Jin-hyeock Choi

A Cross-Layering Design for IPv6 Fast Handover Support in an IEEE 802.16e Wireless MAN

Broadband wireless access networks, such as the IEEE 802.16 standard for wireless metropolitan area networks (WMANs), aim to provide high bandwidth, low-cost, scalable solutions that extend multimedia services from backbone networks to wireless users. Because of a larger coverage area, portability and mobility have become significant issues for providing high quality mobile services, as it is crucial to minimize handover latency and maintain IP session continuity. As a result, such issues were addressed by the IEEE 802.16e task group on the mobile WMAN. However, the scope of the IEEE 802.16e standard did not include cross-layering approaches for the enhancement of upper layer handover performance. This article proposes a new cross-layering design for fast IPv6 handover support over IEEE 802.16e. First, we describe the IEEE 802.16 deployment architectures, as well as the link layer, handover procedures in IEEE 802.16e. Next, we describe the operation of fast IPv6 handover and point out the need for interaction between the network layer and the link layer for proper performance. Then, we propose a new cross-layering design to achieve a proper behavior of the fast IPv6 handover over IEEE 802.16e. Finally, we present handover scenarios for the proposed techniques and discuss the major factors that contribute to the handover latency.

An energy efficient antenna selection for large scale green MIMO systems

This paper proposes an energy efficient antenna selection for large scale (LS) MIMO in green base station (BS). For the maximum energy efficiency (EE) operation of LS-MIMO, antenna selection is necessary, because the RF chains which are connected with antennas are expensive, and consumes a lot of power. However, the excessive amount of antennas in LS-MIMO hinder the efficient antenna selection. We determine optimum antenna number in various circumstances, and show that with LS-MIMO, simple random antenna selection can provide significant EE gain. Moreover, we also show if the EE optimum number of antenna is larger than a certain threshold, the random antenna selection is already very close to the optimum antenna selection. The proposed technique is verified by both mathematical analysis and numerical simulations.

Energy efficient basestation operation with traffic-specific energy consumption

Basestation on-off algorithms for mobile-network energy saving beyond 4 G can be simplified due to absence of interference in multi-user MIMO systems. We discuss an on-off algorithm based on specific energy and its energy savings performance.

An energy efficient PAPR reduction technique for mobile terminals

An energy efficient PAPR reduction technique using adaptive clipping and filtering (CAF) for OFDM uplink transmission is proposed. Even though SC-FDMA is one of good choices for uplink transmission, there are several disadvantages which makes it less attractive to use in practical systems, such as high pilot overhead, link-level performance degradation, receiver complexity increment especially in MIMO mode, etc. There are various alternative PAPR reduction techniques to improve energy efficiency, and the CAF is the simplest and effective one, but oversampling and iteration requirements can be burdens. The proposed technique adaptively adjusts CR (Clipping Ratio) as a function of modulation, and has less burden of oversampling and iteration comparing with conventional Base Station (BS) CAF technique. Also, the effect of NI (Noise Interference) among users could be negligible owing to context-awareness and adaptive characteristics. Moreover it does not require receiver modification, thus improving energy efficiency of both BS and mobile terminals is possible. Simulation results show that the proposed technique presents excellent performance comparing with SC-FDMA.