Seongwon Kim

Wi-Fi could be much more

Wi-Fi has become an essential wireless technology in our daily lives, although the original intention of its introduction was to replace Ethernet cable. In this article, we outline the most remarkable features introduced during its ongoing technological evolution in terms of three major directions: throughput enhancement, longrange extension, and greater ease of use. By stitching these advanced features together, we also envision a promising future that Wi-Fi technology will bring us in terms of spectrum heterogeneity, seamless service provisioning, and possible relations with cellular networks.

Toward realistic WiFi simulation with smartphone “Physics”

Various packet-based simulation tools (e.g., NS-3) have been employed for design, validation, and evaluation of new protocols for WiFi networks since they offer cost efficiency, scalability, and reproducibility. These benefits come, however, at the expense of lack of realism compared to live testbed experiments. This is attributed in a major part to the difficulty of capturing detailed characteristics of channel dynamics, bit-level protocol specification (PHY layer), and application/user behaviors in a high-fidelity manner. The performance gap predicted by simulation and live testbed becomes even more pronounced when one considers a wide diversity of device characteristics and the way each device is used by end users. For example, smartphones generally show worse WiFi performance than other WiFi devices (e.g., laptops and tablets) because smartphones suffer from additional signal loss due to hand-grips and the low antenna gains of their embedded antennas. The goal of this study is to significantly close the gap by incorporating survey- and measurement-based smartphone WiFi characteristics and realistic hand-grip models into traditional WiFi network simulators (NS-3 in this study). The enhanced WiFi simulation tools performance prediction capability is validated through an comparative study between testbed experiments and simulations.

ProCCA: Protective Clear Channel Assessment in IEEE 802.11 WLANs

In wireless local area network, all transmissions are preceded by clear channel assessment (CCA), which determines the availability of wireless medium. Ideally, CCA should enable concurrent transmissions, whenever possible, to improve network capacity via spatial reuse. However, current CCA method is inherently limited in exploiting spatial reuse. Only the received signal strength of an incoming frame is utilized for CCA, and hence, the feasibility of a concurrent transmission should be determined without the knowledge of the frames transmitter, the corresponding receiver, etc. In this letter, we propose a novel CCA method which utilizes additional information delivered in the physical layer header to properly determine the feasibility of concurrent transmissions. Simulation results show that the proposed method increases network throughput by up to 54% by promoting spatial reuse.

Asymmetric Simultaneous Transmit and Receive in WiFi Networks

Many researchers expect to see the efficiency of wireless local area networks (WLANs) increased by in-band simultaneous transmit and receive (STR). While insufficient suppression of self-interference has been a major obstacle to implementing the STR capability, an even bigger obstacle is the fact that enabling STR involves significant modification to the current IEEE 802.11 medium access control (MAC) protocol. In this paper, we propose <italic>MASTaR</italic>, a novel MAC protocol that enables STR in 802.11 WLAN using standard-compliant methods. The feasibility and performance of <italic>MASTaR</italic> are extensively evaluated via 3-D ray-tracing-based simulation. The simulation results demonstrate that significant performance enhancement, e.g., up to <inline-formula> <tex-math notation=LaTeX>

Practical antenna selection for WLAN AP

2.58times

MASTaR: MAC Protocol for Access Points in Simultaneous Transmit and Receive Mode

</tex-math></inline-formula> higher throughput than the current 802.11 MAC protocol, can be achieved by an STR-capable access point.

Load Balancing in Two-Tier Cellular Networks With Open and Hybrid Access Femtocells

Antenna selection, a cost-effective way to enhance network performance, has been employed in a limited manner in wireless local area networks (WLANs) due to the lack of channel information at the transmitter. In this paper, a practical antenna selection system without using channel information is proposed. We first describe the practical issues of antenna selection system for infrastructure-based WLANs, and then, analyze its characteristics through an extensive measurement study. Based on that, we propose antenna selection algorithms of access point (AP) for both (1) unicast transmission and (2) multicast transmission and reception. The proposed algorithms are comparatively evaluated using prototype implementation in a commercial AP. It is demonstrated that the proposed algorithms achieve up to 34% throughput gain and 54% frame error rate reduction for unicast and multicast transmissions, respectively.

Pricing policies for femtocell service adoption in two-tier cellular networks

In-band simultaneous transmit and receive (STR) is expected to increase the efficiency of wireless local area network (WLAN). A major obstacle to implementing STR capability, however, has been insufficient suppression of self-interference. In addition, tackling several problems will require modifications to the current IEEE 802.11 medium access control (MAC) protocol. In this paper, we propose MASTaR, a novel MAC protocol supporting STR in 802.11 WLAN, backward compatible with legacy 802.11. The performance of MASTaR is extensively evaluated via ns-3 simulation. The simulation results demonstrate that significant performance enhancement can be achieved in the current WLANs by an access point (AP) with STR capability and a properly designed MAC protocol.

A novel metric for Dynamic Channel Assignment in enterprise wireless networks

Femtocell base station (BS) is a low-power, low-price BS based on the cellular communication technology. It is expected to become a cost-effective solution for improving the communication performance of indoor users, whose traffic demands are large in general. We propose long-term parameter optimization schemes for open and hybrid femtocells, which maximize the average throughput of macrocell users by offloading the macro users downlink traffic to femtocells. To achieve this goal, load balancing between femtocells and macrocells is needed, and hence, we jointly optimize the ratio of dedicated resources for femtocells as well as the femtocell service area in open access femtocell networks by numerical analysis. Then, we extend our algorithm to hybrid access femtocells, where some intra-femtocell resources are dedicated only for femtocell owners, while remaining resources are shared with foreign macrocell users. Our evaluation results show that the proposed parameter optimization schemes significantly enhance the performance of macrocell users because of the large offloading gain. The benefits provided to femtocell users are also adaptively maintained according to the femtocell users requirements. The results in this paper also provide insights about the situations where femtocell deployment on dedicated channels is preferred to the cochannel deployment.

Quiet ACK: ACK transmit power control in IEEE 802.11 WLANs

Femtocell is a cost-effective solution to both soaring wireless data traffic and coverage hole problems. Along with technical issues, the economic benefit which Wireless Service Providers (WSPs) and mobile users get from the femtocell service is a key to successful adoption of femtocell technology. In this paper, we study pricing issues for femtocell service using game theoretic approach. We propose a realistic and detailed pricing framework, and model the interaction between a monopolist WSP and users by a leader-follower game. We also model the competition between two WSPs in a duopoly market at the adoption of femtocell service by a non-cooperative simultaneous game. The competition between femtocells and repeaters is also considered using the same pricing framework. Analysis results present important factors and pricing strategies for economic success of femtocell technology.