Heterogeneous Networks

MINIMUM NEIGHBOUR SCHEME

3.2 Performance Evaluation

3.2.6 Heterogeneous Networks

switches and iterations respectively at A = 2. Although not shown, similar robust performance has been observed for IEEE 802.11 a.

In order to determine the effectiveness of the MINE scheme when co-existing with other channel assignment schemes in the same network, we have implemented the DSATUR scheme, described in Section 2.3.2. This scheme is chosen because of its simplicity and hence its attractiveness for practical implementation. Although the scheme is intended for small and isolated centralized WLAN networks, it can still be deployed in a heterogeneous network where a group of APs belong to the same owner while the rest of the APs belong to various owners. An example of this is an office block where a big enterprise occupies several floors while other floors are occupied by many smaller firms.

Throughput gains are calculated by taking the convergence throughput over the initial throughput which represents the gains when APs implement the MINE scheme instead of the default random channel assignment scheme. Results are only shown for fEEE 802.11 b which is representative of denser scenarios (with D = 3 channels and Y = 8 interfering APs). The percentage of APs that implement the MINE scheme is varied from PM= 0% to 100%. The remaining APs remain on their initial randomly assigned channels throughout the simulation duration (random channel assignment scheme).

Fig. 3.16 shows the aggregate throughput for various PM percentages of APs that implement the MINE scheme. There is an evident throughput improvement across all percentages with higher gains seen when more APs implement the MINE scheme. Fast convergence times of less than four iterations are also seen across all percentages. The throughput decomposition gains for APs that implement the MINE scheme and the remaining APs (random scheme) are shown in Fig. 3.17. The performance of the MINE scheme is very commendable in that the total throughput gain increases linearly with PM with up to almost 60% improvement when PM = 100%. Furthermore, APs that implement the MINE scheme can expect at least 50% improvement in their throughputs

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Figure 3.17: Throughput decomposition gains for various percentages of APs that implement MINE scheme.

irrespective of how many APs are implementing the scheme in the network. It is equally important to note that even APs that do not implement the MINE scheme also benefit when APs that implement the MINE scheme are present in the network. Their throughput is seen to increase up to 30% with higher gains seen for higher values of PM.

The interaction of the MINE scheme with the DSA TUR scheme is presented here.

Initially, the percentage Po of APs that implement the DSA TUR scheme is set. Due to the centralized nature of this scheme, an algorithm is designed that ensures that the APs chosen to implement the DSATUR scheme are connected to each other. The first AP is chosen randomly. The next AP is chosen randomly from all possible neighbour APs of the reference AP (which is set as the previously chosen AP). In the event that all neighbour APs have already been chosen, the reference AP is selected randomly from the set of previously chosen APs. This process is repeated until the desired number of APs is chosen. After the DSATUR APs have been chosen, the APs that implement MINE scheme are chosen randomly from the rest of the APs. The remaining APs implement the random channel assignment scheme.

Fig. 3.18 shows the throughput decomposition for various percentages PM of APs that implement the MINE scheme when Po= 10% of APs implement the DSATUR scheme.

Note the increase in aggregate throughput as more APs implement the MINE scheme.

Of particular interest is when PM= 40% which means PR =50% (PR is the percentage of APs that implements the random channel assignment scheme and PM + PR + P0 =

I 00%). Even though the number of APs that implement the MINE scheme is lesser, their throughput is higher than APs that implement the random scheme. The throughput decomposition gains for various percentages PM of APs that implement the MINE scheme when Po= 10% of APs implement the DSATUR scheme is shown in Fig. 3.19.

Similar to the case when only the MINE scheme is implemented by a percentage of APs

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in the network, the robust performance of the MINE scheme can be seen from total throughput gains of up to almost 50%. Furthermore, throughput gains of not less than 50% can be noted for the MINE scheme APs across all values of PM. Last but not least, the presence of APs that implement the MINE scheme results in throughput gains for APs that implement other channel assignment schemes such as the DSATUR scheme and the random scheme. This is because the MINE scheme maximizes its own throughput by minimizing interference, which benefits neighbouring APs as well.

Although not shown, similar gains can also be seen for different values of PD which reflect networks with a higher percentage of APs that implement the DSA TUR scheme.