IEEE - Aerospace and Electronic Systems - December 2019 - 22

Cognitive Radar Principles for Defence and Security Applications
an in-depth evaluation of the tracked objects and overall situation assessment is performed, resulting in the attribution of
certain properties to the objects, such as mission criticality
or threat classification.

COGNITIVE RESOURCE MANAGEMENT
The resource management has the task to optimize the use
of the available resources with respect to the current mission and situation. With this information using a performance model of the sensor, the resource management
defines the sequence of the waveforms, appropriate waveform parameters, beam and scan parameters, and processing parameters that will be used to illuminate the
environment and process the reflected signals in an optimized manner. This sequence is defined in a way that the
usefulness of the sensor is maximized regarding a set of
the predefined optimization criteria [10]. The definition of
these criteria is crucial for the behavior of the sensor and
varies depending on its current mission. The detailed tasks
and functionalities of a cognitive resource manager will
be described in more detail in the following sections.

ASPECTS OF COGNITIVE RADARS
COEXISTENCE
The coexistence of systems is a big challenge for all RF
users now and even more so in the future. In recent years,
the number of frequency users has increased continuously
and this trend is ongoing. With the unbroken demand for
more digital bandwidth, the evolution of communication
technology, e.g., mobile communications toward 5G and
wireless LAN systems (WAS/RLAN), requires more RF
bandwidth to satisfy more frequency users being active in
all bands (1-6 GHz and in the future mm-wave). Also, on
the radar side, new systems emerge from the new operational needs (e.g., detect and avoid radars for unmanned
air vehicles, hostile fire indication, and multifunctional
systems). New requirements for radars, such as a better
resolution in range and the detection of small targets in
clutter, result in higher demand for an RF bandwidth. Reliability and immunity to interference become crucial to
ensure radar operation in such dense environments. Especially in the automotive area, where the number of cars
equipped with radar sensors is constantly increasing and
highly automated driving requires a new level of system
safety and reliability.
The frequency spectrum is finite and rare. Coexistence
by fixed spectral separation is, therefore, not realistic anymore in this crowded environment. Caused by the dense
packing of frequency channels, also interference from the
adjacent frequencies increases and new technologies for
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interference mitigation become necessary. The coordination of frequency allocation is getting more and more
important between technologies and beyond borders for
communication as well as for radar. Frequency users and
interferers today are commonly mobile so that a spatial
separation cannot be ensured either.
In military missions, radar systems are often operated
in close neighborhood to the communication systems. The
individual radar and communication systems may be operated by different crews in the multiple military units or
even in the multinational missions.
In coexistence situations, mutual interference between
the radar systems or between the radars and communication systems may occur. Such disturbances can constrain
the effectiveness in particular missions strongly or may
even lead to the mission failure.
Studies were performed analyzing potential influences
between the radars among each other as well as between
the radar sensors and communication equipment. The
mutual interference was analyzed for concrete exemplary
scenarios and radar systems. For these situations, strategies for the improvement of coexistence were evaluated
and the current frequency allocation was assessed [4].
In order to cope with the coexistence situation, cognitive radar concepts and techniques might be useful to
make the radar less vulnerable to interferences. These can
either be the methods concerning the radar signal emission
or signal processing at the radar receiver. Methods for the
reduction of interference from other RF systems are using
separability measures in one of the dimensions time, frequency, space, or signal modulation. Below some measures are described that enable coexistence.

MEASURES FOR IMPROVED COEXISTENCE CAPABILITY
ENABLED BY THE RADAR SIGNAL EMISSION SUBSYSTEM
Waveform design: Specific phase or frequency
modulations can allow for coexistence [5]-[8] (e.g.,
orthogonal waveforms for coexistence of several
radars of the same type). Noise radar and the low
probability of intercept methods can reduce the disturbance from their own radar toward the other
users and vice versa.
Matched illumination: The maximization of the
signal-to-interference-ratio leads to improved coexistence performance. With the matched illumination
techniques, the waveform is adjusted to the dimensions and characteristics of the target of interest.
Frequency, bandwidth, and pulse length as well as
the polarization can be adapted to the specific situation. Also the optimization of energy distribution
over the frequency within the pulse can improve the
signal-to-noise ratio.

IEEE A&E SYSTEMS MAGAZINE

DECEMBER 2019

IEEE - Aerospace and Electronic Systems - December 2019

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