Access Selection And Call Admission Control In Heterogeneous Wireless Networks

As the technology of the third generation mobile communication (3G) slowly marches forward, device manufacturers and network operators have already started to do research on the key technologies of the fourth generation mobile communication system (4G). Among all the proposed mainstream resolving scenarios, the idea of multi-system integration and evolution is the most promising one. It is well accepted by both the industrial circles and the academic circles that 4G should be an open network environment-heterogeneous wireless networks (HWN), which can intelligently integrate the existing and the future radio access systems. In this dissertation, under the guidance of the coordinated radio resource management theory, the problems of access selection and call admission control in HWN are intensively studied. The contents of this work are listed as follows:In order to make full use of the trunking gain and the multi-radio access diversity gain in the HWN, the problem of centralized access selection is studied, which is modelled as an integer linear programming problem optimized to minimize the overall bandwidth occupation in the HWN. Two suboptimal solution algorithms are proposed, which greatly reduce the computational complexity of the optimal algorithm, i.e., the enumeration method. In comparison with the traditional load balancing algorithm, those two algorithms effectively enhance the network capacity and reduce the outage probability during access selection, at the cost of a slight increase in computational complexity.In order to keep the multi-mode mobile terminal (MT) always best connected (ABC) in the HWN, the problem of distributed access selection is studied in the second part. First, an adaptive battery-situation-aware access selection scheme is proposed for MTs with multiple active applications. In the proposed scheme, the weight factors in the cost function are dynamically adjusted according to the available battery energy, and the access selection behaviors of the different applications are adaptively coordinated according to the changing service requirement. As a result, a flexible tradeoff is realized between the satisfaction degree of bandwidth requirement and the battery lifetime. Then, an adaptive handoff time decision scheme is proposed to avoid the handoff synchronization effect, which greatly enhances the sensitivity of the handoff stability periodand reduces the unnecessary vertical handoffs.Call admission control (CAC) in the HWN is studied in the third part, aiming to coordinate the existing CAC schemes in the access systems, and provide seamless quality of service (QoS) to the inter-system roaming MTs. A seamless-QoS-oriented CAC scheme is proposed for an integrated cellular/WLAN network, in which the CAC problem is modelled as an optimization problem aiming to minimize the overall grade of service (GoS). Accordingly, the optimum numbers of guard channels and balance channels are determined under different traffic loads, which guarantees full use of the radio resource and seamless QoS at the same time.Integration of access selection and call admission control in a HWN made up of two soft capacity systems (based on the technologies of CDMA (Code Division Multiple Access) and OFDMA (Orthogonal Frequency Division Multiple Access) respectively) is studied in the fourth part. First, a receive power estimation algorithm and a transmit power estimation algorithm are proposed for the CDMA system and the OFDMA system respectively, in order to estimate the traffic load in these access systems dis-tributedly. Accordingly, a power threshold based call admission prediction algorithm and a transmit power based access selection algorithm are proposed. With the aid of distributed system load estimation, wise access selection decision is made in the MT, achieving a great improvement in resource utilization.