In the next generation wireless communication systems, the need for high data rate will increase. Several kinds of data services will coexist and costumers will receive a service not only from a single system but also from a few systems. However, some problems exist in order to get served from several systems. Seamless communication should be possible between heterogeneous systems and also exact measurement must precede seamless communication.
A critical handoff criterion in horizontal handoff, the received signal strength (RSS), is not enough in heterogeneous environment because the standard for RSS is different for each system. Therefore, more components such as data rate, available bandwidth and pricing should be considered for handoff decision in heterogeneous circumstances. In this thesis, we deal with vertical handoff decision algorithm in heterogeneous environment.
First, we investigate how to evaluate the quality of different kinds of systems. We present utility function that provides a unifying measurement for any kind of system. We show superiority of our algorithm by comparing it with other existing schemes in terms of throughput and handoff rate.
Next, we consider the timing of a handoff after evaluating the utility of the systems. Due to the handoff delay and randomness of user distribution, deciding a handoff timing is quite complicated. We show that there is a tradeoff between throughput and handoff rate according to handoff timing. Also, adaptive handoff scheme relying on the direction of the handoff is introduced.
We propose a vertical handoff decision algorithm based on the utility function to maximize throughput. Simulation results show that the utility function resembles the RSS for switching and effectively increases throughput. Blocking rate and dropping rate are decreased by efficiently utilizing radio resource.