KR20070022077A - Method of selectively adjusting the configuration of an access point antenna to enhance mobile station coverage - Google Patents

Abstract

A wireless communication system includes a plurality of transmit / receive units (WTRUs) and an access point (AP). This AP communicates with the WTRU via an antenna. In one embodiment, the AP configures an antenna for the wide beam configuration covering the desired service area and transmits a Request-To-Send (RTS) control message. When the AP receives a Clear-To-Send (CTS) control message from the one or more WTRUs, the AP determines an optimal antenna configuration and communicates with one WTRU. The AP configures an antenna for narrow beam configuration and transmits one or more data packets to one WTRU. When the AP receives an acknowledgment message indicating that the data packet was successfully received by the WTRU, the AP configures an antenna for the wide beam configuration. In another embodiment, the AP is configured to transmit and receive data packet fragments from WTRUs and thus form an antenna.

Wireless communication system

Description

METHODOLOGY OF SELECTIVELY ADJUSTING THE CONFIGURATION OF AN ACCESS POINT ANTENNA TO ENHANCE MOBILE STATION COVERAGE}

The present invention relates to the field of wireless communications. More particularly, the present invention relates to the control of antenna radiation patterns in a wireless communication system.

In a WLAN system, Distributed Coordination Function (DCF) is a basic access method used to support asynchronous data transmission on a best effort basis. The DCF mode of the WLAN system is used to support contention services that promote fair access to the channel for all stations. The multiple access scheme used to achieve these services is Carrier Sense Multiple Access with Collision Avoidance (CSMA / CA). One way for stations to detect if a channel is in use is to analyze all detected packets sent by other WLAN users and to detect the activity of that channel by relative signal strength from other sources.

Referring to FIG. 1, a wireless communication system 100 includes a plurality of wireless transmit / receive units (WTRUs) 110. 115, 120, that is, access points (APs) 105 that communicate with stations, terminals. It includes. Two WTRUs that are within the coverage area of the AP 105 but outside the coverage area of each other are referred to as being hidden from each other. If two WTRUs are "hidden" with respect to each other, the first WTRU cannot detect the signals transmitted by the second WTRU and thus "collision avoidance" of both WTRUs with respect to each other. Disable.

The WLAN protocol utilizes a Request-To-Send / Clear-To-Send (RTS) handshaking mechanism that resists the effects of collision. For the same reason, RTS / CTS can be used to avoid the problem of hidden terminals.

Referring to FIG. 2, when RTS / CTS is used, the source WTRU that wants to transmit a frame after expiration of Distributed Interframe Space (DIFS) 210 indicating the duration that the WTRU needs to transmit the packet. Send an RTS message 205. If the destination WTRU successfully receives the RTS message 205, the destination WTRU responds with a CTS message 220 that, after expiration of the Short Interframe Space (SIFS) 215, confirms that the source WTRU is allowed to transmit. And reserves a channel for data transmission. The source WTRU then sends a data packet 225, and the destination WTRU sends an acknowledgment (ACK) 230 message to confirm successful receipt of the data packet 225. Using this handshake mechanism, the AP 105 can transmit one of two messages (ie, RTS or CTS), so all WTRUs attempt to receive one or more of the two messages. Upon receipt of an RTS and / or CTS message. Other WTRUs may set their network allocation vector (NAV) 225, 230 for the duration of the data transmission. Thereafter, a CW (Contention Window) 245 is established before accessing that channel. This mechanism solves the problem of hidden terminals by visually ensuring that the source WTRU retains the medium for the desired duration.

Referring to FIG. 3, the DCF mode of operation also supports fragmentation / reassembly of large media access control (MAC) protocol data units (MPDUs). If the size of the MPDU exceeds the configurable threshold, the MPDU is divided into smaller fragments, with the receiver acknowledging each fragment individually. Only the first fragment is transmitted using the RTS / CTS mechanism. In addition, only the duration fields of the initial RTS / CTS messages describe the first fragment. Duration information for subsequent fragments is determined by other WTRUs from the header of the preceding fragments and ACKs.

Increasing demands on the range and capacity of WLAN systems use adaptive antennas associated with such systems. Because of the costs associated with adaptive antenna technologies, the use of an adaptive antenna is often perceived as more relevant for the AP than for the entire WTRUs.

Typically, smart antenna systems use an antenna array and form directional beams to send and receive wireless signals. This added directionality helps to increase coverage and signal-to-noise ratio while reducing interference to neighboring Base Stations System (BSS), which means that when the AP 105 transmits packets to WTRUs in other beams, Impair the ability of the WTRU in a given beam to perform sensing. In such a system, using the RTS / CTS handshaking mechanism, the RTS where WTRUs located in beams other than the beam transmitted by the AP 105 are transmitted by the AP 105 (when the AP 105 is a source). Or because the probability of detecting the CTS (when the AP 105 is the destination) is low, which does not alleviate the problem of hidden terminals.

For example, FIG. 1 illustrates a situation in which the WTRUs 110 and 115 in which beam 1 is located transmit packets to and receive packets from the AP 105. Assuming the WTRU 120 is located outside the coverage area of the WTRU 110 and in a beam (ie, beam 5) that is different from the beam (ie, beam 1) that includes the WTRUs 110 and 115, the AP 105 May not detect packets sent to the WTRUs 110, 115 in beam 1. This is referred to as the problem of hidden beams, and creates collisions when the WTRU 120 has data to transmit. In addition, the fact that the WTRU 120 is outside the coverage area of the WTRU 110 translates into the problem of hidden terminals, which also results in the occurrence of collision. Thus, the RTS and CTS handshakes are transmitted by the AP 105 to the WTRU 110 or 115 via the RTS or CTS message, or beam 1, by which the WTRU 120 is sent by the WTRU 110 to the AP 105. Since it is impossible to detect any of the transmitted RTS or CTS messages, it does not alleviate the problem of hidden terminals or the problem of hidden beams.

There is a great need for a method of successfully transmitting and receiving data packets without experiencing hidden terminal or hidden beam problems.

The present invention is a method used with a wireless communication system including a plurality of WTRUs and an AP.

In one embodiment, the AP is configured to transmit one or more data packets to one or more WTRUs through one or more antennas. This AP configures an antenna for a wide beam configuration covering the desired service area. The AP transmits an RTS message to one or more of the plurality of WTRUs via a wide beam antenna configuration. The AP listens for CTS messages from one or more WTRUs via a wide beam antenna configuration. This AP determines the optimal antenna settings to communicate with one WTRU. The AP then configures an antenna for narrow beam configuration and transmits one or more data packets to one or more WTRUs. The AP listens for an acknowledgment message indicating that this data packet was successfully received by one or more WTRUs. The AP then configures the antenna for the broadband configuration in response to receiving the acknowledgment message.

This system may be a WLAN system that provides services using CSMA / CA. The system may execute a transmission failure procedure if the AP does not receive a CTS control message. The AP may perform a MAC layer protocol to obtain channel access before transmitting the RTS control message.

In yet another embodiment, the AP is configured to transmit data packet fragments. The AP configures the antenna for the wide beam configuration covering the desired service area. The AP transmits an RTS message to one or more of the WTRUs via this wide beam antenna configuration. The AP listens for CTS messages from one or more WTRUs via a wide beam antenna configuration. The AP transmits the first portion of the data packet fragment to one or more WTRUs via a wide beam antenna configuration. The AP configures an antenna for the narrow beam configuration, and transmits a second portion of the data packet fragment via the narrow beam antenna configuration.

The AP configures the antenna for the wide beam configuration after this AP transmits the second portion of the data packet fragment. The AP listens for an acknowledgment message indicating receipt of a data packet fragment by one or more WTRUs. If the AP receives an acknowledgment message and there are more data packet fragments used for processing, the processing is repeated.

The system may execute a transmission failure procedure if the AP does not receive an acknowledgment message. The first portion of the data packet fragment is a preamble. It may include a PLCP header and a MAC header.

In yet another embodiment, the AP is configured to receive data packet fragments. The AP receives an RTS control message sent from one or more WTRUs. The AP configures the antenna for the wide beam configuration. The AP sends a CTS control message to one or more WTRUs via this wide beam antenna configuration. The AP configures the antenna for narrow beam configuration. The AP listens for data packet fragments through a narrow beam antenna configuration. The AP configures the antenna for the wide beam configuration when the data packet fragment is successfully received. The AP sends an acknowledgment message to the one or more WTRUs indicating that the data packet fragment was successfully received.

The AP may configure the antenna for the wide beam configuration when the data packet fragment has not been successfully received. The system may execute a reception failure procedure. If there are more data packet fragments available for processing, the processing is repeated.

The invention will be understood in more detail by way of example in conjunction with the following description and the accompanying drawings.

1 is a wireless communication system incorporating the present invention.

2 shows transmission using the RTS / CTS mechanism.

3 shows transmission using the RTS / CTS mechanism and fragment.

4 is a flow diagram illustrating method steps used to implement AP transmission in the system of FIG. 1 using the RTS / CTS mechanism without fragmentation in accordance with the present invention.

FIG. 5 is a flow diagram illustrating method steps used to implement AP transmission in the system of FIG. 1 using the RTS / CTS mechanism with fragmentation in accordance with the present invention.

6 is a flow diagram illustrating method steps used to perform AP reception with or without fragmentation in the system of FIG. 1 in accordance with the present invention.

Preferred embodiments are described with reference to the drawings, wherein like reference numerals refer to like elements throughout the specification.

Preferably, the methods and systems disclosed herein utilize one or more wireless transmit / receive units (WTRUs). Thereafter, the WTRU includes, but is not limited to, user equipment, mobile station, fixed subscriber unit or mobile subscriber unit, pager, or any other type of device operable in a wireless environment.

The present invention extends its radiation pattern when an access point in which an adaptive antenna system is installed transmits RTS, CTS and ACK packets, and uses more directional patterns when transmitting and / or receiving data packets. It is about. If fragmentation is used, only the initial portions of the PPDU containing the duration information are transmitted using the extended radiation pattern.

The AP 105 has an adaptive antenna system installed in the AP 105 that can focus transmission and / or reception radiation patterns on a specific area within the entire service area, i.e., a cell, or can focus transmission and / or reception radiation patterns from a cell. Assume In addition, the AP 105 may configure an adaptive antenna system for the wide radiating pattern for transmission and / or reception, covering the entire service area of the cell. Expansion of the radiation pattern can be achieved through a variety of methods, including using a separate omni-directional antenna or adjusting beamforming taps to allow uniform coverage in all directions, but are limited to these methods It doesn't work. The AP 105 uses the wide beam to determine an optimal radiation pattern for transmission to and reception from the WTRU while receiving transmissions from the WTRU. For example, the AP 105 may determine the narrow beam radiation pattern using the measurement of the angle of arrival of the received packet.

In the default state, the antenna of the AP 105 should be configured for a wide pattern that covers the entire area of the cell being serviced. As such, the idle AP 105 may detect and receive transmissions from any WTRU located within its coverage area.

If the AP 105 has data to transmit to the WTRU and a narrow beam is used, the AP 105 uses an RTS / CTS handshake mechanism. The initial RTS packet is transmitted using a wide beam. Upon receiving the CTS packet from the destination WTRU, the AP 105 configures the smart antenna and transmits the data packet using the narrow beam. The AP 105 may estimate optimal antenna parameters for transmission to the WTRU based on the CTS packet that was received from the WTRU.

4 is a flow diagram of a process 400 including method steps used to perform an AP transmission using the RTS / CTS mechanism in accordance with the present invention. The transmission failure procedure shown in this flowchart is implemented without departing from the scope of the present invention. Typically, the AP retries the transmission of the data packet following the same procedure as the initial attempt, up to the maximum number of transmission attempts.

The RTS / CTS handshake mechanism introduces significant overhead for very small data packets. As such, the use of RTS / CTS using beamforming may be determined based on the size of the data packet, ie based on the threshold. More specifically, small data packets can be transmitted directly using the wide beam while larger data packets can be transmitted according to the procedure described in FIG. 4.

Referring to process 400 of FIG. 4, the present invention solves the hidden beam problem described above. In step 405, if the AP 105 wishes to transmit a packet to either the WTRU 110 or the WTRU 115, which is located in one particular beam, the AP 105 may be antenna for the wide beam default. Configure (step 410) and execute the 802.11 MAC layer protocol for channel access (step 415). The AP 105 sends a RTS control message to the WTRU using a wide radiation pattern (step 420) to ensure that all users in the cell can detect the message. All users in that cell are notified of the duration that the channel is held for, which is indicated in the RTS control message. This avoids collisions between WTRUs 120 located outside the beam where the destination WTRUs 110 or 115 are located.

Referring back to FIG. 4, at step 425, the AP 105 waits to receive a CTS control message from one or more WTRUs via the wide beam antenna in response to the RTS control message. If the CTS message was not received by the AP 105, a transmission failure procedure is executed (step 430). Once the CTS message is received, the AP 105 determines the optimal antenna settings and communicates with the WTRU (step 435). The AP 105 then configures an antenna for narrow beam configuration (step 440) and transmits this data packet to the WTRU (step 445). At step 450, the AP 105 waits to receive an ACK message indicating that the data packet was successfully received by the WTRU. If this ACK message has not been received by the AP 105, then a transmission failure procedure is executed (step 430). If an ACK message is received, the AP 105 reconstructs the antenna for the wide beam configuration at step 455.

When fragmentation of the data packet is used, only RTS / CTS control packets provide duration information for the first fragment. Duration information for subsequent packets is carried in the MAC header of the preceding fragment and their ACK. After receiving the CTS message from the destination WTRU, the AP 105 uses the beamforming capability of the smart antenna to transmit the remainder of the packet, reduce interference to neighboring cells, and improve its transmission range. Let's do it.

5 is a flow diagram of a process 500 including method steps used to perform AP transmission using an RTS / CTS mechanism with fragmentation in accordance with the present invention. As in the previous case, the RTS packet is transmitted using a wide beam. However, when fragmentation is used, the AP 105 transmits a preamble, a physical layer convergence protocol (PLCP) header and a MAC header of a data packet (ie, fragment) using a wide beam. The remainder of each fragment is transmitted using a narrow beam.

In step 505, when the AP 105 is ready to send a packet to the WTRU 110 or the WTRU 115 located in one particular beam, the AP 105 configures the antenna for the wide beam default (step 510, and execute the 802.11 MAC layer protocol for channel access (step 515). The AP 105 uses the wide radiation pattern to send an RTS control message to the WTRU (step 520) to ensure that all users in the cell can detect the message. At step 525, the AP 105 waits to receive the CTS control message from the WTRU via the wide beam antenna configuration in response to the RTS control message. If no CTS message is received, then a transmission failure procedure is executed (step 530).

When the CTS message is received, the AP 105 transmits a preamble, a PLCP header, and a MAC header of the data packet (ie, fragment) in the wide beam pod (step 535). The AP 105 then determines the optimal antenna settings and communicates with the WTRU (step 540). At step 545, the AP 105 configures an antenna for narrow beam (ie, focused) transmission, and then, at step 550, the AP 105 transmits the remainder of the fragment. At step 555, the AP 105 reconfigures the antenna for the default (wide beam) configuration.

At step 560, the AP 105 waits to receive the CTS control message from the one or more WTRUs via the wide beam antenna configuration when a determination is made whether an ACK message has been received from the WTRU. If no ACK message is received, a transmission failure procedure is executed (step 530). If an ACK message is received, then a determination is made whether there are additional fragments to transmit (step 565). If there is one or more additional fragments to transmit, processing 500 returns to step 535 and the AP 105 transmits the preamble, PLCP header and MAC header of the data packet in the wide beam mode.

In addition, the AP 105 may use an adaptive antenna for the reception of data packets from the WTRU. In this case, the AP 105 focuses its antenna when it receives a data packet. The AP 105 uses the wide beam for transmission of the CTS packet and, if necessary, for transmission of the ACK packet.

6 is a flow diagram of a process 600 including method steps used to perform AP reception in the presence or absence of fragmentation of data packets according to the present invention. As shown in FIG. 1, when the WTRU 110 has data to send to the AP 105, the WTRU 110 sends an RTS message to retain the channel for the duration of the packet transmission. Because the WTRU 120 is out of range of the WTRU 110 (hidden terminal), the WTRU 120 does not detect the RTS message sent by the WTRU 110. However, by performing the method steps of FIG. 6, the CTS packet is transmitted using a wide beam. Thus, the AP 105 guarantees that the WTRU 120 receives the CTS packet, and causes the WTRU 120 to set its NAV to the duration of the data packet transmission. The channel is then reserved for the WTRU 110 to transmit its data packet.

Referring again to FIG. 6, the idle AP 105 receives an RTS or other message indicating that a data packet is waiting to be sent to the destination address of the AP 105 (step 605). At step 610, the AP 105 determines the optimal antenna settings and communicates with the WTRU. At step 615, a determination is made whether an RTS frame has been received. In step 615, if it is determined that the RTS frame has been received, the AP 105 transmits the CTS control message using the wide beam (step 620), and then configures an antenna for narrow beam (i.e., focused) reception of the data packet. Step 625. If it is determined in step 615 that the RTS message has not been received, the AP 105 continues to use the wide beam antenna configuration to transmit the ACK packet when the packet is successfully received.

At step 630, a determination is made whether the packet was successfully received by the AP 105. If the packet is not successfully received, the AP 105 configures an antenna for the wide beam (step 635) and executes a reception failure procedure (step 640). If the packet is successfully received, the AP 105 configures an antenna for the wide beam (step 645) and sends an ACK message to the WTRU (step 650). At step 655, a determination is made as to whether there are any more fragments to transmit. If there is one or more additional fragments to transmit, processing 600 returns to step 625 and the AP 105 configures an antenna for narrow beam (ie, focused) reception.

Although the present invention has been described in terms of the preferred embodiments, other modifications, which are within the scope of the invention outlined in the claims below, are apparent to those skilled in the art.

Claims (18)

In a wireless communication system including a plurality of transmit / receive units (WTRUs) and an access point (AP), the AP is configured to transmit one or more data packets to one or more of the plurality of WTRUs through one or more antennas, (a) configuring an antenna for a wide beam configuration in which the AP covers a desired service area; (b) the AP transmitting a Request-To-Send (RTS) control message to one or more of the plurality of WTRUs through the wide beam antenna configuration; (c) the AP waiting to receive a Clear-To-Send (CTS) control message from the one or more WTRUs through the wide beam antenna configuration; (d) the AP configuring an antenna for a narrow beam configuration; (e) the AP transmitting the one or more data packets to the one or more WTRUs via the narrow beam antenna configuration; (f) the AP waiting to receive an acknowledgment message indicating that the data packet was successfully received by the one or more WTRUs; And (g) configuring the antenna for the wide beam configuration in response to the AP receiving the acknowledgment message. The method of claim 1, wherein the system is a wireless local area network (WLAN) system. The method of claim 2, wherein the system provides a service using carrier sense multiple access with collision avoidance (CSMA / CA). 2. The method of claim 1, wherein the system executes a transmission failure procedure when the AP does not receive the CTS control message. 2. The method of claim 1, further comprising: (h) executing a media access control (MAC) layer protocol to obtain channel access before the AP transmits the RTS control message. In a wireless communication system including a plurality of transmit / receive units (WTRUs) and an access point (AP), the AP is configured to transmit data packet fragments to one or more of the plurality of WTRUs through one or more antennas, (a) configuring an antenna for a wide beam configuration in which the AP covers a desired service area; (b) the AP transmitting a Request-To-Send (RTS) control message to one or more of the plurality of WTRUs through the wide beam antenna configuration; (c) the AP waiting to receive a Clear-To-Send (CTS) control message from the one or more WTRUs through the wide beam antenna configuration; (d) the AP transmitting a first portion of a data packet fragment to the one or more WTRUs via the narrow beam antenna configuration; (e) the AP configuring an antenna for a narrow beam configuration; And (f) the AP transmitting a second portion of the data packet fragment via the narrow beam antenna configuration. The method of claim 6, wherein the system is a wireless local area network (WLAN) system. 8. The method of claim 7, wherein the system provides service using carrier sense multiple access with collision avoidance (CSMA / CA). 7. The method of claim 6, wherein the system executes a transmission failure procedure when the AP does not receive the CTS control message. 7. The method of claim 6, further comprising: (g) executing a media access control (MAC) layer protocol to obtain channel access before the AP transmits the RTS control message. 7. The method of claim 6, further comprising: (g) configuring an antenna for a wide beam configuration after the AP transmits a second portion of the data packet fragment; (h) the AP waiting to receive an acknowledgment message indicating receipt of the data packet fragment by the one or more WTRUs; And (i) the AP further receiving the acknowledgment message and repeating steps (d) to (h) if there are more data packet fragments available for processing. 12. The method of claim 11, wherein the system executes a transmission failure procedure when the AP does not receive the acknowledgment message. 7. The method of claim 6, wherein the first portion of the data packet fragment comprises a preamble, a physical layer convergence protocol (PLCP) header, and a media access control (MAC) header. In a wireless communication system including a plurality of transmit / receive units (WTRUs) and an access point (AP), the AP is configured to receive data packet fragments from one or more of the plurality of WTRUs through one or more antennas, (a) the AP receiving a RTS (Requset-To-Send) control message sent from one or more of the plurality of WTRUs; (b) the AP configuring an antenna for a wide beam configuration; (c) the AP transmitting a Clear-To-Send (CTS) control message to one or more WTRUs through the wide beam antenna configuration; (d) the AP configuring an antenna for a narrow beam configuration; (e) the AP waiting to receive a data packet fragment through the narrow beam antenna configuration; (f) configuring an antenna for a wide beam configuration when the AP successfully receives the data packet fragment; And (g) the AP sending an acknowledgment message to the one or more WTRUs indicating that the data packet fragment was successfully received. The method of claim 14, wherein the system is a wireless local area network (WLAN) system. 16. The method of claim 15, wherein the system provides service using carrier sense multiple access with collision avoidance (CSMA / CA). 15. The method of claim 14, further comprising: (h) the AP configuring an antenna for a wide beam configuration when the data packet fragment is not successfully received; And (i) the system executing a reception failure procedure. 15. The method of claim 14, further comprising (h) repeating steps (d) to (g) if there are more data packet fragments that can be used for processing.

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