Wireless device and wireless communication method

Abstract

A wireless device according to one aspect of the present invention includes: a threshold-value deciding unit that decides a threshold value to be used for determining a usage state of a frequency channel and that sets, when first priority as priority of a frame to be transmitted has a first priority level, a threshold value to a first value, and sets, when the first priority has a second priority level higher than the first priority level, the threshold value to a second value higher than the first value; and a carrier sensing control unit that determines the usage state of the frequency channel on the basis of comparison between received power detected on the frequency channel by carrier sensing and the threshold value.

Description

[Technical field]

[0001] The present invention relates to wireless communications. [Background technology]

[0002] In recent years, with the spread of portable wireless terminals such as laptops and smartphones, IEEE802.11 standard wireless local area networks (LANs) are widely used not only in companies and public spaces but also in ordinary homes. This has resulted in situations where multiple basic service sets (BSSs) using the same frequency channel exist adjacent to each other. In such situations, there are concerns that the reliability of wireless communication will decrease, such as decreasing throughput and increasing transmission delay. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] IEEE P802.11ax / D8.0, “26.10 Spatial reuse operation”, October 2020. Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a technique that enables highly reliable wireless communication. [Means for solving the problem]

[0005] A wireless device according to one embodiment of the present invention includes a threshold determination unit that determines a threshold used to determine the usage status of a frequency channel, the threshold determination unit setting the threshold to a first value when a first priority, which is the priority of a frame to be transmitted, is a first priority level, and setting the threshold to a second value greater than the first value when the first priority is a second priority level higher than the first priority level, and a carrier sense control unit that determines the usage status of the frequency channel based on a comparison between the received power of a frame detected on the frequency channel by carrier sense and the threshold. Effect of the Invention

[0006] According to the present invention, it is possible to provide a technique that enables highly reliable wireless communication. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a diagram showing a communication system according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram showing a frame format according to the embodiment of the present invention. [Diagram 3] FIG. 3 is a block diagram showing a hardware configuration of the base station shown in FIG. [Figure 4] FIG. 4 is a block diagram showing a hardware configuration of the terminal shown in FIG. [Diagram 5] FIG. 5 is a block diagram showing functional configurations of the base station and the terminal shown in FIG. [Figure 6] FIG. 6 is a block diagram illustrating the transmitting unit shown in FIG. [Figure 7] FIG. 7 is a block diagram showing the receiving section shown in FIG. [Figure 8] FIG. 8 is a diagram illustrating an example of a method for determining the CCA threshold in the MAC frame processing unit illustrated in FIG. [Figure 9] FIG. 9 is a flowchart showing an example of the operation of the base station shown in FIG. [Figure 10]FIG. 10 is a flowchart showing an example of the operation of the base station shown in FIG. [Figure 11] FIG. 11 is a time chart showing an example of the operation of the communication system shown in FIG. [Figure 12] FIG. 12 is a diagram for explaining another example of the method for determining the CCA threshold in the MAC frame processing unit shown in FIG. [Figure 13] FIG. 13 is a flowchart showing another example of the operation of the base station shown in FIG. [Figure 14A] FIG. 14A is a time chart showing another example of the operation of the communication system shown in FIG. [Figure 14B] FIG. 14B is a time chart showing another example of the operation of the communication system shown in FIG. [Figure 15] FIG. 15 is a diagram illustrating a further example of the method for determining the CCA threshold in the MAC frame processing unit shown in FIG. [Figure 16] FIG. 16 is a flow chart illustrating a further example of the operation of the base station shown in FIG. [Figure 17] FIG. 17 is a flowchart showing yet another example of the operation of the base station shown in FIG. [Figure 18] FIG. 18 is a diagram for explaining still another example of the method for determining the CCA threshold in the MAC frame processing unit shown in FIG. [Figure 19] FIG. 19 is a time chart showing yet another example of the operation of the communication system shown in FIG. [Figure 20] FIG. 20 is a flowchart showing another example of the operation of the base station shown in FIG. [Figure 21] FIG. 21 is a flowchart illustrating a further example of the operation of the base station shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0009] (First embodiment) [composition] 1 is a schematic diagram of a communication system 50 according to a first embodiment of the present invention. As shown in FIG. 1, the communication system 50 includes base stations 10 and 12, terminals 20 and 22, and a network 40.

[0010] The base stations 10 and 12 operate as access points (APs) of a wireless LAN (Local Area Network). The base station 10 wirelessly communicates with a terminal 20, and the base station 12 wirelessly communicates with a terminal 22. The communications between the base stations 10 and 12 and the terminals 20 and 22 are based on, for example, the IEEE 802.11 standard. The base stations 10 and 12 are connected to a network 40, for example, by wire. The network 40 may include a local area network (LAN), a wide area network (WAN), or both. The base stations 10 and 12 may be connected to different networks.

[0011] The terminals 20 and 22 are wireless terminals. Examples of the wireless terminals include a smartphone, a tablet PC (Personal Computer), a desktop PC, and a laptop PC. The terminals 20 and 22 exchange data with a computer (not shown) (e.g., a server) on the network 40 via the base stations 10 and 12.

[0012] In a communication system 50, two basic service sets (BSSs) 30 and 32 exist adjacent to each other. The BSS 30 is composed of a base station 10 and a terminal 20, and the BSS 32 is composed of a base station 12 and a terminal 22. The BSSs 30 and 32 use the same frequency channel. Hereinafter, the frequency channel will be simply referred to as a channel.

[0013] Hereinafter, wireless station is used as a general term for base stations and wireless terminals. For example, wireless station may refer to each or any of the base stations 10, 12 and terminals 20, 22, depending on the context.

[0014] Before transmitting a frame, a wireless station performs carrier sensing to determine the usage status of a channel used for transmitting the frame. Carrier sensing may be based on a Carrier Sense Multiple Access with Collision Detection (CSMA / CA) algorithm. In CSMA / CA, a threshold called a Clear Channel Assessment (CCA) threshold is used to determine the usage status of the channel. When a wireless station detects a frame by carrier sensing, the wireless station determines a CCA threshold based on information included in the preamble of the detected frame and the priority of the frame to be transmitted (hereinafter, also referred to as a frame scheduled for transmission), and determines whether the channel is busy or idle based on a comparison between the received power value of the detected frame and the determined CCA threshold. The wireless station transmits a frame after confirming that the channel is idle.

[0015] In the IEEE802.11ax standard, the SR (Spatial Reuse) function is added and the BSS color is defined. The SR function makes it possible to identify the BSS to which a frame belongs by setting a different BSS color for each BSS. The BSS color is an identifier for the BSS and is included in the preamble of the frame. A wireless station can identify whether the destination of the detected frame is a wireless station in its own BSS (MyBSS) or a wireless station in another BSS (OBSS: overlapping BSS) based on the BSS color included in the preamble of the detected frame. If the destination of the detected frame is a wireless station in another BSS, the wireless station increases the CCA threshold. Specifically, if the destination of the detected frame is a wireless station in its own BSS, the wireless station uses a CCA threshold of -82 dBm, and if the destination of the detected frame is a wireless station in another BSS, the wireless station uses a CCA threshold defined in the SR function. The CCA threshold defined in the SR function is called an SR value. In one example, a CCA threshold of -77 dBm may be used as the SR value. The IEEE 802.11ax standard addresses the exposed terminal problem by determining the CCA threshold based on whether the frame is destined for a wireless station in the same BSS or a wireless station in another BSS.

[0016] In FIG. 1, the base stations 10, 12 and the terminals 20, 22 are located such that the base station 12 detects a signal from the base station 10 at a power value exceeding the CCA threshold determined by the SR function, the terminal 20 cannot detect a signal from the terminal 22, and the terminal 22 cannot detect a signal from the terminal 20. According to the IEEE802.11ax standard, when the base station 10 is transmitting a frame to the terminal 20, the base station 12 uses the CCA threshold determined by the SR function for the signal from the base station 10 detected by carrier sense. For this reason, the base station 12 determines the channel to be busy and waits for frame transmission. In this way, when the distance between the wireless stations is short, the opportunity to transmit a frame decreases.

[0017] For example, real time applications (RTA) such as network games and industrial robot control applications require low latency communication. The reduction in frame transmission opportunities described above worsens the latency of communication. Hereinafter, frames containing high priority data such as data that requires low latency will be referred to as high priority frames, and frames containing low priority data will be referred to as low priority frames.

[0018] In the first embodiment, when a frame to be transmitted is a high priority frame, the wireless station uses a higher CCA threshold than when the frame to be transmitted is a low priority frame. As a result, when a frame to be transmitted is a high priority frame, the channel is less likely to be determined to be busy, and the transmission opportunity for the high priority frame increases. Therefore, it is possible to ensure the low latency required for high priority frames while avoiding or reducing the exposed terminal problem. In other words, highly reliable wireless communication is possible even in a situation where multiple BSSs overlap.

[0019] In the communication system 50, wireless communication between the base station and the terminal complies with the IEEE 802.11 standard. The IEEE 802.11 standard specifies the first and second MAC sublayers of the OSI (Open Systems Interconnection) reference model. In the OSI reference model, communication functions are divided into seven layers (first layer: physical layer, second layer: data link layer, third layer: network layer, fourth layer: transport layer, fifth layer: session layer, sixth layer: presentation layer, seventh layer: application layer).

[0020] The data link layer includes, for example, an LLC (Logical Link Control) layer and a MAC (Media Access Control) layer. The LLC layer generates LLC packets by, for example, adding a DSAP (Destination Service Access Point) header and an SSAP (Source Service Access Point) header to data input from an upper layer. The MAC layer generates MAC frames by, for example, adding a MAC header to LLC packets. The MAC frames are also called MPDUs (MAC Protocol Data Units). The physical layer generates wireless frames by, for example, adding a preamble to the MAC frames. The wireless frames are also called PPDUs (Physical layer (PHY) Protocol Data Units).

[0021] Fig. 2 illustrates an example of the structure of a radio frame 60 according to the first embodiment. As illustrated in Fig. 2, the radio frame 60 includes a PHY preamble 61, a PHY header 62, and an MPDU 63. The PHY preamble 61 and the PHY header 62 are collectively referred to as a preamble.

[0022] The PHY preamble 61 includes a field for storing information used for synchronization. The PHY header 62 includes a field for storing control information. Specifically, the PHY header 62 includes a field for storing information necessary for data demodulation, a field 611 for storing identification information for identifying a BSS, and a field 612 for storing identification information for identifying a frame priority. The identification information for identifying a BSS may be, but is not limited to, a BSS color defined in IEEE802.11ax.

[0023] In the HE (High Efficiency) frame format defined in IEEE802.11ax, the preamble includes L-STF, L-LTF, L-SIG, HE-SIG-A, HE-STF, HE-LTF, etc. HE-SIG-A includes a field that stores the BSS color. L-STF, L-LTF, HE-STF, and HE-LTF correspond to synchronization information, and L-SIG and HE-SIG-A correspond to control information.

[0024] Hereinafter, the identification information for identifying a BSS is referred to as a BSS color, and the identification information for identifying the priority of a frame is referred to as a QoS (Quality of Service) color. Priority may also be referred to as a QoS value. Frame priority is expressed in two or more levels. When frame priority is expressed in two levels, field 612 may have a one-bit length. For example, when frame priority is a high priority level, "0" is stored in field 612, and when frame priority is a low priority level, "1" is stored in field 612. When frame priority is expressed in four levels, field 612 may have a two-bit length. For example, "00" is associated with the highest priority level, "01" is associated with the second highest priority level, "10" is associated with the third highest priority level, and "11" is associated with the lowest priority level.

[0025] The field 612 may be included in the field 611. In this case, identification information for identifying the BSS and identification information for identifying the priority of the frame are indicated by the information included in the field 611. Also, the field 611 or the field 612 may be included in the PHY preamble 61 instead of the PHY header 62.

[0026] Next, we will explain the configurations of the base station 10 and the terminal 20. The base station 12 can have the same configuration as the base station 10, and the terminal 22 can have the same configuration as the terminal 20. Therefore, the explanation of the configurations of the base station 12 and the terminal 22 will be omitted.

[0027] Fig. 3 illustrates an example of a hardware configuration of the base station 10. In the example illustrated in Fig. 3, the base station 10 includes a CPU (Central Processing Unit) 151, a ROM (Read Only Memory) 152, a RAM (Random Access Memory) 153, a wireless communication module 154, and a wired communication module 155.

[0028] The CPU 151 is a circuit capable of executing various programs and controls the overall operation of the base station 10. The ROM 152 is a non-volatile semiconductor memory and holds programs and control data for controlling the base station 10. The RAM 153 is, for example, a volatile semiconductor memory and is used as a working area for the CPU 151. The wireless communication module 154 is a circuit used for transmitting and receiving data by wireless signals. The wireless communication module 154 includes, for example, a digital circuit, an analog circuit, an A / D converter, and a D / A converter. The digital circuit includes a general-purpose processor such as a CPU. Alternatively or additionally, the digital circuit may include a dedicated processor such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field Programmable Gate Array). The analog circuit includes, for example, a frequency up-converter, a frequency down-converter, a modulation circuit, and a demodulation circuit. The wireless communication module 154 is connected to an antenna. The wireless communication module 154 may include an antenna. The wired communication module 155 is a circuit used for transmitting and receiving data by wired signals and is connected to the network 40.

[0029] FIG. 4 is a schematic diagram showing an example of a hardware configuration of the terminal 20. In the example shown in FIG. 4, the terminal 20 includes a CPU 251, a ROM 252, a RAM 253, a wireless communication module 254, a display 255, and a storage 256. The CPU 251 is a circuit capable of executing various programs, and controls the overall operation of the terminal 20. The ROM 252 is a non-volatile semiconductor memory, and holds programs and control data for controlling the terminal 20. The RAM 253 is, for example, a volatile semiconductor memory, and is used as a working area for the CPU 251. The wireless communication module 254 is a circuit used for transmitting and receiving data by wireless signals, and is connected to an antenna. The wireless communication module 254 may include an antenna. The display 255 displays information such as a GUI (Graphical User Interface) corresponding to application software. The storage 256 is a non-volatile storage device, and holds, for example, system software of the terminal 20.

[0030] The terminal 20 may further include an input interface, for example, a touch screen.

[0031] 5 shows an outline of a functional configuration example of the base station 10 and the terminal 20. The wireless station (each of the base station 10 and the terminal 20) performs LLC layer processing, MAC layer processing, and PHY layer processing on data input from a higher layer to generate a wireless signal including the data, and transmits the wireless signal. The wireless station also receives a wireless signal, performs PHY layer processing, MAC layer processing, and LLC layer processing on the received wireless signal to extract data from the received wireless signal, and outputs the extracted data to the higher layer. The higher layer is, for example, an application layer.

[0032] 5, the base station 10 includes a radio unit 101 and an upper layer 102. The radio unit 101 includes an LLC processing unit 110, a MAC processing unit 120, and a PHY processing unit 130. The radio unit 101 is realized by, for example, a wireless communication module 154 or a combination of the CPU 151 and the wireless communication module 154.

[0033] The LLC processing unit 110 serves as an interface with the upper layer 102, and performs LLC layer processing. For example, when data addressed to the terminal 20 is input from the network 40 to the base station 10, the LLC processing unit 110 receives the data from the upper layer 102, and generates an LLC packet by adding a DSAP header, an SSAP header, and the like to the data. The LLC processing unit 110 receives the traffic type (TID; Traffic Identifier) ​​of the data together with the data from the upper layer 102. The TID is information indicating the priority of the data. For example, a high priority is assigned to data that requires low latency. The LLC processing unit 110 sends the LLC packet and the TID to the MAC processing unit 120. Furthermore, when the LLC processing unit 110 receives an LLC packet from the MAC processing unit 120, it extracts data from the LLC packet and sends the extracted data to the upper layer 102.

[0034] The MAC processing unit 120 performs processing of the MAC layer. In the example shown in FIG.

[0035] When the data processing unit 121 receives an LLC packet and a TID from the LLC processing unit 110, the data processing unit 121 generates a MAC frame by adding a MAC header including a destination address, a source address, BSS information indicating the BSS, a TID, and an error detection code to the LLC packet. The data processing unit 121 transmits the MAC frame to the MAC frame processing unit 122. When the data processing unit 121 receives a MAC frame from the PHY processing unit 130 via the MAC frame processing unit 122, the data processing unit 121 demodulates the MAC frame to obtain a MAC header and an LLC packet. The data processing unit 121 determines whether or not the destination address included in the MAC header indicates the own station (specifically, the base station 10). When the destination address indicates the own station, the data processing unit 121 transmits the LLC packet to the LLC processing unit 110. When the destination address does not indicate the own station, the data processing unit 121 discards the LLC packet.

[0036] The MAC frame processing unit 122 receives a MAC frame from the data processing unit 121 and temporarily stores the MAC frame. Then, the MAC frame processing unit 122 performs carrier sense for a random time, and transmits the MAC frame to the PHY processing unit 130 after confirming that the channel is idle. If the received power observed in the PHY processing unit 130 is higher than the CCA threshold, the MAC frame processing unit 122 determines that the channel is busy, and if not, determines that the channel is idle. The received signal strength (RSSI; Received Signal Strength Indicator) as the received power is measured by the PHY processing unit 130 and provided to the MAC frame processing unit 122. The MAC frame processing unit 122 determines the CCA threshold according to a combination of the value of the BSS color included in the preamble of the wireless frame detected by carrier sense and the priority of the frame to be transmitted to the terminal 20. The MAC frame processing unit 122 specifies the priority of the frame to be transmitted based on the TID information included in the MAC header of the MAC frame received from the data processing unit 121. The MAC frame processor 122 may specify the priority of a frame to be transmitted based on information other than the TID information, for example, AID (Association Identifier) ​​information. A method for determining the CCA threshold will be described later.

[0037] The MAC frame processing unit 122 may control the transmission power when transmitting a frame to be transmitted. The MAC frame processing unit 122 may control the transmission power based on, for example, the priority of the frame to be transmitted. The MAC frame processing unit 122 sends information indicating the transmission power to the PHY processing unit 130 together with the MAC frame.

[0038] In this way, the MAC frame processing unit 122 functions as a threshold determination unit that determines the CCA threshold, and a carrier sense control unit that performs carrier sensing and determines the channel usage status, and may further function as a power control unit that controls the transmission power when transmitting a frame scheduled for transmission.

[0039] The PHY processing unit 130 performs processing of the PHY layer. In the example shown in FIG.

[0040] When the transmitting unit 131 receives a MAC frame from the MAC processing unit 120, the transmitting unit 131 generates a wireless frame by adding a preamble to the MAC frame. The preamble includes a BSS color and a QoS color. The transmitting unit 131 converts the wireless frame into a wireless signal and transmits the wireless signal via an antenna.

[0041] The receiver 136 receives a wireless signal via an antenna and converts the received wireless signal into a wireless frame. The receiver 136 first obtains the BSS color and QoS color contained in the preamble of the wireless frame and sends them to the MAC processor 120. Next, the receiver 136 extracts the MAC frame from the wireless frame and sends it to the MAC processor 120.

[0042] 6 illustrates an example of the configuration of the transmission unit 131. As illustrated in FIG. 6, the transmission unit 131 includes a PHY header processing unit 132 and a radio signal processing unit 133.

[0043] As described above, after confirming that the channel is idle, the MAC processing unit 120 transmits the MAC frame to the transmitting unit 131. That is, the MAC processing unit 120 transmits the MAC frame to the transmitting unit 131 after acquiring the transmission right.

[0044] The PHY header processing unit 132 receives a MAC frame from the MAC processing unit 120. The PHY header processing unit 132 generates a wireless frame by adding a PHY header and a PHY preamble, which include information such as a BSS color and a QoS color, to the MAC frame. The PHY header processing unit 132 determines the value of the BSS color based on the BSS information included in the MAC header, and determines the value of the QoS color based on the TID information included in the MAC header. Note that the QoS color may be determined based on information other than the TID information, for example, AID information. When the QoS color value is determined based on the AID information, it is possible to set a priority for each terminal. For example, all frames transmitted by a terminal to which a specific AID is assigned by the base station 10 are set to a high priority.

[0045] The frame priority is set higher as the data priority is higher. TID is expressed in two or more stages. For example, TID is expressed by two values, #1 and #2, and the data priority is higher in the order of #1, #2. In this case, the transmitter 131 may set the QoS color to a value (e.g., "0") indicating high frame priority when TID is #1, and to a value (e.g., "1") indicating low frame priority when TID is #2. Also, TID is expressed by three values, #1, #2, and #3, and the data priority is higher in the order of #1, #2, and #3. In this case, the transmitter 131 may set the QoS color to a value (e.g., "0") indicating high frame priority when TID is #1, and to a value (e.g., "1") indicating low frame priority when TID is #2 or #3. These are merely examples of methods for determining the QoS color.

[0046] The radio signal processing unit 133 receives a radio frame from the PHY header processing unit 132, performs a predetermined modulation operation on the radio frame to convert the radio frame into a radio signal, and transmits the radio signal via an antenna. The predetermined modulation operation includes, for example, convolutional coding, interleaving, subcarrier modulation, Inverse Fast Fourier Transform (IFFT), Orthogonal Frequency Division Multiplexing (OFDM) modulation, and frequency conversion.

[0047] 7 shows a schematic configuration example of the receiving unit 136. As shown in FIG. 7, the receiving unit 136 includes a radio signal processing unit 137 and a PHY header processing unit 138.

[0048] The radio signal processing unit 137 performs a predetermined demodulation operation on the radio signal received by the antenna, and sends the radio frame obtained thereby to the PHY header processing unit 138. The predetermined demodulation operation includes, for example, frequency conversion, OFDM demodulation, fast Fourier transform (FFT), subcarrier demodulation, deinterleaving, and Viterbi decoding.

[0049] Furthermore, the radio signal processing unit 137 measures the RSSI of the received radio signal and notifies the MAC processing unit 120 of the RSSI via the PHY header processing unit 138.

[0050] The PHY header processing unit 138 receives a wireless frame from the wireless signal processing unit 137 and identifies information contained in the preamble (specifically, the PHY header) of the wireless frame, such as the BSS color and the QoS color. The PHY header processing unit 138 performs the following operations based on the BSS color and the QoS color contained in the preamble.

[0051] When receiving a frame, if the BSS color indicates its own BSS (specifically, the BSS to which the base station 10 belongs), the PHY header processing unit 138 continues the demodulation operation of the radio signal processing unit 137 and sends the BSS color and QoS color extracted from the preamble of the radio frame to the MAC processing unit 120, and then sends the MAC frame extracted from the radio frame to the MAC processing unit 120. If the BSS color does not indicate its own BSS, the PHY header processing unit 138 stops the demodulation operation of the radio signal processing unit 137. Even if the demodulation operation is stopped, the PHY header processing unit 138 sends the BSS color and QoS color to the MAC processing unit 120.

[0052] During carrier sensing, the PHY header processing unit 138 notifies the MAC processing unit 120 of the values ​​of the BSS color and QoS color extracted from the preamble of the wireless frame.

[0053] 5 again, the terminal 20 includes a radio unit 201 and an upper layer 202. The radio unit 201 includes an LLC processing unit 210, a MAC processing unit 220, and a PHY processing unit 230. The radio unit 201 is realized by, for example, a wireless communication module 254 or a combination of a CPU 251 and a wireless communication module 254.

[0054] The LLC processing unit 210, the MAC processing unit 220, and the PHY processing unit 230 perform operations similar to those of the LLC processing unit 110, the MAC processing unit 120, and the PHY processing unit 130, respectively. For this reason, detailed descriptions of the LLC processing unit 210, the MAC processing unit 220, and the PHY processing unit 230 will be omitted.

[0055] The LLC processing unit 210 serves as an interface with the upper layer 202, and performs LLC layer processing. For example, when data is input from the upper layer 202 to the radio unit 201, the LLC processing unit 210 generates an LLC packet by adding a DSAP header, an SSAP header, and the like to the data. The LLC processing unit 210 sends the LLC packet to the MAC processing unit 220. Furthermore, when the LLC processing unit 210 receives an LLC packet from the MAC processing unit 220, it extracts data from the LLC packet and sends the extracted data to the upper layer 202.

[0056] The MAC processing unit 220 performs processing of the MAC layer. In the example shown in Fig. 5, the MAC processing unit 220 includes a data processing unit 221 and a MAC frame processing unit 222. The MAC frame processing unit 222 is also called a carrier sense control unit. The data processing unit 221 and the MAC frame processing unit 222 perform the same operations as the data processing unit 121 and the MAC frame processing unit 122, respectively.

[0057] When the data processing unit 221 receives an LLC packet from the LLC processing unit 210, it generates a MAC frame by adding a MAC header including a destination address, a source address, a TID, etc., and an error detection code to the LLC packet. The data processing unit 221 sends the MAC frame to the MAC frame processing unit 222. When the data processing unit 221 receives a MAC frame from the PHY processing unit 230, it demodulates the MAC frame to obtain a MAC header and an LLC packet. When the destination address included in the MAC header indicates its own station (specifically, the terminal 20), the data processing unit 221 sends the LLC packet to the LLC processing unit 210.

[0058] The MAC frame processing unit 222 receives a MAC frame from the data processing unit 221 and temporarily stores the MAC frame. Then, the MAC frame processing unit 222 performs carrier sense for a random period of time, and transmits the MAC frame to the PHY processing unit 230 after confirming that the channel is idle.

[0059] The PHY processing unit 230 performs PHY layer processing. In the example shown in FIG.

[0060] When the transmitting unit 231 receives a MAC frame from the MAC processing unit 220, it generates a wireless frame by adding a preamble including a BSS color and a QoS color to the MAC frame. The transmitting unit 231 determines the value of the BSS color based on the BSS information included in the MAC header, and determines the value of the QoS color based on the TID information included in the MAC header. The transmitting unit 231 converts the wireless frame into a wireless signal, and transmits the wireless signal via an antenna.

[0061] The receiver 236 receives a radio signal via an antenna and performs demodulation on the received radio signal to obtain a radio frame. When receiving a frame, if the BSS color included in the preamble of the radio frame indicates the own BSS (specifically, the BSS to which the terminal 20 belongs), the receiver 236 sends the MAC frame extracted from the radio frame together with the BSS color and QoS color extracted from the preamble of the radio frame to the MAC processor 220. If the BSS color does not indicate the own BSS, the receiver 236 ends the demodulation operation. Even if the receiver 236 ends the demodulation operation midway, it sends the BSS color and QoS color to the MAC processor 220. During carrier sense, the receiver 236 notifies the MAC processor 220 of the values ​​of the BSS color and QoS color extracted from the preamble of the radio frame.

[0062] Furthermore, the receiver 236 measures the RSSI of the received wireless signal and notifies the MAC processor 220 of the RSSI.

[0063] Next, a method for determining the CCA threshold will be described with reference to Fig. 8. Here, the description will be given for the base station 10, but the same method can be applied to the terminal 20. In Fig. 8, -62 dBm written next to CCA-ED (Energy Detection) is the CCA threshold used when the signal detected by carrier sense is not recognized as a frame based on the IEEE802.11 standard.

[0064] The MAC frame processing unit 122 of the base station 10 determines the CCA threshold based on the value of the BSS color included in the preamble of the wireless frame detected by carrier sense and the priority of the wireless frame that the base station 10 is about to transmit to the terminal 20.

[0065] When the BSS color indicates the BSS to which the base station 10 belongs, the MAC frame processor 122 sets the CCA threshold to Th a Set to Th a For example, Th is -82 dBm. a The threshold value of -82 dBm shown next to CCA-SD (Signal Detection) in Fig. 8 is the default CCA threshold value used when it is recognized that the signal detected by carrier sense is a frame based on the IEEE802.11 standard.

[0066] If the BSS color does not indicate the BSS to which the base station 10 belongs, the MAC frame processor 122 determines the CCA threshold based on the priority of the frame to be transmitted. The MAC frame processor 122 identifies the priority of the frame to be transmitted based on, for example, TID information included in the frame to be transmitted.

[0067] Referring back to the above example, it is assumed that the frame priority is represented by two levels, the TID is represented by two values, #1 and #2, and #1 has the highest data priority, followed by #2.

[0068] When the TID information is "#2", that is, when the frame priority is at a low priority level, the MAC frame processing unit 122 sets the CCA threshold to Th b where Th b Th a Greater than (Th a <Th b ). b For example, is -77 dBm (SR value).

[0069] When the TID information is "#1", that is, when the frame priority is at a high priority level, the MAC frame processing unit 122 sets the CCA threshold to Th c where Th c Th b Greater than (Th c >Th b ). c is typically less than -62 dBm, for example -67 dBm. c may be -62 dBm or greater.

[0070] Assume that frame priority is expressed in four levels, TID is expressed by four values ​​#1, #2, #3, #4, and data priority is highest in the order of #1, #2, #3, #4. The CCA threshold is set to a value according to the priority of the frame to be transmitted. Specifically, the higher the priority of the frame to be transmitted, the higher the CCA threshold is set to.

[0071] When the TID information is "#4", that is, when the frame priority is the lowest priority level, the MAC frame processing unit 122 sets the CCA threshold to Th b where Th b Th a Greater than (Th a <Th b If the TID information is "#3", that is, if the frame priority is the third highest priority level, the MAC frame processing unit 122 sets the CCA threshold to Th c where Th c Th b Greater than (Th c >Thb If the TID information is "#2", that is, if the frame priority is the second highest priority level, the MAC frame processing unit 122 sets the CCA threshold to Th d where Th d Th c Greater than (Th d >Th c When the TID information is "#1", that is, when the frame priority is the highest priority level, the MAC frame processing unit 122 sets the CCA threshold to Th e where Th e Th d Greater than (Th e >Th d ).

[0072] [Operation] Next, the operation of the communication system 50 will be described.

[0073] 9 and 10 show an example of a schematic diagram of a procedure of a transmission process executed by the base station 10. The MAC frame processing unit 122 of the base station 10 executes carrier sense based on CSMA / CA before transmitting a frame. For example, the MAC frame processing unit 122 starts carrier sense in response to receiving a MAC frame from the data processing unit 121. Note that, although the description will be given assuming that the base station 10 executes the flows shown in FIGS. 9 and 10, the flows shown in FIGS. 9 and 10 may be executed by the terminal 22.

[0074] If no frame is detected by carrier sense (step S101 in FIG. 9; No), the process proceeds to step S102. In step S102, the MAC frame processing unit 122 determines that the channel is idle. In step S103, the base station 10 transitions to a frame transmission operation. For example, the MAC frame processing unit 122 sends the MAC frame to the transmitting unit 131, and the transmitting unit 131 generates a wireless frame from the MAC frame and transmits the wireless frame.

[0075] If a frame is detected by carrier sense (step S101; Yes), the process proceeds to step S104. In step S104, the MAC frame processing unit 122 judges whether the destination of the received frame, which is the detected frame, is a wireless station belonging to the own BSS. For example, the receiving unit 136 extracts the BSS color from the preamble of the received frame by demodulating the preamble of the received frame, and the MAC frame processing unit 122 judges whether the BSS color extracted by the receiving unit 136 matches the BSS color of the own BSS. If the BSS color of the received frame matches the BSS color of the own BSS, the MAC frame processing unit 122 judges that the destination of the received frame is a wireless station belonging to the own BSS, and if the BSS color of the received frame does not match the BSS color of the own BSS, it judges that the destination of the received frame is not a wireless station belonging to the own BSS.

[0076] If the destination of the received frame is a wireless station that belongs to the own BSS (step S104; Yes), the process proceeds to step S105. In step S105, the MAC frame processing unit 122 sets the default value Th a Specifically, the MAC frame processor 122 sets the CCA threshold to a value Th a Set to.

[0077] If the destination of the received frame is not a wireless station belonging to the own BSS (step S104; No), the process proceeds to step S106. In step S106, the MAC frame processing unit 122 determines whether the priority of the frame to be transmitted is high or not. For example, the MAC frame processing unit 122 determines whether the priority of the frame to be transmitted is high or not based on the TID information of the frame to be transmitted. For example, the MAC frame processing unit 122 determines that the priority of the frame to be transmitted is low when the TID information is "#2", and determines that the priority of the frame to be transmitted is high when the TID information is "#1".

[0078] If the priority of the frame to be transmitted is not high (step S106; No), in step S108, the MAC frame processing unit 122 sets the SR value Th b We decide to use Th b Th a Greater than (Th a <Th b Specifically, the MAC frame processor 122 sets the CCA threshold to a value Th b Set to.

[0079] If the priority of the frame to be transmitted is high (step S106; Yes), in step S107, the MAC frame processing unit 122 sets a value Th according to the priority of the frame to be transmitted as the CCA threshold. c We decide to use Th c Th b Greater than (Th c >Th b Specifically, the MAC frame processor 122 sets the CCA threshold to a value Th c Set to.

[0080] Once the CCA threshold is determined in step S105, S107, or S108, the process proceeds to step S109 in Fig. 10. In step S109, the MAC frame processing unit 122 compares the power value of the received frame with the CCA threshold.

[0081] If the power value of the received frame is smaller than the CCA threshold (step S109; Yes), the process proceeds to step S110. In step S110, the MAC frame processing unit 122 determines that the channel is idle. In optional step S111, the MAC frame processing unit 122 changes the transmission power when transmitting a frame to be transmitted. For example, the higher the priority of the frame to be transmitted, the higher the transmission power is set by the MAC frame processing unit 122. For example, when the priority of the frame to be transmitted is low, the MAC frame processing unit 122 sets the transmission power to a default power level, and when the priority of the frame to be transmitted is high, the transmission power is set to a power level higher than the default power level.

[0082] The MAC frame processor 122 may set the transmission power to a power level according to the threshold. In this case, multiple values ​​used as the threshold are associated with multiple power levels. For example, the value Th a is associated with the first power level, and the value Th b is associated with a second power level higher than the first power level, and a value Th c is associated with a third power level higher than the second power level. The MAC frame processor 122 sets the CCA threshold to Th a set the transmit power to a first power level when Th is used, and set the CCA threshold to Th b set the transmission power to a second power level when Th is used, and set the CCA threshold to Th c is used, set the transmit power to a third power level.

[0083] In step S112, the base station 10 transitions to a frame transmission operation. For example, the transmission unit 131 starts frame transmission. For example, the MAC frame processing unit 122 sends the MAC frame to the transmission unit 131, and the transmission unit 131 generates a wireless frame from the MAC frame and transmits the wireless frame with the transmission power specified by the MAC frame processing unit 122.

[0084] If the power value of the received frame is equal to or greater than the CCA threshold (step S109; No), the process proceeds to step S113. In step S113, the MAC frame processing unit 122 determines that the channel is busy, and the base station 10 does not proceed to frame transmission operation.

[0085] Fig. 11 shows an example of the operation of the communication system 50. As described in relation to Fig. 1, the BSS 30 includes the base station 10 and the terminal 20, and the BSS 32 includes the base station 12 and the terminal 22. In the example shown in Fig. 11, a situation is assumed in which the base station 10 issues a request to transmit a high priority frame to the terminal 20 while the base station 12 is transmitting a low priority frame to the terminal 22. Furthermore, when the reception power of the frame received by the base station 10 from the base station 12 is greater than Th b FromTh c Let's assume that it is between .

[0086] In step S201 of FIG. 11, the base station 12 starts transmitting a low priority frame to the terminal 22.

[0087] In step S202, a request to transmit a high priority frame to terminal 20 occurs in base station 10, and base station 10 performs carrier sensing based on CSMA / CA. Base station 10 detects a frame from base station 12 to terminal 22 by carrier sensing. Base station 10 checks the BSS color included in the preamble of the detected frame and recognizes that the destination of the detected frame is not a wireless station in BSS 30. In other words, base station 10 recognizes that the detected frame is a frame related to another BSS. Next, base station 10 checks the TID information of the frame to be transmitted and recognizes that the priority of the frame to be transmitted is high. As a result, base station 10 sets the CCA threshold to Th c Set to.

[0088] In step S203, the base station 10 recognizes that the received power of the detected frame is lower than the CCA threshold, and determines the channel to be idle. In step S204, the base station 10 starts transmitting high priority frames to the terminal 20.

[0089] [effect] In the first embodiment, a wireless station performs carrier sensing based on CSMA / CA before transmitting a frame. The wireless station obtains a BSS color from the preamble of a received frame, which is a frame detected by carrier sensing, and determines a CCA threshold based on the BSS color and TID information of a frame to be transmitted. The wireless station determines whether the received frame is a frame related to its own BSS based on the BSS color. If the received frame is a frame related to its own BSS, the wireless station sets the CCA threshold to a default value Th a If the received frame is related to another BSS, the wireless station determines whether the priority of the frame to be transmitted is low or high based on the TID information of the frame to be transmitted. Specifically, the wireless station determines whether the priority of the frame to be transmitted is a first priority level or a second priority level higher than the first priority level. If the priority of the frame to be transmitted is low, the wireless station sets the CCA threshold to a value Th a Greater than Th b If the frame to be transmitted has high priority, the station sets the CCA threshold to the value Th b Higher value Th c The wireless station determines the channel usage status based on a comparison between the received power of the received frame and the CCA threshold.

[0090] When the received frame is a frame related to another BSS, the CCA threshold is set to a value larger than when the received frame is a frame related to the own BSS. This makes it possible to avoid or reduce the exposed terminal problem. Furthermore, when the priority of the frame to be transmitted is high, the CCA threshold is set to a value larger than when the priority of the frame to be transmitted is low. When the priority of the frame to be transmitted is high, the channel is less likely to be determined to be busy, and the transmission opportunity of the high priority frame increases. This makes it possible to ensure the low latency required for the high priority frame. For example, the high priority frame is transmitted overlapping with the frame related to the other BSS, realizing early transmission of the high priority frame. In addition, transmitting the high priority frame overlapping with the frame related to the other BSS leads to utilization of the capture effect. Therefore, even in a situation where multiple BSSs overlap, highly reliable wireless communication is provided.

[0091] The wireless station may control the transmission power such that the transmission power when transmitting a frame to be transmitted is higher as the priority of the frame to be transmitted increases. This allows frames with higher priority to reach their destination more reliably. Alternatively, the wireless station may set the transmission power when transmitting frames to be transmitted to a power level according to a threshold. This allows frames with higher priority to reach their destination more reliably while protecting frames related to other BSSs.

[0092] Second Embodiment In the second embodiment, another example of a method for determining a CCA threshold executed by a wireless station will be described. In the second embodiment, the CCA threshold is determined further based on the priority of a frame detected by carrier sense. In the second embodiment, the description of the same parts and operations as those described in the first embodiment will be omitted as appropriate.

[0093] The base station 10 determines the CCA threshold based on the BSS color and QoS color of a received frame, which is a frame detected by carrier sensing, and the TID information of a frame to be transmitted. The base station 10 judges whether a received frame is a high-priority frame or a low-priority frame based on the QoS color of the received frame. For example, if the QoS color of the received frame is a value indicating high priority (e.g., "0"), the base station 10 judges the received frame to be a high-priority frame, and if the QoS color of the received frame is a value indicating low priority (e.g., "1"), the base station 10 judges the received frame to be a low-priority frame. If the base station 10 detects a high-priority frame during carrier sensing, the base station 10 sets the CCA threshold to Th c Smaller value Th b As an example, as shown in FIG. b is the SR value.

[0094] Fig. 13 shows an example of a threshold determination procedure according to the second embodiment. The flow shown in Fig. 13 is obtained by adding step S151 to the flow shown in Fig. 9. Step S151 is added between step S104 and step S106. Note that, although the description will be given assuming that the base station 10 executes the flow shown in Fig. 13, the flow shown in Fig. 13 may be executed by the terminal 22.

[0095] 13, the MAC frame processing unit 122 of the base station 10 executes carrier sensing based on CSMA / CA before transmitting a frame. If a frame is detected by carrier sensing (step S101; Yes), the MAC frame processing unit 122 determines whether the destination of the received frame, which is the detected frame, is a wireless station belonging to the own BSS (step S104).

[0096] If the destination of the received frame is a wireless station that belongs to the own BSS (step S104; Yes), the MAC frame processing unit 122 sets the default value Th a It is decided to use (step S105).

[0097] If the destination of the received frame is not a wireless station belonging to the own BSS (step S104; No), the process proceeds to step S151. In step S151, the MAC frame processing unit 122 judges whether the priority of the received frame is low or not. For example, the receiving unit 136 of the base station 10 extracts the QoS color from the preamble of the received frame by demodulating the preamble of the received frame, and the MAC frame processing unit 122 judges whether the priority of the received frame is low or not based on the QoS color extracted by the receiving unit 136. For example, the MAC frame processing unit 122 judges that the priority of the received frame is low when the value of the QoS color of the received frame is "1", and judges that the priority of the received frame is high when the value of the QoS color of the received frame is "0".

[0098] If the priority of the received frame is not low, that is, if the received frame is a high-priority frame (step S151; No), the process proceeds to step S108. In step S108, the MAC frame processing unit 122 sets the SR value Th b We decide to use Th b Th a Greater than (Th b >Th a ).

[0099] If the priority of the received frame is low, that is, if the received frame is a low-priority frame (step S151; Yes), the process proceeds to step S106. In step S106, the MAC frame processing unit 122 judges whether the priority of the frame to be transmitted is high or not. If the priority of the frame to be transmitted is not high (step S106; No), the MAC frame processing unit 122 sets the SR value Th as the CCA threshold. b If the priority of the frame to be transmitted is high (step S106; Yes), the MAC frame processing unit 122 determines to use a value Th according to the priority of the frame to be transmitted as the CCA threshold. c (Step S107).c Th b Greater than (Th c >Th b ).

[0100] After the CCA threshold is determined in step S105, S107, or S108, the processing is the same as that described above with reference to FIG.

[0101] 14A and 14B each show an example of the operation of the communication system 50 according to the second embodiment. As described in relation to FIG. 1, the BSS 30 includes the base station 10 and the terminal 20, and the BSS 32 includes the base station 12 and the terminal 22. In the example shown in FIG. 14A, when the base station 12 is transmitting a low-priority frame to the terminal 22, the base station 10 generates a transmission request for a high-priority frame to the terminal 20. In the example shown in FIG. 14B, when the base station 12 is transmitting a high-priority frame to the terminal 22, the base station 10 generates a transmission request for a high-priority frame to the terminal 20. In both of the examples shown in FIG. 14A and FIG. 14B, when the reception power of the frame received by the base station 10 from the base station 12 is Th b FromTh c Let's assume that it is between .

[0102] In step S401 of FIG. 14A, the base station 12 starts transmitting a low priority frame to the terminal 22. In step S402, a request to transmit a high priority frame to the terminal 20 occurs in the base station 10, and the base station 10 performs carrier sensing based on CSMA / CA. The base station 10 detects a frame from the base station 12 to the terminal 22 by carrier sensing. The base station 10 checks the BSS color and QoS color included in the preamble of the detected frame, and recognizes that the detected frame is a low priority frame related to another BSS. Next, the base station 10 checks the TID information of the frame to be transmitted, and recognizes that the frame to be transmitted is a high priority frame. As a result, the base station 10 sets the CCA threshold to Th c Set to.

[0103] In step S403, the base station 10 recognizes that the received power of the detected frame is lower than the CCA threshold, and determines the channel to be idle. In step S404, the base station 10 starts transmitting high priority frames to the terminal 20.

[0104] In step S411 of FIG. 14B, the base station 12 starts transmitting a high priority frame to the terminal 22. In step S412, a request to transmit a high priority frame to the terminal 20 occurs in the base station 10, and the base station 10 performs carrier sensing based on CSMA / CA. The base station 10 detects a frame from the base station 12 to the terminal 22 by carrier sensing. The base station 10 checks the BSS color and QoS color contained in the preamble of the detected frame, and recognizes that the detected frame is a high priority frame related to another BSS. As a result, the base station 10 sets the CCA threshold to Th b Set to.

[0105] In step S413, the base station 10 recognizes that the received power of the detected frame is higher than the CCA threshold and determines the channel to be busy. In step S414, the base station 12 ends the transmission of the high priority frame to the terminal 22, and in step S415, the base station 10 performs carrier sensing again.

[0106] In the above example, the same CCA threshold (Th b In these cases, a different CCA threshold may be used. For example, as shown in FIG. 15, when the frame detected by carrier sense is a high priority frame for another BSS, the CCA threshold is set to the SR value Th b Smaller value Th d may be set to

[0107] Fig. 16 shows an outline of another example of the threshold determination procedure according to the second embodiment. The flow shown in Fig. 16 is a modified example of the flow shown in Fig. 13, and the flow shown in Fig. 16 and the flow shown in Fig. 13 are different in the processing when the received frame is a high priority frame.

[0108] In the example shown in FIG. 16, if the priority of the received frame is not low (step S151; No), the process proceeds to step S152. In step S152, the MAC frame processing unit 122 sets a value Th according to the priority of the received frame as the CCA threshold. d We decide to use Th d Th a Bigger Th b Smaller than (Th a <Th d <Th b Specifically, the MAC frame processor 122 sets the CCA threshold to a value Th d After the CCA threshold is determined in step S152, the process is the same as that described above with reference to FIG.

[0109] In the second embodiment, when a received frame detected by carrier sense is a high priority frame for another BSS, the CCA threshold is set to Th c For example, even if the frame to be transmitted is a high-priority frame, the CCA threshold is set to a value smaller than the SR value Th b Or a smaller value Th d This makes it difficult for the channel to be determined to be idle, and reduces the occurrence of interference with high priority frames related to other BSSs. This makes it possible to ensure the low latency required for high priority frames in other BSSs. In this way, the transmission opportunities for high priority frames related to the own BSS are increased, and high priority frames related to other BSSs are protected. Therefore, highly reliable wireless communication is provided even in a situation where multiple BSSs overlap.

[0110] (Third embodiment) In the third embodiment, a further example of a method for determining a CCA threshold executed by a wireless station will be described. In the third embodiment, the description of the same parts and operations as those described in the first or second embodiment will be omitted as appropriate.

[0111] CSMA / CA implements the RTS / CTS (Request to Send / Clear to Send) method to reduce frame collisions due to the hidden terminal problem. In the RTS / CTS method, a transmitting wireless station transmits a control frame called RTS to a receiving wireless station before transmitting a data frame, and the receiving wireless station transmits a control frame called CTS when it receives the RTS. RTS and CTS include a duration field that describes the planned period for using the channel. Other wireless stations that detect RTS or CTS wait to transmit for the period described in the RTS or CTS. In the IEEE802.11 standard, the mechanism for suppressing transmissions by other wireless stations is called NAV (Network Allocation Vector).

[0112] Referring back to FIG. 1, it is assumed that the base station 10 and the terminal 22 are far enough apart that the base station 10 cannot detect a frame from the terminal 22. When the base station 12 transmits a frame to the terminal 22, the base station 12 transmits an RTS to the terminal 22, and the terminal 22 transmits a CTS to the base station 12 in response to the RTS. The base station 10 receives the RTS from the base station 12, and thereby the base station 10 recognizes that a NAV has been set on the channel. Also, when the terminal 22 transmits a frame to the base station 12, the terminal 22 transmits an RTS to the base station 12, and the base station 12 transmits a CTS to the terminal 22 in response to the RTS. The base station 10 detects the CTS from the base station 12, and thereby the base station 10 recognizes that a NAV has been set on the channel.

[0113] The preamble of an RTS or CTS contains a BSS color and a QoS color. The BSS color of an RTS or CTS indicates the BSS to which the station that transmitted the RTS or CTS belongs. The BSS color of an RTS or CTS enables a station that receives the RTS or CTS to determine whether the NAV was set by a station that belongs to its own BSS. The QoS color of an RTS or CTS indicates the priority of the NAV that is set. The priority of the NAV matches the priority of the data frame that the station that transmitted the RTS is transmitting or is about to transmit.

[0114] Fig. 17 shows an example of a threshold determination procedure according to the third embodiment. Steps S504 to S507 shown in Fig. 17 are the same as steps S105 to S108 shown in Fig. 9, respectively, and therefore detailed description of these processes will be omitted. In addition, the description will be given assuming that the base station 10 executes the flow shown in Fig. 17, but the flow shown in Fig. 17 may be executed by the terminal 22.

[0115] 17, the MAC frame processing unit 122 of the base station 10 receives a transmission queue from the upper layer 102. For example, the LLC processing unit 110 receives data addressed to the terminal 20 from the upper layer 102, generates an LLC packet including the data, and sends the LLC packet to the data processing unit 121. The data processing unit 121 receives the LLC packet from the LLC processing unit 110, generates a MAC frame including the LLC packet, and sends the MAC frame to the MAC frame processing unit 122. The MAC frame processing unit 122 receives the MAC frame from the data processing unit 121 and buffers the MAC frame.

[0116] In step S502, the MAC frame processing unit 122 determines whether or not the NAV is set on the channel. For example, determining whether or not the NAV is set may include determining whether or not the RTS or CTS is received, and determining whether or not the period described in the RTS or CTS has elapsed. The MAC frame processing unit 122 determines that the NAV is not set when the RTS or CTS is not received, or when the RTS or CTS is received and the period described in the RTS or CTS has elapsed. The MAC frame processing unit 122 determines that the NAV is set when the RTS or CTS is received and the period described in the RTS or CTS has not yet elapsed.

[0117] If the NAV is not set (step S502; No), the base station 10 executes the flow shown in any one of FIG. 9, FIG. 13, and FIG.

[0118] If the NAV is set (step S502; Yes), the process proceeds to step S503. In step S503, the MAC frame processor 122 judges whether the NAV is set by a wireless station belonging to the own BSS (specifically, the BSS to which the base station 10 belongs). For example, the receiver 136 extracts the BSS color from the RTS or CTS preamble by demodulating the RTS or CTS preamble, and the MAC frame processor 122 judges whether the BSS color extracted by the receiver 136 matches the BSS color of the own BSS. If the BSS color of the RTS or CTS matches the BSS color of the own BSS, the MAC frame processor 122 judges that the NAV is set by a wireless station belonging to the own BSS, and if the BSS color of the RTS or CTS does not match the BSS color of the own BSS, the MAC frame processor 122 judges that the NAV is not set by a wireless station belonging to the own BSS.

[0119] If the NAV is set by a wireless station belonging to the own BSS (step S503; Yes), the process proceeds to step S504. In step S504, the MAC frame processing unit 122 sets the default value Th a Decided to use.

[0120] If the NAV is not set by a wireless station belonging to the own BSS (step S503; No), the process proceeds to step S505. In step S505, the MAC frame processing unit 122 judges whether the priority of the frame to be transmitted is high or not. If the priority of the frame to be transmitted is not high (step S505; No), in step S507, the MAC frame processing unit 122 sets the SR value Th as the CCA threshold. b Decided to use (Th a <Th b If the priority of the frame to be transmitted is high (step S505; Yes), in step S506, the MAC frame processing unit 122 sets a value Th according to the priority of the frame to be transmitted as the CCA threshold. c Decide to use the value Th c As shown in Figure 18, the SR value Th b Greater than.

[0121] After the CCA threshold is determined in step S504, S506, or S507, the processing is the same as that described above with reference to FIG.

[0122] FIG. 19 shows an example of the operation of the communication system 50 according to the third embodiment. As described in relation to FIG. 1, the BSS 30 includes the base station 10 and the terminal 20, and the BSS 32 includes the base station 12 and the terminal 22. In the example shown in FIG. 19, a situation is assumed in which the base station 10 issues a request to transmit a high priority frame to the terminal 20 while the base station 12 is transmitting a low priority frame to the terminal 22. Furthermore, when the reception power of the frame received by the base station 10 from the base station 12 is greater than Th b FromTh c Let's assume that it is between .

[0123] 19, in step S601, the base station 12 transmits an RTS to the terminal 22 on a channel to be used in order to set a NAV on that channel. In response to receiving the RTS, the terminal 22 transmits a CTS to the base station 12. The base station 10 also receives an RTS from the base station 12. The base station 12 receives the CTS from the terminal 22 and then starts transmitting low priority frames to the terminal 22.

[0124] In step S602, a request to transmit a high-priority frame to terminal 20 occurs in base station 10, and base station 10 performs carrier sense based on CSMA / CA. In step S603, base station 10 determines whether or not NAV is set. Base station 10 receives RTS from base station 12, and since the period described in the RTS has not elapsed, base station 10 determines that NAV is set.

[0125] Furthermore, the base station 10 judges whether or not the wireless station that set the NAV belongs to its own BSS (BSS30 in this example). Since the NAV was set by the base station 12 that belongs to BSS32, the base station 10 judges that the wireless station that set the NAV does not belong to its own BSS. Next, the base station 10 checks the priority of the frame to be transmitted. Since the priority of the frame to be transmitted is high, the base station 10 sets the CCA threshold to Th c Set to.

[0126] The base station 10 detects a low-priority frame from the base station 12 to the terminal 22 by carrier sensing, and compares the received power of the detected frame with the CCA threshold Th c The timing at which a low priority frame from the base station 12 to the terminal 22 is detected may be before the timing at which the CCA threshold is determined. The received power of the detected frame is Th c Since it is lower, the base station 10 determines that the channel is idle (step S604).

[0127] In step S605, the base station 10 starts transmitting a high priority frame to the terminal 20.

[0128] Fig. 20 shows an outline of another example of the threshold determination procedure according to the third embodiment. The flow shown in Fig. 20 is obtained by adding step S551 to the flow shown in Fig. 17. Step S551 is added between step S503 and step S505.

[0129] 20, if the NAV is not set by a wireless station belonging to the own BSS (step S503; No), the process proceeds to step S551. In step S551, the MAC frame processor 122 judges whether the priority of the NAV is low or not. For example, the receiver 136 of the base station 10 extracts the QoS color from the RTS or CTS preamble by demodulating the RTS or CTS preamble, and the MAC frame processor 122 judges whether the priority of the NAV is low or not based on the QoS color extracted by the receiver 136.

[0130] If the priority of the NAV is low, that is, if the priority of the frame being transmitted or being transmitted by the wireless station that has set the NAV is low (step S551; Yes), the process proceeds to step S505. The process from step S505 onwards has been described with reference to FIG. 17, and therefore will not be described here.

[0131] If the priority of the NAV is not low, that is, if the priority of the frame that the wireless station that has set the NAV is transmitting or is about to transmit is high (step S551; No), the process proceeds to step S507. In step S507, the MAC frame processing unit 122 sets the SR value Th as the CCA threshold. b After the CCA threshold is determined in step S507, the process is the same as that described above with reference to FIG.

[0132] Fig. 21 shows a schematic diagram of a further example of the threshold determination procedure according to the third embodiment. The flow shown in Fig. 21 is a modified example of the flow shown in Fig. 20, and the flow shown in Fig. 21 and the flow shown in Fig. 20 are different in the processing when the priority of a frame that a wireless station that has set the NAV is transmitting or is about to transmit is high.

[0133] In the example shown in FIG. 21, if the priority of the NAV is not low (step S551; No), the process proceeds to step S552. In step S552, the MAC frame processing unit 122 sets a value Th according to the priority of the NAV as the CCA threshold. d We decide to use Th d Th a Bigger Th b Smaller than (Th a <Th d <Th b After the CCA threshold is determined in step S552, the processing is the same as that described above with reference to FIG.

[0134] In the third embodiment, the wireless station determines the CCA threshold based on whether the NAV is set by a wireless station in the own BSS and the priority of the frame to be transmitted. If the NAV is set by a wireless station in the own BSS, the wireless station sets the CCA threshold to a default value Th a If the NAV was set by a station in another BSS, the station determines the CCA threshold based on the priority of the frame to be transmitted.

[0135] For example, if the priority of the frame to be transmitted is the first priority level, the CCA threshold is set to a value Th a Greater than Th b and when the priority of the frame to be transmitted is a second priority level higher than the first priority level, the CCA threshold is set to a value Th b Higher value Th cThis increases the chances of transmitting high-priority frames. This makes it possible to ensure the low latency required for high-priority frames. Therefore, highly reliable wireless communication is provided even in a situation where multiple BSSs overlap.

[0136] If the NAV has a high priority, the CCA threshold may be set to a smaller value. For example, even if the frame to be transmitted is a high priority frame, the CCA threshold is set to the SR value Th b Or a smaller value Th d This makes it difficult for the channel to be determined to be idle, and reduces the occurrence of interference with high priority frames related to other BSSs. This makes it possible to ensure the low latency required for high priority frames in other BSSs. In this way, the transmission opportunities for high priority frames related to the own BSS are increased, and high priority frames related to other BSSs are protected. Therefore, highly reliable wireless communication is provided even in a situation where multiple BSSs overlap.

[0137] In the third embodiment, an example has been described in which the wireless station recognizes that the NAV has been set based on the RTS or CTS. Instead of the RTS or CTS, the wireless station may recognize that the NAV has been set based on any frame including a duration field, such as a data frame.

[0138] [Variations] In the embodiment described above, the QoS color is included in the preamble of the radio frame, but alternatively, the QoS color may be included in another part of the radio frame, such as the MAC header.

[0139] The radio section of a wireless station (e.g., the radio section 101 of the base station 10 or the radio section 201 of the terminal 20) may be implemented by a discrete component such as a chip. For example, a chip may be embedded in a substrate of the wireless station when the wireless station is manufactured. The wireless device referred to herein may refer to a wireless station or to a discrete component that realizes the radio section of the wireless station.

[0140] The present invention is not limited to the above-mentioned embodiment, and various modifications can be made in the implementation stage without departing from the gist of the invention. The embodiments may be implemented in appropriate combination, and in that case, the combined effect can be obtained. Furthermore, the above-mentioned embodiment includes various inventions, and various inventions can be extracted by combinations selected from the multiple components disclosed. For example, if the problem can be solved and the effect can be obtained even if some components are deleted from all the components shown in the embodiment, the configuration from which the components are deleted can be extracted as an invention. [Explanation of symbols]

[0141] 10,12...Base station 20,22…Terminal 30,32…BSS 40…Network 50…Communication systems 60...Radio frame 61...PHY preamble 62...PHY header 63...MPDU 101,201…Radio section 102,202…Top tier 110,210…LLC Processing Section 120, 220...MAC processing section 121, 221: Data processing section 122,222...MAC frame processing section 130, 230...PHY processing unit 131,231…Transmitter 132...PHY header processing unit 133...Radio signal processing unit 136,236…Receiver 137...Radio signal processing unit 138...PHY header processing unit 151,251…CPU 152,252…ROM 153,253…RAM 154,254...Wireless communication module 155...Wired communication module 255…Display 256…Storage

Claims

1. A wireless device, a threshold determination unit that determines a threshold used to determine the usage status of a frequency channel; a carrier sense control unit that determines the usage status of the frequency channel based on a comparison between a reception power of a frame detected on the frequency channel by carrier sense and the threshold; Equipped with The detected frame includes identification information for identifying a BSS (Basic Service Set), the wireless device belongs to a first BSS; The threshold determination unit: When the identification information indicates a second BSS different from the first BSS and a first priority, which is a priority of a frame to be transmitted, is a first priority level, the threshold is set to a first value; if the identification information indicates the second BSS and the first priority is a second priority level higher than the first priority level, setting the threshold to a second value higher than the first value; If the identification information indicates the first BSS, the wireless device sets the threshold to a third value that is smaller than the first value.

2. The threshold determination unit: When the identification information indicates the second BSS and a second priority level of the detected frame is a third priority level, the threshold value is set to the first value; setting the threshold to the first value when the identification information indicates the second BSS, the second priority is a fourth priority level lower than the third priority level, and the first priority is the first priority level; setting the threshold to the second value when the identification information indicates the second BSS, the second priority is the fourth priority level, and the first priority is the second priority level.

2. The wireless device of claim 1.

3. The threshold determination unit: When the identification information indicates the second BSS and the second priority level of the detected frame is a third priority level, the threshold value is set to a fourth value that is greater than the third value and less than the first value; setting the threshold to the first value when the identification information indicates the second BSS, the second priority is a fourth priority level lower than the third priority level, and the first priority is the first priority level; setting the threshold to the second value when the identification information indicates the second BSS, the second priority is the fourth priority level, and the first priority is the second priority level.

2. The wireless device of claim 1.

4. A wireless device, a threshold determination unit that determines a threshold used to determine the usage status of a frequency channel; a carrier sense control unit that determines the usage status of the frequency channel based on a comparison between a reception power of a frame detected on the frequency channel by carrier sense and the threshold; Equipped with The threshold determination unit: determining whether or not a network allocation vector (NAV) is set for the frequency channel; and, if the NAV is set, determining whether or not the NAV is set by a wireless station that belongs to a basic service set (BSS) to which the wireless device belongs; If the NAV is not set by a wireless station belonging to the BSS and a first priority, which is a priority of a frame to be transmitted, is a first priority level, the threshold is set to a first value; if the NAV is not set by a radio station belonging to the BSS and the first priority is a second priority level higher than the first priority level, setting the threshold to a second value higher than the first value; A wireless device that sets the threshold to a third value smaller than the first value when the NAV is set by a wireless station that belongs to the BSS.

5. The threshold determination unit: If the NAV is not set by a radio station belonging to the BSS and the third priority level of the NAV is a fifth priority level, the threshold is set to the first value; setting the threshold to the first value when the NAV is not set by a radio station belonging to the BSS, the third priority is a sixth priority level lower than the fifth priority level, and the first priority is the first priority level; setting the threshold to the second value when the NAV is not set by a radio station belonging to the BSS, the third priority is the sixth priority level, and the first priority is the second priority level; 5. The wireless device of claim 4.

6. The threshold determination unit: When the NAV is not set by a radio station belonging to the BSS and a third priority level of the NAV is a fifth priority level, the threshold is set to a fourth value that is greater than the third value and less than the first value; setting the threshold to the first value when the NAV is not set by a radio station belonging to the BSS, the third priority is a sixth priority level lower than the fifth priority level, and the first priority is the first priority level; setting the threshold to the second value when the NAV is not set by a radio station belonging to the BSS, the third priority is the sixth priority level, and the first priority is the second priority level; 5. The wireless device of claim 4.

7. and a power control unit that sets a transmission power for transmitting the frame to be transmitted to a first power level when the first priority is the first priority level, and sets the transmission power to a second power level higher than the first power level when the first priority is the second priority level. A wireless device according to any one of the preceding claims.

8. a power control unit that sets a transmission power when transmitting the frame to be transmitted to a power level according to the threshold determined by the threshold determination unit. A wireless device according to any one of the preceding claims.

9. A wireless communication method performed by a wireless device, comprising: determining a threshold value to be used to determine the usage status of a frequency channel; determining the usage status of the frequency channel based on a comparison between a reception power of a frame detected on the frequency channel by carrier sense and the threshold; Equipped with The detected frame includes identification information for identifying a BSS (Basic Service Set), the wireless device belongs to a first BSS; Determining the threshold value comprises: setting the threshold to a first value when the identification information indicates a second BSS different from the first BSS and a first priority, which is a priority of a frame to be transmitted, is a first priority level; setting the threshold to a second value greater than the first value when the identification information indicates the second BSS and the first priority is a second priority level greater than the first priority level; setting the threshold to a third value less than the first value when the identification information indicates the first BSS; A wireless communication method comprising:

10. A wireless communication method performed by a wireless device, comprising: determining a threshold value to be used to determine the usage status of a frequency channel; determining the usage status of the frequency channel based on a comparison between a reception power of a frame detected on the frequency channel by carrier sense and the threshold; Equipped with Determining the threshold value comprises: determining whether a network allocation vector (NAV) is set to the frequency channel; determining whether or not the NAV has been set by a wireless station belonging to a BSS (Basic Service Set) to which the wireless device belongs when the NAV has been set; setting the threshold to a first value when the NAV is not set by a wireless station belonging to the BSS and a first priority, which is a priority of a frame to be transmitted, is a first priority level; setting the threshold to a second value greater than the first value when the NAV is not set by a radio station belonging to the BSS and the first priority is a second priority level greater than the first priority level; setting the threshold to a third value smaller than the first value when the NAV is set by a wireless station belonging to the BSS; A wireless communication method comprising:

Images