U.S. patent application number 11/399400 was filed with the patent office on 2006-08-17 for wireless lan communication method and apparatus.
This patent application is currently assigned to SAMSUNG ELECTRONICS CO., LTD.. Invention is credited to Jae-hwa Kim, Chang-yeul Kwon, Dong-hwi Roh, Chil-youl Yang.
Application Number | 20060182079 11/399400 |
Document ID | / |
Family ID | 37045539 |
Filed Date | 2006-08-17 |
United States Patent
Application |
20060182079 |
Kind Code |
A1 |
Yang; Chil-youl ; et
al. |
August 17, 2006 |
Wireless LAN communication method and apparatus
Abstract
A wireless local area network (WLAN) communication method and
apparatus are provided. The WLAN communication method includes
allowing a receiving station to receive a multi input multi output
(MIMO) frame, allowing the receiving station to determine whether
the MIMO frame is erroneous and whether the MIMO frame is destined
for the receiving station, allowing the receiving station to
generate a single input single output (SISO) acknowledgement (ACK)
frame if the MIMO frame is not erroneous and is destined for the
receiving station, and allowing the receiving station to transmit
the SISO ACK frame to a sending station that has transmitted the
MIMO frame.
Inventors: |
Yang; Chil-youl; (Yongin-si,
KR) ; Kwon; Chang-yeul; (Yongin-si, KR) ; Kim;
Jae-hwa; (Siheung-si, KR) ; Roh; Dong-hwi;
(Seoul, KR) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W.
SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
SAMSUNG ELECTRONICS CO.,
LTD.
|
Family ID: |
37045539 |
Appl. No.: |
11/399400 |
Filed: |
April 7, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11199118 |
Aug 9, 2005 |
|
|
|
11399400 |
Apr 7, 2006 |
|
|
|
60601135 |
Aug 13, 2004 |
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Current U.S.
Class: |
370/347 |
Current CPC
Class: |
H04L 1/188 20130101;
H04L 2001/125 20130101; H04L 1/1671 20130101; H04L 27/2602
20130101; H04L 5/023 20130101; H04L 1/1607 20130101; H04B 7/02
20130101; H04L 1/1829 20130101; H04W 84/12 20130101; H04L 1/16
20130101 |
Class at
Publication: |
370/347 |
International
Class: |
H04B 7/212 20060101
H04B007/212 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 6, 2004 |
KR |
10-2004-0070931 |
Claims
1. A wireless local area network communication method comprising:
receiving a multi input multi output (MIMO) frame at a receiving
station; determining, at the receiving station, whether the
received MIMO frame is erroneous and a media access control (MAC)
frame is destined for the receiving station; generating a single
input single output (SISO) acknowledgement (ACK) frame at the
receiving station if it is determined that the received MIMO frame
is not erroneous and the MAC frame is destined for the receiving
station; and transmitting the SISO ACK frame to a sending station
that transmitted the MIMO frame.
2. The method of claim 1, wherein the MIMO frame comprises a
plurality of physical layer convergence procedure (PLCP) preambles,
a signal field, and a data field, and the signal field immediately
follows a first PLCP preamble.
3. The method of claim 2, wherein the data field comprises
information regarding a length in bytes of a part of the MIMO frame
following the signal field.
4. A wireless local area network communication method comprising:
generating a multi input multi output (MIMO) frame at a sending
station; transmitting the MIMO frame from the sending station to a
receiving station; and receiving a single input single output
(SISO) acknowledgement (ACK) frame sent by the receiving station in
response to the MIMO frame.
5. The method of claim 4, wherein the MIMO frame comprises a
plurality of physical layer convergence procedure (PLCP) preambles,
a signal field, and a data field, and the signal field directly
follows a first PLCP preamble.
6. The method of claim 5, wherein the data field comprises
information regarding a length in bytes of a part of the MIMO frame
following the signal field.
7. A station comprising: a physical layer which receives a multi
input multi output (MIMO) frame transmitted via a wireless medium
and obtains a media access control (MAC) frame from the MIMO frame
which is received; and an MAC layer which determines whether the
MAC frame is erroneous and whether the MAC frame is destined for
the station, generates an acknowledgement (ACK) frame, and provides
the ACK frame to the physical layer if it is determined that the
MAC frame is not erroneous and is destined for the station, wherein
the physical layer generates a single input single output (SISO)
ACK frame based on the ACK frame provided by the MAC layer, and
transmits the SISO ACK frame via the wireless medium.
8. The station of claim 7, wherein the MIMO frame comprises a
plurality of physical layer convergence procedure (PLCP) preambles,
a signal field, and a data field, and the signal field immediately
follows a first PLCP preamble.
9. The station of claim 8, wherein the data field comprises
information regarding a length in bytes of a part of the MIMO frame
following the signal field.
10. A recording medium storing a computer program to execute a
wireless local area network communication method, the method
comprising: receiving a multi input multi output (MIMO) frame at a
receiving station; determining, at the receiving station, whether
the received MIMO frame is erroneous and a media access control
(MAC) frame is destined for the receiving station; generating a
single input single output (SISO) acknowledgement (ACK) frame at
the receiving station if it is determined that the received MIMO
frame is not erroneous and the MAC frame is destined for the
receiving station; and transmitting the SISO ACK frame to a sending
station that transmitted the MIMO frame.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation of application Ser. No. 11/199,118
filed Aug. 9, 2005. The entire disclosure of the prior application,
application Ser. No. 11/199,118 is considered part of the
disclosure of the accompanying continuation application and is
hereby incorporated by reference.
[0002] This application claims priority from Korean Patent
Application No. 10-2004-0070931 filed on Sep. 6, 2004 in the Korean
Intellectual Property Office, and U.S. Provisional Patent
Application No. 60/601,135 filed on Aug. 13, 2004 in the United
States Patent and Trademark Office, the disclosures of which are
incorporated herein by reference in their entirety.
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] Apparatuses and methods consistent with the present
invention relate to wireless local area network (LAN)
communications, and more particularly, to wireless LAN (WLAN)
communications using an improved carrier sensing mechanism.
[0005] 2. Description of the Related Art
[0006] Recently, there is an increasing demand for ultra high-speed
communication networks due to widespread public use of the Internet
and a rapid increase in the amount of available multimedia data.
Since LANs emerged in the late 1980s, the data transmission rate
over the Internet has drastically increased from about 1 Mbps to
about 100 Mbps. Thus, high-speed Ethernet transmission has gained
popularity and wide spread use. Currently, intensive research into
a gigabit speed Ethernet is under way. An increasing interest in
the wireless network connection and communication has triggered
research into and development of WLANs, greatly increasing
availability of WLANs to consumers. Although use of WLANs may
reduce performance in view of lower transmission rate and poorer
stability as compared to wired LANs, WLANs have various advantages,
including wireless networking capability, greater mobility and so
on. Accordingly, WLAN markets have been gradually growing.
[0007] Due to the need for a greater transmission rate and the
development of wireless transmission technology, the initial IEEE
802.11 standard, which specifies a 1 to 2 Mbps transfer rate, has
evolved into advanced standards including 802.11b and 802.11a.
Currently, a new IEEE standard, 802.11g, is being discussed by the
Standardization Conference groups. The IEEE 802.11g standard, which
delivers a 6 to 54 Mbps transmission rate in the 56 GHz-National
Information Infrastructure (NII) band, uses orthogonal frequency
division multiplexing (OFDM) as transmission technology. With an
increasing public interest in OFDM transmission and use of a 5 GHz
band, much greater attention is been paid to the OFDM than other
wireless standards.
[0008] Recently, wireless Internet services using WLAN, so-called
"Nespot," have been launched and offered by Korea Telecommunication
(KT) Corporation of Korea. Nespot services allow access to the
Internet using a WLAN according to IEEE 802.11b, commonly called
Wi-Fi representing wireless fidelity. Communication standards for
wireless data communication systems, which have been completed and
promulgated or are being researched and discussed, include Wide
Code Division Multiple Access (WCDMA), IEEE 802.11x, Bluetooth,
IEEE 802.15.3, etc., which are known as 3rd Generation (3G)
communication standards. The most widely known, cheapest wireless
data communication standard is IEEE 802.11b, a series of IEEE
802.11x. An IEEE 802.11b WLAN standard delivers data transmission
at a maximum rate of 11 Mbps and utilizes the 2.4 GHz-Industrial,
Scientific, and Medical (ISM) band, which can be used at below a
predetermined electric field without permission. With the recent
widespread use of the IEEE 802.11a WLAN standard, which delivers a
maximum data rate of 54 Mbps in the 5 GHz band by using OFDM, IEEE
802.11g developed as an extension to the IEEE 802.11a for data
transmission in the 2.4 GHz band using OFDM is intensively being
researched.
[0009] The Ethernet and the WLAN, which are currently being widely
used, both utilize a carrier sensing multiple access (CSMA) method.
According to the CSMA method, it is determined whether a channel is
in use or not in use. If the channel is not in use, that is, if the
channel is idle, then data is transmitted. If the channel is busy,
retransmission of data is attempted after a predetermined period of
time. A carrier sensing multiple access with collision detection
(CSMA/CD) method, which is an improvement of the CSMA method, is
used in a wired LAN, whereas a carrier sensing multiple access with
collision avoidance (CSMA/CA) method is used in packet-based
wireless data communications. In the CSMA/CD method, a station
suspends transmitting signals if a collision is detected during
transmission. Compared with the CSMA method, in which it is
pre-checked whether a channel is occupied or not before
transmitting data, in the CSMA/CD method, the station suspends
transmission of signals when a collision is detected during the
transmission of signals and transmits a jam signal to another
station to inform it of the occurrence of the collision. After the
transmission of the jam signal, the station has a random backoff
period for delay and restarts transmitting signals. In the CSMA/CD
method, the station does not transmit data immediately even after
the channel becomes idle and has a random backoff period for a
predetermined duration before transmission to avoid collision of
signals. If a collision of signals occurs during transmission, the
duration of the random backoff period is increased by two times,
thereby further lowering a probability of collision.
[0010] As described above, conventionally, a single input single
output (SISO) approach has been adopted for WLAN communications
based on a CSMA/CA method. That is to say, a station (hereinafter
referred to as an "SISO station") that adopts the SISO approach
receives data from and transmits data to a wireless medium using a
single antenna. However, in recent years, research on wireless
communications based on a multiple input multiple output (MIMO)
approach has been vigorously carried out. A station (hereinafter
referred to as an "MIMO station") that adopts the MIMO approach,
unlike an SISO station, transmits a plurality of data to a wireless
medium via different transmission paths using a plurality of
antennas and receives a plurality of data from another MIMO station
via different transmission paths using the antennas. Accordingly,
an MIMO station achieves higher data rates (data transferring
rates) than an SISO station. However, in a WLAN where an MIMO
station and an SISO station coexist, the SISO station may not be
able to interpret any data transmitted by the MIMO station.
Problems that may arise in such a WLAN will now be described in
detail with reference to FIGS. 1 through 3.
[0011] FIG. 1 is a diagram illustrating the format of an IEEE
802.11a frame.
[0012] Referring to FIG. 1, the IEEE 802.11a frame is comprised of
a physical layer convergence procedure (PLCP) preamble 110, a
signal field 120, and a data field 130.
[0013] The PLCP preamble 110 indicates what data will be
transmitted on a current physical layer. The signal field 120,
which follows the PLCP preamble 110, includes one orthogonal
frequency-division multiplexing (OFDM) symbol that is modulated at
a lowest data rate using a basic modulation method. The data field
130 includes a plurality of OFDM symbols that are modulated at data
rates higher than or equal to the data rate at which the OFDM
symbol of the signal field 120 is modulated.
[0014] The signal field 120 is comprised of a total of 24 bits. In
detail, the first through fourth bits of the signal field 120
constitute a rate field 142, which specifies how and at what coding
rate the data field 130 has been modulated. The fifth bit of the
signal field 120 is a reserved bit. The sixth through seventeenth
bits of the signal field 120 constitute a length field 144, which
specifies the length of the IEEE 802.11a frame.
[0015] The eighteenth bit of the signal field 120 is a bit used for
parity check. The nineteenth through twenty fifth bits of the
signal field 120 are tail bits. The length field 144 specifies the
number of bytes constituting a media access control (MAC) frame
contained in the data field 130. First through sixteenth bits of
the data field 130 constitute a service field. The signal field 120
and the service field constitute a PLCP header 140. The data field
130 also includes a PLCP service data unit (PSDU), six tail bits,
and pad bits. The PSDU corresponds to an MAC frame, which is
comprised of an MAC header, an MAC data field, and a frame check
sequence (FCS) used for determining whether the MAC frame is
erroneous. The data field 130 may be modulated in various manners
and at various coding rates. As described above, information
regarding how and at what coding rate the data field 130 has been
modulated is included in the rate field 142 of the signal field
120.
[0016] FIG. 2 is a diagram illustrating a carrier sensing operation
performed in a WLAN.
[0017] Two carrier sensing methods, i.e., a physical carrier
sensing method and a virtual carrier sensing method, are currently
available for WLAN communications. The physical carrier sensing
method and the virtual carrier sensing method will now be described
in detail with reference to the accompanying drawings. Referring to
FIG. 2, a frame 212, which is received by a physical layer 210, is
comprised of a PLCP preamble 214, a signal field 216, and a data
field 218.
[0018] The physical carrier sensing method enables a station to
recognize whether signals are transmitted by a wireless medium. In
other words, when the PLCP preamble 214 is input to the physical
layer 210, the physical layer 210 notifies an MAC layer 220 that it
is currently used by transmitting a busy signal to the MAC layer
220, as marked by 222. Thereafter, when the reception of the PLCP
preamble 214 is completed, the physical layer 210 notifies the MAC
layer 220 that it is idle by transmitting an idle signal 228 to the
MAC layer 220.
[0019] A physical carrier sensing operation may be performed based
on a result of interpreting a length field included in the signal
field 216. The virtual carrier sensing method is a method that
enables the MAC layer 220 to determine whether a wireless medium is
used based on a result of interpreting a duration value, i.e., a
network allocation vector (NAV) value, contained in an MAC frame
included in the data field 218. Therefore, for a predetermined
period of time specified by the duration value, the MAC layer 220
considers that the wireless medium is used. A station can receive
the data field 218 and then read the NAV value from the MAC frame
included in the received data field 218.
[0020] FIG. 3 is a diagram illustrating a conventional method of
transmitting frames in a contention period in a WLAN where three
MIMO stations, i.e., first through third MIMO stations, and an SISO
station coexist.
[0021] According to the physical carrier sensing method, stations
are prevented from transmitting frames via a wireless channel when
frames are transmitted via the wireless channel by other stations.
In a contention mode, stations cannot transmit a next frame
immediately after the wireless channel becomes empty but are
required to wait for a predetermined amount of time called a
distributed inter-frame space (DIFS) and random back-off time to
obtain the opportunity to transmit a frame via the wireless
channel.
[0022] Referring to FIG. 3, the first MIMO station obtains the
opportunity to transmit data through channel contention and thus
transmits a data frame to the second MIMO station. Since the data
frame transmitted by the first MIMO station is an MIMO frame, the
third MIMO station as well as the second MIMO station can receive
it, but the SISO station cannot receive it. Following a short
inter-frame space (SIFS) after receiving the data frame transmitted
by the first MIMO station, the second MIMO station transmits an
acknowledgement (ACK) frame to the first MIMO frame.
[0023] Since the SIFS is shorter than the DIFS and the second MIMO
station transmits the ACK frame following a short period of time
after receiving the data frame transmitted by the first MIMO
station, the second and third MIMO stations and the SISO station
cannot transmit data until the transmission of the ACK frame is
completed. Since the ACK frame is also an MIMO frame, the third
MIMO station as well as the first MIMO station can receive it, but
the SISO station cannot receive it.
[0024] The first through third MIMO stations can set their
respective NAV values based on MIMO data that they receive by
performing a virtual carrier sensing operation. Accordingly, the
first through third MIMO stations can obtain the opportunity to
transmit a next frame the DIFS and back-off time 310 after the
transmission of the ACK frame is completed.
[0025] However, the SISO station cannot receive the MIMO data and
thus cannot perform a virtual carrier sensing operation. In other
words, while not receiving any data frame, the SISO frame considers
that a collision between data frames has occurred. Therefore, the
SISO station can obtain the opportunity to transmit a frame
following an extended inter-frame space (EIFS) and back-off time
320 after performing a physical carrier sensing operation, and the
EIFS is equal to the sum of the SIFS and a predetermined amount of
time required for transmitting an ACK frame at a lowest data rate.
In other words, the SISO station must wait a long period of time to
obtain the opportunity to transmit a frame in an environment where
it exists together with the first through third MIMO stations.
Thus, the SISO station is in a disadvantageous position in channel
contention with the first through third MIMO stations or other new
MIMO stations. Therefore, it is necessary to develop a WLAN
communication method that can prevent SISO stations from being
discriminated against MIMO stations in an environment where they
exist together with the MIMO stations.
SUMMARY OF THE INVENTION
[0026] The present invention provides a WLAN communication method
and apparatus using an improved carrier sensing method.
[0027] According to an aspect of the present invention, there is
provided a WLAN communication method including allowing a receiving
station to receive a MIMO frame, allowing the receiving station to
determine whether the MIMO frame is erroneous and whether the MIMO
frame is destined for the receiving station, allowing the receiving
station to generate SISO ACK frame if the MIMO frame is not
erroneous and is destined for the receiving station, and allowing
the receiving station to transmit the SISO ACK frame to a sending
station that has transmitted the MIMO frame.
[0028] According to another aspect of the present invention, there
is provided a WLAN communication method including allowing a
sending station to generate an MIMO frame, allowing the sending
station to transmit the MIMO frame to a receiving station, and
allowing the sending station to receive an SISO ACK frame
transmitted by the receiving station in response to the MIMO
frame.
[0029] According to still another aspect of the present invention,
there is provided a wireless LAN communication method including
allowing a sending station to determine how an MAC frame is to be
transmitted, allowing the sending station to generate an MIMO frame
based on the MAC frame if the sending station decides to transmit
the MAC frame in an MIMO approach, and allowing the sending station
to generate an SISO frame based on the MAC frame if the sending
station decides to transmit the MAC frame in an SISO approach, and
allowing the sending station to transmit the generated MIMO or SISO
frame in the selected approach.
[0030] According to a further aspect of the present invention,
there is provided a station including a physical layer, which
receives an MIMO frame transmitted via a wireless medium and
obtains an MAC frame from the received MIMO frame, and an MAC
layer, which determines whether the MAC frame is erroneous and
whether the MAC frame is destined for the station, and generates an
ACK frame and then provides the generated ACK frame to the physical
layer if the MAC frame is not erroneous and is destined for the
station, wherein the physical layer generates an SISO ACK frame
based on the ACK frame provided by the MAC layer and provides the
generated SISO ACK frame to the wireless medium.
[0031] According to a yet another aspect of the present invention,
there is provided a station including an MAC layer, which generates
an MAC frame and determines how the generated MAC frame is to be
transmitted, and a physical layer, which generates an MIMO frame or
an SISO frame based on the MAC frame based on the determination
results and transmits the generated MIMO or SISO frame to a
wireless medium.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] The above and other aspects of the present invention will
become more apparent by describing in detail exemplary embodiments
thereof with reference to the attached drawings in which:
[0033] FIG. 1 is a diagram illustrating the format of an IEEE
802.11a frame;
[0034] FIG. 2 is a diagram illustrating conventional carrier
sensing methods for wireless communications;
[0035] FIG. 3 is a diagram illustrating a conventional method of
transmitting frames in a contention period in a conventional WLAN
where MIMO stations and an SISO station coexist;
[0036] FIG. 4 is a diagram illustrating the formats of a data frame
and an ACK frame according to an exemplary embodiment of the
present invention;
[0037] FIG. 5 is a diagram illustrating a method of transmitting
frames in a contention period in a wireless LAN where MIMO stations
and an SISO station coexist;
[0038] FIG. 6 is a flowchart illustrating the operation of a
sending station according to an exemplary embodiment of the present
invention;
[0039] FIG. 7 is a flowchart illustrating the operation of a
receiving station according to an exemplary embodiment of the
present invention;
[0040] FIG. 8 is a flowchart illustrating a carrier sensing method
performed by an SISO station according to an exemplary embodiment
of the present invention;
[0041] FIG. 9 is a block diagram of an MIMO station according to an
exemplary embodiment of the present invention; and
[0042] FIG. 10 is a block diagram of an MIMO station according to
another exemplary embodiment of the present invention.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION
[0043] The present invention will now be described more fully with
reference to the accompanying drawings, in which exemplary
embodiments of the invention are shown. It is assumed in this
disclosure that an MIMO station has two input ports and two output
ports. However, the present invention is also applicable to an MIMO
station having more than two input ports and more than two output
ports and to an SIMO station having a single input port and
multiple output ports and an MISO station having multiple input
ports and a single output port.
[0044] FIG. 4 is a diagram illustrating the formats of a data frame
and an ACK frame according to an exemplary embodiment of the
present invention.
[0045] In the present exemplary embodiment, an MIMO data frame is
used to facilitate a physical carrier sensing operation, and an
SISO ACK frame is used to facilitate a virtual carrier sensing
operation even when the MIMO data frame is received.
[0046] The structure of a data frame will now be described in
detail with reference to FIG. 4.
[0047] Referring to FIG. 4, a data frame includes a first PLCP
preamble 410, a signal field 420, a second PLCP preamble 450, and a
data field 430. The data frame may optionally include a
supplementary signal field 460. OFDM symbols received by antenna 1
of a receiving station and OFDM symbols received by antenna 2 of
the receiving station coexist in the data field 430.
[0048] The first PLCP preamble 410 is a signal that antenna 1 is to
synchronize itself with, and the second PLCP preamble 450 is a
signal that antenna 2 is to synchronize itself with. In the present
exemplary embodiment, the signal field 420 follows the first PLCP
preamble 410. The first PLCP preamble 410 and the signal field 420
have the same structures as the first PLCP preamble 110 and the
signal field 120, respectively, of FIG. 1. Thus, even an SISO
station can obtain information contained in the signal field 420,
for example, information regarding data rate information and frame
length. The frame length indicates the length in bytes of part of
the data frame following the signal field 420, i.e., the sum of the
lengths in bytes of the second PLCP preamble 450, the supplementary
signal field 460, and the data field 430. In other words, a station
can obtain the duration of the fields following the signal field
460 by dividing the frame length by the data rate.
[0049] For example, if the data rate is 108 Mbps (54 Mbps per
antenna), the duration of the second PLCP preamble 450 is 8
microseconds, the supplementary signal field 460 is 0 bytes, and
the data field 430 contains n-byte data, then the frame length is
calculated in the following manner. The duration of each OFDM
symbol is four microseconds, and the second PLCP preamble 450
corresponds to two OFDM symbols. Since 216.times.2 byte-data per
OFDM symbol can be transmitted at a data rate of 108 Mbps, it
appears that the second PLCP preamble 450 has a length of 432
bytes. Therefore, n+432 is recorded as the frame length in a length
field of the data frame.
[0050] If the data rate is 120 Mbps (6 Mbps per antenna), the
duration of the second PLCP preamble 450 is 8 microseconds, the
supplementary signal field 460 is comprised of 0 bytes, the data
field 430 contains n-byte data, then the frame length is calculated
in the following manner. As described above, the duration of each
OFDM symbol is four microseconds, and the second PLCP preamble 450
corresponds to two OFDM symbols. Since 24.times.2 byte-data per
OFDM symbol can be transmitted at a data rate of 108 Mbps, it
appears that the second PLCP preamble 450 is has a length of 48
bytes. Therefore, n+48 is recorded as the frame length in a length
field of the data frame.
[0051] In the present exemplary embodiment, an SISO frame still
cannot receive an MIMO frame but can obtain information regarding
the data rate and the length of the MIMO frame. Accordingly, an
SISO station can perform a physical carrier sensing operation with
reference to the frame length information as well as a power level.
Therefore, according to the present invention, a station can more
efficiently carry out a clear channel assessment (CCA)
mechanism.
[0052] The structure of an ACK frame will now be described with
reference to FIG. 4. The IEEE 802.11 standard prescribes that an
ACK frame or a clear-to-send (CTS) frame must be transmitted at the
same data rate as a frame that it follows as a response frame.
Therefore, if a station receives an MIMO frame, it must transmit an
MIMO ACK frame in response to the received MIMO frame, in which
case, an SISO station cannot receive the MIMO ACK frame. Thus, in
the present exemplary embodiment, a station is required to transmit
an SISO ACK frame in response to a frame input thereto even though
the input frame is an MIMO frame.
[0053] Referring to FIG. 4, an ACK frame includes a PLCP preamble
412 and a signal field 422. A block ACK frame based on the IEEE
802.11e standard may also include a data field 432.
[0054] The operation of a WLAN in a case where a station transmits
an SISO ACK frame in response to a frame input thereto regardless
of the type of the input frame will now be described in detail with
reference to FIG. 5.
[0055] FIG. 5 illustrates a total of four stations, i.e., first
through third MIMO stations (MIMO stations 1 through 3) and an SISO
station (SISO station).
[0056] Referring to FIG. 5, the first MIMO station obtains the
opportunity to transmit data through channel contention and thus
transmits a data frame to the second MIMO station. Since the data
frame transmitted by the first MIMO station is an MIMO frame, the
third MIMO station can receive it, but the SISO station cannot
receive it. However, in the present exemplary embodiment, unlike in
the prior art, the SISO station can obtain information regarding
data rate and frame length from a signal field of the data frame
transmitted by the first MIMO station, and thus can efficiently
perform a physical carrier sensing operation based on the
information regarding data rate and frame length.
[0057] Following a short inter-frame space (SIFS) after receiving
the data frame transmitted by the first MIMO station, the second
MIMO station transmits an ACK frame to the first MIMO station in
response to the received data frame. In the present exemplary
embodiment, unlike in the prior art, the ACK frame transmitted by
the second MIMO station is an SISO ACK frame. Thus, the SISO
station as well as the first and third MIMO stations can receive
the ACK frame transmitted by the second MIMO station. The third
MIMO station obtains an MAC frame from the data frame transmitted
by the first MIMO station and sets its NAV value 520 by performing
a virtual carrier sensing operation. The SISO station obtains an
MAC frame from the ACK frame transmitted by the second MIMO station
and sets its NAV value 530 by performing a virtual carrier sensing
operation.
[0058] Accordingly, following a DIFS and back-off time 510 after
transmitting or receiving the ACK frame, the first through third
MIMO stations and the SISO station may have the opportunity to
transmit a frame.
[0059] The operations of a sending station and a receiving station
and a carrier sensing operation will now be described in
detail.
[0060] FIG. 6 is a flowchart illustrating the operation of a
sending station according to an exemplary embodiment of the present
invention.
[0061] Referring to FIG. 6, in operation S610, an MAC layer of the
sending station receives data from an upper layer. In operation
S620, the MAC layer of the sending station generates an MAC frame
by attaching an MAC header and a frame check sequence (FCS) to the
received data.
[0062] In operation S630, a physical layer of the sending station
receives the MAC frame and generates a data frame by attaching two
PLCP preambles to the received MAC frame. In operation S640, the
sending station transmits the data frame to a wireless medium.
[0063] In operation S650, the sending station determines whether it
has received an ACK frame within a predetermined amount of time. If
the sending station has received an ACK frame, the entire process
of transmitting the data frame is completed. However, if the
sending station has not received an ACK frame, it determines that
the transmitting of the data frame in operation S640 was
erroneous.
[0064] Therefore, in operation S660, the sending station doubles
the size of a back-off contention window, contends with other
stations, and retransmits the data frame to the wireless
medium.
[0065] In operation S650, the sending station determines again
whether it has received an ACK frame within the predetermined
amount of time. If the sending station has received an ACK frame
within the predetermined amount of time, the entire process of
transmitting the data frame is completed.
[0066] FIG. 7 is a flowchart illustrating the operation of a
receiving station according to an exemplary embodiment of the
present invention.
[0067] Referring to FIG. 7, in operation S710, the receiving
station detects a first PLCP preamble and then recognizes that a
data frame (hereinafter referred to as a "current data frame") is
currently input thereto.
[0068] In operation S720, if a first antenna of the receiving
station is synchronized with the detected first PLCP preamble, the
receiving station receives a signal field which contains
information regarding a data rate and a frame length.
[0069] In operation S730, the receiving station determines whether
the current data frame is an MIMO frame. In operation S740, if the
current data frame is an MIMO frame, the receiving station detects
a second PLCP preamble, and then a second antenna of the receiving
station is synchronized with the detected PLCP preamble. Otherwise,
however, the detecting of the second PLCP preamble is skipped.
[0070] In operation S750, once the receiving station is
synchronized with the current data frame using the first and/or
second preambles, it extracts an MAC frame from a data field of the
current data frame. In operation S760, the receiving station
determines whether the current data frame is erroneous with
reference to an FCS of the extracted MAC frame and whether the
current data frame is destined for it with reference to an MAC
header of the extracted MAC frame.
[0071] In operation S770, if the current data frame is not
erroneous and is destined for the receiving station, the receiving
station generates an ACK frame having one PLCP preamble in response
to the current data frame. In operation S780, the receiving station
transmits the ACK frame to a wireless medium.
[0072] However, if the current data frame is erroneous and is not
destined for the receiving station, the receiving station abandons
the current data frame in operation S790.
[0073] FIG. 8 is a flowchart illustrating a carrier sensing
operation performed by an SISO station according to an exemplary
embodiment of the present invention.
[0074] Referring to FIG. 8, in operation S810, when a data frame is
received via a wireless medium, an SISO station detects a first
PLCP preamble. In operation S820, the SISO station receives a
signal field. In operation S830, the SISO station obtains
information regarding data rate and frame length by interpreting
the received signal field and then performs a physical carrier
sensing operation based on the obtained information. However, the
SISO station cannot obtain an MAC frame yet and thus cannot set its
NAV value yet by performing a virtual carrier sensing
operation.
[0075] In operation S840, the SISO station receives an ACK frame.
In the present exemplary embodiment, the ACK frame received by the
SISO station is an SISO ACK frame, and thus, even the SISO station
can receive it. Accordingly, in operation S850, the SISO station
extracts an MAC frame from the received ACK frame. In operation
S880, the SISO station obtains information necessary for setting
its NAV value from a duration field of an MAC header and sets its
NAV value based on the obtained information.
[0076] FIG. 9 is a block diagram of an MIMO station according to an
exemplary embodiment of the present invention.
[0077] Referring to FIG. 9, the MIMO station includes a physical
layer 910, an MAC layer 920, and an upper layer 930.
[0078] The physical layer 910 includes an SISO PLCP module 912, an
MIMO PLCP module 916, an MIMO codec 914, and a wireless
transmission/reception module 918.
[0079] In a process of transmitting a data frame, the SISO PLCP
module 912, like a conventional SISO PLCP module, receives an MAC
frame from the MAC layer 920 and generates an SISO frame by
attaching a PLCP preamble and additional information to the
received MAC frame. In a process of receiving a data frame, the
SISO PLCP module 912 obtains an MAC frame by removing a PLCP header
from an SISO frame received by the wireless transmission/reception
module 918 and then transmits the obtained MAC frame to the MAC
layer 920.
[0080] In the process of transmitting a data frame, the MIMO PLCP
module 916 obtains MIMO data by coding an MAC frame with the use of
the MIMO codec 914 and then generates an MIMO frame by attaching
first and second PLCP preambles and additional information to the
obtained MIMO data. In the process of receiving a data frame, the
MIMO PLCP module 916 obtains MIMO data by removing a PLCP header
from an MIMO frame received by the wireless transmission/reception
module 918 and then provides the obtained MIMO data to the MIMO
codec 914.
[0081] In the process of transmitting a data frame, the MIMO codec
914 obtains MIMO data by coding an MAC frame received from the MAC
layer 920 and provides the obtained MIMO data to the MIMO PLCP
module 916. In the process of receiving a data frame, the MIMO
codec 914 receives MIMO data from the MIMO PLCP module 916 and
provides the received MIMO data to the MAC layer 920.
[0082] In the process of transmitting a data frame, the wireless
transmission/reception module 918 receives an SISO frame or an MIMO
frame and transmits the received SISO or MIMO frame to a wireless
medium (not shown). In the process of receiving a data frame, the
wireless transmission/reception module 918 receives an SISO frame
or an MIMO frame and transmits the received SISO or MIMO frame to
the SISO PLCP module 912 or the MIMO PLCP module 916.
[0083] The MAC layer 920 includes an MAC frame generation module
924, an MAC frame interpretation module 926, and an ACK frame
generation module 922.
[0084] In the process of transmitting a data frame, the MAC frame
generation module 924 generates an MAC frame by attaching an MAC
header and an FCS to data received from the upper layer 930 and
transmits the generated MAC frame to the physical layer 910. In a
case where the MIMO station transmits an MIMO frame, the MAC frame
generated by the MAC frame generation module 924 is transmitted to
the MIMO codec 914. On the other hand, in a case where the MIMO
station transmits an SISO frame, the MAC frame generated by the MAC
frame generation module 924 is transmitted to the SISO PLCP module
912.
[0085] In the process of receiving a data frame, the MAC frame
interpretation module 926 receives an MAC frame from the physical
layer 910 and determines whether the received MAC frame is
erroneous with reference to an FCS of the received MAC frame. If
the received MAC frame is erroneous, the MAC frame interpretation
module 926 abandons the received MAC frame. However, if the
received MAC frame is not erroneous, the MAC frame interpretation
module 926 determines whether the received MAC frame is destined
for the MIMO station with reference to a header of the received MAC
frame. If the received MAC frame is destined for the MIMO station,
the MAC frame interpretation module 926 transmits an MAC frame PSDU
from which the MAC header and the FCS are removed to the upper
layer 930. However, if the received MAC frame is not destined for
the MIMO station, the MAC frame interpretation module 926 abandons
the received MAC frame.
[0086] The ACK frame generation module 922 generates an ACK frame
if the received MAC frame is not erroneous and is destined for the
MIMO station. Thereafter, the ACK frame generation module 922
transmits the generated ACK frame to the SISO PLCP module 912.
[0087] FIG. 10 is a block diagram of an MIMO station according to
another exemplary embodiment of the present invention.
[0088] Referring to FIG. 10, the MIMO station includes a physical
layer 1010, an MAC layer 1020, and an upper layer 1030. The
physical layer 1010 includes an SISO PLCP module 1012, an MIMO PLCP
module 1016, an MIMO codec 1014, and a wireless
transmission/reception module 1018. The operations of the SISO PLCP
module 1012, the MIMO PLCP module 1016, the MIMO codec 1014, and
the wireless transmission/reception module 1018 are the same as the
operations of the SISO PLCP module 912, the MIMO PLCP module 916,
the MIMO codec 914, and the wireless transmission/reception module
918 of FIG. 9.
[0089] The MAC layer 1020 includes an MAC frame generation module
1024, an MAC frame interpretation module 1026, an ACK frame
generation module 1022, and a selection module 1028. The operations
of the MAC frame generation module 1024, the MAC frame
interpretation module 1026, and the ACK frame generation module
1022 are the same as the operations of the MAC frame generation
module 924, the MAC frame interpretation module 926, and the ACK
frame generation module 922 of FIG. 9.
[0090] The selection module 1028 decides whether an MAC frame
generated by the MAC frame generation module 1024 is to be
transmitted in an MIMO approach or in an SISO approach. If the MAC
frame is long, the MIMO approach is more efficient than the SISO
approach. On the other hand, if the MAC frame is short, the SISO
approach is more efficient than the MIMO approach because the MIMO
approach achieves two times higher data rates than the SISO
approach but incurs more overhead, such as PLCP preambles, than the
SISO approach. The selection module 1028 decides to transmit a
frame to be broadcasted or multicasted, or a control frame or a
management frame in the SISO approach because the frame to be
broadcasted or multicasted must be received by a plurality of
stations and the control frame or the management frame is generally
more important than other frames.
[0091] If the selection module 1028 decides to transmit the MAC
frame in the MIMO approach, it transmits the MAC frame to the MIMO
codec 1014. On the other hand, if the selection module 1028 decides
to transmit the MAC frame in the SISO approach, it transmits the
MAC frame to the SISO PLCP module 1012.
[0092] The term "module", as used herein, means, but is not limited
to, a software or hardware component, such as a Field Programmable
Gate Array (FPGA) or Application Specific Integrated Circuit
(ASIC), which performs certain tasks. A module may advantageously
be configured to reside on the addressable storage medium and
configured to execute on one or more processors. Thus, a module may
include, by way of example, components, such as software
components, object-oriented software components, class components
and task components, processes, functions, attributes, procedures,
subroutines, segments of program code, drivers, firmware,
microcode, circuitry, data, databases, data structures, tables,
arrays, and variables. The functionality provided for in the
components and modules may be combined into fewer components and
modules or further separated into additional components and
modules. In addition, the components and modules may be implemented
such that they are executed one or more computers in a
communication system.
[0093] As described above, since the WLAN communication method and
apparatus according to the present invention use an SISO ACK frame,
SISO stations are not discriminated against MIMO stations in a WLAN
where the SISO stations and the MIMO stations coexist. In addition,
since a signal field is interposed between two PLCP preambles of an
MIMO frame, even the SISO stations can obtain information necessary
for performing a physical carrier sensing operation from the signal
field of the MIMO frame.
[0094] In concluding the detailed description, those skilled in the
art will appreciate that many variations and modifications can be
made to the exemplary embodiments without substantially departing
from the principles of the present invention. Therefore, the
disclosed exemplary embodiments of the invention are used in a
generic and descriptive sense only and not for purposes of
limitation.
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