Page 158 - ITU Journal Future and evolving technologies – Volume 2 (2021), Issue 2

A(x, y, z) = s (x, y, z)
2
Laser mesh points Mesh element
blocked by a target
(x, y, z)
z
Beams intersection
point y
z x
j=1 j=2 j=3 y
x
(a)
j=1 j=2 j=3
(b)
Fig. 5 – Estimated area and shape of the target based on the blocked laser beams at mesh positions. (a) Blocked laser beam intersections are shown in
red at the respective mesh; (b) estimated area at each blockage.

s

j=1
s
j=2

j=3
Fig. 6 – The estimated 3D shape of the target based on blocked laser mesh intersections in Fig. 5.

3.2 Detection of the target based on blockage If there is a blockage to the path of a single laser beam
of laser beam or a bunch of beams due to a potential target, the re‑
ceived intensity, (RX) ( (RX) , ) of each beam is reduced
,
th
The RXs of laser beams at azimuth steering position and a subsequent reduction occurs in the SNR, / . This
G
th
and mesh, at a distance , from the TX, and an aper‑ reduction is due to the re lection and absorption of the
ture radius of (RX) expects an intensity (RX) ( (RX) , ) incident intensity from a target given in (4). Let be
,
(See (3) ) in case there is no blockage. The intensity, (RX) , the threshold for minimum SNR. The detection thresh‑
as a function of (RX) and ) is given as old is obtained using Neyman‑Pearson decision rule and
,
square law detection function for a given probability of
| | 2 0 2 −2 (RX) 2 false alarm (pfa). If / G < , then, this is perceived
0
(RX) ( (RX) , ) = ( ) exp ( ). as the presence of a target at that particular RX position.
,
2
2 0 ( ) ( ) The material of the target does not signi icantly change
,
b
b
,
(5) the blockage characteristics.
The corresponding received power at the RX side is given
as [21] 4. TARGET FEATURES
In this section, details of the features, i.e. 3D shape, max‑
2
(RX)
−2
2
2
∣ | [1 − exp ( ( , ) )] imum velocity, pitch, and drift angles, and maximum alti‑
0
0
2
(RX) ( (RX) , ) = 4 0 . (6) tude, obtainable by the proposed approach are provided.
,
Finally, the Signal‑to‑Noise Ratio (SNR) represented as 4.1 Features associated with target shape
th
th
/ at the RXs of steering position and mesh in Depending on the distance between consecutive beams,
G
the presence of Additive White Gaussian Noise (AWGN) the blockage at the intersection position of laser beams
2
∼ (0, ) can be written as on a mesh due to a target has a corresponding blocked
G
n
area. Fig. 5(a) shows laser beams blocked at different po‑
(RX) ( (RX) , )
/ = 2 , . (7) sitions on laser meshes, = 1, 2, 3, due to a target. The
G
area of each blocked position (i.e., blocked intersection