@article{rhee_warrier_min_xu_2009, title={DRAND: Distributed Randomized TDMA Scheduling for Wireless Ad Hoc Networks}, volume={8}, ISSN={["1558-0660"]}, DOI={10.1109/TMC.2009.59}, abstractNote={This paper presents a distributed implementation of RAND, a randomized time slot scheduling algorithm, called DRAND. DRAND runs in O(\delta ) time and message complexity where \delta is the maximum size of a two-hop neighborhood in a wireless network while message complexity remains O(\delta ), assuming that message delays can be bounded by an unknown constant. DRAND is the first fully distributed version of RAND. The algorithm is suitable for a wireless network where most nodes do not move, such as wireless mesh networks and wireless sensor networks. We implement the algorithm in TinyOS and demonstrate its performance in a real testbed of Mica2 nodes. The algorithm does not require any time synchronization and is shown to be effective in adapting to local topology changes without incurring global overhead in the scheduling. Because of these features, it can also be used even for other scheduling problems such as frequency or code scheduling (for FDMA or CDMA) or local identifier assignment for wireless networks where time synchronization is not enforced. We further evaluate the effect of the time-varying nature of wireless links on the conflict-free property of DRAND-assigned time slots. This experiment is conducted on a 55-node testbed consisting of the more recent MicaZ sensor nodes.}, number={10}, journal={IEEE TRANSACTIONS ON MOBILE COMPUTING}, author={Rhee, Injong and Warrier, Ajit and Min, Jeongki and Xu, Lisong}, year={2009}, month={Oct}, pages={1384–1396} }
 @article{rhee_warrier_aia_min_sichitiu_2008, title={Z-MAC: A hybrid MAC for wireless sensor networks}, volume={16}, ISSN={["1558-2566"]}, DOI={10.1109/TNET.2007.900704}, abstractNote={This paper presents the design, implementation and performance evaluation of a hybrid MAC protocol, called Z-MAC, for wireless sensor networks that combines the strengths of TDMA and CSMA while offsetting their weaknesses. Like CSMA, Z-MAC achieves high channel utilization and low latency under low contention and like TDMA, achieves high channel utilization under high contention and reduces collision among two-hop neighbors at a low cost. A distinctive feature of Z-MAC is that its performance is robust to synchronization errors, slot assignment failures, and time-varying channel conditions; in the worst case, its performance always falls back to that of CSMA. Z-MAC is implemented in TinyOS.}, number={3}, journal={IEEE-ACM TRANSACTIONS ON NETWORKING}, author={Rhee, Injong and Warrier, Ajit and Aia, Mahesh and Min, Jeongki and Sichitiu, Mihail L.}, year={2008}, month={Jun}, pages={511–524} }
 @article{warrier_park_min_rhee_2007, title={How much energy saving does topology control offer for wireless sensor networks? - A practical study}, volume={30}, ISSN={["1873-703X"]}, DOI={10.1016/j.comcom.2007.05.019}, abstractNote={Topology control is an important feature for energy saving, and many topology control protocols have been proposed. Yet, little work has been done on quantitatively measuring practical performance gains that topology control achieves in a real sensor network. This is because many existing protocols either are too complex or make too impractical assumptions for a practical implementation and analysis. A rule of thumb or a practical upper bound on the energy saving gains achievable by topology control would assist engineers in estimating the overall energy budget of a real sensor system. This paper proposes a new topology control protocol simple enough to permit a straightforward stochastic analysis and also a real implementation in Mica2. This protocol is currently deployed in our testbed network of 42 Mica2 nodes. Our contribution is not on the novelty of this protocol but on a practical performance bound we can study using this protocol. The stochastic analysis reveals that topology control can achieve a power gain proportional to network density divided by a factor of eight to ten. Our experiment result from the real testbed tests confirms this finding. We also find a tradeoff in terms of throughput loss due to reduced density by topology control which amounts to about 50% throughput loss. These performance figures represent rough rules of thumb on energy efficiency achievable even by a very simple, unoptimized protocol.}, number={14-15}, journal={COMPUTER COMMUNICATIONS}, author={Warrier, Ajit and Park, Sangjoon and Min, Jeongki and Rhee, Injong}, year={2007}, month={Oct}, pages={2867–2879} }