This paper presents ScaPSM (i.e., Scalable Power-Saving Mode Scheduler), a design that enables scalable competing background traffic scheduling in crowd event 802.11 deployments with Power-Saving Mode (PSM) radio operation. ScaPSM prevents the packet delay proliferation of previous study, if applied in the crowd events scenario, by introducing a new strategy of adequate competition among multiple PSM clients to optimize overall energy saving without degrading packet delay performance. The key novelty behind ScaPSM is that it exploits delay-aware load balance to control judiciously the qualification and the number of competing PSM clients before every beacon frame's transmission, which helps to mitigate congestion at the peak period with increasing the number of PSM clients. With ScaPSM, the average packet delay is bounded and fairness among PSM clients is simultaneously achieved. ScaPSM is incrementally deployable due to only AP-side changes and does not require any modification to the 802.11 protocol or the clients. We theoretically analyze the performance of ScaPSM. Our experimental results show that the proposed design is practical, effective, and featuring with significantly improved scalability for crowd events.

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Abstract:In the building integrated photovoltaic (BIPV) system, the influence of partial shading on the energy efficiency of the BIPV system is large in certain circumstance. Energy efficiency of the centralized system and multi string type system are researched in four typical shading conditions. Results show that, when the shading is not serious, whether the system is in weak light or bright light condition, the energy conversion efficiency of the centralized system and multi string system is high and the difference is small. When the shading is serious, whether the system is in weak light or bright light condition, the system energy efficiency difference of two kinds of energy conversion structure is very big. In general, multi string systems is more higher than centralized system in energy efficiency, so the choice of a better energy conversion structure is the key factor to reduce the shading effect and improve the system energy efficiency.