EP1074100A1 - Synchronisation en temps absolu pour la localisation de terminaux mobiles dans un systeme de communication cellulaire - Google Patents

Synchronisation en temps absolu pour la localisation de terminaux mobiles dans un systeme de communication cellulaire

Info

Publication number
EP1074100A1
EP1074100A1 EP99947059A EP99947059A EP1074100A1 EP 1074100 A1 EP1074100 A1 EP 1074100A1 EP 99947059 A EP99947059 A EP 99947059A EP 99947059 A EP99947059 A EP 99947059A EP 1074100 A1 EP1074100 A1 EP 1074100A1
Authority
EP
European Patent Office
Prior art keywords
time
radio base
value
base stations
cellular communications
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Withdrawn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
EP99947059A
Other languages
German (de)
English (en)
Inventor
Dan Anders Lindqvist
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 EP1074100A1 publication Critical patent/EP1074100A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W56/00—Synchronisation arrangements
    • H04W56/0055—Synchronisation arrangements determining timing error of reception due to propagation delay
    • H04W56/006—Synchronisation arrangements determining timing error of reception due to propagation delay using known positions of transmitter and receiver
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S5/00—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations
    • G01S5/02—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations using radio waves
    • G01S5/0205—Details
    • G01S5/0244—Accuracy or reliability of position solution or of measurements contributing thereto
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S1/00—Beacons or beacon systems transmitting signals having a characteristic or characteristics capable of being detected by non-directional receivers and defining directions, positions, or position lines fixed relatively to the beacon transmitters; Receivers co-operating therewith
    • G01S1/02—Beacons or beacon systems transmitting signals having a characteristic or characteristics capable of being detected by non-directional receivers and defining directions, positions, or position lines fixed relatively to the beacon transmitters; Receivers co-operating therewith using radio waves
    • G01S1/022—Means for monitoring or calibrating
    • G01S1/026—Means for monitoring or calibrating of associated receivers

Definitions

  • the present invention relates in general to the mobile communications field and, in particular, to a method and system for accurately determining the position of mobile terminals (MTs) in a cellular communications system.
  • MTs mobile terminals
  • the prior art discloses numerous methods for determining the geographical position of a MT in cellular communications systems.
  • Some existing positioning methods use the arrival time of the signal transmitted from a MT at the radio base stations (RBSs), as the basis for the positioning calculations. These methods are typically referred to as Time of Arrival (TO A) or Time Difference of Arrival (TDOA) measurement approaches.
  • TO A Time of Arrival
  • TDOA Time Difference of Arrival
  • RBSs measure the arrival time of a signal received from a MT whose position is to be determined.
  • a central computing function converts the different arrival times of the MT's signal to distances, and calculates the results to determine the position of the MT.
  • the precision in this TO A method is determined primarily by the exactness of the burst arrival time at each RBS, with respect to a common time reference. Essentially, for high precision, the RBSs need to receive a highly accurate time reference signal, and the delays in their respective receive antenna signal paths have to be known.
  • FIGURE 1 is a simplified block diagram that illustrates a typical prior art time of arrival MT positioning system (10).
  • the MT 12 whose position is to be determined is synchronized to the RBSs (RBS 1-4).
  • the network orders the MT 12 to generate and transmit one or more bursts.
  • Each RBS (RBS 1-4) measures the respective arrival time of a burst received from the MT 12.
  • the RBSs determine the respective arrival times in comparison with a common time reference, and report the respective arrival times to a central node in the network.
  • a processor in the central node calculates the position of the MT, based on the reported arrival times.
  • an ATu connected to an RBS can comprise a Global Positioning System (GPS) receiver.
  • GPS Global Positioning System
  • a significant problem with the above-described absolute time approach is that the absolute time information needs to be distributed from the ATu to the receiving part of an RBS with a known delay.
  • the delay characteristics for each distribution path need to be known.
  • the delay between the RBS receiver and antenna needs to be known, along with delays within the receiver.
  • the specific antenna installation and receiver implementation used results in a delay that varies widely with the type of installation, operating temperature, age of equipment, type of receiver, type of connecting cables, etc.
  • the number of such delay variables implies that use of such a one-time calibration procedure would provide a time resolution with an unknown accuracy.
  • such an absolute time approach would be difficult to introduce into already existing RBSs without performing a major redesign.
  • synchronization of different base stations to a common "air frame structure" has been considered useful for many applications, such as simplified handovers of MTs between base stations, MT positioning, etc.
  • One approach that can be used for base station synchronization to a common air interface frame structure is terminal-based mobile positioning. For example, one such positioning method uses the arrival time at an MT of the signals generated by the RBSs as the basis for the MT's positioning calculations. The MT whose position is to be determined measures (at a given instant) the arrival times of as many received RBS signals as the MT can "hear,” and calculates the difference in arrival times between the bursts.
  • the MT sends the difference in arrival time information to its serving RBS, which sends the information to the system node that includes the MT positioning calculation function.
  • the precision of this method is determined by the exactness of the arrival time measurements in the MT, and knowledge of the time difference between each RBS.
  • each RBS is generated from a common time reference and can be replicated with relatively high accuracy via the transmitter's antenna system.
  • the MT being positioned "listens" to the broadcast channels from the different RBSs, measures the arrival times of the bursts, and calculates the difference in the delays between them.
  • One such proposed terminal-based approach is to place reference terminals at known locations between the RBSs.
  • the reference terminals can utilize the same positioning algorithm as the MT being positioned to perform a comparative position calculation.
  • this approach would solve the above-described problem of varying RBS delays and non- synchronized RBSs.
  • a method and system are provided for time-synchronizing a plurality of radio base stations in a cellular communications network.
  • a reference terminal e.g., modified standard mobile terminal
  • the reference terminal includes an absolute time reference function, which is used to synchronize the RBSs with respect to a common absolute time reference. Consequently, a positioning algorithm can be used to determine the position of a mobile terminal in the network with a relatively high degree of accuracy.
  • An important technical advantage of the present invention is that no new hardware interfaces are introduced between an RBS and its associated reference terminal.
  • Another important technical advantage of the present invention is that all time-critical components are concentrated in one unit, so that a new positioning system based on the present invention can be introduced in an existing RBS without replacing existing RBS equipment.
  • Still another important technical advantage of the present invention is that time of arrival measurements can be calculated with respect to the radio air interface (i.e., at the antenna), which makes the MT positioning algorithm insensitive to different RBS delay variations.
  • Yet another important technical advantage of the present invention is that the method can be used for antenna supervision both for the uplink and downlink.
  • Still another important technical advantage of the present invention is that positioning measurements can be made independently of delays in the antenna system.
  • Still another important technical advantage of the present invention is that the method can be used for accurate Time Division Multiple Access (TDMA) frame synchronization between RBSs.
  • TDMA Time Division Multiple Access
  • RBSs being used for position determinations can be temporarily located at interim locations (e.g., fairs, sports events, etc.)
  • the reference terminals can be used as a type of positioning reference terminal for terminal-based MT positioning.
  • Still another important technical advantage of the present invention is that a mobile RBS with a satellite link interface can be used as a mobile "tracker" in a positioning system, whereby a reference terminal can function as a user interface to the position algorithm function.
  • FIGURE 1 is a simplified block diagram that illustrates a typical prior art time of arrival MT positioning system
  • FIGURE 2 is a simplified block diagram that illustrates an exemplary system for time-calibrating a radio base station in a cellular communications network, in accordance with a preferred embodiment of the present invention
  • FIGURE 3 is a sequence diagram that illustrates an exemplary method that can be used to update the absolute time information in a radio base station shown in FIGURE 2, in accordance with the preferred embodiment of the present invention
  • FIGURE 4 is a sequence diagram that illustrates an exemplary time of arrival measurement sequence that can be used initially (e.g., at system set-up) for determining the position of a base station in a cellular communications network, in accordance with the preferred embodiment of the present invention.
  • FIGURE 5 is a sequence diagram that illustrates an exemplary time of arrival measurement sequence that can be used while determining the position of mobile terminals in a cellular communications network, in accordance with the preferred embodiment of the present invention.
  • FIGUREs 2-5 of the drawings like numerals being used for like and corresponding parts of the various drawings.
  • FIGURE 2 is a simplified block diagram that illustrates an exemplary system (100) for time-calibrating a radio base station in a cellular communications network, in accordance with a preferred embodiment of the present invention.
  • System 100 includes an RBS 102 coupled to an antenna subsystem 104.
  • the exemplary system 100 shown is described as part of a Global System for Mobile Communications (GSM) network.
  • GSM Global System for Mobile Communications
  • the invention is not intended to be limited to the GSM and can include any appropriate cellular network that utilizes radio signal timing (e.g., TDMA) to determine the position of mobile terminals.
  • TDMA radio signal timing
  • system 100 can be duplicated in a plurality of similar systems for time-calibrating other RBSs (not shown) in a cellular communications network.
  • System 100 also includes a reference terminal (RT) 106 coupled preferably by a wireline connection 108 to the RBS 102.
  • Connection 108 can provide power for RT 106 from RBS 102.
  • connection 108 can provide data communications therebetween, but the full technical advantages of the present invention would not be realized since added hardware (data interface) would be required.
  • RT 106 can be a modified, standard MT.
  • RT 106 is an MT with a calibrated transmission delay.
  • the internal delays inherent in RT 106 are predetermined and stored locally for calibration purposes, along with the delay characteristics of the antenna cable 110.
  • Cable 110 (with the known delay) couples RT 106 to a transmit/receive antenna 112.
  • antenna 112 is a combined GSM transmit/receive antenna section and GPS receive antenna section.
  • RT 106 also includes an absolute time reference unit (not shown).
  • the absolute time reference unit can be a
  • the RT 106 can receive highly accurate timing signals and/or absolute position information for the RT 106 from the GPS receiver. Consequently, if the RT 106 is co-located with, or a known distance and direction from the RBS 102, the RBS's absolute position is also known.
  • the GPS receiver in the RT 106 can be synchronized with a phase-locked loop (PLL) in the RT.
  • PLL phase-locked loop
  • the absolute time information thus derived with the PLL from the absolute time reference unit is used by a processor in the RT 106 to mark precisely the instant in time when the RT transmits each burst over the air interface.
  • the RT stores this burst timing information in local memory, and also forwards this absolute time information (e.g., burst X transmitted at time T) to the RBS 102 preferably via the radio air interface.
  • the burst timing information can also be forwarded to other network components by the RBS 102 using a standard message transfer protocol.
  • the respective absolute burst timing information known by each of a plurality of RBSs in a cellular network can be used by a TO A or TDOA positioning algorithm to more accurately determine the position of a mobile terminal.
  • FIGURE 3 is a sequence diagram that illustrates an exemplary method that can be used to update the absolute time information in the RBS 102 shown in FIGURE 2 (or any similar network RBS), in accordance with the preferred embodiment of the present invention.
  • the absolute time updating method 200 is applied to RBSb (e.g., RBS 102 in FIGURE 2) and its associated RT (e.g., RT 106).
  • RBSb e.g., RBS 102 in FIGURE 2
  • RT e.g., RT 106
  • the method can also be applied to update the absolute time information in each of the other network RBSs (e.g., RBSc l02' and RBSa l02").
  • the RBS 102 connects with the RT 106 (e.g., preferably via the radio air interface) and orders the RT 106 to generate a burst for transmission (measurement- or M-burst).
  • the RT 106 reads in (e.g., via the PLL coupled to the GPS receiver) the absolute time, and simultaneously transmits the M-burst over the air interface via antenna unit 112.
  • the RT 106 stores the M-burst' s reference absolute time value (absolute transmit time of the burst, or At 0 ) in local memory.
  • the transmitted M-burst is received by the RBS 102 via antenna subsystem 104.
  • the RBS 102 measures the arrival time of the received M-burst, and relates that measured arrival time value to an Absolute Time Counter (AT- CNT) value stored in the RBS.
  • the arrival time of the received M-burst (At j ) is stored in local memory in the RBS 102.
  • the RBS 102 connects (preferably via the radio air interface) with its associated RT 106 and requests the M-burst transmit time information (At 0 ).
  • the RT 106 sends the requested information preferably via the air interface to the RBS 102.
  • the RBS 102 (an internal processor) then calculates the difference between the M-burst' s transmit reference time value (At 0 ) and received arrival time value (At,).
  • the processor in the RBS 102 uses the difference value ( ⁇ t) to update the absolute time value in the AT-CNT with the difference value ( ⁇ t) and thus compensate for any pre-existing time error.
  • the RBS 102 uses the AT- CNT to continue providing the absolute time by counting internal clock periods (e.g., the AT-CNT can "free- wheel" in-between the periodic absolute time updating or calibrating events, by use of the internal TDMA clock).
  • the time of arrival for signals received from an MT whose position is to be determined can be based on the highly accurate absolute time reference provided by the present invention, as measured at the receive antenna port of the RBS(s) involved. In other words, the reference point for the highly accurate time of arrival measurement is at the receive antenna port for the RBS involved.
  • the delay between the receive antenna (e.g., 104) and the RBS (102) has been compensated for.
  • the following method can be used to synchronize the TDMA operations in a network of RBSs.
  • a network base station controller (BSC) or mobile services switching center (MSC) sends a message to all RBSs involved (e.g., each similar to RBS 102), which orders the RBSs to time-align the generation of TDMA slots and transmissions based on a given absolute start time value (TDMA-start).
  • Each RBS uses the AT-CNT value described above to await the TDMA- Start command and start (or adjust) the respective RBS's TDMA counter.
  • the above-described absolute time-counter updating method 200 can also be used to enhance the precision of the TDMA timing in the network.
  • the network BSC (or MSC) can request RBSs to provide their respective TDMA counter values at known absolute times, in order to monitor the precision of network synchronization.
  • each RT locked to its respective RBS can continuously measure the arrival time of received bursts expressed as an absolute time value, and store the absolute time value in local memory.
  • a central node e.g., BSC or MSC in the GSM
  • a processor in the central node evaluates the time differences between the RBSs, and calculates a time offset for each RBS.
  • the central node sends a respective time offset as a control parameter to the pertinent RBS, which uses the time offset to adjust its air timing generator accordingly and minimize the time error at the transmitter antenna point.
  • the TO A of bursts received by an MT from these time-calibrated RBSs can be used by a positioning algorithm to more accurately determine the position of the MT.
  • the central node may order the RTs periodically to report the absolute time information for the TDMA structure for verification purposes, or at any time as part of a system supervisory function.
  • the above-described terminal-based synchronization function can be performed in steps, such as, for example, first synchronizing the neighboring RBSs in the same cell, then synchronizing the neighboring RBSs in other cells, and so on until the entire network is synchronized. Consequently, this method will account for all of the delays in the antenna system, and provide a complete "air interface sync.”
  • FIGURE 4 is a sequence diagram that illustrates an exemplary time of arrival measurement sequence 300 that can be used initially (e.g., at system set-up) for determining the position of a base station in a cellular communications network, in accordance with the preferred embodiment of the present invention.
  • each RBS involved e.g., RBS 102 in FIGURE 2
  • orders its associated RT e.g., RT 106
  • the RT's geographical position e.g., X,Y or latitudinal and longitudinal coordinates
  • the RT sends (preferably via the air interface) the requested position information to the RBS (102).
  • the RBS reports this position information to a central positioning function in a network MSC, which can use the reported position information from each such RBS as a basis for MT positioning calculations.
  • FIGURE 5 is a sequence diagram that illustrates an exemplary time of arrival measurement sequence 400 that can be used while determining the position of MTs in a cellular communications network, in accordance with the preferred embodiment of the present invention.
  • Sequence 400 can follow and/or be complementary to the time of arrival measurement sequence 300 described above with respect to FIGURE 4.
  • the RBS e.g., RBSa 102
  • the MT whose position is to be determined e.g., MT 420
  • T- bursts timing measurement bursts
  • the network BSC or MSC orders all of the RBSs involved in the position determinations (e.g., RBSb 102, RBSc 102', and RBSa 102") to perform a time of arrival measurement at a predetermined time, and each with a predetermined frequency and timeslot.
  • each RBS receives the T-burst and measures its respective arrival time. Each RBS then relates the respective measured arrival time with the absolute time value in the respective AT-CNT. The resulting absolute time value associated with each respective measured arrival time is stored in each respective RBS's local memory (Mtime 0 ).
  • the following sequence of steps is virtually identical to the absolute time updating sequence 200 described above with respect to FIGURE 3. However, the following sequence can be performed at each MT positioning event, in order to ensure that the delays experienced for the received burst are the same for the MT whose position is being determined (e.g., MT 420) and the RT for each RBS involved in the positioning events. Consequently, the sequence shown in FIGURE 5 can be used to compensate for delay differences caused by temperature variations and other variations between the different receivers.
  • each pertinent RBS connects with its associated RT and orders the RT to generate one or more M-bursts.
  • each RT reads its absolute time reference (e.g., from a GPS receiver), transmits its M-burst, and stores the absolute time reference value (absolute transmit time of the burst, or At 0 ) in local memory.
  • the pertinent RBS receives the transmitted M-burst from the associated RT, measures the arrival time of that burst, and relates that measured arrival time value with the absolute time reference value in the AT-CNT.
  • the RBS stores the resulting absolute time value for the measured arrival time (At,) in local memory.
  • the pertinent RBS connects with its associated RT and requests the transmission time of the M-burst (At 0 ).
  • RBS reports the calculated absolute time value to the central MT positioning function preferably in the network MSC.
  • the time of arrival measurements used in making MT position determinations are time-aligned precisely with the absolute time reference values provided by the present invention.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Mobile Radio Communication Systems (AREA)
  • Position Fixing By Use Of Radio Waves (AREA)
  • Synchronisation In Digital Transmission Systems (AREA)

Abstract

L'invention concerne un procédé et un système pour la synchronisation dans le temps de plusieurs stations radios fixes (RBS1-4) d'un réseau de communication cellulaire. Un terminal de référence (106)(ex : un terminal mobile standard modifié) est placé à des endroits connus, au niveau de chaque site RBS du réseau, de préférence le plus près possible de l'antenne (104) de la station fixe. Le terminal de référence (106) comprend une fonction de référence dans le temps absolu, utilisée pour la synchronisation des RBS (102) par rapport à une référence commune dans le temps absolu. Par conséquence, un algorithme de localisation peut être utilisé pour la détermination de la position d'un terminal mobile (12) du réseau, avec un degré de précision relativement élevé.
EP99947059A 1998-04-24 1999-04-09 Synchronisation en temps absolu pour la localisation de terminaux mobiles dans un systeme de communication cellulaire Withdrawn EP1074100A1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
US6577198A 1998-04-24 1998-04-24
US65771 1998-04-24
PCT/SE1999/000579 WO1999056413A1 (fr) 1998-04-24 1999-04-09 Synchronisation en temps absolu pour la localisation de terminaux mobiles dans un systeme de communication cellulaire

Publications (1)

Publication Number Publication Date
EP1074100A1 true EP1074100A1 (fr) 2001-02-07

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EP (1) EP1074100A1 (fr)
CN (1) CN1306708A (fr)
AU (1) AU4297999A (fr)
CA (1) CA2330280A1 (fr)
WO (1) WO1999056413A1 (fr)

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AU4297999A (en) 1999-11-16
WO1999056413A1 (fr) 1999-11-04
CA2330280A1 (fr) 1999-11-04
CN1306708A (zh) 2001-08-01

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