Bongjhin Shin

Effects of time-to-trigger parameter on handover performance in SON-based LTE systems

In this paper, we evaluate handover (HO) performance when we apply various time-to-trigger (TTT) methods in self-organizing network (SON)-based long term evolution (LTE) systems. Although TTT can mitigate the wasteful ping-pong HO effect, it also can cause undesirable radio link failure (RLF) due to delayed HO. The optimal HO timings that produce the lowest ping-pong rate within allowable RLF rate vary depending on user equipment (UE) speeds and neighboring cell configurations. To achieve efficient HO timings, we propose and investigate two methods: “adaptive” and “grouping.” In the “adaptive method,” we select the adaptive TTT value for each UE speed based on RLF rate of 2%. The “grouping method” classifies UE speeds into three ranges and assigns the proper TTT value to each range. To apply the LTE specification more effectively, we suggest the criteria of grouping, and propose the proper TTT value for each range. We consider HO in two neighboring cell configurations: from a macro cell to either a macro cell or a pico cell. Simulation results show that the HO performance of the “adaptive method” is greatly improved compared to that of applying fixed TTT values. The results also show that the performance of the “grouping method”, using proposed criteria and proper TTT values, is comparable to that of the “adaptive method.”

Cross-layer resource allocation with multipath routing in wireless multihop and multichannel systems

A joint multipath routing algorithm and channel allocation and scheduling for wireless multihop and multichannel systems is discussed. In packet transmission, distribution of packets to multiroutes makes it possible to reduce the transmission cost of the channels. Cross-layer cooperation of routing, channel allocation, and scheduling is an effective method of packet distribution. As a framework for the cooperation, we propose a multiroute distance vector routing (MDVR) scheme. In the MDVR scheme, the routing table is logically placed in between the routing and link layers, and the table plays the role of a service access point between these two layers. To evaluate the performance of MDVR, simulation is performed in a multichannel, multihop environment. The simulation results show that the MDVR framework can be efficiently implemented in the form of a distributed routing algorithm. It is also shown that in MDVR, the system-wise channel efficiency is almost 25% higher than that in a conventional single-route routing approach.

Adaptive code partitioning for fast h0andover in IEEE 802.16e systems

Ranging is one of the major sources of handover latency in IEEE802.16e systems. It is due to the retransmission of ranging signals because of collision in contention based ranging. To reduce the handover latency, we need to make the possibility of retransmission low. We propose an adaptive code partitioning scheme that we utilize for fast handover in this paper. This scheme allocates a portion of codes only for the retransmission of ranging signals. The portion of this region is also adjusted adaptively in this scheme. Performance of the proposed scheme is evaluated by simulation. We analyzed the system capacity or the number of MSs that can be supported with reliable handover. Simulation results show that the proposed scheme leads to about 28.6% capacity improvement.

Restricted sleep mode for effective cell throughput improvement in vertical handover

In this paper, we propose a “sleep mode restriction” scheme for improving the effective cell throughput of worldwide interoperability for microwave access (WiMAX) systems when a mobile station (MS) switches its serving network from WLAN to WiMAX in heterogeneous networks. In the previous scheme, a MS acquires the information related to vertical handover (VHO) from media independent handover (MIH) server before VHO is performed, and utilizes sleep mode operation (SMO) of the WiMAX. However, in this method, while VHO latency is reduced, the effective cell throughput of WiMAX is degraded because MSs connected to WLAN access point (AP) constantly utilize a certain portion of the WiMAX downlink radio resources. To diminish the performance degradation, we suggest that only MSs with high possibility of VHO can enter SMO and maintain connection with WiMAX. When proposed scheme is applied, the simulation results show that the effective cell throughput degradation of WiMAX is diminished by up to 12.57 % compared to the scheme with non-restriction.

Effects of the Number of Hops on TCP Performance in Multi-hop Cellular Systems

This paper analyzes performance of Transmission Control Protocol (TCP) in multi-hop cellular networks. Multi-hop transmission shortens communication distance and can make channel quality at each hop better. However it needs channel resources at every hop for packet transmission, and thus effective throughput on end-to-end links can be decreased. Related researches have shown that multi-hop transmission may reduce TCP performance in the systems. However, it may be because improvement of channel quality derived by multi-hop transmission has not been considered fairly. We analyze TCP performance with considering channel quality improvement on a multi-hop system. By simulation, we derived the throughput gain by multi-hop transmission for various values of the number of hops. We also have analyzed the gain according to position of active users in a cell. From the results, we show that multi-hop transmission can improve TCP performance, especially for the users near the cell edge. We also show a proper number of hops that gives maximum TCP performance.