KR20030017205A - Dynamic soft handoff method in wireless telecommunication system - Google Patents

Abstract

PURPOSE: A dynamic soft handoff method in a wireless communication system is provided to dynamically decide parameter values used for handoff, according to dynamically variable receiving power of MSs(Mobile Stations), so as to minimize the use of network resources and secure tone quality over a predetermined level. CONSTITUTION: A distance(d) to a BTS(Base Transceiver Station)-A is initialized to 1(one)(201). The received signal strength(S.sub.a(d)) from the BTS-A and the received signal strength(S.sub.b(d)) from a BTS-B are measured(202). The received signal strength(S.sub.a(d)) is compared with a predetermined threshold(A.sub.TH)(203). If the received signal strength(S.sub.a(d)) is not less than the predetermined threshold(A.sub.TH), whether the distance(d) is equal to a distance(D) between the BTS-A and the BTS-B is decided(208). If so, the steps are ended, and otherwise, the distance(d) is added by one to be a distance(d+1)(209), and then the step 202 is returned. If the received signal strength(S.sub.a(d)) is less than the absolute threshold(A.sub.TH) in the step 203, the received signal strength(S.sub.a(d)) is compared with a regular threshold(A.sub.a)(204). If the received signal strength(S.sub.a(d)) is less than the regular threshold(A.sub.a), a difference(S.sub.b(d)-S.sub.a(d)) between the receive signals strengths is compared with a dynamic handoff parameter(T.sup.0.sub.add)(205). If the difference(S.sub.b(d)-S.sub.a(d)) is not less than the value(T.sup.0.sub.add), soft handoff is performed(207) and the step 208 is performed. If the difference(S.sub.b(d)-S.sub.a(d)) is less than the value(T.sup.0.sub.add), soft handoff is not generated and the step 208 is performed. If the received signal strength(S.sub.a(d)) is not less than the regular threshold(A.sub.a) in the step 204, the difference(S.sub.b(d)-S.sub.a(d)) is compared with a dynamic handoff parameter(T.sup.0.sub.add(S.sub.a.(d)))(206). If the difference(S.sub.b(d)-S.sub.a(d)) is not less than the value(T.sup.0.sub.add(S.sub.a.(d))), soft handoff is performed(207) and the step 208 is performed. And if the difference(S.sub.b(d)-S.sub.a(d)) is less than the value(T.sup.0.sub.add(S.sub.a.(d))), soft handoff is not generated and the step 208 is performed.

Description

Dynamic soft handoff method in wireless communication system

The present invention dynamically changes the parameter values used in the handoff according to the received signal strength of a mobile station (MS) in a wireless communication system, thereby guaranteeing a certain level of quality to the subscriber and minimizing the use of network resources, and also unnecessary hands. The present invention relates to a dynamic soft handoff method capable of reducing traffic load of an entire system by suggesting a method of suppressing off, and a computer-readable recording medium recording a program for realizing the method.

First, direct sequence code division multiple access (DS-CDMA: Direct Sequence CDMA) based on the International Standard-95 (IS-95) standard, which may be helpful in understanding the prior art and the technical gist of the present invention. The handoff service provided by the cellular system will be described.

In general, a code division multiple access (CDMA) cellular system divides a service area into cells and reuses used frequencies to efficiently use frequency resources.

As such, since the service area is divided into cellular compartments, when a mobile station (MS) moves to another cell, it starts communication with a base station (BTS) that manages a new corresponding cell, which is referred to as a "handoff". .

The handoff service provided by the DS-CDMA cellular system based on the IS-95 standard includes the "Soft Handoff" method and the "Hard Handoff" method. There is this.

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 disconnected 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, a soft handoff method refers to a mobile station allocated with a call channel from two base stations simultaneously while being in communication between a serving base station and an adjacent base station, and a 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 soft handoff procedure defined in IS-95, a standard for CDMA cellular systems, can be described with reference to FIG.

1 is an explanatory diagram of a soft handoff signal level in a typical wireless communication system. As the base station A moves from base station A to base station B, the strength of the received signal of the base station A decreases, and the strength of the received signal of the base station B gradually increases. Shows.

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

T _add is a value of base station pilot strength that a neighbor base station must satisfy to enter a candidate base station.

T _drop is the lowest signal level value for the base station to remain in the active set.

T _comp (T _compl ) is a value for comparing the difference between the pilot strength of the candidate group, 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.

T _tdrop is a channel drop timer value 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.

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.

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 operates the timer to measure the pilot strength of the base station A after T _tdrop seconds, and if the pilot strength of the base station A is still below the T _drop , the pilot strength measurement message is sent to the base station to release the call path with the base station A. Transmit (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 of T _add , the handoff service is suspended until the time of T _comp of FIG. 1. Here, T _comp point refers to a point when the pilot strength of the neighboring base station becomes equal to or greater than T _comp 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 radio 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 an adjacent cell) as specified in IS-95, two traffic channels allocated from both base stations are used simultaneously in the cell boundary region. .

Therefore, during soft handoff, the mobile station forms a call path simultaneously with 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 two traffic channels, the use efficiency of the traffic channel is also reduced. In other words, whenever the traffic channel usage is increased, interference from other mobile stations is increased, which adversely affects the call quality and system capacity.

In summary, in a mobile communication system, a service area is composed of many cells to increase system capacity. It is necessary to make a handoff so that mobiles can continue a call when moving to an adjacent cell or to an adjacent sector in the same cell. At this time, it is necessary to design a good handoff technique in order to provide good quality services to mobile stations while promoting efficient use of network resources. One of the important characteristics of a CDMA system is soft handoff. In soft handoff, the mobile station communicates with the new base station without disconnecting the old base station. Thus, compared to the hard handoff scheme, the voice quality is improved due to diversity due to an extra channel path at the cell boundary. However, in terms of network operations, more network resources are required to perform these functions. Therefore, the efficient handoff technique of the CDMA system should minimize the network resources required while guaranteeing a certain level of call quality to the subscriber.

In soft handoff, the voice quality is somewhat improved due to the diversity due to the extra channel path at the cell boundary, but the demand for network resources is inevitably increased.

Hard handoff and soft handoff differ in the techniques themselves, but also in the performance indicators that are highlighted. In hard handoffs, the tradeoff between handoff delay and the Ping Pong effect is a major concern, while in soft handoffs the increased quality of diversity and increased network resources during soft handoffs is a major concern. The trade off between the disturbances is a major concern.

The performance of the CDMA soft handoff technique can be seen in three aspects.

First, the subscriber's voice quality is expressed as Outage Probability, which indicates the probability that the received signal strength at the mobile station will fall below the minimum quality level.

The second and third indicate the degree of network resource requirements, which is the number of changes in the active set and the average number of base stations in the active set. The number of changes in the active set is defined as the average number of changes in the active set on the movement path of the mobile station. The average number of base stations in the active set is represented by the average number of base stations in the active set on the mobile path of the mobile station.

There is a trade-off between the three performance factors mentioned above. That is, using a certain handoff method increases the update rate of the active set, but reduces the average number of base stations in the active set, thereby saving network resources. However, the diversity gain will be reduced and the voice quality level will be lowered. In addition, frequent active set updates may cause an increase in the amount of signals between the mobile station and the base station, which may result in another kind of system load. Another type of handoff method can be used to maintain a relatively large number of base stations in an active set. Therefore, the number of active set updates is reduced, which can take a high diversity gain, resulting in a good speech quality level.

Several soft handoff techniques have been proposed since the static threshold handoff method described in the IS-95 standard. However, in most handoff schemes, various parameter values used are determined as specific constant values regardless of the received power of the mobile station. Under these schemes, there is a problem in that optimal handoff performance cannot be expected because the handoff is not performed in consideration of the receiving power of mobile stations that change dynamically.

The present invention has been proposed to solve the above problems, and dynamically determines the parameter values used in the handoff according to the receiving power of the mobile stations that change dynamically in the wireless communication system, thereby minimizing the requirement of network resources. The present invention aims to provide a dynamic soft handoff method capable of guaranteeing a certain level of call quality to a subscriber and a computer-readable recording medium recording a program for realizing the method.

1 is a diagram illustrating a soft handoff signal level in a general wireless communication system.

2 to 5 are flowcharts of first to fourth embodiments of a dynamic soft handoff method according to the present invention.

FIG. 6 is a diagram illustrating an embodiment of a dynamic T _add value according to the received power S _a (d) used in the present invention. FIG.

7 is an exemplary explanatory diagram showing a dynamic T _add value according to the reception power S _b (d) used in the present invention.

8 is a diagram illustrating an exemplary embodiment of a dynamic T _drop value according to the reception power S _a (d) used in the present invention.

9 is a diagram illustrating an exemplary embodiment of a dynamic T _drop value according to the reception power S _b (d) used in the present invention.

According to an aspect of the present invention, there is provided a soft handoff method in a wireless communication system, comprising: a first step of obtaining received signal strengths of adjacent base stations, respectively; A second step of dynamically determining, based on a received signal strength, a value T _add of base station pilot strengths that a neighboring base station must satisfy to enter a candidate base station based on a predetermined threshold value less than an absolute threshold value; And a third step of determining whether to handoff based on a comparison between the received signal strength difference of the neighboring base station and the dynamic T _add value.

In addition, the present invention provides a soft handoff method in a wireless communication system, comprising: a first step of obtaining received signal strengths of adjacent base stations, respectively; A second step of dynamically determining a lowest signal level value T _drop for a base station to remain in an active set based on a predetermined threshold value according to the received signal strength; And a third step of comparing the difference between the received signal strengths of the neighboring base stations and the dynamic T _drop value, and determining whether to handoff based on a time gauge.

In order to achieve the above object, the present invention provides a wireless communication system having a processor for dynamic soft handoff, comprising: a first function of obtaining received signal strengths of adjacent base stations, respectively; A second function for dynamically determining, based on a received signal strength, a value T _add of base station pilot strengths that a neighboring base station must satisfy to enter a candidate base station based on a predetermined threshold value less than an absolute threshold value; And a computer-readable recording medium having recorded thereon a program for realizing a third function of determining whether to handoff based on a comparison between a received signal strength difference of a neighboring base station and a dynamic T _add value.

In addition, the present invention provides a wireless communication system having a processor for dynamic soft handoff, comprising: a first function of obtaining received signal strengths of adjacent base stations, respectively; A second function of dynamically determining a lowest signal level value T _drop for a base station to remain in an active set based on a predetermined threshold value according to the received signal strength; And a computer-readable recording medium having recorded thereon a program for realizing a third function of comparing a received signal strength difference of a neighboring base station with a dynamic T _drop value and determining handoff based on a time gauge according to the comparison result. do.

The present invention is to dynamically change the parameter values used in the handoff according to the receiving power of the mobile station that is changing dynamically, to ensure the subscriber to a certain level of call quality and to minimize the use of network resources. In addition, the present invention proposes a method for suppressing unnecessary handoff, thereby reducing the overall system traffic load.

To this end, in the present invention, in order to guarantee a certain level of call quality to subscribers while minimizing the requirement of network resources, if the relative difference between the signal strengths received from each base station at the mobile station is greater than or equal to a certain value or less than another specific value, the soft hand is used. Instead of turning off the static soft handoff technique, we propose a dynamic soft handoff technique in which these specific values change according to the received signal strength of the mobile stations.

In addition, the present invention, in order to reduce the system load due to frequent changes in the active set, the absolute threshold technique to prevent entry into the active set if the received signal of the pilot (Pilot) in the active set is above a certain value (Absolute Threshold), The Drop Timer technique is used to drop the active set only when the relative difference in signal strength is kept below a certain value for a certain period of time.

Therefore, since the present invention dynamically determines the hysteresis limit value according to the received power values of the terminals, it is possible to guarantee a certain level of call quality while minimizing the requirement of network resources, and the absolute threshold value and the drop-down clock technique. Can be used to reduce the system load due to frequent changes in the active set.

The above objects, features and advantages will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

First, referring to the wireless environment used in the present invention is as follows.

The basic system consists of two base stations A and B, which are separated from each other by D meters.

The propagation environment is characterized by log linear pathloss and shadow fading.

The mobile station moves from A to B along a straight path connecting the two base stations.

In the case where the distance from the base station A is d, the strengths S _a (d) and S _b (d) of the signals received from the base stations A and B are expressed in dB, respectively.

S _a (d) = k ₁ -k ₂ log (d) + u (d)

S _b (d) = k ₁ -k ₂ log (Dd) + v (d) d∈ (0, D)

In Equation 1, k ₁ and k ₂ are parameters representing path loss. Then, u (d) and v (d) follow the zero mean Gaussian process with the following Exponential Auto Correlation Function (Equation 2).

E {μ (d) · μ (d + Δd)} = σ ² (Δd / d ₀ )

In Equation 2, d ₀ is a constant indicating how quickly the correlation disappears as the distance increases. It is also assumed that u (d) and v (d) follow a joint Gaussian distribution with mean 0, variance σ ² , and correlation coefficient p.

Then, a dynamic soft handoff technique in a mobile communication system, i.e., pilots in an active set from A to AB, pilots in an active set from B to AB, pilots in an active set from AB to A, and pilots in an active set are AB. The soft handoff method to B in more detail as follows.

First, the handoff process in which the pilot in the active set goes from A to AB will be described in more detail with reference to FIG.

First, d = 1 is initialized (201), and the received signal strength (received power) S _a (d) and S _b (d) from the base stations A and B are measured (202).

Thereafter, the received signal strength S _a (d) is compared with a predetermined threshold A _TH (203).

As a result of the comparison 203, if the received signal strength S _a (d) is equal to or larger than the predetermined threshold A _TH , no handoff occurs. In other words, the received signal strength from the base station A is large enough to avoid unnecessary handoff. At this time, if d = D (208), the handoff process is finished, or d = d + 1 (208,209), and the process proceeds to step " 202 ".

As a result of the comparison (203), if the received signal strength S _a (d) is less than the predetermined threshold A _TH , the received signal strength S _a (d) is compared with A _a (<A _TH ) (204). This is to determine a _Toff value, which is a handoff parameter, dynamically according to the received signal strength of S _a (d). That is, if S _a (d) is smaller than A _{TH but} greater than a certain threshold A _a , pilot B enters the active set more difficult than S _a (d) is less than _a certain threshold A _a , thus making network resources more efficient. We plan to use. To this end, the T _add value is determined according to the value of S _a (d) as shown in FIG. 6. As shown in FIG. 6, when S _a (d) is equal to or larger than A _{a, the} T _add value is increased to suppress the pilot B from entering the active set.

As a result of the comparison 204, if the received signal strength S _a (d) is less than A _a (<A _TH ), the difference between the two received signal strengths S _b (d) -S _a (d) and the dynamic handoff parameter T ⁰ _add Compare 205 to determine whether to soft hand off.

As a result of the comparison 205, if the difference S _b (d) -S _a (d) between the two signal strengths is equal to or greater than a predetermined value T ⁰ _add , a soft handoff occurs in which the pilot B is included in the active set (207). That is, since the signal strength at the base station B is greater than a predetermined value at the base station A, it is necessary to perform soft handoff to improve the quality of the subscriber. At this time, if d = D (208), the handoff process is finished, or d = d + 1 (208,209), and the process proceeds to step &quot; 202 &quot;. However, if the difference S _b (d) -S _a (d) of the two signal strengths is less than a constant value T ⁰ _add , no soft handoff occurs. At this time, if d = D (208), the handoff process is finished, or d = d + 1 (208,209), and the process proceeds to step " 202 &quot;.

As a result of the comparison 204, if the received signal strength S _a (d) is equal to or larger than A _a (<A _TH ), the difference between the two received signal strengths S _b (d) -S _a (d) and S _a (d) The dynamically changing dynamic handoff parameter T ⁰ _add (S _a (d)) is compared 206 to determine whether to soft hand off.

That is, if the received signal strength S _a (d) is greater than or equal to A _a (<A _TH ), the T _add value is set to T _add (S _a (d)), which changes dynamically according to S _a (d) greater than T ⁰ _add . As a result, the pilot B is prevented from entering the active set.

Thus, if the result of the comparison 206, the difference _b S (d) -S _a (d) of the signal strength is a predetermined value of the two base stations T _add (S _a (d)) or higher, to improve the communication quality of the subscriber cycle A soft handoff is performed to include pilot B in the active set (207). At this time, if d = D (208), the handoff process is finished, or d = d + 1 (208,209), and the process proceeds to step " 202 &quot;. However, if the difference S _b (d) -S _a (d) of the two signal strengths is less than the constant value T _add (S _a (D)), no soft handoff occurs. At this time, if d = D (208), the handoff process is terminated, otherwise, d = d + 1 (208, 209) and the process proceeds to step “202”.

Referring now to FIG. 3, the handoff procedure in which the pilot in the active set goes from B to AB will be described in more detail.

First, d = 1 is initialized (301), and the received signal strength (received power) S _a (d) and S _b (d) from the base stations A and B are measured (302).

Thereafter, the received signal strength S _b (d) is compared with a predetermined threshold A _TH (303).

As a result of the comparison 303, if the received signal strength S _b (d) is equal to or larger than the predetermined threshold A _TH , no handoff occurs. In other words, the received signal strength from the base station B is large enough to avoid unnecessary handoff. At this time, if d = D (308), the handoff process is finished, or d = d + 1 (308, 309), and the process proceeds to step " 302 &quot;.

As a result of the comparison 303, if the received signal strength S _b (d) is less than the predetermined threshold A _TH , the received signal strength S _b (d) is compared with A _a (<A _TH ) (304). This is to determine the _Toff value of the handoff parameter dynamically according to the received signal strength of S _b (d). In other words, if S _b (d) is less than A _{TH but} greater than a certain threshold A _a , it is more difficult for pilot A to enter the active set than if S _b (d) is less than _a certain threshold A _a. We plan to use. To this end, the T _add value is determined according to the S _b (d) value as shown in FIG. 7. As shown in FIG. 7, when S _b (d) is greater than or equal to A _a, T _add is increased to suppress pilot A from entering the active set.

As a result of comparison 304, if the received signal strength S _b (d) is less than A _a (<A _TH ), the difference between the two received signal strengths S _a (d) -S _b (d) and the dynamic handoff parameter T ⁰ _add Compare 305 to determine whether to soft hand off.

As a result of the comparison 305, if the difference S _a (d) -S _b (d) between the two signal strengths is equal to or greater than a predetermined value T ⁰ _add , a soft handoff occurs that includes pilot A in the active set (307). That is, since the signal strength at the base station A is greater than a predetermined value at the base station B, it is necessary to perform soft handoff to improve the quality of the subscriber. At this time, if d = D (308), the handoff process is finished, or d = d + 1 (308, 309), and the process proceeds to step &quot; 302 &quot;. However, if the difference S _a (d) -S _b (d) between the two signal strengths is less than a constant value T ⁰ _add , no soft handoff occurs. At this time, if d = D (308), the handoff process is finished, or d = d + 1 (308, 309), and the process proceeds to step " 302 &quot;.

As a result of the comparison 304, if the received signal strength S _b (d) is equal to or larger than A _a (<A _TH ), the difference between the two received signal strengths S _a (d) -S _b (d) and S _b (d) The dynamically changing dynamic handoff parameter T ⁰ _add (S _b (d)) is compared 306 to determine whether to soft hand off.

That is, if the received signal strength S _b (d) is greater than or equal to A _a (<A _TH ), the T _add value is T _add (S _b (d)), which changes dynamically according to S _b (d) greater than T ⁰ _add . As a result, it is possible to suppress the pilot A from entering the active set.

Therefore, if the difference S _a (d) -S _b (d) between the signal strengths of the two base stations is equal to or greater than a predetermined value T _add (S _b (d)), the comparison result 306 improves the call quality of the subscriber. In operation 307, soft handoff is performed to include pilot A in the active set. At this time, if d = D (308), the handoff process is finished, or d = d + 1 (308, 309), and the process proceeds to step " 302 &quot;. However, if the difference S _a (d) -S _b (d) of the two signal strengths is less than a constant value T _add (S _b (D)), no soft handoff occurs. At this time, if d = D (308), the handoff process is finished, or d = d + 1 (308, 309), and the process proceeds to step " 302 &quot;.

On the other hand, the handoff process in which the pilot in the active set is from AB to A will be described in more detail with reference to FIG.

First, the time meter is fixed at a predetermined time k (401).

Then, the received signal strength (received power) S _a (d) and S _b (d) are measured from the base stations A and B (402).

Next, the received signal strength S _a (d) is compared with a predetermined threshold A _d (403). This is to determine the T _drop value, a handoff parameter, dynamically according to the received signal strength of S _a (d). That is, when the S _a (d) is less than a predetermined threshold value A _d, that the pilot B eliminated S _a (d) is made difficult as compared to the case it is greater than the threshold value A _d enhance subscriber quality by the diversity gain and the active Reduce traffic load due to aggregation changes. To this end, the T _drop value is determined according to the value of S _a (d) as shown in FIG. 8. As shown in FIG. 8, when S _a (d) is less than or equal to A _{d, the} T _drop value is reduced to prevent pilot B from dropping from the active set.

As a result of the comparison (403), if the received signal strength S _a (d) is greater than or equal to A _d , the difference between the two received signal strengths S _b (d) -S _a (d) and the dynamic handoff parameter T ⁰ _drop are compared (404). ), Whether or not soft handoff is determined.

As a result of the comparison (404), if the difference S _b (d) -S _a (d) of the two signal strengths is equal to or less than the constant value T ⁰ _drop and the value of k is 0 (406), the soft hand removes pilot B from the active set. Off occurs (407). That is, because the signal strength at the base station B is low, B is eliminated from the active set, so that network resources can be efficiently operated. At this time, if d = D (408), the handoff process is finished, otherwise d = d + 1 (408, 409), and the process proceeds to step &quot; 401 &quot;. However, if the value of k is not 0 (406), if d = D (410), the handoff process is terminated, otherwise k = k-1 and d = d + 1 (410, 411) to step “402”. Passing The reason for using the time gauge k is to reduce unnecessary traffic load by preventing frequent handoff due to the ping-pong effect of the received signal strength.

As a result of the comparison 403, if the received signal strength S _a (d) is less than A _d , the dynamic hand dynamically varies according to the difference S _b (d) -S _a (d) and S _b (d) of the two received signal strengths. The off parameter T ⁰ _drop (S _a (d)) is compared (405) to determine whether to soft hand off.

That is, if the received signal strength S _a (d) is less than A _d , the T _drop value is set to T _drop (S _a (d)), which varies dynamically according to S _a (d) less than T ⁰ _drop . Suppresses dropping from the active set.

Thus, the result of the comparison 405, the signal strength of the two base difference _b S (d) -S _a (d), the predetermined value T _drop (S _a (d)) or less, k is the value 0 (406) In operation 407, soft handoff is performed to remove pilot B from the active set for efficient operation of network resources. At this time, if d = D (408), the handoff process is finished, otherwise d = d + 1 (408, 409), and the process proceeds to step " 401 &quot;. However, if the value of k is not 0 (406), if d = D (410), the handoff process is terminated, otherwise k = k-1 and d = d + 1 (410, 411) to step “402”. Passing The reason for using the time gauge k is to reduce unnecessary traffic load by preventing frequent handoff due to the ping-pong effect of the received signal strength.

Finally, the handoff procedure in which the pilot in the active set goes from AB to B will be described in more detail with reference to FIG.

First, the time meter is fixed at a predetermined time k (501).

Thereafter, the received signal strength (received power) S _a (d) and S _b (d) are measured from the base stations A and B (502).

Next, the received signal strength S _b (d) is compared with a predetermined threshold A _d (503). This is to determine the T _drop value, which is a handoff parameter, dynamically according to the received signal strength of S _b (d). That is, when the S _b (d) is less than a predetermined threshold value A _d, that the pilot A dropped S _b (d) is made difficult as compared to the case it is greater than the threshold value A _d enhance subscriber quality by the diversity gain and the active Reduce traffic load due to aggregation changes. To this end, the T _drop value is determined according to the S _b (d) value as shown in FIG. 9. As shown in FIG. 9, when S _b (d) is less than or equal to A _{d, the} T _drop value is reduced to prevent pilot A from dropping from the active set.

As a result of the comparison (503), if the received signal strength S _b (d) is greater than or equal to A _d , the difference between the two received signal strengths S _a (d) -S _b (d) and the dynamic handoff parameter T ⁰ _drop are compared (504). ), Whether or not soft handoff is determined.

As a result of the comparison (504), if the difference S _a (d) -S _b (d) between the two signal strengths is equal to or less than the constant value T ⁰ _drop and the value of k is 0 (506), the soft hand removes pilot A from the active set. Off occurs (507). That is, since signal strength at the base station A is low, A is eliminated from the active set, so that network resources can be efficiently operated. At this time, if d = D (508), the handoff process is finished, otherwise d = d + 1 (508,509), and the process goes to step “501”. However, if the value of k is not 0 (506), if d = D (510), the handoff process is finished, otherwise k = k-1 and d = d + 1 (510, 511) to step “502”. Passing The reason for using the time gauge k is to reduce unnecessary traffic load by preventing frequent handoff due to the ping-pong effect of the received signal strength.

As a result of the comparison (503), if the received signal strength S _b (d) is less than A _d , the dynamic hand dynamically varies according to the difference S _a (d) -S _b (d) and S _b (d) of the two received signal strengths. The off parameter T ⁰ _drop (S _b (d)) is compared (505) to determine whether to soft hand off.

That is, if the received signal strength S _b (d) is less than A _d , the T _drop value is set to T _drop (S _b (d)) which varies dynamically according to S _b (d) less than T ⁰ _drop . Suppresses dropping from the active set.

Accordingly, when the comparison result 505 shows that the difference S _a (d) -S _b (d) between the signal strengths of the two base stations is equal to or less than a predetermined value T _drop (S _b (d)), and the k value is 0 (506). In operation 507, soft handoff is performed to remove pilot A from the active set for efficient operation of network resources. At this time, if d = D (508), the handoff process is finished, otherwise d = d + 1 (508,509), and the process goes to step “501”. However, if the value of k is not 0 (506), if d = D (510), the handoff process is finished, otherwise k = k-1 and d = d + 1 (510, 511) to step “502”. Passing The reason for using the time gauge k is to reduce unnecessary traffic load by preventing frequent handoff due to the ping-pong effect of the received signal strength.

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 apparent to those of ordinary knowledge.

The present invention as described above, since the parameter values used in the handoff is dynamically determined according to the changing power of the mobile stations, soft handoff that can guarantee a certain level of call quality while minimizing the network resource requirements It is possible to reduce the system load due to frequent changes of the active set by using the absolute threshold and the drop-down clock technique.

Claims (8)

In the soft handoff method in a wireless communication system, A first step of obtaining received signal strengths of adjacent base stations, respectively; A second step of dynamically determining, based on a received signal strength, a value T _add of base station pilot strengths that a neighboring base station must satisfy to enter a candidate base station based on a predetermined threshold value less than an absolute threshold value; And A third step of determining whether to handoff based on the comparison of the received signal strength difference of the neighboring base station and the dynamic T _add value Dynamic soft handoff method in a wireless communication system comprising a. The method of claim 1, The absolute threshold value is, Substantially, the method of dynamic soft handoff in a wireless communication system, characterized in that the entry into the active set is prevented if the received signal of pilots in the active set is above the absolute threshold value. The method according to claim 1 or 2, The dynamic T _add value is, It is determined according to the received signal strength of the neighboring base station, if the received signal strength of the neighboring base station is more than the predetermined threshold value by increasing the T _add value, characterized in that to suppress the pilot of the neighboring base station enters the active set Dynamic Soft Handoff Method in Communication Systems. In the soft handoff method in a wireless communication system, A first step of obtaining received signal strengths of adjacent base stations, respectively; A second step of dynamically determining a lowest signal level value T _drop for a base station to remain in an active set based on a predetermined threshold value according to the received signal strength; And The third step of comparing the difference between the received signal strength of the neighboring base station and the dynamic T _drop value, and determines whether to hand off based on the time gauge Dynamic soft handoff method in a wireless communication system comprising a. The method of claim 4, wherein The time measuring instrument, Substantially, a dynamic soft handoff method in a wireless communication system is characterized in that it is dropped from the active set only when the relative difference in signal strength continues below a predetermined value for a predetermined period. The method according to claim 4 or 5, The dynamic T _drop value is, It is determined according to the received signal strength of the neighboring base station, if the received signal strength of the neighboring base station is less than the predetermined threshold value, the T _drop value is small to suppress the pilot of the neighboring base station from dropping the active set wireless, characterized in that Dynamic Soft Handoff Method in Communication Systems. In a wireless communication system having a processor for dynamic soft handoff, A first function of obtaining received signal strengths of adjacent base stations, respectively; A second function for dynamically determining, based on a received signal strength, a value T _add of base station pilot strengths that a neighboring base station must satisfy to enter a candidate base station based on a predetermined threshold value less than an absolute threshold value; And A third function of determining whether to handoff based on a comparison of a received signal strength difference of a neighboring base station and a dynamic T _add value A computer-readable recording medium having recorded thereon a program for realizing this. In a wireless communication system having a processor for dynamic soft handoff, A first function of obtaining received signal strengths of adjacent base stations, respectively; A second function of dynamically determining a lowest signal level value T _drop for a base station to remain in an active set based on a predetermined threshold value according to the received signal strength; And A third function of comparing a received signal strength difference of a neighboring base station with a dynamic T _drop value and determining whether to handoff based on a time gauge according to a comparison result A computer-readable recording medium having recorded thereon a program for realizing this.