KR20070041591A - A method and system for link adaptation in wireless networks - Google Patents

Abstract

Provided are methods and systems for adapting a transmission rate of a mobile station among a plurality of transmission rates between a plurality of stations in a wireless local area network (WLAN), with the ability to determine whether transmission errors are caused by increased path loss. do. In response to the transmission timeout condition of the transmitted frame, causing a transmission error associated with the timeout condition to be caused by increased path loss using received signal strength (RSS) from a plurality of incoming frames received by the mobile station. Determine if not. If the decision is true, the RSS threshold is increased, for example the link adaptation rate threshold and the frame are retransmitted.

Description

A METHOD AND SYSTEM FOR LINK ADAPTATION IN WIRELESS NETWORKS

The present invention relates to a communication system. More specifically, the present invention relates to errors due to increased path loss and errors due to interference and collisions to more accurately adjust the transmission rate of each station in a wireless network, such as an IEEE 802.11 wireless local area network (WLAN). A system and method for adapting transmission rates through the distinction between

The IEEE 802.11 standard specifically describes media access control (MAC) and physical characteristics for wireless local area networks (WLANs) to support the physical layer structure. The IEEE 802.11 standard is published in the 1999 edition of International Standard ISO / IEC 8802-11 "Information Technology--Telecommunication and information exchange area network," which is hereby incorporated by reference in its entirety. It is limited.

The IEEE 802.11 physical layer (PHY) limits multiple transmission rates based on different modulation and channel-code designs so that the transmitter of a frame can select one of multiple transmission rates based on radio channel conditions between the receiver and the transmitter itself at a particular time. Can be. In general, the lower the transmission rate, the more reliably the transmission.

In such a wireless system, the propagation and trunk environment changes over time and space by factors such as station mobility, interference and impulse that change over time. As a result, there is no single PHY mode (law and code design) that can be optimal under all scenarios. Link adaptation (LA) algorithms have been proposed to solve this problem somewhat, and the efficiency of the system is improved by adapting the modulation design that is optimal for the current link conditions.

In particular, a particular example of an LA algorithm allows a transmitting station to adapt the transmission rate using reception strength (RSS), measured from a frame received from an access point (AP) as an indicator for link quality. . Without considering fast fluctuations in SNR / SIR due to interference or multipath fading, the LA algorithm considers RSS to have a linear relationship with SNR on average. Therefore, the received power as a function of distance and path loss conditions is very useful for estimating the best matched PHY mode for the next transmission. This link adaptation algorithm is described in pending US patent application number XXXXXXXX, which is incorporated herein by reference.

The change in RSS indicates that the condition of the radio link between the station and the AP changes, and it may be necessary to adapt the transmission rate appropriately according to the long distance and high path loss between the station and the AP. However, the prior art LA adaptation algorithm may always assume that the error is due to low RSS and the adaptation may be executed incorrectly.

For example, other sources of error seen in wireless radio channels are interference noise at the receiving station, collision at the receiving station, and multipath fading. Interference behavior by other stations and other transmitting devices on the same channel, such as microwaves, is nearly pulsed and transient. The LA algorithm must not adapt the transmission rate for transmission errors caused by interference or collision, in which case the RSS threshold does not change. Accordingly, there is a need to distinguish between errors due to interference to the LA algorithm that can provide dynamic ratio adaptation based on received signal strength (RSS) measured from the received frame and errors due to low RSS (distance).

The present invention is directed to errors and high path loss due to interference and collisions, shading, and increased path loss (due to long distances) to better control the transmission rate of wireless networks such as wireless local area networks (WLANs). A system and method for adapting transmission rates with the ability to distinguish between errors due to

One aspect of the invention relates to a method for determining a transmission rate of a mobile station between a plurality of transmission rates, the method comprising: obtaining an average received signal strength (RSS) value from a plurality of incoming frames received by the mobile station; Measuring; Comparing the average RSS value to a predetermined reference table having a minimum RSS required for a particular frame length for transmission at one of the plurality of transmission rates; Selecting a new transmission rate of the mobile station for subsequent transmission of a new frame based on the comparison result, in response to a transmission timeout condition of the transmitted frame; Determining whether a transmission error associated with a timeout condition was caused by increased path loss using an average RSS value, and if yes, the new transmission rate of the mobile station for subsequent transmission of a new frame; Selecting a step.

Another aspect of the invention relates to a method for determining whether a transmission error is caused or not caused by increased path loss for use in determining the transmission rate of a mobile station between a plurality of transmission rates, such as, for example, a link adaptation algorithm. It is about. The method is responsive to a transmission timeout condition of the transmitted frame; Determining whether a transmission error associated with a timeout condition is caused or not caused by an increased path loss using a received signal strength (RSS) value from a plurality of incoming frames received by the mobile station; If yes, increasing the RSS threshold, such as, for example, the link adaptation rate threshold and resending the frame; If no, retransmitting the frame.

Another aspect of the invention relates to a system for adapting a link adaptive transmission rate of a mobile station between a plurality of transmission rates, the system comprising: receiver circuitry for demodulating incoming frames; A power-measuring circuit for measuring a received signal strength (RSS) of the received incoming frame, and a processor coupled to the power-measuring circuit, the processor determining a transmission timeout condition for the transmitted frame and timeout Determine if a transmission error associated with a condition is caused or not caused by an increased path loss using received signal strength (RSS) values from a plurality of incoming frames received by the mobile station, and if yes, an RSS threshold Increase the value and resend the frame or send a new frame.

Another aspect of the invention is directed to a system for determining a transmission rate between a plurality of transmission rates, the system comprising a receiver circuit for demodulating an incoming frame and a received signal strength (RSS) of the received incoming frame. A processor coupled to the power-measure circuit for selecting a new rate and for calculating an average RSS for transmission of a new frame based on a comparison result of a predetermined reference table with the power-measure circuit for measurement, the predetermined The reference table includes the minimum RSS required for a particular frame length for transmission at one of a plurality of said transmission rates, and the singer processor responds to a transmission timeout condition of the transmitted frame so that a transmission error associated with the timeout condition is detected. Use the average RSS to determine whether it is caused by increased path loss or not, The processor selecting a new transmission rate of the mobile station for retransmission of the frame or subsequent transmission of a new frame, and for storing the average RSS and the predetermined reference table for subsequent retrieval. Contains associated memory.

The foregoing and other features and advantages of the present invention will become apparent from the following detailed description of the preferred embodiments as shown in the accompanying drawings, in which like numerals designate the same parts throughout the various views.

1 is a simplified block diagram showing the structure of a wireless communication system to which an embodiment of the present invention is 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.

3 is a graphical representation of transmission criteria used to adjust a transmission rate in accordance with an embodiment of the present invention.

4 is a flow diagram illustrating operational steps for distinguishing between errors due to increased path loss and errors due to interference and collision to adjust transmission rates in accordance with an embodiment of the present invention.

Although the present invention is described below with particular reference to the system block diagram of FIG. 1, at the beginning of the following description the apparatus and method according to the present invention can be used with other infrastructure for the station to communicate with other stations via wireless media. Should understand

1 shows an exemplary network to which an embodiment of the present invention is applied. As shown in FIG. 1, an access point (AP) 2 is connected to a plurality of mobile stations STA _{i in} communication with each other and the AP via a wireless link. The main principle of the present invention is that regardless of receiver performance and channel behavior, frame-error probability depends on the receiver (signal-to-noise ratio SNR), transmission rate, and length. On average, the transmitting STA may keep track of the RSS measured from the frames sent by the receiving STA to relatively estimate the path loss and channel behavior. Note that in a typical IEEE 802.11 STA implementation, RSS is available for the Media Access Control (MAC) protocol. Thus, as long as the receiving STA uses a fixed transmit-power level for all transmissions, the change in RSS can be used to provide a mechanism for generating and updating the transmission rate criteria for subsequent transmissions of the frame, Frames are sent directly at the correct rate.

Referring to FIG. 2, each STA and AP in the WLAN of FIG. 1 may include a system having the structure shown in the block diagram of FIG. 2. Both the AP and the STA use a receiver 12, 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. It may include. Although the present description may refer to terms generally used to describe particular mobile stations, the present description and concepts apply equally to other processing systems, including systems having structures that are not similar to the system shown in FIG. . The processor 20 may represent a microprocessor, a central processing unit, a computer, a circuit card, and special purpose integrated circuits (ASICs). The memory 18 may represent a combination or part of a disk-like optical or magnetic storage device, an electronic memory, and these and other storage devices. However, in other embodiments, hardware circuitry may be used in place of or in combination with software instructions for practicing the present invention.

In operation, receiver 12 and transmitter 26 are connected to an antenna (not shown) for converting and transmitting received signals through corresponding demodulator 14 and modulator 24 to corresponding digital signals, respectively. The power-measuring circuit 16 operates under the control of the processor 20 to detect the RSS of the frame received there. RSS for other stations is estimated and stored in memory 18 coupled to processor 20 for subsequent retrieval. The estimated RSS for the other stations in the BSS is updated and used to generate a reference table that is later used to select the correct transmission rate. Timer 22 is used to remove old RSS estimates stored in memory 18. In an embodiment, the RSS is updated because it tends to change by the time-varying nature of the wireless channel and the potential mobility of the WLAN STA.

As an example, Figure 3 shows a transmission-reference table to select a suitable transmission rate. Each time the transmitting STA sends a frame with a certain length and receives a corresponding acknowledgment signal, the transmitting STA generates or updates a threshold boundary based on the RSS measured in the reference table to be used for subsequent transmission of the frame. If an RSS threshold boundary is established for each other frame interval (e.g., 0-100 bytes, 100-1000 bytes, and 1000-2400 bytes), the transmitting STA is sent to the RSS measured from the frame received from the receiving STA. To adapt the transmission rate. Note that the change in RSS indicates that the condition of the radio link between the transmitting STA and the receiving STA changes. As shown in FIG. 3, each threshold boundary indicates that it is the minimum RSS value needed for a particular transmit PHY rate. For example, if the STA monitoring RSS from a frame sent by the receiving STA detects that the RSS is lower than one of the thresholds (ie, due to the increasing interval between the receiving STA and the transmitting STA), then Attempts to transmit may be made at low transmission rates to ensure accurate reception of the frame.

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

I Index to data rate F: ratio I = {1,2,3,5.5,11} (Mbps) = {1,2,3,4} J Index to frame length G: length J = {0-100,100-1000,1000-2400} (bytes) = {1,2,3} LA_th [i, j] Link Adaptation Rate Threshold 0 <I <5 & 0 <j <4 RSS Measure most recently received signal strength RSS_avg Average received signal strength

For simplicity, the frame-length interval with j = {1,2,3} represents different frame sizes of 0-100 bytes, 100-1000 bytes, and 1000-2400 bytes, respectively. The data rate with i = {1,2,3,4} represents one of four possible data rates in this example, namely 1,2,5.5 and 11 Mbps. The RSS threshold will be defined for each interval. The threshold "LA_th [i, j}" represents the minimum "RSS_avg or RSS threshold" value for transmitting a frame within the length interval "j" at the data rate "i".

4 illustrates the distinction between error 1 due to increased path loss (due to increased spacing), shading and high path loss, and error 2 due to interference and collision to adjust the transmission rate of the wireless network. Shows the whole task.

In general, the mobile device is configured to operate (step 100) in two modes: (1) receive mode, and (2) transmit mode. After the STA transmits the request signal to transmit data, it selects a transmission rate based on the RSS average value (RSS_avg), the threshold value, the frame size, and the number of retransmission attempts. Here, rate adaptation occurs when the average RSS measured from a received frame passes some threshold of the reference table, including the minimum RSS value required for a particular transmission rate. Accordingly, the STA transmits the frame at the selected transmission rate. Depending on whether the transmission was successful and whether the frame error was caused by interference, collision, path loss, the STA updates the corresponding "threshold" in the reference table. Accordingly, the STA selects a transmission rate according to the RSS_avg, the frame length, and the number of retransmission attempts. Note that the block diagram is shown for an 802.11 STA operating with the base service set of FIG. 4, where all frames are always transmitted / received to / from that AP. Thus, the receiving STA described herein is always that AP.

Each time the transmitting STA sends a frame with a certain length, it receives a corresponding acknowledgment signal (ie, an acknowledgment (ACK) frame). When an acknowledgment signal is received this indicates that the transmission rate is adequate. When the acknowledgment signal has not been received at a predetermined time, a acknowledgment signal timeout condition occurs (step 102). In the timeout condition, it is determined whether the error is caused by, for example, too low RSS receiver execution (step 104). If "false", the cause of the error is determined, for example, by interference, collision, multipath, and the like. For example, after the timeout condition (step 102) occurs, at step 104, it is determined whether the received signal strength RSS changes more than a certain RSS threshold at a time of a predetermined period.

는 다음의 수학식에 따라 계산될 수 있다.RSS changes over time, i.e.

May be calculated according to the following equation.

= RSS_avg - RSS_actual

= RSS_avg-RSS_actual

In the determination of step 104, if the change in RSS over a period of time increases, the likelihood of causing an error also increases because the RSS at the receiver is too low. In addition, it represents errors caused by the performance of the receiver (PER) and errors caused by low power at the receiver. Thus, the RSS threshold / link adaptation rate threshold LA_th [i] [j] is increased in step 108 and the frame is calculated after calculating the optimal data rate, as shown in FIG. Is resent). If the decision of step 104 indicates that there is no or small change in RSS over a period of time (for example, when compared with a predetermined threshold), then there is a high probability of an error resulting from a collision or interference at the receiver and Channel conditions do not go bad. Thus, the frame is retransmitted at step 106 without changing the link adaptation rate threshold LA_th [i] [j]. It should be appreciated that the likelihood of a collision at all retransmissions is low, so that those skilled in the art can determine various retransmission thresholds for various conditions.

In step 120 of FIG. 5, the transmission rate is selected. In step 122, the LA_th table is checked for the highest probability of transmission, such as a new (high) rate being selected if (RSSI_avg> = LA_th (I) (J)) is false. Otherwise, the selected ratio is used in step 124.

As is apparent from the above description, the present invention is advantageous in that, unlike the prior art, the RSS threshold is increased only after a channel related error (eg, not updated after a collision or interference). The transmission rate is only adapted after an associated change or long interference (after a predetermined number of bundles) in RSS. In addition, the present invention can select a suitable transmission rate without any change in the current standards for ISSS 802.11 WLAN media access control.

While the preferred embodiments of the invention are shown and described, it will be understood by those skilled in the art that various changes and modifications may occur and equivalents may be substituted for the components thereof without departing from the true scope of the invention. In addition, many modifications may be made to adapt to a particular situation and teaching of the present invention without departing from its scope. Therefore, it is intended that the invention not be limited to the particular embodiments described in the best way contemplated for carrying out the invention, but the invention includes all embodiments falling within the scope of the appended claims.

The present invention is used in a communication system. More specifically, the present invention relates to errors due to increased path loss and errors due to interference and collisions to more accurately adjust the transmission rate of each station in a wireless network, such as an IEEE 802.11 wireless local area network (WLAN). It is used in systems and methods to adapt the transmission rate by discrimination between.

Claims (16)

A method for adapting a link adaptive transmission rate of a wireless device among a plurality of transmission rates, the method comprising: (a) in response to a transmission timeout condition of the transmitted frame, a transmission error associated with a timeout condition results in increased path loss using a received signal strength (RSS) value from a plurality of incoming frames received by the wireless device. Determining whether or not caused by, (b) if yes, increasing the RSS threshold and retransmitting the frame or transmitting a new frame; A method for adapting a link adaptive transmission rate of a wireless device. 2. The method of claim 1, further comprising retransmitting the frame or transmitting a new frame if the transmission error associated with the timeout condition does not result in increased path loss. The method of claim 1, further comprising: measuring an average received elongation intensity (RSS_avg) value from a plurality of incoming frames received by the wireless device and whether the received signal strength changes more or less than a predetermined value at a predetermined time period. Determining the link adaptation transmission rate of the wireless device. The method of claim 1, wherein the RSS threshold is a link adaptation rate threshold. 4. The method of claim 3, wherein if the change in RSS over time is above a predetermined value, the transmission error associated with the timeout condition is caused by a path loss and the RSS threshold is increased. Way. 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 wireless device. A method of determining a transmission rate of a wireless device among a plurality of transmission rates, (a) measuring an average received signal strength (RSS) from a plurality of incoming frames received by the wireless device; (b) comparing the average RSS value with a predetermined reference table having a minimum RSS required for a particular frame length for transmission at one of a plurality of said transmission rates; (c) selecting a new transmission rate of the wireless device for subsequent transmission of a new frame based on the comparison result; (d) in response to a transmission timeout condition of the transmitted frame; Determining whether a transmission error associated with a timeout condition is caused by an increased path loss using an average RSS value, and (e) if yes, selecting a new transmission rate of the wireless device for retransmission of the frame or subsequent transmission of a new frame; A method of determining a transmission rate of a wireless device among a plurality of transmission rates. A wireless device for adapting a link adaptive transmission rate among a plurality of transmission rates, A receiver circuit for demodulating an incoming frame, A power-specific circuit for measuring a received signal strength (RSS) of the incoming frame received; A processor coupled to the power-measuring circuit, the processor determines a transmission timeout condition of a transmitted frame, wherein a transmission error associated with a timeout condition is received from a plurality of incoming frames received by the wireless device. Determine whether caused by increased path loss or not, and if yes, increase the RSS threshold and resend the frame or send a new frame. And a wireless device for adapting a link adaptive transmission rate among a plurality of transmission rates. 10. The link adaptive transmission rate of claim 9, wherein the processor further comprises transmission of a new frame or retransmission of the frame if the transmission error associated with the timeout condition is not caused by increased path loss. Wireless device for adapting. 10. The method of claim 9, wherein the processor is further configured to determine whether the average received elongation intensity (RSS_avg) value from a plurality of incoming frames received by the wireless device and the received signal strength change more than a predetermined value in a predetermined time period. And determining whether or not to adapt the link adaptive transmission rate among the plurality of transmission rates. 10. The wireless device of claim 9, wherein the RSS threshold is a link adaptation rate threshold. 11. The method of claim 10, wherein if the change in RSS over time is greater than or equal to a predetermined value, the transmission error associated with the timeout condition is caused by increased path loss and the RSS threshold is increased. Wireless device to adapt the rate. 10. The wireless device of claim 9, wherein the incoming frame is transmitted by an access point (AP). 10. The wireless device of claim 9, wherein the incoming frame is transmitted by another wireless device. A wireless device for determining a transmission rate among a plurality of transmission rates, A receiver circuit for demodulating an incoming frame, A power-measuring circuit for measuring a received signal strength (RSS) of the received incoming frame; A processor coupled to the power-measuring circuit, the processor calculates an average RSS and determines a new transmission rate for transmission of a new frame based on a comparison result of a predetermined reference table, wherein the predetermined reference table is a plurality of reference tables. A minimum RSS required for a particular frame length for transmission at one of the transmission rates of the processor, and in response to the transmission timeout condition of the transmission frame, the processor increases the transmission error associated with the timeout condition using the average RSS. Determine whether caused or not caused by a lost path; If yes, selecting a harmful transmission rate of the wireless device for retransmission of the frame or subsequent transmission of a new frame; A memory coupled to the processor for storing the average RSS and the predetermined criteria table for subsequent retrieval, A wireless device for determining a transmission rate among a plurality of transmission rates.

Images