KR20080056895A - Method for performing handover of communication terminal for wireless local area network system - Google Patents

Abstract

A handover method for communication terminals in a WLAN(Wireless LAN) system is provided to restrain the generation of a ping-pong state and reduce communication delays by preventing a communication terminal from sensitively responding to even a minute change of RSSIs(Received Signal Strength Indicators) with an access node. A control part in a communication terminal, connected with the first access node, measures the first RSSI periodically(311,313). The control part judges whether the first RSSI exceeds the first threshold(315). If the first RSSI is below the first threshold, the control part judges whether the first RSSI exceeds the second threshold(317). If so, the control part radiates a probe request(319). If a probe response is received, the control part analyzes it and detects the second access node(321-325). Then the control part measures the second RSSI with the second access node(327). The control part calculates the difference between the first RSSI and the second RSSI and compares the calculated difference with a delta value(329,331). If the difference exceeds the delta value, the control part releases the connection with the first access node and executes handover to the second access node(333).

Description

Method for performing handover of communication terminal in wireless LAN system {METHOD FOR PERFORMING HANDOVER OF COMMUNICATION TERMINAL FOR WIRELESS LOCAL AREA NETWORK SYSTEM}

1 is a view schematically showing the configuration of a WLAN system according to an embodiment of the present invention;

2 is a view schematically showing a configuration of a communication terminal according to an embodiment of the present invention; and

3 is a diagram illustrating a handover procedure according to an embodiment of the present invention.

The present invention relates to a method for performing handover in a wireless communication system, and more particularly, to a method of performing a handover in a wireless LAN system.

Currently, a wireless local area network (WLAN) system based on IEEE 802.11 enables low cost effective services. The unlicensed spectrum used in IEEE 802.11-based wireless LAN systems can be used at low cost by any organization. In addition, well-designed Medium Access Control (MAC) provides high bandwidth. As a result, IEEE 802.11 based wireless LAN is expected to emerge as a next generation cellular system or part thereof.

On the other hand, the WLAN system is composed of a plurality of basic service sets (hereinafter referred to as "BSS"), each BSS is composed of an access point (AP) and a plurality of communication terminals connected by a wired network. At this time, communication in the BSS is performed through the access node, and the communication terminal must be connected to the access node in order to access the network. In addition, since the BSS has overlapping service areas and each access node uses a different channel, even if the communication terminal moves, the BSS can perform data communication by connecting to the network without disconnection by performing a handover between the access nodes. have.

However, since the communication terminal performs a handover when it is determined that the received field strength with the currently connected access node is less than or equal to the set threshold value, the communication terminal is sensitive to the minute change in the received field strength with the access node. A ping-pong phenomenon that repeats handover occurs in an overlapping area between each service area. This ping pong phenomenon causes communication delay.

Accordingly, an object of the present invention is to provide a method for performing a handover of a communication terminal capable of reducing a communication delay by suppressing a ping pong phenomenon in a WLAN system.

Another object of the present invention is a handover of a communication terminal capable of suppressing a ping-pong phenomenon when a handover is performed based on a measured value of a received electric field strength with a currently connected access node of a communication terminal in a wireless LAN system. To provide a way to do it.

Accordingly, a method of performing a handover of a communication terminal in a wireless LAN system according to the present invention for achieving the above object comprises the steps of: measuring a received electric field strength with a first access node connected in a wireless LAN system; If the received electric field strength of the first access node exceeds the second threshold for performing the handover and is less than or equal to the first threshold, which is a predetermined value greater than the second threshold, the WLAN system encounters the second access node. If the difference between the measured field strength and the measured difference between the received field strength of the second access node and the received field strength of the first access node exceeds a set value, handover is performed to the second access node. It is characterized by including the process of performing.

Hereinafter, exemplary embodiments will be described in more detail with reference to the accompanying drawings.

In the following description, the communication terminal of the present invention may be a terminal supporting at least a cellular mode or a dual mode capable of accessing a wireless LAN. Hereinafter, an embodiment using a WLAN system and a cellular network will be described. However, the present invention is not limited thereto, and in the method for performing handover according to an embodiment of the present invention, the handover in the homogeneous network is performed in the WLAN system, but the handover to the heterogeneous network is performed in addition to the cellular network. It can also be done with other systems.

In an embodiment of the present invention described below, in a connection node related term, the term “first access node” refers to an access node of a BSS to which a communication terminal currently belongs in a WLAN system. It means the connection node that provides the service. The term " second access node " refers to an access node that a communication terminal wants to continuously receive after moving a service provided from the first access node. The second access node is a homogeneous network, that is, a first access node. It belongs to another BSS of the WLAN system, and in particular, uses the same Service Set ID (SSID) as the first access node.

In terms of the received signal strength indicator (hereinafter referred to as "RSSI"), the terms "first threshold value" and "second threshold value" mean that the communication terminal receives the received field strength from the first access node. The term means RSSI as a criterion for determining whether to perform a handover based on the above. At this time, the first threshold is greater than the second threshold. For example, the first threshold is about -75 dBm to -70 dBm and the second threshold is about -85 dBm to -82 dBm. The term "delta value" refers to a value set to determine whether a communication terminal performs handover in an overlapping area between each service area of a BSS. The delta value is a first threshold value and a second value. The threshold value may be a difference value. That is, the delta value may be an absolute value of the first threshold value-second threshold value or the second threshold value-first threshold value, for example, 8 dBm to 10 dBm.

1 is a view schematically showing the configuration of a WLAN system according to an embodiment of the present invention. In the present embodiment, it is assumed that a communication terminal currently connected to a first access node in a WLAN system moves to a service area to which the second access node belongs.

Referring to FIG. 1, the WLAN system includes a BSS1 110 and a BSS2 120. The BSS1 110 includes a first access node 111 connected through a wired network, and the BSS2 120 includes a second access node 121 connected through a wired network. In addition, the BSS1 110 and the BSS2 120 have service areas overlapping each other, and the first access node 111 and the second access node 121 are allocated with different channels. At this time, the first access node 111 and the second access node 121 are connected to the network 130 through a gateway (not shown).

Accordingly, the communication terminal 200 is connected to the first access node 111 to perform communication, and after moving to the service area to which the second access node 121 belongs, the second access node 121 through handover. Is connected to perform communication. At this time, whether to perform the handover of the communication terminal 200 compares a value obtained by measuring the RSSI with the first access node 111 (hereinafter referred to as “first RSSI”), and the first threshold value and the second threshold value, respectively. It is judged based on the result. Further, when the communication terminal 200 is located in the overlapping area of the service area of each of the BSS1 110 and the BSS2 120, a value of measuring the RSSI between the first RSSI and the second access node 121 (hereinafter, referred to as “the 2 RSSI "is determined based on a result of comparing the difference value with the set delta value.

2 is a diagram schematically illustrating a configuration of a communication terminal capable of performing handover in a WLAN system according to an embodiment of the present invention. In the present embodiment, it is assumed that the communication terminal is a mobile phone.

1 and 2, the communication terminal 200 includes a wireless communication unit 210, a control unit 220, a storage unit 230, an audio processing unit 240, a display unit 250, and a key input unit 260. do.

The wireless communication unit 210 performs a wireless communication function of the communication terminal 200. The wireless communication unit 210 includes an RF transmitter for upconverting and amplifying a frequency of a transmitted signal, and an RF receiver for low noise amplifying and downconverting a received signal. In this case, the wireless communication unit 210 may simultaneously process a frequency band for a service of a cellular network system and a frequency band for a service of a WLAN system according to an exemplary embodiment of the present invention. Meanwhile, although the wireless communication unit 210 is disclosed to include one antenna in the present embodiment, the wireless communication unit 210 may include dual antennas or more to correspond to each system.

The controller 220 performs a function of controlling the overall operation of the communication terminal 200. In addition, the controller 220 includes a data processor including a transmitter for encoding and modulating a transmitted signal and a receiver for demodulating and decoding a received signal. In this case, the data processing unit may be configured of a modem and a codec.

In particular, the control unit 220 measures the first RSSI for the first access node 111 connected through the wireless communication unit 210 at regular intervals according to an embodiment of the present invention. When the controller 220 needs to perform the handover as a result of the determination based on the measured first RSSI, the controller 220 discovers the second access node 121 using an active mode scan method. In this case, when the communication terminal 200 is located in the overlapping area of the service area of each of the BSS1 110 and the BSS2 120, the controller 220 measures the second RSSI for the second access node 121. A handover is performed to the second access node 121 as necessary based on the difference between the first RSSI and the second RSSI.

The storage unit 230 may be composed of a program memory and a data memory. The program memory stores an operation program of the communication terminal 200 and programs for performing handover according to an embodiment of the present invention. The data memory stores data generated during program execution. In addition, the data memory stores a first threshold value and a second threshold value for comparison with the measured first RSSI when the controller 220 determines whether handover is performed according to an embodiment of the present invention. When the 200 is located in the overlapping area of the service area of each of the BSS1 110 and the BSS2 120, a delta value for comparing with a difference value between the first RSSI and the second RSSI is stored.

The audio processor 240 reproduces the received audio signal output from the audio codec of the data processor and generates the received audio signal through the speaker SPK, or transmits the transmitted audio signal generated from the microphone MIC to the audio codec of the data processor. Do this.

The display unit 250 displays the state of the communication terminal 200 under the control of the controller 220. In this case, an LCD may be used as the display unit 250. In this case, the display unit 250 may include an LCD controller, a memory capable of storing display data, and an LCD display device. And when the LCD is implemented in a touch screen (touch screen) method, it may operate as an input unit.

The key input unit 260 includes keys for inputting numeric and character information and function keys for setting various functions.

3 is a diagram illustrating a handover procedure of a communication terminal in a WLAN system according to an embodiment of the present invention.

1 to 3, in a state in which the communication terminal 200 is currently connected to the first access node 111 in the WLAN system (311), the controller 220 measures the first RSSI at regular intervals (313). ).

Subsequently, the controller 220 determines whether the measured first RSSI exceeds the first threshold value (315). As a result of the determination, when the first RSSI exceeds the first threshold value, the controller 220 maintains a state of being connected with the first access node 111 (316), and when the first RSSI is less than or equal to the first threshold value, It is determined whether the RSSI is less than or equal to the first threshold but exceeds the second threshold (317).

Subsequently, as a result of the determination, if the first RSSI is equal to or less than the first threshold and exceeds the second threshold, the controller 220 emits a probe request (319). The controller 220 receives a probe response from the access node neighboring the communication terminal 200 that receives the emitted probe request (321). Thereafter, the controller 220 analyzes the received probe response (323), and detects the second access node from the neighboring access node that transmits the probe response based on the analyzed result (325). At this time, if the second access node is not detected, the controller 220 maintains the state connected with the first access node (316), and when the second access node is detected, the controller 220 measures the second RSSI ( 327).

Finally, the controller 220 calculates the difference between the measured second RSSI and the first RSSI, that is, the absolute value of the second RSSI-first RSSI or the absolute value of the first RSSI-second RSSI (329). The controller 220 compares the difference value and the delta value between the second RSSI and the first RSSI to determine whether the difference value between the second RSSI and the first RSSI exceeds the delta value (331). As a result of the determination, when the difference value between the second RSSI and the first RSSI is equal to or less than a delta value, the controller 220 maintains a connection with the first access node 111. For example, if the second RSSI is measured at -76 dBm and the first RSSI is measured at -79 dBm, the second RSSI has a larger value than the first RSSI, but the difference between the second RSSI and the first RSSI is 4 dBm. Since it is smaller than the delta value, the controller 220 maintains the state of being connected to the first access node 111 (316).

If the difference between the second RSSI and the first RSSI exceeds the delta value, the controller 220 disconnects the first access node 111 and performs a handover to the second access node 121. Perform (333).

On the other hand, as a result of determining whether the first RSSI is equal to or less than the first threshold and exceeds the second threshold (317), if the first RSSI is equal to or less than the first threshold but does not exceed the second threshold, the controller 220 Determines whether the first RSSI is less than or equal to the second threshold (335). If the first RSSI is less than or equal to the second threshold, the controller 220 emits a probe request (337). In operation 339, the controller 220 receives a probe response from an access node neighboring the communication terminal 200 that receives the emitted probe request. Thereafter, the controller 220 analyzes the received probe response (341), and detects the second access node from the neighboring access node that transmits the probe response based on the analysis result (343). In this case, when the second access node is detected, the controller 220 releases the connection with the first access node 111 and performs a handover to the second access node 121 (333).

If the second access node is not detected, the controller 220 performs a handover to a heterogeneous network, that is, a cellular network (345).

As described above, the method for performing a handover of a communication terminal in a wireless LAN system according to an embodiment of the present invention, before the communication terminal performs the handover, the first RSSI, two reference values, that is, the first threshold value and the second Compared with the threshold value, in particular, when the communication terminal is located in an overlapping area of the service area to which the first access node and the second access node respectively belong, the second RSSI is measured and the difference between the first RSS and the second RSSI is determined by a delta value. Based on the result of the comparison with, it is possible to determine whether to perform the handover. In addition, since the communication terminal performs a handover to the second access node based on the determination result, the ping-pong phenomenon occurs by preventing the communication terminal from reacting sensitively to the minute change in the received field strength with the access node. Can be suppressed, and furthermore, communication delay can be reduced.

Claims (5)

Measuring a received electric field strength with a first access node connected in a WLAN system; If the measured reception field strength with the first access node exceeds a second threshold for performing a handover and is less than or equal to a first threshold that is a predetermined value greater than the second threshold, the second access node in the WLAN system. Measuring the received electric field strength with And performing a handover to the second access node when the measured difference between the received field strength with the second access node and the received field strength with the first access node exceeds a set value. Method for performing handover of a communication terminal in a wireless LAN system. The method of claim 1, If the difference is less than the set value, the method of performing a handover of a communication terminal in a WLAN system, characterized in that further comprising the step of maintaining a connection with the first access node. The method of claim 2, If the measured field strength with the first access node is less than or equal to a second threshold, handover of the communication terminal in the WLAN system, further comprising performing a handover to the second access node. How to do it. The method of claim 2, And performing a handover to a heterogeneous network when the received field strength with the measured first access node is less than or equal to a second threshold value. The method of claim 2, And the set value is a difference between the first threshold value and the second threshold value.

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