Research On Access Selection Algorithm In Heterogeneous Wireless Integrated Networks

Heterogeneous Wireless Networks (HWNs) are expected to be the trends of next generation wireless network, which can meet users'demand mostly. It needs to select an access network to provide Always Best Connected (ABC) anytime and anywhere in the multi-layer networks. There are two main problems on access selection algorithm in the prior literatures. Firstly, there is a short of effective study in weight factors, which describes the importance of the attributes. Secondly, it is hard to evaluate the creditability of network services. In order to solve these problems, this dissertation is devoted to research on the access selection algorithm in HWNs. Based on the known access selection algorithms, the dissertation presents a new access selection model, and proposes two access selection algorithms on the basis of the model. The main achievements of this dissertation are as follows:1. An access selection model based on the relative closeness of grey relation (RCGR) is presented. Taking multiple attribute decision making (MADM) for reference, the decision attribute set is defined and normalized to sort the candidate networks with RCGR which provides the theoretical foundation of research for access selection algorithms.2. An access selection algorithm based on combined weight (ASBCW) is proposed. The ASBCW mostly improves the weight factors, and achieves the global consistence of subjective and objective weight factors for decision making through combination optimization, in which the subjective weight reflects the user's demands and the objective weight reflects the difference of candidate networks performance. Simulation results show that the algorithm could attain higher average throughput and smaller transmission delay, and improve the accuracy of access selection.3. An access selection algorithm based on network trustworthiness (ASBNT) is proposed. Based on the study on service creditability, this dissertation presents an access selection mechanism based on trustworthiness and a dynamic trust model based on entity credibility (DTMBC). Then, trustworthiness-weighted decision-making attributes are applied to the access selection model which decreases the probability of unreliable service for users. Finally, an ameliorative trust model with Pre-selection mechanism named Pre-DTMBC is proposed to decrease the delay induced by DTMBC, which improves the efficiency of ASBNT.