Jiwoong Jeong

Achieving weighted fairness between uplink and downlink in IEEE 802.11 DCF-based WLANs

In this paper, we first propose an analytical model of WLANs (wireless LANs) with an arbitrary backoff distribution and AIFS (arbitration inter-frame space). From the analysis, we show that the achievable bandwidth is determined by the mean of backoff distribution regardless of the shape of the backoff distribution. We compare the effectiveness of four parameters on channel access differentiation, namely, the mean of backoff distribution, CWmin (initial contention window), the number of backoff stages, and AIFS. Numerical results show that the mean of backoff distribution provides weighted fair channel access most accurately. Second, based on the proposed analytic frame work, we develop three schemes for the uplink/downlink bandwidth differentiation in order to achieve weighted fairness between uplink and downlink transmissions. Note that IEEE 802.11 is known to have unfairness between uplink and downlink accesses. Each scheme is characterized according to the corresponding channel access rule. The simulation results show that the proposed schemes achieve high system throughput while accurately differentiating bandwidth allocation

New Approach for Reducing DAD delay using Link Layer Assistance in Mobile IPv6

There have been a lot of research and investigation to improve handover latency of mobile IPv6 (MIPv6). The handover latency is one of the most important factors because performance of TCP flows as well as realtime traffic degrades sharply as the latency increases. The MIPv6 handover process consists of movement detection, duplicate address detection (DAD), and binding update. Among the three components, DAD has been identified as the most critical factor. In this paper, we introduce novel schemes to reduce the DAD delay. By utilizing tentative address that an access router provides, a mobile node pre-determines its care-of-address before L2 handover such that the DAD period can be greatly reduced. We also devise a mechanism that reduces the messaging overhead via link layer assistances. Extensive performance analyses show that the proposed scheme significantly enhances the performance of MIPv6.

Physical layer capture aware MAC for WLANs

The physical layer capture (PLC) effect occurs frequently in the real wireless deployment; when two or more nodes transmit simultaneously, a receiver can successfully decode the collided frame if the signal strength of one frame is sufficiently high enough. Although the PLC effect increases the channel utilization, it results in an unfair channel access among the wireless nodes. In this paper, we propose a PLC-aware media access control (MAC) algorithm that employs the average waiting time as a common control reference. It enables the nodes to converge to a fair channel access by changing one of the IEEE 802.11 enhanced distributed channel access parameters: contention window, arbitration interframe space, or transmission opportunity. We then find multiple control references that meet the fair channel access constraint and obtain the near-optimal reference that maximizes the overall throughput. Through ns-2 simulations and real in-door experiments using the universal software radio peripheral platform, we evaluate the fairness and throughput performance of the PLC-aware MAC algorithm.

Design, Analysis and Evaluation of A New Energy Conserving MAC Protocol for Wireless Sensor Networks

Low power listening (LPL) MAC protocols based on duty-cycling mechanism have been studied extensively to achieve ultra low energy consumption in wireless sensor networks (WSNs). Especially, recent ACK-based LPL schemes such as X-MAC employ strobe preambles and an early ACK, and show fair performances in communications and energy efficiencies. However, the state-of-the-art ACK-based LPL scheme still suffers from collision problems due to the protocol incompleteness. These collision effects are not trivial and make WSNs unstable, aggravate energy consumptions. In this paper, we propose two novel schemes; (i) ?-duration CCA to mitigate the collision problem in ACK-based LPL MAC protocols. (ii) Short Preamble Counter (SPC) to conserve more energy by reducing unnecessary overhearing. We demonstrate the performance improvement of our scheme via a mathematical analysis and real-time experiments. Both analysis and experimental results confirm that our proposed scheme saves energy by up to 36% compared to the naive ACK-based LPL MAC protocol thanks to ?-duration CCA and SPC.

Adjacent channel interference aware channel assignment scheme for WLANs

As the deployment of wireless devices becomes widespread, the performance reduction due to interference between wireless channels incur a new research issue. Thus, the channel assignment scheme for reducing the interference is very important in IEEE 802.11-based Wireless LANs. However, most previous approaches have focused on 2.4GHz spectral band or have assumed that there is no interference between non-overlapping channels. In this paper, we investigate adjacent channel interference (ACI) between non-overlapping channels. We find out that the ACI has a great impact on the throughput performance via experimental results. We also propose a new channel assignment scheme which minimizes the ACI. The proposed scheme allocates the channel so as to maximize the system utilization based on the information of neighbor channel state. To evaluate the proposed scheme, we conduct extensive experiments on a wireless testbed. We also show that the proposed scheme achieves superior network performance.

Reference-based fair MAC algorithm in Wi-Fi WLANs with capture effect

The widespread deployment of infrastructure WLANs has made Wi-Fi an integral part of today’s Internet access technology. Due to the inherent characteristics of the wireless medium in WLAN systems, the capture effect significantly affects the system performance; a receiver can successfully decode a collided frame given that its signal-to-interference and noise ratio is sufficiently high enough, but results in an unfair channel access share among the wireless nodes. In this article, we propose fair capture effect aware MAC (FC-MAC) algorithm, which achieves channel access fairness using a feedback control mechanism. We determine the average waiting time as a common control reference, which provides fair channel access even when the capture effect is present. In result, the algorithm enables each node to converge to a fair channel access share. Among multiple points that yields fair channel access, we determine the optimal target reference that maximizes the aggregate throughput. Through both dynamic system modeling and extensive simulation studies, we show that the FC-MAC algorithm is stable and achieves fairness while improving the aggregate throughput.