Communication system, communication apparatus and communication method

The present invention relates to a communication device, a communication method, and a communication system for feeding back channel estimation information to a communication partner device, and more particularly to exchanging channel estimation information related to MIMO (Multi Input Multi Output).

In recent years, technology related to MIMO, which transmits information using a plurality of antennas for transmission and reception, has attracted attention. A wireless communication system using MIMO technology has an advantage that the communication capacity can be expanded without expanding the required frequency band. The use of MIMO is also considered to be promising in IEEE802.11n, a wireless LAN standard that is currently being standardized. However, in the case of a wireless communication system using MIMO, the channel state of each path cannot be estimated even if signal processing is performed on the receiving side, especially under the propagation environment of LOS (Line Of Sight), and the data is multiplexed using a plurality of antennas. There is a problem that the transmitted data may not be separated on the receiving side. One of the reasons for this is that the transmitting side cannot know the receiving characteristics of the receiving side. If the receiving characteristics of the receiving side are not clear, it is possible that the transmitting side transmits multiple numbers or data to be transmitted from the antenna, which cannot normally separate information on the receiving side. As a result, bandwidth is wasted. It also causes the problem of interfering with other communications.

In order to solve this problem, the transmitting side may select the number of data multiplexes and the antenna used for transmission according to the channel state so that the information can be separated normally on the receiving side so that the data can be transmitted. ..

For example, the following techniques are known in which information on the channel state estimated by the receiving side is fed back to the transmitting side, and the transmitting side selects a data transmission method according to the channel state. Those that switch the modulation method of the transmitted data on the transmitting side based on the feedback of channel information from the receiving side (see Patent Document 1 below), those that control the coding rate (see Patent Document 2 below), and the like.

However, in order to feed back the channel estimation information for appropriately controlling the transmitting side using MIMO, a technique not available in the conventional communication performed by one antenna is required. For example, if the conventional technology is simply applied, a method of transmitting data one by one from a plurality of transmitting side antennas, measuring the channel state for each antenna on the receiving side, and feeding back to the transmitting side is conceivable. Be done. However, this method wastes a lot of communication resources depending on the number of antennas, and the communication procedure required for measurement becomes complicated.<patcit num="1"><text>JP-A-2002-290246</text></patcit><patcit num="2"><text>Japanese Patent Application Laid-Open No. 2003-69531</text></patcit>

<p> An object of the present invention is to provide a communication system, a communication device, and a communication method capable of exchanging channel estimation information between communication devices capable of communicating by multiple inputs and multiple outputs (MIMO).</p>

<p> The communication system according to one aspect of the present invention includes first and first communication means capable of communicating according to the first physical layer protocol of multi-input and multi-output and communication by the second physical layer protocol of single input / output. A communication system for exchanging channel state estimation information about a channel used for communication between two communication devices, wherein the first communication device is connected to the second communication device and the second communication device in the second communication device. It is transmitted based on the second physical layer protocol for requesting the first channel state estimation information including the information about the reception state when communicating with the communication device 1 using the first physical layer protocol. The physical frame is further provided with a first transmission means for adding a first preamble transmitted based on the first physical layer protocol to a predetermined position and transmitting the first preamble to the second communication device. The second communication device includes a detection means for detecting that the physical frame requests the first channel state estimation information by decoding the physical frame, and the said physical frame added to the physical frame. A channel state estimation means for obtaining the first channel state estimation information based on the first preamble and a second channel state estimation information obtained by the channel state estimation means are transmitted to the first communication device. Is provided with a means for transmitting.</p><p> The communication device according to one aspect of the present invention is a communication device provided with a communication means capable of communication according to the first physical layer protocol of multi-input and multi-output and communication by the second physical layer protocol of single input / output. To request the other communication device for first channel state estimation information including information on the reception state when the signal transmitted using the first physical layer protocol is received by the other communication device. A first transmission in which a first preamble transmitted based on the first physical layer protocol is added to a predetermined position and transmitted to a physical frame transmitted based on the second physical layer protocol. According to the first physical layer protocol based on the means, the receiving means for receiving the first channel state estimation information from the other communication device, and the first channel state estimation information received from the other communication device. A means for determining a transmission condition for transmitting a physical frame and notifying the communication means of the transmission condition is provided.</p><p> And a communication method according to one aspect of the present invention is provided.</p>

<p> According to the present invention, the channel state representing the reception characteristic when communicating using MIMO in the receiving side communication device is estimated, and this channel state estimation information is fed back to the transmitting side communication device. The transmitting side communication device can appropriately select a transmission method including the number of information multiplex and the number of antennas used for transmission based on the channel state estimation information fed back from the receiving side communication device.</p><p> In addition, it is possible to avoid a situation in which communication is started using MIMO even though the channel condition is poor and communication using MIMO is not possible. As a result, it is possible to prevent wasting the bandwidth of the communication path due to a communication error that is expected to occur.</p>

(First Embodiment) FIG. 1 is an example of a functional block diagram of the communication device according to the embodiment of the present invention. This communication device is a device constituting the communication system according to the present embodiment, and has a processing unit 100 of the MAC layer and a processing unit 200 of the physical layer. These processing units are implemented as analog or digital electronic circuits, depending on the implementation, or, for example, firmware that is executed by a CPU built into the LSI. An example is shown in which, for example, three antennas 300 are connected to the processing unit 200 of the physical layer. As shown in FIG. 1, the processing unit 100 of the MAC layer has the MAC layer management function 101. It also has a function T1 that creates a channel information feedback request frame to be transmitted to the communication partner device in response to an instruction from the MAC layer management function 101. MAC frames such as channel information feedback request frames created in the processing unit 100 of the MAC layer are sent to the processing unit 200 of the physical layer. The processing unit 200 of the physical layer has a function T2 for encoding (encoding) a MAC frame and a function T3 for generating a physical frame by adding a preamble to the coded data. The generated physical frame is transmitted from the antenna 300.

On the other hand, the processing unit 200 of the physical layer has a function R1 that estimates the channel state based on the preamble received by the antenna 300 at the time of reception, and a function R3 that decodes data based on this channel estimation. The channel estimation result is used in the channel estimation result notification frame creation function R2 in the MAC layer processing unit 100. Further, the data decoded in the function R3 determines whether or not the received frame is a channel information feedback request frame, and whether or not the received frame is a channel estimation result notification frame. It has the function R5. If the received frame is a channel information feedback request frame, the function R2 creates a channel estimation result notification frame and sends it to the channel information request destination. On the other hand, when the received frame is a channel estimation result notification frame, at least the information multiplex and the transmitting antenna when transmitting data to the communication device that transmitted this frame are determined based on the frame (R6). The information determined by R6 is transmitted to the coding function T2, which controls the operation at the time of transmission. An example of a method for determining the information multiplex / transmitting antenna by R6 will be described later.

As the communication system according to the embodiment of the present invention, a wireless LAN system using a communication method by MIMO is assumed. The communication terminal (hereinafter referred to as MIMO terminal) used in this communication system shall be able to understand the format used in the communication communication method specified in IEEE802.11a.

FIG. 2 is a diagram showing a configuration example of a MIMO channel in the communication system according to the embodiment of the present invention. As shown in the figure, in the embodiment of the present invention, three antennas 300 are prepared for transmission and reception, and a matrix channel (MIMO channel) is formed. The transmitting side transmits different information from each of the three antennas 300. The receiving side receives the multiplexed signal at each antenna 300, and separates the received information by signal processing.

In the present embodiment, since the matrix channel assumes a wireless channel, the channel state fluctuates drastically, and the transmitting side cannot grasp the signal receiving characteristics on the receiving side without feedback of the channel estimation result information from the receiving side. Have difficulty.

Hereinafter, a mechanism for feeding back channel estimation result information to the transmitting side in a wireless communication system using a MIMO terminal will be described according to the communication procedure of FIG. Feedback of channel information from the receiving side to the transmitting side is mainly performed at the start of communication or when the communication quality deteriorates. Alternatively, feedback may be provided on a regular basis.

As shown in FIG. 3, in this communication procedure, the receiving side estimates the channel based on the first step 5-1 of transmitting the channel information feedback request frame 1 from the transmitting side to the receiving side and the channel information feedback request frame 1. The second step 5-2 of performing the above, the third step 5-3 of notifying the transmitting side of the channel estimation result on the receiving side by frame 2-1 and the transmitting side performing channel estimation based on frame 2-1. The fourth step 5-4 and the fifth step of transmitting one of the channel estimation result notification frames 3-1, 3-2, and 3-3 as the channel estimation result of the transmitting side from the transmitting side to the receiving side. It consists of 5-5.

FIG. 4 is a diagram showing a basic example of the physical frame in the present embodiment, and the physical frame shown here is appropriately modified and used depending on the embodiment of the present invention. The physical frame 400 is roughly divided into a preamble and a MAC frame 411. In the present embodiment, the preamble has two types of preambles, which are a briamble 401 and a preamble 402. Preamble 401 is a preamble transmitted based on the communication method specified in IEEE802.11a, and preamble 402 is a preamble transmitted by MIMO. The MAC frame 411 is basically the same as the frame format specified by IEEE802.11a, and is transmitted by the communication method based on IEEE802.11a unless otherwise specified. It differs from the physical frame specified in IEEE802.11a in that it does not have a field corresponding to preamble 402. The channel information feedback request frame and the channel estimation result information frame, which will be described later, are basically generated based on the format of the physical frame 400.

FIG. 5 is a diagram showing the format of the channel information feedback request frame 1. In the processing unit 100 of the MAC layer, the MAC frame part of the channel information feedback request frame is created in response to the instruction of the channel information feedback request from the MAC layer management function 101 (T1). The frame portion is passed to the processing unit 200 of the physical layer, and is encoded (encoded) specified in IEEE802.11a or encoded when transmitted by MIMO (T2). After that, the preamble specified in IEEE802.11a and the MIMO preamble are added before the MAC frame (T3) and transmitted from the antenna 300.

As shown in FIG. 5, the MAC frame portion needs to be transmitted by the communication method specified in IEEE802.11a. FIG. 6 is a diagram for explaining that in MIMO, data may not be separated depending on the transmission line environment. As shown in Fig. 6, consider MIMO that transmits data S1, S2, and S3 using three transmitting antennas (Tx1, Tx2, Tx3). The transmitting antenna Tx1 transmits the data S1. Similarly, the transmitting antenna Tx2 transmits data S2 and the transmitting antenna Tx3 transmits data S3. The receiving side receives data S1, S2, S3 using three receiving antennas (Rx1, Rx2, Rx3). The receiving antennas Rx1, Rx2, and Rx3 all receive a signal in which three types of data S1, S2, and S3 are mixed. Here, focusing on the receiving antenna Rx1, the signal r1 received by the receiving antenna Rx1 is<maths num="1"><img file="JP2005198213A_D0001.tif" /></maths>

It is expressed as. h1_1, h2_1, h3_1 are the effects of the channel state on the data. That is, the channel state between the transmitting antenna Tx1 and the receiving antenna Rx1 is expressed as h1_1, and the data S1 transmitted by the transmitting antenna Tx1 changes under the influence of the channel state h1_1 during transmission, and S1 * at the receiving antenna Rx1. Received as h1_1. Similarly, the data S2 is received as S2 * h2_1 and S3 is received as S3 * h3_1.

Similarly, the received signal r2 at the receiving antenna Rx2 is<maths num="2"><img file="JP2005198213A_D0002.tif" /></maths>

The received signal r3 in the receiving antenna Rx3 is <maths num="3"><img file="JP2005198213A_D0003.tif" /></maths>

It is expressed as. The above equations (1) to (3) can be summarized as equation (4). <maths num="4"><img file="JP2005198213A_D0004.tif" /></maths>

On the receiving side, if the channel state matrix H can be estimated, S1, S2, S3 can be separated and extracted from the received signals r1, r2, r3 by solving the simultaneous equations of Eq. (4). In order to estimate H, the preamble that is added and transmitted together with the data is used. When a MIMO preamble is added to the data, the channel state matrix H can be estimated on the receiving side, so S1, S2, and S3 can be separated and extracted from the received signals r1, r2, and r3. ..

Using the channel state matrix H estimated on the receiving side, it is possible to determine the information multiplexing number and transmitting antenna (R6) on the transmitting side. Here, an example of a method for determining the multiple number and the transmitting antenna will be described.

First, a method using the correlation coefficient α between each path can be considered. The correlation coefficient α between each path can be obtained from Eq. (4) and the channel state estimation result hx_y (x = 1,2,3, y = 1,2,3) in FIG. For example, if the hx_y values of two paths are approximately equal, the correlation coefficient α between the two paths is high. Conversely, if the hx_y values of two paths differ significantly, then the correlation coefficient α between the two paths is considered low. When communicating using MIMO, multiple signals received through a path with a high correlation coefficient α cannot be separated on the receiving side, so if the correlation between the paths is high, either one of the paths It is desirable to use only. That is, the correlation coefficient α between each path is obtained from the channel estimation result hx_y, and if the correlation coefficient α is larger than the predetermined threshold value α_th, one of the paths with high correlation is selected. Make a selection. On the other hand, paths that are not selected and are highly correlated with each other will not be used. Then, the antenna to be used for transmitting the selected path and the multiple number to be finally used for transmission can be determined.

As another example of the method, a method of obtaining the CNR (Carrier vs. Noise Ratio) of each path and selecting the transmitting antenna so as not to use the path having a low CNR can be considered. Signals received from paths with a low CNR can be difficult to separate by path. Therefore, if the CNR of a certain path is smaller than the preset threshold value CNR_th, that path is set not to be used. The CNR of each path can be obtained from the channel estimation result hx_y (x = 1,2,3, y = 1,2,3) in Eq. (4) and FIG. Further, since the path having a large channel estimation result hx_y value has a high CNR, it is possible to determine the multiple number and the transmitting antenna from the magnitude of the channel estimation result hx_y value without actually obtaining the CNR. In addition, the above CNR used for judgment can be judged in the same way even if it is SNR (Signal vs. Noise Ratio).

However, in the LOS environment, the signals S1, S2, and S3 transmitted from the transmitting antennas Tx1, Tx2, and Tx3 pass through almost the same channels, so that the correlation between the received signals r1, r2, and r3 is high. That is,<maths num="5"><img file="JP2005198213A_D0005.tif" /></maths>

And the channel state matrix H <maths num="6"><img file="JP2005198213A_D0006.tif" /></maths>

Will be. In this case, equation (4) is <maths num="7"><img file="JP2005198213A_D0007.tif" /></maths>

Therefore, the transmission signals S1, S2, and S3 cannot be obtained because the equation cannot be solved. Therefore, when MIMO is used in the LOS environment, it is impossible to separate and extract S1, S2, and S3 from the received signals r1, r2, and r3.

In this way, in MIMO, data may not be separated depending on the environment, so the MAC frame part of channel information feedback request frame 1 must be transmitted by the communication method specified in IEEE802.11a, not by MIMO. There is.

The channel information feedback request frame 1 shown in FIG. 5 may be configured as shown in FIG. This is to decrypt the format transmitted by the communication method specified in IEEE802.11a with the preamble transmitted by MIMO. When using a preamble transmitted by MIMO, the channel state can be estimated for all antenna combinations, and of course, the channel state of the channel that transmitted the MAC frame can also be obtained. That is, it is possible to decode the MAC frame portion of the format transmitted by the communication method specified in IEEE802.11a. Therefore, by using the preamble transmitted by MIMO, it is possible to decode the MAC frame in the format transmitted by the communication method specified in IEEE802.11a, and the frame as shown in FIG. 7 can be used as the channel information feedback request in FIG. It can be used in place of frame 1.

Hereinafter, each step of the communication procedure shown in FIG. 4 will be described in detail. &lt;First step (transmitting side receiving side)&gt; The channel information feedback request frame 1 shown in FIG. 5 is transmitted from the transmitting side to the receiving side. Here, the transmitting side transmits the preamble by the communication method specified in IEEE802.11a using one antenna. In addition, the preamble is transmitted by MIMO using three antennas. Data requesting feedback of channel information is stored in the MAC frame, and this is transmitted using the same single antenna as when transmitting the preamble based on the communication method specified in IEEE802.11a. Here, the data requesting feedback of channel information may be stored in either the header or the payload of the MAC frame.

In this step, a data frame may be used instead of the channel information feedback request frame 1, and data requesting feedback of the channel estimation result information may be added to general transmission data and transmitted by MIMO.

&lt;Second step (channel estimation process on the receiving side)&gt; On the receiving side, the channel information feedback request frame 1 is received. Here, channel estimation is performed using the preamble transmitted by the communication method specified in IEEE802.11a. In addition, channel estimation during communication by MIMO is performed using the preamble transmitted by MIMO. Next, the MAC frame portion is decoded based on the result of channel estimation using the preamble transmitted by the communication method specified in IEEE802.11a. By this decoding, it can be seen that the transmitting side is requesting feedback of the channel estimation result information during communication by MIMO, so the channel estimation result notification frame 2-1 for notifying the channel estimation result during communication by MIMO is set. create. Generally, the channel estimation result is represented by a complex number including phase and amplitude information, but the channel estimation result information fed back to the transmitting side may be simplified information instead of the complex number itself. For example, it is conceivable to feed back an approximate number obtained by quantizing a complex number or a bitmap expressing the quality of the channel state by a truth value (1/0) as channel estimation result information. By using the information summarizing the channel estimation result on the communication device side for channel estimation, it is possible to reduce the processing on the communication device side that receives the information.

&lt;Third step (receiver sender)&gt; The receiver sends back the channel estimation result notification frame 2-2 during communication by MIMO. Figure 8 shows an example of the format. In this step, the preamble is first transmitted by the communication method specified in IEEE802.11a using one antenna. Next, the preamble is transmitted by MIMO using three antennas. Then, the channel estimation result information at the time of communication by MIMO obtained in the second step is stored in the MAC frame, and this is used with the same antenna as when the preamble is transmitted by the communication method specified in IEEE802.11a. And send. Here, the data requesting the channel estimation result information may be stored in either the header or the payload of the MAC frame.

In the transmission of the preamble and the MAC frame, one antenna having a good channel condition can be selected based on the channel estimation result performed in the second step and transmitted by the communication method specified in IEEE802.11a.

Further, in this step, a data frame may be used instead of the channel estimation result notification frame 2-1 and the channel estimation result information may be added to the general transmission data and transmitted by MIMO.

&lt;Fourth step (channel estimation process on the transmitting side)&gt; The transmitting side receives the channel estimation result notification frame 2-1. First, channel estimation is performed using the preamble transmitted by the communication method specified in IEEE802.11a. Next, channel estimation during communication by MIMO is performed using the preamble transmitted by MIMO. The MAC frame part is decoded using the channel estimation result by the preamble of the communication method specified in IEEE802.11a. By this decoding, it can be seen that the channel estimation result information during communication by MIMO has been fed back from the receiving side, so the number of multiplexes when transmitting data by MIMO and the antenna used for transmission are determined based on the channel estimation result information. To do. At this time, it is possible to confirm the correctness of the channel estimation result between the two by comparing the channel estimation result during communication by MIMO with the channel estimation result during communication by MIMO on the receiving side fed back from the receiving side. it can. This is a work to be performed because the channel state from the transmitting side to the receiving side and the channel state from the receiving side to the transmitting side may not be completely equal depending on the configuration of the communication device or the like. In this way, the recognition inconsistency in the channel state between the transmitting side and the receiving side can be found before the data communication is started, and it becomes possible to set the communication parameters that can be tolerated by both.

&lt;Fifth step (sender receiver)&gt; In the fifth step, the transmitting side notifies the receiving side of the result information of the channel estimation performed on the transmitting side in the fourth step. At this time, when it is determined that the signal transmitted by MIMO can be correctly separated from the channel estimation result fed back from the receiving side in the third step, the channel estimation result notification frame 3-1 or 3-2 Is used. Figure 9 shows an example of the format of the channel estimation result notification frame 3-1 and Fig. 10 shows an example of the format of the channel estimation result notification frame 3-2. When using either of these channel estimation result notification frames 3-1 or 3-2, the number of transmission antennas determined in the fourth step and the number of transmitting antennas are used, and the result is obtained in the fourth step. The channel estimation result information on the transmitted side is multiplexed and the MAC frame unit is transmitted. On the other hand, from the channel estimation result fed back from the receiving side in the third step, it is judged that the signal transmitted by MIMO cannot be correctly separated on the receiving side, and it is impossible to multiplex the information and transmit it with multiple antennas. When this is done, channel estimation result notification frame 3-3 is used. Figure 11 shows an example of the format of frame 3-3. In this case, MIMO communication is not possible and only one antenna can be used for transmission and reception. Therefore, the MAC frame unit that stores the channel estimation result information on the transmitting side obtained in the fourth step transmits with one antenna. Also, regardless of whether the signal transmitted by MIMO can be correctly separated on the receiving side, the result of channel estimation performed on the transmitting side in the fourth step using frame 2-1 as in the third step. Information may be sent. Further, in this step, even if a data frame is used instead of the channel estimation result notification frames 3-1, 3-2, and 3-3, and channel estimation result information is added to general transmission data and transmitted by MIMO. Good.

By executing the first to fifth steps described above, the transmitting side communication terminal and the receiving side communication terminal can know each other's channel estimation results. As a result, the transmitting side can transmit data by selecting the information multiplexing number and the antenna used for transmission so that the receiving side can correctly separate the information.

In the present embodiment, in the fourth step, the transmitting side determines the information multiplexing number and the antenna to be used for transmission based on the channel estimation result fed back from the receiving side, but the receiving side performs channel estimation. At that time, it is conceivable that the receiving side determines the information multiplex and the transmitting antenna based on the channel estimation information, and feeds back the information multiplex and the antenna used for transmission to the transmitting side instead of the channel estimation result.

(Second Embodiment) In the second embodiment of the present invention, in the same wireless system as the first embodiment, the communication procedure for feeding back the channel information is different from that of the first embodiment. In the present embodiment, the channel estimation result information is not transmitted to each other between transmission and reception, but only the preamble for channel estimation is transmitted to cause the other party to estimate the channel. FIG. 12 shows a communication procedure according to this embodiment.

&lt;First step (transmitting side receiving side)&gt; The first step is the same as that of the first embodiment.

&lt;Second step (channel estimation process on the receiving side)&gt; First, the receiving side receives the channel information feedback request frame 1. Next, channel estimation is performed using the preamble transmitted by the communication method specified in IEEE802.11a. Next, channel estimation during communication by MIMO is performed using the preamble transmitted by MIMO. Then, the MAC frame portion is decoded using the channel estimation result based on the preamble transmitted by the communication method specified in IEEE802.11a. By this decoding, it can be seen that the transmitting side is requesting feedback of the channel estimation result information at the time of communication by MIMO. In this step, it is also possible to determine the number of information multiplexes and the transmitting antenna to be used when transmitting data from the receiving side to the transmitting side based on the channel estimation result at the time of communication by MIMO.

&lt;Third step (reception side transmission side)&gt; The transmission side returns the channel estimation result frame 2-2 for the transmission side to perform channel estimation during communication by MIMO from the reception side to the transmission side. Figure 13 shows an example of the format of the channel estimation result frame 2-2.

First, the preamble is transmitted by the communication method specified in IEEE802.11a using one antenna. Next, the preamble is transmitted by MIMO using three antennas. Then, the MAC frame containing only the MAC header is transmitted using the same antenna as when the preamble was transmitted by the communication method specified in IEEE802.11a.

The channel estimation result frame to be transmitted at this time may be the channel estimation result frame 2-1 as shown in FIG. 8 as long as the channel can be estimated at the time of transmission by MIMO.

For the transmission of the preamble by the communication method specified in IEEE802.11a, one antenna with a good channel condition can be selected and used based on the channel estimation result performed in the second step.

&lt;Fourth step (channel estimation process on the transmitting side)&gt; The transmitting side receives the channel estimation result frame 2-2. Next, channel estimation is performed using the preamble transmitted by the communication method specified in IEEE802.11a. In addition, channel estimation during communication by MIMO is performed using the preamble transmitted by MIMO. Then, based on the channel estimation result information during communication by MIMO, the number of multiplexes when transmitting data by MIMO and the antenna used for transmission are determined.

According to the second embodiment, by omitting the step of notifying the receiving side of the channel estimation result on the transmitting side from the transmitting side, it is possible to reduce the overhead required for the notification on the receiving side as compared with the first embodiment.

(Third Embodiment) The third embodiment of the present invention is configured to execute a preparatory step prior to the first step in a wireless system similar to the first or second embodiment. In the preparation step, the physical layer capability information such as the number of antennas possessed by each device is exchanged between the transmitting side and the receiving side using the physical layer capability information notification frame shown in FIG. In the channel estimation result information unit of the MAC frame in this physical layer capability information notification frame, physical layer capability information such as the number of antennas possessed by the own device is stored instead of the channel estimation result. By executing the preparation step and obtaining information such as the number of antennas of each other, it is possible to add a preamble of the physical header to the MAC frame so that channel estimation during communication by MIMO according to the number of antennas is possible. Therefore, in the first to fifth steps executed after the preparation step, the preamble used for MIMO communication set to the necessary and sufficient length and configuration for channel estimation during communication by MIMO is set from the channel information feedback request frame 1. It can be used for the physical layer capability information notification frame.

Instead of the preparation step, the beacon frame transmitted by the AP (Access Point) stores physical layer capability information such as the number of antennas of the AP and each terminal and exists in the BSS (Basic Service Set) of the AP. All terminals may be notified. Further, the physical layer capability information of the own terminal may be stored in the probe request frame or probe response frame broadcast by each terminal to the peripheral terminals and notified to the peripheral terminals. Further, the physical layer capability information of the own terminal may be stored in the association request frame from the terminal or the association response frame from the AP and notified to the peripheral terminals.

By either of these methods, each terminal can know the physical layer capability of the other party with whom it wants to communicate in advance, and when executing the first to fifth steps, the physical layer capability information notification from the channel information feedback request frame 1 The preamble used for MIMO communication of the frame can be set to the length and configuration according to each other's physical layer ability.

The present invention is not limited to the above-described embodiment as it is, and at the implementation stage, the components can be modified and embodied within a range that does not deviate from the gist thereof. In addition, various inventions can be formed by an appropriate combination of the plurality of components disclosed in the above-described embodiment. For example, some components may be removed from all the components shown in the embodiments. In addition, components across different embodiments may be combined as appropriate.

<figref num="1">The figure which shows an example of the schematic structure of the communication device which concerns on embodiment of this invention.</figref><figref num="2">The figure which shows an example of the configuration example of the MIMO channel in the communication system which concerns on embodiment of this invention.</figref><figref num="3">The figure which shows an example of the communication procedure which concerns on 1st Embodiment of this invention.</figref><figref num="4">The figure which shows an example of the format of the physical frame which concerns on 1st Embodiment of this invention.</figref><figref num="5">The figure which shows an example of the format of the channel information feedback request frame 1 which concerns on 1st Embodiment of this invention.</figref><figref num="6">Diagram for explaining that in MIMO, data may not be separated depending on the transmission line environment.</figref><figref num="7">Diagram showing another example of the format of channel information feedback request frame 1.</figref><figref num="8">The figure which shows an example of the format of the channel estimation result notification frame 2-1 which concerns on 1st Embodiment of this invention.</figref><figref num="9">The figure which shows an example of the format of the channel estimation result notification frame 3-1 which concerns on 1st Embodiment of this invention.</figref><figref num="10">The figure which shows an example of the format of the channel estimation result notification frame 3-2 which concerns on 1st Embodiment of this invention.</figref><figref num="11">The figure which shows an example of the format of the channel estimation result notification frame 3-3 which concerns on 1st Embodiment of this invention.</figref><figref num="12">The figure which shows an example of the communication procedure which concerns on 2nd Embodiment of this invention.</figref><figref num="13">The figure which shows an example of the format of the channel estimation result frame 2-2 which concerns on 2nd Embodiment of this invention.</figref><figref num="14">The figure which shows an example of the format of the physical layer capacity information notification frame which concerns on 3rd Embodiment of this invention.</figref>

Code description

100 MAC layer 200 Physical layer 300 Antenna 400 Physical frame 401 Preamble (11a) 402 Preamble (MIMO)