本文提出了一種稱為基於軟體定義網路（OHD-SDN）的預先換手分流決策機制，將車建構於軟體定義網路（SDN）下，使用於車到基礎設施通信從行動網路分流到路基台（RSU）的 IEEE 802.11p 網路， 在所提出的控制方案中，當具有車載單元（OBU）的車輛（其具有行動網路介面和 IEEE 802.11p 網路介面）連接到行動網路時，SDN 控制器監控車輛回報的資訊，包括速度，地理位置，方向和感測到的相鄰 RSU 的 ID。一旦車輛接近 IEEE 802.11p路基台，SDN 控制器將判斷車輛是否切換到 RSU 以進行分流。 SDN 控制器（1）計算到做出分流決策的時間，（2）決定使車輛從行動網路切換到即將遇到的 RSU 的 IEEE 802.11p 網路是否合適，（3）通知如果前面的 RSU IEEE 802.11p 網路的網路狀況不合適，則車輛保持在行動網路中，或者如果前面的 RSU 的 IEEE 802.11p 網路的網路狀況是合適，則將車輛從行動網路切換到 RSU IEEE 802.11p 網路。模擬結果表明，使用提出的 OHD-SDN 控制方案，可以降低行動網路的負載和流量，並且可以確保 RSU 的 IEEE 802.11p 網路中的車輛的網路品質。

This paper proposes a prediction control scheme - called Offloading with Handover Decision based on Software-Defined Network (OHD-SDN) for the offloading of the vehicle-toinfrastructure communication from cellular network to IEEE 802.11p network of a Road Side Unit (RSU) using the Software-Defined Network (SDN) Architecture. In the proposed control scheme, when the vehicle with an On Board Unit (OBU), which has a cellular networks interface and an IEEE 802.11p network interface, connects to cellular network, the SDN Controller monitors it to make decision about the offloading indication based on the reported information, including speed, geographical position, direction, and sensed neighboring RSUs’ IDs, from the vehicle. Once the vehicle is approaching the IEEE 802.11p RSUs, the SDN Controller will judge whether it is good or not for the vehicle to switch to the RSU for offloading or not. The SDN Controller (1) calculates when the due time is to make decision, (2) decides whether it is suitable or not to have the vehicle to handoff from cellular network to the ahead IEEE 802.11p network of a RSU, (3) notifies the vehicle to stay in cellular network if the networking situation of the ahead RSUs IEEE 802.11p network is not suitable or to switch from cellular network to the ahead RSUs IEEE 802.11p network if the networking situation of the ahead RSU’s IEEE 802.11p network is suitable. The simulation results show that the cellular networks load and traffic can be reduced and the networking quality of the vehicle being in the IEEE 802.11p network of a RSU can be assured using the proposed OHD-SDN control scheme.

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