毫微微細胞覆蓋式正交分頻多工網路之干擾控制

Abstract

隨著無線通訊容量及高速率需求的增長，催化了新興通訊傳輸技術的發展。於室內放置毫微微細胞 (femtocell)是個增加現有無線網路通訊容量並同時提升室內覆蓋率的可行辦法。它藉由現存的數位用戶迴路或是電纜連接原先核心網路，可視為是種低功率的無線網路橋接器。

雖然目前已有寬頻分碼多工(WCDMA) 系統之毫微微細胞相關產品上市，但由於無法有效解決與原始的網路之間相互干擾的問題，普及度並不高。本文的主旨則在研究於第四代的通訊正交分頻多工(OFDMA)系統內佈建毫微微蜂巢網路之關鍵技術課題：即網路內及網路間的干擾消除與控制。因為干擾的形成主要來自於新（毫微微細胞）、舊（現存）網路之頻率與功率的規劃、統籌各自為政。我們所提的方案乃是從問題的根本著手，透過適當的資源（次載波、傳輸功率）分配將網路內及網路間之干擾控制在可容許的範圍。本文集中於下傳(Downlink)情境之同頻干擾控制，鄰頻干擾需藉由新舊網路之同步及輸出信號之旁波帶規範來解決。我們證明了，藉由適當的系統資源分配不但可以大大降低同頻干擾、提升網路容量與資源使用效益，並可提高毫微微蜂巢網路的建置效益。

Increasing demand for higher wireless system capacity and the need of high speed residential areas has catalyzed several new transmission techniques and network archi-tecture. Deploying femtocells in the house is a candidate solution to solve the capacity problem. Femtocells are low-power wireless access points that operate in licensed spec- trum to connect standard mobile devices to a mobile operator's network using residential DSL, cable broadband or wireless connections. Although some femto-related products are available in the market, they were designed for use in 3G networks and the performance seems to be less than satisfactory. The most critical physical layer design issue in a two-tier (femtocells overlaying existing marco-cells) femtocell network is interference control and management, i.e., to contain femto-to-macro, femto-to-femto and macro-to-femto interference to within speci‾ed bounds such that the network capacity/throughput is maximized with ‾xed femto transmit power. In this study, we focus on OFDMA-based 4G networks and investigate the issue of interference management. We provide a feasible solution by proposing downlink re- source (power and subcarriers) allocation algorithm in an OFDMA-based overlay femto (femto-macro coexisting) network. It is shown that through proper resource allocation,interference in an OFDMA network, as measured by signal-to-noise-plus-interference ratios at the active user terminals, can be controlled to within the tolerable range while the network still maintaining outstanding spectral e±ciency (capacity) performance.