Aerospace and Electronic Systems Magazine May 2018 - 40

FDA-OFDM for Integrated Navigation, Sensing, and Communication Systems

Figure 9.

Schematic illustration of integrated navigation, sensing and communications.

and FDA-OFDM chirp schemes for different values of Ns and Nc,
where the SNR is fixed at -10 dB. It is clear that the FDA-OFDM
chirp scheme achieves better target detection performance than its
counterpart FDA-OFDM scheme.

INTEGRATED NAVIGATION, SENSING, AND
COMMUNICATIONS
In addition, navigation functionality can be further integrated into
the FDA-OFDM radar-communication system. In doing so, the integrated navigation, sensing, and communication system can operate in a cognitive way [30]: (1) The transmitter adaptively learns
about the scenarios through machine learning the interactions with
the receiver; (2) The transmitter adjusts its operating parameters
intelligently according to its learned experiences; (3) The whole
system constitutes a dynamic closed-loop feedback encompassing
the transmitter, scenarios and receiver to update current probabilistic understanding of the operation scenarios for automatic navigation. This idea is illustrated in Figure 9.

IMPLEMENTATION ISSUES AND DISCUSSIONS
DOPPLER FREQUENCY SHIFT

Figure 10.

Doppler frequency shift is an important radar feature for target velocity estimation, but little attention has been paid in the literature.
OFDM-coded radar signal has poorer Doppler tolerance than chirp
waveform [31]. It can be proved that OFDM chirp waveforms are
less sensitive to the Doppler shift than OFDM waveform. That is,
Doppler sensitivity means that the range of the target is sensitive
to the speed of the target and different speeds can result in different
range data for an identical target, namely, the designed waveforms
are less sensitive to Doppler effects, which is an advantage for highresolution radar sensing. Nevertheless, a method to compute the
Doppler shift from OFDM signals, independent of the applied multicarrier coding, has been presented in [32]. Since this correlationbased method has the shortcomings of high computing complexity and Doppler ambiguities, another Doppler processing scheme
regardless of the transmitted signal information and coding was
proposed in [33]. This scheme operates by processing the symbols
that compose the OFDM symbols directly instead of processing the
baseband signals. In doing so, it can be applied in combination with
the transmission of arbitrary user data and is able to resolve multiple
reflecting targets with high dynamic ranges and low sidelobe levels.
40

Comparisons of phase noise impacts between OFDM and OFDM chirp
waveforms: (a) Comparisons of phase noise impact on BER performance. (b) Comparisons of phase noise impact on CCDF performance.

However, for a fixed OFDM chirp symbol index, the Doppler
frequency shift has no individual influence on the different modulation symbols within the same OFDM chirp symbol because it
brings an identical phase shift on every subcarrier. Although both
the distance to the reflecting target and Doppler shift introduce a
linear phase shift in the returned OFDM chirp signals, they have
completely orthogonal influence on the OFDM modulation symbols. Therefore, the target Doppler and target range can be independently estimated with suitable signal processing algorithms.
The details can be found in [1].

IMPACT OF PHASE NOISE
It is well known that OFDM is sensitive to frequency offset
and phase noise, which may destroy the orthogonality among
OFDM subcarriers, cause phase error and intercarrier interference. Frequency offset is a deterministic phenomenon which

IEEE A&E SYSTEMS MAGAZINE

MAY - JUNE 2018

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