| With updating wireless access technologies and emerging new services, wireless communication systems are rapidly developed. Overall, the development contains single system evolution and multiple systems integration. Single system evolution comprises smooth transition or innovation and multiple systems integration are heterogeneous networks. For both the single system and the multiple systems, radio resource management plays an important role. And access control is the foundation of radio resources management. Excellent random access control methods ensure successful user access.Based on the random access control methods, the OFDMA system is considered in the single system and heterogeneous networks is focused on in the multiple systems. Firstly, these two systems are introduced, and then research status about the random access control methods is further described, including some common algorithms. Lastly, this thesis is presented random access methods combinating with the characteristics of OFDMA system, heterogeneous systems and M2M services, respectively. The main contribution of this thesis is as followsFor TDD/OFDMA system, an access method and a backoff strategy are presented based on the pseudo-Bayesian algorithm. The characteristics of OFDMA system are considered in them. The access method includes adaptive random access channels allocation strategy and dynamical access probability algorithm. The adaptive access random access allocation strategy dynamically configures the number of random access channels according to the load of OFDMA system. The dynamical access probability algorithm adjusts the access user probability based on the adaptive random access channels allocation strategy. Hence, the successful access rate is improved. The backoff strategy is also based on the load of OFDMA system. According to the comparison between the number of access users and the number of random access channels, the suitable backoff method is selected. Therefore, the average delay of access users is effectively reduced.For M2M service, the diversion access strategy is presented in heterogeneous environment. Combined with the characteristics of M2M service, it is divided into multiple sub-streams in different networks. Firstly, the access point is set to receive the data from the M2M devices and connect the multiple networks in the network model. And then the economics conception that includes the benefits and the costs is introduced. Based on it, the utility function model is configured using the queuing theory model analysis. The function is modeled as a nonlinear programming problem with equality and inequality constraints and solved by Lagrange multipliers method and KKT method. Finally, the results are got and proved excellent. Considered the M2M service features, the strategy maximize the utility.In heterogeneous networks, the load balancing access strategy is presented basd on multiply terminals. The strategy is consisted of two aspects. One is the access selection mechanism; the other is access control mechanism. The access selection mechanism is mainly to solve the terminals problem that is "how to select the network". The multiple properties that are considered by terminals are into a dimension in space. And then through the improved AHP method, we get the real vector and the target vector based on the multiple properties. According to the two vectors, the set of terminal’access networks is obtained. The access control mechanism is to solve the problem that is "which network to access". The terminal is assigned to the appropriate network by the network side based on the load balancing principle. In this strategy, both the terminal side and the network side are considered. It improves the QoS of terminal. Meanwhile, it makes the heterogeneous networks access more terminals.Finally, conclusions and future work are summarized at the end of this thesis... |
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