The Impact of Fractional Frequency Reuse on Femtocell Resource allocation in multi-cell LTE networks

Femtocell又稱為毫微微蜂巢式基地台，或是家用基地台，在固網與行動網路融合(FMC)中扮演重要腳色。Femtocell通過在建築物內佈置一個小型的低功率發射器/接收器，從而允許3G手機連接到本地蜂巢基站，並通過ADSL線路進行路由呼叫，可達到良好的室內涵蓋率及傳輸速度。 LTE即所謂長期演進技術，是新一代的行動通訊網路技術，底層採用OFDMA的技術，所以在干擾問題上適合採用通道分配的方法去解決。並且在細胞間的干擾問題，LTE已經採取部份頻率重覆使用的方法去解決。有了Femtocell的加入，雖然可以有效地提高頻譜效率，但也使得干擾問題變得更加複雜。然而目前關於femtocell以及細胞資源分配相關的研究結果多半建立在單一細胞的系統，而無法透過簡單地改變直接使用在多細胞的系統。而其他相關的研究，即使考量了多細胞的系統，由於對於不同細胞內的femtocell會造成的干擾沒有加以考慮，所以在細胞的涵蓋率以及傳輸速率上的效能不盡理想。 在此我們提出一個資源分配的方法，同時考量了細胞間及細胞內部的干擾問題，並且能有效降底femtocell會對於造成胞的涵蓋率以及傳輸速率上的效能上造成的干擾，同時保有femtocell所能造成的高頻譜效率的優勢。Femtocells have been recently proposed as a potential good solution to increase not only indoor radio coverage, but also system capacity. However, the interference problem driven by femtocells should been paid more attention to. There are two common methods to solve interference problem such as power control methods and channel allocation methods. OFDMA systems like LTE and WiMAX can assignment different subcarriers to subscribers which make them in a good potential in using channel allocation method to solve the interference problem. However, interference in multi-cell system is much more complex than that in a single cell system and fewer related work discuss interference problem in a multi-cell system. The methods the proposed are good for single cell but will cause the coverage and cell-edge performance of macrocell down to a low level and new method should be proposed. In this work, we analyze the impact of Fractional Frequency Reuse on femtocell resource allocation, and then propose a new channel allocation method for femtocells and macrocells to work in multi-cell system without causing poor performance on cell-edge MSs and macorcell coverage