06 Coloured Petri Net-based Traffic Collision Avoidance System encounter model for the analysis of

1.題目和關鍵詞
Title: Coloured Petri Net-based Traffic Collision Avoidance System encounter model for the analysis of potential induced collisions
用於分析潛在誘發碰撞的基於有色Petri網的空中防撞系統遭遇模型
TCAS（The Traffic Alert and Collision Avoidance System）交通警報和防撞系統；
Encounter model遭遇模型；
State space狀態空間；
Potential collision scenario潛在碰撞場景；
Petri net Petri網.

2.摘要
The Traffic Alert and Collision Avoidance System (TCAS) is a world-wide accepted last-resort means of reducing the probability and frequency of mid-air collisions between aircraft. Unfortunately, it is widely known that in congested airspace, the use of the TCAS may actually lead to induced collisions. Therefore, further research regarding TCAS logic is required. In this paper, an encounter model is formalised to identify all of the potential collision scenarios that can be induced by a resolution advisory that was generated previously by the TCAS without considering the downstream consequences in the surrounding traffic. The existing encounter models focus on checking and validating the potential collisions between trajectories of a specific scenario. In contrast, the innovative approach described in this paper concentrates on quantitative analysis of the different induced collision scenarios that could be reached for a given initial trajectory and a rough specification of the surrounding traffic. This approach provides valuable information at the operational level. Furthermore, the proposed encounter model can be used as a test-bed to evaluate future TCAS logic changes to mitigate potential induced collisions in hot spot volumes. In addition, the encounter model is described by means of the coloured Petri net (CPN) formalism. The resulting state space provides a deep understanding of the cause-and-effect relationship that each TCAS action proposed to avoid an actual collision with a potential new collision in the surrounding traffic. Quantitative simulation results are conducted to validate the proposed encounter model, and the resulting collision scenarios are summarised as valuable information for future air traffic management (ATM) systems.

交通警報和防撞系統（TCAS）是一種世界範圍內公認的降低飛機之間空中碰撞概率和頻率的最終手段。不幸的是，眾所周知，在擁擠的空域中，使用TCAS實際上可能導致誘導碰撞。因此，需要對TCAS邏輯進行進一步的研究。在本文中，遭遇模型被正式化，以識別所有可能發生碰撞的場景，這些場景可能是由TCAS生成的未考慮周圍交通下游後果的解決方案引起的。現有的遭遇模型專注於檢查和驗證特定場景的軌跡之間的潛在碰撞。相比之下，本文描述的創新方法集中於對給定的初始軌跡和周圍交通的粗略規程可能產生的不同誘發碰撞場景的定量分析。這種方法在操作層面提供了有價值的資訊。此外，所提出的遭遇模型可以用作評估未來TCAS邏輯變化的測試平臺，以減輕熱點區域中潛在的誘導碰撞。此外，採用有色Petri網（CPN）描述了遭遇模型。結果狀態空間提供了對因果關係的深刻理解，每個TCAS動作都建議採用這種因果關係來避免實際碰撞與周圍交通中潛在的新碰撞。定量模擬結果驗證了所提出的遭遇模型，並將碰撞場景總結為未來空中交通管理（ATM）系統中有價值的資訊。

3.創新點、學術價值
A mathematical model for the TCAS II algorithm was developed to be potentially used in a TCAS-TCAS encounter. TCAS II provides TAs to warn pilots of the encounter with neighbouring traffic and RAs to prevent a collision by offering a suggested resolution manoeuvre to pilots to execute an avoidance manoeuvre in the vertical direction. Using a series of mathematical equations, this CA process has been conceptually described. The process has also been used as the theoretical basis for construction of the encounter model.
（1）開發了TCAS II演算法的數學模型，可在TCAS-TCAS遭遇中使用。TCAS II提供交通諮詢（TAs）來警告飛行員與鄰近交通的相遇，向飛行員提供決議諮詢（RAs）執行垂直方向上的迴避策略來避免碰撞。利用一系列數學方程，對CA（collision avoidance）過程進行了概念性描述。該過程也被用作構建遭遇模型的理論基礎。
A novel scenario generation process of potential collisions was proposed. The only input of this model is the aircraft trajectory and the number of intruder aircraft, while the inputs of most other encounter models (Netjasov et al., 2013; Kochenderfer et al., 2010; Billingsley et al.,2009; Tang et al., 2014) are the initial states (e.g., trajectories) of all involved aircraft for the analysis of particular traffic geometries. In contrast, the proposed model presented in this paper aims to generate the potential collision scenarios for a certain number of aircraft, based on the trajectory of just one instance representative aircraft, rather than to test whether a multi-aircraft scenario contains a potential collision or not. The generated encounter scenarios may not be credible within the normal operation of the ATC system, as some of them are designed through the use of different cruising flight levels.
（2）提出了一種新的潛在碰撞場景生成過程。該模型的唯一輸入是飛機的軌跡和入侵飛機的數量，而其他大多數遭遇模型的輸入是所有相關飛機的初始狀態（例如，軌跡），用於分析特定的交通幾何形狀。相比之下，本文提出的模型旨在根據一架典型飛機的飛行軌跡，生成一定數量的潛在碰撞場景，而不是測試一個多飛機的場景是否包含潛在的碰撞。在ATC系統的正常執行中，所生成的遭遇情景可能並不可信，因為其中一些情景是通過使用不同的巡航飛行高度而設計的。
The encounter model is represented in the CPN formalism. This causal model depicts the procedure that takes an aircraft with a known initial state into various induced collision scenarios containing multiple TCAS-equipped aircraft. With the state space, the model provides a better understanding of the potential collision occurrences for risk assessment by comprehending the cause-effect relationship of each action. The initial states of multiple aircraft that are involved in the scenarios can be generated one by one. Finally, all of the possible situations (state space) can be represented for subsequent analysis to summarise the typical induced collision scenarios.
（3）遭遇模型用CPN形式表示。該因果模型描述了將具有已知初始狀態的飛機帶入包含多個裝有TCAS的飛機的各種誘發的碰撞場景的過程。在狀態空間中，該模型通過理解每個動作的因果關係，可以更好地理解潛在的碰撞事件，以進行風險評估。可以逐個生成參與場景的多架飛機的初始狀態。最後，所有可能的情況（狀態空間）都可以表示出來，以便進行後續分析，總結出典型的誘導碰撞場景。
A summary is provided of the typical induced collision scenarios based on the simulation results of the causal model. Quantitative measurement experiments were conducted to validate the feasibility and effectiveness of the encounter model. In addition, for scenarios involving three or four aircraft (representative of almost all of the factual situations), the detailed process of a collision and the typical scenarios were illustrated and described in detail.
（4）根據因果模型的模擬結果，總結了典型的誘導碰撞場景。進行定量測量實驗以驗證遭遇模型的可行性和有效性。此外，對於涉及三架或四架飛機的情況（代表幾乎所有的實際情況），詳細說明和描述了碰撞的詳細過程和典型情況。

4.對結論的理解和對學習工作的啟發
TCAS旨在直接向飛行員提供最終的避撞指南，長期的實踐經驗證明了TCAS的實用性和效率。然而， 即使在所有涉及的飛機都裝有TCAS的情況下，也可能在特殊情況下發生碰撞。當涉及多架飛機時，TCAS實際上會引發一場原本不會發生的碰撞，尤其是在周圍交通密集的情況下。公共領域缺乏因果模型來描述可能引發誘導碰撞的周圍交通場景；此類場景可用於比較實際交通場景，以降低碰撞頻率。開發這個因果模型的動機是為了識別TCAS誘發的碰撞，並支援對當前和先進的ATM概念（包括TCAS）進行安全分析的後續研究。

未來研究計劃：
（1）開發模式識別工具以識別可能存在潛在誘發碰撞的交通場景；
（2）利用所提出的因果模型來促進當前TCAS邏輯的改進，其目的是通過增強CA效能來解決未來繁忙和擁擠的交通問題。