KR20070047316A - A method and system for error differentiating in wireless networks - Google Patents

Abstract

A method and system are provided for determining if a transmission error is caused by a channel condition for use in determining a transmission characteristic of a mobile station in a wireless local area network (WLAN). Such a method and system includes detecting a transmission timeout state of a transmitted frame and a channel using a received signal strength (RSS) from a plurality of incoming frames for which a transmission error associated with the timeout state has been received by the mobile station. Determining whether it is caused by a condition.

Description

A METHOD AND SYSTEM FOR ERROR DIFFERENTIATING IN WIRELESS NETWORKS

The present invention relates to a communication system. In particular, the present invention provides a system for distinguishing errors due to channel conditions from errors due to interference and collisions to more accurately adjust station characteristics in wireless networks such as IEEE 802.11 wireless local area networks (WLANs); It is about a method.

The IEEE 802.11 standard specifies the physical characteristics of a medium access control (MAC) and a wireless local area network (WLAN) for supporting physical layer units. The IEEE 802.11 standard is an international standard ISO entitled "Information Technology-Telecommunications and information exchange area networks" entitled 1999 edition, which is hereby incorporated by reference in its entirety. / As defined in IEC 8802-11.

The IEEE 802.11 physical layer (PHY) defines a plurality of transmission rates based on different modulation and channel-coding schemes, such that a frame's transmitter is one of a number of rates based on radio channel conditions between the receiver and itself at a particular point in time. You can choose one. In general, the slower the transmission rate, the more reliable the transmission.

In such a wireless system, the propagation and interference environment changes over time and space due to factors such as station mobility, time-varying interference and collisions. As a result, there is no single PHY mode (modulation and coding structure) that can be optimal under all scenarios. A link adaptation (LA) algorithm has been proposed to alleviate this problem, in which case the efficiency of the system is improved by adapting the modulation scheme that is optimal for the current link state.

In particular, the LA algorithm allows the transmitting station to adapt the transmission rate by using the received signal strength (RSS) measured from the frame received from the access point (AP) as an indicator of link quality. RSS is assumed to have a linear relationship with the SNR on average, without taking into account the sudden fluctuations in SNR / SIR due to interference or multipath fading. Therefore, the received power and path loss conditions as a function of distance are very useful for estimating the best matched PHY mode for the next transmission. Such link adaptation algorithms are described in co-pending US patent application XXXXXXXX, which is incorporated herein by reference.

The change in RSS indicates that the state in the wireless link between the station and the AP is changing, and it may be necessary to adapt the transmission rate accordingly due to the greater distance or higher path loss between the station and the AP. . However, the prior art LA adaptation algorithm always assumes that such error is due to low RSS, so the adaptation can be done incorrectly.

For example, another source of error seen in wireless radio channels is interference noise at the receiving station, collisions and multipath fading at the receiving station. Interference behavior from other stations and other transmitting devices on the same channel, such as microwaves, is nearly pulsed and transient. The LA algorithm must not adapt its speed with respect to transmission errors caused by interference or collisions, in which case the RSS thresholds should not be changed. Thus, there is a need to distinguish between errors due to low RSS (e.g. bad channel conditions) and errors due to interference.

The present invention distinguishes errors due to bad channel conditions such as distance, shading and high path loss from errors due to interference and collisions to adjust station characteristics in wireless networks such as local area networks (WLANs). It relates to a system and a method. This information is then used to determine the type of error that occurs and their different handling for any other application needed to determine the reason for the application, such as power control or missed frames.

One aspect of the invention relates to a method of determining whether a transmission error is caused by a channel condition, which can then be used for use in determining the transmission speed of a mobile station, for example among a plurality of transmission rates. This method comprises the following steps: detecting a transmission timeout state of a transmitted frame, and receiving a signal strength (RSS) from a plurality of incoming frames in which a transmission error associated with this timeout state has been received by the mobile station. Using the value to determine if it is caused by a channel condition.

Another aspect of the invention relates to a mobile station for error discrimination between two mobile stations in a wireless network, the station comprising a receiver circuit for demodulating an incoming frame, the received signal strength of the incoming frame received therein. Power measurement circuitry for measuring (RSS) and a transmission timeout state of the transmitted frame, wherein transmission errors associated with the timeout state are received signal strength from a plurality of incoming frames received by the mobile station. And a processor coupled to the power measurement circuitry to determine if it is caused by a channel condition using an RSS) value.

The foregoing and other features and advantages of the present invention will become apparent from the following more detailed description of the preferred embodiments, as illustrated in the accompanying drawings in which like reference characters indicate like parts throughout the several views.

1 is a simplified block diagram illustrating the architecture of a wireless communication system to which embodiments of the present invention are applied.

2 is a simplified circuit diagram of each station and access point in a particular basic service set (BSS) in accordance with an embodiment of the present invention.

FIG. 3 shows a graphical representation of transmission references used to adjust the transmission speed in accordance with an embodiment of the present invention. FIG.

4 is a flow diagram illustrating operational steps for distinguishing between errors due to bad channel conditions and errors due to interference and collision, in order to adjust the transmission rate in accordance with one embodiment of the present invention.

The invention is hereinafter described with particular reference to the system block diagram of FIG. 1, but at the beginning of the description, the apparatus and method according to the invention can be used with a different infrastructure, in which case one station is radio It should be understood that it communicates with another station via the medium.

1 illustrates an exemplary network to which an embodiment of the present invention is applied. As shown in FIG. 1, an access point (AP) 2 is coupled to a plurality of mobile stations STA _i 10 and communicates these mobile stations with each other and with the AP via a wireless link. The key principle of the present invention is that, regardless of receiver performance and channel behavior, the frame error probability depends on the signal-to-noise ratio (SNR) at the receiver, its transmission rate and its length. On average, the transmitting STA can relatively estimate the path loss and channel behavior by tracking the RSS measured from the frame sent by receiving the STA. Note that in a typical IEEE 802.11 STA implementation, RSS is available for the Media Access Control (MAC) protocol. Therefore, as long as the receiving STA uses a fixed transmit power level for all its transmissions, a change in RSS can be used to provide a mechanism to generate and update a transmission rate reference for the next transmission of the frame, This is transmitted at the right transmission rate.

Referring to FIG. 2, the AP and each STA in the WLAN of FIG. 1 may include a system with the architecture illustrated in the block diagram of FIG. 2. Both the AP and the STA may include a receiver, a demodulator 14, a power measurement circuit 16, a memory 18, a control processor 20, a timer 22, a modulator 24, and a transmitter 26. Although the description may refer to terms commonly used to describe particular mobile stations, the description and concepts apply equally to other processing systems, including those having architectures that are not similar to those shown in FIG. The processor 20 may represent a microprocessor, a central processing unit, a computer, a circuit card, an application specific integrated circuit (ASIC). Memory 18 may represent a portion or combination of disk-based optical or magnetic storage units, electronic memory, and these and other memory devices. However, in other embodiments, hardware circuitry may be used in place of or in combination with software instructions for implementing the present invention.

In operation, receiver 12 and transmitter 26, via demodulator 14 and modulator 24, respectively, convert the received signal into corresponding digital data and transmit it to an antenna (not shown) to transmit the desired data. Combined. The power measurement circuit 16 operates under the control of the processor 20 to detect the RSS of the received frame. RSS for other stations is estimated and stored in memory 18, which is coupled to processor 20 for subsequent retrieval. The estimated RSS for other stations in the same BSS is updated and later used to generate a reference table that is used to select the appropriate transmission rate. Timer 22 is used to remove old RSS estimates, which are stored in memory 18. In this embodiment, the RSS is updated when it tends to change due to the time-varying nature of the wireless channel as well as the potential mobility of WLAN STAs.

3 shows, by way of example, a transmission criteria table for selecting an appropriate transmission rate. Each time a transmitting STA sends a frame with a particular length and receives a corresponding acknowledgment signal, the transmitting STA generates or updates a threshold boundary based on the measured RSS in the reference table to be used in the next transmission of the frame. Once an RSS threshold boundary is established for each of the different frame intervals (ie, 0-100 bytes, 100-1000 bytes, and 1000- 2400 bytes), the transmitting STA depends on the RSS measured from the frame it receives from the receiving STA. Adapt the transmission speed. Note that the change in RSS indicates that the state in the wireless link between the transmitting STA and the receiving STA changes. As shown in FIG. 3, each threshold boundary indicates which minimum RSS values are required for a particular transmission PHY rate. For example, if the STA monitoring RSS from the frame sent by the receiving STA detects that the RSS is lower than one of the thresholds (due to the increasing distance between the receiving STA and the transmitting STA), then the next transmission attempt will be the correct reception of the frame. It can be done at a lower speed to ensure that.

 The following is a list of variables used in FIGS. 3 to 4.

I Index on data rate F: speed i = {1,2,5.5,11} (Mbps) = {1,2,3,4} J The index into the frame length G: length j = {0-100, 100-1000, 1000-2400} (bytes) = {1, 2, 3} LA_th [i, j] Link Adaptation Speed Threshold 0 <I <5 & 0 <j <4 RSS Most recently received signal strength measurement RSS_avg Average received signal strength

In summary, the frame-length interval j = {1, 2, 3} represents different frame sizes of 0 to 100 bytes, 100 to 1000 bytes and 1000 to 2400 bytes, respectively. Data rate i = {1, 2, 3, 4} represents one of four data rates available in this example, namely 1, 2, 5.5 and 11 Mbps. RSS thresholds are defined for each interval. The threshold "LA_th [i, j]" represents the minimum "RSS_avg or RSS threshold" value for transmitting a frame in the length section "j" at the data rate "i".

Figure 4 shows the overall operation of the distinction between (1) errors due to bad channel conditions such as distance, shading, high path loss, and (2) errors due to interference and collision to adjust the transmission speed in the wireless network. To illustrate.

In general, the mobile unit is configured to operate (step 100) in two modes: (1) receive mode and (2) transmit mode. The STA transmits a request signal to transmit data, and then selects a transmission rate based on values of an RSS average (RSS_avg), a threshold value, a frame size, and the number of retransmission attempts. Rate adaptation in this case occurs when the average RSS measured from the received frame passes some threshold in the reference table, which contains the minimum RSS value required for the particular transmission rate. Thereafter, the STA transmits the frame at the selected transmission rate. Depending on whether the transmission was successful, the STA updates the corresponding "threshold" in the reference table. Therefore, the STA selects a transmission rate that depends on RSS_avg, frame length, and retransmission attempt. The block diagram is shown for an 802.11 STA operating in the basic service set in FIG. 4, in which case all frames are always transmitted or received to or from its AP. Therefore, the receiving STA mentioned herein is always its AP.

Each time the transmitting STA transmits a frame having a particular length, the transmitting STA receives a corresponding acknowledgment signal (ie, an acknowledgment (ACK) frame). When an acknowledgment signal is received, it indicates that the transmission speed was adequate. If a confirmation signal is not received at a predetermined time, a confirmation signal time out condition occurs (step 102). In the time-out state, it is determined whether the error is an error caused by the receiver's performance, e. If not, the cause of the error is determined by interference, collision, multiple paths, and the like. For example, after a timeout condition (step 102) occurs, a determination is made at step 104 as to whether the received signal strength RSS has changed more than a particular RSS threshold in a predetermined time period.

The change in RSS over time, ie the delta RSS, can be calculated according to the following equation.

Delta RSS = RSS_avg-RSS_actual

In the decision at step 104, as the change in RSS over a particular time period increases, the probability of causing an error also increases because the RSS at the receiver is too low. In addition, this indicates that the error occurs due to the receiver's performance (PER) and is caused by low power at the receiver. Therefore, the RSS threshold / link adaptation rate threshold LA_th [i] [j] is increased in step 108, and then the frame is retransmitted in step 106. If the decision in step 104 indicates no or small change in RSS over a particular time period (e.g., when compared with a predetermined threshold), then there is a high probability that an error will occur due to collision or interference at the receiver, and There is a high probability that the state will not fall. Therefore, the frame is retransmitted without a change in the link adaptation speed threshold LA_th [I] [j] in step 106. Each retransmission has a lower probability of collision and therefore one skilled in the art can determine various retransmission thresholds for various conditions.

As is evident from the foregoing, the present invention is advantageous in that, unlike the prior art, the RSS threshold increases only after a channel related error (eg, no update after a collision or interference). The transmission rate is only adapted after an associated change or long interference in the RSS (after a certain number of packets). In addition, the present invention makes it possible to select an appropriate transmission rate without making any changes in the current IEEE 802.11 WLAN media access control specification.

While the preferred embodiments of the invention have been illustrated and described, those skilled in the art will recognize that various changes and modifications may be made and elements may be substituted for equivalents without departing from the true scope of the invention. In addition, many modifications may be made to adapt to the teachings and particular circumstances of the present invention without departing from the central scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out the invention, but that the invention will include all embodiments falling within the scope of the appended claims.

As noted above, the present invention distinguishes errors due to communication systems, particularly channel conditions, and errors due to interference and collisions to more accurately adjust station characteristics in wireless networks such as IEEE 802.11 Wireless Local Area Networks (WLANs). It can be used for the system and method.

Claims (10)

A method for error discrimination between two mobile stations in a wireless network, Detecting a transmission timeout state of the transmitted frame; Determining whether a transmission error associated with a time out condition was caused by a channel condition using received signal strength (RSS) from a plurality of incoming frames received by the mobile station. And a method for error discrimination between two mobile stations in a wireless network. The method of claim 1, wherein step (a) Measuring an average received signal strength (RSS_avg) value from a plurality of incoming frames received by the mobile station, and determining whether the received signal strength has changed more than a predetermined value in a predetermined time period; Further comprising a method for error discrimination between two mobile stations in a wireless network. The method of claim 1, wherein the change in RSS over time delta RSS is Delta RSS = RSS_avg-RSS And RSS is indicative of the current received signal strength, wherein the error discrimination between the two mobile stations of the wireless network. The method of claim 1, wherein the incoming frame is transmitted by an access point (AP). The method of claim 1, wherein the incoming frame is transmitted by another mobile station. A mobile station for error discrimination between two mobile stations in a wireless network, A receiver circuit for demodulating an incoming frame, A power measurement circuit for measuring a received signal strength (RSS) of the incoming frame received therein, Received signal strength (RSS) from a plurality of incoming frames received by the mobile station is used to determine the transmission timeout state of the transmitted frame and to determine if a transmission error associated with the timeout state is caused by the channel condition. In order to determine the processor coupled to the power measurement circuitry And a mobile station for error discrimination between two mobile stations in a wireless network. 7. The processor of claim 6, wherein the processor determines an average received signal strength (RSS_avg) from a plurality of incoming frames received by the mobile station, and determines whether the received signal strength has changed more than a predetermined value in a predetermined time period. Further comprising determining a mobile station for error discrimination between two mobile stations in a wireless network. 8. The method of claim 7, wherein the change in RSS over time is Delta RSS = RSS_avg-RSS Mobile station for error discrimination between two mobile stations in a wireless network, wherein the RSS represents a current received signal strength. 7. The mobile station of claim 6, wherein the incoming frame is transmitted by an access point (AP). 7. The mobile station of claim 6, wherein the incoming frame is transmitted by another mobile station.

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