U.S. patent application number 11/201258 was filed with the patent office on 2006-05-04 for communication method for wireless lans.
Invention is credited to Tomoko Adachi, Tetsu Nakajima, Yasuyuki Nishibayashi, Masahiro Takagi, Tomoya Tandai, Yoriko Utsunomiya.
Application Number | 20060092871 11/201258 |
Document ID | / |
Family ID | 36261733 |
Filed Date | 2006-05-04 |
United States Patent
Application |
20060092871 |
Kind Code |
A1 |
Nishibayashi; Yasuyuki ; et
al. |
May 4, 2006 |
Communication method for wireless LANS
Abstract
A physical frame is generated and transmitted to a destination
terminal. In this physical frame, one of a data frame, an
acknowledgement frame, and an acknowledgement request frame, and a
transmission permission frame which is used in place of a normal
Ack frame associated with a delayed Block Ack, and permits the
destination terminal to perform piggyback transmission, are
aggregated.
Inventors: |
Nishibayashi; Yasuyuki;
(Kawasaki-shi, JP) ; Takagi; Masahiro; (Tokyo,
JP) ; Adachi; Tomoko; (Urayasu-shi, JP) ;
Nakajima; Tetsu; (Yokohama-shi, JP) ; Tandai;
Tomoya; (Tokyo, JP) ; Utsunomiya; Yoriko;
(Tokyo, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Family ID: |
36261733 |
Appl. No.: |
11/201258 |
Filed: |
August 11, 2005 |
Current U.S.
Class: |
370/328 ;
370/469; 370/477 |
Current CPC
Class: |
H04L 1/1685 20130101;
H04L 1/1835 20130101; H04L 1/1614 20130101; H04W 72/14 20130101;
H04L 1/1671 20130101; H04L 1/188 20130101; H04W 74/0866
20130101 |
Class at
Publication: |
370/328 ;
370/477; 370/469 |
International
Class: |
H04J 3/22 20060101
H04J003/22; H04J 3/16 20060101 H04J003/16; H04Q 7/00 20060101
H04Q007/00; H04J 3/18 20060101 H04J003/18 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 1, 2004 |
JP |
2004-318487 |
Claims
1. A communication method comprising: generating a physical frame
in which: one of a data frame, an acknowledgement frame, and an
acknowledgement request frame, and a transmission permission frame
which is used in place of a normal Ack frame associated with a
delayed Block Ack, and permits a destination terminal to perform
piggyback transmission, are aggregated; and transmitting the
physical frame to the destination terminal.
2. A communication method comprising: receiving a physical frame in
which: one of a data frame, an acknowledgement frame, an
acknowledgement request frame, and a transmission permission frame
which is used in place of a normal Ack frame associated with a
delayed Block Ack, and permits a destination terminal to perform
piggyback transmission, are aggregated; and detecting notification
of the normal Ack associated with the delayed Block Ack on the
basis of the transmission permission frame.
3. A communication method comprising: generating a physical frame
in which a transmission permission frame for permitting piggyback
transmission and data frames for a plurality of destination
terminals are aggregated; and transmitting the physical frame to
said plurality of destination terminals, wherein after data in an
opposite direction is received from the destination terminal, a
confirmation notification indicating that transmission of a partial
response is performed by a delayed type is replaced with a
transmission permission frame to the destination terminal.
4. A communication method comprising: receiving a physical frame in
which a transmission permission frame for permitting piggyback
transmission and data frames for a plurality of destination
terminals are aggregated; transmitting a data frame to a
transmission source terminal of the physical frame upon
piggybacking the data frame on a partial response frame; and
transmitting a plurality of MAC frames to a plurality of
destination terminals again to a plurality of destination terminals
upon aggregating the MAC frames within a continuous transmission
permission period currently held by a terminal which has
transmitted a physical frame to said plurality of destination
terminals, wherein destination information contained in plural
destination control information contained in the physical frame is
checked, and if an address of a receiving terminal of the physical
frame is not contained, it is determined that application of a
delayed policy to a partial response to a piggybacked and
transmitted data frame has failed.
5. A communication method comprising: receiving a physical frame in
which MAC frames which are addressed to a plurality of destination
terminals and have a plurality of priorities are aggregated;
storing MAC frames of a received physical frame in a reception
buffer prepared for each priority; and managing, on a premise that
a control information frame is aggregated in a head portion of a
MAC frame for each destination and each priority, the reception
buffer by using sequence number information of a data frame
following the control frame if an error calculation result on the
control frame is correct, and the data frame has been successfully
received.
6. A method according to claim 1, wherein the piggyback
transmission comprises transmitting, from the destination terminal
to a transmission source, a physical frame in which an
acknowledgement frame and at least one MAC frame are
aggregated.
7. A method according to claim 1, further comprising determining,
in accordance with a remaining period of a channel use permission
period, whether or not to aggregate the transmission permission
frame in the physical frame.
8. A method according to claim 1, further comprising: determining,
after a lapse of a minimum frame time since transmission of the
physical frame, whether or not an acknowledgement frame is
contained in a physical frame returned from the destination
terminal; and requesting a retransmission of the acknowledgement
frame when the acknowledgement frame is not contained.
9. A method according to claim 1, wherein the presence/absence of
the acknowledgement frame is determined on the basis of error
detection at a specific frame position in a physical frame returned
from the destination terminal.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from prior Japanese Patent Application No. 2004-318487,
filed Nov. 1, 2004, the entire contents of which are incorporated
herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a communication apparatus
and method which perform media access control on the basis of the
carrier sense information of a physical layer and the carrier sense
information of a MAC layer.
[0004] 2. Description of the Related Art
[0005] Media access control (MAC) is control for causing a
plurality of communication apparatuses which perform communication
while sharing the same media to decide how to use the media in
transmitting communication data. Owing to media access control,
even if two or more communication apparatuses transmit
communication data by using the same media at the same time, there
is less chance of the occurrence of a phenomenon (collision) in
which a communication apparatus on the receiving side cannot
separate communication data. Media access control is also a
technique for control-ling access from communication apparatuses to
a media so as to minimize the chance of the occurrence of a
phenomenon in which, despite the presence of communication
apparatuses having transmission requests, the media is not used by
any of the communication apparatuses.
[0006] In wireless communication, since it is difficult for a
communication apparatus to monitor transmission data while
transmitting the data, media access control (MAC) which is not
premised on collision detection is required. IEEE 802.11 is a
typical technical standard for wireless LANs, and uses CSMA/CA
(Carrier Sense Multiple Access with Collision Avoidance). According
to CSMA/CA in IEEE 802.11, in the header of a MAC frame, a period
(Duration) until the end of a sequence comprising one or more frame
exchanges following the frame is set. In this period, a
communication apparatus which is irrelevant to the sequence and has
no transmission right waits for transmission upon determining a
virtual occupied state of the media. This prevents the occurrence
of collision. On the other hand, a communication apparatus which
has a transmission right in this sequence recognizes that the media
is not used except for a period during which the media is actually
occupied. IEEE 802.11 defines that the state of a media is
determined on the basis of such a combination of virtual carrier
sense on a MAC layer and physical carrier sense on a physical
layer, and media access control is performed on the basis of the
determination.
[0007] IEEE 802.11 using CSMA/CA has increased the communication
speed mainly by changing the physical layer protocol. With regard
to the 2.4 GHz band, there have been changes from IEEE 802.11
(established in 1997, 2 Mbps) to IEEE 802.11b (established in 1999,
11 Mbps), and further to IEEE 802.11g (established in 2003, 54
Mbps). With regard to the 5 GHZ band, only IEEE 802.11a
(established in 1999, 54 Mbps) exists as a standard. In order to
develop standard specifications directed to further increase
communication speeds in both the 2.4 GHz band and the 5 GHz band,
IEEE 802.11 TGn (Task Group n) has already been established.
[0008] In addition, several access control techniques designed to
improve QoS (Quality of Service) are known. For example, as a QoS
technique of guaranteeing parameters such as a designated bandwidth
and delay time, HCCA (HCF Controlled Channel Access) which is an
extended scheme of a conventional polling sequence is available.
According to HCCA, scheduling is performed in a polling sequence in
consideration of required quality so as to guarantee parameters
such as a bandwidth and delay time. Jpn. Pat. Appln. KOKAI
Publication No. 2002-314546 refers to QoS in the IEEE 802.11e
standard, and discloses a method of assigning priorities to
communications between communication apparatuses in a wireless
network.
[0009] When the same frequency band as that in the existing
specifications is to be used in realizing an increase in
communication speed, it is preferable to assure coexistence with
communication apparatuses conforming to the existing specifications
and to maintain backward compatibility. For this reason, it is
basically preferable that a protocol on a MAC layer conforms to
CSMA/CA matching the existing specifications. In this case, a
temporal parameter associated with CSMA/CA, e.g., an IFS
(Interframe Space) or backoff period needs to match that in the
existing specifications.
[0010] Even if an attempt to increase the communication speed in
terms of physical layer succeeds, the effective throughput of
communication cannot be improved. That is, when an increase in the
communication speed of the physical layer is realized, the format
of a PHY frame ceases to be effective any more. An increase in
overhead due to this may hinder an increase in throughput. In a PHY
frame, a temporal parameter associated with CSMA/CA is permanently
attached to a MAC frame. In addition, a PHY frame header is
required for each MAC frame.
[0011] As a method of reducing overhead and increasing throughput,
a Block Ack technique introduced in recently drafted IEEE
802.11e/draft 5.0 (enhancement of QoS in IEEE 802.11) is available.
The Block Ack technique can consecutively transmit a plurality of
MAC frames without any backoff, and hence can reduce the backoff
amount to some degree. However, a physical layer header cannot be
effectively reduced. In addition, according to aggregation
introduced in initially drafted IEEE 802.11e, both the backoff
amount and the physical layer header can be reduced. However, since
the length of a physical layer frame containing MAC frames cannot
be increased beyond about 4 kbytes under the conventional
limitation on the physical layer, an improvement in efficiency is
greatly limited. Even if the length of a PHY layer frame can be
increased, another problem arises, i.e., a reduction in error
tolerance.
BRIEF SUMMARY OF THE INVENTION
[0012] The present invention has been made to solve the above
problems, and has as its object to provide a method for a
communication apparatus which can coexist with an existing
apparatus and can improve the substantial communication throughput
by eliminating overhead accompanying the transmission of a
plurality of frames by making a frame format more efficient.
[0013] According to an aspect of the present invention, there is
provided a communication method including generating a physical
frame in which: one of a data frame, an acknowledgement frame, and
an acknowledgement request frame, and a transmission permission
frame which is used in place of a normal Ack frame associated with
a delayed Block Ack, and permits a destination terminal to perform
piggyback transmission, are aggregated; and transmitting the
physical frame to the destination terminal.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0014] FIG. 1 is a block diagram showing the arrangement of a
communication apparatus according to an embodiment of the present
invention;
[0015] FIG. 2 is a view showing the format of a Block Ack Request
frame defined in IEEE 802.11e/Draft 10.0;
[0016] FIG. 3 is a view showing the format of a Block Ack frame
defined in IEEE 802.11e/Draft 10.0;
[0017] FIG. 4 is a view showing an example of an immediate Block
Ack sequence;
[0018] FIG. 5 is a view showing an example of a delayed Block Ack
sequence;
[0019] FIG. 6 is a view showing an example of the aggregation of a
plurality of MPDUs;
[0020] FIG. 7 is a view showing another example of the aggregation
of a plurality of MPDUs;
[0021] FIG. 8 is a view showing the format of a Compressed Block
Ack;
[0022] FIG. 9 is a view showing an example of a Compressed Block
Ack sequence;
[0023] FIG. 10 is a view showing the format of an IAC (Initiator
Aggregation Control) frame;
[0024] FIG. 11 is a view showing an example of piggyback
transmission using IAC frames;
[0025] FIG. 12 is a view showing a case wherein an explicit Block
Ack Request is transmitted upon occurrence of a transmission
error;
[0026] FIG. 13 is a view showing a case wherein an IAC frame is
added to an explicit Block Ack Request;
[0027] FIG. 14 is a view showing a case wherein errors have
occurred in some of frames transmitted in the uplink direction;
[0028] FIG. 15 is a view showing a case wherein errors have
occurred in some of frames transmitted in the downlink
direction;
[0029] FIG. 16 is a view showing another case wherein errors have
occurred in some of frames transmitted in the downlink
direction;
[0030] FIG. 17 is a view a case wherein errors have occurred in
some of frames transmitted in both the uplink direction and the
downlink direction;
[0031] FIG. 18 is a view another case wherein errors have occurred
in some of frames transmitted in both the uplink direction and the
downlink direction;
[0032] FIG. 19 is a view showing a case wherein a timeout has
occurred in Compressed Block Ack transmission in the uplink
direction;
[0033] FIG. 20 is a view showing another case wherein a timeout has
occurred in Compressed Block Ack transmission in the uplink
direction;
[0034] FIG. 21 is a view showing a case wherein errors have
occurred in all MPDUs aggregated and transmitted in the downlink
direction from an HC;
[0035] FIG. 22 is a view showing another case wherein errors have
occurred in all MPDUs aggregated and transmitted in the downlink
direction from an HC;
[0036] FIG. 23 is a view showing a case wherein a Block Ack Request
is contained in the last portion of a physical frame in which a
plurality of data are aggregated;
[0037] FIG. 24 is a view showing how frames are exchanged when
piggybacking is performed by using the delayed Block Ack
Policy;
[0038] FIG. 25 is a view showing piggybacking operation applied to
the delayed Block Ack technique;
[0039] FIG. 26 is a view showing another example of piggybacking
operation applied to the delayed Block Ack technique;
[0040] FIG. 27 is a view showing a case wherein only a busy is
detected in a delayed Block Ack sequence;
[0041] FIG. 28 is a view showing a case wherein errors have
occurred in some of data transmitted in the uplink direction;
[0042] FIG. 29 is a view showing a case wherein errors have
occurred in some of data transmitted in the downlink direction;
[0043] FIG. 30 is a view showing a case wherein a timeout has
occurred in the uplink direction;
[0044] FIG. 31 is a view showing the format of an MRAD frame;
[0045] FIG. 32 is a view showing an example of frame exchange in an
immediate Block Ack sequence to a plurality of destinations;
[0046] FIG. 33 is a view showing another example of frame exchange
in an immediate Block Ack sequence to a plurality of
destinations;
[0047] FIG. 34 is a view showing still another example of frame
exchange in an immediate Block Ack sequence to a plurality of
destinations;
[0048] FIG. 35 is a view for explaining aggregation to a plurality
of destinations and reception buffer management;
[0049] FIG. 36 is a view for explaining aggregation to a plurality
of destinations and reception buffer management; and
[0050] FIG. 37 is a view for explaining aggregation to a plurality
of destinations and reception buffer management.
DETAILED DESCRIPTION OF THE INVENTION
[0051] FIG. 1 is a block diagram showing the arrangement of a
communication apparatus according to the first embodiment of the
present invention. A communication apparatus 1 is an apparatus
configured to communicate with another communication apparatus
through a wireless link, and includes processing units 2, 3, and 4
respectively corresponding to a physical (PHY) layer, MAC layer,
and link layer. These processing units are implemented as analog or
digital electronic circuits in accordance with implementation
requirements. Alternatively, the processing units are implemented
as firmware or the like to be executed by a CPU incorporated in an
LSI. An antenna 5 is connected to the physical layer processing
unit ("processing unit" will be omitted hereinafter) 2. The MAC
layer 3 includes an aggregation processing device 6 for MAC frames.
The aggregation processing device 6 includes a carrier sense
control device 7 and retransmission control device 8, and performs
transmission/reception of Block Ack (acknowledgement for a
plurality of MAC frames) frames (to be described in detail later),
retransmission control based on Block Ack frames, and the like.
[0052] The physical layer 2 is designed to be compatible with two
types of physical layer protocols. The processing unit 2 includes a
first-type physical layer protocol processing device 9 and a
second-type physical layer protocol processing device 10 for the
respective types of protocol processing. The first-type physical
layer protocol processing device 9 and second-type physical layer
protocol processing device 10 often share circuits and are not
necessarily independent of each other in terms of
implementation.
[0053] In this embodiment of the present invention, the first-type
physical layer protocol is assumed to be a protocol defined in IEEE
802.11a, and the second-type physical layer protocol is assumed to
be a protocol using a so-called MIMO (Multiple Input Multiple
Output) technique using a plurality antennas on each of the
transmitting side and the receiving side. Using the MIMO technique
makes it possible to expect an increase in transmission capacity
almost proportional to the number of antennas without changing the
frequency band. The MIMO technique is therefore a technique
directed to further increase the throughput of IEEE 802.11. Note
that the link layer 4 has a normal link layer function defined in
IEEE 802. The technique to be used to increase the transmission
rate is not limited to MIMO. For example, a method of increasing
the occupied frequency band may be used or may be combined with
MIMO.
[0054] According to IEEE 802.11e/Draft 8.0, as a technique of
improving the transmission efficiency at the MAC (Media Access
Control) layer, a Block Ack technique has been proposed. In the
Block Ack technique, a given terminal transmits QoS (Quality of
Service) data at minimum frame intervals called SIFS (Short
Interframe Space) for a given channel use period (TXOP:
Transmission Opportunity). Thereafter, the terminal transmits a
Block Ack Request to the receiving terminal at an arbitrary timing
to request its reception status. The receiving side converts the
reception status into information in the bitmap format on the basis
of the Starting Sequence Number (Block Ack Starting Sequence
Control) determined by the Block Ack Request, and returns the
information as a Block Ack.
[0055] Prior to the detailed description of the embodiments of the
present invention, existing techniques for Block Acks and buffer
management on a receiving terminal of Block Acks will be described.
According to IEEE 802.11e/Draft 10.0, a Block Ack technique is
known as a technique of improving the transmission efficiency at
the MAC (Media Access Control) layer. In the Block Ack technique, a
given transmitting terminal transmits QoS (Quality of Service) data
at minimum frame intervals called SIFS (Short Interframe Space) for
a given channel use period (TXOP: Transmission Opportunity).
Thereafter, the transmitting terminal transmits a Block Ack Request
to the receiving terminal to request its reception status at an
arbitrary timing. The receiving side converts the reception status
into information in the bitmap format on the basis of the Starting
Sequence Number (Block Ack Starting Sequence Control) determined by
the Block Ack Request, and returns the information as a Block
Ack.
[0056] FIGS. 2 and 3 respectively show the formats of a Block Ack
Request frame and Block Ack frame which are defined in IEEE
802.11e/Draft 10.0. Both the frames shown in FIGS. 2 and 3 are MAC
frames, each having the MAC header defined in IEEE 802.11. The MAC
header is comprised of a Frame Control field, Duration field,
Receiver Address field, and Transmitter Address field.
[0057] A BAR Control (Block Ack Request Control) 20 has a 4-bit TID
(Traffic Identifier) field. QoS data exists for each priority (TID)
and is assigned a unique sequence number and fragment number. For
this reason, a reception status in the Block Ack in FIG. 3 also
needs to be prepared for each priority. The TID field of the BAR
Control 20 in the Block Ack Request is used to designate such a
priority.
[0058] A Block Ack Starting Sequence Control 21 in the Block Ack
Request in FIG. 2 is comprised of a 4-bit Fragment Number field and
12-bit Starting Sequence Number field. The Starting Sequence Number
is used by a receiving terminal to generate a Block Ack Bitmap by
tracing back a reception status, on the basis of a relative
reception status from a sequence number corresponding to the
Starting Sequence Number.
[0059] Like the BAR Control 20 in FIG. 2, a BA Control 30 in the
Block Ack in FIG. 3 contains a 4-bit TID field. A Block Ack
Starting Sequence Control (Block Ack Starting Sequence Number) 31
indicates the Starting Sequence Number of the reception status
indicated by a Block Ack Bitmap 32 in the Block Ack. According to
IEEE 802.11e/Draft 10.0, the size of a Block Ack Bitmap is a fixed
length of 1,024 bits, which makes it possible to notify a reception
log corresponding to data of a maximum of 64 MSDUs (MAC Service
Data Units). The process of partitioning a MSDU or MMPDU (MAC
management protocol data unit) into smaller MAC level frames, MPDUs
(MAC Protocol Data Units), is called fragmentation. One MSDU or
MMPDU shall be divided into a maximum of 16 MPDUs with a
Fragmentation Threshold. Note that an FCS (Frame Check Sequence)
for error detection is added to each of the MAC frames shown in
FIGS. 2 and 3.
[0060] FIGS. 4 and 5 each show an example of a Block Ack sequence
in an HCCA (HCF Controlled Channel Access). The HC (Hybrid
Coordinator) shown in each drawing is a QoS access point (QoS-AP)
in IEEE 802.11e and serves as an entity which performs bandwidth
management including the allocation of TXOPs to QSTAs (QoS
stations) and performs downlink (the downlink direction from the HC
to the QSTA) data transmission. The assignment of a TXOP to the
QSTA is performed on the basis of a QoS CF-Poll frame (QoS
Contention Free-Poll: a QoS-compatible polling frame which is
transmitted from the HC to the QSTA to grant transmission
opportunity).
[0061] Referring to FIG. 4, first of all, the HC assigns a channel
use period (TXOP period 1) to QSTA 1 by transmitting a QoS CF-Poll
frame 40 to it. QSTA 1 can transmit any frame in TXOP period 1. In
the example shown in FIG. 4, QSTA 1 transmits QoS Data frames 41 at
SIFS intervals in a burst manner, and then transmits a Block Ack
Request frame 42 at the end of the transmission of the data frames.
Thereafter, QSTA 1 receives a Block Ack frame 43 from QSTA 2. When
TXOP period 1 assigned to QSTA 1 expires, the HC acquires TXOP
period 2. In TXOP period 2, the HC also transmits QoS Data 44 to
QSTA 1 in a burst manner. At the end of TXOP period 2, as in TXOP
period 1 assigned to QSTA 1, the HC transmits a Block Ack Request
45, and receives a Block Ack 46 from QSTA 1. The Block Ack Requests
42 and 45 request the destination to return the relative reception
status designated by a Block Ack Starting Sequence Control value.
FIG. 4 shows an example of an immediate Block Ack sequence. In this
case, the terminal which has received the Block Ack Requests 42 and
45 must return the Block Acks 43 and 46 after the SIFS intervals
without fail.
[0062] FIG. 5 shows an example of a delayed Block Ack sequence.
Upon receiving a Block Ack Request 50, the terminal returns an Ack
frame defined in IEEE 802.11 (called a Normal acknowledgement in
IEEE 802.11e/Draft 10.0) 51, and transmits a Block Ack 52 after a
lapse of an arbitrary period. Upon receiving the Block Ack 52 at
last, the data transmitting terminal returns a Normal
acknowledgement 53, thereby completing the delayed Block Ack
sequence. Note that the receiving side is notified of QoS data
subjected to the Block Ack technique by using an Ack Policy field
in a QoS Control field of a MAC header extended for IEEE 802.11e.
The Ack Policy field allows to designate the Normal ack scheme
defined in IEEE 802.11, the Block Ack scheme defined in IEEE
802.11e, the No acknowledgement scheme which does not require ACK
response, or the like.
[0063] Each embodiment of the present invention is directed to a
communication apparatus designed to aggregate a plurality of MPDUs
(MAC Protocol Data Units) in a PSDU (PHY Service Data Unit) to
transmit a single PPDU (PHY Protocol Data Unit). Note that a PPDU
corresponds to a physical frame (PHY frame) containing a PHY
header, a PHY trailer and PSDU which contains plurality of
MPDUs.
[0064] In order to achieve a high throughput in a wireless LAN, the
overhead of the MAC layer and the overhead of the PHY layer, such
as a frame interval and random backoff period, must be reduced. As
shown in FIGS. 6 and 7, these overheads can be reduced by
transmitting a plurality of MPDUs upon aggregating them into one
PSDU. In the example shown in FIG. 6, header information 61 which
indicates in octets the length of each MPDU containing a MAC header
to an FCS exists in the head of a PSDU 60 in which a plurality of
MPDUs are aggregated. The header information 61 will be referred to
as a "MAC super frame header" hereinafter. A CRC (Cyclic Redundancy
Check) 62 for detecting an error in the header 61 itself is added
to the MAC super frame header 61. "0" is written in an MPDU Length
field corresponding to a portion in which no MPDU exists. In
addition, if the CRC calculation for the MAC super frame header 61
is incorrect, the reception of all the MPDUs is regarded as
failed.
[0065] Referring to FIG. 7, in the front portion of each of the
aggregated MPDUs, information indicating the length of a
corresponding MPDU exists. In addition, a CRC for detecting an
error in the MPDU length information is added to it. A combination
of MPDU length information and a CRC will be referred to as an
"MPDU separation". Upon receiving a physical frame having the
arrangement shown in FIG. 7, a terminal checks the CRC of an MPDU
separation 71. If the first MPDU separation 71 has been
successfully received, the terminal extracts succeeding MPDU and
calculates an FCS. If the FCS calculation result is correct, it is
determined that the MPDU has been successfully received. If the FCS
calculation result is incorrect, the reception of the MPDU is
regarded as failed. The terminal then checks the CRC of a next MPDU
separation 72 upon skipping a portion indicated by the MPDU length
of the MPDU separation 71. If the MPDU separation is incorrect, the
terminal consecutively skips and performs a CRC check on an octet
basis. If the result is correct, the FCS for the MPDU following the
MPDU separation is calculated to determine whether or not the MPDU
has been successfully received.
[0066] Assume that, in each embodiment of the present invention,
for a partial response to a physical frame in which a plurality of
MPDUs are aggregated, an extended one of the Block Ack frame
defined in IEEE 802.11e is used. FIG. 8 shows the frame arrangement
of an extended Block Ack. According to IEEE 802.11e/Draft 10.0, a
Block Ack frame has a bitmap having a fixed length of 1,024 bits in
consideration of fragmentation. Since the overhead of a fragment is
generally large, in order to achieve a high throughput, it is
preferable not to fragment an MSDU. The extended Block Ack frame
shown in FIG. 8 therefore includes a Compressed Block Ack Bitmap 80
corresponding to 64 MSDUs on the premise that no fragmentation is
performed. 1 bit corresponds to the reception status of 1 MSDU. The
size of the Compressed Block Ack Bitmap 80 can be reduced to 1/16
that of a conventional Block Ack frame. A Block Ack frame with the
Compressed Block Ack Bitmap 80 will be referred to as a "Compressed
Block Ack" hereinafter. Note that the Compressed Block Ack Bitmap
80 of a Compressed Block Ack may have a variable length in
accordance with the number of MPDUs aggregated into one physical
frame.
[0067] FIG. 9 shows an example of transmitting a plurality of MPDUs
upon aggregating them. In each embodiment of the present invention,
upon receiving a physical frame in which a plurality of MPDUs are
aggregated, a terminal (STA and HC) returns a Compressed Block Ack
to the transmission source after a lapse of a SIFS which is the
minimum frame interval even if no Block Ack Request is contained in
the physical frame. For example, first of all, the HC assigns TXOP
period 1 to QSTA 1 by transmitting a QoS CF-Poll frame 90 to QSTA
1. In TXOP period 1, QSTA 1 transmits, to QSTA 2, a physical frame
91 in which MPDUs with sequence numbers "1" to "3" are aggregated,
and QSTA 2 returns the reception statuses of the MPDUs in a
physical frame 93 as a Compressed Block Ack 92 to QSTA 1 after a
lapse of a SIFS. In the succeeding TXOP period 2, the HC transmits
the physical frame 93 to QSTA 1, and QSTA 1 returns the reception
statuses of the MPDUs in the physical frame 93 as a Compressed
Block Ack 94 to the HC after a lapse of a SIFS. In TXOP period 3,
the HC transmits a QoS CF-Poll frame 97 to QSTA 2 to assign TXOP
period 3 to QSTA 2. QSTA 2 transmits a physical frame 95 to the HC.
The HC then returns the reception statuses of the MPDUs in the
physical frame 95 as a Compressed Block Ack 96 to QSTA 2 after a
lapse of a SIFS. Each embodiment of the present invention allows a
Compressed Block Ack to be returned even if no Block Ack Request is
contained in a physical frame. This will be referred to as an
"Implicit Block Ack Request" hereinafter. However, as in IEEE
802.11e/Draft 10.0, a Block Ack Request frame may be aggregated at
the end of a physical frame, and the receiving side may return a
Compressed Block Ack in accordance with the information indicated
by the Block Ack Request frame.
[0068] The MAC efficiency can be improved by transmitting a
plurality of MPDUs upon aggregating them, and performing selective
repeat retransmission control using the above Compressed Block Ack
(and Implicit Block Ack Request) technique.
FIRST EMBODIMENT
[0069] In the first embodiment of the present invention, the MAC
efficiency is improved by aggregating a plurality of MPDUs and then
piggybacking the MPDUs in the opposite direction on a partial
response from a destination. Application methods for the immediate
Block Ack and delayed Block Ack techniques defined in IEEE
802.11e/Draft 10.0 will also be described below.
[0070] More specifically, a communication apparatus according to
the first embodiment piggybacks at least one data frame on a Block
Ack frame in immediate Block Ack transmission. For this purpose,
the initiator side of data transmission transmits a transmission
permission frame, which permits a destination terminal to piggyback
a plurality of data frames, upon aggregating the control frame
(Block Ack Request frame, or Block Ack frame) with a data frame.
Such communication apparatus of the first embodiment searches a
physical frame returned from a destination, when operating as a
transmitting terminal. If Block Ack frame is not contained, the
apparatus determines that a timeout has occurred. When a timeout
associated with a Block Ack has occurred, the receiving side
selects either the method of transmitting all the previously
transmitted data frames as retransmission targets in the next
piggyback allowable period or the method of piggybacking a Block
Ack Request.
[0071] The MAC efficiency can be improved by piggybacking a
plurality of MPDUs in the opposite direction (from a destination to
a transmission source) on a partial response frame from the
destination. According to the IEEE 802.11e/Draft 10.0 standard,
however, a destination terminal can only return a response frame to
a data frame to a data transmitting terminal which has acquired a
TXOP. Consider, therefore, a frame like the one having the
arrangement shown in FIG. 10, which is used to give a transmission
permission to the destination terminal to allow it perform
piggyback transmission.
[0072] Assume that a data transmission source is regarded as an
initiator terminal, and a frame 100 in FIG. 10 will be called an
"IAC (Initiator Aggregation Control) frame". As shown in FIG. 10,
the IAC frame 100 has the same MAC header as that defined in IEEE
802.11, which is comprised of a Frame Control field, Duration
field, Receiver Address field, and Transmitter Address field.
[0073] An IAC Mask field 101 following the MAC header designates
the application purpose (RTS, MIMO feedback, or piggyback
transmission permission) of the IAC frame 100 with the bitmask
format. A Next PPDU (PLCP Protocol Data Unit) Size 102 indicates,
in octets, the length of following PPDU to be transmitted next by
the transmission source. A Next PPDU Default MCS field 103
represents a physical transmission rate in the transmission of
following PPDU. A Reverse Direction Limit field 104, Reverse
Direction Grant field 105, and Response Period Offset 106 are
provided to assign the destination terminal a transmission
permission time required for piggybacking. When the destination
terminal is to be assigned a transmission time for piggybacking,
the transmission source terminal extracts an arbitrary period of
time from the currently held TXOP period. The transmission source
is not permitted to extend the assigned TXOP period itself. An
RDTID (Reverse Direction Traffic Identifier) field 107 designates a
TID as a piggyback target. An MCS Feedback field 108 is used to set
a transmission rate in accordance with a propagation path
environment (mainly used for link adaptation). A 4-octet FCS is
added to the tail of the IAC frame 100 according to the IEEE 802.11
standard.
[0074] FIG. 11 is a view showing how a plurality of MPDUs are
aggregated and a piggyback permission is given to a destination
terminal when an IAC frame is to be used. The example shown in FIG.
11 is a frame sequence in the case of HCCA. However, the present
invention can also be applied to EDCA (Enhanced Distributed Channel
Access) which is a contention-based QoS access control scheme.
Referring to FIG. 11, upon obtaining TXOP period 1, the HC
transmits, to QSTA 1, a physical frame 112 in which an IAC frame
110 and a plurality of data frames 111 with sequence numbers "1" to
"14" are aggregated. Upon receiving the physical frame 112, QSTA 1
returns a Compressed Block Ack 113 after a lapse of a SIFS period.
Since piggyback transmission is permitted by the IAC frame 110,
QSTA 1 transmits a physical frame 115 in which data 114 in the
uplink direction to the HC are aggregated. The number of MPDUs
which can be piggybacked on a Compressed Block Ack to the HC by
QSTA 1 is determined within the range of duration indicated by
Reverse Direction Limit or Reverse Direction Grant given by the HC.
Reverse Direction Limit or Reverse Direction Grant is adjusted
within the range of TXOP period 1 of the HC. When QSTA 1 transmits
the physical frame 115 in which the Compressed Block Ack 113 and
the data 114 with sequence numbers "1" to "4" in the uplink
direction are aggregated, the HC returns a Compressed Block Ack 116
to QSTA 1 after a lapse of a SIFS, thereby finishing TXOP period 1.
In TXOP period 2, the HC transmits, to QSTA 2, a physical frame 119
in which an IAC frame 117 and data frames 118 with sequence numbers
"1001" to "1004" are aggregated. If QSTA 2 has no data in the
uplink direction to the HC, i.e., data to be piggybacked, QSTA 2
returns only a Compressed Block Ack 120 to the data from the HC
regardless of whether Reverse Direction Grant (or Reverse Direction
Limit) is given. Referring to FIG. 11, the two TXOP periods are
separated from each other by a PIFS (PCF Interframe Space).
[0075] According to the first embodiment, using an IAC frame makes
it possible to intentionally permit a destination terminal to
perform piggyback transmission. The MAC efficiency can be improved
by causing a destination terminal which has obtained a piggyback
transmission permission to perform piggyback transmission of data
frames and the like.
[0076] Several sequence examples in a case wherein errors have
occurred in physical frames will be described below with reference
to FIGS. 12 to 23.
[0077] FIGS. 12 and 13 each show a sequence example in a case
wherein after the HC transmits, to QSTA 1, a physical frame 123 in
which an IAC frame 121 and a plurality of data frames 122 with
sequence numbers "1" to "4" are aggregated, a busy 124 is detected
by carrier sense within a SIFS plus 1 slot time, and the FCS
calculation result indicates that all the MPDUs are incorrect.
[0078] According to the IEEE 802.11 standard, when power larger
than a predetermined value is detected, a wireless channel is
regarded as being used (busy). According to the IEEE 802.11e/Draft
10.0 standard, when the HC detects a busy a SIFS after transmitting
a QoS CF-Poll frame at the time of channel access by HCCA, and the
FCS calculation result indicates that a received frame is
incorrect, the HC retransmits a QoS CF-Poll frame to acquire a TXOP
period again, a PIFS after the channel is set in an idle state.
When the HC detects a busy after transmitting a data frame, and the
FCS check indicates an error, the HC retransmits the data frame
after a lapse of a SIFS. In poll frame transmission, it is unknown
whether or not a TXOP period has been properly acquired by
destination terminal. In data frame transmission, the transmission
source has already acquired a TXOP period, and hence can transmit
(or retransmit) an arbitrary frame after a lapse of a SIFS.
[0079] Assume that, in the case shown in FIGS. 12 and 13, a
Compressed Block Ack (and piggybacked data) in the direction from
QSTA 1 to the HC is present, and the HC determines by FCS
calculation that all the MPDUs are incorrect. In this case, in the
HC, a timer which counts the duration until a Compressed Block Ack
is received causes a timeout. The HC detects from this timeout that
no Compressed Block Ack has been received, and transmits a
(explicit) Block Ack Request a SIFS after the wireless channel
becomes idle. The HC can transmit this Block Ack Request because it
can be interpreted that the HC is on the initiator side of
piggyback transmission, and has acquired a TXOP. As the Block Ack
Starting Sequence Control value of the Block Ack Request, the
sequence number "1" of the first transmitted MPDU is designated. In
the example shown in FIG. 12, when the HC transmits a Block Ack
Request 125, an IAC frame is not aggregated in the same physical
frame. For this reason, QSTA 1 only returns an acknowledgement to
the data previously received from the HC by using a Compressed
Block Ack 126. This is because since no IAC frame is present, QSTA
1 is not permitted to perform piggyback transmission.
[0080] When operating as a transmitting terminal, the communication
apparatus according to the first embodiment determines, in
accordance with the remaining period of the channel use period
(i.e., the TXOP) assigned to the transmitting terminal, whether or
not to transmit, to the destination terminal, a frame for
permitting the terminal to return a partial response frame upon
aggregating the frame and a plurality of MPDUs.
[0081] As shown in FIG. 12, when the HC receives the Compressed
Block Ack 126 from QSTA 1, TXOP period 1 of the HC expires, and the
next TXOP period 2 starts after a lapse of a PIFS time. In TXOP
period 2, the HC transmits, to QSTA 2, a physical frame 129 in
which an IAC frame 127 and data frames 128 with sequence numbers
"1001" to "1004" are aggregated.
[0082] In contrast to this, in the example shown in FIG. 13, TXOP
period 1 held by the HC is sufficient, and hence permits QSTA 1 to
perform piggyback transmission, by transmitting a physical frame
132 in which an IAC frame 130 and Block Ack Request 131 are
aggregated. Upon receiving the physical frame 132, QSTA 1 is
permitted by the IAC frame 130 to perform piggyback transmission,
and can transmit data frames 134 in the uplink direction to the HC
by piggybacking them on a Compressed Block Ack (corresponding to
the MPDUs with sequence numbers "1" to "4" which were transmitted
first by the HC). The HC transmits a Compressed Block Ack 136 to
the data frame 134 from QSTA 1 after a lapse of a SIFS, and then
finishes TXOP period 1.
[0083] The HC can therefore selectively control
permission/inhibition of piggybacking with respect to a destination
terminal in accordance with the scheduling state on the side where
a TXOP is acquired.
[0084] FIG. 14 shows an example of operation to be performed when
errors have occurred in some of a plurality of aggregated MPDUs
upon uplink transmission from a QSTA to the HC. First of all, the
HC transmits an IAC frame 140 and data frames 141 with sequence
numbers "1" to "4" upon aggregating them into one physical frame
142. After a lapse of a SIFS, QSTA 1 transmits a plurality of data
in the uplink direction to the HC upon piggybacking them on a
Compressed Block Ack 143 to the data frames 141 from the HC. In the
example shown in FIG. 14, an FCS calculation result indicates that
errors have occurred in the Compressed Block Ack and an MPDU 144
with sequence number "4" from QSTA 1.
[0085] In the first embodiment, even if it is detected that the
channel is busy a SIFS after a plurality of MPDUs are aggregated
and transmitted, the transmitted MPDUs are regarded as
retransmission targets as long as there is no normal Compressed
Block Ack in the physical frame which has caused the busy state.
For this reason, it is necessary to prompt the retransmission of a
Block Ack from the destination by transmitting a Block Ack Request
in accordance with the IEEE 802.11e/Draft 10.0 standard.
[0086] In the example shown in FIG. 14, the HC has not been able to
receive a Compressed Block Ack to the MPDUs 141 with sequence
numbers "1" to "4" which the HC has transmitted to QSTA 1. Within
the range of TXOP period 1, therefore, the HC aggregates
(piggybacks) a Block Ack Request 147 on a Compressed Block Ack 146
to QSTA 1, thereby requesting QSTA 1 to retransmit the Block Ack.
In addition, the HC transmits an IAC frame 145 for giving
transmission permission to QSTA 1 upon aggregating it in a single
physical frame 148. After a lapse of a SIFS, QSTA 1 reflectively
transmits the same contents as those of the previously transmitted
Compressed Block Ack (without changing any of the contents), and
piggybacks data in the uplink direction on the basis of the Reverse
Direction Grant (or Reverse Direction Limit) information in the IAC
frame. Referring to FIG. 14, QSTA 1 has detected by the Compressed
Block Ack 146 from the HC that the transmission of a MPDU 150 with
sequence number "4" has failed, and hence piggybacks the MPDU 150
as a retransmission target on a Compressed Block Ack 149 to the HC.
The HC then transmits a Compressed Block Ack 151 to the MPDU 150
with sequence number "4" retransmitted from QSTA 1, thus finishing
TXOP period 1.
[0087] If TXOP period 1 acquired by the HC is short, and the HC
does not have time enough to prompt frame transmission from QSTA 1,
the HC can finish the TXOP period by transmitting a Compressed
Block Ack without aggregating a Block Ack Request nor an IAC.
[0088] In addition, the HC may detect the presence/absence of an
acknowledgement frame on the basis of error detection at a specific
frame position in a physical frame returned from a destination
terminal. Assume that transmitting and receiving terminals have
mutually recognized that a Compressed Block Ack is returned upon
piggybacking of a plurality of data thereon, and the Compressed
Block Ack is always aggregated in the head portion of a physical
frame. In this case, if an FCS calculation result indicates an
error in the first MPDU, the transmitting terminal can cause a
timeout with respect to a partial response frame, i.e., can regard
that the reception of a Compressed Block Ack has failed, without
searching the remaining MPDUs.
[0089] When an IAC frame is aggregated in the head of a physical
frame from the HC in addition to a Compressed Block Ack as in the
example shown in FIG. 14, an FCS up to the second MPDU is
calculated to determine whether or not the Compressed Block Ack has
successfully been received. Assume that an IAC frame is always
aggregated in the head of a physical frame, and a Compressed Block
Ack is aggregated at the first position in the remaining portion
(i.e., next to the IAC frame in the same physical frame). In this
case, if an FCS calculation result on the second MPDU indicates an
error, the terminal which has received the physical frame regards
that the reception of the Compressed Block Ack has failed. That is,
if both the transmitting and receiving terminals recognize in
advance the position where a Compressed Block Ack is to be
aggregated, an FCS calculation result on the corresponding portion
can be used as information for determining the success/failure of
the reception of the Compressed Block Ack.
[0090] FIGS. 15 and 16 each show an example of retransmission to be
performed when errors have occurred in MPDUs in a physical frame in
the downlink direction from an HC to a QSTA. Assume that the HC has
transmitted an IAC frame and a plurality of MPDUs with sequence
numbers "1" to "4" upon aggregating them, and errors have occurred
in MPDUs 152 and 153 with sequence numbers "1" and "4". In this
case, when a SIFS has elapsed since the reception of the physical
frame, QSTA 1 transmits data (with sequence numbers "1" to "4") 155
in the uplink direction from QSTA 1 to the HC upon piggybacking
them on a Compressed Block Ack 154 indicating that the MPDUs with
sequence numbers "1" and "4" are incorrect. When a SIFS has elapsed
since the reception of the physical frame from QSTA 1, the HC
transmits a Compressed Block Ack 156 to the data in the uplink
direction, thereby finishing TXOP period 1. If the HC detects by
carrier sense during a PIFS that the wireless media is idle, the HC
acquires TXOP period 2, and transmits an IAC frame 157 and data
frames 158 with sequence numbers "1" and "4" as retransmission
targets upon aggregating them. After a lapse of a SIFS, QSTA 1
transmits a Compressed Block Ack 159 indicating that the frames
with sequence numbers "1" and "4" retransmitted by the HC have been
successfully received. TXOP period 2 then expires. In this case,
there is an IAC frame in the physical frame, but piggyback
transmission for QSTA1 is not permitted. The HC acquires TXOP
period 3, during which the HC transmits data to QSTA 2, after
carrier sense in a PIFS. If TXOP period 1 assigned to the HC is
sufficient as shown in FIG. 16, the HC can transmit retransmission
data frames 160 in the downlink direction from the HC to QSTA 1 and
an IAC frame 161, together with the Compressed Block Ack 156 to
QSTA 1 to the HC, upon aggregating them. In this case, the MAC
efficiency is higher than that in the example shown in FIG. 15.
[0091] FIGS. 17 and 18 each show an example of retransmission to be
performed when error have occurred in MPDUs in both downlink and
uplink physical frames. Referring to FIG. 17, the HC transmits an
IAC frame and data frames with sequence numbers "1" to "4" in the
downlink direction to QSTA 1 upon aggregating them. Assume that the
data frames with sequence numbers "1" and "4" are incorrect. In
this case, after a lapse of a SIFS since the reception of the
physical frame from the HC, QSTA 1 transmits data frames 171 with
sequence numbers "1" and "4" in the uplink direction to the HC upon
piggybacking them on a Compressed Block Ack 170 to the HC.
Referring to FIG. 17, an FCS calculation result indicates that
errors have occurred in MPDUs of the MPDUs in the uplink direction
to the HC which have sequence numbers "2" and "3".
[0092] TXOP period 1 in FIG. 17 is short, and hence the HC cannot
afford to retransmit the incorrect MPDUs. Therefore, the HC
finishes the TXOP by transmitting a Compressed Block Ack 172 to the
data in the uplink direction from QSTA 1. Referring to FIG. 17,
upon acquiring a TXOP period again (TXOP period 2) after a lapse of
a PIFS, the HC transmits an IAC frame 173 and MPDUs 174 with
sequence numbers "1" and "4" as retransmission targets to QSTA 1
upon aggregating them. QSTA 1 transmits an acknowledgement to the
downlink data from the HC as a Compressed Block Ack 175 upon
piggybacking retransmission MPDUs within the range of the
transmission permission time given by the IAC frame 173. Referring
to FIG. 17, QSTA 1 piggybacks a new MPDU with sequence number "5"
on the Compressed Block Ack 175 to the HC, in addition to the MPDUs
with sequence numbers "2" and "3" as retransmission targets.
Thereafter, the HC transmits a Compressed Block Ack 176 to the data
from QSTA 1, and finishes TXOP period 2.
[0093] In the example shown in FIG. 18, TXOP period 1 held by the
HC is relatively long, and hence the HC transmits an IAC frame 180,
a Compressed Block Ack 181, and data frames 182 with sequence
numbers "1" and "4" which need to be retransmitted, upon
aggregating them, after a lapse of a SIFS since the reception of
the uplink data from QSTA 1. QSTA 1 transmits the MPDUs with
sequence numbers "2" and "31" which need to be retransmitted and a
new MPDU 184 with sequence number "5" upon piggybacking them on a
Compressed Block Ack 183 to the MPDUs with sequence numbers "1" and
"4". Lastly, the HC returns a Compressed Block Ack 185 to QSTA 1,
and finishes TXOP period 1. In this case, if the error rate of the
wireless media is high and retransmission is repeatedly executed in
both the downlink and uplink directions, the fairness of data
transmission may be impaired. Method of improving the
retransmission quality may include setting the upper limit of the
number of MPDUs which can be continuously transmitted to the total
window size, setting an upper limit for the number of times of
continuous transmission including retransmission, and adjusting the
value of Reverse Direction Grant (or Reverse Direction Limit) of
IAC.
[0094] FIGS. 19 and 20 each show an example of retransmission to be
performed when errors have occurred in all the data in the uplink
direction from a QSTA to an HC. Referring to FIG. 19, the HC
transmits an IAC frame 190 and data frames 191 with sequence
numbers "1" and "2" upon aggregating them. After a lapse of a SIFS,
QSTA 1 transmits data frames 193 with sequence numbers "1" and "2"
in the uplink direction upon piggybacking them on a Compressed
Block Ack 192 for notifying the successful reception of the MPDUs.
At this time, if an FCS calculation result indicates that all the
data in the uplink direction from QSTA 1 to the HC are incorrect
(sequence numbers "1" and "2" in FIG. 19), since the HC does not
know the presence of the data from QSTA 1, the HC finishes TXOP
period 1 without generating any Compressed Block Ack. According to
the IEEE 802.11e/Draft 10.0, QSTA 1 transmits data frames to the
HC, and then sets a timer for the reception of a response frame. If
a busy is detected within an (SIFS+1 slot) time after the
transmission of the physical frame, QSTA 1 resets the timer, and
performs FCS calculation for each received MAC frame. This slot
time is used to tolerate a physical processing error, and varies
depending on physical transmission specifications. In contrast, if
no busy is detected even after a lapse of an (SIFS+1 slot) time
since physical frame transmission, the transmitted data frames are
regarded as recovery targets. Obviously, if an FCS calculation
result on a MAC frame indicates that the frame is incorrect, the
transmitted data frame is regarded as a retransmission target
regardless of whether a busy is detected. Referring to FIG. 19, the
HC which holds TXOP period 1 receives the Compressed Block Ack 192
from QSTA 1, and acquires TXOP period 2 after a lapse of a PIFS. In
TXOP period 2, the HC transmits an IAC frame 194 and data frames
195 with sequence numbers "1001" and "1002" upon aggregating them.
At the start of TXOP period 2, QSTA 1 regards the MPDUs with
sequence numbers "1" and "2", which have been transmitted in the
uplink direction, as recovery targets. In TXOP period 2 shown in
FIG. 19, since a response frame which becomes a factor for a busy
state is not transmitted even after a lapse of an (SIFS+1 slot)
time since the transmission of data frames 196 with sequence
numbers "1" and ""2" in the uplink direction from QSTA 2 to the HC,
the data frames 196 are regarded as retransmission targets. The HC
finishes TXOP period 2, and then acquires TXOP period 3 after a
lapse of a PIFS. In TXOP period 3, the HC transmits an IAC frame
197 and data frames 198 with sequence numbers "3" and "4" to QSTA 1
upon aggregating them. The IAC frame 197 allows QSTA 1 to piggyback
a Block Ack Request 200 on a Compressed Block Ack 199 to the data
frames with sequence numbers "3" and "4". According to the IEEE
802.11e/Draft 10.0 standard, in performing immediate Block Ack
transmission, when each QoS data with an Ack Policy Block Ack at
SIFS intervals, and Block Ack frame can not be received from the
destination even after a lapse of a predetermined period of time
since the transmission of a Block Ack Request frame, a Block Ack
Request is retransmitted. In the example shown in FIG. 19, since
QSTA 1 has received no Compressed Block Ack to the data transmitted
in the uplink direction to the HC, QSTA 1 piggybacks the Block Ack
Request frame 200 on the Compressed Block Ack 199 to prompt the HC
to transmit a Compressed Block Ack frame. After a lapse of a SIFS,
the HC transmits, to QSTA 1, an IAC frame 201 and a Compressed
Block Ack 202 to the Block Ack Request frame 200 upon aggregating
them. Since the HC has not successfully received any MPDU of data
from QSTA 1 which is located after the Block Ack Starting Sequence
Control value of the Block Ack Request frame 200, all the bits of
the Compressed Block Ack Bitmap of the Compressed Block Ack 202 are
set to 0. When the HC transmits the IAC frame and Compressed Block
Ack together, QSTA 1 recognizes the presence of the two MPDUs whose
transmission has failed, and retransmits them to the HC.
[0095] As shown in FIG. 20, when a data frame transmitted from QSTA
1 to the HC needs to be recovered, QSTA 1 may directly retransmit
only the data frame in the next allocated transmission period
instead of transmitting a Block Ack Request. According to the IEEE
802.11e/Draft 10.0 standard, since a delay allowable time (delay
bound) is provided for QoS data, when it is known from the
viewpoint of scheduling that QSTA1 cannot afford to retransmit a
data frame upon reception of a Compressed Block Ack from the
destination, as shown in FIG. 19, a data frame 203 is directly
retransmitted as shown in FIG. 20. According to this embodiment,
when data frames need to be recovered, selectively transmitting a
Block Ack Request or directly retransmitting all the data frames
can improve the MAC efficiency as well as meet QoS
requirements.
[0096] In addition, this embodiment can be implemented not only by
the method of performing recovery processing when an HC gives a
piggyback permission to a QSTA as shown in FIG. 19 but also by a
method of performing recovery processing at the first of the
acquisition of a TXOP in an EDCA period or at the beginning of the
acquisition of a TXOP by a QoS CF-Poll from the HC. In the first
embodiment of the present invention, the HC performs bandwidth
management including the allocation of TXOPs to QSTAS. Obviously,
however, the piggyback technique can also applied to a case wherein
QSTA 1 is to completely acquire a TXOP and arbitrarily transmit an
arbitrary MAC frame within the period.
[0097] In TXOP period 3 in FIG. 19, the HC aggregates, for QSTA 1,
the IAC frame 201 with the Compressed Block Ack 202. When the HC
holds a TXOP, the HC also serves as an entity which performs
scheduling for piggybacking. When QSTA 1 is preferably made to
immediately retransmit a data frame from the viewpoint of a delay
allowable time (delay bound), the IAC frame 201 is aggregated with
the Compressed Block Ack 202 as in the example shown in FIG. 19. In
the example shown in FIG. 19, since all the bits of the Compressed
Block Ack Bitmap of the Compressed Block Ack 202 to QSTA 1 are 0,
the HC recognizes that QSTA 1 needs to perform retransmission
processing. In this case, the HC also recognizes that the QSTA
needs to perform retransmission, when bits representing a reception
failure and reception success are alternately arranged in the
Compressed Block Ack Bitmap of a Compressed Block Ack to a QSTA, or
when the Block Ack Starting Sequence Control value of a Block Ack
Request is different from that of a Compressed Block Ack (on the
data transmitting side, all MPDUs with lower sequence numbers than
the Block Ack Starting Sequence Control value of the Compressed
Block Ack are regarded as those whose transmission has failed). In
this case, the HC transmits an IAC frame for permitting a QSTA to
perform piggybacking in accordance with the determination made by
the scheduler device of the HC. Alternatively, since Reverse
Direction Grant (or Reverse Direction Limit) designated by an IAC
frame need not be completely consumed on the QSTA side, an IAC
frame may be transmitted in advance to the QSTA to give it a margin
for retransmission by piggybacking.
[0098] FIGS. 21 and 22 each show an example of retransmission to be
performed when errors have occurred in all the MPDUs aggregated and
transmitted from an HC through a downlink. Referring to FIG. 21,
the HC transmits an IAC frame 210 and data frames 211 with sequence
numbers "1" to "4" to QSTA 1 upon aggregating them. Assume that
errors have occurred in all the MPDUs including the IAC frame due
to collision on a wireless channel or a high bit error rate. In
this case, QSTA 1 cannot understand the MPDUs in the physical frame
transmitted by the HC at all, and cannot determine whether or not
the frame contains any MPDU addressed to itself. For this reason,
even if the HC transmits an IAC frame, QSTA 1 transmits no data in
the uplink direction. According to the IEEE 802.11e/Draft 10.0
standard, in performing channel access by HCCA, when no response is
returned from a destination after an HC transmits the first frame
(data or QoS CF-Poll) in a given TXOP period, the HC needs to
transmit a frame again after performing carrier sense in a PIFS. In
the example shown in FIG. 21, therefore, the HC acquires TXOP
period 2 after a lapse of a PIFS, and transmits a Block Ack Request
212 to make a QSTA set a NAV. In addition, in the example shown in
FIG. 21, an IAC frame 213 is aggregated with the Block Ack Request
212. With this operation, QSTA 1 piggybacks a plurality of data 215
in the uplink direction to the HC on a Compressed Block Ack frame
214 to the MPDUs with sequence numbers "1" to "4" which QSTA 1 has
failed to receive in TXOP period 1. Referring to FIG. 21, the HC
finishes TXOP period 2 by transmitting a Compressed Block Ack 216
to QSTA 1. Also, the Compressed Block Ack Bitmap of the Compressed
Block Ack frame 214 which is transmitted by QSTA 1 to the HC in
TXOP period 2 is filled with 0s to express that QSTA 1 has failed
to receive all the MPDUs. Alternatively, as in the example shown in
FIG. 22, if all the data transmitted from the HC through the
downlink are incorrect, only a Block Ack Request 220 is transmitted
after a lapse of a PIFS. Since the Block Ack Request 220 has no IAC
frame aggregated, QSTA 1 only transmits a Compressed Block Ack 221.
The HC retransmits data frames 222 with sequence numbers "1" to "4"
in TXOP period 3 acquired by the HC. That is, the retransmission
timing of downlink data can be quickened as compared with the
example shown in FIG. 21. Therefore, the scheduling processing unit
of the HC can improve the MAC efficiency by determining whether or
not to transmit an IAC frame to the QSTA, in consideration of a
delay allowable time (delay bound) and the like.
[0099] In the first embodiment of the present invention, upon
receiving a physical frame in which a plurality of data are
aggregated without any Block Ack Request, a terminal returns
reception statuses of the MPDUs as a Compressed Block Ack after a
lapse of a SIFS. The present invention can also be applied to even
a case wherein a physical frame in which a plurality of data are
aggregated contains a Block Ack Request at the end as shown in FIG.
23. Although the basic operation without using Implicit Block Ack
Request like FIG. 9 is the same as that in the case wherein a
physical frame contains no Block Ack Request, a retransmission
example in this case will be described with reference to FIG.
23.
[0100] Referring to FIG. 23, upon acquiring TXOP period 1, the HC
transmits an IAC frame 230, a plurality of data 231 with sequence
numbers "1" to "4", and a Block Ack Request frame 232 with a Block
Ack Starting Sequence Control value of "1" upon aggregating them.
Assume that at this point of time, QSTA 1 has not successfully
received the data 231 with sequence numbers "1" and "4" and the
Block Ack Request frame 232. Since QSTA 1 has not received any
Block Ack Request from the HC, QSTA 1 cannot transmit any
Compressed Block Ack. However, QSTA 1 stores in advance reception
information such as the Block Ack Starting Sequence Control value
"2" and the Compressed Block Ack Bitmap "110 . . . " as the
reception status of one physical frame in the past. In TXOP period
1, QSTA 1 transmits data frames 233 with sequence numbers "1" to
"3" and a Block Ack Request 234 with a Block Ack Starting Sequence
Control value of "1" upon aggregating them. In this case, if the HC
does not successfully receive the Block Ack Request 234, the HC
returns no Compressed Block Ack. If the data frame transmitting
side detects a busy within an (SIFS+1 slot) time, but there is no
Compressed Block Ack frame addressed to itself in the received
physical frame, the transmitted frames are regarded as
retransmission targets. The HC transmits an IAC frame 235 and a
Block Ack Request frame 236 for prompting QSTA 1 to retransmit the
Compressed Block Ack upon aggregating them. QSTA 1 transmits a
Block Ack Request frame 238 to the HC upon piggybacking it on a
Compressed Block Ack 237 indicating that the MPDUs with sequence
numbers "1" and "4" are incorrect. The HC then transmits an IAC
frame 239, a Compressed Block Ack 240 to the Block Ack Request from
QSTA 1, MPDUs 241 with sequence numbers "1" and "4" for
retransmission, and a Block Ack Request frame 242 upon aggregating
them. At the end of TXOP period 1, QSTA 1 transmits a Compressed
Block Ack 243 as an acknowledgement. If piggybacking is permitted
by an IAC frame and data to be transmitted to the HC exists in a
transmission queue, the data is also transmitted together. As
described above, whether or not to permit QSTA 1 to perform
piggybacking is determined in accordance with determination made by
the scheduling processing device of the HC.
[0101] According to the first embodiment of the present invention,
the MAC efficiency can be improved by transmitting a plurality of
MPDUs upon aggregating them and transmitting data in the opposite
direction upon piggybacking it on a partial response frame from the
destination. This embodiment has been described mainly on the basis
of HCCA which is a contention-free QoS access control scheme.
Obviously, however, the present invention can also be applied to
contention-based EDCA. In the case of EDCA, a terminal which has
acquired a TXOP serves as an entity of scheduling and adjusts the
amount of frames piggybacked and transmitted from a destination
terminal by using an IAC frame. In the case of HCCA as well, a QSTA
which has acquired a TXOP upon receiving a QoS CF-Poll frame from
an HC permits a destination terminal to perform piggyback
transmission by suing an IAC frame. These scheduling operations
depend on the delay allowable time (delay bound) and the like
represented by QoS data.
SECOND EMBODIMENT
[0102] The second embodiment of the present invention is directed
to delayed Block Ack transmission, in which a Normal
acknowledgement frame for allowing the transmission of a Block Ack
to be postponed is replaced with the IAC frame described in the
first embodiment. More specifically, a communication apparatus
according to the second embodiment of the present invention
transmits a plurality of data frames and then uses an IAC frame
from a destination terminal to another destination in place of a
Normal acknowledgement to a delayed Block Ack. After a lapse of a
predetermined period of time, the destination terminal transmits
the Block Ack frame and a plurality of data upon aggregating
them.
[0103] According to IEEE 802.11e/Draft 10.0, if it is difficult to
return a Block Ack frame a SIFS after the reception of a Block Ack
Request frame, a delayed Block Ack like the one shown in FIG. 5 can
be used. According to the delayed Block Ack technique, first of
all, an Ack response (Normal acknowledgement) to a Block Ack
Request is returned. After a lapse of an arbitrary period of time,
a Block Ack frame is transmitted, and an Ack response (Normal
acknowledgement) to the frame is returned. In the delayed Block Ack
technique, if Normal acknowledgement frame can not be received
after a lapse of a predetermined period of time since the
transmission of a Block Ack Request or Block Ack, the transmission
of the corresponding frames is regarded as failed. The second
embodiment of the present invention is directed to piggyback
transmission using the delayed Block Ack technique.
[0104] FIG. 24 shows how frames are exchanged when piggybacking
described in the second embodiment of the present invention is
performed by using the conventional delayed Block Ack Policy
defined in IEEE 802.11e. Referring to FIG. 24, upon acquiring TXOP
period 1, the HC transmits an IAC frame 244 and data frames 245
with sequence numbers "1" and "2" upon aggregating them. QSTA 1
transmits data 247 in the uplink direction upon piggybacking it on
a Compressed Block Ack 246 to the data frames 245 from the HC
within the period assigned by the IAC frame 244. In this case, when
the delayed Block Ack Policy is to be used for a response from the
HC, the HC transmits a Normal acknowledgement frame 248 defined in
IEEE 802.11 to notify the reception of the delayed Block Ack
procedure. When the QSTA 1 cannot successfully receive a Normal
acknowledgement frame due to an error, QSTA 1 regards the data
frame (or a Block Ack Request frame) as a retransmission target. In
TXOP period 2 in FIG. 24, as in the case of TXOP period 1, when the
delayed policy is used for a Compressed Block Ack from the HC to
QSTA 2, the TXOP expires after a Normal acknowledgement 249 is
transmitted to QSTA 2. In TXOP period 3, the HC transmits, to QSTA
1, a data frame 250 with sequence number "3" in the downlink
direction and a Compressed Block Ack 251 with a Block Ack Starting
Sequence Control value of "1" whose transmission is delayed in TXOP
period 1 upon aggregating them, and QSTA 1 transmits a Normal
acknowledgement frame 252, thereby completing one delayed Block Ack
sequence. In TXOP period 3 in FIG. 24, a Compressed Block Ack 253
with a Block Ack Starting Sequence Control value of "3" to the
downlink data from the HC is piggybacked on the Normal
acknowledgement frame 252. When piggybacking is to be performed by
using the delayed Block Ack technique in the above manner, the MAC
efficiency inevitably decreases due to the use of the Ack frame
defined in IEEE 802.11. The second embodiment of the present
invention therefore realizes a mechanism for solving such a
problem. Although a case wherein the delayed Block Ack Policy is
mainly applied to the transmission of a Compressed Block Ack from
an HC to a QSTA will be mainly described, it is obvious that the
present invention can be applied to both uplink transmission and
downlink transmission.
[0105] FIGS. 25 and 26 each show a basic embodiment of the present
invention concerning its application to the delayed Block Ack
technique. Referring to FIG. 25, when the transmission of a
Compressed Block Ack to data in the uplink direction from QSTA 1 is
to be delayed, the Normal acknowledgement frame defined in IEEE
802.11 is transmitted in a normal state. Instead of this operation,
however, an IAC frame to another destination is transmitted after a
lapse of a SIFS. An IAC frame can be used for various applications
by setting 1 in each bit of the IAC Mask field shown in FIG. 10. In
this case, in order to indicate that the transmission of a delayed
Block Ack is allowed, a 1-bit identification flag is prepared in
the IAC Mask field.
[0106] When the HC transmits, to QSTA 2, data frames 255 with
sequence numbers "1001" and "1002", the destination MAC address of
an IAC frame 254 to be simultaneously aggregated has been set to
QSTA 2. In the second embodiment of the present invention, when
performing transmission to QSTA 2, the HC sets an extended flag in
the IAC Mask field of an IAC frame to 1, which indicates that a
delayed Block Ack has been accepted (to which negative logic can be
obviously applied). QSTA 1 recognizes in advance that the delayed
Block Ack Policy is applied to a Compressed Block Ack returned from
the HC. Assume that QSTA 1 detects a busy state in the wireless
channel within an (SIFS+1 slot) time after the transmission of data
in the uplink direction to the HC. In this case, if QSTA 1 has
successfully received the IAC frame aggregated in the physical
frame, and the flag in the IAC Mask field in the IAC frame, which
indicates that a delayed Block Ack is accepted, is set to 1 (0 in
the case of negative logic), QSTA 1 recognizes that the
transmission of the delayed Block Ack is accepted on the
destination side.
[0107] In this case, the HC in FIG. 25 transmits data to QSTA 2 a
SIFS after the reception of a physical frame from QSTA 1. According
to the IEEE 802.11e/Draft 10.0 standard, if no busy state is
detected in a wireless channel within an (SIFS+1 slot) time after
the transmission of a Block Ack Request or data, the transmitted
frame is regarded as a retransmission target. Therefore, a frame by
which the HC notifies the QSTA of the acceptance of a delayed Block
Ack needs to be transmitted after a lapse of a SIFS. Upon detecting
a busy a SIFS after the transmission of the frame to the HC, QSTA 1
resets the timer. Even if the destination of an IAC frame in a
physical frame which causes a busy state is other than QSTA 1, when
the flag in the IAC Mask is set to 1, QSTA 1 confirms that a
Compressed Block Ack is returned, according to the delayed Block
Ack Policy. If the flag in the IAC Mask remains 0 (1 in the case of
negative logic), it is determined that the establishment of a
delayed Block Ack sequence has failed. So, the QSTA should
retransmit the data or Block Ack Request frame.
[0108] Referring to FIG. 25, the HC transmits data 256 with
sequence number "3", an IAC frame 257 to QSTA 1, and a Compressed
Block Ack 258 with a Block Ack Starting Sequence Control value of
"1" to QSTA 1 upon aggregating them a SIFS after the reception of a
frame in the uplink direction from QSTA 2. The Compressed Block Ack
258 is an acknowledgement frame to MPDUs with sequence numbers "1"
and "2" transmitted first by QSTA 1. Although the destination of
the IAC frame 257 is QSTA 1, setting a flag in the IAC Mask
notifies that delayed Block Ack transmission of data in the uplink
direction from QSTA 2 is accepted. According to the IEEE
802.11e/Draft 10.0 standard, although it is necessary to return a
Normal acknowledgement to a Block Ack frame, in the second
embodiment of the present invention, when a Normal acknowledgement
frame and a Compressed Block Ack to data in the downlink direction
from an HC are to be aggregated, transmitting the Compressed Block
Ack also serves as transmitting the Ack frame defined in IEEE
802.11. That is, when the HC transmits data with sequence number
"3" and a Compressed Block Ack based on the delayed policy, and the
destination (QSTA 1 in the example shown in FIG. 25) then returns a
Compressed Block Ack according to the immediate policy, it is
regarded that a Normal acknowledgement frame to the Block Ack is
received as defined in IEEE 802.11e/Draft 10.0.
[0109] As shown in FIG. 25, if there is data to be transmitted to
another destination, an IAC frame is also aggregated, and it is
notified by using the frame that the delayed Block Ack technique is
accepted. When there is no downlink data as in the example shown in
FIG. 26, the Normal acknowledgement frame defined in IEEE 802.11 is
transmitted to finish the TXOP period. In the example shown in FIG.
26, after a frame 260 from QSTA 2 is received, since there is no
data to be transmitted after a lapse of a SIFS, the HC transmits a
Normal acknowledgement frame 261 to QSTA 2 to notify that the
delayed Block Ack is accepted. When TXOP period 1 expires and TXOP
period 2 starts, the HC transmits a Compressed Block Ack 262 based
on the delayed policy and a downlink data 263 to QSTA 1 upon
aggregating. As shown in FIG. 25, a Compressed Block Ack from QSTA
1 also serves as a Normal acknowledgement (an Ack to a Block Ack).
In the second embodiment of the present invention, when there are
data to be transmitted at SIFS intervals in a predetermined TXOP
period, an IAC frame to another destination is regarded as an Ack
response to a delayed Block Ack. Therefore, when an IAC frame is
used as a Normal acknowledgement in the delayed Block Ack technique
as shown in FIGS. 25 and 26, the MAC efficiency can be improved as
compared with a case wherein the conventional delayed Block Ack
Policy defined in IEEE 802.11e/Draft 10.0 is used.
[0110] FIGS. 27 to 30 each show how frames are exchanged in the
execution of retransmission due to errors. The basic operation in
this case is the same as that in the first embodiment of the
present invention. First of all, as shown in FIG. 27, the HC
transmits downlink data 271 with sequence numbers "1" and "2" to
QSTA 1. In this case, if an error has occurred in a response frame
transmitted by QSTA 1 after a lapse of a SIFS, the HC detects only
a busy 272. After a lapse of a SIFS, the HC transmits a Block Ack
Request frame 274 and IAC frame 273 to QSTA 1 upon aggregating
them. When the immediate Block Ack Policy is applied to a
Compressed Block Ack from QSTA 1 to the HC, QSTA 1 transmits a
Compressed Block Ack 275 a SIFS after the reception of the Block
Ack Request frame 274 from the HC. In the example shown in FIG. 27,
QSTA 1 transmits the Compressed Block Ack 275 with a Block Ack
Starting Sequence Control value of "1" and data 276 in the uplink
direction to the HC upon piggybacking them. Assuming that the
delayed policy is applied to a Compressed Block Ack from the HC to
the QSTA, the HC uses an IAC frame 277 addressed to QSTA 2 to
notify that the application of the delayed Block Ack Policy is
accepted, as in the example shown in FIG. 25. Assume that when the
frame transmission in the uplink direction from QSTA 2 to the HC
ends, the remainder of TXOP period 1 held by the HC is small, and
the HC transmits a Compressed Block Ack based on the delayed policy
to QSTA 1 from the viewpoint of scheduling. Since there is a
delayed Compressed Block Ack in the physical frame received from
the HC, QSTA 1 completes the delayed Block Ack sequence by
returning the Normal acknowledgement frame defined in IEEE 802.11.
At this time, in the second embodiment of the present invention, as
in the example shown in FIG. 25, if the HC has transmitted downlink
data in response to a delayed Compressed Block Ack, and the
immediate policy is applied to a Compressed Block Ack from QSTA 1
to the HC, transmitting only the Compressed Block Ack can also
serve as transmitting the Normal acknowledgement defined in IEEE
802.11, as described above. In the example shown in FIG. 27, since
the physical frame transmitted by the HC at the end of TXOP period
1 contains no aggregated data, QSTA 1 completes the delayed Block
Ack sequence by transmitting a Normal acknowledgement 278.
[0111] FIG. 28 shows an example of operation to be performed when
errors have occurred in some of the MPDUs in the uplink direction
from a QSTA to an HC. In the example shown in FIG. 28, errors have
occurred in a Compressed Block Ack 280 from QSTA 1 to the HC and
data 281 with sequence number "2" in the uplink direction. The HC
cannot receive any Compressed Block Ack from QSTA 1. The HC
therefore transmits a Block Ack Request 282. An IAC frame 283 is
aggregated in the Block Ack Request 282 transmitted by the HC. The
destination of the IAC frame 283 is QSTA 1, and 1 (0 in the case of
negative logic) is set in the flag in the IAC Mask field. Upon
receiving the IAC frame 283, QSTA 1 confirms that the delayed
policy is properly applied to data with sequence numbers "1" and
"2" transmitted by itself. QSTA 1 then retransmits the Compressed
Block Ack 283 with a Block Ack Starting Sequence Control value of
"1". After a lapse of a SIFS, the HC transmits an IAC frame 284 and
data 285 with sequence numbers "1001" and "1002" to QSTA 2 upon
aggregating them. At this time, the value of the flag in the IAC
Mask field of the IAC frame 284 is kept at 0 which is the initial
value (1 in the case of negative logic). This is because the
notification of the acceptance of the delayed Block Ack Policy for
data from QSTA 1 has already been completed. After QSTA 2 transmits
data to the HC, the HC transmits downlink data (sequence number
"3") 286 and a Compressed Block Ack 287 based on the delayed policy
with a Block Ack Starting Sequence Control value of "1" to QSTA 1.
QSTA 1 makes a Compressed Block Ack 288 to sequence number "3" from
the HC also serve as a Normal acknowledgement frame to the Block
Ack. In addition, when piggybacking is permitted by an IAC frame,
QSTA 1 retransmits data frame 289 with sequence number "2", whose
transmission has failed, upon piggybacking.
[0112] FIG. 29 shows an example of retransmission to be performed
when errors have occurred in some of MPDUs aggregated in a physical
frame in the downlink direction. In the example shown in FIG. 29,
since the immediate policy is applied to Compressed Block Ack
transmission from a QSTA to an HC, QSTA 1 returns a Compressed
Block Ack 290 to indicate that an error has occurred in an MPDU
with sequence number "1" from the HC, and the HC retransmits an
MPDU 291 with sequence number "1". In TXOP period 2, the HC
transmits data frames 292 with sequence numbers "1001" and "1002"
and an IAC frame 293 to QSTA 2 upon aggregating them. QSTA 2
transmits, to the HC, a Compressed Block Ack 294 based on the
immediate policy and data 295 in the uplink direction upon
piggybacking them. In transmitting data to QSTA 1 a SIFS after the
reception of the frame from QSTA 2, the HC sets 1 in the flag in
the IAC Mask field of an IAC frame 297 aggregated with the data.
When the flag in the IAC frame 297 addressed to QSTA 1 is set to 1,
QSTA 2 confirms that the delayed policy is applied to a partial
response from the HC to the uplink data transmitted by QSTA 2.
[0113] FIG. 30 shows a case wherein errors have occurred in all
data in the uplink direction from a QSTA to an HC, and the HC
cannot return a Compressed Block Ack. Referring to FIG. 30, since
QSTA 1 is permitted by an IAC frame from the HC to perform
piggyback transmission, QSTA 1 piggybacks data (sequence numbers
"1" and "2") 300 in the uplink direction on a Compressed Block Ack
301. At this time, if an FCS calculation result indicates that all
the data frames transmitted from QSTA 1 are incorrect, the HC does
not return Compressed Block Ack. The HC then performs downlink
transmission to QSTA 2 within the range of TXOP period 1. In this
case, the flag in the IAC Mask field of an IAC frame 302 to QSTA 2
remains the initial value "0" ("1" in the case of negative logic).
QSTA 1 is monitoring the physical frame transmitted from the HC,
and checks the flag in the IAC frame 302. However, since the value
remains 0, QSTA 1 determines that the application of the delayed
policy to the Compressed Block Ack has failed, and regards the
transmitted data frames 300 as retransmission targets. When the HC
transmits data 303 with sequence number "3" and an IAC frame 304 to
QSTA 1 upon aggregating them afterward, QSTA 1 piggybacks a Block
Ack Request 306 on a Compressed Block Ack (Block Ack Starting
Sequence Control value of "3") 305 to the data 303 from the HC.
Alternatively, as in the first embodiment, QSTA 1 may directly
aggregate the data with sequence numbers "1" and "2" as
retransmission targets. The scheduling processing device of QSTA 1
selects whether to piggyback the Block Ack Request 306 or directly
aggregate the frames as retransmission targets. Assume that after a
lapse of a SIFS since the reception of a frame from QSTA 1, the HC
is to transmit data to another QSTA. In this case, the HC sets 1 (0
in the case of negative logic) in the flag in the IAC Mask field of
an IAC frame. This makes QSTA 1 recognize that Compressed Block Ack
return based on the delayed policy is applied, on the HC side, to
the Block Ack Request (or data) transmitted by itself.
[0114] As described above, according to the second embodiment of
the present invention, the MAC efficiency can be improved by
efficiently applying the piggyback technique to the delayed Block
Ack technique. Note that in the second embodiment, the delayed
policy is applied to a Compressed Block Ack from an HC to a QSTA
(i.e., uplink data from a QSTA), and the immediate policy is
applied to a Compressed Block Ack from a QSTA to an HC (i.e.,
downlink data to a QSTA). Obviously, however, the present invention
allows the delayed policy to be applied to Compressed Block Acks in
both the uplink and downlink directions.
[0115] In addition, as in the first embodiment, the present
invention can be applied to a method in which, upon acquiring a
TXOP by EDCA, a terminal having an access right plays a leading
role in executing the delayed Block Ack technique using an IAC
frame. Furthermore, the present invention can be applied to a case
wherein a Block Ack Request is to be aggregated with the end of a
physical frame (explicit Block Ack Request), as in the first
embodiment. In this case, if an FCS calculation result indicates
that the Block Ack Request is incorrect, the data receiving side
does not transmit Compressed Block Ack. Thereafter, the data
transmitting terminal requests the receiving side to retransmit a
Compressed Block Ack, by, for example, retransmitting a Block Ack
Request frame.
THIRD EMBODIMENT
[0116] The third embodiment of the present invention is directed to
the application of the immediate Block Ack technique and delayed
Block Ack technique in a case wherein a plurality of MPDUs are
aggregated and transmitted to a plurality of destinations. When
only MAC frames addressed to the same destination are to be
aggregated and transmitted, overheads like IFS (Interframe Space)
and random backoff occur every time the destination changes. In
contrast to this, aggregating MAC frames addressed to a plurality
of different destinations into one physical frame makes it possible
to reduce these overheads and improve the MAC efficiency.
[0117] FIG. 31 shows an example of a MAC frame containing
information associated with a plurality of destinations.
Aggregating a MAC frame 310 like this frame in the head of a
physical frame allows a physical frame receiving terminal to
immediately determine whether or not there is any MPDU addressed to
itself exists. The MAC frame 310 like the one shown in FIG. 31 will
be referred to as an "MRAD (Multiple Receiver Aggregation
Descriptor) frame" hereinafter. As shown in FIG. 31, the MAC frame
310 has a conventional MAC header 311 defined in IEEE 802.11 which
includes "Frame control", "Duration", "Receiver Address",
"Transmitter Address", and the like. The MAC frame 310 includes a
Number of receivers field 312 indicating the number of destinations
of MPDUs aggregated in the physical frame, a Receiver Address Info
field 313 indicating destination MAC address information, and
Length field 314 for designating, in octets, an information size to
be occupied for each destination. The example shown in FIG. 31
exemplifies information up to "Receiver Address Info 3". However,
the number of pieces of information is not limited to this, and an
arbitrary variable length can be set. That is, the number of
destinations is arbitrarily set.
[0118] FIG. 32 shows an example of frames which are exchanged when
the immediate Block Ack Policy is applied. Upon acquiring a TXOP,
the HC transmits an MRAD frame 320, an IAC 321 and data frames
(sequence numbers "1" and "2") 322 to QSTA 1, and an IAC 323 and
data frames (sequence numbers "1001" and "1002") 324 upon
aggregating them into one physical frame 325. Using the information
of the MRAD frame 320 allows terminals other than QSTAs 1 and 2 to
freely perform processing such as shifting to the power saving
mode. Offset times from the end of the transmission of a physical
frame from the HC are written in the IAC frames 321 and 323
addressed to QSTAs 1 and 2 to designate the timings at which QSTAs
1 and 2 respond. As this offset time, the Response Period Offset
field in the example shown in FIG. 10 is used. When QSTA 1
successfully receives an IAC frame addressed to itself, it
aggregates uplink data 327 with a Compressed Block Ack 326 to the
HC within the range of piggyback transmission allowable time, and
transmits the resultant data, as shown in FIG. 32. Likewise,
following the frame transmission by QSTA 1, QSTA 2 transmits
Compressed Block Ack 328 and uplink data 329 to the HC upon
aggregating them. At this time, the example in FIG. 32 shows that
all data frames 329 transmitted by QSTA 2 are incorrect. When the
immediate Block Ack Policy is applied, the HC transmits an MRAD
frame 330 and an IAC 331 and Compressed Block Ack frame 332 to QSTA
1 upon aggregating them a SIFS after the end of frame transmission
by QSTA 2. Since all the data from QSTA 2 are incorrect, the
Compressed Block Ack frame from the HC to QSTA 2 is not aggregated.
In this case, if the HC does not permit QSTA 2 to perform frame
transmission in the opposite direction (uplink), the Receiver
Address Info field of the MRAD frame 330 does not contain the MAC
address of QSTA 2. The Number of receivers field is 1, and only the
MAC address of QSTA 1 and length information are written. If the HC
is to permit QSTA 2 to perform transmission, it aggregates an IAC
frame addressed to QSTA 2, sets "Number of receivers" to 2, and
adds the MAC address of QSTA 2.
[0119] In the third embodiment of the present invention, when the
HC transmits a physical frame within TXOP period 1, QSTAs 1 and 2
check the Receiver Address Info field in the MRAD frame aggregated
in the physical frame from the HC. If each QSTA detects no MAC
address of its own, the QSTA regards the transmitted frame as a
recovery target. In the example shown in FIG. 32, QSTA 2 determines
that it has failed to receive an immediate type Compressed Block
Ack to transmitted data with sequence numbers "1" and "2", and
performs appropriate recovery operation.
[0120] FIGS. 33 and 34 each show an application example of the
delayed Block Ack Policy. Referring to FIG. 33, the HC transmits an
IAC 331 and data frame (sequence number "1") 332 to QSTA 1, and an
IAC 333 and data frame (sequence number "1001") 334 to QSTA 2 upon
aggregating them into one physical frame 335. QSTAs 1 and 2
recognize the timings of transmission to uplinks on the basis of
the respective pieces of IAC frame information, respectively
piggyback uplink data 338 and 339 on Compressed Block Acks 336 and
337.
[0121] When the delayed policy is used, there is no need to
transmit a Compressed Block Ack immediately after transmission by a
QSTA. Instead, as in the second embodiment, the HC can regard a
frame for giving a permission to perform transmission in the
opposite direction (permits a terminal having no TXOP to perform
transmission) as a Normal acknowledgement frame to a Block Ack
Request frame by delayed Block Ack transmission defined in IEEE
802.11e/Draft 10.0. In this case, the HC aggregates an IAC frame
340 to QSTA 1, QSTA 2, and QSTA 3 and data (sequence number "2001")
341 in the downlink direction to QSTA 3 and transmits the resultant
data. Both Reverse Direction Grant and Response Period Offset of
the IAC frame to each of QSTAs 1 and 2 are set to 0. That is, the
HC does not permit QSTAs 1 and 2 to perform transmission in the
uplink direction. A flag indicating the acceptance of the delayed
Block Ack technique is set ON. Upon receiving this physical frame,
each of QSTAs 1 and 2 confirms that the delayed Block Ack Policy is
applied to the data transmitted by itself. Thereafter, QSTA 3
transmits a Compressed Block Ack 342 to the data (sequence number
"2001") from the HC and data 343 in the uplink direction upon
aggregating them. Referring to FIG. 33, the HC transmits IAC frames
344 to QSTAs 1, 2, and 3 and Compressed Block Acks 345 to QSTAs 1
and 2. The Compressed Block Ack 345 is a Block Ack based on the
delayed policy to data in the uplink direction from QSTAs 1 and 2.
In this case, values are set in Reverse Direction Grant and
Response Period Offset of the IAC frame 344 to each of QSTAs 1 and
2 to allow each QSTA to transmit at least the Normal
acknowledgement frame defined in IEEE 802.11. In addition, a flag
is set in the IAC Mask field of QSTA 3 to notify the acceptance of
the delayed Block Ack technique. As shown in FIG. 34, when the
remainder of TXOP period held by the HC becomes small, the HC
transmits Normal acknowledgement frames 346 defined in IEEE 802.11
which are prepared for the respective destinations and aggregated.
That is, an aggregation of Normal acknowledgements is performed for
a plurality of destinations.
[0122] Buffer management on the receiving side in a case wherein
data addressed to a plurality of destinations are aggregated will
be described with reference to FIGS. 35 and 36. Consider a case
wherein an MRAD frame 350, an IAC 351 to QSTA 1, data frames 352
and 353 with sequence numbers "1" and "2", an IAC 354 to QSTA 2,
and data frames 355 and 356 with sequence numbers "1001" and "1002"
are aggregated and transmitted. In this case, a format like the one
shown in FIG. 6 may be used to aggregate a plurality of frames.
[0123] Assume that, as shown in FIG. 36, an FCS calculation result
indicates that an error has occurred in the MPDU 352 with sequence
number "1". By using the offset value designated by the IAC 351,
QSTA 1 transmits a Compressed Block Ack 360 with a Block Ack
Starting Sequence Control value of "2", and QSTA 2 transmits a
Compressed Block Ack 361 with a Block Ack Starting Sequence Control
value of "1001". For aggregated data containing no Block Ack
Request (implicit Block Ack Request), the sequence number of the
first MPDU which has been successfully received is used as the
Block Ack Starting Sequence Control value of the Compressed Block
Ack. Referring to FIG. 36, assume that MPDUs with sequence numbers
"0" and "4095" have already been stored in a reception buffer 362
of QSTA 1, and MPDUs with sequence numbers "999" and "1000" have
already been stored in a reception buffer 363 of QSTA 2. In the
third embodiment of the present invention, when an FCS calculation
result on an IAC frame is correct, and an FCS calculation result on
a data frame following it is correct, the sequence number of the
data frame is regarded as proper sequence number information for
reception buffer management. In the example shown in FIG. 36, QSTA
1 transmits a Compressed Block Ack to the HC, but keeps the MAC
frame stored in the reception buffer 362. On the other hand, QSTA 2
has successfully received all frames, and hence performs reception
buffer management by setting the sequence number "1001" as a proper
Block Ack Starting Sequence Control value. According to the IEEE
802.11e/Draft 10.0 standard, all MAC frames having lower sequence
numbers than the Block Ack Starting Sequence Control value must be
released from the reception buffer and forwarded to the upper
layer. For this reason, QSTA 2 in FIG. 36 releases MAC frames with
sequence numbers "999" to "1002" from the reception buffer 363 and
forwards them to the upper layer.
[0124] As shown in FIG. 37, a format containing no IAC frame can
also be used. In the example shown in FIG. 37, an FCS calculation
result indicates that an error has occurred in the data with
sequence number "2" to QSTA 2. In this case, even if an FCS
calculation result on the data frame with sequence number "1001" to
QSTA 2 is correct, it cannot be determined up to which MPDUs to
QSTA 1 are aggregated. For this reason, even if a Compressed Block
Ack is returned, no MAC frame can be released from the reception
buffer. That is, in the third embodiment of the present invention,
if FCS calculation results on two consecutive MPDUs having
different destination addresses are successful, reception buffer
management is performed by determining the sequence number of the
second MPDU (i.e., the MPDU having the new destination) as a proper
Block Ack Starting Sequence Control value for the next
destination.
[0125] According to the IEEE 802.11e/Draft 10.0 standard, MAC
frames are classified according to the priorities of traffic events
and a Block Ack Request and Block Ack frame are required for each
priority. The BAR (Block Ack Request) field of the Block Ack
Request frame in FIG. 2 and the BA (Block Ack) Control field of the
Block Ack in FIG. 3 each include a 4-bit TID (Traffic Identifier),
in which a number 0 to 15 is written. Note that assigning a
numerical value from 0 to 7 to the TID indicates that the MAC frame
is transmitted by prioritized QoS, i.e., EDCA, whereas assigning a
numerical value from 8 to 15 to the TID (which is called TSID:
Traffic Stream Identifier) indicates that the MAC frame is
transmitted by parameterized QoS, i.e., HCCA. A TID is also used
for an RDTID (Reverse Direction Traffic Identifier) of the IAC
frame of the Compressed Block Ack in FIG. 8 or of the IAC frame in
FIG. 10. The RDTID field of an IAC frame is used by a transmitting
terminal which has acquired a TXOP to designate a priority to a MAC
frame to be piggybacked when permitting a destination terminal to
perform piggyback transmission. According to the IEEE 802.11e/Draft
10.0 standard, a sequence number must be independently assigned to
a MAC frame for each TID. The QoS data receiving side therefore
preferably manages the reception buffer for each priority. In
transmission based on the Block Ack technique defined in IEEE
802.11e, all MAC frames having lower sequence numbers than the
Starting Sequence Number (Block Ack Starting Sequence Control)
indicated by a Block Ack Request frame are released from a
reception buffer. In this case, since a Block Ack Request frame is
prepared for each TID, reception buffer management must be done for
each priority (TID). The description of the reception buffer
management which has been made with reference to FIGS. 35 and 37 is
about the case wherein MAC frames addressed to a plurality of
destinations, with a single priority (one kind of TID), are
aggregated into a physical frame. In this embodiment, the present
invention can be applied to a case wherein MAC frames addressed to
a plurality of destinations, with a plurality of priorities, are
aggregated into a single physical frame. Referring to FIG. 35,
following the MRAD, the IAC frame to QSTA 1, the data frames with
sequence numbers "1" and "2", the IAC frame to QSTA 2, and the data
frames with sequence numbers "1001" and "1002" are aggregated in
the order named. Assume, however, that following an MRAD, an IAC
frame with a high priority (the value of the TID is arbitrarily
set) to QSTA 1, data frames with sequence numbers "1" and "2", an
IAC frame with an intermediate priority to QSTA 1, data frames with
sequence numbers "1" and "2", an IAC frame with a high priority
(the value of the TID is arbitrarily set) to QSTA 2, data frames
with sequence numbers "1001" and "1002", an IAC frame with an
intermediate priority to QSTA 1, and data frames with sequence
numbers "1001" and "1002" are aggregated in the order named. In
this case, if an FCS calculation result on a given IAC frame is
correct and an FCS calculation result on the succeeding MPDU is
correct on the assumption that an IAC frame is aggregated before
each destination and each priority, the sequence number of the MPDU
is regarded as a proper Starting Sequence Number (Block Ack
Starting Sequence Control). All MAC frames having lower sequence
numbers than the Starting Sequence Number are then released from a
corresponding buffer prepared for each priority in the receiving
terminal and forwarded to the upper layer. Alternatively, assume
that a physical frame need not necessarily contain any IAC frame,
as shown in FIG. 37. In this case, if FCS calculation results on
two consecutive MPDUs are correct and the two MPDUs have different
destination addresses or different priorities, the sequence number
of the second MPDU is used for the management of a reception buffer
prepared for each priority in the destination terminal of the MPDU.
That is, all MAC frames having lower sequence numbers than the
proper Block Ack Starting Sequence Control are released from the
reception buffer and forwarded to the upper layer.
[0126] This embodiment has exemplified the case wherein in downlink
transmission from an HC (QoS access point) to a QSTA (QoS station),
MAC frames addressed to a plurality of destinations are aggregated
and transmitted. However, a QSTA may serve as an entity of
transmission as long as a TXOP is given by a QoS CF-Poll frame.
When the QSTA serves as an entity of transmission, destination
candidates include, for example, terminals which can directly
communicate with each other between QSTAs through DLS (Direct Link
Set-up), in addition to access points. Obviously, the present
invention can also be applied to contention-based EDCA as well as
HCCA which is a contention-free QoS access control scheme. In EDCA,
a terminal which has acquired a TXOP serves as a start point of
data transmission to a plurality of destinations. In addition, the
permission of piggyback transmission to a destination by an IAC
frame is also realized by the scheduling processing device of a
terminal which has acquired a TXOP.
[0127] Additional advantages and modifications will readily occur
to those skilled in the art. Therefore, the invention in its
broader aspects is not limited to the specific details and
representative embodiments shown and described herein. Accordingly,
various modifications may be made without departing from the spirit
or scope of the general inventive concept as defined by the
appended claims and their equivalents.
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