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In this paper, we investigate the performance of hierarchical base station cooperation (HBSC) techniques in macrocell/ microcell heterogeneous networks for the Third-Generation Partnership Project Long-Term Evolution-Advanced (LTE-A) system. HBSC techniques aim at reducing the cochannel interference between a macrocell and a group of microcells by coordinating the transmissions of distributed antennas in the cell coverage area. We find that joint intra-and intersite cooperation will significantly reduce the intercell interference. Compared with the case without joint intrasite/intersite cooperation, we demonstrate that HBSC in the conventional pentagonal cell architecture can improve spectrum efficiency by 65% at the cell edge. When the narrow-beam trisector cell architecture is considered, the spectrum efficiency can be further improved by 16.42% at the cell edge.Index Terms-Heterogeneous network, hierarchical base station cooperation (HBSC), interference management.

Cognitive radio (CR) technology can be been applied in hierarchical cellular systems to allow concurrent transmissions for licensed (primary) and unlicensed (secondary) users to improve spectrum utilization. The major challenge of hierarchical CR systems is to manage the inter-cell interference between the primary and secondary systems. In the paper, we first present an optimal multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) uplink transmission scheme for hierarchical CR systems that can maximize the sum rate of the underlay secondary CR users, and prevent the primary systems from the severe interference of the secondary systems. The main contribution of this work is to propose a methodology to transform the signal to interference plus noise ratio (SINR) maximization problem of the secondary system into a quasi-convex form, thereby obtaining the optimal beamforming solution using a simple bisection method. Furthermore, we proposed a sub-optimal user scheduling algorithm in the secondary system to effectively mitigate the interference to the primary system.

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ZnO/ZnS nanocomposite-based nanostructures exhibit dual light and gas sensing capabilities. To further boost the light/dual sensing properties, gold nanoparticles (Au NPs) were incorporated into the core-shell structures. Multiple material characterizations revealed that Au NPs were successfully well spread and decorated on ZnO/ZnS nanostructures. Furthermore, our findings show that the addition of Au NPs could enhance both 365 nm UV light sensing and hydrogen gas sensing in terms of light/gas sensitivity and light/gas response time. We postulate that the optimization of gas/light dual sensing capability may result from the induced electric field and inhabitation of electron-hole recombination. Owing to their compact size, simple fabrication, and stable response, ZnO/ZnS/Au NPs-based light/gas dual sensors are promising for future extreme environmental monitoring.