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

• US 6,157,668 A
• Filed: 09/30/1994
• Issued: 12/05/2000
• 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): Bocure, Tesfaldet
• Application Number:
  US08/316,155
• Time in Patent Office: 2,258 Days
• Field of Search: 375/205, 375/130, 375/140, 375/141, 379/59, 379/60, 455/33, 455/436, 455/437, 455/438, 455/442, 455/439, 37/331, 37/332, 37/333, 37/334, 37/335, 37/342
• US Class Current: 375/130
• 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 36/20 for optimising the interference level
• CPC Class Codes: H04W 52/24 using SIR [Signal to Interference Ratio] or other wireless path parameters
• 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 soft or 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. A fourth method adds a new base station or sector only when the mobile unit is in need of additional power to operate properly. In all four methods, reverse link demodulation in each sector may continue with or without the transmission of the forward link. In all four 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. In a spread spectrum communication system in which a mobile user communicates with another user via at least one base station in a system of base stations as directed by a system controller, a method for directing communications between said mobile unit user and said system of base stations comprising the steps of:

communicating by said mobile unit with a first base station wherein said first base station has an entry on a first list stored in said mobile unit wherein said first list comprises an entry for each of the one or more base stations in active communication with said mobile unit;

measuring at said mobile unit signal strength transmitted by a second base station through which active communication is not established;

providing by said mobile unit to said system controller a measured signal strength of said first base station and said measured signal strength of said second base station; and

comparing at said system controller said measured signal strength of said first base station to a desired operating power and sending said mobile unit a new first list comprising said second base station if said measured signal strength of said first base station is less than said desired operating power and said mobile unit is not in communication with any other base station.

2. The method of claim 1 wherein each base station in said system of base stations transmits a pilot signal and wherein said measured signal strength of said second base station is a measurement of signal strength of said pilot signal transmitted by said second base station.

3. The method of claim 1 further comprising the steps of:

communicating by said mobile unit simultaneously with said first and a third base station wherein said third base station has an entry on said first list;

providing by said mobile to said system controller a measured signal strength of said third base station wherein said measured signal strength of said third base station is less than said measured spinal strength of said first base station;

summing at said system controller said measured signal strength of said first base station and said measured signal strength of said third base station; and

comparing said summed measured signal strength of said first and third base stations to said desired operating power and sending said mobile unit a new first list comprising an entry corresponding to said second base station if said summed measured signal strength of said first and third base stations is less than said desired operating power.

4. The method of claim 1 further comprising the steps of:

communicating by said mobile unit with a third base station wherein said third base station has an entry on said first list;

providing by said mobile unit to said system controller a measurement of signal strength of said third base station wherein said measured signal strength of said third base station is less than said measured signal strength of said first and second base stations; and

sending said mobile unit a new first list comprising an entry corresponding to said second base station if said measured signal strength of said first base station is less than said desired operating power.

5. The method of claim 4 wherein said measured signal strength of said third base station is less than said measured signal strength of said first and second base stations by a predetermined threshold amount.

6. The method of claim 4 further comprising the steps of:

summing at said system controller said measured signal strength of said first base station and said measured signal strength of said second base station; and

sending said mobile unit a new first list comprising an entry corresponding to said third base station only if said sum of said measured signal strengths of said first and second base stations is less than said desired operating power.

7. The method of claim 1 wherein said first base station and said second base stations are two different sectors of a common base station cell site.

8. The method of claim 1 wherein said first base station is a multisectored base station and wherein said measured signal strength of said first base station corresponds to a signal strength from a single sector thereof.

9. The method of claim 1 wherein said step of providing by said mobile unit to said system controller said measured signal strength of said first base station and said measured signal strength of said second base station is performed because said measured signal strength of said second base station exceeds said measured signal strength of said first base station.

10. The method of claim 1 wherein said step of providing by said mobile unit to said system controller said measured signal strength of said first base station and said measured signal strength of said second base station is performed periodically at a variable rate.

11. The method of claim 10 wherein said variable rate is a function of a rate at which of frame errors occur.

12. The method of claim 1 wherein said step of providing by said mobile unit to said system controller said measured signal strength of said first base station and said measured signal strength of said second base station is performed in response to a request from said system controller.

13. The method of claim 1 wherein said step of providing by said mobile unit to said system controller said measured signal strength of said first base station and said measured signal strength of said second base station is performed because said measured signal strength of said second base station exceeds a predetermined threshold.

14. The method of claim 1 further comprising the step of receiving and demodulating at said second base station an information signal transmitted by said mobile unit independent of whether said second base station has an entry on said first list or said new first list.

15. In a spread spectrum communication system in which a mobile user communicates with another system user via at least one base station in a system of base stations as directed by a system controller, a method for directing communications between said mobile unit user and said system of base stations comprising the steps of:

communicating by said mobile unit with a first base station wherein said first base station has an entry on a first list stored in said mobile unit wherein said first list comprises an entry for each of the one or more base stations in active communication with said mobile unit;

measuring at said mobile unit signal strength transmitted by a second base station during communication by said mobile unit with said first base station;

comparing said measured signal strength of said second base station to a first predetermined level;

providing by said mobile unit to said system controller a measurement of signal strength of said first base station and said second base station if said measured signal strength of the second base station exceeds said first predetermined level; and

comparing at said system controller said measured signal strength of said first base station to a desired operating power and sending said mobile unit a new list comprising said second base station if said measured signal strength of said first base station is less than said desired operating power and said mobile unit is not in communication with any other base station.

16. In a spread spectrum communication system in which a mobile unit user communicates with another system user via at least one base station in a system of base stations as directed by a system controller, a method for directing communications between said mobile unit user and said system of base stations comprising the steps of:

communicating by said mobile unit with a first base station wherein said first base station has an entry on a first list stored in said mobile unit wherein said first list comprises an entry for each of the one or more base stations in active communication with said mobile unit;

measuring, during communication by said mobile unit with said first base station, at said mobile unit a communication quality index corresponding to a second base station wherein said second base station does not have an entry on said first list;

providing by said mobile unit to said system controller a measured quality index of said first base station and said measured quality index of said second base station; and

comparing at said system controller said measured quality index of said first base station to a desired operating power and sending said mobile unit a new list comprising an entry for said second base station if said measured signal strength of said first base station does not meet said desired operating index.

17. The method of claim 16 wherein said measured quality index of said first and second base stations is a frame erasure rate.

18. The method of claim 16 wherein said measured quality index of said first and second base stations is a signal to noise ratio.

19. The method of claim 16 wherein said measured quality index of said first and second base stations is a bit error rate.