SELF-ORGANIZING MULTI-CHANNEL MESH NETWORK
One
of the most logical progressions for WLANs is to have a structured organization
of access points (APs). This will
result in better coverage of a service area and improved coordination among APs.
The majority of today’s WLANs suffer from piecemeal, uncoordinated and
independent deployments using “hot spot” topology, with only a limited number
of multi-AP deployments utilizing proprietary technologies. This has spurred
various governmental agencies around the world to initiate projects for
wide-area coverage using WLAN technologies.
Meanwhile, many institutions are exploring similar network
deployments.
In
the present scheme, this can be accomplished by using the spare spectrum (e.g.,
available communication channels) to increase bandwidth in a self-organizing
process resulting in a system meeting the requirements of a mesh network. The
central idea is to carve up the system into a number of clusters. Within each
cluster, all nodes can communicate directly with one another, and communication
links are established for each and every pair of nodes in this cluster.
A
fully connected network provides direct links between every pair of nodes,
thereby offering the best network performance within the cluster, in terms of
the number of hops among possible network topologies. Some nodes with
special topological significance, e.g., WAN connectivity (called “portal”),
data source/sink attachment or connection to other clusters (called “edge
node”), normally have more traffic moving through them than other nodes.
Therefore, within the limits of available channels, the disclosed system
attempts to maximize the coverage of clusters centered around these special
nodes.
These
special nodes can take precedence in this cluster forming stage preferably in a
certain order. In a preferred embodiment, this precedence order is
preset, e.g., the priority of portal is higher than that of a source, which is
in turn higher than that of a sink. That is, if we use Pri(c(t)) to denote the
priority assigned to the type of nodes c cluster of certain topology at time
instance t, the precedence relationship inequality in equation 1 holds for the
example above: Pri(WAN(t)) > Pri(Source(t)) > Pri(Sink(t)) >
Pri(Edge(t)). It’s possible to adjust the precedence order depending on
the time of day to suit the dominant activity at that time, e.g., given that
batch download of media files is prevalent early in the morning, higher
precedence can be assigned to the source, where the media server is attached.
Furthermore, this precedence relationship can be adjusted depending on the
resulting topology. For example, an edge node, which can be located between a
source and a sink node, shall have higher priority than these sink and source
nodes. The traffic source and sink nodes can be further refined into different
priority classes based on the nature of their contents. For this reason,
data as a general term can be used to denote these source and sink nodes.
Following
the formation of a cluster, an edge node is selected to reach out to other
nodes belonging to the adjacent or non-adjacent clusters. Taking into account
the capabilities of each node and its topological significance, the disclosed
algorithm establishes communication links between clusters. As a result, the
whole system settles into a topology accustomed to the system conditions and
requirements.
In
each cluster, all nodes can communicate directly with one another. However,
depending on the capabilities of each node, most notably the number of radios
for each node and the capability of performing channel switching on each
particular radio, the communication links are either permanently established or
scheduled using a number of scheduling policies.
When the
number of radios present is less than the links required to connect to
neighbors, connection between nodes will have to be time-shared via a scheme,
called channel hopping. Node ‘hops’ from one channel to the other channel
by adjusting its radio components to tune to the particular frequency
associated with the target channel. Channel hopping can be scheduled based on
the following policies:
·
Round-robin;
·
Fixed order/frequency based on traffic requirements
(recurring rate, frame size); or
·
Once the
scheduling is decided, at each time “slot” a pair of nodes will ‘rendezvous’ in
the same channel with one of this pair transmitting to the other. Each node has
to queue up messages destined for certain nodes for scheduled time slots.
In
summary, the present scheme offers the following benefits:
·
Systematic channel assignment;
·
Self-organizing network topology;
·
Coordination among access points in a system;
·
Spectral reuse leading to bandwidth increase; and
·
Improved routing and communication protocols.