Study On Network Integration And Handoff Mechanism Based On WiMAX And TD-SCDMA

With the rapid development of wireless communication technologies, mobile communications have changed people's life deeply. The existing wireless technologies, such as Wi-Fi, WiMAX, TD-SCDMA and Ad Hoc, have their respective advantages, but any of them cannot support all kinds of services independently. Next generation wireless communication systems are expected to relay on integrated networks consisting of multiple wireless technologies to offer high quality of services to mobile users.WiMAX is a kind of broad band wireless access technology, whose data rate is much faster than that of TD-SCDMA and whose coverage of a base station (BS) is also larger. However, the weakness of WiMAX is its mobility limitation. TD-SCDMA supports seamless access and higher mobility. Given the complementary characteristics of WiMAX (faster data rate, lower-cost, hotspot access, only support lower mobility) and TD-SCDMA (slower data rate, higher-cost, seamless access, support higher mobility), it is significant to combine them to provide multiple services and ubiquitous access for the users.At present, researches on homogeneous networks are relatively mature. In recent years, researches on heterogeneous networks have been gradually developing, but researches on heterogeneous wireless networks based on WiMAX and TD-SCDMA are still rare and immature at home and abroad because both WiMAX and TD-SCDMA are new emerging technologies. Therefore, studies on WiMAX and TD-SCDMA heterogeneous wireless networks are necessary and meaningful.In this paper, we have deeply studied network integration and handoff mechanism based on WiMAX and TD-SCDMA. By comparing the respective characteristics of the two technologies, the feasibility of integration between WiMAX and TD-SCDMA was analyzed and their network integration schemes were proposed in this paper. The schemes were including tightly-coupled scheme and loosely-coupled scheme.For the studies on handoff mechanism of WiMAX and TD-SCDMA, we have laid emphasis on vertical handoff decision algorithm and vertical handoff execution algorithm. In this paper, handoffs were divided into two classes:handoffs initiated by MNs and handoffs initiated by BSs. For the handoffs initiated by MNs, a novel vertical handoff decision algorithm based on fuzzy control in aid of pre-decision method was proposed. Different with the ordinary vertical handoff decision algorithms, this algorithm used pre-decision method which could save system overhead and raise the efficiency of handoff decisions. In addition, fuzzy control was introduced into this algorithm which helped simplify the process on handoff decision criteria and enhanced the adaptability of the algorithm. The simulation results showed that the proposed algorithm could make accurate handoff decisions, reduce unnecessary handoffs and eliminate the ping-pong effect. For the handoffs initiated by BSs, a cost function based vertical handoff decision algorithm was proposed to select the MNs with lower cost values. Then the selected MNs were handed over to relieve heavy load of the current network and decrease the probability of call blocking and dropping. The proposed algorithm took the entire network performance into consideration and balanced the overall load which was more thoughtful than the existing vertical handoff decision algorithms. Vertical handoff execution is critical to the performance of vertical handoffs. In this paper, MIHF based FHMIPv6 vertical handoff execution algorithm was proposed and the WiMAX/TD-SCDMA vertical handoff execution processes were presented. The proposed algorithm introduced MIHF and combined the advantages of HMIPv6 and FMIPv6, which made this algorithm more effective than MIPv6, HMIPv6 and FMIPv6. The simulation results showed that the proposed algorithm could obviously improve the performance of vertical handoffs with lower handoff latency, smaller signal overhead and lower packet loss.