Method of selecting a cell to connect by radio with a mobile station and a mobile communications terminal therefor

• US 7,171,232 B2
• Filed: 12/15/2004
• Issued: 01/30/2007
• Est. Priority Date: 01/30/2004
• Status: Expired due to Fees

• Current Assignee: LAPIS Semiconductor Co., Ltd. (ROHM Co., Ltd.)
• Original Assignee: OKI Electric Industry Company Limited
• Inventors: Akahori, Hiroji, Atsumi, Tsuyoshi
• Primary Examiner(s): Eng; George
• Assistant Examiner(s): Bhattacharya; Sam
• Application Number:
  US11/011,081
• Publication Number:
  US 20050170857A1
• Time in Patent Office: 776 Days
• Field of Search: 455/445, 455/446, 455/450, 455/62, 455/513, 455/522, 455/517, 455/524, 455/525, 455436-439, 370/294, 370/320, 370/350, 375/294, 375/304, 375/344, 375/350, 375/498
• US Class Current: 455/525
• CPC Class Codes: H04B 1/7083 Cell search, e.g. using a three-step approach
• CPC Class Codes: H04W 48/20 Selecting an access point

Abstract

A mobile communications system includes an RF processor for transmitting and receiving radio signals to and from a base station, and a base-band processor for spread-spectrum coding a frame signal to be transmitted to transfer it to the RF processor and spread-spectrum decoding a signal transferred from the RF processor to extract a frame signal. The base-band processor includes a rake receiver for demodulating the received signal and a cell selector and processor for selecting a cell to be connected based upon the propagation path and the power of the received signal. The cell selector and processor includes a search circuit for detecting a cell from the received signal, a cell operator for determining a cell from which received is a signal associated with a shorter propagation path, based on the reception timing of the received signal, and a connecting cell selector for selecting a cell to be connected.

Claims

1. A method of selecting a cell formed by a base station to which a mobile station is to be connected, comprising the steps of:

preparing a mobile communications system having a plurality of cells formed by a corresponding plurality of base stations and a mobile station travelable in a radio service area covered by the plurality of cells to communicate by radio with one of the plurality of base stations;

detecting a first reception timing of a signal received from a first one of the plurality of cells by the mobile station and a second reception timing of a signal received a from second one of the plurality of cells by the mobile station;

calculating a first absolute value of a difference between the first reception timing and the second reception timing, and a second absolute value obtained by subtracting the second reception timing from the first reception timing plus a period of time corresponding to a length of a time slot;

determining a cell from which the signal was received and with which a shorter propagation path is associated, based on a magnitude relation between the first absolute value and the second absolute value calculated; and

selecting the determined cell as the cell to which the mobile station is to be connected.

2. The method in accordance with claim 1, further comprising the step of connecting by radio the mobile station to the base station forming the selected cell.

3. The method in accordance with claim 1, wherein, when the mobile station is located commonly in at least two of the plurality of cells, a cell is selected which is associated with a shorter propagation path of the received signal than a cell associated with the received signal having a higher reception power.

4. The method in accordance with claim 1, wherein the signals transmitted from the base stations in the first and second cells are not synchronous with each other, said method further comprising the steps of:

estimating, when synchronization is not established between the first and second cells, a time offset between the first and second cells;

correcting the first and second reception timings of the received signals based on the estimated time offset; and

using the corrected reception timings to calculate the first and second absolute values.

5. A mobile communications terminal travelable in a radio service area covered by a plurality of cells formed by a corresponding plurality of base stations for selecting one of the plurality of cells which is formed by a base station to be connected, comprising:

a transmitter/receiver for transmitting and receiving a radio signal to and from any of the plurality of base stations; and

a base-band processor for spread-spectrum coding frame signal to be transmitted to deliver the coded frame signal to said transmitter/receiver, and spread-spectrum decoding the signal received by said transmitter/receiver to then extract the frame signal,

said base-band processor comprising;

a signal receiver for demodulating the received signal; and

a cell selecting and processing circuit for selecting a cell to be connected on a basis of a propagation path associated with the received signal and an electric power of the received signal,

said cell selecting and processing circuit comprising;

a detector for generating a time slot to detect a reception timing of the received signal, and for detecting a first reception timing of a signal transmitted from a first one of the plurality of cells and a second reception timing of a signal transmitted from a second one of the plurality of cells;

a cell operator for calculating a first absolute value of a difference between the first reception timing and the second reception timing, and a second absolute value obtained by subtracting the second reception timing from the first reception timing plus a period of time corresponding to a length of the time slot to determine a cell from which the signal was received and which is associated with a shorter propagation path, based on the magnitude relation between the first absolute value and the second absolute value; and

a correlator for determining correlation of the received signals to calculate the electric power of the received signal.

6. The terminal in accordance with claim 5, wherein the signals transmitted from the base stations in the first and second cells are not synchronous with each other,

said cell operator estimating, when synchronization is not established between the first and second cells, a time offset between the first and second cells, correcting the first and second reception timings of the received signals based on the estimated time offset, and using the corrected reception timings to calculate the first and second absolute values.