WO1999057934A1 - Method and apparatus for control of soft handoff usage in radiocommunication systems - Google Patents
Method and apparatus for control of soft handoff usage in radiocommunication systems Download PDFInfo
- Publication number
- WO1999057934A1 WO1999057934A1 PCT/SE1999/000687 SE9900687W WO9957934A1 WO 1999057934 A1 WO1999057934 A1 WO 1999057934A1 SE 9900687 W SE9900687 W SE 9900687W WO 9957934 A1 WO9957934 A1 WO 9957934A1
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- sources
- remote station
- threshold
- evaluating
- substantially stationary
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- 238000000034 method Methods 0.000 title claims abstract description 34
- 230000005540 biological transmission Effects 0.000 claims abstract description 36
- 230000007246 mechanism Effects 0.000 claims description 4
- 238000011156 evaluation Methods 0.000 claims 1
- 230000001413 cellular effect Effects 0.000 description 6
- 238000004891 communication Methods 0.000 description 5
- 230000000694 effects Effects 0.000 description 5
- 230000008569 process Effects 0.000 description 3
- 238000013459 approach Methods 0.000 description 2
- 230000000903 blocking effect Effects 0.000 description 2
- 230000010267 cellular communication Effects 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 238000005562 fading Methods 0.000 description 2
- 230000002411 adverse Effects 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 230000002542 deteriorative effect Effects 0.000 description 1
- 230000003116 impacting effect Effects 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 230000003993 interaction Effects 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012544 monitoring process Methods 0.000 description 1
- 230000010287 polarization Effects 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W36/00—Hand-off or reselection arrangements
- H04W36/16—Performing reselection for specific purposes
- H04W36/18—Performing reselection for specific purposes for allowing seamless reselection, e.g. soft reselection
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L12/00—Data switching networks
- H04L12/28—Data switching networks characterised by path configuration, e.g. LAN [Local Area Networks] or WAN [Wide Area Networks]
- H04L12/42—Loop networks
- H04L12/427—Loop networks with decentralised control
- H04L12/433—Loop networks with decentralised control with asynchronous transmission, e.g. token ring, register insertion
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L12/00—Data switching networks
- H04L12/28—Data switching networks characterised by path configuration, e.g. LAN [Local Area Networks] or WAN [Wide Area Networks]
- H04L12/42—Loop networks
- H04L12/437—Ring fault isolation or reconfiguration
Definitions
- This invention generally relates to the field of communication systems having soft handoff capability and, more particularly, to reducing interference by restricting the application of soft handoff under certain circumstances.
- Mobile stations M1-M10 communicate with the fixed part of a public switched telephone network (PSTN) by transmitting radio signals to, and receiving radio signals from, cellular base stations B1-B10.
- PSTN public switched telephone network
- the cellular base stations B1-B10 are, in turn, connected to the PSTN via a Mobile Switching Center (MSC).
- MSC Mobile Switching Center
- Each base station B1-B10 transmits signals within a corresponding area, or "cell" C1-C10.
- a base station transmits to the mobile units over downlink RF channels, while the mobile units transmit information to the base station over uplink RF channels.
- Conventional spatial diversity techniques employ two or more separated antennas in a single base station, or two or more base stations, to communicate with a mobile station. However, diversity is not limited to spatially offsetting base stations or antennas (i.e., multiple transmission paths).
- Diversity transmission can also be generated using one or more of an offset in time, polarization, or frequency.
- One area in which macro diversity is commonly practiced is during handoff.
- the candidate base station i.e., the base station to which a mobile station is to be handed off
- This usage of macro diversity is commonly referred to as soft handoff.
- Figure 2 illustrates a soft handoff arrangement wherein a first, original base station 202 and a second, candidate base station 204 each transmit a same message 206 to a mobile station 208.
- the message 206 is transmitted to the mobile station 208 over different signal paths in the forms of a first downlink 210 and a second downlink 212.
- the first and second downlink signals 210 and 212 are recombined (or one of the received signals is selected) in the mobile station 208 to extract the message 206.
- the mobile station 208 transmits to the base stations 202 and 204 over first and second uplink paths 214 and 216, respectively.
- the transmission of message information to the mobile station from the first, original base station 202 is terminated and the soft handoff process is concluded.
- Soft handoffs can also be performed using multiple transmissions from a single base station.
- Figure 3 depicts a single base station macro diversity arrangement wherein first and second directional lobes 318 and 320, generated by an antenna array 304, each cover a different area.
- the mobile station 308 can be handed off from one lobe to another in the manner described above. That is, the first directional lobe 318 maintains a first diversity link including a first downlink 310 which carries a message 306.
- the second directional lobe 320 establishes a second diversity link including a second downlink 312 which also carries the message 306.
- First and second uplinks 314 and 316 communicate from the mobile station 308 to the antenna array 304 within each lobe 318 and 320, respectively.
- the base stations and/or antennas communicating with a particular mobile station are known as "active set" members.
- active set members of the active set.
- base stations 202 and 204 would be considered members of the active set.
- TDMA time division multiple access
- CDMA code division multiple access
- one method for controlling interference is to limit the number of base stations and/or antennas in an active set. This technique is described, for example, in published International Patent Application (PCT) WO/ 95/12297 to Gilhousen et al., wherein sectors involved in a softer handoff are monitored for reverse link signal strength. If the signal strength of transmissions from one of the sectors drops below a predetermined threshold for a predetermined period of time, then the base station discontinues transmissions from that sector.
- PCT International Patent Application
- the downlink transmit power may be equally split between each active base station and/or antenna in an active set. That is, in the case where there are three downlinks, and a total transmission power of P is available, each of the downlinks has a transmission power level of P/3.
- the link may, in effect provide a small improvement in communications robustness, but introduce, on balance, a greater amount of disruption to surrounding communications by unduly introducing interference. Consequently, the C/I ratio for adjacent cells can be negatively impacted with only a minimal gain in communications efficiency.
- the present invention solves the forgoing problems by identifying those mobile stations which are stationary or substantially stationary and either adjusting the threshold used to remove weakly received members from the active set or removing the weakest members unconditionally. In this way, additional system capacity is acquired without detrimentally affecting the quality of the stationary mobile station's connection.
- Exemplary embodiments of the present invention use location information associated with a mobile station to determine if it is stationary. Any known locating technique can be used, either based in the mobile station itself or in the system. If the system identifies a particular connection as being associated with a stationary mobile station, then the system applies a higher threshold for keeping a transmission source in the active set for that connection so that it is more likely to reduce the number of members in the active set.
- FIG. 1 depicts a conventional cellular communication system in which the present invention present invention can be utilized
- FIG. 2 depicts a soft handoff scenario wherein two individual base stations communicate with a mobile station
- FIG. 3 depicts a macro diversity scenario wherein an individual base station communicates with a mobile station using an array antenna or plural sector antennas which propagate separate lobes each of which handles a different coverage area;
- FIG. 4 illustrates an exemplary scenario according to the present invention wherein a stationary mobile station and a moving mobile station are receiving signals from two transmission sources; and
- FIG. 5 is a flow chart depicting a method for handling soft handoff/macrodiversity according to an exemplary embodiment of the present invention.
- a base station 400 supports radiocommunication services in a first cell and base station 410 supports radiocommunication services in a second cell.
- the base stations 400 and 410 are in communication with a radio network controller (RNC) via a mobile switching center (MSC), which in turn is connected to a public switched telephone network (PSTN).
- RNC radio network controller
- MSC mobile switching center
- PSTN public switched telephone network
- This example also depicts two mobile stations 420 and 430 disposed near the cell boundary between base stations 400 and 410.
- base stations 400 and 410 would typically support connections with many mobile stations concurrently, however interaction between these two exemplary mobile stations and the network is sufficient to illustrate soft handoff/ macrodiversity techniques according to the present invention.
- mobile station 420 is stationary or substantially stationary relative to the two base stations, while mobile station 430 is moving in the direction of the illustrated arrow away from base station 400 generally toward base station 410.
- both mobile stations are currently receiving transmissions from both base stations, i.e., they are in soft handoff mode.
- the mobile station will monitor the transmissions of neighboring sources, e.g., base stations or antenna elements, while it is connected to the system. Information regarding the received signal quality and/or strength is returned to the system and used to place these neighboring sources in that mobile station's candidate set. At certain times, one or more of the sources in the candidate set may be added to the active set. For example, in many systems and particularly CDMA systems, when a mobile station approaches a cell boundary, the mobile station may enter a region wherein another transmission source (e.g. , another base station and/or another antenna element from the same base station) begins to transmit substantially the same information to that mobile station. The mobile station can then combine the plural received signals to create a composite that has better quality than that which would have resulted from only receiving the information from one source.
- neighboring sources e.g., base stations or antenna elements
- the network recognizes that a mobile station should be added or dropped from the active set by monitoring the signal strength at which the mobile station receives transmissions from its neighboring sources and comparing the monitored values with predetermined thresholds. For example, as described in the article entitled "A Channel Assignment Scheme for Reducing Call Blocking rate in a DS-CDMA Cellular System" by Hyoung-Goo Jeon et al., the system can have a predefined parameter T DROP such that if the measured signal strength is less than T DROP, a transmission source is removed from the active set and a predefined parameter T ADD such that if the measured signal strength exceeds T ADD, the corresponding transmission source is added to the active set.
- the present invention therefore handles the active set associated with mobiles stations 420 and 430 in different ways. More specifically, as depicted in the flow chart of Figure 5, the system first determines whether the mobile station is stationary or substantially stationary at step 500.
- a first technique for implementing the test described by step 500 is to use consecutive position values to determine whether the mobile station is moving.
- a second technique for identifying stationary mobiles is by determining a velocity of the mobile station. This can be accomplished by, for example, measuring the Doppler effects on the signal received at the mobile station to determine a radial velocity of the mobile station relative to the base station.
- a third technique for performing this check is to periodically order measurement reports relating to quality parameters associated with the signal received by the mobile station. For example, checking to see if the received signal strength, bit error rate and/or frame error rate from one of the connections are steady could provide an indication as to whether the mobile station is stationary.
- position information can be determined in many ways.
- the mobile station could estimate its own position and send a message with its coordinates to the system. This could be accomplished by, for example, providing the mobile unit with a Global Positioning System (GPS) receiver that receives location information from the GPS satellite network.
- GPS Global Positioning System
- the base stations which transmit signals to, and receive signals from, the mobile station could be used to determine the mobile station's location.
- Various techniques including attenuation of a mobile station's signal, angle- of-arrival, and difference between the time-of-arrival (TDOA) of a mobile station's signal at different base stations, have been suggested for usage in providing mobile unit location information. See, for example, the article entitled “Time Difference of Arrival Technology for Locating Narrowband Cellular Signals" by Louis A. Stilp, SPIE Vol. 2602, pp. 134-144.
- a third category of strategies for locating mobile stations in radiocommunication systems involves the provision of an adjunct system, i.e., a system which may be completely independent of the radiocommunication system or which may share various components (e.g. , an antenna) with the radiocommunication system but which processes signals separately therefrom.
- an adjunct system i.e., a system which may be completely independent of the radiocommunication system or which may share various components (e.g. , an antenna) with the radiocommunication system but which processes signals separately therefrom.
- This may be advantageous, for example, as an expedient solution to providing mobile unit location without modifying the large number of existing base stations in a system.
- More details regarding exemplary usages of adjunct systems can be found in U.S. Patent No. 5,327,144 to Stilp et al. , entitled “Cellular Telephone Location System", the disclosure of which is incorporated here by reference.
- the system can use any of the above-identified methods, or some other technique, to determine whether the mobile station is stationary or substantially stationary at step 500. Having made this determination, the system selects an appropriate threshold for dropping (and/or adding) a transmission source from (or to) the active set. For example, having determined that mobile station 420 is relatively stationary at step 500, the system can use a first T DROP value (step 510) to determine whether to remove transmission sources from the active set. This may involve comparing the received signal strength (RSS) associated with each transmission source to the selected T DROP value at step 516 and selectively removing those which fall below that value at step 518. Otherwise, if the system determines that the mobile station is moving, e.g. , as in the case of mobile station 430, then the system can use a second value for the T DROP parameter as shown in step 520.
- RSS received signal strength
- the second value of T DROP will be lower than the first value for T DROP so that soft handoff will be continued longer and more frequently 10 for the moving terminals which require the additional received signal(s) to maintain acceptable quality.
- the first and second values of T DROP will likely vary from implementation to implementation based upon the network preferences of the operators.
- the system can evaluate all of the members of the active set and drop the weakest transmission source therefrom.
- T DROP is increased and the signal quality (or the stationary quality of the mobile station) can be continuously or periodically monitored. If the quality starts deteriorating and/or the mobile station starts moving, the call will be put back into soft handoff mode again and T DROP will be lowered.
- T ADD and T DROP are cell level parameters which are provided on the broadcast control channel to all mobile stations in the cell.
- a message can be transmitted on the traffic channel to that mobile station informing it of the new T DROP and/or T ADD values, without changing T ADD and T DROP for all mobile stations in the cell.
- thresholds For example, although only two thresholds were described above, those skilled in the art will appreciate that more than two thresholds may exist and can be modified in view of whether a mobile station is stationary. Moreover, changing a threshold is not necessary to implement the concept of adjusting the active set for substantially stationary mobiles. For example, when a stationary mobile station is identified, the base station with the lowest received signal strength could reduce its transmission power until it eventually falls below an unmodified T DROP threshold. Accordingly, 11 the invention is defined only by the following claims which are intended to embrace all equivalents thereof.
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- Engineering & Computer Science (AREA)
- Computer Networks & Wireless Communication (AREA)
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- Mobile Radio Communication Systems (AREA)
Abstract
Description
Claims
Priority Applications (6)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US09/071,275 US6560205B1 (en) | 1998-05-01 | 1998-05-01 | Method and apparatus for control of soft handoff usage in radiocommunication |
BR9910059-2A BR9910059A (en) | 1998-04-30 | 1999-04-27 | Process for performing transfer of control in a radio communication system, and radio communication systems, and for adjusting an active set of sources that transmit signals to a particular receiver |
JP2000547810A JP4316805B2 (en) | 1998-04-30 | 1999-04-27 | Method and apparatus for controlling soft handoff use in a wireless communication system |
AU43018/99A AU769348B2 (en) | 1998-04-30 | 1999-04-27 | Method and apparatus for control of soft handoff usage in radiocommunication systems |
PCT/SE1999/000687 WO1999057934A1 (en) | 1998-04-30 | 1999-04-27 | Method and apparatus for control of soft handoff usage in radiocommunication systems |
CA002330129A CA2330129A1 (en) | 1998-04-30 | 1999-04-27 | Method and apparatus for control of soft handoff usage in radiocommunication systems |
Applications Claiming Priority (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US09/069,765 | 1998-04-30 | ||
US09/069,765 US6934546B1 (en) | 1998-04-30 | 1998-04-30 | Method and apparatus for control of soft handoff usage in radiocommunication systems |
US09/071,275 US6560205B1 (en) | 1998-05-01 | 1998-05-01 | Method and apparatus for control of soft handoff usage in radiocommunication |
PCT/SE1999/000687 WO1999057934A1 (en) | 1998-04-30 | 1999-04-27 | Method and apparatus for control of soft handoff usage in radiocommunication systems |
Publications (1)
Publication Number | Publication Date |
---|---|
WO1999057934A1 true WO1999057934A1 (en) | 1999-11-11 |
Family
ID=27617346
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/SE1999/000687 WO1999057934A1 (en) | 1998-04-30 | 1999-04-27 | Method and apparatus for control of soft handoff usage in radiocommunication systems |
Country Status (3)
Country | Link |
---|---|
JP (1) | JP4316805B2 (en) |
BR (1) | BR9910059A (en) |
WO (1) | WO1999057934A1 (en) |
Cited By (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP2001197536A (en) * | 1999-12-31 | 2001-07-19 | Mitsubishi Electric Inf Technol Center Europ Bv | Method for relieving overload of base station |
GB2388494A (en) * | 2002-05-08 | 2003-11-12 | Lucent Technologies Inc | Handover of mobile call connection |
EP1460451A1 (en) * | 2003-03-18 | 2004-09-22 | Alcatel | Determining a binary information related to the speed of a mobile terminal |
EP1585357A1 (en) * | 2004-04-07 | 2005-10-12 | TeliaSonera Finland Oyj | Optimizing the resources of the telecommunications network |
GB2492180A (en) * | 2011-06-13 | 2012-12-26 | Neul Ltd | Allocating resources to static terminals in a communications network |
Citations (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO1995016329A1 (en) * | 1993-12-08 | 1995-06-15 | Motorola Inc. | Method for performing a handoff in a communication system |
-
1999
- 1999-04-27 BR BR9910059-2A patent/BR9910059A/en not_active Application Discontinuation
- 1999-04-27 JP JP2000547810A patent/JP4316805B2/en not_active Expired - Lifetime
- 1999-04-27 WO PCT/SE1999/000687 patent/WO1999057934A1/en not_active Application Discontinuation
Patent Citations (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO1995016329A1 (en) * | 1993-12-08 | 1995-06-15 | Motorola Inc. | Method for performing a handoff in a communication system |
Cited By (8)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP2001197536A (en) * | 1999-12-31 | 2001-07-19 | Mitsubishi Electric Inf Technol Center Europ Bv | Method for relieving overload of base station |
GB2388494A (en) * | 2002-05-08 | 2003-11-12 | Lucent Technologies Inc | Handover of mobile call connection |
EP1460451A1 (en) * | 2003-03-18 | 2004-09-22 | Alcatel | Determining a binary information related to the speed of a mobile terminal |
EP1585357A1 (en) * | 2004-04-07 | 2005-10-12 | TeliaSonera Finland Oyj | Optimizing the resources of the telecommunications network |
GB2492180A (en) * | 2011-06-13 | 2012-12-26 | Neul Ltd | Allocating resources to static terminals in a communications network |
GB2492180B (en) * | 2011-06-13 | 2015-09-30 | Neul Ltd | Static Terminals |
US9374753B2 (en) | 2011-06-13 | 2016-06-21 | Neul Ltd. | Static terminals |
US10582434B2 (en) | 2011-06-13 | 2020-03-03 | Huawei Technologies Co., Ltd. | Device and method for deriving alignment information |
Also Published As
Publication number | Publication date |
---|---|
JP4316805B2 (en) | 2009-08-19 |
BR9910059A (en) | 2000-12-26 |
JP2002514872A (en) | 2002-05-21 |
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