Intelligent communication node using beacon in a mobile ad hoc network

<u>Field of the Invention</u>

0001The present invention relates to the field of communication networks, and, more particularly, to mobile ad hoc wireless networks and related methods.

<u>Background of the Invention</u>

0002A rapidly developing area of wireless networks is mobile ad hoc networks. Physically, a mobile ad hoc network includes a number of geographically-distributed, potentially mobile nodes wirelessly connected by one or more radio frequency channels. Compared with other type of networks, such as cellular networks or satellite networks, the most distinctive feature of mobile ad hoc networks is the lack of any fixed infrastructure. A pure mobile ad hoc network is formed of mobile nodes only, and a network is created on the fly as the nodes transmit to or receive from other nodes. Node movement patterns may be anywhere from continuous to start-stop type patterns. The network does not in general depend on a particular node and dynamically adjusts as some nodes join or others leave the network.

0003An ad hoc network can be quickly deployed and provide much needed communications. Ad hoc networks will allow people to exchange data in the field or in a class room without using any network structure except the one they create by simply turning on their computers or PDAs, for example.

0004New applications for mobile ad hoc networks will continue to emerge and become an important part of the communication structure. Due to the lack of a fixed infrastructure, nodes must self-organize and reconfigure as they move, join or leave the network. All nodes could potentially be functionally identical and there may not be any natural hierarchy or central controller in the network. Many network-controlling functions are distributed among the nodes. Nodes are often powered by batteries and have limited communication and computation capabilities. The bandwidth of the system is usually limited. The distance between two nodes often exceeds the radio transmission range, and a transmission has to be relayed by other nodes before reaching its destination. Consequently, a network has a multihop topology, and this topology changes as the nodes move around.

0005The Mobile Ad-Hoc Networks (MANET) working group of the Internet Engineering Task Force (IETF) has been actively evaluating and standardizing routing, including multicasting, protocols. Because the network topology changes arbitrarily as the nodes move, information is subject to becoming obsolete, and different nodes often have different views of the network, both in time (information may be outdated at some nodes but current at others) and in space (a node may only know the network topology in its neighborhood usually not far away from itself).

0006A routing protocol needs to adapt to frequent topology changes and with less accurate information. Because of these unique requirements, routing in these networks is very different from others. Gathering fresh information about the entire network is often costly and impractical. Many routing protocols are reactive (on-demand) protocols: they collect routing information only when necessary and to destinations they need routes to, and do not generally maintain unused routes after some period of time. This way the routing overhead is greatly reduced compared to proactive protocols which maintain routes to all destinations at periodic time intervals. It is important for a protocol to be adaptive. Ad Hoc on Demand Distance Vector (AODV), Dynamic Source Routing (DSR) and Temporally Ordered Routing Algorithm (TORA) are representative of on-demand routing protocols presented at the MANET working group.

0007Examples of other various routing protocols include Destination-Sequenced Distance Vector (DSDV) routing which is disclosed in <patcit id="pcit0001" dnum="US5412654A"><text>U.S. Patent No. 5,412,654 to Perkins</text></patcit>, and Zone Routing Protocol (ZRP) which is disclosed in <patcit id="pcit0002" dnum="US6304556B"><text>U.S. Patent No. 6,304,556 to Haas</text></patcit>. ZRP is a hybrid protocol using both proactive and reactive approaches based upon distance from a source node.

0008These conventional routing protocols use a best effort approach in selecting a route from the source node to the destination node. Typically, the number of hops is the main criteria (metric) in such a best effort approach. In other words, the route with the least amount of hops is selected as the transmission route.

0009Existing communication node advertisement and communication node neighbor discovery approaches including those for ad hoc networks, only use network-condition-independent mechanisms such as constant transmit rate or random transmit rate "hello" messages from nodes to announce, or advertise, their presence. These transmitted announcements are called "beacons" and conventional approaches do not endow these beacons with any degree of intelligence. Other nodes may detect these beacons and either form a network from scratch, add the newly-detected node to the existing network, or disallow further communications to this newly-detected node.

0010Document XP000823968, ROYER E M ET AL: "A REVIEW OF CURRENT ROUTING PROTOCOLS FOR AD HOC MOBILE WIRELESS NETWORKS" discloses various routing protocols for mobile ad-hoc networks, including table based protocols and source initiated on-demand protocols, which in turn includes on-demand dynamic source routing, temporarily ordered routing algorithm, associativity-based routing e.t.c. For dynamic routing protocols document XP000823968 discloses sending discovery packets by the nodes. Further the comparison of the various methods is disclosed.

0011Document <patcit id="pcit0003" dnum="WO0192992A"><text>WO 01/92992</text></patcit> discloses a method and apparatus for varying the rate at which broadcast beacons are transmitted.

<u>Summary of the invention</u>

0012In view of the foregoing background, it is therefore an object of the present invention to provide the general framework, called the "Intelligent Communication Node Object Beacon Framework" (ICBF), for intelligent, adaptive advertisement by any communications node object of its presence and/or the corresponding detection (neighbor discovery) by another node object or the network of those node objects transmitting such beacons.

0013This and other objects, features, and advantages in accordance with the present invention are provided by a method for advertisement of presence by a mobile node or by a group of mobile nodes, in a mobile ad hoc network. The mobile ad hoc network includes a plurality of wireless mobile nodes and a plurality of wireless communication links connecting the nodes together. The group of mobile nodes includes a temporary or permanent association of two or more of the plurality of mobile nodes. The method includes transmitting node/group information using a beacon signal, determining a node/group condition or set of conditions of the corresponding mobile node or group of nodes, and varying the beacon signal based upon the determined condition or set of conditions. The beacon signal includes information relating to a status of the corresponding mobile node or group of nodes.

0014Varying the beacon signal preferably includes varying transmission rate, transmission frequency and transmission pattern. Also, the condition preferably includes node/group movement, such as node velocity, node acceleration and/or node movement pattern of the corresponding mobile node. Here, varying the beacon signal includes increasing the transmission rate based upon increased node movement. The node movement may be determined using global positioning satellites (GPS), local landmarks, triangulation, and/or by measuring inertia of the mobile node.

0015The condition may also or alternatively include quality of service (QoS), such as error rate and/or available bandwidth. Here, varying the beacon signal may include increasing the transmission rate and/or changing the transmission frequency based upon decreased QoS. The transmission rate of the beacon signal should not exceed a rate threshold based upon available bandwidth. Group beacon signals are transmitted by a subset of mobile nodes of the group of mobile nodes. Such a subset includes a range from one mobile node to all the mobile nodes of the group. Also, the beacon signals may include information relating to a status of the mobile ad hoc network, such as information about the links between the nodes of the network.

0016Objects, features, and advantages in accordance with the present invention are also provided by a mobile ad hoc network including a plurality of wireless mobile nodes, and a plurality of wireless communication links connecting the nodes together. Each mobile node includes a communications device to wirelessly communicate with other nodes of the plurality of nodes via the wireless communication links, and a controller to route communications via the communications device. The controller includes at least a beacon signal generator to generate and transmit status signals, and a condition determining unit to determine a condition of the mobile node. The beacon signal generator varies the beacon signal based upon the determined condition of the mobile node. Again, the beacon signal includes information relating to a status of the mobile node.

0017The beacon signals may further include information relating to a status of a group of mobile nodes which are a temporary or permanent association of at least two of the plurality of mobile nodes. Here, the condition determining unit further determines a condition of the group of mobile nodes, and the beacon signal generator varies the beacon signal based upon the determined condition of the group of mobile nodes. The beacon signal generator may vary the transmission rate, transmission frequency and/or transmission pattern of the beacon signal.

0018The node condition may include node movement, and the beacon signal generator may vary beacon signal by increasing the transmission rate based upon increased node movement and decreasing the transmission rate based upon decreased node movement. The node movement includes node velocity, node acceleration and/or node movement pattern of the corresponding mobile node or group of nodes. The condition determining unit may comprise a global positioning satellite (GPS) device for determining the node movement, and/or may ' determine the node movement using local landmarks, by tracking the relative velocity using triangulation and/or by measuring inertia of the mobile node.

0019Furthermore, the node condition may include quality of service (QoS), and the beacon signal generator varies the beacon signal by increasing the transmission rate and/or changing the transmission frequency based upon decreased QoS. The beacon signal generator should not increase the transmission rate of the beacon status signals beyond a rate threshold based upon available bandwidth. Again, the beacon signals may also include information relating to a status of the mobile ad hoc network, such as information about the links connecting the nodes of the network.

0020The invention is carried out by the methods of independent claims 1 and 7 and the system of independent claim 12.

<u>Brief Description of the Drawings</u>

0021<ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001">FIG. 1</figref> is a schematic diagram of a mobile ad hoc network in accordance with the present invention.</li><li><figref idref="f0002">FIG. 2</figref> is a flowchart illustrating the steps of a method for node advertisement by a mobile node, or group of mobile nodes, in a mobile ad hoc network in accordance with the present invention.</li><li><figref idref="f0002">FIG. 3</figref> is a schematic diagram illustrating a router of a node in accordance with the network of the present invention.</li><li><figref idref="f0003">FIG. 4</figref> is a schematic diagram illustrating the details of the controller of the router in <figref idref="f0002">FIG. 3</figref>.</li></ul>

<u>Detailed Description of the Preferred Embodiments</u>

0022The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout, and prime notation is used to indicate similar elements in alternative embodiments.

0023As will be appreciated by those skilled in the art, portions of the present invention may be embodied as a method, data processing system, or computer program product. Accordingly, these portions of the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, portions of the present invention may be a computer program product on a computer-usable storage medium having computer readable program code on the medium. Any suitable computer readable medium may be utilized including, but not limited to, static and dynamic storage devices, hard disks, optical storage devices, and magnetic storage devices.

0024The present invention is described below with reference to flowchart illustrations of methods, systems, and computer program products according to an embodiment of the invention. It will be understood that blocks of the illustrations, and combinations of blocks in the illustrations, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, implement the functions specified in the block or blocks.

0025These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory result in an article of manufacture including instructions which implement the function specified in the flowchart block or blocks. The computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer or other programmable apparatus implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart block or blocks.

0026Referring initially to <figref idref="f0001">FIGs. 1</figref> and <figref idref="f0002">2</figref>, a method for node advertising in a mobile ad hoc network <b>10</b> will now be described. The network <b>10</b> includes a plurality of mobile nodes <b>12</b> including the source node <b>S</b> and the destination node <b>D</b> with intermediate nodes there between. The nodes <b>12,</b> such as laptop computers, personal digital assistants (PDAs) or mobile phones, are connected by wireless communication links <b>14</b> as would be appreciated by the skilled artisan.

0027A description of a problem follows. A snapshot of a mobile ad hoc network <b>10</b> is shown in <figref idref="f0001">FIG. 1</figref>. Through route discovery, two routes <b>R1</b> and <b>R2</b> have been identified from the Source Node <b>S</b> to the Destination Node <b>D.</b> The second route <b>R2</b> has been identified by the source node <b>S</b> as its primary route to the destination node <b>D.</b> The first route <b>R1</b> will only be used if the second route <b>R2</b> becomes invalid.

0028Conventionally, each of the nodes <b>12</b> in both routes <b>R1</b> and <b>R2</b> including the source node <b>S</b> and the destination node <b>D</b> would transmit neighbor discovery beacons at some constant periodic rate. If some nodes <b>12</b> in route <b>R2</b> move too fast and end up out of the range of an adjacent node <b>12</b> in the route before the next beacon transmissions from these nodes, the beacon transmission rates (also called beacon rates) cannot therefore keep up with the rate at which the source node <b>S</b> needs to update its route table or route cache.

0029Since the source node <b>S</b> would falsely believe that route <b>R2</b> is valid, it would attempt to send information to the destination node <b>D using</b> this route <b>R2.</b> Therefore, some links <b>14</b> and nodes <b>12</b> would become tied up performing a task which cannot be completed. This would result in lost time and inefficient use of network <b>10</b> bandwidth. Retransmission along the route <b>R1</b> would then be necessary or the discovery of an entirely new route would be required if a straying node <b>12</b> was common to both the routes <b>R1</b> and <b>R2.</b> This results in lost time, a potentially critical problem, discovering valid routes from the source node <b>S</b> to the destination node <b>D.</b>

0030As mentioned, an object of the present invention is to provide the general framework, called the "Intelligent Communication Node Object Beacon Framework" (ICBF), for intelligent, adaptive advertisement by any communications node object of its presence and/or the corresponding detection (neighbor discovery) by another node object or the network of those node objects transmitting such beacons. Also, conventional beacon schemes do not extend the notion of node beacons and node neighbor discovery to temporary or permanent associations of nodes potentially capable of communication with other temporary or permanent associations of nodes. ICBF defines any such generalized node association as "Node Communication Object Association:" (NCOA) and the corresponding beacons for this association as "NCOA beacons". In the network <b>10</b> shown in <figref idref="f0001">FIG. 1</figref>, a group <b>6</b> (NCOA) of mobile nodes <b>12</b> includes a temporary or permanent association of more than one of the plurality of mobile nodes.

0031The method of the present invention (<figref idref="f0002">FIG. 2</figref>) begins (block <b>100)</b> and includes determining a node/group/network condition of the corresponding mobile node <b>12,</b> group of nodes <b>6</b> or network <b>10</b> (block <b>102),</b> varying the beacon signal waveform based upon the determined condition (block <b>104</b>), and transmitting node/group/network information using beacon signals (block <b>106)</b> before ending at block <b>108.</b> The beacon signals include information relating to a condition of the corresponding mobile node, group of nodes. Also, the beacon signals may include information relating to a condition of the mobile ad hoc network <b>10,</b> such as information about the status of the links <b>14</b> between the nodes <b>12</b> of the network. Transmitting beacon signals may further include transmiting beacon signal information using a beacon properties signal to advertise a type of beacon signal being transmitted to the plurality of nodes <b>12</b> of the mobile ad hoc network <b>10.</b>

0032The beacon signal is preferably made up of transmission rate, transmission frequency and transmission pattern which collectively define the beacon waveform. Also, the condition preferably includes node/group movement, such as velocity, acceleration and/or movement pattern of the corresponding mobile node <b>12</b> or group of mobile nodes (NCOA) <b>6.</b> Here, varying the beacon signals includes increasing the transmission rate based upon increased node movement. The node movement may be determined using global positioning satellites (GPS), local landmarks, triangulation, and/or by measuring inertia of the mobile node <b>12.</b>

0033The condition may also or alternatively include priority of information and/or quality of service measurements (QoS), such as bit/packet error rate and/or usable available bandwidth. Here, varying the beacon signals may include increasing the transmission rate and/or changing the transmission frequency or pattern based upon decreased QoS or increased priority of information. Likewise, varying the beacon signals may include decreasing the transmission rate and/or changing the transmission frequency or pattern based upon increased QoS or decreased priority of information. The transmission rate of the beacon signals should not exceed a rate threshold based upon available bandwidth. Group beacon signals are transmitted by a subset of mobile nodes <b>12</b> of the group <b>6</b> of mobile nodes <b>12.</b> Such a subset includes a range from one mobile node <b>12</b> to all the mobile nodes <b>12</b> of the group <b>6</b> The maximum would be all the mobile nodes <b>12</b> of the group <b>6</b>, while the minimum would be only one node <b>12</b> of the group <b>6</b> transmitting the beacons.

0034A method for neighbor discovery (<figref idref="f0002">FIG. 3</figref>) begins at block <b>200</b> and includes defining the initial detection rate, the initial detection frequency and the maximum detection frequency (block <b>202).</b> At block <b>204,</b> the method continues with searching for the variable beacon signals at a given mobile node <b>12</b> using the initial detection rate and at the initial detection frequency, and (block <b>206)</b> increasing a detection rate from the initial detection rate up to the maximum detection rate while searching for the variable beacon signals at the initial detection frequency.

0035The maximum detection rate may be predetermined or set according to a received maximum detection rate transmitted by a neighboring mobile node <b>12.</b> Also, the detection rate may be increased according to a function defining time varying properties of the variable beacon signal of a neighboring mobile node <b>12.</b> The variable beacon signals may vary in at least one of transmission rate, transmission frequency and transmission pattern as discussed above, and the method may include (block <b>208)</b> changing a detection frequency from the initial detection frequency while searching for the variable beacon signals. The method may also include (block <b>210)</b> determining a type of variable beacon signal being transmitted from a neighboring mobile node <b>12</b> by processing beacon signal information received from the neighboring mobile node via a beacon properties signal, before ending at block <b>212.</b>

0036A system aspect of the invention will now be described with further reference to <figref idref="f0002">FIGs. 3</figref> and <figref idref="f0003">4</figref>. As discussed, the mobile ad hoc network <b>10</b> has a plurality of wireless mobile nodes <b>12,</b> and a plurality of wireless communication links <b>14</b> connecting the nodes together. Each mobile node <b>12</b> includes a router <b>40</b> that has a communications device <b>42</b> to wirelessly communicate with other nodes of the plurality of nodes via the wireless communication links <b>14.</b> Also, the router <b>40</b> includes a controller <b>44</b> to route communications via the communications device <b>42.</b> Also, a memory <b>46</b> may be included as part of the controller <b>44</b> or in connection with the controller.

0037The controller <b>44</b> includes at least a beacon signal generator <b>50</b> to generate and transmit beacon signals, and a condition determining unit <b>52</b> to determine a condition of the mobile node <b>12.</b> The beacon signal generator <b>50</b> varies the beacon signals based upon the determined condition of the mobile node <b>12.</b> Again, the beacon signals include information relating to a condition of the mobile node <b>12.</b> The beacon signals may further include information relating to a status of a group <b>6</b> of mobile nodes <b>12</b> which, as discussed above, are a temporary or permanent association of at least two of the plurality of mobile nodes <b>12.</b>

0038Here, the condition determining unit <b>52</b> further determines a condition of the group <b>6</b> of mobile nodes <b>12,</b> and the beacon signal generator <b>50</b> varies the beacon signals based upon the determined condition of the group <b>6</b> of mobile nodes 12. Again, the beacon signal is made up of transmission rate, transmission frequency and transmission pattern.

0039The node/group condition may include node/group movement, and the beacon signal generator <b>50</b> may vary the beacon signals by increasing the transmission rate or changing the transmission frequency or pattern based upon increased node/group movement and decreasing the transmission rate or changing the transmission frequency or pattern based upon decreased node/group movement. The node/group movement includes node/group velocity, node/group acceleration and/or node/group movement pattern of the corresponding mobile node <b>12</b> or group <b>6</b> of nodes. The condition determining unit <b>52</b> may comprise a global positioning satellite (GPS) device for determining the node/group movement, and/or may determine the node/group movement using local landmarks, by tracking the relative velocity using triangulation and/or by measuring inertia of the mobile node <b>12</b> or group of nodes <b>G.</b>

0040Furthermore, the node/group condition may include quality of service (QoS) and/or priority of information, and the beacon signal generator <b>50</b> varies the beacon signals by increasing the transmission rate and/or changing the transmission frequency or pattern based upon decreased QoS or increased priority of information and decreasing the transmission rate or changing the transmission frequency or pattern based upon increased QoS and/or decreased priority of information. The beacon signal generator <b>50</b> should not increase the transmission rate of the beacon signals beyond a rate threshold based upon available bandwidth. Again, the beacon signals may also include information relating to a condition of the mobile ad hoc network <b>10,</b> such as information about the links <b>14</b> connecting the nodes <b>12</b> of the network. Additionally, the beacon signal generator <b>50</b> may transmit beacon signal information using a beacon properties signal to advertise a type of beacon signal being transmitted to the plurality of nodes <b>12</b> of the mobile ad hoc network <b>10.</b>

0041A beacon signal detector <b>54</b> is included to search for the variable beacon signals at a detection rate, which is increased from an initial detection rate up to a maximum detection rate, and at an initial detection frequency. The maximum detection rate may be predetermined or based upon a received maximum detection rate transmitted by a neighboring mobile node <b>12.</b> The beacon signal detector <b>54</b> may increase the detection rate according to a function defining time varying properties of the variable beacon signal of a neighboring mobile node <b>12,</b> and may determine a type of variable beacon signal being transmitted from a neighboring mobile node <b>12</b> by processing beacon signal information received from the neighboring mobile node via a beacon properties signal.

0042Again, it should be understood that blocks of the illustrations, and combinations of blocks in the illustrations, can be implemented by computer program instructions which may be provided to a processor to implement the functions specified in the block or blocks.

0043In sum, ICBF defines the fundamental framework for development of multiple types of beacons and the corresponding beacon detection mechanisms. One such general capability bestowed upon beacons to account for node movement is a mechanism to accept and intelligently process the velocity and acceleration of a NCOA or group <b>6</b> of nodes <b>12.</b> As either or both of these increase, the NCOA beacon rate is increased so that listening nodes <b>12</b> can adjust their route tables (caches) in time to mark affected routes as stale before they are used to try to send information over. ICBF should not permit a beacon rate to increase to the point of reducing the useful bandwidth of a necessary link <b>14,</b> so rules to limit this appropriately will come into effect when triggered.

0044ICBF defines the framework for other "built-in" network detection parameter detection mechanisms to be defined and linked into the system for adjusting a NCOA beacon waveform. Examples are rate of change of bit errors on a channel, rate of change of the effective bandwidth, rate of change of the number of NCOAs/individual nodes in the neighborhood of S, etc.

0045ICBF includes interface mechanisms to send information to the network's current routing algorithm to stimulate the creation of new routes at more optimal times than what conventional neighbor discovery beacons would allow. This mechanism also increases the likelihood that routes that are in the process of being created will be valid by the time the entire route is determined.

0046ICBF defines a "Broadband Beacon Rate Ramp" (B²R²) search as a default mechanism that enables network or non-network nodes <b>12</b> or groups of nodes <b>6</b> to detect these variable beacons. B²R² Begins with some initial value of the search rate at some initial beacon frequency. From that point in time on, B²R² uses one of several possible tactics for searching for beacons. Examples of such tactics specified by ICBF include: a predefined, fixed maximum detector rate; the maximum detector rate which is passed by the transmitting nodes to other nodes at convenient times; a function specifying the time varying properties of the beacon rate of a given node; and "Beacon Channel Surfing" in which beacon detectors can "surf" across multiple communications channels for a beacon if the network's NCOA/node beacon transmit tactic be that of distributing each NCOA/node beacon across multiple communications channels (This could be useful for security and to avoid noisy channels).

0047ICBF provides the association of a NCOA/node with a predefined beacon and for advertising the type of beacon to the network so appropriate beacon detectors can be chosen. For each type of NCOA/node beacon waveform, a corresponding beacon detector may be defined which is adaptable to the potential variability of the NCOA/node beacon. Beacons are dynamically adaptable, intelligently or nonintelligently, to conditions that affect the ability of the object to be known to its neighbors. Node movement (velocity, acceleration, pattern) and QoS are examples of such classes of conditions that could possibly affect the beacon transmission rate, transmit frequency and pattern (collectively these three characteristics make up the beacon's waveform).

0048ICBF distributes the burden of routing to include neighbor discovery beacons capable of carrying intelligence and knowledge about network conditions, capable of using knowledge about the network.and capable of intelligently interacting with NCOAs and individual nodes. ICBF could support enhanced 3G, 4G, 5G and beyond communications.