KR101084326B1 - Expected capacity based WLAN handoff processing method - Google Patents

Abstract

The present invention calculates in advance the " expected capacity ", which is a transmission capacity that can be expected when an IEEE 802.11 WLAN mobile terminal connects to a new wireless access point by using information such as location, signal strength, moving speed, and direction, and the like. The present invention relates to a method of selecting a wireless access point to be handed off as a reference. Specifically, a method of transmitting a location of a wireless access point to a mobile terminal, a method of calculating an expected capacity by the mobile terminal, and the like are proposed. Existing handoff methods have a disadvantage in that they do not properly reflect the performance of a radio link since the radio handoff target is determined based on only one physical value of a received signal strength or distance having high variability. On the contrary, the expected capacity suggested by the present invention reflects various physical values such as position, signal strength, moving speed, and direction to increase the reliability of the scale. In addition, the present invention reduces the unnecessary handoff and improves the transmission stability by using the interval performance measured for a predetermined time to calculate the expected capacity.

IEEE 802.11, WLAN, Handoff, Expected Capacity, Mobile Communication, Wireless Access Point

Description

Expected Capacity-based Handoff Method for WLAN}

The present invention calculates in advance the " expected capacity ", which is a transmission capacity that can be expected when an IEEE 802.11 WLAN mobile terminal connects to a new wireless access point by using information such as location, signal strength, moving speed, and direction, and the like. The present invention relates to a method of selecting a wireless access point to be handed off as a reference. Specifically, a method of transmitting a location of a wireless access point to a mobile terminal, a method of calculating an expected capacity by the mobile terminal, and the like are proposed.

In an IEEE 802.11 WLAN environment, a wireless terminal periodically checks a state of a connected wireless access point. When it is determined that smooth service is not provided, the mobile terminal performs handoff. In this case, a search process is performed to find nearby wireless access points.

At this time, the IEEE 802.11 standard provides an active scanning and passive scanning function to search for neighboring wireless access points.

In the active search, the mobile station broadcasts a probe request frame and receives a probe response frame from wireless access points that respond to the probe request frame. The time taken here is called a probe response wait time. This process is performed for all channels provided by the wireless radio, thus taking up most of the handoff delay time (about 11 channels for IEEE 802.11b / g and about 19 channels for IEEE 802.11a).

The manual search is received for a predetermined time through a beacon frame generated by the wireless access point periodically to search for neighboring wireless access points. This process is also performed for all channels, which also causes a large delay time.

The fundamental cause of the problem with the handoff delay time is because the IEEE 802.11 WLAN standard is not designed in consideration of the mobility of the terminal. Therefore, the existing handoff methods based on the standard are manually disconnected from the currently connected wireless access point, and then go through a process of searching for a neighboring wireless access point, authentication and connection. At this time, it was confirmed from the existing research that the channel search delay time occupies most of the handoff delay time in the wireless access point search process.

In order to reduce the delay time, many methods for actively predicting the handoff time before the connection with the wireless access point are disconnected have been proposed. However, most of these studies still have a problem in that frequent or unnecessary handoff may occur by taking a method of accessing a radio access point close to a mobile terminal at a specific time or having a large variability of received signal strength.

As such, the WLAN technology is the most popular communication protocol for supporting a broadband wireless access network. Recently, users who want to support real-time multimedia services through the WLAN are increasing even while moving. In order to support the mobility of the WLAN, the handoff function of the mobile terminal is essential. However, it can be seen from the handoff delay problem that only the WLAN handoff scheme based on the existing IEEE 802.11 standard has a limitation in maintaining real-time multimedia services.

Accordingly, the present invention has been made to solve the above problems, based on the moving speed and the direction of the mobile terminal through a real-time positioning device such as GPS to calculate the expected capacity with the neighboring wireless access point in advance to access based on this. An object of the present invention is to provide a WLAN handoff processing method for selecting a wireless access point. In this case, since the expected capacity is calculated in consideration of information such as the location, signal strength, moving speed and direction of the mobile terminal, performing the handoff through this can ensure higher network capacity and connectivity than the conventional handoff method.

Another object of the present invention is to provide an expected capacity-based WLAN handoff processing method applicable to all wireless mobile terminals receiving a service by accessing a wireless network for handoff of the most popular WLAN technology popularly used in a local area network. It is.

It is still another object of the present invention to enable the mobile terminal to seamlessly process data in a space where the wireless access point is appropriately arranged, and thus to realize the economic benefit of the wireless terminal that needs to continuously transmit / receive data. It is to provide a LAN handoff processing method.

Another object of the present invention is an essential requirement for an effective handoff of a mobile vehicle in a road network in which a plurality of wireless access points exist, and an expected capacity-based WLAN handoff can be maximized through the application of the present invention. To provide a treatment method.

A feature of the expected capacity-based WLAN handoff processing method according to the present invention for achieving the above object is (A) when performing the handoff of the WLAN, the wireless positioning equipment and GPS satellites mounted on the mobile terminal; Acquiring a movement level including at least one of position information, a movement direction, and a movement speed of the mobile terminal; and (B) a mobile terminal considering the movement direction of the mobile terminal at a predetermined time based on the movement level of the mobile terminal; Calculating distances between the mobile terminal and each wireless access point by using a change in the position of each other and a position between each wireless access point in the vicinity, and (C) calculating the distance between the mobile terminal and the wireless access point based on the calculated path loss model. Converting the received signal strength value based on a power loss (path loss) according to a distance; and (D) defining the converted received signal strength value in advance. Converting the transmission rate based on the hardware specification and the experimental data, (E) calculating the expected capacity by adding up the transmission rates with the wireless access point for a predetermined time, and (F) all wireless And when the calculation of the expected capacity of the access point is completed, performing the handoff with the wireless access point having the largest expected capacity.

Preferably, the handoff transition of the WLAN is characterized in that the handoff transition is performed when at least one or more of the mobile terminal's mobility level and the average received signal strength value with the wireless access point are larger than the threshold value.

Preferably, before the step (A) (A1) collecting the location information of the wireless access point of the surroundings through the beacon frame of at least one or more wireless access points and periodically storing the location information of the wireless access point in the table, (A2) mobile terminal Based on the location information of the mobile terminal acquired through the wireless positioning equipment and GPS satellites mounted on the mobile terminal and the location of the mobile terminal detected based on the moving direction and the moving speed and the location information of the wireless access point acquired through the beacon frame. Measuring at least one or more of an average received signal strength value of the currently connected radio access point detected; (A3) at least one of an average received signal strength value of the measured mobile terminal and the connected radio access point in advance; And setting whether or not to perform handoff by comparing with a set threshold value. All.

를 적용하여 전력 손실(경로 손실)을 생성하며, 이때 상기 d(t)는 t초에 이동 단말과 무선접속점 사이의 거리를, 상기

는 손실된 신호 세기 값을, 상기

,

는 상수인자인 것을 특징으로 한다.Preferably the path loss model of step (C) is

To generate power loss (path loss), where d (t) is the distance between the mobile terminal and the wireless access point at

Is the lost signal strength value,

,

Is a constant factor.

Preferably, the hardware specification and the experimental data are received signal strength values respectively measured according to the distance between the connected mobile terminal and the wireless access point.

Preferably, in step (F), when the calculation of the expected capacities of all the wireless access points is completed, detecting the wireless access point having the largest expected capacity, and the detected wireless access point is currently connected to the mobile terminal. If it is characterized in that it comprises the step of maintaining a connection with its wireless access point without performing the handoff.

As described above, the IEEE 802.11 WLAN handoff processing method based on the expected capacity according to the present invention obtains the expected capacity by using a combination of the distance of the mobile terminal, the received signal strength, the speed and the moving direction of the mobile terminal, and based on the estimated capacity. By performing handoffs, high network capacity and connectivity can be guaranteed, reducing frequent handoffs and providing stable performance.

In this case, the expected capacity suggested by the present invention may improve reliability of the scale by reflecting various physical values such as distance of the mobile terminal, received signal strength, moving speed, and direction.

In addition, by using the interval performance measured for a predetermined time to calculate the expected capacity, it is possible to further reduce unnecessary handoff and increase transmission stability.

In addition, the expected capacity due to the direction of movement has a greater advantage when the moving path is straight than when the moving path is curved, so that the vehicle moving on the road can be expected to have a great effect when equipped with the terminal applying the present invention technique. have.

Other objects, features and advantages of the present invention will become apparent from the following detailed description of embodiments with reference to the accompanying drawings.

A preferred embodiment of the expected capacity-based WLAN handoff processing method according to the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but can be embodied in various forms, and only the present embodiments are intended to complete the disclosure of the present invention and to those skilled in the art to fully understand the scope of the invention. It is provided to inform you. Therefore, the embodiments described in the specification and the drawings shown in the drawings are only the most preferred embodiments of the present invention and do not represent all of the technical idea of the present invention, various equivalents that may be substituted for them at the time of the present application It should be understood that there may be water and variations.

1 is a block diagram illustrating a handoff prediction time point and an execution process of a wireless mobile terminal according to an embodiment of the present invention.

Referring to FIG. 1, position information, a moving direction, and a moving speed are acquired through the wireless positioning equipment mounted on the mobile terminal A1 and the GPS satellites A8. Then, the mobile terminal A1 calculates the expected capacities of the respective wireless access points by using a combination of the distance, the received signal strength, the speed and the moving direction of the mobile terminal thus acquired (A6, A7). At this time, the location information of each wireless access point is received through a beacon frame for transmitting its own location information from the wireless access point (A2, A3).

The wireless access point having the largest expected capacity is selected among the expected capacity of the neighboring wireless access point thus configured to remove or reduce the time of detecting the broken wireless link and the search time of the new neighboring wireless access point.

In contrast, the handoff methods based on the existing WLAN standard are performed after the radio link between the currently connected wireless access point A2 and the mobile terminal A1 is disconnected. That is, when the mobile terminal A1 moves out of its own direction and moves out of the communication range of the currently connected first wireless access point A2, it performs a series of processes to find another second wireless access point A3 in the vicinity. it means. In this case, the total delay time for handoff includes the time for detecting the disconnection of the radio link and the time for searching for a new neighbor radio access point.

Referring to the accompanying drawings, the operation of the wireless LAN handoff processing apparatus based on the expected capacity according to the present invention configured as described above will be described in detail as follows. The same reference numerals as in FIG. 1 refer to the same members performing the same function.

2 is a flowchart illustrating a method for processing WLAN handoff based on expected capacity according to the present invention.

Referring to FIG. 2, first, each of the wireless access points A2 and A3 transmits its location information in the beacon frames A4 and A5, and the mobile terminal A1 receives the beacon frame A4. Collect the location information of the wireless access point of the surroundings through A5) and periodically store the location information of the wireless access point in the table (S10).

Subsequently, the mobile terminal A1 acquires the location information, the moving direction, and the moving speed through the installed wireless positioning equipment and the GPS satellite A8 to classify the moving level of the mobile terminal in stages, and also receives the current received in the beacon frame. The controller acquires the location information of the connected wireless access point and measures and stores the average received signal strength value with the connected wireless access point (S20).

After comparing the presence or absence of a predetermined threshold value based on the measured movement level of the mobile terminal A1 and the average received signal strength value with the connected wireless access point, the handoff below is greater than the threshold value. Perform the following process for, otherwise repeat the process (S10 ~ S30) (S30). At this time, the threshold value of the movement level is set to the speed value of the medium speed, and the threshold value of the average received signal strength value is preferably set to a value of 10 difference or more from the average value, which can be changed to a value arbitrarily set by an administrator. to be.

As an example, if the movement degree of the mobile terminal A1 is less than the medium speed (threshold value), it is determined that no handoff is necessary. If the movement degree is greater than the medium speed (threshold value), the handoff is determined to be necessary. do. In addition, if the average received signal strength value with the connected wireless access point shows a difference of 10 (threshold value) or less from the average value, it is determined that handoff is not necessary, and the average received signal strength value is 10 (threshold value) or more from the average value. If a difference is indicated, it is determined that handoff is necessary.

As such, when the mobile node A1 is changed from the stopped state to the medium speed or more and the reception signal state with the currently connected wireless access point is not good, it is determined that the handoff is necessary.

In addition, if at least one or more of the moving level of the mobile terminal A1 and the average received signal strength value with the radio access point for the handoff progress is greater than the threshold value, it is determined that the handoff is necessary. That is, it is determined that the handoff is necessary when the moving level of the mobile terminal A1 is greater than or equal to the medium speed or the average received signal strength is more than 10 differences from the average value.

And when the comparison result (S30), when the handoff is necessary, the mobile terminal A1 acquires the position information, the moving direction and the moving speed of the mobile terminal A1 through the mounted radio positioning equipment and the GPS satellite A8 ( S40). In this case, the position information, the moving direction, and the moving speed of the mobile terminal A1 acquired in step S20 may be used again.

In addition, the position change of the terminal in consideration of the moving direction of the mobile terminal A1 for a predetermined time (for example, during T0 to T3) based on the acquired movement level of the mobile terminal A1, and each wireless connection point ( Using the positions between A2 and A3, distances between the mobile terminal A1 and each wireless access point are calculated and stored (S50). That is, the predicted arrival point of the mobile terminal A1 may be predicted after a predetermined time based on the moving speed and the direction of the mobile terminal A1. The distance between the mobile terminal A1 and the wireless access points A2 and A3 is calculated in the moving path. Since the wireless access points A2 and A3 are periodically collected through the beacon frame and stored in a table, the distance between the mobile terminal A1 and the wireless access points A2 and A3 can be calculated.

The calculated distance is converted into a received signal strength value by applying the calculated distance between the mobile terminal A1 and the wireless access points A2 and A3 to the path loss model according to Equation 1 (S60).

는 손실된 신호 세기 값을 의미하며, 상기

,

는 상수인자로서 적용되는 환경에 맞게 조정된다. 따라서 무선접속점의 거리와 수신 신호 세기 특성에 따라 상수 인자(

,

)의 조절을 통해 경로 손실 모델을 보다 정확하게 보정할 수 있다. In this case, the d (t) refers to the distance between the mobile terminal A1 and the wireless access point (A2, A3) in t seconds,

Denotes a lost signal strength value, and

,

Is adjusted to the environment in which it is applied as a constant factor. Therefore, the constant factor (

,

), The path loss model can be calibrated more accurately.

In this way, since the power loss occurs as the distance from the mobile terminal A1 communicating due to the radio signal characteristics, it is defined as the path loss, and by estimating the power value to be lost from the path loss model according to Equation 1 The calculated distance can be converted into a received signal strength value.

Subsequently, the received signal strength value is converted by applying the path loss model to the transmission rate based on the hardware specification and the experimental data of FIG. 3 (S70). In general, wireless network card manufacturers specify the transmission speed according to the received signal strength. 3 is an example of the Cisco Aironet wireless cardbus adapter specification, which may be referred to the specification of a hardware product used in this way.

Basically, as the distance between the connected mobile terminal A1 and the wireless access point increases, the strength of the received signal gradually decreases, and the mobile terminal A1 communicates at a lower transmission speed in order to increase transmission stability. If the specification is not provided by the hardware manufacturer, or in order to calculate a more reliable expected capacity, the configuration diagram may be reconfigured to a value obtained by experimenting the received signal strength according to the distance with the wireless interface card actually used in the mobile terminal A1.

In this manner, the received signal strength value according to the moving path is converted into a transmission speed, and the expected capacity is calculated by summing (transmitting with respect to time) the transmission speeds with the wireless access point for a predetermined time (S80).

The wireless access point from which the expected capacity is calculated is checked whether the neighboring wireless access points are the last wireless access point of the stored table (S90), and if not, the process of handoff (B5 to B9) is repeated.

In addition, in the check result (S90), if the wireless access point whose expected capacity is calculated is the last wireless access point of the stored table, the wireless access point having the largest expected capacity is detected among the wireless access points stored in the table (S100).

In this case, it is determined whether the detected wireless access point is the same as the wireless access point currently connected to the mobile terminal A1 (S110), and if the determination result (S110) is the same, the wireless access point does not perform handoff with its own wireless access point. Maintaining the connection, repeating the process (S10 ~ S110), and if the determination result (S110) is not the same and performs the handoff with the wireless access point having the largest expected expected capacity (S120).

As such, based on the path loss model, the mobile terminal A1 basically calculates the expected capacities A6 and A7 that can be expected as much as actual experimental values (expected values corresponding to the table configuration diagram of FIG. 3). It is determined to perform handoff with the neighboring wireless access point having the largest result value.

Although the technical spirit of the present invention described above has been described in detail in a preferred embodiment, it should be noted that the above-described embodiment is for the purpose of description and not of limitation. In addition, those skilled in the art will understand that various embodiments are possible within the scope of the technical idea of the present invention. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

1 is a block diagram illustrating a handoff prediction time point and an execution process of a wireless mobile terminal according to an embodiment of the present invention;

2 is a flowchart illustrating a method for processing WLAN handoff based on expected capacity according to the present invention.

3 is a table showing the hardware specification and experimental data for inferring the transmission rate from the received signal strength value according to an embodiment of the present invention

DESCRIPTION OF THE REFERENCE NUMERALS

A1: wireless mobile terminal A2, A3: wireless connection point

A4, A5: beacon frame A8: positioning satellite

Claims (7)

(A) when the handoff transition of the wireless LAN is in progress, acquiring a movement level including location information, a moving direction, and a moving speed of the mobile terminal through a wireless positioning device and a GPS satellite installed in the mobile terminal; (B) calculating distances between the mobile terminal and each wireless access point by using the position change of the mobile terminal in consideration of the moving direction of the mobile terminal at a predetermined time based on the movement level of the mobile terminal and the position between the respective wireless access points. Steps, (C) converting the calculated distance between the mobile terminal and the wireless access point into a received signal strength value based on power loss (path loss) according to the distance calculated in the path loss model; (D) converting the converted received signal strength value to a transmission rate based on predefined hardware specifications and experimental data; (E) calculating the expected capacity by summing the converted transmission rates with the wireless access points for a predetermined time; (F) when the calculation of the expected capacities of all the wireless access points is completed, performing the handoff with the wireless access point having the largest expected capacity, the expected capacity-based WLAN handoff processing method. The method of claim 1, The handoff transition of the WLAN is performed according to the expected capacity based on the handoff when the at least one or more of the mobility level of the mobile terminal and the average received signal strength value with the wireless access point is greater than the threshold value. Treatment method. The method of claim 1, wherein before step (A) (A1) collecting location information of wireless access points in the vicinity through beacon frames of at least one wireless access point, and periodically storing the location information of the wireless access points in a table; (A2) The position information of the mobile terminal acquired through the wireless positioning equipment mounted on the mobile terminal and the GPS satellites, and the movement level of the mobile terminal detected based on the moving direction and the moving speed and the wireless access point acquired through the beacon frame. Measuring at least one or more of average received signal strength values of currently connected wireless access points detected based on the location information; (A3) setting whether to perform handoff by comparing at least one of the measured movement level of the mobile terminal and the average received signal strength value with the connected wireless access point with a preset threshold value. Expected capacity based WLAN handoff processing method. The method according to claim 2 or 3, The threshold value of the mobility level is a value of 10Km / h or more difference in the average moving speed, the threshold value of the average received signal strength value is a value of 10dBm difference or more in the average value based on the expected capacity-based WLAN handoff processing method. The method of claim 1, Path loss model of the step (C) is the formula

To generate power loss (path loss), where d (t) is the distance between the mobile terminal and the wireless access point at

Is the lost signal strength value,

,

Expected capacity-based WLAN handoff processing method characterized in that the constant factor. The method of claim 1, The hardware specification and the experimental data are expected capacity-based WLAN handoff processing method, characterized in that the received signal strength value respectively measured according to the distance between the connected mobile terminal and the wireless access point. The method of claim 1, wherein (F) When the calculation of the expected capacities of all the wireless access points is completed, detecting a wireless access point having the largest expected capacity; If the detected wireless access point is a wireless access point currently connected to a mobile terminal, maintaining the connection with its own wireless access point without performing a handoff; Way.

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