IL193755A

IL193755A - Method for identifying concealed nodes in an ad-hoc network

Info

Publication number: IL193755A
Application number: IL193755A
Authority: IL
Original assignee: Rohde & Schwarz
Priority date: 2006-03-10
Filing date: 2008-08-28
Publication date: 2013-03-24
Also published as: IL193755A0; ATE518336T1; PT2030370E; EP2030370B1; WO2007104425A1; EP2030370A2; DE102006014311A1

Abstract

The invention relates to a method for identifying concealed nodes in an ad-hoc network, according to which, respectively, one list comprising all continuously actualised adjacent nodes is sent to each node of the ad-hoc network, and a node concealed for a node of the ad-hoc network is identified in the vicinity of a node which is adjacent to the node, as soon as the target address of a user data packet sent by adjacent nodes differs from all addresses of the adjacent nodes sent in the list.

Description

I, David Charlston, MMus, BA, MIL, MITI, Dipl. Trans., of 26 Castleford Rd, Ludlow, Shropshire, SY8 IDF hereby certify that to the best of my knowledge and belief the following is a true translation made by me of the text of PCT/EP2007/001683 Dated this 2008 METHOD FOR IDENTIFYING CONCEALED NODES IN AN AD-HOC NETWORK pin in nigra onnoi ninm 'in'T1? no' y Eitan-Mehulal Law Group Advocates-Patent Attorneys P-10773-IL 1 Translation of PCT/EP2007/001683 Method for identifying concealed nodes in an ad-hoc network The invention relates to a method for identifying concealed nodes in an ad-hoc network.

A mobile ad-hoc network (MANET) consists of a number of radio devices, which form a dynamic, temporary network, in which each radio device acts as a router for the respectively other radio devices and, accordingly, a central infrastructure is not required.

One important consideration with MANETs is the coordination of access to the jointly-used transmission resource. Only one device can transmit at a given time, because otherwise collisions may occur, which could lead to a loss of information transmitted.

A Medium-Access-Control (MAC) protocol coordinates access and defines how the radio devices can divide up the limited transmission resource in fair and efficient manner. MAC methods, which implement the coordination of channel access on the basis of information regarding channel loading are very widely distributed particularly in the ad-hoc sector. Methods of this kind are combined under the heading Carrier-Sensing-Multiple-Access (CSMA) . One widely distributed WLAN method, IEEE 802.11, is based on CSMA.

With CSMA methods, all stations intending to transmit monitor the medium. If the medium is already loaded, the stations intending to transmit have to wait. If the medium 2 is not loaded, stations intending to transmit can occupy the medium and transmit. Channel access can be controlled by an arbitrary waiting time at the end of the transmission in order to avoid collisions. Different stations have different waiting times at the end of the transmission, so that one station occupies the medium first. The other stations detect this through the channel monitoring and withhold their transmission requests until the end of the current transmission. The medium is considered to be loaded if the received signal strength is disposed above a given threshold value .

MA ETs provide a dynamic, sometimes rapidly-changing, arbitrary topology. The radio devices communicate directly with radio devices adjacent to them (adjacent nodes) , if these are disposed inside the range, or via several radio devices acting as intermediate nodes (multi-hop) , which route information to the target radio device (target node) . As a result of the decentralised structure, networks of this kind are very robust, but they require independent control and coordination by the individual network nodes.

For a multi-hop operation, each radio node provides a routing table with the topology of all participating radio nodes. These routing tables are up-dated in a pro-active routine within a given time raster by means of data exchange with the adjacent radio nodes, and in a reactive routine only at the times of the data exchange with the adjacent radio nodes. If the source node locates the target node in the routing table, the data packet to be transmitted by the radio node intending to transmit is transmitted via the 3 routing path of all known intermediate nodes to the target node .

Network blockage can occur as shown in Figure 1, if two nodes, within whose range the respectively other node is not contained, provide an identical target node, which is disposed within their range. If the two nodes intend to communicate with their identical target node at the same time, their respective signals will collide. This cannot be prevented by the CSMA method because of the lack of coordination between the two nodes. The performance of the mobile ad-hoc network is reduced by a blockage of this kind. Since the two transmitting nodes are each disposed outside the range of the other node, they each represent concealed nodes for the respectively other node.

The identification of concealed nodes of this kind within a MANET therefore represents an important measure for increasing the performance of the mobile ad-hoc network.

The RTS-CTS method shown in Figure 2 is often used to avoid collisions with concealed nodes. In this context, one transmitter first transmits a short message (RTS) , which announces the transmission. The receiver also replies with a short message (CTS) , which is followed by the actual user-data transmission. The RTS and CTS signals inform all stations within the range of the transmitter and receiver regarding the transmission. During the transmission, the other stations themselves must not transmit in order to avoid collisions. 4 A similar method for identifying a concealed node is disclosed in WO 03/079708 Al . In this context, a node intending to transmit transmits a control message to an adjacent node, in the vicinity of which a node concealed from the node intending to transmit is disposed. The control message is then re-routed from the adjacent node to the concealed node, which sends an acknowledgement message via the adjacent node back to the node intending to transmit. The node intending to transmit uses this acknowledgement message as an indicator for the presence of a concealed node disposed in the vicinity of the adjacent node.

One common factor shared by the methods of the prior art is the fact that the transmission of the RTS/CTS message or respectively the control/acknowledgement message unnecessarily uses transmission capacity in mobile ad-hoc networks, which is therefore no longer available for the transmission of user-data. This has a significant impact particularly in the case of small user-data packets.

Accordingly, a minimum user-data packet size is defined when using methods of this kind.

Moreover, methods of this kind provide an interference-range, which is greater than the transmission range of the user-data transmission, so that the concealed nodes in certain spatial ranges cannot be resolved.

The object of the invention is therefore to develop a method for identifying concealed nodes in an ad-hoc network in such a manner that the transmission capacity of a method of this kind does not unnecessarily impair the performance of the network . 5 This object is achieved by a method for identifying concealed nodes in an ad-hoc network with the features of claim 1.

According to the invention, the concealed nodes in a mobile ad-hoc network are identified without signalling and without the use of any control or acknowledgement signals. The broadcast characteristic of the radio transmission, in which a signal broadcast by a radio device is received by all adjacent radio devices disposed within the range of the radio device, is used for this purpose. According to the invention, one radio node observes all user-data transmissions of all nodes adjacent to it, extracts the target address of the user-data packet from every user-data packet transmitted and compares this target address with the addresses of all adjacent nodes disposed in a list, which is obtained from the routing table. If the target address of the user-data packet corresponds with one of the addresses contained in the list, the target node, with which the adjacent node communicates, is not an adjacent node, but rather a concealed node disposed in the vicinity of the adjacent node.

If it is not already contained in the list of the respective radio node, this concealed node identified in the vicinity of an adjacent node is added to the list with an indication of the time of the identification. The transmitted user-data packet is additionally analysed with regard to certain parameters, for example, data type, packet size, service class and transmission time, and supplied to a continuous statistical evaluation stored in the list of data traffic in 6 the respective, adjacent node with the concealed node identified .

After the transmission time of the user-data packets transmitted between adjacent nodes and identified concealed nodes has been stored, a monitoring is implemented at given time intervals regarding whether the respective adjacent node or concealed node has been identified again since the last monitoring time. If the respective adjacent or concealed node has not been updated since the last monitoring time, the respectively-identified, adjacent node or concealed node is deleted from the list.

An exemplary embodiment of the method according to the invention for identifying concealed nodes in an ad-hoc network is explained in greater detail below with reference to the drawings. The drawings are as follows: Figure 1 shows the spatial distribution of transmitting, adjacent and concealed nodes; Figure 2 shows the data exchange in a RTS-CTS network; Figure 3 shows a flow chart of the method according to the invention for identifying concealed nodes in an ad-hoc network; and Figure 4 shows a block-circuit diagram of the system for identifying a concealed node in an ad-hoc network according to the invention in every node of the ad-hoc network. 7 With reference to Figure 3, the following section describes the method according to the invention for identifying a concealed node applied to one node selected from all of the nodes disposed in an ad-hoc network.

In the first procedural stage S10, the user-data packet transmitted by the transmitting node is received by the selected node in the ad-hoc network, which is disposed within the range of a transmitting node.

In the description below, the term source node is understood to mean that node, in which the data packet is currently present, while the term target node is understood to mean that node, to which the source node sends the data packet.

In the next procedural stage S20, after the receipt of the user-data packet in the physical layer of the selected node, the MAC source address of the received user-data packet is extracted in a superordinate layer of the selected node and, since the transmitting node is a node adjacent to the selected node, the extracted MAC source address is compared with a node address of adjacent nodes stored in a list. The adjacent nodes stored in the list are up-dated from a routing table associated with the selected node in a proactive routing process within a given time raster, and within a reactive routing process in the case of a user-data transmission of a node adjacent to the selected node.

The interrogation of procedural stage S30 determines whether the adjacent node identified in procedural stage S20 is already present in the list. If the adjacent node just identified is already present in the list, the adjacent node 8 present in the list is up-dated in the next procedural stage S40 with the transmission time and message parameters of the user-data packet transmitted. The message parameters of the transmitted user-data packet are data such as the packet size, the data type or the service class of the transmitted user-data packet, which are supplied for a statistical evaluation for each adjacent node.

If the adjacent node just identified is not present in the list, it is entered in the list in the next procedural stage S50 together with its node address, the transmission time and the message parameters of the user-data packet just transmitted.

The next procedural stage S60 comprises the extraction of the MAC target address of the user-data packet just received. The interrogation of the next procedural stage S70, determines from the extracted MAC address, whether the selected node is the target node of the user-data packet transmitted. If this is the case, the user-data packet received is routed in the next procedural stage S80 for further processing to the higher protocol layers of the selected node and supplied for statistical evaluation in procedural stage S140.

If the user-data packet just received is not destined for the selected node, the next interrogation in the next procedural stage S90 determines on the basis of the extracted MAC target address, whether an adjacent node of the selected node already entered in the list is the target of the user-data packet just received. 9 If this is the case, the adjacent node entered in the list is up-dated in the next procedural stage S100 with the transmission time and the message parameters of the user-data packet transmitted. Otherwise, the interrogation in procedural stage S110, determines whether the node identified as a concealed node is already present as a concealed node in the list in the selected node.

If the identified concealed node is already present in the list, in procedural stage S130, this concealed node is updated in the list with the transmission time and message parameters of the user-data packet just transmitted. In the event that the concealed node identified is not yet present in the list, the identified concealed node is entered in procedural stage S120 in the list in the selected node with its node address, transmission time and message parameters of the user-data packet just transmitted.

In the penultimate procedural stage S140, a current statistical evaluation is implemented with regard to the individual message parameters stored in the list in the selected node for the user-data packets transferred from and respectively to the individual adjacent and concealed nodes. This statistical evaluation can characterise the data traffic for adjacent and concealed nodes of the respectively selected node. On this basis, appropriate transmission times, in which an absence of data traffic between adjacent and concealed nodes can be assumed with a high probability, can be determined by the respectively-selected node for the transmission of user-data packets. 10 Finally, in the last procedural stage S150, within a given time raster, the list in the selected node is investigated with regard to the up-date status of the adjacent nodes and concealed nodes entered. For this purpose, it is determined whether the up-dated and stored transmission time of the user-data packet transmitted between adjacent and concealed nodes has been up-dated within the last time segment. If the transmission times stored for every adjacent and concealed node have not been up-dated within the last time segment, the entry of the respective adjacent or concealed node has expired and is therefore deleted from the list.

Figure 4 shows a block-circuit diagram of the system according to the invention, which is implemented in every node of the ad-hoc network, in order to implement in this node the method according to the invention for identifying concealed nodes within an ad-hoc network The system according to the invention consists of a monitoring instance 1, which analyses and extracts from all received user-data packets information of the user-data packet relevant for the method according to the invention, such as MAC target address, MAC source address and message parameters. The monitoring instance 1, which is preferably realised in the network layer, can implement the extraction of the relevant data from the received user-data packet either separately for an individual layer, preferably the network layer, or alternatively, in a combined manner for all layers of the node.

The extracted information from the received user-data packet is entered from an evaluation instance 2, which is also 11 preferably implemented in the network layer and connected downstream of the monitoring instance 1, in a list stored in a databank 3 at the correct position respectively for every known or new adjacent or concealed node. The databank 3 can also preferably be realised in the network layer. Alongside the entry of the extracted information in the list, the evaluation instance 2 implements the statistical evaluation of the message parameters for every adjacent and concealed node entered in the list.

The invention is not restricted to the exemplary embodiment presented. All of the features and measures can be combined with one another as required within the framework of the invention.

Claims

12 XXXX/2 Amended claims

1. Method for identifying concealed nodes in an ad-hoc network, by providing in every node of the ad-hoc network a list containing all continuously up-dated adjacent nodes, by identifying a node, which is concealed for one node of the ad-hoc network, in the vicinity of a node adjacent to the respective node, and by adding the said concealed node to the respective list as a concealed node, as soon as the target address of a user-data packet transmitted from the adjacent node differs from all of the addresses of the adjacent nodes contained respectively in the list, characterised In that statistical information regarding the data traffic respectively between the adjacent node and the concealed node disposed in the vicinity of the adjacent node is stored in the list in every node for every adjacent node and every concealed node and statistically evaluated in order to determine appropriate transmission times for the transmission of user-data packets, in which the absence of data traffic between adjacent and concealed nodes can be assumed with a high probability.

2. Method for identifying concealed nodes according to claim 1, characterised In that, 13 XXXX/2 with every identification of a concealed node, the concealed node is up-dated in the list by adding the time of the current identification.

3. Method for identifying concealed nodes according to claim 1 or 2, characterised in that, the statistical information is obtained from the statistical evaluation of the packet size, the data type, the service class and/or the transmission time of the user-data packets exchanged respectively between the adjacent node and the concealed node.

4. Method for identifying concealed nodes according to claim 2, characterised in that those adjacent nodes and/or those concealed nodes, which were not up-dated within the last time interval, are deleted from the list in every node after a given time interval.

5. Method for identifying concealed nodes according to any one of claims 1 to 4, characterised in that the list in every node regarding respectively adjacent and concealed nodes is administered with node-relevant data from the network layer separately within the network layer.

6. Method for identifying concealed nodes according to any one of claims 1 to 4, characterised in that, 14 XXXX/2 the list in every node regarding respectively adjacent and concealed nodes is administered with node-relevant data from all layers in a combined manner within one of the layers. 15

7. The method according to any one of claims 1-6 substantially as described in the specification and in the foregoing claims.

8. The method according to any one of claims 1-6 substantially as illustrated in any of the drawings. P-10773-IL