JP6146866B2 - Wireless communication apparatus and wireless communication method - Google Patents

Description

  The present invention relates to a wireless communication apparatus and a wireless communication method used in a heterogeneous network system in which a wireless LAN system and other wireless systems coexist.

  The amount of traffic required for wireless communication is increasing year by year, and it is required to increase the throughput in the entire wireless section. The wireless LAN standard IEEE802.11 aims to improve throughput even in an environment where wireless terminals are crowded, and has launched HEW (High Efficent Wireless LAN) SG (Study Group), aiming for standardization. . Under such circumstances, it has been newly proposed to control the CCA (Clear Channel Assessment) level in CSMA / CA which is a precondition in the wireless LAN system.

  Since the wireless LAN terminal can perform transmission if the received signal is below the CCA level, the transmission right acquisition rate can be improved by setting the CCA large. However, on the other hand, if each terminal arbitrarily sets the CCA level to increase the acquisition rate of the transmission right, all terminals start transmission freely, and the system throughput decreases due to an increase in interference. In order to prevent the system throughput from decreasing due to such a problem, Non-Patent Document 1 assumes that control is performed so as to increase CCA and simultaneously decrease transmission power. However, if individual wireless LAN terminals attempt to optimize themselves, there is a risk that priority is given to increasing the CCA level.

  FIG. 12 is a block diagram showing a configuration of the wireless terminal 2 in the conventional wireless LAN. 12 includes an antenna 10, a radio system signal transmission / reception circuit 12, a transmission modulation circuit 13, a reception decoding circuit 14, a reception level acquisition circuit 16, and an information signal input / output circuit 17. When receiving a signal, the wireless terminal 2 receives the wireless signal in the wireless system signal transmission / reception circuit 12 via the antenna 10. The wireless system signal transmission / reception circuit 12 performs analog / digital conversion in synchronization with the reception signal, outputs the obtained digital signal to the reception decoding circuit 14, and outputs the reception level of the reception signal to the reception level acquisition circuit 16.

  If the input reception level is higher than a predetermined CCA level, the reception level acquisition circuit 16 notifies the information signal input / output circuit 17 of signal detection. The reception level acquisition circuit 16 notifies the information signal input / output circuit 17 to cancel the signal detection state when the input reception level becomes lower than a predetermined CCA level. Different CCA levels can be used depending on whether the received signal is an unknown system or a radio system of the same type as the radio terminal 2.

  The reception decoding circuit 14 decodes the digital signal input from the radio system signal transmission / reception circuit 12, and if the obtained signal is a signal addressed to the own radio terminal 2, the obtained data bits are input / output to the information signal. Output to the circuit 17. The reception decoding circuit 14 may not perform decoding unless the decoded data bits are destined for the own wireless terminal. When it is determined that the decoded bits have been acquired without error, the reception decoding circuit 14 notifies the radio system signal transmission / reception circuit 12 of normal reception. When normal reception is input, the radio system signal transmission / reception circuit 12 generates an ACK (Acknowledge) signal indicating normal reception, converts the signal into an analog signal suitable for transmission, and up-converts the signal to a carrier frequency. To send through.

  When a transmission signal addressed to another wireless terminal is input to the information signal input / output circuit 17, it is determined whether the wireless terminal 2 is in a signal detection state. If the signal is in a signal detection state, the signal detection state is the reception level acquisition circuit 16. Wait until it is canceled. When the signal detection state is not set or the signal detection state is canceled by the reception level acquisition circuit 16, the data bit is output to the transmission modulation circuit 13 after waiting for a random time according to the CSMA / CA rule. The transmission modulation circuit 13 modulates the input data bits and outputs the generated transmission signal to the radio system signal transmission / reception circuit 12. The radio system signal transmission / reception circuit 12 converts the input modulation signal into an analog signal, up-converts it, and transmits it to a radio terminal as a communication partner via the antenna 10.

Koichi Ishihara, et al., "Simultaneous Transmission Technologies for HEW," IEEE 11-13 / 1395r2, Nov. 2013

  As described above, if the wireless terminal freely controls the CCA level in the reception level determination circuit in order to optimize its own throughput, the system throughput is greatly reduced. That is, in the wireless system based on CSMA / CA, if the CCA level is increased so that each wireless terminal maximizes its own throughput, there is a problem that the system throughput is greatly reduced due to an increase in interference.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a wireless communication apparatus and a wireless communication method capable of preventing a decrease in system throughput when a plurality of wireless systems coexist. .

The present invention is a wireless communication apparatus that performs random access, a signal attenuating unit that gives arbitrary attenuation to a reception signal input from an antenna and a transmission signal output to the antenna, and a reception signal from the signal attenuation unit A reception signal level detection unit that detects a reception signal level, a signal attenuation amount determination unit that determines an attenuation amount of the signal attenuation unit that can be transmitted from the detected reception signal level, and a transmission signal to a communication partner are generated a transmission signal generator, a modulation mode determination unit for determining a modulation mode consisting of a modulation scheme and a coding rate in transmitting attenuates the signal at the signal attenuator, the attenuation determined for the signal attenuator A signal attenuation amount setting unit for setting the amount, and a radio signal transmission unit that performs modulation and encoding according to the modulation mode and transmits the transmission signal through the signal attenuation unit. And features.

The present invention includes a reception level frequency storage unit that stores frequency information of a signal detected by the reception signal level detection unit, and a modulation mode determined in consideration of an attenuation amount in the generated transmission signal. when the calculated throughput evaluation value from the frequency information, further comprising an attenuation usage determination unit determines whether to perform communication using the determined the attenuation is determined that communicates the signal attenuation The setting unit sets the determined attenuation amount in the signal attenuation unit.

The present invention corresponds to an ID acquisition unit that acquires an ID of a wireless communication device that has transmitted a received signal, an ID of a wireless communication device that is a transmission destination of the received signal, or both, and the acquired ID A reception level ID storage unit that stores a signal level as ID reception level information; a signal attenuation amount determination unit that determines an attenuation amount to be used in the signal attenuation unit from the stored ID reception level information; Whether the transmission signal is to be communicated using the determined attenuation amount based on the modulation mode throughput evaluation value determined in consideration of the attenuation amount determined for the ID for the generated transmission signal And an attenuation utilization determining unit for determining the above.

The present invention corresponds to an ID acquisition unit that acquires an ID of a wireless communication device that has transmitted a received signal, an ID of a wireless communication device that is a transmission destination of the received signal, or both, and the acquired ID A reception level ID storage unit that stores signal level and frequency information as ID reception level information, and a signal attenuation amount determination unit that determines, based on the stored ID reception level information, an attenuation amount to be used in the signal attenuation unit for the ID And an attenuation use determination unit that calculates a throughput evaluation value from the modulation mode and the stored frequency information and determines whether or not to perform communication using the determined attenuation amount, and the modulation mode determining unit, modulation mode consisting of a modulation scheme and a coding rate between the transmission of signal is attenuated by signal attenuator using the attenuation being determined for the ID Determined, if it is determined that communicates the signal attenuation amount setting unit, and sets the attenuation amount determined in the signal attenuator.

The present invention provides an ID acquisition unit that acquires an ID of a wireless communication device that is a transmission source of a signal that is being received, a wireless terminal ID that is a transmission destination of a signal that is being received, and an ID of the wireless communication device that is a transmission source A reception level ID storage unit that stores a corresponding signal level as ID reception level information; and a signal attenuation amount determination unit that determines an attenuation amount for each ID stored in the ID reception level information. The unit determines the amount of attenuation determined for the ID of the wireless communication terminal that is the transmission source of the signal being received and the amount of attenuation determined for the ID of the wireless communication terminal that is the transmission destination of the signal that is being received and determining the modulation mode consisting of a modulation scheme and a coding rate in transmitting attenuates the signal at the signal attenuator using the attenuation of the larger of.

The present invention further includes a specific ID designating unit that imposes a penalty for adding a further additional attenuation amount to the attenuation amount determined from the reception level or prohibiting communication using the attenuation amount with respect to the specific ID, and storing the reception level ID The unit stores the prohibition of communication using the attenuation amount in the ID reception level information or the addition of the additional attenuation amount for the ID specified from the specific ID.

  The present invention relates to a wireless communication method performed by a wireless communication apparatus that performs random access, a signal attenuation step that gives arbitrary attenuation to a reception signal input from an antenna and a transmission signal output to the antenna, and the signal attenuation step A received signal level detecting step for detecting a received signal level of the received signal given the attenuation by the signal, a signal attenuation determining step for determining the attenuation in the signal attenuating step from the detected received signal level, and communication A transmission signal generation step of generating a transmission signal to a wireless communication device as a counterpart, a modulation mode determination step of determining a modulation mode when transmitting by attenuating the transmission power of the transmission signal by the signal attenuation step, and According to the modulation mode, the signal having the attenuation amount is transmitted by the signal attenuation step. And having a line signal transmitting step.

  The present invention includes a reception level frequency storage step for storing frequency information of the signal detected in the reception signal level detection step, a modulation mode determined in consideration of the attenuation amount determined in the signal attenuation amount determination step, and storage. An attenuation use determination step for determining whether to perform communication using an attenuation amount with reference to a throughput evaluation value calculated from the received reception level frequency information, and determining that the attenuation amount is used. In this case, transmission is performed using the attenuation determined for the detected received signal level.

  According to the present invention, it is possible to prevent the throughput of the wireless communication system from being lowered.

It is a block diagram which shows the structure of 1st Embodiment of this invention. It is a figure which shows the attenuation value of the corresponding variable ATT11 which can be made into a CCA level or less with respect to the reception level (RSSI) from another BSS. It is a flowchart which shows the processing operation of the 1st method in 1st Embodiment. It is a flowchart which shows the processing operation of the 2nd method in 1st Embodiment. It is a figure which shows terminal ID and reception level (RSSI) which were memorize | stored in the radio | wireless terminal 1 in 2nd Embodiment. It is a flowchart which shows the processing operation of the 1st method in 2nd Embodiment. It is a flowchart which shows the processing operation of the 2nd method in 2nd Embodiment. It is a figure which shows the channel conditions between the radio | wireless terminals defined in order to show the effect of the radio | wireless terminal by this embodiment. It is explanatory drawing which shows an example of a parameter. It is a figure which shows the result of having evaluated the effect at the time of using the control method by this embodiment. It is a figure which shows the result of having evaluated the effect at the time of using the control method by this embodiment. It is a block diagram which shows the structure of the radio | wireless terminal 2 in the conventional wireless LAN.

<< First Embodiment >>
Hereinafter, a wireless communication apparatus according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the embodiment. In this figure, the same parts as those of the conventional apparatus shown in FIG. The apparatus shown in this figure is different from the conventional apparatus in that a variable attenuator (variable ATT) 11 and an ATT control circuit 15 are provided.

  When receiving a signal, the wireless terminal 1 receives the wireless signal in the wireless system signal transmission / reception circuit 12 via the antenna 10 and the variable ATT 11. The wireless system signal transmission / reception circuit 12 performs analog / digital conversion in synchronization with the reception signal, outputs the obtained digital signal to the reception decoding circuit 14, and outputs the reception level of the reception signal to the reception level acquisition circuit 16. If the input reception level is higher than a predetermined CCA level, the reception level acquisition circuit 16 notifies the information signal input / output circuit 17 of signal detection. The reception level acquisition circuit 16 notifies the information signal input / output circuit 17 to cancel the signal detection state when the input reception level becomes lower than a predetermined CCA level. Different values can be used for the CCA level to be considered when the received signal is an unknown system and when the received signal is the same type of wireless system as the wireless terminal 1.

  The reception decoding circuit 14 decodes the digital signal input from the radio system signal transmission / reception circuit 12, and if the obtained signal is a signal addressed to the own radio terminal 1, the obtained data bits are input / output to the information signal. Output to the circuit 17. The reception decoding circuit 14 may not perform decoding unless the decoded data bits are destined for the own wireless terminal. When it is determined that the decoded bits have been acquired without error, the reception decoding circuit 14 notifies the radio system signal transmission / reception circuit 12 of normal reception. When normal reception is input, the radio system signal transmission / reception circuit 12 generates an ACK (Acknowledge) signal indicating normal reception, converts the signal into an analog signal suitable for transmission, and up-converts the signal to a carrier frequency. To send through.

  When a transmission signal addressed to another wireless terminal is input to the information signal input / output circuit 17, it is determined whether or not the wireless terminal 1 is in a signal detection state. If the signal detection state is detected, the signal detection state is a reception level acquisition circuit. It waits until it is canceled from 16. When the signal detection state is not set or the signal detection state is canceled by the reception level acquisition circuit 16, the data bit is output to the transmission modulation circuit 13 after waiting for a random time according to the CSMA / CA rule. The transmission modulation circuit 13 modulates the input data bits and outputs the generated transmission signal to the radio system signal transmission / reception circuit 12. The radio system signal transmission / reception circuit 12 converts the input modulation signal into an analog signal, up-converts it, and transmits it to a radio terminal as a communication partner via the antenna 10.

  A set of wireless terminals including all wireless terminals that perform data communication with the wireless terminal 1 and wireless terminals that perform data communication with the wireless terminal that communicates with the wireless terminal 1 is defined as BSS (Basic service set). If there is no other BSS that communicates at the same frequency in the vicinity, the variable ATT 11 can be set so as not to attenuate the signal (attenuation rate α = 0 dB).

  FIG. 2 is a diagram illustrating an attenuation value of the corresponding variable ATT 11 that can be equal to or lower than the CCA level with respect to a reception level (RSSI: Receive signal strength indication) from another BSS. Here, an example in which a discrete attenuation value in 5 dB increments can be selected is shown, but control can be performed with finer accuracy such as 1 dB increments, or can be controlled with coarser accuracy such as 10 dB increments. Since the CCA level is set to -82 dBm, it is not necessary to attenuate at -82 dBm or less, and the value of the attenuation value is 0 dB. For RSSI of −82 dB to −77 dB, by setting the attenuation value to 5 dB, the RSSI value in the receiving apparatus is reduced to −87 to −82 dBm, and transmission is enabled. Hereinafter, the attenuation value is set to −57 dBm.

  This upper limit value depends on the maximum attenuation value that can be selected by the variable ATT 11, and in the example shown in FIG. 2, the maximum attenuation value is 25 dB. Therefore, when the reception level is greater than −57 dBm, the attenuation value is set. The value does not exist. The higher the attenuation value, the higher the RSSI can be handled. However, since the transmission power also decreases correspondingly, there is a practical modulation scheme for the communication partner of the wireless terminal 1 even if a very large value is set. No longer exists.

<First method>
Next, the first method in the first embodiment will be described. When the information input / output circuit 17 of the wireless terminal 1 has a transmission signal to a communication partner to perform data transmission and the wireless terminal 1 is receiving a signal from another BSS, the ATT control circuit 15 receives a reception level acquisition circuit. 16 determines whether there is a modulation mode consisting of a modulation scheme and a coding rate that can be used with the attenuation value set for the RSSI value of the received signal acquired from 16, and if the modulation mode exists, it is variable. The attenuation value is set in ATT11. When the attenuation value is set in the variable ATT 11, the RSSI evaluated by the reception level acquisition circuit 16 decreases, so that the CSI level or lower is reached, and the information signal input / output circuit 17 is notified of the cancellation of the communication detection state.

  When the signal detection state is canceled, the information signal input / output circuit 17 outputs an attenuation value and a data bit for transmission to the transmission modulation circuit 13. The transmission modulation circuit 13 modulates and encodes the input data bits according to the modulation mode determined by the ATT control circuit 15 and converts the data bits into a form suitable for transmission from the antenna 10 by the radio system signal transmission / reception circuit 12. (For example, digital-analog conversion, etc.), and transmit via the variable ATT 11 and the antenna 10. Here, the modulation mode determined in consideration of using the attenuation value determined by the variable ATT 11 corresponds to a lower bit amount than the case where the normal attenuation value is 0 dB (not attenuated). May be a modulation mode that is not different from the case where the attenuation value is 0 dB.

  Next, with reference to FIG. 3, the processing operation of the wireless terminal 1 using the first method in the first embodiment will be described. FIG. 3 is a flowchart showing the processing operation of the first method in the first embodiment. When a radio signal exceeding the CCA level is detected and a data signal to be transmitted from the radio terminal 1 to another radio terminal is generated (step S1), an attenuation value used according to the reception level is set in the variable ATT 11 (step S1). S2) Since there is no radio signal exceeding the CCA level, transmission of a data signal or acquisition of a transmission right by an RTS signal is started (step S3). Then, when the detection of the radio signal exceeding the CCA level is finished, this processing is finished.

<Second method>
Next, the second method in the first embodiment will be described. In the second method in the first embodiment, the communication probability in the table shown in FIG. 2 is measured, and control is performed using this value. When the reception level acquisition circuit 16 acquires the RSSI of the signal from the other BSS, the reception level acquisition circuit 16 notifies the information signal input / output circuit 17 of the signal detection state and collects information on the continuation state of the signal detection state. Specifically, the time ratio of the signal detection state in the entire waiting time is measured. It is also possible to simply measure the ratio (probability) at which a signal is detected, or to evaluate the ratio corresponding to the RSSI at that time. An example in which the frequency of occurrence of communication is evaluated with respect to the RSSI range shown in FIG. By using the communication probability information, it is possible to prevent the variable ATT 11 from being used in unnecessary scenes and to use it only when an improvement in throughput can be expected. The communication probability in FIG. 2 can also be evaluated by the time excluding the time during which transmission from the own wireless terminal 1 and reception to the own wireless terminal 1 are performed.

  In Example 1, since there is a 60% probability (RSSI <−82 dBm) that communication can be performed without using the variable ATT 11, the merit of performing communication using the variable ATT during communication by other BSSs is small. The communication probability when the RSSI value is between −82 and −57 dBm is 10 + 15 + 10 = 35%, but this is not an inaccessible time, and based on CSMA / CA, a certain percentage of this is due to the communication of the own wireless terminal. You can get it. If it is assumed that there are four wireless terminals using the same channel other than the own wireless terminal and the wireless resources can be obtained evenly, 20% is the access time that can be used by the own wireless terminal, so 35% × 0. 2 = 7% can be communicated without using the variable ATT11. That is, by using the variable ATT 11 according to the present embodiment, when the access right can be acquired with a probability of 60 + 7 = 67%, the access right acquisition rate is improved to 60 + 35 = 95%. Can be evaluated.

  When the position between the wireless terminal 1 and the communication partner is far and the channel strength is weak, it is necessary to change the modulation mode to one having a low bit number according to the attenuation value, and a total of 35 using the attenuation value of 5 to 15 dB. % Communication throughput may be low. Furthermore, since the communication that requires a large attenuation value has a large decrease in throughput between the wireless terminal 1 and the communication partner, in this case, communication with the variable ATT 11 is not performed during reception of data with a high attenuation value. I can judge.

  In Example 2, the ratio that communication is not possible without using variable ATT 11 is greater than in Example 1. For this reason, the merit of using the variable ATT 11 is greater than that of Example 1. The communication probability that can be communicated using the variable ATT 11 is 30 + 15 + 10 + 10 = 65%. As in Example 1, if there are four wireless terminals using the same channel other than the own wireless terminal and the wireless resources can be obtained evenly, 20% is the access time that the own wireless terminal can use. 65% × 0.2 = 13% can be communicated without using the variable ATT 11. Therefore, the probability that the access right can be acquired increases from 30 + 13 = 43% to 95%, and can be regarded as a throughput improvement effect of about 2.2 times.

Compared to Example 1, the merit is large, and the merit of acquiring the transmission right according to the present embodiment is large even in view of the attenuation value of the variable ATT 11. Whether or not to use variable ATT when actually transmitting from the wireless terminal 1 to the communication partner can be determined as follows. A first evaluation method for determining one attenuation value of the variable ATT 11 for the surrounding environment and commonly used for all reception levels, and a second evaluation method for setting an attenuation value appropriately for the reception level are shown. . First, in the first evaluation method, the access right acquisition rate before using the variable ATT 11 is set to ρ ₀ . The acquisition rate ρ ₀ is evaluated as 67% in Example 1 and 43% in Example 2. The access right acquisition rate obtained when the attenuation value α is used is defined as ρ (α). In Example 1, ρ (−15) = 95%, and in Example 2, ρ (−20) = 95%. Here, the value of α is expressed in dB.

Next, assuming that a certain wireless terminal 1 is a wireless terminal 1-j to transmit, the bit rate corresponding to the modulation mode in the case where communication is performed without giving attenuation in the variable ATT 11 to the wireless terminal 1-j is represented by B _{It is} assumed that _{0 and ij,} and the bit rate corresponding to the modulation mode used when the attenuation value α is used is B _ij (α). At this time, when the communication according to the present embodiment is not used, the throughput evaluation value T _{0, ij} from the wireless terminal 1 to the wireless terminal 1-j is T _{0, ij} = ρB _{0, ij} (1)
It can be expressed. The evaluation value T _ij (α) when the attenuation value by this method is introduced is T _ij (α) = ρ (α) B _ij (α) (2)
As obtained. By substituting the possible attenuation value α into the expression (2) to calculate a throughput evaluation value _, and when compared with the evaluation value T _{0, ij of the} expression (1), Communication can be performed using the attenuation value α. For example, when T _ij is K times T _{0, ij} , the transmission access right can be acquired by setting the attenuation value α to the variable ATT. Here, K is a positive number of 1 or more.

  Next, a second evaluation method is shown. In this evaluation method, the individual access right acquisition rate obtained when the attenuation value α is used is defined as ρ ′ (α), and is set individually for the attenuation value. In Example 1, ρ ′ (0) = 60%, ρ ′ (− 5) = 10%, ρ ′ (− 10) = 15%, ρ ′ (− 15) = 10% from FIG. '(0) = 30%, ρ' (-5) = 30%, ρ '(-10) = 15%, ρ' (-15) = 10%, ρ '(-20) = 10% The

Next, assuming that a certain wireless terminal 1 is a wireless terminal 1-j to transmit, the bit rate corresponding to the modulation mode used when the attenuation value α is used can be expressed as B _ij (α). In the second evaluation method, since α is changed for each reception level, evaluation is performed by the sum of all combinations using attenuation values from the communication probability. Throughput evaluation value T ′ _ij according to the second evaluation method is T ′ _ij (α ′) = ρ (0) B _{0, ij} + ρ (−5) B _ij (−5) +... + Ρ (α ′) B _ij (α ′) (3)
As a result, the throughput is evaluated for all attenuation values that are equal to or less than the attenuation value α ′. Even in the second evaluation method, when T ′ _ij is K times T _{0, ij} , the transmission access right can be acquired by setting the attenuation value α to the variable ATT. Here, K is a positive number of 1 or more.

  Next, the processing operation of the wireless terminal 1 using the second method in the first embodiment will be described with reference to FIG. FIG. 4 is a flowchart showing the processing operation of the second method in the first embodiment. When a radio signal exceeding the CCA level is detected and a data signal to be transmitted from the radio terminal 1 to another radio terminal is generated (step S11), the throughput evaluation value is a threshold value when the corresponding attenuation value is used. (Step S12), if it exceeds, the attenuation value used according to the reception level is set in the variable ATT11 (step S14), and there is no radio signal exceeding the CCA level. Alternatively, acquisition of the transmission right by the RTS signal is started (step S15). If the threshold value is not exceeded in step S12, transmission of the data signal is waited until the communication of the other wireless terminal is completed (step S13). When the detection of the radio signal exceeding the CCA level is completed, this process is terminated.

<< Second Embodiment >>
Next, a wireless communication device according to a second embodiment of the present invention will be described with reference to the drawings. Since the device configuration of the wireless terminal 1 according to the second embodiment is the same as the configuration shown in FIG. 1, detailed description thereof is omitted here. In the second embodiment, as indicated by the dotted line in FIG. 1, the ID of the transmission source wireless terminal obtained as a result of decoding is output from the reception decoding circuit 14 to the reception level acquisition circuit 16. By controlling in this way, the reception level acquisition circuit 16 can store the reception level obtained from the wireless system signal transmission / reception circuit 12 and the wireless terminal ID obtained from the reception decoding circuit 14 in association with each other.

<First method>
Next, the first method in the second embodiment will be described. FIG. 5 is a diagram illustrating a terminal ID and a reception level (RSSI) stored in the wireless terminal 1 in the second embodiment. In the second embodiment, unlike the first embodiment, control based on information on the wireless terminal ID is possible. The RSSI, communication probability, wireless terminal type and communication partner information can be managed in the ATT control circuit 15 for each ID. The information signal input / output circuit 17 acquires the ID of the wireless terminal that is the transmission source of the signal received from the reception decoding circuit, the wireless terminal that is the transmission destination, or both, and outputs the ID to the ATT control circuit 15. The ATT control circuit 15 can store it together with the RSSI input from the reception level acquisition circuit 16 as shown in FIG. At this time, information such as the type of wireless terminal obtained by the information signal input / output circuit 17 regarding the communication can be stored in the ATT control circuit 15 together. The ATT control circuit 15 can also evaluate the communication probability of the communication of the corresponding ID by acquiring the signal detection state and its cancellation from the reception level acquisition circuit 16.

  Furthermore, as a method of using the ID, it is possible to specify from the outside via the network whether or not the control based on the attenuation value is performed for each ID. It is possible to input ID information from the outside to the information signal input / output circuit 17 to determine whether or not to perform control using an attenuation value, and to specify an attenuation value. For example, when the information signal input / output circuit 17 is designated not to perform communication using an attenuation value for communication relating to ID1 from the outside, the ATT control circuit 15 does not set the attenuation value for communication of ID1. be able to. Further, by prohibiting all communication relating to ID1, it is possible to set no attenuation value for the IDs of all wireless terminals belonging to ID1 (ID2 and ID3 in the example of FIG. 5). Further, the ATT control circuit 15 can reduce the influence of the ID on the communication by adding a further attenuation value to the attenuation value that can be estimated from the reception level according to the ID. By doing in this way, it can control so that communication of specific ID is not influenced by the radio | wireless terminal 1. FIG.

  In addition, the information signal input / output circuit 17 can be designated to increase the attenuation value for all communications related to ID1 from the outside. In the example of FIG. 5, the attenuation value of the variable ATT 11 can also be set by adding the designated additional attenuation value to the attenuation value setting for the transmission signals from ID2 and ID3 communicating with ID1. Similar to the second method in the first embodiment, the communication probability can be used to calculate a throughput evaluation value and determine whether to use an attenuation value. For example, by taking the sum of the corresponding communication probabilities for the attenuation values determined for the IDs in FIG. 5, a table similar to that in FIG. 2 is created, and the throughput is as shown in Equation (2) and Equation (3). Can be evaluated. Further, in FIG. 5, it is possible not to consider an ID for which communication using an attenuation value is prohibited. In the first method in the second embodiment, the reception level acquisition circuit 16 determines the setting of the attenuation value in the variable ATT 11 based on the wireless terminal ID of the reception signal obtained from the reception decoding circuit 14.

  Next, with reference to FIG. 6, the processing operation of the wireless terminal 1 using the first method in the second embodiment will be described. FIG. 6 is a flowchart showing the processing operation of the first method in the second embodiment. First, when a radio signal having a reception level exceeding the CCA level is detected, the ID of the radio terminal transmitting the radio signal is acquired (step S21), and stored in association with the corresponding reception level (step S21). S22).

  Further, when a data signal to be transmitted from the wireless terminal 1 to another wireless terminal is generated (step S23), it is determined whether the acquired wireless terminal ID is the wireless terminal ID corresponding to the use of the attenuation value. (Step S24) If it is compatible, the attenuation value corresponding to the wireless terminal ID is set to the variable ATT (Step S26), and there is no wireless signal exceeding the CCA level. Acquisition of the transmission right by is started (step S27). If the wireless terminal is not compatible in step S24, it waits for transmission of the data signal until communication of the other wireless terminal is completed (step S25). Then, when the detection of the radio signal exceeding the CCA level is finished, this processing is finished.

<Second method>
Next, the second method in the second embodiment will be described. In this method, the reception decoding circuit 14 outputs both the ID of the wireless terminal that is transmitting the received signal and the ID of the transmission destination to the reception level acquisition circuit 16. Unlike the conventional control method, the reception level acquisition circuit 16 refers to the information shown in FIG. 5 for the ID of the transmission destination wireless terminal. For example, it is assumed that the transmission source ID of the wireless signal currently received by the wireless terminal 1 is ID1, the transmission destination is ID3, and reception is performed at a reception level of −81 dBm. In the second method according to the second embodiment, the RSSI corresponding to the communication partner ID3 is referred to, and the corresponding attenuation value 20 dB is used.

The attenuation value set for the level of the received signal is Γ _S (S is an abbreviation for Source), and the attenuation value set for the wireless terminal 1 that is the transmission destination of the received signal is Γ. _{When D} is an abbreviation of Destination, the first method in the first and second embodiments uses the attenuation value Γ _S = 5 dB with a reception level of −81 dBm, whereas the second embodiment In the second method, Γ _D or max (Γ _D , Γ _S ) is used. max () is a function that extracts the largest value in parentheses. By controlling in this way, the influence on other wireless terminals can be minimized.

  Next, the processing operation of the wireless terminal 1 using the second method in the second embodiment will be described with reference to FIG. FIG. 7 is a flowchart showing the processing operation of the second method in the second embodiment. First, when a wireless signal having a reception level exceeding the CCA level is detected, the ID of the wireless terminal that is transmitting this wireless signal and the ID of the wireless terminal that is the transmission destination are acquired (step S31), and the transmission source The wireless terminal ID and the reception level are stored in association with each other (step S32).

  When a data signal to be transmitted from the wireless terminal 1 to another wireless terminal is generated (step S33), the acquired ID of the wireless terminal serving as the transmission destination, or the ID of the wireless terminal serving as the transmission destination and the wireless serving as the transmission source. With reference to the attenuation value corresponding to both of the terminal IDs, it is determined whether the evaluation value of the throughput by using this attenuation value exceeds the threshold value (step S34).

If the result of this determination is exceeded, the attenuation value determined by the above-described Γ _S or max (Γ _S , Γ _D ) is set in the variable ATT 11 (step S36), and transmission of the data signal or acquisition of the transmission right by the RTS signal is performed. Is started (step S37). If the threshold value is not exceeded in step S34, transmission of a data signal is waited until communication with other wireless terminals is completed (step S35). Then, when the detection of the radio signal exceeding the CCA level is finished, this processing is finished.

Next, effects of the above-described control method will be described with reference to the drawings. Consider that the wireless terminals 1-1 and 1-3 according to the present embodiment transmit data packets to the wireless terminals 1-2 and 1-4 that are communication partners, respectively. FIG. 8 is a diagram illustrating channel conditions between wireless terminals defined to show the effects of the wireless terminals according to the present embodiment. G ₂₁ from the radio terminal 1-1 to the radio terminal _{1-2, G 31} is the radio terminal 1-3 from the radio terminal _{1-1, G 13} is the radio terminal 1-1 from the radio terminal _{1-3, G 43} each of the radio terminal 1-3 to the radio terminal _{1-4, G 23} from the radio terminal 1-3 to the radio terminal _{1-2, G 41} is the channel gain from the radio terminal 1-1 to the radio terminal 1-4 Represent. Here, assuming the symmetry of the _channel, and G 31 _{= G 13,} the range of _{G ij} 0 _{<was G ij} <1.

Another wireless terminal 1 using the same frequency in the periphery has a problem of greatly reducing the system throughput if the wireless terminal 1 freely controls the CCA level in the reception level determination circuit for self-throughput optimization. If the wireless terminal 1-3 and the wireless terminal 1-1 are close enough to detect each other,
G ₁₃ P + N ≧ T
Satisfy the relationship. Here, P is transmission power, N is a thermal noise level, and T is a CCA level for determining that the wireless terminal does not transmit data.

と表すことができる。シャノン容量により、ＳＩＮＲから、ｌｏｇ_２（１＋ＳＩＮＲ）として周波数利用効率を評価した。ログの前についた１／２は、無線端末１−３と無線端末１−１が時間領域を半分ずつシェアしているためである。 Under such conditions, if the wireless terminal 1-3 and the wireless terminal 1-1 always try to transmit to the wireless terminal 1-4 and the wireless terminal 1-2 that are communication partners, a system that considers these two wireless terminals The overall frequency utilization efficiency is

It can be expressed as. The frequency utilization efficiency was evaluated as log ₂ (1 + SINR) from the SINR based on the Shannon capacity. 1/2 before the log is because the wireless terminal 1-3 and the wireless terminal 1-1 share the time domain by half.

として表せる。ここではまだＣＣＡレベルを上回る信号が無線端末１−１と無線端末１−３で受信されている。減衰率を受信信号がＣＣＡレベルを下回るように設定すると、

として周波数利用効率が得られる。 With the configuration of the present embodiment, it is considered that the level of the reception signal and the transmission signal is reduced by the attenuation rate a _{i in} the wireless terminal 1 by the variable ATT 11. In the description of this embodiment, what was expressed as an attenuation value was expressed in dB, so it was expressed as a true value, and the attenuation rate satisfying 0 <a _i ≦ 1 was defined in different terms. Is the same. The frequency utilization efficiency when the attenuation rate is set as a _i is

It can be expressed as Here, signals that still exceed the CCA level are received by the wireless terminals 1-1 and 1-3. If you set the decay rate so that the received signal is below the CCA level,

As a result, frequency utilization efficiency can be obtained.

と定義できる。 That is, the frequency utilization efficiency is set by the attenuation rate setting.

Can be defined.

Here, the change in the frequency utilization efficiency due to the attenuation rate a _i is evaluated using the parameters shown in FIG. The transmission power was 13 dBm, the threshold value was -82 dBm, the noise level was -91 dBm, and the frequency was 2.4 GHz. In order to simplify the following description, an environment where the SINR is sufficiently large is assumed, the conventional frequency utilization efficiency without using the attenuation factor is η ₀ ′, and the frequency utilization efficiency of the present embodiment using the attenuation factor is η _S. 'Is defined as follows.

As a propagation loss, free space is assumed,
G _ji = (λ / 4πD _ji ) ²
It was. Here, considering the environment where the distance between wireless terminals is very short as used in tethering, D ₂₁ = D ₄₃ = 1 [m] and D ₃₁ = D ₄₁ = D ₂₃ = D. In the configuration of the present embodiment, the variable ATT 11 is used only on the transmission side, and a ₂ = a ₄ = 1. Furthermore, the frequency utilization efficiency evaluation formula has a practical modulation scheme for any high SINR, and is a condition that becomes a theoretical upper limit value, which may cause a deviation from the actual system performance. There is. For this reason, the highest modulation scheme (64QAM) used in the wireless LAN standard IEEE802.11a and the bit rate at the coding rate (3/4), 2.7 bits / s / Hz are used as the upper limit.

Further, referring to a document that approximates the frequency utilization efficiency for SINR to a practical modulation scheme and coding rate, instead of setting the evaluation equation for frequency utilization efficiency for SINR to c (SINR) = log ₂ (1 + SINR),
c (SINR) = min {2.7, 0.52 log ₂ (1 + 0.25 SINR)
It was. FIG. 10 shows a result of evaluating the frequency use efficiency η _ATT of the present embodiment with respect to the attenuation factor of the variable _{ATT 11} with respect to D with a1 = a3. It was confirmed that there was a value of a _i that increased the frequency utilization efficiency under the condition that D was farther than 5 m, and the frequency utilization efficiency could be increased up to twice as much.

  Further, under the conditions shown in FIG. 8, when the wireless terminal 1-1 is a wireless terminal according to the present embodiment and the wireless terminal 1-3 is a conventional wireless terminal, the value of the variable ATT 11 is obtained only by the wireless terminal 1-1. The result of controlling is shown in FIG. D is set to 160 m. By setting the attenuation value of the wireless terminal 1-1 to 0.08 (−11 dB) or less, it becomes possible for the wireless terminal 1-1 and the wireless terminal 1-3 to communicate simultaneously, and throughput increases in both wireless terminals. I can confirm that. As described above, it was confirmed that the transmission power and the CCA level are integrally controlled, thereby improving the throughput of the own radio terminal without lowering the throughput of other radio terminals.

  Conventionally, there has been proposed a technique for preventing a decrease in system throughput due to an increase in interference by simultaneously controlling the CCA / CA CCA level and transmission power (Non-patent Document 1). However, since this control is performed by individual terminals, there is still a problem that the system throughput is reduced.

  In this embodiment, for example, an attenuation value corresponding to the reception power from the communication partner is set, and at the same time as the CCA level increases, the transmission power decreases, and the modulation mode corresponding to the transmission power is changed. I sent it. In order to realize these, the CCA level is substantially increased by inserting a common attenuator for the transmission antenna and the reception antenna to attenuate the reception power by a certain amount. With this configuration, due to the reversibility of radio wave propagation, fairness among the wireless devices can be maintained, and a decrease in system throughput can be prevented. In addition, by realizing with one attenuator, it is possible to realize miniaturization and simplification of the radio.

  Further, instead of using the variable ATT according to the present embodiment, the same control can be performed with a digital signal. That is, for the transmission signal, the output of the radio system signal transmission / reception circuit is reduced to a signal level equivalent to that attenuated by the variable ATT, and the reception power level compared with the CCA level is also attenuated by the attenuation used by the variable ATT. For example, the reception level can be reduced by the attenuation amount and compared with the CCA level.

  The wireless terminal 1 in the embodiment described above may be realized by a computer. In that case, a program for realizing this function may be recorded on a computer-readable recording medium, and the program recorded on this recording medium may be read into a computer system and executed. Here, the “computer system” includes an OS and hardware such as peripheral devices. The “computer-readable recording medium” refers to a storage device such as a flexible medium, a magneto-optical disk, a portable medium such as a ROM and a CD-ROM, and a hard disk incorporated in a computer system. Furthermore, the “computer-readable recording medium” dynamically holds a program for a short time like a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line. In this case, a volatile memory inside a computer system serving as a server or a client in that case may be included and a program held for a certain period of time. Further, the program may be for realizing a part of the functions described above, and may be a program capable of realizing the functions described above in combination with a program already recorded in the computer system. It may be realized using hardware such as PLD (Programmable Logic Device) or FPGA (Field Programmable Gate Array).

  As mentioned above, although embodiment of this invention has been described with reference to drawings, the said embodiment is only the illustration of this invention, and it is clear that this invention is not limited to the said embodiment. is there. Therefore, additions, omissions, substitutions, and other modifications of the components may be made without departing from the technical idea and scope of the present invention.

  In a wireless system based on CSMA / CA, it is possible to realize a wireless communication system that prevents a wireless terminal from unjustly acquiring an access right from being generated by equally attenuating a transmission signal and a reception signal by an attenuator.

  DESCRIPTION OF SYMBOLS 1, 2 ... Wireless terminal, 11 ... Variable ATT (signal attenuation part), 12 ... Radio system signal transmission / reception circuit (radio signal transmission part), 13 ... Transmission modulation circuit (radio signal transmission part) , 14... Reception decoding circuit, 15... ATT control circuit (signal attenuation amount determination unit, modulation mode determination unit, signal attenuation amount setting unit, attenuation use determination unit, reception level ID storage unit), 16. Reception level acquisition circuit (reception level detection unit), 17... Information signal input / output circuit (reception level ID storage unit)

Claims (8)

A wireless communication device that performs random access,
Giving any attenuation in the transmission signal to be output to the antenna, and the signal attenuator for Ru given the same amount of attenuation and the transmission signal to the reception signal input from the antenna,
A received signal level detector that detects a received signal level of the received signal from the signal attenuator;
A signal attenuation amount determination unit that determines an attenuation amount of the signal attenuation unit that can be transmitted from the detected received signal level;
A transmission signal generator for generating a transmission signal to the communication partner;
A modulation mode determination unit for determining a modulation mode consisting of a modulation scheme and a coding rate in transmitting attenuates the signal at the signal attenuator,
A signal attenuation amount setting unit for setting the attenuation amount determined in the signal attenuation unit;
A radio communication apparatus comprising: a radio signal transmission unit that performs modulation and encoding according to the modulation mode and transmits the transmission signal via the signal attenuation unit. A reception level frequency storage unit for storing frequency information of signals detected by the reception signal level detection unit;
A throughput evaluation value is calculated from the modulation mode determined in consideration of the attenuation amount in the generated transmission signal and the stored frequency information, and it is determined whether or not communication is performed using the determined attenuation amount. An attenuation use determination unit that
The wireless communication apparatus according to claim 1, wherein when it is determined that communication is performed, the signal attenuation amount setting unit sets the determined attenuation amount in the signal attenuation unit. An ID acquisition unit that acquires the ID of the wireless communication device that has transmitted the received signal or the ID of the wireless communication device that is the transmission destination of the received signal, or both IDs;
A reception level ID storage unit for storing a signal level corresponding to the acquired ID as ID reception level information;
A signal attenuation amount determination unit that determines an attenuation amount to be used in the signal attenuation unit for the ID from the stored ID reception level information;
Whether to perform communication of the transmission signal using the determined attenuation amount based on the throughput evaluation value of the modulation mode determined in consideration of the attenuation amount determined for the ID for the generated transmission signal An attenuation use determination unit for determining whether or not
The wireless communication apparatus according to claim 1, further comprising: An ID acquisition unit that acquires the ID of the wireless communication device that has transmitted the received signal or the ID of the wireless communication device that is the transmission destination of the received signal, or both IDs;
A reception level ID storage unit for storing signal level and frequency information corresponding to the acquired ID as ID reception level information;
A signal attenuation amount determination unit that determines an attenuation amount to be used in the signal attenuation unit for the ID from the stored ID reception level information;
An attenuation use determination unit that calculates a throughput evaluation value from the modulation mode and the stored frequency information, and determines whether to perform communication using the determined attenuation amount ;
The modulation mode determination unit determines the modulation mode consisting of a modulation scheme and a coding rate in transmitting attenuates the signal at the signal attenuator using the attenuation being determined for the ID,
The wireless communication apparatus according to claim 1, wherein when it is determined that communication is performed, the signal attenuation amount setting unit sets the determined attenuation amount in the signal attenuation unit. An ID acquisition unit that acquires an ID of a wireless communication device that is a transmission source of a signal being received and a wireless terminal ID that is a transmission destination of a signal that is being received;
A reception level ID storage unit that stores a signal level corresponding to the ID of the wireless communication device as a transmission source as ID reception level information;
A signal attenuation amount determining unit that determines an attenuation amount for each ID stored in the ID reception level information;
The modulation mode determination unit is determined for the attenuation determined for the ID of the wireless communication terminal serving as the transmission source of the signal being received and the ID of the wireless communication terminal serving as the transmission destination of the signal being received. to claim 1, wherein the determining the modulation mode consisting of a modulation scheme and a coding rate in transmitting attenuates the signal at the signal attenuator using the attenuation of the larger of the amount of attenuation is The wireless communication device described. A specific ID designating unit that imposes a penalty for adding a further additional attenuation amount to the attenuation amount determined from the reception level or the prohibition of communication using the attenuation amount with respect to the specific ID;
6. The reception level ID storage unit stores, for an ID specified from a specific ID, communication prohibition using an attenuation amount in ID reception level information or provision of an additional attenuation amount. The wireless communication device according to any one of the above. A wireless communication method performed by a wireless communication device that performs random access,
Giving any attenuation in the transmission signal to be output to the antenna, and the signal attenuation steps of Ru given the same amount of attenuation and the transmission signal to the reception signal input from the antenna,
A received signal level detecting step of detecting a received signal level of the received signal given the attenuation by the signal attenuating step;
A signal attenuation determination step for determining the attenuation in the signal attenuation step from the detected received signal level;
A transmission signal generation step for generating a transmission signal to a wireless communication device as a communication partner;
A modulation mode determination step for determining a modulation mode when transmitting the transmission signal after attenuating the transmission power of the transmission signal by the signal attenuation step;
And a radio signal transmission step of transmitting a signal given the attenuation amount by the signal attenuation step according to the modulation mode. A reception level frequency storage step for storing frequency information of the signal detected in the reception signal level detection step;
Whether communication is performed using the attenuation amount with reference to the throughput evaluation value calculated from the modulation mode determined in consideration of the attenuation amount determined in the signal attenuation amount determination step and the received reception level frequency information An attenuation use determination step for determining whether or not,
8. The wireless communication method according to claim 7, wherein when it is determined that the attenuation amount is used, transmission is performed using the attenuation amount determined for the detected received signal level.

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