Modeling, Analysis and Design for Carrier Aggregation in Heterogeneous Cellular Networks

Carrier aggregation (CA) and small cells are two distinct features of next-generation cellular networks. Cellular networks with small cells take on a very heterogeneous characteristic, and are often referred to as HetNets. In this paper, we introduce a load-aware model for CA-enabled \textit{multi}-band HetNets. Under this model, the impact of biasing can be more appropriately characterized; for example, it is observed that with large enough biasing, the spectral efficiency of small cells may increase while its counterpart in a fully-loaded model always decreases. Further, our analysis reveals that the peak data rate does not depend on the base station density and transmit powers; this strongly motivates other approaches e.g. CA to increase the peak data rate. Last but not least, different band deployment configurations are studied and compared. We find that with large enough small cell density, spatial reuse with small cells outperforms adding more spectrum for increasing user rate. More generally, universal cochannel deployment typically yields the largest rate; and thus a capacity loss exists in orthogonal deployment. This performance gap can be reduced by appropriately tuning the HetNet coverage distribution (e.g. by optimizing biasing factors).Comment: submitted to IEEE Transactions on Communications, Nov. 201

Dry Machining of AA7075 by H-DLC Coated Carbide End Mill

AbstractPresent investigation evaluates the performance of a hydrogenated diamond like carbon (H-DLC) coating on carbide end mills during machining of an Al-Zn-Mg based alloy i.e. AA7075. Although diamond is known to be the most potential hard coating on carbide tools to deal with the challenges of machining aluminium, DLC coating offers economic solution in dealing with this material at medium cutting speeds. Present study explores the feasibility of using a H-DLC coating, which is eventually softer than non-hydrogenated DLC, in machining this alloy and compares its performance with that of uncoated carbide tools under dry environment. In terms of surface finish and cutting force this H-DLC coated tool substantially outperformed uncoated carbide one in the cutting speed range of 60 to 180 m/min. The coating was able to substantially arrest built up edge (BUE) formation, however, found to be with minor trace of built up layer (BUL)