CN101959132A - Base station selection method and device for wireless communication system - Google Patents

Abstract

The invention provides a base station selection method for a wireless communication system. The wireless communication system comprises a plurality of base stations and a plurality of wireless devices, wherein the signal coverage areas of the base stations and the wireless devices are overlapped. The method includes simulating the base stations into variable nodes in a factor graph; emulating the plurality of wireless devices into a plurality of restriction nodes of the factor graph; and using the factor graph to perform operation to select a base station for transmission from the plurality of base stations. Each variable node represents a channel state of each base station, and each restriction node is connected to the variable node corresponding to the base station including the corresponding wireless device in the signal coverage area, and represents that the channel states of the base stations including the corresponding wireless device in the signal coverage area cannot be all closed.

Description

Base station selection method and device for wireless communication system

technical field

The present invention refers to a base station selection method and device for a wireless communication system, especially a method and device for selecting a transmission base station by using a graphical interface to simulate the overlapping coverage of base stations in multicast mode .

Background technique

In a wireless communication system, such as a wireless local area network, if two or more base stations (not associated with each other) have overlapping wireless signal coverage and operate on the same frequency channel, one of the base stations Signals transmitted by a wireless device operating within the coverage area may affect wireless devices operating within the coverage area of another base station. In the field of wireless networks, it is called the Overlapping Basic Service Sets (OBSS) problem.

In unicast mode (unicast), the problem of hidden terminal (hidden terminal) caused by overlapping base station coverage can be solved through a Request To Send (RTS)/Clear To Send (CTS) mechanism to solve. Through the request-to-send/accept-to-send mechanism, the sender sends a request-to-send packet before sending data, and when the receiver receives the request-to-send message, it sends an accept-to-send packet to tell the sender that data can be sent and tell other wireless devices No data can be transmitted during this time to avoid collisions. However, the request transmission/acceptance transmission mechanism cannot be applied to the multicast mode (multicast). Therefore, in the multicast mode, different frequency channels must be assigned to adjacent base stations with overlapping areas to solve the above-mentioned problem of overlapping coverage areas of the base stations. However, as the network topology becomes more and more complex, how to allocate channels efficiently is still an unsolved problem under the condition that the number of channels available to base stations is limited.

In addition, when the signal coverage of the base stations overlaps, when the multicast data is to be transmitted to the wireless devices located in the signal overlapping area, the wireless communication system must properly select the base station for transmission, so as to prevent the data from being incorrectly transmitted. necessary copying. For example, please refer to FIG. 1 . FIG. 1 illustrates a case where a wireless communication system 10 selects a base station when performing multicast transmission under the condition that signal coverages of base stations overlap. As shown in FIG. 1 , it is assumed that a wireless device STA1 is located in the signal overlapping area of the base stations BS1 and BS2, and belongs to the multicast list of the base stations BS1 and BS2 at the same time. Therefore, when the multicast data is to be transmitted to the wireless device STA1, the wireless communication system 10 must select an appropriate base station between the base stations BS1 and BS2 for transmission, for example, only select the base station BS1 to avoid data being unnecessary Duplication, resulting in a waste of transmission resources. However, the prior art does not teach how to efficiently select base stations for transmission to minimize unnecessary data duplication.

Contents of the invention

Therefore, the main purpose of the present invention is to provide a base station selection method and device for a wireless communication system.

The invention discloses a base station selection method for a wireless communication system. The wireless communication system includes multiple base stations and multiple wireless devices with overlapping signal coverage areas. The method includes simulating the plurality of base stations as a plurality of variable nodes of a factor graph, each variable node having a variable representing a channel state of each base station; simulating the plurality of wireless devices as the factor There are a plurality of restricted nodes in the graph, each restricted node is connected to a variable node corresponding to a base station containing the wireless device within the signal coverage, each restricted node has a restriction condition, and the restriction condition represents that the wireless device is included in the signal coverage area The channel states of the base stations of the device cannot all be turned off; and using the factor graph to perform calculations to select a base station for transmission from the plurality of base stations.

The present invention also discloses a device used in a wireless communication system, which is used to execute the aforementioned method to select a base station for transmission in the wireless communication system.

Description of drawings

FIG. 1 illustrates the situation of selecting a base station when a wireless communication system performs multicast transmission under the condition that signal coverages of base stations overlap.

Figure 2 is a schematic diagram of a factorial graph.

FIG. 3 is a schematic diagram of a process in Embodiment 1 of the present invention.

FIG. 4 is a schematic diagram of a wireless communication system with overlapping coverage of base stations.

FIG. 5 illustrates a factor graph generated by simulating the network type in FIG. 4 according to an embodiment of the present invention.

FIG. 6 is a factor diagram generated by simulating the network type in FIG. 4 according to another embodiment of the present invention.

[Description of main component labels]

10, 40 Wireless communication system

STA1～STA5 wireless device

BS1～BS5 base station

F _A ~ F _E channel

f ₁ , f ₂ , f ₃ , CN1～CN5 limit nodes

x ₁ ~ x ₅ , VN1 ~ VN5 variable nodes

SI soft information

30 Process

300, 302, 304, 306, 308 steps

Detailed ways

Through the decentralized nature of the network itself, the present invention uses Factor Graphs with decentralized computing characteristics to simulate the problem of overlapping coverage of base stations in multicast mode, so as to efficiently The base station used for transmission is selected to improve the disadvantages of the known techniques.

The factor graph uses the Sum-Product Algorithms to process various codes in the fields of communication, signal processing, and artificial intelligence with a consistent and efficient graphical view. First, please refer to Figure 2, which is a schematic diagram of a factor graph, which is used to solve an equation:

f(x ₁ ,x ₂ ,x ₃ ,x ₄ ,x ₅ )=f ₁ (x ₁ ,x ₃ )·f ₂ (x ₂ ,x ₃ )·f ₃ (x ₃ ,x ₄ ,x ₅ ) ,(Formula 1)

It can be seen from formula 1 that the f function can be expressed as the product of f ₁ function, f ₂ function and f ₃ function. At the same time, the f ₁ function is only related to x ₁ and x ₃ , the f ₂ function is only related to x ₂ and x ₃ , that is, the f ₃ function is only related to x ₃ , x ₄ and x ₅ . The concept of factor graph is to deal with the relationship between variables and functions from a graphical point of view. Taking Figure 2 as an example, each function is represented by a square, also called a constraint node (Constraint Node) or an agent node (Agent Node), while x ₁ ~ x ₅ is represented by a circle, also called a variable node (Variable Node) ). The connection between the restriction node and the variable node is determined according to the relationship between the function and the variable. For example, the f ₁ function is only related to x ₁ and x ₃ , then the restriction node represented by the f ₁ function is only connected to x ₁ and x ₃ Represents a variable node. By analogy, the factor diagram shown in Figure 2 can be drawn. In addition, the data transmitted between the restriction node and the variable node is soft information (Soft-information) SI, and each soft information is only related to the adjacent restriction node and variable node, and its content can be judged according to other related soft information. For example, the soft information SI(x ₃ , f ₃ ) of node x ₃ to node f ₃ can be expressed as:

SI(x ₃ , f ₃ ) = SI(f ₁ , x ₃ ) · SI(f ₂ , x ₃ )

By analogy, as long as the number of executions is sufficient, the result of f(x ₁ , x ₂ , x ₃ , x ₄ , x ₅ ) can be obtained.

In addition to simplifying complex calculations, factor graphs represent the relationship between functions and variables in a graphical view. Therefore, when expanding the calculation conditions, as long as the relationship between the newly added node and the original node is judged, it can be easily expanded. factor graph.

Please refer to FIG. 3 . FIG. 3 is a schematic diagram of a process 30 according to an embodiment of the present invention. The process 30 is used to implement a base station selection method for a wireless communication system. The wireless communication system, such as a wireless local area network system, includes multiple base stations and multiple wireless devices with overlapping signal coverage areas. Process 30 includes the following steps:

Step 300: start.

Step 302: Simulate the plurality of base stations as a plurality of variable nodes of a factor graph, each variable node has a variable representing a channel status of each base station.

Step 304: Simulate the plurality of wireless devices as a plurality of restricted nodes of the factor graph, each restricted node is connected to a variable node corresponding to a base station containing the wireless device within the signal coverage, and each restricted node has a restriction condition, the restriction condition means that the channel statuses of the base stations including the wireless device within the signal coverage area cannot all be turned off.

Step 306: Use the factor graph to perform calculations to select a base station for transmission from the plurality of base stations.

Step 308: end.

According to the process 30, the embodiment of the present invention simulates base stations and wireless devices with overlapping signal coverage in the wireless communication system as variable nodes and restricted nodes of the factor graph respectively. Wherein, the variable represented by each variable node is the channel status of each base station, and each restricted node is connected to the variable node corresponding to the base station containing the wireless device within the signal coverage range, and the restricted condition represented by it is signal coverage The channel status of the base stations that contain the wireless device within range cannot all be turned off. In this way, the embodiment of the present invention can use the factor graph with distributed computing characteristics to simulate the problem of base station coverage overlap in multicast mode, so as to select base stations for multicast transmission in various network forms. In addition, since the restriction conditions are only defined by the variable nodes connected to the restriction nodes, the embodiments of the present invention can perform distributed computation between the wireless device and the base station, and greatly reduce the complexity of the computation.

For example, please refer to FIG. 4 . FIG. 4 is a schematic diagram of a wireless communication system 40 having coverage overlap of base stations. As shown in FIG. 4 , the wireless communication system 40 includes base stations BS1 - BS5 and wireless devices STA1 - STA5 with overlapping signal coverage areas. In this case, if the variable nodes are represented by circles and the limit nodes are represented by squares, then the one-factor graph generated by simulating the network type in FIG. 4 according to the embodiment of the present invention will be as shown in FIG. 5 . In Fig. 5, the variable nodes VN1-VN5 correspond to the base stations BS1-BS5, which are respectively used to represent the channel states F _A - _FE of each base station; and the restriction nodes CN1-CN5 correspond to the wireless devices STA1-STA5, It is connected to the variable node corresponding to the base stations including the wireless device within the signal coverage area, and is used to indicate that the channel states of the base stations including the wireless device within the signal coverage area cannot all be closed.

For example, the wireless device STA5 is located within the signal coverage of the base stations BS1, BS2, and BS3, so the restricted node CN5 corresponding to the wireless device STA5 needs to be connected to the variable nodes VN1, VN2, and VN3 corresponding to the base stations BS1, BS2, and BS3. In addition, since at least one of the base stations BS1, BS2, and BS3 needs to transmit multicast data to the wireless device STA5, the channels of the base stations BS1, BS2, and BS3 cannot be turned off at the same time. Similarly, the wireless device STA4 is located in the signal coverage of the base stations BS4 and BS5, so the restricted node CN4 corresponding to the wireless device STA4 needs to be connected with the variable nodes VN4 and VN5 corresponding to the base stations BS4 and BS5, and the base stations BS4 and BS5 channels cannot be closed at the same time.

Preferably, the channel states F _A ~ F _E of each base station can be represented by "0" and "1" respectively, "0" represents that the channel of the base station is closed, and "1" represents that the channel of the base station is activated . In this case, in the embodiment of the present invention, a logic equation can be used to express the restriction condition of each restriction node. For example, the restriction conditions of the restriction nodes CN4 and CN5 can be represented by the following equations respectively: F _A +F _B +F _C ≠0 and F _D +F _E ≠0, and so on.

After defining the restriction conditions of each restriction node in the factor graph, the soft message can be transmitted repeatedly between the variable node and the restriction node through the following four steps to determine the channel state of each base station: Step 1: initial variable node ( For example, the initial channel state of each base station channel); Step 2: transfer the soft message from the variable node to the restricted node; Step 3: return the soft message from the restricted node to the variable node; and Step 4: according to the predefined The stop condition stops the delivery of soft messages and makes hard decisions. After the hard decision is made, the embodiment of the present invention can determine the channel state of each base station according to the coordination result between the variable node and the limit node, so as to select the base station for multicast transmission. The operation of the above-mentioned factor graph is known to those skilled in the art, and the detailed operation method will not be repeated here.

Further, the present invention can also increase the performance of calculation by weighting the restriction conditions. For example, when a certain base station is in the signal overlapping area of two base stations, compared with the situation where the channel states of both base stations are in the open state, the embodiment of the present invention can set the channel of only one base station to be in the open state. A higher weight is set for the ON status to increase the efficiency of determining the channel status of the base station. Such corresponding changes also belong to the scope of the present invention.

Generally speaking, after selecting the base station for multicast data transmission, the wireless communication system must also allocate different frequency channels to adjacent and overlapping base stations to avoid transmission data collisions due to hidden nodes. Case. In this case, the embodiment of the present invention can further combine the problem of selecting the transmission base station and the problem of channel allocation of the base station together by using the above-mentioned factor graph. For example, please refer to FIG. 6 . FIG. 6 is a factor diagram generated by simulating the network type in FIG. 4 according to another embodiment of the present invention. In this embodiment, the restriction condition of the restriction node means that all the base stations including the wireless device within the signal coverage cannot be turned off, and also means that the selected channels of the base stations including the wireless device within the signal coverage must be allocated to a different channel. For example, taking the restricted node CN5 as an example, since the wireless device STA5 is within the signal range of the base stations BS1, BS2 and BS3 at the same time, except that the channels of the base stations BS1, BS2 and BS3 cannot be turned off at the same time, the base stations BS1, The channels of BS2 and BS3 shall be allocated to different channels to avoid data transmission collisions. Therefore, the restriction conditions of the restriction node CN5 can be respectively expressed by the following equations: F _A +F _B +F _C ≠0 and F _A ≠F _B ≠F _C . In this case, besides "0" representing the channel of the base station being closed, each variable node also represents an available channel of the base station with "1"-"N". The rest of the limit nodes can be deduced in the same way.

In this way, in the embodiment of the present invention, in addition to selecting the base station used to transmit multicast data, the channel used by the base station can also be determined at the same time, so as to avoid transmission data collision due to the problem of hidden nodes.

In terms of hardware implementation, the present invention can define the meanings represented by base stations and wireless devices according to the requirements of different wireless communication systems. For a wireless local area network system, a base station represents a wireless network access point (Access Point), and a wireless device represents a device equipped with a wireless network card, such as a notebook computer, or related network equipment.

To sum up, the present invention utilizes the decentralized nature of the network itself, and uses a factor graph with decentralized computing characteristics to simulate the problem of base station coverage overlap in multicast mode, so as to efficiently select the base stations in various network forms. The base station for transmission improves the disadvantages of the known technology.

The above descriptions are only preferred embodiments of the present invention, and all equivalent changes and modifications made according to the claims of the present invention shall fall within the scope of the present invention.

Claims (8)

1. base station system of selection that is used for wireless telecommunication system, this wireless telecommunication system include a plurality of base stations and a plurality of wireless device that signal cover overlaps, and this method includes:

These a plurality of base station emulation are become a plurality of variable nodes of a factor graph, and each variable node has a variable, and this variable is represented a channel state of each base station;

These a plurality of wireless device emulation are become a plurality of restriction nodes of this factor graph, the pairing variable node of base station that comprises this corresponding wireless device in each restriction node and signal cover is connected, each restriction node has a restrictive condition, and the channel state that comprises the base station of this corresponding wireless device in this restrictive condition representation signal coverage can not all be closed; And

Utilize this factor graph to carry out computing, with the base station of from these a plurality of base stations, selecting to be used for transmitting.

2. method according to claim 1, wherein on behalf of one of each base station, this variable of each variable node also select channel.

3. method according to claim 2, wherein this restrictive condition of each restriction node selection channel of also comprising the base station of this corresponding wireless device in the representation signal coverage must be assigned to different channels.

4. method according to claim 1 wherein utilizes this factor graph to carry out computing, and the step with the base station selecting to be used for transmitting from these a plurality of base stations includes:

Initial these a plurality of variable nodes;

Between variable node that is connected and restriction node, transmit the flexible message that is relevant to the channel state data repeatedly; And

Stop the transmission repeatedly of flexible message according to a default stop condition, and carry out hard decision, to determine the channel state of these a plurality of base stations.

5. method according to claim 1, it also comprises:

Utilize a weighting scheme to change the restrictive condition of these a plurality of restriction nodes.

6. method according to claim 1, wherein these a plurality of base stations operate in the pattern that multicasts.

7. method according to claim 1, wherein this wireless telecommunication system is a WLAN system.

8. a device that is used for wireless telecommunication system is used for carrying out the method for claim 1, with the base station of selecting to be used for transmitting in this wireless telecommunication system.

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