Kwanghun Han

Performance Analysis of Sleep Mode Operation in IEEE 802.16e Mobile Broadband Wireless Access Systems

In this paper, we analytically evaluate the sleep mode operation of the IEEE 802.16e, defined for the power saving. In the sleep mode, an mobile subscribe station (MSS) sleeps for a sleep window and wakes up at the end of the sleep window in order to check pending download packet(s) destined to itself. If there is no such a packet, the MSS doubles the sleep window up to the maximum value and sleeps again. For a quantitative analysis, we model the sleep mode operation as a semi-Markov chain. Then, the average packet delay and average power consumption are analytically derived. Based on the performance analysis, we discuss selecting the proper set of operational parameter values for a given traffic arrival pattern

Optimization of femtocell network configuration under interference constraints

Femto BS (Base Station) is emerging as a key technology to secure the coverage and capacity in indoor environments. However, since the existing macrocell network is overlaid on femtocell networks utilizing the same set of frequency channels, femtocell networks can originate severe co-channel interference to the macrocell network unless the femtocell network is carefully configured. Therefore, according to a desired network-wide objective, we optimize the femtocell network with constraints such that the service connectivity with a femto BS is secured in the target indoor area while the signal emitted out of the building, playing as interference to the outdoor users, should be controlled with an appropriate strength in order not to interrupt the communication between macro BS and outdoor users. Each optimization problem is formulated as a mixed integer programming, and as the results, we obtain not only the transmit power and operational frequency channel of each femto BS, but also the optimal femto BS-to-user association pair at each geographical position.

Opportunistic band sharing for point-to-point link connection of cognitive radios

Cognitive radios are typically known to exploit vacant spectrum resources yet not interfering with primary communication systems. However, cognitive radios may not be able to secure a clear spectrum band, i.e., white hole, in certain environments. Underlay spectrum sharing provides a way to cope with such a spectrum sharing problem in a bustling spectrum band; cognitive radios share the spectrum band with the spectrum licensees, i.e., primary users, by adjusting signal transmit power so as not to severely deteriorate the performance of the primary users. In this paper, we propose an underlay spectrum sharing policy for cognitive radios. Primary users are assumed to form a cellular network, and a point-to-point link of cognitive radio leverages uplink spectrum resource of the primary network. We formulate the transmit power constraints of the cognitive radio transmitter and propose a practical uplink band sharing framework. We also demonstrate that such an uplink band sharing can enhance the throughput performance of point- to-point link, while the interference to the primary users can be regulated under the allowed level decided by the primary users.

Idle mode for deep power save in IEEE 802.11 WLANs

Along with the wide acceptance of IEEE 802.11 wireless local area network (WLAN), new applications such as Internet protocol (IP) telephony over WLAN are fast emerging today. For battery-powered IP phone devices, the life time extension is a key concern for the market acceptance while todays 802.11 is not optimized for such an operation. In this paper, we propose a novel idle mode operation, which comprises paging, idle handoff, and delayed handoff. Under the idle mode operation, a mobile host (MH) without any active session does not need to perform hand-off within a predefined paging area (PA). Only when it enters a new PA, an idle handoff is performed. The proposed idle mode allows an MH without traffic to extend its life time. We develop a new analytical model in order to comparatively evaluate our proposed scheme. The numerical results demonstrate that the proposed scheme outperforms the existing schemes with respect to power consumption.

A MAC/PHY cross-layer design for efficient ARQ protocols

In many wireless data systems, automatic repeat request (ARQ) and hybrid automatic repeat request (HARQ) work independently. In this paper, we introduce a new ARQ feedback scheme called Cross-Layer ARQ (CL-ARQ), where ARQ closely interoperates with HARQ by making use of the acknowledgement of HARQ internally. By doing so, CL-ARQ not only removes the overhead for ARQ acknowledgement messages, but also improves the average delivery delay and TCP throughput. Especially, when the entities in charge of HARQ and ARQ are located far apart geographically, CL-ARQ remarkably outperforms the legacy scheme.

Power amplifier characteristic-aware energy-efficient transmission strategy

The energy consumption in transmitting an information bit, i.e., energy-per-bit, has been known to decrease monotonically as the transmission time increases [1]. However, when considering the power amplifier (PA) characteristics, we learn that the energy-per-bit starts to increase as the transmission time becomes long over a certain threshold. This is caused by the fact that, in a wireless device, it is not the transmission power, which determines the energy consumed during transmissions, but the input power to the PA whose output power is used as the transmission power. Based on our new trade-off model between the energy-per-bit and transmission time, we revisit known energy-efficient scheduling algorithms. Finally, we evaluate the impact of the new trade-off model and the performance of algorithms via simulations.

A Novel Idle Mode Operation in IEEE 802.11 WLANs

While the IEEE 802.11 Wireless Local Area Network (WLAN) became a prevailing technology for the broadband wireless Internet access, new applications such as Internet Protocol (IP) telephony are fast emerging today. For the battery-powered IP phone devices, the standby time extension is a key concern for the market acceptance while todays 802.11 is not optimized for such an operation. In this paper, we propose a novel Idle Mode operation, which comprises paging, idle handoff, and delayed handoff. Under the idle mode operation, a Mobile Host (MH) does not need to perform a handoff within a predefined Paging Area (PA). Only when the MH enters a new PA, an idle handoff is performed with a minimum level of signaling. Due to the absence of such idle mode operation, both IP paging and Power Saving Mode (PSM) have been considered the alternatives so far even though they are not efficient. We develop a new analytical model to comparatively evaluate our proposed scheme. Our numerical results demonstrate that the proposed scheme outperforms the legacy alternatives with respect to power consumption, thus extending the standby time dramatically.

A novel idle mode operation in IEEE 802.11 WLANs: prototype implementation and empirical evaluation

While the IEEE 802.11 Wireless Local Area Network (WLAN) became a prevailing technology for the broadband wireless Internet access, new applications such as Internet Protocol (IP) telephony are fast emerging today. For the battery-powered IP phone devices, the standby time extension is a key concern for the market acceptance while todays 802.11 is not optimized for such an operation. In this paper, we propose a novel Idle Mode operation, which comprises paging, idle handoff, and delayed handoff. Under the idle mode operation, a Mobile Host (MH) does not need to perform a handoff within a predefined Paging Area (PA). Only when the MH enters a new PA, an idle handoff is performed with a minimum level of signaling. Due to the absence of such idle mode operation, both IP paging and Power Saving Mode (PSM) have been considered the alternatives so far even though they are not efficient. We develop a new analytical model to comparatively evaluate our proposed scheme. Our numerical results demonstrate that the proposed scheme outperforms the legacy alternatives with respect to power consumption, thus extending the standby time dramatically.

Game Based Self-Organizing Scheme for Femtocell Networks

A femto base station (BS) is an emerging candidate solution to guarantee wireless coverage and enhance capacity in indoor environments. Ideally, femto BSs should be designed to be installed by customers without their manual configuration. Hence, a femtocell network should be automatically organized by configuring the operating frequency channel and transmit power level of the femto BSs adaptively according to the interference environment. However, in order to enhance the capacity of femtocell users, the femto BSs in the network should be carefully configured since they can cause severe co-channel interference to the existing macrocell networks operating in the same frequency channel. In this work, we propose an automatic self-organizing scheme for a femtocell network by jointly considering transmit power control and dynamic frequency selection, which tries to maximize the mean sum downlink achievable rate of the femtocell users and to guarantee the performance of the macrocell users by limiting the co-channel interference from the femtocells. The proposed scheme is based on a potential game which guarantees a convergence property, and we enhance the scheme with a Tabu search, which attempts to achieve the optimality.

On the multi-channel access schemes of the evolving WLANs

Today wireless local area networks (WLAN) are evolving with an aim to enhance the throughput performance leveraging various cutting-edge technologies. In this paper, we compare the aggregate throughput performance of two different multi-channel access schemes, namely, channel bonding (of the emerging IEEE 802.11n standard) and multi-radio MAC. Numerical analysis demonstrates that even though the channel bonding scheme can provide the higher physical layer transmission rate with the wider bandwidth, this does not always guarantee a higher aggregate throughput due to the relatively larger MAC overhead. Moreover, it is shown that distributing stations across multiple channels with multi-radio MAC can further enhance the aggregate throughput performance due to the reduced contention overhead.