Information Technology Reference
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is a quite small memory requirement compared with the hardware resources of
today's mobile devices.
For a node with
M
neighbors, the number of multiplications/divisions it needs
to calculate in Equation (1) is 2
M
+1, For a network with
C
channels, the number
of multiplications/divisions the node needs to do is
C
(2
M
+ 1). With
C
=12
and
M
= 256, the calculation time is quite small compared with the seconds
long refreshing period for the conflict probabilities.
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5 Evaluations
We implemented this channel usage based multichannel assignment algorithm
for MIMC VANETs (MIMC-Chan-Usage) in NS2 [1]. The parameters used in
Section 4 to describe the algorithm are listed in Table 2. We use AODV [14] to
evaluate the network performance, and compare MIMC-Chan-Usage with Single
Interface Single Channel (SISC), Fix-Switch [9], and MIMC-Road [24]. In order
to compare with Fix-Switch, the number of channels is set to a small number of
3, and the interfaces is 2. A channel switch delay of 10ms is also implemented in
the simulations. The communication range is set to 150m. The channel segment
size is set to about 300m according to the rules in [24].
Tabl e 2.
The Parameters of the Mutli-Channel Assignment Algorithm
Parameters
Values
T
varying randomly between 1.25 and 1.75 seconds
T
switch
varying randomly between 2.5 and 4.5 seconds
α
0.15
P
threshold
0.2275
We simulate the network with 100, 200, 300 and 400 moving vehicles on a real
road topology shown in Fig. 3 (the black lines). It's the main roads extracted
from a 2000
1700
m
2
area in south Beijing. The roads are simulated with several
separated lanes. And the vehicles are moving according to the Intelligent Driver
Motion (IDM) Model [20].
Fig. 4 is the comparison of the number of all the packets delivered during the
simulations on different network sizes. It shows that the channel usage based
MIMC outperforms the others. With two interfaces, the channel usage based
MIMC can keep the total delivered packets about double of the the SISC's,
while Fix-Switch and MIMC-Road can not. This shows the channel usage based
MIMC can better utilize the channel resources under different scenarios. The
average delays of the packets in Fig. 5 show that the channel usage based MIMC
still performs the best in all the configurations.
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