Algorithms comparison

In this section, we compare the throughput of different algorithms in hybrid WMNs. There are four algorithms. The descriptions are as following:

1. Hash: randomly assign role and channel for the radios with two constraints due to the properties of hybrid WMNs :

(i)At least one fixed radio and at least one switchable radio per node.

(ii)The fixed radios on a mesh node are on different channels.

2. MRF+MCUF: role assignment is obtained from MRF, and channel assignment MCUF is based on [11]. Fixed radios will change its channel when the number of user of the channel in two-hop neighborhood is too large.

For convenience, in our implemented MCUF algorithm the mesh nodes have the same number of chances to change the channel of its fixed radios as the times the nodes using MIIF to choose its best channel in centralized way.

3. MRF+MIIF: the two algorithms are designed for MAX SL and MIN TIL problem. We will get an integrated assignment through algorithm MRF and algorithm MIIF sequentially.

4. Joint: the Joint algorithm is designed for joint assignment problem. Through considering the role assignment and channel assignment simultaneously. We try to obtain the global optimum of TCL of network.

The first two algorithms are existing method for hybrid WMNs. But they are just designed for the convenience of implementation. The two algorithms do not consider the whole network situation and use limited information to determine the assignment. But our algorithms are based on the design and analysis of hybrid approach WMNs and target to different problems in [15]. In the comparison of algorithms, the number of flows is varied from 100 to 400 in order to present the change of traffic loading.

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Fig. 5.2 shows the performance of the network under 2-radio mesh node environment. It is clear that both of our algorithms are much better than the remaining algorithms and the performance between MIIF and Joint algorithm are almost the same. MCUF is 22% better than Hash. The performances of our algorithms MIIF and Joint are 25% better than MCUF and 54% better than Hash.

But in 2-radio environment due to the basic constraint in hybrid WMNs, at least one fixed radio and at least one switchable radio on a node, there is no necessary to choose the role of radio on the mesh nodes. So the algorithm MRF does not work here.

(a) (b)

(c)

Fig. 5.2: Throughput comparison under 2 radios environment:

(a)3 channels; (b)5 channels; (c)12 channels

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Fig. 5.3 represents the throughput with 12 available channels for 3-radio and 4-radio environment. Compare to the 2-radio environment result in Fig 5.2, the performances of Joint algorithm and MIIF algorithm in 3-radio and 4-radio environment the throughput have an obvious gap between Joint algorithm and MIIF algorithm. In 3-radio and 4-radio environment the performances of Joint are 22% and 24% better than MIIF. The performance of MIIF is 3% better than MCUF in 3-radio environment and almost the same as MCUF in 4-radio environment. This is because the role assignment generated from the MRF algorithm increases the number of switchable links and brings the constraint to MIIF algorithm for channel assignment. The above phenomenon presents that the integrated solution obtained from sequentially solving MAX SL and MIN TIL cannot achieve global optimum of MIN TCL. The joint algorithm simultaneously considers the role and channel assignment for MIN TCL. So the throughput of Joint algorithm is much better than other three scenarios.

(a) (b)

Figure. 5.3: Throughput comparison under 12 channels: (a)3 radios; (b)4 radios.

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Chapter 6 Conclusion

In this thesis, we propose two assignment algorithms based on the theorem of [15]. We target different problems, such as MAX SL, MIN TIL, and MIN TCL, to design the algorithms. We have compared the performance of the proposed algorithms and other algorithms used in hybrid WMNs. The results show that our algorithm performs better without question. For the further research, we may develop the distributed algorithm for wide use.

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