1. Field of the Invention
The present invention relates to a land mobile communication system constituted by two independent systems such as a macro-cellular system represented by a car telephone and a micro-cellular system represented by a cordless telephone. More particularly, the present invention relates to a constitution of a radio control channel for integrating these two systems and to a method of estimating the moving speed of a mobile station.
2. Description of the Related Art
Recent mobile land communication systems are classified into two large groups as described in for example "THIRD GENERATION WIRELESS INFORMATION NETWORKS", ISBN 0-7923-9218-3, published by Kluwer Academic Publishers, pages 12 and 13. One group is cellular car telephone systems having a macro cell structure for users moving rapidly. The other group is cordless telephone systems having a micro cell structure for users moving slowly.
In the cellular land mobile communication systems, each cell is constituted by a macro cell having a large radius of about half to several kilometers. The communication between a base station of the macro cell and a mobile station (terminal) located within this macro cell is executed via a radio link with a high transmitting power about several to several hundreds watt. Thus, such the mobile station consumes large power causing the life period of its battery to be limited to short, for example less than one day. Furthermore, since the size of the cell is large, the distance between the cells using the same frequency (co-interference distance) has to be large causing the number of subscribers capable of simultaneous communication to be reduced in comparison with that in the micro-cellular systems. However, as each macro cell covers relatively large area, the number of handovers will be reduced. This is advantageous for the rapidly moving mobile station.
On the other hand, in the cordless telephone systems, each cell is constituted by a micro cell having a small radius of about several tens to one hundred meters. Thus, the distance between the cells using the same frequency (co-interference distance) has to be short causing the number of subscribers capable of simultaneous communication to be increased in comparison with that In the macro-cellular systems. Since the cell size is small, the communication between a base station of the micro cell and a mobile station located within this micro cell can be executed via a radio link with a low transmitting power of about several milliwatt. Therefore, the battery life of the mobile station will last long for example one week. However, as each micro cell covers relatively small area, handover will frequently occur for the rapidly moving mobile station resulting the control to extremely complicate. Thus, these micro-cellular systems will be utilized only for mobile terminals moving at a low speed such as walking speed.
As aforementioned, the cellular mobile communication system using macro cells and the cordless telephone system using micro cells have both advantages and problems. Namely, the cellular mobile communication system has an advantage of being used in the user moving rapidly, but has problems of low spectrum efficiency and of short battery life. The cordless telephone system has advantages of high spectrum efficiency and of long battery life, but has a problem of being used only in the user moving slowly.
In order to access both the cellular mobile communication system and the cordless telephone system to obtain the above-mentioned advantages of each of the systems, since these systems are constituted by two independent systems, the user must use two different mobile terminals.