Robust Sensing and Fusion over Disadvantaged Networks

Sensors/estimators can generate state estimates of dynamic targets and send them to the fusion center. The state estimate from an individual sensor is prone to error and can be biased due to the limitation of the sensing device and the noise/interference incurred to the sensing signals. In addition, the estimation errors from multiple sensors could be correlated. The fusion center combines individual estimates to generate combined estimates in order to achieve performance superior to individual sensor estimates. During the fusion process, the state estimates within a window W from a sensor will be considered, and the fusion will be carried over M sensors. A larger W could potentially improve fusion quality, at the cost of potentially a higher processing complexity and a larger initial detection delay.

In some application scenarios, the sensors could be far away from each other and far from the fusion center. The communications have to be carried over long-haul links such as satellite, fiber or the mix of the two. The long-haul communications could lead to significant transmission delay (in the order of W), delay jitter, and loss. This is especially the case with satellite links. Although fiber transmission has much lower loss and error rate per link, a transmission over multiple fiber links through a wide area network could also experience packet droppings. TCP has been commonly used in network transmissions to ensure reliable end-to-end transmissions. However, the retransmission through TCP could significantly increase delay and jitter, and the problem will be even more severe over satellite links where link loss is a norm. As a result of TCP congestion control procedures, it may even throttle the transmission. These transmission problems would significantly impact the fusion quality.

The objective of this work is to investigate techniques that could provide timely and effective state estimates in such a wide-area transmission scenario. This includes the investigation of network techniques that improve transmission quality and robust fusion methods. To focus on the problem due to long-haul transmission, the investigation will start with single target or fixed number of targets. Some potential directions that may be explored are as follows.