EP1192830A1 - Passage intercellulaire avec evaluation par le reseau, assiste a la fois par les stations mobiles et par les stations de base - Google Patents

Passage intercellulaire avec evaluation par le reseau, assiste a la fois par les stations mobiles et par les stations de base

Info

Publication number
EP1192830A1
EP1192830A1 EP00937442A EP00937442A EP1192830A1 EP 1192830 A1 EP1192830 A1 EP 1192830A1 EP 00937442 A EP00937442 A EP 00937442A EP 00937442 A EP00937442 A EP 00937442A EP 1192830 A1 EP1192830 A1 EP 1192830A1
Authority
EP
European Patent Office
Prior art keywords
handover
downlink
condition
base station
mobile
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP00937442A
Other languages
German (de)
English (en)
Inventor
Walter Müller
Magnus Persson
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Telefonaktiebolaget LM Ericsson AB
Original Assignee
Telefonaktiebolaget LM Ericsson AB
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Telefonaktiebolaget LM Ericsson AB filed Critical Telefonaktiebolaget LM Ericsson AB
Publication of EP1192830A1 publication Critical patent/EP1192830A1/fr
Withdrawn legal-status Critical Current

Links

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
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W36/00—Hand-off or reselection arrangements
    • H04W36/24—Reselection being triggered by specific parameters
    • H04W36/30—Reselection being triggered by specific parameters by measured or perceived connection quality data
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W36/00—Hand-off or reselection arrangements
    • H04W36/24—Reselection being triggered by specific parameters
    • H04W36/30—Reselection being triggered by specific parameters by measured or perceived connection quality data
    • H04W36/302—Reselection being triggered by specific parameters by measured or perceived connection quality data due to low signal strength

Definitions

  • the present invention relates to wireless communication systems, and more particularly, to a method and apparatus for efficiently handing over mobile radios among neighboring cells.
  • a geographical area is divided into cell areas served by base stations which are connected to a radio network.
  • Each user (mobile subscriber) in the cellular radio system is provided with a portable, pocket, hand-held, or car mounted mobile station which communicates voice and/or data with the mobile network.
  • Each base station- includes a plurality of channel units including a transmitter, a receiver, and a controller and may be equipped an omni-directional antenna for transmitting equally in all directions or with directional antennas, each directional antenna serving a particular sector cell.
  • Each mobile station also includes a transmitter, a receiver, a controller, and a user interface and is identified by a specific mobile station identifier.
  • the first public mobile radio systems were introduced in the late 1970's and early 1980's.
  • first generation systems those now well-known systems were referred to as “first generation” systems. They included the “Advanced Mobile Phone System” (AMPS) in the United States, “NordisktMobilTelefon-system” (NMT) in Scandinavia, “Total Access Communications System” (TACS) in England, and “Nippon Mobile Telephone System” (NAMTS) in Japan. They had certain transmission characteristics that were generally common to all, such as analog frequency modulation at the radio and digital control at the network. Otherwise, however, each system used a communication standard unique to itself in comparison to the others.
  • AMPS Advanced Mobile Phone System
  • NMT Total Access Communications System
  • NAMTS Nippon Mobile Telephone System
  • a mobile station when a mobile station is idle, (not using a traffic channel), it tunes to and continuously monitors a control channel corresponding to its current cell in the network. As a result, the mobile can continuously determine whether a page message addressed to it has been received over a control channel. If so, the mobile then transmits a page response over the control channel to the base station which forwards the page response to the radio network. Upon receiving the page response, the radio network selects an available voice channel in the cell from which the page response was received and requests the base station in that cell to order the mobile station via the control channel to establish a through connection.
  • a mobile station may access the network to initiate a call by dialing the telephone number and pressing the "SEND" button on the telephone handset. A control signal including the mobile station identifier and the dialed telephone number is transmitted over the control channel to the base station and forwarded to the radio network which validates the mobile station, assigns a traffic channel, and establishes a through connection.
  • a "handover" of that connection takes place between the cells.
  • the handover can occur as a result of a variety of changes that can occur in the communications between a mobile station and a network.
  • One common handover occurs when the mobile station is in communication with a single base station servicing a cell in which the mobile station resides. As the mobile station commutes from that cell into a new cell serviced by a new base station, the first base station hands over the communication to the new base station. In this way, the mobile station ends communication with a first base station and begins communication with a second base station as it moves from cells serviced by the respective base stations.
  • a mobile station may be receiving redundant communication from multiple base stations to ensure quality of transmission.
  • a radio network core 100 receives a communication 102 from a network (not shown).
  • the communication 102 is intended to be directed to mobile station MS via an established traffic channel TCH for the communication.
  • the radio network core 100 delivers the communication 102 to a diversity handoff DHO entity 101, which splits the signal 102 into redundant messages destined for base station BS1 and base station BS2.
  • Base stations BS1 and BS2 deliver the communication via the same traffic channel TCH to the mobile station MS.
  • a variety of techniques are known for providing the diversity handoff described above.
  • the mobile station receives the message via redundant communications over traffic channel TCH, it is able to improve the quality of reception (and conversely, transmission) by opportunistically selecting the signal from the traffic channels or by combining the signals received on the traffic channel in accordance with known protocols.
  • Mobile station MS and current Base Stations BS 1 and BS2 may, at some point in the communication, benefit from the addition of Base Station BS3 in the diverse communication scheme. That is, the mobile station MS may be said to be in communication with a current group of Base Stations (BS1 and BS2) and has available neighboring Base Stations (BS3) as future communication link prospects.
  • Base Station 2 maintains communication with the mobile station MS during its entire travel and Base Stations BS1 and BS3 may or may not remain in communication depending upon signal quality.
  • the mobile station is communicating using the traffic channel TCH, regardless of the base stations to which it is communicating.
  • the mobile station maintains a record of its current Base Stations, and may test (or be instructed to test) neighboring cells for inclusion in that record. As conditions dictate, Base Stations in current communication are added to or removed from the current record.
  • a handoff can also occur even within the confines of a single base station, as shown in Figure 2.
  • a base station is shown having four antennas A1-A4 defining four geographical service areas.
  • the mobile station MS at position A communicates with the base station BS over traffic channel TCH.
  • the mobile station communicates with the base station over redundant reception/ transmissions to antennas Al and A4.
  • mobile station MS may begin transmitting/receiving to antennas Al and A2.
  • a handoff occurs as between antennas A1/A4 and antennas A1/A2.
  • the handoff scenario occurs as a result of the existence of defined conditions, such as signal strength between the mobile station and the receptor.
  • defined conditions such as signal strength between the mobile station and the receptor.
  • BS3 Base Station
  • BS1-BS3 measured the current radio conditions between the mobile station and the neighboring cells (often measured and reported by the MS) and the resource conditions (finding free channels in the cell pointed out by the MS measurements).
  • the MS measures the cell conditions and reports the results to the network which the evaluates the handover in light of the required resources.
  • both uplink and downlink signals to/from the mobile radio and the radio network are involved in a handover evaluation.
  • the invention is particularly useful whenever the uplink and downlink conditions are different in one network or when the mobile station is near the border of two different network operators.
  • handover related measurement reports from a mobile station may be delivered to the radio network and used by the network to determine when the base station should measure the quality of an uplink transmission from the mobile station. Both measurements are used to make the handoff determination.
  • the invention allows the BS to take some measurements upon the MS in parallel with the MS measurements on the BS: Also, some BSs listen to the uplink without sending anything on the downlink other than to use the existing downlinks from other BSs to transfer power control commands.
  • the invention also permits the network to correct channel and/or power level uplink conditions before a radio hands over to a new cell broadcast area.
  • FIGURE 1 is a schematic diagram of a simplified mobile radio communication system
  • FIGURE 2 is a schematic diagram of a simplified mobile station to base station communication system
  • FIGURE 3 is a schematic representation of a mobile station to base station communication link
  • FIGURE 4 is a schematic representation of a simplified mobile station communication network
  • FIGURE 5 is a schematic representation of a simplified radio network controller connected to a and base station ;
  • FIGURE 6 is a schematic representation of a simplified mobile station
  • FIGURE 7 is a graphical representation of the current set and neighbor set thresholds employed by an example embodiment of the present invention.
  • FIGURE 8 is a schematic representation of a simplified mobile communications system in which mobile stations communicate to different base stations for uplinks and for downlinks;
  • FIGURE 9 is a schematic representation of an example embodiment of the present invention in use across borders between different operators.
  • a representative, connection- oriented, external core network, shown as a cloud 12 may be for example the Public Switched Telephone Network (PSTN) and/or the Integrated Services Digital Network (ISDN).
  • PSTN Public Switched Telephone Network
  • ISDN Integrated Services Digital Network
  • a representative, connectionless-oriented external core network shown as a cloud 14 may be for example the Internet. Both core networks are coupled to corresponding service nodes 16.
  • the PSTN/IDSN connection-oriented network 12 is connected to a connection- oriented service node shown as a Mobile Switching Center (MSC) node 18 that provides circuit-switched services.
  • MSC Mobile Switching Center
  • the MSC 18 is connected over an interface A to a Base Station Subsystem (BSS) 22 which in turn is connected to radio base station 23 over interface A'.
  • the Internet connectionless-oriented network 14 is connected to a General Packet Radio Service (GPRS) node 20 tailored to provide packet- switched type services sometimes referred to as the serving GPRS service node (SGSN).
  • GPRS General Packet Radio Service
  • Each of the core network service nodes 18 and 20 connects to a UMTS Terrestrial Radio Access Network (UTRAN) 24 over a radio access network (RAN) interface.
  • UTRAN 24 includes one or more radio network controllers 26.
  • Each RNC 26 is connected to a plurality of base stations (BS) 28 and to any other RNCs in the UTRAN 24.
  • radio access is based upon wideband, Code Division Multiple Access (WCDMA) with individual radio channels allocated using CDMA spreading codes.
  • WCDMA Code Division Multiple Access
  • Other access methods may be employed.
  • WCDMA provides wide bandwidth for multimedia services and other high transmission rate demands as well as robust features like diversity handoff and RAKE receivers to ensure high quality.
  • the mobile stations 30 use transmission codes so base station 28 can identify transmissions from that particular MS 30.
  • codes are supposed to be allocated as follows for the dedicated channels:
  • the uplink and downlink transmission is using channelization codes, and on top of that a scrambling code
  • the channelization code determines e.g., the spreading factor, and the spreading factor determines the maximum bitrate
  • d) mobiles in other cells use the same channelization codes but different scrambling codes.
  • the scrambling codes secure the integrity, between downlink transmissions using the same channelization code but in different cells.
  • the scrambling code used in uplink secure the integrity between uplink transmissions from different mobile stations in the same or in other cell.
  • the MS gets its own scrambling code while the BS transmission to a specific mobile on a dedicated channel will use a common scrambling code but a unique channelization code.
  • the MS have the ability to combine a downlink transmission using a different scrambling codes and different channelization codes (one limitation today is that the spreading factor of the channelization codes must be the same from all cells).
  • the radio network controller 26 and base station 28 shown in Fig. 5 are radio network nodes that each include a corresponding data processing and control unit 32 and 33 for performing numerous radio and data processing operations required to conduct communications between the RNC 26 and the mobile stations 30.
  • Part of the equipment controlled by the base station data processing and control unit 33 includes plural radio transceivers 34 connected to one or more antennas 35.
  • the mobile station 30 shown in Fig. 6 also includes a data processing and control unit 36 for controlling the various operations required by the mobile station.
  • the mobile's data processing and control unit 36 provides control signals as well as data to a radio transceiver 37 connected to an antenna 38. Both the data processing and control unit 36 and transceiver 37 are powered from voltage supplied by battery 39.
  • the amount of power supplied by the battery 39 to the data processing and control unit 40 and transceiver 37 is regulated by one or more control signals from the data processing and control unit 36.
  • the present invention may be employed in the context of the example mobile communications system 10 shown in Fig. 4 in which the radio network controllers 26 and base stations 28 form a radio access network between a core network node (like the MSC 16) and the mobile stations 30.
  • the mobile station performed radio condition evaluations and the network performed resource evaluations to determine if a handover should occur.
  • a principal problem that occurs as a result is over- or under-power conditions in which the MS is broadcasting at too great a signal strength or too little signal strength for the conditions existing in a neighboring hand-over cell.
  • the present invention allows the network to make measurements in lieu of, or (more likely) in parallel with measurement reports received from the mobile radio before the network sends the handover command.
  • FIG. 3 illustrates these conditions in more detail.
  • traffic channel TCH provides an uplink from the mobile station MS to base station BS1 and a downlink from base station BS 1 to mobile station MS.
  • Communication quality between the mobile station and the base station is defined by reference to both the uplink conditions and the downlink conditions.
  • a handoff determination will have to be made as between Base Station BS1 and Base Station BS2.
  • the handoff determination is made by uplink and downlink communication quality between the mobile station and Base Station BS1 in comparison to the mobile station in Base Station BS2.
  • the network is unsure of the downlink conditions as between Mobile Station MS and Base Station BS 1 vis-a-vis Base Station BS2. .
  • the current protocol allows the network to make the resource evaluation regardless of whether the MS or the BS makes the radio condition evaluation. That is, the MS may report the radio condition information for use by the network in evaluating the handoff or the BS may provide the radio condition evaluation based on the uplink conditions.
  • the radio condition information can be estimated by using pathloss estimates measured by the MS but the information could be explicitly measured by the BS to be more accurate.
  • the presently preferred embodiment of the present invention has the mobile station reporting to the RNC 100 regarding downlink profiles which the RNC uses to order handoff operations.
  • the MS will use the BCCH channel to measure upon also for the cells to which it is in communication with (the cells that are included in the active set).
  • MS maintains a record of current Base Stations to which it is in communication.
  • the MS is also continually monitoring neighboring cells for quality of downlink signal based on a reception quality of a common pilot channel. Alternatively, any channel containing pilot bits having a constant output power, and covering a whole cell can be used for neighboring cell measurements.
  • the MS measures the BCH downlink conditions from Base Station BS3.
  • the MS reports those measurement profiles from the downlink to the RNC 100 whenever the profile from a neighboring cell exceeds a standard.
  • the RNC informs the base station, such as BS3, that an MS has identified the Base Station as a prospective Base Station for current or near-term communication.
  • the RNC 100 instructs BS3 to measure uplink transmission power received from MS as it moves from position A to position B. If the mobile station is transmitting at high power (uplink) as reported by the base station and is receiving at high power (downlink) as reported by the mobile station at the Base Station BS3 (the neighboring cell), the RNC 100, using existing links between MS-BS1 and
  • MS-BS2 orders the mobile station to lower its power levels to an appropriate non-interfering level for the cell defined by BS3.
  • BS3 uplink is protected from excessive interference until a radio link is established between the MS and BS3 with full support for fast power control.
  • the Base Stations BS l and BS2 continue communicating with mobile station MS over the transmission channel TCH that has been previously setup. At first, only power control is provided between MS and BS3 until BS3 reports to the RNC 100 that the uplink from MS is at an appropriate level.
  • RNC 100 notifies MS that it should setup a handoff to include BS3 in its current communication report on TCH (or if the mobile station capacity can accept no more base stations, to take away the weakest base station from the current report and replace it with BS3).
  • the RNC 100 has informed the mobile station MS to reduce its transmission power to the appropriate level as it includes BS3 in the current report of base stations to which the mobile station is communicating on TCH.
  • the MS can be instructed to lower its power. This is typically achieved by changing the signal-to-interference ratio target in the BSl and BS2 since BSl and BS2 have fast power control connection with the MS on downlink.
  • the preferred embodiment of the present invention removes any links where both the downlink and the uplink are both weak.
  • a mobile station keeps within its active communication set communications with base stations in which a strong uplink i.e., low pathloss and low disturbance (factors that makes it possible to use low power to reach the quality goal), is coupled with a weak downlink (or vice versa).
  • strong uplink and downlink signals will ensure the continuation of communications between a mobile station and any base station with a possible power reduction instruction being given by RNC to the MS.
  • a mobile station reports BCH power levels for all neighboring cells, whether the signals are weak or strong.
  • the RNC uses the measurements from the mobile station to determine, based on the reported downlink information, when a neighboring base station should measure uplink information transmitted by the mobile station. When the uplink information meets the threshold, a handoff is triggered.
  • Other reasons for starting BS measurements could also be that a BS suffers from a high interference level, that the MS output power is about to reach its limits, or that a BS member in the active set is running out of power. Another reason could be that the frequency used by the MS is getting overloaded and the MS must be handed over to another frequency.
  • the BS could then measure upon the MS and evaluate which BS the UE should use after the frequency change assuming that the other frequency is not supported by all cells in an area.
  • the MS measures on a MS the MS is identified by its unique scrambling code.
  • the MS is identified by its unique scrambling code. And the system should be able to do a much more reliable inter-frequency handover decision.
  • Figure 7 illustrates a comparison of the signal quality (downlink) received at a mobile station from various base stations as the mobile station moves through geographic regions proximate to BSl, BS2, and BS3 over time.
  • the mobile station is in voice communication solely with BSl (and may be monitoring downlink conditions from BS2 and BS3).
  • BS2 nor BS3 are included in the mobile stations current base station active set.
  • the mobile station continues to report to the RNC 100 what the downlink signal strengths are for neighboring cells BS2 and BS3.
  • the signal strength for the BS2 downlink reaches a threshold for inclusion in the current communication active set, )CS. This can be seen as a request for update. (In IS 95 the request is more explicit, such as "the MS gives the network an offer it cannot refuse").
  • the mobile station continues to test the downlink signal strength from Base Station BS3.
  • the mobile station reports that BS3 is now a candidate for inclusion in the mobile station current set.
  • RNC notifies BS3 to evaluate uplink conditions and report on possible interference and power level conditions.
  • RNC reports back to MS when the connection with BS3 can begin and at what power levels.
  • BS3 will then be added to the current report when the RNC notifies the MS that appropriate handover specifications exist (and appropriate power levels) and MS detects a )CS downlink threshold from BS3.
  • the MS does not adjust its power explicitly; it adjusts its power when the power control bits that are transferred by the downlink in the active set indicates that the MS power should be decreased.
  • FIG 8 illustrates another example embodiment in which the present invention provides advantageous application.
  • mobile station MS I begins at position A with uplink and downlink communications on TCH from three Base Stations BSl, BS2 and BS3.
  • MS thus has a current communication set equal to BS l, BS2 and BS3.
  • Mobile Station MS I monitors BCH from BS4 and BS5, eventually adding them to its proposed neighboring cells. Problems exist, however, with adding BS4 and BS5 into the current report. As for BS4, signal strength is too great and should be reduced as quickly as possible.
  • BS 4 could instruct the BSl, 2, 3, to lower their signal-to- interference target and thereby force the MS power down quickly by using fast power control bits so it would not disturb BS4. It would also be beneficial if the BS4 uplink is included in the DHO combining at the same time to compensate for the reduced uplink power of the UE.
  • the BS4 downlink could be started and the MS active set could be updated later on when the network considers it to be appropriate.
  • MS communication on TCH causes unacceptable interference with communications already established between MS2 and BS5 on channel TCHp.
  • MS I detects BCH downlinks from BS4 and BS5 as it moves to position B and reports to the network when )NS is exceeded for each neighboring base station. When the threshold is reached, the network does not immediately command the handoff procedure, but signals the base station to make an uplink evaluation.
  • the Base Station BS4 or BS5 Upon doing so, the Base Station BS4 or BS5 will detect the power level problems or interference conditions and will report the conditions to the network. If BS4 and BSl, 2, 3 are operating on the same frequency, the handover should be considered an early power control that is taking place to penalize this MS to the benefit of all other MSs using BS4. If the MS power is reduced the BS5 may not suffer from this MS anymore. The RNC then awaits further downlink informational input from the mobile station vis-a-vis other neighboring cells.
  • FIG 9 illustrates yet another example embodiment which makes good use of the present invention.
  • mobile station is serviced by operator 1 to the left of the border indicated and, once it moves to position B, will be serviced by a different operator, operator 2, to the right of the border.
  • the mobile station MS While in cell 1 of operator 1, the mobile station MS uplinks at frequency FI. If the mobile station moves into cell 2 of operator 2, the mobile station may uplink at frequency FI in interference with other transmissions.
  • a current list is created by the MS for operator 1 (those base stations that exceed )CS threshold) and a neighbor list for operator 2 ()NS threshold) by detecting the BCH downlinks of operator 2 cells.
  • This information is reported to the RNC of operator 2 which instructs the base station in cell 2 to measure the uplink from mobile station MS.
  • This uplink measurement may reveal high signal strength from this specific MS and hence the cell 2 is suffering from interference from this MS as long as the MS is not connected to cell 2.
  • the RNC for operator 2 then reports to the RNC for operator 1 that the neighbor list will not allow mobile station to uplink at frequency FI in cell 2. There are at least 3 options to do after receiving that information from operator 2.
  • the RNC for operator 1 could request a handover to be performed from cell 1 to cell 2 and RNC operator 2 would order the BS in cell 2 to measure on the user entity and answer the request for handover based on the measurement results.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Mobile Radio Communication Systems (AREA)

Abstract

Cette invention se rapporte à un système de télécommunication, dans lequel les passages intercellulaires sont déterminés et spécifiés sur la base des conditions de liaison montante et de liaison descendante entre une radio mobile et une station de base de cellule voisine. La radio mobile rapporte les conditions de liaison descendante pour les cellules voisines à un réseau, lequel donne à la station de base de cellule voisine l'instruction de rapporter les conditions de liaison montante à partir de la station mobile. Le réseau rapporte les spécifications du passage intercellulaire et le niveau de puissance de la station mobile sur la base des informations concernant les conditions de liaison montante et de liaison descendante.
EP00937442A 1999-06-24 2000-05-23 Passage intercellulaire avec evaluation par le reseau, assiste a la fois par les stations mobiles et par les stations de base Withdrawn EP1192830A1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
US34412299A 1999-06-24 1999-06-24
US344122 1999-06-24
PCT/SE2000/001039 WO2001001720A1 (fr) 1999-06-24 2000-05-23 Passage intercellulaire avec evaluation par le reseau, assiste a la fois par les stations mobiles et par les stations de base

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EP1192830A1 true EP1192830A1 (fr) 2002-04-03

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EP (1) EP1192830A1 (fr)
JP (1) JP2003503922A (fr)
CN (1) CN1254144C (fr)
AU (1) AU5261500A (fr)
TW (1) TW573435B (fr)
WO (1) WO2001001720A1 (fr)

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JP2003503922A (ja) 2003-01-28
TW573435B (en) 2004-01-21
CN1254144C (zh) 2006-04-26
AU5261500A (en) 2001-01-31
CN1371581A (zh) 2002-09-25
WO2001001720A1 (fr) 2001-01-04

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