KR100467530B1 - Method of soft handoff controlling in mobile telecommunication system - Google Patents

Abstract

1. TECHNICAL FIELD OF THE INVENTION

The present invention relates to a soft handoff control method of a mobile station in a mobile communication system and a computer-readable recording medium having recorded thereon a program for realizing the method.

2. The technical problem to be solved by the invention

The present invention provides a soft handoff control method and a method for realizing a soft handoff of a mobile station for minimizing soft handoff in the form of excessively occupying radio resources in order to effectively use radio resources while minimizing call disconnection in a mobile communication system. Its purpose is to provide a computer-readable recording medium that records the program.

3. Summary of the Solution of the Invention

The present invention provides a soft handoff control method for a mobile station in a mobile communication system, wherein a parameter (FLAG, T_Excellent, T_ADD_HIGHER) for suppressing the soft handoff timing of the mobile station is set, when entering a mobile station call channel state from another state. Setting a value of the FLAG to zero (“0”), a value of the T_Excellent to a predetermined value greater than the T_ADD_HIGHER, and a value of the T_ADD_HIGHER to a predetermined value greater than T_ADD; An active set analyzing step of analyzing an active set registered in the mobile station call channel state; And when the analysis result of the active set analysis step indicates that at least two registered active sets have a maximum pilot strength of pilot strengths of neighboring base stations in soft handoff in the active set greater than the T_Excellent, the neighboring base station is a candidate base station. The T_ADD_HIGHER is used instead of the base station pilot strength value T_ADD that must be satisfied in order to set a value, and the channel drop timer value T_TDROP necessary for the pilot belonging to the active set to be deleted from the active set is set to zero ("0"). And a soft handoff control step of suppressing the soft handoff timing.

4. Important uses of the invention

The present invention is used for soft handoff control and the like in a mobile communication system.

Description

Method of soft handoff controlling of mobile station in mobile communication system

The present invention relates to the technical field related to mobile communication handoff, and more particularly, in order to effectively use radio resources while minimizing call disconnection in a mobile communication system, it is possible to minimize soft handoff in the form of excessively occupying radio resources. And a computer readable recording medium having recorded thereon a program for realizing the above method.

In general, a code division multiple access (CDMA) cellular mobile communication system divides a service area into small areas called cells and reuses the same frequency to efficiently use frequency resources.

As such, since the service area is divided into cellular compartments, when the mobile station moves to another cell, communication with the base station managing the new corresponding cell is started, which is referred to as "handoff".

Direct-sequence CDMA (DS-CDMA) cellular mobile communication systems based on the International Standard-95 (IS-95) standard include the 'Soft Handoff' method and the handoff service. There is a 'hard handoff' method.

Hard handoff is a method in which a communication channel established between a current base station and a mobile station is instantly changed to a channel between an adjacent base station and a mobile station, and a call is dropped for a short time, and a soft handoff is performed. A mobile station maintains a communication channel with two or more base stations for a predetermined time, thereby changing the service area without disconnecting the call.

For example, the soft handoff method refers to a mobile station allocated with a call channel from two base stations at the same time while it is between a serving base station and an adjacent base station, and the hard handoff method is a service. When a frequency used by a base station and a neighboring base station is different from each other, the current frequency is disconnected and the call is continued by changing to a new frequency supported by the neighboring base station.

The terms used in the present invention are defined as follows.

A pilot strength measurement message (PSMM) is a pilot strength measurement message received by a base station / base station controller from a mobile station.

A handoff direction message (HDM) is a message used by a base station / base station controller to request handoff to a mobile station.

The soft handoff procedure defined in IS-95, which is a standard of the CDMA cellular mobile communication system, can be described with reference to FIG.

1 is an explanatory diagram of a soft handoff signal level in a code division multiple access (CDMA) mobile communication system to which the present invention is applied. As shown in FIG. It shows that the strength of the received signal of the base station B gradually increases.

The parameters for measuring pilot strength used to determine handoff timing are as follows.

T_ADD is a value of base station pilot strength (hereinafter referred to as "T_ADD") that the neighboring base station must satisfy to enter the candidate base station.

T_DROP is a lowest signal level value (hereinafter, referred to as "T_DROP") for the base station to remain in an active set.

T_COMP (T_COMPL) is a value for comparing the difference between the pilot strength of the candidate group and the pilot strength of the active set and the strength difference of the pilots belonging to the active set for the base station of the candidate group to enter the active set (hereinafter referred to as "T_COMP"). )to be.

T_TDROP is a channel drop timer value (hereinafter referred to as "T_TDROP") required for the pilot belonging to the active set to be deleted from the active set.

ADD refers to the pilot addition of a neighboring sector or cell as an active set when the mobile station moves to a neighboring sector or cell in a code division multiple access (CDMA) handoff scheme.

DROP means that pilots present in the active set are deleted in a code division multiple access (CDMA) handoff scheme.

Ec / Io is the ratio of the pilot energy Ec accumulated during one pseudo-noise (PN) chip period to the total power spectral density (Io) in the reception bandwidth (hereinafter referred to as Ec / Io).

Looking at the soft handoff procedure with reference to Figure 1 as follows.

First, when the mobile station moves from base station A to base station B, if the pilot signal strength of base station B is greater than T_ADD, the mobile station sends a pilot strength measurement message (PSMM) to the base station.

The base station then instructs the mobile station to allocate the traffic channel of the base station B through the handoff indication message (HDM) and to include the base station B's pilot in the active set. At this time, the mobile station forms a call path simultaneously with the base stations A and B.

Next, as the mobile station gradually approaches the base station B, the strength of the pilot signal of the base station A falls below T_DROP. At this time, the mobile station starts a timer to measure the pilot strength of the base station A by T_TDROP seconds, and if the pilot strength of the base station A is still less than or equal to T_DROP, a pilot strength measurement message ( PSMM).

Subsequently, the base station receiving the pilot strength measurement message PSMM releases the channel talking to the base station A through the handoff indication message HDM to the mobile station, at which time the handoff ends.

As shown in FIG. 1, the area where the channel is released by T_TDROP from the time T_ADD is called a soft handoff area.

As described above, if the mobile station does not receive the handoff service due to the traffic load and channel conditions of the base station B at the time T_ADD, the handoff service is suspended until the time T_COMP of FIG. Here, the T_COMP time point is a time point when the pilot strength of the neighboring base station becomes T_COMP or more than the pilot strength of the serving base station.

Therefore, the mobile station, which has not been provided with the handoff service, becomes farther from the base station A while approaching the T_COMP point, so that the call is more likely to be disconnected when the propagation environment becomes poor.

If the mobile station does not receive the handoff service even at the time of T_COMP, a handoff service failure occurs, and the call is stopped when the signal from the base station A becomes weak.

As noted above, when soft handoff occurs (ie, when a mobile station moves from one cell to a neighboring cell) as specified in IS-95, it is possible to simultaneously use multiple traffic channels allocated from neighboring base stations in a cell boundary region. do. Therefore, during soft handoff, the mobile station forms a call path at the same time as both base stations, so that power control of the base station with better radio wave environment can be achieved and good call quality can be maintained.

However, since the mobile station occupies several traffic channels, the use efficiency of radio resources is inferior. In other words, whenever the traffic channel usage is increased, interference is increased for other mobile stations, which adversely affects the call quality and system capacity.

Therefore, there have been suggested methods for maintaining the call quality while keeping the soft handoff time as short as possible.

The prior art defined in IS-95 uses fixed thresholds (T_ADD, T_DROP, T_COMP, T_TDROP, etc.) as far as handoff is concerned. In this case, using a fixed threshold value means that the handoff algorithm does not flexibly cope with a change in state of various channels, thereby inefficiently processing radio resources.

For example, if the fixed handoff threshold is set very high and strictly so that the sectors in the measurement set must have a fairly good quality in order to be added to the active set, the mobile station will not find any sectors that are good enough for the active set. If the call is dropped, this means that the handoff algorithm unnecessarily increases the probability of the call break. On the contrary, if the threshold is set lower and looser, the more likely the sector is to be added to the active set, the more likely the mobile station is to be connected to a large number of sectors, and thus more than is actually needed to maintain the call. Many radio resources are allocated.

Therefore, in the current technical field, in order to effectively use radio resources while minimizing call disconnection, there is an urgent need for a method capable of minimizing soft handoff in the form of excessively occupying radio resources.

The present invention has been proposed to meet the above-mentioned demands, and in order to minimize the disconnection in a mobile communication system to effectively use radio resources, to minimize soft handoff in the form of excessively occupying radio resources. It is an object of the present invention to provide a soft handoff control method of a mobile station and a computer-readable recording medium having recorded thereon a program for realizing the method. Other objects and advantages of the present invention can be understood by the following description, It will be more clearly understood by the embodiments of the present invention. Also, it will be readily appreciated that the objects and advantages of the present invention may be realized by the means and combinations thereof indicated in the claims.

1 is an explanatory diagram of a soft handoff signal level in a code division multiple access (CDMA) mobile communication system to which the present invention is applied;

2 is an explanatory diagram showing a T_TDROP value in a code division multiple access (CDMA) mobile communication system to which the present invention is applied;

3 is a state transition diagram of a mobile station in a code division multiple access (CDMA) mobile communication system to which the present invention is applied.

4 is a flowchart illustrating a method for controlling soft handoff of a mobile station in a code division multiple access (CDMA) mobile communication system according to the present invention;

In order to achieve the above object, the present invention provides a soft handoff control method of a mobile station in a mobile communication system, wherein the parameters FLAG, T_Excellent, and T_ADD_HIGHER are set for suppressing the soft handoff timing of the mobile station. A first value for setting the value of the FLAG to zero (“0”), the value of the T_Excellent to a predetermined value greater than the T_ADD_HIGHER, and the value of the T_ADD_HIGHER to a predetermined value greater than T_ADD when entering a mobile station call channel state; Parameter setting step; An active set analyzing step of analyzing an active set registered in the mobile station call channel state; And when the analysis result of the active set analysis step indicates that at least two registered active sets have a maximum pilot strength of pilot strengths of neighboring base stations in soft handoff in the active set greater than the T_Excellent, the neighboring base station is a candidate base station. The T_ADD_HIGHER is used instead of the base station pilot strength value T_ADD that must be satisfied in order to set a value, and the channel drop timer value T_TDROP necessary for the pilot belonging to the active set to be deleted from the active set is set to zero ("0"). It characterized in that it comprises a soft handoff control step of suppressing the soft handoff time.

In addition, the present invention provides T_ADD and T_TDROP as a criterion for the soft handoff time when one active set is registered or when the maximum pilot strength among pilot strengths of neighboring base stations in soft handoff in the active set is smaller than the T_Excellent. Characterized in that it further comprises a second parameter setting step using.

On the other hand, the present invention is to set the parameters (FLAG, T_Excellent, T_ADD_HIGHER) for suppressing the soft handoff time of the mobile station in the mobile communication system having a processor for soft handoff control of the mobile station, in the other state A first parameter for setting a value of the FLAG to zero ("0"), a value of the T_Excellent to a predetermined value greater than the T_ADD_HIGHER, and a value of the T_ADD_HIGHER to a predetermined value greater than T_ADD when entering a call channel state; Setting function; An active set analysis function for analyzing an active set registered in a mobile station call channel state; And when the analysis result of the active set analysis step indicates that at least two registered active sets have a maximum pilot strength of pilot strengths of neighboring base stations in soft handoff in the active set greater than the T_Excellent, the neighboring base station is a candidate base station. The T_ADD_HIGHER is used instead of the base station pilot strength value T_ADD that must be satisfied in order to set a value, and the channel drop timer value T_TDROP necessary for the pilot belonging to the active set to be deleted from the active set is set to zero ("0"). There is provided a computer-readable recording medium having recorded thereon a program for realizing a soft handoff control function for suppressing a soft handoff point.

In addition, the present invention provides T_ADD and T_TDROP as a criterion for the soft handoff time when one active set is registered or when the maximum pilot strength among pilot strengths of neighboring base stations in soft handoff in the active set is smaller than the T_Excellent. A computer readable recording medium having recorded thereon a program for further realizing a second parameter setting function using the present invention.

The present invention relates to a method for handoff of a mobile station in a mobile communication system. In order to minimize call disconnection during soft handoff, an excessive soft handoff is minimized to effectively use radio resources.

That is, according to the present invention, the soft handoff area is set too wide due to an incorrect cell arrangement of the base station, or because of the geographical influence, that is, the mobile station is located on an elevated roadway or in the upper part of a building in an urban area, and pilots of several adjacent base stations besides the base station to which the mobile station belongs. In the situation where the T_ADD is detected harder than the T_ADD, the conventional problem that the soft handoff in the form of over-taking several radio channels is inevitable will occur.

To this end, the present invention focuses on the fact that it is not necessary to waste valuable radio resources by occupying the forward channel of an adjacent base station if the strength of the base station pilot to which the mobile station belongs is sufficient to prevent call disconnection or call quality degradation. If it is determined that one of the pilot strengths of the neighboring base stations in the soft handoff is sufficiently above a certain level, the existing thresholds (T_ADD, T_TDROP) are changed to strictly limit the conditions included in the new active set and exclude them from the active set. By mitigating the necessary conditions, the time for soft handoff to occur is as short as possible. That is, some of the handoff related parameters are appropriately adjusted according to the state of the channel.

The above objects, features and advantages will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, whereby those skilled in the art may easily implement the technical idea of the present invention. There will be. In addition, in describing the present invention, when it is determined that the detailed description of the known technology related to the present invention may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted. Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The present invention uses T_Excellent and T_ADD_HIGHER in addition to T_ADD and T_TDROP, which are part of parameters used to determine handoff timing in the IS-95 series, which is an existing CDMA mobile communication standard. Here, the value of T_ADD_HIGHER is operated with a threshold higher than T_ADD, and the value of T_Excellent is operated with a threshold higher than T_ADD_HIGHER.

In the present invention, when it is determined that one of the pilot strength values of neighboring base stations in soft handoff is greater than T_Excellent, T_ADD_HIGHER is used instead of the existing T_ADD value, and T_TDROP is set to "0" to maximize the time for soft handoff. Keep it short

For reference, the value of T_TDROP defined in the IS-95 series is to be used for the mobile station according to the information transmitted from the base station from 0 to 15 as shown in FIG.

The mobile station according to the present invention stores and operates new variables FLAG, T_Excellent and T_ADD_HIGHER in memory.

The present invention performs an initialization operation when entering the "mobile station call channel state (see Fig. 3)" in the other state (401). Here, the initialization operation includes a procedure of setting the value of FLAG to "0" and setting the T_Excellent and T_ADD_HIGHER values to predetermined values.

Then, it is determined whether there is more than one currently registered active set (402).

As a result of the determination, if there is more than one active set, it is checked whether the energy intensity value of the active set having the maximum energy intensity value is higher than T_EXCELLENT (403).

As a result of the test, if the energy value of the active set having the maximum energy intensity value among the active sets is higher than T_EXCELLENT, it is analyzed whether the FLAG variable value is "0" (404).

As a result of analysis, if the FLAG variable value is "0", FLAG is set to "1", the current T_TDROP value is backed up to a separate memory, the T_TDROP value to be used is set to "0", and the current T_ADD value is set separately. It backs up to the memory, and performs a series of operations of replacing the T_ADD value to be used with the T_ADD_HIGHER value (405).

As a result of the analysis, if the FLAG variable value is not "0", the mobile station talk channel state is maintained (408).

In the above process (402, 403), if the active set is not more than two, or the energy value of the active set having the maximum energy intensity value is not higher than T_EXCELLENT, it is analyzed whether the FLAG variable value is "1" (406).

As a result of analysis, if the FLAG variable value is "1", FLAG is set to "0", the T_TDROP value backed up in the separate memory is restored to the T_TDROP value currently used, and the T_ADD value backed up in the separate memory is After performing a series of operations to restore the T_ADD value to be used (407), the mobile station talk channel state is maintained (408).

As a result of the analysis, if the FLAG variable value is not "1", the mobile station talk channel state is maintained (408).

As described above, the present invention has been described using IS-95A, which is a standard of the CDMA digital cellular mobile communication system as an example, but is not limited thereto. IS-95B, IS-95C, and IS-95C have evolved from IS-95. Applicable to -2000 is obvious.

The method of the present invention as described above may be implemented as a program and stored in a computer-readable recording medium (CD-ROM, RAM, ROM, floppy disk, hard disk, magneto-optical disk, etc.).

The present invention described above is not limited to the above-described embodiments and the accompanying drawings, and various substitutions, modifications, and changes are possible in the art without departing from the technical spirit of the present invention. It will be clear to those of ordinary knowledge.

As described above, the present invention minimizes call disconnection during soft handoff, minimizing soft handoff in the form of excessively occupying radio resources in order to effectively use radio resources. There is an effect that can be increased.

Claims (7)

A method for controlling soft handoff of a mobile station in a mobile communication system, Set the parameters FLAG, T_Excellent, T_ADD_HIGHER to suppress the soft handoff time of the mobile station, when entering the mobile station call channel state from other states, the value of the FLAG is zero ("0"), the value of the T_Excellent Setting a value of the T_ADD_HIGHER to a predetermined value greater than T_ADD_HIGHER and setting the value of the T_ADD_HIGHER to a predetermined value greater than T_ADD; An active set analyzing step of analyzing an active set registered in the mobile station call channel state; And As a result of the analysis of the active set analysis step, when at least two registered active sets are present, if the maximum pilot strength among the pilot strengths of the neighboring base stations in the soft handoff in the active set is greater than the T_Excellent, the neighboring base station is determined to the candidate base station. The T_ADD_HIGHER is used instead of the base station pilot strength value T_ADD that must be satisfied to enter, and the channel drop timer value T_TDROP necessary for the pilot belonging to the active set to be deleted from the active set is set to zero ("0"). Soft handoff control step of suppressing soft handoff timing Soft handoff control method of a mobile station in a mobile communication system comprising a. The method of claim 1, A second using T_ADD and T_TDROP as a criterion for the soft handoff time when one active set is registered or the maximum pilot strength among pilot strengths of neighboring base stations in soft handoff in the active set is smaller than the T_Excellent Parameter setting step Soft handoff control method of a mobile station in a mobile communication system further comprising. The method of claim 2, The second parameter setting step, Analysis step of analyzing whether the FLAG variable value is one ("1") when there is only one registered active set or the maximum pilot strength among pilot strengths of neighboring base stations in soft handoff in the active set is smaller than T_Excellent. ; If the FLAG variable value is one ("1"), the FLAG variable is set to zero ("0"), and the T_TDROP value backed up in a separate memory is restored to the currently used T_TDROP value. Restoring the T_ADD value backed up to a separate memory to the T_ADD value currently to be used, and then maintaining the mobile station call channel state; And If the FLAG variable value is not one ("1") as a result of the analysis in the analyzing step, maintaining a mobile station call channel state Soft handoff control method of a mobile station in a mobile communication system comprising a. delete The method according to any one of claims 1 to 3, The soft handoff control step, A test step of checking whether the pilot energy intensity value of the active set having the maximum energy intensity value is higher than the T_EXCELLENT when the analysis result of the active set analysis step is at least two; A determination step of determining whether the FLAG variable value is zero ("0") when the pilot energy intensity value of the active set having the maximum energy intensity value is higher than the T_EXCELLENT as a result of the inspection of the inspection step; If the FLAG variable value is zero ("0"), the FLAG is set to one ("1"), the current T_TDROP value is backed up in a separate memory, and the T_TDROP value to be used is zero. Setting to "0", backing up the current T_ADD value to a separate memory, and replacing the T_ADD value to be used with the T_ADD_HIGHER value; And If the FLAG variable value is not zero ("0") as a result of the determination in the determination step, maintaining a mobile station call channel state Soft handoff control method of a mobile station in a mobile communication system comprising a. In a mobile communication system having a processor for soft handoff control of a mobile station, Set the parameters FLAG, T_Excellent, T_ADD_HIGHER to suppress the soft handoff time of the mobile station, when entering the mobile station call channel state from other states, the value of the FLAG is zero ("0"), the value of the T_Excellent A first parameter setting function for setting a value of the T_ADD_HIGHER to a predetermined value greater than T_ADD to a predetermined value greater than the T_ADD_HIGHER; An active set analysis function for analyzing an active set registered in a mobile station call channel state; And As a result of the analysis of the active set analysis step, when at least two registered active sets are present, if the maximum pilot strength among the pilot strengths of the neighboring base stations in the soft handoff in the active set is greater than the T_Excellent, the neighboring base station is determined to the candidate base station. The T_ADD_HIGHER is used instead of the base station pilot strength value T_ADD that must be satisfied to enter, and the channel drop timer value T_TDROP necessary for the pilot belonging to the active set to be deleted from the active set is set to zero ("0"). Soft handoff control to suppress soft handoff points A computer-readable recording medium having recorded thereon a program for realizing this. The method of claim 6, A second using T_ADD and T_TDROP as a criterion for the soft handoff time when one active set is registered or the maximum pilot strength among pilot strengths of neighboring base stations in soft handoff in the active set is smaller than the T_Excellent Parameter setting function A computer-readable recording medium that records a program for further realization.