Page 105 - 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

(a) (b) (c)
∘
∘
Fig. 8 – Evaluation of the instantaneous data rate [Gbps] vs. the beam width and the vehicle speed, in case of (a) = [0.1, 10] and (b) = [30, 120] ,
both by considering different speeds i.e., 1 = 25, 2 = 50, and 3 = 75 [m/s]. (c) Instantaneous data rate [Gbps] vs. vehicle speed and distances, in
∘
case of = [20, 70, 120] .

Finally, in Fig. 8 (c) we analyze the impact of the speed 1 °
RIM, = 20
b
i.e., from 10 to 100 km/h, with respect to specific values of RIM, = 90 °
∘
beam width i.e., = [20, 70, 120] . The behavior follows 0.8 no RIM b

the same trend as observed in Fig. 8 (a) and (b), where,
as expected, for higher beam width the data rate perfor- 0.6
mance is strongly reduced. Also, lower distances provide Outage Probability
higher performance. 0.4
0.2
5.2 Outage Probability
0
The outage probability is a crucial metric for vehicular 0 100 200 300 400 500
Distance [m]
communication [24, 25], and can be defined as the instan-
taneous mutual information rate that falls below a certain Fig. 9 – Outage Probability vs. the distance, in case of (i) a meta-surface
∘
∘
threshold , i.e.: with beam width = 20 and = 90 , and (ii) without a meta-
surface.
[ < ] = 1 − , (16)
meta-atoms needed in the metastructure for a high tun-
ing of the phase. In practice, the higher is the number of
where is the success probability that SNR is unit cells of the full structure, the better is the control of
higher than , and can be expressed as the whole system, but also the control logic to drive the
controllable meta-surface is more sophisticated/compli-

= [ > ] = (− ) , (17) cated, since it is demanding a higher precision and could
make the system more vulnerable to misalignment errors.
with as the transmitting power.
Based on the outage probability, given a specific target 6. DISCUSSION
rate as a Quality of Service (QoS) parameter, we can de-
In order to assess the performance of the system and to
rive the throughput of success delivery with constrained
evaluate the potential impact of the RIM in a vehicular
outage probability , as [24]:
context, we have considered some assumptions to sim-
= (1 − ) (1 + ). (18) plify the analysis and give some useful insights for fu-
2
ture work. Firstly, a perfect alignment between the relay
In order to evaluate the impact of the presence of the coatedwith the RIM and the receiverhasbeen considered.
meta-surface, in Fig. 9, we consider a target rate of 1 Gbps This assumption cannot be ensured above all in a con-
and derive the corresponding outage probability as com- text characterised with high speed. In order to account
puted in Eq. (16). In order to better appreciate the ef- for that, we need to introduce an error factor of the speed
fect of the meta-surface, we consider two different beam to account for the misalignment. A possible approach for
∘
∘
widths of 20 and 90 . As expected, the lower is the beam accounting the misalignment has been proposed in [26].
width, the lower is the outage probability and the system We believe that this misalignment could be translated as a
has better performance in terms of capacity (see Fig. 10). reduction of the received power and then in a decreasing
The better performance is related to a higher precision of of the SNR.
the system, that corresponds to an increased number of Another simplification introduced is the ideal configura-

© International Telecommunication Union, 2020 85