A study on the load reduction of the emergency multi-system access method in mobile cellular systems during large-scale disasters

摘要

When a massive disaster occurs, the traffic on communication systems increases suddenly and dramatically because people want to check on their families and friends in the stricken area. In this situation, cellular phones are very useful communication tools because of their portability. However, many calls are blocked because increasing the capacity of mobile systems is difficult due to limited radio-frequency resources. Therefore, we proposed a method for emergency multi-system access(EMSA), in which, during heavy call demand, cellular phone users are permitted access not only to their own system but also to any other cellular phone systems. The EMSA method increased users that could access a cellular system but it also increased the total access load in the whole system. For the purpose of the reduction of this access load, in this paper, we propose EMSA with Fixed Access (EMSA-FA) method. In this method, users can access only the system which is assigned by their own system. We estimate the EMSA-FA performance in a macro (PDC) and micro (PHS) overlay cell structure through computer simulations. The simulations showed that the EMSA-FA method yields higher blocking rate than the EMSA but it decreases the access load in the whole system. They also showed that the appropriate system assignment ratio in the EMSA-FA method varies with the number of micro-cells overlaid by macro-cells.