一個性能增強的長期演進技術車對車通訊下行排程演算法

Abstract

車間通訊是基於通訊技術來提升交通安全性與效率的一種服務。在基於LTE-Uu的車間通訊服務服務中，車對車的協同告知訊息會先上行傳送到基地台，然後基地台內的車間通訊應用伺服器會將協同告知訊息轉發到適當的基地台做下行傳送。在這車間通訊工作模式中，基地台的下行資料量可能會發生暫時超載的情況。而對於典型的尾部丟棄先進先出排程器，訊務超載會發生緩衝鎖死的現象，某些車輛會遭受極高的封包丟失率。因此，我們提出了一個性能增強的長期演進技術車對車通訊下行排程演算法。在我們的演算法中，訊務超載時會從緩衝器中挑選適當的封包丟棄，以改善封包接收間隔時間的分布。從我們的模擬中可以見到，相較於典型的尾部丟棄先進先出排程器，我們的排程演算法可以提高封包丟失公平性，和降低較長的封包接收間隔時間的發生機率。

Vehicle to everything (V2X) service is based on connectivity technology; aim to improve traffic safety and efficiency. In LTE-Uu based V2X service, the V2V CAM traffic is transmitted from vehicles to eNodeB, and the V2X application server forwards it to appropriate eNodeB(s) for downlink transmission. In this V2X operation, eNodeB downlink capacity may suffer temporary overload. Under traffic overload condition, buffer lock-out phenomenon will occur when using tail-drop FIFO queue management. As the result, some vehicles will suffer extremely high packet loss rate. Therefore, we propose a performance enhanced downlink scheduling algorithm for LTE V2V communications. In our algorithm, we select the appropriate CAM packet to drop, in order to improve the packet inter-reception time distribution instead of tail-drop. From our simulation results, comparing to tail-drop FIFO queue management, our algorithm can improve the fairness of packet loss rate and reduce the black events due to long packet inter-reception time.