KR20200002154A - Method for wireless communication handoff and apparatus thereof - Google Patents

Abstract

The present invention relates to a handoff technique in which a terminal switches communication from one access point (AP) to another access point, wherein the connection with the first access point with which the terminal is currently communicating is maintained. Periodically monitor the received signal strength with the first access point and the surrounding access point in the state, and if the preset condition is satisfied with respect to the termination of communication with the first access point, among the neighboring access points based on the monitoring result. Select a second access point to which to switch communication, request a connection to the selected second access point, and when a response to the connection request is received, the terminal switches the communication from the first access point to the second access point.

Description

Wireless communication handoff method and apparatus according to the method

The present invention relates to a communication technology between an access point (AP) and a terminal connected via wireless communication, and in particular, a method for performing a high speed handoff for switching communication from one access point to another and It relates to a terminal according to the method.

The Wi-Fi handoff process according to the IEEE 802.11 standard is composed of a channel scanning process, an authentication phase, and an association phase. Among them, in the channel search process for searching for a new AP, the user's smartphone searches all Wi-Fi channels, and the handoff time increases rapidly by repeatedly performing the search process according to the surrounding channel environment.

Many researchers have proposed various modifications to reduce the Wi-Fi handoff delay time, but it is widely used in the market because it is often adopted as a standard and requires modification of the Wi-Fi protocol applied to communication devices. It is difficult to apply it immediately to commercially available wireless devices.

A. Mishra, M. Shin, and W. Arbaugh, "An empirical analysis of the IEEE 802.11 MAC layer handoff process," ACM SIGCOMM Comput. Commun. Rev., vol. 33, no. 2, pp. 93-102, Apr. 2003.

The technical problem to be solved by the present invention, in the conventional Wi-Fi handoff technology is to establish a communication by searching for a new access point from the point of communication disconnection by searching for and connecting a new access point after the communication with the previous access point is disconnected. It takes a lot of time to solve the inconvenience of delayed user experience, and the proposed techniques to reduce the Wi-Fi handoff delay time are required to change the standard Wi-Fi protocol to apply to current commercial devices I want to overcome difficult limits.

In order to solve the above technical problem, the handoff method of the wireless communication according to an embodiment of the present invention, (a) the connection with the first access point (AP) that the terminal is currently communicating with the maintenance (main) Periodically monitoring received signal strength with the first access point and the surrounding access point in a controlled state; (b) when the preset condition is met regarding the termination of communication with the first access point, selecting, by the terminal, a second access point to which to switch communication among the surrounding access points based on a monitoring result; (c) the terminal requesting to connect to the selected second access point; And (d) when the response to the connection request is received, the terminal switches communication from the first access point to the second access point.

In the handoff method of wireless communication according to an embodiment, the step (a) of periodically monitoring the received signal strength may include receiving, by the terminal, an event according to a received signal strength indicator (RSSI) change from a neighboring access point, or The received signal strength of the first access point may be measured periodically using a timer.

In the handoff method of the wireless communication according to an embodiment, the step (b) of selecting a second access point to which to switch the communication, (b1) the received signal strength from the first access point is greater than the signal threshold value Determining that maintaining a communication with the first access point is difficult if at least one or a combination of the two conditions is met if the first small condition and the second condition in which the distance between the terminal and the first access point is greater than a distance threshold are satisfied; It may include.

In the handoff method of the wireless communication according to an embodiment, the step (b) of selecting a second access point to switch communication to, (b2) the terminal receives the received signal strength from the surrounding access point from the monitoring result; And selecting a second access point to which to switch communication based on the reference. Also, in the step (b2), the received signal strength is compared with the value of the largest received signal strength among the neighboring access points and the received signal strength of the currently connected first access point, and the difference is greater than the efficiency threshold value. An access point corresponding to the largest value may be selected as the second access point. Furthermore, in the step (b2), when the difference between two values of the largest received signal strength among the neighboring access points is smaller than the comparison threshold value, the step (b2) may include the latest received signal from the change rate of the received signal strength of the corresponding two access points. An access point having the highest priority may be selected as the second access point by giving a relatively high weight to the strength.

In the handoff method of wireless communication according to an embodiment, the step (b) of selecting a second access point to which to switch communication may include: (b3) the terminal among the surrounding access points based on GPS information and a rotation angle; Selects an opposing candidate access point, calculates a distance between the terminal and the selected candidate access point, and communicates an access point whose calculated distance is smaller than a distance between the terminal and the first access point. May be selected as a second access point to be switched. In addition, the step (b3), considering the change in the distance between the terminal and the candidate access point with the passage of time, and the farther away from the terminal to give a relatively low weight to the candidate access point having the highest priority The second access point may be selected.

In the handoff method of wireless communication according to an embodiment, in the step (c) of requesting connection to the second access point, the terminal may request connection to the second access point in a unicast manner. .

On the other hand, the following provides a computer-readable recording medium having recorded thereon a program for executing the handoff method of wireless communication described above on a computer.

In order to solve the above technical problem, a terminal for performing a handoff (access point) with an access point (AP) according to an embodiment of the present invention, a communication unit for communicating with the access point according to the Wi-Fi protocol; A memory for storing a program for establishing communication with an access point based on the received signal strength received through the communication unit; And a processor configured to drive the program to perform handoff between access points, wherein the program stored in the memory is configured to maintain the connection with a first access point (AP) to which the terminal is currently communicating. The terminal periodically monitors the received signal strength with the first access point and the neighboring access points, and when a preset condition is met with respect to the termination of communication with the first access point, the terminal is configured to perform the control based on the monitoring result. Selecting a second access point to which communication is to be switched among neighboring access points, the terminal requests a connection to the selected second access point, and when a response to the connection request is received, the terminal accesses the first access point To divert communication from a second access point to a second access point May include words.

In a terminal performing a handoff with an access point according to an embodiment, the program stored in the memory may receive an event according to a change in a received signal strength indicator (RSSI) from a neighboring access point, or a timer. By using, it is possible to periodically measure the received signal strength of the first access point.

In a terminal performing handoff with an access point according to an embodiment, the program stored in the memory may include a first condition in which a received signal strength from the first access point is less than a signal threshold and the terminal and the first condition; If at least one or a combination of the two of the second conditions in which the distance between the access points is larger than the distance threshold is satisfied, it may be determined that maintaining communication with the first access point is difficult.

In a terminal performing a handoff with an access point according to an embodiment, a program stored in the memory may include a second access point for which the terminal intends to switch communication based on a received signal strength among the neighboring access points from a monitoring result. Can be selected. The program stored in the memory may compare the received signal strength of the neighboring access point with the largest received signal strength with the currently connected first access point, and if the difference is greater than the efficiency threshold, the received signal strength. An access point corresponding to the largest value may be selected as the second access point. Furthermore, when the difference stored in the two received signal strengths among the neighboring access points is smaller than the comparison threshold, the program stored in the memory may have the latest received signal from the change rate of the received signal strengths of the corresponding two access points. An access point having the highest priority may be selected as the second access point by giving a relatively high weight to the strength.

In one embodiment, a terminal performing handoff with an access point includes a GPS receiver configured to receive GPS information; And an acceleration sensor for detecting rotation, wherein the program stored in the memory selects a candidate access point facing the terminal among the surrounding access points based on GPS information and a rotation angle, and selects the candidate from the terminal. The distance between the access point is calculated, and an access point corresponding to a value whose calculated distance is smaller than the distance between the terminal and the first access point may be selected as a second access point to which communication is to be switched. The program stored in the memory may consider a change in the distance between the terminal and the candidate access point over time, and give a relatively low weight to the candidate access point having the highest priority as the distance from the terminal increases. The second access point may be selected.

In a terminal performing a handoff with an access point according to an embodiment, the program stored in the memory may request the terminal to connect to the second access point in a unicast manner.

Embodiments of the present invention, without changing the standard Wi-Fi protocol, periodically check the received signal strength from the currently connected access point and search for a new access point around before disconnecting from the previous access point By performing Wi-Fi handoff at a high speed using an algorithm based on received signal strength or distance, the handoff delay time can be greatly reduced.

1 and 2 are diagrams for explaining a problem of the conventional handoff method in the technical field in which the embodiments of the present invention are implemented.
3 is a flowchart illustrating a fast handoff method of wireless communication according to an embodiment of the present invention.
4 is a view for explaining a process of selecting an access point to switch in the fast handoff method of the wireless communication of FIG. 3 according to an embodiment of the present invention.
FIG. 5 is a pseudo-code implementing the process of FIG. 4 as an example.
6 and 7 are pseudo codes embodying a process of selecting an access point to switch based on received signal strength and proximity distance as an example.
8 is a block diagram illustrating a terminal performing a fast handoff with an access point according to an embodiment of the present invention.
FIG. 9 illustrates a terminal user interface (UI) of a prototype implementing a fast handoff method proposed by embodiments of the present invention.
10 and 11 are diagrams illustrating an experimental environment and a method of measuring handoff delay time through a prototype of the fast handoff method proposed by the embodiments of the present invention, respectively.

Before describing embodiments of the present invention, a brief review of various methodologies for reducing latency in implementing handoff for switching communication to an access point in an environment employing wireless communication, in particular the Wi-Fi protocol, is described. In order to solve the problems which are expected through these methodologies, ideas and technical means adopted by embodiments of the present invention are sequentially presented.

1 and 2 are diagrams for explaining a problem of the conventional handoff method in the technical field in which the embodiments of the present invention are implemented.

1 assumes a situation in which a terminal 10 for wireless communication is performing communication with an access point 20A to which a connection is currently established. In this situation, assume that as the user carrying the terminal 10 moves, it becomes difficult to continue the connection with the currently connected access point 20A. In this case, in the conventional Wi-Fi handoff technique, first, the terminal 10 terminates the connection with the currently connected access point 20A, searches for the surrounding new access points 20B and 20C, and then searches for the found access point. A suitable one 20B is selected to establish a connection.

Since the handoff process is performed according to this sequential flow, a time difference occurs from the connection termination point of the original access point 20A to the connection establishment point of the new access point 20B. User inconvenience has been pointed out due to the large time delay incurred during the channel search process.

More specifically, the Wi-Fi handoff process according to the IEEE 802.11 standard is composed of a channel scanning process (Scanning phase), an authentication process (Authentication phase), and an association phase (Association phase) as shown in FIG. In the commercialized implementation method, first, after the connection with the conventional access point 210 is terminated, a process of searching for a new access point and handing off proceeds. The user terminal searches for all Wi-Fi channels from channel 1 to channel 13 in the search process 220 for searching for a new AP. However, the search process 220 is repeatedly performed according to the surrounding channel environment, which causes a problem in which the handoff time increases rapidly.

In order to reduce such Wi-Fi handoff delay time, algorithms such as SyncScan to DueceScan based on pre-scanning that search for an access point before handoff occurs have been proposed. However, in order to apply the conventional handoff techniques to a real environment, a change in the Wi-Fi protocol, which is adopted as a standard and widely used, requires a hand according to the changed standard in an environment using a common commercial wireless terminal / smartphone. It is very difficult to apply the off technique immediately.

The Wi-Fi protocol, which currently operates on wireless terminals / smartphones, works in a so-called "Break-Before-Make (BBM)" method, which searches for and connects to a new access point after disconnection from a previous access point, thus searching for a new access point. It takes at least tens of seconds to do so, so it takes a long time for Wi-Fi handoff.

Accordingly, embodiments of the present invention devised to solve the above-mentioned problems do not change the conventional Wi-Fi protocol adopted and utilized as a standard, and search for a new access point before disconnecting from the previous access point. In this paper, we propose a fast Wi-Fi handoff algorithm based on "Listen-Before-Talk (LBT)".

In terms of implementation, embodiments of the present invention periodically check the received signal strength from the currently connected access point, and use the received signal strength based algorithm and the distance based algorithm depending on whether the GPS function of the smartphone is activated. Perform Wi-Fi handoff.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, in the following description and the accompanying drawings, detailed descriptions of well-known functions or configurations that may obscure the subject matter of the present invention will be omitted. In addition, the term 'comprising' a certain component throughout the specification means that it may further include other components, without excluding other components unless specifically stated otherwise.

In addition, terms such as first and second may be used to describe various components, but the components should not be limited by the terms. The terms may be used for the purpose of distinguishing one component from another component. For example, without departing from the scope of the present invention, the first component may be referred to as the second component, and similarly, the second component may also be referred to as the first component.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, the terms "comprise" or "include" are intended to indicate that there is a feature, number, step, action, component, part, or combination thereof that is described, and that one or more other features It should be understood that it does not exclude in advance the possibility of the presence or addition of numbers, steps, operations, components, parts or combinations thereof.

Unless specifically defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art. Terms such as those defined in the commonly used dictionaries should be construed as meanings consistent with the meanings in the context of the related art and shall not be construed in ideal or excessively formal meanings unless expressly defined in this application. .

As introduced above, embodiments of the present invention are optimized to determine and pre-receive received signal strengths of currently connected access points and surrounding access points to support high speed Wi-Fi handoff without changing the Wi-Fi standard protocol. We propose a Wi-Fi handoff algorithm for determining the access point. The proposed fast Wi-Fi handoff algorithm can be divided into three algorithms according to its function.

First, the Handoff Trigger Algorithm receives an event caused by a change in a received signal strength indicator (RSSI) or periodically detects the received signal strength of a currently connected access point by using a timer. At this time, when the received signal strength of the connected access point is weakened or the distance between the terminal (client) and the access point is far, the handoff operation starts.

Second, an RSSI-based algorithm scans the received signal strength of neighboring access points and determines an optimal access point based on the received signal strength of the access point. Once the optimal access point is determined, it then attempts to unicast to that access point.

Third, in the distance-based algorithm, unlike an RSSI-based algorithm, the distance-based algorithm determines the optimal access point by measuring the distance between the neighboring access point and the terminal (client). Attempt to connect in a unicast fashion.

Hereinafter, each algorithm will be described sequentially.

3 is a flowchart illustrating a fast handoff method of wireless communication according to an embodiment of the present invention. The series of processes may be implemented through a wireless communication terminal having at least one processor and communication means, and the terminal and the access point are preferably in accordance with the IEEE 802.11 standard.

In step S310, the terminal periodically monitors the received signal strength of the first access point and the neighboring access point while maintaining a connection with the first access point (AP) currently communicating. That is, without changing the Wi-Fi protocol widely used in the prior art, the search process is performed in parallel with the situation in which the connection with the conventional access point is maintained. In this process, the terminal may receive an event according to a change in a received signal strength indicator (RSSI) from a neighboring access point, or periodically measure the received signal strength of the first access point by using a timer.

In step S320, when a preset condition is met regarding termination of communication with the first access point, the terminal selects a second access point to switch communication among the surrounding access points based on a monitoring result. The communication termination condition is a criterion for determining whether to perform a handoff in consideration of the status of the access point with which the current connection is maintained and the information of the neighboring access point previously monitored, which will be described later in detail with reference to FIGS. 4 and 5. Do it.

In step S330, the terminal requests a connection to the selected second access point. In terms of implementation, in this process, the terminal preferably requests the connection to the second access point in a unicast manner.

In step S340, when the response to the connection request is received, the terminal switches the communication from the first access point to the second access point, thereby minimizing the handoff delay time.

4 is a view for explaining in more detail a process (step 320) of selecting an access point to switch in the fast handoff method of the wireless communication of FIG. 3 according to an embodiment of the present invention. The process performed continuously in the process of monitoring the received signal strength with the surrounding access point.

First, through step S321, it is checked whether a communication termination condition is satisfied. The communication termination condition includes a first condition in which a received signal strength from the first access point (current access point) is less than a signal threshold value, and a second condition in which a distance between the terminal and the first access point is greater than a distance threshold value. At least one or a combination of the two, if one of the conditions set or if the two conditions at the same time, it is determined that maintaining the communication with the first access point is difficult, and selects another access point for handoff You will proceed to the process.

Embodiments of the present invention propose two algorithms in selecting an access point for handoff. In step S322, the terminal selects a second access point from which the communication is to be switched based on the received signal strength among the surrounding access points from the monitoring result, and in step S323, the terminal is selected based on the proximity distance among the surrounding access points. The second access point to which to switch communication is selected. Each algorithm will be described in detail later with reference to FIGS. 6 and 7.

FIG. 5 illustrates a handoff trigger algorithm as a pseudo-code implementing the process of FIG. 4 as an example.

The main function of the algorithm illustrated in FIG. 5 is to receive an event according to the RSSI change or to determine a handoff time by periodically checking the received signal strength of a currently connected access point using a timer. Existing Wi-Fi handoff technologies attempt to connect to a new access point when the currently connected access point is disconnected, resulting in a long handoff delay time. Therefore, in this embodiment, the state of the currently connected access point is confirmed in advance to reduce the handoff delay time. In FIG. 5, when the terminal (client) determines the handoff time, a received signal strength based algorithm (RSSI-based algorithm) (S550) or distance based algorithm (Distance-based algorithm) (S590) is determined according to a user's setting. Perform and request a connection to a new access point.

More specifically, referring to FIG. 5, the meaning of the variable used to examine the operation of the handoff trigger algorithm is as follows. γ _current is the RSSI of the currently connected access point, γ _th is the RSSI threshold for attempting handoff, d ' _current is the distance between the terminal and the currently connected access point, and d' _th is the distance for determining whether to attempt handoff. Means the threshold.

When the algorithm is first started, the terminal (eg, a smartphone) sets a timer (S510) and waits for an event. The event is generated when the RSSI of the connected access point changes. When the event occurs (S520), the terminal updates the RSSI value γ _current of the currently connected access point (S530). In this case, in order to prevent the RSSI from being changed for a long time, when the set timer expires, the RSSI value of the currently connected access point is acquired to periodically check the state of the connected access point.

If the RSSI value γ _current of the currently connected access point is lower than the threshold value γ _th of the received signal strength (S540), it is determined that communication with the currently connected access point is difficult and ready to perform handoff. In this case, when GPS is turned off or the user does not select a distance-based mode, a received signal strength based algorithm (RSSI-based algorithm) connecting to an optimal access point based on the received signal strength (S550) It works.

On the other hand, if the user selects the distance-based mode while the GPS is on (S560), the terminal compares the distance d ' _current between the terminal and the currently connected access point and the threshold value d' _th of the distance. If the distance d ' _current between the terminal and the currently connected access point is greater than the threshold d' _th of the distance or γ _current is smaller than γ _th (S580), it is determined that communication with the currently connected access point is difficult and the distance between the access points is A distance-based algorithm for connecting to an optimal access point is performed based on S (S590).

6 and 7 are pseudo codes embodying a process of selecting an access point to switch based on received signal strength and proximity distance as an example.

If the RSSI of the currently connected access point is lower than the threshold, an RSSI-based algorithm illustrated in FIG. 6 may be performed for handoff. First, variables and descriptions used in FIG. 6 are as follows. R _AP is the set of access point lists sorted by RSSI size, R _RSSI is the set of RSSI values sorted by size, AP _j is the jS largest access point, RSSI _j is the RSSI value of AP _j , N Is the number of scanned access points, γ _current is the RSSI of the currently connected access point, and α is the threshold (to ensure the efficiency of the handoff). Is the threshold of time, β is the threshold for determining whether to trace previous RSSI, H _j is the set of RSSI values of AP _{j over} time, PR _j is the handoff priority value of AP _j , and ω _i is for time i It means the weight.

Referring to FIG. 6, the terminal performs a scan to obtain received signal strength of neighboring access points. Next, the scanned access points are arranged in low order in the RSSI order (S610). At this time, if the highest RSSI value RSSI ₁ among the neighboring access points is larger than α by RSSI γ _current of the currently connected access point (S620), the connection of the currently connected access point is interrupted and an optimal access point is attempted. That is, in this process, when the received signal strength of the neighboring access points has the largest received signal strength compared to the currently connected first access point, and the difference is greater than the efficiency threshold value α, the received signal strength is the most. The access point corresponding to the large value is selected as the second access point for handoff.

If the total number of access points scanned is '1', it attempts to connect to AP ₁ having the highest RSSI. On the other hand, if it is determined that the total number of scanned access points is greater than '1' and a certain time has passed, the terminal compares the difference between the highest RSSI and the second highest RSSI among the scanned access points. In this case, when the difference between the two values is smaller than the threshold β (S630), it is determined that the received signal strengths of the two access points are similar and the priority is determined through the rate of change of the RSSI (S640). At this time, the priority of each access point may be derived through Equation 1 below (S650).

Here, PR _j means the handoff priority value of AP _j . The larger the value, the higher the connection priority. ΔRSSI _j (i) denotes an amount of change in RSSI of AP _j at time i, and ω _i denotes a weight for time i. That is, the priority of each access point means the sum of RSSI change amounts of the access point during the recent τ time. Therefore, when the difference between the RSSI values of the two access points is smaller than β, the access point having a higher RSSI among the two access points has a higher priority. That is, in this process, when the difference between two values of the largest received signal strength among the neighboring access points is smaller than the comparison threshold value β, the latest received signal strength from the change rate of the received signal strength of the corresponding two access points A relatively high weight is given to select the access point with the highest priority as the second access point for handoff. Finally, the terminal requests a connection in an unicast manner to an access point having a higher priority among the two access points (S660).

In the RSSI-based algorithm proposed in FIG. 6, the access point to be handed off is determined by tracking the change amount of the RSSI value during the previous time without using the RSSI of the access point obtained by scanning once. Through this, it is possible to reduce the variation of RSSI due to fast fading and shadow fading occurring in a wireless communication environment and to determine an optimal access point.

사이의 수직 거리, N은 스캔된 액세스 포인트들의 개수, d'_current는 단말기와 현재 연결된 액세스 포인트 사이의 거리, d_th는 액세스 포인트와 단말기의 진행 방향 벡터

사이 수직 거리의 기준 값, PD_j는 AP_j의 핸드오프 우선순위 값, R은 우선순위 값을 증가시켜 우선순위를 낮추기 위한 상수를 의미한다.FIG. 7 illustrates a distance-based algorithm. Variables and descriptions used in FIG. 7 are as follows. where s is the starting position of the client, n is the current position of the terminal, AP _j is the access point with the jth largest RSSI, d ' _j is the distance between AP _j and the terminal, d _j is the direction vector of AP _j and the terminal

The vertical distance between N, N is the number of scanned access points, d ' _current is the distance between the terminal and the currently connected access point, d _th is the direction of travel of the access point and the terminal vector

The reference value of the vertical distance therebetween, PD _j is a handoff priority value of AP _j , R is a constant for decreasing the priority by increasing the priority value.

The main function of the distance-based algorithm of FIG. 7 is to perform a handoff to an optimal access point by predicting the direction of the terminal based on the location information of the terminal and the location information of the neighboring access points. If the RSSI of the currently connected access point is lower than the threshold value or the distance from the currently connected access point is far from the handoff trigger algorithm, the terminal performs a distance-based algorithm to perform the handoff.

More specifically, in FIG. 7, the terminal stores the current location coordinates (latitude and longitude) in n using GPS (S710). Next, the terminal stores the starting position in s. When the distance-based algorithm is first performed, the position coordinates of the current terminal are stored in the starting position s. Next, the terminal detects the rotation. The reason for detecting the rotation of the terminal is to initialize the starting position to accurately predict the direction of movement of the terminal. A method for detecting a rotation by the terminal proposed in this embodiment is as follows. Current location information confirmed by the terminal is stored in the internal storage. The location information of the terminal stored in the internal storage may be represented by M ₁ , M ₂ ,..., M _k according to the stored order, where k is the maximum number of location information that can be stored in the internal storage. In this case, the direction in which the terminal bypasses may be obtained through the rotation angle θ between two vectors (generated from two consecutive points) as shown in Equation 2.

를 얻을 수 있다. 단말기의 진행 방향 벡터

를 얻으면 주위 액세스 포인트들을 스캔한다. 단말기는 스캔된 각 액세스 포인트들과의 거리 d'_j를 계산하고, 단말기의 진행 방향 벡터와 각 액세스 포인트들 사이의 수직 거리 d_j를 계산한다(S730). Since the movement direction can be expressed as a vector in a two-dimensional plane, the direction in which the terminal bypasses can be known by obtaining the rotation angle between the two vectors. For example, at two recently stored points, the moving direction may be represented by NM ₃ = (x ₁ , y ₁ ) and M ₃ -M ₂ = (x ₂ , y ₂ ) vectors, respectively. At this time, if the sinθ value is greater than '0', it means to move in the counterclockwise direction (left turn), and if it is smaller than '0', it means to move in the clockwise direction (right direction). When the rotation of the terminal is detected by the above method (S720), the starting position of the terminal is initialized to the current position to proceed the direction vector of the terminal

Can be obtained. Terminal direction vector

If it is found, it scans the surrounding access points. The terminal calculates the distance d ' _j from each of the scanned access points, and calculates a vertical distance d _j between the direction vector of the terminal and each of the access points (S730).

와 스캔된 Ap_j 사이의 직선거리 d_j가 기준 값보다 작은지 확인한다(S760). 만일 단말기의 진행 방향과 스캔된 AP_j 사이의 직선거리 d_j가 임계값 d_th보다 작으면 이동 경로에 스캔된 AP_j가 있다고 판단하고 PD_j에 단말기와 AP_j와의 거리 d'_j를 입력한다. 마지막으로 단말기는 위 세 단계를 반복하여 스캔된 모든 액세스 포인트에 대한 우선순위를 결정한다(S770). 다음으로 가장 우선순위가 높은 액세스 포인트에 유니캐스트 방식으로 연결을 요청하여 핸드오프 지연시간을 단축시킨다(S780).The distance-based algorithm determines the optimal access point in four steps based on the calculation result. First, if the distance d ' _j from the scanned AP _j is greater than the distance d' _current from the currently connected access point (S740), it is determined that the wireless environment of the scanned AP _j is worse than that of the currently connected access point, and the threshold value is set to PD _j . Add 2R to lower the priority of AP _j . At this time, the priority of AP _j is higher as the value of PD _j is smaller. Second, it is checked whether the position of the terminal approaches AP _j according to time (S750). If it is determined that the scanned AP _j is moving away from the terminal, it predicts that the wireless environment of the AP _j scanned in the future may deteriorate and adds a threshold R to PD _j to lower the priority of AP _j . Third, the terminal is a direction vector of the terminal

And d _j is a linear distance between the scanned Ap _j a check is less than the reference value (S760). If the straight line distance d _j between the traveling direction and the scanning AP _j of the terminal is smaller than the threshold d _th is determined that the AP _j scans the travel path, and enter the distance between the terminal and the AP _j to PD _j d _'j . Finally, the terminal repeats the above three steps to determine the priority of all scanned access points (S770). Next, by requesting a connection in the unicast method to the highest priority access point to reduce the handoff delay time (S780).

In summary, in the above-described process, the candidate access point facing the terminal is selected from the surrounding access points based on the GPS information and the rotation angle, the distance between the terminal and the selected candidate access point is calculated, and the calculated distance is determined by the terminal. And an access point corresponding to a value smaller than the distance between the first access point and the second access point. In addition, while considering the change in the distance between the terminal and the candidate access point over time, the farther away from the terminal is given a relatively lower weight to select the candidate access point having the highest priority as the second access point.

The distance-based algorithm proposed in this embodiment initializes the starting position every time the terminal rotates, predicts the moving direction of the terminal, and determines whether the scanned access point is close to the moving direction of the terminal based on the predicted result. In order to determine the optimal access point.

FIG. 8 is a block diagram illustrating a terminal 10 performing a fast handoff with an access point 20 according to an embodiment of the present invention, and corresponds to a series of processes of the handoff method described above with reference to FIG. 3. Therefore, in order to avoid duplication of description, only the functions / operations of the components of the terminal 10 will be outlined.

The communication unit 11 is a means for communicating with the access point 20 according to the Wi-Fi protocol.

The memory 13 stores a program for establishing communication with the access point 20 based on the received signal strength received through the communication unit 11, and the processor 15 drives the program to access the access point 20. The handoff is performed.

Here, the program stored in the memory 13 is received with the first access point and the neighboring access point while the connection with the first access point (AP) to which the terminal 10 is currently communicating is maintained. Periodically monitoring signal strength, and when a preset condition is met with respect to the termination of communication with the first access point, a second terminal to switch communication among the neighboring access points based on a monitoring result; Select an access point, the terminal requests a connection to the selected second access point, and when a response to the connection request is received, the terminal switches communication from the first access point to the second access point; Contains the command.

In the program stored in the memory 13, the terminal 10 receives an event according to a change in a received signal strength indicator (RSSI) from a neighboring access point, or periodically receives the first access point using a timer. Signal strength can be measured. In addition, the program stored in the memory 13, the terminal may request the connection to the second access point in a unicast (unicast) manner.

The program stored in the memory 13 may include one of a first condition in which a received signal strength from the first access point is less than a signal threshold value, and a second condition in which a distance between the terminal and the first access point is greater than a distance threshold value. If at least one or a combination of both is satisfied, it may be determined that maintaining communication with the first access point is difficult.

In order to perform the handoff, the program stored in the memory 13 may select the second access point to which the terminal 10 intends to switch communication based on the received signal strength among the surrounding access points from the monitoring result. In this case, the program stored in the memory 13 compares the received signal strength of the neighboring access point with the largest received signal strength with the currently connected first access point and the difference is greater than the efficiency threshold. An access point corresponding to a value having the largest received signal strength may be selected as the second access point. In addition, the program stored in the memory 13, when the difference between the two values of the largest received signal strength among the neighboring access points is smaller than the comparison threshold value, the program stored in the memory 13 from the rate of change of the received signal strength of the corresponding two access points; An access point having the highest priority may be selected as the second access point by giving a relatively high weight to the received signal strength of the.

On the other hand, the terminal 10 further includes a GPS receiver 17 for receiving GPS information and an acceleration sensor 19 for detecting rotation, and the program stored in the memory 13 is based on the GPS information and the rotation angle. Selecting a candidate access point facing the terminal from among the neighboring access points based on the neighboring access point, calculating a distance between the terminal and the selected candidate access point, and the calculated distance is greater than the distance between the terminal and the first access point. An access point corresponding to a small value may be selected as the second access point to which communication is to be switched. In this case, the program stored in the memory 13 considers a change in the distance between the terminal and the candidate access point over time, but the candidate having the highest priority by giving a relatively low weight as it moves away from the terminal. An access point may be selected as the second access point.

A prototype was implemented to confirm the feasibility of embodiments of the present invention. The high-speed Wi-Fi handoff prototype proposed by the embodiments of the present invention is implemented in the form of an Android app so that it can be easily used in a smartphone terminal.

High-speed Wi-Fi Handoff Prototype (hereinafter referred to as myWiFiRoam) is a program that reduces communication disconnection time during handoff by applying the high-speed Wi-Fi handoff algorithm proposed above. In particular, the developed myWiFiRoam uses the LBT method of determining the optimal access point before the current access point is disconnected using the Android Application Programming Interface (API) without changing the conventional Wi-Fi protocol adopted as a standard. Support handoff. FIG. 9 is a diagram illustrating a terminal user interface (UI) screen of a prototype myWiFiRoam implementing the fast handoff method proposed by embodiments of the present invention.

The myWiFiRoam developed according to the embodiment of FIG. 9 may be configured with the device components or modules as shown in FIG. 8. myWiFiRoam acquires the location information of the current terminal by using the Wi-Fi received signal strength or GPS information to support high-speed Wi-Fi handoff, and the pre-stored location information of the access point and the received signal strength of the surrounding Wi-Fi Use to find the best access point to hand off. At this time, myWiFiRoam is a Wi-Fi signal receiving module (communication unit), GPS receiving module (GPS receiving unit), a series of algorithms stored in memory (access point location module, high-speed Wi-Fi handoff algorithm module and access point handoff connection) Module, a GUI (Graphic User Interface) for displaying the access point connection status, and the like. The function of each component is outlined as follows.

● Wi-Fi Signal Receiving Module (Communication Unit): A smartphone equipped with myWiFiRoam program acquires the received signal strength of the beacon signal in real time through the Wi-Fi signal receiving module. The received received signal strength is used for the fast Wi-Fi handoff algorithm and thus is transmitted to the fast Wi-Fi handoff algorithm module. At this time, the SSID and BSSID information of the neighboring access points and the received signal strength may be acquired using APIs such as ScanResult and WifiManager provided by Android.

● GPS receiver module (GPS receiver): When using the distance-based algorithm in the high-speed Wi-Fi handoff algorithm, the location information of the terminal should be used. Therefore, the GPS receiving module acquires latitude and longitude information of the current smartphone using satellite signals or network location. Latitude and longitude information of the acquired smartphone is transmitted to the high speed Wi-Fi handoff algorithm module.

● Access point location module: The access point location module scans the surrounding access points and uses the scan results to determine the location information of the corresponding access point stored in the internal database. Since the high-speed Wi-Fi handoff algorithm performs handoff based on the distance between the smartphone and the neighboring access point, the location information of the neighboring access point acquired from the access point location module is transmitted to the high-speed Wi-Fi handoff algorithm module. .

● Fast Wi-Fi Handoff Algorithm Module: The Fast Wi-Fi Handoff Algorithm Module uses the received signal strength from the access point signal receiving module, GPS receiving module, and access point positioning module, and location information of surrounding access points. Determine the best access point to hand off. When the optimal access point is determined in the high-speed Wi-Fi handoff algorithm module, myWiFiRoam transmits the BSSID and SSID of the determined access point to the access point handoff access module. If the optimal access point is secured, the password is also sent.

Access Point Handoff Access Module: The Access Point Handoff Access Module uses the BSSID, SSID, and password of the access point received from the high-speed Wi-Fi handoff algorithm module to unicast to the corresponding access point. When connected to the access point, the GUI of the smartphone is updated to inform the user.

● GUI: The GUI shows the status of the currently connected access point and the operation of the program. The SSID, channel information and RSSI values are shown in the status of the currently connected access point, and the operation process of the simple program such as start time and end time of the developed myWiFiRoam is displayed in the log.

10 and 11 are diagrams illustrating an experimental environment and a method of measuring handoff delay time through a prototype of the fast handoff method proposed by the embodiments of the present invention, respectively.

In order to experiment with the prototype app to which the embodiment of the present invention is applied, a test-bed was constructed as shown in FIG. Figure 10 (b) is a picture showing a test bed actually constructed. The Wi-Fi handoff testbed consists of two access points 100 meters away on a straight road. The WLAN access point uses an integrated access point that supports both backhaul and user Wi-Fi services. At this time, the 5GHz band with low ambient interference is used as the wireless backhaul, and the Wi-Fi mobile network is configured to support the Wi-Fi service using the 2.4GHz band.

The method for measuring handoff delay time is illustrated in FIG. 11. First, the traffic server 1 repeatedly transmits an 'echo request' packet through the WLAN AP1. At this time, the payload size included in the 'echo request' packet is about 1.4MB and is repeatedly transmitted every 100ms. Next, the traffic server 2 repeatedly transmits the 'echo request' packet through the WLAN AP2. The terminal moves from the WLAN AP1 position to the WLAN AP2 position to measure the handoff delay time. At this time, if the terminal successfully receives the 'echo request' packet, the terminal sends an 'echo reply' packet to the traffic server through the connected access point. send. Each traffic server uses the WireShark program to sniff the packet and measure the time that the 'echo reply' packet arrived. The handoff delay time was defined as in Equation 3.

Here, T _handoff means handoff delay time, t ₁ means the time when the last 'echo reply' packet arrived at traffic server 1, and t ₂ means the time when the first 'echo reply' arrived at traffic server 2.

The average Wi-Fi handoff delay time for three repeated Wi-Fi handoff experiments is shown in Table 1.

Referring to Table 1, it can be seen that the handoff delay time is significantly reduced in the case of the smart phone to which the handoff method according to the embodiment of the present invention is applied.

According to embodiments of the present invention, without changing the standard Wi-Fi protocol, periodically check the received signal strength from the currently connected access point and search for a new access point around before disconnecting from the previous access point. By performing a Wi-Fi handoff at a high speed using an algorithm based on received signal strength or distance, the handoff delay time can be significantly reduced.

Meanwhile, embodiments of the present invention can be implemented by computer readable codes on a computer readable recording medium. The computer-readable recording medium includes all kinds of recording devices in which data that can be read by a computer system is stored.

Examples of computer-readable recording media include ROM, RAM, CD-ROM, magnetic tape, floppy disk, optical data storage device, and the like. The computer readable recording medium can also be distributed over network coupled computer systems so that the computer readable code is stored and executed in a distributed fashion. And functional programs, codes and code segments for implementing the present invention can be easily inferred by programmers in the art to which the present invention belongs.

The present invention has been described above with reference to various embodiments thereof. Those skilled in the art will understand that the present invention can be implemented in a modified form without departing from the essential features of the present invention. Therefore, the disclosed embodiments should be considered in descriptive sense only and not for purposes of limitation. The scope of the present invention is shown in the claims rather than the foregoing description, and all differences within the scope will be construed as being included in the present invention.

10: terminal
11: communication unit 13: memory
15: Processor
17: GPS receiver 19: acceleration sensor
20, 20A, 20B, 20C: access point

Claims (20)

(a) periodically monitoring received signal strength between the first access point and the neighboring access point while the terminal maintains a connection with a first access point (AP) with which the terminal is currently communicating;
(b) when the preset condition is met regarding the termination of communication with the first access point, selecting, by the terminal, a second access point to which to switch communication among the surrounding access points based on a monitoring result;
(c) the terminal requesting to connect to the selected second access point; And
(d) if the response to the connection request is received, the terminal switching communication from the first access point to the second access point. The method of claim 1,
In step (a),
A method for handoff in wireless communication in which a terminal receives an event according to a change in a received signal strength indicator (RSSI) from a neighboring access point or periodically measures a received signal strength of the first access point using a timer. The method of claim 1,
In step (b),
(b1) at least one or a combination of a first condition in which the received signal strength from the first access point is smaller than a signal threshold and a second condition in which a distance between the terminal and the first access point is greater than a distance threshold; Determining that it is difficult to maintain communication with the first access point, if satisfied. The method of claim 3, wherein
In step (b),
(b2) the terminal selecting, from the monitoring result, a second access point to which the communication is to be switched based on the received signal strength among the neighboring access points. The method of claim 4, wherein
Step (b2),
When the received signal strength of the neighboring access points is greater than the received signal strength of the first access point currently connected and the difference is greater than an efficiency threshold, the access point corresponding to the received signal strength is the largest value. Is selected as the second access point. The method of claim 4, wherein
Step (b2),
If the difference between the two received signal strengths among the neighboring access points having the largest value is smaller than the comparison threshold value, the weight of the recent received signal is relatively high from the rate of change of the received signal strength of the corresponding two access points. Selecting the access point having the highest priority as the second access point. The method of claim 3, wherein
In step (b),
(b3) selecting a candidate access point facing the terminal among the surrounding access points based on the GPS information and the rotation angle, calculating a distance between the terminal and the selected candidate access point, and the calculated distance is determined by the terminal; Selecting an access point corresponding to a value less than the distance to the first access point as a second access point to which communication is to be switched. The method of claim 7, wherein
Step (b3),
Considering a change in distance between the terminal and the candidate access point as time passes, selecting a candidate access point having the highest priority as the second access point by giving a relatively low weight as the distance from the terminal increases. A handoff method of wireless communication characterized by the above-mentioned. The method of claim 1,
In step (c),
The terminal requests a connection to the second access point in a unicast manner. The method of claim 1,
The terminal and the access point
A handoff method of wireless communication, characterized by the IEEE 802.11 standard. A computer-readable recording medium having recorded thereon a program for executing the method of any one of claims 1 to 10. A terminal performing a handoff with an access point (AP),
A communication unit communicating with an access point according to a Wi-Fi protocol;
A memory for storing a program for establishing communication with an access point based on the received signal strength received through the communication unit; And
A processor for driving the program to perform handoff between access points;
The program stored in the memory,
Periodically monitoring the received signal strength between the first access point and the neighboring access point while maintaining a connection with the first access point (AP) to which the terminal is currently communicating;
When a preset condition is met with respect to the termination of communication with the first access point, the terminal selects a second access point to which to switch communication among the surrounding access points based on a monitoring result,
The terminal requests a connection to the selected second access point,
And when the response to the connection request is received, the terminal to switch communication from the first access point to the second access point. The method of claim 12,
The program stored in the memory,
Wherein the terminal receives an event according to a change in a received signal strength indicator (RSSI) from a neighboring access point, or periodically measures a received signal strength of the first access point by using a timer. The method of claim 12,
The program stored in the memory,
At least one or a combination of a first condition in which the received signal strength from the first access point is smaller than a signal threshold and a second condition in which the distance between the terminal and the first access point is greater than a distance threshold are satisfied And determining that it is difficult to maintain communication with the first access point. The method of claim 14,
The program stored in the memory,
And the terminal selects, from the monitoring result, a second access point from which the communication is to be switched based on the received signal strength. The method of claim 15,
The program stored in the memory,
When the received signal strength of the neighboring access points is greater than the received signal strength of the first access point currently connected and the difference is greater than an efficiency threshold, the access point corresponding to the received signal strength is the largest value. Terminal is selected as the second access point. The method of claim 15,
The program stored in the memory,
If the difference between the two received signal strengths among the neighboring access points having the largest value is smaller than the comparison threshold value, the weight of the recent received signal is relatively high from the rate of change of the received signal strength of the corresponding two access points. And selecting the access point having the highest priority as the second access point. The method of claim 14,
A GPS receiver for receiving GPS information; And
Further comprising an acceleration sensor for detecting rotation,
The program stored in the memory,
A candidate access point facing the terminal is selected from among the surrounding access points based on GPS information and a rotation angle, a distance between the terminal and the selected candidate access point is calculated, and the calculated distance is determined by the terminal and the first access point; And selecting an access point corresponding to a value smaller than a distance from the access point as a second access point to which communication is to be switched. The method of claim 18,
The program stored in the memory,
Considering a change in distance between the terminal and the candidate access point as time passes, selecting a candidate access point having the highest priority as the second access point by giving a relatively low weight as the distance from the terminal increases. Terminal characterized in that. The method of claim 12,
The program stored in the memory,
And the terminal requests a connection to the second access point in a unicast manner.

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