JP2008054347A - Communication apparatus, communication system, communication method, and communication control program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To attain throughput improvement by aggregating multiple communication frames addressed to different destinations. <P>SOLUTION: A communication apparatus includes a physical frame generating device configured to generate a single physical frame which includes a plurality of media access control frames having different destinations and in which frames, of the media access control frames, which have the same destination are consecutively arranged, and a transmitting device configured to transmit the physical frame generated by the physical frame generating device. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a communication device, a communication system, a communication method, and a communication control program for performing medium access control (MAC), and more particularly, frame aggregation for transmitting a plurality of medium access control frames (MAC frames) in one physical frame. About what to do.

  Media access control (MAC) determines how a plurality of communication apparatuses that communicate by sharing the same medium use the medium to transmit communication data. In medium access control, as a result of two or more communication devices transmitting communication data using the same medium at the same time, the number of events (collisions) in which communication data on the receiving side cannot be separated is minimized. On the other hand, this is a technique for controlling access from a communication device to a medium so that the number of events in which the medium is not used by any communication device despite the presence of a communication device having a transmission request is minimized.

  However, particularly in wireless communication, since it is difficult for a communication apparatus to monitor transmission data while transmitting data, medium access control (MAC) that does not assume collision detection is required. IEEE802.11, which is a typical technical standard for wireless LAN, employs CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance). In the IEEE802.11 CSMA / CA, a period (Duration) until a sequence of one or more frame exchanges following the frame ends is set in the header of the MAC frame. During this period, a communication apparatus that is not related to the sequence and has no transmission right waits for transmission by determining the virtual occupation state of the medium. Therefore, the occurrence of a collision is avoided. On the other hand, the communication apparatus 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 based on the combination of the virtual carrier sense of the MAC layer and the physical carrier sense of the physical layer to control the medium access.

IEEE802.11, which employs CSMA / CA, has so far attempted to increase the communication speed mainly by changing the physical layer protocol. The 2.4 GHz band is changing from IEEE802.11 (1997, 2 Mbps) to IEEE802.11b (1999, 11 Mbps) and to IEEE802.11g (2003, 54 Mbps). For the 5 GHz band, only IEEE 802.11a (1999, 54 Mbps) exists as a standard so far. And IEEE802.11 TGn (Task Group n) has already been established in order to formulate a standard aiming at further speeding up in both 2.4 GHz band and 5 GHz band.
US Pat. No. 5,329,531

  Even if the communication speed of the physical layer can be increased, there is a problem that the substantial throughput of communication cannot be improved. That is, when the physical layer is speeded up, the PHY frame format is no longer efficient, and the overhead caused by this is considered to hinder the improvement of the throughput. In the PHY frame, temporal parameters related to CSMA / CA are fixedly attached to the MAC frame. A PHY frame header is required for each MAC frame.

  One of the methods for improving the throughput by eliminating the overhead is a block response (Block ACK) mechanism introduced in the recent draft IEEE802.11e draft 5.0 (IEEE802.11 QoS enhancement). However, according to the block response mechanism, a plurality of MAC frames can be continuously transmitted without back-off, and the back-off amount can be reduced somewhat, but the overhead of the physical layer header is not effectively reduced. Also, according to the aggregation introduced in the early draft IEEE802.11e, it is possible to reduce both the backoff amount and the physical layer header, but due to restrictions of the conventional physical layer, the physical layer including the MAC frame Since the frame length cannot be more than about 4k bytes, there is a big restriction on improving efficiency. Even if the frame of the physical layer can be lengthened, another problem that the error resistance is lowered occurs.

  Therefore, it is necessary to eliminate the overhead associated with transmitting a plurality of frames by increasing the efficiency of the frame format and to improve the substantial throughput of communication.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a communication device, a communication system, a communication method, and a communication control program capable of improving throughput by aggregation of communication frames to a plurality of different destinations. To do.

  A communication apparatus according to an aspect of the present invention is a physical frame that includes a plurality of medium access control frames with different destinations in one physical frame, and has the same destination among the medium access control frames in the physical frame. And a transmission unit for transmitting the physical frame generated by the physical frame generation unit. The communication apparatus includes: a physical frame generation unit configured to generate physical frames arranged in a continuous manner;

  According to the present invention, it is possible to provide a communication device, a communication system, a communication method, and a communication control program that can improve throughput by aggregation of communication frames to a plurality of different destinations.

  Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a block diagram showing a configuration of a communication apparatus according to an embodiment of the present invention. The communication device 100 is a device that communicates with another communication device via a wireless link, and includes processing units 101, 102, and 103 corresponding to a physical layer, a MAC layer, and a link layer, respectively. These processing units are realized as analog or digital electronic circuits according to mounting, or as firmware executed by a CPU incorporated in an LSI. An antenna 104 is connected to the physical layer processing unit 101. The MAC layer 102 includes an aggregation processing unit 105 according to the present invention.

  The aggregation processing unit 105 creates a PHY (physical) frame including a plurality of medium access control (MAC) frames (MPDU). MPDU is an abbreviation for MAC Protocol Data Unit. PSDU is an abbreviation for Physical Layer Convergence Protocol Service Data Unit.

The created physical frame is processed by the physical layer processing unit 101 and transmitted from the antenna 104. Such a communication method is referred to as “frame aggregation” in this specification. Frame aggregation is suitable for next-generation ultra-high-speed wireless LAN communication (IEEE 802.11n standard) that is currently being developed. In the embodiment of the present invention, the aggregation processing unit 105 performs frame aggregation of a plurality of MAC frames having different destinations. More specifically, in the first embodiment of the present invention, wireless communication that improves channel utilization during downlink transmission from an AP by aggregating a plurality of MAC frames with different destinations into one physical frame. System.

  FIG. 2A is a diagram illustrating a downlink between an access point (AP) and a plurality of terminals (STA), and a unicast frame transmission sequence in the downlink. On the downlink 20, a frame is transmitted from the AP toward STA 1, 2, 3. Conversely, transmission of a frame from STA1, 2, 3 toward the AP is called uplink transmission. The example of FIG. 2A is a case where frame aggregation is applied to access by DCF (Distributed Coordination Function), and a frame sequence for data transmission and ACK reception is executed according to DCF. The embodiment of the present invention is not limited to DCF, but can be applied to access using PCF (Point Coordinate Function) and access considering QoS. Note that the case of considering QoS will be described in the second and subsequent embodiments.

  Consider a case where a unicast frame is transmitted from an AP to a plurality of STAs. As can be seen from FIG. 2B, a frame cannot be sent to the next destination until ACK is received and a carrier sense (here, the DIFS period) and a back-off period have elapsed. When transmitting to a large number of destinations, the channel unused period increases, and the frame transmission efficiency decreases.

  In the wireless LAN MAC layer, generally, transmitting one MAC frame to one destination terminal is called “unicast”, and one MAC frame having a plurality of destinations as reception targets. Sending is called “multicast”. On the other hand, in the description of the embodiment of the present invention, aggregating a plurality of MAC frames into one physical frame and transmitting a plurality of destinations as reception targets will be referred to as “simulcast”.

  Here, it is considered that a plurality of destination MAC frames are simply aggregated into one physical frame and simulcast from the AP to each STA. In this case, as shown in FIG. 3, there is a problem that the partial ACK frames 30, 31, and 32 from the receiving terminals collide with the simulcast MAC super frame 33, and communication cannot be normally performed. According to the IEEE802.11 standard, an STA that receives a unicast data frame returns an ACK frame as soon as the SIFS period elapses without checking the channel state. Therefore, it is inevitable that ACK frames from a plurality of STAs collide as shown in FIG.

  Therefore, in the communication system according to the first embodiment of the present invention, the MAC super frame including a plurality of destinations is simulcast from the AP to the STA, and each STA transmits an ACK frame to the AP. The transmission timing is controlled so as to avoid collision with ACK frames from other STAs.

  First, the transmission side (AP here) will be described. As shown in FIG. 4, the AP adds information 41 indicating that there are a plurality of addresses (destination) to the MAC super frame header 40. Hereinafter, this information 41 is referred to as a “Multi Address Bitmap”. FIG. 5 shows a format example of the entire MAC super frame extended in this way. In the multi-address bitmap 41 in FIG. 4, the size of 8 bits is specified as the corresponding bitmap information when the maximum number of aggregates is 8, but this information size is the aggregate size of the MAC frame. It may be arbitrarily determined according to the maximum number of gates (implementation-dependent).

  Next, the multi-address bitmap according to the embodiment of the present invention will be described. The multi-address bit map is information indicating the presence of a plurality of destinations, and the information includes bits corresponding to each of the aggregated MAC frames and indicates a delimiter between the plurality of destinations. That is, the multi-address bitmap is also information regarding the position where a frame whose destination changes compared to the destination of the previous MAC frame among the MAC frames in the physical frame including the MAC super frame is included.

  As shown in FIG. 6, by setting a bit at a corresponding position when a certain destination is started, it is possible to indicate that the bit position is a destination delimiter. In the multi-address bitmap 43 shown in FIG. 6, the bit is designated as 1 when the destination starts, but 0 may be used instead of 1. In this case, the multi-address bitmap in FIG. 6 is indicated as “01101011”.

  In addition, a multi-address bitmap can be used to indicate that the destination has changed. In this case, as shown in FIG. 7, the corresponding bit is set when the destination changes to the next different destination. In the multi-address bitmap 44 shown in FIG. 7, 1 bit is specified at the time of change, but 0 may be used instead of 1 as described above.

  A transmitting terminal (AP) that creates a MAC super frame having a plurality of destinations needs to divide and aggregate the MAC frames for each destination. Here, “separating MAC frames for each destination” includes arranging the frames having the same destination in the MAC super frame so as to be continuous.

  In the frame aggregation method, if there is no error in the MAC super frame header on the receiving side of the MAC super frame, each aggregated MAC frame is extracted and an error is calculated for each extracted MAC frame and received. Detect the status. The reception status result thus detected is returned to the transmitting side by a partial ACK (partial response). FIG. 8 shows an example of partial ACK bitmap information. In the MAC super frame body 42 of FIG. 8, a portion with a cross indicates that the MAC frame aggregated in the MAC super frame is incorrect. FIG. 8 shows a case where “1” is normally received when a partial ACK is returned to the MAC super frame transmitting terminal, and “0” indicating that an incorrect MAC frame portion could not be received correctly. Is described.

  Here, as shown in FIG. 9 (a), when the destinations of the MPDU (s) 90 are aggregated in any order, on the receiving terminal (STA) side, how many destination frames exist and how many frames are received. The situation cannot be determined and the partial response cannot be correctly transmitted to the transmission side.

  For example, even if the multi-address bitmap 40 is added to the state of FIG. 9A, the multi-address bitmap 40 is used for the purpose of reporting that the destination has changed (0 1 1 1 1 1 1 1) It is impossible to determine how many MAC frames exist for each destination. In this situation, the terminal that has received the MAC super frame determines from the information in the multi-address bitmap 40 that there are eight types of destinations, but there are actually only three destinations.

  On the other hand, as shown in FIG. 9B, even if the data is delimited for each destination and aggregated, in the case of the header 91 that does not include information indicating the delimitation (that is, the multi-address bitmap), all frames to DEST2 are erroneous If it is, it is impossible to determine where the DEST3 frame starts, and it is impossible to correctly transmit the partial response bitmap information to the transmission side.

  In order to solve these problems, when a transmitting terminal (AP) aggregates a plurality of frames with different destinations into one physical frame, the transmitting terminal (AP) divides each destination and sets the information on the MAC super frame header. It is necessary to describe.

  After aggregating the MAC frames of a plurality of destinations into one physical frame for each destination and writing the information of the plurality of destinations in the header of the MAC super frame, the AP simulcasts the MAC super frame to the STA.

  Next, the receiving side (STA) will be described. As described above, in the communication system according to the first embodiment of the present invention, when the AP simulcasts a MAC super frame including a plurality of destinations to the STA, each STA transmits an ACK frame to the AP. In this case, the transmission timing is controlled so as to avoid collision with ACK frames from other STAs.

  That is, each STA identifies and extracts a MAC frame destined for the STA based on the multi-address bitmap from the received physical frame, and sends a response frame (partial ACK) to the extracted MAC frame as a destination. Send according to the time interval corresponding to the order of the breaks.

  FIG. 10 is a flowchart showing the operation of the receiving terminal. After receiving the MAC super frame having a plurality of destinations (step S1), the receiving terminal performs error calculation on the header of the MAC super frame (step S2). If the error calculation results in an error, the MAC super frame is discarded (step S3). After the channel becomes idle, carrier sense is performed for an EIFS (Extended Inter Frame Space) period (step S4).

  If the header is not in error, an error check for each MAC frame is performed (step S5). Next, the number (M) of destinations of the MAC frame aggregated in the MAC super frame and the number (Nth) destination of the MAC address of the own terminal are inspected (step S9).

  For example, as shown in FIG. 11, the MAC frame to the receiving terminal corresponding to DEST1 is first aggregated (N = 1), and this receiving terminal has a SIFS period (in the same sequence as the normal frame aggregation) After step S15), the partial ACK frame 110 (or block ACK) is transmitted (step S16). Note that 111 is a corresponding partial ACK bitmap. Thereafter, while other terminals (DEST2 and DEST3 in the example of FIG. 11) send back partial ACKs with a time difference, NAV112 is set and transmission of data frames and the like is stopped (step S17). Note that the period of the NAV 112 is determined by (the number of remaining terminals × (SIFS + ACK transfer time)). In the embodiment of the present invention, it is assumed that the transfer rate of ACK from each STA is the same. However, when the ACK transfer rate is different for each STA, the corresponding ACK transfer time is calculated. To do.

  The second aggregated DEST 2 transmits a partial ACK 113 representing the partial ACK bitmap 114 after the SIFS period has elapsed (step S 12) after DEST 1 transmits the partial ACK 110 (step S 11) (step S 12). S13). Then, after the terminal transmits the partial ACK 113, the NAV 115 is set during the period during which the remaining terminals transmit the partial ACK, as in the case of DEST1 (step S14). DEST3 waits for the destination aggregated before its own terminal to return partial ACKs 110 and 113, and then further passes SIFS, and then receives partial ACK 116 (partial ACK bitmap is 114) from its own terminal. Send. This waiting time is determined by the number of destinations aggregated ahead of the own terminal × (SIFS + ACK transfer time). If the terminal is the last destination (DEST3 in this case) aggregated in the MAC super frame, the NAV period is 0, that is, not set.

  If there is no MAC frame destined for the terminal in the MAC super frame, the NAV 118 is set for (the number of aggregated destinations × (SIFS + ACK transfer time)) (steps S7 to S8). In addition, the number of aggregated destinations is obtained from the information of the multi-address bitmap (Step S7). That is, when a bit indicating the information is set at the destination start location, the number of valid bits corresponds to the number of aggregated destinations. Since the multi-address bitmap is added to the header of the MAC super frame, the location information and the number of destinations can be determined even if each MAC frame is incorrect unless the MAC super frame header is incorrect.

  As shown in FIG. 12 (a), if both of the two frames destined for DEST2 are incorrect, DEST2 cannot determine whether or not the destination address to its own terminal is included. NAV 120 is set for a period of (number of destinations × (SIFS + ACK transfer time)) (steps S7 to S8). Since the DEST3 terminal can determine where the MAC frame addressed to itself starts from and the reception status based on the information in the multi-address bitmap, as shown in FIG. The partial ACK 121 can be transmitted to the transmitting side at an appropriate timing.

  If there is no destination frame to the terminal that has received the MAC super frame, the number of destinations may be extracted from the multi-address bitmap information and the NAV period may be calculated as in the above example. When creating a super frame, a value of (number of aggregated destinations × (SIFS + ACK transfer time)) may be described in the Duration field of each MAC frame. In this case, the MAC super frame receiving terminal may set the NAV during the period specified in the Duration field when there is no destination addressed to the own terminal.

  According to the first embodiment of this invention, throughput can be improved by aggregation of communication frames to a plurality of different destinations. FIG. 13 shows a state in which the embodiment of the present invention is applied to the frame sequence shown in FIG. Specifically, according to FIG. 13, by transmitting the MAC super frame 130 in which MPDUs of a plurality of destinations (three examples in the figure) are mixed, the carrier required for each destination in FIG. It can be seen that the sense and back-off time can be shortened. The partial ACK from the STA to the MAC super frame 130 is transmitted to the AP with a time difference, and they do not collide. If the number of destinations to be aggregated is increased, overhead can be further reduced accordingly. Further, if the present invention is applied to the frame of the “No ACK” policy, there is no need to wait for the reception of a partial ACK, so that the transfer efficiency can be further improved.

  Therefore, it is possible to shorten the carrier sense and back-off period required for each destination, effectively use the channel utilization rate, and enhance the transmission effect.

(Second Embodiment)
Several access controls for improving quality of service (QoS) are known. For example, as QoS that guarantees parameters such as specified bandwidth and delay time, HCCA performs scheduling in consideration of required quality in a polling procedure so that parameters such as bandwidth and delay time can be guaranteed. As QoS according to the second embodiment of the present invention, HCCA that guarantees the quality of each traffic stream is assumed. The QoS in the IEEE802.11e standard includes DCF (Distributed Coordination Function), PCF (Point Coordination Function), EDCA (HCF Contention Access), and HCCA (HCF Controlled Access). HCCA is a conventional PCF expansion method that performs polling control from an AP. In the PCF, a QoS-AP called HC (Hybrid Coordinator) is a subject that performs polling (scheduling), and centrally controls wireless terminals. The AP polls the terminals in order based on the polling list. The STA gets an opportunity to transmit a frame when its own station is designated by polling.

  As shown in FIG. 14, when starting communication, QoS-nonAP-STA (hereinafter QSTA) sets up HC and TS (Traffic Stream) (Uplink, Downlink, Bidirectional). TS is a path of data indicating what kind of traffic (Voice over IP or FTP) the terminal uses and how much bandwidth is required, and it is unique by TSPEC (Traffic Specification). The specifications are determined. At the start of TS setup, TSPEC from QSTA is notified. The TSPEC includes information such as “TSID (TS identifier determined by the TSPEC)” and “Mean Data Rate” (TS throughput to be guaranteed at least by MAC_SAP). Multiple TSs can be stretched, and the HC needs to perform scheduling to meet the requirements of each TS. However, a specific algorithm related to scheduling is not defined in IEEE802.11e and depends on the implementation. QSTA obtains TXOP (transmittable time) by polling given from HC and transmits a frame.

  When frame aggregation is performed in such HCCA, each MAC frame has its own MAC header, and is present in the TID in the header (the QoS Control field extended for IEEE802.11e, identifying traffic). Since TSID can be uniquely identified by using TSID No. 8-15), it is possible to aggregate multiple streams.

  The second embodiment of the present invention mainly focuses on improving the efficiency of the downlink traffic 150 from the HC shown in FIG.

  As shown in FIG. 16, first, the HC creates downlink traffic destination queues 1100 and 1101 for each QSTA that has a TS. In these destination queues 1100 and 1101, frames destined for the respective QSTAs are packed. The required bandwidth of QSTA can be determined from the mean data rate in TSPEC (the sum of the values for each TS of QSTA), and the ratio is calculated, and for QSTA that requires a lot of bandwidth, WRR Send more with (weighted round robin).

  For example, if QSTA1 requires 8 Mbps for downlink traffic from HC, QSTA2 requires 4 Mbps, and QSTA3 also requires 4 Mbps, HC transmits with a weight of 2: 1: 1. By creating a queue for each priority level in each destination queue, frame aggregation considering the frame priority level is also possible.

  Here, as a scheduling method other than WRR, for downlink traffic from HC to QSTA, the bandwidth is divided by the number of terminals connected to HC by extending TS. As shown in FIG. 17, a frame is transmitted to the destination terminal by RR (round robin: round once evenly). For example, a certain QSTA (a user terminal paying a telecommunications carrier with a higher amount of money) issues a bandwidth securing request to the HC, and returns a response message if the QSTA is registered in the HC. Thereafter, the transmission cycle from the HC to the QSTA becomes WRR, and the transmission opportunities to the corresponding QSTA may be increased.

  As shown in FIG. 18, HC weights the number of transmissions for downlink traffic to QSTA. “Transmit once” means once when a frame is correctly sent to the destination (including retransmission) when sending a certain MAC super frame (all partial ACK bitmaps are 1). And count. For example, assume that frames are aggregated as [1] [2] [3] [4] [5] [6] [7] [8]. Here, the number of each priority frame in one physical frame varies according to the Mean Data Rate of TSPEC. If all the frames [1] to [8] are correctly transmitted (partial ACK reception) in the first transmission, “one transmission” is counted. Alternatively, if retransmission of [2] is necessary and the MAC super frame is retransmitted as in [2] [9] and a partial ACK is received, it is counted as “one transmission” at that time. Thus, the number of transmissions is defined, and the number of transmissions to each QSTA calculated from TSPEC is weighted.

  The purpose of this embodiment is only to improve the efficiency of downlink traffic. The downlink transmission from the HC to the QSTA is separated from the uplink transmission that gives TXOP (transmission opportunity) by polling the QSTA. Think. In other words, the HC performs scheduling by alternately repeating “time to transmit a frame on the downlink” and “time to poll each QSTA and give TXOP” alternately.

  Before starting transmission (continuous) to the downlink, the HC determines the TXOP period based on the delay bound (Delay Bound) in the TSPEC of each TS. The delay bound also considers retransmission due to an error on the transmission path, and therefore the TXOP period that is initially determined by the HC is a relatively large value. However, the specific method for determining the delay bound is not defined by IEEE802.11e.

  HC simulcasts QoS data frames towards QSTA. In the data frame, the TXOP value required by the HC for transmission of downlink traffic is included as a duration, and each QSTA is in a state in which it cannot transmit any frame with a NAV. When there are many errors on the transmission path and the frame is retransmitted many times, the TXOP specified in advance is not sufficient (the frames are transmitted to all QSTAs in order), so the CAP (Controlled Access Phase) shown in FIG. If it is between, after waiting SIFS, TXOP (2nd time) 2 is obtained again. When the frame has been transmitted to all QSTAs (with WRR), the reserved TXOP period may be left, but at that time, a QoS-Null frame is sent to cancel the NAV attached to each QSTA. CAP is a period acquired again when HC performs carrier sense during PIFS and the channel state is idle. If a new CAP is acquired, QoS CF-Poll is sent to QSTA to allow transmission of uplink traffic (or communication between QSTAs by DLP). In the polling frame, the value of TXOP given to each QSTA is included as a duration, and during that period, other terminals cannot transmit anything with NAV.

  As an actual processing sequence, for example, consider the case shown in FIG. 20A (when QSTA1 requires a weight of 2, QSTA2 has a weight of 1, and QSTA3 has a weight of 1).

  As shown in Fig. 20 (b), the first transmission to QSTA1 is as follows: “[1] [2] [3] [4] [5] [6] [7] [8] to QSTA1” Assume that the frame 201 is aggregated and transmitted. The partial ACK 202 is returned to the MAC super frame 201, and when the transmission is correctly performed, the MAC super frame 201 is counted once. And this time, since it is assumed that the transmission right is passed by WRR (weighted cyclic method), QSTA1 with a weight of 2 is changed to “[9] [10] [11] [12] to QSTA1” again. Assume that frame 203 is transmitted.

  If there are not many frames in the queue, a smaller number of frames may be packed than the maximum number of aggregates determined for each terminal. (Frame 203) When frame transmission to QSTA1 (twice) is completed, the process proceeds to the transmission sequence of frame 205 to QSTA2 following partial ACK 204 ("[1] [2] [3] [4] to QSTA2" ).

  After the partial ACK 206 for the frame 205 to QSTA2, the MAC super frame 207 to QSTA3 is similarly transmitted (“[1] [2] [3] [4] [5] [6] [7] to QSTA3” ).

  Here, in this embodiment, for example, the HC bundles and transmits the second frame transmission to QSTA1 and the frame transmission to QSTA2 in one MAC super frame 211, and receives partial ACKs 212 and 213 with a time difference. That is, instead of aggregating frames of one destination (QSTA1) in one MAC super frame 214, the HC creates a physical frame including MAC super frames having a plurality of destinations.

  Also in the present embodiment, as shown in FIG. 4 of the first embodiment, the MAC super frame header 40 is expanded and a multi address bitmap field 41 is added. This field 41 is a bit field indicating information when there are MPDUs having different destination addresses in the aggregated MAC super frame. The bit field is used by setting the bit of the portion to 1 when the destination changes for the MPDU aggregated for each destination in the MAC super frame.

  Similarly to the case shown in FIG. 5, it is assumed that MAC frames (MPDUs) 42 for two destinations are aggregated in one MAC super frame, and MPDUs for DEST2 appear from the fifth part. In this case, the multi-address bit map 41 is indicated as “0 0 0 1 0 0 0”. Here, the portion where the bit value changes from 0 to 1 corresponds to the frame position where the destination has changed.

  In the example of FIG. 5, since the maximum number of MPDUs that can be aggregated is 8, the multi-address bitmap is also 8 bits, but this size is variable according to the number of aggregates. In addition, by using the multi-address bitmap 41, the receiving side can determine how many destinations exist in the MAC super frame. In the above example, since the number of times the destination has changed is 1, it can be determined that the number of destinations existing in the MAC super frame is two. If only MPDUs for one destination are aggregated, it is indicated as “0 0 0 0 0 0 0 0”. That is, it can be seen that the value of all bits is 0 in the multi-address bitmap.

  In the implementation of frame aggregation for the same destination, each terminal that has received a MAC super frame can determine whether or not the entire frame is destined for itself by checking only the address of the head MPDU. In the case of the present invention in which frames with different destinations are aggregated, the multi-address bitmap field is added so that the value is all 0 (when a multi-address bitmap is used in the meaning of destination change. If the number of destinations is 1, the first bit is 1 and all subsequent bits are 0.), the MPDU (s) in the MAC superframe is used. Since the number of destinations is limited to one, in this case, only the address of the head MPDU is checked, and subsequent checks are unnecessary.

If any bit field of the multi-address bitmap contains a value of 1, it is possible to determine the destination of the MPDU by directly accessing the bit position. By using the multi-address bitmap field in this manner, the number of times the contents of the MPDU header are checked can be compared only once when there is only a single destination in the MAC super frame. Also, since the part where the bit of the multi-address bitmap is 1 is the place where the destination is changing, if you check that part directly, whether the destination addressed to your terminal is included, It can be judged more easily. (When “1” is used to indicate the beginning of each destination)
The QSTA that has determined that there are a plurality of destination MPDUs (determined from the multi-address bitmap) in the MAC super frame determines whether any of the destinations contains the address of the terminal itself. Then, the order in which the partial ACK is returned is determined depending on whether the address of the own terminal is relatively forward or backward. For example, if a MAC superframe “[DEST1] [DEST1] [DEST1] [DEST1] [DEST2] [DEST2] [DEST2] [DEST2]” is received and the address of the receiving terminal is “DEST1” It is required to send a partial ACK after SIFS. Then, the terminal with the address “DEST2” returns a partial ACK to the HC after SIFS when the terminal with the address “DEST1” transmits the partial ACK. At this time, the QSTA of DEST1 returns the CRC (cyclic redundancy check) calculation result for the 1-4th MPDU, and the QSTA of address 2 returns the CRC calculation result for the 5-8th MPDU.

  When the destination addressed to the own terminal is not included in the MAC super frame, the terminal sets NAV. In the MAC protocol defined in IEEE802.11, when a unicast data frame is received, a duration corresponding to [SIFS time + ACK transfer time] is basically set. In this proposal, which returns a partial ACK, the duration value of ((number of aggregated destinations-number of destinations) x ([SIFS time + ACK transfer time])) is set to HC (MAC superframe transmission). Terminal) sets each MAC frame. In the embodiment of the present invention, it is assumed that the transfer rate of ACK from each QSTA is the same. However, when the ACK transfer rate differs for each QSTA, the corresponding ACK transfer time is calculated. To do.

  A terminal having an address addressed to itself in the MAC super frame can determine at what timing the terminal should return a partial ACK from the relative position of the aggregated destination. Then, a terminal for which there is no destination addressed to itself in the MAC super frame applies NAV only during the duration of Duration.

  Also, the terminal that sent the partial ACK does not need to set NAV if the terminal is the last aggregated MPDU from the relative address information in the MAC super frame, but it is not like DEST1 and DEST2. If the subsequent partial ACK is expected to be transferred, the NAV is set until the NAV end period set by the HC (MAC superframe terminal).

  For example, as shown in FIG. 11, when all the MPDUs for DEST2 are wrong and it is determined which part of the MPDU to DEST3 starts, by utilizing the multi-address bitmap field, the MAC super It is possible to determine how many destinations exist in the frame and where those breaks start.

  For example, as shown in FIG. 12, if all the MPDUs to DEST2 are wrong, there are three destinations from the multi-address bitmap field and where the beginning of the MPDU to DEST3 is It is possible to judge whether there is. Therefore, DEST2 does not know whether the MPDU addressed to its own terminal was included, so NAV is set up only for (number of aggregated destinations x (SIFS + ACK transfer time). DEST3 finds the MPDU addressed to its own terminal. At this point, it is determined from the multi-address bitmap what number the destination of the terminal is and where the MPDU addressed to the terminal is, and a partial ACK is returned after an appropriate time. As in the example of FIG. 12, the terminal 2 itself does not respond with a partial ACK, but the terminal 3 returns its own partial ACK in consideration of the time of the partial ACK (+ SIFS) that the terminal 2 should originally send.

  The MAC super frame transmitting terminal caches information indicating how many MPDUs are packed and transmitted to which destination, and after receiving all the time-sequential partial ACKs sent from the destination terminal, the frame to be retransmitted. To decide.

  FIG. 20 shows a case where frames of different destinations are not aggregated from HC to QSTA. On the other hand, as shown in FIG. 21, it is understood that the SIFS period can be shortened by mixing and transmitting MPDUs of a plurality of destinations (two in the example in the figure). If the number of destinations to be aggregated is increased, the overhead of SIFS (× α) can be further reduced accordingly. Further, if the present invention is applied to the frame of the “No ACK” policy, there is no need to wait for the reception of a partial ACK, so that the transfer efficiency can be further improved.

  The HC that has transmitted downlink traffic to a plurality of destinations waits for the number of destinations to return partial ACKs, and then performs processing such as retransmission. Since it is divided for each destination, a new MPDU may be packed and transmitted to one destination. Therefore, the value of the ACK timer to be set by the HC is represented by (number of destinations × (SIFS + partial ACK transmission time) +1 slot time).

  According to the second embodiment of the present invention described above, even when QoS is considered, throughput is improved by aggregation of communication frames to a plurality of different destinations as in the first embodiment described above. it can. Further, if the number of destinations to be aggregated is increased, the overhead of SIFS (× α) can be further reduced accordingly. Therefore, it is possible to shorten the carrier sense and back-off period required for each destination, effectively use the channel utilization rate, and enhance the transmission effect.

  Specifically, for example, when streaming video distribution is performed via the Internet at a hot spot in a city, the transmission efficiency of downlink traffic from the AP can be improved. More client terminals can be accommodated in the hot spot.

  QoS guarantees the quality of delay-sensitive applications and can keep jitter even, for example, and realizes efficient forwarding by aggregating flows for multiple different destinations (low priority flow It has the effect of being able to guarantee the bandwidth.

  In addition, by assigning weights to each destination STA (user), it is possible to easily realize service quality classification based on a charging system. Thereby, for example, a user terminal paying a high amount can preferentially transmit a frame from the AP by WRR.

(Third embodiment)
The third embodiment of the present invention relates to a communication apparatus that transmits a plurality of block ACK control frames (BlockAckReq / BlockAck for each TS) defined in IEEE802.11e in one PHY frame. IEEE802.11e defines a block ACK that transmits data frames in bursts at SIFS intervals. The communication procedure using the block ACK can be performed even when the frame aggregation described so far is not performed.

  In the present embodiment, block ACK (response) request frames to a plurality of different destinations are transmitted by simulcast as in the first and second embodiments described above. Similarly to the above-described first and second embodiments, the block ACK frame is transmitted with a time difference in order to avoid collision of response frames.

  A frame sequence based on a block ACK defined by IEEE802.11e is shown in FIG. An example of the frame sequence in FIG. 22 is a case of an immediate block ACK. There are two types of block ACK procedures: the sender sends an ACK request (Block ACK request), the receiver immediately sends a response (block ACK), and the sender sends a block ACK. There is a delay type that transmits a request and returns a response (block ACK) after a while by the receiving side. The embodiments of the present invention are applicable to both cases.

  As shown in FIG. 22, in the block ACK procedure, a plurality of unicast data frames 220 are continuously transmitted for each SIFS period during a transmission period (TXOP: Transmission Opportunity) determined for each terminal. Then, block ACK requests 221 and 223 are transmitted to each destination terminal to transmit a block ACK frame having bitmap information of the reception status. For this reason, the block ACK request frames 221 and 223 need to be transmitted separately for each destination. In response to the block ACK request 221, QSTA1 transmits a block ACK 222 to the HC. In response to the block ACK request 223, QSTA2 transmits a block ACK 224 to the HC.

  In the third embodiment of the present invention, as shown in FIG. 23, a plurality of block ACK request frames 230, 231, 232,... 23n are aggregated into one frame. Similar to the frame aggregation to the multiple destinations described so far, the block ACK request transmitting terminal aggregates the block ACK request frames by dividing each destination, and adds the MAC super frame header 40. Then, the delimiter information is written in the multi-address bitmap 41. The MAC super frame header 40 includes a header CRC 44, and if a header error occurs, a block ACK request frame obtained by aggregating a plurality of destination block ACK requests is discarded. Then, after the channel becomes idle, carrier sense for the EIFS period is set. This means that the procedure is the same as that in the flowchart described above.

  As described above, the terminal that has received the aggregated block ACK request checks how many times the destination of the own terminal is aggregated, and as in the first and second embodiments described above, it is time-dependent. Block ACK is transmitted to. After the terminal transmits the block ACK, the NAV is set while the remaining destination is transmitting the block ACK. FIG. 24 shows the sequence. In the example of FIG. 24, by transmitting the frame 240 in which block ACK requests to a plurality of destinations are aggregated, the SIFS period can be shortened and the channel utilization efficiency can be improved. In FIG. 24, blocks ACKs 241 and 242 are transmitted with a time difference. Further, after transmission of block ACK241, QSTA1 sets NAV243 so as to avoid collision with block ACK242.

  Furthermore, as shown in FIG. 25, it is possible to aggregate not only with block ACK requests 230, 231,... 23n but also with data frames 250, .. 25n (not requiring ACK). In this case as well, aggregation is performed for each destination, and the frame size of each frame (data, block ACK request) is described in the MPDU Length field, so that data frame extraction and block ACK transmission over time can be performed correctly. Can be done.

(Fourth embodiment)
FIG. 26 is a block diagram showing a configuration of a communication apparatus according to the fourth embodiment of the present invention. The communication device 100 is a device that communicates with another communication device via a wireless link, and includes processing units 101, 102, and 103 corresponding to a physical layer, a MAC layer, and a link layer, respectively. These processing units are realized as analog or digital electronic circuits according to mounting, or as firmware executed by a CPU incorporated in an LSI. An antenna 104 is connected to a physical layer processing unit (hereinafter, “processing unit” is omitted) 101. The MAC layer 102 includes an aggregation processing unit 105 according to the present invention. The aggregation processing unit 105 includes a carrier sense control unit 106, a retransmission control unit 107, and a power saving control unit 108.

  The physical layer 101 is configured to be compatible with two types of physical layer protocols. For each protocol processing, the physical layer 101 includes a first type physical layer protocol processing unit 109 and a second type physical layer protocol processing unit 110. In implementation, circuit sharing is often performed between the first-type physical layer protocol processing unit 109 and the second-type physical layer protocol processing unit 110, and therefore they do not necessarily exist independently. .

  In the fourth embodiment of the present invention, the first type physical layer protocol is a so-called MIMO (Multiple Input Multiple Output) protocol that uses a plurality of antennas on the transmitting side and the receiving side, respectively, and the second type physical layer protocol is used. The protocol is assumed to be a protocol defined in IEEE802.11a. Even if the frequency band is kept the same, the transmission capacity can be expected to increase almost in proportion to the number of antennas. Therefore, MIMO is a technology for further increasing the throughput of IEEE802.11. The link layer 103 has 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 occupation band and a combination thereof and MIMO may be used.

  FIG. 27 is a diagram showing an example of a frame format used by the communication apparatus according to the embodiment of the present invention. The frame format 200 schematically shows a frame structure related to the physical layer and the MAC layer, and specifically, the frame format 200 is assumed to conform to IEEE802.11 or its extension. Note that IEEE802.11 frames are roughly classified into three types: control frames, management frames, and data frames, and it is assumed that the embodiment of the present invention is mainly applied to data frames. Application to the management frame is not excluded. As shown in FIG. 27, the frame format 200 includes 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 a PHY payload described later.

The PHY header 201 is processed by the physical layer 101 of the receiving communication apparatus. That is, based on the received PHY header 201, the physical layer 101 detects the beginning of the frame, establishes carrier synchronization, establishes timing synchronization, controls the gain of the amplifier (AGC: Automatic Gain Control), tracks the carrier frequency on the transmission side (Automatic Frequency Control ), Transmission path estimation, etc. The physical layer 101 also detects the modulation method and coding rate of the PHY payload following the PHY header 201, and the transmission rate and data length. FIG. 27 shows aggregation of MAC frames directed to a single destination. In this embodiment, as in the above-described embodiment, as shown in FIG. 28, a “simult cast” is performed in which MAC frames directed to a plurality of destinations are aggregated into one physical frame, and a plurality of destinations are transmitted as reception targets. Do.

  In this case, based on the multi-address bitmap (Multi Address Bitmap) shown in FIG. 28, for example, the transmission source AP (access point) receives a partial ACK (partial delivery confirmation) frame from each destination terminal (STA). Receive in a time lag (FIG. 29). The time difference reception of the partial ACK is the same as that in the above-described embodiment.

  FIG. 30 is a diagram showing a carrier sense state according to the fourth embodiment of the present invention. HT0 (address: a0) which is the first type of communication device (hereinafter referred to as HT: High Throughput (high throughput) terminal) shown in FIG. 30 is HT1 (address: a1), HT2 (address: a2), HT3. Assume that a MAC frame directed to (address: a3) is aggregated into one physical frame and transmitted. The MAC header of each MAC frame that is aggregated to the MAC super frame includes information on the period during which the channel is used (duration values d1, d2, d3), and NAV (Network Allocation Vector) is set.

  According to the IEEE802.11 standard, the NAV value when a unicast data frame is transmitted is the sum of the time required to receive an ACK from the destination, that is, the SIFS (Short Inter Frame Space) time and the ACK transmission time. be equivalent to. In this case, as shown in FIG. 31, DEST1 sets the NAV for the duration of DEST1, DEST2 sets the NAV for the duration of DEST2 after transmitting the partial ACK. In this method, for example, a case where a terminal that transmits a partial ACK with a time difference aggregates and transmits a data frame with one ACK together with one physical frame, NAV (SIFS time, ACK transmission time specified in advance) is considered. The total).

  On the other hand, according to the regulations of IEEE802.11e, when HC transmits QoS data to QSTA, it is possible to piggyback a polling frame to the destination. That is, it is determined from the type and subtype information of the MAC header that the frame is QoS Data + CF-Poll. By aggregating the IEEE 802.11e QoS Data + CF-Poll frame to the MAC super frame as shown in FIG. 32, HT1, HT2, and HT3 in FIG. In addition to the ACK response, the data frame for HT0 can be aggregated and transmitted.

  That is, when HT1, HT2, and HT3 in FIG. 30 receive the MAC super frame from HT0, the destination MAC frame to itself is a QoS Data + CF-Poll frame and is specified by CF-Poll. If it falls within the range of the transmission permission time (TXOP), the data frame to HT0 can be aggregated into the partial ACK and transmitted. At this time, SIFS time + channel use period (TXOP) of the wireless terminal is specified as Duration (channel use period) of the aggregated MAC frame, not SIFS time + ACK transmission time. As a result, while HT1 aggregates and transmits a partial ACK (+ data frame) to HT0 in one physical frame, other terminals (HT2, HT3) set NAV to detect frame collision. Can be avoided. In addition, (partial) ACK responses to MAC data frames aggregated into partial ACKs from HT1, HT2, and HT3 may be sent sequentially from HT0 to each destination, or partial ACK responses to multiple destinations are aggregated. May be transmitted. When receiving a MAC super frame that aggregates MAC frames to multiple destinations, if the frame to the destination contains only a partial ACK, there is no need to set a NAV by Duration and it is also necessary to return an ACK response. It goes without saying that there is nothing.

  In the example of FIG. 30, in addition to the high-throughput terminals (HT0 to HT3) realized by the first type physical layer protocol, there are legacy terminals (Legacy) realized by the second type physical layer protocol. . Since the legacy terminal cannot be interpreted even if it receives a MAC super frame of the form shown in FIG. 33, after the channel shifts from busy to idle, it performs EIFS (Extended IFS) carrier sense and then idles If the condition persists, take a backoff.

  According to the fourth embodiment of the present invention described above, when the timing of the time-sequential partial ACK can be appropriately set based on TXOP or the like specified by CF-Poll, the data is piggybacked (joined) to the partial ACK. Throughput can be improved.

(Fifth embodiment)
As shown in the example of FIG. 30, when a high-throughput terminal realized by the first type physical layer protocol and a legacy terminal realized by the second type physical layer protocol coexist, the legacy terminal is high. The frame of the throughput terminal cannot be received, and EIFS carrier sense is performed. In general, EIFS has a longer period than the frame interval AIFS (Arbitration Inter Frame Space) for each priority specified in DIFS (Distributed Coordinate Function inter frame Space) and IEEE802.11e, so media access rights are not equal. . Therefore, as shown in FIG. 34, when a partial ACK to a plurality of destinations is aggregated, a MAC header that can be understood by the legacy terminal is added to the head of the MAC super frame, and the MAC header and the MAC super frame main body (multiple FCS for error calculation for the destination (partial ACK) is added to the end.

  Further, such a MAC super frame in which the partial ACK is aggregated is transmitted by the second type physical layer protocol (legacy transmission by 802.11a). If the legacy terminal that has received the frame is able to receive correctly based on the error calculation by FCS added to the end of the PSDU (Protocol Size Data Unit), after the channel becomes idle, FIG. As shown in FIG. 5, the DIFS carrier sense is performed in the same manner as the high-throughput terminal.

  Note that since the type and subtype are not values recognized by legacy terminals, the contents after the first MAC header are not readable by the legacy terminal, but unless PSDU is incorrect, it is not EIFS but a DIFS carrier. It is possible to take a sense. By applying this embodiment, even if a partial ACK is transmitted to multiple destinations after data transmission to multiple destinations and partial ACK (including aggregated data) within the transmission period, FCS errors in legacy terminals After DIFS, high-throughput terminals as well as legacy terminals can perform media access equally.

(Sixth embodiment)
In the previous embodiments in which a plurality of MPDUs (MAC Protocol Data Units) are aggregated into one physical frame, the length information (multiples) of each MPDU is added to the front part of the aggregated MPDUs, and One CRC (Cyclic Redundancy Check) is added to the above, and each MPDU is cut out and FCS (Frame Check Sequence) is calculated on the receiver side. On the other hand, in the sixth embodiment according to the present invention, as shown in FIG. 36, information for identifying the length of each MPDU is added.

  As shown in FIG. 36, the “MPDU length” field (element) located in front of each MPDU indicates the length of the aggregated MPDU in octets, and the “order” field in this case is PSDU. Write consecutive numbers from the beginning of. In the following description of the embodiment, such information added to the head of each aggregated MPDU including “MPDU length”, “order”, and CRC fields for them is referred to as “MPDU separation”. . In the description of the sixth and seventh embodiments, the number of MPDUs to be aggregated is 8. However, the number of MPDUs that can be aggregated can be arbitrarily determined depending on the situation.

  In the sixth and seventh embodiments, various bitmaps can be added to frames in which a plurality of MPDUs are aggregated in order to support IEEE802.11e QoS and to transmit to a plurality of destinations. .

  37 and 38 show an example format of MPDU separation. The MPDU separation includes an “MPDU length” field indicating the length of the subsequent MPDU in octets, an “order” field indicating the number of the MPDU separation, and a CRC for the MPDU separation.

  In the example 1 of FIG. 37, an example in which one bit of the “reserved” field exists in addition to the “MPDU length”, “order”, and “CRC” is shown. However, the length of these fields is not limited. Needless to say, an arbitrary fixed length can be taken as in Example 2 of FIG. For example, in Example 2 of FIG. 37, the size of the “order” field can be expanded by setting the “reservation” field to a size of 0 bits. In Example 1 and Example 2 in FIG. 37, when the order of MPDU separation is continuously counted from the beginning of the PSDU, it is assumed that the number is described in the “order” field. As described above, for the order field, it is also possible to specify a sequence number, or a sequence number and a fragment number, that the MPDU following the MPDU separation has. When assigning sequential numbers from the top of PSDU, if numbers are continuous, you may assign them as 0, 1, 2, 3, 4, or assign them as 1, 2, 3, 4, 5. May be. When making it correspond to the sequence number (including the fragment number in some cases) of the MPDU, the terminal transmitting the aggregated frame writes the corresponding value in the MPDU separation while referring to the MAC header of each MPDU.

  Typically, a terminal that has received a frame having an MPDU separation field as shown in FIG. 36 performs an FCS check for each aggregated MPDU, and returns a reception status to the transmitting side as a partial ACK. The CRC associated with the MPDU separation is protected including information such as “MPDU length” and “order”. If the CRC calculation result is correct, it is determined that the MPDU separation has been received normally.

  FIG. 39 and FIG. 40 show an example of a reception situation in a terminal that receives a PSDU in which a plurality of MPDUs are aggregated and an MPDU separation is added in front of each MPDU. As shown in FIG. 39, when the first MPDU separation has been successfully received as a result of the CRC check, it is determined that the “MPDU length” information described therein is correct. The MPDU 1) in FIG. 39 can be cut out. Since each MPDU is accompanied by an FCS, if the MPDU FCS is normal, it can be determined that the MPDU has been received correctly.

  Here, when the CRC calculation result of a certain MPDU separation is diagnosed as an error as in “MPDU separation 2” in FIG. 39, the search process is continuously performed until the next MPDU separation. This search processing method is shown in the flowchart of FIG. The pointer p in the flowchart shown in FIG. 41 is an identifier indicating a relative position from the beginning in the PSDU, and moves toward the back of the PSDU in units of octets. For example, as shown in the flowchart, the pointer p first points to the beginning of PSDU (step S1), and the length of the MPDU separation from this portion (this length includes CRC. MPDU separation error calculation is performed (step S2). As a result, if the MPDU separation is normal, the subsequent MPDU is cut out by the length specified by the “MPDU length” in the MPDU separation, and the FCS is calculated for the MPDU (step S4). As described above, if the FCS of the MPDU is correct, it is considered that the MPDU has been received normally. If the CRC of the MPDU separation is incorrect, the pointer p is shifted toward the back of the PSDU by 1 octet (step S3). Then, CRC calculation for MPDU separation is performed again. At this time, CRC calculation is performed from the position indicated by the pointer p in consideration of the length of MPDU separation (including CRC). If the CRC calculation result for the MPDU separation is incorrect, the pointer p is shifted again by 1 octet, and the CRC check for MPDU separation is performed. Continuing this process, if the CRC check for MPDU separation is normal, the MPDU separation field search routine is exited, and the FCS of the subsequent MPDU is checked. Judgment of successful or unsuccessful reception of MPDU shall follow the above procedure.

  In the example of FIG. 39, it is assumed that “MPDU separation 2” is an error and “MPDU separation 3” has been normally received as a result of the MPDU separation search. The length of the MPDU separation is fixed, and considering the case where the value is recognized by both the transmitting and receiving devices, from “MPDU 1” in FIG. 39 to “MPDU separation 3” that has been successfully received. It can be considered that the length between them is an area occupied by “MPDU separation 2” and “MPDU 2”. That is, since it can be estimated that the MPDU length is obtained by subtracting the MPDU separation length (fixed) therefrom, it is possible to check the reception status of the MPDU by checking the FCS for the MPDU. That is, the error calculation is performed assuming that the end of the MPDU is immediately before the next normal MPDU separation to be found by scanning. That is, in the example of FIG. 39, even if “MPDU separation 2” is incorrect, if the result of inspecting the FCS by estimating the length of “MPDU 2” is normal, it is determined that the MPDU has been successfully received. To do. Needless to say, if the FCS result for “MPDU 2” in FIG. 39 is incorrect, it is determined that the MPDU could not be received correctly. Also, if the “order” for MPDU separation is continuously given, as shown in FIG. 40, if two or more successfully received MPDU separation numbers are separated by two or more, It is determined that a plurality of sandwiched MPDUs ("MPDU2" and "MPDU3" in FIG. 40) are incorrect.

  Here, consider the examples of FIGS. 42 and 43. Assume that MPDUs with sequence numbers “1” to “8” are aggregated and transmitted to one PSDU, and “2”, “4”, and “6” are normally received. The method for confirming the reception status of the MPDU is as described above. When the aggregated frame is retransmitted, the MPDUs “2”, “4”, and “6” do not need to be retransmitted (sent), so the size of the MPDU following the MPDU separation is set to 0 as shown in FIG. That is, all 0 is specified in the MPDU length fields in “MPDU separation“ 2 ”,“ 4 ”, and“ 6 ”” in Fig. 43. The "order" of the MPDU separation here is the sequence number of the MPDU. Needless to say, it may be supported, or may be a relative serial number from the beginning of PSDU, or for MPDUs that do not need to be retransmitted as shown in FIG. "Can also be skipped. In the example of Fig. 53, the numbers" 2 "," 4 "and" 6 "that were successfully transmitted are skipped and" 1 "" 3 "" 5 "" 7 "" 8 " It shows a state where MPDU separation and MPDU having “order” are aggregated into one physical frame.

(Seventh embodiment)
In the sixth embodiment described above, the (sub) field element of “order” (number based on the beginning of the PSDU, or the number corresponding to the MPDU sequence number and fragment number) exists in the MPDU separation field. However, the MPDU separation according to the seventh embodiment of the present invention has a format that does not include the “order” field, as shown in FIG.

  FIG. 45 shows a specific format of MPDU separation when the “order” field does not exist. As shown in FIGS. 37 and 38 of the sixth embodiment, CRCs for the “MPDU length” field, the “MPDU length” field, and the remaining “reserved” field that specify the length of the MPDU following the MPDU separation in octets are shown. Will be described.

FIG. 46 and FIG. 48 show an example of receiving PSDU (a plurality of MPDUs are aggregated) including an MPDU separation field that does not include an “order” field. In FIG. 46, as in the sixth embodiment, if the CRC calculation result of the MPDU separation is normal, it can be determined that the “MPDU length” information is correct, so the subsequent MPDU is cut out and the FCS is inspected. By doing so, it can be determined whether or not the MPDU has been normally received. In FIG. 46, the first “MPDU separation” and “MPDU1” are normally received. Here, in FIG. 46, consider a case where the CRC of the second “MPDU separation” from the beginning of PSDU is an error. In this case, as described in the sixth embodiment, the next correctly received MPDU separation is searched by continuously checking the CRC one octet according to the procedure of the flowchart shown in FIG. . In the example of FIG. 46, it is assumed that the third “MPDU separation” from the beginning of PSDU is normally received. At this time, as in the sixth embodiment, it is assumed that there is an MPDU between “MPDU 1” that can be normally received and the third “MPDU separation” from the beginning of the PSDU, and the MPDU separation length ( The FCS is inspected for the MPDU by subtracting the fixed length) that is mutually recognized between the transmitting and receiving terminals. That is, the error calculation is performed assuming that the end of the MPDU is immediately before the next normal MPDU separation found by scanning. As a result, if the FCS is normal, it is determined that the MPDU has been received normally. In the example of FIG. 46, even if the first and third “MPDU separation” from the top are successfully received as a result of the CRC check, the second “MPDU separation” occupied between them is incorrect. An example is shown in which “MPDU2” can be normally received by directly performing error calculation by FCS on “MPDU2”. Needless to say, if the FCS calculation result for the MPDU is invalid, a partial ACK indicating that the MPDU could not be received correctly is created.
In the example of FIG. 47, the transmitting terminal aggregates and transmits a plurality of MPDUs as shown in FIG. 46, and as a result of error calculation for each MPDU separation and MPDU on the receiving side, some MPDU separations (FIG. 47). (In the third from the beginning), even if the MPDU separation information received correctly before and after was correct, the MPDU sandwiched between them was normal (inspecting the FCS of the MPDU). In the partial ACK bitmap created by the side that has received the aggregated frame, “1” indicating all normal is described. Needless to say, the bit indicating whether data is normally received can be realized not only in positive logic but also in negative logic.

  Here, as shown in FIG. 48, when a certain MPDU separation (second in the example in the figure) is erroneous as a result of the CRC check, and continuously searching for a normal MPDU separation, the number of octets moved during the search However, if the maximum MPDU length (specified by IEEE802.11 standard, the maximum size that can be taken by one MPDU, specified in octets) is exceeded, two or more MPDU separations (and MPDUs) are incorrect. to decide. The notation “exceeding the maximum MPDU length” in FIG. 48 indicates that the length exceeds the maximum MPDU length and will be treated in the same manner. In this case, when creating a partial ACK bitmap indicating the reception status for the partial ACK frame returned by the receiver, the relative position of the frame that has been successfully received is speculative. In this way, the receiving side is notified of the reception status.

  In the example of FIG. 49, a certain MPDU separation (in the figure, the MPDU separation for the third MPDU) is incorrect, and as a result of sequentially calculating the CRC by one octet to retrieve the next MPDU separation, 5 This is a case where the MPDU separation to the MPDU is normal as a result of the CRC check. As a result of continuous scanning, the number of movements (octets) required for the search exceeds the maximum MPDU length, so two or more MPDU separations (and MPDUs) existing between two successfully received MPDU separations. ) Is wrong. Here, since the lengths of multiple MPDUs aggregated to one PSDU are not uniform, it is not possible to determine how many MPDU separations (and MPDUs) exist between two normal MPDU separations. Absent. Therefore, as shown in FIG. 49, it can be considered that all the MPDUs subsequent to the fifth MPDU (that is, the sixth MPDU) are erroneous and a partial ACK bitmap is created. In the example of FIG. 49, reception of the first two MPDUs is successful, and the subsequent MPDUs are all notified by a partial ACK to the transmission side. As a result, the transmitting side retransmits all the third and subsequent MPDUs. However, since the receiving side normally received the “5” MPDU in the first transmission, Discard duplicate frames.

  As the reception status at the time of creating a partial ACK, all subsequent MPDUs are regarded as errors as shown in FIG. 49, and a method of estimating retroactively from the end of PSDU as shown in FIG. Here, it is assumed that the number of MPDU separations existing in one PSDU is fixed, and the transmitting and receiving terminals recognize each other. In the example of FIG. 50, it is assumed that the first, fourth, seventh, and eighth MPDU separations from the top have been successfully received as a result of the CRC calculation. In the seventh embodiment, information indicating the order is not included. Assuming that the number of MPDU separations present in the PSDU is fixed, there are two MPDU separations (and MPDUs) between the first and fourth MPDU separations, and two between the fourth and seventh MPDU separations. It can be determined that MPDU separation (and MPDU) exists. If the number of octets required for searching between normal MPDU separations exceeds the maximum MPDU length, the FCS for the MPDUs sandwiched between MPDU separations cannot be calculated, so these MPDUs are regarded as errors. As a result, as shown in FIG. 50, the partial ACK bitmap returned from the receiving side to the transmitting side correctly indicates the reception status of the MPDU corresponding to the MPDU separation position calculated speculatively (as a result of the FCS, it can be received correctly). For the portion where the writing and search period exceeds the maximum MPDU length, a bit map indicating that reception was not successful is transmitted to the transmission side.

When the partial ACK is created speculatively, as shown in FIG. 51, a bit indicating the reception status in the partial ACK bitmap may be erroneously transmitted (shifted). In this case, as shown in FIG. 51, even if two MPDU separations in the PSDU are correctly detected and the FCS of the subsequent MPDU is normal, the MPDU is located in which part of the aggregated PSDU relatively. There is a possibility that the estimation of existence exists. In the example of FIG. 51, it is assumed that MPDUs with sequence numbers “1” to “8” are aggregated and transmitted, and the first and fifth MPDU separations and MPDUs are normally received. At this time, the partial ACK created by the receiving terminal can have a plurality of reception statuses as shown in FIG. This is because it is not possible to determine how many MPDU separations (and MPDUs) exist between two normal MPDU separations when the length of searching between MPDU separations exceeds the maximum MPDU length. Of the two types of partial ACK bitmaps created in the example of FIG. 51, the lower bitmap (1 0 0 0 1 0 0 0) is a case where the estimation is successful, and a partial ACK having this information is received The terminal that has transmitted the aggregated frame can appropriately perform window control and retransmission control. Here, if a partial ACK having a state in which the reception status is shifted (the upper part of FIG. 51: 1 0 0 1 0 0 0 0) is returned, the frame of sequence number “4” can be normally transmitted on the transmission side. It is assumed that the frame has the sequence number “5” as a retransmission target (“5” has been successfully transmitted).
FIG. 52 shows frame control at the time of retransmission. In the lower example where the estimation at the time of creation of the partial ACK was successful, "2", "3", "4", "6", "7", "8" for retransmission, and a new "9" MPDU were aggregated by window control. It shows a state. In the upper example, “5” received correctly on the receiving side is the retransmission target. However, even in the upper example, when retransmitting a frame in which multiple MPDUs are aggregated, as a result of using partial ACK from the receiving side (returning the reception status for the aggregate frame received at that time) and duplication check, By giving up the MPDU with the sequence number “4” on the receiving side, the subsequent frame sequence is not affected. Partial ACK is a means to notify the transmission side of the reception status for each MPDU at the time when a frame in which multiple MPDUs are aggregated is received, so there is no problem in window control on the transmission side, There is no such thing as repeated retransmissions indefinitely. The impact is only about a loss of one MPDU.

  In the seventh embodiment, when setting the traffic stream defined by IEEE802.11e, the MSDU size that can be transmitted is fixed, or by padding an appropriate amount of bits, the PSDU When all the aggregated MPDUs have an equal fixed length, the relative position of each MPDU can be determined more accurately.

(Eighth embodiment)
Consider a case in which a certain transmitting terminal aggregates and transmits a plurality of MPDUs to one PSDU as shown in FIG. The terminal that receives the aggregated frame checks the reception status of each MPDU, creates a partial ACK bitmap, and returns it to the transmitting side after the SIFS period. However, as shown in FIG. 54, when the partial ACK is incorrect and is not correctly received on the transmission side, the AIFS (Distributed Coordination Function Inter Frame Space) or the frame interval for each priority defined in IEEE802.11e is used. There is a problem that all MPDUs must be retransmitted after performing carrier sense and backoff in the period of Arbitration Inter Frame Space).

  Therefore, in the eighth embodiment of the present invention, as shown in FIG. 55, a terminal that has aggregated and transmitted a plurality of MPDUs to one PSDU detects an IEEE802.11 physical frame after the SIFS period. If the PSDU is an error as a result of the FCS check, a partial ACK retransmission request is transmitted to the destination after PIFS or SIFS. This PIFS or SIFS period is for the purpose of preventing interruption of frame transmission from other terminals during that period, and it goes without saying that it is not limited to either one in this embodiment. These frame intervals may be negotiated in some way between transmitting and receiving terminals, or may be premised on agreement among all terminals.

  If a terminal that has received a partial ACK retransmission request has transmitted a partial ACK before PIFS or SIFS (that is, immediately before) and corresponds to a terminal that has transmitted a partial ACK retransmission request, the terminal transmits the partial ACK retransmission request. The content of the ACK is transmitted as it is to the partial ACK retransmission request transmission terminal. Therefore, it is desirable that a terminal that receives the aggregated PSDU keeps the reception status for a certain period (minimum PIFS). FIG. 56 shows the frame format of the partial ACK retransmission request. The receiving side identifies the partial ACK retransmission request frame based on the type and subtype information in the IEEE802.11 MAC header. Alternatively, instead of defining a new frame as shown in FIG. 56, PSDU in which MPDU length information (in the MPDU separation or MAC superframe header) is specified as 0 (at this time, the MPDU itself is not aggregated) When the MPDU length in the PSDU is all 0 on the receiving side, it may be determined between the transmitting and receiving terminals so that the partial ACK transmitted immediately before is retransmitted. In addition, when defining a new frame as shown in FIG. 56, a plurality of partial ACK retransmission request frames for a plurality of destinations are aggregated, and time-sequential partials are obtained as in the first and second embodiments. A method of transmitting / receiving ACK (for retransmission) can also be adopted.

  According to the eighth embodiment of the present invention, it is not necessary to retransmit all MPDUs on the transmission side, and more efficient retransmission control can be performed. Needless to say, it can be used together with QoS control such as IEEE802.11e.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

The block diagram which shows the structure of the communication apparatus which concerns on embodiment of this invention. The figure which shows the transmission sequence of the unicast frame in the downlink between an access point (AP) and several terminal (STA) and this downlink Diagram for explaining collision of partial ACK frame The figure which shows the format example of the MAC super-frame header which concerns on embodiment of this invention The figure which shows the example of a format of the whole MAC super-frame which concerns on embodiment of this invention The figure which shows the multi-address bit map showing the start position of the destination based on embodiment of this invention The figure which shows the multi-address bit map showing the change of the destination which concerns on embodiment of this invention The figure which shows an example of the bit map information of partial ACK Diagram illustrating problems when destinations are aggregated out of order and when multi-address bitmaps are not used The flowchart which shows operation | movement of the receiving terminal which concerns on embodiment of this invention. The figure which shows a mode that it concerns on embodiment of this invention and transmits a partial ACK at a different time interval. FIG. 10 is a diagram illustrating a state in which partial ACKs are transmitted at different time intervals according to the embodiment of the present invention, and is a diagram for explaining a case where a reception error occurs in all MAC frames of a certain destination The figure which shows the frame sequence which concerns on the 1st Embodiment of this invention Schematic of communication procedure when implementing QoS The figure which shows the down traffic based on the 2nd Embodiment of this invention Diagram showing destination queue for downlink traffic per QSTA Diagram for explaining frame transmission by round robin Diagram for weighting the number of transmissions in downlink traffic to QSTA Diagram showing CAP (Controlled Access Phase) Diagram showing the case where aggregation of different destinations is not performed The figure which shows the case where frame aggregation of several destination is implemented with QoS according to the 2nd Embodiment of this invention. The figure which shows the frame sequence by the block ACK which is stipulated in IEEE802.11e The figure which shows the frame format in the case of aggregating several block ACK request | requirement frames to one frame concerning the 3rd Embodiment of this invention. The figure which shows the frame sequence which concerns on the 3rd Embodiment of this invention. The figure which shows the case where it aggregates with not only a block ACK request | requirement but the data frame (it does not require ACK) concerning the 3rd Embodiment of this invention. The block diagram which shows the structure of the communication apparatus which concerns on the 4th Embodiment of this invention. The figure which shows an example of a format of MAC super-frame The figure which shows an example of the MAC super frame with a several destination Diagram showing time difference reception of transmission to multiple destinations and partial ACK The figure which shows the carrier sense state which concerns on the 4th Embodiment of this invention The figure which shows the setting of NAV for every destination The figure which shows the example of an aggregation of QoS data and a CF-Poll frame The figure which shows the example of aggregation of the partial ACK frame to a several destination The figure which shows an example of the format which can concern on the 5th Embodiment of this invention and can perform a frame check with a legacy terminal. The figure which shows the carrier sense state which concerns on the 5th Embodiment of this invention The figure which shows the aggregation of the MPDU separation field and MPDU which concerns on the 6th Embodiment of this invention Diagram showing the format of MPDU separation Diagram showing the format of MPDU separation Diagram for explaining PSDU reception status and MPDU extraction Diagram for explaining PSDU reception status and MPDU extraction Flow chart showing search procedure for MPDU separation Diagram showing aggregate transmission and partial ACK Diagram showing an example of aggregation during retransmission The figure which shows the aggregation of the MPDU separation field and MPDU which concerns on the 7th Embodiment of this invention Diagram showing the format of MPDU separation Diagram for explaining PSDU reception status and MPDU extraction Diagram showing aggregate transmission and partial ACK Diagram for explaining PSDU reception status and MPDU extraction Diagram showing aggregate transmission and partial ACK Diagram showing aggregate transmission and partial ACK Diagram for explaining estimation of partial ACK bitmap Diagram for explaining estimation of partial ACK bitmap Diagram showing an example of aggregation during retransmission The figure for demonstrating the partial ACK retransmission request which concerns on the 8th Embodiment of this invention. The figure for demonstrating the partial ACK retransmission request which concerns on the 8th Embodiment of this invention. The figure which shows the frame format of a partial ACK resending request

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Communication apparatus, 101 ... Physical layer, 102 ... MAC layer, 103 ... Link layer, 104 ... Antenna, 105 ... Aggregation process part

Claims (17)

In a communication system having a communication device on the transmission side and a communication device on the reception side,
The transmission side communication device is:
A plurality of MAC frames corresponding to a plurality of destinations, each of the MAC frames comprising means for transmitting a single physical frame including data to be transmitted to the destination and transmission opportunity grant information;
The communication device on the receiving side is
Means for receiving the physical frame and extracting a MAC frame destined for the receiving communication device from the physical frame;
Based on the transmission opportunity grant information included in the MAC frame, whether or not a transmission opportunity for transmitting data is given from the receiving-side communication apparatus and a sufficient period for sending the data is given. Means for determining;
Communication comprising: a transmission means for transmitting a MAC frame representing delivery confirmation and a MAC frame of data to be transmitted from the reception side communication device in a single physical frame according to a determination result based on the transmission opportunity grant information. system. Means for creating a plurality of delivery confirmation MAC frames representing delivery confirmation for each of the MAC frames transmitted from the plurality of first kind communication devices by the first kind physical frame;
Error detection information used for error detection when handled as a single MAC frame, and the plurality of delivery confirmation MAC frames, received by both the first type communication device and the second type communication device A means to build possible single and second kind physical frames;
And a transmission unit configured to transmit the physical frame for delivery confirmation. Means for constructing a frame representing one PSDU (physical layer conversion protocol service data unit) including a plurality of MPDUs (MAC protocol data units) and transmitting the frame to a destination communication device;
Each MPDU included in the PSDU of the frame includes MPDU length information, frame number information, and one CRC (cyclic redundancy check) information corresponding to the length information and order information. Communication device. 4. The communication apparatus according to claim 3, wherein the frame number information is a sequential number assigned continuously from the beginning of the PSDU. 4. The communication apparatus according to claim 3, wherein the frame number information is a sequence number described in an MPDU or a designated sequence number and fragment number. Means for receiving a partial response from the destination communication device;
Means for constructing a retransmission frame in response to the partial response,
The communication apparatus according to claim 3, wherein a zero value is set in the length information of the MPDU for an MPDU that is not subject to retransmission. Means for receiving a partial response from the destination communication device;
Means for constructing a retransmission frame in response to the partial response,
4. The communication apparatus according to claim 3, wherein a discontinuous number excluding MPDUs not to be retransmitted is set in the number information of the frame. It represents one PSDU (physical layer conversion protocol service data unit) including a plurality of MPDUs (MAC protocol data units), and each MPDU included in the PSDU of the frame includes MPDU length information, frame number information, Means for receiving a frame having one CRC (Cyclic Redundancy Check) information corresponding to length information and order information;
Means for checking whether or not reception abnormality has occurred in the length information of the MPDU and the frame number information using the CRC information;
Means for checking whether or not the MPDU has been normally received using the FCS (frame check sequence) of the MPDU specified based on the length information of the MPDU;
Means for creating and transmitting a partial response indicating whether or not the MPDU has been successfully received. If reception abnormality is detected by the inspection using the CRC information, means for retrieving length information of the next MPDU received normally;
Means for identifying the FCS of the corresponding MPDU based on the retrieved MPDU length information;
The communication apparatus according to claim 8, further comprising: a unit that checks whether the MPDU has been normally received using the identified FCS. On the premise that number information is continuously given at the time of receiving the frame,
If reception abnormality is detected by the inspection using the CRC information, search the length information of the next MPDU successfully received,
Identifying the FCS of the corresponding MPDU based on the retrieved MPDU length information, and checking whether the MPDU was successfully received using the FCS,
If the number interval between the first MPDU and the second MPDU received normally is 2 or more, the MPDU between the first MPDU and the second MPDU could not be received normally. The communication device according to claim 8, wherein the communication device is determined to be a device. It represents one PSDU (physical layer conversion protocol service data unit) including a plurality of MPDUs (MAC protocol data units), and each MPDU included in the PSDU of the frame corresponds to the length information of the MPDU and the length information. Means for receiving a frame having two CRC (Cyclic Redundancy Check) information;
Means for inspecting whether or not reception abnormality has occurred in the length information of the MPDU using the CRC information;
If reception abnormality is detected by the inspection using the CRC information, means for retrieving length information of the next MPDU received normally;
Means for checking whether or not the MPDU has been normally received using the FCS (frame check sequence) of the MPDU identified based on the length information of the retrieved MPDU;
Means for speculatively creating and transmitting a partial response indicating whether or not the MPDU has been successfully received. 12. The communication apparatus according to claim 11, wherein when the length information of the retrieved MPDU exceeds a maximum MPDU length, it is determined that all subsequent MPDUs are broken. After receiving the frame, the MPDU length information is continuously searched, and when the error calculation result is normal, if the searched length exceeds the maximum MPDU length, it is aggregated in the PSDU. The communication apparatus according to claim 11, wherein the reception status is speculatively determined retroactively from the end of the PSDU, assuming that the MPDU length information is a fixed number. Means for receiving a retransmission frame based on the speculatively generated partial response;
The communication apparatus according to claim 11, further comprising: a partial response frame that responds to the retransmission frame. Means for transmitting a frame representing one PSDU (physical layer translation protocol service data unit) including a plurality of MPDUs (MAC protocol data units);
Means for transmitting a retransmission request for a partial response to a destination after a period during which no interruption from another terminal including an SIFS period or a PIFS period is permitted after transmission of the frame. Means for receiving a frame representing one PSDU (physical layer translation protocol service data unit) including a plurality of MPDUs (MAC protocol data units);
Means for transmitting a partial response frame in response to receipt of the frame;
And a means for retransmitting the partial response frame if a partial response retransmission request is received after the SIFS period or PIFS period. 17. The communication apparatus according to claim 16, further comprising means for storing a reception status represented by the partial response frame for a predetermined period or more from the time of transmission of the first partial response frame for retransmission of the partial response. .

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