無線蜂巢式系統下排程演算法與無線資源配置之研究

Abstract

本論文旨在研究無線系統中封包排程演算法以及無線資源配置。 本論文提出一新穎的「個人機會」(Self-opportunity)概念，在眾多典型排程演算法會考慮的多使用者分集指標(Multiuser diversity)之外，進一步用個人機會指標區分出各使用者的通道傳輸效率，提供給排程器額外資訊，以增進封包排程的效能，特別是針對即時性的應用服務。且此個人機會的概念可以廣泛地應用在各式演算法上使用。 此外，本論文針對可調式影像編碼(Scalable Video Coding)之視訊串流服務，提出一跨層次系統設計，透過具移動性的使用者設備端(如手機)、基地台、與視訊串流伺服器三者之間的合作，根據無線介面的頻寬變化來調節視訊串流的資料流量，並且利用”Importance-based intra-service packet scheduling”的方式，在單一服務流(service flow)下的資料封包擁有不同程度的重要性時，藉由對重要的影像資料提供較好的保護，來提升影像的服務品質。 另外，本論文以數學分析的角度出發，建構一個資源配置的數學分析模型，來分析一無線通訊系統的傳輸能力如系統吞吐量以及使用者容量，此分析模型包含調變編碼分佈模型以及資源配置模型，根據無線資源使用上的調變編碼分佈以及無線資源的有限性，評估一無線系統的吞吐量上限。

In this dissertation, we investigate the problem of scheduling and resource allocation in wireless cellular systems. We propose a new physical indicator which can be considered in the scheduling metrics function to further improve scheduling performance. The new physical indicator is named by “self-opportunity,” which means the chance of benefit from users’ point of view. The propose self-opportunity introduces a new dimension to scheduling metrics function and it can cooperate with conventional scheduling algorithms. We will show that the concept of self-opportunity can help the scheduler improve transmission performance, especially for scheduling real-time applications. To identify the performance improvement, a system-level simulator is established to evaluate the scheduling performance of each algorithm. In addition, we investigate a special case of scheduling H.264/AVC scalable video coding (SVC) based traffic. Due to the layered characteristic of SVC traffic, we propose a cross-layer system architecture to adapt the traffic amount of SVC video streaming according to the transmission bandwidth of last-mile wireless environment. Besides, we use “importance-based intra-service packet scheduling” to further improve the transmission performance and QoS of the SVC-encoded traffic. Importance-based intra-service packet scheduling can be applied if the arriving SDUs of a service flow can be categorized to multiple levels of importance, which is the main characteristic of SVC-encoded traffic. Simulation results and subject test show that the proposed system architecture can provide better performance for SVC-encoded traffic. Furthermore, we propose an analytical model to evaluate the system throughput and user capacity of a wireless cellular system. The analytical model contains two components including the MCS distribution model and resource allocation model. The analytical model is derived based on the resource allocation behavior and the constraint of limited wireless resources. Besides, we also use an example of two-hop relay networks to demonstrate how to use the analytical model. The proposed analytical model can provide the engineering sense for the system deployment.