MXPA97008410A - Celu radio localization system - Google Patents

Abstract

The present invention relates to the location of a mobile unit M of a cellular radio system is determined by determining the differences in the synchronization of a characteristic aspect of the transmission of the control channel of each base station A, B, C, D , E as measured in the mobile unit. Preferably, the characteristic aspect is the training sample that has already been used by the mobile unit in cellular systems to measure the strength of the signal in order to inform the delivery decisions. By determining the differences between the arrival time of the transmissions from four base stations A, B, C, D, the position can be derived in two dimensions without prior knowledge of the actual distance to any of the base stations. A fifth base station E allows to determine the position in three dimensions

Description

CELLULAR RADIO LOCALIZATION SYSTEM DESCRIPTION OF THE INVENTION This invention relates to radio location systems. A number of systems have been developed to identify the location of a mobile unit, using radio propagation characteristics. One such system is the Global Positioning System (GPS), in which a portable unit obtains a fixed position using radio transmissions from space satellites. This system is highly accurate, but requires special equipment, and is not reliable in locations that have poor visibility of the sky, because several widely separated satellites must be in a line-of-sight relation to the micro-telephone apparatus to obtain a fixed position. Various proposals have been made for systems that utilize the radio propagation characteristics of a cellular radio system to provide a position determination for a mobile cellular radio unit. This would allow the mobile unit itself to act as a position location device. As is well known, cellular radio systems allow the user having a portable micro-telephone device (a "mobile unit") to make and receive telephone calls, either to another mobile unit or to a conventional fixed termination, by means of a radio link. The radio link is established between the mobile unit and one of a network of fixed radio base stations distributed over the area to be covered, the system allows any mobile unit to communicate through any base stations; usually the mobile unit will communicate through the base station providing the best radio signal quality. Because the mobile unit can move during the course of a call, it may become necessary for it to move outside the range of the base station with which the call was initially established. Cellular radio systems therefore include delivery systems to allow communication to be established with a second base station, and to exit the first, without interrupting the call itself as it is perceived by any of the parties to the call . In the system known as GSM (Global System for Mobile Communications), the mobile unit frequently monitors the BCCH (Transmission Control Channels) of the surrounding base stations in order to establish which base station is providing the best signal, and therefore through which base station a new call can be established, or if a delivery should be initiated. This process occurs in both idle and active modes, that is, there is no need for the user to make a call. Developments in GPS technology mean that a highly accurate synchronization supply can now be implemented at a relatively low cost at each cellular radio base site. A good synchronization supply has a number of benefits, these include; improved delivery, a capability to reduce the interference effect between neighboring base stations, and allow highly accurate radiation frequencies over the radio interface. It should be noted that unlike simple transmission time signals, the GPS synchronization signal takes into account the position of the GPS receiver, and can therefore compensate for the time delay caused by the finite speed of the radio waves. European Patent Specification EP0320913, (Nokia), describes a system in which the synchronization pulses derived from the GPS system are transmitted from each of three or more base stations, and their different arrival times to the mobile unit are used to identify the position of the unit. This prior art system requires the mobile unit to interrogate each base station in turn, which requires to establish communication between the different base stations in order to ask this question. This requires the use of various traffic channels, or an auxiliary channel and also requires that reliable radio communication be established with each nearby base station. In International Patent Application W095100821 (Omniplex) and in US Patent 5,293,645 (Sood), each base station transmits data signals in synchronized packets. The mobile unit monitors all packet data channels of the base stations simultaneously, which requires either a mobile unit capable of receiving different radio frequencies at a time, or that all base stations transmit their data packets over the same channel. None of these aspects are conventional in a cellular radio system. Both of these systems also require the transmission of synchronization pulses or special synchronization from the cell sites (base stations) to the mobile unit, and in recognition of these pulses by means of the mobile unit. This requirement not only imposes an overload of signaling on the mobile unit, but requires additional functionality in the mobile unit to recognize the synchronization pulses. According to the invention, there is provided a method for determining the location of a mobile unit of a cellular radio system having a plurality of base stations, comprising the steps of determining the differences in synchronization between the transmissions of the stations of base as measured in the mobile unit, determine from the synchronization differences the differences in the distance of the mobile unit from each of the base stations, and derive the location of the mobile unit from the difference in the distance determined in this way, characterized in that the time division frame structures of the control channels of at least some of the base stations within the radio range of the mobile unit are synchronized, and the mobile unit determines the differences in the synchronization in the mobile unit of a characteristic aspect of the transmission of structure of division frame of t time by means of the control channel of each base station. Using the control channel, the mobile unit is able to make use of the existing radio link quality monitoring systems used to establish whether a delivery should take place, and does not need to establish full communication with any of the base stations. Preferably, the characteristic aspect used is a training signal transmitted by each base station, which is correlated with a reference training signal stored by the mobile unit. Such "synchronization explosion" (SCH), and its correlation process are already part of the GSM standard to characterize the radio path. The method of the invention can therefore make use of these existing signals and the programming of the correlation analysis. However, for position determination it is preferred that the system uses the first identified correlation of the reference signal, instead of the strongest one as used for delivery determination. This ensures that the path of the most direct signal, instead of the strongest but most indirect path, is used for the calculation of the distance. The derived location can also be averaged over time to minimize the effects of spurious results from the reflected signals, which would make the apparent distance between the station and the mobile unit bigger than it really is. The derived location can communicate through the cellular radio network to a remote user, rather than to the user of the mobile unit itself. An alarm signal can be transmitted if the derived location corresponds to a predetermined location. According to another aspect of the invention, a mobile unit is provided for use with a cellular radio system, the mobile unit comprising apparatus for determining the position of the mobile unit; apparatuses comprising means for detecting the time differences between the signals received from the different radio base stations, and means for determining, from the time differences, the differences in the distances of the mobile unit from each of the base stations; and means for deriving, from differences in distance, the location of the mobile unit, characterized in that the mobile unit has means to determine the time differences in the mobile unit of an aspect of a frame structure transmission. division of time synchronously by means of the control channel of each base station; the mobile unit may further comprise data means for receiving data from the station currently serving with respect to the base stations within the radio regime of the mobile unit, the information including the geographical locations of the base stations. The cellular radio station can be complementary in the mobile unit of the second aspect of the invention as defined in the above. Alternatively, the location determination functions can be performed by the network itself. Accordingly, the cellular network may comprise means for determining the difference in time between the signals transmitted by the base stations as measured in the mobile unit; means for determining, from the time differences, the differences in the distances of the mobile unit from each of the base stations; and means for deriving, from differences in distance, the location of the mobile unit, characterized in that the base stations have transmission control channels operating with synchronized time division frame structures that have a characteristic appearance for the detection by means of the mobile units and having means to receive from the mobile unit an indication of the arrival time in the mobile unit of characteristic appearance from each base station. According to a further aspect of the invention, there is provided an apparatus for determining the position of a mobile unit using a cellular beam system having one or plurality, such apparatus comprising means for determining the time differences of the operation of the cells. base stations as measured in the mobile unit; means for determining, from the time differences, the differences in the distances of the mobile unit from each of the base stations; and means for deriving, from differences in distance, the location of the mobile unit, characterized in that the apparatus comprises means in the cellular radio system to synchronize the time division frame structures of the transmission of control channels by means of at least a plurality of base stations within the radius of the mobile unit, and means in the mobile unit to determine the differences in time in the mobile unit of a characteristic aspect of the transmission of the structure of the mobile unit. time division frame by means of the control channel of each base station. The time difference measuring means, the distance difference determining means and the means deriving the location can each form part of the mobile unit or the fixed network. If they are in the mobile unit, this unit may further comprise means for receiving data from the base station currently serving the base stations within the radio regime of the mobile unit, the information including geographical locations of the stations of base. In existing GSM systems, each base station transmits a control channel (BCCH) having a TDMA frame structure. This frame structure is composed of temibrarmarches "each of 235.38 milliseconds Each multimarco has a substructure of fifty-one frames, each frame having eight explosions. Each explosion is composed of three bits of "tail", 142 bits of information, three more bits of "tail" and a protection period equivalent in duration to 8-114 bits. The frame therefore has 156-114 bits of duration, and each bit lasts for approximately 3.9 microseconds, such that the explosion lasts for 0.577 milliseconds. The frames in each multi-frame are conventionally numbered from 00 to 50, of which five are frequency control frames (FCCH), (00, 10, 20, 30 and 40); and five are synchronization frames (SCH); 01, 11, 21, 31, 41. The interval between the synchronization frames so generally is 46.15 milliseconds, (80 explosions), but the interval between the frames 41 and 01 has a duration greater than 50.77 milliseconds (88 explosions ) due to the presence of the additional frame 50. The synchronization frames each include a training sequence that is used in this embodiment of the invention as the characteristic aspect. In GSM, the use of time division multiple access (TDMA) means that the mobile station and the base station that is serving must be highly synchronized. In order for the mobile unit to decode the BSIC identity code of a base station, it has to briefly self-synchronize with the base station. Accordingly, the mobile unit always has an indication of what fraction of a frame (ie how many bits) each of the neighboring base stations differ from the base station that is serving, as seen by the mobile unit. If the frame cycles of all the base stations were absolutely synchronized (ie all base stations transmit simultaneously the same part of the frame) the amount of the mobile unit would have to change its frame structure (with respect to the base station which is providing service) to decode the BSIC of the other base stations would only be a function of the difference in the length of the path between the base station that is providing service and the neighboring ones. In existing systems, mobile units are synchronized with respect to their base stations that provide service at a point better than 114 bit, 0.923 microseconds, which, at the speed of light (3x108 mis), corresponds to a resolution of 277 m . This accuracy can be significantly improved for location purposes by using data present in the mobile unit equalizer. In GSM practice, the frame structure of each base station is in fact not synchronized in the absolute sense, but only in the relative sense in that for each base station there is some point in the frame structure that is synchronized with the external synchronization signal. Therefore, the synchronization of the frame structures of the base stations differs from the others by an arbitrary but constant amount, designated here as "displacement". The term "synchronized", as used in this specification, is used in the relative sense (that is, differentiated by a constant amount), unless the context clearly requires otherwise. It will be possible (although undesirable for other reasons) to reconfigure the GSM system in such a way that the base stations are all synchronized in the absolute sense. However, in a preferred arrangement, for each base station, the respective displacement is subtracted from the arrival time in the mobile unit of the characteristic aspect of the frame to obtain the difference between the distance at which the base station is located with respect to the mobile unit and the distance at which the base station that is serving with respect to the mobile unit is located. These calculations can be made in the fixed part of the network, but in a preferred arrangement the displacement data associated with each base station is transmitted from the base station serving the mobile unit, and the synchronization difference is determines by means of the mobile unit from such displacement data and the arrival times of the characteristic aspect of each base station. Accordingly, another aspect of the invention provides a cellular radio network for use with the mobile units defined in the foregoing, comprising a plurality of base stations operating with control channels that transmit synchronous time division frame structures., means for identifying which of the base stations are in the radio regime of the specific mobile unit, and means for transmitting data relating to the location and synchronization offsets of each base station with respect to the mobile unit. The synchronization differences provide the differences in the path lengths between the various base stations, however they do not provide an absolute path length. The prior art systems described above, the synchronization of the signals from a minimum of three base stations is considered sufficient to provide a single fixed position (in two dimensions).

In order to achieve this, it is necessary to know not only the difference in arrival times of the signals from the different base stations, but also their absolute arrival times with respect to some fixed time scale. This requires that the mobile unit have a clock synchronized with those of the base stations. The base stations can be synchronized using the GPS system, but the mobile units can not by themselves be synchronized with the GPS system unless they also incorporate GPS receivers, thereby reintroducing the complexity that was expected to be avoided when using the GPS. cellular radio characteristics. It has been suggested in advance that the synchronization advance can be used to determine the distance from the base station that is serving. The synchronization advance is the amount by means of which the serving base station instructs the mobile unit to advance its transmissions with respect to the signals received by the mobile unit, to allow transmissions from the mobile unit to arrive to the base station at its point located in the TDMA frame. The synchronization advance corresponds to the time taken by the radio waves to cover the round trip distance between the base station and the mobile unit, that is, twice the length of the path. However, synchronization progress is only determined when a mobile unit has a call in progress. In addition, the synchronization advance is determined for the strongest signal, which is not necessarily the most direct if multipath interference is present, and its accuracy is also relatively coarse. Instead, in a preferred arrangement according to the invention, the differences in synchronization between at least four base stations are determined (conveniently these are the differences between the base station currently serving and each of the three neighbors), which allows the determination of the absolute location of the mobile unit in two dimensions. As will be described later, the use of four base stations provides a unique result in two dimensions, without the need for an absolute reference in the mobile unit. In another preferred arrangement, the differences in synchronization between at least five base stations (the base station that is serving and four others) is determined, thereby allowing the absolute location of the mobile unit in three dimensions. This last arrangement is preferred if the differences in the attitudes of the base stations and / or the mobile unit are large in relation to the overall accuracy of the system. The embodiments of the invention can, however, use synchronization advance information to supplement the basic method in circumstances where less than the minimum number of base stations are detected by means of the mobile unit. Other supplementary information may be used when circumstances require, such as information regarding the direction of the mobile unit with respect to the antenna. If one or more of the plurality of base stations in the cellular radio system have a very limited regime, the method may comprise an additional step wherein if it is recognized that the mobile unit is within the regime of one of the radio stations. Based on the regime, it is determined that the location of the mobile unit is the location of such a base station limited by the regime.

One embodiment of the invention will now be described with reference to the drawings in which: Figure 1 shows part of a cellular radio system; Figure 2 is a part illustrating schematically the system of Figure 1 in more detail, and indicating the various parameters used in the calculations performed in the method of the invention; Figure 3 illustrates the propagation of multiple trajectories; Figure 4 shows a correlation diagram against time for a training sequence. Figure 1 shows a cellular radio system including a mobile unit M, a base station A, currently serving the mobile unit M, and six neighboring base stations B, C, D, E, F, G. Each base station is shown to have a hexagonal cover area, or "cell", however in practice the cells are more irregular due to topographical reasons, and the base station sitting. In addition, the propagation characteristics of the radio waves mean that the coverage areas are superimposed in practice, and the mobile unit can detect signals coming from several nearby base stations, although with less force than those coming from the A station of base that currently serves. For purposes of illustration, it is assumed that the mobile unit M can detect the BCCH (control channel) of the base stations A, B, C, D and E at least. The coverage area of the base station A is subdivided into three sectors A1, A2, A3 of 120 degrees each of which is served by a respective sector antenna in the base station A having its own channel location. Also within the coverage of base station A there is a micro-shed H. This is a cell that has its own low-energy (and therefore short-rate) base station, provided to serve a limited area that has a high call traffic demand, and / or to which the main cellular structure serves poorly, for example due to tall buildings. In Figure 2, the mobile unit M and five base stations A, B, C, D, E are shown, together with their coordinates in three dimensions (Xa, Ya, Za, Xb, Yb, Zb, Xc, Ye , Zc; Xd, Yd, Zd; Xe, Ye, Ze), and the distance of the mobile unit from each base station gives, db, of, dd, of, respectively. The unknown coordinates of the mobile unit M are represented as (x, y, z). For illustrative purposes, the modality will be described as operating in accordance with standard GSM, using GPS data, but it is not intended to be limiting. In GSM, each base station, (for example, base station A) has information relating to itself and six stations B, C, D, E, F, G of nearby bases. For the purpose of the present invention only four stations B, C, D, E of near bases of the six are used, the four in question being generally those that provide the strongest signal in the mobile unit M.

The base station transmits the data to the mobile unit M on its BCCH (Transmission Control Channel). These data include the radio frequency of each BCCH of the base station, allowing the mobile unit to periodically display the signal quality of each BCCH, and allow deliveries based on the results of this sampling. In this embodiment of the invention, the additional information with respect to that required by the GSM system is transmitted to the mobile unit, either on the BCCH or in a separate data message. This information includes the location of each of the base stations A, B, C, D, E and their relative frame shifts (as defined above). This offset indicates how the synchronization of the TDMA frame structure relates to the reference time frame, which may be the time frame of the base station A that is serving, or of universal reference. The radio link between the mobile unit M and the base station A is a time division multiple access (TDMA) system, in which different mobile units communicate with the base station A on the same radio frequency, in different times. At times when the base station A is transmitting to other mobile units (not shown), the mobile unit M monitors the BCCH frequencies of the base stations B, C, D, E, (F, G) as shown in FIG. identified with respect to it by means of base station A. Each base station periodically transmits a training sequence (SCH). Specifically, the GSM, the SCH is transmitted five times in each BCCH multiple frame, in the frames of TDMA 01, 11, 21, 31 and 41. This training sequence corresponds to the sequence stored in the mobile unit, which is arranged to identify correlations between the stored sequence and the BCCH transmissions, thereby allowing the mobile unit and the base station to synchronize and make a calculation of the quality of the signal. Figure 3 illustrates a phenomenon known as "multiple trajectory formation". In a typical environment radio signals can be passed between a base station A and a mobile unit M by means of a number of different paths, as a result of reflections and refraction caused by buildings and other constructions. These trajectories are, in general, of different length; for example a direct path 41 is shorter than a path 42 reflected by a building 40. The correlation of the training sequence can therefore identify more than one correlation, which occurs at different times. This is illustrated in Figure 4, in which there is a first correlation 31 at time t31 and a second correlation 32 stronger at time t32. This situation can occur when the direct path 41 is subject to attenuation, for example by means of the foliage, and the direct path 42 is not attenuated. In the example of Figure 3, an indirect, strong signal 42 will occur without the building 40 being a good radio wave reflector. For the purpose of properly determining the delivery, and synchronization with a base station, the strongest correlation 32 will be used, although this corresponds to a trajectory 42 longer than the first, weakest correlation. However, for the purpose of identifying the position, the distance of the straight line from the base station is required and thus it is used at the time of arrival of the first correlation 31, and not the strongest correlation 32. The first correlation can be related to a reflected signal, if there is no direct path line, however it will be the closest to the time of a direct signal that has arrived. The mobile unit M identifies from the respective BCCH the arrival times TB, TC, TD, TE of the first case of the training sequence from each nearby base station B, C, D, E and compares them with the time of arrival TA of the training sequence from the base station A that is serving, to identify the time intervals TI = TB - TA; T2 = TC-TA; T3 = TD-TA; T4 = TE - TA. These intervals can be measured accurately by counting the number of digital bits that occur between the arrivals of these signals. This provides an accuracy of the order of 1 microsecond. The intervals will be different, as a result of three factors: difference in the length of the trajectory; difference regarding the displacements of the frame; and the transmission in different frames. First it is necessary to eliminate the last two factors in order to determine the differences in the length of the trajectory. Each base station transmits the same synchronization training sequence five times in each control channel multiple frame, i.e. in a time interval tF. Because the mobile unit monitors the multiple control channel frames as a presynchronization method it will not always identify the correlations from all the base stations A, B, C, D, E on the same part of the cycle structure. multiple frame. However, the time difference tF between the synchronization frames (SCH) within the multiple frame of the control channel is approximately 46 ms, as previously described, which is large enough for the radio wave to propagate approximately 13,800 km . Consequently, the multiple of the frame length can easily be eliminated. The different shifts of SCH within the multiple frame can be allowed by measuring, at each base station, the transmission time of the control frame multiple frame sequence with respect to a universal reference such as the GPS synchronization signal. The base station A that is providing service transmits on the BCCH a signal representing the displacements of the neighboring base stations (with respect to either the universal reference or, preferably, with respect to their own transmissions), thus allowing these displacements are compensated. In this way a time difference ti = TI - (nltf + QB) can be derived, where QB is the displacement of the base station B with respect to the base station A, tF is the frame length, and it is not a integer in the selected normal circumstances such that the magnitude of you is a minimum. GPS provides precise time signals at 50 nanoseconds, and this can be used as the base stations to provide the synchronization information required to determine the displacement Q values. The frame of length tF is a system constant. The precision of the value of ti is therefore determined to a large extent by the precision with which TI is measured (typically of the order of 1 microsecond, as already discussed). Note that the value of ti may be negative, if the base station B is closer to the mobile unit than the base station A that is serving, as may occur if the base station A has a stronger signal in the base station. 20 mobile unit than the base station B, in spite of its greater distance, or if there is no traffic channel available on base station B. As stated in the above, the interval between SCH frames is either 88 explosions or 80 and therefore there are two possible values for tF (46.15 or 50.77 milliseconds). The position within the multiple frame can be easily determined by means of the mobile unit, and the appropriate value of tF selected. The values t2 = T2 - (n2tF + QC), t3 = T3 - (n3tF + QD), and t4 = T4 - (n4tF + QE) can be derived in a similar way. The values ti, t2, t3 and t4 when multiplied by C, the speed of the propagation of the radio waves, produce values di, d2, d3 and d4 which are the differences between the length of the trajectory and the lengths db, of, dd and of respectively (see Figure 1). Specifically, di = da - db; d2 = da - of; d3 = da - dd; and d4 = da - of.

It will be appreciated that the mobile unit does not have means to detect the GPS synchronization pulse itself, since this is not a GPS receiver. The arrival times of the training sequence can therefore be measured with respect to each other, not against an absolute time scale, and therefore the time ta required by the training signal to reach the mobile unit M from station A of base is unknown. In this way the distance given from the mobile unit M from the base station A (which is simply the distance at which the radio waves propagate in this unknown time ta) can not be derived directly (and similarly for the stations of base B, C, D, E). The relative arrival times indicate only that the base station B, for example, is also from the mobile unit M that the base station A by means of a distance di = da-db. To allow the mobile unit to calculate its position, you must know the location of the base station locations in your area. This information can be passed to the mobile unit either by using a "Cell Transmission" message or a Short Message Service (SMS) as provided on some cellular systems; both are capable of message lengths of up to 160 characters in amplitude. The information sent to the mobile unit from a base station will include; the coordinates of that base station and the information about the neighboring base stations such as their locations and their shifts (the synchronization of the training sequence relative to a universal standard, or relative to the base station that is providing service ), a flag to indicate if a base station was synchronized precisely, time and date. The base station A that provides the service transmits not only its own details but also the details of its neighbors B, C, D, E. The mobile unit M can thus obtain all the information it needs without having to deliver to other stations. base. The speed at which such information is transmitted will have to be sized to allow the mobile unit to calculate its position quickly, this is especially important if a tracking service is going to use the information. The "Short Message Service" (SMS) available in the GSM system can be used when a client initially requests the service, to provide authentication and prevent unauthorized use. Once a client has been validated as a user, the SMS can then pass a key in figures to the mobile unit to enable it to decode the cell transmission message. This system will be relatively secure as the messages that pass over the radio interface are already protected by the GSM encryption system. The SMS can be used in place of the Cell Transmission system to pass all location information from the base station to a mobile unit and allow it to calculate its position. This method will tend to make fewer errors than a Cell Transmission, since SMS is a point-to-point system. However, the large number of messages required to reach a potentially large number of mobile units could be a very high overhead over the network. Another problem with a system based on the SMS is the identification of which details of the base station locations are to be sent to a particular mobile unit without first knowing where the mobile unit is. Therefore a base station ID that is serving the mobile unit must be known by the network before the corresponding information from its neighboring base stations is transmitted over the SMS. A tracking service will require the use of SMS originating from the mobile unit if the location is to be passed to a remote center, for example emergency services or a fleet control center. The position information transmitted from the mobile unit may include a timestamp to allow delays in the SMS network and movement of the mobile unit.

The determination of the position from the synchronization differences will now be described in detail. It will be observed from the following that five base stations is the minimum necessary to ensure an unambiguous result in three dimensions if the absolute distance from any of them is known. If only two dimensions are considered, four base stations are sufficient. Figure 2 shows the information available regarding the mobile unit. The values x, y and z represent the position of the mobile unit in three dimensions, which are to be calculated. The values Xa, etc., indicate the known positions of the base stations, as they were transmitted to the mobile unit M on the BCCH. Consider five base stations: Base station A in (Xa, Ya, Za): the distance to the mobile unit is Base station B in (Xb, Yb, Zb): the distance to the mobile unit is db Station C base in (Xc, Ye, Zc): the distance to the mobile unit is from Base Station D in (Xd, Yd, Zd): the distance to the mobile unit is dd Station E base in (Xe, Ye, Ze): the distance to the mobile unit is from The mobile unit scrutinizes the base stations and measures the synchronization differences ti, t2, t3, t4 between the base station that is serving and each surrounding base station, as described in the above. These synchronization differences are directly proportional to the differences in the path length: di = tIC, where C is the propagation velocity of the radio waves, approximately 300 meters per microsecond. Therefore the mobile unit can easily calculate di a d4 where: d > = d. d "- = _ '..? ? - d. d.

The following five equations represent the location of the mobile unit, based on the equation for a sphere: (t - X.r - / Y 2 - tt Z.I '= d.! - Equation! - X,)' + i? Y,) 2 - 12 - z-, 12 = d Equation (21 ¡x - Xr i-, and Y í2 * • íz - Z! = De- - Equation ¡3! Fx X i2 -? Yi) 1 - ^ Iz - ZJ - = d - Equation fd] (x - Xl- T Y.) 1 - (¿. Zj1 =? - Equation [51 Now, di = da - db. Rewritten as di = d = -db, and taking the square root of both sides gives: Equation 6! d - 2d < ci. - d-: = du2 Replace [1] and [2] in [6] , '- 2 d, d. - (x - X''2 + IY Y.) '- iz z.r = (X -x.) 1 - < ? ? > - > ! + 'Zal Changing the order to place the known variables on the right side gives: - d, d. - x (X. -X ») - ylY. And *) -zlZ. - Zt) = k, / 2 - Equation (7a) When kl consists of the known values: k, = -d, 1 - x- 'Y-' - z. ' + x. ' + v »+ z.2 For simplicity we define: x- = x «'X-. ? «= Y > - w Equation 7a becomes: ? ¡, / O - Equation [7] dtd., -? X'i > -? '' "- z ji = k, / Repeating this process with the equations [3] to [51] gives: The stations A and C - d d - Xic - Y V.c - ZZJC = k? / 2 - Equation [81 Where. k = - i2 - X- -? «2 - Z + Xc2 and 2 - _.-" Stations A and D Equation [91 d-sd * - * X. «- v -» - zZ., A = k? Y2 Where kj = - do '- X .. - W - _T.J - ^ *' - Y- * Z < Stations A and E Equation flOJ - s, - xX «- y / V_. - _ • -_-. = * - «/ -? Where * - = - rf- '- -2 - W - ZX + X. »+ Wr * • Changing the order of the equation [7] in terms of: k_ d. =. - > v-Y -yY «• = z. - Equation [111 Substituting [11] in [8] leads to: Equation [121 c (X,? D, - X..d,) + y. { Yt? D: - Yn, dl) +:. { Z,? D. - Za.d,) - (-_l _-_-______ l. | = 0 Substituting [11] in [9] leads to: - Equation (131 - X ", dt) + y. { * - Y "rld,) H-: (Z" -, - Z &?) - (ÍÍLG¿'1-0 Substitution of [11] in [10] leads to: Equation í 741 * (- \ "rf - V." ._ /,) - < -, (Y..h b? +, ..-,) - z (Z. "d. - Z," d,) - í ________________ For the two-dimensional position, all z coordinates can be ignored. This will induce an error due to the fact that it will be unlikely that the four base stations and the mobile unit are all in exactly the same plane. In particular, base stations are, whenever possible, mounted on mountains or high structures (buildings or masts built for that purpose) to improve their regime, while mobile units usually operate close to ground level. However, when the differences in altitude are small (in the order of the accuracy of the system as a whole) the error will be negligible. Subject to these limitations, it is possible to solve in two dimensions ignoring the z coordinates from the equations and from the calculation of the terms kl, k2, etc. Equation [12] then becomes: - d, k, c (X, ". rf - V.,, /,) - (- y (Y" "d - Y d,) = 0 and equation [13] becomes: f d. { k. - d, k, c (X, .., '',) + (Y.? d, - Y,, ^,) - Both of these equations represent straight lines in the xy plane. The point where these two lines cross represents the position of the mobile unit. This point can be found by substituting one equation in the other. In the three-dimensional equations [12], [13] and [14] each one presents planes in space. The intersection of the two planes represents a straight line, therefore the three equations are needed to find the location of the mobile unit (x, y, z) only. The general equation of a plane is: Ax + By + Cz + D = Y.cd¡: C = Z. "d2- X.cdi; and For equation 1121. A X. "d? - X. < d ?; B = Y -'- di .'d.k. d.k, D To solve the intersection of the three planes, it is necessary to put the equations in the Hessian form. For the equation [12]: A- + B: + C: n. = < - > "+5 + C2 A1 + B1 + C2 The plane can now be represented simply as a vector: nx = -p. where • '«=«,' + 'z? - "• > ' Once all the planes are represented in this way, the intersection can be calculated easily. It should be noted that much of the software required to process the information of the time difference already exists in the mobile units. As described above, the time of the arrival of the information can be communicated from the mobile unit to the network, allowing the function or location determination to be developed by the network. Alternatively, the position calculation can be made in the mobile unit itself with very little overload of the network. This system will be able to support a large number of users since it does not need to make calls, apart from the initial authentication SMS messages. However, such a system will require the addition of special software in the mobile unit to perform the necessary calculations. Improvements in signal processing can also be used, for example using data obtained from the mobile unit equalizer, to solve in a better way than the 114 bit (0.923 microseconds, equivalent to 277 meters) required only for bit synchronization. The data present in the equalizer of the mobile unit must allow the revolution to 4% of a bit, equivalent to approximately 50 meters. Factors such as multiple trajectory, shading and weakening can cause the pressure of the location calculation to vary over time. Therefore, it is desirable to use time averaging in the location calculation algorithm to improve accuracy. There are a number of possible services that can be provided as assistants for a positioning service. Fraud with large amounts of money has been converted into the cellular radio industry through illegal practices such as "cionación", which is the fraudulent practice of giving a mobile unit, usually a stolen one, the electronic identity of another legitimate unit. The calls made on the "cion" are then loaded by the cellular network to the legitimate user. The existence of a connection is usually only detected when the legitimate user obtains his account statement, or if both the user and the legitimate user try to enter the system simultaneously. Providing a location service built in its place will mean that a stolen or otherwise suspicious mobile unit can be located and recovered quickly.

Similarly, building a mobile unit in a vehicle would allow the vehicle to be located, if stolen. For such services to be effective the location software would have to be enabled remotely, either by the official owners or by the police. The precise position information will be invaluable for emergency services in other ways. This service would allow the help to be directed quickly and efficiently to the person in distress making an emergency call from a mobile unit adjusted in this way. It may be desirable for the client to have control over whether the service is activated, to prevent the client from realizing that he is being watched by the authorities. Emergency services, and other organizations with large field forces such as utility companies, can make use of the cellular network, rather than a private mobile network (PMR), and the tracking service will allow a controller to monitor the distribution of field force personnel. A tracking service can be used to monitor the progress of value or sensitive loads. The system may be arranged to warn of deviations from a pre-set route. Another application would be an alarm service to alert train passengers who are tired when they have reached the station in which they have to get off. As mentioned in the above, a signal needs to be received from four base stations in order to provide a fixed position in two positions, (five base stations for three dimensions). There are some circumstances in which there are fewer base stations within the regime. Under these circumstances, several complementary methods can be used to obtain a fixed position. In a possible arrangement the mobile unit may be forced to be delivered from the base station A that currently serves a neighboring base station, for example base station B (See Figure 1). This base station will have a "neighbor list" different from that of base station A (although the lists will have several base stations in common). Between the two neighbor lists there may be enough base stations in the mobile unit's regime to obtain a fixed position. The base stations in each neighbor list will have their displacements determined according to the respective base station A or B, but this can be allowed because the displacement of the base station B relative to the base station A is known, since both are in the neighbor lists of the other. Other complementary methods may be employed. For example, the absolute distance to the base station that is currently serving can be derived from the synchronization base; that is, the amount that the transmissions of the Mobile Unit need to be advanced with respect to the signals received from the base station in such a way that they arrive at the base station in the correct time slot, This is only accurate to approximately 600 meters , and the synchronization advance is normally only calculated when a call is in progress, not when the mobile unit is on hold. As shown in Figure 1 for the base station A, one (or more) cells can be divided into sectors, ie, the base station has several antennas each serving an azimuth regime (typically 60 or 120 degrees). The identification of the sector that serves the mobile unit can be used to identify which solution of the equation is correct. However, this method is not practical when the base station has an omnidirectional antenna, nor when two or more possible outcomes occur in the same Al sector. In particular, because the division into sectors is azimuthal, it will not resolve an ambiguity in the z coordinate (altitude). In addition, there is a possibility that a side or rear lobe of the sector antenna is detected. An additional possibility is to identify, from the possible solutions, the one that is closest to the previously identified location of a mobile unit because it is the one with the greatest possibility of being the new one. This can be reasonably reliable if the mobile unit is traveling slowly compared to the time between location updates. Figure 1 also shows a microcell H. Microcells are very small cells served by low energy base stations often mounted well below roof level or even indoors to provide additional coverage at very high demand locations. . It is very possible that a GPS receiver does not work in such a base station, since it will not be reliably visible with respect to satellites, and because it is also prohibitively expensive. In addition, because the microceed H 1 5 antenna is most likely at a low level or indoors, it is likely that a mobile unit in the microceed base station regime is not in the 4-station radio regime of base, and possibly it is in the regime of a station that is not of base different from that which is serving the microcepida H. However, because the microcell H only covers a very small area, the information that the The mobile unit is within the regime of the microcell H can provide sufficient precision to locate the mobile unit with the same precision as the basic system. All these complementary processes can potentially present systematic errors, and accuracy less than the basic system, and in addition they require additional processing, but they can be used, individually or in combination, to maintain the service at least base stations that the minimum of four ( five) are within the regime of the mobile unit. The GPS system has systematic errors in it, resulting in an accuracy of approximately 100 meters. For some applications, such as plane surveys, greater accuracy is required, and a system known as "GPS difference" has been developed to overcome this. This involves placing a GPS receiver in a known "radio beacon" position accurately and measuring the error in its position as mediated by the GPS, whose error value is then transmitted to other users. The location location system of the present invention requires a significant number of cellular base stations to have adjusted GPS receivers, to provide accurate synchronization signals. Because the positions of the cellular base stations are fixed, they can be determined by other means with greater precision, allowing them to be used to provide such a differential GPS beacon radio service.

Claims (9)

RE I V I ND I C AC I ONE S

1. A method for determining the location of a mobile unit of a cellular radio system having a plurality of base stations, comprising the steps of determining the difference in synchronization between the transmissions of the base stations as measured in the unit mobile, determine from the synchronization differences the differences in the distance of the mobile unit from each of the base stations, and derive the location of the mobile unit from the differences in the distance determined in this way, characterized in that the time division frame structures of the control channels of at least some of the base stations within the radio regime of the mobile unit are synchronized, and the mobile unit determines the differences in synchronization in the mobile unit of a mobile unit. characteristic aspect of the time division frame structure transmission through the control channel of each station n base.

The method according to claim 1, characterized in that the differences in the synchronization in at least four base stations are determined, thereby allowing the determination of the absolute location of the mobile unit in two dimensions.

3. The method in accordance with the claim 1, characterized in that the differences in synchronization between at least five base stations are determined, thereby allowing the determination of the absolute location of the mobile unit in three dimensions.

4. The method according to claim 2 or claim 3, characterized in that, if at least the required number of base stations are detected by the mobile unit, the synchronization advance required for communication with the base station is is presented the service is used to derive the distance between the mobile unit and the base station that is presenting the service. 5.- The method according to the claim 2, 3 or 4, characterized in that if less than the required number of base stations are detected by the mobile unit, information regarding the detection of the mobile unit relative to one or more base stations is additionally used to identify the correct location . The method according to any of the preceding claims, characterized in that the synchronizations of the time division frame structures of the base stations are deviated from one another, and in which for each base station the displacement respective is subtracted from the arrival time of the characteristic aspect of the frame to obtain the difference between the distance at which that base station is located from the mobile unit and the distance at which the base station that is providing the service from the mobile unit The method according to claim 6, characterized in that the data relating to the displacement associated with each base station is transmitted from the base station that is presenting the service to the mobile unit, and the calculation of the distance is determined by the mobile unit from the displacement data and the arrival times of the characteristic aspect. The method according to any of the preceding claims, characterized in that the characteristic aspect is used in a training signal transmitted by each base station and the mobile unit identifies the correlations of the signals received from each base station with a signal of reference training stored by a mobile unit. The method according to claim 8, characterized in that the cellular radio system operates in accordance with the GSM standard, and the training signals are the synchronization burst (SCH) transmitted in accordance with that standard. 10. The method according to claim 8 or claim 9, characterized in that the first identified correlation of the reference signal, io corresponding to the most direct signal path, is used for the calculation of the distance. 11. The method according to any of the preceding claims, characterized in that the derived location is averaged over time. The method according to any of the preceding claims, characterized in that one or more of the plurality of base stations in the cellular radio system has a very short rate, and comprises the additional stage where if the mobile unit is recognized being within the regime of one of such base stations limited by the regime, it is determined that the location of the mobile unit is the location of such base station located by the regime. The method according to any of the preceding claims, characterized in that the derived location is communicated through the cellular radio network is communicated through the cellular radio network to a remote user. The method according to any of the preceding claims, characterized in that if the derived location corresponds to a location for predetermined, an alarm signal is transmitted. 15. A mobile unit for use with a cellular radio system, the mobile unit comprising an apparatus for determining the position of the mobile unit, the apparatus comprises means for detecting the synchronization differences of the signals received from different radio base stations and means for determining, from the synchronization differences, the differences in the distances of the mobile unit from each of the base stations; and means for deriving, from the differences in distance, the location of the mobile unit, characterized in that the mobile unit has means to determine the differences in the synchronization in the mobile unit of a characteristic aspect of a division frame structure of time transmitted synchronously through the control channel of each base station. The mobile unit according to claim 15, characterized in that it comprises means for detecting the differences in synchronization in the mobile unit of at least 4 base stations, and means for thereby determining the position of the mobile unit in two. dimensions. The mobile unit according to claim 15, further characterized in that it comprises means for detecting the differences in synchronization in the mobile unit of at least five base stations, and means for determining thereby the mobile unit position in three dimensions. The mobile unit according to claim 16 or 17, characterized in that it has means for deriving the distance between the mobile unit and the base station that is providing the service from the synchronization progress required for communication with the base station which is providing service if less than the required number of base stations are detected by the mobile unit. 19. The mobile unit according to claim 16, 17 6 18, characterized in that it has means for determining the address of the mobile unit relative to one or more of the base stations and that they detect less than the required number of base stations by means of the mobile unit The mobile unit according to claim 15, 16, 17, 18 or 19, further characterized in that it comprises means for receiving data relating to the location of the base stations. The mobile unit according to claim 20, further characterized in that it comprises means for receiving data relating to the amount by which the frame synchronizations of the base stations are shifted with respect to the base station that is providing the service currently, and means to subtract, for base station, the displacement of the frame arrival time to obtain the difference between the distance between that base station and the mobile unit, and the distance between the base station that is serving and the mobile unit 22. The mobile unit according to any of claims 15 to 21, characterized in that it is arranged to operate in accordance with the GSM standard, and wherein the characteristic aspect is the synchronization burst (SCH) transmitted in accordance with that normal. 23. The mobile unit according to any of claims 15 to 22, characterized in that it further comprises means for identifying the base stations within a radio regime of the mobile unit. 24. The mobile unit according to any of claims 15 to 23, further characterized in that it comprises means for identifying a predetermined geographical location, and alarm means for signaling to the user io that the geographical location of the device corresponds to the predetermined location. 25. In combination with the mobile unit according to any of claims 21, 22, 23 or 24, a cellular radio network characterized in that it comprises a plurality of base stations operating with the control channels transmitting frame structures of division of synchronous time, means for identifying which of the base stations are in the radio regime of a specific mobile unit, and means for transmitting data relating to the location and synchronization of displacement of each of the base stations with respect to the unit mobile. 26. A cellular radio unit comprising a plurality of base stations operating with control channels transmitting synchronous time division frame structures, means for identifying which of the base stations are in the radio mode of a mobile unit specific, means for identifying the difference in synchronization between the signals transmitted by the base stations as measured in the mobile unit; means for determining, from the synchronization differences, the differences in the distances of the mobile unit from each of the base stations; and means for deriving from the differences in distance, the location of the mobile unit, characterized in that the base stations have transmission control channels operating with synchronized time division frame structures that have a characteristic appearance for the detection by the mobile units, and because they have means to receive from the mobile unit an indication of arrival time in the mobile unit of the characteristic aspect transmitted from each base station. 27. A cellular radio network according to claim 25 or 26, characterized in that it is arranged to operate in accordance with the GSM standard, and wherein the characteristic aspect is the synchronization explosion (S C H) transmitted in accordance with that standard. 28. The cellular radio network according to claim 25, 26 or 27, characterized in that it comprises means for detecting the differences in the synchronization in the mobile unit of at least four base stations, and means for determining thereby the position of the mobile unit in two dimensions. 29. The cellular radio network according to claim 25, 26 or 27, characterized in that it comprises means for detecting the differences in the synchronization in the mobile unit of at least 5 base stations, and means for determining with it the position of the mobile unit in three dimensions. 30. The cellular radio network according to claim 27, 28 or 29, characterized in that it has means for deriving the distance of the mobile unit from the base station that is providing the service from the synchronization advance required for the communication with the base station that is providing the service, if less than the required number of base stations are detected by the mobile unit. The cellular radio network according to claim 27, 28, 29 or 30, characterized in that it has means for determining the direction of the mobile unit with respect to one or more of the base stations and less than the required number of stations of base are detected by the mobile unit. 32. The cellular radio system according to any of claims 26 to 31, characterized in that the frame synchronizations of the base stations move with respect to each other, and furthermore comprise means for subtracting the respective displacement from the time of arrival of the characteristic aspect of the frame in the mobile unit to obtain the difference between the distance at which that base station is located from the mobile unit and the distance at which the base station that is providing the service from the unit is located mobile. 33. An apparatus for determining the position of a mobile unit using a cellular radio system having a plurality of base stations, the apparatus comprising means for determining the differences in the synchronization of the operation of the base stations as measured in the mobile unit; means for determining, from the synchronization differences, the differences in the distances of the mobile unit from each of the base stations; and means for deriving, from differences in distance, the location of the mobile unit, characterized in that the apparatus comprises means in the network for synchronizing the time division frame structures of the control channels transmitted through the network. at least a plurality of base stations within the radio regime of the mobile unit, and means in the mobile unit for determining the differences in synchronization in the mobile unit of a characteristic aspect of the time division frame structure transmitted by the mobile unit. means of the control channel of each base station. 34. The apparatus in accordance with the claim 33, characterized in that the time difference measuring means, the distance difference determining means and the location derivation means form part of the mobile unit. 35. The apparatus according to claim 34, further characterized in that it comprises means for identifying the base stations within the radius regime of the mobile unit, and means for transmitting data to the mobile unit with respect to the geographical locations of the mobile stations. base. 36. The apparatus according to claim 25, 34 or 35 further characterized in that it comprises means for determining and compensating the shifts in synchronization between the transmissions of the base stations. 37. The apparatus according to any of claims 33 to 36, arranged to operate in accordance with the GSM standard, and characterized in that the characteristic aspect is the synchronization burst (SCH) transmitted in accordance with that standard. 38. The apparatus according to any of claims 33, 34, 35, 36 or 37, characterized in that it comprises means for detecting the differences in the synchronization in the mobile unit of at least four base stations, and means for determining thereby the position of the mobile unit in the two dimensions. 39. The apparatus according to any of claims 33, 34, 35, 36, 37 or 38, characterized in that it comprises means for detecting the synchronization differences in the mobile unit of at least five base stations, and means for determining with it the position of the mobile unit in 3 dimensions. 40. The apparatus according to claim 38 or 39, characterized in that it has means for deriving the distance of the mobile unit from the base station that is providing the service from the synchronization advance required for communication with the base station that is providing the service, if less than the required number of base stations are detected by means of the mobile unit. 41. The apparatus according to claim 38, 39 or 40, characterized in that it has means for determining the direction of the mobile unit with respect to one or more of the base stations, if less than the required number of the base stations are detected. by means of the mobile unit. 42. A position locator device according to any of the means of the preceding claim, characterized in that it identifies a predetermined geographical location, and alarm means to signal to the user that the geographical location of the device corresponds to the predetermined location.