The cycle life and capacity fading mechanisms of secondary sulfur electrodes prepared by two different electrode fabrication methods were studied in an effort to improve the energy density of the cathode. Cycle life improved substantially when the uniformity of carbon distribution around the sulfur particles improved and electrode density increased, improving the overall structural integrity of the carbon matrix. Capacity fading in a high-energy-density cathode is mainly due to structural failure by physical crack propagations of the electrode structure and subsequent formation of the electrochemically irreversible Li 2 S layer at cracked surfaces of carbon particles or masses. The capacity fading due to these mechanisms appears to be reduced substantially and significantly by improved structural integrity with uniform pore structure of the carbon matrix. A Li/S cell containing a cathode fabricated by the improved technique cycled over 400 cycles without any severe structural damage of the electrode structure.

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In ubiquitous networking environments, we generally need two or more heterogeneous communication systems coexisting in a single place. Especially, wireless local area networks (WLANs) based on IEEE 802.11 specifications and wireless personal area networks (WPANs) based on IEEE 802.15.4b or g specifications need to coexist in the same Industrial, Science and Medial (ISM) band. If the WPAN communication coverage is expanded using a cluster-tree network topology, then the 802.15.4 network is more susceptible to interference from neighboring WLANs. In this paper, we propose an adaptive interferenceaware clustering algorithm using multiple channels in a WPAN in the presence of WLAN interference. The algorithm includes interference detection and avoidance schemes to adaptively reconfigure multiple channels in an IEEE 802.15.4 cluster-tree network to avoid interference from WLANs. To evaluate the performance of the proposed algorithm, the frame error rate (FER) is measured in a real network testbed. The measurement result shows that the proposed algorithm is effective in an IEEE 802.15.4 cluster-tree network in the presence of multiple IEEE 802.11 interferers.

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y 2) Interference Mediation Part N N II. INTERFERENCE MEDIATION SCHEME FOR COLLOCATED ZIGBEE AND WLAN NETWORKSIn this paper, we propose a proactive and network-centric interference mediation scheme in an overlaid network environment of WLAN and ZigBee devices. In order to solve this problem, we propose fairness-based TDMA schemes to guarantee the ZigBee data transmission. y Fig. 1. Block Diagram of the Proposed Interference Mediation Scheme Zigbee channel observation using FER 1) Channel Status Observation Part WLAN channel observation using WLAN Dev.To mediate this inter-system interference, we propose an interference mediation scheme in which an interference mediator(IM) coordinates the interference between WLAN and Zig-Bee networks using its internal WLAN and ZigBee modules. This 1M plays an important role as a coordinator of mutual interference mediation between a ZigBee piconet and a WLAN BSS. Fig. 1 shows a block diagram of the proposed interference mediation scheme which consists of a Channel Status Observation Part and an Interference Mediation Part.Abstract-In emerging ubiquitous wireless environments, mobile devices can have multiple communication modules such as WLAN and ZigBee. Since IEEE802.15.4 ZigBee devices and IEEE802.11b WLAN devices share the same 2.4GHz ISM band, a ZigBee network operating in a low power environment can be severely interfered by overlapped WLAN networks with much larger bandwidth due to higher transmission power. To overcome this inter-system interference problem and guarantee the ZigBee communications, we propose an interference mediation scheme in an overlaid network environment of WLAN and ZigBee devices by using an interference mediator, and evaluate the performance of ZigBee and WLAN networks for three different resource allocation schemes in terms of throughput and channel occupancy time.