Ad-hoc networks are groups of interconnected devices, such as computers or transceivers, in which the topology and/or connectivity of the network may change at any time. Ad-hoc networks are advantageously used in circumstances where a plurality of devices desire or are required to communicate with each other.
In a wireless network, bandwidth is driven by the available RF spectrum, which is currently a scarce commodity. In this environment the most significant challenge associated with a broad-band wireless network is efficiently using the limited bandwidth provided by the network. This problem is made worse by the needs of a distributed network, which requires most or all of the nodes in the network to broadcast and/or multicast information to thereby pass the information through the network. Such broadcasting can take up a great deal of system bandwidth since a message may need to be repeated throughout the system. In a wired internet procotol (IP) based network, reducing the system load of broadcast services is resolved by isolating the broadcast area to a defined region of the network. In a mobile ad-hoc network, however, such isolation is not possible because the IP addresses do not represent a defined group of people within a fixed geographic region or location.
One type of mobile ad-hoc network in which broadcast communications may be overtaxed comprises a plurality of military resources or nodes such as tanks, infantry, unmanned aerial vehicles (UAVs), autonomous sensors, helicopters, and fixed-wing aircraft. Distributed situational awareness information for everyone in a theater of operation is helpful in supporting local decision makers in discovering resource availability and status, and in forming ad hoc force groups in order to engage the enemy. Using situational awareness information, local decision makers are given a visual representation of what is happening in the battlefield and are able to make decisions such as the makeup of a force group and the direction and way in which targets are engaged. Situational awareness information includes such attributes as location, type of resource, weapons availability, fuel status, resource availability and any other type of attribute that can be used to determine ability of a resource to engage an enemy. Unfortunately, transmitting distributed situational awareness information is a major source of broadcast and/or multicast traffic in a military wireless network and can overload many legacy networks. For example, a command center may periodically desire to know what military resources are within a specific geographic region for which the command center has responsibility. A request, broadcast by a command center or command node throughout a wireless network, may needlessly use broadcast resources if the request is transmitted to nodes outside of the specific geographic region. Furthermore, in even a moderately interconnected network the responses sent by the relevant nodes toward the command node may be returned using a plurality of broadcast paths, thereby wasting broadcast resources. What is therefore needed is a communications protocol that conserves communications resources while ensuring messages are transmitted to the desired nodes in a mobile ad-hoc network.
It is therefore an object of the invention to provide a communications protocol that conserves communications resources such as broadcast bandwidth.
It is another object of the invention to transmit situational awareness information in an ad-hoc mobile network only to nodes that have a need to receive the information.
It is still another object of the invention to permit a node to request and receive situational awareness information from some or all nodes in a network regardless of the distance between each node and the requesting node.
A feature of the invention is distance-limited re-transmission of periodically transmitted situational awareness messages, and non-distance limited re-transmission of responses to a situational awareness request from a command node.
An advantage of the invention is the conserving of communications resources by limiting the actual distance a situational awareness message is transmitted through the network.