L. Zhang et al.: Energy-Aware Dynamic Resource Allocation in UAV-Assisted MEC Over SIoV
FIGURE 2. The system model.
and are distributed as Poisson point process on the straight
unidirectional multi-lane road segment with length d
S
and
width d
W
. We assume that each vehicle drives in a straight
line at a constant speed denoted by V, and never leaves
the road. The UAV is mounted with a transceiver, a single
antenna, and a MEC server. In particular, the MEC server
connects to the core network through wireless backhaul and
provides computation resources to vehicles by adopting a
powerful computing processor. A RSU is installed along
the road to make drivers and passengers enjoy the socially-
inspired services and require the cached popular social con-
tents via the social content caching server. The cacheable
RSU with a radius d
R
≤ d
S
/2 is stationary after deployment.
We assume that M vehicles are within the coverage region of
the RSU. Thereby, M vehicles can request the cached social
contents from the RSU via V2I link. Each vehicle is equipped
with a single-antenna OBU which can communicate with the
UAV, the RSU and other vehicles. Here, the vehicle-carried
OBU has an on-chip microprocessor with limited computing
capability to execute local computation task. In this context,
the computation task of each vehicle can be partitioned in
bitwise for partial local computing and partial computation
offloading.
Without loss of generality, we consider a three dimen-
sional Cartesian coordinate system to describe the loca-
tions of the ground vehicles and the flying UAV. As shown
in Fig. 3, the finite time horizon T is divided into N time
slots with equal length τ , i.e., τ = T /N . Let t
n
corre-
spond to the instant time within the nth time slot, for t
n
∈
[
t
0
+
(
n − 1
)
τ, t
0
+ nτ
]
, where t
0
is an initial time of time
horizon T . It is should be noted that there exist continuous
time during each time slot, which differs from fixed time slot
division in a discrete way. At the nth time slot, the instant
location of the mth vehicle over the horizontal plane coor-
dinate can be denoted as q
m
(
t
n
)
=
[
x
m
(
t
n
)
, y
m
(
t
n
)
]
. Under
such circumstances, the mobility constraint of the mth vehicle
is determined as
k
q
m
(
T
)
− q
m
(
0
)
k
= VT ≤ 2d
R
, ∀m (1)
FIGURE 3. The time slot allocation for computation offloading from
M vehicles to UAV by using a TDMA-based co-channel media access.
In this system, we focus on the scenario where the UAV
flies at a fixed hovering altitude H aiming to keep contin-
uous flying over the air. This stable hovering of the UAV
contributes to avoidance of frequent aircraft ascending and
descending owing to terrain or building blockage. Then the
instant location of the UAV mapped onto the horizontal
plane coordinate at the nth time slot can be denoted by
q
U
(
t
n
)
=
[
x
U
(
t
n
)
, y
U
(
t
n
)
]
. We further assume that the start
and end locations of the UAV are pre-determined, which
can be also given as q
s
U
= [x
s
U
, y
s
U
] and q
e
U
= [x
e
U
, y
e
U
],
respectively. Technically, τ can be chosen to be sufficiently
small such that the location of the UAV stays approximately
at a fixed location at each time slot [20], [28], [32]. In this
way, by incorporating the locations of N time slots, the flying
trajectory of the UAV within time horizon T can be modeled
by q
U
=
q
s
U
, q
U
(
t
1
)
, ··· , q
U
(
t
N
)
, q
e
U
. Thereby, the tra-
jectory constraints of the UAV can be represented as
k
q
U
(
t
n
)
− q
U
(
t
n−1
)
k
≤ τ V
max
U
, ∀n
q
s
U
= q
U
(
0
)
, ∀n
q
e
U
= q
U
(
T
)
, ∀n (2)
where V
max
U
is the UAV’s maximum flight speed. We assume
that the wireless channel from ground vehicles to the UAV
is dominated by the line-of-sight (LoS) transmission link
[20], [28], [32]. A quasi-static block fading channel model is
utilized to represent the ground-UAV LoS link. In this case,
the channel remains unchanged within each fading block, and
is subject to distance dependent power attenuation. Therefore,
at the nth time slot, the channel gain between the mth vehicle
and the UAV can be formulated as
h
m
(
t
n
)
= η
0
d
−ζ
m
(
t
n
)
=
η
0
k
q
U
(
t
n
)
− q
m
(
t
n
)
k
2
+ H
2
ζ /2
(3)
where η
0
is the channel gain at a reference distance d
0
, d
m
(
t
n
)
is the distance between the mth vehicle and the UAV over the
horizontal plane, and ζ ≥ 2 is the path-loss exponent.
A. COMPUTATION MODEL
In this paper, we assume that the vehicles adopt a partial com-
putation offloading model. That is, the computation task can
either be executed locally at the vehicles, or be offloaded to
and executed by the UAV assisted MEC server. Here, we use
the size of computation input data including the program
codes and input parameters to describe the computation task
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