Page 100 - ITU Journal, Future and evolving technologies - Volume 1 (2020), Issue 1, Inaugural issue

ITU Journal on Future and Evolving Technologies, Volume 1 (2020), Issue 1

main beam for beam stearing objective. capacity, by demonstrating the great potentiality of
this type of structure.
In [18], it is demonstrated how this type of meta-surface
allows a digital control of EM waves, by associating two
coding elements with opposite reflection phases (i.e., 0 ∘ The rest of the article is organized as follows. Section 2
∘
and 180 ) and considering them as digital bits (i.e., 0 and describes the specific scenario considered and details the
proposed unit cell structure. Section 3 presents simu-
1 in the binary case). Reconfigurable meta-surface struc-
lated results for the proposed RIM unit cell in two ON and
tures can be applied to manipulate EM waves in a sim-
OFF states, expressed in terms of (i) reflection magnitude
ple and effective way, by changing the coding elements on
a 2D plane with predesigned coding sequences [19]. In and phase, and (ii) effective permittivity and permeabil-
ity. In Section 4 we validate the full RIM structure, while in
order to independently control and create different cod-
Section 5 the performance of the proposed RIM has been
ing sequences a Field Programmable Gate Array (FPGA)
exploited for vehicular communications, by considering
is used. By changing the coding sequences stored in
that the RSU and the receiver vehicle are coated with the
the FPGA, many different functionalities can be switched
implemented 10 × 10 unit cells RIM. Instantaneous data
in real time, thereby leading to programmable meta-
rate, outage probability and channel capacity have been
surfaces.
obtained as validation results. In Section 6, we present a
In this paper, we formulate the specific features that a fewconsiderationsrelatedtotheobtainedresults. Finally,
meta-surface for vehicular communication applications conclusions are drawn at the end of the article.
needs to have in the frequency range of [5, 5.9] GHz. In
particular, we consider a tracking application with beam 2. UNIT-CELL DESIGN AND CONFIGURA-
steering, for which is of paramount importance to con- TION
trol the phase and to concentrate the power in the main
lobe of the reflected signal, as much as possible. In or- The envisioned vehicular communications paradigm
der to meet these specific requirements, we will design based on using RIM is shown in Fig. 1. In particular, we fo-
a unit cell and then derive a full structure constituted by cus on a RIM relay based scheme. An RSU (Road Side Unit)
the periodic repetitions of these unit cells, behaving as a is at the side of the road and is coated with the specific
reflector for a pair of transmitter receivers. We will focus meta-surface structure we will detail later. We assume
on the phase shift and the main beam width in order to that the RSU, as represented in Fig. 1, is re-transmitting
design a beam tracking system which is able to “follow” data to the receiver (i.e., the green vehicle). In order to
the mobile receiver node for improving the efficiency in maximize the SNR to the destination, the RIM RSU will be
“beam tracking” the receiver. This specific behavior can
terms of data rate and outage probability. Based on that,
we will present a multifunctional reconfigurable meta- be realized by designing a unit cell with specific features
surface structure based on the radiation pattern modu- as explained to the follow.
lation of the reflection coefficient. Firstly, we will design
a reconfigurable U-shaped unit cell using a pin diode via The proposed unit cell structure is shown in Fig. 2 (a). In
∘
a hole, which can provide 180 -phase difference between this structure we proposed a U-shaped microstrip struc-
ON and OFF states. Specifically, a 10 × 10 meta-surface ture which is able to be reconfigurable by a PIN diode. By
loadedwithPINdiodesisdesignedformultifunctionalbe- creating a rectangular slot in the corner of the rectangu-
havior, such as coding and beam steering. The simulated lar patch a new path of surface current will be created.
results in both scenarios of unit cell and full structures Hence, we can control the input impedance of the unit cell
will show the effectiveness of the proposed structure for which is suitable for such an application of RIM. Moreover,
vehicular communications. the relevant equivalent circuit for this structure is shown
in Fig. 2 (b). Regarding the ON and OFF states of the PIN
Our main contributions can be summarized as follows:
diode, we put two different equivalent circuits for this sec-
• We design a specific meta-atom working at 5.3 GHz tion. All the dimensions are summarized in Table 1.
for automotive applications and based on this unit
cell, we design a full structure and validate it to as-
sess its suitability for the vehicular application con- Table 1 – Parameters of the proposed unit cell
sidered;
Parameter Value [mm] Parameter Value [mm]
• We design a full structure and validate it to assess its 10 9
suitability for the vehicular application considered; 10 6

ℎ 1.6 1 2
• We consider the integration of the designed Recon-
1 1 3
figurable Intelligent Meta-surface (RIM) in a vehicu- 3 0.25
lar system and we numerically evaluate the perfor-
mance; We compare the results of the system with
and without RIM in terms of outage probability and In meta-surface structures, beam steering can be consid-

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