I Introduction
The heterogeneous wireless network is an open communication system, where various access networks will be integrated to provide an optimum service at anytime from anywhere. However, it also brings some new challenges for security. The traditional access control mechanisms have been proven inadequate and inflexible for the heterogeneous network which is governed by uncertainty. Among the networks, some might be honest and provide high-quality services, some might be buggy and can not provide services with the quality that they advertise, some might be even malicious by providing bad services. Transaction of the user with an unknown network is more a norm than an exception. A security mechanism employed a satisfactory trust model that can effectively evaluate trustworthiness of the network becomes more and more necessary.