Research And Simulation Of RoF System Dynamic Load Balancing Strategy

With the rapid development of mobile communication, more and more bandwidth is needed. In order to meet this requirement, RoF (Radio over Fiber) technology has recently been researched widely in wireless communication systems. This technology has the advantages of broad coverage, high data rate transmission capability, low power consumption and interference. However, system overload is easily caused by the special network structure of RoF system. The load balancing and QoS guarantee for RoF system are emphatically studied in this thesis.First, a preventive load balancing strategy is proposed to reduce the system handoff frequency, avoid the system overload. On the basis of the structure characteristics of RoF system such as microcell, high speed environment, multiple distributed antenna etc, RoF network model and RoF cell group handoff are discussed. According to the mobility model and system load conditions, formula of normalization sojourn time predication and estimation are deduced. Then the size of the RoF cell group is set to adaptive adjust by the sojourn time threshold. Second, in order to ensure that the system would be restored from overload with a minimum load transfer price, a restorative load balancing strategy is studied. A function of load transfer cost is discussed. Genetic algorithm is used to realize the RoF cell group selection for load transfer, this part stresses the issue of improving on the chromosome decoding and genetic algorithm termination etc.Furthermore, this thesis compared several RoF cell group size adjustment methods. Also, the performances of genetic algorithm and restorative load balancing strategy are assessment by experiment. Simulation results demonstrate that the dynamic load balancing scheme can gain the lowest number of handoffs, call dropping probability (CDP) and call blocking probability (CBP) both in normal RoF system and overload RoF system, and the load is balanced.