WO2013055034A1

WO2013055034A1 - Method of transmitting and receiving packets in wireless local area network system and apparatus for supporting the same

Info

Publication number: WO2013055034A1
Application number: PCT/KR2012/006825
Authority: WO
Inventors: Ill Soo Sohn; Hyang Sun YOU; Yong Ho Seok; Jong Hyun Park
Original assignee: Lg Electronics Inc.
Priority date: 2011-10-11
Filing date: 2012-08-27
Publication date: 2013-04-18

Abstract

A method of transmitting packets in a Wireless Local Area Network (WLAN) system is provided. The method includes: performing a packet repetition configuration in order to transmit a plurality of packets along with a receiver; repeatedly transmitting the plurality of packets one by one at packet spacing to the receiver; and receiving an acknowledgement frame, informing that one or more of the plurality of packets have been received, from the receiver. The plurality of packets includes identical data, The performing the packet repetition configuration includes receiving a packet repetition request frame from the receiver and the packet repetition request frame requests to repeatedly transmit the packets.

Description

METHOD OF TRANSMITTING AND RECEIVING PACKETS IN WIRELESS LOCAL AREA NETWORK SYSTEM AND APPARATUS FOR SUPPORTING THE SAME

The present invention relates to wireless communication and, more particularly, to a method of transmitting and receiving packets in a Wireless Local Area Network (WLAN) system and an apparatus for supporting the same.

With the advancement of information communication technologies, various wireless communication technologies have recently been developed. Among the wireless communication technologies, a wireless local area network (WLAN) is a technology whereby Internet access is possible in a wireless fashion in homes or businesses or in a region providing a specific service by using a portable terminal such as a personal digital assistant (PDA), a laptop computer, a portable multimedia player (PMP), etc.

The IEEE 802.11n is a technical standard relatively recently introduced to overcome a limited data rate which has been considered as a drawback in the WLAN. The IEEE 802.11n is devised to increase network speed and reliability and to extend an operational distance of a wireless network. More specifically, the IEEE 802.11n supports a high throughput (HT), i.e., a data processing rate of up to above 540 Mbps, and is based on a multiple input and multiple output (MIMO) technique which uses multiple antennas in both a transmitter and a receiver to minimize a transmission error and to optimize a data rate.

With the widespread use of the WLAN and the diversification of applications using the WLAN, there is a recent demand for a new WLAN system to support a higher throughput than a data processing rate supported by the IEEE 802.11n. A next-generation WLAN system supporting a very high throughput (VHT) is a next version of the IEEE 802.11n WLAN system, and is one of IEEE 802.11 WLAN systems which have recently been proposed to support a data processing rate of above 1 Gbps in a MAC service access point (SAP).

The next-generation WLAN system supports transmission using a Multi-User Multiple Input Multiple Output (MU-MIMO) method of allowing a plurality of non- AP STAs to access a radio channel at the same time in order to efficiently use the radio channel. In accordance with the MU-MIMO transmission method, an AP may transmit frames to one or more MIMO-paired STAs at the same time.

With the wide spread of a WLAN, problems related to the service coverage of a WLAN system may occur. In general, an AP may use great transmit power in order to transmit a radio signal. This is related to the wide coverage of WLAN service provided by the AP. That is, an AP capable of using great transmit power can support wide service coverage. In contrast, an STA may inevitably use lower transmit power than an AP because of a limit to the transmit power supported by the STA or a limit to transmit power regulated in a WLAN system. If this STA is placed in the outer wall of service coverage, a radio signal transmitted by the STA may reach an AP, but the AP may not normally receive the signal. A failure in the transmission and reception of a radio signal may be generated by interference due to signals transmitted by other STAs or interference due to heterogeneous wireless communication systems. Accordingly, there is a need for improving the reliability of the transmission and reception of radio signal between an AP and an STA in a WLAN system providing wide service coverage.

An object of the present invention is to provide a method of transmitting and receiving packets in a WLAN system and an apparatus for supporting the same.

In an aspect, a method of transmitting packets in a Wireless Local Area Network (WLAN) system is provided. The method includes: performing a packet repetition configuration in order to transmit a plurality of packets along with a receiver; repeatedly transmitting the plurality of packets one by one at packet spacing to the receiver; and receiving an acknowledgement frame, informing that one or more of the plurality of packets have been received, from the receiver. The plurality of packets includes identical data, The performing the packet repetition configuration includes receiving a packet repetition request frame from the receiver and the packet repetition request frame requests to repeatedly transmit the packets.

The packet repetition request frame my include a request repetition number field indicating a number of packets requested to be repeatedly transmitted and a request packet spacing field indicating request packet spacing.

The number of the plurality of transmitted packets may be the number of requested packets indicated by the request repetition number field.

The packet spacing may be the requested packet spacing indicated by the request packet spacing field.

The performing the packet repetition configurations may further include transmitting a packet repetition response frame in response to the packet repetition request frame. The packet repetition response frame may include a response type field indicating a response to the request according to the packet repetition request frame.

The repeatedly transmitting the plurality of packets one by one may be performed when the response type field indicates acceptance of the request according to the packet repetition request frame.

The packet repetition response frame may include a response repetition number field indicating the number of plurality of packets repeatedly transmitted one by one and a response packet spacing field indicating the packet spacing.

The response repetition number field may be set differently from the request repetition number field and the response packet spacing field may be set differently from the request packet spacing field.

When the response type field is set to deny the request according to the packet repetition request frame, the response type field may be further set to indicate a reason code indicating a reason of the denial.

Each of the packets may include a packet ID related to order of its own transmission in the plurality of packets.

Each of the packets may include a remainder packet indicator indicating a number of remaining packets to be subsequently transmitted.

The remainder packet indicator may be included in a Medium Access Control (MAC) header.

The remainder packet indicator may be combined with a bit sequence for resetting a scrambler included in a service field of the packet.

The method may further include transmitting a packet repetition response frame, informing that the repeated transmission of the plurality of packets is stopped, to the receiver.

The packet repetition response frame may include a response type field indicating that the repeated transmission of the plurality of packets is stopped, and the response type field further indicates a reason of the stop.

In another aspect, a wireless apparatus configured to transmit packets in a Wireless Local Area Network (WLAN) system is provided. The wireless apparatus includes: a transceiver configured to transmit and receive the packets; and a processor functionally connected to the transceiver. The processor is configured to: perform a packet repetition configuration in order to transmit a plurality of packets along with a receiver; repeatedly transmit the plurality of packets one by one at packet spacing to the receiver; and receive an acknowledgement frame, informing that one or more of the plurality of packets have been received, from the receiver. The plurality of packets includes identical data. The performing the packet repetition configuration includes receiving a packet repetition request frame from the receiver and the packet repetition request frame requests to repeatedly transmit the packets.

In accordance with according to the present invention, an STA which is placed within the service coverage of an AP, but is far from the AP can transmit packets repeatedly. The AP can receive data normally by receiving one of the packets which are repeatedly transmitted several times and which include the same data. Accordingly, the reliability of data transmission and reception between an AP and an STA can be improved.

A packet ID is included in each of the packets that are repeatedly transmitted, and an AP can know the number of packets that are repeatedly transmitted and the number of remaining packets. Accordingly, the AP can transmit an acknowledgement response frame in synchronization with a point of time at which the packets are repeatedly transmitted. Furthermore, when data is normally received through a specific packet, power can be reduced until the repeated transmission of packets is completed. Accordingly, reliability in the exchange of packets between an AP and an STA can be improved, and unnecessary power consumption by a receiver can be prevented.

FIG. 1 is a diagram showing the configuration of a WLAN system to which embodiments of the present invention may be applied.

FIG. 2 shows a physical layer architecture of a WLAN system supported by IEEE 802.11.

FIG. 3 is a block diagram showing the format of an MAC frame that may be applied to an embodiment of the present invention.

FIG. 4 is a block diagram showing an example of a PPDU format used in a WLAN system which provides HT service.

FIG. 5 shows an example of a PPDU format used in a WLAN system.

FIG. 6 is a diagram showing an example of a WLAN system to which an embodiment of the present invention may be applied.

FIG. 7 is a diagram showing a method of transmitting and receiving packets based on packet repetition according to an embodiment of the present invention.

FIG. 8 is a diagram showing a method of transmitting and receiving packets based on packet repetition according to an embodiment of the present invention.

FIG. 9 is a block diagram showing the format of a packet repetition request frame according to an embodiment of the present invention.

FIG. 10 is a block diagram showing the format of a packet repetition response frame according to an embodiment of the present invention.

FIG. 11 is a block diagram showing a wireless apparatus to which an embodiment of the present invention may be applied.

Referring to FIG. 1, A WLAN systemincludes one or more Basic Service Set (BSSs). The BSS is a set of stations (STAs) which can communicate with each other through successful synchronization. The BSS is not a concept indicating a specific area

An infrastructure BSS includes one or more non-AP STAs STA1, STA2, STA3, STA4, and STA5, an AP (Access Point) providing distribution service, and a Distribution System (DS) connecting a plurality of APs. In the infrastructure BSS, an AP manages the non-AP STAs of the BSS.

On the other hand, an Independent BSS (IBSS) is operated in an Ad-Hoc mode. The IBSS does not have a centralized management entity for performing a management function because it does not include an AP. That is, in the IBSS, non-AP STAs are managed in a distributed manner. In the IBSS, all STAs may be composed of mobile STAs. All the STAs form a self-contained network because they are not allowed to access the DS.

An STA is a certain functional medium, including Medium Access Control (MAC) and wireless-medium physical layer interface satisfying the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard. Hereinafter, the STA refers to both an AP and a non-AP STA.

A non-AP STA is an STA which is not an AP. The non-AP STA may also be referred to as a mobile terminal, a wireless device, a wireless transmit/receive unit (WTRU), a user equipment (UE), a mobile station (MS), a mobile subscriber unit, or simply a user. For convenience of explanation, the non-AP STA will be hereinafter referred to the STA.

The AP is a functional entity for providing connection to the DS through a wireless medium for an STA associated with the AP. Although communication between STAs in an infrastructure BSS including the AP is performed via the AP in principle, the STAs can perform direct communication when a direct link is set up. The AP may also be referred to as a central controller, a base station (BS), a node-B, a base transceiver system (BTS), a site controller, etc.

A plurality of infrastructure BSSs including the BSS shown in FIG. 1 can be interconnected by the use of the DS. An extended service set (ESS) is a plurality of BSSs connected by the use of the DS. APs and/or STAs included in the ESS can communicate with each another. In the same ESS, an STA can move from one BSS to another BSS while performing seamless communication.

In a WLAN system based on IEEE 802.11, a basic access mechanism of a medium access control (MAC) is a carrier sense multiple access with collision avoidance (CSMA/CA) mechanism. The CSMA/CA mechanism is also referred to as a distributed coordinate function (DCF) of the IEEE 802.11 MAC, and basically employs a “listen before talk” access mechanism. In this type of access mechanism, an AP and/or an STA senses a wireless channel or medium before starting transmission. As a result of sensing, if it is determined that the medium is in an idle status, frame transmission starts by using the medium. Otherwise, if it is sensed that the medium is in an occupied status, the AP and/or the STA does not start its transmission but sets and waits for a delay duration for medium access.

The CSMA/CA mechanism also includes virtual carrier sensing in addition to physical carrier sensing in which the AP and/or the STA directly senses the medium. The virtual carrier sensing is designed to compensate for a problem that can occur in medium access such as a hidden node problem. For the virtual carrier sending, the MAC of the WLAN system uses a network allocation vector (NAV). The NAV is a value transmitted by an AP and/or an STA, currently using the medium or having a right to use the medium, to anther AP or another STA to indicate a remaining time before the medium returns to an available state. Therefore, a value set to the NAV corresponds to a period reserved for the use of the medium by an AP and/or an STA transmitting a corresponding frame.

An IEEE 802.11 MAC protocol, together with a DCF, provides a Hybrid Coordination Function (HCF) based on a Point Coordination Function (PCF) in which a reception AP or a reception STA or both periodically poll a data frame using the DCF and a polling-based synchronous access scheme. The HCF includes Enhanced Distributed Channel Access (EDCA) in which a provider uses an access scheme for providing a data frame to a number of users as a contention-based scheme and HCF Controlled Channel Access (HCCA) employing a non-contention-based channel access scheme employing a polling mechanism. The HCF includes a medium access mechanism for improving the Quality of Service (QoS) of a WLAN and can transmit QoS data both in a Contention Period (CP) and a Contention-Free Period (CFP).

The next-generation WLAN system tries to support 80 MHz bandwidth transmission, contiguous 160 MHz bandwidth transmission, non-contiguous 160 MHz bandwidth transmission or higher. Furthermore, an MU-MIMO transmission method is provided for a higher throughput. The AP of the next-generation WLAN system can transmit a data frame to one or more MIMO-paired STAs at the same time.

In a WLAN system, such as that shown in FIG. 1, an AP 10 can transmit data to an STA group, including at least one of a plurality of

STAs

21, 22, 23, 24, and 30 associated therewith, at the same time. In a WLAN system, such as that shown in FIG. 1, the AP 10 may transmit data to an STA group including at least one STA, from among the plurality of

STAs

21, 22, 23, 24, and 30 associated therewith, at the same time. An example where the AP performs MU-MIMO transmission to the STAs is shown in FIG. 1. In a WLAN system supporting Tunneled Direct Link Setup (TDLS), Direct Link Setup (DLS), or a mesh network, however, an STA trying to send data may send a PPDU to a plurality of STAs by using the MU-MIMO transmission scheme. An example where an AP sends a PPDU to a plurality of STAs according to the MU-MIMO transmission scheme is described below.

The data respectively transmitted to each of the STAs may be transmitted through different spatial streams. The data packet transmitted by the AP 10 may be a PPDU, generated and transmitted by the physical layer of a WLAN system, or a data field included in the PPDU, and the data packet may be referred to as a frame. That is, a PPDU or a data field for SU-MIMO and/or MU-MIMO, which is included in the PPDU, may be referred as a MIMO packet. In an example of the present invention, it is assumed that a target transmission STA group MU-MIMO-paired with the AP 10 includes the STA 1 21, the STA 2 22, the STA 3 23, and the STA 4 24. Here, data may not be transmitted to a specific STA of the target transmission STA group because spatial streams are not allocated to the specific STA. Meanwhile, it is assumed that the STAa 30 is associated with the AP 10, but not included in the target transmission STA group.

When the AP transmits a PPDU to a plurality of STAs by using a MU-MIMO transmission scheme, the AP transmits the PPDU by inserting information indicating a group ID into the PPDU as control information. When the STA receives the PPDU, the STA confirms the group ID field and thus confirms whether the STA is a member STA of a transmission target STA group. If it is confirmed that the STA is the member of the transmission target STA group, the STA can determine at which position a spatial stream set to be transmitted to the STA is located among all spatial streams. Since the PPDU includes information indicating the number of spatial streams allocated to a reception STA, the STA can receive data by searching for spatial streams allocated to the STA.

Meanwhile, a TV White Space (WS) has been in the spotlight as a frequency band that may be newly used in a WLAN system. TV WS (White Space) refers to a frequency band that remains unused as analog TV broadcast evolves into digital in the U.S., and which occupies a range between 54 to 698MHz. However, this is merely an example, and TV WS may be a band authorized for a licensed user to have priority for use. The licensed user means any user authorized to use a permitted band, and may be also referred to as ‘licensed device’, ‘primary user’, or ‘incumbent user’.

APs and/or STAs which operate on the TV WS band need to provide protection functions for licensed users because the licensed users have priority in using the TV WS band. For instance, in the case that a licensed user, such as a microphone, has been already using a specific WS channel having a specified bandwidth divided from the TV WS band, the APs and/or STAs cannot use the frequency band corresponding to the WS channel to protect the licensed user. Also, when the licensed user uses a frequency band for transmission and/or reception of a current frame, the APs and/or STAs should stop using the frequency band.

Accordingly, the APs and/or STAs first perform a process to figure out whether a specified frequency band in the TV WS band can be used—i.e., whether there is any licensed user for the frequency band. Such process is referred to as ‘spectrum sensing.’ As mechanisms for spectrum sensing, energy detection or signature detection are used. When the strength of a received signal is not less than a predetermined value or when a DTV preamble is detected, it is determined that the frequency band is used by a licensed user.

The IEEE 802.11 PHY architecture includes a PHY layer management entity (PLME), a physical layer convergence procedure (PLCP) sub-layer 210, and a physical medium dependent (PMD) sub-layer 200. The PLME provides a PHY management function in cooperation with a MAC layer management entity (MLME). The PLCP sub-layer 210 located between a MAC sub-layer 220 and the PMD sub-layer 200 delivers to the PMD sub-layer 200 a MAC protocol data unit (MPDU) received from the MAC sub-layer 220 under the instruction of the MAC layer, or delivers to the MAC sub-layer 220 a frame received from the PMD sub-layer 200. The PMD sub-layer 200 is a lower layer of the PDCP sub-layer and serves to enable transmission and reception of a PHY entity between two STAs through a radio medium. The MPDU delivered by the MAC sub-layer 220 is referred to as a physical service data unit (PSDU) in the PLCP sub-layer 210. Although the MPDU is similar to the PSDU, when an aggregated MPDU (A-MPDU) in which a plurality of MPDUs are aggregated is delivered, individual MPDUs and PSDUs may be different from each other.

The PLCP sub-layer 210 attaches an additional field including information required by a PHY transceiver in a process of receiving the PSDU from the MAC sub-layer 220 and delivering the PSDU to the PMD sub-layer 200. The additional field attached to the PSDU in this case may be a PLCP preamble, a PLCP header, tail bits required to reset an convolution encoder to a zero state, etc. The PLCP sublayer 210 receives a TXVECTOR parameter, including control information necessary to generate and transmit a Physical Layer Convergence Procedure (PLCP) Protocol Data Unit (PPDU) and control information necessary for a receiving STA to receive and interpret the PPDU, from the MAC sublayer 220. The PLCP sublayer 210 uses the information included in the TXVECTOR parameter in order to generate the PPDU including the PSDU.

The PLCP preamble serves to allow a receiver to prepare a synchronization function and antenna diversity before the PSDU is transmitted. In the PSDU, the data field may include padding bits, a service field including a bit sequence for initializing a scrambler, and a coded sequence obtained by encoding a bit sequence to which tail bits are attached. In this case, either binary convolutional coding (BCC) encoding or low density parity check (LDPC) encoding can be selected as an encoding scheme according to an encoding scheme supported in an STA that receives a PLCP protocol data unit (PPDU). The PLCP header includes a field that contains information on a PPDU to be transmitted, which will be described below in greater detail with reference to FIG. 5.

The PLCP sub-layer 210 generates a PPDU by attaching the aforementioned field to the PSDU and transmits the generated PPDU to a reception STA via the PMD sub-layer. The reception STA receives the PPDU, acquires information required for data recovery from the PLCP preamble and the PLCP header, and recovers the data. The PLCP sublayer of the receiving STA transfers an RXVECTOR parameter, including control information included in a PLCP preamble and a PLCP header, to an MAC sublayer so that the MAC sublayer can interpret the PPDU and obtain data in a reception state.

Referring to FIG. 3, the MAC frame 300 that may be used in a WLAN system chiefly includes an MAC header 310, a frame body 320, and a Frame Check Sequence (FCS) 330. The frame body 320 may include management information, control information and/or data that may be transmitted through the MAC frame 300. The FCS 330 is set to indicate an FCS value calculated for a bit sequence that forms the MAC header 310 and the frame body 320.

The MAC header 310 includes control information about the MAC frame that is exchanged between a transmission STA and a reception STA. The MAC header 310 includes a frame control field 311, a duration/ID field 312, one or

more address fields

313a, 313b, 313c, and 313d, a sequence control field 314, a Quality of Service (QoS) control field 315, and an HT control field 316.

The frame control field 311 includes information related to the characteristics of the MAC frame 300. The frame control field 311 may include pieces of information, such as a protocol version, a type, and a sub type of the MAC frame.

The duration/ID field 312 may be set to indicate duration and/or an Association ID (AID) for transmitting the MAC frame.

Each of the one or more address fields is set to indicate the address of a specific AP and/or STA. For example, the first address field 313a may be set to indicate the MAC address of a source STA, the second address field 313b may be set to indicate the MAC address of a destination STA, the third address field 313c may be set to indicate the MAC address of a transmission STA, and the fourth address field 313d may be set to indicate the MAC address of a reception STA.

The sequence control field 314 may be set to indicate the sequence number of a MAC Service Data Unit (MSDU), an Aggregation MSDU (A-MSDU) and/or an MAC Management Protocol Data Unit (MMPDU). Furthermore, the sequence control field 314 may be set to indicate the fragment number of each MSDU and/or each MMPDU fragment.

The QoS control field 315 may include control information related to QoS.

Meanwhile the HT control field 316 may be embodied as the HT control field of an HT format when an MAC frame is for WLAN service for HT and may be embodied as the HT control field of a VHT format if the MAC frame is for WLAN service for VHT.

The HT control field of an HT format may be identified by an indicator indicating that the HT control field has the HT format. The HT control field may be embodied so that it includes control information related to link adaptation, information related to calibration, channel state information, and NDP notification information informing the transmission of a Null Data Packet (NDP). For example, the HT control field may include an MCS feedback sequence identifier (MFSI) subfield in relation to link adaptation. The MFSI subfield may be set to an MCS request (MRQ) Sequence Identifier (MSI) value that is included in a frame related to MCS feedback (MFB) information. The MSI is ID information about a sequence for identifying a request when MCS estimation is requested.

The HT control field of a VHT format may be identified by an indicator indicating that the HT control field is the VHT format. The VHT control field may be embodied so that it includes control information related to link adaptation and control information related to channel sounding. For example, the HT control field may include an MSI subfield and an MFSI subfield. The MSI subfield may include information about the ID of a sequence for identifying a request when MCS estimation is requested. The MFSI may be set to an MSI value that is included in a frame related to MFB information.

The HT control field 316 may be used to feed back MCS-related information that has been estimated based on subfields related to the above MRQ/MFB. That is, the HT control field 316 may include MCS-related information that has been estimated by an STA. MCS information that is recommended based on the estimated MCS-related information may be implicitly fed back. Meanwhile, the MSI and/or MFSI may be used to identify a frame itself that includes the MSI and/or MFSI. The MSI and/or MFSI may be used to indicate the number of remaining packets in embodiments of the present invention to be described later.

FIG. 4 is a block diagram showing an example of a PPDU format used in a WLAN system which provides HT service. Hereinafter, an STA capable of providing only service in the existing WLAN system is called a legacy STA (L-STA and an STA capable of providing service in an HT WLAN system is called an HT-STA, for convenience of description of a PPDU format related to FIG. 4.

Referring to FIG. 4, a PPDU supported by IEEE 802.11n, that is, a WLAN system standard which provides HT service, has three formats.

FIG. 4(a) shows a Legacy PPDU (L-PPDU) format, that is, a PPDU format used in IEEE 802.11a/b/g, that is, the existing WLAN system standards. Accordingly, in a WLAN system to which the IEEE 802.11n standard has been applied, an L-STA can transmit and receive an L-PPDU having this format.

Referring to FIG. 4(a), an L-PPDU 410 includes an L-STF field 411, an L-LTF field 412, an L-SIG field 413, and a data field 414.

The L-STF field 411 is used for frame timing acquisition, automatic gain control (AGC) convergence, coarse frequency acquisition, etc.

The L-LTF field 412 is used for frequency offset and channel estimation.

The L-SIG field 413 includes control information for demodulation and decoding of the data field 414.

The L-PPDU may be transmitted in the order of the L-STF field 411, the L-LTF field 412, the L-SIG field 413, and the data field 414.

FIG. 4(b) is a diagram showing an HT-mixed PPDU format in which an L-STA and an HT-STA can coexist. An HT-mixed PPDU 420 includes an L-STF field 421, an L-LTF field 422, an L-SIG field 423, an HT-SIG field 424, an HT-STF field 425, a plurality of HT-LTF fields 426, and a data field 427.

The L-STF field 421, the L-LTF field 422, and the L-SIG field 423 are identical to those shown in FIG. 4(a). Therefore, the L-STA can interpret the data field by using the L-STF field 421, the L-LTF field 422, and the L-SIG field 423 even if the HT-mixed PPDU 420 is received. The L-LTF field 422 may further include information for channel estimation to be performed by the HT-STA in order to receive the HT-mixed PPDU 420 and to interpret the L-SIG field 423, the HT-SIG field 424, and the HT-STF field 425.

The HT-STA can know that the HT-mixed PPDU 420 is a PPDU dedicated to the HT-STA by using the HT-SIG field 424 located next to the L-SIG field 423, and thus can demodulate and decode the data field 427.

The HT-STF field 425 may be used for frame timing synchronization, AGC convergence, etc., for the HT-STA.

The HT-LTF field 426 may be used for channel estimation for demodulation of the data field 427. Since the IEEE 802.11n supports single user-MIMO (SU-MIMO), a plurality of the HT-LTF fields 426 may be configured for channel estimation for each of data fields transmitted through a plurality of spatial streams.

The HT-LTF field 426 may consist of a data HT-LTF used for channel estimation for a spatial stream and an extension HT-LTF additionally used for full channel sounding. Therefore, the number of the plurality of HT-LTF fields 426 may be equal to or greater than the number of spatial streams to be transmitted.

The L-STF field 421, the L-LTF field 422, and the L-SIG field 423 are transmitted first so that the L-STA also can acquire data by receiving the HT-mixed PPDU 420. Thereafter, the HT-SIG field 424 is transmitted for demodulation and decoding of data transmitted for the HT-STA.

Up to fields located before the HT-SIG field 424, transmission is performed without beamforming so that the L-STA and the HT-STA can acquire data by receiving a corresponding PPDU. In the subsequently fields, i.e., the HT-STF field 425, the HT-LTF 426, and the data field 427, radio signal transmission is performed by using precoding. In this case, the HT-STF field 425 is transmitted so that an STA that receives a precoded signal can consider a varying part caused by the precoding, and thereafter the plurality of HT-LTF fields 426 and the data field 427 are transmitted.

Even if an HT-STA that uses 20 MHz in an HT WLAN system uses 52 data subcarriers per OFDM symbol, an L-STA that also uses 20 MHz uses 48 data subcarriers per OFDM symbol. Since the HT-SIG field 424 is decoded by using the L-LTF field 422 in a format of the HT-mixed PPDU 420 to support backward compatibility, the HT-SIG field 424 consists of 48＊2 data subcarriers. The HT-STF field 425 and the HT-LTF 426 consist of 52 data subcarriers per OFDM symbol. As a result, the HT-SIG field 424 is supported using 1/2 binary phase shift keying (BPSK), each HT-SIG field 424 consists of 24 bits, and thus 48 bits are transmitted in total. That is, channel estimation for the L-SIG field 423 and the HT-SIG field 424 is performed using the L-LTF field 422, and a bit sequence constituting the L-LTF field 422 can be expressed by Equation 1 below. The L-LTF field 422 consists of 48 data subcarriers per one symbol, except for a DC subcarrier.

FIG. 4(c) is a diagram showing a format of an HT-Greenfield PPDU 430 that can be used by only an HT-STA. The HT-GF PPDU 430 includes an HT-GF-STF field 431, an HT-LTF1 field 432, an HT-SIG field 433, a plurality of HT-LTF2 fields 434, and a data field 435.

The HT-GF-STF field 431 is used for frame timing acquisition and AGC.

The HT-LTF1 field 432 is used for channel estimation.

The HT-SIG field 433 is used for demodulation and decoding of the data field 435.

The HT-LTF2 434 is used for channel estimation for demodulation of the data field 435. Since the HT-STA uses SU-MIMO, channel estimation is required for each of data fields transmitted through a plurality of spatial streams, and thus a plurality of HT-LTF2 fields 434 may be configured.

The plurality of HT-LTF2 fields 434 may consist of a plurality of data HT-LTFs and a plurality of extension HT-LTFs, similarly to the HT-LTF 426 of the HT-mixed PPDU 420.

Each of the data fields 414, 427, and 435 respectively shown in FIG. 4(a), (b), and (c) may include a service field, a scrambled PSDU field, a tail bits field, and a padding bits field. The service field may be used to reset a scrambler. The service field may be set to 16 bits. In this case, bits for resetting the scrambler may be 7 bits. A tail field may include a bit sequence necessary to return a convolution encoder to a state 0. The tail field may be assigned a bit size that is proportional to the number of Binary Convolutional Code (BCC) encoders used to encode data to be transmitted. More particularly, the tail field may be embodied so that it has 6 bits per BCC.

FIG. 5 shows an example of a PPDU format used in a WLAN system.

Referring to FIG. 5, a PPDU 500 includes an L-STF field 510, an L-LTF field 520, an L-SIG field 530, a VHT-SIGA field 540, a VHT-STF field 550, a VHT-LTF field 560, a VHT-SIGB field 570, and a data field 580.

A PLCP sub-layer constituting a PHY converts a PSDU delivered from a MAC layer into the data field 580 by appending necessary information to the PSDU, generates the PPDU 500 by appending several fields such as the L-STF field 510, the L-LTF field 520, the L-SIG field 530, the VHT-SIGA field 540, the VHT-STF field 550, the VHT-LTF field 560, the VHT-SIGB field 570, or the like, to the data field and delivers the PPDU 500 to one or more STAs through a physical medium dependent (PMD) sub-layer constituting the PHY. Control information required by the PLCP sub-layer to generate the PPDU and control information used by a reception STA to interpret the PPDU and transmitted by being included in the PPDU are provided from a TXVECTOR parameter delivered from the MAC layer.

The L-SFT 510 is used for frame timing acquisition, automatic gain control (AGC) convergence, coarse frequency acquisition, etc.

The L-LTF field 520 is used for channel estimation for demodulation of the L-SIG field 530 and the VHT-SIGA field 540.

The L-SIG field 530 is used when the L-STA receives the PPDU 500 and interprets it to acquire data. The L-SIG field 530 includes a rate sub-field, a length sub-field, a parity bit and tail field. The rate sub-field is set to a value indicating a bit state for data to be currently transmitted.

The length sub-field is set to a value indicating an octet length of a PSDU to be transmitted by the PHY layer at the request of the MAC layer. In this case, an L_LENGTH parameter which is a parameter related to information indicating the octet length of the PSDU is determined based on a TXTIME parameter which is a parameter related to a transmission time. TXTIME indicates a transmission time determined for PPDU transmission including the PSDU by the PHY layer in association with a transmission time requested for transmission of the PSDU. Therefore, since the L_LENGTH parameter is a time-related parameter, the length sub-field included in the L-SIG field 530 includes information related to the transmission time.

The VHT-SIGA field 540 includes control information (or signal information) required by STAs for receiving the PPDU to interpret the PPDU 500. The VHT-SIGA 540 is transmitted on two OFDM symbols. Accordingly, the VHT-SIGA field 540 can be divided into a VHT-SIGA1 field and a VHT-SIGA2 field. The VHT-SIGA1 field includes channel bandwidth information used for PPDU transmission, identifier information related to whether space time block coding (STBC) is used, information indicating either SU or MU-MIMO as a PPDU transmission scheme, and, if the transmission scheme is MU-MIMO, information indicating a transmission target STA group of a plurality of STAs which are MU-MIMO paired with the AP, and information regarding a spatial stream allocated to each STA included in the transmission target STA group. The VHT-SIGA2 field includes information related to a short guard interval (GI).

The information indicating the MIMO transmission scheme and the information indicating the transmission target STA group can be implemented as one piece of MIMO indication information, and for example, can be implemented as a group ID. The group ID can be set to a value having a specific range. A specific value in the range indicates an SU-MIMO transmission scheme, and other values can be used as an identifier for a corresponding transmission target STA group when the MU-MIMO transmission scheme is used to transmit the PPDU 500.

When the group ID indicates that the PPDU 500 is transmitted using the SU-MIMO transmission scheme, the VHT-SIGA2 field includes coding indication information indicating whether a coding scheme applied to the data field is binary convolution coding (BCC) or low density parity check (LDPC) coding and modulation coding scheme (MCS) information regarding a channel between a transmitter and a receiver. In addition, the VHT-SIGA2 field can include an AID of a transmission target STA of the PPDU and/or a partial AID including a part of bit-sequence of the AID.

When the group ID indicates that the PPDU 500 is transmitted using the MU-MIMO transmission scheme, the VHT-SIGA field 500 includes coding indication information indicating whether a coding scheme applied to the data field which is intended to be transmitted to MU-MIMO paired reception STAs is BCC or LDPC coding. In this case, MCS information for each reception STA can be included in the VHT-SIGB field 570.

The VHT-STF 550 is used to improve performance of AGC estimation in MIMO transmission.

The VHT-LTF 560 is used when the STA estimates a MIMO channel. Since the next generation WLAN system supports MU-MIMO, the VHT-LTF field 560 can be configured by the number of spatial streams in which the PPDU 500 is transmitted. In addition, when full channel sounding is supported and is performed, the number of VHT-LTFs may increase.

The VHT-SIGB field 570 includes dedicated control information required when the plurality of MIMO-paired STAs receive the PPDU 500 to acquire data. Therefore, the STA may be designed such that the VHT-SIGB field 570 is decoded only when the control information included in the VHT-SIGA field 540 indicates that the currently received PPDU 500 is transmitted using MU-MIMO transmission. On the contrary, the STA may be designed such that the VHT-SIGB field 570 is not decoded when the control information in the VHT-SIGA field 540 indicates that the currently received PPDU 500 is for a single STA (including SU-MIMO).

The VHT-SIGB field 570 may include MCS information and rate-matching information for each STA. Further, the VHT-SIGB field 570 may include information indicating a PSDU length included in the data field for each STA. The information indicating the PSDU length is information indicating a length of a bit-sequence of the PSDU and can be indicated in the unit of octet. Meanwhile, when the PPDU is transmitted based on single user transmission, the information about the MCS may not be included in the VHT-SIGB field 570, because that is included in the VHT-SIGA field 540. A size of the VHT-SIGB field 570 may differ according to the MIMO transmission method (MU-MIMO or SU-MIMO) and a channel bandwidth used for PPDU transmission.

The data field 580 includes data intended to be transmitted to the STA. The data field 580 includes a service field for initializing a scrambler and a PLCP service data unit (PSDU) to which a MAC protocol data unit (MPDU) of a MAC layer is delivered, a tail field including a bit sequence required to reset a convolution encoder to a zero state, and padding bits for normalizing a length of the data field. In case of MU transmission, each data unit intended to be respectively transmitted to each STA may be included in the data field 580. The data unit may be aggregate MPDU (A-MPDU).

In the WLAN system of FIG. 1, if the AP 10 intends to transmit data to the STA1 21, the STA2 22, and the STA3 23, then a PPDU may be transmitted to an STA group including the STA1 21, the STA2 22, the STA3 23, and the STA4 24. In this case, as shown in FIG. 5, no spatial stream may be allocated to the STA4 24, and a specific number of spatial streams may be allocated to each of the STA1 21, the STA2 22, and the STA3 23 and thus data can be transmitted. In the example of FIG. 2, one spatial stream is allocated to the STA1 21, three spatial streams are allocated to the STA2 22, and two spatial streams are allocated to the STA3 23.

Meanwhile, with the wide spread of a WLAN system, problems related to the service coverage of a WLAN may occur. Problems related to service coverage are directly related to the reliability of WLAN service. The problems are described in detail with reference to FIG. 6.

Referring to FIG. 6, it is assumed that three STAs exist within the coverage of an AP. A coverage where each STA transmits and receives a signal for exchanging frames is indicated by a dotted line.

The intensity of a signal received by the AP from each STA may vary depending on the position of the STA. The intensity of a signal received by the AP from an STA which is far from the AP may be smaller than the intensity of a signal received by the AP from an STA which is relatively close to the AP. In the example of FIG. 6, the intensity of a signal received from the STA1 may be weaker than the intensity of each of signals received from the STA2 and the STA3. The transmission of this weak signal may fail owing to the signals transmitted by the STA2 and/or the STA3 which are placed outside the coverage of the STA1, if the weak signal is not protected by an RTS-CTS mechanism. The signal of the STA1 may not be normally received owing to interference due to a radio signal transmitted by a wireless apparatus which is placed in another BSS and operated in the same frequency band in an Overlapping BSS (OBSS) environment, in addition to the signals transmitted by the STA2 and/or the STA3. Furthermore, an interference signal in a WLAN environment having wide coverage may be generated by not only another WLAN system, but also other systems operated in an Industrial Scientific and Medical Equipment (ISM) band. The interference signals may be burst in terms of the time.

Accordingly, in order for an AP to precisely receive the signal of an STA distant from the AP when an interference signal exists, there is a need for a method of protecting transmitted data. For example, the STA can reduce the error rate of a received signal by lowering the modulation order and the code rate of the transmitted data. A current system according to a WLAN standard uses BPSK modulation at the lowest code rate and a 1/2 code rate. A WLAN system operated in wide coverage may use a 1/3 or 1/4 or lower code rate.

As another method, the error rate can be reduced by using Forward Error Correcting (FEC) coding even in the MAC layer, unlike the above method of using the FEC coding even in the PHY layer.

The above methods are effective in reducing the reception error rate of an interference signal when the data part of a WLAN frame is received. However, if the interference signal is received in the preamble part of a WLAN frame, the above method of controlling the code rate is not effective because carrier frequency offset compensation, timing synchronization, and channel estimation cannot be properly performed.

The present invention proposes a method of consecutively transmitting packets including the same data when transmitting data, such as a PPDU, in order to precisely receive a signal from an STA which is placed within the service coverage of an AP, but is far from the AP. This method is called packet repetition, for convenience of description.

FIG. 7 is a diagram showing a method of transmitting and receiving packets based on packet repetition according to an embodiment of the present invention. The method of transmitting and receiving packets according to the example of FIG. 7 shows the transmitting type of packet repetition for consecutively transmitting N packets. It is hereinafter assumed that an STA sends packets and an AP receives the packets, for convenience of description, but the scope of the present invention is not limited thereto.

Referring to FIG. 7, the STA consecutively transmits the N packets. Each of the packets transmitted by the STA may include a packet ID. The STA does not need to receive another signal, such as acknowledgement, while performing transmission based on packet repetition. After transmitting the last packet during the consecutive packet transmission, the STA may check whether the transmission of the packets is successful or not by checking whether acknowledgement has been received from the AP or not. Packet spacing equal to the time T may be placed between the packets consecutively transmitted. If the spacing of the time T is short, it is possible to prevent another STA from occupying a relevant channel and starting transmission and the total transmission time can be reduced. The STA can protect the consecutive transmission period based on packet repetition through length information within the signal field of a PLCP header. Here, the length of each packet may be set so that all the lengths and packet spacings of the remaining packets are included in order to prevent another STA from breaking in the consecutive transmission and from starting transmission.

The AP that receives the signal may receive some of the consecutively transmitted packets or may not receive some of the consecutively transmitted packets depending on a varying environment, such as a channel state and an interference signal. When one or more of the packets transmitted based on packet repetition are received, the AP may predict a point of time at which the transmission based on packet repetition is finished based on the packet IDs of the successfully received packet although the remaining packets are not received. Accordingly, if any one of the plurality of transmitted packets has been successfully received, the AP can know that the transmission has been successfully completed by transmitting acknowledgement to the STA at a point of time at which the last packet is transmitted. In the example of FIG. 7, the AP normally receives the third packet although the first and the second packets are not received and thus can transmit acknowledgement to the STA after the packets are repeatedly transmitted.

At the time of transmission based on packet repetition, power can be reduced by using a characteristic that the same data is repeatedly transmitted. When a receiver recognizes that a received packet is a packet transmitted based on packet repetition, the receiver can know the time length of the packets which include the same data and which are repeatedly transmitted and does not receive redundant data during the time, thus being capable of reducing power. In FIG. 7, the AP may enter a sleep state until sending acknowledgement after receiving the third packet.

Packet transmission based on packet repetition may be embodied using various methods. For example, a method of informing the start or end of transmission between an AP and an STA in advance based on packet repetition may be used. That is, after a process of configuring packet repetition transmission before starting transmitting and receiving packets based on packet repetition is performed, the transmission and reception of the packets may be started. This is described below with reference to the accompanying drawing.

Referring to FIG. 8, for the purpose of packet repetition between an AP and an STA, a packet repetition configuration (S810) is performed. The packet repetition configuration corresponds to a process of requesting, responding to, and instructing packet repetition before starting the transmission and reception of packets based on packet repetition and setting an information parameter value for the packet repetition.

The packet repetition configuration may be embodied by one-sided indication by the AP. The AP may perform the packet repetition configuration by transmitting a packet repetition request frame, instructing that subsequent packet transmission be performed based on packet repetition, to the STA distant from the AP (S811).

Referring to FIG. 9, the packet repetition request frame 900 may include a category field 910, an action field 920, a packet repetition start/end field 930, a repetition number field 940, and a packet spacing field 950.

The category field 910 and the action field 920 may be set to indicate that a frame is the packet repetition request frame 900.

The packet repetition start/end field 930 may be set to indicate whether or not the AP starts the transmission and reception of packet based on packet repetition or may be set to instruct that transmission and reception based on the existing packet repetition be finished.

The repetition number field 940 may be set to indicate the number of times that packets including the same data are repeatedly transmitted. The packet spacing field 950 may be set to indicate spacing for which each packet is transmitted. An AP may determine the number of times of packet repetition N and/or a packet spacing T that are suitable for the transmission of packets based on packet repetition by taking the reception state of a signal received from an STA into consideration and may set the packet number field 940 and/or the packet spacing field 950 by taking the number of times of packet repetition N and/or a packet spacing T into consideration.

In addition, the packet repetition request frame 900 may include the request type field 960. The request type field 960 may be defined as in Table 1 below depending on a characteristic of a request made by an AP.

request type field value	description
0	New Request
1	Cancel the former request with reason code 1
2	Cancel the former request with reason code 2
…	…

The request type field 960 may indicate that a request is a new request when it is set to ‘0’. Furthermore, the request type field 960 may transmit a request that cancels the existing request. The request to cancel the existing request may mean only cancel simply or may inform a reason of the cancel by defining a reason code particularly.

Referring back to FIG. 8, the AP may perform the packet repetition configuration one-sidedly by transmitting the packet repetition request frame, and the packet repetition configuration may be embodied as a request/response mechanism through an additional response of the STA. In this case, the STA may transmit a packet repetition response frame to the AP in response to the packet repetition request frame (S812).

Referring to FIG. 10, the packet repetition response frame 1000 may include a category field 1010, an action field 1020, a response type field 1030, a repetition number field 1040, and a packet spacing field 1050.

The category field 1010 and/or the action field 1020 may be set to indicate that a frame is the packet repetition response frame 1000.

The response type field 1030 is a response to a packet repetition configuration request according to the packet repetition request frame. The response type field 1030 may be set to a value for controlling an STA in response to the transmission of preset packets based on packet repetition. The response type field 1030 may be embodied as in Table 2 below.

response type field value	description
0	Accept
1	Deny with reason code 1
2	Deny with reason code 2
…	…
n	Terminate with reason code 1
n+1	Terminate with reason code 2
…	…

As in the example of the response type field 1030, when an STA accepts a packet repetition request from an AP, the response type field 1030 may be set to ‘0’. In this case, the STA may set the repetition number and/or the packet spacing as requested by the AP or may set the repetition number and/or the packet spacing to another values intended by the STA. If the repetition number and/or the packet spacing are set as requested by the AP, the STA may set the repetition number field 1040 and the packet spacing field 1050 to values in which the repetition number field and the packet spacing field of the packet repetition request frame are set, or the repetition number field 1040 and the packet spacing field 1050 may not be included in the packet repetition response frame. If the STA changes the repetition number and/or the packet spacing to intended values, the STA may set the repetition number field 1040 and/or the packet spacing field 1050 to the intended values.

If the STA does not accept the packet repetition request, the response type field 1030 may inform the AP of a reason through a previously defined reason code.

In addition, the STA may stop packet transmission based on packet repetition that is now started by sending the packet repetition response frame although a packet repetition request has not been received. In this case, likewise, the response type field 1030 may be set to indicate that the stop is a stop according to a specific reason through a previously defined reason code.

Referring back to FIG. 8, if the packet repetition configuration through the packet repetition request frame and/or the packet repetition response frame is performed, the AP can know that a radio signal transmitted by the STA is transmitted in the state in which the N packets are repeatedly transmitted at the T spacing. Accordingly, the STA repeatedly transmits the packets having the same data at the T spacing N times (S820).

When transmitting the N packets based on packet repetition, the STA may assign a packet ID to each of the packets. Accordingly, although only one of the packets which include the same data and which are repeatedly transmitted is successfully received, the AP can induce a point of time at which the entire packet repetition is terminated. In order to implement this, the STA may include information about the number of remaining packets in each packet. The AP may determine a point of time at which the transmission of the last packet will be terminated based on the length of a successfully received packet, packet spacing, and the number of remaining packets. Furthermore, the AP may transmit acknowledgement to the STA at a point of time at which the determined packet transmission is terminated (S830).

The information about the number of remaining packets may be embodied as follows.

- A method of transmitting a data field including the information about the number of remaining packets

1. The number of remaining packets may be indicated by using a bit sequence for resetting the scrambler of a service field that is included in the foremost of the data field and that indicates encoding information. For example, the information about the number of remaining packets may be combined with a bit sequence for resetting a scrambler reset.

2. Information indicating the number of remaining packets may be included as part of data that forms the PSDU of a data field.

- A method of transmitting an MAC header including the information about the number of remaining packets

1. Information indicating the number of remaining packets may be embodied by utilizing the reserved bit of the MAC header.

2. Information indicating the number of remaining packets may be embodied by utilizing a bit stream number, such as an MSI or an MFSI included in an HT control field.

- A method of transmitting a PLCP header including the information about the number of remaining packets

Information indicating the number of remaining packets may be embodied by utilizing the reserved bit of an L-SIG field, an HT-SIG field and/or a VHT-SIG field.

In the above examples, it is assumed that the AP and the STA perform the packet repetition configuration by exchanging a packet repetition request frame and packet repetition response frame in advance. Here, the STA may start the transmission of packets based on packet repetition without the previous setting process. In this case, the STA has to be able to inform the AP of not only the number of remaining packets, but also that the packets are transmitted based on packet repetition. Accordingly, the STA may signalize that packet transmission based on packet repetition has been started by further allocating 1 bit when using one of the methods of loading the information onto each packet (i.e., the method of transmitting a data field including the information about the number of remaining packets, the method of transmitting an MAC header including the information about the number of remaining packets, and the method of transmitting a PLCP header including the information about the number of remaining packets).

FIG. 11 is a block diagram showing a wireless apparatus to which an embodiment of the present invention may be applied. The wireless apparatus may be an AP or an STA.

The wireless apparatus 1100 includes a processor 1110, memory 1120, and a transceiver 1130. The transceiver 1130 is configured to transmit and receive radio signals, and the physical layer of IEEE 802.11 is embodied in the transceiver 1130. The processor 1110 is functionally connected to the transceiver 1130 and is configured to embody the MAC layer and the physical layer of IEEE 802.11. The processor 1110 is configured so that it supports packet transmission based on packet repetition according to the embodiment of the present invention. The processor 1110 may be configured to perform the packet repetition configuration based on a packet repetition request frame and a packet repetition response frame according to the embodiment of the present invention. The processor 1110 may be configured to transmit and receive packets including the same data through the packet repetition configuration. The processor 1110 may be configured to embody the embodiments of the present invention which have been described with reference to FIGS. 6 to 10.

The processor 1110 and/or the transceiver 1130 may include Application-Specific Integrated Circuits (ASICs), other chipsets, logic circuits, or data processors or all of them. The memory 1120 may include Read-Only Memory (ROM), Random Access Memory (RAM), flash memory, memory cards, storage media and/or other storage devices. When the above-described embodiment is embodied in software, the above-described scheme may be embodied by using a module (process or function) that performs the above function. The module may be stored in the memory 1120 and executed by the processor 1110. The memory 1120 may be placed inside or outside the processor 1110 and may be connected to the processor 1110 using a variety of well-known means.

Claims

A method of transmitting packets in a Wireless Local Area Network (WLAN) system, the method comprising:
performing, by the transmitter, a packet repetition configuration in order to transmit a plurality of packets along with a receiver;
repeatedly transmitting, by the transmitter, the plurality of packets one by one at packet spacing to the receiver; and
receiving, by the transmitter, an acknowledgement frame, informing that one or more of the plurality of packets have been received, from the receiver,
wherein the plurality of packets comprises identical data,
wherein the performing the packet repetition configuration comprises receiving a packet repetition request frame from the receiver, and
the packet repetition request frame requests to repeatedly transmit the packets.
The method of claim 1, wherein the packet repetition request frame comprises:
a request repetition number field indicating a number of packets requested to be repeatedly transmitted; and
a request packet spacing field indicating request packet spacing.
The method of claim 2, wherein the number of the plurality of transmitted packets is the number of requested packets indicated by the request repetition number field.
The method of claim 3, wherein the packet spacing is the requested packet spacing indicated by the request packet spacing field.
The method of claim 2, wherein the performing the packet repetition configurations further comprises transmitting a packet repetition response frame in response to the packet repetition request frame,
wherein the packet repetition response frame comprises a response type field indicating a response to the request according to the packet repetition request frame.
The method of claim 5, wherein the repeatedly transmitting the plurality of packets one by one is performed when the response type field indicates acceptance of the request according to the packet repetition request frame.
The method of claim 6, wherein the packet repetition response frame comprises:
a response repetition number field indicating the number of plurality of packets repeatedly transmitted one by one; and
a response packet spacing field indicating the packet spacing.
The method of claim 7, wherein:
the response repetition number field is set differently from the request repetition number field, and
the response packet spacing field is set differently from the request packet spacing field.
The method of claim 6, wherein when the response type field is set to deny the request according to the packet repetition request frame, the response type field is further set to indicate a reason code indicating a reason of the denial.
The method of claim 1, wherein each of the packets comprises a packet ID related to order of its own transmission in the plurality of packets.
The method of claim 1, wherein each of the packets comprises a remainder packet indicator indicating a number of remaining packets to be subsequently transmitted.
The method of claim 11, wherein the remainder packet indicator is included in a Medium Access Control (MAC) header.
The method of claim 11, wherein the remainder packet indicator is combined with a bit sequence for resetting a scrambler included in a service field of the packet.
The method of claim 1, further comprising,
transmitting, by the transmitter, a packet repetition response frame, informing that the repeated transmission of the plurality of packets is stopped, to the receiver.
The method of claim 14, wherein:
the packet repetition response frame comprises a response type field indicating that the repeated transmission of the plurality of packets is stopped, and
the response type field further indicates a reason of the stop.
A wireless apparatus configured to transmit packets in a Wireless Local Area Network (WLAN) system, the wireless apparatus comprising:
a transceiver configured to transmit and receive the packets; and
a processor functionally connected to the transceiver,
wherein the processor is configured to:
perform a packet repetition configuration in order to transmit a plurality of packets along with a receiver;
repeatedly transmit the plurality of packets one by one at packet spacing to the receiver; and
receive an acknowledgement frame, informing that one or more of the plurality of packets have been received, from the receiver,
wherein the plurality of packets comprises identical data,
wherein the performing the packet repetition configuration comprises receiving a packet repetition request frame from the receiver, and
the packet repetition request frame requests to repeatedly transmit the packets.