Method and system for controlling forward transmit power in a wireless system

• US 6,496,531 B1
• Filed: 09/02/1999
• Issued: 12/17/2002
• Est. Priority Date: 09/02/1999
• Status: Expired due to Term

• Current Assignee: WSOU Investments, LLC (WSOU Holdings, LLC)
• Original Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: Wu, Xiao Cheng, Weaver, Carl Francis, Meyers, Martin Howard, Kuo, Wen-Yi, Kamel, Raafat Edward
• Primary Examiner(s): Pham, Chi
• Assistant Examiner(s): Bayard, Emmanuel
• Application Number:
  US09/389,080
• Time in Patent Office: 1,202 Days
• Field of Search: 375/220, 375/222, 375/130, 375/219, 455/69, 455/450, 455/452, 455/442, 455/522, 370/331, 370/332
• US Class Current: 375/130
• CPC Class Codes: H04W 52/12 Outer and inner loops
• CPC Class Codes: H04W 52/146 Uplink power control
• CPC Class Codes: H04W 52/40 during macro-diversity or soft handoff
• CPC Class Codes: H04W 52/50 at the moment of starting communication in a multiple access environment

Abstract

A method and system for controlling down link transmit power during a soft hand-off in a spread-spectrum wireless system supports independent power control of multiple forward channels to reduce fading. For a soft hand-off, a mobile switching center determines if a forward control channel is transmitted from different sectors of base stations than a forward data channel is. The base stations preferably adjust transmit powers of the forward channels grouped into different physical channels by receiving power control data over the allocated reverse power control channels to compensate for fading of the forward channels during a soft hand-off.

Claims

1. A method for controlling downlink transmit power in a wireless system, the method comprising:

instructing allocation of multiple reverse power control channels if a forward control channel serving a mobile station is transmitted from a different set of sectors than a forward data channel of the mobile station, the forward data channel associated with the forward control channel, and if base stations associated with the forward control channel are participating in a soft hand-off of the forward control channel; and

adjusting transmit powers of the forward channels based on the reverse power control channels associated with the forward channels.

2. The method according to claim 1 wherein the instructing step comprises determining if active control sectors of the forward control channel are different in number from at least one active data sector of the forward data channel participating in the soft hand-off.

3. The method according to claim 1 wherein the instructing step comprises determining if active control sectors of the forward control channel are different in identity from at least one active data sector of the forward data channel participating in the soft hand-off.

4. The method according to claim 1 wherein the instructing step comprises determining a number of the reverse power control channels based on a total number of different forward physical channels, each forward physical channel associated with at least one corresponding pilot code representing one of said sectors.

5. The method according to claim 1 wherein the adjusting step comprises adjusting the transmit power of the data channel independently from the transmit power of the control channel serving the mobile station during the soft hand-off.

6. The method according to claim 1 wherein the instructing step comprises instructing multiple reverse power control channels over separate channels, each separate channel defined by bit robbing to provide a channel with a transmission capacity of 400 bits per second to 800 bits per second to compensate for fading.

7. The method according to claim 1 wherein the instructing step comprises instructing multiple reverse power control channels over separate channels, each separate channel defined by bit robbing from a reverse pilot channel.

8. The method according to claim 1 wherein the adjusting step further comprises the step of:

maintaining multiple inner-loop power control schemes to control the forward transmit power of different base stations participating in the soft hand-off of the mobile station.

9. A method for controlling downlink transmit power in a wireless system, the method comprising:

instructing the allocation of multiple reverse power control channels if a forward control channel is transmitted in association with a different set of pilot code offsets than a forward data channel, associated with the forward control channel, and if base stations associated with the forward control channel are participating in a soft hand-off; and

determining a number of the reverse power control channels based on a total number of distinct physical channels associated with the different sets of pilot code offsets of the forward channels, where the physical channels are realized by the base stations.

10. The method according to claim 9 wherein the instructing step further comprises defining different sets of pilot code offsets, including a full set of pilot code offsets and at least one reduced set, with a lesser number of pilot code offsets than the full set, for participation in the soft hand-off.

11. The method according to claim 9 wherein the determining step comprises requiring at least two power control channels if the forward control channel is simulcasted and associated with a full set of pilot code offsets and if the data channel is associated with a reduced set, with a lesser number of pilot code offsets than the full set.

12. The method according to claim 9 wherein determining step comprises requiring at least three power control channels if the forward control channel is simulcasted and associated with a full set of pilot code offsets, if a first data channel is associated with first reduced set, and if a second data channel is associated with a second reduced set having at least one different constituent pilot code offset from the first reduced set.

13. The method according to claim 9 further comprising the steps of:

receiving different physical downlink channels associated with corresponding distinct pilot sets of the pilot code offsets serving the mobile station during the soft hand-off;

allocating a target signal parameter value associated with each distinct pilot set of pilot code offsets received at the mobile station;

measuring a received signal parameter at the mobile station during the soft hand-off for each distinct pilot set of pilot code offsets;

comparing the measured signal parameter to the target signal parameter value for each distinct pilot set of pilot code offsets; and

transmitting power adjustment data over the multiple power control channels based on the comparison between the target signal parameter value and its corresponding measured signal parameter value for each distinct pilot set.

14. The method according to claim 9 further comprising determining a number of reverse power control channels based on a total number of distinct physical channels associated with corresponding distinct sets of pilot code offsets, where the physical channels are associated with a plurality of base stations participating in the same soft hand-off.

15. The method according to claim 14 wherein the physical channels include a data physical channel for the data channel and a control physical channel for the control channel.

16. A method for controlling downlink transmit power in a spread-spectrum wireless system, the method comprising:

determining if a new pilot channel is to be added to service a forward control channel for a mobile station;

placing the forward control channel in a soft hand-off mode and determining whether an affiliated forward data channel, affiliated with the control channel, is placed into the soft hand-off mode;

receiving at least one reverse power control channel for the control channel and its affiliated data channel; and

adjusting the forward transmit powers of the forward channels based on any distinct pilot sets of pilot codes by sending power control data over the at least one of the reverse power control channels.

17. The method according to claim 16 wherein the determination of whether the data channel is placed into the soft hand-off mode is based upon available channel capacity at base stations participating in the soft hand-off mode for the mobile station.

18. The method according to claim 16 wherein the determination whether a data channel is placed into the soft hand-off mode is based upon an interference reduction goal of using a lesser number base stations for the forward data channel than a simulcasted control channel participating in the soft hand-off mode.

19. The method according to claim 16 further comprising the step of:

opting the data channel out of the soft hand-off mode and reestablishing the data channel after the soft hand-off mode terminates for the mobile station.

20. The method according to claim 16 further comprising the step of:

re-establishing the data channel when an active set size equals one after the soft hand-off mode of the mobile station.

21. The method according to claim 16 wherein the determining step comprises providing the new pilot channel to service the control channel based on measured signal parameters of a neighbor set at the mobile station.

22. A communications system for controlling downlink transmit power, the communications system comprising:

a switching center for determining if a forward control channel serving a mobile station, the forward control channel being affiliated with a forward data channel of the mobile station, is participating in a soft hand-off;

a receiver of a base station for receiving at least one reverse power control channel based on a total number of distinct pilot sets of pilot codes associated with said forward channels;

a downlink power controller of the base station for adjusting the forward transmit powers of any of the distinct pilot sets of pilot codes independently by sending power control data over the at least one of the power control channels to compensate for fading of the forward channels.

23. The system according to claim 22 further comprising:

a receiver of the base station for receiving data relating to multiple inner-loop power control schemes to control the forward transmit power of the base station participating in the soft hand-off of the mobile station.

24. The system according to claim 22 wherein the downlink power controller is adapted to adjust the forward transmit powers of the base station on an active set-by-active set basis for each of the pilot sets.

25. A wireless communications system for controlling downlink transmit power comprising:

a switching center for determining whether a forward data channel serving a mobile station is to be placed into a soft hand-off mode upon placement of a forward control channel in a soft hand-off mode, the forward control channel being a forward control channel of the mobile station and being affiliated with the forward data channel;

a receiver for receiving at least one reverse power control channel for the control channel and its affiliated data channel; and

a power controller of a base station for adjusting the forward transmit powers of the forward channels based on distinct pilot sets of pilot codes by receiving power control data over the at least one of the reverse power control channel to compensate for fading of the forward channels.

26. The system according to claim 25 wherein the switching center is adapted to determine whether the data channel is placed into the soft hand-off mode based upon available channel capacity at base stations participating in the soft hand-off mode for the mobile station.

27. The system according to claim 25 wherein the switching center adapted to determine whether a data channel is placed into the soft hand-off mode is based upon an interference reduction goal of using a lesser number base stations for the forward data channel than for a simulcasted forward control channel participating in the soft hand-off mode.

28. The system according to claim 25 further comprising:

memory associated with the switching center for storing packet data messages associated with opting the data channel out of the soft hand-off mode and reestablishing the data channel after the soft hand-off mode terminates for the mobile station.

29. The system according to claim 25 wherein the switching center determines whether to add a new pilot channel to service the control channel and engage in the soft hand-off mode based on measured signal parameters of a neighbor set at the mobile station.

30. A mobile station for controlling downlink transmit power during a soft hand-off:

a measurer for determining at least one relatively strong pilot channel for a forward data channel and a forward control channel during a soft hand-off;

a processor for establishing multiple power control channels based on a total number of distinct pilot sets of pilot codes associated with the forward channels;

a transceiver for sending power control data over the established multiple power control channels to compensate for fading of the downlink signal.

31. The mobile station according to claim 30 wherein the distinct pilot sets include a control pilot set for the forward control channel and a data pilot set for the forward data channel, wherein the control pilot set and the data pilot set each contain a different number of pseudo-random noise code offsets.

32. The mobile station according to claim 30 wherein the distinct pilot sets include a control pilot set for the forward control channel and a data pilot set for the forward data channel, wherein the control pilot set and the data pilot set each contain a different identity of pseudo-random noise code offsets.