Hyun-Il Yoo

A Preamble Design Technique for Efficient Handover in IEEE 802.16 OFDM-Based Mobile Mesh Networks

In this paper, a hierarchical design concept of a preamble for orthogonal frequency-division multiplexing (OFDM)-based mobile mesh networks (MMNs) is proposed to reduce the handover overhead by distinguishing an intercluster handover event from an intracluster handover event at the physical layer. The handover procedure using the proposed preamble can simplify the scanning procedure and skip/simplify the network entry procedure, resulting in a significant reduction of the handover overhead. The performance of the handover procedure using the proposed preamble is evaluated using the parameters in the IEEE 802.16 mesh mode.

Channel Estimation for OFDM SYstems with Transparent Multi-Hop Relays

In this letter, the effect of a propagation delay resulting from the use of an OFDM system with a transparent mobile multi-hop relay (MMR) is initially analyzed. Then, a least square (LS) channel estimation technique for the OFDM system with throughput enhancement (TE) MMR or cooperative MMR is proposed. It is demonstrated by computer simulation that the proposed LS channel estimation technique for OFDM systems with transparent MMR is superior to the conventional technique in terms of mean square error (MSE) and bit error rate (BER).

A transmission of paging indicator information for mobile communication systems

In a cellular system, efficient power saving techniques for a mobile station (MS) are necessary because of its inherently limited battery of MS. The paging indicator (PI) transmission scheme in CDMA cellular systems is known to be an effective power saving strategy. However, in OFDM-based cellular systems, the MS has to operate FFT for PI symbol detection, resulting in a significant power consumption. In this paper, a reduced power consumptive PI transmission technique using the preamble in OFDM-based cellular systems, especially for mobile WiMAX systems, is proposed for the MS under power saving mode. Simulations indicate a 30∼50% power saving result from our proposed PI transmission technique, at the expense of a slight increase of paging response delay.

A Channel Assignment Technique for OFDMA-based Wireless Mesh Network with Different Time Delays

In this paper, a channel assignment technique to mitigate interferences due to ISI(Inter Symbol Interference) and ICI(Inter Carrier Interference) caused by TDoA(Time Difference of Arrival) among distributed MRs(Mesh Routers) in OFDMA(Orthogonal Frequency Division Multiple Access)-based WMN(Wireless Mesh Network) is proposed. The SINR(Signal to Interference and Noise Ratio) associated with the channel assignment for each MR is defined to minimize the effect of ISI and ICI due to TDoA in WMN, which is then used to propose an channel assignment technique considering fairness constraint. It is verified by computer simulation that the proposed channel assignment technique can improve the performance of BER(Bit Error Rate) in WMNs with compared to the conventional technique.