DE102007044558A1 - Data rate and packet size adjusting method for wireless local area network radio channel in Car2X-network, involves providing subscribers, and reducing data rate and packet size with diminishing signal quality - Google Patents

Abstract

The method involves providing subscribers using multiple transmission or receiving units, where a subscriber of radio communication comprises an evaluation unit for evaluation of signal quality of radio communication. Data rate and packet size of radio communication are reduced with diminishing signal quality. The data rate and the packet size are increased when the signal quality lies over a preset value for a pre-defined period. Messages containing information about vehicle speed and driving direction are periodically sent by the subscriber to another subscriber.

Description

The The invention relates to a method and a device for adaptation the data rate of WLAN radio channels and / or the packet size on WLAN radio channels in a Car2X network.

at All WLAN radio systems find an adaptation of the data rate depending on the signal quality instead. It can be from 1 Mbps in poor quality up to 11 Mbps (802.11b) or 6 Mbps up to 54 Mbps (802.11a / g / h) or 3 MBit / s up to 27 MBit / s (802.11p) with very good quality increase. New standards such as 802.11n even point a maximum data rate of up to 300 Mbps. These algorithms but are optimized for stationary nodes.

From the DE 20 2004 017 120 U1 For example, a base station configured for use in a wireless local area network (WLAN) and using a predefined wireless frame format is implemented, with a traffic congestion control implemented in the base station. The base station includes a transmitter and receiver configured to transmit and receive wireless communications in the predefined frame format. A processing unit coupled to the transmitter and receiver is configured to process received communication frames and format information for transmission in frames, the processing unit recognizing traffic prediction information embedded in wireless communication frames received from the receiver from a wireless transceiver unit (WTRU) is received. The processing unit evaluates the received traffic information from the WTRU in conjunction with other communication traffic data to generate a corresponding command to be sent in a formatted communication frame with instructions to the WTRU.

From the DE 602 06 606 T2 For example, a method is known for improving a data throughput of a transmission over a communication network with a management unit for managing channels having transmission parameters and with a provisioning unit for providing, distributing and sending data over the channels. The management unit informs the providing unit of a channel change from an old to a new channel, the information comprising the transmission parameters of the new and the old channel as well as the time of performing the channel change, based on this information, an adjustment of the transmission parameters of the old channel to the Transmission parameters of the new channel are performed.

From the DE 600 15 510 T2 US-A-5 011 031 is a method of wireless-specific communication between a wireless network hardware component connected to a computer and a software component on the computer, wherein an interface to the wireless network hardware component is invoked. An input for the interface is provided, the input indicating the location of a parameter and the input including an object identifier indicating a wireless-specific request from the software component to the wireless network hardware component, the wireless-specific dynamic query data for a packet requests. The response of the wireless network hardware component is then received. The wireless-specific request is preferably a request for a frequency of a beacon signal of a sender of an incoming packet received from the wireless network hardware component, the sender being a connection point. Based on the percentage of correctly received beacon signals sent from the connection point (base station), the reliability of the transmission from the base station can be determined.

at Car2X network, however, prove the known methods for data adaptation as problematic.

measurements the course of the data rate when a vehicle is a second Vehicle approaches or gets away from the vehicle again, show a frequent switching of the data rate. Disadvantage of this Behavior is that during the switching no communication is possible and that, on the other hand, too "optimistic" Choice of data rate piling up transmission errors. More often, mistakes can be made more frequently Vehicles, so decreasing signal quality, watch. But even if the data rate too early too high there can be mistakes.

at the use of WLAN, but also when using TCP / IP or UDP / IP in general, larger data sets like For example, graphics or videos are usually not in a single Package, but are pieced into small individual packages and transmitted one after the other. This denomination generates overhead and additional network load. For WLAN maximum allowed are 2304 bytes, which is also called maximum transfer Unit MTU is called. Usually, however, only 1500 bytes used what the MTU of Ethernet corresponds to.

Especially at low signal levels, so usually at longer distances, the risk of transmission errors and thus the need for repetition increases. This is bigger, the larger the packages. So there are two really contradictory requirements. To the One should be as large individual packets are transmitted to minimize the overhead of the segmentation, on the other hand, the packets should be as small as possible to avoid transmission errors.

Of the The invention is therefore based on the technical problem of a method and a device for adjusting the data rate of WLAN radio channels and / or the packet size on WLAN radio channels in a Car2X network, by means of which transmission errors can be reduced.

The Solution of the technical problem results from the objects with the features of claims 1, 2, 6 and 7. Further advantageous embodiments of the invention will become apparent from the dependent claims.

A The first solution is to decrease signal quality immediately the data rate and / or the packet size of the Reduce radio link, with an increase in the data rate and / or the package size is only made if the signal quality for a predefined Period is above a predetermined value. The predefined Period is preferably between 0.1-10 seconds. As a parameter for the evaluation of signal quality Different values can be considered, respectively individually or in combination may be used. In the simplest case, the signal strength is evaluated. Another possibility is that the failure periodic messages (beacons) is evaluated or the failure of receipt acknowledgment signals. The basic principle of the procedure is that in doubt it is assumed that the signal quality worse because the participants move away from each other immediately the reduction of the data rate and / or the packet size is done to reduce transmission errors.

Around To prevent being too optimistic assumptions too soon on an excessively high data rate and / or packet size is switched back, the signal quality over a longer period of time above the given one Value. The evaluation of signal quality can be at a participant or all participants.

In An alternative solution sends at least one participant periodically messages (beacons) to the at least one other Participant of the radio connection, the message being at least includes the current position of the subscriber, wherein from the transmitted Position the distance between the participants is determined, where at least as a function of the determined distance the Package size is selected, and / or off the transmitted position is determined, whether the Participants move towards or away from each other and the data rate increases or stays the same when approached and is lowered when moving away from each other. The position data will be thereby for example by means of a satellite-supported Position determining device such as GPS determined. To determine the relative movement, it is necessary that even the other participant knows his position, either stuck and is known (eg permanently installed access point) or determined (eg stationary or moving vehicle). especially the Adjusting the packet size can be erratic or continuous respectively. For example, each fixed to a distance range be associated with a packet size, in the extreme case only two package sizes are used.

Preferably In addition to the position also information about the Vehicle speed and / or the direction of travel transmitted. These are easily from the GPS data or other vehicle sensor sizes derivable. This already allows a relatively accurate estimate the future reception situation are met. Is moving For example, a subscriber very quickly, so the data rate and / or the package size also reduced more become.

In Another preferred embodiment is additionally the signal strength of the received periodic messages (Beacons) and / or the transmitted network signals in the Adjustment of the data rate and / or the packet size taken into account, with the signal strength too Note that these are not only the distance, but also of depending on possible obstacles and other characteristics is. It should be noted that the alternative method either only with one participant or with several participants of a radio connection can be carried out.

Emotional a vehicle on an access point or another vehicle too, the signal strength (signal level) tends to increase and the data rate and / or packet size becomes elevated. The short-time shutdown breaks the signal level one. In order now to prevent that due to the possibly only short-term drop in signal level, the data rate again lowers In this case, a time is waited if the signal level is restored improved and as long as the data rate is left equal. This prevents too frequent changing of the data rate and increases the maximum throughput. With an increase in the data rate when approaching so is the signal strength in the short term not taken into account the connection quality appreciate. This wait can be very short, though Due to GPS or vehicle signals it is known that the participants to move towards each other.

The Invention will be described below with reference to a preferred embodiment explained in more detail. The figures show:

1 a schematic sequence of adaptation of the data rate and

2 a schematic sequence of adaptation of the packet size.

In 1 on the one hand, the signal strength S of a received signal at a subscriber of a WLAN radio connection is shown and below the data rate DR of this radio link. At time t ₀ , the signal strength is above a threshold value S _G and the radio connection is made with a high data rate DR2. At time t ₁ , the signal strength S falls below the threshold value S _G and the data rate DR is immediately reduced from DR2 to DR1. At time t ₂ , the signal strength S again exceeds the threshold value S _G , but the data rate DR remains at the reduced value DR1. The signal strength S remains above S _G until the time t ₃ , so that after the predefined time period Δt = t ₃ -t ₂ has elapsed, it is switched back to the higher data rate DR2. At time t ₄ , the signal strength S then again falls below the limit value S _G , so that switching back to the smaller data rate DR1 takes place. Subsequently, the signal strength S initially does not remain above the threshold value S _G for a period Δt. Only at the time t ₅ does the signal strength S then exceed the limit value S _G and then remain above it for the time period Δt, so that at the time t ₆ the system switches back to the higher data rate DR 2. It should be noted that the period .DELTA.t is preferably user-individually adjustable, in particular when a vehicle communicates with a base station. A radio connection can generally be made directly between vehicles or between a vehicle and a road-side unit or a stationary access point. The proposed method is suitable for all types of applications such as media download, transfer of POI data, traffic control data, but also security relevant.

In the 2 is the basic principle for adjusting the packet size shown. Here, on the one hand, the distance A or the distance of a subscriber to another subscriber, for example an access point over time, is shown. The radio link is assigned a limit distance A _G , that is, the distance between two participants small AG, a packet size P2 is selected, which corresponds for example to the MTU. This is the case at time t ₁ until time t ₂ . Otherwise, a smaller packet size P1 is used.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• DE 202004017120 U1 [0003]
• - DE 60206606 T2 [0004]
• - DE 60015510 T2 [0005]

Claims (8)

Method for adapting the data rate of WLAN radio channels and / or the packet size on WLAN radio channels in a Car2X network, wherein the subscribers are formed with transceiver units, wherein at least one subscriber of a radio connection has means for assessing the signal quality of the radio link, characterized in that with decreasing signal quality, the data rate of the radio link and / or the packet size is reduced immediately, with an increase in the data rate and / or packet size is only made if the signal quality for a predefined period .DELTA.t is above a predetermined value S _G. Method for adapting the data rate of WLAN radio channels and / or the packet size on WLAN radio channels in a Car2X network, with subscribers having transceiver units are formed, wherein at least one participant of a radio link Means for assessing the signal quality of the radio link having, characterized in that at least one Participants periodically send messages to the at least one other Participant sends, the message at least the current Position of the participant includes, from the transmitted Position of the other participants the distance between the participants determined, at least depending on the determined Distance the package size is selected and or is determined from the transmitted position, whether the participants move towards or away from each other and the Data rate at an approximation remains the same or increases and is lowered when moving away from each other. A method according to claim 2, characterized in that the Message information about the vehicle speed and / or the direction of travel contains. A method according to claim 2 or 3, characterized in that a signal strength of a received message and / or a useful signal in the adaptation of the data rate and / or packet size taken into account becomes. A method according to claim 4, characterized in that after waiting for an increase in the data rate one time before the signal strength again when assessing the signal quality is taken into account. Subscriber in a Car2X network, wherein the data transmission takes place via WLAN radio channels, wherein the subscriber comprises a transmitting / receiving unit and means for assessing the signal quality of a radio link, characterized in that with decreasing signal quality, the data rate of the radio link and / or the packet size is reduced immediately, wherein an increase in the data rate is only made if the signal quality for a predefined period .DELTA.t is above a predetermined value S _G. Subscribers in a Car2X network, with data transmission via WLAN radio channels takes place, wherein the participant a Transmitter / receiver unit comprises and means for assessing the Signal quality of a radio link, characterized, that the means of assessing signal quality based on a received message from another participant of Radio communication, the message being at least the position of other participant includes the distance between the participants determine, at least depending on the determined Distance the package size is selected and or is determined from the transmitted position, whether move the participants toward or away from each other and one Data rate of the radio connection at an approximation of participants equal stays or is raised and when moving from each other is immediately degraded. Subscriber according to claim 7, characterized in that the Means for assessing signal quality in addition a transmitted vehicle speed and / or direction of travel and / or a received signal strength during the adaptation take into account the data rate and / or packet size.