Hybrid cellular radio communication system

• US 5,822,697 A
• Filed: 04/07/1997
• Issued: 10/13/1998
• Est. Priority Date: 06/05/1995
• Status: Expired due to Term

• Current Assignee: Hitachi America Limited (Hitachi, Ltd.)
• Original Assignee: Hitachi America Limited (Hitachi, Ltd.)
• Inventors: Matsuzawa, Naoto
• Primary Examiner(s): LE, THANH C
• Application Number:
  US08/834,560
• Time in Patent Office: 554 Days
• Field of Search: 455/422, 455/436, 455/437, 455/438, 455/439, 455/440, 455/443, 455/444, 455/450, 455/451, 455/452, 455/560, 370/329, 370/330, 370/331
• US Class Current: 455/443
• CPC Class Codes: H04W 36/04 Reselecting a cell layer in multi-layered cells

Abstract

A hybrid cellular mobile communication system is disclosed that contains a first layer having a plurality of radio communication micro-cells, and a second layer of radio communication cells of a larger size which, in operation, overlay the micro-cells. The hybrid cellular system provides that when a control switching center detects rapid amounts of micro-cell to micro-cell transfers of an ongoing call (such as when a call is occurring from a car moving on a highway), the call is transferred to the second cellular layer for handling. The second cellular layer includes cells which cover a larger geometric area, thereby reducing the number of "hand-offs" or transfers that the call would undergo when the mobile telephone user is traveling quickly across the geographic areas covered by the micro-cells.

Claims

1. A method of reducing the number of transfers of an ongoing call of a mobile telephone user between micro-cells of a cellular radio system, said cellular radio system having a first layer of micro-cells, a second layer of cells overlaying said micro-cells, wherein each cell covers the geographic area of a plurality of micro-cells and a centralized switching station having at least one register for storing data, said method comprising the steps of:

storing the micro-cell location of the mobile telephone user in the register;

changing the micro-cell location in the register after the mobile telephone user moves into another micro-cell and the transfer of the call between micro-cells is confirmed;

monitoring the frequency of the changes in the register for a predetermined time duration;

comparing the frequency of the changes in the register to a first predetermined threshold;

transferring the ongoing call from a micro-cell in the first layer to a cell in the second layer when the switching station determines that the frequency of the changes in the register for the predetermined time duration is greater than the first predetermined threshold;

wherein said transferring of the ongoing call between a micro-cell in the first layer and a cell in the second layer comprises altering the frequency of the ongoing call from a frequency associated with the micro-cell in the first layer to a new frequency associated with a cell in the second layer;

monitoring the time duration that a cell in the second layer is handling the ongoing call;

comparing the time that the ongoing call is handled by a cell in the second layer to a second predetermined threshold; and

transferring the ongoing call back to a micro-cell in the first layer when the switching station determines that the time that the ongoing call handled by a cell in the second layer is greater than the second predetermined threshold;

wherein said transferring of the ongoing call between a cell in the second layer and a microcell in the first layer comprises altering the frequency of the ongoing call from the frequency associated with the cell in the second layer to a frequency associated with a microcell in the first layer.

2. A method of reducing the number of transfers of an ongoing call of a mobile telephone user between micro-cells of a cellular radio system according to claim 1 further comprising the step of increasing the signal power of the ongoing call after the call is transferred from a micro-cell in the first layer to a cell in the second layer, and decreasing the signal power of the ongoing call after the call is transferred from a cell in the second layer to a micro-cell in the first layer.

3. A method of reducing the radio communications in a cellular radio communications system having a plurality of micro-cells to control the radio communications of a mobile telephone user, a plurality of cells overlaying the micro-cells, wherein each cell functions as a micro-cell and covers the geographic area of several adjacent micro-cells, and at least one switching station having a storage register for recording data indicative of the micro-cell or cell controlling the radio communications of the mobile telephone user, said method comprising the steps of:

recording in the register data indicative of the micro-cell controlling the radio communications of a mobile telephone user after a call connection is established;

updating the micro-cell location in the register only after the mobile telephone user has moved to another micro-cell and a micro-cell to micro-cell transfer of the radio communication for the mobile telephone user has been confirmed;

monitoring the number of confirmed micro-cell to micro-cell transfers for a preset time period, said time period being activated after the first micro-cell to micro-cell transfer has been completed;

changing the frequency of the radio communications of the mobile telephone user from a frequency used by the micro-cell controlling the radio communications to a new frequency used by a cell covering the area of the micro-cell when the switching station determines that the number of updates to the register exceeds a first preset threshold within the preset time period;

monitoring the time duration that a cell is controlling the radio communications of a call; and

changing the frequency of the radio communications of the mobile telephone user from a frequency used by the cell to a frequency used by the micro-cell when the switching station determines that the time that the call is controlled by a cell exceeds a second preset threshold.

4. A method of reducing the radio communications in a cellular radio communications system according to claim 3 further comprising the step of increasing the signal power of the call after the call is changed from a frequency used by the micro-cell to a frequency used by the cell.

5. A method of reducing the radio communications in a cellular radio communications system according to claim 3 further comprising the step of decreasing the signal power of a call after the call is changed from a frequency used by a cell to a frequency used by a micro-cell.

6. A method of reducing the radio communications in a cellular radio communications system according to claim 3 wherein the step of monitoring the frequency of changes in the register is activated after a first micro-cell to micro-cell call transfer has occurred.