IEEE Circuits and Systems Magazine - Q1 2021 - 68

and affect performance. The tradeoff of these essential
parameters in such situations has yet to be investigated
[96]. A concept was presented in [97], with a system that
can be used as radar or as communication device. The
proposed system uses off-the-shelf components with
orthogonal frequency division multiplexing (OFDM)
architecture. Next, the work in [98] presented a similar concept applied to drones or unmanned systems.
A practical mobile imaging device utilizing the 60 GHz
band was introduced. The components for the communication were reused to image an object and perform
measurements along the trajectory of this system. The
authors in [99] proposed a wireless sensor network for a
home environment, in which the sensors are dual mode
radars for remote localization and fall detection. In this
work, the network consists of multiple sensor nodes
and a base station. The most important validation in the
dual mode operation is that the radars' functionality will
not interfere with the operation of the wireless communication module. Time division multiplexing (TDM) is
adopted to ensure that the wireless communication and
each radar sensor do not function at the same time. In
addition to this, frequency division multiplexing (FDM)
is used to minimize interference between the radars. Experimental results of this work validated the feasibility
of this method in conducting real time detection without interference. In [100], a system of using a common
waveform for vehicle radar as well as vehicle communication system based on the WLAN standard was proposed. Specifically, an IEEE 802.11(ad)-based radar for
long-range application was designed in the 60 GHz unlicensed band. Despite being intended for vehicle application, it illustrates the same concept of coexistence and
functionality of radars and communication systems.
On the other hand, the work in [101] introduced the
concept of personal mobile radar using a large number of arrays to map the environment. This radar operates in the millimeter(mm)-wave band and it enables
the integration of such large arrays within the users'
5G mobile devices. This work proposed a grid-based
Bayesian mapping approach by introducing a new state
space model. This research highlighted the correlation
between the angular resolution, scanning time, signal
bandwidth and ranging accuracy, besides methods to
trade-off between these parameters. Results validated
the feasibility of the introduced system concept, and a
significant performance improvement in environment
mapping is attained. This could be potentially attractive for applications such as indoor mapping using lowcost massive array antennas embedded in next generation smartphones. Meanwhile, realizing the spectrum
scarcity, Awais et al. [102] introduced a spectrum sharing methodology. The proposed method is a spatial
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approach for spectrum sharing between a MIMO radar
and an LTE cellular system with a number of base stations. Since the MIMO radar and LTE standard share a
number of channels, an interference-channel-selection
algorithm is introduced. Signals from the MIMO radar
were projected onto the interference channel with maximum null space. Careful selection of the interference
channels minimizes interference from the MIMO radar
and at the same time, protects the LTE base station
from interference from the radar. Meanwhile, the coexistence between IEEE802.11 WLAN and radars operating in adjacent channels (5 GHz) was studied in [103].
A modified WLAN receiver link was designed to mitigate the interference by impulse radar. Two proposed
approaches for interference detection were reported,
firstly the time domain cyclic prefix auto-correlation
detection, and secondly, the frequency domain data
subcarrier-based detection. The proposed system can
significantly mitigate radar interference at high and
low interference to noise ratios (INRs), whereas partial
interference mitigation is also possible within the INR
of 3 < INR < 30 dB.
In the future, it is expected that a massive number of
communication devices and radar systems will need to
share the same spectrum. As a result, techniques and
approaches to mitigate and minimize interference are of
vital importance. It is safe to assume that the new norm
will be to have these networks providing different and
complementary services, sharing the same bandwidth
in an uncoordinated way [96].
VII. Discussion and Future Perspectives
Generally, it can be summarized that the detection of
human vital signs by radar techniques involves the selection of the radar type, the appropriate algorithms, as
well as the right processing platforms. A special focus,
was provided to identify where and how FPGA was implemented in these radars, either as a processing/preprocessing platform, or as the control, or an interfacing
device in Section V. The flexibility and reconfigurability nature of the FPGA place it as an excellent candidate
for parallel processing and for implementation of algorithms that are computationally more complex.
It can be observed that there is more research directed towards real-time detection, as such feature is highly
practical. Real-time detection requires a very powerful processing platform, which is not always affordable
for everyday use. Alternative solutions that are being
investigated include innovative parallel processing
structures on reconfigurable processing devices. Nonetheless, recent developments in reconfigurable devices
such as FPGA, enable the processing of multiple operations on hundreds of thousands of logic elements. This
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