KR20070022074A - Wireless communication system, wireless communication device for use as a station in a wireless communication system, a method of communication within a wireless communication system - Google Patents

Abstract

The present invention provides a wireless communication system including a master station, a first additional station, and a second additional station, wherein the master station includes a first high speed mode and the first channel using a first channel and at least one second channel. Operable to communicate with the first and second additional stations in a second low speed mode using a second channel, the first additional station to communicate in a first mode using at least one second channel with the first channel. Wherein the second additional station is arranged to communicate in a second mode using either the first channel or the second channel, wherein the master station is in communication in the first mode. Define a plurality of first time slots for the first channel and a plurality of second time slots for the second channel, for communication in the second mode. And a plurality of third time slots for the first channel and a plurality of fourth time slots for the second channel.

Description

WIRELESS COMMUNICATION SYSTEM, WIRELESS COMMUNICATION DEVICE FOR USE AS A STATION IN A WIRELESS COMMUNICATION SYSTEM, A METHOD OF COMMUNICATION WITHIN A WIRELESS COMMUNICATION SYSTEM}

The present invention relates to a wireless communication system as defined in the preamble of claim 1.

The invention also relates to a station for use in a wireless communication system and a method of communicating within a wireless communication system.

This wireless communication system is described in IEEE Standard 802.11a (1999), "Wireless LAN Medium Access Control (MAC) and Physical (PHY) specifications: High Speed Physical Layer in the 5 ㎓ Band" (IEEE, New York, 1999). It is. Wireless communication systems conforming to this standard can support orthogonal frequency division multiplexing (OFDM) to support raw data rates in the range of 6 to 54 megabits / sec. It operates in the 5GHz license free ISM band. IEEE Standard 802.11b discloses a similar communication system for operating in the 2.4 GHz ISM band. In order to meet the requirements of delay limited applications, a new specification was proposed in p802.11e that incorporates data link layer functionality to provide statistical and parameterized QoS.

In order to support data rates up to about 100 Mbit / sec at the data link layer, a new specification p802.11n has been proposed. In this proposal, an proposal was introduced to extend to the 11a-based PHY and 11e-based MAC standards, while maintaining backward compatibility with certain levels of backward compatibility. This PHY extension is based on multi-in-multi-out (MIMO) and support for transmission in the 40 MHz band, so-called dual channel operation.

A wireless local area network (WLAN), such as a wireless communication system conforming to IEEE standard 802.11 or one of the extensions proposed by this standard, consists of a cell, a so-called basic service set. Such a cell includes a number of wireless stations. One station in such a cell is arranged to provide communication with another cell, master station or access point via an inter-cell system or distribution system.

In such a wireless communication which aims at a first mode of high speed or high-throughput communication while maintaining compatibility for a communication device or station capable of communicating in a second low speed mode, the master station is in communication with the first high speed mode. It should be arranged to facilitate communication in the second low speed mode.

In such a wireless communication system, sub-bands or communication channels are used to establish a communication link. For example, in IEEE standards 802.11a and 11g, 20 MHz wide communication channels are used within the 5 GHz and 2.5 ISM bands, respectively. In IEEE P802.11n, it is proposed that the basic set of services can operate in single channel mode (20 MHz bandwidth) or dual channel mode (40 MHz bandwidth). In the dual channel mode, the first channel is defined as a so-called control channel and the second channel is defined as a so-called expansion channel. This control channel allows the presence of legacy devices (e.g., 802.11a stations). However, if the presence of the legacy device is detected in the extension channel, the master station must select another communication channel.

The disadvantage of communicating in this way is that such communication is rather inflexible and may make the use of available communication channels less than optimal.

Accordingly, it is an object of the present invention, among other things, to provide a wireless communication system with higher flexibility in communication between stations having a wireless communication system.

To this end the invention provides a wireless communication system as defined in the preamble of claim 1, characterized by the features of claim 1.

By creating separate time slots for slow mode communication and fast mode communication in the control and extension channels, the number of channels that can be used for communication in the high speed mode is increased. This increases the flexibility of the wireless communication system.

The master station is arranged to facilitate communication in the first high speed mode and the second low speed mode by creating a time slot that permits transmission in the first mode and another time slot that permits communication in the second mode. In IEEE P802.11n, this is achieved by the master station transmitting an assignment signal that assigns a time frame or time slot for high speed communication and another time frame or time slot for low speed communication. For this purpose, a so-called Clear-To-Send frame or beacon that includes a so-called network allocation vector (NAV), for example a contention-free period. This can be used.

The above and other objects and features of the present invention will become more apparent from the following detailed description considered in conjunction with the accompanying drawings.

1 shows a general overview of a communication system according to one of the IEEE standard 802.11 specification groups.

2 is an overview of a high throughput basic service set of a communication system.

3 shows an overview of a mixed basic service set of a communication system according to the present invention.

4 illustrates a signaling diagram for a 20 MHz based management mixed mode.

In these figures, like parts are identified with like reference numerals.

1 shows a general overview of a communication system according to one of the IEEE standard (Std.) 802.11 specification groups. In the network architecture, the basic elements are called Basic Service Sets (BBSs). This BSS _n is typically limited to a group of stations (wireless nodes) located within a constrained physical area, within which each station (STA) is (communication barrier, physical barrier or other). It is theoretically possible to communicate with all other STAs in the ideal environment without barriers). There are two basic wireless network design architectures that are limited to ad hoc networks and infrastructure networks.

An infrastructure based IEEE 802.11 wireless network or communication system consists of one or more BSS _n interconnected via another network, such as an IEEE 802.3 wired Ethernet network. This connection infrastructure is called a distribution system (DS). According to this infrastructure, each BSS _n must have exactly one radio station connected to the DS. This station provides a function for relaying messages from other STAs of BSS _n to the DS. This STA is called an Access Point (AP) for its associated BSS _n . An entity consisting of a DS and its associated BSS is called an Extended Service Set (ESS). For IEEE 802.11, it is assumed that the DS can move data to / from an external portal between BSSs, but the method used by the DS to achieve this functionality is not limited.

Ad hoc wireless networks are basically the opposite of infrastructure-based wireless LANs (WLANs). Ad hoc WLANs do not have the infrastructure and therefore are not capable of communicating with external networks. Ad hoc WLANs are typically purely set up to allow multiple radio stations to communicate with each other, requiring as little external hardware or management support as possible. The BSS of the ad hoc network is referred to as Independent BSS (IBSS), which is not shown.

Wireless communication systems that extend existing IEEE 802.11 specifications, for example, wireless communication systems according to the proposed P802.11n, need to support different communication modes while maintaining compatibility with older versions. In order to provide compatibility with legacy (IEEE 802.11a / g) devices, in infrastructure mode, basic services controlled by High-Throughput Access Points (HTAPs) complying with P801.11n. The Basic Service Set (BSS) has three modes of operation:

Pure mode: where the legacy STS cannot be connected to the BSS; There is no legacy station in this pure mode.

Managed-mixed mode: legacy STAs may be connected and coexistence between the high throughput STA (HT-STA) and the legacy STA is managed by HTAP via time division; There are two sub modes in the mixed management mode. The first mode is a mixed capable mode. In this mode, there is no legacy station, but the HTAP can accept connections from legacy stations that discover or register with this HTAP by receiving legacy beacons from the HTAP. This means that the beacon is transmitted in the operating mode and can be recognized by the legacy station. The second mode is a management mixed mode. In this mode, the time is divided between the contention free period for the HTSTA and the legacy station by selectively selecting a Network Allocation Vector (NAV). The HTAP transmits a header that can be recognized by the legacy station, where the header includes the time period of the data packet and / or the end of the data packet, thereby preserving the time that the medium is blocked. Furthermore, the time for transmitting an acknowledgment signal is included in this header. The station receiving this header sets the NAV at the end time of the packet. So these stations will not have access to the medium for the time signaled. Part of the management mixed mode may be a 20 MHz based management mixed mode. In this mode, the BSS includes legacy stations and HT stations. Here, there may be a legacy station that overlaps with the BSS on both channels or on one channel. The legacy station and the HT station are connected to the BSS of the AP in the control channel. The AP manages the generation of 40 MHz or HT periods and 20 MHz or slow periods. During the 40 MHz period, the HT station is allowed to access the medium at 40 MHz. Legacy stations are not allowed to access the medium at this time. During the 20 MHz period, the legacy station is allowed to access the medium at 20 MHz.

Unmanaged mixed mode: Here, legacy STAs may be connected and coexistence between high throughput stations and legacy stations is not managed by the HTAP.

In addition, the high throughput station (HT-STA) can operate in three different modes:

Pure mode: STA communication does not require protection of high throughput frames.

Mixed Mode: This mode provides a protection mechanism (spoofing, etc.) for legacy communications.

Legacy Mode: In this mode, the STA communicates as if it is a legacy station.

In managed mixed BSS and pure BSS, high throughput HT-STA uses pure mode. In unmanaged BSS, high throughput STAs use mixed mode. Legacy mode is used if HTAP is not detected.

In managed mixed mode, HTAP divides the time between high speed or high throughput communication and low speed or legacy communication. This division into separate time slots for high speed and low speed communication is accomplished by using a so-called network allocation vector (NAV), for example by transmitting a transmittable (CTS) frame or beacon that includes a contention free period. It will be appreciated that legacy stations and / or stations with high throughput may not transmit for a limited period of time without circuit competition.

In the basic service set of the wireless communication system, a lower band or communication channel is used to establish a communication link. For example, in IEEE standards 802.11a and 11g, 20 MHz wide communication channels are used within the 5 GHz and 2.5 ISM bands, respectively. In IEEE P802.11n, it is proposed that the basic set of services can operate in single channel mode (20 MHz bandwidth) or dual channel mode (40 MHz bandwidth). In dual channel mode the first channel is limited to the so-called control channel and the second channel is limited to the so-called expansion channel. The presence of legacy devices (eg 802.11a stations) in the control channel is allowed. However, if the presence of the legacy device is detected in the extension channel, the master station must select another communication channel.

2 shows an overview of a high throughput basic service set (H-BSS) of a communication system that extends the existing IEEE 802.11 specification. The illustrated H-BSS includes three STAs, a High-Throughput Access Point (HTAP) and two other High-Throughput Stations (HTSTA1, HTSTA2). The H-BSS may be, for example, a wireless communication system according to the proposal P802.11n operating in infrastructure mode The first high throughput station (HTSTA1) in the high throughput basic service set (H-BSS). Communicates with a high throughput access point (HTAP) via a first high throughput communication link 201. A second high throughput station (HTSTA2) communicates with a high throughput via a second high throughput communication link (202). Communicating with an Access Point (HTAP) A high throughput access point (HTAP) is coupled to a distribution system via a communication link 200.

3 illustrates an overview of a mixed basic service set (M-BSS) of a communication system according to the present invention. The illustrated M-BSS includes a high throughput access point (HTAP), a high throughput station (HT-STA), and a station that conforms to legacy communication standards (STA). Therefore, stations that follow the legacy communication standard can communicate only in low speed mode, while HTAP and HT-STA can communicate in both high speed mode and low speed mode. The HTAP and HT-STA communicate with each other on the communication link 301. The HTAP and the STA communicate with each other in a low speed mode on the communication link 302. The HTAP may communicate with other basic service sets through the communication link 300 and the distribution system.

In the known wireless communication system shown in FIG. 1, the M-BSS can operate in both single channel mode and dual channel mode. As described in connection with the system shown in FIG. 1, a known manner of facilitating high speed mode communication and slow mode communication when operating in dual channel mode controls low mode communication and the first channel or control channel conforming to legacy communication standards. Assign to communication of messages and broadcast messages. In known wireless communication systems, a second channel or extension channel is reserved for high speed mode communication only. If low speed legacy communication is detected in the extended channel, the HTAP should select a new communication channel in known wireless communication.

The system according to the invention allows low speed mode legacy communication in the control channel and the expansion channel. The system according to the invention operates in the following manner.

Before determining the operational mode of the basic service set (pure mode, managed mixed mode, or unmanaged mixed mode), the HTAP will scan the channel for the presence of a legacy station (STA). The HTAP will attempt to select the channel pair on which the minimum number of STAs operate. If the HTAP detects two adjacent channels without any STA, the HTAP will establish operation in either pure mode or mixed mode. If the HTAP does not detect two adjacent channels without the STA, the HTAP will attempt to select a channel pair (of two adjacent channels) that the STA is only in one channel. In this case, the HTAP will establish operation in managed mixed mode or unmanaged mixed mode. If only the HTAP detects a channel pair where the legacy station is in both channels, the HTAP will establish operation in managed mixed mode.

If the HTAP has selected two channels (control channel and extended channel) for communication and established operation of the base set of services in pure mode, mixed mode, or unmanaged mixed mode, one or more legacy stations may control or extend the control channel. It can happen to start operating on the channel. If the HTAP operates in one of these modes and detects the presence of a slow legacy station in the extension channel, the HTAP is switched to managed mixed mode. Alternatively, the HTAP may decide to switch to single channel mode if the traffic or communication generated by the legacy station increases.

As described above in the management mixed mode, the HTAP defines a time slot through which the legacy slow station can communicate and another time slot through which the high speed station can communicate. The method of protecting the transmission of HTSTA in dual channel mode is that HTAP transmits legacy transmit request (RTS: Request-To-Send) or transmittable (CTS: Clear-To-Send) frame at the same time or with specific offset on both channels. It is to make it. This method is described in European patent application 03104273.

In an alternative method used in another wireless communication system in the present invention, the HTAP transmits two legacy beacons in a control channel and an extension channel, respectively, at a predetermined predetermined offset relative to each other or simultaneously. This legacy beacon limits the contention-free period on two channels that can be used for fast mode communication by HTAP and HT-STA.

With reference to Fig. 4, the present invention will be explained in more detail. The HTAP controls the operation mode of the STA through the information element included in this beacon. In pure mode, the HTAP ignores any probe request sent by the legacy STA and ignores any legacy beacon sent by the overlapping co-channel legacy device. The HTAP transmits its beacon using an HT-Physical Channel Protocol Data Unit (PPDU) type that cannot be recognized by the legacy station. This beacon contains an HT management element that requires pure mode operation of that STA. Note that using pure mode in HTAP is only suitable for managed installations where legacy APs are not allowed to share the same channel as HTAP.

In mixed capable mode, the HTAP transmits its beacon using a legacy PPDU. This beacon contains an HT management element that indicates that this is HTAP. This stops other co-channel mixed capable APs from considering the AP as a legacy AP.

In a mixable BSS, the HT STA operates in pure mode except when communicating with the legacy STA using DLP (direct link protocol, also referred to as direct link setup (DLS)).

In the mixable mode, the AP may receive a connection and probe request from a legacy STA. This AP will respond to the legacy probe request with a legacy probe response. This AP will respond to the legacy connection request with a legacy connection response. This AP may choose to accept or reject the connection request. If the AP transmits a connection response with status = OK, this AP may enter either managed mode, unmanaged mode or 20 MHz based management mixed mode operation, which AP has any associated legacy STAs. Will stay in action for a while. This AP monitors the channel for the legacy co-channel BSS and, if a channel is detected, transitions to mixed mode or attempts to discover another channel.

In unmanaged mixed mode, the AP transmits its beacon using a legacy PPDU type. This beacon contains an HT management element that requests the mixed mode operation of the STA. STAs in an unmanaged mixed mode BSS may use legacy or HT transmissions.

In the 20 MHz based management mixed mode, the AP transmits its beacon using a legacy PPDU type. This beacon is transmitted on the control channel, but in order to reserve the extension channel, the AP can also transmit the beacon on the extension channel. Beacons in the extended channel may cause the legacy STA to attempt to connect, but HTAP may reject this connection or ignore these requests. This beacon contains an HT management element that requests the mixed mode operation of the STA.

As described above, the HT STA supports three possible modes of operation in the infrastructure system as shown in FIG. 2, namely legacy mode, mixed mode and pure mode.

In pure mode, there is no overlapping legacy STA. Protection of HT frames from legacy devices is not required.

In mixed mode, the HT STA operates in the presence of a legacy STA common channel on the control channel and / or the extension channel. These STAs may be part of the same BSS or may be associated with overlapping legacy BSSs. In mixed mode, it is required to use legacy protection mechanisms such as MAC layer protection, long NAV, TXOP or spoofing truncation. The spoofed NAV duration during spoofing is effectively set in the PHY header using the length and rate fields of the legacy SIGNAL field. This rate field declares the rate at which the packet is coded after the PHY header, and the length field declares the length of the packet in bytes (after the PHY header). When a legacy node receives this signal field, it begins to decode the remaining packets at a particular rate and continues to decode so until the end of the length / rate time. The spoofed NAV uses this property of this length and rate field so that the length / rate is equal to the intended NAV duration. Legacy nodes spoofed into these two fields are prevented from starting transmission during that period. Transmission protection in this manner can be achieved without requesting that the legacy node can receive MAC-PDU content.

A 40 MHz capable HT STA with licensed bandwidth settings of 20 and 40 MHz may be switched to 20 MHz mode to communicate with the 20 MHz HTSTA.

In the 20 MHz based management mixed mode, the 40 MHz capable HT STA may communicate in the 40 MHz mode for a 40 MHz period. If the 40MHz capable HT STA wants to communicate with the HT STA or legacy STA in the 20MHz mode, the 40MHz capable HT STA will communicate with the HT STA in the 20MHz mode in the 20MHz period.

In legacy mode, the HT STA operates as exactly one legacy device, except that this HT STA can switch from legacy mode to mixed mode or pure mode during scanning to detect HTAP.

The coexistence mechanism is now described, which operates in 20MHz mode and transitions to a 40MHz capable phase under the control of HTAP. Legacy STA and HTSTA may be connected in the BSS. The HT STA may be a 40 MHz capable HTSTA or a 20 MHz HTSTA. The legacy STA is connected with the HTAP on the control channel.

According to the present invention, superposition of a BSS including a legacy STA in a control channel and an extension channel in a 20 MHz based management mixed mode is allowed. Due to the 40MHz duration protection on both channels, the overlapping BSS is resistant. Before HTAP selects a control channel, an extended channel, and an operation mode, the HTAP may consider the performance benefits that may be possible using 20 MHz based mode operation. The HTAP specifically attempts to avoid overlapping 802.11e or 802.11b STAs on the extension channel. As described above in the 20 MHz based management mixed mode, the legacy STA and the HTSTA may coexist. Two types of STAs are 40MHz capable HTSTA in 20MHz based management mixed mode; It can coexist with legacy STA and 20 MHz HTSTA. The legacy STA may not receive the HT PPDU and may not interpret the MAC duration value. The 20 MHz HTSTA may not receive a 40 MHz mode HT PPDU and may not interpret its MAC duration value. In 20MHz-based management mode, HTAP provides legacy protection for legacy STAs and 20MHz HTSTAs.

Reference is now made to FIG. 4. The 40 MHz capable HTAP operates in a 20 MHz based management mixed mode. This HTAP divides the time into a 20 MHz period and a 40 MHz period as shown in FIG. In the 20 MHz period, this HTAP ensures that a NAV of 40 MHz mode operation is set in a 40 MHz capable HTSTA. In the 40 MHz period, the NAV of the legacy STA and the 20 MHz HTSTA is set.

This base period is the period during which operation is strictly on the 20 MHz control channel. To begin the 40 MHz period, the HTAP first reserves the control channel by setting the NAV of the legacy STA and the 20 MHz HTSTA to a legacy beacon frame (Bcn) or ICB frame. The transmission rate of the ICB frame is selected from the BSS base rate set. Due to the range of the Duration / ID field in the MAC header, the ICB frame cannot be used to start a 40 MHz period longer than 32767 ms. The HTAP then moves to the extension channel ch_b for its reserve. The extended channel ch_b is reserved by transmission of CTS-to-self or legacy beacon (Bcn) frames after the appropriate channel access is performed on the extended channel ch_b.

The beacon frame Bcn transmitted to reserve the control channel ch_a includes a channel extension indication information element. When a 40 MHz capable HTSTA associated with the HTAP receives a beacon frame (Bcn), the HTSTA extends its channel bandwidth to 40 MHz according to the information in the extended channel offset information element. The 40 MHz capable HTSTA operates in the same way when receiving an ICB (Channel Bandwidth Increase) control frame.

After completing setting the NAV in the extended channel ch_b, the HTAP resets the NAV of the 40 MHz capable HTSTA by transmitting a CF end frame. This initiates a 40 MHz period during which the HTSTA can communicate in 40 MHz mode.

To end the 40 MHz period, the HTAP first sets the NAV for 40 MHz mode operation in a 40 MHz capable HTSTA by sending a DCB (Channel Bandwidth Reduction) frame. The 40 MHz capable HTSTA switches back to the 20 MHz control channel (ch_a). The HTAP then resets the NAV in the extended channel ch_b by transmitting a CF end frame. The AP may reset the NAV in the control channel ch_a by the CF end frame, but this AP may also continue the CFP (line contention free period) that was set in the last beacon frame Bcn on the control channel ch_a. . At this point, the HTAP and all STAs operate on the control channel using a 20 MHz channel bandwidth. This process can be repeated periodically, for example with respect to the beacon interval. The superframe thus generated is divided into a phase for communicating on a 40 MHz channel and a phase for communicating on a 20 MHz channel. One cycle for this process is illustrated in FIG. 4.

A 40 MHz capable HTSTA attempting to access the channel for a 40 MHz period stops the backoff counter during 20 MHz operation and resumes the suspended back off for the next 40 MHz period, or initiates a new random backoff at the beginning of the 40 MHz period. Choose. Similarly, if the HTSTA is trying to access the channel for a 20 MHz period, this HTSTA stops the backoff counter for 40 MHz operation and resumes the suspended backoff for the next 20 MHz period, or this HTSTA is new at the beginning of the 20 MHz period. Select random backoff.

To begin the 40 MHz period, the HTAP transmits a legacy beacon frame (Bcn) or ICB frame on the control channel (ch_a) to obtain a control channel (ch_a) and a NAV of 20 MHz HTSTA with the legacy STA on this control channel (ch_a). Set the control access phase to block this channel by setting The duration field of the ICB frame or the contention free period (CFP) of the beacon can be set to cover the period of 40 MHz phase plus the transition period between 20 and 40 MHz operation.

The HTAP declares an "extension channel access timeout" value in its beacon and probe response frame to limit the maximum transition time to a 40 MHz period. When the HTAP transmits a beacon frame (Bcn) or ICB frame on the control channel (ch_a), the HTAP starts a timer with a duration of "extended channel access timeout" minus the duration of the beacon or ICB frame. The "extended channel access timeout" is the maximum time, after which the STA may receive the beacon or the CTS itself on the extended channel ch_b. One reason why the HTAP may not be able to transmit beacons or CTS itself frames within the "extended channel access timeout" time is that the extended channel ch_b may be a busy medium.

After setting the NAV in the control channel ch_a, the HTAP can switch to 40 MHz analog mode and 20 MHz digital mode and will listen to the control channel ch_a and the expansion channel ch_b. Since the control channel ch_a is assumed to have been reserved by the previous operation, this phase is mainly given to wait for the expansion channel ch_b to go idle. However, while waiting for the expansion channel ch_b to be idle, the control channel ch_a can be maintained without any operation and the STA which has not received the beacon Bcn or ICB frame on the control channel ch_a is reserved. Note that it may interfere with The purpose of mode transition to 40 MHz analog mode and 20 MHz digital mode is to omit the switching of the analog channel at the beginning of the transmit phase on the 40 MHz channel. If the extended channel ch_b is idle, the AP will transmit the CTS itself or the legacy beacon Bcn in the extended channel ch_b after a period of time PIFS in the idle state. The CTS itself or the beacon Bcn blocks the extension channel ch_b by setting the NAV of the legacy STA in the extension channel ch_b. The NAV covers the transition time between the 20 MHz period and the 40 MHz period and the intended duration of the 40 MHz period as shown at the bottom of FIG. 4.

If the "extended channel access timeout" timer expires in HTAP while attempting to transmit the CTS itself or beacon (Bcn), the HTAP may give up switching to the 40 MHz bandwidth and try again later. The HTAP further transmits a CF end frame in the 20 MHz control channel to reconfigure the NAV of the legacy STA in the control channel ch_a. Since the HTSTA has started the "extended channel access timeout" timer after receiving the first beacon or ICB frame on the control channel ch_a, it does not need to be notified by the HTAP about the expiration of this timer.

NAV setting in the extended channel ch_b occurs through the CTS itself or beacon Bcn. The CTS itself may provide less overhead, but in the extended channel ch_b, the beacon Bcn may avoid generating another BSS because other STAs may detect the presence of H-BSS. to be. Furthermore, the duration of the NAV that can be signaled by the CTS itself is limited. Therefore, it is required to set the NAV by the beacon frame Bcn for a long time. According to this analysis, it may be decided to transmit a beacon on the extension channel ch_b.

If the "extended channel access timeout" timer has not yet expired, the HTAP sends a CF termination signal in 40 MHz mode to the HTSTA that the 40 MHz channel is available. The CF end frame is transmitted at least "maximum 40 MHz analog switching time" after the end of the first beacon or ICB frame in the control channel ch_a. The "maximum 40 MHz analog switch time" is the maximum allowable time for the STA and HTAP to perform analog channel switch from 40 MHz to 20 MHz, or vice versa. The HTAP must wait at least "up to 40 MHz analog switch time" before starting the 40 MHz phase to consider the STA with the lowest possible switch time. If the "up to 40 MHz analog switch time" time has already expired after the end of the beacon (Bcn) or ICB frame on the control channel (ch_a), the HTAP is the SIFS-time after the CTS itself or beacon (Bcn) on the extended channel (ch_b). Send a CF end frame to.

After the 40 MHz frames are exchanged, the HTAP sets the NAV of the 40 MHz HTSTA until the intended end of the 20 MHz period by means of a DCB-frame (a decrease in bandwidth). The HTAP then frees the extension channel ch_b and the control channel ch_a for communication in the 20 MHz mode by transmitting CF end frames on both channels. The CF end frame in the control channel ch_a is not needed if the HTAP wants to continue the period without contention. The CF end frame in the control channel ch_a is not sent earlier than the "maximum 40 MHz analog switch time" after the CF end in the expansion channel ch_b. In the extended channel ch_b, the first CF end frame may be transmitted in 40 MHz analog mode and 20 MHz digital mode to avoid additional analog channel switching. After the first CF end frame, the HTAP switches to the control channel ch_a in 20 MHz analog mode and transmits a second CF end frame.

The ratio between the 40 MHz and 20 MHz periods should be adjusted according to the type of traffic and priority. Whether a frame is transmitted in a 40 MHz period or in a 20 MHz period is scheduled according to its traffic type.

It should be noted that in scenarios where there is a large interference between the control channel ch_a and the extension channel ch_b, the HTAP may choose to switch to another 40 MHz channel where time sharing with the legacy STA may not be required. The choice of channel affects the efficiency and performance of the 20MHz-based management mixed mode. While operating in a 20MHz-based mixed mode, monitoring the channel as well as the initial channel selection is necessary to combat state changes.

The 40 MHz capable HTSTA is allowed to operate in 20 MHz mode on the control channel ch_a or in 40 MHz mode on both channels ch_a and ch_b. Operation in the 20 MHz mode is not allowed in the extended channel ch_b.

The 40 MHz capable HTSTA stores the "extended channel access timeout" value contained in the beacon (Bcn) or probe response frame sent by the HTAP.

When the HTSTA receives a beacon (Bcn) or ICB frame with a set of channel extended indication information elements, this HTSTA starts an associated timer with a duration of the "extended channel access timeout" and the HTAP sends its NAV by the CF end frame. You can wait in 40MHz analog mode to reset. Furthermore, when receiving a beacon (Bcn) or ICB frame on the control channel (CH_a), a 40 MHz capable HTSTA is included in the CFP parameter set element in the beacon frame (Bcn) or in the duration / ID field of the ICB frame. Start a timer. If the HTSTA operates in the 20 MHz mode, the HTSTA moves to the 40 MHz analog mode by receiving a beacon Bcn or ICB frame on the control channel ch_a. The HTSTA switches to 40MHz analog mode within at least "up to 40MHz analog switch time" time.

If the "extended channel access timeout" timer expires before receiving the CTS itself or beacon (Bcn) on the extended channel, the 40 MHz capable HTSTA remains waiting. The HTSTA switches back to the 20 MHz mode in the control channel ch_a according to the operation mode of the HTAP.

When a 40 MHz capable HTSTA receives a CF end frame, the NAV for the 40 MHz channel is reset and this 40 MHz channel is then freed to access in 40 MHz mode. The 40 MHz capable HTSTA switches back to the 20 MHz mode on the control channel ch_a if the timer expires before receiving a DCB frame (a decrease in bandwidth) indicating the end of the 40 MHz period. By receiving a DCB frame from the HTAP on the 40 MHz channel, the 40 MHz capable HTSTA sets up the NAV for the 40 MHz channel. The HTSTA can switch back to 20 MHz mode if it wants to communicate in a 20 MHz period when receiving a DCB frame.

A 40 MHz capable HTSTA attempting to access the channel for a 40 MHz period stops the backoff counter during 20 MHz operation and then resumes the suspended back off for a 40 MHz period. Likewise, if the HTSTA attempts to access the channel for a 20 MHz period, the HTSTA stops the back off counter for 40 MHz operation and then resumes the suspended back off for the 20 MHz period.

During the operation of the legacy STA and the 20 MHz HT STA, the NAV of the legacy STA and the 20 MHz HT STA is determined by the beacon (Bcn) or ICB frame in the control channel (ch_a) or by the CTS itself or the beacon frame (Bcn) in the extended channel (ch_b). Is set. This NAV is reset when receiving a CF end frame on its operating channel.

The embodiments of the invention described herein are intended to be illustrative and are not intended to limit the scope thereof. Various modifications may be made to these embodiments by one skilled in the art without departing from the scope of the invention as defined in the appended claims.

For example, although the present invention has been discussed in connection with a wireless communication system using two channels, a control channel and an extended channel, the skilled person will have the same time to create a time slot for slow mode communication and another time slot for high speed communication. It will be clearly understood that the method can be used in a wireless communication system using three or more channels.

As noted above, the present invention is available to provide higher flexibility for communication between stations in a wireless communication system.

Claims (9)

A wireless communication system comprising a master station, a first additional station and a second additional station, the master station comprising a first high speed mode using the first channel and at least one second channel and the first channel or the second channel. Operable to communicate with the first and second additional stations in a second low speed mode of use, wherein the first additional station is operable to communicate in a first mode using at least one second channel with the first channel, In the wireless communication system, the second additional station is arranged to communicate in a second mode using the first channel or the second channel; The master station defines a plurality of first time slots for the first channel and a plurality of second time slots for the second channel to communicate in the first mode, and communicates in the second mode. Arranged to define a plurality of third time slots for the first channel and a plurality of fourth time slots for the second channel. The system of claim 1 wherein the plurality of first time slots and the plurality of second time slots coincide with each other. 2. The wireless communication system of claim 1, wherein the plurality of first time slots and the plurality of second time slots have an offset relative to each other. 4. The wireless communication system according to any one of claims 1 to 3, wherein the plurality of third time slots and the plurality of fourth time slots coincide with each other. 4. The wireless communication system according to any one of claims 1 to 3, wherein the plurality of third time slots and the plurality of fourth time slots have offsets relative to each other. The wireless communication system according to any one of claims 1 to 5, wherein the communication in the second mode conforms to IEEE standard 802.11a, IEEE standard 802.11b, or IEEE standard 802.11g. A wireless communication device for use as a master station in a wireless communication system, the wireless communication system further comprising a first additional station and a second additional station, the wireless communication device comprising a first channel and at least one second channel. Is arranged to communicate with the additional station in a first high speed mode using the wireless communication device, further configured to detect whether the second additional station transmits in a second low speed communication mode on the first channel or the second channel. In the wireless communication device, The communication device includes a plurality of first time slots for the first channel and a plurality of second channels for communicating in the first mode in response to the detection of a low speed mode transmission in the first or second channel. Further define a plurality of third time slots for the first channel and a plurality of fourth time slots for the second channel to define a second time slot of the second channel and to communicate in the second mode. A wireless communication device. 8. The device of claim 7, wherein the communication in the second mode is in accordance with IEEE Standard 802.11a, IEEE Standard 802.11b, or IEEE Standard 802.11g. 10. A method of communicating in a wireless communication system comprising a master station, a first additional station and a second additional station, the master station comprising a first high speed mode using the first channel and at least one second channel and the first channel; Communicate with the first and second additional stations in a second low speed mode using a second channel, wherein the first additional station communicates in a first mode using at least one second channel with the first channel; 2. The method of communicating in the wireless communication system, wherein the additional stations communicate in a second mode using the first channel or the second channel. The master station defines a plurality of first time slots for the first channel and a plurality of second time slots for the second channel to communicate in the first mode, and communicates in the second mode. Defining a plurality of third time slots for the first channel and a plurality of fourth time slots for the second channel.

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