Communication device, communication method and communication system

The present invention relates to a communication device, a communication method, and a communication system that perform medium access control based on the carrier sense information of the physical layer and the carrier sense information of the MAC layer.

Media access control (MAC) determines how a plurality of communication devices that share the same medium and communicate with each other use the medium to transmit communication data. In media access control, as a result of two or more communication devices transmitting communication data using the same medium at the same time, the event (collision) in which the communication device on the receiving side cannot separate the communication data is reduced as much as possible. On the other hand, it is a technique for controlling access from a communication device to a medium so that there are as few events as possible in which the medium is not used by any communication device even though there is a communication device having a transmission request.

However, especially in wireless communication, it is difficult for a communication device to monitor transmitted data at the same time as transmitting data, so medium access control (MAC) that does not presuppose collision detection is required. IEEE 802.11, which is a typical technical standard for wireless LAN, is CSMA / CA (Carrier Sense Multiple Access with Collision). Avoidance) is adopted. In IEEE802.11 CSMA / CA, a period (Duration) until the end of a series of sequences consisting of one or more frame exchanges following the frame is set in the header of the MAC frame. During this period, the communication device, which has nothing to do with the sequence and does not have the transmission right, waits for transmission by determining the virtual occupancy state of the medium. Therefore, the occurrence of collision is avoided. On the other hand, the communication device having the transmission right in the sequence recognizes that the medium is not used except for the period when the physical medium is actually occupied. IEEE802.11 stipulates that the state of the medium is determined by the combination of the virtual carrier sense of the MAC layer and the physical carrier sense of the physical layer, and the medium access is controlled.

IEEE 802.11, which uses CSMA / CA, has been trying to increase the communication speed mainly by changing the physical layer protocol. The 2.4GHz band has changed from IEEE 802.11 (1997, 2Mbps) to IEEE 802.11b (1999, 11Mbps) and then to IEEE 802.11g (2003, 54MHz). For the 5GHz band, only IEEE802.11a (1999, 54MHz) currently exists as a standard. And IEEE 802.11 TGn (Task Group n) has already been established to formulate standards aiming for further speedup in both the 2.4 GHz band and the 5 GHz band.<patcit num="1"><text>U.S. Pat. No. 5,329,531</text></patcit>

<p> If the same frequency band as the existing standard is used to realize high communication speed, the newly provided communication device can coexist with the communication device that complies with the existing standard, and is backward compatible. It is preferably maintained. Therefore, it is considered that the MAC layer protocol should basically follow CSMA / CA, which is consistent with existing standards. In this case, it is necessary to align the time parameters related to CSMA / CA, such as the interframe space (IFS) and backoff period, with the existing standards.</p><p> Here, even if the communication speed of the physical layer can be increased, there is a problem that the actual throughput of communication cannot be improved. That is, when the physical layer is increased in speed, the PHY frame format is no longer efficient, and the overhead caused by this is considered to hinder the improvement in throughput. In the PHY frame, the temporal parameters related to CSMA / CA are fixedly attached to the MAC frame. In addition, a PHY frame header is required for each MAC frame.</p><p> One way to reduce overhead and improve throughput is Block ACK, which was introduced in the recent draft IEEE802.11e draft 5.0 (IEEE802.11 QoS enhancements). By using this, since a plurality of MAC frames can be transmitted continuously without backoff, the amount of backoff can be reduced, but the header of the physical layer is not reduced. Also, according to the aggregation introduced in the early draft IEEE802.11e, both the backoff amount and the physical layer header can be reduced, but due to the restrictions of the conventional physical layer, the frame length of the physical layer including the MAC frame. Since it cannot be more than about 4 kbytes, there is a big limitation in improving efficiency. Even if the frame of the physical layer can be lengthened, there is a problem that the error tolerance is lowered.</p><p> The present invention has been made to solve such a problem, can coexist with an existing device, and eliminates the overhead associated with transmitting a plurality of frames by improving the efficiency of the frame format for communication. It is an object of the present invention to provide a communication device, a communication method, and a communication system capable of improving a substantial throughput.</p>

<p> The communication device according to one aspect of the present invention includes a physical frame construction means for constructing a physical frame having a medium access control superframe payload including a plurality of medium access control frames, and the physical frame constructed by the physical frame construction means. The virtual carrier sense information is set in the plurality of medium access control frames so that the result of the carrier sense is the same even by the virtual carrier sense based on the plurality of medium access control frames in the medium access control super frame payload. It includes one setting means and a transmission means for transmitting a physical frame in which virtual carrier sense information is set by the first setting means to a destination communication device.</p>

<p> According to the present invention, a communication device that can coexist with an existing device and can improve the substantial throughput of communication by eliminating the overhead associated with transmitting a plurality of frames by improving the efficiency of the frame format. , Communication methods, and communication systems can be provided.</p>

(First Embodiment) FIG. 1 is a block diagram showing a configuration of a communication device according to the first embodiment of the present invention. The communication device 100 is a device that communicates with other communication devices via a wireless link, and has processing units 101, 102, and 103 corresponding to the physical layer, the MAC layer, and the link layer, respectively. These processing units are realized as analog or digital electronic circuits depending on the mounting, or as firmware executed by a CPU incorporated in an LSI. An antenna 104 is connected to a processing unit (hereinafter, the notation of "processing unit" is omitted) 101 of the physical layer. The MAC layer 102 has an aggregation processing unit 105 according to the present invention. The aggregation processing unit 105 includes at least a carrier sense control unit 106 in the first embodiment. The retransmission control unit 107 shown in the figure relates to the second embodiment of the present invention, and the power saving control unit 108 relates to the third embodiment. These will be described in detail in the applicable embodiments. The physical layer 101 is configured to support two types of physical layer protocols. For each protocol processing, the physical layer 101 has a first-class physical layer protocol processing unit 109 and a second-class physical layer protocol processing unit 110. In the implementation, circuits are often shared between the first-class physical layer protocol processing unit 109 and the second-class physical layer protocol processing unit 110, so these do not necessarily exist independently. ..

In the embodiment of the present invention, the first-class physical layer protocol is a protocol specified in IEEE802.11a, and the second-class physical layer protocol uses a plurality of antennas on the transmitting side and the receiving side, respectively, so-called MIMO (. Multiple Input Multiple Output) is assumed. MIMO is one of the technologies that can be used to aim for even higher throughput of IEEE 802.11 because the transmission capacity can be expected to increase in proportion to the number of antennas even if the frequency band is kept the same. The link layer 103 shall have a normal link layer function defined by IEEE802. The technology adopted to improve the transmission rate is not limited to MIMO. For example, a method of increasing the frequency occupied band or a combination of the method and MIMO may be used.

FIG. 2 is a diagram showing an example of a frame format used by the communication device according to the embodiment of the present invention. The frame format 200 roughly shows the frame structure related to the physical layer and the MAC layer, and specifically, it is assumed that the frame format conforms to IEEE 802.11 or its extension. The IEEE802.11 frame is roughly classified into three types, a control frame, a management frame, and a data frame. It is assumed that the embodiment of the present invention is mainly applied to the data frame, but the control frame, The application to the management frame is not excluded. As shown in FIG. 2, the frame format 200 is composed of a PHY header 201, a MAC super frame header 202, a MAC super frame payload 203, and a PHY trailer 204. The MAC super frame header 202 and the MAC super frame payload 203 correspond to the PHY payload described later.

The PHY header 201 is processed by the physical layer 101 of the receiving communication device. That is, the physical layer 101 detects the frame head, carrier sense, timing synchronization establishment, amplifier amplification control (AGC: Automatic Gain Control), and follows the transmitting carrier frequency (Automatic Frequency Control) based on the received PHY header 201. ), Estimate the transmission line, etc. The physical layer 101 also detects the modulation method and coding rate of the PHY payload following the PHY header 201, as well as the transmission rate and data length.

FIG. 3 is a diagram showing an example of the format of the first type PHY frame. This format is the same as that specified in IEEE 802.11a. The first-class PHY frame is used when the communication device according to the present invention communicates with an existing communication device, and is processed by the first-class physical layer protocol processing unit 109 of the physical layer 101 (here, IEEE802. Communication by 11a). As shown in FIG. 3, the first-class PHY frame, that is, the first-class PLCP frame is composed of a PLCP (Physical Layer Convergence Protocol) short preamble 301 and a PLCP long preamble 302, a signal field 303, and a data field 304. Will be done. The signal field 303 corresponds to the PCLP header 305 and has a transmission rate (Rate) field 306 and a data length (Length) field 307 as shown in the figure. Needless to say, the first-class PHY frame is not limited to those specified in IEEE802.11a.

FIG. 4 is a diagram showing an example of the format of the second type PHY frame. The second type PHY frame, that is, the second type PLCP frame, has a first header part 401 for the first type physical layer protocol and a second header part 402 for the second type physical layer protocol. Has. The first header section 401 and the second header section 402 are arranged in chronological order and correspond to the PHY header 201 shown in FIG. Further, the second type PHY frame has a PHY payload 403 following the second header portion 402, and a tail and pad bits 404. The PHY payload 403 corresponds to the MAC super frame header 202 and the MAC super frame payload 203 in FIG. 2, and corresponds to the PSDU (PLCP Service Data Unit) in the physical layer format. In addition, the tail and pad bit 404 correspond to the PHY trailer 204 in FIG.

The first header section 401 for the first-class physical layer protocol is composed of a PLCP short preamble 405, a PLCP long preamble 406, and a signal field 407. The signal field 407 corresponds to all or part of the PLCP header, and at least the transmission rate field 408 and the data length field 409 are set with valid values so that physical carrier sense can be performed. Such a signal field 407 has the same information content and modulation method as those of the PLCP header 305 of the first-class PHY frame shown in FIG.

The second header section 402 for the second type physical layer protocol is composed of a PLCP long preamble 410 for MIMO, a MIMO signal field 411, and a MIMO service field 412. The MIMO signal field 411 has a transmission rate field 413 and a data length field 414 as shown in the figure and is referred to in the physical carrier sense. The PLCP long preamble 410 for MIMO is used when the receiving side communication device of MIMO capable of interpreting the second type physical protocol acquires the transmission line information necessary for the decoding process.

By formatting the second type PHY frame as shown in FIG. 4, an existing communication device that can operate only according to the first type physical layer protocol can interpret at least the first signal field 407, so that the signal field. The carrier sense of the physical layer can be correctly performed based on 407. Therefore, it is possible to share the carrier sense information of the same physical layer between such an existing communication device and a communication device that can operate according to the second type physical layer protocol in addition to the first type. Become. It should be noted that the existing communication device cannot share the carrier sense information of the MAC layer, but this does not become a problem due to the partial ACK described later.

Information representing the medium occupancy period (hereinafter, referred to as physical occupancy period) by the PHY payload when the PHY payload is transmitted on the physical medium is used as carrier sense information of the physical layer together with the signal strength. When the receiving side communication device knows the physical occupancy period of the PHY payload by the physical carrier sense, it interprets the period as PHY busy. In addition, it is interpreted that the physical medium is occupied even during the period when the signal strength exceeds a certain threshold value. The physical occupancy period of the PHY payload can be calculated from the transmission rate (408 or 413) and data length (409 or 414) of the PHY payload detected by the receiving communication device. Specifically, it can be obtained by dividing the value of the data length field represented by the octet length by the value of the transmission rate field. This also applies to the first-class PHY frame shown in FIG.

Note that the maximum data length of the PHY payload allowed by the first-class physical layer protocol (4096 octets in IEEE802.11a) is actually larger than the maximum data length of the PHY payload allowed by the second-class physical layer protocol. If it is short, the carrier sense information of the physical layer can be shared by intentionally falsely setting the transmission rate field 408 and the data length field 409 so that the physical occupancy period of the PHY payload is appropriate. ..

Now, we return to the description with reference to FIG. One MAC superframe consists of a single PHY frame containing multiple MAC frames. In the frame format 200 shown in the figure, the MAC super frame header 202 has eight MAC frame data length fields 1 to 8 fixedly. In the present embodiment, the MAC super frame header 202 has a fixed length, but the MAC super frame header 202 may have a variable length by adding information indicating the number of MAC frames.

As shown in FIG. 2, if the MAC superframe payload 203 contains only four MAC frames 1 to 4, the MAC frame data length fields 5 to corresponding to MAC frames 5 to 8 that do not exist in the payload 203 8 is filled with a value of zero. Further, in the case of retransmission control described later, for example, when MAC frame 1 and MAC frame 3 need to be retransmitted, but MAC frame 2 and MAC frame 4 do not need to be retransmitted, MAC frame data length 1&gt; 0, MAC frame. The MAC frame data length can be set to zero even when a MAC frame that is not the target of retransmission is specified, such as data length 2 = 0, MAC frame data length 3&gt; 0, and MAC frame data length 4 = 0.

HCS205 is a header check sequence, and is added to the header 202 in order to detect an error in the MAC super frame header 202. When the receiving communication device detects an error in the MAC super frame header 202 by the HCS 205, it is interpreted that all the MAC frames included in the MAC super frame payload 203 are broken.

In order to prevent buffer overflow in the receiving communication device, it is preferable to dynamically limit the number of MAC frames included in the MAC superframe payload 203. For this, for example, the Sliding Window control described later can be used.

FIG. 5 is a diagram showing an example of the MAC frame format. One MAC frame included in the MAC super frame payload 203 of FIG. 2 is composed of a MAC header 500, a frame body 501, and an FCS (frame check sequence) 502. The MAC header 500 is composed of a frame control field 503, a duration field 504, address fields 505 to 507,509, and a sequence control field 508. The frame body 501 has a variable length in the range of 0 to 2312 octets, and is a payload of a MAC frame corresponding to an MPDU (MAC Protocol Data Unit).

With the speeding up of the physical layer by the second type physical layer protocol (MIMO in this embodiment), in this embodiment, the format is efficiently configured by including a plurality of MAC frames in the PHY frame as MAC super frames. Therefore, it is possible to avoid the overhead of each PHY frame due to the format, that is, PLCP header, various IFS (Inter Frame Space), backoff, etc., and improve the substantial throughput of communication.

Medium access control is performed based on the carrier sense of the physical layer and the carrier sense of the MAC layer. Hereinafter, the robust MAC layer carrier sense related to the characteristics of the first embodiment will be described. FIG. 6 is a diagram showing an example of a communication system according to an embodiment of the present invention. In this communication system, communication devices 1 to 4 shall communicate via a wireless link. The communication devices 1 to 3 shown in the figure have the configuration shown in FIG. On the other hand, the communication device 4 includes only the first-class physical layer protocol processing unit 109 and does not include the second-class physical layer protocol processing unit 110, and therefore does not transmit the MAC superframe. Corresponds to. Hereinafter, the description will be made on the assumption that communication is performed with the communication device 1 as the transmitting side and the communication device 2 as the receiving side, and the communication device 3 and the communication device 4 are not involved in this communication.

As described with reference to FIGS. 2 and 5, each of the MAC frames contained in the MAC superframe payload 203 can detect an error in the MAC header 500 and the entire MAC frame including the MAC header 500, FCS502. And include. When constructing the MAC superframe payload 203 to be transmitted, the communication device 1 on the transmitting side sets the value of the period field 504 of each MAC header 500 of each MAC frame as follows. That is, if at least one MAC frame included in the MAC superframe payload 203 is normally received, a value is set so that the communication device 2 that has received the MAC frame can correctly recognize the carrier sense state of the MAC layer. Specifically, for example, either method 1 or method 2 described below is followed.

(Method 1): The value of the period starting from the time when the PHY frame including the MAC super frame 203 ends and ending when the exchange of MAC frames defined as a continuous sequence in the MAC layer is completed. Alternatively, the period field 504 is set to the value of the period ending at the time when the medium reservation performed in the MAC layer is completed. According to Method 1, the same value is set in the period field 504 of at least a plurality of MAC frames included in the MAC superframe 203 (see FIG. 7).

(Method 2): The value of the period starting at the end of the MAC frame containing the period field and ending at the end of the exchange of MAC frames defined as a continuous sequence in the MAC layer, or MAC. Set the period field 504 to the value of the period ending at the end of the medium reservation performed in the layer. According to the method 2, different values are set in the period field 504 of the MAC frame included in the MAC superframe 203 (see FIG. 8).

Further, the destination address set in any of the address fields 505 to 507,509 (specifically, corresponding to address 1 or address 3) in the MAC header 500 in each MAC frame is set as follows. That is, the MAC address of the corresponding communication device is set so that each MAC frame in the same MAC super frame indicates the same destination.

In this example, the communication device 2 having the MAC address corresponding to the destination address is normally involved in the MAC frame exchange sequence of the period specified in the period field 504, and has the transmission authority according to the rules of the MAC frame exchange sequence. On the other hand, the communication devices 3 and 4 that do not correspond to the destination address are not involved in the MAC frame exchange sequence and do not have the transmission authority during this period.

The communication device 3 that is not involved in the MAC frame exchange sequence refers to the value of the period field 504 in the MAC header 500 of any of the received MAC frames, and the medium is virtual (logical) for the period corresponding to this value. It is interpreted as being occupied, and the frame is not transmitted until the end of the period. Such a period is referred to as a "virtual medium occupancy period". Therefore, the communication device 3 sets a NAV (Network Allocation Vector) to prevent transmission during the virtual medium occupancy period. The NAV setting based on the virtual carrier sense of the MAC layer is performed regardless of the physical medium occupancy period based on the carrier sense of the physical layer. On the other hand, the existing communication device 4 which is not involved in the MAC frame exchange sequence like the communication device 3 enters the standby state during the EIFS (Extended IFS) period. The details of the operation of the existing communication device 4 in this case will be described later.

In the embodiment of the present invention, since a plurality of MAC frames are integrated into one PHY frame, it is possible to robustly perform the carrier sense of the MAC layer and appropriately set the virtual medium occupancy period.

FIG. 7 shows an example of the carrier sense state of each communication device when the value of the period field 504 is determined according to the above method 1. The value of the period field 504 of MAC frame 1, MAC frame 2, MAC frame 3 and MAC frame 4 is set to the sum of SIFS (Short IFS) and the transmission time of the partial ACK frame shown in FIG. ..

It is necessary to set a rule so that the receiving side can uniquely select the method of transmitting the partial ACK so that the transmitting side communication device 1 can calculate the transmission time of the partial ACK. Partial ACK is carried by the PHY frame of IEEE802.11a, which is the first type of physical protocol shown in Fig. 3, and is assumed to be transmitted at the maximum required transmission rate of IEEE802.11a. As will be described later, it is important for backward compatibility that the partial ACK can be decoded and interpreted by a communication device that can interpret only the first-class physical protocol.

When the receiving side communication device 2 receives the frame transmitted by the transmitting side communication device 1, the receiving side communication device 2 first recognizes that the medium is busy, that is, in an occupied state by the carrier sense of the physical layer. In addition, the communication device 3 (the local address is different from the destination address and the source address specified in the MAC frames 1 to 4 and can interpret the first-class and second-class physical protocols), the communication device 4 (the first). (Only one type of physical protocol can be interpreted) also recognizes that the medium is occupied by the carrier sense of the physical layer.

Next, if any of MAC frame 1 to MAC frame 4 is determined by FCS to be correct, the communication device 2 on the receiving side sets the NAV because the destination address is the address of the communication device 2. Know that you don't have to. The communication device 2 on the receiving side transmits a partial ACK after SIFS has elapsed from the completion of receiving the second type PHY frame including the MAC super frame, in accordance with the rules of the MAC frame exchange sequence.

If any of MAC frame 1 to MAC frame 4 is determined by FCS to be correct, the communication device 3 knows that the destination address should be set to NAV instead of the address of the communication device 3. .. The communication device 3 has a period corresponding to the value of the period field 504 included in any of MAC frame 1 to MAC frame 4 determined to be correct by the FCS from the completion of receiving the second type PHY frame including the MAC super frame. Set the NAV of.

The existing communication device 4 cannot interpret the signal field and subsequent fields of the second type PHY frame, and proceeds with the processing assuming that this is the first type PHY frame. Then, at the end of the frame, the FCS is calculated and an error is detected. Alternatively, it also detects an error at the end of the frame, assuming it is an uninterpretable type of PHY frame. In these cases, the communication device 4 does not correctly recognize the virtual carrier sense state of the MAC layer to be set by receiving the PHY frame, and therefore enters the error recovery state. That is, it enters the waiting state for the EIFS period, which is the longest IFS. In this standby state, the communication device 4 receives the partial ACK issued by the receiving side communication device 2 before the end of EIFS. As described above, since the partial ACK is transmitted at the required rate of IEEE802.11a, which is a first-class physical layer protocol, it can be interpreted by the existing communication device 4. If this partial ACK is received correctly, the carrier sense of the MAC layer is performed correctly, so the standby state by EIFS is canceled and there is no problem. Therefore, the communication device according to the present invention can coexist with the existing (conventional) communication device.

The transmitting side communication device 1, the communication device 3, and the existing communication device 4 receive the partial ACK transmitted by the receiving side communication device 2. The value of the period field 504 in this partial ACK is set to 0, and each communication device sets the NAV to zero accordingly. In the MAC sequence, a MAC frame exchange sequence following the partial ACK may be defined. In that case, the value of the period field 504 in the partial ACK becomes a value indicating the end point of the MAC sequence.

If all communication devices have data to be transmitted, they continue to enter the standby state by DIFS (DCF IFS, that is, Distributed Coordinate Function IFS). In this DIFS period, if the carrier sense of the physical layer and the MAC layer indicates an idle state, the backoff period is entered and the countdown is started. The communication device whose counter, which has been initialized with a random number, first reaches zero, gains transmission authority.

Here, an error when receiving a second type PHY frame will be described. Consider the case where the communication device 2 decodes the MAC frame included in the second type PHY frame, and as a result, there is no MAC frame determined to be correct by the FCS. If there is no MAC frame determined by FCS to be error-free, the communication device 2 cannot correctly recognize the virtual carrier sense state of the MAC layer that should be set based on the reception of the second type PHY frame. Therefore, it transitions to the error recovery state. In other words, it transitions to the waiting state for the EIFS period, which is the longest IFS. When the communication device 3 that is not the receiving side transitions to the standby state during the EIFS period, the partial ACK transmitted by the receiving communication device 2 is subsequently received. If the partial ACK is correctly received, the carrier sense of the MAC layer is correctly performed as described later, and the standby state by EIFS is canceled at this time.

If the above error at the time of reception occurs, the receiving side communication device 2 will transition to the standby state during the EIFS period without sending a partial ACK. In this case, if the EIFS period is longer than the period by NAV and DIFS, there will be a situation in which none of the communication devices can transmit at least during this period. Since this event reduces the utilization efficiency of the physical medium used for communication, it should be avoided as much as possible.

However, according to the embodiment of the present invention, since the MAC superframe payload 203 includes a plurality of MAC frames, it is possible to obtain carrier sense information of the MAC layer based on any of these plurality of MAC frames. As a result, the above-mentioned error at the time of reception is less likely to occur. Specifically, a plurality of MAC frames among the MAC frames included in the MAC superframe are necessary for the carrier sense of the MAC layer, that is, the carrier sense of the MAC layer including at least the period field 504 and the destination address. Have information. Since each of these MAC frames has an FCS, it is possible to detect the presence or absence of an error, and even if an error occurs in the reception of any of the MAC frames, at least one of the remaining MAC frames will be normal. It should be received. Therefore, the carrier sense of the MAC layer can be robustly performed based on at least one MAC frame that can be normally received, and the error tolerance at the time of reception per one PHY frame can be relatively increased.

FIG. 8 shows an example of the carrier sense state of each communication device when the value of the period field 504 is determined according to the above method 2. To briefly explain only the difference from FIG. 7, the value of the period field 504 of MAC frame 1 is the transmission time of MAC frame 2, MAC frame 3, and MAC frame 4, the SIFS period, and the transmission time of the partial ACK frame. Set to the sum value. The value of the period field 504 of MAC frame 2 is set to the value of the sum of the transmission time of MAC frame 3 and MAC frame 4, the SIFS period, and the transmission time of the partial ACK frame. The value of each period field 504 of MAC frame 3 and MAC frame 4 is also set in the same manner. That is, unlike the case of FIG. 7, the value of the period field 504 is different for each MAC frame, and the NAV setting is also different accordingly.

For NAV by communication device 3 (the local address is different from the destination address and source address of MAC frame 1 to MAC frame 4 and can interpret the first and second type physical protocols), the period field 504 is included. The value will be set starting from the end point of the MAC frame that was there.

Even in such method 2, the media occupancy time due to the transmission of the MAC super frame ends at the same time as can be seen from FIG.

(Second Embodiment) The second embodiment of the present invention relates to power saving control. FIG. 10 is a diagram for explaining power saving control according to the second embodiment of the present invention. According to the present embodiment, the transmitting side communication device 1 and the receiving side communication device 2 during communication can be controlled so as not to switch to the power saving state, and the communication device not involved in communication can be controlled to switch to the power saving state. It becomes.

When any of the MAC frames included in the MAC super frame included in the second type PHY frame is recognized by the FCS, the communication device 3 terminates the NAV set by the communication device 3 itself. Knowing that it is not necessary to receive or transmit for the period up to, the power saving operation is started from that point. However, this is conditioned on the fact that each MAC frame is encoded in a PHY frame so that each MAC frame is decoded in chronological order on the receiving side.

Since it is necessary to perform carrier sense during the DIFS period and backoff period after the end of NAV, the power saving state ends at the end of NAV. By recognizing the power saving state, it is possible to save power by stopping unnecessary circuits. Specifically, which circuit is stopped at what timing and restarted at what timing depends on the implementation.

The existing communication device 4 also recognizes the duration of the second type PHY frame based on the signal of the second type PHY frame, and this PHY frame is transmitted in a manner that the communication device 4 cannot decode. When it is recognized that the PHY frame is present, the period until the end of the PHY frame can be recognized as a power saving state. However, since it is necessary to perform carrier sense during the EIFS period, it is not in a power saving state.

(Third Embodiment) The third embodiment of the present invention relates to retransmission control. From the viewpoint of communication fairness and QoS (Quality Of Service), it is preferable to control retransmission in order to avoid continuity to the same terminal. FIG. 11 is a diagram showing a transmission management table used for retransmission control according to the third embodiment of the present invention. In this transmission management table, a sliding window is represented. For convenience of explanation, the transmission management table shows all the histories of transmission and reception including retransmission, but the actual communication device does not necessarily have to store all the histories listed here.

Consider a situation in which the same transmitting side communication device continuously transmits a MAC frame (MPDU) to the same receiving side communication device in preference to the communication of other frames. To avoid biased transmission and reception rights to a particular communication device, limit the number of MAC frames that can be transmitted continuously based on the transmission management table. This restriction is in effect until either the transmitting side communication device or the receiving side communication device is changed.

In the transmission management table shown in FIG. 11, the maximum number of MAC frames that can be transmitted continuously is set to 16, which is called the total window W_all. In addition, a sequence number (Seq.No.) Is assigned to a series of MAC frames (MPDUs) to be continuously transmitted in the transmission management table. The start point of the total window W_all is SEQ1, and its end point corresponds to SEQ16. The transmission (or retransmission) of the frames included in this total window W_all is set as one delimiter, and is performed based on a series of transmission sequences (or retransmission sequences) described later. The total window W_all may be made variable in consideration of the congestion situation, the priority given to the receiving side communication device, and the like. Increasing the total window W_all increases delays and jitter, inequity between communication devices, etc., but tends to improve overall throughput. Therefore, when it is recognized that real-time communication of voice or moving image exists, dynamic control such as reducing the size of the total window may be performed. Since such control tends to reduce the overall throughput itself, it is better to use it in combination with some kind of traffic control such as priority control according to the traffic type.

In addition, the maximum value of the total window W_all and the window W_n (n = 1, 2, 3, ...) at each time point is set by negotiating with some protocol for each pair of communication devices on the transmitting side and the receiving side. Alternatively, the values may be common to the entire system. Even if the value is common to all systems, it does not necessarily have to be a fixed value.

The retransmission control unit 107 of the communication device on the transmitting side constructs a MAC superframe while referring to the transmission management table. At this time, the retransmission control unit 107 selects the MAC frame to be included in the MAC super frame while considering the necessity of retransmission.

Multiple MAC frames are included in a single MAC superframe, but the maximum number of MAC frames that can be stored is limited. In this embodiment, a maximum of eight MAC frames can be included. The receiving communication device needs to be able to buffer up to this maximum number of MAC frames. The receiving side communication device passes the MAC frame to the upper part of the MAC layer in a stored order. As a result, even if the MAC frame is normally received, it is determined that the MAC frame having the sequence number preceding it is not normally received by retransmission, or the MAC frame having the preceding sequence number is not retransmitted. Need to be stored in the buffer. In the buffer, MAC frames having the lowest sequence number that has not yet succeeded in normal reception to MAC frames having the lowest sequence number + 7 sequence number are accumulated.

In FIG. 11, the range of this sequence number at each time point is represented by windows W1 to W5 as a start point and an end point, respectively. The MAC frame that the transmitting communication device should include in the MAC superframe and send is within the range of this window, the MAC frame that needs to be resent because the delivery has not been confirmed, or the MAC frame that needs to be resent within the range of this window is newly transmitted. Limited to MAC frames. In FIG. 11, when "LenX" is written in TX1 to TX5, the MAC frame of sequence number X is transmitted by the transmission of the corresponding MAC super frame, and when it is written as "zero", it corresponds. The MAC frame of the sequence number to be used is not transmitted. These values correspond to the data length fields 1 to 8 of the MAC frame in the MAC super frame header 202 shown in FIG. If it is "" in RX1 to RX5, it means that the MAC frame of the corresponding sequence number has already been received normally. When RX1 to RX5 are "x", this indicates that the MAC frame of the corresponding sequence number has not been normally received by that time. These "" and "×" correspond to boolean values, and correspond to the value of Partial ACK Bitmap 91 in the partial ACK frame shown in FIG.

The head of windows W1 to W5 at each time point is the sequence number of the MAC frame that the receiving communication device has never normally received. A lower limit of the progress rate of the start point of this window is set, and the limit is limited to exceeding the lower limit after passing a predetermined number of retransmissions, that is, the window size (here, 8) or more must be advanced. In short, the condition that the continuous transmission of the MAC frame is continued is that the MAC frame is received by the receiving side within the retransmission limit.

In the case of the present embodiment, assuming that the retransmission limit is three times, in the example shown in FIG. 11, it is determined that the MAC frame of sequence number 15 fails even though the MAC frame of sequence number 15 has been retransmitted three times from TX3 to TX5. Therefore, at this point, a series of retransmission sequences to the retransmission destination communication device is stopped. According to such retransmission restrictions, depending on the situation where the transmission path condition with the receiving side communication device has deteriorated for a relatively long period of time, for example, when the receiving side communication device has already come out of the wireless range. , It is effective because it can avoid unnecessary transmission.

At this point, only the transmitting communication device knows that the retransmission sequence has ended. The communication device on the receiving side passes sequence numbers 1 to 14 from the buffer to the upper level, but since sequence number 15 is not normally received, sequence number 16 remains in the buffer. In this case, the communication device on the receiving side receives the MAC super frame starting with the MAC frame having a sequence number larger than the sequence number of the MAC frame that the own device has not confirmed to deliver, thereby communicating on the transmitting side. The device learns that it has given up resending a MAC frame that has not yet been confirmed for delivery. Then, the communication device on the receiving side passes all MAC frames having a sequence number smaller than the first sequence number of the new MAC super frame to the higher-level processing, and emptys the buffer. Since the sequence number is continuously assigned to each MAC frame within a single MAC superframe, even if the first MAC frame is broken, there is one or more other MAC frames that can be received normally. If so, the communication device on the receiving side can know the sequence number of the first MAC frame.

Further, if the receiving side communication device does not receive a new MAC super frame from the transmitting side communication device for a certain period of time, the receiving side communication device sets the MAC frame staying in the buffer assigned to the transmitting side communication device. Pass it to higher-level processing.

The operations of the transmitting side communication device and the receiving side communication device when the retransmission control based on the transmission management table described above is performed will be described. In the following description, the transmitting side communication device is referred to as STA0, and the receiving side communication device is referred to as STA1.

FIG. 12 is a diagram showing an example of a main queue 121 and a sub queue 122 used for retransmission control of the transmitting side communication device in the present embodiment. The subqueue 122 corresponds to the buffer described with reference to FIG. 11 above.

FIG. 13 is an example of a flowchart showing a processing procedure for retransmission control of the transmitting side communication device in the present embodiment. First, the MAC frame to be resent is selected (step S1). In this step S1, from the main queue 121 in which MAC frames in which the destination addresses of various communication devices (here, STA1 to STA4) are specified are stored, the communication device (in this case, the communication device addressed to the destination to be retransmitted in a series of sequences). Here, the MAC frame specified as the destination address by STA1) is selected within the range that does not exceed the range of the total window (W_all) and the window at that time (for example, W1,). After that, the selected MAC frames are extracted into the sub queue 122 having the same size as the window in the order in which the circumstances to be retransmitted occur as shown in FIG. Since the MAC frame extracted at this time is the first retransmission, the state of the sub queue 122 in FIG. 12 is referred to as the window W1 in FIG. After that, the number of windows increases to W2, W3, and so on. The sub queue 122 may be configured even when the number of MAC frames related to the target of the series of retransmission sequences in the main queue 121 is small and the size is less than the window size. The MAC frames extracted in the sub queue 122 are assigned consecutive sequence numbers SEQ1 to SEQ8. It also stores the data lengths LEN1 to LEN8 of these MAC frames. Further, as the initial state of the delivery confirmation of each MAC frame, "N" indicating that the delivery confirmation is not completed is set.

At this time, if the MAC frame to be retransmitted is not extracted to the sub queue 122, it is not necessary to continue retransmitting at least to the communication device (STA1), so the current series of retransmission control processes is terminated (step S2). ..

Next, even if there is an undelivered MAC frame that exceeds the retransmission limit, the series of retransmission sequences to the communication device is stopped (step S3). At this time, the undelivered MAC frame in the sub queue 122 is discarded (step S9). If there are undelivered MAC frames remaining in the main queue, they are retransmitted in the next series of retransmission sequences. As described above, the number of times to set the retransmission limit is not limited to a specific number of times, and may be appropriately selected depending on the situation of the communication partner and the communication medium.

Next, the MAC frames are taken out in order from the beginning of the sub queue 122 to construct the MAC super frame header and the MAC super frame payload (step S4), and the MAC super frame is transmitted to the destination communication device (in this case, STA1) (step). S5). As a result, the destination communication device receives the MAC super frame and transmits a partial ACK for the MAC super frame. The transmitting communication device receives this partial ACK from the destination communication device (step S6).

Next, in step S7, based on the partial ACK bitmap 91 in the partial ACK frame, it is confirmed whether or not the delivery of each MAC frame in the sub queue 122 is confirmed, that is, whether or not the delivery of the MAC frame is received by the destination communication device. .. Based on the result, the delivery confirmation status in the sub queue 122 is updated. At this time, each bit of the bitmap 91 and the sequence number corresponding to the position in the sub queue 122 are stored so as to correspond to each other, and are configured so that the mutual correspondence can be easily understood. In the example shown in FIG. 11, only the MAC frames of SEQ3 and SEQ5 are still undelivered N, that is, undelivered, and the MAC frames other than SEQ3 and SEQ5 are confirmed Y (RX1). In this way, the delivery confirmation information of each MAC frame shown in the partial ACK bitmap 91 included in the partial ACK can be easily determined by associating it with the MAC frame position of the sub queue 122 corresponding to the retransmitted MAC super frame payload. become.

In step S8, the frame with the lowest sequence number among the undelivered frames (for example, SEQ3 in RX1) is determined as the window start point. This starting point corresponds to the starting point of the window W2 in the transmission (TX2) for the second retransmission. By moving the start point in this way, it is possible to prevent the extraction of MAC frames from the minimum sequence number (SEQ1 in TX1) to the sequence number without the first confirmation of delivery (SEQ3 in TX1) to the sub queue 122. .. Compared to window W1, this means that there is space for two window MAC frames. Further, the determination of the retransmission limit exceeding in the previous step S3 can be easily determined by grasping the position of the start point of this window. For example, if the start point of the window after retransmitting SEQ8 assigned to the last MAC frame of window W1 by the retransmission limit does not exceed, it can be determined that one of the undelivered MAC frames has exceeded the retransmission limit.

When the window start point is newly set in step 8, the process returns to step S1 again, and two MAC frames having the same destination address STA1 from the main queue 121 are added in order to the tail of the sub queue 122, and a new sequence number SEQ9, Assign SEQ10. At this time, the data lengths LEN9 and LEN10 of the two added MAC frames are stored, and the delivery confirmation status is set to "N". Update subqueue 122 in this way.

That is, in step S1, the subqueue 122 updated in step S8 is referred to, and the delivery confirmation status is Y according to the stored data length LEN for the MAC frame whose delivery confirmation status is N. Set this to zero for MAC frames that are. Then, in step S4, the MAC super frame header and the MAC frame whose delivery confirmation status is "N" are selectively extracted from the beginning of the sub queue 122 based on the information of the sub queue 122, and the MAC super frame payload is constructed. Next, the MAC super frame to be resent is completed.

Then, the second transmission (TX2) is executed in step S5, and the above-mentioned operations are repeated thereafter (TX3 ~).

Beacons have a higher transmission priority than ordinary data frames and may interrupt the transmission of a series of MAC frames as described above. In such a case, when a discontinuity occurs in the sequence number, the series of retransmission sequences up to that point may be terminated and another series of retransmission sequences may be started before the discontinuity occurs.

On the other hand, FIG. 14 is a diagram showing a sub queue used in the receiving side communication device, and FIG. 15 is a flowchart showing a processing procedure of the receiving side communication device.

Receive a MAC superframe in step S1. The data length of each MAC frame is obtained from the MAC superframe header, and the sequence number is obtained from the MAC header of each MAC frame. Even if an error occurs in one of the MAC frames in the MAC super frame, the sequence number is assigned so that the value is continuous, so it is based on the sequence number of the other MAC frame that could be received normally. Therefore, the sequence numbers of all the MAC frames in the MAC super frame can be obtained. Further, the source address, that is, the MAC address of the transmitting communication device (here, STA0) is also stored.

In the example of FIG. 11, since the MAC frames other than the MAC frames of SEQ3 and SEQ5 are normally received, the reception state is stored in that way (step S2). That is, the reception state of SEQ3 and SEQ5 is set to "N", and the other states are set to "Y".

Next, the partial ACK bitmap 91 is constructed so as to reflect this reception state (step S3), and the partial ACK is transmitted to the communication device on the transmitting side (step S4).

As shown in FIG. 14, the processing cost required for ACK creation can be reduced by setting the partial ACK bitmap 91 corresponding to the arrangement of MAC frames included in the received MAC superframe payload.

Then, the MAC frames from the lowest sequence number (SEQ1 in this case) to before the first reception state "N" (SEQ3 in this case) are taken out from the sub queue 131, and these are passed to the higher-level processing (step S5).

Next, it is determined whether or not all the MAC frames in the sub queue 131 have been received (step S6). When the reception status of all the MAC frames in the sub queue 131 becomes "Y", all the received MAC frames are taken out from the sub queue 131 and become empty. Therefore, this subqueue 131 assigned to STA0 is released and terminated (step S7). On the other hand, if any MAC frame in the sub queue 131 has not been received, the process returns to step S1. In the second reception (RX2), SEQ9 is taken out from SEQ3 and passed to the upper level. Hereinafter, the processes of steps S1 to S6 are repeated for the reception of the MAC super frame for the third to fifth times.

Even if any MAC frame in the sub queue 131 has not been received, if the state in which the MAC super frame is not received from the communication device STA0 on the transmitting side continues for a certain period of time, the machine stays in the sub queue 131. Pass all MAC frames to higher-level processing such as link layer processing. Also, when the sequence number of the first MAC frame of the MAC super frame from the communication device STA0 on the transmitting side is larger than the sequence number of the MAC frame waiting for retransmission in the reception state "N", the MAC of the sub queue 131 Pass all frames to higher-level processing and create a new subqueue for a new MAC superframe. In these cases, MAC frame loss occurs.

When the communication device on the receiving side constructs the partial ACK bitmap, even if the delivery status of the MAC frame included in the previous MAC superframe is shown without referring to the history of the delivery status up to that point. good. In this case, when the transmitting communication device receives the partial ACK, the delivery-confirmed MAC frame is deleted from the subqueue, or the corresponding MAC frame is marked as delivery-confirmed to display the delivery status. The history should be memorized.

Further, when the receiving side communication device returns a partial ACK, the PHY Feedback Information field 92 in FIG. 9 is used to feed back the physical layer information to the transmitting side communication device in an appropriately reduced form. You may. The communication device on the transmitting side is independent of the transmission method (modulation method, code rate, MIMO of the physical layer) based on both the delivery state of each MAC frame represented by the partial ACK bit map 91 and the PHY feedback information 92. You can switch (such as the number of streams in). For example, when all MAC frames are received normally, it is checked whether the margin of the physical layer is large, and if it is large, it is switched to a faster transmission method, or when there is an error in some MAC frames, it is modulated. It is possible to determine whether to reduce the method and coding rate to increase the margin, or to reduce the number of independent MIMO streams. In this way, it is possible to transmit information necessary for communication in the physical layer while transmitting and receiving MAC frames.

(Fourth Embodiment) In the present embodiment, it is permissible to include a partial ACK frame in addition to the data frame as the MAC frame constituting the MAC super frame. Further improvement in throughput can be expected by carpooling (piggyback) the partial ACK into a MAC super frame.

FIG. 16 shows a frame configuration in which a partial ACK frame is allowed as the first MAC frame of the MAC super frame payload 203. The carrier sense state in this case is shown in FIG. Hereinafter, differences from the above-described embodiments will be mainly described.

The partial ACK frame of FIG. 16 contains only address 1, that is, only the address of the receiving communication device, and does not include addresses 2 to 4. The values in the address 1 and period fields are sufficient information for virtual carrier sense of the MAC layer.

In the present embodiment, once the transmission right to use the communication medium is secured, a plurality of MAC superframes and the last partial ACK are continuously arranged at SIFS intervals (that is, without a procedure for securing a new transmission right). You can configure the sequence to be sent and received.

FIG. 17 shows an example of a carrier sense state that determines the value of the period field in the communication device of the present embodiment. Although FIG. 17 shows an example in which a series of communications is completed by exchanging three frames, the sequence may be continued. The maximum TXOP (Transmission Opportunities) in Figure 17 shows the maximum time allowed for a sequence. TXOP is notified to each communication device as a value common to all communication devices by, for example, a beacon. Alternatively, a communication device that centrally manages the right to use a communication medium may dynamically assign a transmission right having an individual TXOP value to each communication device.

In addition, when setting the value of the period (Duration) corresponding to the sum of SIFS and the partial ACK frame transmission time, which the communication device occupies the communication medium at the time of transmission, the partial ACK included in the response is the first type of PHY frame. It must be taken into account that it is not always clear whether it is transmitted by or by a second type PHY frame. Normally, when there is no data frame to be transmitted by the communication device of the other party, or when the data frame cannot be accommodated in the TXOP when the data frame is inserted, the data frame is transmitted in the first type PHY frame. Otherwise, a partial ACK is transmitted by the second type PHY frame. Because the PHY header of the second type PHY frame is longer than the PHY header of the first type PHY frame, and the data length of the partial ACK itself is short and the time required to transmit it does not depend much on the transmission rate. , The transmission time of the frame including the partial ACK is shorter when the first type PHY frame is used. If the longer value is set as the duration value, the communication medium is unnecessarily occupied and wasteful time that is not used in other communications is likely to occur. Therefore, the shorter value is set as the duration value. To set as.

In FIG. 17, as the value of the period (Duration) of MAC frame 1 and MAC frame 2, the value when it is assumed that the partial ACK is transmitted by the first-class PHY frame is set. Actually, the case where a partial ACK (corresponding to MAC frame 3) is transmitted by the second type PHY frame is shown. Period 1 (Duration 1) is indicated by a value that ends before the completion of partial ACK transmission, but communication device 3 and communication device 4 are detecting the PHY busy state during the NAV period set by period 1. .. Partial ACK (MAC frame 3) while the PHY busy state of communication device 3 continues. And since the NAV of the communication device 3 is updated by the value of the period 2 (Duration 2) included in the MAC frame 4, the carrier sense state of the communication device 3 does not pose a problem for the virtual medium occupancy period of the communication. .. As for the communication device 4, since the EIFS period is started again after the reception of the second type PHY frame including the partial ACK is completed, there is no problem in the carrier sense state of the communication device 4. From this, it can be seen that even if the value of the period (Duration) is calculated on the assumption that the partial ACK is transmitted in the first-class PHY frame, no problem occurs in each communication device in the communication. Therefore, when configured as in this embodiment, the partial ACK can be efficiently transmitted while coexisting with other communication devices.

If the partial ACK included in the MAC super frame is not received correctly, it is not necessary to retransmit this partial ACK. In this case, recovery should be performed in the same way as when the partial ACK without aggregate is lost. That is, after detecting that the partial ACK has not been received, the same MAC super frame as the MAC super frame transmitted immediately before including the partial ACK is retransmitted.

(Fifth Embodiment) The present embodiment relates to a case where a plurality of MPDUs generated by fragmentation of one MSDU are aggregated.

FIG. 18 shows an example of the MAC super frame header in this embodiment. In addition to each MAC frame length, it contains the fragment number of each MAC frame. The handling of fragment numbers will be described next.

As a premise, it is assumed that the MPDUs that make up one MSDU do not span different MAC superframes. Sequence numbers are assigned consecutive values for the MSDU. That is, MPDUs generated from the same MSDU have the same sequence number. The fragment number is a value representing the relative position of the MPDU in the MSDU, and usually takes a continuous value starting from 0. Ultimately, the sequence number, fragment number, and relative position of each MAC frame in a series of transmission / retransmission of MAC superframes are determined at the time of transmission. Therefore, the communication device on the transmitting side can specify the corresponding MAC frame only by the bitmap information of the partial ACK, and the retransmission control can be performed by a simple extension of the method described above.

Alternatively, even if the fragment number is not explicitly indicated in the MAC super frame header and only the first and last MPDUs of the MSDU are indicated (one of which may be implicitly indicated), the retransmission control according to the present embodiment is similarly performed. Can work.

(Sixth Embodiment) In the MAC super frame header according to the present embodiment, the MAC super frame header itself has the same format as the MPDU. The communication device on the receiving side can branch the processing of the normal MAC frame and the MAC super frame only by the processing of the MAC layer without receiving the information from the physical layer.

Figure 19 shows an example of the MAC superframe header 1900, which has the same format as the MPDU. For example, a value indicating that it is a MAC super frame header is newly specified and assigned to the Type / Sub-type area included in the Frame Control field. The MAC layer of the communication device on the receiving side determines whether to process the MAC super frame or the normal MAC frame according to this value. The value of the period (Duration) 504 is set according to the calculation method of the period value of another MAC frame included in the MAC super frame. The value of the address 1 field 505 (Receiver Address) is set to be the same as the address 1 of other MAC frames included in the MAC super frame. In this way, an address that identifies the communication device on the receiving side is set in the address 1 field 505.

The value of Sequence Control field 508 has no particular meaning because the MAC superframe header 1900 is neither fragmented nor retransmitted. Therefore, it is more preferable to assign the type of the MAC super frame as the control frame because the sequence control field 508 is omitted.

When Type is defined as Management or Data, it is necessary to have a sequence control field 508, but its value needs to be handled so as to be consistent with the retransmission control of the embodiment according to the present invention. In existing communication, for example, the sequence number (Sequence) of the MAC frame to be retransmitted in a series of retransmission control of the MAC super frame. Since number) is assumed to take a continuous value, when setting a discontinuous value for the sequence number, it is necessary to temporarily end the series of retransmission control of the MAC superframe and start the retransmission control by another sequence. There is. Therefore, it is necessary to prevent the sequence number from being discontinuous, or to be able to continue a series of retransmission controls even if the sequence number is discontinuous. As an example of solving this, when window control at the time of retransmission as shown in another embodiment of the present invention is performed, the maximum sequence that may be assigned to the MAC frame to be retransmitted by a series of retransmission controls. Since the value of the number is known, there is a method of sequentially assigning the sequence number so that the value exceeds this maximum value. In addition, it is necessary to assign a continuous value to this value including the MAC frame to be retransmitted, but when performing retransmission control, the sequence number of the MAC frame to be retransmitted may be ignored to make it discontinuous. It is also possible to control it in this way.

The length of each MAC frame included in the MAC super frame is set in the portion 1901 corresponding to the payload shown in FIG. As described in another embodiment of the invention, the payload 1901 may include a fragment number to accommodate the fragment.

Further, the FCS502 corresponds to the HCS205 shown in FIG. 2, and in the case of this embodiment as well, the FCS502 may be used and treated in the same manner as a normal MPDU. For example, in FCS502, the calculated CRC value is set for the entire MAC super frame header. When the FCS502 attached to the MAC super frame header 1900 recognizes that the MAC super frame header 1900 is broken by the receiving communication device, it is treated in the same way as when an error is detected by HCS205, and the detected reception The side communication device discards the entire MAC super frame.

(7th Embodiment) In this embodiment, a partial ACK and a MAC super frame header that can be handled in the same manner as the MAC frame shown in another embodiment of the present invention are stored in the same MAC super frame.

FIG. 20 shows an example of the format of the MAC superframe 2000 in this embodiment. Here, a partial ACK frame is placed at the beginning of the MAC super frame payload 203, and then the MAC frame of the MAC super frame header is set in that order. The essential information contained in the MAC superframe header 2001 is the length of each MAC frame required for the receiver to recognize the boundaries of each MAC frame in the MAC superframe payload 203. Since the length of the partial ACK can be basically fixed, there is no problem in processing by the receiving side communication device even if the partial ACK is placed at the beginning. By putting the partial ACK at the beginning, there is a high possibility that the preceding partial ACK can be received without any problem even if the MAC super frame header is broken. If the partial ACK is received without any problem, the carrier sense state of the MAC layer is set correctly, so that the next required retransmission can be performed without waiting for error recovery. By eliminating the waiting time for error recovery in this way, improvement in communication throughput can be expected.

On the contrary, even if the positional relationship between the partial ACK and the MAC super frame header 2001 is reversed in the MAC super frame payload 203, if the MAC super frame header 2001 has a fixed length, the preceding MAC super frame header 2001 will be Even if it is broken, there is a high possibility that the partial ACK that exists after that can be received correctly. Similarly, if carrier sense and retransmission control are performed based on the partial ACK, the same effect can be obtained.

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">A block diagram showing a configuration of a communication device according to a first embodiment of the present invention.</figref><figref num="2">The figure which shows an example of the frame format used by the communication apparatus which concerns on embodiment of this invention.</figref><figref num="3">The figure which shows an example of the format of the first kind PHY frame</figref><figref num="4">The figure which shows an example of the format of the 2nd kind PHY frame</figref><figref num="5">Diagram showing an example of MAC frame format</figref><figref num="6">The figure which shows an example of the communication system which concerns on one Embodiment of this invention.</figref><figref num="7">The figure which shows an example of the carrier sense state of each communication device when the value of the period field is determined according to method 1.</figref><figref num="8">The figure which shows an example of the carrier sense state of each communication device when the value of the period field is determined according to method 2.</figref><figref num="9">The figure which shows an example of the format of a partial ACK frame.</figref><figref num="10">The figure for demonstrating the power saving control which concerns on 2nd Embodiment of this invention.</figref><figref num="11">The figure which shows the transmission management table used for the retransmission control which concerns on 3rd Embodiment of this invention.</figref><figref num="12">The figure which shows the main queue and the sub queue used for the retransmission control of a transmitting side communication device.</figref><figref num="13">Flow chart showing the processing procedure of retransmission control of the transmitting side communication device</figref><figref num="14">The figure which shows the sub queue used in the receiving side communication device.</figref><figref num="15">Flowchart showing the processing procedure of the receiving side communication device</figref><figref num="16">The figure which shows an example of the frame format used by the communication apparatus which concerns on 4th Embodiment of this invention.</figref><figref num="17">The figure which shows an example of the carrier sense state of each communication device when the value of the period field in the communication device which concerns on 4th Embodiment of this invention is determined.</figref><figref num="18">The figure which shows an example of the super frame header format used by the communication apparatus which concerns on 5th Embodiment of this invention.</figref><figref num="19">The figure which shows an example of the frame format used by the communication apparatus which concerns on 6th Embodiment of this invention.</figref><figref num="20">The figure which shows an example of the frame format used by the communication apparatus which concerns on 7th Embodiment of this invention.</figref>

Code description

100 ... communication device, 101 ... physical layer, 102 ... MAC layer, 103 ... link layer, 104 ... antenna, 105 ... aggregation processing unit, 106 ... carrier sense control unit , 107 ... Retransmission control unit, 108 ... Power saving control unit, 109 ... First-class physical layer protocol processing unit, 110 ... Second-class physical layer protocol processing unit.