JP2008060699A - Wireless lan device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wireless LAN device capable of precisely determining an unnecessary signal. <P>SOLUTION: The wireless LAN device includes: a reception signal intensity detector 108 which detects the intensity of a reception signal; a reception signal intensity threshold setting part 115 which dynamically changes a threshold; a reception signal intensity threshold determination part 114 which determines whether the intensity detected by the reception signal intensity detector 108 is equal to or lower than the threshold set by the reception signal intensity threshold setting part 115; a training signal correlation operation and determination part 116 which operates an autocorrelation value of a training signal included in the reception signal and determines whether the operated autocorrelation value is equal to or lower than a threshold set by a training signal correlation threshold setting part 117 or not; and a base band signal processing part 118 which determines whether the reception signal should be rejected or not on the basis of a determination result of the reception signal intensity threshold determination part 114 and that of the training signal correlation operation and determination part 116. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a wireless LAN device compliant with IEEE802.11. In particular, the present invention relates to a wireless LAN device used for network devices, printers, MFPs (Multi Function Peripherals), and the like.

  In a wireless LAN device stipulated in IEEE 802.11, an infrastructure mode that is communication between station terminals (hereinafter simply referred to as “STA”) via an access point (hereinafter simply referred to as “AP”), and a STA There is an ad-hoc mode that communicates directly.

  Generally, when constructing a wireless LAN environment, it is often configured in an infrastructure mode. Data communication via the AP is performed after establishing a link between the STA and the AP. The link establishment method here is a method in which the STA attempts to connect based on a beacon signal periodically issued from the AP, and the STA issues a probe request to the AP. As a result, there is a method of attempting connection based on the probe response returned from the AP. The former is called passive scan, and the latter is called active scan. Based on the respective scan results, authentication (Authentication) and association (Association) are executed, and the connection with the AP is successfully established.

  Here, in the area called the MAC header of the beacon signal transmitted from the AP, as shown in FIG. 4, the AP MAC address is included in the source address and BSSID. The frame body includes time management information, an AP permission function, and the like. In addition, depending on the standard, there is also one that notifies the strength of the signal transmitted by the AP itself.

  Also, today, wireless LANs based on the IEEE 802.11 standard have become widespread, and wireless devices are installed at various locations. Accordingly, the frequency channels used with the spread of wireless LANs are becoming scarce. For example, a plurality of APs may be installed in the same channel in one office.

  Until now, it was not a big problem even if STAs and APs were accessing data at the maximum power level. However, as described above, when the environment is such that many APs are installed, If the transmission power is not suppressed, interference will occur, and the convenience of the original wireless LAN cannot be enjoyed.

  In the IEEE 802.11 standard, signal collision avoidance using CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance) can be cited as a method for avoiding interference. In this method, when a signal carrier is detected, it goes to backoff and waits for the next transmission opportunity. However, in the first place, in a situation where APs are turbulent, most wireless devices detect signals, so they go back-off, and transmission opportunities do not easily go around.

  Further, when a signal from an AP installed far away from the STA is picked up, the STA must analyze the frame of the received signal and notify the upper layer of data. However, in general, there is almost no connection with a remote AP, and data transmission / reception is usually performed after establishing a connection with a nearby AP. Therefore, picking up signals from APs installed far away and increasing software processing such as frame analysis is not very good from a functional standpoint and from the viewpoint of reducing power consumption.

  In addition, it is preferable to reject unnecessary signals at the lower layer (physical layer) as much as possible instead of processing them at the protocol level. Here, as a method of rejecting in the physical layer, a method of making a determination while comparing the received carrier signal strength with a threshold value is known (for example, see Patent Document 1).

  Here, there are various methods for obtaining the signal strength. For example, there is a method of using an RSSI (Receive Signal Strength Indicator) signal generated by an RF (Radio Frequency) block. There is also a method of calculating from the baseband IQ component of the received signal.

  In the former method, the intensity of the received signal cannot always be accurately detected due to the noise component of the circuit, temperature dependency, and the like. In the latter method, the calculation from the baseband IQ signal is saturated beyond the input range of the ADC when a signal exceeding the input range is input depending on the accuracy of the ADC (Analog to Digital Converter). As a result, there were some aspects that could not be calculated accurately.

In order to solve such a problem, Patent Document 1 describes that a threshold value is dynamically changed to determine whether the signal is a target AP signal.
JP 2004-7504 A

  However, in the technique described in Patent Document 1, detection of unnecessary signals depends only on signal strength determination, so there is room for improvement in terms of determining unnecessary signals with high accuracy.

  The present invention has been made in view of the above-described circumstances, and an object thereof is to provide a wireless LAN device capable of accurately determining an unnecessary signal.

  The wireless LAN device of the present invention includes a received signal strength detecting means for detecting the strength of a received signal, a first threshold changing means for dynamically changing a first threshold, and an intensity detected by the received signal strength detecting means. Received signal strength threshold value determining means for determining whether or not is equal to or less than the first threshold value, training signal correlation calculating means for calculating an autocorrelation value of a training signal included in the received signal, and the training signal correlation calculating means Training signal correlation threshold value determining means for determining whether or not the autocorrelation value calculated by the above is less than or equal to a second threshold value, a determination result by the received signal strength threshold value determining means, and a determination result by the training signal correlation threshold value determining means And a reception signal rejection determination means for determining whether or not to reject the reception signal based on the above.

  With this configuration, the threshold value to be compared with the strength of the received signal is dynamically changed, and the received signal is a signal that conforms to the IEEE 802.11 standard using the autocorrelation value of the training signal in addition to the strength of the received signal. Therefore, it is possible to determine an unnecessary signal with high accuracy.

  The wireless LAN device of the present invention has a configuration including a second threshold value changing unit that dynamically changes the second threshold value.

  With this configuration, since the threshold value to be compared with the autocorrelation value of the training signal is dynamically changed, the unnecessary signal can be determined with higher accuracy.

  The wireless LAN device of the present invention further comprises first threshold value determining means for determining the first threshold value based on a received signal from the access point when establishing a connection with the access point, The signal strength threshold value determining means has a configuration for determining whether or not the intensity detected by the received signal strength detecting means is equal to or less than the first threshold value determined by the first threshold value determining means.

  With this configuration, since the threshold value is determined based on the reception signal from the access point, it is possible to maintain a signal reception state from an appropriate access point.

  The wireless LAN device of the present invention has a configuration including transmission signal strength determining means for determining the strength of the transmission signal based on the first threshold value.

  With this configuration, the power consumption can be reduced because the strength of the transmission signal is optimized. In addition, since it is possible to suppress radio waves coming to terminals other than the access point to be connected, the processing load on the terminals other than the connected access point can be reduced. Therefore, even in an environment where there are many access points, unnecessary radio waves do not appear on the medium more than necessary, and transmission / reception communication performance of the entire wireless LAN is improved.

  The wireless LAN device of the present invention has a configuration including transmission signal strength determining means for determining the strength of a transmission signal based on the first threshold value and the second threshold value.

  With this configuration, it is possible to further optimize the strength of the transmission signal as compared with the case where only the strength of the received signal is used as a basis for determination.

  In addition, the wireless LAN device of the present invention includes a MAC address holding unit that holds the MAC address of the access point that has been successfully established, and a signal from the access point of the MAC address that the received signal is held by the MAC address holding unit MAC address determination means for determining whether or not the received signal rejection determination means determines whether or not to reject the reception signal based on a determination result by the MAC address determination means. Have.

  With this configuration, it is determined that the strength of the signal detected by the received signal strength detection unit is not less than the first threshold value, and the autocorrelation value calculated by the training signal correlation calculation unit is not less than the second threshold value. Even in such a case, it is possible to reject a reception signal from an unconnected access point close to the wireless LAN device in order to determine whether or not the reception signal is a signal from an access point for which connection establishment was successful. .

  As described above, according to the present invention, it is possible to provide a wireless LAN device having an effect that an unnecessary signal can be determined with high accuracy.

  Hereinafter, a wireless LAN device according to an embodiment of the present invention will be described with reference to the drawings.

(First embodiment)
In this embodiment, a case where a wireless receiver is applied as a wireless LAN device will be described.

  FIG. 1 is a configuration diagram showing a radio receiver according to the first embodiment of the present invention.

  As shown in FIG. 1, the radio receiver includes antennas 101 and 102, a switch 103, an LNA (Low Noise Amplifier) 104, mixers 105 and 109, filters 106 and 110, and a VGA (Variable Gain Amplifier). An amplifier) 107, a received signal strength detector 108, ADCs (Analog to Digital Converter) 111 and 112, a baseband processing circuit 113, and the like.

  In the present embodiment, reception signal strength detector 108 constitutes reception signal strength detection means in the present invention.

  The baseband processing circuit 113 includes a reception signal strength threshold determination unit 114, a reception signal strength threshold setting unit 115, a training signal correlation calculation determination unit 116, a training signal correlation threshold setting unit 117, a baseband signal processing unit 118, and the like. Is done.

  In the present embodiment, received signal strength threshold determination section 114 constitutes a received signal strength threshold determination means in the present invention. In the present embodiment, received signal strength threshold setting section 115 constitutes a first threshold changing means in the present invention. In the present embodiment, the training signal correlation calculation determination unit 116 constitutes a training signal correlation calculation unit and a training signal correlation threshold determination unit in the present invention. Furthermore, in the present embodiment, baseband signal processing section 118 constitutes a received signal rejection determination means in the present invention.

  Of the antennas 101 and 102, an antenna having a high reception level is selected by the switch 103, and a weak signal received by the selected antenna is amplified by the LNA 104. The signal amplified by the LNA 104 is frequency-converted to an intermediate frequency by the mixer 105, and then the image signal is removed by the filter 106.

  The signal that has passed through the filter 106 is converted to an optimum signal level by the VGA 107 and then frequency-converted to the baseband by the mixer 109. The signal frequency-converted by the mixer 109 passes through the filter 110, is converted to a digital signal by the ADC 112, and is demodulated by digital processing in the baseband processing circuit 113.

  On the other hand, the intensity of the signal that has passed through the filter 106 is detected by the received signal intensity detector 108. The signal detected by the received signal strength detector 108 is converted into a digital signal by the ADC 111 and input to the baseband processing circuit 113.

  The reception signal strength threshold determination unit 114 determines whether the strength of the signal detected by the reception signal strength detector 108 is equal to or less than the threshold set by the reception signal strength threshold setting unit 115. Here, if it is determined that the intensity of the signal detected by the received signal strength detector 108 is not less than or equal to the threshold set by the received signal strength threshold setting unit 115, it is determined that the signal conforms to the IEEE 802.11 standard. The

  On the other hand, when it is determined that the intensity of the signal detected by the received signal strength detector 108 is equal to or less than the threshold set by the received signal strength threshold setting unit 115, it is determined that the signal conforms to the IEEE 802.11 standard. Not.

  Note that the threshold set by the received signal strength threshold setting unit 115 is dynamically changed according to the strength of the received signal and surrounding radio wave conditions. For example, when the number of access points (hereinafter simply referred to as “AP”) existing around a wireless receiver is small, it is preferable to set the threshold value to a low value so that as many signals as possible can be picked up. Good. On the other hand, when there are a large number of APs present around the wireless receiver, it is preferable to set the threshold value to a high value so that signals from other than the nearby APs currently connected are not picked up. .

  Here, it is possible to determine whether the number of APs present around the wireless receiver is large or small by counting address information of an AP different from the connected AP. Alternatively, a method of examining the number of APs by reducing the threshold value in advance or a method of acquiring information on APs other than the connected AP while dynamically changing the threshold value can be considered.

  Further, a training signal correlation calculation and determination are performed by the training signal correlation calculation determination unit 116 for a signal that has entered the baseband processing circuit 113 from the ADC 112. The training signal is a signal that is defined in advance for gain adjustment and synchronization of the radio receiver separately from the original logically valid signal, and is also called a preamble. Further, since the training signal is a signal in which the same vector value is repeated every 0.8 μs, autocorrelation can be obtained. The signal received from the autocorrelation value can be synchronized.

  Whether the autocorrelation value obtained as a result of the training signal correlation calculation is equal to or less than the threshold set by the training signal correlation threshold setting unit 117 is determined by the training signal correlation calculation determination unit 116. Here, if there is an autocorrelation value obtained as a result of the training signal correlation calculation that exceeds the threshold set by the training signal correlation threshold setting unit 117, the signal is a signal compliant with the IEEE 802.11 standard. It can be judged that there is.

  On the other hand, if no autocorrelation value obtained as a result of the training signal correlation calculation exceeds the threshold set by the training signal correlation threshold setting unit 117, the signal can be determined as a signal of another standard, noise, or the like. .

  Next, the determination result by the received signal strength threshold determination unit 114 and the determination result by the training signal correlation calculation determination unit 116 are input to the baseband signal processing unit 118.

  When the determination result by the reception signal strength threshold determination unit 114 and the determination result by the training signal correlation calculation determination unit 116 indicate that the received signal is a signal compliant with the IEEE 802.11 standard, the baseband signal processing unit Demodulation processing is performed at 118, and the received signal is sent to the upper layer from the baseband processing circuit and MAC control circuit shown in FIG.

  On the other hand, if the determination result indicates that the received signal is not a signal conforming to the IEEE 802.11 standard, the received signal is rejected by the baseband signal processing unit 118, that is, the demodulation process is not performed. . Accordingly, the reception signal is not transmitted from the baseband processing circuit or the MAC control circuit to the upper layer.

  As described above, according to the wireless receiver according to the first embodiment of the present invention, the threshold value to be compared with the strength of the received signal is dynamically changed, and the self-training signal is added to the strength of the received signal. Since it is determined whether or not the received signal is a signal compliant with the IEEE 802.11 standard using the correlation value, the unnecessary signal can be determined with high accuracy.

  Similar to the threshold value set by the received signal strength threshold value setting unit 115 described above, the threshold value set by the training signal autocorrelation threshold value setting unit 117 is dynamically changed according to the strength of the received signal and the surrounding radio wave conditions. You may be made to do. In this case, in the present embodiment, the training signal autocorrelation threshold value setting unit 117 constitutes a second threshold value changing unit in the present invention.

  Thereby, since the threshold value compared with the autocorrelation value of the training signal is dynamically changed, it is possible to determine the unnecessary signal with higher accuracy.

  Further, the threshold set by the received signal strength threshold setting unit 115 may be determined based on a received signal from the AP when establishing a connection with the AP. The signal received after the threshold value is determined is determined by the received signal strength threshold value determination unit 114 using the determined threshold value. In this case, in the present embodiment, received signal strength threshold setting section 115 constitutes a first threshold determining means in the present invention.

  In the IEEE802.11h standard, the strength of the transmission signal of the AP itself can be added to the beacon signal from the AP. At this time, the wireless receiver can estimate the distance to the AP in terms of the intensity of the transmission signal of the AP itself and the intensity of the actually received signal. Specifically, the intensity of the signal that has been converted into the inverse and converted into the antenna end is estimated from the gain setting information of the RF block shown in FIG. Then, since the attenuation amount between the AP and the wireless receiver is known from the strength of the signal at the antenna end that is inversely converted from the strength of the transmission signal of the AP itself, the distance can be estimated based on the attenuation amount. A threshold of received signal strength is determined from the estimation result of the distance, and the determined threshold is set.

  Thereby, since a threshold value is determined based on the received signal from AP, the signal reception state from appropriate AP can be maintained.

  Even if the signal transmitted from the AP does not include the strength of the transmission signal of the AP itself, the strength of the signal from the AP can be determined from the magnitude using only the strength of the received signal. .

  Specifically, the received signal strength threshold value determination unit 114 determines based on the threshold value table. For example, a default threshold table is created, and an AP corresponding to a signal having the highest intensity among the received signals is determined as an AP to be connected. At this time, if the connection with the AP is established, the threshold table is updated based on the received signal strength. If the strength of the received signal is smaller than the default threshold value, the AP is not connected to the AP or is connected to the AP corresponding to the signal having the highest strength among the received signals.

  In this case, it is assumed that the AP to be connected is the closest AP, but generally there are few problems because the AP is often connected to the nearest AP. In addition, when an AP that outputs a received signal having an intensity greater than the threshold is found after connection, there is a countermeasure method such as reconnecting.

(Second Embodiment)
In this embodiment, a case where a wireless transceiver is applied as a wireless LAN device will be described. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description of the components is omitted.

  FIG. 3 is a block diagram showing a radio transceiver according to the second embodiment of the present invention.

  As shown in FIG. 3, in addition to the configuration of the wireless receiver according to the first embodiment, the wireless transceiver includes VGAs 201 and 204, mixers 202 and 205, filters 203 and 206, DAC (Digital to Analog Converter: Digital-analog converter) 207, transmission signal strength setting unit 209, switch 301, and the like.

  In the present embodiment, transmission signal strength setting section 209 constitutes transmission signal strength determination means in the present invention.

  The digital transmission signal generated by the baseband processing circuit 113 is converted into an analog signal by the DAC 207. The analog signal passes through the filter 206 and is up-converted to an intermediate frequency by the mixer 205, and then the transmission gain of the first stage is adjusted by the VGA 204.

  The signal whose transmission gain is adjusted by the VGA 204 passes through the filter 203 and the mixer 202 to generate an RF (Radio Frequency) band signal. The VGA 201 adjusts the second stage transmission gain. The switch 301 switches input / output of each analog signal at the time of transmission and at the time of reception.

  The transmission signal strength setting unit 209 estimates the distance from the AP based on the threshold set by the reception signal strength threshold setting unit 115, and the transmission signal strength is determined and set based on the estimated distance. . When the distance to the connected AP is short, a low strength is set. On the other hand, when the distance to the connected AP is far, a high strength is set. At this time, the set strength should not exceed the regulation value set in each country. Then, the strength set by the transmission signal strength setting unit 209 is reflected in the VGAs 201 and 204 so that the strength of the transmission signal can be controlled.

  As described above, according to the radio transceiver according to the second embodiment of the present invention, the power consumption can be reduced because the strength of the transmission signal is optimized. Moreover, since it is possible to suppress radio waves coming to terminals other than the AP to be connected, the processing load of terminals other than the connected AP can be reduced. Therefore, even in an environment where there are many APs, unnecessary radio waves do not appear on the medium more than necessary, and the transmission / reception communication performance of the entire wireless LAN is improved.

  The transmission signal strength setting unit 209 determines and sets the strength of the transmission signal based on the threshold set by the reception signal strength threshold setting unit 115 and the threshold set by the training signal correlation threshold setting unit 117. You may do it.

  This is because, when only the strength of the received signal is used as the basis for determination, it is affected by noise and temperature characteristics of the RF circuit. Since the correlation value is a correlation value that is purely based on the signal waveform, the accuracy of the threshold set by the training signal correlation threshold setting unit 117 is good.

  As a result, the strength of the transmission signal can be further optimized as compared with the case where only the strength of the reception signal is used as a basis for determination.

  Further, the MAC address information of the AP included in the beacon frame shown in FIG. 4 may be managed to determine whether or not to reject the received signal. In this case, the final decision of rejection is made not by the baseband processing circuit 113 but by the MAC control circuit shown in FIG. That is, in the present embodiment, the MAC control circuit constitutes a MAC address determination unit and a reception signal rejection determination unit in the present invention. In the present embodiment, the storage means (not shown) constitutes the MAC address holding means in the present invention.

  Specifically, the MAC address of the AP whose connection has been successfully established is stored in the storage means, and when the signal is received, the source address (MAC address) included in the received signal and the stored MAC address are It is compared with the MAC control circuit. As a result of the comparison, if it is determined that the received signal is not a signal transmitted from the connected AP, the received signal is rejected by the MAC control circuit. On the other hand, when it is determined that the received signal is a signal transmitted from the connected AP, the received signal is transmitted from the MAC control circuit to the upper layer.

  Thereby, it is determined that the strength of the signal detected by the received signal strength detector 108 is not less than or equal to the threshold set by the received signal strength threshold setting unit 115, and the autocorrelation value obtained as a result of the training signal correlation calculation is Even if it is determined that the received signal is not equal to or less than the threshold set by the training signal correlation threshold setting unit 117, the wireless transceiver is used to determine whether the received signal is a signal from an AP that has successfully established a connection. A received signal from a nearby non-connected AP can be rejected.

It is a block diagram which shows the radio receiver which concerns on the 1st Embodiment of this invention. It is a block diagram which shows a general wireless LAN apparatus. It is a block diagram which shows the radio | wireless transmitter / receiver which concerns on the 2nd Embodiment of this invention. It is a figure which shows the MAC frame structure of IEEE802.11 standard.

Explanation of symbols

101, 102 Antenna 103, 301 Switch 104 LNA
105, 109, 202, 205 Mixer 106, 110, 203, 206 Filter 107, 201, 204 VGA
108 Received signal strength detector 111, 112 ADC
113 Baseband Processing Circuit 114 Reception Signal Strength Threshold Determination Unit 115 Reception Signal Strength Threshold Setting Unit 116 Training Signal Correlation Calculation Determination Unit 117 Training Signal Correlation Threshold Setting Unit 118 Baseband Signal Processing Unit 207 DAC
209 Transmission signal strength setting section

Claims (6)

Received signal strength detecting means for detecting the strength of the received signal;
First threshold value changing means for dynamically changing the first threshold value;
A received signal strength threshold determination unit that determines whether or not the intensity detected by the received signal strength detection unit is equal to or lower than the first threshold;
Training signal correlation calculating means for calculating the autocorrelation value of the training signal included in the received signal;
Training signal correlation threshold determination means for determining whether or not the autocorrelation value calculated by the training signal correlation calculation means is equal to or less than a second threshold;
Receiving signal rejection determining means for determining whether or not to reject the received signal based on the determination result by the received signal strength threshold determining means and the determination result by the training signal correlation threshold determining means. A wireless LAN device.   The wireless LAN device according to claim 1, further comprising second threshold value changing means for dynamically changing the second threshold value. A first threshold value determining means for determining the first threshold value based on a received signal from the access point when establishing a connection with the access point;
The received signal strength threshold determining means determines whether or not the intensity detected by the received signal strength detecting means is equal to or less than a first threshold determined by the first threshold determining means. Item 3. The wireless LAN device according to item 1 or item 2.   The wireless LAN device according to any one of claims 1 to 3, further comprising transmission signal strength determining means for determining the strength of a transmission signal based on the first threshold value.   The radio according to any one of claims 1 to 3, further comprising transmission signal strength determining means for determining the strength of a transmission signal based on the first threshold and the second threshold. LAN device. MAC address holding means for holding the MAC address of the access point for which connection establishment was successful;
MAC address determination means for determining whether or not the received signal is a signal from an access point of the MAC address held by the MAC address holding means,
6. The radio according to claim 1, wherein the reception signal rejection determination unit determines whether or not to reject the reception signal based on a determination result by the MAC address determination unit. LAN device.

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