Communication system employing multiple handoff criteria

• US 20030002460A1
• Filed: 06/29/2001
• Published: 01/02/2003
• Est. Priority Date: 06/29/2001
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: English, Sean
• Granted Patent: US 7,058,035 B2
• Time in Patent Office: Days
• US Class Current: 370/331
• CPC Class Codes: H04W 36/18 for allowing seamless reselection, e.g. soft reselection
• CPC Class Codes: H04W 72/542 using measured or perceived quality

Abstract

Disclosed herein is a communication system which manages guarantee of service (GOS) requirements for various users while efficiently managing backhaul network traffic and optimizing overall system capacity. In one aspect, armed handoff is used to transmit forward link data from a single base station to a particular mobile station as long as certain minimum requirements are met, such as minimum data throughput, minimum data rate, and GOS requirements. If these criteria are not met, soft and softer handoff can be employed to transmit forward link data from one or more base stations to a particular mobile station until the conditions for armed handoff are met. In another aspect, the test to add a base station sector to the active set differs based on whether other sectors of that base station already exist in the active set. The test is less stringent when a sector is not the first of its base station to enter the active set, and more stringent when it is the first.

Claims

1. A method for high speed data transmission from one or more base stations to a mobile station comprising:

measuring the quality of forward link signals from one or more base stations;

transmitting from one base station having the highest measured forward link signal quality to the mobile station during a time slot when that measured forward link signal quality meets certain criteria; and

transmitting from one or more base stations in soft handoff to the mobile station during a time slot when the highest measured forward link signal quality does not meet certain criteria.

2. The method of claim 1 wherein the quality of each forward link signal is determined by the received signal-to-noise-and-interference ratio (C/I).

3. The method of claim 2 wherein the criteria includes a minimum C/I corresponding to a minimum data rate.

4. The method of claim 2 wherein the criteria includes a guarantee of service requiring a minimum C/I.

5. The method of claim 3 wherein the criteria further includes a measure of system loading.

6. The method of claim 1 wherein the quality of each forward link signal is determined by the sustainable data rate.

7. The method of claim 6 wherein the criteria includes a minimum data rate.

8. The method of claim 6 wherein the criteria includes a guarantee of service requiring a minimum data rate.

9. The method of claim 6 wherein the criteria includes a statistical measure of data throughput.

10. The method of claim 9 wherein the statistical measure of data throughput is average throughput over a certain time duration.

11. The method of claim 7 wherein the criteria further includes a measure of system loading.

13. The method of claim 12 further comprising:

transmitting from the sector having the highest measured forward link signal quality to the mobile station during a time slot when that measured forward link signal quality meets certain criteria; and

transmitting from one or more sectors in soft handoff to the mobile station during a time slot when the highest measured forward link signal quality does not meet certain criteria.

14. The method of claim 12 wherein the higher threshold is determined by adding a minimum marginal improvement factor to the quality of forward link signals from the sectors currently in the active set.

15. The method of claim 12 wherein the lower threshold is determined by adding a minimum marginal improvement factor to the quality of forward link signals from the sectors currently in the active set.

16. The method of claim 12 further comprising removing a sector from the active set when the forward link signal from that sector falls below a removal threshold.

17. The method of claim 16 wherein the removal threshold is the lower threshold when more than one sector from one base station are in the active set, and the removal threshold is the higher threshold when the sector is the only sector of its base station in the active set.

19. The method of claim 18 wherein the quality of each forward link signal is determined by the received signal-to-noise-and-interference ratio (C/I).

20. The method of claim 19 wherein the criterion is a C/I corresponding to a minimum sustainable data rate.

12. A method for high speed data transmission from one or more sectored base stations to a mobile station comprising:

measuring the quality of forward link signals from one or more sectors of one or more base stations;

adding one or more of the sectors of one or more base stations to an active set when the quality of the forward link signal from each sector exceeds a higher threshold; and

adding one or more of the sectors of one or more base stations to an active set when the quality of the forward link signal from each sector exceeds a lower threshold and at least one other sector of that sector'"'"'s base station is in the active set.

18. A method for high speed data transmission from one or more base stations to a mobile station comprising:

measuring the quality of forward link signals from one or more base stations;

selecting one base station according to the measured quality of forward link signals from one or more base stations;

when the measured quality of the forward link signal from the selected base station meets a criterion;

sending a data request message to the selected base station; and

transmitting data from the selected base station to the mobile station at a rate in accordance with the measured quality of the forward link signal from the selected base station; and

when the measured quality of the forward link signal from the selected base station does not meet a criterion;

selecting one or more additional base stations such that the combined quality of forward link signals of the first selected base station and the additional one or more base stations meets the criterion; and

transmitting data from the selected base station and the additional one or more base stations to the mobile station at a rate in accordance with the combined quality of the forward link signal from the selected and additional base stations.

21. A communications system, comprising:

a plurality of base stations which transmit respective pilots and respective code channels comprising a forward traffic channel;

a mobile station which has the plurality of base stations assigned to an active set thereof, comprising;

a diversity receiver which measures respective signal qualities of the pilots;

a processor which produces a signal quality standard, prepares a message directing one of the base stations to transmit data on its respective forward traffic channel when the quality of the pilot of the one base station equals or surpasses the standard, and prepares a message directing more than one base station to transmit data simultaneously on their respective forward traffic channels when the quality of a single pilot of any of the base stations does not equal or surpass the standard; and

a transmitter which transmits the message to the system controller via the plurality of base stations;

a system controller communicatively connected to the plurality of base stations and maintaining data queues for the mobile station'"'"'s forward traffic data in those base stations contained in the mobile station'"'"'s active set;

wherein the one base station receives, and transmits in response to, a message directing the one base station to transmit data from its data queue on its respective forward traffic channel; and

wherein the system controller receives a message directing more than one base station to transmit data simultaneously on their respective forward traffic channels and directs the respective base stations accordingly.

22. A system controller, communicatively connected to a plurality of base stations and a mobile station, comprising:

a processor for maintaining data queues for the mobile station'"'"'s forward traffic data in those base stations contained in the mobile station'"'"'s active set; and

wherein the system controller receives a message directing more than one base station to transmit data simultaneously on their respective forward traffic channels and directs the respective base stations accordingly.

23. A base station, communicatively connected to a base station controller, a plurality of other base stations, and one or more mobile stations, comprising:

a transmitter for transmitting pilots and code channels comprising a forward traffic channel; and

a receiver for receiving messages from a mobile station;

wherein the base station receives, and transmits in response, to a message directing it to transmit data on its forward traffic channel;

wherein the base station receives from a mobile station and delivers to the base station controller a message directing more than one base station to transmit simultaneously on their respective forward traffic channels; and

wherein the base station transmits accordingly under direction of the base station controller.

24. A mobile station which communicates with a plurality of base stations, the base stations communicatively connected to a base station controller, comprising:

a diversity receiver configured to measure respective signal qualities of the pilots;

a processor configured to produce a signal quality standard, prepare a message directing one of the base stations to transmit data on its respective forward traffic channel when the quality of the pilot of the one base station equals or surpasses the standard, and prepare a message directing more than one base station to transmit data simultaneously on their respective forward traffic channels when the quality of a single pilot of any of the base stations does not equal or surpass the standard; and

a transmitter configured to transmit the message to the system controller via the plurality of base stations.