JP2750207B2 - Optimal channel assignment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial application field) The present invention relates to a local area network (LAN).
The present invention relates to an optimal channel assignment method for accommodating a wireless terminal constituting a communication network in a wireless base station.

(Prior Art) As a communication network, there is a wide area network that is established through a public line or the like, or a network formed in a limited area such as a building or a factory.

Generally, in a limited area, a network formed by connecting a host computer and a large number of terminals is often a wired network. These are connected via, for example, a bus line, a coaxial cable, or an optical fiber cable.

However, this type of wired network has a drawback that the degree of freedom in arranging terminals and the like is low.

That is, if the rearrangement of the terminals and the like is performed by changing the pattern, complicated wiring work and connection work are required each time. In order to secure the degree of freedom in this type of network layout, it is effective to use wireless communication.
However, if a network is configured only by radio, various problems such as line quality and overhead at the end of communication start occur due to restrictions on frequency band and output.

Therefore, in order to obtain sufficient characteristics while securing the degree of freedom of the network layout, a two-layer communication network as shown in FIG. 2 was previously developed (Japanese Patent Application No. 2-4561).
No. 8, 2-45619).

FIG. 2 shows a conceptual diagram of the two-layer communication network.

The communication network shown in the figure is composed of one wired network 1 composed of a coaxial cable or the like and a plurality of wireless networks 2A, 2B, 2C.

A large number of transceivers 3 for performing input / output control are connected to the wired network 1, and a host computer 4 and a wired terminal 5 are connected to each of the transceivers 3. Enables data communication.

This communication network includes several transceivers 3
In response, the radio base stations 6A, 6B acting as gateways
6C is connected. The wireless base stations 6A, 6B, and 6C relay communication between the wireless terminal 7 and the wired terminal 5 and the host computer 4, respectively, which are arranged within the coverage area (in a circle surrounded by a dashed line in the figure). I do.

Here, for example, the wired network 1 is set up in a building, and each wireless network 2A, 2B, 2C is arranged on each floor of the building or an appropriately partitioned room. In this way, the coverage of the wireless base stations 6A, 6B, 6C themselves is narrow, and the size of the device can be reduced. Further, in the wireless networks 2A, 2B and 2C which are sufficiently separated from each other, completely the same frequency can be used at the same time, and there is no competition between channels. In addition, if the defense range is narrow, the transmission output is small, and the occurrence of interference or the like can be prevented. In addition, the radio base stations 6A, 6B, 6C can be relatively freely added, and the service area can be expanded.

In the above wireless networks 2A, 2B, 2C,
The following control is performed.

FIG. 3 shows the wireless network 2 and the wired network 1
FIG. 3 is an explanatory diagram of a communication protocol for controlling communication with the communication device.

In the figure, a wireless terminal 7 includes a wireless protocol control unit.
7a is provided, and the wireless base station 6A is provided with a wireless protocol controller 6a and a wired network protocol controller 6b. Communication control is performed between the wireless terminal 7 and the wireless base station 6A using a protocol for wireless communication such as known packet communication.

On the other hand, the wireless base station 6A is connected to the wired network 1 via the transceiver 3, and communication control is performed on the wired network 1 by a wired network protocol. This communication control is also based on, for example, packet communication. Then, the wireless base station 6A relays communication between the wireless terminal 7 and another terminal or the like connected to the wired network 1 while mutually performing protocol conversion.

Here, the coverage areas of the wireless networks 2A, 2B, 2C shown in FIG. 2 are not necessarily clearly limited, and may overlap each other. Therefore, there is a possibility that a plurality of wireless base stations receive transmission data from one wireless terminal 7. Therefore, it is necessary to connect the wireless terminal 7 and a specific wireless base station in advance. This is hereinafter referred to as a wireless base station accommodating a wireless terminal.

FIG. 4 shows a sequence chart of a basic terminal accommodation system of the communication network shown in FIG.

The communication network shown in FIG. 2 is not limited to the case where each of the radio base stations 6A, 6B and 6C not only accommodates a fixed radio terminal 7 preset in advance, but also a portable portable computer. It is based on the premise that it may be used in different wireless networks depending on the use situation, such as mobile phones and mobile phones.

In FIG. 4, when the power of a certain wireless terminal 7 is turned on, the wireless terminal 7 first sends an accommodation request to be accommodated in any of the wireless base stations 6A, 6B or 6C (step).

In the example of the communication network shown in FIG. 2, for example, the accommodation request and the like are executed by packet communication. On the other hand, the radio base stations 6A, 6B, and 6C that have received the accommodation request respond to the radio terminal 7. Here, for example, the wireless terminal 7
Is located in the range of the wireless base station 6A, and is outside the range of the wireless base station 6B and the wireless base station 6C.

In this case, the wireless base station 6B or the wireless base station 6C may not always correctly receive the accommodation request of the wireless terminal 7. Even if an accommodation request is received, an error occurs if the received signal level is low, and a retransmission request or the like is made. Even when each of the wireless base stations 6A, 6B, and 6C responds to the wireless terminal 7, the wireless terminal 7 may not correctly receive the response. Therefore, the wireless terminal 7
Receives a correct response at various timings in time. Here, the endless terminal 7 responds to the first correct response from the wireless base station 6A (step in FIG. 4), and transmits an accommodation confirmation to the wireless base station 6A (step in FIG. 4). That is, the responses (steps in FIG. 4) output from the other radio base stations 6B and 6C are ignored.

Upon receiving the accommodation confirmation, the wireless base station 6A determines accommodation of the wireless terminal 7 (step in FIG. 4). Thus, the wireless base station 6A thereafter performs an operation of connecting the wireless terminal 7 to the wired network 1 (FIG. 2).

(Problems to be Solved by the Invention) In the above-described wireless network, available frequency resources are limited, and effective use of frequencies is an important problem. In a mobile phone, which is a typical example of this type of network, the frequency is effectively used by multi-channel access communication using a small zone method. In multi-channel access communication,
The same frequency can be assigned to wireless networks that are sufficiently far from each other.

Determining which frequency is used in which network is called channel allocation, and determining which channel a wireless terminal uses in a predetermined network is called channel assignment.

Here, the channel allocation method includes a fixed channel allocation method in which channels used by each zone are fixedly allocated in advance, and a dynamic channel determination method in which a channel to be allocated is determined in consideration of the entire frequency usage situation every time a communication request is made. There is a channel arrangement method.

When the peak time of the traffic volume of each wireless network varies, it is generally said that the dynamic channel allocation improves the allocation efficiency.

However, the following problem occurs in the two-layer communication network as described in FIG.

That is, unlike a car telephone system, the environment in which a local area network is deployed is harsh. For example, various factors such as variations in the propagation distance of radio waves due to obstacles such as walls, the effects of transmitted and reflected waves, the three-dimensional configuration of wireless base stations on the upper and lower floors, and the traffic density of each wireless network. Considering this, it is extremely difficult to fixedly determine the optimal channel of each radio base station at the design stage before operating the system.

On the other hand, when using the dynamic channel allocation method,
If at least each wireless base station does not know the positional information indicating the positional relationship of each wireless network, an appropriate channel cannot be allocated.

In a network with many wireless base stations,
It is extremely complicated and requires a great deal of labor to individually input the position information of the wireless network to each wireless base station. In addition, in the case where the wireless base station is relocated, or the system is expanded by expanding the system, it is necessary to newly input the position information.

The background of the development of the two-layer network as shown in FIG. 2 is based on the degree of freedom such as rearrangement and expansion of the system. .

The present invention has been made in view of the above points, and an object of the present invention is to provide an optimal channel assignment method capable of automatically acquiring position information and realizing an appropriate channel arrangement.

(Means for Solving the Problems) According to an optimal channel allocation method of the present invention, a plurality of wireless base stations are mutually connected via a wired network, and each of the wireless base stations is connected to an arbitrary one of a plurality of wireless terminals. In the case of accommodating a wireless terminal, each of the wireless base stations selects another one of a plurality of assignable channels and assigns it to a wireless terminal accommodated by itself, and then, in advance, assigns another wireless base station. Receiving all receivable control information transmitted by the base station, and using the signal level and the number of reception times of the control information for each channel as elements, the area multiplicity as an index of the probability of occurrence of communication interference is determined. In this case, the channel allocation is performed by selecting the areas having the lowest area multiplexing in order.

(Operation) According to this optimal channel assignment method, each radio base station obtains the area multiplexing based on the signal level and the number of receptions of the control information for each channel. The control information has a simpler configuration than other communication data, and can be received by a long-distance wireless base station. Therefore, by receiving the control information of the nearest wireless base station in a wide range to some extent and comparing the properties of the signals, it is possible to select a channel in which communication interference is likely to occur in practice. Thus, if channels are allocated from the lowest area multiplicity, optimal channel arrangement becomes possible.

Hereinafter, the present invention will be described in detail with reference to an embodiment shown in the drawings.

FIG. 1 is an explanatory diagram of an optimal channel assignment method according to the present invention.

The method of the present invention is employed in a two-layer communication network as shown in FIG.

Before describing FIG. 1, first, a basic frequency allocation operation between a wireless terminal and a wireless base station will be described.

FIG. 5 is a sequence chart showing an uplink wireless communication procedure, and FIG. 6 is a sequence chart showing a downlink wireless communication procedure. Note that the term “uplink” refers to a direction in which a wireless terminal transmits data to a terminal or the like on a wired network.
Downlink refers to a direction in which a terminal on a wired network or another wireless terminal transmits to a wireless terminal.

FIG. 5 shows a radio base station as described above with reference to FIG.
The wireless terminal 7 issues an accommodation request to 6A, 6B, and 6C, and shows, for example, a communication procedure after the wireless terminal 7 is accommodated in the wireless base station 6A.

Here, first, the wireless terminal 7 transmits a communication request (step in FIG. 5). This communication request is received by the three wireless base stations 6A, 6B, 6C. However, since the wireless terminal 7 has already been determined to be accommodated in the wireless base station 6A, only the wireless base station 6A returns a response to the wireless terminal 7 (step in the figure). In this response, a channel is assigned to the wireless terminal 7. Upon receiving this response, the wireless terminal 7 transmits data to the wireless base station 6A using the assigned channel. Thus, data transmission for one packet becomes possible, and when transmitting for the next packet, the same procedure is repeated.

On the other hand, in FIG. 6, for example, when the radio base station 6C receives communication data for the radio terminal 7, the radio base station 6C transmits the data to another radio base station 6 through the wired network.
A packet containing the identification number of the wireless terminal 7 is generated for A and 6B and a reception request is made (step). Wireless base station 6A
Recognizes that it is a reception request to the wireless terminal 7 accommodated therein, and sends an acknowledgment response to the wireless base station 6C (step). Further, thereafter, the radio base station 6A allocates a channel to the endless terminal 7 (step in the figure), and subsequently transmits communication data (step in the figure).

Next, the concept of area multiplicity serving as a reference for channel allocation in the method of the present invention will be described.

 FIG. 7 is a conceptual explanatory diagram of the area multiplicity.

This figure shows a spatial arrangement of four wireless base stations 10A to 10D.

Here, a plurality of frequency channels are prepared for a wireless network surrounded by a dashed-dotted line, which is a coverage area of each wireless base station. One of them is allocated for communication control, and the other is allocated for data communication, and a multi-channel access method is adopted.

Therefore, in FIG. 7, the range surrounded by the dashed-dotted circle is
As long as the coverage is for the reliable communication of each of the wireless base stations 10A to 10D, the control information can be received in a wider range as indicated by a broken-line circle.

The control information for communication control is, for example, a signal having a relatively simple configuration, which includes commands such as the accommodation request and response described above. On the other hand, communication data is relatively complicated and long.
Therefore, when the quality of the communication line is equal, the bit error probability that a packet is erroneously transmitted is lower in the control information. In general, the longer the distance, the higher the error rate. Therefore, the probability that a control packet can be received at a greater distance than a data packet is higher.

Since the design of the coverage area of the wireless network is designed based on the communication range of communication data that is difficult to reach, the control information reaches the wireless base station from a far distance compared to the coverage area of the wireless base station.

On the other hand, each radio base station has already made the accommodation decision shown in FIG. 4 immediately after the power of the radio terminal has been turned on, and if any radio terminal makes a transmission request,
From the identification number included in the packet, it can be easily determined whether or not the wireless terminal is accommodated by itself. Of course, the control information transmitted by each wireless base station also includes the identification number of the wireless base station.

Then, as the number of times of receiving the control information transmitted by another wireless base station is larger and the average of the received signal levels is larger, it can be determined that the wireless base station is closer. Therefore, if the signal level and the number of times of reception of control information are obtained for each channel and a certain analysis is performed, it is possible to numerically determine the likelihood of occurrence of communication disturbance. The index of the probability of occurrence of the communication disturbance is defined as the area multiplicity in the present invention.

 Hereinafter, a procedure for obtaining the area multiplicity will be described.

FIG. 8 shows a reception history of control information in the radio base station 10A shown in FIG. 7, for example.

FIG. 8 shows the radio wave reception level of the control information of another radio base station received by the radio base station 10A within the past fixed time on the control channel. It is assumed that, for example, five reception histories are stored from the latest one.

In this chart, 1
Numbers are assigned, such as ~ 5.

For example, the reception history 1 is control information transmitted from the radio base station 10B, and its signal level is set to “4”. It is assumed that the signal level increases as the numerical value increases. That is, it can be understood that the higher the signal level, the closer the wireless base station is arranged.

FIG. 9 shows an area multiplicity table in which the area multiplicity in the radio base station 10A is obtained based on the reception history as shown in FIG.

For example, the radio base station 10B receives the radio waves of the signal level "4" in the reception histories 1 and 4, respectively, as shown in FIG. Therefore, the value “8” obtained by integrating these is set as the area multiplicity. As shown in FIG. 8, the radio base station 10C receives radio waves of signal levels "2" and "3" in the reception histories 2 and 5, respectively. If both are integrated, the area multiplicity becomes “5”. The radio base station 10D receives only the radio wave of the signal level "1" in the reception history 3 in FIG. Therefore, the area multiplicity is “1”.

In FIG. 9, it can be considered that a wireless base station having a larger value of the area multiplicity is more likely to cause communication interruption in the wireless base station 10A. Therefore, this makes it possible to determine the degree of overlap of the wireless networks.

For example, if there is a wireless base station having an area multiplicity of “0”, it can be determined that the wireless base station is in a place completely isolated from the wireless base station 10A. Here, when the wireless base station assigns a channel to a communication request from a wireless terminal, the wireless base station follows the principle of assigning a channel that is least likely to interfere with communication at present.

In the dynamic channel allocation method, it is necessary to know the surrounding channel usage in order to determine the optimal channel where interference is less likely to occur. Conventionally, the surrounding channel usage status can be easily obtained by exchanging information between wireless base stations using a wired network. However, if such information exchange is performed, the traffic on the wired network increases.

Therefore, in the present invention, only before each wireless base station uses the channel and only when the use is over and the channel is released, the broadcast function of the wired network is used to determine the usage status of the channel with very simple contents. Added notification of update.

FIG. 10 illustrates a channel use state table used for such notification of the channel use state.

For example, at the start and end of use of a channel, the radio base station 10A transmits information on the used channel to each radio base station using a group broadcast function. Each wireless base station that has received this updates the channel use status table therein as shown in FIG. 10 based on the update data. That is, the content is updated to "1" if the corresponding channel is in use and "0" if the channel is open.

The example of FIG. 10 is a channel use situation when the number of channels is “8”, and it is assumed that a base station having an area multiplicity of “0” is located in a completely isolated place. Does not appear. That is, the channel usage table is
Only those having an area multiplicity of “1” or more need be considered.

When assigning a channel to a communication request from a wireless terminal accommodated therein, the data shown in FIGS. 8 to 10 is used.

Hereinafter, the optimal channel assignment method of the present invention will be described with reference to FIG.

First, when receiving a communication request from a wireless terminal accommodated therein, the wireless base station does not interfere most recently with the nearest station based on the channel usage table managed by itself as shown in FIG. The channel which seems to be assigned as a channel for communication. In this case, if there are a plurality of channels that can be assigned, the channel to be assigned is selected from the one with the lowest area multiplicity based on the area multiplicity described above.

In this case, as shown in FIG. 1, data of the number of used channels is calculated for all the channels.

That is, for example, for the channel “3”, the radio base station 10
A and 10B are unused, and the radio base stations 10C and 10D are in use. In this case, attention is paid only to the radio base station using the channel “3”, and the sum of the area multiplicity at the radio base station is obtained. This is the channel usage count.

Similarly, the channel usage frequency is calculated for each channel.

For example, when the radio base station 10A performs channel assignment, its own channel, that is, in the figure, channel “1” and channel “6” are immediately excluded from assignment targets. In addition, when there is a channel that is not used by any of the radio base stations, the channel usage number becomes “0”, and this is assigned the highest priority.

However, in the example shown in FIG. 1, one of the radio base stations is in a state of using all the channels. In this case, the channel usage numbers are compared numerically. It can be said that the higher the channel usage number, the higher the rate of occurrence of interference. Therefore, the smallest channel usage,
That is, in this case, it is determined that the channel “8” should be assigned.

If there are two or more channels indicating the lowest channel usage frequency, any one of them may be selected at random.

After this channel is determined, another wireless base station is notified through the wired network that the channel is to be used. Further, if a notification using the channel is received from another base station before the notification is correctly transmitted, the channel assignment is restarted from the beginning. Of course, in the case of communication from the wireless base station to the wireless terminal, similarly, after determining the channel to be assigned, the wireless terminal is called, and at the same time, the assigned channel is notified to other wireless base stations.

With the above configuration, before and after data communication, a total of 2 channel usage status update packets having very simple contents are obtained.
Only the transmission is required, and a reduction in the communication volume of the wired network can be expected.

The channel use status update packet is composed of an identification number of the radio base station, a channel number, and a code indicating start or end of use. In addition, this method does not require information conversion at the time of channel allocation,
Channel placement operation is speeded up.

On the other hand, for example, according to a conventional general dynamic channel allocation method, first, it is necessary to input position information at the time of installing a radio base station, but in the method of the present invention, position information is automatically created.

In addition, since only information on the adjacent wireless base station that actually affects communication is provided as position information, there is an advantage that the amount of information is small and the load is small.

 The present invention is not limited to the above embodiments.

In the above embodiment, the example in which the determination of the area multiplicity is performed based on the control information transmitted from the wireless base station has been described. However, the control information transmitted from the wireless terminal may be used.

Various networks such as a token passing bus, a token passing ring, a broadband bus, and a CSMA / CD system can be adopted as the wired network constituting the communication network.

(Effects of the Invention) According to the above-described optimal channel assignment method of the present invention, for the control information received farther than the communication data, the area multiplexing degree is obtained based on the signal level and the number of receptions. Since the channel assignment is performed in order from the one with the lowest severity, the appropriate channel arrangement and channel assignment can be performed by using the dynamic channel method even if the position information of the radio base station is not accurately known in advance. Can be realized. Therefore, it is possible to freely add or move the wireless base station, and when a part of the wireless base station is broken or the power is not turned on, the wireless base station is ignored by another wireless base station. As a result, an effect that the adjacent station complements the communication range of the failed wireless base station can be expected.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an optimum channel allocation method of the present invention, FIG. 2 is a conceptual diagram of a communication network having a two-layer structure, FIG. 3 is an explanatory diagram of a communication protocol of the communication network of FIG.
Fig. 5 is a sequence chart showing a basic terminal accommodating method of the communication network shown in Fig. 2, Fig. 5 is a sequence chart showing an uplink wireless communication procedure of the same communication network, Fig. 6 is a sequence chart showing a downlink wireless communication procedure, Seventh
FIG. 8 is a conceptual explanatory diagram of the area multiplicity in the present invention, FIG. 8 is a chart showing a reception history in the radio base station 10A, FIG. 9 is a chart showing an area multiplicity table in the radio base station 10A, and FIG. It is a chart of a use situation table. 7 ... Wireless terminals, 10A to 10D ... Wireless base stations.

Claims (1)

(57) [Claims] A plurality of wireless base stations connected to each other via a wired network, wherein each of said plurality of wireless base stations accommodates an arbitrary one of a plurality of wireless terminals; When selecting and allocating one of a plurality of assignable channels to a wireless terminal accommodated therein, all the receivable control information transmitted by another wireless base station is transmitted in advance. Receiving, obtaining an area multiplicity as an index of the probability of occurrence of communication disturbance, using the signal level and the number of receptions of the control information for each channel as elements, and selecting in order from the lowest area multiplicity An optimal channel assignment method, wherein channel assignment is performed.