Problem

TTNT (Tactical Targeting Networking Technology) is an advanced tactical data link currently under development by Rockwell Collins Government Systems and the Advanced Technology Center.  The incorporation of network centric warfare concepts into military operations creates a technological challenge that the packet exchanges within the network are susceptible to eavesdropping, traffic analysis, and distortion. Thus, modes supporting Low Probability of Intercept (LPI) and Low Probability of Detection (LPD) are a highly desirable addition to existing TTNT functionality. 

From the networking perspective, critical to LPI/LPD is a detection aware routing scheme for mobile ad hoc networks (MANET) which TTNT will operate on. By using a LPI/LPD aware routing scheme, system detectability can be improved and usable data rate for given detectability level can be maximized.

Current routing schemes mostly use the shortest path or the least hop count to determine the routing path. In the last few years, power aware routing and mobility aware routing have received some attentions in the research communities. However, no one has considered using possibility of being intercept, threat level / detectability, or node characteristics as the factors for routing.

Description of LPI/LPD aware routing for MANET

This invention presents a method and scheme that provides LPI/LPD aware routing. The method can be used for secure communications in a high detectability threat environment.

1. Routing path selection factors:

In this invention, the routing path selection considers the following three factors:

•         Intercept radius, Ri, of node, which is related to the required transmission power level

•         Detectability / threat level of node

•         Availability of non-LO nodes for rerouting

The intercept radius, or range of intercept, is a concept used to define link detectability. It is determined by transmission power and data rate which affects communication range, channel fading, and jamming. Different data rates needs different signal to noise ratio for demodulation of data, which in turn is driven by coding efficiency and chip rate. For a given range of communication, the intercept radius decreases with decreasing data rate. Low data rates allow for a long transmission time per bit, and thus for an equivalent Eb/No operations lower data rates require lower transmission power levels and decrease signal detectability.

Another concept we introduce for controlling the detectability of packet transmission in LPI/LPD aware routing is the threat level or detectability level of routing nodes. The purpose is to route away from the high detection / threat area. This can be accomplished by using the sensor information collected by the physical layer to guide the layer 3 routing.

One method to minimize packets being detected is to route the packets to nodes that are not Low Observable (LO) platforms. This method works especially well for long range broadcasting. Thus the third parameters we use for LPI/LPD routing is node characteristics. Also, TTNT supports receive-only and silent mode operations. One consideration of routing node selection is that the node is able to transmit in high threat environment.

2. Node selection procedure

Below is the procedure of node selection in route discovery:

•         Each node keeps a table containing information of its neighbor nodes: Required Ri, threat/detectability level, suitability, etc.

•         The table is updated periodically (though infrequently) by locally-broadcasted information (beacon) from each neighbor node.

•         At a certain time period, called synchronization time, each node examines its LPI/LPD parameters.

•         If a certain parameter has changed above a threshold, it will locally broadcast a beacon.

•         Assuming there are N nodes within the communication range, the source node selects top M nodes (M<N) for the first hop relay.

•         The selection criteria are based on the heuristic analysis of the three LPI/LPD routing path selection factors.

•         The source node sends a Route Notification (RN) packet to each desired node, which will reply using a Route Reply (RR) packet if it is available.

•         After a preset time period, if the source node does not receive RR from one of the desired node, it will pick the node with the M+1 priority for routing, if it is available.

•         Starting from the second hop, each node in the M-path selects its next hop node using the same selection criteria.

Innovations claimed

1. We claim a method of providing LPI-LPD aware routing by selecting the next hop routing node based on LPI/LPD factors.
2. The method of claim 1, wherein the LPI/LPD factors include intercept radius, threat level, and node security characteristics. These parameters are controlled by transmission power, data rates, geographically dependent detection level, and platform characteristics.
3. The method of claim 1 further comprises of each node keeping a table containing the above LPI/LPD information of neighboring nodes.
4. The method of claim 2, wherein the LPI/LPD routing table is updated periodically by beacons emitted by neighbor nodes.
5. The method of claim 3, wherein the step of beacon broadcast comprises of each node examining its LPI/LPD parameters at a preset time interval, called synchronization time, and if any of the values of the parameters exceed the threshold, then a beacon will be broadcasted.
6. The method of claim 1, wherein the step of path selection comprises of the source node selecting the top M nodes out of the N nodes within communications range for its first hop relay.
7. The method of claim 1, wherein the path selection is a heuristic based algorithm.
8. The method of claim 5, wherein the path selection protocol comprises of the source code and the desired next hop nodes exchanging Route Notification (RN) and Route Reply (RR) packets.
9. The method of claim 7, wherein the step of packet exchange comprises of picking the node with the M+1 priority for routing, if the source node does not receive RR from one of the M desired nodes after a preset time period.
10. The method of claim 1, wherein the step of path selection comprises of starting from the second hop, each node in the M-path selects its next hop node using the same selection criteria as specified in claim 1.