Research On Radio Resource Management Technology In Heterogeneous Wireless System

With the rapid development of wireless communications, the various wireless networks will coexist. In order to relize the final goal of future wireless communications, accommodate mobile users increased enormously and offer multimedia traffic services with high quality, different wireless networks overlaid each other must be integrated to cooperate and form an uniform heterogeneous system. The radio resource management is a key technology and a research hotspot in the heterogeneous system. It includes many sub-areas such as call access control, handoff control, layer selection, load control, power control, packet schedule, capacity analysis and so on. The call access control (CAC) of bidirectional call-overflow, handoff, load control and others are emphatically studied in this thesis.Firstly, various call-overflow schmems in the heterogeneous hierarchical wireless system are analysed with uniform theory. On the basis of real mobile model builded, the control method of bidirectional call-overflow is improved, the speed of call and size of cell are considered simultaneously. Simulation results show that the improved call-overflow scheme can gain maximum channel utilization, the lowest blocking probability of new calls and dropping probability of handoff calls.On the basis of making the best of call-overflow scheme, a handoff strategy based on guard channel, queuing and channel preemption is proposed. Simulation results show that compared with the scheme of only guard channel adopted and the scheme of both guard channel and queuing used, the proposed handoff scheme can dramatically decrease the dropping probabilities of fast and slow real-time traffic, and guarantee the performance of fast and slow nonreal-time handoff traffic.In order to decrease the call blocking probability (CBP) and call dropping probability (CDP), heighten the utilization of overall heterogeneous system, the load control is researched and several load balancing algorithms are proposed.A load balancing scheme based on traffic selection is proposed for the heterogeneous wireless system composed of same layer wireless networks, in which non-periodical load control mechanism of half-centralization and half-distribution is employed. For the sake of QoS guaranteed, only nonreal-time traffic are selected to transfer. A handoff signal strength threshold for transfer is set to avoid ping-pong handoff. Simulation results show that the CBP and CDP are greatly decreased, system utilization is also enhanced.For the heterogeneous hierarchical syetem, three load balancing algorithms based on sojourn time are proposed. A model is used to calculate the cell sojourn time. The first algorithm is called load balancing algorithm based on sojourn time, only one call can be selected to transfer from overloaded cell to under-loaded cell overlaid per load balancing period. This algorithm has lower CBP and CDP than those of random selection algorithm.The second is a dynamic load balancing algorithm, in which the number of transferred calls in a load balancing period is calculated according to call arrival rate and the workload states of overlaid cells with the hot spot cell. The second algorithm outperforms the first algorithm. The third algorithm is based on the second algorithm and considers the type of call service. Only nonreal-time traffic calls can be transferred in the third load balancing algorithm, so the handoff frequency of real-time traffic in the third algorithm is lower than those of other two load balancing algorithms.In order to further increase the channel utilization of hotspot cell system, a hybrid dynamic load balancing algorithm is proposed based on the combination of channel borrowing scheme and load transfer scheme. The hotspot cells can borrow channels from homogeneous cells with light workload in the compact pattern. At the same time, some ongoing calls can be transferred from hotspot cells into the overlapping heterogeneous cells with light workload according to certain conditions. The total number of channels borrowed and ongoing calls transferred per load balancing period is computed by the remainder available channels and new calls arrival rates of hotspot cell. Simulation results show that the proposed hybird dynamic load balancing algorithm can decrease CBP, CDP of hot-spot cell system and overall heterogeneous system, and the system utilization of overall heterogeneous system is increased accordingly.Finally, it concludes the dissertation briefly, and the future research work is indicated.