Aerospace and Electronic Systems Magazine May 2018 - 35

offsets between the transmitted signal and returned signal for estimating the range and velocity of a target. It was pointed out that
OFDM-coded signal is comparable with LFM waveforms without range-Doppler coupling, but traditional OFDM signals usually
have high PAPR, which brings design difficulties for subsequent
RF hardware systems. As chirp waveform has been widely used in
practical radars due to its attractive properties in large time-bandwidth product and constant envelope, OFDM chirp waveforms are
proposed [19], but only radar sensing applications are considered.
Nevertheless, it is shown that OFDM chirp waveform is comparable with classic chirp signals and furthermore experiences no
range-Doppler coupling problem.
In this article, we present the use of frequency diverse array
(FDA) and OFDM chirp waveform, referred to as FDA-OFDM,
for integrated navigation, sensing and communications. Different
from conventional phased-array which generates range independent transmit beampattern, FDA produces both angle and range
dependent transmit beampattern by adopting a small frequency
offset across its array elements [20]. FDA range-dependent beampattern characteristics under monochromatic continuous-wave signal has been investigated in the literature [21]. The multipath FDA
characteristics analyzed in [22] show that FDA has the capability
to form a quasi-flat interference pattern for desired ranges, which
is particularly beneficial for potential applications [23]. This is
also why FDA has emerged to address pressing shortcomings in
phased-arrays [24]. In [25], a pulsed-FDA with quasi-static beampattern was discussed, while the mathematical analysis and conceptual design of a linearly frequency modulated continuous-wave
FDA were reported in [26]. Due to promising potentials of FDA
in future radar and communication applications, a special issue on
FDA signal processing was also published recently in Institute of
Electrical and Electronics Engineers Journal of Selected Topics in
Signal Processing [27].
This article extends the FDA technique by embedding communication codes through OFDM chirp modulation for integrated radar, communication, and navigation applications. FDA and OFDM
were initially exploited for secure wireless communications [28],
but only monochromatic continuous-wave carrier is considered. In
this article, the new FDA-OFDM scheme is presented from a toplevel system description, with an aim to call for more publications
MAY - JUNE 2018

and investigations on this promising topic. Note that the difference
between the discussed OFDM chirp and standard OFDM schemes
lies in that the former uses chirp-frequency carriers, instead of
single-frequency carriers as the latter, to improve the PAPR performance of the transmitted signals and enhance the detection
performance for the integrated radar sensing and communication
systems.

COMMUNICATION-EMBEDDED FDA-OFDM WAVEFORM
FDA
Figure 1 illustrates the comparisons between conventional phasedarray and a standard M-element FDA. FDA involves modulating
a single waveform to slightly different center frequency for each
transmit element of the array. The center frequency for the mth
element is
f m = f 0 + Δf m , m = 0,1,..., M − 1

(1)

where f0 and Δfm denote the carrier frequency for the reference element and frequency offset for the mth element, respectively. The
FDA electric field in far-field region can be expressed as

Figure 1.

Comparisons between phased-array and FDA antennas. The former
uses an equal carrier frequency, while the latter uses incremental carrier
frequencies.

IEEE A&E SYSTEMS MAGAZINE

Table of Contents for the Digital Edition of Aerospace and Electronic Systems Magazine May 2018