LTE-A系統下具彈性部分頻率重複使用之效益導向多點傳輸資源分配機制

Abstract

由於細胞之間的干擾(iner-cell interference, ICI)是降低行動通訊系統效能的主要原因，許多方法已被提出來解決ICI問題。部分頻率重複使用(FFR)是一種藉由使相鄰的細胞邊緣操作在不同的主頻帶來有效降低干擾的方式。協調式多點傳輸(CoMP)是藉由多個傳輸點同時服務一個使用者，使得原本的干擾轉變為信號的方法。由於FFR是將頻譜固定切成幾個特定的附頻帶，如此的作法無法適應多變的細胞環境，因此我們提出藉由頻率感知的方法來使頻率重複使用具有彈性。即使有了上述的各種方法，我們還是需要一個好的資源分配(resource allocation)來使系統達到最大的吞吐量(Throughput)。 在本論文中我們提出了LTE-A系統下具彈性部分頻率重複使用之效益導向多點傳輸資源分配機制。彈性部分頻率重複使用(FFFR)是由FFR、CoMP以及頻率感知。FFR與CoMP可有效處理ICI，配合頻率感知則可進一步提高頻譜使用效率。效益導向多點傳輸資源分配包含了效益函數(utility function)以及三個啟發式演算法，其中效益函數的設計考慮了滿足使用者的QoS需求、系統吞吐量最大化，以及有效率的傳輸點分配，最後藉由迭代執行三個啟發式演算法，便可找到當下最佳的資源分配組合。

Since inter-cell interference (ICI) is a main performance limiting issue in wireless cellular networks, several solutions are proposed to mitigate ICI problem. Fractional frequency reuse (FFR) is proposed to mitigate the cell edge ICI problem by making the adjacent cells operate in different subbands at cell edge. Coordinated multiple-point (CoMP) transmission can turn interference into signal by allowing multiple transmission points to transmit same signal to single user. Since FFR cannot adapt to the traffic variation, by spectrum sensing we can make the frequency reuse more flexible. Although there are several way to mitigate ICI, we still need a good resource allocation to maximize system throughput. In this thesis, we propose a flexible fractional frequency reuse (FFFR) strategy with utility-based multiple-point coordination resource allocation (UCRA) scheme. The FFFR strategy is formed by a conventional FFR, multiple-point coordination, and a CQI-based spectrum sensing technique. The conventional FFR and multiple-point coordination effectively mitigate ICI, and the CQI-based spectrum sensing improves spectrum efficiency. The UCRA scheme includes a well-designed utility function and three heuristic algorithms. The utility function considers QoS guarantee, throughput maximization, and efficient transmission point assignment. Three heuristic algorithms operate in an iterative approach to achieve the best resource allocation to the system.