Carrier aggregation (CA) is one of the key features for LTE-Advanced. By means of CA, users gain access to a total bandwidth of up to 100 MHz in order to meet the IMT-Advanced requirements. The system bandwidth may be contiguous, or composed of several non-contiguous bandwidth chunks, which are aggregated. This paper presents a summary of the supported CA scenarios as well as an overview of the CA functionality for LTE-Advanced with special emphasis on the basic concept, control mechanisms, and performance aspects. The discussion includes definitions of the new terms primary cell (PCell) and secondary cell (SCell), mechanisms for activation and deactivation of CCs, and the new cross-CC scheduling functionality for improved control channel optimizations. We also demonstrate how CA can be used as an enabler for simple yet effective frequency domain interference management schemes. In particular, interference management is anticipated to provide significant gains in heterogeneous networks, envisioning intrinsically uncoordinated deployments of home base stations.

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DC is one of the most important features introduced in Release 12 of the 3GPP specifications. DC aims at increasing the per-user throughput by improving the utilization of radio resources across two base stations connected via non-ideal backhaul (X2) and operating on different carrier frequencies. By making it possible to maintain the connection to the primary cell located in the macro base station while accessing the extra capacity provided by the small cell layer, DC can also improve the mobility performance in small cell deployments. This article gives an overview of the DC feature as standardized in Release 12. We summarize the supported scenarios and the DC functionality, and also demonstrate by means of detailed system-level simulations how DC can improve end-user throughput and mobility performance.

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