Chang-Yeong Oh

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Femtocells are expected to be one of the emerging technologies for next generation communication systems. For successful deployment of femto-cells in the pre-existing macrocell networks, there are some challenges such as the cell planning for interference management, handoff, and power control. In this paper, we focus on frequency planning which can provide(More)
The interference mitigation technique based on fractional frequency reuse (FFR) provides improved cell-edge performance with similar overall cell capacity as that of systems with the frequency reuse factor of one. Furthermore, frequency sub-band allocation by FFR has the benefit of allowing flexibility for the deployment of femto-cells through frequency(More)
In multiuser OFDMA systems, adaptive resource allocation has been identified as one of the key technologies to have more flexibility and higher efficiency. Several adaptive subcarrier allocation algorithms with the objective to maximize spectral efficiency or fairness have been proposed. However, quality of service (QoS) requirement of each user may not be(More)
Cooperative communications using relays in wireless networks have similar effects of multiple-input and multiple-output without the need of multiple antennas at each node. To implement cooperation into a system, efficient protocols are desired. In IEEE 802.11 families such as a/b/g, mobile stations can automatically adjust transmission rates according to(More)
—We consider the joint relay and pre-coder selection in the decode-and-forward (DaF) relay network, where multiple relays are employed with multiple antennas. Depending on the channel information, the destination informs the relay and pre-coder selection information to the source and relays with finite bits of information. The source and the selected relay(More)
In IEEE 802.11, the rate of a station (STA) is dynamically determined by link adaptation. Low-rate STAs tend to hog more channel time than high-rate STAs due to fair characteristics of carrier sense multiple access/collision avoidance, leading to overall throughput degradation. It can be improved by limiting the transmission opportunities of low-rate STAs(More)
In this paper, we propose a mechanism to increase performance by using cooperative communications in IEEE 802.11. Existing algorithms use one relay between a source and a destination, which is a 2 hop relay. There may be cases that relays cannot be found. We propose a cooperative communication protocol for three hops. The proposed algorithm manages network(More)