The rapid growth of mobile traffic has heavily overloaded the cellular networks, making it increasingly desirable to offload mobile users' (MUs') traffic to small-cell networks. In this paper, we study the MUs' optimal uplink traffic offloading scheme based on the new paradigm of small-cell dual-connectivity (DC). Through DC, an MU can flexibly schedule its traffic between a macro-cell base station (BS) and a small-cell access point (AP) via two different radio interfaces. To optimize the overall network radio resource usage, we jointly optimize the BS' bandwidth allocation as well as the MUs' traffic scheduling and power allocation. Specifically, for reducing the bandwidth usage, the BS prefers to allocate the MUs small amount of bandwidth to encourage the MUs to utilize the small-cell networks. However, excessive traffic offloading can lead to severe interferences among MUs, which increase the MUs' power consumption. Hence, our joint optimization strikes a proper balance between these two aspects. Despite the non-convexity of the proposed joint optimization problem, we propose an efficient algorithm to compute the optimal offloading solution. The key idea is to exploit the layered-structure of the joint optimization problem, and decompose it into the BS' bandwidth allocation problem (on the top-level) and the MUs' traffic scheduling and power allocation problem (as a subproblem). Such a decomposition enables us to exploit the hidden convexity of the MUs' problem and the monotonic structure of the BS' problem for an effective algorithm design. Numerical results show that our proposed algorithm can achieve the global optimum solution with significantly reduced computational time. Moreover, the proposed traffic offloading scheme can significantly reduce the overall system cost, in comparison with using the fixed bandwidth allocation or traffic scheduling schemes.

In this paper, we investigate how the mobile users (MUs) can effectively offload traffic by taking advantage of the capability of dual-connectivity, which enables an MU to simultaneously communicate with a macro base station (BS) and a small-cell access point (AP) via two radio-interfaces. We formulate an optimization problem that jointly determines each MU's traffic schedule (between the BS and AP) and power allocations (between two radio-interfaces), with the objective to minimize all MUs' total cost. We first propose an effective scheme to characterize the feasibility of the joint optimization problem. Then, by exploiting the layered structure, we propose an efficient layered scheme to solve it. Numerical results are provided to validate the proposed schemes and show the performance gain via properly offloading MUs' traffic via dual-connectivity.