**4.2 Simulation results**

6 Mobile Networks

Fig. 7 shows only a small part of the entire model for simplicity although there are a lot of cdma2000 and WiBro cells. WiBro network cells and cdma2000 network cells are attached one by another in the simulation. Picocells and microcells are only used to generate frequent handoffs of mobile stations. Since the Markov mobility model used in the simulation, as shown in Fig. 8, is designed for mobile stations at low-speed (20 60km/h), and the following probability density function is used, where *m* represents the average speed of a mobile station

2.4 (EV-DO), < 2 (WiBro)

> ≤ 1500 or 1502

10−1, 10−2, 7 ∗ 10−3,10−3, 10−4, 10−<sup>5</sup>

Max. Bit Rate (Mb/s) 2.4 (EV-DO),

Max Packet Size (byte) <sup>≤</sup> 1500 or

Fig. 5. Simulation model for performance evaluation

Packet Error Ratio

Table 1. Simulation parameters

in a cell (Janevski, 2003).

Fig. 6. Mobility model for mobile stations

< 2 (WiBro)

1502

<sup>10</sup>−2, 7 <sup>∗</sup> 10−3,10−3, 10−4, 10−<sup>5</sup>

Conversational Streaming Interactive Background

2.4 (EV-DO), < 2 (WiBro)

> ≤ 1500 or 1502

10−3, 10−4, 10−<sup>6</sup>

2.4 (EV-DO), < 2 (WiBro)

> ≤ 1500 or 1502

10−3, 10−4, 10−<sup>6</sup>

Both L3 and L2 handoff schemes are simulated to prove the superiority of the proposed L2 handoff over L3 handoff on most popular services in mobile environment, such as streaming, web browsing, and Email services. These services are categorized into streaming, interactive, and background traffic class, respectively. In addition, conversational class is also added for video conferencing environment. As mentioned earlier, the low latency handoff for Mobile IPv4 in Fig. 3 has been implemented for the L3 handoff scheme.

Fig. 7 - 10 show that the proposed L2 handoff scheme outperforms the L3 handoff on all kinds of service classes. In fact, performances resulted in each scheme should be the same except when handoffs occur. Therefore, performance differences shown in Fig. 9 - 12 are due to handoff processes. Figures also show that handoff occurrence is very frequent at interval times of 6 to 23, 32 to 35, and 55 to 57.

Fig. 7. Packet delay on conversational traffic class

Fig. 8. Packet delay on streaming traffic class

Fig. 11. Average delay according to MS's speed (conversational traffic class)

A Fast Handover Scheme for WiBro and cdma2000 Networks 63

Fig. 12. Average delay according to MS's speed (streaming traffic class)

handoffs. We summarize the average packet delay in Table 2.

packet delay and loss.

the larger differences in delay performance arise, because the fast moving causes frequent

Finally, Fig. 15 describes the packet loss ratio in both schemes. Since the L3 handoff scheme

In summary, the OPNET simulation results in this section indicate that the proposed L2 handoff scheme is an efficient and practical solution because it can be implemented with minimal modification of existing cdma2000 and WiBro networks while providing the reduced

employs mobile IP techniques, there may be relatively large number of packet loss.

Fig. 9. Packet delay on interactive traffic class

Fig. 10. Packet delay on background traffic class

Fig. 7 and Fig. 8 are the simulation results of conversational and streaming traffic classes, respectively. The graph of the L2 handoff scheme is more stable with small deviation than the L3 handoff because the L2 handoff reduces packet losses and delays.

Fig. 9 shows the case of interactive traffic class using HTTP, where differences in packet delays between L3 and L2 handoff are larger than those of Fig. 7 and Fig. 8 of the burst property of web traffic. We can find from Fig. 10 that background traffic class like Email shows almost no difference in delay performance because background traffic has the lowest priority.

In addition, we performed simulations with different moving speed of mobile stations. Fig. 11 - 14 show the average delay times of each traffic class of MS at different speed. The graph shows the superiority of the L2 handoff scheme over the L3 handoff scheme on all kinds of traffic classes and moving speeds. We can also find that the faster a mobile station moves, 8 Mobile Networks

Fig. 7 and Fig. 8 are the simulation results of conversational and streaming traffic classes, respectively. The graph of the L2 handoff scheme is more stable with small deviation than the

Fig. 9 shows the case of interactive traffic class using HTTP, where differences in packet delays between L3 and L2 handoff are larger than those of Fig. 7 and Fig. 8 of the burst property of web traffic. We can find from Fig. 10 that background traffic class like Email shows almost no

In addition, we performed simulations with different moving speed of mobile stations. Fig. 11 - 14 show the average delay times of each traffic class of MS at different speed. The graph shows the superiority of the L2 handoff scheme over the L3 handoff scheme on all kinds of traffic classes and moving speeds. We can also find that the faster a mobile station moves,

difference in delay performance because background traffic has the lowest priority.

Fig. 9. Packet delay on interactive traffic class

Fig. 10. Packet delay on background traffic class

L3 handoff because the L2 handoff reduces packet losses and delays.

Fig. 11. Average delay according to MS's speed (conversational traffic class)

Fig. 12. Average delay according to MS's speed (streaming traffic class)

the larger differences in delay performance arise, because the fast moving causes frequent handoffs. We summarize the average packet delay in Table 2.

Finally, Fig. 15 describes the packet loss ratio in both schemes. Since the L3 handoff scheme employs mobile IP techniques, there may be relatively large number of packet loss.

In summary, the OPNET simulation results in this section indicate that the proposed L2 handoff scheme is an efficient and practical solution because it can be implemented with minimal modification of existing cdma2000 and WiBro networks while providing the reduced packet delay and loss.

Fig. 15. Packet loss ratio

In this paper, we proposed a low-latency L2 handoff procedure between cdma2000 and WiBro which creates a promising next generation wireless network. Even though several efforts are actively in progress to improve mobility services based on Mobile IP, mobility services between different wireless networks, e.g., WiBro and cdma2000 still need more attention. From this viewpoint, we devise an L2 handoff scheme which can provide better performance compared with the L3 handoff. We also define required functionalities of each network

A Fast Handover Scheme for WiBro and cdma2000 Networks 65

The proposed L2 handoff procedure does not require additional signaling messages to reduce packet loss which can occur in signaling L3 messages. However, in order to apply our scheme, the necessary functional change of network elements is inevitable. For completion,

3GPP (2003). 3gpp tr 22.934, *Feasibility study on 3GPP system to Wireless Local Area*

3GPP2 (2002). 3gpp2 a.s0011-a, *Interoperability Specification (IOS) for cdma2000 Access Network*

Ahmavaara, K., Haverinen, H. & Pichna, R. (2003). Ieee communications magazine, *Interworking Architecture between 3GPP and WLAN Systems* Vol. 41(No. 11): 74–81. Buddhikot, M., Chandranmenon, G., Han, S., Lee, Y., Miller, S. & Salgarelli, L. (2003).

IEEE (2001). Ieee std. 802.16, *IEEE Standard for Local and Metroploitan Area Network Part 16 : Air*

Janevski, T. (2003). Artech house, *Traffic analysis and design of wireless IP networks* pp. 186–190.

Ieee communications magazine, *Design and Implementation of a WLAN/cdma2000*

the detailed protocols above L3, e.g., session control remains to be further studied.

element, ACR of WiBro, PDSN of cdma2000, and mobile station.

*Network(WLAN) Interworking (Release 6)* .

*Interworking Architecture* Vol. 41(No. 11): 90–100.

*Interface for Fixed Broadband Wireless Access System* .

*Interfaces : Part 1 Overview* .

URL: *http://www.wimaxforum.org*

**5. Conclusion**

**6. References**

Forum, W. (n.d.).

Fig. 13. Average delay according to MS's speed (interactive traffic class)

Fig. 14. Average delay according to MS's speed (background traffic class)


Table 2. Summary of average delay according to MS's speed

Fig. 15. Packet loss ratio
