| Summary: | 碩士 === 國立成功大學 === 電腦與通信工程研究所 === 103 === The development of small cells which shifts the traditional macro-based homogeneous network to the heterogeneous networks (HetNets) is regarded as one of the major breakthroughs to improve the network capacity. With the traditional Max-SINR association scheme, a user will choose the base station (BS) which offers the strongest received signal strength as its serving BS. Consequently, severe congestions may happen at the high-power macro base stations (MBSs) because most users tend to associate with the more powerful MBS rather than the low-power pico base stations (PBSs). To release the congestion problem, users can be shifted from the overloaded BSs to other BSs, known as user offloading. However, without taking the BS load into consideration, users may be offloaded to a neighboring BS that is overloaded, leading to failure cell association that is undesirable from both users' and operators' perspectives. In this work, we propose a load-based offloading scheme to address the aforementioned issue. We first formulate the optimal load-based offloading problem and shows that it is NP-hard. To facilitate practical implementation, a heuristic algorithm is proposed that is featured by the use of an offset parameter to mitigate offloading users to over-loaded BSs. From simulation results, the proposed heuristic algorithm is shown to increase the association rate and the average user rate, as compared to the traditional offloading scheme without considering the BS load.
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