CN100344120C - Method of transmittng down data from insertion site in radio local network - Google Patents

Abstract

The invention discloses a method for an access point in a wireless local area network to use a fixed beam smart antenna to send downlink data, including predetermining and storing the position of a terminal; the access point sends an inquiry message using the beam covering the terminal according to the position information; The access point judges whether a response message from the terminal is received within the preset time, if so, the access point uses the beam to send downlink data, otherwise the access point determines the current location of the terminal, and uses the beam to cover the beam according to the current location information. The beam at the terminal's current location sends downlink data. Using the present invention effectively solves the difficulty of processing downlink data existing when the fixed beam smart antenna is installed on the access point at present, which is conducive to the further application of the smart antenna in the wireless local area network, thereby improving the coverage of the wireless local area network. Expanded the working capacity of the wireless LAN.

Description

A method for sending downlink data from an access point in a wireless local area network

technical field

The invention relates to a smart antenna technology of a wireless local area network, in particular to a method for an access point in a wireless local area network to use a fixed beam smart antenna to send downlink data.

Background technique

Wireless local area network is a kind of local area network that follows the International Institute of Electrical and Electronics Engineers (IEEE) 802.11 protocol and uses electromagnetic waves as the transmission medium. The IEEE 802.11 protocol includes two physical layer standards: 802.11a and 802.11b. Their working frequency bands are 2.4G and 5G respectively, and the highest supported physical interface rates are 11Mbps and 54Mbps respectively. 802.11a and 802.11b use the same media access control protocol (MAC).

A wireless LAN is mainly composed of a terminal and an access point inserted into a wireless LAN card. The terminal can form a peer-to-peer (Adhoc) mode without a central point, and can also form an infrastructure (Infrastructure) mode in which a central point forwards with an access point, and interconnect with a wired network through an access point. Figure 1 shows a basic Basic structure of wireless LAN in facility mode. In this configuration, the access point communicates with the terminal using an omni-directional antenna.

WLAN was originally designed for indoor and small-scale application environments, so the coverage area is small and the anti-interference ability is weak. At present, access points and terminals generally use omnidirectional antennas. Under the specified transmission power, the indoor coverage can only be about 30 meters, and the outdoor coverage is about 100 meters. Smaller coverage and weaker anti-interference limit the further development of WLAN.

In this case, in order to improve the coverage of WLAN, people consider adopting advanced smart antenna technology. Smart antennas were initially used in radar, sonar and military communications. Figure 2 shows the principle of smart antenna technology. The basic principle is to achieve directional beams in space by weighting multiple antennas. And by adjusting the weighted value, the beam of the antenna array can be dynamically adjusted to adapt to the change of the signal environment and obtain a better wireless transmission effect. After adopting the smart antenna, the system coverage capability can be improved, and the requirements for the transmitting power amplifier can be reduced at the same time.

Current smart antennas can be divided into two categories: fixed beam smart antennas and adaptive smart antennas. The fixed-beam smart antenna uses the antenna array to form multiple fixed beams, and selects the beam with the largest enhanced signal for receiving and transmitting; while the adaptive smart antenna can adjust the antenna pattern according to noise, interference, multipath and mobile user distribution, and can be in the expected While there is a large gain in the signal direction, a spatial beam zero point is formed in the direction of strong interference, thereby improving the signal quality. Adaptive smart antennas can achieve better results, but the implementation is more complicated. Although the fixed beam smart antenna is not optimal, it is relatively simple to implement.

The existing scheme of combining wireless local area network and smart antenna generally installs the smart antenna on the terminal side, but due to the limitation of the current technical level, the cost of implementing the smart antenna on the terminal side is high, the product is not easy to promote, and the terminal installed with the smart antenna is generally bulky Huge, very inconvenient for users to use. In order to overcome this shortcoming, people thought of installing the smart antenna on one side of the access point. Since the access point is shared by multiple users, the cost allocated to a single user does not increase much, and the access point is relatively large, which does not have any impact on user use. Therefore, it is more reasonable to use smart antennas for access points.

But to install the smart antenna on the side of the access point, there are currently the following difficulties:

1. Broadcast data is difficult to process

Because the smart antenna can only cover part of the surrounding area at a certain moment, but cannot cover all terminals in the wireless local area network. Therefore, the broadcast information that all terminals must listen to cannot be processed according to the current protocol. In the wireless local area network, the beacon frame (Beacon) is the most important broadcast information, and the access point and the terminal must broadcast and receive periodically respectively. Therefore, to install the smart antenna on the side of the access point, it is necessary to solve how to send the broadcast message problem.

2. The downlink data sent actively is difficult to process

For the data transmission initiated by the terminal, the access point can determine the location of the terminal according to the signal sent by the terminal, so as to determine the beam for sending downlink data. However, for data transmission initiated by the access point, it is difficult to deal with since there is no reference signal such as the terminal location that can be used to help select the beam.

3. The point coordination function is difficult to handle

In the media access control protocol of the wireless local area network, the access point has a point coordination function. In this working mode, all terminals cannot actively send data, but the access point sequentially sends a CF_Poll frame for polling the terminals to the terminals. The terminal receiving CF_Poll can only start sending if there is data to send. CF_Poll also belongs to the downlink data actively sent by the access point, so it is also difficult to process. Moreover, when the point coordination function ends, the access point will send a broadcast frame CF_End indicating the end of the contention-free phase to announce the end of the point coordination function to all terminals, and as described above, this broadcast data is also difficult to process.

Contents of the invention

In view of this, the purpose of the present invention is to provide a method for an access point in a wireless local area network to send downlink data using a fixed beam smart antenna, so as to solve the current problem that the downlink data actively sent by the access point is difficult to process.

Above-mentioned purpose of the present invention is solved by following technical scheme:

A method for sending downlink data by an access point in a wireless local area network using a fixed beam smart antenna, comprising the following steps:

a. Predetermine the location of the terminal;

b. The access point sends an inquiry message using the beam covering the terminal according to the location information of the terminal;

c. The access point judges whether a response message from the terminal is received within the preset time, if yes, the access point uses the beam to send downlink data, otherwise, execute step d;

d. The access point sends inquiry messages in other beams in turn until it receives a response message from the terminal, and determines the current location information of the terminal according to the response message, or the access point caches downlink data and marks the access The broadcast message that needs to send downlink data to the terminal is sent to all terminals until a response frame from the terminal is received, and the current location information of the terminal is determined according to the response frame; and the current location of the terminal is covered by using the current location information of the terminal beam to send downlink data.

The sequentially sending inquiry messages in other beams in step d includes: sequentially sending inquiry messages in other beams according to the principle of increasing distance from the current beam.

In the above method for sending downlink data, after sending the broadcast message indicating that the access point needs to send downlink data to the terminal to all terminals in step d, and before receiving the response frame from the terminal, it further includes: The terminal determines whether the access point needs to send downlink data to itself by analyzing the broadcast message, if not, the terminal does not respond; if so, the terminal sends a response frame indicating its location information to the access point. Here, the connection identifier of the terminal in the service indication mapping information may be set to mark that the access point needs to send downlink data to the terminal, and the service indication mapping information may be attached to the broadcast message for transmission. The broadcast message here may be a beacon frame.

In the above method for sending downlink data, the position information of the terminal is indicated by using the number of the beam covering the terminal.

In the above method for sending downlink data, in step a, the location of the terminal can be determined by reading the location information of the terminal stored in the access point. Here, the access point can determine and store the initial location information of the terminal according to the connection request message sent by the terminal to the access point; each time the access point performs data communication with the terminal, it uses the current location of the terminal to update the stored location of the terminal information.

It can be seen from the technical solution of the present invention that the wireless local area network first stores the location information of the terminal, and when it needs to send downlink data to the terminal, it first uses the location information to send an inquiry frame using the corresponding beam, and if the terminal responds, it uses the beam to send an inquiry frame. For downlink data, if there is no response from the terminal within the specified time, an inquiry frame will be sent on other beams, and the location information of the terminal will be determined according to the response frame returned by the terminal, and then the downlink data will be sent to the terminal using the location information. Or when no response from the terminal is received within the specified time, the AP considers the terminal to be in power-saving mode, buffers the downlink data, and sets the connection identifier (AID) corresponding to the user in the TIM. Since each beacon frame contains a TIM, the terminal can find its own buffer data by parsing the beacon frame, and then send the PS_Poll frame to the access point, and the access point can determine the terminal through the PS_Poll frame from the terminal location information, and then use the location information to send downlink data to the terminal. In this way, by pre-storing the location information of the terminal, sending an inquiry frame to the terminal, and determining the actual location of the terminal through the terminal response, the downlink data can be sent to the terminal with certainty according to the location information. The problem that the downlink data sent actively is difficult to handle.

Since the CF_Poll frame sent in the point coordination function is essentially a downlink data, it can be sent using the first scheme of the present invention, so the present invention also partially solves the problem that the current point coordination function is difficult to handle.

The technical solution proposed in the applicant's patent application for the method of sending broadcast messages by access points in wireless local area networks can successfully solve the existing problems of difficult processing of broadcast messages and the difficulty of processing CF_End frames in the point coordination function Therefore, in combination with the present invention, the three major problems in the prior art can be completely solved, and the obstacles are cleared for installing the fixed-beam smart antenna on the access point in the wireless local area network and normal operation.

Therefore, it is possible to install fixed-beam smart antennas on the side of the access point in the wireless local area network. Compared with the use of omnidirectional antennas, the coverage of the wireless local area network is expanded, and the disadvantages of high cost and large size of the terminal are avoided. . With this method, only the MAC layer of the access point needs to be modified appropriately, while the MAC layer of the terminal does not need any modification, so it is easy to implement.

Description of drawings

FIG. 1 is a schematic diagram of an access point communicating with a terminal using an omnidirectional antenna in the prior art;

Fig. 2 is a schematic diagram of the working principle of the smart antenna in the prior art;

3 is a schematic diagram of the access point of the present invention using a fixed beam smart antenna to communicate with a terminal;

FIG. 4 is a schematic diagram of a basic working mode of a smart antenna;

Fig. 5 is a timing diagram of the first method for sending a beacon frame in the present invention;

FIG. 6 is a schematic diagram of a timing sequence of a second method for sending a beacon frame in the present invention;

FIG. 7 is a schematic timing diagram of a first method for sending downlink data in the present invention;

FIG. 8 is a schematic diagram of the sequence of the first method for sending a CF_Poll message in the present invention.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

In a WLAN system where fixed-beam smart antennas are installed on APs, terminals still use existing omnidirectional antennas, and APs use fixed-beam smart antennas to communicate with terminals. As can be seen in Figure 3, each A terminal is located within the coverage of the fixed beam of the fixed beam smart antenna, and the AP communicates with the terminal through the beam where the terminal is located. The fixed beams of the fixed beam smart antenna can be divided in a 360-degree range according to the actual situation, and all the fixed beams can be combined to cover the entire wireless LAN area.

According to the working principle of the fixed-beam smart antenna, the fixed-beam smart antenna can only cover part of the area at a certain moment when sending data, and can cover the entire area at one moment when receiving data. The basic working process of the AP is: when receiving data, receive from multiple beams at the same time, and select the beam with the best signal quality to receive; 1 covers the area that beam 1 can reach, and at the second moment, beam 2 covers the area that beam 2 can reach, and this cycle repeats, that is, the entire surrounding area can be covered. This process is shown in Figure 4. In Figure 4, there are two terminals that need to communicate with the AP, and the AP will cover the two terminals at different times during the fast handover process, so that the AP can send messages to the terminals.

The following describes the method for the AP to send broadcast messages and downlink data to the terminal.

First, take the beacon frame as an example to illustrate how the AP sends broadcast messages to all terminals. As mentioned in the prior art section, the beacon frame is a very important broadcast message in the wireless local area network, and the AP needs to periodically send the beacon frame to all terminals. However, since the AP can only cover part of the area at a certain moment when polling between fixed beams, in order not to affect the use of the terminal, it is necessary to modify the sending mode of the beacon frame in the case of an omnidirectional antenna. Three methods for an AP to send a broadcast message by using a fixed-beam smart antenna are proposed below, all of which are described by taking a beacon frame as an example.

Method 1 for sending broadcast messages:

FIG. 5 shows a schematic diagram of a timing sequence of a first method in which an AP uses a smart antenna with four fixed beams to send a beacon frame. As shown in Figure 5, the AP still periodically sends beacon frames, but selects a different beam every time it sends. In Figure 5, the AP first selects beam 1 to send a beacon frame in the first round of scanning, and does not send it on other beams, and then selects beam 2 to send a beacon frame in the second round of scanning, and also does not send it on other beams , so that after four rounds of scanning, the terminals within the coverage of each beam will receive a beacon frame. Subsequently, the AP repeats the cycle in the same manner, and sends another beacon frame in four rounds of scanning after a predetermined period.

In this method, if the period of the AP sending the beacon frame is T, then for the terminal covered by each beam, the period of the actually received beacon frame is n×T, where n represents the total number of beams. Therefore, when using this method, it is necessary to modify the parameter aBeaconPeriod indicating the period of the AP sending the beacon frame to n×T in the protocol.

Method 2 for sending broadcast messages:

FIG. 6 shows a schematic diagram of a second method for sending beacon frames by an AP using a smart antenna with four fixed beams. As shown in Figure 6, when it is necessary to send a beacon frame, the AP does not select only one beam to send a beacon frame in a scanning round as in method 1, but simultaneously sends a beacon frame in all 4 beams in a scanning round. 4 beacon frames are sent in each beam. Then, after a time interval T, beacon frames are sent to all beams simultaneously in one scanning round. If this method is used, the period for each terminal to receive the beacon frame is still T, then there is no need to modify the setting of the parameter aBeaconPeriod, but it is necessary to modify the existing beacon frame sending method, because in the current wireless local area network only One beacon frame needs to be sent, and this method needs to send beacon frames corresponding to the fixed number of beams.

Method 3 for sending beacon frames:

In this method, an existing omnidirectional antenna can be added to the AP, and the beacon frame can be sent in the same way as in the prior art by using the omnidirectional antenna. Although using this method needs to add an omnidirectional antenna, this method is simpler to implement.

The above describes how to send broadcast messages to terminals in the present invention by taking the three methods of sending beacon frames as examples. It should be noted that for broadcast messages that require high timeliness, that is, broadcast messages that are required to be received by all terminals when they are sent, such as the beacon frame that marks the beginning of the PCF phase and the CF_End frame that marks the end of the PCF, then Only method 2 or method 3 introduced above can be used, because in method 1, the time interval for different terminals to receive broadcast messages is relatively large, which is not suitable for situations with high timeliness requirements.

The following describes how the AP sends downlink data to a specific terminal in the present invention. The present invention also proposes three methods for sending downlink data.

Method 1 for sending downlink data:

FIG. 7 shows a schematic diagram of a timing sequence for sending downlink data. In this method, the AP needs to first store the location information of each terminal, that is, the number of the beam covering the terminal. For example, beam 3 covers STA1, and the position of STA1 is recorded as beam 3; if beam 1 covers STA2, the position of STA2 is recorded as beam 1. When the terminal is turned on, it will send a connection request message to the access point, and the access point can determine the location information of the user through the connection request message and store the location information in the memory of the access point. initial location information. The process of storing location information here is a well-known technology for those skilled in the art, and will not be described in detail here. Each time the AP communicates with the terminal, it updates the location information with the current beam number of the terminal.

After recording the location information of a specific terminal, when the AP sends downlink data to the terminal, it first sends an RTS frame with the beam that records the location information of the terminal, that is, for STA1, first sends an RTS frame with beam 3 of the current location information of STA1 , if STA1 is now within the coverage of beam 3, it will return a CTS frame to the AP. The RTS frame and the CTS frame here are both control frames defined in the wireless local area network. The RTS frame is used by the data sender to send to the receiver before sending data, and the CTS is used to respond to the RTS frame. After receiving the CTS frame from the terminal, the AP can confirm that the terminal is within the coverage of beam 3, then use beam 3 to send downlink data, and receive the ACK frame returned by the terminal after the transmission is completed.

If STA1 is not within the coverage of beam 3 and the AP does not receive the CTS frame from STA1 within the specified time ACK_Timeout, it will send RTS frames in other beams in turn until it receives the CTS frame from STA1. The order in which the RTS frames are sent here is from near to far from the current beam. For example, there are 5 fixed beams and the current beam is beam 3. The RTS frames may be sent in the order of 3-2-4-1-5.

It should be noted that in the original protocol used by the wireless LAN, the MAC layer stipulates that the RTS/CTS mechanism should only be used when the length of the sent data is greater than a specific value. In this method, this setting is modified. For all downlink data regardless of Both long and short must use the RTS/CTS mechanism.

Method 2 for sending downlink data:

This method is the same as the first half of method 1 in sending downlink data, that is, the AP needs to store the location information of each terminal first. When the AP sends downlink data to a certain terminal, it first sends an RTS frame with the beam that records the location information of the terminal. If it receives the CTS frame returned by the terminal, it uses the current beam to send the downlink data, and receives the CTS frame returned by the terminal after the transmission is completed. ACK frame. If the terminal is not currently within the coverage of the current beam, and the AP does not receive a CTS frame from the terminal within the specified time ACK_Timeout, the following steps are different from method 1.

If the AP does not receive a CTS response within the specified time, it considers that the terminal is in power-saving mode, caches the user data, and sets the flag AID corresponding to the user in the service indication mapping information (TIM) indicating the user. Since the TIM is included in each beacon frame, a specific terminal will find its own cached data by parsing the beacon frame, and then the terminal sends a Ps_Poll frame to the AP. After the AP receives the Ps_Poll from a specific terminal, it can obtain the user location information, and then send the data to the terminal in the response frame.

It should be noted that this method is different from existing wireless local area network protocols. In existing protocols, the AP only caches data for terminals in power saving mode. Whether the terminal enters the power saving mode is identified in the data frame sent by the terminal. Only in the power saving mode, the terminal parses the TIM field in the beacon frame to determine whether there is cached data. However, this method requires the AP to cache data even if the downlink beam cannot be determined, and requires the terminal to parse the relevant information of the TIM no matter what state it is in. If there is a cache of the terminal, the terminal can obtain it by sending a Ps_Poll frame. This modification is obtained by modifying the corresponding setting of the MAC layer.

Method 3 for sending downlink data:

Add an omnidirectional antenna to the AP, and use the omnidirectional antenna to send an RTS frame to a specific terminal. After receiving the RTS frame, the terminal returns a CTS frame to the AP, and the AP determines the location of the terminal according to the CTS frame returned by the terminal, that is, The beam number of the terminal, and then use this beam to send downlink data to a specific terminal.

The above describes the method for the AP to send downlink data to a specific terminal. The point coordination function used by the wireless local area network is also mentioned in the prior art part, which actually includes two parts, that is, when the point coordination function starts, the AP needs to send a CF_Poll frame indicating the start of the point coordination function to a specific terminal, and in When the point coordination function ends, the AP needs to send a CF_End frame broadcast message indicating the end of the point coordination function to all terminals. Therefore, it can be seen that the use of the point coordination function is actually a combination of two processes in which the AP sends a broadcast message to all terminals and sends a downlink data message to a specific terminal.

The CF_Poll frame sent by the AP can be processed by method 1 of sending downlink data, that is, firstly, according to the recorded location information of a specific terminal, a corresponding beam is selected to send the CF_Poll frame. If there is no response from the terminal, the AP sends CF_Poll frames in each beam in turn. Here, the order of beam polling can be from near to far, until it receives a response from the terminal when a certain beam is sent, completes the data transmission, and sends the frame to the terminal. A CF_ACK frame, and then send the next CF_Poll frame to the next terminal in the same way, and Figure 8 is a schematic diagram of its timing. It can be seen from Figure 8 that the AP does not receive a response from the terminal in beam 1 and beam 2, but receives a response from STA1 in beam 3, thereby completing the data transmission with STA1.

In addition to method 1 for sending downlink data, the AP can also use method 3 for sending downlink data when sending CF_Poll frames. At this time, the AP uses an omnidirectional antenna to transmit omnidirectionally to all terminals at the beginning, and then determines the beam position of the terminal according to the response information of the terminal, and then directly uses the fixed beam of the terminal to receive data from the user.

Since the wireless local area network requires that all terminals can quickly receive the CF_Poll frame from the AP when using the point coordination function, it is not suitable to use the method 2 of sending downlink data. Because in method 2, if the response from the terminal is not received within the specified time, the data will be cached and the TIM will be sent through the beacon frame, so that the terminal will not be able to satisfy the system in terms of time after receiving the beacon frame and parsing the TIM. Requirements, so it is not suitable to use this method for point coordination function.

The CF_End frame is a broadcast frame, and its sending method is no different from sending a broadcast message. However, because the wireless LAN has high timeliness requirements for it, that is, when the AP sends the frame, all terminals must receive it, so method 1 of sending broadcast messages cannot be used, but only method 2 or method of sending broadcast messages can be used. Method 3, the specific sending method has been introduced in detail above, so it will not be repeated here.

The present invention proposes a series of solutions after the fixed beam smart antenna is installed on one side of the access point, and the corresponding technical problems can be solved by using any one of each method. It can be understood that not all the specific methods for sending data and receiving data that can be used are listed in the description, so the above is only a specific description of the spirit of the present invention, and is not intended to limit the present invention.

Claims (9)

1. access point uses fixed beam intelligent antenna to send the method for downlink data in the WLAN (wireless local area network), comprises the steps:

A. pre-determine the position of terminal;

B. access point uses the wave beam that covers this terminal to send an apply for information according to described positional information;

C. access point judges whether to receive the response message from this terminal in the time that sets in advance, if access point uses this wave beam to send downlink data, otherwise execution in step d;

D. access point sends apply for information successively in other wave beams, till the response message that receives from this terminal, determine the current location information of this terminal according to described response message, perhaps, access point buffer memory downlink data, and the mark access point need be sent to all terminals to the broadcast that this terminal sends downlink data, up to the response frame that receives from this terminal, determine current location information of terminal according to described response frame; And the wave beam that covers this terminal current location according to described current location information use sends downlink data.

2. the method for transmission downlink data according to claim 1 is characterized in that, sends apply for information described in the steps d successively and comprise in other wave beams: send apply for information successively in other wave beams according to the current wave beam of distance principle from the close-by examples to those far off.

3. the method for transmission downlink data according to claim 1 is characterized in that, when steps d adopted the method for described transmission apply for information, described downlink data was the CF_Poll frame that the expression point coordination function begins.

4. the method for transmission downlink data according to claim 1, it is characterized in that, after described in the steps d mark access point need being sent to all terminals to the broadcast that this terminal sends downlink data, and further comprised before the response frame that receives from this terminal: terminal determines by resolving described broadcast whether access point needs to send downlink data to oneself, if not, terminal does not respond; If described terminal sends the response frame of the own positional information of expression to access point.

5. the method for transmission downlink data according to claim 4, it is characterized in that, come the mark access point to send downlink data by connection identifier set in the steps d, and this traffic indication map information is attached in the broadcast sends to this terminal with this terminal in the traffic indication map information.

6. the method for transmission downlink data according to claim 5 is characterized in that, described broadcast is a beacon frame.

7. the method for transmission downlink data according to claim 1 is characterized in that, by using the wave beam numbering expression location information of terminals that covers terminal.

8. the method for transmission downlink data according to claim 1 is characterized in that, determines the position of terminal by reading the terminal positional information that is stored in access point in step a.

9. the method for transmission downlink data according to claim 8 is characterized in that, the connection request message that access point sends to access point according to terminal is determined the also initial position message of storage terminal; Access point carries out after the data communication with terminal each time, uses the current location of terminal to upgrade this location information of terminals of being stored.

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