Numerical Results

Figure 12 and Figure 13 shows the evaluation result of the two handoff mechanisms, CSN anchored mobility (case 1) and R4 mobility (case 2). We can see the packet sequence number accumulates in Figure 12 and Figure 13, there are three broken points in the graph, the first and the third broken points are resulting in the ASN anchored mobility between BS_1 and BS_2, BS_3 and BS_4. The second broken point is the handoff between BS_2 and BS_4, and we can clearly see that in Figure 12 the broken interval is longer than that in Figure 13. The Result shows that if we could use the R4 mobility to replace the R3 mobility in roaming between different ASN domains, the packet loss will decrease. The pre-constructing data path method (case 3) evaluation result is showed in Figure 14, there are also three broken point in the data packet accumulation graph. We could saw that pre-constructing data path case has fewer packet losses than the other two cases.

Table 2 shows the total packet loss of handoff in the three cases, we could find that the R4 mobility handoff could decrease the 20% packet loss than the R3 mobility handoff. But the pre-constructing case does not show the significant improvement than the R4 mobility method, although it still has less 10% packet loss. We can figure out the result is that the emulator is not in a real WiMAX hardware and the procedure delay occurs because the experiment setting is six emulator in one kernel, and the pre-constructing data path is still need the PATH_REQ/PATH_RSP message to make the data path active. Although the active message is shorter and fewer, the procedure also speed time in handoff and it causes the packet loss. Table 2 also shows the data packet delay in case 1 and case 2, it apparently presents that the R4 mobility will

spend more time sending a packet than R3 mobility because R4 mobility will not route the path to the serving ASN-GW. Even the data packet delay is a tinny difference, but the experiment is on the emulator. If we experiment in the real WiMAX environment, the data packet delay will increase and R4 mobility also has its trade-off in MS roaming. We will test this experiment in real WiMAX hardware in future, and we believe that the pre- constructing data path method will show better significant result than other methods.

Figure 12 Case 1: CSN Anchored Mobility (R3 mobility)

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Figure 13 Case 2: R4 mobility

Figure 14 Case 3: Pre-establish Data Path

Case 1:

R3 mobility

Case 2:

R4 mobility

Case 3:

Predictive

R6 Mobility between BS_1 and BS_2 59 42 35

Inter-ASN mobility between BS_2 and BS_3 74 45 40

R6 Mobility between BS_3 and BS_4 42 50 38

Total packet loss (loss/total) 175/1640 137/1640 113

Packet loss rate 10.67% 8.35% 6.89%

The inter-ASN handoff delay 4.44 sec 2.7 sec 2.4 sec The data packet delay after inter-ASN HO 64ms 93ms

Table 2 The Packet Loss Comparison While Handoff

Chapter 5

Conclusion and Future Work

In our thesis, we implement the R4 mobility between two ASN-GWs to replace the CSN anchored mobility of inter-ASN mobility and use the R4 mobility to implement a pre-establishment data path method. In the highly mobility environment, the seamless handoff is an very popular topic in WiMAX network, and the improvement of handoff could not only in the IEEE 802.16 PHY and MAC layer protocol but also could be in the End-to-End Network Architecture. Because the network architecture is the special feature of WiMAX, the network environment assistant handoff would be a workable method to improve the handoff in WiMAX network. We have emulated the WiMAX End-to-End Network Architecture and evaluated the packet loss of R3, R4, and R6 mobility in this article, but it only uses hard HO method between MS and BS.

In the future, we will do the experiment in the real WiMAX hardware and try other mobility methods according to the network architecture or the MS/BS handoff scenarios to improve the network assistant handoff by the design of ASN-GW and BS.

And also we will implement the data integrity method in ASN-GW for buffering the

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data packet to reduce the data packet loss when MS roaming. Because ASN-GW is an central role in ASN network, the information gathering in ASN-GW can be numerous MSs, so how to make the resource in better using is also a research topic in our future work.

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