JP2014017627A - Radio communication system and radio communication method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the utilization efficiency of frequency resources in a multiple access system achieving multi-user communication.SOLUTION: A setting unit 10 sets a total communication period, a sub-communication period, the number of sub-channels, and the number of unallocated terminals. A multi-user data frame construction unit 11, until the total communication period becomes shorter than the sub-communication period or the number of allocated terminals reaches the number of unallocated terminals and using the number of sub-channels as an upper limit, performs allocation of terminals participating in implementation of multiple access while updating the remaining number of unallocated terminals, and constructs a multi-user data frame for all the terminals allocated for implementation of multiple access while updating the remaining total communication period. An ending unit 12 deletes the remaining communication period portion if the remaining total communication period is not 0, and carries over communication of remaining terminals to multi-user communication opportunities at the next time or after if the number of remaining unallocated terminals is not 0.

Description

  The present invention relates to a wireless communication system and a wireless communication method.

  In wireless communication, it is desired to improve the use efficiency of frequency resources in order to accommodate a huge number of terminals in a limited frequency resource and provide a high-quality communication service. For this reason, a method of introducing a multiple access method within a single acquired communication opportunity and performing multiuser communication between an access point AP (Access Point) and a plurality of terminals has been proposed (for example, Patent Documents 1 and 2). reference).

  Compared to single-user communication, in multi-user communication, downlink multi-user communication addressed to a plurality of terminals from an access point AP or uplink multi-address addressed to an access point AP from a plurality of terminals in one communication opportunity. User communication is performed. For this reason, the amount of data that can be communicated in one communication opportunity increases, communication can be completed early, and the waiting time and delay time of other terminals are reduced. In a multiple access method capable of communicating at the same time, such as an OFDMA method or an SDMA method, a plurality of terminals can share frequency resources at the same time. In these systems, one channel is divided into a plurality of subchannels in frequency or space, and each terminal communicates using the one or a plurality of subchannels. For example, in the case of OFDMA (Orthogonal Frequency Division Multiple Access), multi-user diversity effect), and in the case of SDMA (Spatial Division Multiple Access), channel capacity expansion improves frequency resource utilization efficiency and throughput. To do.

Daewon Jung, Hyuk Lim, “Opportunistic MAC Protocol for Coordinating Simultaneous Transmissions in Multi-User MIMO Based WLANs,” IEEE Communications Letters, Vol. 15, No. 8, pp. 902-904, Aug. 2011. Stefan Valentin, Thomas Freitag, Holger Karl, “Integrating Multiuser Dynamic OFDMA into IEEE 802.11 WLANs-LLC / MAC Extensions and System Performance,” Proc. Of 2008 IEEE International Conference on Communications (ICC'08), pp. 3328-3334, May 2008.

  However, in a wireless local area network (LAN), wireless signals are not communicated continuously as in a mobile phone system, but wireless signals are communicated in frame units (also referred to as packet mode communication). Therefore, synchronization needs to be established for each frame, and communication is made to or from a plurality of terminals through one subchannel #i (i = 1, 2, 3, 4) within one frame time. It is not possible. For example, in a wireless LAN, communication as shown in FIG. 13 cannot be performed. That is, as shown in FIG. 14, the upper limit of the number of terminals that can be accommodated by the multiple access scheme OFDMA or SDMA in the wireless LAN matches the number of subchannels. Here, since one data frame of one terminal may occupy a plurality of subchannels by space-time frequency coding, the number of terminals that can be accommodated is always limited to the number of subchannels or less.

  In addition, the number of subchannels is limited by regulations of the Radio Law or physical limits on the mounting of terminals. Specifically, the number of OFDMA subchannels is limited to the channel bandwidth determined by the Radio Law. For example, in a wireless LAN, one basic channel bandwidth is defined as 20 MHz. Among them, there are only 52 effective subcarriers, and in the case of applying the OFDMA scheme in which 13 subcarriers are bundled to form one subchannel, a maximum of 4 terminals can be accommodated in one communication.

  In the case of SDMA, the number of subchannels is limited to the number of antennas and high frequency circuit chains that can be mounted on the terminal. For example, in a wireless LAN, it is specified that only four or eight antennas are mounted on one terminal, and in the case of applying an SDMA system in which one antenna is one subchannel, one communication is performed. Only a maximum of 4 or 8 terminals can be accommodated.

  In addition to the limitation on the number of subchannels, when the time length for which each terminal accommodated in one multiple access uses the subchannel, that is, the user data frame length is different, as shown in FIG. Frequency resources are generated. This is due to the difference in data packet size, modulation and coding scheme, space-time frequency coding scheme, and the number of available subchannels of each terminal accommodated in one multiple access. The presence of frequency resources that are not used for information communication leads to a decrease in frequency utilization efficiency, leading to degradation of throughput characteristics.

  In addition to the difference in user data frame length, if there is a terminal having a long user data frame among the terminals accommodated in a single multiple access, the other terminals not accommodated in the multiple access You have to wait until the data frame communication ends. That is, during a single multi-access communication, other terminals cannot be interrupted, so the delay time of the other terminals increases by the length of the multi-connection communication period.

  Furthermore, since the number of terminals that can be accommodated in one multiple access is limited to the number of subchannels, in order to provide communication services to more terminals, communication is performed at a plurality of communication opportunities as shown in FIG. There is a need. For this purpose, communication of control signals for acquiring / releasing a communication opportunity is required a plurality of times, which further reduces the efficiency of use of frequency resources.

  For example, in the case of a wireless LAN, in order to communicate with 15 terminals, even if the above OFDMA scheme is applied, only a maximum of 4 terminals can be accommodated at a time. For this reason, it is necessary to acquire and release communication opportunities by four times of CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance).

  In a medium access control method that autonomously acquires a communication opportunity such as CSMA / CA used in a wireless LAN, generally, it takes time for a long-term frequency resource to be idle to acquire a communication opportunity. . Accordingly, the acquisition / release of a plurality of communication opportunities due to the limitation of the number of subchannels for one multiple access causes a decrease in the efficiency of use of frequency resources. Further, acquisition / release of a plurality of communication opportunities also causes an increase in delay time by a time during which long-term frequency resources are unused.

Therefore, when a multiple access method for realizing multi-user communication is applied to a system that performs wireless signal communication in units of frames, the following problems occur.
(1) The number of terminals that can accommodate one downlink (or uplink) is limited to the number of subchannels or less.
(2) A frequency resource for a control signal for acquiring / releasing a plurality of communication opportunities must be allocated.
(3) Delay time increases due to acquisition / release of multiple communication opportunities.
(4) Unused frequency resources are generated due to uneven user data frame length.
(5) When the communication period of one multiple access increases, the delay time of other terminals that are not accommodated in the multiple access increases.

  As described above, in the related art, the above-described problems occur, and these problems cause a decrease in throughput characteristics and delay characteristics of the wireless communication network.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a radio communication system capable of improving the use efficiency of frequency resources in a multiple access scheme for realizing multi-user communication, and a radio It is to provide a communication method.

  In order to solve the above-described problem, the present invention is a wireless communication system that communicates with a terminal for each of a plurality of subchannels using a frame having a length corresponding to a communication period in one communication opportunity, A setting unit that sets a plurality of sub-communication periods, and a multi-user data frame construction unit that constructs a multi-user data frame in which each of a plurality of terminals is assigned to one of the plurality of sub-communication periods. Is a wireless communication system.

  In addition, the present invention is characterized in that the setting unit described above sets a terminal accommodated in one communication opportunity according to a data frame length with which the terminal communicates among a plurality of terminals.

  Further, the present invention is characterized in that the setting unit described above sets a preselected terminal among a plurality of terminals as a terminal accommodated in one communication opportunity.

  Further, the present invention is characterized in that the multi-user data frame construction unit described above assigns terminals having a short data frame length or a ratio close to an integer to the same sub-communication period.

  Further, the present invention is characterized in that the multi-user data frame construction unit described above preferentially assigns a terminal having a long data frame length with which the terminal communicates.

  In addition, the present invention provides the above-described multi-user data frame construction unit, which transmits a terminal data frame to a plurality of sub-communications for a terminal whose data frame length communicated by the terminal is longer than a frame length capable of communication in the sub-communication period. Dividing into multi-user data frames in a period.

  Further, the present invention provides a multiuser for each sub-communication period so that the multiuser data frame construction unit described above constructs a multi-user data frame so that the multi-user data frames in a plurality of sub-communication periods are independent from each other. It is characterized in that an end point for marking the end of the data frame is determined.

  The present invention is also a wireless communication method of a wireless communication system that communicates with a terminal for each of a plurality of subchannels using a frame having a length corresponding to a communication period in the above-described one communication opportunity. A wireless communication method comprising: setting a plurality of sub-communication periods; and constructing a multi-user data frame in which each of the plurality of terminals is assigned to any one of the plurality of sub-communication periods. It is.

  According to the present invention, it is possible to improve the use efficiency of frequency resources in a multiple access scheme that realizes multi-user communication.

FIG. 3 is a conceptual diagram showing a data frame of multiuser communication in a communication network based on a wireless LAN according to the first embodiment. It is a block diagram which shows the structure of access point AP by this 1st Embodiment. It is a flowchart for implement | achieving construction | assembly of a highly efficient multiuser data frame by this 1st Embodiment. It is a conceptual diagram which shows an example of the determination method of an end point by this 1st Embodiment. It is a conceptual diagram which shows the other example of the determination method of an end point by this 1st Embodiment. It is a conceptual diagram which shows the other example of the determination method of an end point by this 1st Embodiment. It is a conceptual diagram which shows an example of the determination method of an end point by this 1st Embodiment. It is a conceptual diagram which shows the data frame of multiuser communication in the communication network based on wireless LAN by this 2nd Embodiment. It is a block diagram which shows the structure of access point AP by this 2nd Embodiment. It is a flowchart for implement | achieving construction | assembly of a highly efficient multiuser data frame by this 2nd Embodiment. In order to show the quantitative effect of this invention, it is a conceptual diagram which shows the numerical experiment example (simulation evaluation result) of 1st Embodiment. It is a conceptual diagram which shows the relationship characteristic of an offer load (traffic amount of each terminal) and 90% delay time in this invention and a prior art. It is a conceptual diagram for demonstrating the communication system by the multiple access system which can share a frequency resource by the several terminal at the same time by a prior art. It is a conceptual diagram for demonstrating the subject by the multiple access system which can share a frequency resource by the several terminal at the same time by a prior art. It is a conceptual diagram which shows the example which performs several communication in the several communication opportunity by a prior art.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
A. First Embodiment First, a first embodiment of the present invention will be described.
FIG. 1 is a conceptual diagram showing data frames for multi-user communication in a communication network based on a wireless LAN according to the first embodiment. The access point AP acquires a communication opportunity (communication right) for a certain arbitrary k-th communication channel, and performs downlink (or uplink) multi-user communication. In this one-time multi-user communication opportunity, as shown in FIG. 1, four times of multiple access, that is, multiple times of multiple access is performed. It can be seen that the total communication channel occupation period is significantly shortened as compared with the single implementation of multiple times of multi-user communication according to the prior art shown in FIG. The reason is that the acquisition of a plurality of communication opportunities necessary for a plurality of multiple access communications according to the prior art has been reduced to one time, and a highly efficient multi-user data frame has been constructed.

  FIG. 2 is a block diagram showing the configuration of the access point AP in the wireless communication system according to the first embodiment. In FIG. 2, the access point AP includes a setting unit 10, a multiuser data frame construction unit 11, and a termination unit 12.

The setting unit 10 sets the total communication period T _all , the sub communication period T _min , the number of sub channels N _sub, and the number of unassigned terminals. More specifically, for example, the setting unit 10 once sets a time length in which the communication channel hardly fluctuates and the communication quality hardly deteriorates even when the same demodulation process is applied from the start to the end of the communication period. The total communication period T _all (that is, the communication time length) that can be used for the downlink (or uplink) multi-user communication is set. In addition, the setting unit 10 sets, for example, the frame length necessary to send the minimum packet size to one multiple access in a plurality of multiple connections in one downlink (or uplink) multiuser communication. The sub-communication period T _min necessary for communication is set. Here, the sub-communication period T _min can be determined according to the data frame length communicated in each multiple access communication in the iterative process.

In addition, the setting unit 10 may use a frequency axis, a spatial axis, or a code that can be used for one-time multi-access communication among a plurality of times of multi-access that is communicated for one downlink (or uplink) multi-user communication. An axis or the number of subchannels N _sub combining these axes is set. In addition, the setting unit 10 determines the number of terminals N _all that can be accommodated in one downlink (or uplink) multi-user communication as the number of unallocated terminals (multi-user communication has been decided, but scheduling has not been performed yet. The number of terminals that are not.

The multi-user data frame construction unit 11 sets the remaining number of subchannels as the upper limit until the total communication period T _all becomes shorter than the sub communication period T _min or the number of allocated terminals reaches the number of unassigned terminals N _all . While updating the number of unallocated terminals, allocation of terminals participating in the implementation of multiple access is performed, and a multi-user data frame of all terminals allocated to the implementation of multiple access is constructed while updating the remaining total communication period.

Specifically, for example, the multi-user data frame construction unit 11 sets the sub-channel number N _sub as an upper limit, the sub-communication period T _min is longer than the total communication period T _all , or the terminal number N _all is 0 The terminal number of the multiple access communication is executed for the frame (aggregation multi-user data frame) that acquired the communication opportunity while updating the remaining number of unassigned terminals N _all (subtracting one each time a terminal is assigned) Then, by updating the remaining total communication period T _all (subtracting the length of the multi-user data frame length every time a terminal is assigned), the end point of the subframe is efficiently determined, thereby 1 A frame is constructed so that a subcarrier can be shared by multiple terminals.

The termination unit 12 deletes the remaining communication period after the multi-user data frame construction by the multi-user data frame construction unit 11 if the remaining total communication period is not zero, and the remaining number of unassigned terminals is zero. Otherwise, the remaining terminal communication is carried over to the next and subsequent multi-user communication opportunities. Specifically, for example, the termination unit 12 deletes the remaining communication period if the remaining total communication period T _all is not 0, and remains if the remaining number of unallocated terminals N _all is not 0. The terminal communication is carried over to the next downlink (or uplink) multi-user communication opportunity.

  FIG. 3 is a flowchart for realizing the construction of a multi-user data frame by the access point AP of the first embodiment. The procedure shown in this flowchart may be executed either before or after the communication opportunity is acquired, and there is no limitation on the timing.

In order to communicate multiple access multiple times in one downlink (or uplink) multi-user communication opportunity, in the multiple access multiple communication, one downlink (or uplink) multi As shown in FIG. 3, a total communication period T _all that can be used for user communication opportunities is set, and as many terminals as possible are accommodated during the period, so that multiple access can be integrated and implemented with high efficiency. The following initialization process, iterative process, and finalization process are performed according to the flowchart.

First, in the initialization process in step S1, the following settings are made.
A total communication period T _all (that is, a communication time length) that can be used for one downlink (or uplink) multi-user communication is set. For example, it is sufficient to set a time length in which the communication channel hardly fluctuates and the communication quality is hardly deteriorated even when a similar demodulation process is applied from the start to the end of the communication period.

A sub-communication period T _min necessary for one-time multi-access communication among a plurality of multi-accesses in one downlink (or uplink) multi-user communication is set. For example, the frame length necessary to send the minimum packet size may be set.

・ Frequency axis, space axis, code axis, or a combination of these axes that can be used for one-time multi-access communication among a plurality of multiple connections in one downlink (or uplink) multi-user communication The number of subchannels N _sub is set. In FIG. 1, the number of subchannels N _sub is set to 4. This may be the frequency axis, the spatial axis, or another axis. Moreover, the number of subchannels combining these axes may be used.

The number N _all of terminals that can be accommodated in one downlink (or uplink) multi-user communication is set as the number of unassigned terminals. For example, let N _all be the number of _all terminals that can be accommodated by one AP, and N _all = 15 in accordance with FIG. 15, that is, there are 15 terminals that can be accommodated. The number 15 is the number of unassigned terminals. To do.

  However, in this case, it is not known whether or not the terminal participates in the current downlink (or uplink) multi-user communication among the 15 terminals. That is, the selection of terminals participating in communication is not performed. That is, here, a terminal to be assigned to the k-th communication opportunity is not selected in advance, but is selected by subsequent iterative processing.

Next, in the iterative process of steps S2 to S6, the following process is performed.
First, the variable k is set to 1 (step S2), and the determination of the execution of the k-th multiple access is that the total communication period T _all is equal to or greater than the sub communication period T _min and the number of terminals N _all that can be accommodated is greater than 0 (allocation) It is determined whether or not the number of terminals has reached the number of terminals N _all that can be accommodated set in the initialization process (step S3). When the total communication period T _all is equal to or longer than the sub communication period T _min and the number of allocated terminals has not reached the accommodable terminal number N _all set in the initialization process (YES in step S3), Terminal allocation for the kth multiple access is executed (step S4), a multiuser data frame for the kth multiple access is constructed (step S5), the variable k is incremented by 1 (step S6), and the process returns to step S3. .

That is, when it is determined that the repetition is continued (YES in step S3), in the repetition process, first, in step S4, the terminal participating in the communication of the present multiple access up to the number of subchannels N _sub set in the initial process is set as an upper limit. Assigns. Then, by subtracting the number of allocated terminals from unallocated terminal number N _all, it updates the remaining unallocated terminal number N _all. In terminal allocation, for example, terminals having a short data frame length or a ratio close to an integer are allocated to the same multiple access communication. As a result of this terminal allocation, for example, in the prior art shown in FIG. 15, terminal # 2 and terminal # 6 accommodated in separate multiple access communications are shown in FIG. 1 when the present invention is applied. Thus, they are accommodated together in the second multiple access. As a result, frequency resources that are not used due to the difference in data frame length, that is, padding of padding data is reduced.

  Furthermore, in order to shorten the total communication channel occupation period in which multiple access is performed a plurality of times, a terminal having a long data frame length is preferentially assigned early. Then, it becomes possible to advance the timing of interruption of other terminals by dividing long data frames, leading to a reduction in the total communication channel occupation period. Terminal # 5 and terminal # 11 are accommodated the second and third times in the prior art shown in FIG. On the other hand, when the invention is applied, as shown in FIG. 1, terminal # 5 and terminal # 11 are applied to the first multiple access communication, and the timing at which another terminal can interrupt is advanced. Yes.

In the iterative process, in step S5, the multi-user data frame of all terminals allocated to the communication of the present multiple access is constructed, and the remaining sub-communication period T _min is subtracted from the total communication period T _all . The total communication period T _all is updated. For a terminal having a long data frame length, the data frame is divided and distributed to a plurality of multiuser data frames corresponding to a plurality of multiple access for communication. This avoids monopolization of the communication channel due to communication of a long data frame, enables interruption of other terminals, and is effective for both reduction of unused frequency resources and reduction of delay time. Terminal # 5, terminal # 9, and terminal # 11 shown in FIG. 1 divide long data frames to enable interrupt communication with other terminals.

  Furthermore, in a wireless system such as a wireless LAN that implements packet mode communication, each multi-user data frame is set so that multi-user data frames of each multiple access are independent from each other so that synchronization can be easily obtained in units of frames. Add an end delimiter to. In FIG. 1, a total of four independent multi-user data frames are constructed, each corresponding to one multi-access communication.

  As described above, each multi-user data frame is marked with an end so that the multi-user data frames of each multiple access are independent of each other. For this reason, the end point of the multi-user data frame of each multiple access is determined. In addition, it is necessary to embed padding data (that is, dummy data) at the end point so that the data frame lengths of all terminals participating in each session are made uniform. Since the communication of padding data that does not include information is a waste of frequency resources, it is desirable to determine the end point as follows so that the amount thereof is minimized. As a method for determining the end point, the multi-user data frame construction unit 11 may, for example, use the frame point with the longest accumulated communication period in the available subchannel, or the end point of the data frame with the shortest frame length, or the frame The end point of the longest data frame or a fixed period length can be set, and either the frame point that has passed the period length from the start point of the multi-user data frame can be selectively determined as the end point. it can. Such a determination method will be described below.

(Frame point with the longest cumulative communication period in available subchannels)
4A and 4B are conceptual diagrams illustrating an example of an end point determination method according to the first embodiment. FIG. 4A shows a state in which no end point has been determined and the current multi-user data frame is not separated. Here, in order to quantitatively express the time axis, time slots are shown in the horizontal direction and subchannels are shown in the vertical direction. The unit of the time slot may be set according to the requirements of the communication system. For example, if it can be one hour sample, it can be any number of OFDM signals.

  As shown in FIG. 4B, in time slot # 5, the accumulated communication period in usable subchannel # 1 and subchannel # 3 that are not occupied by data is 10 slots. This is longer than the other time slots # 1, # 2, # 3, # 4, # 6, # 7, # 8, # 9, # 10. For this reason, this multi-user data frame is marked with an end point, with this time slot # 5, that is, the frame point with the longest accumulated communication period in the available subchannel as the end point.

(Terminate the data frame with the longest frame length)
In addition to the end point determination criterion described above, the data frame having the longest frame length can be used as the end point.
FIGS. 5A and 5B are conceptual diagrams showing another example of the end point determination method according to the first embodiment. FIG. 5A shows a state in which the end point has not been determined and the division of the current multi-user data frame is not performed, as in FIG. 4A. As shown in FIG. 5 (b), the end point of the longest data frame in the data frame of the terminal accommodated in the current multiple access, and the end point of time slot # 10, and the end of the current multi-user data frame Add a separator.

(Terminate the data frame with the shortest frame length)
It is also possible to use the data frame with the shortest frame length as the end point.
6A and 6B are conceptual diagrams showing another example of the end point determination method according to the first embodiment. FIG. 6A shows a state in which the end point is not determined and the current multi-user data frame is not separated, as in FIG. 4A. As shown in FIG. 6 (b), the end point of the shortest data frame in the data frame of the terminal accommodated in the current multiple access, the time slot # 3 as the end point, and the end of the current multi-user data frame Add a separator.

(A fixed period length is set, and the frame point that has passed the period length from the start point of the multi-user data frame is the end point)
Furthermore, it is possible to set a fixed period length and use the frame point that has passed the period length from the start point of the multi-user data frame as the end point.
FIGS. 7A and 7B are conceptual diagrams illustrating another example of the end point determination method according to the first embodiment. FIG. 7A shows a state in which the end point has not been determined and the current multi-user data frame is not separated, as in FIG. 4A. As shown in FIG. 7B, a fixed time length of 4 hours slot is set for the current multiple access, and the frame point that has passed 4 slots from the start point of the current multi-user data frame is set as the end point. Thus, an end delimiter is added to the current multi-user data frame.

  As described above, various end point criteria are conceivable, but any end point determination criteria is not beyond the scope of the present invention.

  After the end point is determined and an end delimiter is added to the current multi-user data frame, the excess portion and the lack portion are adjusted with respect to the end point. If the data frame length may exceed the end point among the terminals participating in this multiple access, the excess information data will be sent to the multi-user communication opportunity this time for multiple access. Carry over to the next multiple access in the middle.

  Also, if the data frame length of the terminals participating in this multiple access is insufficient to the end point, padding data (that is, dummy data) is embedded and the data frame length is set to the end point. To match.

When the total communication period is limited as in the first embodiment, the length of the multi-user data frame length from the start point to the end point of the multi-user data frame corresponding to the current multiple access implementation sub communication period _{T min} which corresponds to amount corresponding to subtract from the total communication period _{T all,} and updates the total communication period _{T all.}

In addition, a control signal or a control section may be inserted between multi-user data frames corresponding to each time multiple access is performed. For example, in a wireless LAN, a preamble control signal may be inserted at the beginning of a data frame, or a SIFS (Short Inter Frame Space) may be inserted between communication frames. In such a case, the total communication period T _all, the length of the control signal and a control section in addition to the sub-communication period T _min which corresponds to the multi-user data frame length also subtracted, updates the total communication period T _all To do.

On the other hand, when the total communication period T _all is not equal to or longer than the sub communication period T _min (when the total communication period is insufficient), or when the allocated number of terminals reaches the accommodated number of terminals N _all set in the initialization process If all the terminals that can be accommodated are allocated (NO in step S3), the iterative process is terminated, and finally the termination process is executed (step S7).

In the termination process of step S7, if the remaining total communication period T _all is not 0, the remaining communication period is deleted, and the communication opportunity is released without performing communication in the deleted communication period. By doing so, it leads to reduction of frequency resources that are not used. A portion with a cross after the fourth multiple access shown in FIG. 1 is the deleted remaining communication period. If the number of remaining unassigned terminals N _all is not 0 after the end of the iterative process, the remaining terminal communication is carried over to the next downlink (or uplink) multi-user communication opportunity. Thereafter, the process ends.

In the first embodiment, since the limit T _all is provided for the total available communication period, not all accommodable terminals are necessarily accommodated. As shown in FIG. 1, as a result, a single multi-user communication is performed for all 15 terminals in four multiple access implementations except for terminal # 8, terminal # 10, terminal # 13, and terminal # 15. I accommodate all of them on occasion. Moreover, the communication period is guaranteed in advance.

  In the first embodiment, there is only one terminal in downlink (or uplink) communication. In other words, in the case of single user communication between a single terminal and an access point or a base station, multicarrier multiplex communication system OFDM, multiantenna multiplex communication system SDM, or multiantenna space-time code A system STC (Space Time Code), an interleaver multiplex communication system IDM (Interleaved Division Multiplexing), or a combination of these multiplex communication systems is applied.

  Further, when the downlink (or uplink) link communication becomes multi-user communication between a plurality of terminals and an access point or a base station, the multi-carrier multiple access scheme OFDMA, or the multi-antenna multiple access scheme SDMA, Alternatively, interleaver multiple access scheme IDMA (Interleaved Division Multiple Access), a combination of these multiple access schemes, or a combination of these multiple access schemes and the above-described multiple communication schemes, for example, OFDMA-SDMA, OFDMA-SDM, OFDM -SDMA or the like can be applied. The application of any communication method does not exceed the scope of the present invention. Further, different multiple access methods may be applied to multiple access multiple times. For example, OFDMA-SDM can be applied the first time and SDMA-OFDM can be applied the second time.

B. Second Embodiment Next, a second embodiment of the present invention will be described.
FIG. 8 is a conceptual diagram showing data frames for multiuser communication in a communication network based on a wireless LAN according to the second embodiment. The access point AP acquires a communication opportunity for a certain arbitrary k-th communication channel, and performs downlink (or uplink) multi-user communication. In this one-time multi-user communication opportunity, as shown in FIG. 8, five times of multiple access, that is, multiple times of multiple access is performed. It can be seen that the total communication channel occupation period is significantly reduced as compared with the single implementation of multi-user communication multiple times according to the prior art shown in FIG. The reason is that the acquisition of a plurality of communication opportunities necessary for implementing a plurality of multiple connections according to the prior art has been reduced to one time, and a highly efficient multi-user data frame has been constructed.

FIG. 9 is a block diagram showing the configuration of the access point AP according to the second embodiment. In FIG. 2, the access point AP includes a setting unit 20 and a multiuser data frame construction unit 21. The setting unit 20 selects a terminal that participates in one downlink (or uplink) link communication, and sets the selected terminal number N _STA to the number of unassigned terminals. The setting unit 20 includes a frequency axis, a spatial axis, or a code axis that can be used for one-time multi-access communication among a plurality of times of multi-access performed for one downlink (or uplink) multi-user communication. Alternatively, the number of subchannels N _sub combining these axes is set. In the second embodiment, there is no restriction on the total communication period set in the first embodiment.

The multiuser data frame construction unit 21 updates the remaining number of unassigned terminals N _STA with the upper limit of the number of subchannels N _sub until the number of unassigned terminals N _STA becomes 0 (subtracts one each time a terminal is assigned). On the other hand, by performing terminal assignment of multiple access communication for a frame (aggregation multi-user data frame) that has acquired a communication opportunity, and efficiently determining the end point of the subframe, one subcarrier in one frame is determined. Build a frame so that it can be shared by multiple terminals.

  FIG. 10 is a flowchart for realizing the construction of a multi-user data frame by the access point AP of the second embodiment. The procedure shown in the flowchart of FIG. 10 may be applied either before or after the acquisition of a communication opportunity, and there is no limitation on the application timing.

  In order to integrate and implement multiple multiple access within a single downlink (or uplink) multi-user communication opportunity, one downlink (or uplink) link in advance in the multiple multiple access. Select a group of terminals that will participate in communication at a multi-user communication opportunity, shorten the communication period as much as possible for the selected terminal group, and integrate multiple multiple access with high efficiency. The following initialization process and iterative process are applied according to the flowchart shown in FIG.

First, in the initialization process in step S10, the following settings are performed.
A terminal that participates in one downlink (or uplink) link communication is selected, and the selected number of terminals N _STA is set as the number of unassigned terminals. For example, all 15 terminals shown in FIG. 15 are selected to participate in the current multi-user communication. Therefore, the number of unassigned terminals is also 15. However, since there is no restriction on the total communication period that can be used, all 15 terminals continue to communicate until the end.

-Frequency axis, space axis, code axis, or those axes that can be used for one-time multi-access communication among a plurality of times of multi-access performed for one downlink (or uplink) multi-user communication The number of subchannels N _sub combined is set. In FIG. 8, the number of subchannels N _sub is set to 4. This may be the frequency axis, the spatial axis, or another axis. Moreover, the number of subchannels combining these axes may be used.

Next, in the iterative process of steps S11 to S14, the following process is performed until all terminals participating in the communication selected in the initialization process are allocated.
First, the variable k is set to 1 (step S11), and it is determined whether or not the selected number of terminals N _STA is larger than 0 as an execution determination for the k-th multiple access (step S12). If the number of terminals N _STA is larger than 0 (YES in step S12), the number of subchannels N _sub set in the initial process is set as the upper limit, and the terminals participating in the current multiple access are allocated. (Step S13), the multi-user data frame of all terminals allocated to the implementation of the current multiple access is constructed (Step S14), the variable k is incremented by 1 (Step S15), and the process returns to Step S12.

That is, if it is determined that the repetition is continued (YES in step S12), in the repetition process, first, in step S13, the terminals participating in the implementation of the present multiple access up to the number of subchannels N _sub set in the initial process are set as the upper limit. Perform the allocation of. Thereafter, the remaining number _NSTA of unassigned terminals is updated. For terminal allocation, the same method as in the first embodiment is applied. Next, in step S14, a multi-user data frame is constructed for all terminals assigned to the current multiple access implementation. The same method as in the first embodiment is applied to the construction of the multiuser data frame.

  In the second embodiment, since there is no restriction on the total communication period, all terminals participating in the communication selected in the initialization process are allocated, and the entire aggregation multi-user data frame is constructed. In the example of FIG. 8, multiple access is performed 5 times in total, and a total of 15 terminals are accommodated in one multiuser communication opportunity. However, the necessary communication period is not guaranteed in advance.

  In the second embodiment, when there is only one terminal for downlink (or uplink) link communication, that is, when single user communication is actually performed between a single terminal and an access point or a base station. Is applicable to the multicarrier multiplex communication system OFDM, the multi-antenna multiplex communication system SDM, the multi-antenna space-time code system STC, the interleaver multiplex communication system IDM, or a combination of these multiplex communication systems. .

  Further, when the downlink (or uplink) link communication becomes multi-user communication between a plurality of terminals and an access point or a base station, the multi-carrier multiple access scheme OFDMA, or the multi-antenna multiple access scheme SDMA, Alternatively, an interleaver multiple access scheme IDMA, or a combination of these multiple access schemes, or a combination of these multiple access schemes and the above multiplex communication scheme, for example, OFDMA-SDMA, OFDMA-SDM, OFDM-SDMA, or the like is applied. be able to. The application of any communication method does not exceed the scope of the present invention. Further, different multiple access methods may be applied to multiple access multiple times. For example, the first time is OFDMA-SDM and the second time is SDMA-OFDM.

C. Numerical Experiment Results of Invention Next, quantitative effects of the present embodiment will be shown. FIG. 11 is a conceptual diagram showing a numerical experiment example (simulation evaluation result) of the first embodiment. FIG. 12 is a conceptual diagram showing a relationship characteristic between offered load (traffic amount of each terminal) and 90% delay time in the present invention and the prior art. A wireless LAN system is assumed as a system for introducing the present invention, and communication characteristics when the present invention is applied in downlink communication of the wireless LAN system are evaluated.

  As the MAC protocol, those shown in the upper and middle stages of FIG. 11 are used. When using the present invention, FIG. 11 is generated and they are communicated in one communication opportunity. On the other hand, in the case of the prior art, as shown in the lower right side (b) of FIG. 11, one multiuser data frame is communicated in one communication opportunity. As shown in FIG. 12, it can be seen that the present invention reduces the delay time by 90% compared to the prior art.

  Here, parameters conforming to IEEE 802.11g, which is a wireless LAN standard, are applied to both the conventional technology and the present invention. As a medium access method for acquiring a communication opportunity, the CSMA / CA method adopted in the IEEE 802.11 standard is used. An orthogonal frequency multiple access OFDMA scheme is used as a multiple access scheme for realizing downlink multiuser communication and uplink multiuser communication. Multi-user communication in which 13 subcarriers 15 OFDMA symbols can be multiple-accessed up to 4 users at a time as one basic unit was performed. Of course, since the effectiveness of the present invention is not limited to OFDMA, the same effect can be obtained by applying space division multiple access SDMA or interleave division multiple access IDMA.

According to the first and second embodiments described above, the following effects can be obtained.
(1) By performing multiple access multiple times in a single communication opportunity, the number of terminals that can be accommodated is not limited by the number of subchannels in a single multiple access, and more terminals can be accommodated. Communication services can be provided.
(2) By performing multiple access multiple times within a single communication opportunity, communication opportunity acquisition processing (random access) with low frequency utilization efficiency can be reduced, so multiple access The control signals for a plurality of times required for carrying out the operations separately can be reduced to one time, the use efficiency of frequency resources can be improved, and the delay time can be shortened.
(3) By performing multiple access multiple times in a single communication opportunity, terminal allocation, multiple access mode selection and data frame in each multiple access included in the implementation of multiple access The flexibility of construction is improved, and as a result, it is possible to construct a multi-data frame with few unused frequency resources, and the utilization efficiency of frequency resources is improved. Further, during communication with a terminal having a long user data frame, interrupt communication with other terminals is possible, and the delay time can be shortened.

S1, S10 Initialization processing S2-S6, S11-S14 Iterative processing S7 Finalization processing AP Access point (base station)
10, 20 Setting unit 11, 21 Multi-user data frame construction unit 12 Termination unit

Claims (8)

A wireless communication system that communicates with a terminal for each of a plurality of subchannels by a frame having a length corresponding to a communication period in one communication opportunity,
A setting unit for setting a plurality of sub-communication periods within the communication period;
A multi-user data frame construction unit for constructing a multi-user data frame in which each of a plurality of terminals is assigned to any of the plurality of sub-communication periods;
A wireless communication system comprising: The radio according to claim 1, wherein the setting unit further sets a terminal accommodated in the one communication opportunity according to a data frame length with which the terminal communicates among the plurality of terminals. Communications system. The wireless communication system according to claim 1, wherein the setting unit further sets a preselected terminal among the plurality of terminals as a terminal accommodated in the one communication opportunity. The multi-user data frame construction unit allocates terminals having a short data frame length with which the terminals communicate or a ratio close to an integer in the same sub-communication period. The wireless communication system according to any one of the above. The multi-user data frame construction unit allocates a terminal having a long data frame length with which the terminal communicates to an earlier sub-communication period among the plurality of sub-communication periods. The wireless communication system according to any one of the above. The multi-user data frame construction unit, for a terminal whose data frame length communicated with a terminal is longer than a frame length that can be communicated in the sub-communication period, The wireless communication system according to claim 1, wherein the wireless communication system is divided into frames. The multi-user data frame constructing unit separates the end of the multi-user data frame in each sub-communication period so that the multi-user data frames in the plurality of sub-communication periods are independent from each other when constructing the multi-user data frame. The wireless communication system according to any one of claims 1 to 6, wherein an end point to which the mark is added is determined. A wireless communication method of a wireless communication system for communicating with a terminal for each of a plurality of subchannels by a frame having a length corresponding to a communication period in one communication opportunity,
Setting a plurality of sub-communication periods within the communication period;
Constructing a multi-user data frame in which each of a plurality of terminals is assigned to any of the plurality of sub-communication periods;
A wireless communication method comprising:

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