Fusion in Signal Processing - Information Fusion in Signal and Image Processing - page 23

They involve the basic mechanisms of information combination, or the choice of data
that has to be retrieved (complementarity or redundancy). The allocation of multi-
sensor resources is the optimization of the overall performances of a set of sensors or
measuring instruments, according to operational criteria or depending on the mission
of this set. Another, more concise and pragmatic definition is given by [MCI 96]: “a
multi-sensor system generally has to answer four questions: which sensor should I
use? for what purpose (mode)? where should I direct it? when should I begin?”
This set of sensors is also characterized by six major functions, in the case of
military applications, by using the information on targets as input and the control of
the sensors as output [BUE 90]:
- events are predicted in order to evaluate the periods of time during which events
occur that require sensors to observe them;
- predicting the sensor's state makes it possible to model the performances of the
sensor in order to determine its abilities to accomplish the tasks it was assigned to do;
- arranging targets by order of priority is done for all of the targets, according to
information needs and urgency, depending on criteria based on threat (in defense),
opportunity (in attack), or surveillance;
- the assignment of sensors to targets is determined based on the previous two
functions (prediction on the sensor and target ranking), in order to quantify the use-
fulness [POP 89], the adequacy of each possible assignment (an optimal assignment
is obtained by maximizing this usefulness);
- assignment control makes it possible to organize and program the sensor's vari-
ous tasks over time;
- the interface with the sensors makes it possible to dispatch the orders to the
various sensors.
These functions give an overview of how a sensor system works, particularly in
terms of the sequence in time.
A systems architecture mostly involves how the sensors are organized with respect
to each other, particularly in terms of communications, but also depending on how the
information is processed. The choice of an architecture immediately leads to choosing
the system's control, as well as its co-ordination. The architectures of multi-sensor
systems used to be strongly centralized. These architectures had the advantage of pro-
viding information on different levels of abstraction, but the system is then vulnerable
to possible breakdowns of the central processor, which has to process an increasingly
large and heterogenous volume of data. Needs have evolved towards a more inde-
pendent system. System control has therefore become more delocalized: it is either
semi-distributed, allowing for partial fusions of information at different intermediate
levels, with a final decision based on the processed information or distributed, making
it possible to make many decisions locally and independently. If the system has to