JP2007142722A - Wireless communication apparatus and wireless communication method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem of carrier sensing in conventional CSMA/CA systems, wherein there is the possibility that an error is generated on the occurrence of packet collision due to unsatisfied CIR requirements, when desired wave power is small, even when the RSSI is a carrier sense threshold or lower and that the transmission propriety is determined even though the conventional method determines the transmission propriety, by comparing the RSSI being an interference power with the carrier sense level threshold value. <P>SOLUTION: A wireless communication method disclosed herein calculates permissible interference power, on the basis of the reception power of desired waves on the receiver side and the CIR requirements, obtains transmission propriety threshold on the basis of the permissible interference power, and determines whether the transmission is to be executed, by comparing a power on a channel with the transmission propriety threshold. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a wireless communication device and a wireless communication method for suppressing occurrence of errors due to data collision on a receiving side in a wireless communication system including a plurality of wireless communication devices.

In the conventional wireless LAN system of IEEE802.11 and IEEE802.11a, b, g method, the CSMA / CA (Carrier Sense Multiple Access / Collision Avoidance) method is used as an access method, and before transmission, other stations Carrier sense is performed to determine whether or not the signal of the signal exists on the channel. FIG. 9 shows an example of carrier sense in the conventional CSMA / CA system.
When a transmission request is generated at terminal X, the channel is searched (carrier sense) before transmission, and when no carrier is detected on the channel, the channel is determined to be in an idle state and transmission is started. On the other hand, when a transmission request is generated at the terminal Y while the terminal X is transmitting, the carrier of the terminal X is detected by performing carrier sense. In this case, terminal Y determines that the channel is busy and refrains from transmission (see, for example, Non-Patent Document 1).

Here, the carrier sense compares the RSSI (Received Signal Strength Indicator) value measured by itself with a predetermined carrier sense level threshold, and when the RSSI value is equal to or higher than the carrier sense level threshold, the channel is busy. Judgment is made in a state, transmission is avoided, and collision is avoided. This carrier sense level threshold is determined by the standard, and takes two values depending on whether IEEE802.11b, g is a constant value, and IEEE802.11a indicates whether a preamble signal has been detected. In addition, a method of obtaining high signal quality by changing a channel at the time of interference has been proposed (see, for example, Patent Document 1).

JP 2003-249935 A (pages 2 to 7) Matsue, Morikura, “IEEE802.11 High-Speed Wireless LAN Textbook”, IDG Japan Publishing, pages 15-16

As described above, the conventional carrier sense is performed by using RSSI as the interference power and comparing the interference power and the carrier sense level threshold value. It is determined by a ratio CIR (Carrier to Interference Ratio) between the power (received signal power from the other party to communicate originally) and the intensity of the interference power. Therefore, even when it is determined that transmission is possible with the interference power below the carrier sense threshold, if the desired signal power is small, an error may occur at the time of packet collision. This is a problem that occurs because the prescribed carrier sense level threshold is a constant value and does not consider the magnitude of the desired wave power.

The present invention was made to solve the above problems, and by setting a carrier sense level threshold dynamically based on the desired wave power, a system that is less prone to error and has a high throughput is realized. The purpose is to do.

The present invention relates to a wireless communication device in a wireless communication system including a plurality of wireless communication devices, wherein the counterpart communication device acquired from a counterpart communication device that is a counterpart to which data is wirelessly transmitted from the wireless communication device. Based on the acquired information on the communication status, the allowable interference power calculation means for obtaining the allowable interference power that is the allowable value of the intensity of the interference signal with respect to the desired signal in the wireless communication device, and the allowable interference power calculated by the allowable interference power calculation means A transmission availability threshold value calculating means for obtaining a transmission availability threshold value, which is a criterion for determining whether or not the wireless communication device performs data transmission to the counterpart communication device, and the wireless communication device is connected to the counterpart communication device. Based on the power on the channel to be used, which is the power on the channel to be used for communication, and the transmission availability threshold obtained by the transmission availability threshold calculating means, the other party side Is a wireless communication device, characterized in that a transmission capability determining means for determining whether to perform data transmission to signal machine.

In this invention, the transmission-side radio communication device determines the transmission permission threshold from the allowable interference power obtained based on the acquired information on the communication status of the reception-side counterpart communication device. There is an effect that errors can be reduced.

Embodiment 1 FIG.
The first embodiment will be described with reference to FIGS.
FIG. 1 is a configuration diagram of a wireless communication (wireless LAN) system according to this embodiment, FIG. 2 is a configuration diagram of a main part of a terminal or access point according to this embodiment, and FIG. 3 is a carrier sense of this embodiment. It is a flowchart which shows operation | movement.

The system shown in FIG. 1 includes a terminal (STA) 1, a terminal (STA) 2, an access point (AP) 3 and an access point (AP) 4. The terminal 1 and the access point 3 and the terminal 2 and the access point 4 are connected by wireless lines, respectively, and the access point 3 and the access point 4 form a cell 5 and a cell 6 around them, respectively. For convenience of explanation, the cells 5 and 6 are described here, but the number of cells is not limited to two and may be three or more. Further, the access point 3 may perform data communication not only with the terminal 1 but also with a plurality of terminals.

  FIG. 2 is a principal block diagram of the internal configuration of the terminals 1 and 2 and the access points 3 and 4. The terminal and the access point include a transmission / reception unit 7, an RSSI measurement unit 8, a threshold calculation unit 9, an RSSI comparison unit 10, and a control unit 11.

  Next, the operation will be described. In this description, it is assumed that the received power at the access point of the signal transmitted from the terminal to the access point is equal to the received power at the terminal of the signal transmitted from the access point to the terminal. . Further, it is assumed that the reception performance of the terminal and the reception performance of the access point are equal.

When data communication is performed from the access point 3 to the terminal 1 using the access point 3 as a transmission end and the terminal 1 as a reception end (that is, in the case of “downlink data communication”), the access point 3 transmits data to other access points or terminals. In order to check whether or not it is in the middle, carrier sense for detecting the strength of the carrier by another communication device on the channel to be used is performed before transmitting data.

In this embodiment, a threshold value of carrier strength (carrier sense level threshold value) for determining whether or not the access point 3 performs data transmission to the terminal 1 is determined based on the received power from the terminal 1.

A carrier sense flowchart in the access point 3 is shown in FIG.
A signal from the terminal 1 as a communication partner received by the transmission / reception unit 7 of the access point 3 is sent to the RSSI measurement unit 8, and received power (RSSI) is measured as acquired information (step 11). In parallel with this, the threshold calculation unit 9 calculates the required desired signal power to interference power ratio (required CIR, Carrier to Interference Ratio) of the access point 3 itself (step 12). Here, the required CIR represents a CIR capable of obtaining a desired error rate.

Next, the allowable interference power is calculated by the RSSI measurement unit 8 from the RSSI obtained in step 11 and the required CIR obtained in step 12 (step 13). The calculation of allowable interference power is shown in the following equation.
Allowable interference power = RSSI / required CIR
Here, by calculating the allowable interference power of the access point 3, the allowable interference power at the terminal 1 is calculated equivalently.

Subsequently, the threshold value calculation unit 9 receives the allowable interference power from the RSSI measurement unit 8, and calculates the carrier sense level threshold value (CSth) as a transmission availability threshold value based on the allowable interference power (step 14). The calculation method is, for example,
Carrier sense level threshold = allowable interference power + α: α ≦ 0
And

Here, when there is a transmission request from the control unit 11 (when step 15 is YES), the transmission / reception unit 7 observes the channel (step 16) and the received received signal strength value (RSSI: Received Signal Strength Indicator). Is measured as the power on the channel to be used (step 17).
The RSSI comparison unit 10 compares the RSSI with the carrier sense level threshold value described above (step 18). If the observed RSSI is larger, the channel is determined to be busy, and the control unit 11 is notified. In response to an instruction from the control unit 11, the transmission / reception unit 7 refrains from transmission and waits for the back-off time to elapse (step 19). If the observed RSSI is smaller, the channel is determined to be in an idle state, the control unit 11 is notified, and transmission is performed from the transmission / reception unit 7 according to an instruction from the control unit 11 (step 20).

As described above, the allowable interference power is calculated from the RSSI of the received power from the terminal 1 at the access point 3 and the required CIR of the access point 3, and the carrier sense level is dynamically changed. There is an effect that the occurrence of an error due to the collision can be reduced because the collision is less likely to occur.
Further, in this embodiment, the access point 3 that is the transmitting station without using the exchange of feedback information (status notification from the receiving station to the transmitting station) from the terminal 1 that is the receiving station to the access point 3 that is the transmitting station. Since the closed process is performed, there is an effect of not causing an increase in traffic.

In the above example, the case where data is transmitted from the access point to the terminal in the wireless LAN system has been described. However, data communication (uplink data communication) from the terminal 1 to the access point 3 by replacing the terminal 1 and the access point 3 in the above description. In the same manner as described above, it is possible to obtain an effect that the occurrence of errors at the access point 3 can be reduced. Needless to say, the present invention can be applied not only to a wireless LAN system but also to other communication systems.

Embodiment 2. FIG.
The second embodiment will be described with reference to FIGS.
In the first embodiment, the carrier sense level threshold is determined based on the received power and the required CIR at the access point 3 that is the transmitting station. In this embodiment, the terminal that is the receiving station is used. The example which changes a carrier sense level threshold value on the basis of 1 information is shown.

FIG. 4 is a flowchart showing an operation at the access point 3 in the second embodiment, and FIG. 5 is a diagram showing a communication sequence in the second embodiment.
The configuration diagram of the radio communication system and the main configuration diagram of the terminal or access point in the second embodiment are the same as those in FIGS. 1 and 2 shown in the first embodiment, respectively.
In FIG. 4, the same operations as those in the flowchart shown in FIG. 3 in the first embodiment are denoted by the same step numbers, and a part of the description is omitted.

In this second embodiment, instead of the received power (RSSI value) acquired from the terminal 1 in step 11 of FIG. 3 in the first embodiment and the required CIR at the access point 3 acquired in step 12, FIG. The feedback information 21 from the terminal 1 acquired in step 21 is used. As feedback information, here, the received power at the terminal 1 and the required CIR at the terminal 1 are used.

Next, the operation will be described with reference to FIGS.
First, as shown in FIG. 5, when arbitrary (or predetermined) data is transmitted from the access point 3 serving as a transmitting station to the terminal 1 serving as a receiving station, the terminal 1 measures the received power (RSSI value) at this time. To do. Further, the required CIR is defined by the terminal 1. These two pieces of information are fed back to the access point 3 which is a transmitting station. The access point 3 receives feedback information (step 21), and calculates allowable interference power from the information (step 13). The calculation of the allowable interference power is performed based on the following equation as in the first embodiment.
Allowable interference power = RSSI / required CIR

Subsequent operations are the same as those in the first embodiment, and then a carrier sense level threshold CSth is calculated based on the allowable interference power (step 14).
The calculated carrier sense level threshold value CSth is compared with the RSSI value observed in the channel (step 18). When the observed RSSI value is larger (when step 18 is NO), the channel is busy. Refrain from sending. If the observed RSSI value is smaller (YES in step 18), the channel is determined to be idle and transmission is performed (step 20).

In this embodiment, the carrier sense level threshold value can be set based on information at the receiving terminal where the error actually occurs regardless of the performance difference between the transmitting station and the receiving station. Therefore, there is an effect that an error due to one interference in the receiving terminal 1 can be further reduced.

Also in this embodiment, the case where data is transmitted from the access point to the terminal has been described. However, data communication (uplink data communication) is performed from the terminal 1 to the access point 3 by exchanging the terminal 1 and the access point 3 in the above description. It may be applied to the case, and the effect of reducing the occurrence of errors at the access point 3 can be obtained in the same manner as described above.
Furthermore, although an example in which the calculation of allowable interference power (step 13) and subsequent steps is performed on the transmission side is shown, the calculation up to the carrier sense level threshold may be performed in the terminal 1 on the reception station side, and the same effect is exhibited. To do.

Embodiment 3 FIG.
In the above embodiment, an example in which the carrier sense level threshold is dynamically changed to reduce errors due to collisions has been shown. However, in the third embodiment, errors frequently occur even after the carrier sense level threshold is changed. An example of further changing the carrier sense level threshold when it occurs is shown.

FIG. 6 shows a flowchart of the operation of the access point 3 in the third embodiment.
Here, an example is shown in which a function for changing the carrier sense level threshold value according to the error rate is added to the operation of the first embodiment, and the same operations as those of the first embodiment are denoted by the same reference numerals. Is omitted.

Even after the carrier sense level threshold is changed in step 14, if the error status in the terminal 1 exceeds the predetermined threshold (YES in step 31), the carrier sense level threshold is changed (step 32). The carrier sense is changed by, for example, lowering by 1 dB when the error situation exceeds the error situation threshold, or when a predetermined relationship is established between the error situation and the carrier sense level threshold, and the carrier sense is deteriorated. For example, the level threshold value may be lowered.

The detection of the error situation in the terminal 1 is performed by the transmission / reception unit 7. For example, a predetermined error threshold is set in advance for the number of consecutive errors or the error rate, and the terminal 1 receives the data correctly. This is done by detecting an error situation by not reaching ACK (reception confirmation response) transmitted from the terminal 1 and comparing the error situation with a preset threshold (for example, frequency of ACK not reached). If the detected error status is equal to or greater than the predetermined error threshold, the transmitting / receiving unit 7 determines that an error has occurred due to interference, and further sets the carrier sense level threshold low. As described above, ACK is a technique applied to an existing wireless LAN, in which a data receiving station returns data to a data transmitting station when the data is correctly received.

According to this embodiment, the carrier sense level threshold value can be set according to the actual error situation. For this reason, it is possible to perform control directly related to an error as compared with the first embodiment.

  Although the above has been described using the flowchart based on the first embodiment, the second embodiment may be used as a basis, and the same effect can be obtained. In this case, steps 11 and 12 in FIG. 6 are replaced with step 21 in FIG. 4 described in the second embodiment.

Embodiment 4 FIG.
In the third embodiment, the example in which the carrier sense level threshold is changed according to the error occurrence state has been described. In the fourth embodiment, the carrier sense level threshold according to the error occurrence state in the third embodiment is used. An example in which a change and a transmission rate control method according to an existing error occurrence state are combined will be described.

For example, as described in the third embodiment, the occurrence state of an error on the reception side (terminal 1) is grasped by the transmission side (transmission / reception unit 7 of the access point 3) from the ACK non-arrival frequency, and the error occurrence state is high. In this case, the transmission rate is lowered, and the transmission rate is first lowered to a transmission rate (for example, 6 Mbps in IEEE802.11a) where the error is hardly caused by the existing transmission rate control method. If errors still occur on the receiving side exceeding a predetermined value, the carrier sense level threshold value is determined by the operation from step 1 in FIG. 3 or FIG. 4 as described in the first or second embodiment. Set.

Alternatively, first, the carrier sense level threshold is set as in the first embodiment or the second embodiment, and the existing transmission rate control is performed after reaching the predetermined lower limit of the carrier sense level threshold. May be. In this case, a step for determining whether or not the carrier sense level threshold value has reached the lower limit value is provided between step 14 and step 15 in FIGS. 3 and 4, and when it is determined that the lower limit value has been reached. Instead of proceeding to step 15, the existing transmission rate control method may be adopted. This determination is executed by the transmission / reception unit 7 of the access point 3.

In this way, by combining the carrier sense threshold value changing method and the conventional transmission rate control method, as shown in the first embodiment or the second embodiment, errors generated by a collision on the receiving side are reduced, and at the same time, the receiving side. It is possible to avoid errors due to interference caused by a decrease in the desired received power at.

Embodiment 5
In the above embodiment, an example in which the carrier sense level threshold value is changed to reduce the error due to the collision has been shown. However, in the fifth embodiment, RTS / CTS ( An example of switching to the (transmission request / reception confirmation response) method is shown.

Here, the RTS / CTS method means that RTS (Request To Send) is transmitted before the transmitting station transmits data, and if the receiving station can receive the RTS and receive data, CTS (Clear To Send: Ready to receive). All terminals monitor RTS and CTS so that other terminals refrain from transmission and avoid collisions. However, when the RTS / CTS method is used, there is a problem that the data communication speed is lowered due to the overhead of RTS and CTS.

FIG. 7 is a flowchart showing the operation of the wireless LAN system in such a case. First, the carrier sense level threshold is set to a predetermined fixed value (step 40). Next, the carrier sense described in the first to third embodiments is performed (steps 15 to 18). Thereafter, the interference state is detected (step 41), and switching to the RTS / CTS method is performed according to the interference state (step 43). Thereafter, the RTS / CTS method is used until the interference amount is reduced, and the CSMA / CA method of normal transmission is restored when the reduction of the interference amount is detected (FIG. 8).

The detection of the interference state in step 41 is performed, for example, when a Beacon is received from an access point that is an interfering station (having a different SSID from the own station). Alternatively, a predetermined RSSI threshold value is set in advance for the power value (RSSI value) that causes interference, and the preset threshold value is compared with the RSSI value of a signal not addressed to the user. Then, when the RSSI value of the signal not addressed to itself is larger, switching to the RTS / CTS system is performed. Furthermore, the traffic volume at the access point is notified by broadcast information, and the notified traffic volume is compared with a predetermined traffic threshold value set in advance. Then, when the received traffic volume is equal to or greater than a set traffic threshold, the RTS / CTS system is switched.
The above operation is performed in the transmission / reception unit 7.

As described above, errors due to interference can be avoided with only the minimum necessary overhead by dynamically changing the normal transmission and the RTS / CTS method according to the interference state.

In each of the above embodiments, the access point 3 corresponds to the wireless communication device in the present invention, and the terminal 1 corresponds to the counterpart communication device in the present invention. Hereinafter, the transmission / reception unit 7 includes feedback information acquisition means, error situation determination means, Data transmission rate changing means and transmission method determining means, RSSI measuring section 8 is received power intensity measuring means, threshold calculating section 9 is allowable interference power calculating means and transmission enable / disable threshold calculating means, control section 11 is error condition determining means, RSSI comparison The unit 10 corresponds to transmission permission / inhibition determining means.

1 is a diagram illustrating an overall configuration of a wireless LAN system according to an embodiment of the present invention. It is a figure which shows the internal structure of the wireless LAN apparatus which is embodiment of this invention. 3 is a flowchart illustrating a carrier sense procedure of the wireless LAN system according to the first embodiment. 6 is a flowchart illustrating a carrier sense procedure of the wireless LAN system according to the second embodiment. It is a figure which shows the communication sequence in the case of using feedback information. 12 is a flowchart illustrating a carrier sense procedure of the wireless LAN system according to the third embodiment. FIG. 10 is a diagram showing a wireless communication system switching procedure of the wireless LAN system of the fourth embodiment. FIG. 10 is a diagram showing a communication sequence when switching the communication method of the fifth embodiment. It is a figure which shows the example of the carrier sense in the conventional CSMA / CA system.

Explanation of symbols

1, 2 Terminal 3, 4 Access point 5, 6 Wireless cell.

Claims (10)

A wireless communication device in a wireless communication system including a plurality of wireless communication devices,
Based on the acquired information on the communication status of the counterpart communication device acquired from the counterpart communication device that is the counterpart to which data is to be wirelessly transmitted from the radio communication device, the interference signal strength tolerance for the desired signal in the radio communication device A permissible interference power calculating means for obtaining a permissible interference power which is a value;
A transmission enable / disable threshold calculating means for obtaining a transmission enable / disable threshold that is a criterion for determining whether or not the wireless communication apparatus performs data transmission to the counterpart communication apparatus from the allowable interference power calculated by the allowable interference power calculating means; ,
Based on the power on the channel to be used, which is the power on the channel that the wireless communication device intends to use for communication with the counterpart communication device, and the transmission availability threshold obtained by the transmission availability threshold calculating means, A wireless communication device comprising: transmission permission / non-permission determining means for determining whether or not to perform data transmission to a side communication device. (Embodiment 1)
Receiving power strength measuring means for measuring the strength of the signal from the counterpart communication device as received power strength,
2. The wireless communication device according to claim 1, wherein the allowable interference power calculation means obtains the allowable interference power using the reception power intensity measured by the reception power intensity measurement means as the acquired information. (Embodiment 1)
The allowable interference power calculation means includes interference between a received power intensity that is acquired information obtained by the received power intensity measuring means, and a desired wave power necessary for the wireless communication device to receive a desired wave at a predetermined error rate. The wireless communication device according to claim 2, wherein the allowable interference power is obtained based on a required CIR (Carrier to Interference Ratio) which is a ratio of electric power. (Embodiment 2)
Interference reception power that is received power at the counterpart communication device of the signal transmitted from the wireless communication device and interference with desired wave power necessary for the counterpart communication device to receive a desired wave with a predetermined error rate Provide feedback information acquisition means for acquiring the other party's required CIR which is the ratio of power,
2. The radio according to claim 1, wherein the allowable interference power calculation unit obtains the allowable interference power by using the other party received power acquired by the feedback information acquisition unit and the other party required CIR as acquisition information. Communication machine. (Embodiment 3)
An error situation determination unit that compares an error situation of received data with a predetermined error situation threshold in a counterpart communication device, and the transmission availability threshold value calculation means calculates the transmission availability threshold value based on a judgment result of the error situation judgment unit. The wireless communication apparatus according to claim 1, wherein the wireless communication apparatus is changed. (Embodiment 3)
The error situation of the received data in the counterpart communication device is an ACK unreachable frequency to be transmitted from the counterpart receiver, and the error situation threshold is a predetermined threshold regarding the non-arrival frequency. The wireless communication device according to claim 5. (Embodiment 4)
When a predetermined lower limit value is provided for the transmission permission threshold value and the transmission permission threshold value obtained by the transmission permission threshold value calculation unit exceeds the lower limit value, the data transmission rate from the wireless communication device to the partner communication device is set. The wireless communication device according to claim 1, further comprising a data transmission rate changing means for reducing the data transmission rate.   2. The wireless communication device according to claim 1, wherein one of the wireless communication device and the counterpart communication device is a terminal in a wireless LAN system, and the other is an access point in the wireless LAN system. (Embodiment 5)
A wireless communication device in a wireless communication system including a plurality of wireless communication devices,
The wireless communication device
Transmission that determines whether to adopt the RTS / CTS method or the CSMA / CA method depending on the strength of an interference signal from a communication device other than the counterpart communication device that is a partner to which data is wirelessly transmitted from the wireless communication device A wireless communication method comprising a method determining means. A wireless communication method employed by a wireless communication device in a wireless communication system including a plurality of wireless communication devices,
The wireless communication device
Based on the acquired information on the communication status of the counterpart communication device acquired from the counterpart communication device that is the counterpart to which data is to be wirelessly transmitted from the radio communication device, the interference signal strength tolerance for the desired signal in the radio communication device An allowable interference power calculation step for obtaining an allowable interference power that is a value;
A transmission availability threshold calculation step for obtaining a transmission availability threshold, which is a criterion for determining whether or not the wireless communication device performs data transmission to the counterpart communication device, from the allowable interference power calculated in the allowable interference power calculation step; ,
Based on the power on the channel scheduled to be used, which is the power on the channel that the wireless communication device intends to use for communication with the communication device on the other side, and the transmission availability threshold obtained in the transmission availability threshold calculation step, A wireless communication method comprising: a transmission permission / inhibition determining step for determining whether or not to perform data transmission to a side communication device.

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