JP2008153821A - Radio communication system, terminal, base station, and control program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radio communication system capable of securing excellent communication quality by allowing a terminal to select an optimum base station out of a plurality of base stations. <P>SOLUTION: The terminal 1 transmits answer request signals 61, 62, 63, and 64 to base stations 31, 32, 33, and 34. The respective base stations transmit answer signals 71, 72, 73, and 74 to the terminal 1. The terminal 1 measures an answer time from the transmission of each answer request signal to the reception of each answer signal and reception levels and signal quantities of arbitrary signals that the respective base stations transmit. The terminal 1 calculates connection indexes of the respective base stations from answer speeds, reception levels, and signal quantities, and selects a base station having the best communication quality based upon the connection indexes. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a wireless communication system in which a terminal communicates via a base station, and more particularly to a wireless communication system in which a terminal can select an optimal base station from a plurality of base stations.

  In recent years, with the spread of personal computers (hereinafter referred to as “PCs”), PC peripheral devices, and the Internet, LANs have become popular not only in companies but also in general households. Among them, the wireless LAN has an advantage that it does not require a communication cable, so that it is rapidly spreading, and not only information processing apparatuses such as PCs but also mobile information devices such as mobile phones and PDAs are being installed. .

  Mobile phones are also popular all over the world. In Japan, the number of contracts exceeds 90 million and the service area covers almost the whole country.

  A wireless communication system such as a wireless LAN or a mobile phone is a system in which a terminal is directly connected to one base station and communicates with other terminals and servers via the base station. Such wireless communication systems have specific problems.

  For example, in a wireless LAN, an access point (corresponding to a “base station”; hereinafter referred to as “AP”) is easy to install and move, so that the AP and the AP approach each other, and the radio wave coverage of one AP is different from that of another AP. It may overlap with the radio wave coverage of the AP. Furthermore, when the signal output power of the AP is large or the distance between adjacent APs is short, not only the radio wave coverage is overlapped but also the interference between the APs becomes large. Connecting a wireless LAN terminal (hereinafter referred to as “STA”) to an AP in which communication degradation has occurred due to interference leads to a decrease in communication quality. In such a place where APs are densely populated, the STA needs to appropriately select an AP to be connected from a plurality of APs in order to ensure communication quality.

  Various techniques for selecting an optimal AP have been conventionally devised. For example, there is a wireless LAN device that selects a base station using electric field strength (see, for example, Patent Document 1). The technique described in Patent Document 1 uses the electric field strength of a signal from an AP as a criterion for judging communication stability. That is, an AP is selected based on a preset priority order from APs whose electric field strength of a response signal to a search signal from the wireless LAN device is a predetermined value or more.

  Alternatively, there is a wireless LAN system that selects a base station using response time (see, for example, Patent Document 2). The technique described in Patent Document 2 uses response time as a criterion for determining communication efficiency. That is, it is determined that the communication area managed by the AP having the shortest response time to a predetermined frame transmitted from the STA has the lowest congestion and the communication efficiency is good, and the AP is selected.

  In addition, there is a wireless LAN system that selects a base station using electric field strength in addition to response time (see, for example, Patent Document 3). The technique described in Patent Document 3 is to select an AP having the shortest response time from among APs that transmit radio waves having an electric field strength equal to or higher than a predetermined threshold.

JP 2001-308866 A (page 3-4, FIG. 2, FIG. 3) JP 2004-112171 A (page 9-10, FIG. 6) JP 2004-80228 A (Page 5-6, FIG. 5)

  As in the technology described in Patent Document 1, the signal strength from the AP (received level, received signal level, received strength, received signal strength, etc. is essentially determined as a material for judging the quality of communication quality. In the present invention, “reception level” is mainly used in the present invention, which has the following problems. That is, as described above, even an AP having a strong electric field strength of a radio wave to be transmitted may have a strong signal output power of an adjacent AP and receive a large amount of interference from the AP. Such an AP is not necessarily an optimum AP from the viewpoint of communication quality in terms of STA.

  As in the technique described in Patent Document 2, a technique for selecting an AP using only response time may not select a base station even if there is a base station with higher electric field strength and stable communication. There is a problem of having sex.

In the technique described in Patent Document 3, an AP having an electric field strength of a certain value or more is selected, and an AP is selected from the selected AP. Therefore, similarly to the technique described in Patent Document 2, there is a problem that even if there is a base station with higher electric field strength and stable communication can be expected, the base station may not be selected.
(Object of invention)
The present invention has been made in view of the technical problems as described above, and a wireless communication capable of ensuring good communication quality when a terminal selects an optimal base station from a plurality of base stations. An object is to provide a system, a terminal, a base station, and a control program.

  The wireless communication system of the present invention measures the response time of the base station to the response request signal from the terminal, and the reception level and signal quality of the signal transmitted by the base station. Then, from these three measured values, a connection index serving as a determination criterion for selecting one from a plurality of base stations is obtained, and a base station to be connected is determined.

  That is, the wireless communication system of the present invention is a wireless communication system comprising a plurality of base stations and terminals, a response request signal transmitting means for transmitting a response request signal from the terminal to each of the plurality of base stations, and a response request signal A response signal receiving means for receiving a response signal transmitted from each of the plurality of base stations using a terminal, and a response time which is a time from transmission of the response request signal to reception of the response signal. Response time measuring means for measuring using a terminal, reception level measuring means for measuring the reception level of a base station transmission signal transmitted by a base station, signal quality of a base station transmission signal, A signal quality measuring means for measuring using, a connection index calculating means for calculating a predetermined connection index corresponding to each base station based on response time, reception level and signal quality, and a plurality of based on the connection index Providing the connected base station determining means for determining a base station to connect a terminal from a base station, characterized in.

  Furthermore, the wireless communication system of the present invention measures individual response times to a plurality of response request signals transmitted from a terminal to a base station, and reception levels and signal qualities of the plurality of base station transmission signals, and A predetermined calculation process may be performed on the response time, the reception level, and the signal quality, and the connection index may be calculated based on the calculation result.

  That is, the wireless communication system of the present invention receives, using a terminal, response request signal transmitting means for transmitting a plurality of response request signals and each response signal transmitted in response to each of the plurality of response request signals. Response signal receiving means, individual response time measuring means for measuring an individual response time, which is a time from transmission of each of a plurality of response request signals to reception of each response signal, using a terminal, and individual response time Response time calculation means for calculating a response time by performing a predetermined first calculation process; individual reception level measurement means for measuring an individual reception level that is a reception level of each of the plurality of base station transmission signals using a terminal; A reception level calculation means for calculating a reception level by performing predetermined second arithmetic processing on the individual reception level, and measuring individual signal quality, which is each signal quality of a plurality of base station transmission signals, using a terminal And signal quality measuring means may comprise a signal quality calculation means for calculating a signal quality performs third arithmetic processing given to the individual signal quality. This calculation process may be an averaging process or a majority process.

  The wireless communication system of the present invention calculates a connection index from three measurement values, response time, reception level, and signal quality, using a predetermined coefficient for each of the three measurement values, A connection index may be obtained based on the calculation result.

  That is, the wireless communication system of the present invention includes a response time converted value that is a calculation result of the response time and the first coefficient, a reception level converted value that is a calculation result of the reception level and the second coefficient, and signal quality. You may provide the connection parameter | index calculation means which calculates a connection parameter | index based on the signal quality conversion value which is a calculation result with a 3rd coefficient. As signal quality, a signal-to-noise ratio, a bit error rate, or a frame error rate may be used.

  The terminal of the present invention measures the response time of the base station to the signal to the base station, and the reception level and signal quality of the signal transmitted by the base station. Then, from these three measured values, a connection index serving as a determination criterion for selecting one from a plurality of base stations is obtained, and a base station to be connected is determined.

  That is, the terminal of the present invention is a terminal that performs communication via a base station, and a response request signal transmitting unit that transmits a response request signal to each of a plurality of base stations, and a plurality of terminals in response to the response request signal A response signal receiving means for receiving a response signal transmitted from each base station of the base station, a response time measuring means for measuring a response time from a response request signal transmission to a response signal reception, and a base station Each of the base stations based on the response time, the reception level, and the signal quality, the reception level measurement means for measuring the reception level of the base station transmission signal transmitted by the receiver, the signal quality measurement means for measuring the signal quality of the base station transmission signal, And a connection base station determining means for determining a base station to be connected from among a plurality of base stations based on the connection index.

  Furthermore, the terminal of the present invention measures individual response times to a plurality of response request signals transmitted to the base station, and reception levels and signal qualities of the plurality of base station transmission signals, and the plurality of response times and receptions. A predetermined calculation process may be performed on the level and the signal quality, and the connection index may be calculated based on the calculation result. In addition, when calculating the connection index from the three measurement values, the response time, the reception level, and the signal quality, the terminal of the present invention performs an operation using a predetermined coefficient for each of the three measurement values, and the three calculation results Based on the above, a connection index may be obtained. As signal quality, a signal-to-noise ratio, a bit error rate, or a frame error rate may be used.

  The operation of the terminal of the present invention may be controlled by a control program. That is, the terminal of the present invention is a terminal that performs communication via a base station, and a response request signal transmitting unit that transmits a response request signal to each of a plurality of base stations, and a plurality of terminals in response to the response request signal A response signal receiving means for receiving a response signal transmitted by each base station, a response time means for measuring a response time from a response request signal transmission to a response signal reception, and a base station Reception level measuring means for measuring the reception level of the base station transmission signal to be transmitted, and signal quality means for measuring the signal quality of the base station transmission signal are provided. Then, the control program for the terminal includes a response request signal transmitting step for instructing the response request signal transmitting means to transmit a response request signal to each of the plurality of base stations, and a response for inputting the response time from the response time measuring means. Based on the time measurement step, the reception level measurement step of inputting the reception level from the reception level measurement means, the signal quality measurement step of inputting the signal quality from the signal quality measurement unit means, the response time, the reception level and the signal quality, respectively A connection index calculation step of calculating a predetermined connection index corresponding to the base station, and a connection base station determination step of determining a base station to be connected from a plurality of base stations based on the connection index .

  Further, the terminal control program of the present invention includes a step of measuring individual response times to a plurality of response request signals transmitted to the base station, a step of measuring reception levels and signal qualities of the plurality of base station transmission signals, You may provide the process of performing predetermined | prescribed arithmetic processing to several response time, reception level, and signal quality, and the process of calculating a connection parameter | index based on the calculation result. The terminal control program of the present invention calculates a connection index from three measurement values, response time, reception level, and signal quality, using a predetermined coefficient for each of the three measurement values, and You may provide the process of calculating a connection parameter | index based on three calculation results. As signal quality, a signal-to-noise ratio, a bit error rate, or a frame error rate may be used.

  In the wireless communication system of the present invention, a time from when a terminal transmits a response request signal to the base station and when the base station receives a response signal transmitted in response, that is, a “response time” and a signal transmitted by the base station A connection index is calculated based on the reception level and signal quality of the selected base station, and a base station to be connected is selected using the connection index. Therefore, it is possible to connect to the most stable base station, and there is an effect that high communication quality can be ensured.

  The best mode for carrying out the present invention will be described in detail with reference to the drawings, taking a wireless LAN system as an example. There are various types of wireless LANs, but the one that is standardized as IEEE 802.11 is the most common. Therefore, in the description of the best mode for the present embodiment and the embodiment, a wireless LAN of the IEEE 802.11 standard is taken as an example. Unless otherwise specified, a wireless LAN of the IEEE 802.11 standard is simply referred to as “wireless LAN”.

  IEEE802.11a, 802.11b, and 802.11g are added to the IEEE802.11 compliant wireless LAN as physical layer standards in which the frequency band, modulation method, and the like are changed in order to expand the transmission speed. In the present invention, the physical layer standard is arbitrary, and the present invention can be applied to a wireless LAN compliant with any physical layer. Therefore, in the following description, it is assumed that the physical layer conforms to the IEEE 802.11b standard.

  FIG. 1 is a block diagram showing an internal configuration of a wireless LAN terminal (STA) according to the best mode for carrying out the present invention. FIG. 2 is a block diagram showing the internal configuration of the best mode wireless LAN access point (AP). FIG. 3 shows the system configuration of the best mode wireless LAN. FIG. 4 is a sequence diagram of the operation of the best mode. FIG. 5 is a flowchart of the AP selection process in the best mode. FIG. 6 is a flowchart showing processing of a subroutine in the flowchart of FIG.

  First, the system configuration and basic operation of the wireless LAN will be briefly described. When a STA communicates with another terminal or server using a wireless LAN, it normally connects to one AP. This connection form is called infrastructure mode. The wireless LAN also has an ad hoc mode in which the STA and the STA are directly connected. However, since the present invention targets communication using the base station, only the infrastructure mode is handled.

  The STA needs to search for neighboring APs before connecting to the AP. There are various methods for searching for APs, and one method is to send a probe request (referred to as “Probe Request” in the wireless LAN standard), which is a signal for requesting a response, to each of the neighboring APs. is there. Each probe request includes an identification code of the wireless LAN network managed by the AP (hereinafter simply referred to as “AP identification code”). If the identification code in the received probe request matches its own identification code, the AP transmits a probe response (referred to as “Probe Response” in the wireless LAN standard) to the STA. By receiving the probe response, the STA can know that there is an AP having the identification code transmitted in the probe request. The STA can search for neighboring APs and know the existence of APs by transmitting probe requests a plurality of times while sequentially changing the identification codes. Note that the above description of the operation is simplified to the minimum content necessary for the description of the present invention. The exact operation is defined by the wireless LAN standard.

  Next, the internal configuration of the best mode STA will be described. FIG. 1 shows an example of the internal configuration of the STA. The STA 1 includes a radio unit 2, an antenna 3, a data processing unit 4, a response time measurement unit 5, a reception level measurement unit 6, an SNR measurement unit 7, and a connection AP selection unit 8.

  The radio unit 2 converts the radio wave received by the antenna 3 into an electrical signal and outputs it as a received signal 9 to the data processing unit 4. The wireless unit 2 transmits the transmission signal 10 from the data processing unit 4 as a radio wave from the antenna 3.

  Based on the frame transmission instruction signal 11 from the connected AP selection unit 8, the data processing unit 4 configures a probe request frame including an identification code, a channel designation code for designating a frequency to be used, and the like. Is output. At the same time, the data processing unit 4 outputs a response time measurement start signal 12 to the response time measurement unit 5. The data processing unit 4 also analyzes the received signal 9 and detects whether the received signal 9 is a probe response frame that is a response frame to the probe request frame. The probe response frame is a response frame to the probe request frame transmitted from the AP. When it is detected that the received signal 9 is a probe response frame, the data processing unit 4 outputs a response time measurement stop signal 13 to the response time measurement unit 5.

  The response time measurement unit 5 starts measuring the response time according to the response time measurement start signal 12, stops measuring the response time according to the response time measurement stop signal 13, and outputs the response time signal 14 to the connected AP selection unit 8. . Thus, the “response time” is the time from the transmission of the STA probe request frame to the reception of the STA probe response signal.

  The reception level measuring unit 6 measures the reception level of the reception signal 9 of a signal (hereinafter referred to as “AP transmission signal”) transmitted by the AP whose response time is to be measured, and connects the reception level signal 15 to the connected AP. Output to the selector 8. As the reception level, any parameter can be used as long as it is a numerical value that can indicate the intensity of the reception signal 9 such as voltage, current, and power.

  The SNR measurement unit 7 measures a signal-to-noise ratio (Signal to Noise Ratio, hereinafter referred to as “SNR”) of the reception signal 9 of the AP transmission signal, and outputs the signal quality signal 16 to the connected AP selection unit 8.

  A normal wireless LAN includes a correlator to process a received signal. Therefore, as a method for measuring the SNR, there is a method for measuring the SNR of the output of the correlator. In the present embodiment, the correlator is provided inside the SNR measurement unit 7. The correlator may be provided in the radio unit 2 or the data processing unit 4, and in this case, the correlator output may be output to the SNR measurement unit 7.

  There are various methods other than those described above for measuring the SNR, and those skilled in the art can easily select and use an appropriate method. Therefore, description of other SNR measurement methods is omitted.

  The signal whose reception level and SNR are to be measured may be arbitrarily selected as long as the signal is transmitted by the AP (AP transmission signal). For example, a method of using a beacon signal transmitted from the AP at regular intervals is simple. Alternatively, the received signal of the probe response frame may be used for processing in conjunction with response time measurement. This is because it is considered that the reception level and SNR of the signal transmitted by the AP do not depend on the signal content (frame type).

  In the present embodiment, the SNR is used as a measure for measuring the “signal quality” of the AP transmission signal. “Signal quality” in the present invention is a numerical value representing quality and quality as an AP transmission signal, and is not limited to SNR. For example, it may be a bit error rate, a frame error rate, or the like. An embodiment using these as signal quality will be described in a second embodiment.

  The connection AP selection unit 8 calculates a “connection index” to be described later based on the response time signal 13, the reception level signal 14, and the signal quality signal 15, and selects an AP to be connected based on the calculated “connection index”. Then, the STA1 connects to the selected AP and performs subsequent communication via the AP.

  Note that the “connection” here is not limited to simply exchanging signals, but after the STA performs a predetermined authentication process with the AP, it can perform subsequent communication after entering the management. It means becoming a state. In a wireless LAN, such a connection is called “association”.

  FIG. 2 shows an example of the internal configuration of the AP. The AP 21 includes a wireless unit 22, a data processing unit 24, and a control unit 25. The AP 21 only has a function provided in a normal wireless LAN AP, and does not have a function specific to the present invention. In other words, in implementing the present invention, it is not necessary to make any changes to the normal AP, and it can be used as it is.

  The radio unit 22 converts the radio wave received by the antenna 23 into an electric signal and outputs it as a received signal 26 to the data processing unit 24. The wireless unit 22 transmits a transmission signal 27 from the data processing unit 24 as a radio wave from the antenna 3.

  The control unit 25 controls the entire AP based on the wireless LAN standard. Then, the control signal 28 is output to the data processing unit 24.

The data processing unit 24 performs frame transmission / reception control in accordance with the wireless LAN standard according to the control signal 28. As an important function related to the present invention, the data processing unit 4 analyzes the received signal 9 and detects whether or not the received signal 9 is a probe request frame. When detecting that the received signal 9 is a probe response frame, the data processing unit 4 forms a probe response frame and outputs the probe response frame to the radio unit 22 as a transmission signal 27.
(Best mode of operation)
Next, the operation of the best mode will be described. FIG. 3 shows an example of a wireless LAN system in which one STA and four APs exist. AP31, AP32, AP33, and AP34 are installed around the STA1, and these are connected to the wired LAN 41. AP31, AP32, AP33, and AP34 all have the same internal configuration as AP21. A terminal 42 and a server 43 are connected to the wired LAN 41. The STA 1 communicates with the terminal 42 and the server 43 via the wireless LAN and the wired LAN 41. The communicable area 51, the communicable area 52, the communicable area 53, and the communicable area 54 are areas in which transmission signals of the AP 31, AP 32, AP 33, and AP 34 reach the STA 1 and good communication can be performed.

  Even when the STA1 is located outside the communicable area 51, the communicable area 52, the communicable area 53, and the communicable area 54, communication with the AP may be possible although it is not good. Even in such a case, by using the present invention, it is possible to select an AP that can secure the best communication quality and perform stable communication.

  In this best mode, it is assumed that the output signal power of the AP 32 is large, and the AP 32 gives large interference to the adjacent communicable area 51, communicable area 53, and communicable area 54. It is assumed that STA1 is located between AP32 and AP34 and exists in a region where the communicable area 52 and communicable area 54 overlap.

  FIG. 4 shows a sequence when the STA 1 transmits a probe request signal to the AP 31, AP 32, AP 33, and AP 34 and receives a probe response signal in the wireless LAN system of FIG. As described above, in the present invention, the physical layer standard of STA1 and APs 31, 32, 33, and 34 is IEEE802.11b. Therefore, the available channels are 1, 6, 11, and 14ch, and the channels set in each AP are 1ch for AP31, 6ch for AP32, 11ch for AP33, and 14ch for AP34.

  The STA1 transmits a probe request signal to each AP to search for the AP. The probe request signal is transmitted in the order of channels 1ch, 6ch, 11ch, and 14ch that STA1 can use.

  The STA1 transmits the probe request signal 61 to the AP 31 set to 1ch at the timing t1, and receives the probe response signal 71 from the AP 31 at the timing t2. The STA1 transmits the probe request signal 62 to the AP 32 set to 6ch at the timing t3, and receives the probe response signal 72 from the AP 32 at the timing t4. The STA1 transmits the probe request signal 63 to the AP 33 set to 11ch at the timing t5, and receives the probe response signal 73 from the AP 33 at the timing t6. The STA1 transmits the probe request signal 64 to the AP 34 set to 14ch at the timing t7, and receives the probe response signal 74 from the AP 34 at the timing t8.

  The “response time” here is the time from the transmission of each probe request signal by the STA 1 to the reception of the corresponding probe response signal. The response times to the probe request signals 61, 62, 63, 64 are Tr1, Tr2, Tr3, Tr4, respectively. The lengths of Tr1, Tr2, Tr3, Tr4 are not constant, and there are differences depending on the distance from STA1 to AP31, AP32, AP33, AP34, the visibility between STA1 and each AP, and the number and arrangement of people around Arise.

  FIG. 5 is a flowchart showing processing of the connection AP selection unit 8 of the STA1. The connection AP selection unit 8 first calculates the connection index of the AP 31 (step S1), calculates the connection index of the AP 32 (step S2), calculates the connection index of the AP 33 (step S3), and calculates the connection index of the AP 34 ( Step S4) is performed in order. Here, the “connection index” is a numerical value for determining the communication quality between the STA 1 and each AP, and the STA 1 determines the AP to be connected by comparing the magnitude of the connection index of each AP. The connection index calculation process is a subroutine because only the identification code for designating the AP is different and the other processes are the same. The processing contents of the connection index calculation subroutine will be described later. After calculating the connection index of each AP, the connection AP selection unit 8 compares the four connection indices (step S5), and selects the AP with the largest connection index as the AP to be connected (step S6). Thereafter, the STA1 connects (associates) with the selected AP, and thereafter performs communication via the AP.

  Next, processing contents of the connection index calculation subroutine will be described. FIG. 6 is a flowchart illustrating a procedure of connection index calculation processing. The connected AP selection unit 8 first sets an AP identification code for designating an AP in the data processing unit 4 (step S11). Here, it is assumed that the connected AP selection unit 8 specifies the AP 31. Then, the connected AP selection unit 8 instructs the data processing unit 4 to transmit the probe request signal 61 to the AP 31 (step S12).

  When the data processor 8 outputs the transmission signal 10 to the wireless unit 2 in response to an instruction to transmit the probe request signal 61, the probe request signal 61 is transmitted from the antenna 3. Further, the data processing unit 8 outputs a response time measurement start signal 12 to the response time measurement unit 5.

  When receiving the probe response signal 71, the data processing unit 8 outputs the response time measurement stop signal 13 to the response time measurement unit 5. Then, the response time measurement unit 5 outputs the response time signal 14 to the connection AP selection unit 8.

  The reception level measurement unit 6 measures the reception level of an AP transmission signal (not shown) that is an arbitrary signal transmitted by the AP, and outputs a reception level signal 15 to the connected AP selection unit 8. The SNR measurement unit 7 measures the SNR of the AP transmission signal and outputs a signal quality signal 16 to the connected AP selection unit 8. As described above, the measurement of the reception level and the SNR may be performed on the probe response signal 71.

  The connected AP selection unit 8 receives the response time signal 14 and records it as the response time Tr1 of the AP 31 (step S13). Further, the connection AP selection unit 8 receives the reception level signal 15 and the signal quality signal 16, and records the SNR as the reception level and signal quality (steps S14 and S15).

  Next, the connection AP selection unit 8 performs a weighting process on the response time Tr1 using the reception level Ir and the signal quality Q, and calculates a connection index of the AP 31 (step S16).

  In this embodiment, an AP having a large connection index is selected as an AP to be connected. Therefore, the basic concept of weighting when calculating the connection index is that weighting is performed so that the connection index increases when the reception level and signal quality are large so that the connection index increases when the response time is small. Just do it.

Therefore, for example, the calculation formula of the connection index P is
P = k1 / Tr + k2 × Ir + k3 × Q (1)
There is a method.

  Here, k1, k2, and k3 are weighting factors for response time, reception level, and signal quality, respectively, and values may be obtained experimentally so that STA1 can connect to the AP with the best communication quality.

  It is not limited as to what judgment criteria “communication quality” is evaluated. For example, there is a method for determining that the communication quality is good when the throughput is equal to or higher than a predetermined value.

  The method for determining the weighting factor is also arbitrary. For example, if the response time is most important, k1 may be set so that the ratio of k1 / Tr to P is relatively larger than the other two terms.

  The units of numerical values for response time, reception level, and signal quality are arbitrary. Whatever the unit is measured, it can be used without any problem if the weighting factors k1, k2, and k3 are appropriately adjusted. However, it should be noted that whether the numerical value is displayed in a linear or logarithmic manner directly affects the weight of each numerical value.

  For the calculation of the connection indices of AP32, AP33, and AP34, the same processing is performed except that the identification code of each AP is set in step 11.

  In the arrangement of STA1, AP31, AP32, AP33, and AP34 in FIG. 3, the AP closest to STA1 is AP32, and then AP34. Further, the communicable area 52 of the AP 32 completely includes the location where the STA 1 exists. The communicable area 54 of the AP 34 also includes the location where the STA 1 exists. Therefore, Tr2 is the smallest with respect to the response time, and the reception level Ir2 of the AP transmission signal from the AP 32 is also the highest with respect to the reception level. Therefore, if the SNR2 of the AP transmission signal from the AP 32 is the largest, the connection index of the AP 32 is the largest.

  When the calculation of the connection indexes of all APs is completed, the processing after step S5 in FIG. 5 is performed. That is, the connection indices of all APs are compared (step S5), the AP with the largest connection index is selected (step S6), and the process is terminated.

The main process of FIG. 5 and the process of each step of the subroutine of FIG. 6 by the connection AP selection unit 8 may be executed using hardware such as a sequencer. Alternatively, a CPU may be provided inside or outside the connection AP selection unit 8 and executed as program processing by the CPU.
(Effect of the best embodiment)
As described above, the wireless LAN system of the present invention selects the base station based on the response time of the base station to the signal transmitted by the terminal, the reception level of the AP transmission signal, and the signal quality. There is an effect that a stable communication can be performed by connecting to a base station.

Other examples of weighting when calculating the connection index In the best embodiment, the connection index is obtained by multiplying the response speed Tr, the reception level Ir, and the signal quality Q by weighting factors, respectively, as in equation (1). It was.

Other than the equation (1), the weighting may be performed so that the connection index becomes large when the reception level and the signal quality are large so that the connection index becomes large when the response time is small. In the first embodiment, another connection index calculation formula is shown. For example,
P = 1 / Tr × Ir × Q (2)
It is good. In this case, the weights of the three variables are determined depending on whether the numerical value is linearly displayed or logarithmically displayed. Therefore, in order to further adjust the weight of each variable,
P = Tr ^ k4 * Ir ^ k5 * Q ^ k6 (3)
("N ^ m" means n to the power of m). Here, k4, k5, and k6 are response time, reception level, and signal quality weight coefficients, respectively, and values may be obtained experimentally so that STA1 can connect to the AP with the best communication quality. It is desirable that k4 is a negative number and k5 and k6 are positive numbers so that the connection index increases when the reception level and signal quality are large so that the connection index increases when the response time is small.

Alternatively, the connection index may be obtained by a combination of addition and multiplication of Tr ^ k4, Ir ^ k5, and Q ^ k6. That is,
Connection index = Tr ^ k4 # Ir ^ k5 # Q ^ k6 (4)
(# Is + (addition) or x (multiplication)).

As described above, in the present invention, based on the basic idea of performing weighting so that the connection index becomes large when the reception level and the signal quality are large so that the connection index becomes large when the response time is small, Set the connection index calculation formula. The form of the weighting coefficient and the expression may be obtained experimentally, and the specific form of the weighting coefficient and the calculating expression is not limited in the present invention.
(Effect of Example 1)
The calculation formula of the connection index of the first embodiment is configured by three variables or a combination of addition and multiplication of numerical values obtained by multiplying each of the three variables by a weight coefficient, and an optimum connection coefficient is obtained as the weight coefficient and the expression format. Can be set as follows. Therefore, there is an effect that a complicated calculation formula capable of calculating a desired connection coefficient is configured, and an optimum AP can be selected based on the calculation formula.

Other Examples of Signal Quality In the best mode, the SNR is used as a measure for measuring the signal quality of the received AP transmission signal. In the present invention, any numerical value other than SNR can be used as long as the signal quality can be displayed.

  For example, the number of error bits in the AP transmission signal may be counted to obtain a bit error rate (hereinafter referred to as “BER”) and used as the signal quality. The probe response frame of the wireless LAN standard only includes an error detection code (Frame Check Sequence (FCS)), and error bits cannot be counted. Therefore, if the predetermined expected value data is transmitted from the STA 1 and returned to the AP as it is, the number of error bits can be counted and the BER can be obtained. If such a special protocol is defined, the BER can be obtained. However, it is assumed that the BER of the AP transmission signal including various frames can be regarded as equal.

  FIG. 7 is a block diagram of an internal configuration of the STA 1 having a BER measurement function. The STA 1 includes a BER measurement unit 17. The BER measurement unit 18 outputs arbitrary BER measurement data for BER measurement to the data processing unit 4 as transmission data 18. The transmission data 18 is transmitted from the wireless unit 2 to the AP. The AP that has received the transmission data returns the data to the STA 1 as it is. The returned signal is received by the wireless unit 2, and the data processing unit 4 outputs the received data 19 to the BER measuring unit 17. The BER measurement unit 17 compares the transmitted BER measurement data with the received data, counts the number of error bits, and divides by the total number of bits of the BER measurement data to obtain the BER.

  The connection AP selection unit 8 calculates a connection index using BER as signal quality, and selects an AP to be connected.

  In addition to the above BER measurement method, when a frame having an error correction code can be received from the AP, the BER can be obtained by another method. That is, there is a method of obtaining the BER by obtaining the number of error bits from the difference between the bit patterns of the received frame data before error correction and after error correction and dividing by the total number of bits.

  Alternatively, a frame error rate (hereinafter referred to as “FER”) may be used as the signal quality. In this case, it is not necessary to transmit a FER measurement frame in particular, and a probe request frame is transmitted a plurality of times, and a plurality of probe response frames that are responses to each are received. And FER can be calculated | required from the frequency | count of reception of the probe response frame containing an error with respect to the total frequency | count of reception. Whether an error is included in the frame can be determined by the FCS described above.

  FIG. 8 is a block diagram of the internal configuration of the STA 1 having the FER measurement function. The STA 1 includes a FER measurement unit 20. The number of times the response time measurement start signal 12 is output is counted to determine the number of probe request frame transmissions. Further, the FER measuring unit 20 confirms the presence or absence of FCS in the received data 19, counts the number of received frames including an error, and divides by the number of transmissions to obtain the FER.

The connection AP selection unit 8 calculates a connection index using FER as signal quality, and selects an AP to be connected.
(Effect of Example 2)
As described above, in the second embodiment, the connection index is calculated using BER and FER as signal quality. Since BER and FER can be obtained only by digital processing without using special analog processing as in SNR measurement, there is an effect that calculation of a connection index is easy. Furthermore, since the FER can be obtained by receiving a normal probe response of the wireless LAN standard a plurality of times, a special protocol is not required, and the connection index can be calculated more easily.

By the way, in order to avoid collision with radio waves transmitted by other STAs and APs, the wireless LAN uses a CSMA / CA (Carrier Sense Multiple Access Collision Aidance) method. In the wireless LAN CSMA / CA, it is detected that there is no radio wave transmitted by other STAs and APs before transmission, and then transmission is started after waiting for a random time (back-off time). Therefore, when the present invention is applied to a wireless LAN, the measured response time includes an uncertain time corresponding to the back-off time of the STA and the AP. Since the back-off time is a minimum of 31 us and a maximum exceeds 1 ms, the influence of the back-off time on the response time may not be ignored. To be precise, a fixed transmission interval time is included in addition to the back-off time, but this is not considered because it is a time common to all APs.

In the third embodiment, response time, reception level, and signal quality are measured a plurality of times, a connection index is calculated based on a plurality of obtained measurement values, and an AP to be connected is selected.
(Operation of Example 3)
The main process is the same as the process of the best embodiment of FIG.

  In the third embodiment, the processing content of the connection index calculation subroutine is different. FIG. 9 is a flowchart illustrating a procedure of connection index calculation processing according to the third embodiment. The processing from step S11 to step S15 is the same as the processing in the subroutine of the best embodiment of FIG.

  The operations of the data processing unit 8, the radio unit 2, the response time measurement unit 5, the reception level measurement unit 6, and the SNR measurement unit 7 are the same as those in the best embodiment.

  The third embodiment is different in that the processing from step 12 to step 15 is performed a plurality of times. Although three measurements are performed in FIG. 9, the number of times is arbitrary. Steps 12 to 15 are the first measurement, steps 16 to 19 are the second measurement, and steps 20 to 23 are the third measurement. The processing content of step 16 and step 20 is the same as step S12. The processing content of step 17 and step 21 is the same as that of step S13. The processing content of step 18 and step 22 is the same as step S14. The processing content of step 19 and step 23 is the same as that of step S15.

  The connection AP selection unit 8 calculates an average value of each from the measured values of response time, reception level, and signal quality obtained by three measurements (step 24). The average value of response time, reception level, and signal quality is weighted using equations (1), (2), (3), (4), etc., and a connection index is obtained (step 25).

  The method of the third embodiment is also effective when used in a system other than a communication system that performs transmission control using a back-off time. For example, when the AP is communicating with another STA, the response from the STA to the probe request frame may be delayed depending on the communication state of the AP. In such a case, the measured response time becomes longer than the original response time. If the response is steadily delayed, the response time may include the effect. However, if the response time suddenly increases for a certain time, it can be said that the response time does not represent the actual situation.

  Even in such a case, the response time can be approximated to the original response time by measuring the response time multiple times and adopting the average value. At least by using the average value for all APs, it can be said that the accuracy of the relative magnitude relation of the response time is high.

  Regarding the reception level and signal quality, values may be suddenly affected by the influence of transmission radio waves from neighboring STAs and APs. Even in such a case, it can be expected to approach the true value by measuring multiple times and adopting the average value.

  Instead of adopting an average value of a plurality of measured values, a median value may be adopted, or a value to be adopted may be determined by majority vote. Alternatively, assuming that the maximum value or the minimum value means a value under the best condition or the worst condition, the maximum value or the minimum value may be adopted.

For example, for the response time, it can be estimated that the minimum value is the value under the best condition and the maximum value is the value under the worst condition. Therefore, considering the worst case, the maximum response time may be adopted. Or conversely, in consideration of the best case, the minimum response time may be adopted. In the present invention, how to process a plurality of measured values and which value is adopted is not limited.
(Effect of Example 3)
In the third embodiment, response time, reception level, and signal quality are measured a plurality of times, a connection index is calculated using the average value, and an AP to be connected is selected based on the connection index. Therefore, even if the measured values of response time, reception level, and signal quality are affected by a sudden cause of CSMA / CA using a random backoff, the influence on the connection index can be mitigated. There is an effect.

It is a block diagram which shows the internal structure of the wireless LAN terminal of the best form of this invention. It is a block diagram which shows the internal structure of the wireless LAN base station of the best form of this invention. 1 is a system configuration of a wireless LAN according to the best mode of the present invention. It is a sequence diagram of the operation | movement of the best form of this invention. It is a flowchart which shows operation | movement of the best form of this invention. It is a flowchart which shows the process of the subroutine in the flowchart of FIG. 6 is a block diagram of an internal configuration of a wireless LAN terminal having a BER measurement function of Embodiment 2. FIG. 6 is a block diagram of an internal configuration of a wireless LAN terminal having a FER measurement function according to Embodiment 2. FIG. 10 is a flowchart illustrating processing of a subroutine of Example 3.

Explanation of symbols

1 Wireless LAN terminal (STA)
DESCRIPTION OF SYMBOLS 2,22 Radio | wireless part 3 Antenna 4, 24 Data processing part 5 Response time measurement part 6 Reception level measurement part 7 SNR measurement part 8 Connection AP selection part 17 BER measurement part 18 FER measurement part 21, 31, 32, 33, 34 Wireless LAN base station (AP)
25 Control unit 41 Wired LAN
42 terminal 43 server 51, 52, 53, 54 communication area

Claims (20)

A wireless communication system comprising a plurality of base stations and terminals,
Response request signal transmitting means for transmitting a response request signal from the terminal to each of the plurality of base stations;
Response signal receiving means for receiving, using the terminal, a response signal transmitted from each of the plurality of base stations in response to the response request signal;
Response time measuring means for measuring, using the terminal, a response time that is a time from transmission of the response request signal to reception of the response signal;
A reception level measuring means for measuring a reception level of a base station transmission signal transmitted by the base station using the terminal;
Signal quality measuring means for measuring the signal quality of the base station transmission signal using the terminal;
Connection index calculating means for calculating a predetermined connection index corresponding to each of the base stations based on the response time, the reception level and the signal quality;
A wireless communication system comprising connection base station determination means for determining the base station to which the terminal is connected from the plurality of base stations based on the connection index. The response request signal transmitting means for transmitting a plurality of the response request signals;
The response signal receiving means for receiving each of the response signals transmitted in response to each of the plurality of response request signals using the terminal;
Individual response time measuring means for measuring an individual response time, which is a time from transmission of each of the plurality of response request signals to reception of each of the response signals, using the terminal;
Response time calculation means for performing the predetermined first calculation process on the individual response time and calculating the response time;
An individual reception level measuring means for measuring, using the terminal, an individual reception level that is the reception level of each of the plurality of base station transmission signals;
A reception level calculating means for performing a predetermined second calculation process on the individual reception level to calculate the reception level;
Signal quality measuring means for measuring individual signal quality, which is the signal quality of each of the plurality of base station transmission signals, using the terminal;
The radio communication system according to claim 1, further comprising signal quality calculation means for performing the predetermined third arithmetic processing on the individual signal quality and calculating the signal quality. The wireless communication system according to claim 2, wherein the arithmetic processing is averaging processing or majority processing. Response time converted value that is a calculation result of the response time and the first coefficient, reception level converted value that is a calculation result of the reception level and the second coefficient, and calculation of the signal quality and the third coefficient The wireless communication system according to any one of claims 1 to 3, further comprising the connection index calculating means for calculating the connection index based on a signal quality converted value as a result. 5. The wireless communication system according to claim 1, wherein the signal quality is a signal-to-noise ratio, a bit error rate, or a frame error rate. A terminal that communicates via a base station,
Response request signal transmitting means for transmitting a response request signal to each of the plurality of base stations;
Response signal receiving means for receiving a response signal transmitted from each of the plurality of base stations in response to the response request signal;
Response time measuring means for measuring a response time which is a time from transmission of the response request signal to reception of the response signal;
A reception level measuring means for measuring a reception level of a base station transmission signal transmitted by the base station;
Signal quality measuring means for measuring the signal quality of the base station transmission signal;
Connection index calculating means for calculating a predetermined connection index corresponding to each of the base stations based on the response time, the reception level and the signal quality;
A terminal comprising: a connection base station determining means for determining the base station to be connected from among the plurality of base stations based on the connection index. The response request signal transmitting means for transmitting a plurality of the response request signals;
The response signal receiving means for receiving each response signal transmitted in response to each of the plurality of response request signals;
Individual response time measuring means for measuring individual response time which is a time from transmission of each of the plurality of response request signals to reception of each of the response signals transmitted in response to each of the plurality of response request signals When,
Response time calculating means for calculating the response time by performing a predetermined first calculation process for the individual response time Individual reception level measuring means for measuring the individual reception level that is the reception level of each of the plurality of base station transmission signals When,
A reception level calculating means for performing a predetermined second calculation process on the individual reception level to calculate the reception level;
Signal quality measuring means for measuring individual signal quality which is the signal quality of each of the plurality of base station transmission signals;
7. The terminal according to claim 6, further comprising a signal quality calculation unit that performs a predetermined third calculation process on the individual signal quality to calculate the signal quality. The terminal according to claim 7, wherein the calculation process is an averaging process or a majority process. Response time converted value that is a calculation result of the response time and the first coefficient, reception level converted value that is a calculation result of the reception level and the second coefficient, and calculation of the signal quality and the third coefficient The terminal according to any one of claims 6 to 8, further comprising the connection index calculating means for calculating the connection index based on a signal quality converted value as a result. The terminal according to claim 6, wherein the signal quality is a signal-to-noise ratio, a bit error rate, or a frame error rate. A method for controlling a wireless communication system comprising a plurality of base stations and terminals,
A response request signal transmitting step of transmitting a response request signal from the terminal to each of the plurality of base stations;
A response signal receiving step of receiving, using the terminal, a response signal transmitted from each of the plurality of base stations in response to the response request signal;
A response time measuring step of measuring, using the terminal, a response time that is a time from transmission of the response request signal to reception of the response signal;
A reception level measuring step of measuring, using the terminal, a reception level of a base station transmission signal transmitted by the base station;
A signal quality measurement step of measuring the signal quality of the base station transmission signal using the terminal;
A connection index calculation step of calculating a predetermined connection index corresponding to each of the base stations based on the response time, the reception level, and the signal quality;
A control method for a wireless communication system, comprising: a connection base station determination step for determining the base station to which the terminal is connected from the plurality of base stations based on the connection index. The response request signal transmission step of transmitting a plurality of the response request signals;
The response signal receiving step of receiving each of the response signals transmitted in response to each of the plurality of response request signals using the terminal;
An individual response time measuring step of measuring, using the terminal, an individual response time which is a time from transmission of each of the plurality of response request signals to reception of each of the response signals;
A response time calculation step of calculating a response time by performing a predetermined first calculation process for the individual response time, and measuring an individual reception level that is the reception level of each of the plurality of base station transmission signals using the terminal. Individual reception level measurement process,
A reception level calculating step of performing a predetermined second calculation process on the individual reception level to calculate the reception level;
A signal quality measurement step of measuring, using the terminal, individual signal quality that is the reception level of each of the plurality of base station transmission signals;
12. The method of controlling a radio communication system according to claim 11, further comprising a signal quality calculation step of performing a predetermined third calculation process on the individual signal quality to calculate the signal quality. The wireless communication system control method according to claim 12, wherein the calculation process is an averaging process or a majority process. Response time converted value that is a calculation result of the response time and the first coefficient, reception level converted value that is a calculation result of the reception level and the second coefficient, and calculation of the signal quality and the third coefficient The method of controlling a wireless communication system according to any one of claims 11 to 13, further comprising the connection index calculation step of calculating the connection index based on a signal quality converted value as a result. 15. The method according to claim 11, wherein the signal quality is a signal-to-noise ratio, a bit error rate, or a frame error rate. A terminal that communicates via a base station, a response request signal transmitting means for transmitting a response request signal to each of the plurality of base stations, and each of the plurality of base stations in response to the response request signal Response signal receiving means for receiving a response signal transmitted by the base station, response time means for measuring a response time that is a time from transmission of the response request signal to reception of the response signal, and transmission by the base station A control program for a terminal comprising reception level measuring means for measuring a reception level of a base station transmission signal and signal quality means for measuring the signal quality of the base station transmission signal,
A response request signal transmitting step for instructing the response request signal transmitting means to transmit the response request signal to each of the plurality of base stations;
A response time measuring step of inputting the response time from the response time measuring means;
A reception level measuring step of inputting the reception level from the reception level measuring means;
A signal quality measuring step of inputting the signal quality from the signal quality measuring unit means;
A connection index calculating step of calculating a predetermined connection index corresponding to each of the base stations based on the response time, the reception level, and the signal quality;
A control program comprising a connection base station determination step of determining a base station to be connected from among the plurality of base stations based on the connection index. The response request signal transmission step instructing transmission of a plurality of the response request signals;
An individual response time, which is a time from transmission of each of the plurality of response request signals to reception of each of the response signals transmitted in response to each of the plurality of response request signals, is obtained from the response time measuring unit. Individual response time measurement process to be input,
A response time calculating step of calculating the response time by performing a predetermined first calculation process on the individual response time;
An individual reception level measuring step of inputting an individual reception level, which is the reception level of each of the plurality of base station transmission signals, from the reception level measurement means;
A reception level calculating means for performing a predetermined second calculation process on the individual reception level to calculate the reception level;
Signal quality measuring means for inputting individual signal quality, which is the signal quality of each of the plurality of base station transmission signals, from the signal quality measuring means;
17. The control program according to claim 16, further comprising signal quality calculation means for performing a predetermined third calculation process on the individual signal quality and calculating the signal quality. The control program according to claim 17, wherein the arithmetic process is an averaging process or a majority process. Response time converted value that is a calculation result of the response time and the first coefficient, reception level converted value that is a calculation result of the reception level and the second coefficient, and calculation of the signal quality and the third coefficient The control program according to any one of claims 16 to 18, further comprising the connection index calculation step of calculating the connection index based on a signal quality converted value as a result. 20. The control program according to claim 16, wherein the signal quality is a signal-to-noise ratio, a bit error rate, or a frame error rate.

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