Junhee Lee

Implementing utility-optimal CSMA

Hundreds of papers over the last two decades have studied the theory of distributed scheduling in wireless networks, including a number of them on stability or utility maximizing random access. Several publications in 2008 studied an adaptive CSMA that in theory can approach utility optimality without any message passing under a number of assumptions. This paper reports the results from the first deployment of such random access algorithms through an implementation over conventional 802.11 hardware, an on-going effort that started in summer 2009. It shows both a confirmation that utility optimal CSMA may work well in practice even with an implementation over legacy equipment, and a wide array of gaps between theory and practice in the field of wireless scheduling. This paper therefore also brainstorms the discovery of and bridging over these gaps, and the implementation-inspired questions on modeling and analysis of scheduling algorithms.

A Group of People Acts like a Black Body in a Wireless Mesh Network

A wireless mesh network (WMN) is being considered for commercial use in spite of several unaddressed issues. In this paper we focus on one of the most critical issues: the impact of ambient motion of entities like people on the channel characteristics and on the WMN performance. A human body in an electro-magnetic (EM) field acts as an scatterer that absorbs 60% of incident EM energy, thereby shadowing the receiver. This human body model along with the human mobility behavior gives rise to a black body (a group movement) effect that traps the incident EM wave with repetitive internal reflections. The black body theory is verified by simulating the WiSEMesh testbed in picoKAIST, a tool based on deterministic ray tube method. Experimental results show each link exhibiting a unique channel variation pattern in presence of the black body. Based on the pattern we provide several insights in WMN deployment and protocol design.

Commoncode: a code-reuse platform for wireless network experimentation

Experimentation of a wireless network protocol over the air is of significant interest. However, it is more rarely performed than simulation because of the difficulties in coding and debugging as well as lack of scalability and repeatability. In this article, the concept of a code-reuse platform making use of a simulation code directly for real experiments is revisited as an efficient and easy means of experimentation. Furthermore, an architecture and key components of an idealistic code-reuse platform are suggested, and then CommonCode, the most advanced codereuse platform, is proposed. Through extensive simulations and experiments using Common-Code for the same codes, we demonstrate that CommonCode is valid and accurate in terms of protocol performance, and simultaneously fast and easy in terms of protocol development.

CommonCode: a code reuse platform for co-simulation and experimentation

Experimentation of a wireless network protocol over the air is of significant interest. However it is rarely performed compared to the simulation because of the difficulties in coding and debugging as well as scalability and repeatability. CommonCode is a unique protocol validation platform reusing the simulation codes for the experiments. It helps fast, convenient and accurate validation of protocols.

A TCP starvation problem in combining TCP and max-weight scheduling of cross-layer algorithms in WMNs

In this paper, we investigate the problem coming from the adaptation of legacy protocol TCP to the cross-layer protocols that is likely happen in future Internet. We point out named a TCP starvation problem in combining TCP and max-weight scheduling of cross-layer algorithms in wireless mesh networks. TCP starvation occurs when neighbor nodes are already scheduled with large queue length. To overcome TCP starvation as denoted in this paper, we propose a simple remedy named fake-ACK algorithm.

Alternative Attempts can Increase Transmission Opportunities in 802.11-Based Wireless Mesh Networks

Every station within carrier sense zone must keep quiet till the end of transmission which originates that carrier sense zone. We observe futile transmission attempts into this carrier sense zone. With thorough understanding of transmission zone, carrier sense zone, interference zone and corruption zone through equations we derive, we propose alternative attempts which effectively remove inefficiency in the multi-hop WMNs (wireless mesh networks). We show the gain of alternative attempts with analytic approaches and prove the performance improvement with extensive simulations. Our proposed MAC scheme is compatible with the existing 802.11 MAC and requires only subtle modification on commercially available 802.11 devices.