IL190430A - Method and system for transmitting messages in a temporary radio network - Google Patents

Description

'■■■■■Ill 190430 ,7.* , 453605 METHOD AND SYSTEM FOR TRANSMITTING MESSAGES IN A TEMPORARY RADIO NETWORK j anT I 'ΤΊ nura mirnn n-pii i rmym nu'ty Eitan-Mehulal Law Group Advocates-Patent Attorneys P-10392-IL 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 Dated this day of 2008 1 Translation EP2006009388 Method and system for message transmission in a temporary radio network The invention relates to a method and system for message transmission in a temporary radio network (mobile ad-hoc network) .

A mobile ad-hoc network (e.g. MANET) is a radio network consisting of several radio stations, which is set up in an arbitrary region at an arbitrary time without maintaining a central infrastructure and which is disassembled again at a subsequent arbitrary time. Mobile ad-hoc networks of this kind are suitable primarily for military applications, in which a radio network is set up between a given number of radio stations communicating with one another within an arbitrary war zone or crisis region for the duration of the application .

In view of the absence of a central infrastructure, for example, base stations or satellites, useful data and control data are communicated in a decentralised manner between the individual radio stations disposed within the range. A message transmission between two radio stations is implemented over a distance greater than the range of the radio station by interconnecting one or more radio stations which are disposed spatially between the transmitting radio station and the receiving radio station (multi-hop operation) . Controlling and monitoring a mobile ad-hoc 2 network of this kind between a radio station acting as the source node with one or more radio station (s) acting as intermediate nodes and a radio station acting as the target node can be implemented in an autonomous manner by the network nodes participating in the mobile ad-hoc network.

The substantial challenges for controlling and monitoring a mobile ad-hoc network of this kind include the following: - efficient exploitation of the limited network capacity; - fairness in channel allocation for each transmitting network node; - avoidance of collisions (especially in the case of hidden and exposed terminals); - routing in the case of mobile network nodes, in multi-hop operating mode, with changing network participants in the ad-hoc network and with variable properties of the transmission channel resulting from regional conditions.

Current realisations of mobile ad-hoc networks are substantially based on the TCP/IP protocol standard (Internet standard) . Channel access for each network node of the mobile ad-hoc network is implemented in the medium-access-control layer (MAC-layer) .

The most widely-distributed method for channel access in mobile ad-hoc networks is the carrier-sensing-multiple-access method (CSMA method) . With the CSMA method, every network node, which competes with regard to its transmission requirement for access to the network with other network nodes, monitors the network until free network capacities are available. With the CSMA method according to the IEEE standard 802.11 used in WLAN ad-hoc networks, a relatively long free network period (distributed inter-frame space DIFS) is identified; a stochastically-distributed waiting time (random back-off time) in order to avoid a collision with another network node, which has a transmission requirement at the same time, is waited; and the network access is started by the transmission of the message. A successful receipt of the message transmitted from the source node to the target node is acknowledged by the target node and by each intermediate node after the expiration of a relatively-short free network period (short inter-frame space SIFS) with an acknowledgement (ACK) . If the source node or respectively the transmitting intermediate node does not receive the acknowledgement from the target node or the receiving intermediate node within a given time interval or if it receives a message deviating from its transmitted message, an error message transmission is present, and the source node or respectively the transmitting intermediate node restarts the transmission of the lost or erroneously-transmitted message after identifying a distributed inter-frame space and waiting for the stochastic waiting period.

The CSMA method in the WLAN standard 802.11 allows a comparatively-fair distribution of the transmission channel among all network participants with a transmission requirement and reduces the number of collisions within the ad-hoc network. Additional collision avoidance can be achieved according to the WLAN-standard IEEE 802.11 by introducing the RTS/CTS operating mode, in which the transmitting network node notifies the receiving network node of an exclusive network access before transmission of the message with a request (request-to-send-signal, RTS-signal), and the exclusive network access is acknowledged by 4 the receiving network node with an allocation (clear-to-send-signal, CTS-signal). Since the allocation (CTS-signal) is also received by all other transmitting network nodes within the range of the receiving network node, it can be guaranteed that, on the one hand, only one transmitting network node, which is disposed within the range of the receiving network node but not within the range of the other transmitting network nodes, receives an access to the transmission channel (hidden-terminal problem) and, on the other hand, two transmitting network nodes for each respective receiving network node simultaneously receive an access to the transmission channel, if the two receiving network nodes are not disposed within the range relative to one another (exposed-terminal problem) .

If the message transmission in the mobile ad-hoc network between the source node and the target node is implemented according to Figure 1 in the multi-hop operating mode via one or more intermediate nodes, further channel accesses are required. As shown in Figure 2 for the case of one intermediate node, the transmission channel is unnecessarily burdened in the direction towards the source node with the message to be transmitted from the intermediate node to the target node, and unnecessarily burdened in the direction towards the target node with the acknowledgement to be transmitted from the intermediate node to the source node. This unnecessary burdening of the transmission channel reduces the efficiency of exploitation of the limited network capacity.

A method for increasing the efficiency of exploitation of the limited network capacity is presented in Xiao, Y. : "Concatenation and Piggyback Mechanisms for the IEEE 802.11 MAC", Proceedings of the IEEE Wireless Communications and Networking Conference, 2004, Atlanta, in which the acknowledgement of the successful receipt of the message to be transmitted from the source node to the target node is sent by piggyback traffic with a message to be transmitted from the target node to the source node. Since a message to be transmitted from the target node to the source node is not generally immediately present when the message to be transmitted from the source node to the target node arrives in the target node, a considerable delay in the piggyback traffic, and therefore also a delay in the arrival of the acknowledgement in the source node, must be taken into account under some circumstances. This delayed acknowledgement can lead to an expiration of a timer in the source node and therefore to an error notification and an undesired re-transmission of the message from the source node to the target node.

The object of the invention is therefore to develop further a method and a system for message transmission between a source node and a target node within a mobile ad-hoc network with an interconnection of at least one intermediate node in such a manner that the acknowledgement of receipt to be transmitted from the intermediate nodes does not unnecessarily burden the limited network capacities and arrives promptly in the source node or respectively in the preceding intermediate nodes.

This object is achieved with reference to the method by the features of claim 1 and with reference to the system by the 6 features of claim 10. The dependent claims specify advantageous further developments.

According to the invention, the acknowledgement by an intermediate node of the successful receipt of a message transmitted from the source node or from a preceding intermediate node is packaged in a piggyback arrangement with the same message, which is to be transmitted from the intermediate node to a downstream intermediate node or to the target node via the multi-hop operating mode. The burden on the transmission channel is minimised, and the transmission channel is therefore sufficiently exploited by packaging the acknowledgement and the message in a piggyback arrangement. Since the message to be transmitted via piggyback traffic with the acknowledgement from the intermediate node is transmitted immediately after the expiration of a short inter-frame space (SIFS) , the acknowledgement of successful receipt of the message by the target node can be received from the source node before the expiration of a permissible time interval. An undesirable re-transmission of the messages from the source node to the target node is not required in this case.

The correct allocation by the source node transmitting the message of the acknowledgement received via piggyback traffic together with the associated message is also implemented with reference to the message contained in the piggyback data packet and the address of the piggyback data packet, which agrees with the address of the target node.

In the multi-hop operating mode, the transmission by the intermediate node of a piggyback data packet, which contains 7 the received message and the acknowledgement of successful receipt of the messages, requires an evaluation by the radio station integrated in the mobile ad-hoc network, which receives the message, on the basis of which the radio station determines whether it is acting as an intermediate node or a target node for the message received. This evaluation is implemented in the medium-access-control layer of the mobile ad-hoc network operating according to a packet-orientated protocol standard, for example, the TCP/IP protocol standard.

The evaluation by the radio station, regarding whether it is acting as an intermediate node or a target node for a received message, forms the content of the route planning (routing) . In a first variant of this routing - "source/path routing" - in the context of a message transmission implemented according to a packet-orientated protocol standard, the addresses of the target node and of all intermediate nodes are stored by the source node in the status component (header) of the transmission frame containing the message. The radio station receiving a message need therefore only evaluate this header of the transmission frame of the received message, in order to determine whether it must act as an intermediate node or a target node. In a second variant of the routing ("hop-by-hop-routing") the next intermediate node is determined from the address of the target node stored in the header of the transmission frame of the received message and a local database stored in the radio station. This local database (forward database, FDB) is generally stored in the network layer, for example, in the IP-layer. For reasons of speed, this local database is rolled out into a memory region, for 8 example, within the medium-access-control layer, to which the medium-access-control layer has rapid access and which is updated at a given rhythm by a routing instance in the network layer cooperating with the FDB management.

If the radio station recognises that it is acting as a target node for the received message, it transmits the acknowledgement of successful receipt without the use of piggyback traffic. Furthermore, it routes the received message to the higher layers - application layer and transport layer - for further evaluation.

An exemplary embodiment of the method and the system according to the invention for message transmission in a temporary radio network (mobile ad-hoc network) is explained in greater detail below with reference to the drawings. The drawings are as follows: Figure 1 shows a schematic presentation of a multi-hop operating mode of a message transmission in a temporary radio network (mobile ad-hoc network) according to the prior art; Figure 2 shows a channel-loading diagram for a message transmission in a temporary radio network (mobile ad-hoc network) according to the prior art; Figure 3 shows a flow chart for a method according to the invention for message transmission in a temporary radio network (mobile ad-hoc network) ; 9 Figure 4 shows a layer structure of a system according to the invention for message transmission in a temporary radio network (mobile ad-hoc network) ; and Figure 5 shows a channel-loading diagram for a method and a system according to the invention for message transmission in a temporary radio network (mobile ad-hoc network) .

In the first procedural stage SIO of the method according to the invention/ the transmission frame is built up in the medium-access-control layer of the source node, in the case of a routing by means of "hop-by-hop-routing", from the message in the data component, which is to be transmitted; and, in the case of a routing by means of "source/path routing", in the status component (header) from the address of the target node or from the addresses of all intermediate nodes and of the target node.

In the next procedural stage S20, the transmission frame prepared in the MAC-layer in procedural stage SIO is transmitted from the physical layer of the source node in the broadcast operating mode of the radio station acting as the source node. Additionally, a timer is set and started in the MAC-layer of the source node in order to monitor the transmission time of the message.

In procedural stage S30, the transmission frame transmitted from the source node, intermediate node or target node is received in the physical layer of a radio station disposed within the range of the source node, intermediate node or target node. Also in procedural stage S30, the received frame is unpacked in the MAC-layer of the radio station.

If a timer was started by the radio station and an acknowledgement is contained in the unpacked transmission frame, the timer is reset and, the transmission time of the message from the radio station to the next intermediate node or respectively to the target node, with the addition of the re-transmission time for the acknowledgement from the next intermediate node or respectively target node to the radio station, is determined from the timer status.

If the comparison of the transmission time determined in procedural stage S40 with a specified reference time results, in procedural stage S50, in an overshooting of the reference time by the determined transmission time, a retransmission of the message is implemented in procedural stage S60 by once again building up a frame from the message to be transmitted and the address of the target node and/or intermediate node in the MAC-layer of the radio station.

If the comparison of the transmission time determined in procedural stage S40 with a specified reference time results, in procedural stage S50, in an undershooting of the reference time by the determined transmission time, the status component (header) is evaluated in procedural stage S70 in the MAC-layer of the radio station receiving the transmission frame, in order to determine whether the receiving radio station is a node between the source node and the target node, and whether the receiving radio station represents an intermediate node or the target node. For this 11 purpose, in the case of a "hop-by-hop-routing", the address of the target node stored in the header of the transmission frame, and, in the case of a "source/path routing", the addresses of all intermediates nodes and of the target node, are read out. In the case of a "hop-by-hop-routing", it is determined whether the radio station is disposed between the source node and the target node. In the case of a "source/path-routing", it is determined whether the address of the radio station agrees with the address of an intermediate node or of the target node. If the radio station is not disposed along the connection between the source node and the target node, and if there is no identity between the radio station and one of the planned intermediate nodes and the target node, the further processing in the MAC-layer and in all superordinate layers of the radio station is terminated.

If, in procedural stage S80, the comparison of the address of the radio station with the address of an intermediate node stored in the header of the transmission frame results in an identity, and, as a result, if the radio station is disposed between the source node and the target node and is therefore an intermediate node, then - only in the case of a "hop-by-hop-routing" - the next intermediate node is determined in the subsequent procedural stage S90 in the MAC-layer of the radio station acting as the intermediate node. The next intermediate node is determined from the address of the target node and connection data, which are stored in a local database present in the intermediate node. Since this local database ("forward database" FDB) is generally stored and processed in the network layer and is not therefore generally suitable for rapid determination 12 within the context of a smooth message transmission, a copy of the FDB databank is rolled out into a memory region, to which the MAC-layer has rapid access. To guarantee that the data in the FDB layer are up-to-date, these data are updated within a given time interval by a routing instance of the network layer.

In the next procedural stage S100, the transmission frame is built up from the message to be transmitted to the target node in the piggyback arrangement together with the acknowledgement of successful receipt of the message transmitted to the intermediate node and, in the case of a "hop-by-hop routing", from the address of the next intermediate node determined in the status component of the current intermediate node; or from the addresses of all intermediate nodes and target nodes planned by means of the "source/path routing".

After waiting for a short inter-frame space (SIFS) following the receipt of the message to be transmitted to the target node, in procedural stage S30, the transmission frame built up in procedural stage S60 or procedural stage S100 is transmitted from the current radio station in procedural stage S110, and a timer is set and started in the MAC-layer of the radio station for the renewed monitoring of the transmission time.

This transmission frame transmitted from the current radio station is received and unpacked according to procedural stage S30 by a radio station disposed within the range. 13 If, according to procedural stage S80, the radio station is the target node, an acknowledgement of the successful receipt of the message is packed and transmitted by the target node, in procedural stage S120, together with the next message to be transmitted from the target node.

Finally, in the concluding procedural stage S130, the message unpacked in the MAC-layer is routed via the network layer to the applications layer of the target node for further processing.

Figure 4 presents the layer structure of a system according to the invention for message transmission in a temporary radio network (mobile ad-hoc network) with a single intermediate node. In this context, the units provided for routing by means of "hop-by-hop routing" (FDB management and rolled-out FDB databank) are presented in the individual layers .

It is evident that all of the nodes participating in the message transmission provide a physical layer, substantially for control and monitoring of the transport of the messages via a physical medium (continuous lines in the drawing) , a MAC-layer, substantially for management of the transmission frame (set up and unpacking) and for external routing by means of "hop-by-hop routing", and a connection layer, for example, an IP layer, substantially for superordinate route management .

Beyond this, additional layers (marked in Figure 4 by dot-and-dash lines) are essential to the idea of the invention only in the source node and target node. These layers are 14 the transport layer, for example, the TCP layer, substantially for the logical set up and cancellation of a connection between network participants (dotted line in Figure 4) and the applications layer, in which the messages to be transmitted are subjected to pre-processing and postprocessing .

In the channel-loading diagram for a method and a system according to the invention for message transmission within a temporary radio network (mobile ad-hoc network) , which is illustrated in Figure 5, two advantages are evident by comparison with the channel-loading diagram without piggyback traffic as shown in Figure 2: - significant reduction of the channel loading through the piggyback bundling of the message to be transmitted to the target node together with the acknowledgement of successful receipt of the message to be transmitted to the target node within a single transmission frame by comparison with two transmission frames (acknowledgement (ACK) and message) in the case of a transmission frame without piggyback arrangement; - significant reduction in the transmission time of the message from the source node to the target node including the acknowledgement message.

By comparison with the prior art, the significant reduction in transmission time must be emphasised, because the next possible transmission frame to be transmitted from the intermediate node is used for a transmission of the acknowledgement from an intermediate node or target node to a preceding intermediate node or to the source node.

The invention is not restricted to the exemplary embodiment presented. Other protocol standards in addition to the TCP/IP protocol standard are also covered by the invention.

Claims (1)

1. ^Amended claims Method for message transmission according to a packet-orientated protocol standard via a temporary radio network between a radio station acting as a source node and a radio station acting as a target node with an interconnection of at least one radio station acting as an intermediate node, wherein an acknowledgement of successful receipt is transmitted from the intermediate node which has successfully received the message transmitted from the source node together with a message to be transmitted from the intermediate node, wherein the message to be transmitted from the intermediate node together with the acknowledgement of successful receipt is the message successfully received from the source node, characterised in that the radio station successfully receiving a message and acting as an intermediate node determines the next intermediate node or target node from a local database and from the status component of a transmission frame of the target node containing the message to be transmitted, that the database is a local routing databank rolled out from the network layer into the medium-access- control layer, and that the local routing databank is updated by a routing instance of the network layer. Method for message transmission according to claim 1, characterised in that a radio station, which successfully receives a message transmitted from the source node, determines by evaluating the received message, whether it fulfils the function of an intermediate node or a target node for the received message. Method for message transmission according to claim 1 or 2, characterised in that the message transmission is implemented according to a packet-orientated protocol standard. Method for message transmission according to claim 3, characterised in that the evaluation of a radio station successfully receiving a message with regard to its function as an intermediate node or a target node is implemented in a medium-access-control layer of the message transmission implemented according to the packet-orientated protocol standard. Method for message transmission according to claim 4, characterised in that the radio station successfully receiving a message determines its function as an intermediate node or a target node from the status component of a transmission frame containing the message to be transmitted . Method for message transmission according to claim 5, characterised in that XXXX/2 the radio station successfully receiving a message and acting as an intermediate node determines the next intermediate node or target node from the status component of a transmission frame containing the message to be transmitted, which contains all of the intermediate nodes and target nodes determined by the source node. Method for message transmission according to claim 5, characterised in that the radio station successfully receiving a message and acting as a target node transmits only the acknowledgement of the successfully-received message. System for message transmission according to a packet-orientated protocol standard via a temporary radio network between a radio station acting as a source node and a radio station acting as a target node with an interconnection of at least one radio station acting as an intermediate node, characterised in that the evaluation of the radio station successfully receiving a message with regard to its function as an intermediate node or target node is implemented in a medium-access-control layer, that the radio station successfully receiving a message and acting as an intermediate node provides a local routing databank rolled out from the network layer into the medium-access-control layer in order to determine the next intermediate node or target node, and that the local routing databank is updated by a routing instance of the network layer. 19 190430/3 that the local routing databank is updated by a routing instance of the network layer. Λ the Applicant, Advocates - P-10392-IL