KR100946053B1 - Wireless lan system and medium access control method of wireless lan based on radio over fiber technolgies - Google Patents

Abstract

Disclosed are a wireless LAN system and a wireless medium access control method based on a radio over fiber technology. The WLAN system includes a central controller for transmitting communication data to be provided to a mobile node; And a plurality of access points connected to the central controller through an optical fiber and wirelessly transmitting communication data received from the central controller to the mobile node through different frequency channels. The central controller sets a handover support section starting at the same time point and ending at the same time point for the plurality of access points, and in the handover support section, a frequency used by each access point adjacent to the access point. The channel can be used to transmit information including its address and channel frequency.

Optical Wireless, Wireless LAN, Millimeter Band, Handover

Description

WIRELESS LAN SYSTEM AND MEDIUM ACCESS CONTROL METHOD OF WIRELESS LAN BASED ON RADIO OVER FIBER TECHNOLGIES}

The present invention relates to a wireless LAN system and a wireless medium access control method based on a radio over fiber technology. More particularly, the entire access point included in the wireless LAN network starts and ends at the same time. The present invention relates to a WLAN system and a WLAN medium access control method capable of handovering a mobile node with a short delay time by transmitting its information on a channel frequency used by an adjacent access point in a handover support interval.

Recently, the millimeter band has received much attention as an alternative frequency band of the next generation WLAN. This millimeter band can provide a wider bandwidth compared to the 2.4 GHz or 5.0 GHz band used in the existing wireless LAN, and is suitable for a gigabit bps high-speed wireless communication, and in particular, the 60 GHz band can be used without a license. There is this. In addition, the millimeter band has the advantage of less external eavesdropping because the transmission distance in the atmosphere is very short compared to the 2.4 GHz or 5.0 GHz band.

However, since the millimeter band has a very short transmission distance, a large number of access points are required to cover a large space such as a large building with a millimeter band wireless LAN, which requires a lot of installation cost to implement the WLAN system. do. In order to solve this problem, a wireless LAN service using Radio over Fiber (ROF) technology, which implements a wireless LAN system by connecting an access point having a simple structure that performs only signal conversion and transmission by optical fiber, Proposed.

In the optical wireless technology, the access point performs only a function of simply converting data received in the form of an optical signal through an optical fiber into a wireless signal form from a central controller that performs most of the processing related to the wireless LAN communication and transferring the data to the mobile node. This can lower the cost of the access point itself. However, even if the optical radio technology is applied, the problem that the area (cell) covered by one access point is smaller than that of the conventional WLAN due to the characteristics of the millimeter band cannot be solved. That is, since the area covered by one access point in the millimeter band is very narrow, the mobile node using the mobile LAN service moves a large number of handovers during the service period. To change the value of. Therefore, the millimeter band WLAN system should be designed in consideration of frequently occurring handover.

In general, as a handover method supported by IEEE 802.11, which is a conventional WLAN standard, a passive scan method and an active scan method are defined. The passive scan method is a method in which a mobile node receives signals while sequentially shifting channels defined in IEEE 802.11, and the active scan method transmits packets according to an access method defined in IEEE 802.11 to determine whether an AP exists. How to ask. Such a handover method according to the conventional WLAN standard has a problem in that a lot of time delay occurs when the cell area is very narrow and frequent handover needs to be performed, such as a millimeter band WLAN system.

According to the present invention, by allowing an access point in a WLAN system to periodically transmit its channel information at a channel frequency used by an adjacent access point, the mobile node can perform handover without performing a scan for handover. It is a technical problem to provide a wireless LAN system and a wireless medium access control method based on optical wireless technology.

As a means for solving the above technical problem, the present invention,

A central controller for transmitting communication data to be provided to the mobile node; And

A plurality of access points connected to the central controller through an optical fiber and wirelessly transmitting communication data received from the central controller to the mobile node through different frequency channels,

The central controller sets a handover support section starting at the same time point and ending at the same time point for the plurality of access points, and in the handover support section, a frequency used by each access point adjacent to the access point. Provided is a wireless LAN system based on optical wireless technology, characterized in that for transmitting information including its own address and channel frequency using a channel.

According to an embodiment of the present invention, the central controller includes its own address and channel frequency by sequentially using frequency channels used by a plurality of access points adjacent to each access point in the handover support section. Information can be sent.

According to an embodiment of the present invention, the mobile node is set to a reception mode capable of wirelessly receiving data through a channel that has been previously used in the handover support section, and an access point that has been previously communicating during the handover support section. When receiving an address and a channel frequency of an access point different from the, the central controller may request a channel change to the received other access point.

As another means for solving the above technical problem, the present invention,

A plurality of access points connected to the central controller and the central controller for transmitting the communication data to be provided to the mobile node through the optical fiber, and wirelessly transmits the communication data received from the central controller to the mobile node through different frequency channels. In the WLAN system comprising a WLAN medium access control method for providing a WLAN service to the mobile node,

Setting, by the central controller, a handover support section starting at the same time point and ending at the same time point for the plurality of access points; And

In the handover support section, causing the central controller to transmit information including its address and channel frequency in each of the access points using a frequency channel used by an adjacent access point; Provide access control methods.

According to one embodiment of the present invention, the step of causing the information to be transmitted includes, in the handover support section, the central controller sequentially using frequency channels used by a plurality of access points adjacent to each other at the access points. Transmitting information including the address and the channel frequency of the.

According to an embodiment of the present invention, in the handover support section, the mobile node may be set to a reception mode capable of wirelessly receiving data through a channel used previously; And requesting a channel change to the received other access point from the central controller when the mobile node receives an address and a channel frequency of an access point different from an existing access point during the handover support period. It may further include.

According to the present invention, since the mobile node can perform the handover without performing the scan for the handover, there is an excellent effect of minimizing the delay time for the handover.

Hereinafter, various embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, embodiments of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below. Embodiment of this invention is provided in order to demonstrate this invention more completely to the person skilled in the art to which this invention belongs. Therefore, it should be noted that the shape and size of the components shown in the drawings may be exaggerated for more clear explanation.

1 is a configuration diagram of a wireless LAN system based on optical wireless technology according to an embodiment of the present invention.

Referring to FIG. 1, a wireless LAN system based on an optical wireless technology according to an embodiment of the present invention includes a central controller 11 and a central controller for transmitting communication data to be provided to a mobile node 14. 11 to a plurality of access points 121 to 123 connected to the mobile node 14 via the optical fiber 13 and wirelessly transmitting the communication data received from the central controller 11 to the mobile node 14 through different frequency channels. Include.

In the case of a downlink (data link from the central controller 11 to the mobile node 14), the central controller 11 may transmit communication data to the mobile node 14 via the access points 121 to 123. Can be. That is, the central controller 11 is connected to the plurality of access points 121 to 123 using optical fibers, and the access points 121 to 123 have a structure in which the mobile node 14 communicates with the mobile node 14. Therefore, the central controller 11 transmits an optical signal that modulates a radio signal of a form including communication data and which can be transmitted from the access points 121 to 123 to the mobile node 14, to the access points 121 to 123. Done. The access points 121 to 123 convert the optical signal received from the central controller 11 into an initial radio signal and then transmit the radio signal to the mobile node 14 through the antenna. In this process, the access points 121 to 123 simply perform an operation of converting an optical signal into an initial wireless signal and amplifying it, and do not perform other complicated data processing.

In the case of the uplink (the link from the mobile node 14 to the central controller 11), the access points 121 to 123 receive a radio signal transmitted from the mobile node 14 via an antenna, The radio signal is modulated into an optical signal and transmitted to the central controller 11 through the optical fiber.

The central controller 11 receives various requests (eg, WLAN access request, data request, etc.) from the mobile node 14 through the access points 121 to 123, processes them, and processes them. Through 123, the mobile node 14 may transmit a result of the request. That is, the central controller 11 may perform overall system control necessary to configure and maintain the WLAN network.

The access points 121 to 123 may perform a function of a simple remote antenna for converting, amplifying and transferring data between the central controller 11 and the mobile node 14. A large number of access points are required to cover a large area with a wireless based millimeter band WLAN. In addition, a communication range in which one access point can communicate with a mobile node is called cells C1 to C3. In order to avoid co-channel interference between adjacent cells covered by adjacent access points, You must use a channel of frequency. In the example shown in FIG. 1, three access points 121 to 123 are shown to use different frequency channels of f1, f2, and f3, respectively. The same channel may be used for a cell at a long distance where cochannel interference is less likely to occur. Although FIG. 1 illustrates an access point arranged in a simple straight line structure for convenience of description, a frequency channel may be allocated between adjacent cells as shown in FIG. 2 on an actual two-dimensional plane. FIG. 2 (a) shows an example of covering the entire area using three different frequencies, and in case of (b), seven different frequencies are allocated to cover the entire area.

In the optical wireless LAN system of the present invention configured as described above, the central controller 11 sets a handover support interval starting at the same time point and ending at the same time point in the process of operating the system. In the over support interval, information including its own address and channel frequency is transmitted using a frequency channel used by an adjacent access point, that is, a frequency channel of an adjacent cell, through each of the entire access points. With reference to the accompanying drawings will be described in more detail the operation of the WLAN system in the handover support interval.

FIG. 3 is a timing diagram illustrating sections of a wireless communication type by a WLAN medium access control method based on an optical wireless technology according to an embodiment of the present invention. In particular, FIG. 3A illustrates an operation performed by the access point 121 of FIG. 1, and FIG. 3B illustrates an operation performed by the access point 122 of FIG. 1, and FIG. 3. (C) illustrates an operation performed in the access point 123 of FIG. Although the example illustrated in FIG. 3 describes the present invention using three access points, this is merely for convenience of description and does not limit the present invention. Also, those skilled in the art will be able to apply the technical idea of the present invention to four or more access points by modifying the present invention with reference to the description of FIG. 3.

Referring to FIG. 3, the central controller 11 controls the operation of each of the access points 121 to 123, and as shown in FIG. The data transmission section and the handover support section can be divided on the time axis. The central controller 11 knows the length of the optical fiber connected to the central controller 11 and each of the access points 121 to 123, that is, the magnitude of the transmission delay between the central controller 11 and each of the access points 121 to 123. As such, the operation section of the access points 121 to 123 may be performed at the same time point at all the access points connected to the central controller 11. That is, the operation section of each of the access points 121 to 123 may be synchronized by the central controller 11.

The central controller 11 allows the access points 121 to 123 to perform normal data transmission and reception with nodes located in the cells C1 to C3, which are respective communication ranges, in the data transmission period. Subsequently, in the handover support section, the central controller 11 sequentially uses the channel frequencies of the access points adjacent to the respective access points 121 to 123 so as to use the frequencies of the channels allocated to them and their own. Broadcast information necessary for communication such as address.

In this handover support interval, adjacent access points should not broadcast simultaneously on the same frequency in order to avoid co-channel interference. For example, in FIG. 3A, the access point 121 transmits handover information using f2 in the t1 section and f3 in the t2 section during the handover support section. Access points 122 and 123 adjacent to the access point 121 should use a frequency other than f1 in the t1 section, and use a frequency other than f2 in the t2 section. Otherwise, co-channel interference may occur and the mobile node may not receive accurate information in the handover support interval. Accordingly, as shown in FIG. 3B, the access point 122 uses f3 in the t1 section and f1 in the t2 section, and as shown in FIG. 3C, the access point 123 f1 is used in the t1 section and f2 is used in the t2 section. As such, various techniques may be used to prevent co-channel interference from occurring in the handover support interval. For example, assuming that the entire system uses n frequencies (f1, f2, ..., fn), an access point using fi sequentially f (i + 1 mod n) in the handover support interval. Broadcasting using the frequencies f (i + 2 mod n), ..., f (i + n-1 mod n) can prevent co-channel interference. Here, mod represents modulo operation.

In this handover support section, the mobile node 14 is set to a reception mode capable of wirelessly receiving data through an existing channel, and the access point of an access point different from that of the access point previously communicating during the handover support section. When receiving communication information such as an address and a channel frequency, handover can be performed without delay by requesting the central controller to change the channel to the other access point.

For example, as shown in FIG. 1, for the handover process performed while the mobile node 14 moves from the cell C2 by the access point 122 to the cell C3 by the access point 123. Let's explain.

It is assumed that the mobile node 14 moves from the cell C2 by the access point 122 to the cell C3 by the access point 123 while receiving the WLAN service on the frequency channel of f2. Moving to cell C3, the mobile node can no longer be served on the f2 frequency channel by access point 122. When the handover support interval is repeated periodically, the mobile node 14 starts to operate in a reception mode, and each of the access points 121 to 123 communicates with each other by using a frequency channel used by an adjacent access point. Send information (your address, the frequency channel assigned to you). In the handover support interval, the mobile node 14 is in a state capable of receiving a previously used f2 frequency channel, and the access point 123 uses its channel frequency f2 of the adjacent access point 122 to receive its own. It transmits information that the address and the channel frequency assigned to it are f3. Since the mobile node 14 has moved to the cell C3, the access point 123 can receive communication information transmitted using the channel frequency f2. This allows the mobile node 14 to find out that it has entered the cell C3 of the access point 123 using the frequency channel of f3. Mobile node 14 then changes the frequency channel to f3 and requests a resource through a new access point 123. The central controller 11 knows that the mobile node 14 has changed the access point with which it can communicate, and allocates resources using the information of the mobile node 14 that it has.

As such, according to the present invention, since the mobile node 14 does not have to spend a separate time to scan a new frequency channel as in a conventional WLAN, time delay required for handover can be minimized.

1 is a configuration diagram of a wireless LAN system based on optical wireless technology according to an embodiment of the present invention.

FIG. 2 illustrates an example of a cell according to a frequency allocated to each of a plurality of access points in a WLAN system.

3 is a timing diagram illustrating sections of a wireless communication type by a WLAN medium access control method based on an optical wireless technology according to an embodiment of the present invention.

* Description of the symbols for the main parts of the drawings *

11: central controller 121, 122, 123: access point

13: fiber 14: mobile node

Claims (6)

A central controller for transmitting communication data to be provided to the mobile node; And A plurality of access points connected to the central controller through an optical fiber and wirelessly transmitting communication data received from the central controller to the mobile node through different frequency channels, The central controller sets a handover support section starting at the same time point and ending at the same time point for the plurality of access points, and in the handover support section, a frequency used by each access point adjacent to the access point. A wireless LAN system based on optical wireless technology, characterized in that for transmitting information including its own address and channel frequency using a channel. The method of claim 1, wherein the central controller, In the handover support section, each access point sequentially transmits information including its own address and channel frequency by using each frequency channel used by a plurality of adjacent access points. One wireless LAN system. The method of claim 1, wherein the mobile node, In the handover support section is set to a reception mode capable of wirelessly receiving data through the existing channel, and receives the address and channel frequency of the access point different from the access point that was previously communicated during the handover support section. And requesting a channel change to the received other access point from the central controller. A plurality of access points connected to the central controller and the central controller for transmitting the communication data to be provided by the mobile node through the optical fiber, and wirelessly transmits the communication data received from the central controller to the mobile node through different frequency channels In the WLAN system comprising a WLAN medium access control method for providing a WLAN service to the mobile node, Setting, by the central controller, a handover support section starting at the same time point and ending at the same time point for the plurality of access points; And Causing the central controller to transmit information including its address and channel frequency in each of the access points using a frequency channel used by an access point adjacent to the access point; WLAN medium access control method comprising a. The method of claim 4, wherein the transmitting of the information comprises: In the handover support section, allowing the central controller to transmit information including its own address and channel frequency by sequentially using frequency channels used by a plurality of adjacent access points in each access point; WLAN medium access control method. The method of claim 4, wherein Setting a reception mode in which the mobile node can wirelessly receive data through a channel used by the mobile node in the handover support section; And During the handover support period, when the mobile node receives an address and a channel frequency of an access point different from an existing access point, requesting a channel change to the received other access point from the central controller; WLAN medium access control method, characterized in that.

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