V2X communication system with non-orthogonal multiple access: outage performance perspective

Indonesian Journal of Electrical Engineering and Computer Science
Vol. 21, No. 2, February 2021, pp. 854∼864
ISSN: 2502-4752, DOI: 10.11591/ijeecs.v21i2.pp854-864 r 854
V2X communication system with non-orthogonal multiple
access: outage performance perspective
Tu-Trinh Thi Nguyen, Dinh-Thuan Do
Faculty of Electronics Technology, Industrial University of Ho Chi Minh City (IUH), Ho Chi Minh City, Vietnam
Article Info
Article history:
Received Jun 9, 2020
Revised Sep 11, 2020
Accepted Sep 25, 2020
Keywords:
Non-orthogonal multiple
access
Outage probability
Vehicle-to-everything
ABSTRACT
To achieve low-latency and high-reliability (LLHR) for applications in the vehicle-
to-everything (V2X) networks, the non-orthogonal multiple access (NOMA) is pro-
posed for Long Term Evolution (LTE)as a promising technology. NOMA-V2X pro-
vides higher spectrum efficiency compared with the orthogonal multiple access (OMA)
based V2X. The vehicles are expected to serve different services with variety of data
transmission. The cluster of vehicles could be grouped to achieve better service from
the transmitter sources. This study presents two-way relay assisted NOMA-V2X trans-
mission by exploiting amplify-and-forward (AF) and full-duplex technique. We can
benefits from potential applications of NOMA-V2X system with respect to serving
massive users and adapting higher bandwidth efficiency. We derive expressions of
outage probability to evaluate performance of two vehicles and to improve the quality
of service (QoS) for the device with the poor channel conditions. The main investi-
gation related two users’ performance which provides guidelines to design practical
system. These expressions are further verified by Monte-Carlo simulations.
This is an open access article under the CC BY-SA license.
Corresponding Author:
Dinh-Thuan Do,
Faculty of Electronics Technology,
Industrial University of Ho Chi Minh City (IUH),
Ho Chi Minh City, Vietnam.
Email: dodinhthuan@iuh.edu.vn
1. INTRODUCTION
As a candidate technique for forthcoming 5G networks, non-orthogonal multiple access (NOMA) net-
work has recently drawn in considerable attentions [1]-[8]. In particular, the higher spectral efficiency benefits
can be achieved by the deployment of NOMA and it outperforms the traditional orthogonal multiple access
(OMA) scheme [1]-[3]. In practical NOMA systems, to achieve low complexity, the successive interference
cancellation (SIC) decoding technique is needed to satisfy the performance of the NOMA system and it re-
quires the user grouping as an important issue. In the recent works regarding NOMA system, the improved
performance can be achieved as by employing relaying networks [4]-[7], [9]-[13] with NOMA to introduce
new paradigm termed as cooperative NOMA [8]. Regarding system performance, the optimal sum rate [14],
[15], and the minimal transmit power [16] are introduced with respect to the user grouping.
Recently, to provide smarter, safer and more efficient road traffic, vehicle-to-everything (V2X) com-
munications have a lot of achievements in both academia and industry [16]–[18]. Three kinds of V2X net-
works including vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I) and vehicle-to-pedestrian (V2P) are
implemented to enable real-time traffic information exchange among infrastructure, vehicles, and pedestrians
[19]–[21]. In such a V2X, low access efficiency and data congestion are caused by the fast growth of number
Journal homepage: http://ijeecs.iaescore.com

Indonesian J Elec Eng & Comp Sci ISSN: 2502-4752 r 855
of connected vehicles. The development of V2X communications need be tackled the challenges in vehicular
networks such as [22], [23]. This paper considers the ability of two pairs of vehicle can be communicated via
the Roadside Unit (RSU).
2. NETWORK ARCHITECTURE AND PROTOCOL DESCRIPTIONS
2.1. System architecture
Figure 1 depicts a scenario of AF relay assisted two-way NOMA-V2X systems, all nodes are with
single antenna except for relay with two antennas for FD mode. The base stations (BSs) employ a RSU to
serve group of two vehicles. In the multicasting scenario, RSU serves multiple users using NOMA. In this case,
vehicles in the same group require to receive different information (e.g., vehicle-specific control information)
from the BS. The source S1, S2 are able to send the corresponding signals x1, x2 ( with power allocation factors
α1, α2) to the RSU in the same time. The constraint of power allocation factors, i.e., α1 > α2 and α1 +α2 = 1.
It can be shared by two source-destination Group1 = {S1, U1} and Group2 = {S2, U2} pairs. The transmit
power at sources S1, S2 are the same, i.e. equals to Ps. The channels for links S1-RSU, S2-RSU, RSU-U1 and
RSU-U2 are h1, h2, g1, g2.
U2
U1
h1
h2
g2
g1
RSU
S2
S1
Figure 1. System model of NOMA V2X
2.2. SINR calculation
The received signal at RSU is given by
yRSU =
p
α1Psh1x1 +
p
α2Psh2x2 + PRSUf + ηRSU, (1)
where ηRSUis AWGN noise with variance of σ2
0. We call f as self-channel due to FD mode applied at the
RSU. The received signal at Ui, (i = 1, 2) can be expressed as follows:
yUi =
p
PRSUβgi
p
α1Psh1x1 +
p
α2Psh2x2 +
p
PRSUf + ηRSU

+ ηUi . (2)
The amplify factor is defined as follows:
β =
1
q
α1Ps|h1|
2
+ α2Ps|h2|
2
+ PRSU|f|
2
+ σ2
0
, (3)
where ρs
∆
= Ps

σ2
0 and ρRSU
∆
= PRSU

σ2
0 are transmission SNR of source and relay node, respectively.
V2X communication system with non-orthogonal multiple access: outage... (Tu-Trinh Thi Nguyen)

856 r ISSN: 2502-4752
The SINR at destination 1 in order to decode its own data can be written by
γU1
=
α1ρsρRSU|g1|
2
|h1|
2
α2ρsρRSU|g1|
2
|h2|
2
+ ρRSU|g1|
2
+ α1ρs|h1|
2
+ ρRSUρRSU|f|
2
|g1|
2
+ 1
. (4)
The received SINR for destination 2 to decode message x1 is given by
γU2→1 =
α1ρRSUρs|g2|
2
|h1|
2
α2ρRSUρs|h2|
2
|g2|
2
+ ρRSU|g2|
2
+ α1ρs|h1|
2
+ ρRSUρRSU|f|
2
|g2|
2
+ 1
. (5)
Destination 2 detects its own message with the following SINR.
γU4 =
α2ρRSUρs|h2|
2
|g2|
2
ρRSU|g2|
2
+ α1ρs|h1|
2
+ ρRSUρRSU|f|
2
|g2|
2
+ 1
. (6)
3. OUTAGE AND THROUGHPUT PERFORMANCE ANALYSIS
3.1. The outage probability for group 1
The outage probability is basic metric showing probability to SINR less than threshold value. In
particular, the outage probability of group 1 can be written as:
OPFD
Σ1
= Pr γU1
γ1
0

. (7)
Next, OPFD
Σ1
can be computed as
OPFD
Σ1
= Pr
α1ρsρRSU|g1|
2
|h1|
2
α2ρsρRSU|g1|
2
|h2|
2
+ ρRSU|g1|
2
+ α1ρs|h1|
2
+ ρRSUρRSU|f|
2
|g1|
2
+ 1
γ1
0
!
= Pr

1, |g1|
2
≤
γ1
0
ρRSU

+ Pr

|h1|
2

ρRSU|g1|
2

α2ρs|h2|
2
+ ρRSU|f|
2
+ 1

+ 1
α1ρs

ρRSU
γ1
0
|g1|
2
− 1
, |g1|
2

γ1
0
ρRSU


=1 −
1
λg1
∞
Z
γ1
0
ρRSU
exp

−
ρRSUxX
λh1
α1ρs

ρRSU
γ1
0
x − 1
−
x
λg1
−
1
λh1
α1ρs

ρRSU
γ1
0
x − 1


dx
(8)
Putting t = ρRSU
γ1
0
x − 1 ⇒ x =
γ1
0
ρRSU
(t + 1) then OPFD
Σ1
has become
OPFD
Σ1
=1 −
γ1
0
ρRSUλg1
exp

−
γ1
0
λg1 ρRSU
−
γ1
0 X
λh1 α1ρs

×
∞
Z
0
exp

−

1
λh1
α1ρs
+
γ1
0 X
λh1
α1ρs

1
t
−
γ1
0 t
λg1
ρRSU

dt
=1 − exp

−
γ1
0
λg1
ρRSU
−
γ1
0 X
λh1
α1ρs

2
s
γ1
0
λg1
ρRSU

1
λh1
α1ρs
+
γ1
0 X
λh1
α1ρs

× K1 2
s
γ1
0
λg1 ρRSU

1
λh1 α1ρs
+
γ1
0 X
λh1 α1ρs
!
(9)
Indonesian J Elec Eng Comp Sci, Vol. 21, No. 2, February 2021 : 854 – 864

Indonesian J Elec Eng Comp Sci ISSN: 2502-4752 r 857
where X =

α2ρs|h2|
2
+ ρRSU|f|
2
+ 1

. Let Y = α2ρs|h2|
2
+ ρRSU|f|
2
⇒ X = Y + 1 then the outage
probability of group 1 written again as follows
OPFD
Σ1
(Y ) =1 − e
−
γ1
0
λg1 ρr
−
γ1
0 (Y +1)
λh1
α1ρs
2
s
γ1
0
λg1 ρRSU

1
λh1 α1ρs
+
γ1
0 (Y + 1)
λh1 α1ρs

× K1 2
s
γ1
0
λg1
ρRSU

1
λh1
α1ρs
+
γ1
0 (Y + 1)
λh1
α1ρs
!
=1 − e
−
γ1
0 Y
λh1
α1ρs
−
γ1
0
λg1 ρRSU
−
γ1
0
λh1
α1ρs
2
s
γ1
0
λg1 ρRSU

γ1
0 Y
λh1 α1ρs
+
1
λh1 α1ρs
+
γ1
0
λh1 α1ρs

× K1 2
s
γ1
0
λg1 ρRSU

γ1
0 Y
λh1 α1ρs
+
1
λh1 α1ρs
+
γ1
0
λh1 α1ρs
!
=1 − 2e−ϑ1Y −ϑ2
p
ϑ3Y + ϑ4K1

2
p
ϑ3Y + ϑ4

(10)
where ϑ1 =
γ1
0
λh1
α1ρs
, ϑ2 =
γ1
0
ρRSUλg1
+
γ1
0
α1ρsλh1
, ϑ3 =
γ1
0 γ1
0
α1ρsρRSUλg1
λh1
, ϑ4 =
γ1
0
λg1
ρRSU

1
λh1
α1ρs
+
γ1
0
λh1
ϑ1ρs

.
OPFD
Σ1
can be calculated as
OPFD
Σ1
=EY
n
1 − 2e−ϑ1Y −ϑ2
p
ϑ3Y + ϑ4K1

2
p
ϑ3Y + ϑ4
o
=
∞
Z
0

1 − 2e−ϑ1Y −ϑ2
p
ϑ3Y + ϑ4K1

2
p
ϑ3Y + ϑ4

fY (y) dy
=OPFD
Σ11 + OPFD
Σ1,2
(11)
We have
FY (y) =
Y
Z
0
fY (y) dy
=
1
λf
y
ρRSU
Z
0
e
− x
λf dx −
1
λf
e
− y
λh2
υ2ρs
y
ρRSU
Z
0
e
−

1
λf ρr
− 1
λh2
α2ρs

x
dx.
(12)
Here we look at two cases for CDF and PDF:
3.1.1. Case 1
If 1
ρRSUλf
− 1
λh2
α2ρs
6= 0, we have
FY (y) = 1 −
ρRSUλf
ρRSUλf − α2ρsλh2
e
− y
ρRSUλf −
α2ρsλh2
α2ρsλh2
− ρRSUλf
e
− y
α2ρsλh2 , (13)
fY (y) =
e
− y
ρRSUλf
ρRSUλf − λh2
υ2ρs
+
e
− y
λh2
υ2ρs
λh2
υ2ρs − ρRSUλf
. (14)
OPFD
Σ11 can be computed as

858 r ISSN: 2502-4752
OPFD
Σ11 =EY
n
1 − 2e−ϑ1Y −ϑ2
p
ϑ3Y + ϑ4K1

2
p
ϑ3Y + ϑ4
o
=1 −
2e−ϑ2
ρRSUλf − λh2
υ2ρs
θ1 −
2e−ϑ2
λh2
υ2ρs − ρRSUλf
θ2
(15)
where τ1 =

1
ρRSU λf
+ ϑ1

,
θ1
∆
=
∞
Z
0
e−τ1y
p
ϑ3y + ϑ4K1

2
p
ϑ3y + ϑ4

dy
=e
τ1ϑ4
ϑ3
ϑ3
2τ1
2
e
ϑ3
τ1 Γ

−1,
ϑ3
τ1

−
1
2
M
X
m=0
(−τ1)
m
ϑ4
m+1
ϑ3
m+1 G2,1
1,3 ϑ4|−m
1,0,−m

!
, .
(16)
By using the lase equation in [25], vol. 4, (3.16.2.4)], we have:
τ2
∆
=
∞
Z
0
e−τ1y
p
ϑ3yK1

2
p
ϑ3y

dy
=
ϑ3
2τ1
2
e
ϑ3
τ1 Γ

−1,
ϑ3
τ1

.
(17)
and τ3 = 1
ϑ3
ϑ4
R
0
e−
τ1
ϑ3
y√
yK1 2
√
y

dy. Putting t = Cy → y = ϑ4t → dy = ϑ4dt when y = 0 → t = 0,
y = ϑ4 → t = 1 → C = 1
ϑ4
. Based on (18) we have:
τ3 =
ϑ4
ϑ3
1
Z
0
e−
τ1ϑ4
ϑ3
t
p
ϑ4tK1

2
p
ϑ4t

dt
=
1
2
M
X
m=0
(−τ1)
m
ϑ4
m+1
ϑ3
m+1 G2,1
1,3 ϑ4|−m
1,0,−m

.
(18)
Where the lase equation follows the fact that ex
=
∞
P
k=0
xk
k! in [24], (1.211.1)] and
1
R
0
xλ
(1 − x)
µ−1
Kν (a
√
x) dx =
2ν−1
aν Γ (µ) G2,1
1,3

a2
4 |
ν
2 −λ
ν,0, ν
2 −λ−µ

in [24], (6.952.2)].
And
θ2
∆
=
∞
Z
0
e−τ4y
p
ϑ3y + ϑ4K1

2
p
ϑ3y + ϑ4

dy
=e
τ4ϑ4
ϑ3
ϑ3
2τ4
2
e
ϑ3
τ4 Γ

−1,
ϑ3
τ4

−
1
2
M
X
m=0
(−τ4)
m
ϑ4
m+1
ϑ3
m+1 G2,1
1,3 ϑ4|−m
1,0,−m

!
.
(19)

where τ4 = 1
λh2
α2ρs
+ ϑ1. By using the equation xν/2
Kν (a
√
x) = Γ(ν+1)
(2p)ν+1 e
a2
4p Γ

−ν, a2
4p

in [25], vol. 4, eq.
(3.16.2.4)], we can computed τ5 :
τ5
∆
=
∞
Z
0
e−τ4y
p
ϑ3yK1

2
p
ϑ3y

dy
=
ϑ3
2τ4
2
e
ϑ3
τ4 Γ

−1,
ϑ3
τ4

,
(20)
τ6 =
1
ϑ3
ϑ4
Z
0
e−
τ4
ϑ3
y√
yK1 (2
√
y) dy
=
1
2
M
X
m=0
(−τ4)
m
ϑ4
m+1
ϑ3
m+1 G2,1
1,3

4ϑ4
4
|−m
1,0,−m

.
(21)
3.1.2. Case 2:
If 1
ρRSUλf
− 1
λh2
α2ρs
= 0, we have
FY (y) = 1 − e
−y
ρRSUλf −
y
ρRSUλf
e
−y
λh2
α2ρs
, (22)
fY (y) =
y
λY λY
e
−y
λY . (23)
OPFD
Σ1,2 is given as
OPFD
Σ1,2 =EY
n
1 − 2e−ϑ1Y −ϑ2
p
ϑ3Y + ϑ4K1

2
p
ϑ3Y + ϑ4
o
=1 −
2
λY λY
∞
Z
0
e
−

−1
λY
−ϑ1

y−ϑ2

1
ϑ3
(yϑ3 + ϑ4) −
ϑ4
ϑ3

p
ϑ3y + ϑ4K1

2
p
ϑ3y + ϑ4

dy
=1 − θ4 + θ5.
(24)
where
θ4 =τ7
∞
Z
0
e−τ8y
(ϑ3y + ϑ4)
3/2
K1

2
p
ϑ3y + ϑ4

dy
=τ7e
τ8ϑ4
ϑ3 (∆1 − ∆2)
=τ7e
τ8ϑ4
ϑ3

ϑ3
τ8
2
W−2,1/2

ϑ3
τ8

−
1
2
M
X
m=0
(−τ8)
m
ϑ4
m+2
ϑ3
m+1 G2,1
1,3 ϑ4|−m
1,0,−m

#
(25)
By using the equation
∞
R
0
xν/2
Kν (a
√
x) dx = p−µ−1/2
a Γ µ + ν
2 + 1

Γ µ − ν
2 + 1

exp

a2
8p

×W−µ−1/2,ν/2

a2
4p

in [25], vol. 4, eq. (3.16.2.3)] and
∞
R
0
xν/2
Kν (a
√
x) dx = Γ(ν+1)
(2p)ν+1 exp

a2
4p

Γ

−ν, a2
4p

in [25], vol. 4, eq.
(3.16.2.4)], we can computed ∆1, ∆2:
∆1 =
∞
Z
0
e−τ8y
ϑ3
3/2
y3/2
K1

2
p
ϑ3y

dy
=
ϑ3
τ8
2
W−2,1/2

ϑ3
τ8

,
(26)

860 r ISSN: 2502-4752
∆2 =
1
ϑ3
ϑ4
Z
0
e−
τ8
ϑ3
y
y3/2
K1 (2
√
y) dy
=
1
2
M
X
m=0
(−τ8)
m
ϑ4
m+2
ϑ3
m+1 G2,1
1,3 ϑ4|−m
1,0,−m

,
(27)
and
θ5 =τ7ϑ4
∞
Z
0
e−τ8y
p
ϑ3y + ϑ4K1

2
p
ϑ3y + ϑ4

dy
=e
τ8ϑ4
ϑ3
τ7ϑ4ϑ3
2τ8
2
e
ϑ3
τ8 Γ

−1,
ϑ3
τ8

−
τ7
2
M
X
m=0
(−τ8)
m
ϑ4
m+2
ϑ3
m+1 G2,1
1,3 ϑ4|−m
1,0,−m

! (28)
where
τ7 = 2e−ϑ2
λY λY ϑ3
, τ8 = 1
λY
+ ϑ1, τ9 = ϑ3
2τ8
2 e
ϑ3
τ8 Γ

−1, ϑ3
τ8

, τ10 = 1
2
M
P
m=0
(−τ8)m
ϑ4
m+1
ϑ3
m+1 G2,1
1,3
4ϑ4
4 |−m
1,0,−m

.
3.2. The outage probability for group 2
The exact outage probability of group 2 can be written as
OPFD
Σ2
=1 − Pr γU2←1 ≥ γ1
0 , γU2
≥ γ2
0

(29)
The outage probability in (29) can be computed as
OPFD
Σ2
=1 − Pr


α1ρRSUρs|g2|2
|h1|2
α2ρRSUρs|h2|2
|g2|2
+ρRSU|g2|2
+α1ρs|h1|2
+ρRSUρRSU|f|2
|g2|2
+1
≥ γ1
0 ,
α2ρRSUρs|h2|2
|g2|2
ρRSU|g2|2
+α1ρs|h1|2
+ρRSUρRSU|f|2
|g2|2
+1
≥ γ2
0


=1 − OPFD
Σ2,1 + OPFD
Σ2,2

.
(30)
3.2.1. Case 1:
If max = 1
α1ρs
γ1
0
|h1|2
−α2ρs|h2|2
−1−ρRSU|f|2 , we have:
OPFD
Σ2,1 =
∞
Z
0
f|f|2 (z) dz
∞
Z
γ2
0
α2ρs
(ρRSUz+1)
f|h2|2 (y) dy
×
γ1
0 α2
α1

1
γ2
0
+1

y
Z
γ1
0
α1ρs
(α2ρsy+ρRSUz+1)
1 − F|g2|2
1
ρRSU
α1ρsx + 1
α1ρs
γ1
0
x − α2ρsy − ρRSUz − 1
!!
f|h1|2 (x) dx
| {z }
∆
=∆4
,
(31)

Continuing the calculation process, we have
OPFD
Σ2,1 =
∞
Z
0
f|f|2 (z) dz











1
λh2
∞
Z
γ2
0
α2ρs
(ρRSUz+1)
e
−
γ1
0
ρRSUλg2 e
−

γ1
0 α2
α1λh1

1
γ2
0
+1

+ 1
λh2

y
dy
| {z }
∆
=ϑ1
−
1
λh2
∞
Z
γ2
0
α2ρs
(ρRSUz+1)
e
−
γ1
0
ρRSUλg2 e
−

α2γ1
0
α1λh1
+ 1
λh2

y
e
−
ρRSUγ1
0
α1ρsλh1
z
e
−
γ1
0
α1ρsλh1 dy
| {z }
∆
=ϑ2











=
e
−
γ1
0 γ2
0
α1ρsλh1

1
γ2
0
+1

−
γ2
0
α2ρsλh2
−
γ1
0
ρRSUλg2
λh2

γ1
0 α2
α1λh1

1
γ2
0
+ 1

+ 1
λh2

∞
Z
0
e
−

γ1
0 α2
α1λh1

1
γ2
0
+1

+ 1
λh2

ρRSUγ2
0
α2ρs
z
f|f|2 (z) dz
| {z }
∆
=ϑ3
−
e
−
γ1
0
ρrλg2
−
γ1
0
α1ρsλh1
−

α2γ1
0
α1λh1
+ 1
λh2

γ2
0
α2ρs
λh2

α2γ1
0
αλh1
+ 1
λh2

∞
Z
0
e
−

ρRSUγ1
0
α1ρsλh1
+
ρRSUγ2
0
α2ρs

α2γ1
0
α1λh1
+ 1
λh2

z
f|f|2 (z) dz
| {z }
∆
=ϑ4
=
e
−
γ1
0 γ2
0
α1ρsλh1

1
γ2
0
+1

−
γ2
0
α2ρsλh2
−
γ1
0
ρRSUλg2
λh2 λf

γ1
0 α2
α1λh1

1
γ2
0
+ 1

+ 1
λh2
h
γ1
0 α2
α1λh1

1
γ2
0
+ 1

+ 1
λh2

ρRSUγ2
0
α2ρs
+ 1
λf
i
−
e
−
γ1
0
ρRSUλg2
−
γ1
0
α1ρsλh1
−

α2γ1
0
α1λh1
+ 1
λh2

γ2
0
α2ρs
λh2
λf

α2γ1
0
α1λh1
+ 1
λh2
h
ρRSUγ1
0
α1ρsλh1
+
ρrγ2
0
α2ρs

α2γ1
0
α1λh1
+ 1
λh2

+ 1
λf
i.
(32)
where ∆4 = 1
λh1
e
−
γ1
0
ρRSUλg2
γ1
0 υ2
υ1

1
γ2
0
+1

y
R
γ1
0
υ1ρs
(υ2ρsy+ρRSUz+1)
e
− x
λh1 dx,
ϑ1 = e
−
γ1
0 γ2
0
α1ρsλh1
1
γ2
0
+1
!
−
γ2
0
α2ρsλh2
−
γ1
0
ρRSUλg2 e
−
γ1
0 α2
α1λh1
1
γ2
0
+1
!
+ 1
λh2
!
ρRSUγ2
0
α2ρs
z
γ1
0 α2λh2
α1λh1

1
γ2
0
+1

+1
,
ϑ2 = e
−
γ1
0
ρRSUλg2
−
γ1
0
α1ρsλh1
−
α2γ1
0
α1λh1
+ 1
λh2
!
γ2
0
α2ρs
e
−
ρRSUγ1
0
α1ρsλh1
+
ρRSUγ2
0
α2ρs
α2γ1
0
α1λh1
+ 1
λh2
!!
z
λh2

α2γ1
0
α1λh1
+ 1
λh2
,
ϑ3 = e
−
γ1
0 γ2
0
α1ρsλh1
1
γ2
0
+1
!
−
γ2
0
α2ρsλh2
−
γ1
0
ρRSUλg2
λh2
λf

γ1
0 α2
α1λh1

1
γ2
0
+1

+ 1
λh2

γ1
0 α2
α1λh1

1
γ2
0
+1

+ 1
λh2

ρRSUγ2
0
α2ρs
+ 1
λf
,
ϑ4 = e
−
γ1
0
ρRSUλg2
−
γ1
0
α1ρsλh1
−
α2γ1
0
α1λh1
+ 1
λh2
!
γ2
0
α2ρs
λh2
λf

α2γ1
0
α1λh1
+ 1
λh2

ρRSUγ1
0
α1ρsλh1
+
ρRSUγ2
0
α2ρs

α2γ1
0
α1λh1
+ 1
λh2

+ 1
λf
.

862 r ISSN: 2502-4752
3.2.2. Case 2:
If max = 1
α2ρs
γ2
0
|h2|2
−1−ρRSU|f|2 , we have:
OPFD
Σ2,2 =
∞
Z
0
f|f|2 (z) dz
∞
Z
γ2
0
α2ρs
(ρRSUz+1)
f|h2|2 (y) dy
×
∞
Z
γ1
0 α2
α1

1
γ2
0
+1

y
1 − F|g2|2
1
ρRSU
α1ρsx + 1
α2ρs
γ2
0
y − ρRSUz − 1
!!
f|h1|2 (x) dx
| {z }
∆
=∆3
=
2γ2
0
α2ρsρRSUλf
∞
X
k=1
kλk
g2
(−α1ρsλh1
)
k−1
e
−Ξ4−
γ2
0
α2ρsλh2
s

Ξ2 (1 + E)
Ξ1λg2
k+1
ρRSUΞ2Ξ5
Ξ1λg2
k+1
×
∞
Z
0
e
−

1
λf
+
Ξ1ρRSUρRSU
Ξ2
+
ρRSUγ2
0
α2ρsλh2

z
zk+1
Kk+1 2
s
Ξ1 (1 + ρRSUΞ5z + Ξ5)
Ξ2λg2
!
dz.
(33)
where Ξ1 =
γ1
0 α2
λh1
α1

1
γ2
0
+ 1

, Ξ2 = α2ρsρRSU
γ2
0
, Ξ4 =
ρsλh1
α1Ξ1
λg2
Ξ2
+ Ξ1ρRSU
Ξ2
, Ξ5 =
ρsρRSUλh1
α1Ξ1
Ξ2
.
3.3. Throughput
The throughput in delay-limited transmission mode is given by
Υ1 = 1 − OPFD
Σ1

R1,
Υ2 = 1 − OPFD
Σ2

R2.
(34)
4. RESULT AND DISCUSSION
Figures 2 and 3 demonstrate outage probability of two vehicles. It can be observed that outage prob-
ability improves significantly at high SNR. There is existence performance gap among two vehicles due to
different power allocation factors. It is further confirmed that outage probability cannot improve at very high
SNR regardless of changing target rates R1, R2. In these simulations, Monte-Carlo and analytical simulations
are matched tightly and it confirmed our derivations are correct. Figure 4 examines impact of interference chan-
nel related to FD mode on outage probability. When changing λf from 0 (dB) to 30 (dB) outage probability
becomes worse significantly. Figure 5 shows throughput versus transmit SNR ρ. Increasing ρ from -20 (dB) to
15 (dB), throughput increases significantly, but it meets the ceiling at high SNR region.
-10 -5 0 5 10 15 20 25 30 35 40
10-2
10-1
100
Figure 2. Outage probability: R1 = 0.5
bps/Hz, R2 = 1 bps/Hz.
-10 -5 0 5 10 15 20 25 30 35 40
10-3
10-2
10-1
100
Figure 3. Outage probability: α1 = 0.9,
α2 = 0.1.

-20 -15 -10 -5 0 5 10 15 20 25 30
10-3
10-2
10-1
100
Figure 4. Outage probability: R1 = 0.1 bps/Hz,
R2 = 0.1, α1 = 0.9, α2 = 0.1.
-20 -15 -10 -5 0 5 10 15 20 25 30
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.1
Figure 5. Throughput: α1 = 0.9, α2 = 0.1.
5. CONCLUSION
In this paper, two pairs of users in NOMA-V2X systems have been proposed for 5G cellular V2X
communications. The fixed power allocation factors are applied to highlight different outage performance of
each group of user. We provided exact expressions of outage probability to evaluate system performance. We
show that the formulated expression is verified via simulations. Fortunately, it indicates reasonable performance
of two vehicles in NOMA-V2X if self-interference channel is controlled well. Simulation results demonstrate
that the proposed scheme exhibits better performance at high SNR at sources.
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