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usually required to make the channel hopping ecient. And the protocols are
tightly bounded with the MAC protocol. These shortcomings make the single
interface multichannel methods dicult to deploy in reality. In [13], a compar-
ison of these works in MANET is given out. In VANET, there are also some
multichannel MAC protocol design [22,10,11].
Here, our main concern is the multichannel problem with multi-interface ar-
chitecture (MIMC), which is independent of MAC protocols, and more ecient
than single interface architecture [8]. The MIMC algorithms can be divided into
the following categories.
2.1 Fixed Multichannel Assignment
The algorithms of fixed multichannel assignment will not change the assignment
within a quite long period after an assignment is determined. These algorithms is
suitable for networks with static topologies and known trac profiles. In [18], the
authors proposed a centralized channel assignment algorithm for mesh networks.
The algorithm assumes that the trac load is known in advance. The channel
with few conflicts is assigned to link with high load. This algorithm cannot
adapt to dynamic topology and trac. When some links need re-allocate the
channels, they may cause the ripple-effect [18]. In [12], the authors presented
a new multichannel assignment algorithm based on a connectivity graph and a
conflict graph in mesh network. This algorithm does not cause ripple-effect, but
it does not take the trac load into consideration.
2.2 Dynamic Multichannel Assignment
In this sort of algorithms, the interfaces can switch dynamically between available
channels to adapt to the dynamic trac load. In [17] and [16], the authors
propose mechanisms to allocate channels dynamically based on the spanning
tree in mesh network. the gateway node is treated as the root of the tree. The
spanning tree is reconfigured dynamically according to the trac from and to
the gateway.
2.3 Mixed Multichannel Assignment
This sort of algorithms combine the above two assignment strategies. some repre-
sentative algorithms are [9,23]. In [9], each node's interfaces are divided into fixed
interfaces and switchable interfaces. The fixed interfaces only receive packets.
The switchable interfaces switch to the fixed listening channels of the neighbors
to send the packets. The connecitivity is dynamically maintained by exchanging
the listening channels of the nodes. In [23], the channels are assigned based on
clusters. By selecting the vehicles with the same moving directions, quite steady
clusters may be formed. The DSRC channels are then partitioned into intra-
cluster and inter-cluster channel sets. Neighboring clusters select channels by
observing the busy status of channels.
