Patent Description:
Particularly, the present invention relates to processing that selects a TXOP responder that is a STA to which an AP grants a TXOP, in order to perform uplink data transmission.

Wireless Local Area Network (LAN) systems in a standard IEEE <NUM> have been improved in throughput year after year, and have come into widespread use as one example of main wireless access (Non-Patent Document <NUM>). Because the wireless LAN system can be used in an unlicensed band that is a frequency band which does not require a license, various types of wireless stations have come into widespread use. Particularly, the spread of smartphones remarkably increases an opportunity to use the wireless LAN system.

A <NUM> band, a <NUM> band, and a <NUM> band are assigned as unlicensed bands that are frequency bands which are used by the wireless LAN system. In microbands, a <NUM> band and a <NUM> band, a band that can be used by the wireless LAN system in Japan is approximately <NUM>. Furthermore, a band that is equal to or greater than <NUM> is assigned as a band that is possibly used abroad by the wireless LAN system. On the other hand, because wireless communication in an unlicensed band is performed based on a random access scheme such as CSMA/CA, a hidden terminal problem is a great obstacle. Flow control that uses request-to-send (RTS) and clear-to-send (CTS) is proposed for the purpose of solving the hidden terminal problem.

At this point, as illustrated in <FIG>, two wireless LANs, a basic service set (BSS) a and a BSS b, are present in a communication area where an AP <NUM> and a STA <NUM>-<NUM> to a STA <NUM>-<NUM> communicate with each other, using an unlicensed band. The AP <NUM> and the STA <NUM>-<NUM> are present in positions where wireless signals of an AP a and a STA a on one wireless LAN, the BSS a, can be detected. The STA <NUM>-<NUM> and the STA <NUM>-<NUM> are present in positions where wireless signals of an AP b and a STA b on the other wireless LAN, the BSS b, can be detected. The STA <NUM>-<NUM> is present in a position where communication between the BSS a and the BSS b cannot be detected.

First, in the uplink data transmission (transmission from the STA to the AP) that is illustrated in (a) of <FIG>, a case where the STA <NUM>-<NUM> acquires a TXOP and transmits a data frame does not pose any problem. However, when the STA <NUM>-<NUM> is set to acquire the TXOP and transmit the data frame, a collision occurs in the AP <NUM> due to communication over the BSS a that is a hidden terminal from the standpoint of the STA <NUM>-<NUM>, or a failure in the uplink data transmission occurs because of a Network Allocation Vector that is set for the AP <NUM>. In this case, the AP <NUM> acquires the TXOP, and grants the acquired TXOP to the STA <NUM>-<NUM>. Thus, an influence of a hidden terminal that is viewed from the STA <NUM>-<NUM> is reduced and throughput of the uplink from the STA <NUM>-<NUM> to the AP <NUM> can be improved (Non-Patent Document <NUM>).

Next, the downlink data transmission (transmission from the AP to the STA) in (b) of <FIG> will be considered. In communication that is based on the RTS/CTS, before the AP <NUM> transmits user data to the STA <NUM>-<NUM>, an RTC frame is transmitted when a wireless signal over a wireless channel, which is transmitted by the AP <NUM>, cannot be detected, the STA <NUM>-<NUM> transmits a CTS frame according to the RTS frame, and the AP a and the STA a on the BSS a set the network allocation vector (NAV) according to the RTS frame or the CTS frame. Furthermore, the AP b and the STA b on the BSS b set the NAV according to the CTS frame that is transmitted by the STA <NUM>-<NUM>. Accordingly, the BSS a stops the communication, and along with this, the BSS b that is a hidden terminal from the standpoint of the AP <NUM> can stop the communication, and can perform transmission to the STA <NUM>-<NUM> over a wireless channel over which the AP <NUM> acquires the TXOP.

In this manner, when it comes to exchange of the RTS frame and the CTS frame, even if the wireless signal over the BSS b, which cannot be detected from the AP in the STA, is present, the STA sets the NAV using the CTS frame, according to the RTS frame from the AP. Thus, it is possible that the hidden terminal problem is solved and that a decrease in throughput is prevented.

Incidentally, in 3GPP, a standardization organization, the discussion on a cellular system that uses an unlicensed band for a wireless LAN has begun (Non-Patent Document <NUM>) as well, and attention has been focused on a method of utilizing the unlicensed band. That is, in the cellular system, the utilization of a frequency band (the unlicensed band) for the wireless LAN in compliance with specifications for the unlicensed band has been discussed as well. The description as the wireless LAN is provided here, but any communication system in which communication is performed with the random access in the unlicensed band may be available.

For example, in a situation that is illustrated in (b) of <FIG>, when a data frame from the AP <NUM> to the STA <NUM>-<NUM> is transmitted, an environment where wireless resources are insufficient for the wireless signal of the terminal in the BSS b that is the hidden terminal from the AP <NUM> (an environment where the wireless signal is always transmitted) is considered. In this case, a frame that is transmitted from the AP <NUM> experiences a collision, and thus is not received in the STA <NUM>-<NUM>, or due to the NAV that is set by the BSS b, the STA-<NUM> cannot transmit the CTS frame in response to the RTS frame that is transmitted from the AP <NUM>. As a result, a problem occurs in that although control which is based on the RTS and CTS is performed, throughput decreases. To cope with this problem, the STA <NUM>-<NUM> sets the NAV or a transmission prohibition section that has the same function as the NAV, for the BSS b that is the hidden terminal from the AP <NUM> and thus acquires the TXOP. Then, the STA <NUM>-<NUM> grants the acquired TXOP to the AP <NUM>, and transmits the data frame using the TXOP that is granted by the AP <NUM>. Thus, an influence of the hidden terminal in the AP <NUM> is reduced and throughput of downlink from the AP <NUM> to the STA <NUM>-<NUM> can be improved (Non-Patent Document <NUM>).

<CIT> refers to mobile communications including a radio base station that can achieve high throughput while attending to a target quality for each mobile station and fairly assigning a transmission opportunity. In the radio base station, a mobile station selection unit which don't achieve a service quality. A mobile station to which a transmission opportunity is assigned is determined.

<CIT> refers to medium access protection and band with negotiation in a wireless local area network. Sub channels of an OFDM channel are allocated by a first device to second devices. A control frame transmitted to the second devices indicates a request to return a control frame to the first device. A second control frame indicates that at least part of a sub channel is available.

However, there is a problem in that the unfairness in throughput between the STAs is caused to occur depending on how to make a selection, that is, how to select the STA to which the AP grants the TXOP in order to perform the uplink data transmission, or how to select the STA that grants the TXOP to the AP in order to perform the downlink data transmission. For example, although like the STA <NUM>-<NUM> that is illustrated in (a) of <FIG>, the STA itself acquires the TXOP in order to perform the transmission, if throughput of the uplink data transmission decreases remarkably due to the communication over the BSS a that is in a hidden-terminal relation, it is effective to grant the TXOP that is acquired by the AP <NUM> to the STA <NUM>-<NUM>. On the other hand, as is the case with the STA <NUM>-<NUM> that is in a position of the hidden terminal from the BSS a, although the TXOP that is acquired by the AP <NUM> is uniformly granted to an arbitrary STA, this does not necessarily contribute to an improvement in throughput.

Furthermore, if the TXOP that is to be granted to the AP <NUM> in order to perform the downlink data transmission is set to be acquired by all STAs, the number of nodes that participate in random access on the downlink increases dramatically and system throughput of the downlink is greatly improved. However, a problem occurs as well in that one STA occupies many wireless resources in contrast to the BSS in the vicinity and the unfairness between the BSSs is caused to occur. In this case, if the number of STAs that are set to acquire the TXOP is configured to be as small as possible, an influence that is exerted to the communication over the BSS in the vicinity can be decreased, but there is a need to suitably select the STA in which the throughput is greatly improved by granting the TXOP to the AP <NUM>.

A preposition of the present invention is to provide a wireless communication system and a wireless communication method that are capable of efficiently performing selection of an STA to which an AP grants a TXOP in order to perform uplink data transmission and selection of the STA that grants the TXOP to the AP in order to perform downlink data transmission in the wireless communication system that is based on random access.

The preposition of the invention is solved by the subject matter of independent claim <NUM>. An advantageous embodiment is disclosed by the subject matter of claim <NUM>.

According to the present invention, a wireless station in which user experience decreases because low quality of uplink data transmission can be selected as a TXOP responder, based on statistical information or an empirical assumption, and a TXOP that is acquired by an AP can be preferentially granted to the TXOP. Thus, throughput in the uplink data transmission can be ensured in terms of fairness and can be improved.

According to the present invention, the wireless station in which the user experience decreases because low quality of downlink data transmission can be selected as a TXOP holder, based on the statistical information or the empirical assumption, and a STA grants the TXOP to the AP. Thus, throughput in the downlink data transmission can be ensured in terms of fairness and can be improved.

<FIG> illustrates an example of a configuration of a wireless communication system according to the present invention. (a) of <FIG> illustrates uplink data transmission that results from an AP granting a TXOP, and (b) of <FIG> illustrates downlink data transmission that results from a STA granting the TXOP.

In (a) and (b) of <FIG>, an AP <NUM> and a STA <NUM>-<NUM> to a STA <NUM>-<NUM> communicate with each other, and two wireless LANs, a BSS a and a BSS b are present in the vicinity of the AP <NUM> and the STA <NUM>-<NUM> to STA <NUM>-<NUM>. The AP <NUM> and the STA <NUM>-<NUM> are present in positions where wireless signals of an AP a and a STA a on one wireless LAN, the BSS a, can be detected. The STA <NUM>-<NUM> and the STA <NUM>-<NUM> are present in positions where wireless signals of an AP b and a STA b on the other wireless LAN, the BSS b, can be detected. The STA <NUM>-<NUM> is present in a position where communication between the BSS a and the BSS b cannot be detected. A basic configuration is the same as illustrated in <FIG>, and the AP <NUM> is connected to a network <NUM>.

The AP <NUM> has a function of granting the acquired TXOP to one or more STAs and thus causing the one or more STAs to perform the uplink data transmission (uplink TXOP granting). Furthermore, the STA <NUM> has a function of granting the acquired TXOP to an AP and thus causing the AP to perform the downlink data transmission (downlink TXOP granting).

The present invention has a feature of including a scheduling unit <NUM> for TXOP granting that performs processing which selects a STA to which the AP <NUM> grants the TXOP for the uplink data transmission from the STA <NUM>-<NUM> to the STA <NUM>-<NUM> to the AP <NUM> and processing which selects a STA that grants the TXOP to the AP <NUM> from the downlink data transmission from the AP <NUM> to the STA <NUM> to the STA <NUM>-<NUM>. The scheduling unit <NUM> for TXOP granting may be included within the AP <NUM> and may be included on the network <NUM> to which the AP <NUM> makes a connection.

<FIG> illustrates an example of the uplink data transmission that results from the AP granting the TXOP. (a) of <FIG> illustrates a sequence for granting the TXOP acquired by the AP to the STA if the AP has downlink data. (b) of <FIG> illustrates a sequence for granting the TXOP acquired by the AP to the STA if the AP does not have the downlink data. It is noted that the same is true for a sequence for the downlink data transmission that results from the STA granting the TXOP, and that the AP and the STA may have a relation as opposed to that which is illustrated in <FIG>.

Under the control of the scheduling unit <NUM> for TXOP granting, the AP grants the TXOP to a designated STA and the designated STA is caused to perform the uplink data transmission. The AP transmits an RTC frame after acquiring the TXOP, and receives a CTS frame that is transmitted from the corresponding STA. As illustrated in (a) of <FIG>, if the AP has downlink data, the AP transmits TXOP granting signal to the STA after transmitting the data to the STA. Furthermore, as illustrated in (b) of <FIG>, if the AP does not have the downlink data, the TXOP granting signal is transmitted to the STA after the CTS is received. With the reception of the TXOP granting signal, the STA transmits uplink data based on the TXOP that is granted by the AP. At this point, with the RTS that is transmitted by the AP or the CTS that is transmitted by the STA, along with the time at which the uplink data transmission that results from granting TXOP is performed, an NAV is set for neighboring nodes A and B.

An important point here is a function of the scheduling unit <NUM> for TXOP granting that selects a STA to which the AP grants the TXOP with the uplink data transmission, or a STA that grants the TXOP to the AP with the downlink TXOP, considering throughput of each STA. A processing procedure for granting the TXOP for uplink and the TXOP for downlink will be described below along with examples of configurations of the AP <NUM> and the STA <NUM>, and the scheduling unit <NUM> for TXOP granting.

<FIG> illustrates the example of the AP <NUM>.

In <FIG>, the AP <NUM> is configured with an antenna <NUM>, a transmission and reception unit <NUM>, a transmission preparation unit <NUM>, a network communication unit <NUM>, and a TXOP granting signal generating unit <NUM>. When user data that is transmitted on the downlink from an external network through the network communication unit <NUM> is input, the AP <NUM> stores the received user data in a storage unit of the transmission preparation unit <NUM>, and the transmission and reception unit <NUM> acquires the TXOP with random access control, performs RTS/CTS, and then builds a data frame for transmission through the antenna <NUM>. At this point, the AP can have a function of performing transmission to a plurality of STAs using orthogonal frequency domain multiplexing access (OFDMA) or spatial multiplexing, and a plurality of STAs that are transmission targets may be available.

On the other hand, if the AP <NUM> grants the TXOP to the STA <NUM> in order to receive the user data on the uplink, the TXOP granting signal generating unit <NUM> performs its function. When acquiring a TXOP grant schedule from the scheduling unit <NUM> for TXOP granting that will be described above, the TXOP granting signal generating unit <NUM> notifies the transmission preparation unit <NUM> that the TXOP is granted to the STA which is designated with the TXOP grant schedule. If downlink data is present, the transmission preparation unit <NUM> acquires the TXOP, transmits the downlink data, and then transmits the TXOP granting signal from the transmission and reception unit <NUM> ((a) of <FIG>), but, if the downlink data is not present, acquires the TXOP and then transmits the TXOP granting signal directly from the transmission and reception unit <NUM> ((b) of <FIG>).

<FIG> illustrates the example of the configuration of the STA <NUM>.

In <FIG>, the STA <NUM> is configured with an antenna <NUM>, a transmission and reception unit <NUM>, a transmission preparation unit <NUM>, a network communication unit <NUM>, and a TXOP granting signal generating unit <NUM>. When the STA <NUM> stores user data from the network communication unit <NUM>, which is transmitted on the uplink, in a storage unit of the transmission preparation unit <NUM>, the transmission and reception unit <NUM> acquires the TXOP with the random access control, performs the RTS/CTS control, and then builds a data frame for transmission from the antenna <NUM>. The network communication unit <NUM> possibly performs communication with a functional block within the STA, and can input and output a signal from and to other functional blocks within the STA, such as blocks for a portable communication network, wired communication, optical communication, and infrared communication.

Furthermore, if the STA <NUM> receives a signal on the downlink, the signal that is received in the antenna <NUM> is decoded in the transmission and reception unit <NUM>, and the decoded code is output to the network communication unit <NUM> through the transmission preparation unit <NUM>. If the TXOP granting signal that is transmitted from the AP <NUM> is included in the decoded signal, the uplink data that waits for transmission in the transmission preparation unit <NUM> is transmitted from the transmission and reception unit <NUM> on the uplink at a designated timing.

On the other hand, if the STA <NUM> grants the TXOP to the AP <NUM> in order to receive the signal on the downlink, the TXOP granting signal generating unit <NUM> performs its function. When acquiring the TXOP grant schedule from the scheduling unit <NUM> for TXOP granting, which will be described above, through the AP <NUM>, the TXOP granting signal generating unit <NUM> notifies the transmission preparation unit <NUM> that the STA to which the TXOP granting signal generating unit <NUM> belongs acquires the TXOP with the TXOP grant schedule and grants the acquired TXOP to the AP <NUM>. If uplink data is present, the transmission preparation unit <NUM> acquires the TXOP, transmits the uplink data, and then transmits the TXOP granting signal from the transmission and reception unit <NUM>, but, if the uplink data is not present, acquires the TXOP and then transmits the TXOP granting signal directly from the transmission and reception unit <NUM>.

<FIG> illustrates an example of the configuration of the scheduling unit <NUM> for TXOP granting.

In <FIG>, the scheduling unit <NUM> for TXOP granting is configured with a network communication unit <NUM>, a communication quality determining unit <NUM>, and the schedule fixing unit <NUM> for TXOP granting. The communication quality determining unit <NUM> collects information relating to communication quality of the uplink or the downlink, or both. As the information to the communication quality, there is a frame error rate of the uplink/downlink or a TXOP acquisition rate of the uplink/downlink, a ratio of throughput to a quality of service (QoS) condition or a traffic volume demand in the uplink/downlink, or a frame retransmission of the uplink/downlink. Moreover, the communication quality determining unit <NUM> collects information on a function of the STA, contract information of an owner of the STA, positional information on the STA, information on traffic that occurs to the STA or on a packet awaiting transmission, and information on an application that is used by the STA, and can use these pieces of information for determining the TXOP grant schedule.

Based on communication quality information of the communication quality determining unit <NUM>, the schedule fixing unit <NUM> for TXOP granting selects a STA to which the AP grants the TXOP or a STA that grants the TXOP to the AP, or a STA to which the TXOP is granted and which grants the TXOP, determines schedule information for TXOP granting that is set for each of the selected STA, and notifies the AP or the STA, or both of the determined schedule information through the network communication unit <NUM>.

When the scheduling unit <NUM> for TXOP granting notifies the AP <NUM> of the schedule information for TXOP granting, a channel for a network that connects between the scheduling unit <NUM> for TXOP granting and the AP <NUM> can be used. When the scheduling unit <NUM> for TXOP granting notifies the STA <NUM> of the schedule information for TXOP granting, the scheduling unit <NUM> for TXOP granting may notify the STA <NUM> of whether to use the channel for the network that connects between the scheduling unit <NUM> for TXOP granting and the AP <NUM> or a wireless channel between the AP <NUM> and the STA <NUM>, using a channel on which an external communication apparatus serves as an intermediary. However, if the scheduling unit <NUM> for TXOP granting is included in the AP <NUM>, the schedule information for TXOP granting can be input and output directly within a circuit, without using the channel for the network between the scheduling unit <NUM> for TXOP granting and the AP <NUM>.

Uplink TXOP granting will be described in detail below.

If the STA itself acquires the TXOP in the uplink, a probability that a signal of the neighboring BSS will be always detected and thus the TXOP will be able to be acquired is considerably low, a collision with a signal that is transmitted from a node which is a hidden terminal from the standpoint of the STA in the AP on the reception side is experienced and thus the communication is not successful, and so forth. Thus, the scheduling unit <NUM> for TXOP granting selects a STA that has communication quality of the uplink that results from the acquisition of the TXOP, which causes user experience to decrease, and sets the selected STA to be a "TXOP responder" to which the AP <NUM> grants the TXOP.

In an example in (a) of <FIG>, when the STA <NUM>-<NUM> is set to acquire the TXOP on the uplink, a probability that the TXOP will be acquired by the communication over the BSS b decreases. Furthermore, when the STA <NUM>-<NUM> is set to acquire the TXOP on the uplink, the communication over the BSS a that is in a hidden-terminal relation cannot be detected, the collision with the signal occurs in the AP <NUM> and thus a probability that the communication will fail increases. The TXOP that is acquired by the AP <NUM> is preferentially granted to the STA <NUM>-<NUM> and the STA <NUM>-<NUM> as in such cases, and thus the user experience can be improved.

<FIG> illustrates an example of a processing procedure for the uplink that results from the AP granting TXOP.

In <FIG>, the communication quality determining unit <NUM> of the scheduling unit <NUM> for TXOP granting collects communication quality information on the uplink or the uplink/downlink (Step S01). Next, based on the collected communication quality information, the schedule fixing unit <NUM> for TXOP granting determines the schedule information for TXOP granting that is made up of information on one or more STAs to which the AP <NUM> grants the TXOP or information which includes prioritization of the one or more STAs, and notifies the AP <NUM> of the determined schedule information (Step S02). When the schedule information for TXOP granting is input, the TXOP granting signal generating unit <NUM> of the AP <NUM> determines a combination of one or more STAs to which the AP <NUM> grants the TXOP, and outputs the determined combination to the transmission preparation unit <NUM> (Step S03). The transmission preparation unit <NUM> determines a transmission type of the TXOP granting signal in accordance with the presence or absence of the downlink data, and notifies the transmission and reception unit <NUM> of the determined transmission type (Step S04). If downlink data is present, the transmission and reception unit <NUM> transmits the TXOP granting signal after transmitting the downlink data. If the downlink data is not present, the transmission and reception unit <NUM> transmits the TXOP granting signal after acquiring the TXOP (Step S05). The STA <NUM> that receives the TXOP granting signal transmits the user data on the uplink at a timing that is set by the TXOP granting signal (Step S06).

At this point, in the STA, if it is determined that throughput of the uplink data transmission which results from the acquisition of the TXOP causes the user experience to decrease, four selection methods of selecting the STA to which the AP grants the TXOP will be described.

The scheduling unit <NUM> for TXOP granting collects information relating to transmission-awaiting user data from the STA that is an AP <NUM>'s partner in the uplink data transmission, request traffic information, and application information. Then, in each STA, the throughput of the uplink data transmission in the acquisition of the TXOP is compared against the condition, and the TXOP responder is preferentially selected from among STAs in which the throughput of the uplink data transmission is in the poorest condition. A transmission resource that is allocated by the OFDMA or the spatial multiplexing may be determined from a PHY rate between the AP <NUM> and the STA and bits of a shortest packet, and the TXOP may be granted to a plurality of STA's partners. On this occasion, the TXOP responder may be selected from among the STAs that transmit the user data on the downlink. Regardless of a transmission destination on the downlink, the TXOP responder may be selected.

With this control, the uplink data transmission can be prevented from causing the user experience to decrease due to low quality, and the TXOP that is acquired by the AP can be preferentially granted to the STA that has low quality of the uplink data transmission.

The AP <NUM> measures the frame error rate of the uplink that results from the STA acquiring the TXOP, and based on a result of the measurement, the scheduling unit <NUM> for TXOP granting preferentially selects the STA that has a high frame error rate, as the TXOP responder. Accordingly, from the frame error rate of the uplink, it can be simply detected that the uplink is in a poor condition, and the TXOP that is acquired by the AP can be preferentially granted to the STA that has the low quality of the uplink data transmission.

The scheduling unit <NUM> for TXOP granting evaluates the communication quality of the uplink and the downlink that results from the STA acquiring the TXOP, for example, the throughput or the frame error rate. As the communication quality of the uplink that results from the acquisition of the TXOP is poorer by comparison with the communication quality of the downlink that results from the acquisition of the TXOP, the scheduling unit <NUM> for TXOP granting more preferentially makes a selection as the TXOP responder.

With this control, the comparison of the quality of the uplink/downlink is performed, and thus it can be more precisely detected that a specific STA is in a condition where the TXOP is difficult to acquire due to a hidden terminal/ exposed terminal problem, than in the selection method <NUM>, and the TXOP that is acquired by the AP can be preferentially granted to the STA that has the low quality of the uplink data transmission.

The scheduling unit <NUM> for TXOP granting collects pieces of information that have high correlation with the communication quality, such as positional information on the STA or average received signal strength information from the STA, and information on the time at which the communication is performed, and selects the TXOP responder based on machine learning or an empirical assumption, from information other than the communication quality and the performance of the TXOP granting so far. For example, throughput characteristics of the uplink and the downlink, which relates to location information on the STA, are stored in the communication quality determining unit <NUM> of the scheduling unit <NUM> for TXOP granting, and thus the STA that is assumed to have the low communication quality of the uplink or the downlink can be determined using the location information, or if the location information on the STA and time information satisfy a fixed condition, it can be determined that the communication quality of the uplink or the downlink is low. In addition, the communication quality may be determined from information other than direct communication, such as a function of, owner information on, and application use information on the STA, and the TXOP grant schedule may be determined.

With the methods of selecting the TXOP responder, which are described above, based on statistical information or the empirical assumption, the TXOP that is acquired by the AP can be preferentially granted to the STA that has the low quality of the uplink data transmission, and the user experience can be prevented from decreasing because of the low quality of the uplink data transmission.

Furthermore, based on the methods of selecting the TXOP responder, which are described above, weight to the STA or a ratio of resources on which the TXOP granting is performed may be determined, and a probability of granting TXOP to a plurality of STAs or a method of allocating a frequency or time resource block may be as the schedule information for TXOP granting.

Furthermore, the schedule fixing unit <NUM> for TXOP granting may acquire wireless environment information on the vicinity of the AP <NUM>, and may limit the number of STAs that grants the TXOP or the frequency with which the TXOP is granted, depending on the number of or communication states of unmanaged APs and unmanaged STAs in the vicinity of the AP <NUM>.

Downlink TXOP granting will be described in detail.

If the AP itself acquires the TXOP in the downlink, a probability that a signal of the neighboring BSS will be always detected and thus the TXOP will be able to be acquired is considerably low, a collision with a signal that is transmitted from a node which is a hidden terminal from the standpoint of the AP in the STA on the reception side is experienced and thus the communication is not successful, and so forth. Thus, the scheduling unit <NUM> for TXOP granting selects a STA that has communication quality of the downlink that results from the acquisition of the TXOP, which causes user experience to decrease, and sets the selected STA to be a "TXOP holder" which grants the TXOP to the AP <NUM>.

In an example in (b) of <FIG>, when the AP <NUM> is set to acquire the TXOP on the downlink, a probability that the TXOP will be acquired by the communication over the BSS a decreases. Furthermore, although the AP <NUM> acquires the TXOP and performs the transmission to the STA <NUM>-<NUM>, because the communication over the BSS b that is in a hidden-terminal relation cannot be detected, a packet collision in the STA <NUM>-<NUM> occurs and thus a probability that the communication will fail increases. The STA <NUM>-<NUM> as in such a case is selected and the TXOP that is acquired by the STA is granted to the AP <NUM>, and thus the user experience on the downlink can be improved.

<FIG> illustrates an example of a processing procedure for the downlink data transmission that results from the STA granting the TXOP.

In <FIG>, the communication quality determining unit <NUM> of the scheduling unit <NUM> for TXOP granting collects communication quality information on the downlink or the uplink/downlink (Step S11). Next, based on the collected communication quality information, the schedule fixing unit <NUM> for TXOP granting determines the schedule information for TXOP granting that is made up of information on one or more STAs to which the AP <NUM> grants the TXOP or information which includes TXOR acquisition conditions of the one or more STAs, and notifies the corresponding STA <NUM> of the determined schedule information through the AP <NUM> (Step S12). When the schedule information for TXOP granting is input, the TXOP granting signal generating unit <NUM> of the STA <NUM> outputs the information that the TXOP is granted to the AP <NUM> and the TXOR acquisition condition to the transmission preparation unit <NUM> (Step S13). The transmission preparation unit <NUM> determines a transmission type of the TXOP granting signal in accordance with the presence or absence of the uplink data, and notifies the transmission and reception unit <NUM> of the determined transmission type (Step S14). If uplink data is present, the transmission and reception unit <NUM> transmits the TXOR granting signal after transmitting the uplink data. If the uplink data is not present, the transmission and reception unit <NUM> transmits the TXOR granting signal after acquiring the TXOP (Step S15). The STA <NUM> that receives the TXOR granting signal transmits the downlink data at a timing that is set by the TXOR granting signal (Step S16).

At this point, in the AP, if it is determined that throughput of the downlink data transmission that results from the acquisition of the TXOP causes the user experience to decrease, or that the communication quality that results from the acquisition of the TXOP for the uplink data transmission is high, three methods of selecting the STA that grants the TXOP to the AP will be described.

The scheduling unit <NUM> for TXOP granting collects information relating to transmission-awaiting user data for the STA that is an AP <NUM>'s partner in the downlink data transmission, the request traffic information, and the application information. Then, in each STA, the throughput of the downlink data transmission that results from the acquisition of the TXOP from the AP is compared against the condition, and the TXOP holder is preferentially selected from among STAs in which the throughput of the downlink data transmission is in the poorest condition. The transmission resource that is allocated by the OFDMA or the spatial multiplexing may be determined from the PHY rate between the AP <NUM> and the STA and bits of a transmission packet, and the downlink data transmission from a plurality of STA's may be performed.

The AP <NUM> measures the frame error rate of the downlink that results from the AP acquiring the TXOP, and based on a result of the measurement, the scheduling unit <NUM> for TXOP granting preferentially selects the STA that has a high frame error rate, as the TXOP holder.

The scheduling unit <NUM> for TXOP granting evaluates the communication quality (the throughput or the frame error rate) of the uplink and the downlink that results from the acquisition of the TXOP. As the communication quality of the downlink that results from the acquisition of the TXOP is poorer by comparison with the communication quality of the uplink that results from the acquisition of the TXOP, the scheduling unit <NUM> for TXOP granting more preferentially makes a selection as the TXOP holder.

With the methods of selecting the TXOP holder, which are described above, based on the statistical information or the empirical assumption, the TXOP can be preferentially granted to the STA that has the low quality of the downlink data transmission, and the user experience can be prevented from decreasing because of the low quality of the downlink data transmission.

Claim 1:
A wireless access point (<NUM>) characterized by:
a scheduling unit (<NUM>, <NUM>) for transmission opportunity, TXOP, granting configured
to determine one or more wireless stations (<NUM>) as TXOP responders to which the wireless access point (<NUM>) grants a TXOP based on a parameter indicating a quality of an uplink data transmission, and
a unit (<NUM>, <NUM>) that is configured
to acquire the TXOP using a random access scheme after the determination of the TXOP responders,
to transmit a TXOP granting signal indicating a timing to perform the uplink data transmission to the TXOP responders; and
to transmit an RTS and receive a CTS, before transmission of the TXOP granting signal, and setting a NAV to reserve a channel necessary to transmit at least both the TXOP granting signal and uplink data with the RTS.