IEEE - Aerospace and Electronic Systems - April 2022 - 50

Frequency-Hopping MIMO Radar-Based Communications: An Overview
Table 1.
Parameter Definitions and Settings for Simulations and
Illustrations Throughout the Article (Unless Otherwise
Specified)
Variable Value
H
Definitions
10
M
B
K
T
Ts
D
t
10
100
MHz
20
0:2ms
1=ð2BÞ
1
0:2
number of hops per radar
pulse
number of antennas at radar
transmitter
radar bandwidth
number of subbands
time duration of a hop
sampling time
BT=K
duty cycle of a radar pulse
channels. This validates the high accuracy of the channel
estimation method. We also see from the figure that,
employing the estimated channel parameters, FHCS outperforms
BPSK w.r.t the SER against Eb=N0, which owes
to the improved data rate of FHCS over BPSK. Since the
combination of FHCS and BPSK further improves the
data rate, the SER performance of the combination is
improved over those of the individual modulations.
We further see from Figure 6 that khm has a much
stronger impact on the SER of BPSK compared with the
channel parameters b0 and u0. To achieve the SER of
104, using the true value of khm can reduce the required
Eb=N0 by 5 dB, compared with using the estimated khm.
On one hand, this observation indicates that the final SER
performance ofFH-MIMO DFRC should be carefully analyzed
after taking the detection performance of khm into
account, as discussed in the section " Comparing Signaling
Table 2.
Comparing Existing Signaling Schemes for FH-MIMO DFRC
Modulation
Data Rate
Range Sidelobe
Spectral Containment
Necessary Information for
Demodulation
50
good
(I1), (I2) and
(I3)
NEW SIGNALING STRATEGIES ENABLING HIGHER DATA
RATES
As shown in (8), the overall data rate achieved by FH-MIMO
DFRC is 27 Mb/s, under the condition that BPSK and FHCS
are combined, the radar has 10 antennas and a bandwidth of
100 MHz, and the UE has a single antenna. To provide an
effective high-speed G2A communication link using FHMIMODFRC,
new signaling strategies are required.
We remark that the information conveyed in the hopping
frequencies has not been fully explored yet. In light
of FHCS as illustrated in the section " Information Modulation, "
the permutations of hopping frequencies can be
employed to convey information bits [18]. Using permutations
is expected to increase the data rate dramatically,
since the number of permutations can be huge. Take the
parameters used in Figure 6 for an example. The number
of permutations that permutes Mð¼ 10Þ out of Kð¼ 20Þ
subbands can be larger than 670 billion, which, in theory,
is able to convey up to 39 bits per radar hop. Similar to the
rate calculation given in (8), the data rate achieved by
using permutations can be given by 39 10=10 106 ¼
39 Mb/s. As a result, an increase of 12ð¼ 39 27Þ Mb/s
in data rate can be achieved through using permutations.
This improvement of data rate, however, requires a proper
demodulation method to be developed at the UE. One
challenge is to deal with the reduced Euclidean distances
Schemes for FH-MIMO DFRC. " On the other hand, this
observation suggests that new methods should be developed
to improve the estimation performance ofkhm.
MAJOR RESEARCH CHALLENGES IN FH-MIMO DFRC
As a newly conceived DFRC architecture based on FHMIMO
radar, there are still many challenging issues to be
addressed effectively. In this section, we discuss the major
challenges and suggest potential solutions for future research.
PSK[11] DPSK[12]
lower
CPM[13]
FHCS[14]
PRFHMJ PRFHMJ PRFHMlog 2M PRFHblog 2CM
low
lowest
better
(I1) and
(I2)
IEEE A&E SYSTEMS MAGAZINE
best
(I1), (I2) and
(I3)
poor
(I1) (not strictly
necessary)
Notes: J is the PSK modulation order. For instance, J ¼ 1; 2, and 3 denotes BPSK, QPSK, and 8-PSK, respectively.
APRIL 2022
K c
high with periodic
spikes

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