아주대학교

초록/요약

The current wireless networks with orthogonal frequency division multiple access (OFDMA) system gives us high speed wireless communication. With high speed, variety mobile services that have different traffic characteristics and requirements have been produced. However, the interference sensitivity of OFDMA system degrades performances of cell-edge users. In addition, the diversity of mobile services causes a channel quality asymmetry between a downlink and an uplink in OFDMA system. Unfortunately, conventional mobility management schemes have not taken account the channel quality asymmetry and the diversity of service traffic. Therefore, this dissertation presents advanced mobility schemes considering the channel quality asymmetry and the diversity of service traffic for improving service continuity and user-perceived performance. The first proposed mobility scheme is a handover scheme considering downlink-uplink channel quality asymmetry. The proposed handover scheme determines an appropriate handover timing and handover direction according to an estimated uplink channel quality and a measured downlink channel quality. For exploiting an uplink channel quality in handover, an efficient uplink channel estimation method is also proposed. The proposed method estimates an uplink signal strength using the measured downlink signal strength and predicts an uplink interference on the basis of the interference-level information that is from neighbor base stations. To improve user-perceived performances, the proposed handover scheme adjusts weights of handover criteria according to service traffic pattern. Simulation results show that the proposed uplink estimation method can accurately compute the uplink channel quality of neighbor cells where the estimation error rate is less than 0.7%. The simulation results also show that the proposed handover scheme reduces handover-call-dropping probability by up to 69% compared to LTE-Advanced system and the proposed scheme outperforms previous studies in terms of throughput and mean opinion score (MOS). In addition, the end-to-end delay of the proposed scheme is better than that of LTE-Advanced system by 26%. The second proposed mobility scheme is the user-centric mobility scheme that exploits multipath communication to support seamless mobility. For that, the service continuity management (SCM) protocol is newly designed. SCM has four functional blocks which are located between the application layer and the transport layer. SCM monitors quality of experience (QoE) and makes multiple sessions for one service using multiple radio adaptors in order to maintain QoE requirements. To improve the efficiency of the proposed multipath communication scheme, a high efficiency transport method is proposed. The proposed scheme sends identical packets over multiple paths to improve reliability; likewise, different packets are sent to improve throughput, simultaneously. The simulation results show that the user-centric mobility scheme enable a mobile device to reduce service interruptions during handover in heterogeneous networks. Numerical results indicate that the proposed transport scheme achieves the maximum transport control protocol (TCP) throughput when the proportion of same and different packets is adjusted according to link conditions.