IEEE Signal Processing - July 2018 - 113

Introduction

ocean to rivers and estuaries [23]. Of course, it is not trivial to
implement in a real radar or sonar system all of the functionality of a well-trained biosonar that has been evolving over
millions of years, although some efforts along these lines
have been successfully pursued [72].

IEEE Signal Processing Magazine

|

July 2018

Receiver

Transmitter

The idea of cognitive radar was first introduced by Haykin in
2006 [28]. However, the first papers on knowledge-based
systems and agile waveform design, which are the foundations of the modern concept of cognitive radar, can be traced
back to the late 1990s (see [1], [9], and [21] and the references therein). Quoting [28], a cognitive radar "continuously
Cognitive active radars that adapt to the
learns about the environment through experience gained
environment: The evil of spectrum erosion
from interactions with the environment, the transmitter
Radar technology has recently been evolving toward higher
adjusts its illumination of the environment in an intelligent
resolution, high-precision multifunction systems with an evermanner, the whole radar system constitutes a dynamic closed
increasing list of capabilities, all available simultaneously, such
feedback loop encompassing the transmitter, environment,
as surveillance, tracking, confirmation of false alarm, backand receiver."
scanning, and clutter and interference estiThe new feature of a cognitive radar that
mation. These capabilities are traditionally
in nature, all of the
differentiates it from a classical radar is the
associated with dedicated individual radars
desired features of a
active feedback between receiver and trans[73]. For these reasons, multifunction radar
cognitive radar system
mitter, as shown in the block diagram in
systems should be able to work with freare embedded in the
Figure 1. The classical concept of adaptivquency bands wider than traditional ones.
echolocation systems
ity, already known in the radar community
Clearly, however, this is in conflict with the
since the early 1960s, is extended to the
growth of activities in the area of civil comof bats and dolphins.
transmitter. A classical adaptive radar is
munications, where the emergence of new
able to extract information from the target and the disturbance
technologies and new services that have a high demand for
signals through appropriate signal processing algorithms and
spectrum allocation puts strong pressure on the frequency
to use that information at the receive level to improve its perchannels currently allocated to radars.
formance. Conversely, a cognitive radar is able to use all of
The allocation of spectrum is regulated by the International
the extracted information not only at the receive level but also
Telecommunication Union (ITU) and is continually reviewed
at the transmit level by changing, on the fly, the transmit freat an international level by the World Radiocommunication
quency channel, waveform shape, time on target, pulse repetiConference [26]. Some portions of the radar bands have been
tion frequency (PRF), power, number of pulses, polarization,
recently allocated to communication services. For instance, in
and so forth. In an adaptive radar, all of these parameters are
the United States, the National Telecommunications and Inforpreset and cannot be changed on the spot.
mation Administration [48], [17] has recently devoted efforts
The cognitive radar system mimics the perception-action
to identifying frequency bands that could be made available
cycle of cognition [19], [30]. It senses the environment and
for wireless broadband service. A total of 115 MHz of addilearns from it important information about the target and the
tional spectrum (the 1,695-1,710-MHz and 3,550-3,650-MHz
background (perception) and then adapts the transmitted wavebands) has been identified for wireless broadband systems
form to optimally suit the needs of its mission (surveillance,
[69]. Moreover, high ultrahigh frequency (UHF) radar systems
tracking, and the like) according to a desired goal (action). In
overlap with Global System for Mobile Communications systhis decision-action phase, there are two main approaches that
tems, and S-band radars already partially overlap with longcan be applied: 1) the Bayesian approach, which builds on prior
term evolution (LTE) and WiMax systems [13]. Some results
distributions and knowledge-aided models of the environment
on the impact of S-band radars on WiMax systems are shown
obtained from past measurements in the same or similar enviin [10], and the impact of very-high-frequency (VHF)/UHF
ronments [30], and 2) the machine-learning approach, which
radars on Digital Video Broadcasting-Terrestrial (DVB-T)
determines the next action based only on the measured data
and knowledge of actions commonly taken in the same or similar environments [45].
In nature, all of the desired features of a cognitive radar
Feedback
system are embedded in the echolocation systems of bats and
Information
Environmental
Environmental
dolphins. It is well known (e.g., [55] and [67]) that both bats
Scene Actuator
Scene Analyzer
and dolphins are able to see very small prey (compared to
their own size) and track them by adjusting both the duration and the repetition frequency of their emitted pulse bursts
Observables
Actions
Radar
based upon the range and the velocity of the targets. Some
Environment
dolphin species, such as the bottlenose, are able to detect,
classify, and localize targets the size of a sardine in a cluttered background over ranges from 0 m to about 150 m in
FiguRe 1. A block diagram of a cognitive radar seen as a dynamic closedany sea condition and maritime environment, from the open
loop feedback system with the perception-action cycle [25].

|

113



Table of Contents for the Digital Edition of IEEE Signal Processing - July 2018

Contents
IEEE Signal Processing - July 2018 - Cover1
IEEE Signal Processing - July 2018 - Cover2
IEEE Signal Processing - July 2018 - Contents
IEEE Signal Processing - July 2018 - 2
IEEE Signal Processing - July 2018 - 3
IEEE Signal Processing - July 2018 - 4
IEEE Signal Processing - July 2018 - 5
IEEE Signal Processing - July 2018 - 6
IEEE Signal Processing - July 2018 - 7
IEEE Signal Processing - July 2018 - 8
IEEE Signal Processing - July 2018 - 9
IEEE Signal Processing - July 2018 - 10
IEEE Signal Processing - July 2018 - 11
IEEE Signal Processing - July 2018 - 12
IEEE Signal Processing - July 2018 - 13
IEEE Signal Processing - July 2018 - 14
IEEE Signal Processing - July 2018 - 15
IEEE Signal Processing - July 2018 - 16
IEEE Signal Processing - July 2018 - 17
IEEE Signal Processing - July 2018 - 18
IEEE Signal Processing - July 2018 - 19
IEEE Signal Processing - July 2018 - 20
IEEE Signal Processing - July 2018 - 21
IEEE Signal Processing - July 2018 - 22
IEEE Signal Processing - July 2018 - 23
IEEE Signal Processing - July 2018 - 24
IEEE Signal Processing - July 2018 - 25
IEEE Signal Processing - July 2018 - 26
IEEE Signal Processing - July 2018 - 27
IEEE Signal Processing - July 2018 - 28
IEEE Signal Processing - July 2018 - 29
IEEE Signal Processing - July 2018 - 30
IEEE Signal Processing - July 2018 - 31
IEEE Signal Processing - July 2018 - 32
IEEE Signal Processing - July 2018 - 33
IEEE Signal Processing - July 2018 - 34
IEEE Signal Processing - July 2018 - 35
IEEE Signal Processing - July 2018 - 36
IEEE Signal Processing - July 2018 - 37
IEEE Signal Processing - July 2018 - 38
IEEE Signal Processing - July 2018 - 39
IEEE Signal Processing - July 2018 - 40
IEEE Signal Processing - July 2018 - 41
IEEE Signal Processing - July 2018 - 42
IEEE Signal Processing - July 2018 - 43
IEEE Signal Processing - July 2018 - 44
IEEE Signal Processing - July 2018 - 45
IEEE Signal Processing - July 2018 - 46
IEEE Signal Processing - July 2018 - 47
IEEE Signal Processing - July 2018 - 48
IEEE Signal Processing - July 2018 - 49
IEEE Signal Processing - July 2018 - 50
IEEE Signal Processing - July 2018 - 51
IEEE Signal Processing - July 2018 - 52
IEEE Signal Processing - July 2018 - 53
IEEE Signal Processing - July 2018 - 54
IEEE Signal Processing - July 2018 - 55
IEEE Signal Processing - July 2018 - 56
IEEE Signal Processing - July 2018 - 57
IEEE Signal Processing - July 2018 - 58
IEEE Signal Processing - July 2018 - 59
IEEE Signal Processing - July 2018 - 60
IEEE Signal Processing - July 2018 - 61
IEEE Signal Processing - July 2018 - 62
IEEE Signal Processing - July 2018 - 63
IEEE Signal Processing - July 2018 - 64
IEEE Signal Processing - July 2018 - 65
IEEE Signal Processing - July 2018 - 66
IEEE Signal Processing - July 2018 - 67
IEEE Signal Processing - July 2018 - 68
IEEE Signal Processing - July 2018 - 69
IEEE Signal Processing - July 2018 - 70
IEEE Signal Processing - July 2018 - 71
IEEE Signal Processing - July 2018 - 72
IEEE Signal Processing - July 2018 - 73
IEEE Signal Processing - July 2018 - 74
IEEE Signal Processing - July 2018 - 75
IEEE Signal Processing - July 2018 - 76
IEEE Signal Processing - July 2018 - 77
IEEE Signal Processing - July 2018 - 78
IEEE Signal Processing - July 2018 - 79
IEEE Signal Processing - July 2018 - 80
IEEE Signal Processing - July 2018 - 81
IEEE Signal Processing - July 2018 - 82
IEEE Signal Processing - July 2018 - 83
IEEE Signal Processing - July 2018 - 84
IEEE Signal Processing - July 2018 - 85
IEEE Signal Processing - July 2018 - 86
IEEE Signal Processing - July 2018 - 87
IEEE Signal Processing - July 2018 - 88
IEEE Signal Processing - July 2018 - 89
IEEE Signal Processing - July 2018 - 90
IEEE Signal Processing - July 2018 - 91
IEEE Signal Processing - July 2018 - 92
IEEE Signal Processing - July 2018 - 93
IEEE Signal Processing - July 2018 - 94
IEEE Signal Processing - July 2018 - 95
IEEE Signal Processing - July 2018 - 96
IEEE Signal Processing - July 2018 - 97
IEEE Signal Processing - July 2018 - 98
IEEE Signal Processing - July 2018 - 99
IEEE Signal Processing - July 2018 - 100
IEEE Signal Processing - July 2018 - 101
IEEE Signal Processing - July 2018 - 102
IEEE Signal Processing - July 2018 - 103
IEEE Signal Processing - July 2018 - 104
IEEE Signal Processing - July 2018 - 105
IEEE Signal Processing - July 2018 - 106
IEEE Signal Processing - July 2018 - 107
IEEE Signal Processing - July 2018 - 108
IEEE Signal Processing - July 2018 - 109
IEEE Signal Processing - July 2018 - 110
IEEE Signal Processing - July 2018 - 111
IEEE Signal Processing - July 2018 - 112
IEEE Signal Processing - July 2018 - 113
IEEE Signal Processing - July 2018 - 114
IEEE Signal Processing - July 2018 - 115
IEEE Signal Processing - July 2018 - 116
IEEE Signal Processing - July 2018 - 117
IEEE Signal Processing - July 2018 - 118
IEEE Signal Processing - July 2018 - 119
IEEE Signal Processing - July 2018 - 120
IEEE Signal Processing - July 2018 - 121
IEEE Signal Processing - July 2018 - 122
IEEE Signal Processing - July 2018 - 123
IEEE Signal Processing - July 2018 - 124
IEEE Signal Processing - July 2018 - 125
IEEE Signal Processing - July 2018 - 126
IEEE Signal Processing - July 2018 - 127
IEEE Signal Processing - July 2018 - 128
IEEE Signal Processing - July 2018 - 129
IEEE Signal Processing - July 2018 - 130
IEEE Signal Processing - July 2018 - 131
IEEE Signal Processing - July 2018 - 132
IEEE Signal Processing - July 2018 - 133
IEEE Signal Processing - July 2018 - 134
IEEE Signal Processing - July 2018 - 135
IEEE Signal Processing - July 2018 - 136
IEEE Signal Processing - July 2018 - 137
IEEE Signal Processing - July 2018 - 138
IEEE Signal Processing - July 2018 - 139
IEEE Signal Processing - July 2018 - 140
IEEE Signal Processing - July 2018 - Cover3
IEEE Signal Processing - July 2018 - Cover4
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_201809
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_201807
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_201805
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_201803
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_201801
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_1117
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0917
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0717
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0517
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0317
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0117
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_1116
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0916
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0716
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0516
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0316
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0116
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_1115
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0915
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0715
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0515
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0315
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0115
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_1114
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0914
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0714
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0514
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0314
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0114
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_1113
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0913
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0713
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0513
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0313
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0113
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_1112
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0912
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0712
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0512
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0312
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0112
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_1111
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0911
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0711
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0511
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0311
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0111
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_1110
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0910
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0710
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0510
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0310
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0110
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_1109
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0909
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0709
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0509
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0309
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0109
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_1108
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0908
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0708
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0508
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0308
https://www.nxtbook.com/nxtbooks/ieee/signalprocessing_0108
https://www.nxtbookmedia.com