Fusion in Signal Processing - Information Fusion in Signal and Image Processing - page 24

be efficient, the implementation of control rules is difficult and many problems occur
because of local decision conflicts between agents. A comparative study in tracking
mode of these three types of architectures can be found in [BLA 86].
Modeling the sensor resource [BUE 90] can help realize which characteristics play
a role:
- the passive mode (the sensor merely receives information), the active mode
(transmitting and receiving) or the protected mode (the transmitted and received infor-
mation is in the form of a pulse);
- the direction; the frequency (changing the frequencies used by active sensors is
a significant need in a military context);
- the type of wave, pulse or continuous; the power (greater range and quality of
measurement, particularly in noisy or jammed environments);
- the size of the beam, thin or wide;
- the illumination time (identification requires a longer time than simple detec-
tion).
On some sensors, there are four types of control available [WAL 90]:
- global (this control mode is used to establish the default values of the sensor's
parameters);
- sectoral (the surveillance volume is partitioned into different sectors, for which
the sensor's parameters can be adapted);
- targeted (the parameters are adapted based on the various targets that are
present);
- the last mode involves the search for targets (the precise volume or other
attributes are specified).
Data retrieval plays a particular role. The first mode is the push mode, which means
that the data processing system expects the data and processes them as they come
along. The sensors continuously send observation sequences and it is up to the system
to manage the waiting queue (the time sequence). The drawback of such a system is
the lack of reactivity because the elements of information arrive in a pre-defined order
(generally based on the sensors' acquisition times). The other data retrieval mode is
the pull mode. In this case, the system sends sensors requests, in other words informa-
tion queries, specifying among other things which target the sensor should be aimed
at and the observation time. This way, the system controls the information it needs and
the information retrieval sequence can be different for each target. Over the course of
a tracking function, additional information requests are sent when the target is maneu-
vering. In a classification process, if the target's speed is very high, and if the system is
hesitating between a missile and a plane, the following request may involve wingspan
and the decision will then be immediate. In the pull mode, an operator can act on the