Method and apparatus for mitigating power-control error during a soft handoff in a wireless communication system
A plurality of base stations (600) are programmed (702) with a uniform power-control bit pattern to be sent to a mobile unit during a plurality of power-control bit times, before the mobile unit is acquired on a reverse link. The plurality of base stations are further arranged and programmed to synchronize (704) transmissions of the uniform power-control bit pattern such that the plurality of base stations, when transmitting, send identical power-control bits during each of the plurality of power-control bit times.
This invention relates in general to wireless communication systems, and more specifically to a method and apparatus for mitigating power-control errors during a soft handoff in a wireless communication system.
BACKGROUND OF THE INVENTIONPrior-art wireless communication systems have employed a special “slow-power-up” power control technique to prevent power spikes on the reverse channel from the mobile unit to the base station during the initiation of a call and during a handoff. Recently, “soft” handoffs have become increasingly popular, because of the advantages they can provide. In a soft handoff, the mobile unit initially monitors more than one base station simultaneously in order to facilitate a handoff to the base station that can provide the best signal quality.
Unfortunately, monitoring more than one prior-art base station can result in conflicting power-control information being sent to the mobile unit, sometimes causing the mobile unit to decrease power when, in fact, all the monitored base stations are signaling the mobile unit to increase power!
Thus, what is needed is a method and apparatus for mitigating power-control errors during a soft handoff in a wireless communication system.
BRIEF DESCRIPTION OF THE DRAWINGSThe accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views and which together with the detailed description below are incorporated in and form part of the specification, serve to further illustrate various embodiments and to explain various principles and advantages in accordance with the present invention.
In overview, the present disclosure concerns wireless communication systems that provide service for communications units or more specifically a user thereof operating therein. More particularly, various inventive concepts and principles embodied as a method and apparatus for mitigating power-control errors during a soft handoff in a wireless communication system for use in equipment with such communications systems will be discussed and disclosed. The communications systems of particular interest are those being deployed and developed such as CDMA (Code Division Multiple Access), W-CDMA (Wideband-CDMA), CDMA2000, 2.5G (Generation), 3G, UMTS (Universal Mobile Telecommunications Services) systems and evolutions thereof that utilize spread spectrum signals, although the concepts and principles have application in other systems and devices as well.
The instant disclosure is provided to further explain in an enabling fashion the best modes of making and using various embodiments in accordance with the present invention. The disclosure is further offered to enhance an understanding and appreciation for the inventive principles and advantages thereof, rather than to limit in any manner the invention. The invention is defined solely by the appended claims including any amendments made during the pendency of this application and all equivalents of those claims as issued.
It is further understood that the use of relational terms, if any, such as first and second, top and bottom, and the like are used solely to distinguish one from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions.
Much of the inventive functionality and many of the inventive principles are best implemented with or in one or more conventional processors, or with integrated circuits (ICs) such as custom or application specific ICs. It is expected that one of ordinary skill, notwithstanding possibly significant effort and many design choices motivated by, for example, available time, current technology, and economic considerations, when guided by the concepts and principles disclosed herein will be readily capable of programming such processors, or generating such ICs with minimal experimentation. Therefore, in the interest of brevity and minimization of any risk of obscuring the principles and concepts according to the present invention, further discussion of such processors and ICs, if any, will be limited to the essentials with respect to the principles and concepts employed by the preferred embodiments.
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It is worth noting that, in the prior-art system 100, the exact structure of the power-control bit sequence can be selected by the system operator. For example, one system operator may choose to use a power-control bit sequence exactly like the exemplary power-control bit sequence 200, while another system operator may choose to move the two pairs 202, 204 of consecutive power-up bits to a different location in the frame, while yet another system operator may choose a faster power-up sequence that uses two pairs of three consecutive power-up bits, and so on. Further complicating the issue, some systems use a power-control bit sequence that is longer than one frame, and thus does not repeat in every frame. These differences can cause operational difficulties during soft handoff, as will be explained next.
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It will be appreciated that, in yet another embodiment, a power-control bit sequence can require more than a single transmission frame of the forward link from the base station to the mobile unit before the pattern repeats. In that embodiment, timing the transmissions comprises synchronizing the transmissions from each of the base stations attempting to communicate with the mobile unit such that the transmissions start at substantially identical times.
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In addition, the base station 600 includes a memory element 608 coupled to the processor 604 for storing software instructions for programming or for execution by the processor 604 in accordance with the present invention. The memory element 608 comprises a uniform power-control bit pattern 612 to be sent by different ones of a plurality of base stations to the mobile unit during a plurality of power-control bit times, before the mobile unit is acquired on a reverse link. The memory element 608 also includes a synchronization program 614 for programming the processor 604 to cooperate with the synchronizer 606 to synchronize the transmissions. In addition, the memory element 608 includes a conventional communications program 616 for programming the processor 604 to control the communications of the base station 600 in accordance with the protocol employed by the base station 600.
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In one embodiment, programming the plurality of base stations with the uniform power-control bit pattern comprises programming a pattern that requires more than a single transmission frame of a forward link from a base station to the mobile unit before the pattern repeats. In that embodiment, timing the transmissions comprises synchronizing the transmissions from each of the plurality of base stations such that the transmissions start at substantially identical times.
In another embodiment, programming the plurality of base stations with the uniform power-control bit pattern comprises programming a pattern that repeats after a single one of a plurality of transmission frames of a forward link from the base station to the mobile unit, and timing the transmissions comprises starting the transmissions at substantially identical points within different ones of the plurality of transmission frames.
In yet another embodiment, programming the plurality of base stations with the uniform power-control bit pattern comprises programming a pattern that repeats after a single one of a plurality of transmission frames of a forward link from the base station to the mobile unit, and timing the transmissions comprises starting the transmissions at substantially identical points within a specific one of the plurality of transmission frames.
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Thus, it should be clear from the preceding disclosure that the present invention provides a method and apparatus for mitigating power-control errors during a soft handoff in a wireless communication system. The method and apparatus advantageously is simple to implement in the base stations.
This disclosure is intended to explain how to fashion and use various embodiments in accordance with the invention rather than to limit the true, intended, and fair scope and spirit thereof. The foregoing description is not intended to be exhaustive or to limit the invention to the precise form disclosed. Modifications or variations are possible in light of the above teachings. The embodiments were chosen and described to provide the best illustration of the principles of the invention and its practical application, and to enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims, as may be amended during the pendency of this application for patent, and all equivalents thereof, when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.
Claims
1. A method in a wireless communication system for mitigating power-control errors during a soft handoff of a mobile unit, the method comprising:
- programming a plurality of base stations with a uniform power-control bit pattern to be sent to the mobile unit during a plurality of power-control bit times, before the mobile unit is acquired on a reverse link; and
- timing transmissions of the uniform power-control bit pattern such that the plurality of non-co-located base stations, when transmitting for use during the soft handoff of the mobile unit and not for use during softer handoff of the mobile unit, send identical power-control bits during each of the plurality of power-control bit times.
2. The method of claim 1,
- wherein programming the plurality of base stations with the uniform power-control bit pattern comprises programming a pattern that requires more than a single transmission frame of a forward link from a base station to the mobile unit before the pattern repeats, and
- wherein timing the transmissions comprises synchronizing the transmissions from each of the plurality of base stations such that the transmissions start at substantially identical times.
3. The method of claim 1,
- wherein programming the plurality of base stations with the uniform power-control bit pattern comprises programming a pattern that repeats after a single one of a plurality of transmission frames of a forward link from the base station to the mobile unit, and
- wherein timing the transmissions comprises starting the transmissions at substantially identical points within different ones of the plurality of transmission frames.
4. The method of claim 1,
- wherein programming the plurality of base stations with the uniform power-control bit pattern comprises programming a pattern that repeats after a single one of a plurality of transmission frames of a forward link from the base station to the mobile unit, and
- wherein timing the transmissions comprises starting the transmissions at substantially identical points within a specific one of the plurality of transmission frames.
5. The method of claim 1,
- wherein timing the transmissions comprises synchronizing the transmissions through a synchronization signal made available to the plurality of base stations.
6. An apparatus for use in a wireless communication system for mitigating power-control errors during a soft handoff of a mobile unit, the apparatus for use with a base station of a plurality of base stations attempting to communicate with the mobile unit, the apparatus comprising:
- a processor for controlling the base station;
- a memory element coupled to the processor for programming the processor, the memory element comprising a uniform power-control bit pattern to be sent by different ones of the plurality of base stations to the mobile unit during a plurality of power-control bit times, before the mobile unit is acquired on a reverse link; and
- a synchronizer coupled to the processor for cooperating with the processor to time transmissions of the uniform power-control bit pattern such that the plurality of non-co-located base stations, when transmitting for use during the soft handoff of the mobile unit and not for use during softer handoff of the mobile unit, send identical power-control bits during each of the plurality of power-control bit times.
7. The apparatus of claim 6,
- wherein the uniform power-control bit pattern is a pattern that requires more than a single transmission frame of a forward link from the base station to the mobile unit before the pattern repeats, and
- wherein the synchronizer is arranged and programmed such that the transmissions of the uniform power-control bit pattern from the plurality of base stations start at substantially identical times.
8. The apparatus of claim 6,
- wherein the uniform power-control bit pattern is a pattern that repeats after a single one of a plurality of transmission frames of a forward link from the base station to the mobile unit, and
- wherein the synchronizer is arranged and programmed such that the transmissions of the uniform power-control bit pattern from the plurality of base stations start at substantially identical points within different ones of the plurality of transmission frames.
9. The apparatus of claim 6,
- wherein the uniform power-control bit pattern is a pattern that repeats after a single one of a plurality of transmission frames of a forward link from the base station to the mobile unit, and
- wherein the synchronizer is arranged and programmed such that the transmissions of the uniform power-control bit pattern from the plurality of base stations start at a substantially identical point within a specific one of the plurality of transmission frames.
10. The apparatus of claim 6,
- wherein the synchronizer is arranged and programmed to synchronize the transmissions through a synchronization signal made available to the plurality of base stations.
11. A base station for use in a wireless communication system for mitigating power-control errors during a soft handoff of a mobile unit, the base station being one of a plurality of base stations attempting to communicate with the mobile unit, the base station comprising:
- a processor for controlling the base station;
- a wireless transceiver coupled to the processor for providing wireless communications for the base station;
- a memory element coupled to the processor for programming the processor, the memory element comprising a uniform power-control bit pattern to be sent by different ones of the plurality of base stations to the mobile unit during a plurality of power-control bit times, before the mobile unit is acquired on a reverse link; and
- a synchronizer coupled to the processor for cooperating with the processor to time transmissions of the uniform power-control bit pattern such that the plurality of non-co-located base stations, when transmitting for use during the soft handoff of the mobile unit and not for use during softer handoff of the mobile station, send identical power-control bits during each of the plurality of power-control bit times.
12. The base station of claim 11,
- wherein the uniform power-control bit pattern is a pattern that requires more than a single transmission frame of a forward link from the base station to the mobile unit before the pattern repeats, and
- wherein the synchronizer is arranged and programmed such that the transmissions of the uniform power-control bit pattern from the plurality of base stations start at substantially identical times.
13. The base station of claim 11,
- wherein the uniform power-control bit pattern is a pattern that repeats after a single one of a plurality of transmission frames of a forward link from the base station to the mobile unit, and
- wherein the synchronizer is arranged and programmed such that the transmissions of the uniform power-control bit pattern from the plurality of base stations start at substantially identical points within different ones of the plurality of transmission frames.
14. The base station of claim 11,
- wherein the uniform power-control bit pattern is a pattern that repeats after a single one of a plurality of transmission frames of a forward link from the base station to the mobile unit, and
- wherein the synchronizer is arranged and programmed such that the transmissions of the uniform power-control bit pattern from the plurality of base stations start at a substantially identical point within a specific one of the plurality of transmission frames.
15. The base station of claim 11,
- wherein the synchronizer is arranged and programmed to synchronize the transmissions through a synchronization signal made available to the plurality of base stations.
16. A wireless communication system infrastructure for mitigating power-control errors during a soft handoff of a mobile unit, the infrastructure comprising:
- a central controller for controlling the communication system infrastructure; and
- a plurality of base stations coupled to the central controller for handling communications of the infrastructure, wherein a base station of the plurality of base stations comprises:
- a processor for controlling the base station;
- a wireless transceiver coupled to the processor for providing wireless communications for the base station;
- a memory element coupled to the processor for programming the processor, the memory element comprising a uniform power-control bit pattern to be sent by different ones of the plurality of base stations to the mobile unit during a plurality of power-control bit times, before the mobile unit is acquired on a reverse link; and
- a synchronizer coupled to the processor for cooperating with the processor to time transmissions of the uniform power-control bit pattern such that the plurality of non-co-located base stations, when transmitting for use during the soft handoff of the mobile unit and not for use during softer handoff of the mobile unit, send identical power-control bits during each of the plurality of power-control bit times.
17. The infrastructure of claim 16,
- wherein the uniform power-control bit pattern is a pattern that requires more than a single transmission frame of a forward link from the base station to the mobile unit before the pattern repeats, and
- wherein the synchronizer is arranged and programmed such that the transmissions of the uniform power-control bit pattern from the plurality of base stations start at substantially identical times.
18. The infrastructure of claim 16,
- wherein the uniform power-control bit pattern is a pattern that repeats after a single one of a plurality of transmission frames of a forward link from the base station to the mobile unit, and
- wherein the synchronizer is arranged and programmed such that the transmissions of the uniform power-control bit pattern from the plurality of base stations start at substantially identical points within different ones of the plurality of transmission frames.
19. The infrastructure of claim 16,
- wherein the uniform power-control bit pattern is a pattern that repeats after a single one of a plurality of transmission frames of a forward link from the base station to the mobile unit, and
- wherein the synchronizer is arranged and programmed such that the transmissions of the uniform power-control bit pattern from the plurality of base stations start at a substantially identical point within a specific one of the plurality of transmission frames.
20. The infrastructure of claim 16,
- wherein the synchronizer is arranged and programmed to synchronize the transmissions through a synchronization signal made available to the plurality of base stations.
Type: Application
Filed: Nov 29, 2005
Publication Date: May 4, 2006
Inventors: Daniel DeClerk (Lake Barrington, IL), Dean Thorson (Grayslake, IL)
Application Number: 11/289,043
International Classification: H04Q 7/20 (20060101);