JP2008078698A - Radio channel selection method, communication device, wireless access point and program for radio channel selection - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a radio channel selection method with interference from other channels taken into consideration. <P>SOLUTION: A specific communication device determines a method for calculating an interference influence degree showing degrees of influences of interference channels on available radio channels (use candidate channels) and receives signals of all the use candidate channels and measures and stores signal intensities of respective channels and reads out stored signal strength (interference signal strength) of all the interference channels per use candidate channel and calculates degrees of interference influences on the basis of the interference influence degree calculation method determined in an interference influence degree calculation method determination step by using respective interference signal strength and selects maximum degrees of interference influences from degrees of interference influences of interference channels, which are calculated in the interference influence degree calculation step, per use candidate channel and uses degrees of interference influences selected per use candidate channel in the interference influence degree selection step, to select a use candidate channel giving the minimum degree of the interference influence. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a radio channel selection method, a communication apparatus, a radio access point, and a radio channel selection program when performing communication using radio such as a wireless LAN (Local Area Network), and more particularly from among a plurality of radio channels. The present invention relates to wireless communication for selecting a wireless channel optimal for communication.

  In recent years, wireless computer networks have become widely used. In particular, in a company, unlike a wired LAN, a wireless LAN is often used because there is no need to re-install a cable due to cable laying or layout change. There is also a movement to use a wireless LAN as a public connection service.

  The physical layer and the MAC (Medium Access Control) layer of the wireless LAN are standardized by the following (Non-Patent Document 1), and this standard is generally used in wireless LANs for businesses and homes. Since the wireless LAN radio wave reaches about 100 m, it is necessary to install a plurality of wireless APs in order to cover a wide range. In addition, there is a limit to the number of communication channels for wireless communication, and interference may occur between communication channels. There is a need to devise and set a channel to prevent interference.

  However, even if wireless AP channels are allocated within an organization (for example, within a department) and are appropriately installed so that interference does not occur between the wireless APs, radio waves may arrive from wireless APs in other departments, depending on circumstances. Radio waves from other companies across the street may arrive. Such radio waves from other wireless LANs adversely affect wireless communication within the department as interference radio waves. In addition, when public wireless LAN services become common and service providers start to install wireless APs everywhere, radio wave interference problems are expected to become even more serious.

  Radio wave interference occurs not only when the same channel is used by other wireless devices but also when other channels are used. FIG. 18 shows the channel arrangement of the IEEE802.11b / g wireless LAN shown in the following (Non-Patent Document 1), and each channel is standardized so as to be separated by 5 MHz. FIG. 19 shows energy spread in the transmission channel of the IEEE 802.11 wireless LAN. As can be seen from FIGS. 18 and 19, in IEEE802.11b / g, a band of 22 MHz is used in one communication channel, so that the band used in one communication channel is larger than the difference in the center frequency between channels. Interchannel interference is likely to occur. For this reason, it has been conventionally recommended to use at least 5 channels apart.

  By the way, in the wireless LAN, according to the following (Non-patent Document 1), a wireless terminal in a wireless system called an ad hoc network and a wireless terminal in a wireless system called an infrastructure network. There is a network in which wireless terminals communicate indirectly with each other through a wireless AP. The advantage of using the infrastructure network is that, as shown in FIG. 20, when the wireless terminals are separated by a long distance so that the wireless terminals cannot communicate directly with each other, they pass through two wireless APs connected by a wired LAN. Communication is possible without worrying about the position of the communication partner.

  In homes and hot spots, an infrastructure network using this wireless AP is often constructed. However, when a wireless LAN is used in an apartment or a condominium, a wireless LAN signal may leak from an adjacent room or upper and lower rooms. In this case, if the channel setting of the wireless AP is not properly performed, the leaked radio wave using a close channel becomes an interference signal, a packet error due to the interference occurs, and communication efficiency decreases. Similarly, even with hot spots that have recently increased, if appropriate channel settings are not set, wireless APs installed by each service company will interfere with each other and a packet error will occur, and a wireless LAN that maintains sufficient performance The service cannot be provided.

  In order to avoid such interference, the following (Patent Document 1) adopts a method in which the interference signal levels measured at each wireless station are aggregated at the wireless master station, and a channel is selected based on the temporal sum of the interference signal levels. ing. In the following (Patent Document 2), a channel with low interference wave power is selected from channels not used in the own radio communication system. Further, in the following (Patent Document 3), the duration of received power above a certain level is measured, the amount of interference is measured based on the ratio to the observation time, and channel selection is performed based on the amount of interference.

  On the other hand, in a wireless LAN such as IEEE802.11b / g, the influence of interference becomes stronger as the channel used becomes closer to the interference source channel. According to “15.4.7.4 Transmit spectrum mask” in the following (Non-Patent Document 1), as the energy spread in the wireless transmission channel is closer to the center frequency as shown in FIG. 19, the output level becomes higher. Therefore, when adjacent channels are only 5 MHz apart as in IEEE802.11b / g, the closer the channels that generate radio waves, the greater the overlap between the outputs, and the higher the overlap. , More susceptible to interference. For this reason, in channel selection, it is important to evaluate the signal level of other channels and the degree of separation from other channels.

For example, FIG. 21 shows an example of radio wave intensity for each channel. In this example, the vacant channels are 1, 2 and 13, and among the vacant channels, the channel 1 has no radio wave in the adjacent channel 2, but the adjacent channel 3 has a strong radio wave. . On the other hand, in channel 13, the condition is that adjacent channel 12 has a weaker radio wave than channel 3. In such a case, the probability of occurrence of a packet error in either channel 13 or channel 2 depends on the signal strength of other channels, the degree of channel separation, and the characteristics of the individual devices corresponding to them.
JP 2004-320249 A JP 2002-186019 A Japanese Patent No. 3149928 ANSI / IEEE Std 802.11, 1999 Edition Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications

  However, in the devices disclosed in the above-mentioned conventional (Patent Documents 1 to 3), channel selection that avoids interference is performed using the interference intensity of the own channel that is a candidate for use (the radio wave intensity that leaks into the own channel). Therefore, there is a problem that channel selection cannot be performed by directly evaluating the influence of interference radio waves of other channels from the signal strength of other channels.

  In the conventional technology, channel selection is performed based on the radio wave intensity leaking into the own channel. However, due to the characteristics of the wireless system, there is no possibility that communication will be affected even if a certain amount of interference signals exist. There is a problem that the evaluation value used for channel selection does not necessarily correspond to the packet error occurrence rate.

  The present invention has been made in view of the above, and a radio channel selection method, a communication apparatus, which can evaluate the influence of other radio channels and can predict a realistic packet error rate when a radio channel is selected. An object is to obtain a wireless access point and a wireless channel selection program.

  In order to solve the above-described problem, the present invention provides a communication system including a plurality of communication devices, in which a specific communication device selects an optimum radio channel from available radio channels (use candidate channels). An interference influence degree calculation method determining step for determining an interference influence degree calculation method representing a degree of influence from an interference channel on the use candidate channel, and receiving signals of all use candidate channels. A scanning step of measuring and storing the signal strength of each channel, and reading out the signal strengths (interference signal strengths) of all the interference channels stored in the scanning step for each of the use candidate channels, Based on the interference influence calculation method determined in the interference influence calculation method determination step using the signal strength, An interference influence degree calculating step for calculating an influence degree, and an interference influence degree selection for selecting the maximum interference influence degree among the interference influence degrees of the interference channels calculated in the interference influence degree calculating step for each use candidate channel And a radio channel selection step of selecting a use candidate channel having a minimum interference influence level using the interference influence level selected for each use candidate channel in the interference influence level selection step.

  According to the present invention, the channel selection is performed based on the interference signal strength and the interference adjacency based on the transmission power of the use candidate channel and the correlation between the interference signal and the packet error, so that interference from other channels is taken into consideration. Channel selection is possible.

  The radio channel selection method according to the first aspect of the present invention is a communication system constituted by a plurality of communication devices, wherein a specific communication device selects an optimum radio channel from among usable radio channels (use candidate channels). A radio channel selection method in the case of selecting an interference influence degree calculation method determining step for determining a calculation method of an interference influence degree representing a degree of influence from an interference channel on a use candidate channel, and signals of all use candidate channels Scanning step of receiving, measuring and storing the signal strength of each channel, and reading out the signal strengths (interference signal strengths) of all interference channels stored in the scanning step for each use candidate channel Interference based on the interference influence calculation method determined in the interference influence calculation method determination step using the signal strength An interference influence degree calculating step for calculating a reverberation degree; an interference influence degree selecting step for selecting the maximum interference influence degree from the interference influence degrees of the interference channels calculated in the interference influence degree calculating step for each use candidate channel; And a radio channel selection step for selecting a use candidate channel having a minimum interference influence level using the interference influence level selected for each use candidate channel in the interference influence level selection step. There is an effect that channel selection in consideration of interference from other channels becomes possible.

  The radio channel selection method according to the second invention of the present invention is characterized in that the interference influence level is a value that increases or decreases according to the packet error rate (PER) occurrence characteristics in the use candidate channel. It is possible to select a channel in consideration of interference from the.

  The radio channel selection method according to the third aspect of the present invention is characterized in that the interference influence level is calculated using the interference signal strength and the interference adjacency degree indicating the inter-channel distance between the use candidate channel and the interference channel. And has the effect of allowing channel selection in consideration of interference from other channels.

  In the radio channel selection method according to the fourth aspect of the present invention, in the interference influence degree calculation method determination step, the received power pair PER according to the combination of the interference adjacency degree and the interference signal strength value for each manufacturer or each manufacturing model number. The characteristics are measured in advance for all the use candidate channels, and the calculation method of the interference influence level is determined based on the measurement result. This enables channel selection in consideration of interference from other channels. It has the effect of becoming.

  A radio channel selection method according to a fifth aspect of the present invention is characterized in that a PER predicted value is calculated based on a measured received power versus PER characteristic, and a communication throughput predicted value is calculated from the PER predicted value. And has an effect of enabling channel selection in consideration of interference from other channels.

  A radio channel selection method according to a sixth aspect of the present invention is characterized in that the processing of the scanning step, the interference influence degree calculation step, the interference influence degree selection step, and the radio channel selection step is performed at the start of communication. There is an effect that channel selection in consideration of interference from other channels becomes possible.

  A radio channel selection method according to a seventh aspect of the present invention is characterized in that the processing of the scanning step, the interference influence degree calculation step, the interference influence degree selection step, and the radio channel selection step is periodically performed during wireless communication. Thus, channel selection is possible in consideration of interference from other channels.

  A radio channel selection method according to an eighth aspect of the present invention is characterized in that the scanning step, the interference influence degree calculating step, the interference influence degree selection step, and the radio channel selection step are performed according to a request from a user. And has an effect of enabling channel selection in consideration of interference from other channels.

  According to a ninth aspect of the present invention, in a communication system constituted by a plurality of communication apparatuses, a specific communication apparatus selects an optimum radio channel from usable radio channels (use candidate channels). Communication device, a radio channel list storage means for storing signal strengths of signals of all use candidate channels, signals of all use candidate channels are received, signal strengths of each channel are measured, and the signals Scanning means for storing the strength in the wireless channel list storage means, and signal strengths (interference signal strengths) of all interference channels are read from the wireless channel list storage means for each use candidate channel, and each interference signal strength is used. Calculate the interference influence level indicating the degree of influence from the interference channel, and then calculate the maximum interference from the interference influence degrees for each candidate channel. An interference influence degree calculating means for selecting a reverberation degree, and a radio channel selection means for selecting a use candidate channel having a minimum interference influence degree by using the interference influence degree selected for each use candidate channel. This has the effect of enabling channel selection in consideration of interference from other channels.

  The communication apparatus according to the tenth aspect of the present invention is characterized by comprising an activation unit that activates a scanning unit at the start of communication, and allows channel selection in consideration of interference from other channels. It has the action.

  According to an eleventh aspect of the present invention, there is provided a communication device comprising a timer means for periodically starting a scanning means, which makes it possible to select a channel in consideration of interference from other channels. Has an effect.

  According to a twelfth aspect of the present invention, there is provided a communication apparatus comprising: a user operation detection unit that activates a scanning unit in response to a request from a user; and channel selection in consideration of interference from other channels. It has the effect of becoming possible.

  The communication apparatus according to a thirteenth aspect of the present invention is characterized in that the interference influence level is a value that increases or decreases in accordance with a packet error rate (PER) occurrence characteristic in a use candidate channel. It has the effect that channel selection in consideration of interference becomes possible.

  The communication apparatus according to the fourteenth aspect of the present invention is characterized in that the interference influence degree is calculated using the interference signal intensity and the interference adjacency degree indicating the interchannel distance between the use candidate channel and the interference channel. And has an effect of enabling channel selection in consideration of interference from other channels.

  The communication device according to the fifteenth aspect of the present invention measures, for each manufacturer company or each manufacturing model number, a received power versus PER characteristic corresponding to a combination of interference adjacency and interference signal strength values for all use candidate channels. Based on the measurement result, a method for calculating the interference influence degree is determined, and the interference influence degree calculating means calculates the interference influence degree by the calculation method, and considers interference from other channels. The channel selection can be performed.

  The communication device according to the sixteenth aspect of the present invention further comprises a communication throughput creating means for calculating a PER predicted value based on the measured received power versus PER characteristic and calculating a communication throughput predicted value from the PER predicted value. It has a feature that it is possible to select a channel in consideration of interference from other channels.

  According to a seventeenth aspect of the present invention, there is provided a wireless access point having the function of the communication device according to any one of claims 9 to 16, and channel selection in consideration of interference from other channels becomes possible. It has the action.

  According to an eighteenth aspect of the present invention, there is provided a program for selecting a radio channel, which causes a computer to execute the process of the radio channel selection method according to any one of claims 1 to 8, and the other channel. It is possible to select a channel in consideration of interference from the.

  Embodiments of the present invention will be described below.

(Embodiment 1)
FIG. 1 is a block diagram showing a functional configuration example of a first embodiment of a wireless channel selection unit according to the present invention. As shown in FIG. 1, the radio channel selection unit includes a data transmission unit 1, a data reception unit 2, a transmission / reception control unit 3, a scanning unit 4, a radio channel list storage unit 5, an interference influence degree calculation unit 6, and a radio channel selection unit. It comprises means 7, communication throughput calculation means 8, and antenna 9.

  FIG. 2 is a diagram illustrating a functional configuration example of a wireless communication apparatus (hereinafter simply referred to as a communication apparatus) equipped with the wireless channel selection unit of the present embodiment. As shown in FIG. 2, the communication apparatus according to the present embodiment includes a radio channel selection unit 20 and a radio channel selection unit activation unit 21. The radio channel selection unit activation means 21 activates the radio channel selection unit 20 when the communication device is turned on.

  Here, first, the definition of the interference adjacency and the interference influence degree used in the present embodiment will be described.

  In the present embodiment, the interference adjacency degree is defined as representing how many channels are separated from channels that are candidates for use by the wireless AP that is an example of the communication apparatus. For example, when the use candidate channel of the wireless AP is CH1, the interference adjacency when CH2 has an interference radio wave is 1 (same as adjacent interference), and the interference adjacency when CH3 has an interference radio wave is 2 (2 The interference adjacency when CH4 has an interference radio wave is 3 (same as 3 adjacent interference), and the interference adjacency when CH5 has an interference radio wave is 4 (same as 4 adjacent interference). To do.

  Further, the interference influence degree is defined as indicating the degree of influence from other channels in the channel to be used. Specifically, this corresponds to the minimum reception sensitivity in the use candidate channel when there is interference from other channels. Hereinafter, the interference influence degree will be described with reference to the drawings.

  FIG. 3 is a schematic diagram showing the relationship between the received signal strength and the packet error rate (PER), and FIG. 4 is a schematic diagram of the receivable range. In any of the figures, the solid line is a graph when there is no interference and the broken line has interference with a certain intensity. In the example shown in FIG. 3, the PER increases rapidly from a certain received signal strength. It can be considered that the signal strength at which such PER begins to occur represents the minimum received signal strength necessary for maintaining the communication quality (the occurrence of packet errors is small), that is, the minimum reception sensitivity. Generally, since the received signal strength is inversely proportional to the square of the distance between wireless devices, the range in which communication is possible becomes narrower when the minimum receiving sensitivity is lowered. Therefore, as shown in FIG. 3, when there is no interference, the PER is low even if the received signal strength is considerably weak, and it is possible to communicate with a wider range of wireless devices as shown by the solid line in FIG. However, when there is interference, the PER increases even if the received signal strength is strong to some extent, and communication is possible only with a wireless device in a narrow range as indicated by the broken line in FIG.

  In such an environment where interference radio waves exist, the communicable range of the wireless AP becomes narrower than when there is no interference. Alternatively, when the received signal strength is the same, the PER increases when there is interference. For this reason, in order to select a channel with good communication quality, it is necessary to select a channel that is less affected by the interference signal, that is, a channel that has less deterioration in minimum reception sensitivity. For these reasons, in this embodiment, the minimum reception sensitivity in the channel used when there is an interference radio wave from another channel is defined as the interference influence degree, and the interference influence degree is used as an index for channel selection. By selecting a channel having a small interference influence level, it is possible to secure a wide communication range with few packet errors.

  Next, functions of each unit of the radio channel selection unit 20 of the present embodiment will be described. The data transmission means 1 converts the data to be transmitted into a radio signal and performs transmission processing, and the data reception means 2 performs processing to receive the radio signal and convert it into a data signal. The transmission / reception control means 3 performs control related to data transmission or reception, for example, retransmission control during transmission.

  The scanning means 4 performs scanning in order to investigate the radio wave status of each wireless channel. Here, scanning in the IEEE 802.11 standard is a process for searching for wireless APs that can communicate. Specifically, each channel used in the wireless LAN is searched by receiving a beacon from the wireless AP or receiving a probe response that is a response to a probe request addressed to the wireless AP. In the scanning according to the present embodiment, such scanning is performed, or a method of receiving any packet in a channel including a beacon and a probe response is performed. In the former method, a packet from the wireless AP is received, and in the latter method, a packet from the wireless AP and the wireless terminal is received. Which scanning method is used may be freely determined for each wireless system.

  The result of scanning by the scanning unit 4 is stored in the wireless channel list storage unit 5. The transmitter address of the packet received on each channel and the average received signal strength of the packet from the transmitter are stored in the MAC address column and the signal strength column, respectively, as shown in the table of FIG. 5, for example.

  In the present embodiment, the wireless channel list storage means 5 stores the MAC address and signal strength in a table format, but may store in any format such as a list format.

  In the 802.11 MAC layer header, as shown in the table of FIG. 6, the address field stores the address of the access point, the type of wireless and wired, etc. in addition to the source and destination addresses. For wireless devices, the “To DS” bit (0 if the destination is wireless, 1 if the destination is wired) and the “From DS” bit (0 if the transmission source is wireless, the transmission source) In the case of a wired connection, all of the bits (1) are 0, and the address 2 indicates the transmitter address of the packet. Therefore, in this embodiment, the received signal strength of the packet is held for each address of the transmission source wireless device indicated in the address 2 field.

  The interference influence degree calculation means 6 receives from interference signals in all the radio channels based on the interference signal intensity and the interference adjacency degree that are the received signal intensity of the packet received in each channel stored in the radio channel list storage means 5. The interference influence degree and the PER predicted value are calculated. The calculation is performed using a calculation formula or a table. The calculation formula or table for the interference influence degree has different characteristics depending on the manufacturer of the wireless AP as will be described later. Therefore, a calculation formula corresponding to the wireless AP is set in the interference influence degree calculating means 6. Further, the calculated interference influence degree is stored in the wireless channel list storage means 5 as shown in FIG.

  The radio channel selection means 7 reads out the interference influence degree of the wireless channel list storage means 5 and selects the wireless channel with the lowest interference influence degree.

  The communication throughput calculation means 8 calculates the communication throughput that is the most important parameter in actual communication using the selection result of the radio channel selection means 7 and the PER predicted value calculated by the interference influence calculation means 6. . The communication throughput can be calculated according to the following (Equation 1) using the PER predicted value. However, the unit of communication throughput is bps (bit per second: bit / second).

(Total number of bytes of packets received per second) × 8 × (100−PER) / 100 (Equation 1)
The antenna 9 transmits and receives radio waves.

  Subsequently, the operation of the radio channel selection unit 20 of the present embodiment will be described.

  First, when the wireless AP is turned on, the wireless channel selector 20 is activated by the wireless channel selector activation means 21. The scanning unit 4 scans all channels. As described above, the scanning method is a method of receiving a beacon transmitted by another wireless AP, a method of receiving a probe response from another wireless AP in response to a probe request, or all packets other than the probe response. It is a method of receiving. Further, the MAC address of the transmitter of each received packet and the average received signal strength for each transmitter are calculated and stored in the wireless channel list storage means 5.

  Next, the interference influence degree calculation means 6 receives the search result and calculates the interference influence degree for each channel. The channel selection procedure will be described based on the channel selection flowchart of the present embodiment shown in FIG.

  First, the interference influence degree calculating means 6 sets a candidate channel (use candidate channel) for calculating the interference influence degree to an initial value (1 in this example) (step 1). Next, the interference influence degree work area is cleared to zero, and an initial value (1 in this example) of a channel (interference channel) that interferes with the candidate channel is set (step 2).

  Next, the interference influence degree calculation means 6 reads the radio channel list storage means 5 and extracts the maximum radio wave intensity from the signal intensity of the interference channel (step 3). Next, the absolute value of the difference between the candidate channel and the interference channel is obtained as the interference adjacency (step 4). Based on the interference adjacency obtained in step 4 and the maximum radio wave intensity obtained in step 3, the interference influence degree is calculated using a calculation formula or a table obtained in advance based on the measurement result (step 5). The calculated interference influence degree is stored in the interference influence degree work area of the radio channel list storage means 5 corresponding to this interference channel (step 6). Next, the interference channel is incremented by 1 (step 7), and the interference channel is compared with the maximum channel (step 8). If the interference channel exceeds the maximum channel, go to step 9. If not, the process returns to step 3 to calculate the interference influence degree of the next interference channel.

  Next, the interference influence degree calculation means 6 takes out the maximum value from the interference influence degree work area of each channel, sets it as the interference influence degree to the candidate channel, and sets the candidate channel of the radio channel list storage means 5. Write in the column of interference influence degree (step 9). Next, the candidate channel is incremented (step 10), and the candidate channel is compared with the maximum channel (step 11). If the candidate channel exceeds the maximum channel, go to step 12. If not, the process returns to step 2 to calculate the interference influence degree of the next candidate channel. After the interference influence levels of all channels are calculated, the radio channel selection unit 7 reads the interference influence levels from the radio channel list storage unit 5 and selects a channel with the minimum interference influence level (step 12).

  Although the interference influence work area is included in the table of the wireless channel list storage unit 5, another buffer memory or the like may be prepared and held.

  Next, an example of a procedure for obtaining a calculation formula or table used in the interference influence degree calculating means 6 will be described. In the present embodiment, in order to obtain the relationship between the intensity and adjacency of the interference signal and PER, as shown below, first to fourth experiments for measuring PER under different conditions are performed, and based on the results. The calculation formula of the interference adjacency is determined. These experiments were performed for two wireless APs, a wireless AP of S company and a wireless AP of T company. In each experiment, for wireless signal transmission, a wireless terminal is prepared in addition to the wireless AP to be evaluated for both the evaluation symmetric channel and the interference source channel, and a signal is generated from the wireless terminal.

  First, as a first experiment, the PER of the receiving side (wireless AP) was measured while changing the transmission power of the transmitting side (wireless terminal) of the channel to be evaluated in an environment where there is no interference. FIG. 8 shows the results for AP of S Company at that time, and FIG. 9 shows the results for AP of T Company. However, the reception power (reception signal strength) in FIGS. 8 and 9 is calculated by (Equation 2).

Received power (received signal strength) = transmitted power−signal attenuation in transmission path (Equation 2)
Here, the transmission power is an actually measured value, and the signal attenuation in the transmission path is obtained by calculating a predicted value under experimental conditions.

  As shown in FIG. 8, in the case of the wireless AP of company S, when the received power falls below a certain value (XdBm), a packet error occurs suddenly (hereinafter, a packet error occurs suddenly, It describes that it will stand up). In this experiment, when X was obtained from the graph, it was about -90 dBm. Since the reception level X is a level at which PER starts to occur, and can be regarded as the minimum reception sensitivity in the transmission channel of the wireless AP used in the experiment, here, X represents the minimum reception sensitivity. From this experimental result, it can be seen that when there is no interference, communication can be performed with the PER almost zero until the reception power (reception signal strength) of the minimum reception sensitivity XdBm is reached.

  A communication environment without interference as in the first experiment is an ideal state from the viewpoint of interference. Therefore, if a radio channel showing the PER characteristic closest to the PER characteristic at this time is selected, it can be expected that the channel is a good communication environment with the least influence of interference. By the way, in the experimental results of FIG. 8, the PER characteristics change rapidly in the vicinity of the reception power X dBm, and even if the reception power fluctuates slightly, the PER becomes 0% or several 10%. It fluctuates greatly. Therefore, when the PER is predicted using this experimental result, if the received power is close to the level X, it is desirable to predict the PER larger in consideration of the variation of the received power. In this example of the experimental result, instead of the chart of the experimental result, for example, as shown in (Equation 3), a reception power vs. PER approximate expression in consideration of a margin for a variation in received power is used.

PER = 20000 × (7 × x / 8 + 94) ^ (− 3.8531) (Equation 3)
Here, x is received power. In (Equation 3), as described above, since fluctuations in received power are taken into account, there is a possibility that PER may occur even when the received power is smaller than the received power X dBm that causes a packet error measured in an experiment. It is a curve. As described above, by using an approximate expression in which a packet error occurs earlier than the actual power with respect to the received power, more stable radio channel selection can be aimed at. Also, by using this approximate curve, if the received power (received signal strength) from the wireless terminal is known, the PER at the time of packet reception can be easily calculated, so the PER characteristic when this channel is selected is Predictable. In the case of communication apparatuses having different minimum reception sensitivities, for example, a graph obtained by translating (Equation 3) in the received power direction may be used.

Moreover, the approximate expression shown by (Formula 3) is an example, and may be approximated by any calculation expression.
For example,
PER = 2.7697 × e ^ (− 0.1642 × (7 × x / 8 + 94)) (Equation 3 ′)
It may be approximated by a function such as

  Since the result of using the wireless AP of company T shown in FIG. 9 is almost the same as the experiment using the wireless AP of company S, the approximate curve of (Equation 3) is used. In the experimental result of the wireless AP of T company, X was about -90 dBm.

  Subsequently, as a second experiment, in order to investigate the influence of interference, an interference signal was generated in an adjacent channel and PER was measured. The strength of the interference signal is the strength of the signal received by the adjacent channel of the wireless AP to be evaluated when the wireless terminal transmits the signal of the adjacent channel. The interference signal strength of the wireless terminal so that the strength of the interference signal received by the adjacent channel of the wireless AP is in three stages (in this example, a, (a−k), (a−2 × k): unit is dBm). Then, for each interference signal intensity, the transmission power of the channel to be evaluated was changed as in the case where there was no interference signal, and the PER was measured. However, the received power (received signal strength) is calculated by (Equation 2) as in the first experiment.

  FIG. 10 shows the measurement result of the wireless AP of company S in this experiment, and FIG. 11 shows the measurement result of the wireless AP of company T. The case where there is no interference signal is indicated by a circle and a solid line in the figure. If there is an interference signal in the adjacent channel, the measurement results of the interference signal with adBm, (ak) dBm, (a-2 × k) dBm are indicated by triangles, diamonds, and squares, respectively. Shown with accompanying lines.

  First, it can be seen that in the wireless AP of company S shown in FIG. 10, the packet error is more likely to occur as the intensity of the interference signal increases. That is, when there is an interference signal in the adjacent channel, the stronger the interference signal strength, the worse the received signal strength vs. PER characteristics, and the weaker the interference signal strength, the better the received signal strength vs. PER characteristics.

  In detail, the received power at which PER rises in proportion to the interference signal intensity is large. When the received power at which PER rises based on the measurement result is expressed as interference adjacency = 1 and interference signal strength I is I = (a + r) (a is -58.5 dBm in this example), for example, (Equation 4) It can be expressed as In this example, X is the minimum received power when there is no interference, and is −90 dBm, and k is about 10 dBm.

Received power at which PER rises = (X + 40) + (r / k) × 10 (Expression 4)
Next, looking at the experimental results of the wireless AP of company T shown in FIG. 11, when there is an interference signal, the PER characteristic does not tend to drop below about 40% even when the received power is sufficiently large. However, this tendency is the same at any interference strength, and the relationship between the interference strength and the received power at which PER rises is proportional to the interference signal strength. This is common with the AP. Therefore, the received power at which PER rises can be approximated as in (Equation 4 ′), with interference adjacency = 1 and interference signal strength I = (a + r) as variables, as in the case of Company S. In this example, X is the minimum received power when there is no interference, and is −90 dBm, and k is about 10 dBm.

Received power at which PER rises = (X + 37) + (r / k) × 10 (Equation 4 ′)
Next, as a third experiment, PER was measured by generating an interference signal in two adjacent channels (channels with a degree of adjacency of 2). The strength of the interference signal is the strength of the signal received by the two adjacent channels of the wireless AP to be evaluated when the wireless terminal transmits the signal of the two adjacent channels. The interference signal strength of the wireless terminal is adjusted so that the strength of the interference signal received on the two adjacent channels of the wireless AP is in two or three steps, and each interference signal strength is evaluated in the same way as when there is no interference signal. The PER was measured while changing the transmission power of each channel.

  FIG. 12 shows the result of the wireless AP of company S at this time, and FIG. 13 shows the result of the wireless AP of company T. However, the received power (received signal strength) is calculated by (Equation 2).

  As shown in FIG. 12, in the third experiment, it is understood that the received power at which PER rises in proportion to the interference signal intensity, as in the second experiment. The received power at which PER rises can be expressed as (Equation 5), for example, when the interference adjacency = 2 and the interference signal strength I are expressed as I = (a + r) (a is -58.5 dBm in this example). Note that X is the minimum received power when there is no interference, -90 dBm, a is about -58.5 dBm, and k is about 10 dBm.

Received power at which PER rises = (X + 27) + (r / k) × 10 (Expression 5)
As shown in FIG. 13, in the wireless AP of company T, it can be seen that the same result as in the second experiment is obtained with respect to the relationship between the interference intensity and the received power at which the PER rises. The reception power at which the PER rises is expressed as (Equation 5 ′), for example, when the interference adjacency = 2 and the interference signal strength I are expressed as I = (a + r) (a is −58.5 dBm in this example). it can. Note that X is the minimum received power when there is no interference, -90 dBm, a is about -58.5 dBm, and k is about 10 dBm.

Received power at which PER rises = (X + 27) + (r / k) × 10 (Equation 5 ′)
Next, as a fourth experiment, an experiment for changing the interference adjacency was performed. That is, a state in which interference radio waves are generated in order for channels of interference adjacency 1 (adjacent), interference adjacency 2 (2 adjacency), interference adjacency 3 (3 adjacency), and interference adjacency 4 (4 adjacency). Then, the PER of the receiving side (wireless AP) was measured while changing the transmission power of the transmitting side (wireless terminal). The strength of the interference signal is the strength of the signal received on the channel of the interference source of the wireless AP to be evaluated when the wireless terminal transmits the signal of the channel of the interference source. The intensity of the interference signal was not changed, and the PER was measured by changing the transmission power of the channel to be evaluated for each degree of adjacency as in the case where there was no interference signal.

  FIG. 14 shows the result of the wireless AP of company S at this time, and FIG. 15 shows the result of the wireless AP of company T. However, the received power (received signal strength) is calculated by (Equation 2).

  As shown in FIG. 14, the smaller the interference adjacency (the closer the two channels are), the worse the received signal strength vs. PER characteristics, and the larger the interference adjacency (the two channels are separated) are the received signal strength vs. PER. The characteristics will be good. From this measurement result, the interference adjacency d is used as a variable and the received power at which PER rises is approximated. When the interference adjacency = d and the interference signal strength is a (a is -58.5 dBm in this example), for example, ( It can be expressed as Equation 6). In this example, X is the minimum received power when there is no interference, and is −90 dBm, and a is about −58.5 dBm.

Received power at which PER rises = (X + 40) − (d−1) × 10 (Equation 6)
Further, as shown in FIG. 15, in the wireless AP of company T, when the reception power is sufficiently large, PER is approximately constant at about 40% from adjacent interference to 3 adjacent interference, whereas 4 adjacent interference In this case, there is a difference that the PER changes at almost 0% above the rising received signal strength. However, as for the relationship between the interference adjacency and the received power at which the PER rises, there is a common point with the wireless AP of Company S that the smaller the interference adjacency, the worse the received signal strength versus the PER characteristic. Therefore, the received power at which PER rises can be expressed as (Equation 6 ′), for example, when the interference adjacency = d and the interference signal strength is a (a is −58.5 dBm in this example). In this example, X is the minimum received power when there is no interference, and is −90 dBm, and a is about −58.5 dBm.

Received power at which PER rises = (X + 37) − (d−1) × 10 (Equation 6 ′)
As a result of the above second to fourth experiments, from (Equation 4), (Equation 5), and (Equation 6), for the wireless AP of company S, interference signal strength I = (a + r), interference adjacency d For example, the received power at which the PER rises can be approximated by the following (Equation 7). The power represented by (Equation 7) serves as an index representing the influence of interference from other channels. In this embodiment, the interference adjacency is obtained by (Equation 7). In this example, X is the minimum received power when there is no interference, and is −90 dBm, and k is about 10 dBm.

Received power at which PER rises (interference influence level) = (X + 53−13 × d) + (r / k) × 10 (Expression 7)
Similarly, in the case of the wireless AP of company T, the received power at which the PER rises when the interference signal strength (a + r) and the interference adjacency d are from (Equation 4 ′), (Equation 5 ′), and (Equation 6 ′). Can be expressed as follows (Equation 7 ′), for example. Similar to the AP of company S, in this embodiment, the interference adjacency of the wireless AP of company T is a value represented by (Expression 7 ′). In this example, X is the minimum received power when there is no interference, and is −90 dBm, and a is about −58.5 dBm.

Received power at which PER rises (interference influence level) = (X + 47−10 × d) + (r / k) × 10 (Expression 7 ′)
As described above, the interference adjacency is obtained from the interference signal intensity and the interference adjacency by (Equation 7) and (Equation 7 ′). Further, if the interference adjacency, that is, the reception power at which PER rises is known, the received power can be obtained by translating the received power versus PER approximate expression (Equation 3) when there is no interference by (reception power at which PER rises -X). A power versus PER approximation curve can be determined. On the other hand, in the case of the wireless AP of company T, if there is interference from other channels, the PER does not become 0% when the received power is larger than the received power at which the PER rises. For example, as shown in FIG. %. In such a case, the reception power versus PER approximate curve in the case of the wireless AP of company T needs to be translated not only in the reception power direction but also in the PER direction. Specifically, when x is the received power, when (the received power at which x-PER rises)> 0, the PER can be calculated by the following equation.

The PER characteristic curve obtained in (Equation 7 ′) is moved by + 40% in the PER direction (Equation 7 ″)
However, in channel selection, since the PER characteristics can be compared only with the interference influence level, that is, the received power and the received power at which the PER rises, (Equation 7 ′) may be used.

  FIG. 10 shows an example in which the approximate curve of (Equation 3) is translated in the +20 received power direction. Similarly, FIG. 11 shows an example in which the approximate curve of (Equation 3) is translated by +17 in the received power direction. The amount of translation is obtained from the measured value by (received power at which PER rises -X) for each case. As described above, a curve obtained by translating (Equation 3) by this amount of translation is the case's case. It can be regarded as a reception power versus PER approximate curve.

  Note that the PER characteristics of wireless devices are expected to vary depending on the device manufacturer, etc., but as shown here, for example, the PER characteristics as described above were measured for each device manufacturer, and obtained from there. A calculation formula or the like may be determined for each device manufacturer from the result. If there are devices with different characteristics (model numbers are different) even in the same manufacturer, the characteristics may be measured for each device (model number) in the same manner, and a calculation formula or the like may be defined. If the characteristics of the same device are different depending on the channel, a calculation formula or the like may be similarly defined for each channel.

  As described above, it is possible to define the received power versus PER approximate expression (Expression 3) and the received power expression (Expression 7) and (Expression 7 ′) where PER rises based on the experimental results. As a result, if the interference signal intensity and the arbitrary degree of interference adjacency are known, the PER characteristic can be predicted. The calculation formula is an example, and any format may be used as long as the formula can approximate the characteristic. In addition, although the interference influence degree is calculated using an equation here, for example, the relationship between the interference signal strength, the interference adjacency degree, and the interference influence degree is held in a table, and the interference influence degree is calculated using this table. You may take such a method.

  As described above, according to the present embodiment, the PER characteristic of the device itself is measured in advance, and the calculation formula of the interference influence degree that is an index of the PER characteristic is obtained from the result, and the signal strength of channels other than the use candidate radio channel is obtained. Since the interference influence degree of the candidate radio channel is calculated using the (interference intensity) and the interference adjacency degree, and the channel selection is performed by comparing the calculation result, the packet error caused by the interference of the other channel is surely detected. A small number of channels can be selected, and communication can be performed with few communication errors.

(Embodiment 2)
FIG. 16 is a block diagram showing a functional configuration example of a second embodiment of a communication apparatus equipped with a radio channel selection unit according to the present invention. In this embodiment, radio channel selection is performed periodically.

  As shown in FIG. 16, the communication apparatus according to the present embodiment includes a radio channel selection unit 20, a radio channel selection unit activation unit 21, a radio channel switching unit 22, and a timer unit 23.

  The radio channel selection unit 20 has the same function as that of the first embodiment, and thus description thereof is omitted. The timer unit 23 periodically activates the radio channel selection unit activation unit 21 at regular intervals during communication with the wireless terminal. When started by the timer means 23, the radio channel selection unit activation unit 21 activates the scanning unit 4 of the radio channel selection unit 20. The operation of selecting a radio channel after the scanning means 4 is activated is the same as in the first embodiment. The interference influence degree calculation means 6 of the radio channel selection unit 20 calculates the interference influence degree of each channel, and the wireless channel selection means selects the channel having the lowest interference influence degree. The radio channel switching means 22 acquires the channel selected by the radio channel selection unit 20, and switches to the selected channel when the selected channel is different from the currently used radio channel. At this time, switching may be performed when a difference in interference influence between the channel being used and the channel selected by the radio channel selection unit 20 is equal to or larger than a certain difference so that channel switching does not occur unnecessarily.

  As described above, in the present embodiment, the radio channel is periodically selected by the timer. Therefore, even when the interference influence level changes due to a change in the usage status of the radio channel during communication, etc. Reselection of the optimum channel can be performed automatically.

(Embodiment 3)
FIG. 17 is a block diagram showing a functional configuration example of a third embodiment of a communication apparatus equipped with a radio channel selection unit according to the present invention. In the present embodiment, radio channel selection is performed for user operation. In the present embodiment, when the user recognizes that the communication state has deteriorated, for example, the voice is interrupted while using the wireless AP, the channel selection is performed based on the wireless channel selection request by the user. .

  As shown in FIG. 17, the communication apparatus according to the present embodiment includes a radio channel selection unit 20, a radio channel selection unit activation unit 21, a radio channel switching unit 22, and a user operation detection unit 24. The functions of the radio channel selection unit 20, the radio channel selection unit activation unit 21, and the radio channel switching unit 22 are the same as those in the first or second embodiment, and thus the description thereof is omitted. When the user operation detection unit 24 detects a request from the user, the user operation detection unit 24 activates the wireless channel selection unit activation unit 21. Subsequent channel selection and channel switching operations are the same as in the case of periodically performing radio channel selection in the second embodiment.

  As described above, according to the present embodiment, when the user recognizes the deterioration of the communication state, the radio channel can be selected by the user's operation. Even when the interference influence level changes due to the above, the optimum channel can be reselected.

  As described above, the radio channel selection method, the radio access point, the communication device, and the radio channel selection program according to the present invention are useful for communication using radio such as a wireless LAN (Local Area Network), It is suitable for wireless communication in which the optimal wireless channel for communication is selected from among the wireless channels.

Block diagram of radio channel selector of the present invention The block diagram of the communication apparatus containing the radio channel selection part of this invention Schematic explanatory diagram of received signal strength versus PER when there is no interference and when there is interference Schematic illustration of receivable range when there is no interference and when there is interference The figure which shows the example of the various information memorize | stored in a wireless channel list memory | storage means The figure which shows the contents of the IEEE 802.11 address field Flowchart of radio channel selection of the present invention The figure which shows the measurement result of the reception power versus PER in the wireless AP of S company when the interference by the experiment of this invention does not exist The figure which shows the measurement result of the reception power versus PER in the wireless AP of T company when the interference by the experiment of this invention does not exist The figure which shows the measurement result of the reception power versus PER in the wireless AP of S company when interference exists in the adjacent channel by experiment of this invention The figure which shows the measurement result of the reception power versus PER in the wireless AP of T company when interference exists in the adjacent channel by experiment of this invention The figure which shows the measurement result of the reception power versus PER in the wireless AP of S company when interference exists in two adjacent channels by experiment of this invention The figure which shows the measurement result of the reception power versus PER in the wireless AP of T company when interference exists in two adjacent channels by experiment of this invention The figure which shows the measurement result of the reception power versus PER in the wireless AP of S company when the interference of various interference adjacency exists by the experiment of this invention The figure which shows the measurement result of the reception power versus PER in the wireless AP of T company when the interference of various interference proximity degree by the experiment of this invention exists. The block diagram of the apparatus which performs radio channel selection periodically of the present invention The block diagram of the apparatus which performs a radio channel selection by user operation of this invention The figure which shows the radio | wireless channel arrangement | positioning in IEEE802.11b / g. Diagram showing energy spreading in an IEEE 802.11 transmission channel Diagram explaining communication between wireless devices far away Diagram showing examples of signal strength of each channel

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Data transmission means 2 Data reception means 3 Transmission / reception control means 4 Scanning means 5 Radio channel list storage means 6 Interference influence degree calculation means 7 Radio channel selection means 8 Communication throughput calculation means 9 Antenna 20 Radio channel selection part 21 Radio channel selection part Starting means 22 Wireless channel switching means 23 Timer means 24 User operation detecting means

Claims (18)

In a communication system configured by a plurality of communication devices, a specific communication device is a radio channel selection method in a case where an optimal radio channel is selected from available radio channels (use candidate channels),
An interference influence degree calculation method determining step for determining an interference influence degree calculation method representing a degree of influence from an interference channel on the use candidate channel;
A scanning step of receiving signals of all use candidate channels and measuring and storing the signal strength of each channel;
For each use candidate channel, the signal strength (interference signal strength) of all the interference channels stored in the scanning step is read, and the interference influence determined in the interference influence degree calculation method determining step using each interference signal strength. An interference influence degree calculating step for calculating the interference influence degree based on the degree calculation method;
An interference influence degree selection step for selecting the maximum interference influence degree from the interference influence degrees of the interference channels calculated in the interference influence degree calculation step for each of the use candidate channels;
A radio channel selection step of selecting a use candidate channel having a minimum interference influence level using the interference influence level selected for each of the use candidate channels in the interference influence level selection step;
A wireless channel selection method comprising: The radio channel selection method according to claim 1, wherein the interference influence level is a value that increases or decreases according to a packet error rate (PER) generation characteristic in the use candidate channel. 3. The radio channel selection method according to claim 1, wherein the interference influence degree is calculated using the interference signal intensity and an interference adjacency degree indicating a channel-to-channel distance between a use candidate channel and an interference channel. . In the interference influence degree calculation method determining step, the received power versus PER characteristic corresponding to the combination of the interference adjacency degree and the interference signal strength value is measured in advance for all use candidate channels for each manufacturer or each manufacturing model number. 4. The radio channel selection method according to claim 3, wherein a calculation method of the interference influence degree is determined based on the measurement result. The radio channel selection method according to claim 4, wherein a PER predicted value is calculated based on the measured received power versus PER characteristic, and a communication throughput predicted value is calculated from the PER predicted value. The radio channel according to claim 1, wherein the scanning step, the interference influence degree calculating step, the interference influence degree selecting step, and the radio channel selection step are performed at the start of communication. Selection method. The process of the scanning step, the interference influence degree calculating step, the interference influence degree selecting step, and the radio channel selecting step is periodically performed during wireless communication. Wireless channel selection method. The radio according to any one of claims 1 to 7, wherein the scanning step, the interference influence degree calculating step, the interference influence degree selecting step, and the radio channel selecting step are performed according to a request from a user. Channel selection method. In a communication system composed of a plurality of communication devices, a specific communication device is a communication device for selecting an optimal wireless channel from available wireless channels (use candidate channels),
Wireless channel list storage means for storing signal strengths of signals of all use candidate channels;
Scanning means for receiving signals of all use candidate channels, measuring the signal strength of each channel, and storing the signal strength in the wireless channel list storage means;
For each candidate channel, the signal strength (interference signal strength) of all the interference channels is read from the wireless channel list storage means, and the interference influence degree representing the degree of influence from the interference channel is calculated using each interference signal intensity Then, for each use candidate channel, an interference influence degree calculating means for selecting a maximum interference influence degree from among the interference influence degrees,
Radio channel selection means for selecting a use candidate channel that minimizes the interference influence level using the interference influence level selected for each of the use candidate channels;
A communication apparatus comprising: Starting means for starting the scanning means at the start of communication;
The communication apparatus according to claim 9, further comprising: Timer means for periodically activating the scanning means;
The communication apparatus according to claim 9, further comprising: User operation detection means for activating the scanning means in response to a request from a user;
The communication apparatus according to claim 9, 10, or 11. The communication apparatus according to claim 9, wherein the interference influence level is a value that increases or decreases according to a packet error rate (PER) generation characteristic in the use candidate channel. The interference influence degree is calculated using the interference signal intensity and an interference adjacency degree indicating an inter-channel distance between a use candidate channel and an interference channel, according to any one of claims 9 to 13. The communication device described. For each manufacturing company or each manufacturing model number, measure the received power versus PER characteristics according to the combination of interference adjacency and interference signal strength values for all use candidate channels, and calculate the interference influence based on the measurement results. 15. The communication apparatus according to claim 14, wherein the interference influence degree calculating unit calculates an interference influence degree by the calculation method. Further, a communication throughput creating means for calculating a PER predicted value based on the measured received power versus PER characteristic and calculating a communication throughput predicted value from the PER predicted value;
The communication apparatus according to claim 15, comprising: A wireless access point having the function of the communication device according to claim 9. A program for selecting a radio channel, which causes a computer to execute the process of the radio channel selection method according to any one of claims 1 to 8.

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