適用於長程演進網路上行傳輸之預測式資源排程法

Abstract

長期演進技術(LTE)為第三代合作夥伴計劃(3GPP)制定之標準，並且被公認為是邁向4G網路時期的一項很有前景的科技。由於在下行鏈路中使用正交分頻多工存取(OFDMA)技術，以及在上行鏈路中使用單載波分頻多工存取(SC-FDMA)技術，因此LTE相較於3G網路可以在頻寬最高20MHz上面提供極高的傳輸速率。 為了增加基地台的整體傳輸速率與使用者多樣性增益之目的， LTE在以OFDMA為技術的下行鏈路中是採納傳統的通道相依排程演算法(CDS)。CDS演算法會優先將各個資源區塊(RB)各別的配置給在這個RB頻道品質較好的使用者，然而這個方法若同樣的套用在以SC-FDMA為技術的上行鏈路中，則可能會讓整體的傳輸表現變得不盡理想。會發生這個問題的主要原因是因為SC-FDMA技術比OFDMA技術在配置資源的時候多了兩個限制，第一個是使用者在配置資源時必須符合連續限制，第二個則是針對一個使用者在所有被配置的RBs都必須使用相同的調變技術(MCS)。此次論文將把目標鎖定在探討上行鏈路以SC-FDMA為技術的排程演算法。由於上行鏈路的資源配置最佳解已經被証明為NP-hard問題，因此我們將藉由提出新的概念以發展出一個啟發式演算法，並且嘗試去逼近問題的最佳解。最後將以模擬評估本論文提出之演算法，結果顯示此方法在系統總傳輸率相較於傳統以CDS為基礎的方法有明顯的改善。

Long Term Evolution (LTE) is a promising technology for 4G mobile networks standard by 3rd Generation Partnership Project (3GPP). Due to utilize OFDMA in downlink and SC-FDMA in uplink, the LTE system is expected to provide significantly high throughput with 20 MHz spectrum allocation compared to 3G 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 Scheme (MCS). In this thesis, since the optimization problem of resource allocation in SC-FDMA is NP-hard, we hence propose an estimation-based heuristic algorithm, which will take the two inherent constraints of SC-FDMA into consideration. In the algorithm, each time it will try to allocate one RB to the User Equipment (UE), which can maximize the current upper bound estimation. We evaluate the proposed algorithm by conducting simulation. The simulation results show that our method can achieve significant performance improvement in system throughput.