IEEE - Aerospace and Electronic Systems - September 2023 - 7

Ksi ˛e_zyk et al.
a third user perspective. In this article, the focus is put on
those downlink physical signals and channels that are not
user specific. Then, downlink channel reference signals
will be described.
As an introduction to the detailed analysis of 5G signals'
and physical channels' morphology given in the following,
a rough description of their usage during UE
access to the 5G network is presented in Table 1.
NR RG AND NUMEROLOGY
Figure 2.
General signal processing diagram for radar using a 5G network
as a source of illumination.
but operating in option 4, at least two receiving antennas
have to be provided.
As mentioned, the processing in both types of radar,
active and passive, is very similar. In passive radars, the
signal can be additionally synchronized allowing for the
increase of the SNR at the output of the detector, but this
operation is not mandatory. The range compression is performed
according to matched filtering (1) or correlation (2)
for active and passive radar, respectively. The next steps
rely on clutter removal, velocity estimation, target detection,
and tracking. These steps are close in passive and
active systems and operate on the base of the same
principles.
5G SIGNAL MORPHOLOGY
A passive radar approach relies on the concept of utilizing
an existing signal produced by ongoing communication
between a transmitter and a receiver. In the 5G NR cellular
network, these devices correspond to the BTS and UE.
A key requirement is to identify the signals that are useful
in active and passive location techniques presented in
Figure 1. The 5G NR waveform is constructed from several
physical channels and signals. Each of them has a different
purpose, occurs in different places in the time-
frequency (TF) grid, and is coded in a different way. It is
important to identify the position of those signals in the
TF resource grid (RG) and, if possible, decode them from
SEPTEMBER 2023
Filtered orthogonal frequency division multiplex (FOFDM)
was chosen as a 5G NR access scheme. Similar to
the 4G long term evolution (LTE) deployment, all 5G
physical channels and signals in both uplink and downlink
form an RG on which particular symbols are placed in the
frequency and time domain. The main differences
between NR and LTE are i) scalable (so-called) numerology,
identified by parameter m ¼f0; 1; 2; ...g, and ii)
max carrier bandwidth. Parameter m directly identifies
subcarries spacing (SCS), symbol and cyclic prefix duration,
and slot length. Possible values of all options for general
parameters are presented in Table 2.
Table 1.
Some 5G Physical Channels/Signals Which Are
Important for Radar Purposes
Analyzed Receiving/
Decoding
SSB
PSS
SSS
DM-RS and
PBCH
MIB from
PBCH
Goal
Frequency and
symbol synchron
Physical cell
identification
Frame synchro,
spacial filter selection
Finding PDCCH
configuration
PDCCH PDCCH Obtaining info about
SIB1 position
PDSCH PDSCH Obtaining SIB1, i.e.,
min system info
CSI-RS
CSI-RS
Finding 5G channel
characteristics
1. PSS: Primary synchronization signal. 2. SSS: Secondary synchronization
signal. 3. DM-RS: Demodulation reference signal.
4. PBCH: Physical broadcast channel. 5. SSB = 1+2+3+4: Synchronization
signal block. 6. MIB = Master information block
from PBCH. 7. PDCCH: Physical downlink control channel.
8. PDSCH: Physical downlink shared/data channel. 9. SIB1: System
information block type 1from PDSCH. 10. CSI-RS: Channel
state information reference signal.
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