A Cross-Layer-Aware FDD/TDD Carrier Aggregation Framework for LTE-A Networks

In this paper, we study the aggregation between the frequency division duplex and time division duplex (TDD) spectrum bands within the context of 3GPP LTE-A system. To be specific, we first provide a cross-layer design analysis to obtain the achievable throughput using the TDD mode for transmission in LTE-A system. Under particular QoS requirements and certain channel conditions, the achievable throughput is derived and evaluated. The QoS requirements required from the upper layers, where the file size, the TCP window size and the latency for efficient transmission are incorporated in the final formulation. Having obtained the formulation, simulation results highlight the impact of the QoS parameters to different TDD frame format, wherein the number of DL and UL subframes vary. Having taken into account this design aspects, we propose a framework for TDD frame adaptation within the LTE-A system. The aim of this framework is to provide the dynamic configuration of different TDD frame formats by calculating the DL:UL subframes ratio under certain channel conditions and QoS requirements. We also provide flowchart procedures of how such a solution could be implemented within the 3GPP LTE-A context. Simulation results are carried out, which reveal the probability of choosing the different TDD frame formats from the system under certain channel conditions and QoS requirements.