Information Technology Reference
In-Depth Information
As discussed in the introduction section, connectivity invariant property is
valuable to the VANET QoS and layered network protocol design. Here, we want
to preserve the connectivity invariant property from MIMC-Road and overcome
its shortcomings. Generally, the connectivity invariance can be achieved by in-
suring that there always exists at least one common channel between any two
nodes within the communication range. In MIMC-Road, this is guaranteed by
arranging the channels geographically. But more generally, for a network with
C
available channels, we can insure the common channel between nodes by equip-
ping at lease
2
+ 1 interfaces for every node. Letting these interfaces work
on different channels and the existence of common channels are insured by the
Pigeon Hole Principle. This condition constrains the interface number of the
vehicles. Considering that there is fewer hardware and energy limitations on
the vehicles than on the conventional mobile devices, the requirement can be
satisfied with reasonable costs. Specifically, for 3 channels in 802.11b/g, 7 chan-
nels in DSRC and 12 channels in 802.11a, the required number of interfaces are
2, 4 and 7. It is suitable for a vehicle to equip 2 or 4 interfaces. 7 interface per
vehiclelooksabittoocostlyatfirstglance. But MIMC architecture does not
need to modify the MAC, which means the hardware can be obtained off the
shelf. And the connectivity invariance simplifies the protocol design and reduces
the implementation cost. The total cost may not be as much as one would expect
at first glance.
With the above connectivity invariant condition, the topology of multichannel
network is identical to that of the single channel network. There's no constraints
of using channels geographically as MIMC-Road did, or timely as channel hop-
ping methods did. Idle nodes will not be required to switch the channels to keep
the connectivity anymore. For the dense networks, the nodes can freely switch
their channels to find unbusy channels. This gives nodes more opportunity to
use more channels for a better performance in a small area than MIMC-Road.
The channel usage based dynamic multichannel assignment method in Section
4 achieves this. Moreover, only the interfaces on the same node are required
to have the same communication ranges. The interfaces of different vehicles are
no longer required to be identical. Different vehicles can equip hardwares from
different manufacturers with various characters. This also simplifies the VANET
deployment.
4 Channel Usage Based Multichannel Assignment
When vehicles encounter high communication conflicts, they can switch inter-
faces from busy channels to spare ones to improve the performance. This is the
design philosophy of channel usage based assignment. Based on the connectivity
invariant condition in Section 3, we do not need to worry about the connectivity
and can concentrate our attention on the channel usage conditions. In the fol-
lowing subsections, we first give out the mathematic expression of channel usage
in Section 4.1. Then, the design of the dynamic channel assignment algorithm is
described in detail in Section 4.2.
