[C6] Flexible Array Signal Processing
The aim of this project is to carry out comprehensive investigation of sensor-arrays where the position of the individual sensors is described by a time varying function, that is the geometry changes during the observation interval. Thus the proposed work is concerned with the development of novel suitable superresolution flexible array signal processing techniques for accurate detection, localisation and tracking of narrowband and/or wideband targets in complex environments. This objective is motivated by the military needs for the flexible sensor arrays (e.g. radar, sonar) that have not only high resolution location estimation capabilities but also robustness against the unwanted effects of jammers and noise.
In general, two different types of time-varying sensor-arrays can be distinguished. The first type is "rigid" array of sensors mounted on mobile platforms. In this type, the geometry of the array is preserved at least during the observation interval - if not throughout the movement of the platform. The second type is "flexible" array of sensors where the array geometry changes during the observation interval of the incoming signals from the targets. The geometry of the problem in the first type is equivalent to the case of a fixed array and a moving source since only the relative motion of the source and the array is of importance in this case. While the problem formulation of this proposal is quite general, particular emphasis will be placed on the second type of array systems namely where the shape of the array changes significantly during the observation interval.
Within the type of flexible sensor arrays, two categories of movement can be identified. Firstly, the sensors of the array may change their positions in an arbitrary but known way. A good example of this movement is sensors attached to Unmanned Aerial Vehicles (UAVs) where each sensor element has its own propulsion system and they group together to form a large aperture array of moving sensors. In the
second category, the geometry of the flexible array may change in an unpredictable and immeasurable way. For example, due to imperfections in vehicle control, it is common for UAV arrays systems to undergo significant yaw and pitch oscillations. Another example is large towed hydrophone arrays in real situations where sensors may be displaced from their nominal positions due to various kinds of forces on the array. In these examples, time varying uncertainties are introduced in the sensor locations that may degrade the performance of the array system and can only be described stochastically. In both types of movement, the motion of flexible array elements causes the array manifold (i.e. the locus of all sensor array responses) to be a function of time.
