Kazunori Okada

Limiting the Holding Time Considering Emergency Calls in Mobile Cellular Phone Systems during Disasters

During devastating natural disasters, numerous people want to make calls to check on their families and friends in the stricken areas, but many call attempts on mobile cellular systems are blocked due to limited radio frequency resources. To reduce call blocking and enable as many people as possible to access mobile cellular systems, placing a limit on the holding time for each call has been studied [1], [2]. However, during a catastrophe, emergency calls, e.g., calls to fire, ambulance, or police services are also highly likely to increase and it is important that the holding time for these calls is not limited. A method of limiting call holding time to make provision for emergency calls while considering the needs of ordinary callers is proposed. In this method, called the HTL-E method, all calls are classified as emergency calls or other according to the numbers that are dialed or the terminal numbers that are given in advance to the particular terminals making emergency calls, and only the holding time of other calls is limited. The performance characteristics of the HTL-E method were evaluated using computer simulations. The results showed that it reduced the rates of blocking and forced call termination at handover considerably, without reducing the holding time for emergency calls. The blocking rate was almost equal for emergency and other calls. In addition, the HTL-E method handles fluctuations in the demand for emergency calls flexibly. A simple method of estimating the holding-time limit for other calls, which reduces the blocking rate for emergency and other calls to the normal rate for periods of increased call demand is also presented. The calculated results produced by this method agreed well with the simulation results.

Spectrum efficiency of sectorization for distributed dynamic channel assignment in cellular systems

This paper investigates the performance of distributed dynamic channel assignment (DDCA) strategies in sector cell layout systems using directional antennas. Simulations are done under the same propagation conditions and with the same system parameters. They show that DDCA strategies in sector cell layout systems gain 2.3/spl sim/8.2 times higher capacity than do the fixed channel assignment (FCA) strategy in conventional cellular systems using omnidirectional antennas and 1.5/spl sim/2.5 times higher than do DDCA strategies in conventional systems.

Dynamic channel assignment using a channel framework for traffic congestion in a highway micro cellular system

Traffic congestion often occurs on highways and results in a heavy call traffic load that impairs the performance of dynamic channel assignment (DCA) strategies. The authors therefore propose a channel framework in which all the available channels are divided into two subsets according to the directions in which the mobile stations move. The decision of the division ratio depends on the offered load of each direction. The authors investigate, through simulations, DCA performances with channel framework for one-sided and both-sided traffic congestion and compare these performances with that of DCA without the framework. They show that the channel framework increases call blocking but considerably reduces the occurrence of forced call termination and of channel changing during a call.