Downlink power control at soft handover

A cellular radio network, comprising:

• a first base station to communicate with a mobile station and to measure an uplink signal strength received by the first base station from the mobile station;
• a second base station to communicate with the mobile station and to measure a corresponding uplink signal strength received by the second base station from the mobile station;
• a mobile radio in simultaneous diversity communication with plural base stations and to measure a power level for downlink transmissions from the first base station to the mobile station and a power level for downlink transmissions from the second base station to the mobile station;
• and
• a radio network core to receive 1) the uplink signal strength received by the first base station from the mobile station, 2) the corresponding uplink signal strength received by the second base station from the mobile station, 3) the power level for downlink transmissions from the first base station to the mobile station, and 4) the power level for downlink transmissions from the second base station to the mobile station, to calculate 1) an uplink signal strength ratio equal to the measured uplink signal strength received by the first base station divided by the uplink signal strength received by the second base station and 2) a downlink power level ratio equal to the measured power level for downlink transmissions from the first base station divided by the measured power level for downlink transmissions from the second base station, and to compare the uplink signal strength ratio to the downlink power level ratio;
• wherein:
• if the uplink signal strength ratio substantially equals the downlink power level ratio, then the radio network core adapted to handover the mobile radio without adjusting the downlink power levels of the first or second base station;
• if the uplink signal strength ratio is greater than the downlink power level ratio, then the radio network core adapted to handover the mobile radio after reducing the downlink power from the second base station relative to the downlink power from the first base station;
• and
• if the uplink signal strength ratio is less than the downlink power level ratio, then the radio network core adapted to handover the mobile radio after increasing downlink power from the second base station relative to the downlink power from the first base station.

A method of controlling transmission power from first and second base stations involved in a soft diversity handover of a mobile radio, comprising the steps of:

• determining an uplink signal strength to interference ratio between the first base station and the mobile station;
• determining a corresponding uplink signal strength to interference ratio between the second base station and the mobile station;
• measuring a power level for downlink transmissions from the first base station to the mobile station;
• measuring a power level for downlink transmissions from the second base station to the mobile station;
• calculating an uplink signal strength ratio equal to the measured uplink signal strength to interference ratio at the first base station divided by the uplink signal strength to interference ratio at the second base station;
• calculating a downlink power level ratio equal to the measured power level for downlink transmissions from the first base station divided by the measured power level for downlink transmissions from the second base station;
• comparing the uplink signal strength ratio to the downlink power level ratio;
• and
• if the uplink signal strength ratio substantially equals the downlink power level ratio, then handing over the mobile radio without adjusting the downlink power levels of the first or second base station;
• if the uplink signal strength ratio is greater than the downlink power level ratio, then handing over the mobile radio after reducing the downlink power from the second base station relative to the downlink power from the first base station;
• and
• if the uplink signal strength ratio is less than the downlink power level ratio, then handing over the mobile radio after increasing downlink power from the second base station relative to the downlink power from the first base station.