Method and system for aggregating frames to be transmitted over channel in wireless network

The present invention relates collectively to wireless communication networks, and more specifically to combining frames in such networks.

Recent advances in the fields of wireless communications, smart antennas, digital signal processing and VLSI have made it possible to provide very high data rate channels at the physical layer of wireless communications networks. These technologies provide data rates that are at least an order of magnitude higher than those currently available.

The Open Systems Interconnection (OSI) model defines the application layer, presentation layer, session layer, transport layer, network layer, data link layer and physical layer. The data link layer includes a logical link control (LLC) layer and a medium access control layer. The MAC layer controls how to access the network, and the LLC layer controls frame synchronization, flow control and error checking. The physical layer transmits signals over the network. The present invention relates to the data link layer and the physical layer.

"IEEE 802.11n PAR: Draft Amendment to STANDARD for Information Technology -Telecommunications and information exchange between systems-Local and Metropolitan networks --Specific requirements --Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications: Enhancements for "Higher Throughput" specifies the data speed up to 100Mbps in the MAC layer. "IEEE P802.15.SG3a PAR: amendment to Standard for Telecommunications and Information Exchange Between systems --LAN / MAN Specific Requirements: The Higher Speed Physical Layer Extension for the High Rate Wireless Personal Area Networks (WPAN) defines data rates of 110 Mbps and above based on ultra-wideband (UWB) communications for personal area networks (PANs).

However, in order to pass 100Mbps throughput to the layers above the MAC Service Access Point (SAP), it is simply a physical layer solution due to the significant amount of protocol overhead caused by the current protocol for the MAC layer. Is not enough. Therefore, current MAC layer protocols must be improved to accommodate wider bandwidth.

Frame formation As shown in Figure 1, for transmitter 100 in a wireless local area network (WLAN) designed to comply with the IEEE 802.11 standard, each MAC received from the logical link control layer (LLC) 110. A service data unit (MSDU) or frame 111 is added with a MAC header and frame check sequence (FCS) trailer at MAC layer 120 to form a MAC layer protocol data unit (MPDU) or frame 121. At the physical layer, the MPDU is received as a physical layer service data unit (PSDU) or frame 122. At physical layer 130, a physical layer convergence procedure (PLCP) header, PLCP preamble, and tail and pad bits are added to PSDU frame 122 to provide a physical layer protocol data unit (PPDU) or frame 131 for transmission over the channel. It is formed.

FIG. 2 shows format 200 for MPDU frame 121 at medium access control (MAC) layer 120, and FIG. 3 shows format 300 for PPDU frame 131 at physical (PHY) layer 130. The PPDU frame includes the PLCP preamble field 311, the signal field 312 and the data field 313. Details of the other fields in these formats are specified in the standard.

Frame transmission Networks designed to comply with the IEEE 802.11 standard have distributed coordination function (DCF) and point coordination (PCF). Use function) to regulate channel access. DCF applies to both infrastructure and ad hoc modes and follows a known MAC tier method called CSMA / CA. Before each packet is transmitted, the transmitting station detects the channel and waits until the channel is no longer used. The station then deferes the DCF frame interval (DIFS) time interval, enters the backoff stage, and determines a random time interval called the backoff time. The backoff time is evenly distributed from 0 to the contention window (CW) size. After the backoff timer expires, only one frame is transmitted on that channel, after which the receiving station sends an ACK message. The frame notified to all stations is not acknowledged. To reduce the probability of collision, the size of the CW is increased after each collision is detected until the maximum CW value is reached. After successfully transmitting the frame, the CW is reset to a constant minimum.

Bandwidth is a scarce resource in wireless networks. For high-throughput WLANs that comply with the requirements of the IEEE 802.11n standard, the MAC protocol achieves 70-80% efficiency in MAC Service Access Point (SAP) to meet design requirements for 100 Mbps bit rates. Must. The overhead associated with frame transmission conforming to the current IEEE 802.11 standard wastes bandwidth. If each frame is acknowledged individually, the following items correspond to significant overhead for frame transmission: MAC header, physical layer header (PLCP header), PLCP preamble, backoff, DIFS time. , SIFS time and ACK message.

<p> It is desirable to reduce this overhead so that the bandwidth available on the radio channel can be increased.</p>

<p> Future IEEE 802.11n standards will require 100 Mbps throughput in MAC SAP. The various mechanisms of the current IEEE 802.11 and IEEE 802.11e MAC protocols have significant overhead, resulting in reduced bandwidth.</p><p> Therefore, it is not possible to apply the current MAC protocol to the IEEE 802.11n standard as is, unless the efficiency of the protocol is significantly increased.</p><p> The present invention provides a method for combining a MAC service data unit (MSDU) and a physical service data unit (PSDU). The frame coupling method according to the invention achieves a significant improvement in throughput without further complicating the protocol.</p>

The present invention provides methods and systems for combining frames in a wireless communication network. The coupling can be done at two levels: the MSDU level within the MAC layer and the PSDU level within the PHY layer. The MSDU level, our same destination address frames having and traffic class are combined into a single MPDU. MPDU frames with different destination addresses are combined at the PSDU level and share one PLCP preamble. Thus, both excessive overhead at the MSDU level, such as the MAC header per MSDU, and excessive overhead at the PSDU level, such as the PLCP preamble, are reduced to the maximum, thereby significantly increasing throughput. As mentioned above, the method of performing coupling at the PSDU level also resolves the internal collisions faced by systems designed according to the current IEEE802.11e standard. The coupling can be done at either or both levels, depending on the application and traffic requirements. Frame coupling can work during contention or contention-free. Furthermore, the present invention also provides a method for confirming and responding to a coupling frame.

For the purposes of this description and the appended claims, the following terms shall be familiar and defined in the readily available IEEE Standards Association. MSDU MAC service data unit MPDU MAC layer protocol data unit PSDU Physical Layer Service Data Unit FCS frame check sequence OFDM Orthogonal Frequency Division Multiplexing PPDU Physical Layer Protocol Data Unit

Frame coupling-at contention Join at MSDU level FIG. 20 shows a transmitting station according to the present invention. The LLC layer 110 determines whether or not the MSDU frames 111 placed in the queues 2001 to 2002 of the MAC layer 120 are combined. The decision is based on the destination address and traffic class (TID) of those frames. If the destination address and TID are both the same, then those frames are combined into a single MPDU frame.

FIG. 4 shows a coupled MPDU frame 400 according to the present invention. The frame 400 includes a MAC header 410 and a combined frame body 600. The combined MPDU frame can have any length that meets the physical layer requirements and the corresponding transmit duration limit requirements specified by the Transmission Opportunity (TXOP). The format of MAC header 410 is specified by the IEEE 802.11e standard. However, here, the sequence control field 211 of standard format 200 shown in FIG. 2 is referred to as the "start" sequence control field 411. This field represents the sequence number of the "first" MSDU frame in the join frame body field 600. The format of the start sequence control field 411 is specified by the IEEE 802.11 standard. Since each MSDU frame in the body of the coupled frame has its own FCS, the coupled MPDU 400 according to the present invention does not need to have the FCS 212 shown in FIG.

The QoS control field 500 is shown in Figure 5. This field includes a TID field 511, an End of Service Time (EOSP) field 512, an ACK field 513, an MPDU join field 514, and a TXOP field 515. The MPDU field 514 is set to 1 if the frame is combined with multiple MSDUs in the body 600.

FIG. 6 shows the format of the coupled frame body 600 with multiple MSDU triplets. Each MSDU610 triplet contains a header 700, an MSDU frame 612, and an FCS613 for that MSDU frame. FCS613 is determined according to the IEEE 802.11 standard. Note that this FCS is relevant to only one MSDU.

FIG. 7 shows the format 700 of the header field 700, which includes a length field 711, an additional MSDU data field 712, a reserved field 713, and a sequence control field 714. The length field indicates the total number of bytes up to 2048 bytes in the immediately following MSDU payload field. The 1-bit "additional MSDU data" field 712 in the header indicates whether there is a subsequent MSDU. Sequence control is specified by the IEEE 802.11 / 11e standard. Sequence control is unique for each traffic TID.

Binding at PSDU level All PSDUs at transmit station 2000 can be combined regardless of their destination address or transmission rate. PSDUs with different TIDs may also be eligible to combine if certain conditions described below are met. Each frame from LLC layer 110 received by MAC layer 120 competes for a channel according to an appropriate channel access method with a set of QoS control parameters 500 corresponding to the TID as defined by the IEEE 802.11e standard. .. After one of the frames in a particular queue has accessed the channel, all frames in that queue can be combined as long as the TXOP for that TID is justified.

According to current standards, internal collisions occur when the backoff counters for frames of various TIDs are simultaneously decremented to 0. According to the current IEEE 802.11e standard, internal conflicts are resolved by transmitting the highest priority frames, and the lower priority frames are rescheduled according to the new backoff time.

In contrast, the present invention combines all frames involved in an internal collision with all frames stored in the same queue as frames that "win" access contention.

FIG. 8 shows a format 800 for a combined PPDU according to the invention, which includes a PLCP preamble field 811 and a PLCP header field 812 and a corresponding PSDU field 813, a combined BlockACK request field 814, and a tail field 815. , Includes pad field 816 and. PLCP preambles, tails and pads are specified by the IEEE 802.11a standard, as shown in Figure 3.

Since each PSDU can have a different destination address, the transmission rate for the PSDU can be different from the rate for the adjacent PSDU. This is a problem not found in conventional methods.

Therefore, the OFDM symbol 801 is inserted between multiple fields to allow the transmitter to adjust the speed even if the speeds of adjacent PSDUs are different. The OFDM symbol 801 is not needed if the velocities are the same. The OFDM symbol has a unique pattern that allows the receiving station to distinguish between the start of the next PLCP header 812 and the end of the preceding PSDU frame 813. Note that the preceding PSDUn and subsequent PLCP header n + 1 are used to control the acknowledgment, as will be explained in more detail later.

FIG. 9 shows format 900 for header 812, which has a speed field 911, a parity field 913, a tail field 914, and a service field 915, as defined in the IEEE802.11a standard. Including. The length field 912 indicates the length of the corresponding PSDU813.

FIG. 10 shows format 1000 for service field 915, which includes scrambling initialization field 1011, parameter field 1012, and reserved field 1013. According to the IEEE802.11a standard, the initial state of the scrambler is set to a non-zero pseudo-random state. All symbols belonging to a MAC frame are transmitted by using the same initial state for scrambling. The receivers reverse scramble in the same order.

Table A shows the possible values for parameter field 1012. The receiver uses the parameter fields to determine the type of coupling used in the current PSDU frame and whether subsequent PSDUs in the same PPDU have the same transmission rate as the current PSDU frame. This information can also imply whether or not the OFDM symbol 801 delimits the current PSDU frame.

<tables num="1"><img file="JP4680263B2_D0001.tif" /></tables>

As mentioned earlier, the combined BlockACK request function is performed using the immediately preceding combined PSDUn 813 shown in FIG. 8 and the subsequent PLCP header n + 1 812.

Figure 11 shows the format 1100 of PSDUn + 1 (also known as a combined BlockACK request), which includes the frame control field 1101, the duration field 1102, the receiver address field 1103, and the transmitter address field 1104. Contains the join BlockACK request frame body field 1105 and the FCS field 1106. The receiver address (RA) is set to the broadcast address so that the frame body 1105 is decoded by all stations in the network. The transmitter address (TA) is the MAC address of the transmitter. Both the duration field 1102 and the FCS field 1106 apply to all BlockACK request messages that are joined within the join BlockACK request frame body field 1105.

FIG. 12 shows format 1200 of the join BlockACK request frame body field 1105. This information is transmitted at the basic transmission rate and ensures that it is received reliably. The body 1200 contains at least one BlockACK request element, including a duration field 1201, a receiver address field 1202, a BAR control field 1203, a BlockACK start sequence control (TID) field 1204, and an FCS field 1205. Duration field 1201 applies to individual BlockACK request elements. The receiver address (RA) 1202 is the MAC address of the receiving station. Each receiving station corresponds to one element in the combined BlockACK request frame body. One BlockACK request element can contain up to four BlockACK start sequence numbers.

FIG. 13 shows the BlockACK request control field format 1300. The fields include a type field 1301, a TID bitmap 1302, an initial backoff value (IBV) field 1303, and a reserved field 1304. Type field 1301 indicates the type of current BlockACK session. Possible values for type field 1301 are shown in Table B.

<tables num="2"><img file="JP4680263B2_D0002.tif" /></tables>

The TID bitmap field 1302 has one bit for every four possible sequence control fields 1204. For example, if bit 2 is 1, TID0 of the transmitting station (TA) requests a BlockACK from the receiving station (RA) for a set of frames, and the first of those frames is , Has a sequence control field as BlockACK start sequence control (TID0). The number of "1" s in the TID bitmap field is equal to the number of BlockACK start sequence control fields contained in the BlockACK request element. Using this information, the receiver can estimate the length of the BlockACK request element. The IBV field 1303 indicates the number of backoff time slots to use before sending the BlockACK message, as shown in FIG.

FIG. 14 shows the timing for the block acknowledgment. After receiving the join frame 1401, the receiving station j responds with a BlockACK message 1405 when a BlockACK element is present in the last PSDU of the received join frame. To send a BlockACK message, the station first sets the initial value of its backoff counter to IBV1303. The receiving station then backs off the IBV by 1403 slots before sending the BlockACK message. For each BlockACK message, the station accesses the channel using a CSMA-like technique. When the channel is no longer in use, after receiving frame 1401, the station initiates a backoff at SIFS time 1402, so that BlockACK message has the highest priority in channel contention and is of another type. There will be no conflict with BlockACK messages that have frames. In addition, all BlockACK messages resulting from the receipt of a PSDU combined within the same PPDU are designated with a different number of backoff slots. Therefore, potential conflicts between these BlockACK messages are avoided and various receivers can acknowledge and respond to MSDUs contained within the same join frame to prevent conflicts.

Figure 15 shows the format 1500 of the BlockACK message 1405, which includes the frame control field 1501, the duration field 1502, the RA field 1503, the TA field 1504, the BlockACK control (BA) field 1505, and the BlockACK start. Includes a sequence control field 1506, a BlockACK bitmap field 1507, and an FCS field 1508. These fields are defined according to the IEEE 802.11e standard, except that a single BlockACK message can contain acknowledgments for multiple TID frames.

FIG. 16 shows the format 1600 of the BlockACK (BA) control field 1505, which includes a type field 1601, a TID bitmap field 1602, a NAK field 1603, and a reserved field 1604. The TID bitmap field 1602 is the same as the field inside the BlockACK request element. NAK field 1603 can indicate whether an acknowledgment is used or a negative response is used.

Figure 17 shows the format 1700 of the BlockACK bitmap field 1507, which contains a pair of relative sequence number 1701 and encoded TID field 1702. Each relative sequence number (RSN) is determined as follows. RSN = (TIDx sequence number-TIDx start sequence number) The encoded TID field 1702 is a binary representation of the TID associated with the frame of the relative sequence number. Two bits are sufficient, as there are only four priorities at the time of contention.

Instead of including a fixed-length BlockACK bitmap, you can acknowledge only the correct frame or the incorrect frame, whichever is less. Please refer to US Patent Application No. 10 / 917,053, "Method for Acknowledging Data Packet in a Network," filed by Gu et al. On August 12, 2004 and incorporated herein by reference.

Combined frame size adaptation In wireless networks, channel conditions change rapidly, especially if the station is a mobile station. If the quality of the channel deteriorates, the larger the frame size, the higher the probability of loss than the smaller frame. Therefore, it is desirable to have a frame size that can be dynamically adjusted for momentary channel conditions. In addition, the transmission rate can also be adapted to the instantaneous conditions of the channel. Therefore, the combined frame size adjustment should work with the rate adaptation scheme.

When contention is free When contention-free, for example HCCA, a parameterized channel access method is used. The transmission opportunity (TXOP) is specified for each traffic stream (TS). If the TXOP assigned to one traffic stream cannot be used up at a particular time, the TS will confiscate the unfinished TXOP and allow the next scheduled TS to start the TXOP. Therefore, the coupling of frames with various TIDs is inappropriate. Moreover, since each TS is assigned a unique pair of source and destination addresses, combining frames with different destination addresses also violates the basic principles of parameterized traffic transmission. Therefore, when contention-free, such as HCCA, frames are coupled only at the MSDU level. However, at other contention-free times, such as the IEEE 802.11 standard PCF, the PCF can send multiple frames with different destinations in a single polling operation, so at both the MSDU and PSDU levels. Frames can be combined.

The MSDU coupling when the contention is free is also shown in FIGS. 4 to 7 in the case of the coupling when the contention is free. Here, the BlockACK request and BlockACK message described in Related Patent Application No. 10 / 917,053 can be used. The format of the BlockACK request frame is that the BA field has a format 1800 as shown in FIG. 18, including a type field 1801, a block size field 1802, a reserved field 1803, and a TID field 1804. It is a format as defined in the IEEE802.11e standard. As mentioned above, type field 1801 indicates that the BlockACK is for the frame that was joined when contention free. The block size field 1802 stores the number of frames requesting an acknowledgment. TID field 1804 points to the traffic stream associated with that BlockACK message.

Frame join parameters As described herein, is the transmitting station that joins the frames inspected the MPDU binding field 514 of the QoS control field 500 of the MAC header 410 and is given the ability for the receiving station to handle the binding field? Judge whether or not. This is accomplished by sending an additional join level 1/2 (ADDAL) request frame and receiving an ADDAL response frame. The receiving station has the option of accepting or rejecting the request. If the receiving station accepts the request, it can negotiate the maximum size of the frame join. Table C shows the possible action field values.

<tables num="3"><img file="JP4680263B2_D0003.tif" /></tables>

The ADDAL request and ADDAL response have the same frame format as listed in Table D.

<tables num="4"><img file="JP4680263B2_D0004.tif" /></tables>

The category field is set to 4, which represents a frame join. The action fields are set to 0 and 1 to indicate an ADDAL request or ADDAL response, respectively. The dialog token field is set to a non-zero value selected by the station. The frame join parameters are shown in FIG. 19 and include a join level field 1901, a maximum frame size field 1902, and a TID field 1903.

The format of the join level field 1901 is shown in Table E.

<tables num="5"><img file="JP4680263B2_D0005.tif" /></tables>

When frame coupling at the MSDU level is supported, the maximum coupling frame size 1902 indicates the maximum size, which can be determined by the transmitter or receiver, whichever is smaller. The TID field 1903 represents the TID for which the frame join is negotiated.

System structure Transmitter FIG. 20 shows the structure 2000 for frame coupling in the transmitter. The structure includes an LLC layer 110, a MAC layer 120, and a PHY layer 130. The MAC layer includes queue 2001 for prioritized traffic streams and queue 2002 for parameterized traffic streams. Blocks 2010 and 2020 perform MSDU and PSDU level coupling as described herein, respectively, at the MAC and PHY layers. Note that MSDU joins are done on a queue-by-queue basis, but PSDU joins are done on all queues with different TIDs at the same time.

After MSDU frames from LLC layer 110 are received at MAC layer 120, they are stored in queues 2001 and 2002 according to priority and traffic class. At the time of contention, channel access begins immediately after a frame becomes head of line (HOL) in the corresponding queue. After successful channel competition, the MSDU join scans the queue to locate all frames with the same destination address, after which those frames are combined into a single MPDU and the appropriate header for that frame. And a trailer is added.

Note that the total size of the combined frame at the MSDU level is constrained by the limits set by the corresponding TXOP, the current physical channel conditions, and the maximum frame size limit imposed by the physical layer. PSDU binding is called by the event of successful channel competition. PSDU Join 2020 first checks the "winning" queue and requires MSDU Join 2010 to collect all frames with the same TID but different destinations.

In the event of an internal conflict, the PSDU coupling unit 2020 communicates with the MSDU unit 2010, which has a lower priority and is associated with the queue involved in the internal conflict. These units are required to search the corresponding queue for head of line (HOL) frames. The MSDU unit also has the right to decide whether or not to perform the join in these retrieved frames. Finally, the PSDU unit adds a PLCP header for each MPDU frame collected and passes the combined frame to a lower functional block for modulation and transmission. When contention-free, only the MSDU unit applies to frames in the queue that have the same traffic class and destination address.

Receiving machine FIG. 21 shows the receiver structure 2100. In this case, units 2110 and 2120 perform MSDU decomposition and PSDU decomposition, respectively. The PSDU decomposition unit 2120 removes the PLCP header and passes the MPDU frame to the MSDU decomposition unit 2110, and the MSDU decomposition unit 2110 removes the MAC header and trailer and temporarily transfers all priority MSDU frames to the shared memory 2101. The LLC layer 110 retrieves frames from its memory for subsequent processing.

Effect of the invention According to the present invention, it becomes possible to communicate in a wide band width in a high-speed wireless local area network (WLAN). The present invention provides efficient and flexible frame coupling methods and systems for high throughput WLANs. When the present invention is applied, frames can be combined at both the MSDU level and the PSDU level, resulting in a significant reduction in the overhead associated with prior art frame transmission. The present invention is compatible with networks designed according to the IEEE 802.11 standard. The present invention is useful for frame transmission during contention, eg, EDCA, ADCA, and frame transmission during contention-free, eg HCCA, SCCA. The present invention can be applied to networks operating in either infrastructure mode or ad hoc mode, and to other networks such as networks designed according to the IEEE 802.15.3 standard.

Although the present invention has been described by way of example in preferred embodiments, it should be understood that various other modifications and modifications can be made within the spirit and scope of the invention. Therefore, the object of the appended claims is to cover all such modifications and modifications that fall within the true spirit and scope of the invention.

<figref num="1">It is a block diagram of the layer in the transmission station of the wireless communication network by this invention.</figref><figref num="2">It is a block diagram of the MPDU frame of the prior art.</figref><figref num="3">It is a block diagram of the PPDU frame of the prior art.</figref><figref num="4">It is a block diagram of the combined MPDU frame by this invention.</figref><figref num="5">It is a block diagram of the QoS control field according to this invention.</figref><figref num="6">It is a block diagram of the coupling frame main body by this invention.</figref><figref num="7">It is a block diagram of the header field for MSDU in the coupling frame body by this invention.</figref><figref num="8">It is a block diagram of the combined PPDU according to the present invention.</figref><figref num="9">It is a detailed block diagram of the PCLP header field of FIG.</figref><figref num="10">It is a detailed block diagram of the service field according to this invention.</figref><figref num="11">It is a detailed block diagram of the coupling BlockACK according to the present invention.</figref><figref num="12">FIG. 6 is a block diagram of a frame body field in a combined BlockACK request according to the present invention.</figref><figref num="13">FIG. 3 is a block diagram of a BlockACK request (BAR) control field according to the present invention.</figref><figref num="14">It is a timing diagram of the block confirmation response by this invention.</figref><figref num="15">It is a block diagram of the BlockACK message according to the present invention.</figref><figref num="16">It is a block diagram of the block ACK (BA) control field by this invention.</figref><figref num="17">It is a block diagram of the BlockACK bitmap field according to the present invention.</figref><figref num="18">It is a block diagram of the block ACK request frame by this invention.</figref><figref num="19">It is a block diagram of a frame coupling parameter by this invention.</figref><figref num="20">It is a block diagram of the transmitting station by this invention.</figref><figref num="21">It is a block diagram of the receiving station by this invention.</figref>