KR20070061736A - Method of vertical handoff - Google Patents

Abstract

A vertical handoff method is provided to prevent degradation of performance due to an increase in a delay time of vertical handoff, degradation of data throughput, degradation of terminal battery efficiency, and an increase in probability of a failure of vertical handoff. A serving network of a terminal is determined(S110). When the serving network is the first network and an RSSI(Received Signal Strength Indication) received from the second network is greater than the first threshold value, it is determined whether to perform the first vertical handoff by using a result obtained by estimating a transition pattern of the RSSI(S103,S105,S107,S109). When the serving network is the second network and the RSSI received from the second network is smaller than the second threshold value, it is determined whether to perform the second vertical handoff by using a result obtained by estimating a transition pattern of the RSSI(S111,S113,S115,S117,S119).

Description

Vertical handoff method {METHOD OF VERTICAL HANDOFF}

1 is a diagram illustrating a ping pong effect occurring when the conventional vertical handoff method is implemented.

2 is a diagram illustrating a network configuration in which a third generation cellular network and a WLAN network hotspot are overlapped according to an embodiment of the present invention.

3 to 5 illustrate various examples in which the ping-pong effect is prevented in the vertical handoff method according to an exemplary embodiment of the present invention.

6 to 7 illustrate examples of prediction of a received signal strength variation pattern in a vertical handoff method according to an exemplary embodiment of the present invention.

8 illustrates a vertical handoff method according to a first embodiment of the present invention.

9 illustrates a vertical handoff method according to a second embodiment of the present invention.

10 illustrates a vertical handoff method according to a third embodiment of the present invention.

The present invention relates to a vertical handoff method, i.e., to a vertical handoff method of a terminal connectable to a first network and a narrow second network having a relatively wide service coverage in an area where service coverage overlaps between heterogeneous networks.

The next generation network is expected to evolve into a form in which IP (Internet Protocol) based wireless networks with various characteristics have overlapping service areas. That is, the service areas of wireless networks having different characteristics and interworking with each other are hierarchically overlapped. These heterogeneous wireless networks have different characteristics, and service areas of interworking wireless networks are hierarchically overlapped, so that service subscribers are located, propagated environment, service characteristics, and user preferences. This allows for selective and flexible access to the optimal network.

In particular, interworking between 3G Cellular networks and Wireless Local Area hotspots is one of the greatest concerns among heterogeneous wireless networks.

In general, third generation cellular networks provide global coverage, but data rates are slow and expensive. WLAN networks, on the other hand, have limited coverage, such as hotspots, but are cheaper and have higher data rates.

Therefore, these heterogeneous wireless network environments have different characteristics and provide optimal service to subscribers by providing service switching of service connection paths between complementary 3G cellular networks and WLAN hotspot networks to guarantee service continuity. can do.

Here, a handoff between heterogeneous wireless networks, such as a third generation cellular network and a wireless LAN hotspot network, is called a vertical handoff or inter-system handoff (ISHO). This is different from Horizontal Handoff occurring between cells on homogeneous wireless networks.

Vertical handoff has a different signal strength value than that of horizontal handoff. The horizontal handoff determines a handoff by comparing signal strength values corresponding to each other among base stations to be compared. However, vertical handoffs do not have corresponding signal strength values corresponding to each other. However, since the third generation cellular network has wide area service coverage, its signal strength value cannot be used as triggering information for handoff determination. Accordingly, vertical handoff is determined using signal strength values of a network having limited service coverage, such as a hotspot of a WLAN network.

In addition, the vertical handoff has a relatively high probability of a ping-pong effect compared to the horizontal handoff.

That is, in the case of horizontal handoff, the ping-pong effect can be reduced by using a timer and a hysterisis technique in addition to the difference in signal strength between adjacent base stations. However, in case of vertical handoff, since there is no comparable triggering information other than the signal strength of the WLAN hotspot network providing limited service coverage, the ping-pong effect is likely to occur.

1 is a diagram illustrating a ping pong effect occurring when the conventional vertical handoff method is implemented.

That is, according to FIG. 1, the vertical handoff threshold is set to one.

As such, when only one vertical handoff threshold ( χ _thresh ) is assumed, received signal strengths received by terminals staying in a border area of the WLAN hotspot network fluctuate slightly around the vertical handoff threshold. When a fluctuation occurs, a ping-pong effect may occur.

In addition, due to the limited coverage of the WLAN hotspot network, the UE may perform the vertical handoff to the third generation cellular network while performing the vertical handoff to the WLAN hotspot network. This phenomenon may increase the probability of failure of vertical handoff.

However, since the generation of the ping-pong effect due to the characteristic of the vertical handoff brings a very large load on the system compared to the horizontal handoff, a method for minimizing the ping-pong effect is urgently needed.

In addition, the subscriber needs to stay in a wireless LAN hotspot network for a long time, which provides low rates and high data rates.

Here, the following two methods are proposed as a conventional technique for minimizing the ping-pong effect.

According to one conventional technology, a terminal selects a network that provides the highest performance by using a cost function. And before performing vertical handoff to the selected network, while defined as the settling time (stability period, T _S) time monitor that provides a consistent performance in selected network and evaluate the results.

Where the settling time (T _S ) is l _handoff + T _makeup can be defined. l shows a vertical _handoff is the handoff delay time, _makeup T represents the time it takes to compensate for the loss caused by the vertical hand-off.

In addition, the performance of the selected network for monitoring and evaluation includes a change in the effective bandwidth and a change in the received signal strength (RSS) according to the mobility of the terminal.

Therefore, if the terminal can maintain consistent performance in the target wireless network during the settling time (T _S ), that is, it is expected that the effective bandwidth does not decrease above the reference value according to the change in the received signal strength, the vertical handoff is performed.

However, even if the target wireless network guarantees consistent performance during the settling time T _S , thereafter, the target wireless network may not guarantee consistent performance due to irregular mobility of the terminal.

Thus, according to this prior art, the ping-pong effect is not effectively prevented.

According to another prior art, it is determined whether the received signal strength RSS received from the WLAN hotspot network in the transition region t is above or below the vertical handoff threshold χ _thresh . After that, it is determined whether or not to perform the vertical handoff by monitoring the received signal strength continuously transmitted by a predetermined number λ _n .

However, due to the nature of the irregular wireless environment, the received signal strength received by the terminal is never linear. Therefore, even if the received number of received signal strengths λ _n is greater than or equal to the vertical handoff threshold, the received signal strength that is less than or equal to the vertical handoff threshold may be detected.

In this case, the process of monitoring the received signal strength again by a predetermined number λ _n without repeating the vertical handoff is repeated. That is, the vertical handoff from the third generation cellular network to the wireless LAN hotspot network and the vertical handoff from the wireless LAN hotspot network to the third generation cellular network are repeated.

Therefore, the ping-pong effect does not find a suitable time to perform vertical handoff, thereby increasing the probability of failure of vertical hand-off and causing performance degradation.

In addition, in the related art, it is decided not to perform the vertical handoff even with only one signal attenuation among the received signal strengths detected within a predetermined time period.

However, depending on the wireless situation, the received signal strength received from the WLAN hotspot network may be temporarily attenuated rapidly. However, when the vertical handoff is determined by one received signal strength detection, the vertical handoff may not be determined even though sufficient received signal strength is received from the WLAN hotspot network.

In addition, similarly, the received signal strength received from the WLAN hotspot network may temporarily increase rapidly. However, when the vertical handoff is determined by one received signal strength detection, the vertical handoff may not be determined despite receiving the weak received signal strength from the WLAN hotspot network. This phenomenon occurs because the actual received signal strength received by the terminal is not linear even if the terminal is not moving.

Therefore, the technical problem to be achieved by the present invention is to use the first threshold when determining whether the first vertical handoff from the first network to the second network, and whether or not the second vertical handoff from the second network to the first network. In the case of determining, it provides a vertical handoff method using a second threshold having a value less than the first threshold.

In addition, another technical problem to be achieved by the present invention is to provide a vertical handoff method using the result of predicting the variation pattern of the signal strength received from the second network.

In addition, another technical problem to be achieved by the present invention is to provide a vertical handoff method using the result of predicting the variation pattern of the signal strength using the least square method.

In addition, another technical problem to be achieved by the present invention is to provide a vertical handoff method for determining whether the first vertical handoff by predicting the variation pattern of the signal strength when the signal strength received from the second network is greater than the first threshold. .

In addition, another technical problem to be achieved by the present invention is to provide a vertical handoff method for determining whether or not the second vertical handoff by predicting the variation pattern of the signal strength when the signal strength received from the second network is less than the second threshold.

According to a feature of the present invention for achieving the above-described problem,

Vertical handoff method,

A method for vertical handoff of a terminal that can be connected to a first network and a narrow second network having relatively wide service coverage in a region where service coverage overlaps between heterogeneous networks, the method comprising: (a) selling a serving network of the terminal; Cutting step; (b) when the serving network is the first network, when the received strength of the signal is greater than or equal to a first threshold, a variation pattern of the signal strength is estimated using a result of predicting a variation pattern of the signal strength; Determining whether 1 vertical handoff is made; And (c) when the serving network is the second network, when the signal strength received from the second network is less than or equal to a second threshold, whether a second vertical handoff is performed by using a result of predicting a variation pattern of the signal strength. And determining, the first threshold having a value greater than the second threshold.

According to another feature of the invention,

Vertical handoff method,

A method of vertical handoff of a terminal that can be connected to a first network and a narrow second network having relatively wide service coverage in an area where service coverage overlaps between heterogeneous networks, the method comprising: (a) from the second network during a predetermined time interval. Predicting the variation pattern by converting the received signal strengths into a linear form; (b) determining whether to perform a first vertical handoff from the first network to the second network by using the result of predicting the variation pattern; And (c) determining whether to perform a second vertical handoff from the second network to the first network by using the result of predicting the variation pattern.

According to another feature of the invention,

Vertical handoff method,

In a vertical handoff method when a serving network of a terminal accessible to a first network having a relatively broad service coverage and a narrow second network in a region where service coverage overlaps between heterogeneous networks is a first network, (a) the first handoff method Detecting the presence or absence of a signal strength corresponding to the first threshold or more among signal strengths received from a network; (b) when detecting a signal strength above the first threshold, predicting a variation pattern based on the signal strengths received for a predetermined time; (c) if the signal strength increases as a result of the prediction of the variation pattern, determining a first vertical handoff that uses a target network as the second network; And (d) waiting in the serving network when the signal strength decreases as a result of the prediction of the variation pattern.

According to another feature of the invention,

Vertical handoff method,

A vertical handoff method in a case where a serving network of a terminal accessible to a first network having a relatively broad service coverage and a narrow second network in a region where service coverage overlaps between heterogeneous networks is a second network, (a) the first handoff method Detecting the presence or absence of a signal strength corresponding to the second threshold value among signal strengths received from a network; (b) when detecting a signal strength below the second threshold, predicting a variation pattern based on the signal strengths received for a predetermined time; (c) when the signal strength decreases as a result of the prediction of the variation pattern, determining a second vertical handoff that uses a target network as the first network; And (d) waiting in the serving network when the signal strength increases as a result of the prediction of the variation pattern.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and like reference numerals designate like parts throughout the specification. In addition, when a part is said to "include" a certain component, this means that it may further include other components, except to exclude other components unless otherwise stated.

A vertical handoff method according to an embodiment of the present invention will now be described in detail with reference to the accompanying drawings.

First, the vertical handoff is divided into a first vertical handoff and a second vertical handoff.

In this case, the first vertical handoff is a vertical handoff performed in a MI (moving in) scenario, that is, the first network to the second network. The second vertical handoff is a moving out (MO) scenario, that is, a vertical handoff performed from the second network to the first network.

Here, the first network may be referred to as an overlay network as a network having a relatively large service coverage in an area where service coverage overlaps between heterogeneous networks. For example, it is a network providing global coverage, such as a third generation cellular network.

In addition, the second network may be referred to as an underlay network as a network having a relatively narrow service coverage in an area where service coverage overlaps between heterogeneous networks. For example, it is a network that provides limited coverage, such as a WLAN hotspot network.

Heterogeneous wireless networks also refer to wireless networks having different characteristics from one another. In this case, the criteria of different characteristics may be a service coverage and a wireless access scheme.

Meanwhile, the vertical handoff between the heterogeneous wireless networks is performed through the following three processes.

That is, the first process is a process of detecting an access network available to the terminal, which is referred to as "network detection."

The second process is a process in which the terminal makes a decision on when to use any access network, which is called a "handoff decision." This is expected to have the greatest impact on subscribers' quality of service.

The third process is a process in which the terminal performs handoff for accessing the selected target access network after the handoff decision, which is referred to as 'handoff execution'.

Among these, the 'handoff decision' may use the following measurements for selecting the optimal network. That is, it is desirable to consider all of the received signal strength, service type, data rate, QoS, and terminal speed / direction of the networks detected by the terminal.

However, in the vertical handoff determination method according to an embodiment of the present invention, the received signal strength (RSS) received from the second network having a narrow coverage from the service will be considered.

FIG. 2 is a diagram illustrating a network configuration in which a third generation cellular network and a WLAN network hotspot are overlapped according to an embodiment of the present invention, illustrating a theoretical propagation range of each network.

According to this overlapped network configuration, several micro or pico cells are gathered in one macro cell to form a single hot-spot area, which has an overlapping service area. The base heterogeneous wireless network systems interwork.

As shown in FIG. 2, the network configuration includes a third generation cellular network 100, a wireless LAN hotspot network 200, and a common core network 300.

Here, the common core network 300 provides interworking between the third generation cellular network 100 and the WLAN hotspot network 200.

The common core network 300 is called a GGSN (Gateway GPRS Support Node, hereinafter referred to as GGSN) / SGSN (Serving GPRS Support Node, hereinafter referred to as SGSN) 301, RNC (Radio Network Controller, hereinafter referred to as RNC) 303, border gateway 305, media gateway 307, and router 309.

Here, the GGSN / SGSN 301 and the RNC 303 are respective access nodes constituting the wireless access network and the core network of the third generation cellular network 100.

The border gateway 305 is a gateway for accessing the Internet from the common core network 300.

The media gateway (MG) 307 is a connection point to the third generation cellular network 100 and the common core network 300.

The router 309 is a router for accessing the common core network 300 in the WLAN hotspot network 200.

In this common core network 101, there is an interworking service server (311).

In this case, the propagation ranges 101 and 201 of the third generation cellular network 100 and the wireless LAN hotspot network 200 are different from each other and overlap each other.

In addition, the terminal 400 is a multi-mode terminal capable of accessing all wireless network systems connected to the common core network 300. The multi-mode terminal 400 may perform vertical handoff of a moving-in (MI) scenario and a moving-out (MO) scenario.

3 to 5 illustrate various examples in which the ping-pong effect is prevented in the vertical handoff method according to an exemplary embodiment of the present invention.

First, according to FIGS. 3 to 5, the first threshold TH _MI for the first vertical handoff decision and the second threshold TH _MO for the second vertical handoff decision are set differently. The relationship between the first threshold TH _MI and the second threshold TH _MO is as follows.

At this time, the first threshold TH _MI is set larger than the second threshold TH _MO . Accordingly, when determining the first vertical handoff, the vertical handoff is performed when the received signal strength is sufficiently larger than when determining the second vertical handoff.

That is, after determining the second vertical handoff from the second network (wireless LAN hotspot network) to the first network (third generation cellular network), requesting the first vertical handoff from the second network (wireless LAN hotspot network) immediately. prevent.

In addition, by lowering the second threshold for the second vertical handoff decision relatively, it provides an additional effect of staying in the second network (wireless LAN hotspot network) for as long as possible and providing high data rate.

In addition, the ping-pong effect can be prevented by setting different threshold values between the first vertical handoff and the second vertical handoff.

That is, as shown in FIG. 3, the first vertical handoff is determined at a point where the received signal strength is greater than or equal to the first threshold TH _MI , that is, P point. In addition, the second vertical handoff is determined at a point where the received signal strength is equal to or less than the second threshold TH _MO , that is, Q point. Therefore, the ping-pong effect does not occur even if the received signal strength causes variation A in a small width between the P point and the Q point.

As shown in FIG. 4, the first vertical handoff is determined at the R point. Therefore, even if the received signal strength causes variation B after the R point, the ping-pong effect does not occur.

As shown in FIG. 5, the first vertical handoff is determined at S point. Therefore, even if the received signal strength causes variation C before the S point, the ping-pong effect does not occur.

6 to 7 illustrate examples of prediction of a received signal strength variation pattern in a vertical handoff method according to an exemplary embodiment of the present invention.

)을 토대로 선형 형태의 수신 신호 세기 변이 패턴을 예측한다. 그리고 이와 같이 예측한 수신 신호 세기의 변이 패턴을 이용하여 제1 또는 제2 버티컬 핸드오프를 결정한다. That is, as shown in FIG. 6, a set of approximations of received signal strengths periodically detected during a predetermined time period (variation section)

) To predict the received signal intensity variation pattern in the linear form. The first or second vertical handoff is determined using the predicted variation pattern of the received signal strength.

In this case, the variation pattern of the signal strength received from the second network may be predicted by a best-fitting curve derived by using a method of least squares.

Then, the performance of the vertical handoff is determined using the sign (ie, positive, '+' or negative, '-') of the variation pattern of the received signal strength.

Therefore, we propose a method of predicting the variation pattern of the received signal strength using the least square method. Here, the least square method is to obtain a least squares line having a minimum sum of deviations squared from a set of received signal strengths received from the second network during a certain time interval.

A method of predicting the variation pattern of the received signal strength using the least square method will be described in detail as follows.

, n≥2})을 근사화한 것으로 다음 수식으로 표현되는 직선이다.First, the minimum square line S representing the variation pattern of the received signal strength is a set of samples of the received signal strength ({

, n≥2}), which is a straight line represented by the following equation.

S _i = σ + θ t _i

Where n is the total number of detections (n ≧ 2) of the received signal strength for accurate vertical handoff determination and is based on experimental values. And ti represents a predetermined time (x-axis) until completion of received signal strength detection for vertical handoff determination. Si also corresponds to the Y-axis as the received signal strength of the least squares (S). σ is the point where the least square line S and the Y-axis intersect, and θ is the slope of the least square line S.

In this case, when both ti and Si are given, σ and θ are unknown coefficients. Θ is an important variable for determining the variation pattern of the received signal strength.

At this time, the best fitting curve function f (X) having estimated the least squares has a least square error (π). For example,

Then, the unknown coefficients σ and θ calculate the zero first derivatives by the following equation to obtain the least square error Π.

Then, σ and θ can be obtained by expanding Equation 4 as shown below.

Using the above-described Equations 2 to 5, the least square line representing the received signal intensity variation pattern may be calculated.

Here, if the slope of the least square line is positive (+), it is predicted that the terminal enters the second network, that is, the wireless LAN hotspot network region. In addition, when the slope of the least square line is negative, it is predicted that the terminal leaves the second network, that is, the wireless LAN hotspot network area.

The first or second vertical handoff is determined according to whether the minimum square line, that is, the variation pattern of the received signal strength is positive (+) or negative (−).

However, some abnormal situations may occur when predicting the variation pattern of the received signal strength using the least square method. This will be described with reference to FIG. 7.

That is, as shown in FIG. 7, even though the variation pattern of the received signal strength, that is, the slope of the minimum square line is positive, the received signal strength of the minimum square line is not greater than the first threshold TH _MI . Things can happen. This is due to the temporary increase in the received signal strength according to the wireless environment. For example,

In order to prepare for such an abnormal situation, after determining whether the variation pattern of the received signal strength is positive (+), the received signal strength of the least square line becomes the first threshold value when the interval ends at a certain time as shown in the following equation. TH _MI ).

은 일정 시구간이 종료되는 시점에서 최소 자승선의 값 즉 수신 신호 세기를 의미한다.here

Denotes the value of the minimum square line, that is, the received signal strength at the end of a certain time period.

In this case, when the following Equation 7 is satisfied, the first vertical handoff is determined.

However, if the Equation 7 is not satisfied, it decides to wait in the serving network. A process of detecting a received signal strength that is greater than or equal to a first threshold is performed.

Based on the above description, a series of processes of the vertical handoff method will be described.

8 illustrates a vertical handoff method according to a first embodiment of the present invention.

As shown in FIG. 8, first, a procedure of determining a serving network to which a terminal is connected is performed.

That is, it is determined whether the serving network is the first network (S101).

If it is determined in step S101 that the serving network is the first network, a procedure for determining the first vertical handoff is performed.

That is, the signal strength received from the second network is detected (S103).

Then, the received signal strength detected in the step S103 is compared with the first threshold value TH _MI (S105).

In operation S107, a variation pattern of the received signal strength is predicted.

Then, it is determined whether to perform the first vertical handoff using the target network as the second network by using the comparison result in step S105 and the variation pattern prediction in step S107.

On the other hand, as a result of the determination in step S101, if the serving network is not the first network, it is determined whether the serving network is the second network (S111).

As a result of the determination in step S111, when the serving network is the second network, a procedure for determining a second vertical handoff is performed.

That is, signal strength received from the second network is detected (S113).

Then, the received signal strength detected in the step S113 is compared with the second threshold TH _MO (S115).

In operation S117, the variation pattern of the received signal strength is predicted.

Then, it is determined whether to perform the second vertical handoff using the target network as the first network by using the comparison result in step S115 and the variation pattern prediction in step S117 (S119).

9 is a view showing a vertical handoff method according to a second embodiment of the present invention, showing a first vertical handoff method when the serving network is the first network.

As shown in FIG. 9, first, the terminal, which is connected to the first network (S201), detects the received signal strength periodically transmitted by the second network (S203).

Then, it is determined whether there is a detection of the received signal strength having a strength equal to or greater than a first threshold TH _MI among the received signal strengths detected in the step S203 (S205). In this case, if the received signal strength of the first threshold value TH _MI or more is not detected, the steps S203 and S205 are repeated.

Then, in step S205, when detecting a received signal strength having a strength equal to or greater than the first threshold TH _MI , a timer, that is, a predetermined time period (variation interval), is set for a guard time. (S207).

Then, the received signal strength received from the second network is measured and collected periodically until the end of the predetermined time period set in step S207 (S209 and S211).

When the predetermined time period ends, one minimum square line representing a variation pattern of the received signal strength is derived by approximating the set of received signal strengths measured in the steps S209 and S211 (S213).

For detailed description of the step S213, refer to the description of FIGS. 6 to 7.

Next, the slope sign of the least square line derived in the step S213 is determined to determine whether to perform the first vertical handoff.

That is, it is determined whether the slope θ is greater than zero (S215).

As a result of the determination in step S215, when the slope θ is greater than zero, since the variation pattern of the received signal strength is positive, the first vertical handoff is determined. However, at this time, in step S209, S211, and S213, the received signal strength and the magnitude of the first threshold value TH _MI received at the end of the predetermined time period are compared (S217).

As a result of the comparison (S217), when the received signal strength is greater than the first threshold TH _MI , a first vertical handoff is determined (S219). That is, the terminal may perform the first vertical handoff using the target network as the second network.

And, the comparison result (S217). When the received signal strength is smaller than the first threshold TH _MI , the terminal waits in the serving network, that is, the first network, of the terminal (S223).

Here, with reference to FIGS. 6 to 7, the contents of performing the step S217 are described.

In addition, when the slope θ is not greater than zero (0), as a result of the determination in step S215, since the slope θ is negative (S221), the terminal waits in the serving network of the terminal (S223). ).

After the step S223, the process returns to the step S203 and the steps S203 to S223 are repeated.

10 is a view showing a vertical handoff method according to a third embodiment of the present invention, showing a second vertical handoff method when the serving network is the second network. The second vertical handoff method is also similar to the first vertical handoff method.

As shown in FIG. 10, first, a terminal connected to a second network (S301) periodically detects a received signal strength received from the second network (S303).

Then, it is checked whether there is a detection of the received signal strength having a strength equal to or greater than a second threshold TH _MO among the received signal strengths detected in the step S303 (S305). At this time, if the received signal strength of the second threshold TH _MO or more is not detected, the steps S303 and S305 are repeated.

Next, when detecting a received signal strength having a strength equal to or less than the second threshold TH _MO in step S305, the terminal sets a timer for the guard time, that is, a predetermined time period (variation interval) (S307).

In addition, the received signal strengths received from the second network are measured and collected periodically until the end of the predetermined time period (S307 and S309).

When the predetermined time period ends (S311), a set of received signal strengths measured in steps S307 and S309 is approximated to derive a minimum square line representing a received signal strength variation pattern (S313).

Then, it is checked whether the inclination θ of the least square line derived in step S313 is negative (S315).

As a result of the check, when the inclination θ of the least square line is negative, the variation pattern of the received signal strength is positive, so that the terminal has a second network having the target network as the first network. Determine vertical handoff. However, at this time, the received signal strength received at the end of the predetermined time period in the step (S307, S309, S311) is compared with the second threshold ( TH _MO ) (S317).

Then, when the received signal strength is less than the second threshold TH _MO , the comparison result (S317) determines the second vertical handoff (S319). That is, the terminal may perform the second vertical handoff using the target network as the first network.

However, when the received signal strength exceeds the second threshold TH _MO , the comparison result S317 waits in the serving network of the terminal, that is, the second network S323.

As in FIG. 9, the description of FIG. 6 to FIG. 7 is referred to for the contents of performing the step S317.

On the other hand, when the slope of the least square line is not negative (-) in the step (S315), the slope is positive (S321) and waits in the serving network (S323).

After the step S323, the process returns to the step S303, and the steps S303 to S323 are repeated.

The embodiments of the present invention described above are not implemented only through the apparatus and the method, but may be implemented through a program for realizing a function corresponding to the configuration of the embodiment of the present invention or a recording medium on which the program is recorded. Implementation may be easily implemented by those skilled in the art from the description of the above-described embodiments.

The scope of the present invention is not limited to the above-described embodiments, but various modifications and improvements of those skilled in the art using the basic concept of the present invention as defined in the following claims are also within the scope of the present invention.

By the above configuration, it is possible to prevent the ping-pong effect due to unnecessary vertical handoff.

In addition, performance degradation due to an increase in delay time of vertical handoff, a decrease in data throughput and terminal battery efficiency, and an increase in the probability of a vertical handoff failure can be prevented.

Claims (20)

In the vertical handoff method of a terminal capable of connecting to a first network and a narrow second network having a relatively wide service coverage in an area where service coverage overlaps between heterogeneous networks, (a) determining a serving network of the terminal; (b) when the serving network is the first network, when the received strength of the signal is greater than or equal to a first threshold, a variation pattern of the signal strength is estimated using a result of predicting a variation pattern of the signal strength; Determining whether 1 vertical handoff is made; And (c) when the serving network is the second network, when the signal strength received from the second network is less than or equal to a second threshold value, determining whether the second vertical handoff is performed using a result of predicting a variation pattern of the signal strength; Including the steps of: And wherein the first threshold has a value greater than the second threshold. The method of claim 1, The first network comprises a third generation cellular network providing global service coverage, And the second network comprises a wireless lan hotspot network that provides limited service coverage. The method of claim 1, In step (b), (Iii) predicting a variation pattern based on signal strengths received from the second network during a predetermined time interval when signal strengths greater than or equal to the first threshold are received; (Ii) determining a first vertical handoff to the second network when the signal strength increases as a result of the prediction of the variation pattern; And (Iv) waiting in the first network when the signal strength decreases as a result of the prediction of the variation pattern Vertical handoff method comprising a. The method of claim 1, Step (c) is, (Iii) predicting a variation pattern based on the signal strengths received from the second network during a predetermined time period when a signal strength less than the second threshold is received; (Ii) determining a second vertical handoff to the first network when the signal strength decreases as a result of the prediction of the variation pattern; And (Iv) waiting in the second network when the signal strength increases as a result of the prediction of the variation pattern Vertical handoff method comprising a. The method according to claim 3 or 4, In the step (iii), And converting the signal strengths into a linear form to predict the variation pattern. The method of claim 5, In the step (iii), A vertical handoff method comprising predicting the disparity pattern using a method of least squares. In the vertical handoff method of a terminal connectable to a first network and a narrow second network having a relatively wide service coverage in an area where service coverage overlaps between heterogeneous networks, (a) predicting a variation pattern by converting signal strengths received from the second network into a linear form during a predetermined time period; (b) determining whether to perform a first vertical handoff from the first network to the second network by using the result of predicting the variation pattern; And (c) determining whether to perform a second vertical handoff from the second network to the first network by using the result of predicting the variation pattern. Vertical handoff method comprising a. The method of claim 7, wherein In step (a), (Iii) calculating minimum square lines of the signal strengths using a least squares method; (Ii) when the slope of the least square line is positive (positive, '+'), the shift pattern predicts that the terminal enters the second network; and (I) when the slope of the least square line is negative (eg, negative), the variation pattern predicts that the terminal deviates from the second network Vertical handoff method comprising a. The method of claim 8, In step (b), Determining to perform the first vertical handoff when the slope of the least square is positive ('+'); and Determining a standby in the first network if the slope of the least square is negative (−−); Vertical handoff method comprising a. The method of claim 8, Step (c) is, Determining to perform the second vertical handoff when the slope of the least square is negative (+); and Determining a wait in the second network if the slope of the least square is positive (−−); Vertical handoff method comprising a. The method according to claim 8, wherein In step (iii), Approximating the set of sampling the signal strength to obtain a linear minimum square line (S); And Obtaining a slope θ of the least square line using a zero-first derivative of the least square error Π of the least square line S Vertical handoff method comprising a. In the vertical handoff method when the serving network of a terminal that can be connected to a first network having a relatively wide service coverage and a narrow second network in a region where service coverage overlaps between heterogeneous networks is a first network, (a) detecting the presence or absence of a signal strength corresponding to the first threshold or more among the signal strengths received from the second network; (b) when detecting a signal strength above the first threshold, predicting a variation pattern based on the signal strengths received for a predetermined time; (c) if the signal strength increases as a result of the prediction of the variation pattern, determining a first vertical handoff that uses a target network as the second network; And (d) waiting in the serving network if the signal strength decreases as a result of the prediction of the variation pattern Vertical handoff method comprising a. The method of claim 12, Step (c) is, Checking whether the received signal strength is greater than or equal to the first threshold when the predetermined time interval ends when the signal strength increases; And Determining the first vertical handoff when the signal strength received at the end of the predetermined time interval is greater than or equal to the first threshold value; Vertical handoff method comprising a. The method of claim 13, Waiting in the serving network when the signal strength received at the end of the predetermined time interval is less than the first threshold; Vertical handoff method comprising a. In the vertical handoff method when the serving network of a terminal that can access a first network having a relatively wide service coverage and a narrow second network in a region where service coverage overlaps between heterogeneous networks is a second network, (a) detecting the presence or absence of a signal strength corresponding to the second threshold or less among the signal strengths received from the second network; (b) when detecting a signal strength below the second threshold, predicting a variation pattern based on the signal strengths received for a predetermined time; (c) when the signal strength decreases as a result of the prediction of the variation pattern, determining a second vertical handoff that uses a target network as the first network; And (d) if the signal strength increases as a result of the prediction of the variation pattern, waiting in the serving network Vertical handoff method comprising a. The method of claim 15, Step (c) is, If the signal strength decreases, checking whether the received signal strength at a time point when the predetermined time ends is less than or equal to the second threshold; And Determining the second vertical handoff when the signal strength is below the second threshold Vertical handoff method comprising a. The method of claim 16, Step (c) is, Waiting in the serving network when the signal strength exceeds the second threshold Vertical handoff method further comprising. The method according to any one of claims 12 to 17, After waiting in the serving network, Vertical handoff method characterized in that to repeat the steps (a) to (d). The method according to any one of claims 12 to 17, In step (b), A vertical handoff method using the least squares derived using the least square method as the variation pattern of the signal strength. The method according to any one of claims 12 to 17, And wherein the first threshold has a value greater than the second threshold.

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