Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W74/00—Wireless channel access
  • H04W74/08—Non-scheduled access, e.g. ALOHA
  • H04W74/0808—Non-scheduled access, e.g. ALOHA using carrier sensing, e.g. carrier sense multiple access [CSMA]
  • H04W74/0816—Non-scheduled access, e.g. ALOHA using carrier sensing, e.g. carrier sense multiple access [CSMA] with collision avoidance
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
  • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
  • H04B7/0413—MIMO systems
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/12—Arrangements for detecting or preventing errors in the information received by using return channel
  • H04L1/16—Arrangements for detecting or preventing errors in the information received by using return channel in which the return channel carries supervisory signals, e.g. repetition request signals
  • H04L1/1607—Details of the supervisory signal
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/12—Arrangements for detecting or preventing errors in the information received by using return channel
  • H04L1/16—Arrangements for detecting or preventing errors in the information received by using return channel in which the return channel carries supervisory signals, e.g. repetition request signals
  • H04L1/18—Automatic repetition systems, e.g. Van Duuren systems
  • H04L1/1829—Arrangements specially adapted for the receiver end
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/12—Arrangements for detecting or preventing errors in the information received by using return channel
  • H04L1/16—Arrangements for detecting or preventing errors in the information received by using return channel in which the return channel carries supervisory signals, e.g. repetition request signals
  • H04L1/18—Automatic repetition systems, e.g. Van Duuren systems
  • H04L1/1867—Arrangements specially adapted for the transmitter end
  • H04L1/188—Time-out mechanisms
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L27/00—Modulated-carrier systems
  • H04L27/26—Systems using multi-frequency codes
  • H04L27/2601—Multicarrier modulation systems
  • H04L27/2602—Signal structure
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L5/00—Arrangements affording multiple use of the transmission path
  • H04L5/02—Channels characterised by the type of signal
  • H04L5/023—Multiplexing of multicarrier modulation signals, e.g. multi-user orthogonal frequency division multiple access [OFDMA]
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W74/00—Wireless channel access
  • H04W74/002—Transmission of channel access control information
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/12—Arrangements for detecting or preventing errors in the information received by using return channel
  • H04L1/16—Arrangements for detecting or preventing errors in the information received by using return channel in which the return channel carries supervisory signals, e.g. repetition request signals
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/12—Arrangements for detecting or preventing errors in the information received by using return channel
  • H04L1/16—Arrangements for detecting or preventing errors in the information received by using return channel in which the return channel carries supervisory signals, e.g. repetition request signals
  • H04L1/1607—Details of the supervisory signal
  • H04L1/1671—Details of the supervisory signal the supervisory signal being transmitted together with control information
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/12—Arrangements for detecting or preventing errors in the information received by using return channel
  • H04L2001/125—Arrangements for preventing errors in the return channel
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W84/00—Network topologies
  • H04W84/02—Hierarchically pre-organised networks, e.g. paging networks, cellular networks, WLAN [Wireless Local Area Network] or WLL [Wireless Local Loop]
  • H04W84/10—Small scale networks; Flat hierarchical networks
  • H04W84/12—WLAN [Wireless Local Area Networks]

Definitions

• 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.
• LAN local area network
• WLAN wireless LAN
• the initial IEEE 802.11 standard which specifies a 1 to 2 Mbps transfer rate, has evolved into advanced standards including 802.1 Ib and 802.11a.
• 802.1 Ig a new IEEE standard, 802.1 Ig, is being discussed by the Stan ⁇ dardization Conference groups.
• the IEEE 802. Hg standard which delivers a 6 to 54 Mbps transmission rate in the 56 GHz-National Information Infrastructure (Nil) band, uses orthogonal frequency division multiplexing (OFDM) as transmission technology.
• OFDM orthogonal frequency division multiplexing
• Wi-Fi Wireless Fidelity
• Wi-Fi Wireless Fidelity
• An IEEE 802.1 Ib 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.
• ISM 2.4 GHz-Industrial, Scientific, and Medical
• the Ethernet and the WLAN which are currently being widely used, both utilize a carrier sensing multiple access (CSMA) method.
• CSMA carrier sensing multiple access
• 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 commu ⁇ nications.
• a station suspends transmitting signals if a collision is detected during transmission.
• 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.
• the station has a random backoff period for delay and restarts transmitting signals.
• 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.
• 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.
• a station hereinafter referred to as an 'SISO station'
• MIMO multiple input multiple output
• 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.
• an MIMO station achieves higher data rates (data transferring rates) than an SISO station.
• 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.
• FIG. 1 is a diagram illustrating the format of an IEEE 802.1 Ia frame.
• the IEEE 802.1 Ia frame is comprised of a physical layer convergence procedure (PLCP) preamble 110, a signal field 120, and a data field 130.
• PLCP physical layer convergence procedure
• 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.
• the signal field 120 is comprised of a total of 24 bits.
• 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.
• 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.
• 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 de ⁇ termining 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.
• FIG. 2 is a diagram illustrating a carrier sensing operation performed in a WLAN.
• 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.
• the physical carrier sensing method enables a station to recognize whether signals are transmitted by a wireless medium.
• 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.
• a physical carrier sensing operation may be performed based on a result of in ⁇ terpreting 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.
• NAV network allocation vector
• 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.
• stations are prevented from transmitting frames via a wireless channel when frames are transmitted via the wireless channel by other stations.
• 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.
• DIFS distributed inter-frame space
• 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.
• SISO short inter-frame space
• 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.
• 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. Ac ⁇ cordingly, 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.
• the SISO station cannot receive the MIMO data and thus cannot perform a virtual carrier sensing operation.
• 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.
• 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.
• the SISO station is in a disadvantageous position in channel contention with the first through third MIMO stations or other new MIMO stations.
• the present invention provides a WLAN communication method and apparatus using an improved carrier sensing method.
• a WLAN com ⁇ munication 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.
• 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.
• 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 tra nsmit the generated MIMO or SISO frame in the selected approach.
• 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.
• 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.
• FIG. 1 is a diagram illustrating the format of an IEEE 802.1 Ia frame
• FIG. 2 is a diagram illustrating conventional carrier sensing methods for wireless communications ;
• 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;
• 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
• 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;
• FIG. 6 is a flowchart illustrating the operation of a sending station according to an exemplary embodiment of the present invention.
• FIG. 7 is a flowchart illustrating the operation of a receiving station according to an exemplary embodiment of the present invention.
• FIG. 8 is a flowchart illustrating a carrier sensing method performed by an SISO station according to an exemplary embodiment of the present invention
• FIG. 9 is a block diagram of an MIMO station according to an exemplary embodiment of the present invention.
• FIG. 10 is a block diagram of an MIMO station according to another exemplary embodiment of the present invention.
• an MIMO station has two input ports and two output ports.
• 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.
• 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.
• an MIMO data frame is used to facilitate a physical carrier sensing operation
• an SISO ACK frame is used to facilitate a virtual carrier sensing operation even when the MIMO data frame is received.
• a data frame includes a first PLCP preamble 410, a signal field
• 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.
• the first PLCP preamble 410 is a signal that antenna 1 is to synchronize itself with
• the second PLCP preamble 450 is a signal that antenna 2 is to synchronize itself with.
• 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.
• a station can obtain the duration of the fields following the signal field 460 by dividing the frame length by the data rate.
• the frame length is calculated in the following manner.
• the duration of each OFDM symbol is four mi ⁇ croseconds, and the second PLCP preamble 450 corresponds to two OFDM symbols. Since 216x2 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.
• the frame length is calculated in the following manner. As described above, the duration of each OFDM symbol is four mi ⁇ croseconds, and the second PLCP preamble 450 corresponds to two OFDM symbols. Since 24x2 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.
• an SISO frame still cannot receive an
• 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.
• CCA clear channel assessment
• 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.
• an ACK frame includes a PLCP preamble 412 and a signal field 422.
• a block ACK frame based on the IEEE 802.1 Ie standard may also include a data field 432.
• FIG. 5 illustrates a total of four stations, i.e., first through third MIMO stations
• MIMO stations 1 through 3 MIMO stations 1 through 3
• SISO station SISO station
• 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.
• the second MIMO station transmits an ACK frame to the first MIMO station in response to the received data frame.
• the ACK frame transmitted by the second MIMO station is an SISO ACK frame.
• 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.
• the first through third MIMO stations and the SISO station may have the opportunity to transmit a frame.
• FIG. 6 is a flowchart illustrating the operation of a sending station according to an exemplary embodiment of the present invention.
• an MAC layer of the sending station receives data from an upper layer.
• 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.
• FCS frame check sequence
• 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.
• the sending station transmits the data frame to a wireless medium.
• 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.
• 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.
• FIG. 7 is a flowchart illustrating the operation of a receiving station according to an exemplary embodiment of the present invention.
• 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.
• a data frame hereinafter referred to as a 'current data frame'
• 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.
• the receiving station 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.
• the receiving station 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.
• FIG. 8 is a flowchart illustrating a carrier sensing operation performed by an SISO station according to an exemplary embodiment of the present invention.
• an SISO station detects a first PLCP preamble.
• the SISO station receives a signal field.
• 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.
• the SISO station cannot obtain an MAC frame yet and thus cannot set its NAV value yet by performing a virtual carrier sensing operation.
• the SISO station receives an ACK frame.
• the ACK frame received by the SISO station is an SISO ACK frame, and thus, even the SISO station can receive it.
• the SISO station extracts an MAC frame from the received ACK frame.
• 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 in ⁇ formation.
• FIG. 9 is a block diagram of an MIMO station according to an exemplary embodiment of the present invention.
• the MIMO station includes a physical layer 910, an MAC layer 920, and an upper layer 930.
• 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.
• the SISO PLCP module 912 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.
• 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.
• the MIMO PLCP module 916 obtains
• 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.
• 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.
• 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.
• the MAC layer 920 includes an MAC frame generation module 924, an MAC frame interpretation module 926, and an ACK frame generation module 922.
• the MAC frame generation module 924 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.
• 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.
• the MAC frame interpretation module 926 transmits an MAC frame MSDU 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 inter ⁇ pretation module 926 abandons the received MAC frame.
• the ACK frame generation module 922 generates an ACK frame if the received
• the ACK frame generation module 922 transmits the generated ACK frame to the SISO PLCP module 912.
• FIG. 10 is a block diagram of an MIMO station according to another exemplary embodiment of the present invention.
• 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.
• 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.
• 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.
• 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.
• a module means, but is not limited to, a software or hardware component, such as a Field Programmable Gate Array (FPGA) or Ap ⁇ plication 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.
• 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 func ⁇ tionality provided for in the components and modules may be combined into fewer components and modules or further separated into additional components and modules.
• the components and modules may be implemented such that they are executed one or more computers in a communication system.
• the WLAN communication method and apparatus according to the present invention use an SISO ACK frame, SISO stations are not dis ⁇ criminated against MIMO stations in a WLAN where the SISO stations and the MIMO stations coexist.
• 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.

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