# 论文概况

Cooperative vehicle collision warning system is made possi- ble by recent progress in advanced positioning systems and wireless com- munication technology. In this paper we report our work in developing a cooperative intersection collision warning system that is not limited by the requirement of line-of-sight. The novel elements of the system include the use of a dynamic ad hoc wireless network for peer-to-peer data sharing, a new intersection collision warning algorithm, and a flexible and extensible software architecture and system design. The very same system is also ca- pable of collision warning for other scenarios such as frontal and rear-end. Further, the tunable parameters in the algorithm make it possible for the system to adapt to the preference and capability of each individual driver.

# 背景讨论

intersection collisions 不如 forward collision 受重视，因为更复杂，以及雷达的硬件水平限制。

# intersection collisions 碰撞模型

top-down 的设计了 specification

## Top-Level ICWS Specification

ICWS 是 Intersection Collision Warning System 的缩写

1. At most one warning is given at one intersection.
2. No warning if there is no route contention.
3. No warning if the driver has already taken appropriate action.

## 两车相碰的数学描述

the expected path intersection $(x_+, y_+)$ 计算方法如下：

\begin{align}
x_+ &= \frac {(y_2 −y_1)−(x_2 \tan \theta_2 −x_1 \tan \theta_1) } {\tan \theta_1 - \tan \theta_2} \\
y_+ &= \frac {(x_2 − x_1)−(y_2 \cot\theta_2 −y_1 \cot\theta_1)} {\cot\theta_1 − \cot\theta_2}
\end{align}

\begin{align}
\text{TTX}_1 &= \frac {| \vec r_+ - \vec r_1 | } { | \vec v_1 | } \mathrm{sign} ((\vec r_+ - \vec r_1) \cdot \vec v_1) \\
\text{TTX}_2 &= \frac {| \vec r_+ - \vec r_2 | } { | \vec v_2 | } \mathrm{sign} ((\vec r_+ - \vec r_2) \cdot \vec v_2)
\end{align}

$$\text{TTC}_i = \begin{cases} \text{TTX}_i \quad & \text{if there is a route contention}\\ \text{Undefined} \quad & \text{otherwise} \end{cases}$$

$$| TTX_1 - TTX_2 | < \alpha$$

## time to avoidance(TTA)

1. 车辆已采取规避措施
2. 距离 TTC 时间还远（见前面 ICWS specification 第 4 条）

# 总结

1. ICWS Specification 和 CWS Algorithm 是非常有意义的工作。
2. 这是一篇比较有实操意义的作弊神器，insight 一般。
3. 文章有一半篇幅讨论用 GPS 作为车车通信，解决 line of sight 问题。不是我关注的内容，未整理到笔记里。
4. 虽然笔记给出了详细公式和推导过程，但仅供参考，落地的时候，照着原文抄更安全。