HK1109971A - Method of selectively adjusting the configuration of an access point antenna to enhance mobile station coverage - Google Patents

Description

Method for selectively adjusting access point antenna configuration to enhance mobile station coverage

Technical Field

The present invention relates generally to wireless communications, and more particularly to controlling antenna transmit modes in a wireless communication system.

Background

In a Wireless Local Area Network (WLAN) system, Distributed Coordination Function (DCF) is a basic access method for supporting asynchronous data transmission on a best effort basis. The DCF mode of WLAN system is used to support the contention service for promoting fair Access to all stations, and the Multiple Access mechanism for achieving this service is Carrier Sense Multiple Access with Collision Avoidance protocol (CSMA/CA). One way for a station to detect whether the channel is busy is by analyzing all detection packets sent by other WLAN users and detecting activity in the channel via the associated signal strength from other sources.

Referring to fig. 1, a wireless communication system 100 includes an Access Point (AP)105 that communicates with a plurality of wireless transmit/receive units (WTRUs)110, 115 and 120, i.e., stations, terminals. Two WTRUs within the coverage area of the AP105 but outside of the mutual coverage area are said to be concealed from each other, and if the two WTRUs are "concealed" from each other, the first WTRU is unable to detect the signal sent by the second WTRU, thereby defeating the ability of the two WTRUs to "collision avoidance" with each other.

The WLAN communication protocol uses a "request to send/clear to send (RTS/CTS)" handshake mechanism to combat collision effects, which can be used to avoid hidden terminal problems by the same client.

Referring to fig. 2, when RTS/CTS is used, a source WTRU, to transmit a frame, sends an RTS message 205 after a distributed interframe space (DIFS)210 indicates that the WTRU must transmit its packet duration expires. If the target WTRU successfully receives the RTS message 205, the target WTRU responds with a CTS message 220 after a short interframe space (SIFS)215 expires to confirm that the source WTRU allowed transmission and to reserve the data transmission channel. The source WTRU then sends a data packet 225 and the target WTRU then sends an acknowledgement message (ACK)230 to confirm successful receipt of the data packet 225. Using this handshake mechanism, all WTRUs may receive one of at least two messages (RTS or CTS) because the AP105 will transmit one of the two messages, and upon receipt of the RTS and/or CTS messages, the other WTRUs can set the Network Allocation Vector (NAV)225, 230 during their data transmissions, and then establish a Contention Window (CW)245 prior to accessing the channel. This mechanism effectively ensures that the medium is reserved for the source WTRU for the required duration, thus solving the hidden terminal problem.

Referring to fig. 3, DCF mode operation also supports fragmentation and reassembly of large Medium Access Control (MAC) protocol data units (MPDUs). When the size of an MPDU exceeds a configured threshold, it is broken into smaller fragments, and the receiver can acknowledge each fragment separately. Only the first segment is sent using the RTS/CTS mechanism, except that the duration range of the initial RTS/CTS message is only responsible for the first segment, and the duration information of the subsequent segments is determined by other WTRUs via the header of the preamble segment and an Acknowledgement (ACK) message.

As the demand for higher range and higher capacity of LAN systems increases, the use of adaptive antennas has attracted the attention of such systems, and is considered more attractive to APs than to all WTRUs due to the cost concerns associated with adaptive antenna technology.

Typically, smart antenna systems use an antenna array and form a directional wave to transmit and receive wireless signals. While the increased directivity helps increase coverage and signal-to-noise ratio while reducing interference to neighboring Base Station Systems (BSSs), it also impairs the ability of WTRUs to perform carrier sensing on a given wave when the AP105 transmits packets to WTRUs on other waves. In such systems, the use of the RTS/CTS handshake mechanism does not alleviate hidden terminal problems except for WTRUs transmitted by the AP105, since WTRUs in the radio wave have a low probability of detecting the RTS (in the case of AP105 being the source) or CTS (when the AP105 is the target) sent by the AP 105.

For example, fig. 1 shows WTRUs 110 and 115 in a radio 1 state, which transmit packets to AP105 or receive packets from AP 105. Assuming that the WTRU 120 is outside the coverage limits of the WTRU110 and is in a different wave (i.e., wave 5) than the waves in which the WTRUs 110 and 115 are located (i.e., wave 1), it is likely that the packets sent by the AP105 to the WTRUs 110 and 115 in wave 1 will not be detected, which is considered a hidden wave problem and would result in a data collision if the WTRU 120 had data to transmit. Similarly, the fact that the WTRU 120 is outside the coverage limits of the WTRU110 is also considered a hidden terminal problem, which also leads to the possibility of collisions. Therefore, using the RTS and CTS handshake mechanism does not alleviate hidden terminal or hidden radio problems because the WTRU 120 cannot detect the RTS or CTS message sent by the WTRU110 to the AP105 via radio 1, nor the RTS or CTS message sent by the AP105 to the WTRU110 or 115 via radio 1.

A method of successfully transmitting and receiving data packets without encountering hidden terminals or hidden radio problems is therefore highly desirable.

Disclosure of Invention

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

In one embodiment, the AP is configured to transmit at least one data packet to one or more WTRUs via at least one antenna. The AP configures the antenna into a wide beam configuration that covers the desired service area. The AP transmitting an RTS message to at least one of the WTRUs via the wide antenna configuration, the AP waiting to receive a CTS message from at least one of the WTRUs via the wide antenna configuration. The AP determines optimal antenna settings for communicating with a WTRU, the AP then configures the antenna to a narrow beam configuration and transmits the at least one data packet to the at least one WTRU, the AP waits to receive an acknowledgement message indicating that the data packet has been successfully received by the at least one WTRU, the AP then configures the antenna to a wideband configuration in response to receiving the acknowledgement message.

The system may be a WLAN system that provides services using CSMA/CA, and may perform transmission disablement procedures if the AP fails to receive the CTS control message, the AP may perform a MAC layer communication protocol to gain channel access prior to transmitting the RTS control message.

In another embodiment, the AP is configured to transmit data packet fragments. The AP configures the antenna into a wide beam configuration that covers the desired service area. The AP transmitting an RTS message to at least one of the WTRUs via the wide antenna configuration, the AP waiting to receive a CTS message from at least one of the WTRUs via the wide antenna configuration. The AP transmits a first portion of a data packet fragment to the at least one WTRU via the wide beam antenna configuration, the AP then configures the antenna into a narrow beam configuration, and transmits a second portion of the data packet fragment via the narrow beam antenna configuration.

After the AP transmits the second portion of the data packet fragment, the AP may configure the antenna to a wide beam configuration, the AP waits to receive an acknowledgement message indicating that the data packet fragment has been received by the at least one WTRU, and repeats the procedure if the AP receives the acknowledgement message and there are more data packet fragments pending.

If the AP does not receive the acknowledgment message, the system may perform a transmission failure procedure. The first portion of the data packet fragment may include a preamble, a PLCP header and a MAC header.

In another embodiment, the AP is configured to receive a data packet fragment. The AP receiving an RTS control message sent by at least one WTRU, the AP configuring the antenna to a wide beam configuration, the AP transmitting a CTS message to the at least one WTRU via the wide beam configuration, the AP configuring the antenna to a narrow beam configuration, the AP waiting to receive a data packet fragment via the narrow beam antenna configuration, the AP configuring the antenna to a wide beam configuration if the data packet fragment is successfully received, the AP sending an acknowledgement message to the at least one WTRU indicating that the data packet fragment is successfully received.

If the data packet fragment is not successfully received, the AP can configure the antenna to a wide beam configuration and the system can perform a reception failure procedure. If there are more data packet fragments waiting for processing, the process is repeated.

Drawings

The invention may be understood in more detail by reference to the following description of a preferred embodiment, given as an example, and the accompanying drawings, in which:

FIG. 1 illustrates a wireless communication system incorporating the present invention;

FIG. 2 illustrates transmissions using an RTS/CTS mechanism;

FIG. 3 illustrates transmissions using RTS/CTS mechanisms and segmentation;

fig. 4 is a flow chart illustrating steps of a method for performing AP transmissions in the system of fig. 1 using an RTS/CTS without fragmentation mechanism in accordance with the present invention;

fig. 5 is a flow chart illustrating steps of a method according to the present invention for performing AP transmissions in the system of fig. 1 using a segmented RTS/CTS mechanism; and

fig. 6 is a flow chart illustrating steps of a method according to the present invention for performing AP reception in the system of fig. 1 using RTS/CTS with/without segmentation.

Detailed Description

The preferred embodiments will now be described with reference to the drawings, wherein like reference numerals refer to like elements throughout.

Preferably, the methods and systems disclosed herein employ one or more wireless transmit/receive units (WTRUs), which include but are not limited to a User Equipment (UE), a mobile station, a fixed or mobile subscriber unit, a pager, or any other type of device capable of operating in a wireless environment.

The invention relates to a method in which an access point equipped with an adaptive antenna system, whose transmission mode is relaxed when RTS, CTS and ACK packets are transmitted and more directional modes are used when data packets are transmitted and/or received, in the case of using segmentation, only the initial part of the PPDU containing information of the duration is transmitted using the relaxed transmission mode.

It is assumed that the AP105 is equipped with an adaptive antenna system that can focus its transmission mode for transmission and/or reception to/from a particular area within the overall service area (i.e., cell). In addition, the AP105 may configure its adaptive antenna system to a wide transmission mode for transmission and/or reception, which covers the entire area served by the cell. The relaxation of the transmission mode can be achieved by various methods including, but not limited to, using a distinctive omni-directional antenna, or adjusting the beamforming valves to allow for homogeneous coverage in all directions. When receiving transmissions from a WTRU using its wide beam, the AP105 determines the best transmit mode to transmit to or receive from the WTRU, for example, the AP105 may use angle of arrival measurements of received packets to determine a narrow beam transmit mode.

In a default state, the antenna of the AP105 should be configured in a wide mode that covers the entire area of the serving cell. As such, an idle AP105 may detect and receive transmissions from any WTRU located within its coverage area.

When the AP105 has data to transmit to an ATRU and uses a narrow radio wave, the AP105 utilizes an RTS/CTS handshaking mechanism, the initial RTS packet is transmitted using a wide radio wave, upon receiving the CTS packet from the target WTRU, the AP105 configures its smart antenna and transmits the data packet using a narrow radio wave. Note that the AP105 may evaluate the optimal antenna parameters for transmission to the WTRU based on receiving a CTS packet from the WTRU.

Fig. 4 is a flow chart of a process 400 including steps for performing AP transmission using the RTS/CTS mechanism according to the present invention, wherein the transmission failure process is performed independently and is outside the scope of the present invention. Typically, the AP will reattempt transmission of the data packet according to the same steps of the first attempt until the maximum number of transmission attempts.

The RTS/CTS handshaking mechanism creates a significant burden on small data packets. As such, the use of RTS/CTS and beamforming may be determined based on the data packet size, e.g., based on a threshold. More precisely, small data packets may be transmitted directly using a wide electric wave, whereas large data packets may be transmitted according to the procedure described in fig. 4.

Referring to the process 400 of FIG. 4, the present invention solves the problem of hidden radio waves described above. In step 405, when an AP105 wants to send a packet to a WTRU110 or 115 on a particular beam, the AP105 configures its antenna to a wide beam default (step 410) and performs 802.11MAC layer protocol for channel access (step 415). The AP105 transmits an RTS control message to the WTRU using a wide transmit mode (step 420) to ensure that every user in the cell can detect. Each user in the cell is informed of the duration of the channel reservation, which is indicated by the RTS control message. This avoids collisions between the WTRU 120 located outside the radio wave and the target WTRU110 or 115 located inside the radio wave.

Still referring to fig. 4, in step 425, the AP105 waits to receive a CTS control message from the at least one WTRU via the wide beam antenna in response to the RTS control message. If the AP105 does not receive the CTS message, a transmission failure procedure is performed (step 430). If a CTS message is received, the AP105 determines the optimal antenna settings for communicating with the WTRU (step 435). The AP105 then configures the antenna to a narrow beam configuration (step 440) and transmits the data packet to the WTRU (step 445). In step 450, the AP105 waits to receive an ACK message indicating that the data packet was successfully received by the WTRU. If the AP105 does not receive an ACK message, a transmission failure procedure is performed (step 430). If an ACK message is received, the AP105 configures the antenna back to the wide beam configuration in step 455.

If data packet fragments are used, the RTS/CTS control packet provides duration information only in the first fragment. The duration information of the succeeding packet is transmitted in the MAC header of the preamble segment and its ACK. Upon receiving the CTS message from the target WTRU, the AP105 uses the beamforming capabilities of its smart antenna to transmit the remainder of the packet, reducing interference to neighboring cells and improving its transmission range.

Fig. 5 is a flow chart of a process 500 including steps for performing AP transmission using RTS/CTS mechanisms and fragments in accordance with the present invention. As described above, RTS packets are transmitted using wide waves, however, when using fragments, the AP105 transmits the preamble, Physical Layer Convergence Protocol (PLCP) header and MAC header of a data packet (i.e., fragment) using the wide waves, and the remainder of each fragment is transmitted using narrow waves.

When the AP105 is ready to send packets to the WTRU110 or 115 on a particular beam in step 505, the AP105 configures its antenna to a wide beam default (step 510) and performs 802.11MAC layer protocol for channel access (step 515). The AP105 transmits an RTS control message to the WTRU using a wide transmit mode (step 520) to ensure that each user in the cell is detectable. In step 525, the AP105 waits to receive a CTS control message from the WTRU via the wide beam antenna configuration in response to the RTS control message. If the CTS message is not received, a transmission failure procedure is performed (step 530).

If the CTS message is received, the AP105 transmits a preamble, physical layer integration protocol (PLCP) header and MAC header of a data packet (i.e., fragment) in a wide beam mode (step 535). The AP105 then determines the optimal antenna settings for communicating with the WTRU (step 540). In step 545, the AP105 configures the antenna for a narrow beam (i.e., concentrated) transmission, and then in step 550, the AP105 transmits the remainder of the segment. In step 555, the AP105 sets the antenna configuration back to the preset (wide wave) configuration.

In step 560, the AP105 waits to receive a CTS control message from at least one WTRU via the wide beam antenna configuration, determining whether an ACK message was received by the WTRU. If an ACK message is not received, a transmission failure procedure is performed (step 530). If an ACK message is received, it is determined whether there are more fragments to transmit (step 565), and if there is at least one additional fragment waiting to be transmitted, the process 500 returns to step 535, whereby the AP105 transmits the preamble, Physical Layer Convergence Protocol (PLCP) header and MAC header of a data packet (i.e., fragment) in a wide beam mode.

An AP105 may also use its adaptive antenna to receive data packets from a WTRU. In this case, the AP105 need only concentrate its antennas when receiving data packets. The AP105 transmits the CTS packet using a wide radio wave and, if necessary, transmits the ACK packet.

Fig. 6 is a flow chart of a process 600 including steps for performing AP reception with/without data packet fragmentation in accordance with the present invention. As shown in fig. 1, if the WTRU110 has data to send to the AP105, it sends an RTS message to reserve the channel for a packet transmission duration. Because the WTRU 120 is out of range of the WTRU110 (blind channel), the WTRU 120 will not be able to detect the RTS message sent by the WTRU 110. However, by performing the steps of fig. 6, the CTS packet is transmitted using a wide radio, so the AP105 can ensure that the WTRU 120 receives the CTS packet, causing the WTRU 120 to set its NAV for the data packet transmission duration, which is then reserved for the WTRU110 to transmit the data packet.

Still referring to fig. 6, an idle AP105 receives an RTS or other message indicating that a data packet is waiting to be sent to the target address of the AP105 (step 605). In step 610, the AP105 determines the optimal antenna settings for communicating with the WTRU. In step 615, it is determined whether an RTS message has been received. If it is determined in step 615 that an RTS frame has been received, the AP105 transmits a CTS control message using a wide beam (step 620), and then configures the antenna to be a narrow beam (i.e., focused) to receive data packets (step 625). If it is determined in step 615 that the RTS was not received, the AP105 then sends an ACK using a wide beam antenna configuration if the packet has been successfully received.

In step 630, it is determined whether a packet has been successfully received by the AP 105. If the packet is not successfully received, the AP105 configures the antenna to a wide beam (step 635) and performs a reception failure procedure (step 640). If the packet is successfully received, the AP105 configures the antenna to be 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 more segments waiting to be transmitted, and if there is at least one additional segment waiting to be transmitted, the process 600 returns to step 625, whereby the AP105 configures the antenna to receive as a narrow beam (i.e., concentrated).

While the present invention has been particularly shown and described with reference to preferred embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the scope of the invention.

Claims (18)

1. A method in a wireless communication system including a plurality of wtrus and an ap configured to transmit at least one data packet via at least one antenna to one or more of the plurality of wtrus, the method comprising:

(a) the ap configuring the antenna to a wide beam configuration that covers a desired service area;

(b) the ap transmitting a request-to-send control message to at least one of the wtrus via the wide beam antenna configuration;

(c) the ap waiting to receive a cts control message from the at least one wtru via the wide beam antenna configuration;

(d) the ap configuring the antenna to a narrow beam configuration;

(e) the ap transmitting the at least one data packet to the at least one wtru via the narrow beam antenna configuration;

(f) the ap waiting to receive an acknowledgement message indicating that the data packet was successfully received by the at least one wtru; and

(g) the ap configures the antenna to the wide beam configuration in response to receiving the acknowledgment message.

2. The method of claim 1 wherein the system is a wireless local area network system.

3. The method of claim 2 wherein the system provides services using a carrier sense multiple access collision avoidance protocol.

4. The method of claim 1 wherein the system performs a transmission failure procedure if the ap does not receive the cts control message.

5. The method of claim 1, further comprising:

(h) the ap performs a mac layer protocol for channel access prior to transmitting the request-to-send control message.

6. A method in a wireless communication system including a plurality of wtrus and an ap configured to transmit a data packet fragment to one or more of the plurality of wtrus via at least one antenna, the method comprising:

(a) the ap configuring the antenna to a wide beam configuration that covers a desired service area;

(b) the ap transmitting a request-to-send control message to at least one of the wtrus via the wide beam antenna configuration;

(c) the ap waiting to receive a cts control message from the at least one wtru via the wide beam antenna configuration;

(d) the ap transmitting a first portion of a data packet fragment to the at least one wtru via the wide beam configuration;

(e) the ap configuring the antenna to a narrow beam configuration; and

(e) the ap transmits a second portion of the data packet fragment via the narrow beam configuration.

7. The method of claim 6 wherein the system is a wireless local area network system.

8. The method of claim 7 wherein the system provides services using a carrier sense multiple access collision avoidance protocol.

9. The method according to claim 6, wherein if said ap does not receive said cts control message, said system performs a transmission failure procedure.

10. The method of claim 6, further comprising:

(g) the ap performs a mac layer protocol for channel access prior to transmitting the request-to-send control message.

11. The method of claim 6, further comprising:

(g) after the ap transmits the second portion of the data packet fragment, the ap configuring the antenna to a wide beam configuration;

(h) the ap waiting to receive an acknowledgement message indicating that the data packet fragment was received by the at least one wtru; and

(i) if the AP receives the acknowledgment message and there are more data packet fragments waiting to be processed, then steps (d) - (h) are repeated.

12. The method according to claim 11, wherein if the ap does not receive the acknowledgment message, the system performs a transmission failure procedure.

13. The method of claim 6 wherein the first portion of the data packet fragment comprises a preamble, a PHY layer integrated protocol header and a MAC layer.

14. A method in a wireless communication system including a plurality of wtrus and an ap configured to receive via at least one antenna data packet fragments from one or more of the plurality of wtrus, the method comprising:

(a) the ap receiving a request-to-send control message from at least one of the wtrus;

(b) the ap configuring the antenna to a wide beam antenna configuration;

(c) the ap transmitting a clear-to-send control message to the at least one wtru via the wide beam antenna configuration;

(d) the ap configuring the antenna to a narrow beam configuration;

(e) the ap waiting to receive a data packet fragment via the narrow beam antenna configuration;

(f) if the data packet fragment is successfully received, the access point configuring the antenna to a wide beam configuration; and

(g) the ap sends an acknowledgement message to the at least one wtru indicating successful reception of the data packet fragment.

15. The method of claim 14 wherein the system is a wireless local area network system.

16. The method of claim 15 wherein the system provides services using a carrier sense multiple access collision avoidance protocol.

17. The method of claim 14, further comprising:

(h) if the data packet fragment is not successfully received, the AP configuring the antenna to a wide beam configuration; and

(i) the system executes a reception failure procedure.

18. The method of claim 14, further comprising:

(h) if there are more data packet fragments waiting to be processed, repeating steps (d) - (g).