Kyeong Hur

A Distributed-Request-Based DiffServ CAC for Seamless Fast-Handoff in Mobile Internet

The next-generation wireless networks are evolving toward an IP-based network that can provide various multimedia services seamlessly. To establish such a wireless mobile Internet, the registration domain supporting fast handoff is integrated with the DiffServ mechanism. In this paper, a Distributed-request-based CDMA DiffServ call admission control (CAC) scheme is proposed for the evolving mobile Internet. Numerical examples show that the forced termination ratio of handoff calls is guaranteed to be much less than the blocking ratio of new calls for a seamless fast-handoff while proposed scheme provides quality of service guarantee for each service class efficiently.

Tiny Function-Linking for Energy-Efficient Reprogramming in Wireless Sensor Networks

The remote and automatic reprogramming is an indispensable part in the wireless sensor networks. Especially, the energy saving problem is an important challenge because of a limited energy characteristic. Many kinds of conventional researches about reprogramming have tried to solve the energy saving problem. But they do not consider the energy consumption model and still have inefficient memory access times. In this paper, we propose a tiny function-linking scheme. It performs function relocation to decrease program code shift and connects relocated function with a tiny function-linker to eliminate function caller changes. This proposed scheme reduces access times to Electrically Erasable Programmable Read-Only Memory (EEPROM) and program memory during the decoding procedure of the reprogramming. Experimental results show that our scheme outperforms the previous reprogramming schemes in terms of the energy consumption.

Minimum TCP throughput guarantee on minimum rate guaranteed networks

The performance of Transmission Control Protocol (TCP) entirely depends on the network traffic conditions. It will be greatly advantageous if the throughput of the TCP is always maintained above a certain level. However, it is difficult to guarantee minimum throughput for each TCP connection even when enough bandwidth is reserved for it. This is because the TCP congestion control algorithm makes its transmission rate fluctuate so that, in some cases, the connection cannot fully utilize the portion of the bandwidth reserved for it. We propose a slightly modified traffic shaper that can help maintain the TCP transmission rate. It normally regulates traffic just as the conventional shapers, but when necessary, it adjusts its transmission rate depending on its own state, namely its queue length and packet-receiving rate, without explicit notification of the network conditions. It only requires a simple modification of the conventional shapers. However, this simple modification can improve TCP performance significantly and help guarantee minimum throughput when the network guarantees minimum bandwidth for the connection. Simulation results are presented for performance evaluation. The proposed scheme is practical in that it does not require end-host modifications. Also, it has scalability since it requires per-flow management only in the network access routers and not in the core routers.

Performance analysis of CDMA reservation ALOHA for multi-traffic system with adaptive access permission probability

A CDMA reservation ALOHA scheme is proposed to support multi-traffic such as voice, data with and without priority. To reduce MAI (multiple access interference), the time slot is divided into access and transmission stages and only packets with codes allocated from the base station in the access stage can be transmitted in the transmission stage. And to reduce packet collisions in the access stage, the code reservation allowed for voice and data traffic with priority using piggyback and access permission probability is adaptively applied to each traffic. Also, numerical performances for each traffic in a cell are analyzed and simulated through Markov-chain modeling.