Method and apparatus for reducing the average transmit power from a sectorized base station

• US 5,864,760 A
• Filed: 06/20/1997
• Issued: 01/26/1999
• Est. Priority Date: 10/28/1993
• Status: Expired due to Term

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Gilhousen, Klein S., Padovani, Roberto
• Primary Examiner(s): Urban, Edward F.
• Application Number:
  US08/880,001
• Time in Patent Office: 585 Days
• Field of Search: 455/436, 455/442, 455/524, 455/525, 455/63, 455/562, 455/522, 455/69, 375/200, 375/205, 370/332, 370/334
• US Class Current: 455/442
• CPC Class Codes: H04B 7/0491 using two or more sectors, i.e. sector diversity
• CPC Class Codes: H04W 16/24 Cell structures
• CPC Class Codes: H04W 36/06 Reselecting a communication resource in the serving access point
• CPC Class Codes: H04W 36/18 for allowing seamless reselection, e.g. soft reselection
• CPC Class Codes: H04W 52/34 TPC management, i.e. sharing limited amount of power among users or channels or data types, e.g. cell loading
• CPC Class Codes: H04W 52/40 during macro-diversity or soft handoff

Abstract

A plurality of methods for achieving the softer handoff process such that the performance of a system is improved. A first method is based on delaying the softer handoff process. A second method is based on reducing the power of transmissions from the sector having the weakest signal strength. A third method is based on eliminating transmissions from the sector having the weakest signal strength. In all three methods, reverse link demodulation in each sector may continue with or without the transmission of the forward link. In all three methods the operation could be based on the signal strength of the reverse link signal or the forward link. It is also possible to combine two or more of these methods to create a hybrid method.

Claims

1. A method for improving the signal-to-interference ratio in a communication system having a set of base stations with at least one base station comprised of multiple sectors comprising the steps of:

communicating between a mobile unit and a first sector of said base station and simultaneously communicating between said mobile unit and a second sector of said base station, and combining a signal from said mobile unit received through said first sector with a signal from said mobile unit received through said second sector;

measuring signal strength of said signal from said mobile unit received through said first sector;

measuring signal strength of said signal from said mobile unit received through said second sector;

comparing the signal strength of said signal from said mobile unit received through said first sector and the signal strength of said signal from said mobile unit received through said second sector in order to identify the sector receiving the weakest signal of said signals from said mobile unit received through said first and said second sector; and

reducing signal strength of a signal from said identified sector to said mobile unit while continuing to combine signal energy from said mobile unit received through said first sector with signal energy from said mobile unit received through said second sector.

2. The method of claim 1 wherein said step of communicating between said mobile unit and said first sector of said base station includes the step of establishing bi-directional communication by both transmitting and receiving signal energy, and wherein the step of communicating between said mobile unit and said second sector of said base station includes the step of establishing bidirectional communication by both transmitting and receiving signal energy.

3. A method for reducing interference in a communication system having a base station comprised of multiple sectors comprising the steps of:

receiving through a first sector antenna of said base station a first signal from a mobile unit;

receiving through a second sector antenna of said base station a second signal from said mobile unit and combining said second signal with said first signal;

transmitting signal energy through said first sector antenna to said mobile unit and simultaneously transmitting signal energy through said second sector antenna to said mobile unit, thereby simultaneously communicating between said base station and said mobile unit through said first and second sector antennas;

measuring the signal strength of said first signal;

measuring the signal strength of said second signal and comparing the signal strength of said second signal to the signal strength of said first signal; and

terminating forward link information transmission from said base station to said mobile unit through said second sector antenna by ceasing transmission of said signal energy through said second sector antenna when the signal strength of said second signal is less than the signal strength of said first signal, said base station subsequently continuing to combine signal energy received from said mobile unit through said first and second sector antennas.

4. A method for reducing interference in a communication system having a base station comprised of multiple sectors comprising the steps of:

receiving through a first sector antenna of said base station a first signal from a mobile unit;

receiving through a second sector antenna of said base station a second signal from said mobile unit and combining said first signal and said second signal;

transmitting signal energy through said first sector antenna to said mobile unit and simultaneously transmitting signal energy through said second sector antenna to said mobile unit;

measuring the signal strength of said signal energy received from said first sector antenna at said mobile unit;

measuring the signal strength of said signal energy received from said second sector antenna at said mobile unit and comparing the signal strength of said signal energy received from said first and said second sector antennas; and

terminating forward link information transmission from said base station to said mobile unit through said second sector antenna by ceasing transmission of said signal energy therethrough when the signal strength of said signal energy received from said second sector antenna is less than the signal strength of said signal energy received from said first sector antenna, said base station continuing to combine signal energy received from said mobile unit through said first and second sector antennas subsequent to said ceasing of transmission of said signal energy through said second sector antenna.

5. A method for reducing interference in a communication system having a base station comprised of multiple sectors comprising the steps of:

communicating bi-directionally between a mobile unit and a first sector of said base station;

transmitting through an antenna of a second sector of said base station a pilot signal;

measuring, at said mobile unit, signal strength of said pilot signal from said antenna of said second sector of said base station and comparing said signal strength to a predefined threshold;

notifying by said mobile unit said base station through said first sector when said signal strength of said pilot signal from said antenna of said second sector exceeds said predefined threshold;

receiving through said antenna of said second sector of said base station a reverse link signal from said mobile unit and combining said reverse link signal with signal energy received from said mobile unit through said first sector; and

delaying transmission of a forward link signal from said second sector of said base station to said mobile unit until signal energy of said pilot signal received at said mobile unit through said second sector exceeds a second predefined threshold.

6. The method for reducing interference in a communication system of claim 5 further comprising the step of combining at said base station said reverse link signal from said mobile unit received through said second sector of said base station with a reverse link signal received through said first sector from said mobile unit to produce an aggregate signal independent of whether said step of transmitting said forward link signal has begun.

7. The method for reducing interference in a communication system of claim 6 further comprising the steps of:

creating a power control command for said mobile unit based on an energy level of said aggregate signal; and

transmitting said power control command to said mobile unit from said antenna of said first sector of said base station.

8. A method for reducing interference in a communication system having a base station comprised of multiple sectors comprising the steps of:

communicating bi-directionally between a mobile unit and a first sector of said base station;

transmitting through an antenna of a second sector of said base station a pilot signal;

measuring, at said mobile unit, signal strength of said pilot signal from said antenna of said second sector of said base station and comparing said signal strength to a predefined threshold;

notifying said base station through said first sector when said signal strength of said pilot signal from said antenna of said second sector exceeds said predefined threshold;

receiving through said antenna of said second sector of said base station a reverse link signal from said mobile unit and combining said reverse link signal with signal energy received from said mobile unit through said first sector; and

delaying transmission of a a forward link signal from said second sector of said base station to said mobile unit until signal energy of said reverse link signal received at said base station through said second sector exceeds a second predefined threshold.

9. The method for reducing interference in a communication system of claim 8 further comprising the step of combining at said base station said reverse link signal from said mobile unit received through said second sector of said base station with a reverse link signal received through said first sector from said mobile unit to produce an aggregate signal independent of whether said step of transmitting said forward link signal has begun.

10. The method for reducing interference in a communication of claim 9 further comprising the steps of:

creating a power control command for said mobile unit based on an energy level of said aggregate signal; and

transmitting said power control command to said mobile unit from said antenna of said first sector of said base station.

11. A method for improving the signal-to-interference ratio in a spread spectrum communication system having a set of base stations with at least one base station comprised of multiple sectors comprising the steps of:

receiving through a first sector antenna of said base station a first spread spectrum signal from said mobile unit;

receiving through a second sector antenna of said base station a second spread spectrum signal from said mobile unit;

combining said first and second spread spectrum signals in order to simultaneously establish communication between said base station and said mobile unit through said first and second sector antennas;

measuring the signal strength of said first spread spectrum signal;

measuring the signal strength of said second spread spectrum signal and comparing the signal strength of said second spread spectrum signal to the signal strength of said first spread spectrum signal; and

reducing a power level of a transmission from said base station to said mobile unit through said second sector antenna based on the signal strength of said second spread spectrum signal and the signal strength of said first spread spectrum signal and continuing to combine said first and second spread spectrum signals.

12. The method for improving the signal-to-interference ratio in a spread spectrum communication system of claim 11 wherein in said step of reducing, said transmission power is reduced to zero and said first and second spread spectrum signals are continued to be combined.

13. A method for improving the signal-to-interference ratio in a spread spectrum communication system having a set of base stations with at least one base station comprised of multiple sectors comprising the steps of:

receiving through a first sector antenna of said base station a first spread spectrum signal from said mobile unit;

receiving through a second sector antenna of said base station a second spread spectrum signal from said mobile unit;

combining said first and second spread spectrum signals in order to simultaneously establish communication between said base station and said mobile unit through said first and second sector antennas;

transmitting from said first sector antenna of said base station a signal;

transmitting from said second sector antenna of said base station a signal;

measuring the signal strength of said signal from said first sector at said mobile unit;

measuring the signal strength of said signal from said second sector at said mobile unit;

comparing the signal strength of said signal from said first sector to the signal strength of said signal from said second sector; and

reducing a power level of a transmission from said base station to said mobile unit through said second sector antenna based on the signal strength of said signal from said second sector and the signal strength of said signal from said first sectors and continuing to combine said first and second spread spectrum signals.

14. The method for improving the signal-to-interference ratio in a spread spectrum communication system of claim 13 wherein in said step of reducing, said transmission power is reduced to zero.

15. A method for improving the signal-to-interference ratio in a spread spectrum communication system having a set of base stations with at least one base station comprised of multiple sectors comprising the steps of:

receiving through a first sector antenna of said base station a first spread spectrum signal from said mobile unit;

receiving through a second sector antenna of said base station a second spread spectrum signal from said mobile unit;

combining said first and second spread spectrum signals in order to simultaneously establish spread spectrum communication between said base station and said mobile unit through said first and second sector antennas;

measuring the signal strength of said first spread spectrum signal;

measuring the signal strength of said second spread spectrum signal;

comparing the signal strength of said second spread spectrum signal to the signal strength of said first spread spectrum signal in order to identify the sector receiving the weakest one of said first and second spread spectrum signals; and

reducing signal strength of the spread spectrum signal from said identified sector to said mobile unit and continuing to combine said first and second spread spectrum signals.

16. A method for improving the signal-to-interference ratio in a communication system having a set of base stations with at least one base station comprised of multiple sectors comprising the steps of:

communicating between a mobile unit and a first sector of said base station and simultaneously communicating between said mobile unit and a second sector of said base station, and combining a signal from said mobile unit received through said first sector with a signal from said mobile unit received through said second sector;

measuring signal strength of a forward link signal from said first sector received at said mobile unit;

measuring signal strength of a forward link signal from said second sector received at said mobile unit;

comparing the signal strength of the signal from said first sector and the signal strength of the signal from said second sector in order to identify the sector providing the weakest signal; and

reducing signal strength of a signal from said identified sector to said mobile unit while continuing to combine signal energy from said mobile unit received through said first sector with signal energy from said mobile unit received through said second sector.