Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W64/00—Locating users or terminals or network equipment for network management purposes, e.g. mobility management
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W64/00—Locating users or terminals or network equipment for network management purposes, e.g. mobility management
  • H04W64/006—Locating users or terminals or network equipment for network management purposes, e.g. mobility management with additional information processing, e.g. for direction or speed determination

Definitions

• the invention relates to a location method employed in a radio system which comprises at least one base station and a mobile station.
• the invention also relates to a radio system which comprises at least one mobile station and a base station and which is arranged to determine a location estimate of the mobile station.
• One of the most common methods of determining the location of a mobile station is to measure the timing between the mobile station and at least three base stations, whereby the signal propagation time between the mobile station and each of the base stations is found out.
• the distance of the mobile station from the base stations can be represented as a circle about each base station, since in most cases the direction of the mobile station from the base stations is not known, and the radius of each circle represents the distance of the mobile station from the base station. All, at least three, circles have one common intersection, which is a location estimate of the mobile station.
• Known measuring methods used for mobile station location include TOA (Time Of Arrival) measuring and TDOA (Time Difference Of Arrival) measuring.
• US Patent 5,508,708 which is incorporated herein by reference, also discloses a solution to determine a location estimate of the mobile station, by means of at least three base stations, based on measuring the timing of the signals.
• the radio systems have a drawback concerning these location methods, which results from the distance between the subscriber termi- nal and the base station, i.e. a near-far problem.
• this problem is also known as an audibility problem.
• a mobile station locating close to one base station cannot be heard by other base stations, and due to interfering transmission of the nearby base station, the mobile station cannot hear the other base stations.
• the signal propagation time between the mobile station and at least three base stations cannot be measured, the location of the mobile station cannot be determined either in this manner.
• US Patent 5,508,708 attempts to reduce the audibility problem by using a so-called PUF (Power Up Function), by means of which transmission power is increased for the duration of location measuring.
• PUF Power Up Function
• the increase in power increases interference in the radio system, which considerably decreases the capacity of the radio system, and therefore it is not a suitable solution for the problem, if the locations of a plurality of mobile stations have to be estimated in the same area within a short period of time.
• the PUF function also increases power consumption of the mobile station and accelerates the battery discharge.
• the object of the invention is thus to provide a method and a radio system implementing the method to the effect that the above drawbacks can be eliminated.
• This is achieved with a method of the type described in the preamble, which is characterized in that, in order to determine a current location estimate of the mobile station, at least one previous measuring data item relating to the location of the mobile station is stored; new timing of signals between the mobile station and at most two base stations is measured; the current location estimate of the mobile station is determined by means of the new timing and at least one previous measuring data item relating to the location of the mobile station.
• the radio system of the invention is characterized by comprising: a memory, in which is stored at least one location data item of the mobile station or a signal timing data item determining the location estimate of the mobile station; timing means for measuring the timing of the signal between the mo- bile station and at least one base station; location calculating means for determining the current location estimate of the mobile station by means of the new timing and at least one previous location data item or the timing data item determining the location estimate.
• the audibility problem alleviates or is eliminated altogether. There is no need for three base stations to determine the location estimate of the mobile station, but in many cases, the location estimate of the mobile station can be determined with two base stations, and in favourable conditions even with one base station.
• Figure 1 shows a radio system
• Figure 2 shows location determination of a mobile station by means of two base stations
• Figure 3 shows location determination of a mobile station by means of two base stations
• Figure 4 shows location determination of a mobile station, the transmission of the base station being sectorized
• Figure 5 shows location determination of a mobile station by means of one base station
• Figure 6 shows location determination of a mobile station by means of location area data of the mobile station
• Figure 7 shows location determination of a mobile station by means of a Kaiman filter
• Figure 8A is a block diagram of a mobile station
• Figure 8B is a block diagram of a base station
• Figure 9 is a block diagram of a transceiver
• Figure 10 is a block diagram of a transceiver.
• Figure 1 shows a radio system, which comprises a mobile station
• the mobile station 100 which is preferably a mobile telephone, communicates with the base station 102, for instance.
• Base stations 104 and 106 are neighbouring base stations of the base station 102.
• the base stations 102 to 106 preferably have a common base station controller 108, from which there is a further connection, for instance via a mobile services switching centre (not shown in Figure 1), to other parts of the mobile telephone network and to other telephone networks.
• the network part of the radio system is determined to comprise all other parts of the radio system than the mobile stations 100. For measuring the location of the mobile station, or more precisely the location estimate, a signal propagation time between the mobile station and at least one base station is needed.
• the signal propagation time between the mobile station and the base station can be measured by the base station or the mobile station in a known manner. Timing measurement of the mobile station signal will be studied in the following. First the mobile station measures a time of arrival TOA of the signals transmitted by each base station. Time differences of arrival TDOA between the base station signals or an observed time difference OTD can be formed by calculating the differences of the times of arrival TOA of the base stations. In the CDMA system, the time of arrival can be determined by utilizing the synchronization of a spreading code.
• the signal propagation time between the mobile station and the base station is t2 less t1.
• the mobile station measures the time t1 and the base station measures the time t2.
• the clock need not be synchronized with the base station clocks.
• the round-trip measuring has to be performed with all those base stations whose signal timing the mobile station measures.
• the round-trip signal is not needed when using the TDOA method based on time differences for determining the location. In the TOA method based on propagation time delays the round-trip signal is thus only needed to a serving base station.
• the base stations can measure the propagation time and/or the difference in propagation times (TDOA; OTD) of the signal transmitted by the mobile station in a known manner.
• TDOA difference in propagation times
• the measurings in accordance with the invention are preferably carried out on so-called lines of sight. If there is no line of sight, the determined location estimate of the mobile station may deviate up to hundreds of metres from the true location in a hilly terrain, and also in an urban area typically several tens of metres.
• the location estimate of the mobile station is determined in at least one measuring, by means of at most two base stations, utilizing at least one previous location-related data item of the mobile station.
• the location-related data item can be a previ- ously determined location estimate of the mobile station or a signal timing data item measured for the previous location estimate.
• These location-related data can be stored in the mobile station or in a unit in the fixed network part. Since data to be stored accumulate all the time, and storing cannot be continued endlessly, it is preferable that stored data items are reduced, when the mem- ory capacity is running out or the maximum number of data items to be stored is achieved.
• the inventive solution requires the memory to comprise data items starting from the moment when the position of the mobile station could last have been estimated, the stored data items can be reduced, if need be, for instance such that every second data item is deleted from the memory when more memory capacity is needed. However, it is not advisable to delete the last formed, location-related data item, unless the data item is clearly erroneous. Moreover, the storing of data needed for location can be discontinued, when the mobile station is stationary. The movement of the mobile station can be determined as a change in the mobile station location at different measur- ing instants. If the location estimate of the mobile station, the TOA or TDOA measuring result does not change substantially in successive measurings, it can be assumed that the mobile station is stationary.
• the movement of the mobile station and particularly its speed can be determined by known methods of measuring movement, independent of the invention.
• Figure 2 illustrates a situation, in which the true location or a location estimate of the mobile station 204 is known at a given instant of time T1.
• the locations of the mobile station 204 on measuring occasions preceding the measuring instant T1 are indicated with the letters X.
• the location estimate of the mobile station 204 could have been determined at the instant of time T1 by any known mobile station location method.
• the location estimate of the mobile station 204 is generally determined by means of one or more base stations 200, 202.
• the location estimate of the mobile station 204 is deter- mined at the instant of time T1 by means of three or more base stations.
• the location estimate of the mobile station 204 is determined by the method of the invention utilizing at most two base stations. It is known on the basis of the signal timing that, at the measuring in- stant TO, the mobile station 204 is located at a distance R1 from the base station 200 and at a distance R2 from the base station 202. Consequently, the mobile station 204 must be located at either one of the intersections 206 and 208 of the circles with radii R1 and R2.
• the highest speed of the mobile station 204 is utilized by assessing how far from the loca- tion of the measuring instant T1 the mobile station 204 can move between the measuring instants T1 and TO.
• Said distance which is here defined as a travel estimate
• D Said distance
• the travel estimate is an estimate on the travel possibly or probably made by the mobile station between the measuring instants.
• these three circles having the radii R1 , R2 and D determine the intersection 208 to be a new location estimate of the mobile station 204. If the mobile station is assumed to continue its travel with a high probability in a given direction, the travel esti- mate can be depicted by other means than a circle.
• the shape of the travel estimate can be an ellipse, for instance, at one center of gravity of which the mobile station 204 is located at the instant of time T1. Moreover, more than one locations of the mobile station 204 or the location-related signal timing prior to the measuring instant TO can be utilized when determining a new loca- tion estimate of the mobile station 204 at the instant of time TO. All measured distances R1 , R2 and D involve a measuring error, but for the sake of clarity, the errors have not been shown in the figures (only Figure 5 shows the error limits of the radius R1).
• the speed of the mobile station 204 can be estimated at each measuring instant by using a map over the location area, since in a given environment the mobile station tends to move at given speeds. For instance, speeds in urban areas are typically less than 50 km/h, even though the fastest possible means would be used for moving. In a region between densely populated areas, it is common to move a lot faster than 50 km/h.
• the speed of the mobile station can also be estimated by utilizing the information on what kind of travel routes there are in the location area of the mobile station. When the mobile station can be localized to a road, railway, or for instance, to a waterway, it is also easy to estimate the speed of the mobile station on said travel route.
• Speed can also be estimated by statistical methods, in which case advance measur- ings on the speeds of the mobile stations and dispersion of the speeds have been carried out in each area to be measured. Hence, it can be estimated that the speed of the mobile station is, for instance, the average speed in the area and a travel estimate can be formed thereby.
• Figure 6 shows an example of utilizing the information on the mobile station location for determining a loca- tion estimate of the mobile station.
• Figure 3 illustrates a situation, in which the mobile station 304 moves so fast that, at the measuring instant TO, the intersections 306 and 308 of the base station 300 and 302 circles with radii R1 and R2 are within a circle with radius D belonging to the instant of time T1.
• a point which is in the middle of the overlapping areas of the circles having the radii R1 and R2 is in this case determined as the location estimate of the mobile station, whereby the location estimate error is substantially minimized.
• the location estimate of the mobile station 304 is the middle point of the line connecting the intersections of the circles.
• Figure 4 illustrates a situation, in which the base station 400 transmits or receives signals in a sectorized manner.
• the mobile station 404 is at a distance R1 in a sector of the base station 400.
• the mobile station 404 is also simultaneously at a distance R2 from the base station 402.
• the sector defined by the antenna beam of the base station 400 and the omnidirectional antenna beam of the base station 402 have only one intersection.
• the location estimate of the mobile station 404 is determined at the intersection 406.
• Figure 5 illustrates an inventive solution employing only one base station 500 for the location of the mobile station 502.
• the distance of the mo- bile station 502 from the base station 500 is determined to equal the radius R1 on the basis of the timing of the signals.
• Said distance R1 involves inaccuracy, which is indicated with the letter E.
• a circular travel estimate having a radius D is associated with the mobile station 502. Consequently, the new location area of the mobile station 502 will be a curved zone 504, which is the common intersec- tional area of the travel estimate circle and the inaccuracy E in the distance R1.
• any one of the points of the zone 504, for instance the middle point of the zone is determined as the location estimate of the mobile station 502.
• a point in the overlapping areas of the circles having the radii R1 and D can be determined as the location estimate of the mobile station, at which point the maximum error in the location is minimized. Said point is approximately the middle point of the line connecting the intersections of the circles having the radii R1 and D.
• the location of the base station (base sta- tion 500) included in the measuring can be determined as the location estimate of the mobile station 204.
• Figure 6 shows a situation, in which the mobile station's location area data are utilized for determining the location.
• the location estimate 606 of the mobile station can be determined by means of two base stations 600 and the signal timing 602, as clearly appears from Figure 6.
• the other intersection of the circles cannot be the location of the mobile station, since it is not on the route 604, where the mobile station was already located in accordance with a plurality of previous location estimates.
• Figure 7 illustrates determination of the location estimate of the mobile station 704 by means of two base stations 700 and 702 when using Kal- man filtering (referring herein in particular to the Extended Kalman Filter), or the like, for the measuring data.
• Kal- man filtering referring herein in particular to the Extended Kalman Filter
• ⁇ x and ⁇ x are variances of speed errors ⁇ x and ⁇ y and ⁇ xy is a cross correlation of the speed errors ⁇ x and ⁇ y .
• the variances describe how much each speed component may change during an iteration cycle. The greater the variances, the greater the assumed change of speed.
• the values in the cross-correlation matrix Q of speed errors can be calculated statistically, if applicable measuring data is available.
• the matrix C can be used as an initial value of a matrix M of the Kalman Filter.
• the matrix C values in various ranges can be calculated statistically, if suitable measuring data is available. When the variances of measuring errors grow, the location estimates calculated by the Extended Kalman Filter will be more and more based on the model of the filter and less on the measurings.
• solutions only employing a simple travel estimate circle and extended Kalman filtering can be combined into a solution which is similar to extended Kalman filtering but simpler.
• the speed and direction of the mobile station are estimated from history data, i.e. from previous location estimate data and/or from signal timing measurings.
• the mobile station's location estimate, speed and direction at the instant T1 are known, it is possible to provide an estimate on the location of the mobile station at a subsequent measuring instant TO.
• the timing of signals between the mobile station and the base station are measured, on the basis of said timings are determined the mobile station's preliminary location estimates, which are two in number, if the meas- uring included only two base stations. Of these two preliminary location estimates the one that is closer to the location estimated at the instant T1 is determined as the actual location estimate in the inventive solution.
• Figure 8A is a transceiver block diagram illustrating a mobile station.
• the mobile station determines its own location estimate.
• the mobile station hears signals of at most two base stations for new location measuring (previous signal measurings could have been performed by using three or more base stations).
• the mobile station receives and transmits through an antenna 800. Transmission and reception are possible through the same antenna 800, since a transmitter block 804 and receiver blocks 806 to 816 are separated with a duplex block 802 in a known manner.
• the signal propagates from the antenna 800 via the duplex block 802 to an RF block 806, where the signal is converted from a radio frequency to a base band in accordance with the prior art.
• the baseband signal is also transformed to digital.
• the digital signal propagates to a signal processing block 816 of the receiver, which block is irrelevant to the invention and where demodulating, channel decoding, de-interleaving and so on are performed on the signal, for instance.
• the digital signal also propagates to a block 808, which is relevant to the invention, and where the signal timing is determined, by means of which timing the mobile station knows how far the mobile station is from the base station that transmitted the signal.
• Information on the signal timing or the distance from the base station is transferred to a location calculation block 814, whereto the travel estimate from the block 810 is also transferred.
• Stored data on previous locations of the mobile station or signal timings from the block 812 can also be supplied to the location calculation block 814.
• the location data on the base stations that are included in determining the location estimate of the mobile station are also needed.
• the data on timing differences of the base station clocks are also needed.
• the base stations transmit these data to the mobile station, when necessary, in prior art signalling.
• Figure 8B depicts a base station, which measures the timing of the signal transmitted by the mobile station and thus determines the distance of the mobile station from the base station.
• the block diagram is very similar to that of Figure 8A.
• the base station can determine the location estimate of the mobile station.
• Signal timing data or location data of other base stations which preferably come to the base station through a fixed network part, can be fed to the location calculation block 814, when necessary.
• the measuring base station needs location data on the base stations that are included in determining the location estimate of the mobile station.
• the timing differences of the base stations in the radio system have to be signalled to the measuring base station.
• the base station receives these data in prior art signalling between other base stations.
• Figure 9 shows a mobile station block diagram, which comprises an antenna 900, a duplex filter 902, radio frequency parts 906, a signal processing block 908, a timing block 910 and a transmitter block 904.
• the mobile station measures the timing of the signal coming from the base station in the block 910 and transmits the timing data to the base station, which determines the location estimate of the mobile station, or the base station forwards the timing data to a base station controller, for instance, or to some other unit of the fixed network part for determining the location estimate of the mobile station.
• Figure 9 can also be a block diagram of the base station, whereby the base station measures, by means of the timing block 910, the timing of the signal transmitted by the mobile station and transmits the timing data to the mobile station for determination of the location estimate.
• Figure 10 illustrates a situation, in which the base station determines the location estimate of the mobile station, after the mobile station has measured the timing of the received signals and transmitted said timing data to the base station.
• the base station receives the measuring data signal of the mobile station with the antenna 1000, wherefrom the signal propagates through a duplex filter 1002 to a radio frequency block 1006.
• the baseband signal typically passes to a digital signal processing block 1008, where the signal information is detected and the timing data are transferred to the location calculation block 1010, to which are also supplied the travel estimate of the mobile station from the block 1012, and if necessary, the data on previous location estimates or signal timings from the block 1014.
• the block entity can also be in the base station controller or some other unit of the fixed network part.
• the measuring base station needs location information on those base stations that are included in determining the mobile station location estimate. In addition, the timing differences of the base stations in the radio system have to be signalled to the measuring base station. The base station receives these data in prior art signalling between other base stations. Transmission from the base station to the mobile station is performed by means of the transmitter block 1004 through the duplex filter 1002 and the antenna 1000.
• the solutions of the invention can be implemented, particularly as far as digital signal processing is concerned, by ASIC (Application-Specific Integrated Circuit) or VLSI (Very Large Scale Integration) circuits, for instance.
• ASIC Application-Specific Integrated Circuit
• VLSI Very Large Scale Integration
• the operations to be per ormed are preferably implemented as software based on microprocessor techniques.

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• Engineering & Computer Science (AREA)
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• Mobile Radio Communication Systems (AREA)

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Cited By (7)

Citations (5)

• 1998
  • 1998-05-28 FI FI981192A patent/FI106908B/fi active
• 1999
  • 1999-05-25 AU AU43750/99A patent/AU4375099A/en not_active Abandoned
  • 1999-05-25 WO PCT/FI1999/000448 patent/WO1999062284A2/fi active Application Filing

Patent Citations (5)

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