| Summary: | 博士 === 國立中央大學 === 通訊工程學系 === 102 === How to associate a femto user (FU) to an appropriate femto base station (FBS) to avoid interference and maximize the achievable data rate (ADR) of FUs have attracted much more attention in 2-tier mobile networks. The evidence provided in this dissertation proves it as an NP-complete problem. To maximize the ADR of the FUs, the methods for assigning FUs to neighboring FBSs are examined to determine the required transmit power level adjustments for the FBSs to mitigate the downlink (DL) interference among the FBSs and the macro base station (MBS). Traditionally, the linear programming (LP) approach is adopted to obtain the optimal solution for this problem but requires substantially more time to obtain the solution. To improve the drawback, we propose an easy but smarter scheme, named smart FBS selection algorithm (SFSA), to distribute FUs to non-interfered FBSs as well as to obtain the maximal ADR for each FU. If the SFSA fails to solve this problem, a DL power-control algorithm (DPCA) is employed to find a solution that causes the least amount of interference. The simulation results show that the SFSA and DPCA require only a minor amount of computation time to obtain a feasible solution.
Then, this dissertation investigates how to adjust the transmit power of each FBS to mitigate interference problems between the FBSs and mobile users (MUs). A common baseline of deploying the FBS to increase the indoor access bandwidth requires that the FBS operation will not affect outdoor MUs operation with their quality-of-service (QoS) requirements. To tackle this technical problem, an FBS transmit power adjustment (FTPA) algorithm is proposed to adjust the FBS transmit power (FTP) to avoid unwanted co-channel interference (CCI) with the neighboring MUs in downlink transmission. FTPA reduces the FTP to serve its FUs according to the QoS requirements of the nearest neighboring MUs to the FBS so that the MU QoS requirement is guaranteed. Simulation results demonstrate that FTPA can achieve a low MU outage probability as well as serve FUs without violating the MU QoS requirements.
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