Mobile communication system capable of performing soft-handover between base station controllers connected to different mobile communication exchanges

• US 6,574,475 B1
• Filed: 08/26/1999
• Issued: 06/03/2003
• Est. Priority Date: 08/26/1998
• Status: Expired due to Fees

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Suzuki, Takayuki
• Primary Examiner(s): NGUYEN, DAVID Q
• Assistant Examiner(s): Contee, Joy K.
• Application Number:
  US09/383,215
• Time in Patent Office: 1,377 Days
• Field of Search: 455/422, 455/432, 455/436, 455/442, 455/560, 455/561, 455/437, 455/438, 455/439, 455/440
• US Class Current: 455/438
• CPC Class Codes: H04W 36/12 Reselecting a serving backbone network switching or routing node
• CPC Class Codes: H04W 36/18 for allowing seamless reselection, e.g. soft reselection

Abstract

A mobile communication system comprises connection lines as communication lines and a control signal line for transmission/reception of a control signal between base station controllers. In soft-handover control sections arranged within the base station controllers, respectively, the connection lines are established with reference to received electric field strength at a mobile terminal. Switching sections arranged within the base station controllers, respectively, perform path-connection among the communication lines, the soft-handover control sections, a QCELP/PCM conversion section of communicating base station controller, the connection lines, and the control signal line.

Claims

1. A mobile communication system including a plurality of base stations including cells for being connected to through which a mobile terminal may be connected by radio, and a plurality of base station controllers connected between said base stations and a mobile exchange, said mobile communication system comprising:

control signal lines connected among said base station controllers operable to transmit control signals to perform soft-handover and to put corresponding base station controllers into a soft-handover state independent of said mobile exchange when said mobile terminal moves between cells; and

connection lines connected among said base station controllers operable to maintain communication between said mobile terminal and another terminal in the soft-handover state;

each of said base station controllers operable to maintain transmitting/receiving communication signals to/from said mobile exchange during the soft-handover state regardless of the location of said mobile terminal, when the communication starts through said mobile exchange.

2. A mobile communication system as claimed in claim 1, wherein said mobile communication system further comprises one or more other mobile exchanges, each of said base station controllers connected to any one of the mobile exchanges.

3. A mobile communication system as claimed in claim 1, said base stations broadcasting predetermined radio waves over said cells, respectively, said mobile terminal detecting the predetermined radio waves to produce a field strength report signal representative of the detected predetermined radio waves, wherein each of said base station controllers comprises:

a soft-handover control section for performing the soft-handover on the basis of the field strength report signal;

a conversion section for converting the communication signals between a first type which is for said base stations and a second type which is for said mobile exchange; and

a switching section connected to said soft-handover control section, said conversion section, predetermined ones of said base stations, predetermined ones of said connection lines of said base stations, and predetermined ones of said control signal lines for switching paths among them.

4. A mobile communication system as claimed in claim 3, wherein each said soft-handover control section establishes a plurality of connections on said connection lines connected among the base station controller including it and other base station controllers, on the basis of the field strength report signal.

5. A method of performing a soft-handover in a mobile communication system, said method comprising the steps of:

receiving at a first base station controller a field strength report signal transmitted by a mobile terminal which communicates with another terminal through said first base station controller;

establishing a connection on a connection line connected between said first base station controller and at least a second base station controller which is connected to a base station indicated by field strength report signal;

establishing a connection on at least two connection lines connected between a first mobile exchange and each of said first base station and said at least a second base station; and

maintaining communication with said mobile terminal through said first base station controller and said first mobile exchange throughout the soft-handover regardless of which base station in said mobile communication system said mobile terminal communicates with.

6. A method as claimed in claim 5, wherein the step of establishing a connection includes a step of establishing a plurality of connections on connection lines according to a plurality of base stations indicated by the field strength report signal.

7. A mobile communication system including first and second base stations having first and second cells adjacent to each other, respectively, through which a mobile terminal may be connected by radio, and first and second base station controllers connected to said first and said second base stations, respectively, which in turn connect said first and said second base stations with a first mobile exchange, said mobile terminal operable to transmit and receive communication signals to/from another terminal through said first base station, said first base station controller, and said first mobile exchange when said mobile terminal is located in the first cell, said mobile communication system comprising:

a control signal line connected between said first base station controller and said second base station controller for performing soft-handover between said first base station controller and said second base station controller independent of said first mobile exchange to put said first base and said second base station controllers into a soft-handover state when said mobile terminal moves from said first cell to said second cell; and

a connection line connected between said first base station controller and said second base station controller for operable to transmit the communication signals between said first base station controller and said second base station controller in the soft-handover state in order to maintain communication through said first base station controller and said first mobile exchange.

8. A mobile communication system as claimed in claim 7, wherein said second base station controller is connected to a second mobile exchange different from said first mobile exchange instead of said first mobile exchange.

9. A mobile communication system as claimed in claim 7, said first and said second base stations periodically broadcasting predetermined radio waves, said mobile terminal detecting electric field strength of the predetermined radio waves to produce a field strength report signal representative of said electric field strength, wherein each of said first and said second base station controllers comprises:

a soft-handover control section for performing the soft-handover on the basis of the field strength report signal;

a conversion section for converting the communication signals between a first type which is for said first and said second base stations and a second type which is for said first mobile exchange; and

a switching section connected to said soft-handover control section, said conversion section, one of said first and said second base stations, said connection line, and said control signal line for switching paths among them.

10. A mobile communication system has including a plurality of mobile terminals, a plurality of base stations each of which includes a cell through which each of said mobile terminals may be connected by a radio communication wave, a plurality of base station controllers each of which is connected to predetermined ones of said plurality of base stations through communication lines operable to carry out transmission and reception of control signals, speech signals, and data signals to and from said predetermined ones of said base stations through said communication lines, a mobile communication exchange which is connected to each of said base station controllers through a communication line and which is operable to control an exchanging operation with said base station controllers, and a system operable to perform soft-handover between one of said plurality of base station controllers when one of said mobile terminals is moved between two cells, said mobile communication system comprising:

a connection line as a communication line and a control signal line for transmission of control signals both of which are connected between said base station controllers; and

said system operable to perform soft-handover operative to maintain communication between said one of said plurality of mobile terminals, a particular one of said plurality of base station controllers in communication with said one of said plurality of mobile terminals just prior to the time when such mobile terminal is moved between two cells and said mobile communication exchange throughout the soft-handover process.

11. A mobile communication system as claimed in claim 10, each of said base station controllers comprising:

a soft-handover control section which establishes said connection line in response to a received electric field strength at said mobile terminal;

a QCELP/PCM conversion section for synthesizing QCELP signals from the speech signals and the data signals transmitted/received to and from said mobile terminal via said base station to produce a synthesized signal and converting the synthesized signal into a PCM signal; and

a switching section for path-connection between a particular one of said plurality of communication lines connected to a particular predetermined one of said plurality of base stations, said soft-handover control section, said QCELP/PCM conversion section, said connection line, and said control signal line;

said soft-handover control section being connected to another soft-handover control section in another one of said plurality of base station controllers through said switching section and said control signal line.

12. A mobile communication system as claimed in claim 11, said mobile communication system further comprising one or more other connection lines as communication lines which are connected between said base station controllers, wherein said soft-handover control section establishes a plurality of connection lines to one of said base station controllers connected to particular ones of said plurality of base stations which have transmitted the radio waves received at a particular one of said mobile terminals with high levels of electric field strength.

13. A soft-handover processing method in a mobile communication system claimed in claim 12, the method comprising the steps of:

measuring at said particular one of said plurality of mobile terminals the received electric field strength of the radio waves transmitted from said particular ones of said plurality of base stations;

reporting the result of the measurement to a particular one of said base station controllers through a particular communicating base station; and

establishing, in response to said result of the measurement, a plurality of connection lines between base station controllers connected to said particular ones of said plurality of base stations which have transmitted radio waves received at said particular one of said plurality of mobile terminals with high levels of electric field strength.

14. A soft-handover processing method as claimed in claim 13, the method further comprising the steps of:

reporting, to said particular one of said base station controllers, said result of the measurement together with identification codes given to the base stations which have transmitted radio waves received at said particular one of said plurality of mobile terminals with high levels of electric field strength;

establishing, with reference to said result of the measurement and the identification codes, a plurality of connection lines between the base station controllers connected to the particular ones of said plurality of base stations which have transmitted radio waves received at said particular one of said plurality of mobile terminals with high levels of electric field strength.

15. A recording medium containing said soft-handover processing method claimed in claim 14.