High mobility is the essential feature of vehicular ad-hoc networks (VANETs), which however challenges the low cost and real-time security of the network. The concept of Trust Communication (TC) is proposed to address the issue. Following this concept, each vehicle gains a trust value depending on its performance of communication. Then, other vehicles choose to communicate with the vehicle owning a high enough trust value. In this way, the security of VANETs is improved with low cost and high timeliness, since the storage space and computing time are obviously reduced compared with traditional methods. However, how to allocate the trust value and how to make a trust communication method to adapt the complex scenario of VANETs are crucial and unsolved problems. In this paper, we make an in-depth investigation on the Trust Communication issue in VANETs. Firstly, we introduce the background of the Trust Problems in VANETs. Then, the most basic trust models for VANETs and a classification of these models are surveyed and discussed. Given the limitations of these basic models, we further present various improvement measures for each model. Finally, we discuss the performances of the trust models under various application scenarios. In particular, the suitable application scenario for each model and potential improvements are proposed.

高移动性是车载自组织网络（VANET）的基本特征，但是，这挑战了网络的低成本和实时安全性。信任沟通的概念建议（TC）解决此问题。遵循此概念，每辆车都将根据其通信性能获得信任值。然后，其他车辆选择与具有足够高的信任值的车辆进行通信。这样，与传统方法相比，由于显着减少了存储空间和计算时间，因此以低成本和高及时性提高了VANET的安全性。然而，如何分配信任值以及如何制定一种信任通信方法以适应VANET的复杂情况是至关重要且尚未解决的问题。在本文中，我们对VANET中的信任通信问题进行了深入研究。首先，我们介绍了VANET中信任问题的背景。然后，调查和讨论了VANET的最基本信任模型以及这些模型的分类。考虑到这些基本模型的局限性，我们进一步针对每种模型提出了各种改进措施。最后，我们讨论了各种应用场景下信任模型的性能。特别是，提出了每种模型的合适应用场景和潜在的改进。