長程演進網路上傳系統以增進總吞吐量為目標的資源排程機制

Abstract

LTE為3GPP制訂的標準，是目前4G網路最具前景的科技之一，其目標為提供高速資料傳輸、彈性頻寬使用、減少傳輸延遲時間、以及支援高速移動傳輸等技術性服務。為了達成此目的，LTE在下行系統和上行系統分別使用OFDMA與SC-FDMA的編碼技術，使它能突破傳統無線網路技術上的限制，晉升為4G網路的一員

為了達到提升系統效能與使用者多樣性增益的目的，在LTE下行系統中是採行傳統的通道相依排程演算法(CDS)，此方法會收集所有使用者的通道狀況資訊，之後讓通道較佳的使用者能優先分配到資源區塊(RB)來傳輸封包。然而因為SC-FDMA有兩大先天的限制：第一個為資源區塊配置連續性的規定，第二個為所有配置區塊需使用相同的編碼技術，因為這兩個限制使得通道相依排程演算法並不適用於LTE上行系統。在此論文中，我們首先考量此兩大先天限制，提出在LTE上行系統中資源分配問題的表示式，並找出其最佳可行解。由於此問題已經被證實是一個NP-hard的問題，為了降低計算複雜度，我們進而提出兩個啟發式的演算法，嘗試去逼近問題的最佳解。模擬結果顯示我們的方法不僅增加了系統的資料總吞吐量，減少了傳輸延遲的時間，同時也降低了拿不到傳輸資源的使用者比例。

Long Term Evolution (LTE), one of most promising technology for 4G mobile networks, is the latest standard of 3rd Generation Partnership Project (3GPP). The goal of LTE is to provide high data rate transmission, flexible frequency usage, smaller latency, and supportable transmission in high mobility. To achieve this, LTE employs the modulation technique by OFDMA in downlink and SC-FDMA in uplink, breaking the technical limitations of traditional wireless, and makes itself be the one of members of 4G mobile networks.

To increase the cell throughput and multi-user diversity gain, channel dependent scheduling (CDS) is implemented for the OFDMA-based multi-user scenario to allocate resource blocks (RBs) to users experiencing better channel conditions. Nevertheless, CDS may not perform well in SC-FDMA due to its two inherent constraints－one is contiguous RB assignment and the other is robust modulation and coding mode. In this paper, the formulation of resource allocation for a SC-FDMA system upon considering two inherent constraints is proposed. Since the optimization problem of resource allocation in SC-FDMA is NP-hard, we further propose two heuristic algorithms to find feasible solutions. We evaluate the proposed formulation and heuristic algorithms by conducting simulation. The simulation results show that our methods achieve significant performance improvement in not only system sum throughput, but also transmission delay and outage ratio.