Abstract-Sleep scheduling is a widely used mechanism in wireless sensor networks (WSNs) to reduce the energy consumption since it can save the energy wastage caused by the idle listening state. In a traditional sleep scheduling, however, sensors have to start up numerous times in a period, and thus consume extra energy due to the state transitions. The objective of this paper is to design an energy efficient sleep scheduling for low data-rate WSNs, where sensors not only consume different amounts of energy in different states (transmit, receive, idle and sleep), but also consume energy for state transitions. We use TDMA as the MAC layer protocol, because it has the advantages of avoiding collisions, idle listening and overhearing. We first propose a novel interference-free TDMA sleep scheduling problem called contiguous link scheduling, which assigns sensors with consecutive time slots to reduce the frequency of state transitions. To tackle this problem, we then present efficient centralized and distributed algorithms that use time slots at most a constant factor of the optimum. The simulation studies corroborate the theoretical results, and show the efficiency of our proposed algorithms.

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Abstract-In this paper, we address the problem of gateway placement for throughput optimization in multi-hop wireless mesh networks. Assume that each mesh nodes in the mesh network has a traffic demand. Given the number of gateways to deploy (denoted by k) and the interference model in the network, we study how to place exactly k gateways in the mesh network such that the total throughput that can be supported is maximized while it also ensure a certain fairness among all mesh nodes. We propose a novel grid-based gateway deployment method using a cross-layer throughput optimization. Our proposed method can also be extended to work with multi-channel and multi-radio mesh networks. Our extensive evaluation demonstrates that our method can effectively exploit the resources available and it performs much better than random deployment and fixed deployment methods.

The informal dimension has always been important in Chinese politics, due to a traditional bias against legalism and favoring the sentimentalization of personal qualities. We contend that it remains so still, albeit in altered form. Rather than being oriented solely to personal or in-group security, factionalism in the context of the more secure bureaucratic environment of the reform era has come to embrace policy goals and material interests as well. Thus, informal politics proliferates, and factional fortunes tend tofluctuateaccording to the patterns of China's political business cycle.In the post-Mao era the radical reformers led by Deng Xiaoping have favored rapid growth, even at the expense of stability. The conservatives surrounding Chen Yun consider stability the paramount goal, believing that it should override considerations of growth. The synchronization of reform and business cycles, plus the appearance of periodic social movements whenever the growth rate slumps, makes reformers and conservatives vulnerable to charges of mismanaging the economy for their respective policy preferences. As long as the business, reform, and movement cycles coincide, wide policyfluctuationsdriven by a politics of blame are inevitable.

Energy ef cient routings and power control techniques in wireless networks have drawn considerable research interests recently. In this paper, we address the problem of energy ef cient reliable routing in wireless networks in the presence of unreliable communication links or devices or lossy wireless link layers by integrating the power control techniques into the energy ef cient routing. We study both the case when the link layer implements a perfect reliability and the case when the reliability is implemented through the transport layer, e.g., TCP. We study the energy ef cient unicast when the links are unreliable. Subsequently, we study how to perform power control (thus, controlling the reliability of each communication link) such that the unicast routings use the least power when the communication links are unreliable. We presented both centralized algorithms and distributed algorithms for all the questions we studied. We conducted extensive simulations to study the power consumption, the end-to-end delay, and the network throughput of our protocols compared with existing protocols.