BTS) for allocating channels to mobile stations in a wireless channel environment, and a vocoder / selector that manages the transmission and reception of traffic data between the mobile station and the base station and selects data. A reverse link release method in soft handoff having a Vocoder) and a Call Control Processor (CCP) that performs call control and handoff control, When the base station serving as a power control criterion selected for a good transmission state and the drop target base station requested by the mobile station to be identical when the reverse link is handed off, the call control processor selects the drop target base station. A method of reverse link release in soft handoff, wherein an internal timer is counted without immediately dropping and a predetermined time is counted, and when the timer count expires, the radio target environment is re-measured by the mobile station to drop the drop target base station. The method of claim 6, The base station as the power control reference, The power strength of the current base station that is in charge of the region where the mobile station is currently located and the power strength of the next base station which is in charge of the region to be forwarded are transmitted to the current base station and the next base station, respectively. A base station serving as the power control reference is selected by reporting to a voice / selector (Vocoder), by selecting a specific base station in which the vocoder / selector has a good transmission state, The vocoder / selector determines a reverse power control value based on data of the base station that is the power control reference and transmits the data to the current base station and the next base station, and the current base station and the next base station By transmitting a power control bit to each of the mobile stations, the mobile station performs fast reverse power control according to the power control bits transmitted from the current base station and the next base station. Reverse link release method. The method of claim 6, The internal timer is an internal time counting timer of the call control processor, and counts a predetermined time. The method of claim 6, If the base station serving as the power control reference and the drop target base station requested by the mobile station do not match, the call control processor sends a message to the mobile station to drop the drop target base station to drop the drop target base station. Reverse link release method in soft handoff. The method of claim 9, When the base station serving as the power control reference and the drop target base station coincide with each other, the call control processor internally drives a timer to maintain a predetermined time, and then the mobile station compares a forward propagation environment and parameters to generate a handoff message. When transmitting to the call control processor, the call control processor drops the drop target base station. The method of claim 9, The call control processor (CCP) transmits a Reset Report message to the mobile station, and the mobile station does not drop the drop target base station to be dropped at present by initializing an internally managed timer. And driving the (T_Tdrop Timer) again to send a message requesting the drop again to the call control processor, so that the call control processor drops the drop target base station.