1. A Survey on Channel Assignment for Multi-Radio Meshed Networks
Maria Dolores Salmerón Pérez

2. Introduction: Wireless mesh networks
Wireless Mesh Networks (WMNs): mix between two wireless networks topologies: ad-hoc networks and structural topology.
Differences between ad-hoc networks and WMNs
Topology changes
Mobility
Scenario of application
Important research area
Increasing the coverage area of the network
Larger number of access points

3. Introduction: Wireless mesh networks
WMNs and Ad hoc networks: Normally single radio systems
Disadvantages:
Lower throughput
Nodes with half-duplex mode
Many channel changes due to dynamic network traffic
Interference from external sources
Shared Spectrum
Solution: Multiradio systems (most of the current WMN deployments adopt the multi-radio multi- channel architecture)

4. Introduction: Wireless mesh networks
Based on the standards:
IEEE a (5 GHz) / IEEE b (2.4 GHz)
IEEE a/b standards provide respectively 12 and 3 non-overlapped frequency channel
Ability to use multiple channels substantially increase the effective bandwidth available to wireless networks

5. Introduction: Wireless mesh networks
In the standard IEEE b there are 12 available channels but only the channels 1, 6 and 11 have low interference and/or overlapping with each other.

6. Problem formulation
A pair of nodes that use the same channel and within interference range may interfere with each other’s communication
Figure (b) is an example of channel assignment for figure (a) that minimizes the number of interfering links for nodes A and B

7. Solution: channel assignment
For any mesh network, there are multiple ways to assign channels to the radios
Solution: Find a proper channel assignment in every node of the network
CA algorithms
Goals:
Increased bandwidth
Performance improvement

8. Solution: channel assignment
Classification of Channel Assignment approaches for MR-MC WMNs :
Centralized: central control
Distributed: no central control

9. Solution: channel assignment
Centralized algorithm: CLICA (Connected Low Interference Channel Assignment)
Polinomial time greedy heuristic
Traffic independent
Based on the connectivity graph and on the conflict graph
Every node is associated with a priority
Coloring decisions are made node by node basis in the order of this priority
Reducing interference

10. Solution: channel assignment
Example of CLICA algorithm:

11. Solution: channel assignment
Distributed algorithm: DCA (Distributed Coloring Algorithm)
Clustering algorithm is applied previously to make set of nodes.
Distributed Clustering Algorithm that find the cluster-head
Cluster-head is the responsible of the graph coloring i.e. of the channel assignment
Every cluster-head has a priority or weight and knows the priorities of its neighbours nodes
Cluster-head colors its cluster only if highest priority cluster-head neighbors have colored completely their clusters

12. Solution: channel assignment
Example of DCA algorithm:
There are 3 types of messages that determine the action of every node:
CA: allows any node to know its color
UP: updates the color of one node
INF: inform about forbidden colors

13. Solution: channel assignment
Distributed algorithm: MIX (Minimum Interference Channel Selection)
Clustering algorithm is applied previosly to make set of nodes.
Highest Connectivity Cluster algorithm that find a cluster-head
MIX is based on minimizing co-channel interference between clusters
Access points have two interfaces:
First interface: for inter-cluster communication
Second interface: for intra-cluster communications using the channel selected by the cluster-head through MIX algorithm

14. Solution: channel assignment
Example of MIX algorithm:

15. Conclusions
DCA is an algorithm designed for devices on a single radio interface and a relatively low consumption
MIX algorithm is the most appropriate algorithm for a larger size of network and the throughput is better than DCA
CLICA has some limitations but compared with the distributed algorithms the performance is a bit better

16. Conclusions
Centralized algorithms usually have in the most of the cases a better performance because they used entire network information
Centralized algorithms: nearer throughput to the optimal
Problem of the algorithms NP-hard problems (difficult to find an optimal solution and exponential runtime )
Heuristics approximation modes (not optimal results)

17. QUESTIONS