KR20120035970A - Opportunistic concurrent transmission method of wireless network and wireless network system using per-station queue - Google Patents

Abstract

PURPOSE: A method of wireless network opportunistic concurrent transmission using a per-station queue and a system thereof are provided to perform opportunistic concurrent transmission when a signal has a sufficient SINR(Signal to Interference plus Noise Ratio) value while the other AP corresponding to an interference signal is being transmitted. CONSTITUTION: When a transmission target packet exists in a per-station queue, a system acquires information of a transmitting link through transmission from the other access point. The system identifies an SINR value of the link. When an identified SINR value is greater than a predetermined capture threshold value, the system schedules concurrent transmission of an available packet for concurrent transmission from stored packets in the per-station queue.

Description

Opportunistic Concurrent Transmission Method of Wireless Network and Wireless Network System using Per-station Queue}

The present invention relates to a method and system for opportunistic simultaneous transmission of a wireless network, and more particularly, to a method and system for opportunistic simultaneous transmission of a wireless network that can maximize the opportunity of simultaneous transmission by using individual queues.

Wireless Local Area Networks (WLANs) complying with the IEEE 802.11 standard have the powerful advantages of being cheap, easy to install, and fast. However, the explosive spread of wireless LANs causes a problem of using limited wireless resources more efficiently.

The IEEE 802.11 Distributed Coordination Function (DCF) has been used as a representative MAC protocol for wireless LANs because of its ease of implementation and distributed characteristics in most environments. DCF does not allow concurrent transmissions because it operates on a carrier sense multiple access / collision avoidance (CSMA / CA) basis. This is to prevent transmissions from failing due to interference or collision of simultaneously transmitted signals.

However, the use of the CSMA / CA method inevitably leads to a waste of limited radio resources in terms of spatial reuse. However, even if signals are transmitted simultaneously, successful reception may be achieved, not failure, depending on the packet delivery order and the relative signal strength. This is called a capture effect.

Conventional LAN cards have physical signal capture when the Intended signal arrives before the interference signal with sufficient signal to interference plus noise ratio (SINR) or within the preamble transmission time of the interference signal. Layer Capture) is enabled. In addition, the WLAN card using Atheros chipset with Message In Message (MIM) function adopts the advanced preamble detection technology, so that the preamble time of the interference signal if the intended signal has a sufficient SINR value (10dB). Since it can be captured even later, the capture probability is much greater.

This is illustrated in FIG. 1. FIG. 1 (a) shows a case of PHY capture, and FIG. 1 (b) shows capture when using a wireless LAN card implementing the MIM function.

As shown in (a) of FIG. 1, if an intended signal having a sufficient SINR of about 10 dB arrives before the preamble transmission of the interfering signal ends, the intended signal can be captured.

In contrast, in the case of implementing the MIM function, even if the intended signal arrives after the preamble transmission of the interference signal is completed, it can be captured.

US Pat. No. 5,987,033 is a prior art for maximizing the capture of a physical layer using such a MIM function. In US Patent No. 5,987,033, when an increase in energy above a certain level is detected during the reception of a message, a carrier is detected according to the increase in energy, and when a carrier is detected, a new message corresponding to the detected carrier is completed as soon as reception of a message currently being received is completed. Disclosed is a method for a receiver to begin retraining so as to receive.

The present invention has been made on the basis of the above technical background, to provide a simultaneous method and system for the simultaneous transmission of a wireless network that can efficiently use a limited radio resources by enabling simultaneous transmission in a wireless LAN system to the problem do.

Another object of the present invention is to provide a method and system for opportunistic simultaneous transmission of a wireless network that can maximize the opportunity of simultaneous transmission to more efficiently use radio resources.

The packet transmission method of the present invention for solving this problem is a packet transmission method of an access point existing in a wireless network system, two or more separate queues for storing packets to be transmitted to two or more client devices connected to the access point, respectively. Maintaining the packet; if there is a packet to be transmitted to the individual queue, intercepting transmission from another access point to obtain information of a link being transmitted from the other access point; signal to interference of the link and confirming a plus noise ratio) value, and when the identified SINR value is equal to or greater than a predetermined capture threshold value, scheduling to simultaneously transmit a packet that can be transmitted simultaneously among the packets stored in the individual queue.

Here, the SINR value may refer to an interference map, and the wireless network system includes a central controller connected to the access point and the other access point, and the interference map is provided by the central controller. Can be.

In addition, the simultaneous transmittable packet refers to a packet having an SINR value equal to or greater than the capture threshold.

According to another aspect of the present invention, a wireless network system includes a wireless network system including two or more access points, each of which includes two or more separate queues for storing packets to be transmitted to two or more client devices connected thereto. If there is a packet to be transmitted to the individual queue of any one of the access point, to intercept the transmission from another access point to obtain information of the link being transmitted from the other access point, the SINR of the link A signal to interference plus noise ratio value is checked, and when the identified SINR value is greater than or equal to a predetermined capture threshold value, the packet is scheduled to be simultaneously transmitted among packets stored in the individual queue.

According to another aspect of the present invention, an access point in a wireless network system is provided, wherein the access point includes two or more separate queues, each holding packets for transmission to two or more connected client devices, and transmitting to the individual queues. If there is a packet to be present, the transmission of the other access point is intercepted to obtain information on the link being transmitted from the other access point, and the SINR (Signal to Interference plus Noise Ratio) value of the link is checked. If the SINR value is equal to or greater than a predetermined capture threshold, the packet is scheduled to be transmitted at the same time among packets stored in the individual queue.

According to the present invention having the above configuration, even if there is transmission of another AP corresponding to the interference signal, in the case of a signal having a sufficient SINR value to perform simultaneous transmission in the opportunity to efficiently utilize the resources of the entire WLAN system Can be.

In addition, since each AP intercepts transmissions of other APs to determine simultaneous transmission, the AP operates in a distributed manner without a large computational load on the central processing unit, thereby making it easy to expand. In particular, the opportunistic simultaneous transmission method of the present invention can be implemented by changing only the AP without changing the client, and thus has an advantage of being gradually applied to the existing WLAN system.

In addition, each AP maintains a separate queue while maximizing simultaneous transmission, enabling more efficient use of total radio resources.

1 is a diagram illustrating a transmission schedule in which physical layer capture is performed.
2 is a view showing the operation of a wireless LAN system according to an embodiment of the present invention.
3 is a flowchart illustrating an opportunistic simultaneous transmission method according to an embodiment of the present invention from the perspective of one AP.
4 is a diagram illustrating an example of a frame schedule in a case where it is determined to perform simultaneous transmission in an opportunistic simultaneous transmission method according to an embodiment of the present invention and when it is not.
5 is a graph showing the predicted throughput of the conventional DCF and the embodiment of the present invention.
6 shows another example of a wireless LAN system to which an opportunistic simultaneous transmission method according to an embodiment of the present invention is applied.
7 illustrates a packet transmission process in the case of using a packet queue according to a conventional method.
8 illustrates a packet transmission process in the case of using a per-station queue according to an embodiment of the present invention.

Advantages and features of the present invention and methods for achieving them will be apparent with reference to the embodiments described below in detail with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in various forms, and only the present embodiments are intended to complete the disclosure of the present invention, and the general knowledge in the art to which the present invention pertains. It is provided to fully convey the scope of the invention to those skilled in the art, and the present invention is defined only by the scope of the claims. It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. In the present specification, the singular form includes plural forms unless otherwise specified in the specification. As used herein, “comprises” and / or “comprising” refers to the presence of one or more other components, steps, operations and / or elements. Or does not exclude additions.

2 is a diagram illustrating a wireless LAN system to which an opportunistic simultaneous transmission method according to an embodiment of the present invention is applied.

As shown in FIG. 2, a wireless LAN system according to an embodiment of the present invention includes a central controller 210, two access points (APs) (AP1; 221, AP2; 222), and a client connected to each AP. Device R1 231, R2; 232, R3; Meanwhile, for convenience of description, FIG. 2 shows two APs and three client devices connected thereto, but the number of APs and clients is not limited thereto.

In the figure, an arrow between the AP and the client indicates a transmission link, and a portion connected by a dotted line between the AP and the client indicates interference. The number in the square next to each transmission link indicates the strength (dB value) of the received signal as a result of simultaneous transmission at two APs. That is, the clients R1 and R2 are connected to the AP1, and the signal from the AP2 becomes an interference signal for the R1 and R2. In contrast, the client R3 is connected to the AP2, so that the signal from AP1 becomes an interference signal to R3. When simultaneous transmission is performed from AP1 and AP2, R1, R2, and R3 receive signals having strengths of 1 dB, 5 dB, and 13 dB, respectively.

AP1 and AP2 may determine a simultaneous transmission by referring to an interference map. The interference map is a table that records the relative signal strength due to the difference in the transmission order. In the embodiment shown in FIG. 1, the central controller 210 generates an interference map and transmits the interference map to each AP. However, the central control unit 210 does not necessarily need to exist in order to generate the interference map, and each AP may generate and refer to the interference map without the central control unit 210.

Now, a process of performing an operation according to the simultaneous transmission method according to an embodiment of the present invention in the WLAN system as shown in FIG. 2 will be described. Since it is for explaining the operation when the simultaneous transmission is made, it is assumed that AP1 and AP2 each have a packet to transmit to their clients.

Considering the case where AP1 first transmits to R1 and then AP2 transmits after the preamble interval of AP1, AP1 will fail to transmit as a result. This is because the SINR value of 1 dB of the packet received by R1 does not satisfy 4 dB, which is a capture threshold for capturing the packet. However, AP2's transmission has a high SINR value of 13dB, which makes it a natural success.

Now consider the case where AP1 transmits to R2 instead of R1. In this case, simultaneous transmission of AP2 does not cause the transmission of AP1 to fail. This is because 5dB of SINR value of R2 is higher than 4dB of capture threshold.

From this point of view, AP2 can transmit simultaneously when AP1 is transmitting to R2. That is, each AP of the WLAN system overhears transmissions of other APs, and performs simultaneous transmission in an opportunity under the condition that its own transmission does not fail the ongoing transmission of other APs.

AP2 knows which link AP1 is transmitting on by looking at the MAC header of the packet being transmitted. Next, since the SINR value for this link is in the interference map, it can be determined about simultaneous transmission by referring to it.

If such simultaneous transmission is determined to cause a problem, that is, if it is determined that transmission of another AP will fail due to simultaneous transmission, the transmission is delayed as in the conventional DCF scheme. In other words, it enters the backoff.

3 is a flowchart illustrating an opportunistic simultaneous transmission method according to an embodiment of the present invention from the perspective of one AP.

First, if the AP determines whether there is a packet to transmit (S310), the AP overhears the transmission from another AP and acquires information on the link being transmitted (S320). Next, the SINR value for the link being transmitted is checked with reference to the interference map (S330). By comparing the checked SINR value with the capture threshold value (S340), if the SINR value is greater than or equal to the capture threshold value, simultaneous transmission is possible, so simultaneous transmission starts (S350). If the SINR value is below the capture threshold, it enters the backoff (S360) and waits for the ongoing transmission to complete. When the ongoing transmission is completed (S370), it transmits its own packet (S380).

4 shows an example of a frame schedule when it is decided to perform simultaneous transmission and when it is not.

4A illustrates a case where it is decided to perform simultaneous transmission. First, when AP1 is transmitting a frame, AP2 determines whether simultaneous transmission is possible through the MAC header and the interference map of the frame that AP1 is transmitting, and if it decides to perform simultaneous transmission, transmits its own frame.

In contrast, (b) of FIG. 4 shows a case where it is decided not to perform simultaneous transmission. If AP2 listens to AP1 and decides not to transmit simultaneously, AP2 waits for AP1 to complete its transmission and transmits its own frame.

On the other hand, the opportunistic simultaneous transmission method according to the embodiment of the present invention can operate according to the above-described method in a broadcast environment that does not use an ACK frame, but uses an ACK frame for acknowledgment like unicast. In this case, a more complex schedule is required. However, such frame scheduling can also be done by referring to the MAC header. That is, since the transmission time of the ACK frame can be known by referring to the MAC header of the packet being transmitted from another AP, it is necessary to schedule its frame schedule so as not to overlap with the ACK frame of the packet being transmitted by the other AP.

Simulation was performed to compare the performance of the opportunistic simultaneous transmission method and the DCF transmission method according to the embodiment of the present invention. As the basis of the comparison, predicted throughput was used, which is the length of the delivered packet divided by the transmission time. For ease of analysis, only broadcast environment is considered and no collision is assumed since ACK is not used. Therefore, the predicted throughput of the DCF scheme is expressed as shown in Equation 1 below.

From here,

to be.

In the case of an opportunistic simultaneous transmission method according to an embodiment of the present invention, it takes additional time to transmit a preamble and a time to receive a MAC header compared to DCF. Therefore, the predicted throughput of the opportunistic simultaneous transmission method according to the embodiment of the present invention is represented by Equation 3 below. Here, OMCT stands for Opportunistic MIM-aware Concurrent Transmission and means opportunistic simultaneous transmission according to an embodiment of the present invention.

From here,

 to be.

In the above [Equation 1] to [Equation 4], the general factor values in IEEE 802.11b were compared to compare the results. The transmission rate was fixed at 6Mbps and the data length was changed from 10 bytes to 1500 bytes. 5 is a graph showing the difference between the DCF and the predicted throughput according to the embodiment of the present invention according to the change of the data length. As can be seen from the results shown in FIG. 5, it can be seen that the embodiment of the present invention has an overall predicted throughput about 2 times higher than that of DCF.

Meanwhile, in the above-described embodiment, the case where the opportunistic simultaneous transmission method of the present invention is applied to a wireless LAN system has been described as an example. However, the present invention is not limited thereto, and other wireless networks such as a wireless ad hoc network and the like are described. It can also be applied to the system.

The opportunistic simultaneous transmission method according to the embodiment of the present invention applies only to the transmission from the downlink, that is, the access point to the client, and the uplink, that is, the transmission from the client to the access point is transmitted according to the conventional DCF scheme. It is preferable. Even in this case, a sufficient transmission efficiency can be improved, since most transmissions are performed in a downlink in a general wireless LAN system. In addition, since it is possible to apply the opportunistic simultaneous transmission method according to the embodiment of the present invention by modifying only the access point without modification of the client, it is progressively compared to the method of modifying both the client and the access point. Easy to use

Now, a queue management scheme for maximizing the transmission opportunity of the opportunistic simultaneous transmission method according to the embodiment of the present invention as described above will be described.

To maximize throughput, it is important to increase the chance of simultaneous transmissions as much as possible. However, even though the AP has a chance of simultaneous transmission, there is a case where the chance of simultaneous transmission is lost due to the order of the packets in the packet queue. Such an example will be described with reference to the drawings.

6 shows another example of a wireless LAN system to which an opportunistic simultaneous transmission method according to an embodiment of the present invention is applied. 7 illustrates a packet transmission process in the case of using a packet queue according to a conventional method, and FIG. 8 illustrates a packet transmission process in the case of using a per-station queue according to an embodiment of the present invention.

In the WLAN system as shown in FIG. 6, when AP1 transmits to R2 (AP1-> R2), AP2 has an opportunity to perform simultaneous transmission (AP2-> R4) using the MIM function to R4. However, even in the situation as shown in FIG. 6, availability of simultaneous transmission may vary depending on the arrangement of the packet queues of AP1 and AP2.

According to the conventional method, as shown in FIG. 7, one AP has one packet queue. That is, AP1 stores packets to be transmitted to client devices R1 and R2 connected to it in packet queue Q1, and AP2 stores packets to be transmitted to client devices R3 and R4 connected to itself in packet queue Q2. If there is more than one client connected to an AP, packets to be sent to both client devices are placed in a queue in the order in which they arrived.

Therefore, if AP2 attempts to transmit to R2 when AP1 attempts to transmit to R2, there is an opportunity for simultaneous transmission. However, if AP2 has a packet queue arrangement as shown in the upper part of FIG. 7, R3 rather than R4 in the packet queue header of AP2. Since simultaneous transmission cannot be performed, packets are individually transmitted in the order of R2-> R3-> R1-> R4 as shown in the lower part of FIG.

In contrast, an embodiment of the present invention uses a method of allocating a per-station queue to a plurality of client devices connected to each AP.

That is, as shown in FIG. 8, AP1 and AP2 each have separate queues Q11, Q12; Q21, Q22 for two client devices R1, R2; R3, R4 connected to each other. Hold a packet to be sent to each client device in a queue.

In the case of having the queue arrangement as shown in the upper part of FIG. 8 according to an embodiment of the present invention, packets are sequentially sent out from each individual queue Q11, Q12; Q21, Q22, as shown in the lower part of FIG. Simultaneous transmission to R2 and R4 is possible. That is, the transmission sequence at this time may be repeated in a cycle of R2: R4 (simultaneous transmission)-> R1-> R3.

In this case, when two packets are transmitted to each client device, only six transmissions are possible. In the case of using the queue arrangement as shown in FIG. 7, two transmissions can be reduced compared to eight transmissions.

Of course, when not transmitting at the same time, it is necessary to extract packets from each individual queue Q11, Q12; Q21, Q22 in order and transmit them.

6 to 8 illustrate a case in which two client devices are connected to one AP for convenience of description, of course, two or more client devices may be connected to one AP. In this case, one individual queue is assigned to each client device so that each AP has as many individual queues as the number of connected client devices.

Although the present invention has been described above with reference to preferred embodiments, the present invention is not necessarily limited to the above-described embodiments, and various modifications or changes can be made without departing from the spirit and scope of the invention. The appended claims will cover such modifications and variations as long as they fall within the spirit of the invention.

Claims (12)

A packet transmission method of an access point existing in a wireless network system,
Maintaining at least two separate queues each holding packets for transmission to at least two client devices connected to the access point,
If there is a packet to be transmitted to the individual queue, intercepting transmission from another access point to obtain information of a link being transmitted from the other access point,
Checking a signal to interference plus noise ratio (SINR) value of the link;
If the identified SINR value is greater than or equal to a predetermined capture threshold, scheduling the simultaneous transmission of packets that can be transmitted among the packets stored in the individual queues. The method of claim 1,
The method of claim 1, wherein the SINR value is checked with reference to an interference map. The method of claim 2,
The wireless network system includes a central control unit connected to the access point and the other access point,
And the interference map is provided by the central controller. The method of claim 1,
And the simultaneous transmittable packet is a packet having an SINR value equal to or greater than the capture threshold. A wireless network system comprising two or more access points,
The access point includes two or more separate queues, each holding packets for transmission to two or more client devices connected thereto;
If there is a packet to be transmitted to the individual queue of any of the access points, the transmission from another access point is intercepted to obtain information of a link being transmitted from the other access point,
By checking the Signal to Interference plus Noise Ratio (SINR) value of the link,
And when the checked SINR value is equal to or greater than a predetermined capture threshold value, scheduling to transmit simultaneous packets among packets stored in the individual queue. The method of claim 5,
And confirming the SINR value with reference to an interference map. The method of claim 6,
The wireless network system further includes a central controller connected to the two or more access points,
And the central controller generates the interference map and provides the interference map to the two or more access points. The method of claim 5,
And the simultaneous transmittable packet is a packet having an SINR value equal to or greater than the capture threshold. As an access point in a wireless network system,
Contains two or more separate queues, each holding packets for transmission to two or more connected client devices.
If there is a packet to be transmitted to the individual queue, the transmission from another access point is intercepted to obtain information of a link being transmitted from the other access point,
By checking the Signal to Interference plus Noise Ratio (SINR) value of the link,
And when the checked SINR value is equal to or greater than a predetermined capture threshold, scheduling of simultaneous transmission of packets that can be transmitted in the individual queues. 10. The method of claim 9,
The SINR value is confirmed by referring to the interference map. The method of claim 10,
The wireless network system further includes a central controller,
And the access point receives the interference map from the central controller. The method of claim 9, wherein the packet capable of simultaneous transmission,
An access point that is a packet having an SINR value equal to or greater than the capture threshold.

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