Result Analysis

A. Average frame size under 100% reserve ratio.

As shown in figure 26, the relationship between average frame size and different network density under 100% reserve ratio. Each protocol in higher density requires the larger frame size. As the result of the simulation: the frame size under 100%

reserve ratio is based on the nodes density. The result shown that PC-ALOHA and AFP-ALOHA require smaller frame size than RR-ALOHA and A-ADHOC, since PC-ALOHA and AFP-ALOHA can find free slot by reducing the node’s transmission range.

Figure 26. Average frame size under 100% reserve ratio in different network density.

(Range = 250 m)

And the average frame size in 250 meters range is larger than 150 meters range, because in 250 meters range, the number of one-hop members and two-hop members is more than the number of one-hop members and two-hop members in 150 meters range.

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Figure 27. Average frame size under 100% reserve ratio in different network density.

(Range = 150 m)

B. Average hop counts under 100% reserve ratio

As shown in figure 28 and 29, the average hop counts under 100% reserve ratio in different network density. Because of the RR-ALOHA and A-ADHOC do not reduce the node’s transmission range, the average hop counts lower than PC-ALOHA and AFP-ALOHA.

Figure 28. Average hop counts under 100% reserve ratio in different network density.

(Range = 250 m)

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Figure 29. Average hop counts under 100% reserve ratio in different network density.

(Range = 150 m)

C. Average relaying delay under 100% reserve ratio

Figure 30 is shown the relaying delay under 100% reserve ratio. The relaying delay is the value of average frame size * average hop counts * slot time. We can know the trend of delay by figure 30.

Figure 30. The average relaying delay under 100% reserve ratio in different network density. (Range = 250 m)

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Figure 31. The average relaying delay under 100% reserve ratio in different network density. (Range = 150 m)

D. Average end-to-end delay under 100% reserve ratio

We analyzed the average end-to-end delay under 100% reserve ratio. As shown in figure 32, the average end-to-end delay of AFP-ALOHA is lower than RR-ALOHA, PC-ALOHA and A-ADHOC in dense network.

Figure 32. The average end-to-end delay under 100% reserve ratio in different network density. (Range = 250 m)

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Figure 33. The average end-to-end delay under 100% reserve ratio in different network density. (Range = 150 m)

E. The results in mobility environment

We analyzed the reserve ratio and average end-to-end delay in mobility environment at 30 seconds. As shown in figure 34, the reserve ratio at 30 seconds. All protocols cannot achieve 100% reserve ratio, because of the merging collision [14].

The merging collision is the opposite vehicles used the same time slot without collision, but when they approached to each other, the collision happened.

Figure 34. The reserve ratio of node mobility.

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The average end-to-end delay at 30 seconds as shown in figure 35. We gave the frame size of RR-ALOHA and PC-ALOHA as 30, because the reserve ratio cannot fix at 100% in mobility environment. The result shown the end-to-end delay of AFP-ALOHA is lower than RR-ALOHA, PC-ALOHA and A-ADHOC.

Figure 35. The end-to-end delay of node mobility.

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Chapter 6 Conclusion

In this thesis, we have proposed an adaptive low-delay schedule-based MAC protocol with RR-ALOHA called Adaptive Frame size adjustment and Power control ALOHA (AFP-ALOHA). We combine RR-ALOHA with frame size adjustment mechanism and power control mechanism to solve the slot congestion problem in RR-ALOHA.

There are two important features of our protocol: (1) AFP-ALOHA can adaptively adjust the frame size and transmission power range at the time to solve slot congestion problem, and (2) achieve the lower end-to-end delay at the same time.

As the simulation results, the end-to-end delay of our AFP-ALOHA is lower than RR-ALOHA, PC-ALOHA and A-ADHOC in the dense network. It means that our AFP-ALOHA can provide the lower delay of safety applications. In the future, we will consider the problems at node mobility environment (e.g. merging collision [14]).

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