In this section, we report the simulative performance comparison with the RCL al-gorithm proposed in [6]. The simulator used for experiments is ns-2 [2] with multi-radio extension. Two-ray ground model is adopted for the radio propagation path loss. Note that to the best of our knowledge, our work is the first to address the optimization of the number of equipped radios at each mesh router. As described in Section 2, we have a different problem scope from the RCL algorithm. To provide a fair comparison, let us make the following assumptions in the simulations for both the RCL and our algorithms.
First, up-link and down-link traffics are assumed to be symmetric, though our algorithm handles asymmetric up- and down-link traffics. Second, we also adopt the protocol model of interference, and assume the interference sources consist of 2-hop neighbors of both the sender and receiver (with RTS/CTS enabled). Third, equal data rate (capacity) for all channels and links is assumed. Fourth, gateway capacity is limited. Fifth, given a fixed total number of available radios, RCL will allocate equal number to each mesh router, while our proposed algorithm will assign heterogeneous numbers to nodes in order to balance the loads.
To demonstrate the importance of network planning, we use the same parameter set-tings as in Fig. 4.2 with total available number of orthogonal channels C = 2. Experiments are performed using three different grid topologies: 3 × 3, 4 × 4, and 5 × 5. Table 4.1 summarizes the aggregate network throughput yielded by the three algorithms under dif-ferent network sizes. Here N denotes the total number of required radio interfaces by each algorithm. As we can see from this table, to achieve comparable network through-put, our proposed DIM and IIM approaches always result in a smaller total number of radio interfaces needed. Under the 5 × 5 topology, our IIM algorithm even requires only half as many as the number of radio interfaces used by RCL (N = 27 vs. N = 50) to achieve similar throughput performance, thus saving deployment costs. Consequently,
network planning by distributing available radios based on different (forwarding) traffic requirements at mesh routers has been effectively exercised by the proposed DIM and IIM algorithms.
Table 4.1: Comparison of the RCL algorithm equipping two radio interfaces at each mesh router with our proposed approaches having the capability of distributing radio interfaces based on load-sensitivity.
3x3 4x4 5x5
RCL (Mbps) 18.0341 N=18 17.2148 N=32 15.7682 N=50
DIM (Mbps) 18.0341 N=15 17.1631 N=21 15.5473 N=31
IIM (Mbps) 18.0593 N=13 17.1902 N=20 15.7504 N=27
Chapter 5 Conclusions
In this thesis, we propose an M4wireless mesh architecture and design related resource allocation and channel assignment mechanisms to maximize the possible network capacity at the deployment stage. The numerical results show encouraging potential in terms of network throughput improvement. We plan to investigate on the optimal arrangement by letting the channel vector ci[k] become unknown and solving the non-linear programming model in the near future, so that we can observe how close our proposed linear method-ology is to the optimal non-linear solution. On the other hand, due to the relatively high computational complexity incurred by the linear programming calculations, we only perform this optimization task at the WMN deployment stage as an initialization setup.
Once mesh nodes are well configured, the LP modeling will be re-evaluated periodically in an infrequent basis. Based on the current insights observed from this work, we plan to explore a sub-optimal tree-induced flow designation strategy, which requires less computa-tional complexity. These results and possible improvements will be reported in our future research. In addition, we are interested in the fairness problem in WMNs. In this thesis, we realize the network-level fairness by setting reasonable user traffic bounds (ui and li) in our linear programming model and performing flow control in the packet forwarding function. However, there is still short of a link-level technique to prevent bandwidth
oc-cupancy from favoring those users closer to Internet gateways. This MAC-layer fairness issue will also be directed into our future research.
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