Handover method based upon channel quality

• US 5,649,290 A
• Filed: 12/14/1994
• Issued: 07/15/1997
• Est. Priority Date: 12/14/1994
• Status: Expired due to Term

• Current Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Original Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: Wang, Robert Chuenlin
• Primary Examiner(s): Urban, Edward F.
• Assistant Examiner(s): ARTHUR JEANGLAUDE, GERTRUDE
• Application Number:
  US08/355,890
• Time in Patent Office: 944 Days
• Field of Search: 455/33.1, 455/33.2, 455/34.1, 455/54.1, 455/54.2, 455/56.1, 455/58.2, 455/63, 455/34.2, 455/67.1, 455/67.3, 379/59, 379/60, 379/63
• US Class Current: 370/332
• CPC Class Codes: H04W 36/08 Reselecting an access point
• CPC Class Codes: H04W 36/302 due to low signal strength

Abstract

A method is disclosed for executing handovers in a cellular network, based upon channel quality measurements. For AMPS service, the method involves the monitoring of a supervisory audio tone (SAT) signal which is superimposed on the voice signal that is transmitted between base stations and mobile terminals traveling within a cellular network, and handovers are executed in dependence upon noise power measurements associated therewith. For TDMA service, the method involves the monitoring of a raw data signal associated with digital transmissions, and handovers are executed in dependence upon noise power measurements associated therewith.

Claims

1. A method for handing over an ongoing radio transmission of a mobile terminal traveling within a cellular network, said network having a plurality of adjoining cells each having a base station, and a multiplicity of channels, comprising the steps of:

handing over the ongoing radio transmission of a mobile terminal traveling in one of said plurality of cells to an idle channel in a target adjacent cell, said handing over including;

(i) determining whether to commence a handover in dependence upon at least a baseband noise power level measured by the base station in said one cell; and

(ii) selecting said target adjacent cell based upon a measurement of the baseband noise power of a supervisory audio tone (SAT) signal superimposed on a voice signal received by ones of a plurality of baseband signal processing units each associated with one of said base stations in the cellular network.

2. A method according to claim 2, wherein said step of handing over an ongoing radio transmission of a mobile terminal includes the step of selecting an idle channel having the highest baseband SAT noise power level in a selected target cell.

3. A method for handing over an ongoing radio transmission of a mobile terminal traveling within a cellular network, said network having a plurality of adjoining cells each having a base station, and a multiplicity of channels, comprising the steps of:

handing over the ongoing radio transmission of a mobile terminal traveling in one of said plurality of cells to an idle channel in an adjacent cell, said handing over including the step of measuring at least a baseband raw data noise power level associated with a digital voice/data signal generated in a time divisional multiple access (TDMA) system, said measuring being performed by the base station of said one cell to determine whether to hand over said radio transmission.

4. A method according to claim 3, wherein said step of handing over an ongoing radio transmission further involves a measurement of raw data signal power and wherein said raw data signal power and said raw data noise power are measured during a synchronization word interval in said TDMA system.

5. A method for handing over an ongoing radio transmission of a mobile terminal traveling within a cellular network, said network having a plurality of adjoining cells each having a base station, and a multiplicity of channels, comprising the steps of:

handing over the ongoing radio transmission of a mobile terminal traveling in one of said plurality of cells to an idle channel in an adjacent cell, said handing over including the step of measuring at least a raw data noise power associated with a digital voice/data signal generated in a time divisional multiple access (TDMA) system, said measuring being performed by the base station of said one cell to determine whether to hand over said radio transmission, and said handing over further including the step of selecting an idle channel having the highest raw data noise power level in a selected target cell.

6. A method of allocating channels to mobile terminals traveling within a cellular network having a plurality of adjoining cells, each of said cells having therein a base station and a multiplicity of channels for call allocation, each base station having a signal processing unit for generating and monitoring a baseband voice/data signal having a supervisory audio tone (SAT) superimposed thereon, said method comprising the steps of:

a) calculating the SAT signal power to SAT noise power ratio for an ongoing radio transmission between a mobile terminal and a base station;

b) determining whether the ratio between the SAT signal power and the SAT noise power is below a predetermined threshold value;

c) commanding each base station adjacent to the base station in communication with the mobile terminal to determine the SAT signal power to SAT noise power ratio for the mobile terminal;

d) selecting the adjacent cell having the highest determined SAT signal power to SAT noise power ratio as a target cell for receiving the ongoing radio transmission;

e) selecting an idle channel within the target cell having the highest SAT noise power; and

f) handing-over the ongoing radio transmission to the selected idle channel within the target cell.

7. A method of allocating channels to mobile terminals travelling within a cellular network having a plurality of adjoining cells, each of said cells having therein a base station and a multiplicity of channels for call allocation, each mobile terminal configured to transmit a digital voice/data signal in accordance with a time division multiple access system, the method comprising the steps of:

a) calculating the raw data signal power to raw data noise power ratio for an ongoing digital transmission between a mobile terminal and a base station during a synchronization word interval;

b) determining whether the raw data signal power to raw data noise power ratio is below a predetermined threshold value;

c) commanding each base station adjacent to the base station in communication with the mobile terminal to determine the raw data signal power to raw data noise power ratio for the mobile terminal;

d) selecting an adjacent cell having the highest determined raw data signal power to raw data noise power ratio as a target cell for receiving the ongoing radio transmission;

e) selecting an idle channel within the target cell having the highest raw data noise power; and

f) handing-over the ongoing radio transmission to the selected idle channel within the target cell.