JP6270147B2 - Wireless communication method, wireless communication system, and wireless communication program - Google Patents

Description

  The present invention relates to a communication method and a communication protocol in a wireless communication network, and in particular, in a wireless network configured in units of cells, a wireless communication method in which a base station of each cell performs wireless communication with a terminal station of the cell. The present invention relates to a wireless communication system and a wireless communication program.

  Currently, the wireless LAN system is operated in an unlicensed band that does not require a radio station license, and in order to share a frequency band with other wireless systems, the wireless LAN system is a CSMA / CA as a medium access control method. (Carrier Sense Multiple Access with Collision Avoidance) is adopted. The CSMA / CA system is an autonomous distributed medium access control system defined as a DCF (Distributed Coordination Function) system in the IEEE 802.11 standard (see, for example, Non-Patent Document 1). By using the CSMA / CA scheme, each terminal can acquire transmission rights in an autonomous and distributed manner while avoiding signal collision by carrier sense and random backoff.

  However, when the CSMA / CA method is used, the terminal tries to acquire the transmission right randomly, so even if there is a terminal requesting QoS (Quality of Service) in the same BSS (Basic Service Set), the system Communication with guaranteed QoS cannot be performed. In addition, when a terminal whose reception SNR (Signal-to-Noise power Ratio) has decreased due to the influence of fading of the radio propagation path acquires the transmission right, the use efficiency of the radio resource decreases and the reception SNR Compared with a case where a terminal having a higher acquisition right acquires a transmission right, the throughput decreases.

  In order to achieve high throughput by guaranteeing QoS with high probability and improving utilization efficiency of radio resources, information on traffic status and channel status of each terminal is collected, and radio resources are based on the collected information. Need to be assigned. As a technique for realizing such transmission, centralized control type resource management in which an operator who centrally manages radio resources like a cellular system dynamically allocates radio resources according to the status of the terminal can be considered (for example, non-patented). Reference 2).

  However, since it is not easy for an operator to centrally manage all systems with different standards operated in the unlicensed band like a cellular system, the centralized control type resource management in the cellular system is introduced directly into the wireless LAN system. That is not desirable.

  Therefore, a BSS centralized control OFDMA (Orthogonal Frequency Division Multiple Access) wireless LAN system has been proposed as a technique for improving QoS utilization and improving the utilization efficiency of radio resources while sharing frequencies with different types of radio systems. (For example, refer nonpatent literature 3).

  In an intra-BSS centralized control type OFDMA wireless LAN system, a terminal (hereinafter referred to as an intra-BSS terminal) connected to an AP (base station; Access Point) in the BSS acquires a transmission right using the CSMA / CA scheme. An RTS (Request to Send) frame is transmitted, and after the AP receives this, a CTS (Clear to Send) frame is transmitted. Thereafter, each terminal in the BSS transmits a CTS frame in order. Reserving the wireless medium by notifying other terminals that have received these control frames and not participating in the BSS (hereinafter referred to as non-BSS terminals) the time to occupy the radio resources, Resources can be shared within the BSS.

  Through the above procedure, the system configured with the terminals in the BSS performs centralized control type resource management centering on the AP while sharing the frequency with other peripheral wireless systems. Further, the AP estimates the channel status while collecting the traffic status of each terminal using the RTS frame and the CTS frame. Based on the collected information, QoS is guaranteed with high probability by preferentially allocating radio resources to terminals that request QoS. Further, by assigning a subchannel to a terminal having the highest received SNR for a certain subchannel, the data frame transmission rate is improved and the throughput is improved.

IEEE 802.11-2012, “IEEE Standard for Information Technology- Telecommunications and Information Exchange Between Systems- Local and Metropolitan Area Networks- Specific Requirements-Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications,” 2012. S. Xie, Y. Liu, Y. Zhang, and R. Yu, “A Parallel Cooperative Spectrum Sensing in Cognitive Radio Networks,” IEEE Trans. Vehic. Technol., Vol. 59, pp. 4079-4092, Oct. 2010 . S. Miyamoto, S. Sampei, and W. Jiang, “Novel DCF-Based Multi-User MAC Protocol for Centralized Radio Resource Management in OFDMA WLAN Systems,” IEICE Trans. Commun., Vol. E96-B, no. 9, pp. 2301-2312, Sept. 2013.

In the BSS centralized control type wireless LAN system described above, it is necessary to perform the following (1) and (2).
(1) In order to allocate radio resources so that higher throughput can be achieved while guaranteeing QoS with a high probability, traffic information and channel information of all intra-BSS terminals are collected in the AP.
(2) In order to prevent a collision with each BSS non-BSS terminal that may be an interference source during radio resource occupation, the radio medium is notified to the non-BSS terminals in the form of a time length for occupying the radio medium. Make a reservation.

  On the other hand, the “collect information of terminals in BSS to AP” and “reservation of wireless medium for terminals outside BSS” are not data frames themselves that store information to be transmitted, but to transmit data frames with high quality and high efficiency. It's just pre-processing. Therefore, in order to finally achieve a high system throughput, the frame time length of control frames and management frames (hereinafter referred to as preprocessing frames) generated from these preprocessings is minimized, and the preprocessing frames are transmitted through the wireless medium. It is desirable to minimize the period of occupation. There are various names for the presence of a preprocessing frame for information transmission, and it is sometimes called a signaling overhead, a MAC overhead, a control overhead, a communication overhead, or the like. The essence is exactly the same.

  In the following, first, the relationship among the three parties of “channel information estimation”, “wireless medium reservation”, and “time length of preprocessing frame” will be organized. Next, problems of the BSS centralized control type wireless LAN system, which is a conventional technique, will be described.

<Relationship between channel information estimation and preprocessing frame time length>
Many current wireless systems, including wireless LANs, employ a synchronous detection method. In this case, the pre-processing frame (the same applies to other radio frames, but here the description will be focused on the pre-processing frame) includes a normal training signal portion and a data signal portion. When the preprocessing frame is transmitted from the transmitting station to the receiving station, the receiving station first estimates channel information CSI (Channel State Information) based on the received training signal portion. Next, based on the channel information CSI obtained by the estimation, an attempt is made to restore the transmission information stored in the data signal portion through a series of signal processing such as demodulation and decoding.

  Since high-accuracy channel estimation using a training signal is a prerequisite for reliable communication, a fixed pattern signal is often used as a normal training signal, and the time length cannot be basically adjusted.

  On the other hand, the data signal only needs to be able to accurately restore the information finally transmitted through the demodulation / decoding process based on the highly accurate channel information CSI by the receiving station. Therefore, a data signal is often constructed by appropriately combining various modulation schemes, coding schemes, multiple access schemes and the like within an allowable error rate range so that highly efficient information transmission is possible. As a result, the modulation code method, multiple access method, etc. can be selected within an allowable error rate range so that the time length of the data signal is the shortest, and the occupation period of the wireless medium by the data signal can be minimized.

  Therefore, the adjustment of the time length of the preprocessing frame is basically realized by adjusting the time length of the data signal portion, not the training signal portion. In an actual wireless LAN system (Non-Patent Document 1), a preamble portion that is a fixed pattern signal corresponds to a training signal portion of a preprocess frame.

  On the other hand, the payload portion to which adaptive modulation coding, multiple access method, etc. can be applied corresponds to the data signal portion of the preprocessed frame. Although the time length of the preamble portion used for estimating the channel information CSI cannot be adjusted, the time length of the payload portion can be minimized by selecting a modulation code method or a multiple access method within an allowable error rate range. By minimizing the payload portion in this way, the time length of the wireless LAN preprocessing frame can be minimized.

<Relationship between wireless medium reservation and preprocessing frame time length>
In order to prevent a collision with a non-BSS terminal while the radio medium is occupied, it is necessary to reserve the radio medium by notifying each non-BSS terminal that can be an interference source of the length of time that the radio medium is occupied. .

  In the current wireless LAN, this wireless medium reservation can be realized by exchanging RTS / CTS frames between the AP and the terminal in the BSS. This RTS / CTS frame is a kind of wireless LAN pre-processing frame, and includes a preamble portion which is also a training signal portion and a payload portion which is a data signal portion.

  The preamble portion of the RTS / CTS frame is composed of a fixed pattern signal as a training signal so that the receiving station can estimate the channel information CSI, similarly to the pre-processing frame of other wireless LANs. Therefore, the time length of the preamble part cannot be shortened.

  On the other hand, in the payload portion of the RTS / CTS frame, reservation information of the wireless medium is described. The payload portion of the RTS / CTS frame is low-efficiency and reliable modulation so that the purpose of wireless medium reservation can be maximized, that is, the error rate is minimized when received by a terminal outside the BSS. Only the 6 Mbps mode by the coding method can be applied. As a result, unlike other wireless LAN pre-processing frames, the time length of the payload portion cannot be minimized by selecting a modulation code method or multiple access method within an allowable error rate range.

  As described above, the time length of the RTS / CTS frame cannot be minimized by minimizing the payload portion in the same manner as other wireless LAN preprocessing frames. In other words, since the frame time length of individual RTS / CTS frames cannot be adjusted, the number of RTS / CTS frames used for RTS / CTS frame exchange can be reduced in order to reduce the occupation period of the radio medium by RTS / CTS frame exchange. There is no other way to reduce it.

<Problems of conventional BSS centralized control type wireless LAN system>
In the above-described conventional BSS centralized control type wireless LAN system, it is necessary to perform the following (3) and (4).
(3) To allocate radio resources so that higher throughput can be achieved while guaranteeing QoS with high probability, traffic information and channel information of terminals in all BSSs are collected in the AP.
(4) In order to prevent a collision with each BSS non-BSS terminal that can be an interference source during radio resource occupation, the length of time to occupy the radio medium is notified to those non-BSS terminals. Make a reservation.

  In conventional BSS centralized control type wireless LAN, attention is paid to the fact that the preamble portion of the RTS / CTS frame can be used for channel information estimation and the payload portion can be used for reservation of the wireless medium. (3) and (4) are realized through pre-processing of RTS / CTS frame exchange.

  Specifically, RTS / CTS frame exchange is performed between the AP and each intra-BSS terminal, and the channel information of the corresponding intra-BSS terminal is obtained using the preamble portion of the RTS / CTS frame from each intra-BSS terminal. By estimating, channel information of terminals in all BSSs is collected (the above (3)). At the same time, the payload portion of the RTS / CTS frame from each terminal within the BSS notifies each non-BSS terminal that can be an interference source of the time of medium occupation and reserves the wireless medium (the above (4)).

  However, the time length of each RTS / CTS frame cannot be adjusted not only in the preamble portion but also in the payload portion (by adapting the modulation code scheme so that the reception error rate is minimized). That is, the time length of the RTS / CTS frame cannot be shortened. Therefore, as the number of terminals in the BSS increases, the number of frames used for RTS / CTS frame exchange also increases proportionally. As a result, the medium occupation period of preprocessed frames becomes longer, resulting in a decrease in system throughput. is there.

  SUMMARY An advantage of some aspects of the invention is that it provides a wireless communication method, a wireless communication system, and a wireless communication program capable of suppressing a decrease in system throughput.

The present invention is a wireless communication method in a communication configuration in which a base station and a plurality of terminal stations exist in the wireless cell in an arbitrary wireless cell belonging to a wireless communication network, and combines an indirect collection method and a direct collection method, Collecting channel information from the terminal station in the radio cell to the base station, and combining the indirect collection method and the direct collection method , from among the terminal stations in the radio cell, the radio The minimum number of the terminal stations to which indirect channel information collection is applied is selected so that there is at least one of the terminal stations in the radio cell within the coverage area of each of the terminal stations outside the cell, and the terminal stations are not selected. by applying a direct collection method to the terminal stations in the radio cell, the radio medium said to minimize the terminal station performs Ri by the RTS / CTS frame Reservation, the steps of the terminal stations in all cells make a reservation to be equal to the reservation of the wireless medium by RTS / CTS frame, in combining the direct collection method and the indirect acquisition method, direct channel information Applying a modulation code scheme and a multiple access scheme to minimize the frame time length of the CSI frame used for collection, and after collecting channel information from the terminal station in the radio cell to the base station, The base station allocates radio resources so that a communication quality index is improved based on the channel information, notifies the terminal station in the radio cell of the allocation result, and the radio cell notified of the allocation result A terminal station performs information transmission with the base station according to an allocation result, and performs a success / failure response to the base station. And wherein the door.

The present invention is a wireless communication system in a communication configuration in which a base station and a plurality of terminal stations exist in the wireless cell in an arbitrary wireless cell belonging to a wireless communication network, and combines an indirect collection method and a direct collection method, When combining the means for collecting channel information from the terminal station in the radio cell to the base station, and the indirect collection method and the direct collection method , the radio The minimum number of the terminal stations to which indirect channel information collection is applied is selected so that there is at least one of the terminal stations in the radio cell within the coverage area of each of the terminal stations outside the cell, and the terminal stations are not selected. by applying a direct collection method to the terminal stations in the radio cell, the radio medium said to minimize the terminal station performs Ri by the RTS / CTS frame Reservation, means for performing reserved for the terminal stations in all cell becomes equal to the reservation of the wireless medium by RTS / CTS frame, in combining the direct collection method and the indirect acquisition method, direct channel information After collecting channel information from the terminal station in the radio cell to the base station, means for applying a modulation code scheme and a multiple access scheme for minimizing the frame time length of the CSI frame used for collection, Means for allocating radio resources so that a communication quality index is improved based on the channel information by the base station, and notifying the terminal station in the radio cell of the allocation result; and the radio cell in which the allocation result is notified The terminal station comprises means for transmitting information with the base station in accordance with an assignment result and performing a success / failure response to the base station.

  The present invention is a wireless communication program for causing a computer to execute the wireless communication method.

  According to the present invention, it is possible to achieve an effect that communication quality improvement such as higher system throughput and short transmission delay can be realized while ensuring the same QoS as compared with a wireless network to which the related art is applied.

It is a figure which shows an example of the radio station arrangement | positioning in an object radio | wireless cell. It is a figure which shows the BSS centralized control type wireless LAN technique by a prior art. 1 is a diagram illustrating a BSS centralized control type wireless LAN technology according to an embodiment of the present invention. FIG. It is a figure which shows an example of the radio station arrangement | positioning in an object radio | wireless cell. It is a figure which shows the BSS centralized control type wireless LAN technique by a prior art. 1 is a diagram illustrating a BSS centralized control type wireless LAN technology according to an embodiment of the present invention. FIG. It is a figure which shows the example of a setting of the simulation of uplink communication. It is a figure which shows the relationship between an NRT terminal and an overhead rate. It is a figure which shows the relationship between the number of NRT terminals, and the total throughput in BSS.

  Hereinafter, a wireless communication system according to an embodiment of the present invention will be described. First, a method for collecting channel information will be organized, and a wireless communication system according to an embodiment of the present invention will be described. As a method of collecting channel information from each BSS terminal to the AP, there are two methods of normal indirect collection (Implicit CSI Feedback) and direct collection (Explicit CSI Feedback). In the following, two methods will be described with a wireless LAN as an example.

  In the indirect collection method, a preamble signal necessary for channel information estimation is transmitted from each intra-BSS terminal to the AP, and the AP collects channel information of all intra-BSS terminals in a form in which channel information is estimated based on the received preamble signal. .

  When the indirect collection method is performed in a wireless LAN, the RTS / CTS frame includes a preamble portion. Therefore, if RTS / CTS frame exchange as preprocessing is used, the preamble can be sent to the AP in order from all the terminals in the BSS. . The AP indirectly collects channel information of terminals in all BSSs by estimating channel information based on the preambles received in order. The channel information collection method of the BSS centralized control type wireless LAN (Non-Patent Document 3) according to the prior art can be classified into this indirect collection method.

  The advantage of the indirect channel information collection by the RTS / CTS frame is that the payload portion is suitable for medium reservation because the low-speed and high-reliability 6 Mbps mode is adopted, and both the medium reservation by the payload and the channel information collection by the preamble are simultaneously performed. It can be done. On the other hand, the RTS / CTS frame cannot reduce the time length of both the preamble part and the payload part, and as the number of terminals in the BSS increases, the number of RTS / CTS frames used for RTS / CTS exchange increases proportionally. For this reason, the medium occupation period of the preprocessing frame becomes long, resulting in a decrease in system throughput.

  In the direct collection method, a preamble signal necessary for estimating channel information is transmitted from the AP to each intra-BSS terminal, and each intra-BSS terminal first estimates its own channel information based on the received preamble signal, and then estimates The channel information is stored in the payload portion of the CSI frame and sent back to the AP. The AP collects channel information of all intra-BSS terminals in a form of receiving channel information stored in the payload portion of these received CSI frames.

  When the direct collection method is implemented in the wireless LAN, since the RTS / CTS frame includes a preamble portion, it is conceivable that the RTS / CTS frame is first transmitted from the AP to each terminal in the BSS. Next, each intra-BSS terminal first estimates its own channel information based on the preamble from the AP, then stores the estimated channel information in the payload of the CSI frame and sends it back to the AP, so that the AP receives the channel information. The channel information of all intra-BSS terminals is collected directly.

  The advantage of direct channel information collection using the CSI frame is that the payload portion can be shortened by applying a highly efficient modulation scheme or multiple access scheme within an allowable error rate range. As a result, the CSI frame is shortened, the pre-processing medium occupation period is shortened, and the system throughput is improved. On the other hand, because the payload portion of the CSI frame applies a high-efficiency modulation method or multiple access method, the reception error rate is lower than the low-efficiency and high-reliability 6 Mbps mode applied to the payload portion of the RTS / CTS frame. Therefore, it is difficult to achieve the purpose of medium reservation for making medium reservation information known to terminals outside the BSS to the maximum extent.

  Of course, there is an option not to make a medium reservation, but in this case, there is a possibility of interference with and collision with neighboring wireless systems that use the same frequency band during the information transmission period between the AP and the terminal in the BSS. . In particular, in today's communication situation where wireless devices operating in unlicensed wireless bands such as wireless LANs are rapidly increasing, starting information transmission without making a medium reservation can cause interference and collisions with other systems. As a result, the throughput of the entire wireless network may be reduced.

  As described above, the indirect collection method and the direct collection method for channel information have respective advantages and disadvantages. The channel information collection method of the BSS centralized control type wireless LAN according to the prior art can be classified into this indirect collection method, and thus receives both advantages and disadvantages of the indirect method.

  In this embodiment, the channel from the terminal in the BSS to the AP is combined by combining the indirect collection method and the direct collection method so that the advantages of both channel information collection methods can be maximized and the disadvantages can be avoided to the maximum. Collect information.

  In addition, when combining the indirect acquisition method and the direct acquisition method, a radio cell to which indirect channel information collection by the RTS / CTS frame is applied in order to avoid a prolonged radio medium occupation period due to an increase in the number of RTS / CTS frames Minimize the number of internal terminals.

  Further, when minimizing the number of terminals in the radio cell to which the indirect channel information collection method using the RTS / CTS frame is applied, the terminal that has minimized the radio medium reservation by the RTS / CTS frame and the terminals in all the cells A reservation effect equivalent to or close to the reservation of the wireless medium by the RTS / CTS frame is ensured.

  In addition, when combining the indirect collection method and the direct collection method, various high-efficiency modulation code schemes and multiple access schemes are used so that the frame time length is the shortest as the configuration policy of the CSI frame used in the direct channel information collection method. Allow application.

  Also, after collecting channel information from terminals in the radio cell to the base station AP, the base station AP allocates radio resources so that communication quality indicators such as system throughput and QoS are improved based on the channel information. And the allocation result is made known to terminals in the radio cell.

  Further, the terminal of the wireless cell whose allocation result is known performs information transmission with the base station AP according to the allocation result, and performs a success / failure response with the AP.

<First Embodiment>
Next, a radio communication system according to the first embodiment of the present invention will be described. 1, 2, and 3 illustrate uplink communication in a BSS centralized control type wireless LAN system. FIG. 1 is a diagram illustrating an example of radio station arrangement in a target radio cell. FIG. 2 is a diagram showing a BSS centralized control type wireless LAN technology according to the prior art. FIG. 3 is a diagram illustrating an intra-BSS centralized control type wireless LAN technology according to an embodiment of the present invention.

  In the prior art (FIG. 2), first, terminal # 1 in the BSS transmits an RTS frame after random backoff. Upon receiving this, the AP transmits a CTS frame and requests all intra-BSS terminals other than terminal # 1 that has transmitted the RTS frame to request transmission of the CTS frame.

  In-BSS terminals # 2, # 3, # 4, # 5, # 6, and # 7 other than terminal # 1 transmit CTS frames in order and non-BSS terminals #a, #b, and #c that can become interference sources Reserving a wireless medium for

  So far, the RTS / CTS frames transmitted by the terminals in BSS # 1, # 2, # 3, # 4, # 5, # 6, and # 7 contain their traffic information. By receiving the RTS / CTS frame, the traffic information of the terminals in each BSS can be collected.

  In addition, the RTS / CTS frame transmitted by the terminals in BSS # 1, # 2, # 3, # 4, # 5, # 6, and # 7 includes a preamble portion used for channel information estimation. The AP can indirectly collect the channel information of all intra-BSS terminals by receiving these RTS / CTS frames and estimating the channel information of each intra-BSS terminal.

  The AP allocates communication resources based on the information collected by these frames, and notifies the allocation result to all terminals in the ARBI frame. Each intra-BSS terminal that has received the ARBI frame transmits a data frame according to the allocation result, and releases the communication right after receiving a success / failure response from the AP.

  Next, the radio communication system according to the present embodiment will be described with reference to FIG. First, terminal # 1 in the BSS transmits an RTS frame after random backoff (FIG. 3 (1)).

  Upon receiving this, the APs # 1, # 2, # 3, # 4, # 5, # 6, and # 7 in all the BSSs need to reserve the wireless medium using the RTS / CTS frame because the reservation space overlaps. Focusing on the tendency to spread more than the above, it is decided to secure the reservation effect equivalent to or close to the reservation by all terminals by transmitting the CTS frame with only the minimum number of terminals in BSS # 2 and # 7 To do.

  On the other hand, for terminals # 3, # 4, # 5, and # 6 in the BSS that do not need to reserve a wireless medium by transmitting a CTS frame, the collection of channel information of these terminals is performed directly by transmitting a CSI frame. Decide to do with collection. Further, these determinations are described in a CTS frame transmitted by the AP and notified to each BSS terminal (FIG. 3B).

  Next, the terminals # 2 and # 7 in the BSS transmit the CTS frame based on the determination described in the CTS frame from the AP, and the wireless medium is transmitted to the terminals B outside the BSS #a, #b, and #c. A reservation is made (FIG. 3 (3)). In the case of the arrangement of the radio stations shown in FIG. 1, in this case, the reservation effect equivalent to the radio medium reservation by all the terminals in the BSS can be obtained as in the prior art.

  Next, the intra-BSS terminals # 3, # 4, # 5, and # 6 first estimate their channel information CSI based on the preamble portion of the CTS frame from the AP. Subsequently, the channel information CSI obtained by the estimation is described in the payload portion of the CSI frame and transmitted to the AP. In this case, as a CSI frame configuration policy, application of a high-efficiency modulation code method or multiple access method within an allowable error rate range is permitted so that the frame time length is shortened (FIG. 3 (4)).

  Next, in the RTS / CTS frame and the CSI frame transmitted by the terminals # 1, # 2, # 3, # 4, # 5, # 6, and # 7 in the BSS so far, their traffic information is described. Therefore, the AP can collect the traffic information of the terminals in each BSS by receiving these frames. In addition, since the RTS / CTS frames transmitted by the intra-BSS terminals # 1, # 2, and # 7 include a preamble portion used for channel information estimation, the AP receives these RTS / CTS frames. Thus, the channel information of the corresponding terminal can be indirectly collected by estimating the channel information of the terminals # 1, # 2, and # 7 in the BSS.

  On the other hand, the CSI frame transmitted by the intra-BSS # 3, # 4, # 5, and # 6 includes the payload portion describing the channel information. Therefore, the AP receives these CSI frames to receive the BSS. The channel information of the inner terminals # 3, # 4, # 5, and # 6 can be directly collected (FIG. 3 (5)).

  As described above, in this embodiment, channel information of terminals in all BSSs can be collected in the AP by combining the channel information indirect collection method and the direct collection method while maintaining the wireless medium reservation effect. However, the channel information CSI (Channel State Information) referred to here is not limited to the propagation response of the radio propagation path, but a modulation / decoding code scheme MCS (Modulation Coding Scheme) according to the propagation response or other channels. A generic term for indicators that reflect the situation. The AP performs communication resource allocation based on the collected information, and notifies the allocation result to all terminals in the ARBI frame.

  Next, each intra-BSS terminal that has received the ARBI frame transmits a data frame according to the allocation result (FIG. 3 (6)).

  Next, after receiving the success / failure response from the AP, each intra-BSS terminal releases the communication right (FIG. 3 (7)).

  As can be seen from FIG. 3, by performing communication between the AP and the terminal as in the present embodiment, the pre-processing wireless medium occupation period can be shortened as compared with the prior art, resulting in an improvement in system throughput in the uplink. realizable.

Second Embodiment
Next, a radio communication system according to the second embodiment of the present invention will be described. 4, 5, and 6 illustrate downlink communication in the BSS centralized control type wireless LAN system. FIG. 4 is a diagram illustrating an example of radio station arrangement in the target radio cell. FIG. 5 is a diagram showing a BSS centralized control type wireless LAN technology according to the prior art. FIG. 6 is a diagram illustrating a BSS centralized control type wireless LAN technology according to an embodiment of the present invention.

  In the prior art (FIG. 5), first, the AP in the BSS transmits an RTS frame after random backoff. Terminals # 1, # 2, # 3, # 4, # 5, # 6, and # 7 in each BSS that have received this transmit CTS frames in order, and terminals outside BSS #a and #b that can become interference sources , #C reserves a wireless medium.

  Up to this point, since the traffic information of each of the CTS frames transmitted by the terminals # 1, # 2, # 3, # 4, # 5, # 6, and # 7 in the BSS has been described, the AP can use these RTSs. By receiving the / CTS frame, the traffic information of the terminals in each BSS can be collected.

  In addition, since the CTS frame transmitted by the terminals # 1, # 2, # 3, # 4, # 5, # 6, and # 7 in the BSS includes a preamble portion used for channel information estimation, the AP By receiving these RTS / CTS frames, the channel information of all intra-BSS terminals can be indirectly collected by estimating the channel information of each intra-BSS terminal.

  The AP allocates communication resources based on the information collected by these frames, and notifies the allocation result to all terminals in the ARBI frame. Each intra-BSS terminal that has received the ARBI frame transmits a data frame according to the allocation result, and releases the communication right after receiving a success / failure response from the AP.

  Next, with reference to FIG. 6, the radio | wireless communications system by this embodiment is demonstrated. First, the APs in the BSS have the same reservation space for all the intra-BSS terminals # 1, # 2, # 3, # 4, # 5, # 6, and # 7 when the wireless medium is reserved by the RTS / CTS frame. Pay attention to the tendency to spread more than necessary, and ensure the reservation effect equivalent to or close to the reservation by all terminals by transmitting the CTS frame with only the minimum number of terminals in BSS # 2 and # 7 decide.

  On the other hand, for terminals # 1, # 3, # 4, # 5, and # 6 in BSS that do not need to reserve a wireless medium by transmitting a CTS frame, the collection of channel information of those terminals is performed in the CSI frame. Decided to do so by direct transmission. Furthermore, these determinations are described in the RTS frame transmitted by the AP, and the RTS frame is transmitted after random backoff (FIG. 6 (1)).

  Next, the terminals # 2 and # 7 in the BSS transmit a CTS frame based on the decision described in the RTS frame from the AP, and the wireless medium is transmitted to the terminals outside the BSS #a, #b, and #c. A reservation is made (FIG. 6 (2)). With the arrangement of the radio stations shown in FIG. 4, in this case, a reservation effect equivalent to the radio medium reservation by the terminals in all the BSSs can be obtained as in the prior art.

  Next, the intra-BSS terminals # 1, # 3, # 4, # 5, and # 6 first estimate their channel information CSI based on the preamble portion of the CTS frame from the AP. Subsequently, the channel information CSI obtained by the estimation is described in the payload portion of the CSI frame and transmitted to the AP. In this case, as a CSI frame configuration policy, application of a highly efficient modulation code scheme or multiple access scheme within an allowable error rate range is permitted so that the frame time length is shortened ((3) in FIG. 6).

  Next, since the CTS frame and the CSI frame transmitted by the terminals # 1, # 2, # 3, # 4, # 5, # 6, and # 7 in the BSS are described so far, their traffic information is described. The AP can collect the traffic information of the terminals in each BSS by receiving these frames. In addition, since the CTS frame transmitted by the intra-BSS terminals # 2 and # 7 includes a preamble portion used for estimating channel information, the AP receives the RTS / CTS frame, thereby allowing the intra-BSS terminal The channel information of the corresponding terminal can be indirectly collected by estimating the channel information of # 2 and # 7.

  On the other hand, the CSI frame transmitted by # 1, # 3, # 4, # 5, and # 6 in BSS includes the payload portion describing the channel information, so the AP receives these CSI frames. Thus, channel information of the terminals # 1, # 3, # 4, # 5, and # 6 in the BSS can be directly collected.

  As described above, in this embodiment, channel information of terminals in all BSSs can be collected in the AP by combining the channel information indirect collection method and the direct collection method while maintaining the wireless medium reservation effect. However, the channel information CSI (Channel State Information) referred to here is not limited to the propagation response of the radio propagation path, but a modulation / decoding code scheme MCS (Modulation Coding Scheme) according to the propagation response or other channels. A generic term for indicators that reflect the situation. The AP performs communication resource allocation based on the collected information, and further notifies the allocation result to all terminals in the ARBI frame as a result of resource allocation (FIG. 6 (5)).

  Next, each intra-BSS terminal that has received the ARBI frame transmits a data frame in accordance with the allocation result (FIG. 6 (5)).

  Next, each intra-BSS terminal releases the communication right after receiving the success / failure response from the AP ((6) in FIG. 6).

  As can be seen from FIG. 6, by performing communication between the AP and the terminal as in the present embodiment, the pre-processing radio medium occupation period can be shortened as compared with the prior art, resulting in an improvement in system throughput in the downlink. realizable.

  Next, a numerical experiment of the above-described wireless communication system will be described. In order to evaluate the transmission characteristics of the wireless communication system described above, a computer simulation was performed for uplink communication. FIG. 7 is a diagram illustrating a setting example of simulation of uplink communication. The terminal arrangements assumed as simulation specifications are as shown here.

  The terminals in the BSS are arranged uniformly and randomly on a circle (dashed circle) whose distance from the AP is d (m). Note that one of the terminals in the BSS is an RT (Real Time) terminal that transmits a packet that requests QoS, and the other terminals are NRT (Not Real Time) terminals that transmit packets with no restrictions on QoS.

  A circle centered on the non-BSS terminal (STA) indicates a region where a signal from the non-BSS terminal can be detected.

  A BSS centralized control type OFDMA wireless LAN system (Non-patent Document 3) is used as a comparison target. In the throughput evaluation, comparison with the DCF method is also performed.

FIG. 8 is a diagram showing the relationship between the NRT terminal and the overhead rate. Here, the overhead rate refers to the proportion of the time during which no data frame is transmitted among the total time during which the terminal in the BSS occupies resources.

As shown in FIG. 8, the wireless communication system according to the present invention (compared to the original OFDMA WLAN system) in the BSS centralized control type OFDMA wireless LAN system (
It can be seen that the Proposed OFDMA WLAN System) overhead rate is decreasing.

  This is because the terminals that make reservations for the wireless medium are limited, and a highly efficient modulation and coding scheme is used when transmitting CSI frames that are transmitted to collect traffic conditions and channel conditions. Further, the difference in overhead rate increases as the number of NRT terminals increases, and it can be confirmed that the above-described wireless communication system is effective in reducing signaling overhead in an environment where the number of terminals in the BSS is increased.

FIG. 9 is a diagram showing the relationship between the number of NRT terminals and the total throughput in the BSS after satisfying the condition that the QoS satisfaction rate is 99% or more. Here, the QoS satisfaction rate refers to a ratio of packets transmitted within the requested delay time among all packets transmitted by the RT terminal.

  In the prior art (Non-Patent Document 3), when the number of terminals increases, the difference from the DCF characteristics decreases as the signaling overhead increases.

  However, in the wireless communication system according to the present invention, it can be confirmed that high throughput can be achieved even when the number of terminals is increased by reducing the signaling overhead described above. Further, although the distance between the AP and the terminal is 20 m and 40 m, respectively, it can be confirmed that the wireless communication system according to the present invention is effective without depending on the distance.

  As described above, in the BSS (Basic Service Set) centralized control type wireless LAN system capable of improving QoS utilization and improving the use efficiency of radio resources while sharing frequencies with different types of radio communication systems, The pre-processing such as collection of terminal information in the BSS at the AP and notification of radio resource occupation time to other terminals not participating in the BSS increases the frame time length of the control frame and management frame, thereby increasing the system throughput. There is a problem that decreases.

  In this embodiment, a terminal that can secure a reception error rate equivalent to that of the indirect collection method by the direct collection method is a terminal that performs the direct collection method, and channel information collected by the AP is collected by combining the indirect collection method and the direct collection method. It is characterized by that.

  With this configuration, channel information of terminals in all BSSs can be collected in the AP by combining the indirect collection method and the direct collection method of channel information. Further, when combining, the number of terminals in the radio cell to which indirect channel information collection by the RTS / CTS frame is applied can ensure a reservation effect that is equal to or close to the reservation of the radio medium by all the terminals in the cell by the RTS / CTS frame. Therefore, it is possible to avoid an increase in the period of occupation of the wireless medium due to an increase in the number of RTS / CTS frames.

  In addition, in order to allow the application of various high-efficiency modulation code schemes and multiple access schemes so that the frame time length is minimized as the CSI frame configuration policy used in the direct channel information collection method when combined, the CSI frame And the pre-processing radio medium occupation period spent for collecting channel information of all radio cell terminals can be shortened.

  As a result of the above effects, the above-described wireless communication network finally achieves improved communication quality, such as higher system throughput and shorter transmission delay, while ensuring the same QoS as compared to the wireless communication network to which the conventional technology is applied. it can.

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

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

  Compared to a wireless network to which the prior art is applied, it is applicable to an application in which it is indispensable to realize an improvement in communication quality such as a higher system throughput and a shorter transmission delay while ensuring equivalent QoS.

  AP ... access point (base station), # 1 to # 7 ... terminals in BSS, #a to #c ... terminals outside BSS

Claims (3)

In any radio cell belonging to a radio communication network, a radio communication method in a communication configuration in which a base station and a plurality of terminal stations exist in the radio cell,
Collecting channel information from the terminal station in the radio cell to the base station by combining an indirect collection method and a direct collection method;
When combining the indirect collection method and the direct collection method, the terminal station in the radio cell is within the communicable area of each of the terminal stations outside the radio cell from the terminal stations in the radio cell. The minimum of the terminal stations to which indirect channel information collection is applied is selected so that there is at least one, and is minimized by applying the direct collection method to the terminal stations in the radio cell that are not selected Book of wireless medium said terminal station is performed Ri by the RTS / CTS frames, the steps of the terminal stations in all cells make a reservation to be equal to the reservation of the wireless medium by RTS / CTS frames,
Applying a modulation code scheme and a multiple access scheme to minimize the frame time length of a CSI frame used for direct channel information collection when combining the indirect collection method and the direct collection method;
After collecting channel information from the terminal station in the radio cell to the base station, the base station allocates radio resources so that a communication quality index is improved based on the channel information, and the base station in the radio cell Notifying the terminal station of the allocation result,
The terminal station of the radio cell to which the allocation result is notified performs information transmission with the base station in accordance with the allocation result, and performs a success / failure response to the base station. Method. In any radio cell belonging to a radio communication network, a radio communication system in a communication configuration in which a base station and a plurality of terminal stations exist in the radio cell,
Means for collecting channel information from the terminal station in the radio cell to the base station by combining an indirect collection method and a direct collection method;
When combining the indirect collection method and the direct collection method, the terminal station in the radio cell is within the communicable area of each of the terminal stations outside the radio cell from the terminal stations in the radio cell. The minimum of the terminal stations to which indirect channel information collection is applied is selected so that there is at least one, and is minimized by applying the direct collection method to the terminal stations in the radio cell that are not selected Book of wireless medium said terminal station is performed Ri by the RTS / CTS frame, and means for terminal stations in all cells make a reservation to be equal to the reservation of the wireless medium by the RTS / CTS frames,
Means for applying a modulation code scheme and a multiple access scheme for minimizing the frame time length of a CSI frame used for direct channel information collection when combining the indirect collection method and the direct collection method;
After collecting channel information from the terminal station in the radio cell to the base station, the base station allocates radio resources so that a communication quality index is improved based on the channel information, and the base station in the radio cell Means for notifying the terminal station of the allocation result;
The wireless communication system comprising: the terminal station of the wireless cell to which the allocation result is notified includes means for transmitting information to and from the base station according to the allocation result and performing a success / failure response to the base station. system.   A wireless communication program for causing a computer to execute the wireless communication method according to claim 1.

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