第四代行動通訊異質網路具混合式可調適性保護配置之研究

Abstract

在異質性網路(Heterogeneous Network, HetNet) 下， 利用Cell Range Expansion(CRE) 技術，藉由一個指定的偏差值(bias)，可以有效率地將使用者從巨型細胞卸載(Offload) 至小型細胞，從而獲得Cell Splitting 增益以提升系統的頻譜效益。但為了保護這些經由CRE 卸載至小型細胞的使用者免於受到巨型細胞的干擾，3GPP LTE-A 於Relesase 10 提出enhanced Intercell Interference Coordination(eICIC) 技術，利用幾乎空白子訊框(Almost Blank Subframe, ABS) 之具保護作用子訊框(Protected Subframes, PSF) 的架構，來降低巨型細胞對小型細胞的干 擾。然而當偏差值提高以獲得更好的卸載效果時，將需要更大比例的ABS 以保護由巨型細胞卸載至小型細胞的使用者，如此雖然可以提升在小型細胞使用者的Throughput，但另一方面卻也因此降低巨型細胞使用者的Throughput。相較於ABS，另一種提出的PSF 架構，即降低傳送功率子訊框(Reduced Power Subframe,RPS)，則是在維持巨型細胞使用者的Throughput，以及降低對小型細胞使用者的干擾間做一個取捨。因此，為了能提升小型細胞使用者的Throughput，同時能維持巨型細胞使用者的Throughput，在本篇論文中，我們提出了一個混合式具保護作用子訊框(Hybrid Protected Subframes, HPS) 的資源分配技術，藉由結合ABS 與RPS 架構來提升位於細胞邊緣地帶的使用者的效能。相較於現行的技術，我們所提出的HPS 資源分配技術可以更有效率的提升系統的效能。

Cell Range Expansion(CRE) with a bias in heterogeneous network(HetNet) can encourage macro user equipment(UE) offloading to increase spectral efficiency through cell splitting. To protect offloaded UE from severe macrocell interference, a specific Protected Subframes(PSF) is introduced in the 3rd Generation Partnership Project(3GPP) Long Term Evoluction Advanced(LTE-A) Release 10. The PSF of current enhanced InterCell Interference Coordination(eICIC) is known as Almost Blank Subframes(ABS). In order to obtain the offloading benefit, a large bias for handover criteria such as Reference Signal Received Power(RSRP) needs to be used. When a large bias is applied, more victim UEs need to be protected by large ABS percentage. On the other hand, when ABS percentage increase, the throughput of pico UEs increase, but the throughput of macro UEs decrease. Therefore, in order to improve pico UEs throughout while ensuring macro UEs throughput, a new PSF pattern need to be considered. Compared to ABS, Reduce Power Subframes(RPS) which is the trade-off between the macro UEs throughput and interference of pico UEs. Thus we propose a PF-aware Hybrid Protected Subframes(HPS) resource allocation method which jointed ABS and RPS to improve the overall throughput for cell edge users. Furthermore, when HPS and Proportional Fair Scheduling(PFS) are applied, based on Proportional Fair(PF) metrics, the proposed method can adaptively reallocate HPS pattern. Compared to related work, the proposed HPS resource allocation technique can maintain the throughput as increasing HPS percentage.