Junhua Zhu

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This paper studies the tradeoff between energy consumption and application performance in wireless sensor networks by investigating the interaction between network lifetime maximization and rate allocation problems. To guarantee the individual performance of sensor nodes, we adopt the network utility maximization (NUM) framework to ensure certain fairness(More)
The network lifetime and application performance are two fundamental but conflicting desig objectives in wireless sensor networks. Hence there is an intrinsic tradeoff between network lifetime maximization and application performance maximization. Often application performance correlates to the application data rate obtained in sensor networks. We can thus(More)
—Proper admission control in cognitive radio networks is critical in providing QoS guarantees to secondary unlicensed users. In this paper, we study the admission control and channel allocation problem in overlay cognitive radio networks under the maximum cumulative delay constraint. We formulate it as a Markov decision process problem, and then solve it by(More)
— This paper considers the problem of routing in sensor networks from the point of view od data collection. That is, given the initial amount of battery energy in each node, the aim is to determine how much data can each source transmit until the network is partitioned (i.e., until the nodes cannot find end-to-end routes to their respective sinks). In(More)
In this paper, we propose and study two adaptive media access control protocols to support probabilistic data delivery reliability in sensor networks using MAC layer retransmissions. Since retransmissions consume energy, our adaptive <i>p-persistent</i> CSMA protocols tune their persistence probabilities in an effort to minimize the expected number of(More)
—Key-based workload partitioning is a common strategy used in parallel stream processing engines, enabling effective key-value tuple distribution over worker threads in a logical operator. While randomized hashing on the keys is capable of balancing the workload for key-based partitioning when the keys generally follow a static distribution, it is likely to(More)
In this work, we find the optimal relay location for a secondary user in a cognitive radio network subject to outage constraints. With selection decode-and-forward relay protocol, we formulate this problem as a nonlinear optimization problem, and then derive an approximation formulation that gives a close-optimal relay location, which means that we can use(More)
Hydrogenation of levulinic acid (LA) and its esters to produce γ-valerolactone (GVL) and 2-methyl tetrahydrofuran (2-MTHF) is a key step for the utilization of cellulose derived LA. Aiming to develop a commercially feasible base metal catalyst for the production of GVL from LA, with satisfactory activity, selectivity, and stability, Al2O3 doped Cu/SiO2 and(More)
Many sensor network applications only require probabilistic data delivery, as they can tolerate some missing data samples. For example, in environmental monitoring, missing temperature, pressure and humidity level samples can often be inferred by spatial and/or temporal interpolations. In this paper we propose and study an adaptive <i>p-persistent</i>(More)