DE10116798C2 - Method for improving the accuracy of position determination in a digital mobile radio network - Google Patents

Description

The present invention relates to a method for Improve the accuracy of positioning a Mobile station in a digital cellular network, and in particular on a method to improve the accuracy of the Position determination of a mobile station in a digital mo bilfunknetz according to the GSM standard, in which information in data packets structured bit by bit, so-called "bursts" be replaced. Such "bursts" are e.g. B. in the GSM Specification (GSM 05.02 Section 5.2.2).

The most accurate localization of mobile radios, which is covered in a digital cellular network ten reception and transmission area, is increasingly important tiger.

For example, the mobile network operators want to enable their customers localize as precisely as possible in the mobile network in order to be able to current location of the user of a mobile station indivi to be able to send duellly adapted advertising notices. This who evidence can e.g. B. Notes on the closest right restaurant, the closest bookstore or similar his.

On the part of the legislator, in turn, is the mobile phone network operator z. B. made the request as accurately as possible determine the position of a user of a mobile station, who requests an emergency service via his mobile station. because abuse is to be prevented and accident victims should be prevented can be located precisely.

For all of these applications, those achieved so far are sufficient Accuracies for locating a mobile station in one Cellular network not out.  

Various known methods for determining a position Mobile stations in a digital cellular network are included play in "Positioning GSM Telephones" by C. Drane et. al. in IEEE Communications Magazine, April 1998, p. 46 ff tert. In particular there are also so-called "timing advan ce "measurements (" lead time "measurements) explains how are explained in more detail below.

In digital cellular networks, and especially in GSM systems data transfer between a base station and a mobile station by so-called "bursts" instead, the are data packets of pre-specified length and pre-specified internal structure.

In common mobile network specifications, especially in the GSM standard, are used to exchange a burst between a sen end station and a receiving station time slots predetermined length provided in the data transmission protocol, within which a sending station send a burst and a related receiving station Burst can receive.

To the capacities of a base station, in its receiving and Broadcast area are a variety of mobile stations can make optimal use of it, the base station is not for everyone de Mobile station permanently ready to receive, but can only during certain time slots one from a certain one Mobile station incoming burst actually received. This leads to a certain distance from a base station already has a burst must send out while the base station is not yet is ready to receive this burst. The base station must rather during the duration of the burst from the mobile station be switched to the base station so that they can then be switched to Time of arrival of the burst at the base station is ready to receive.  

Fig. 1 shows the relationship between the timing advance Δt and the distance Δx between a mobile station and a base station. c is the speed of light (approx. 3.10 ⁸ m / s). The factor 1/2 must be taken into account, since the mobile station sees the synchronization burst shifted by the duration between the mobile station and the base station. If the mobile station sends an RACH signal (RACH = "Random Access Channel"), this is again delayed by the running time between the mobile station and the base station. The timing advance is therefore twice the running time.

Lead time measurements ("timing advance" measurements) have a resolution that corresponds to the duration of a GSM symbol, ie 3.77 µs. GSM 05.04 Section 2.1.1 contains more detailed specifications on the "symbols" used in the GSM standard and their properties. The duration of a symbol thus corresponds to a distance of approx. 3.10 ⁸ m / s. 3.77 µs = 555 m between base station and mobile station.

However, a spatial resolution of approx. 555 m is not sufficient for the requirements that the American federal authority FCC for Location services. (see e.g. Christopher Dra ne, Malcolm Macnaughtan, and Craig Scott, "Positioning GSM Telephones ", IEEE communications magazine, April 1998 or Sirin Tekinay, Ed Chao and Robert Richton "Performance Bench marking for wireless location systems ", IEEE communications magazine, April 1998.

WO 99/27738 A1 describes a method for determining the position known in which signals in a Di for the determination of the transit time medical procedures are received and at which a middle is carried out over several bursts.

WO 01/19112 A1 describes a method for determining the position known, in which the running time directly from the channel impulsant word is determined.  

WO 01/06275 A1 describes a method for determining the position known, in which the runtime determined from a function that is the difference between a signal of many ge averaged channel impulse responses and a signal from the same represents much averaged burst energies. That difference is logarithmic and then processed further.

WO 01/18560 A1 describes a method for determining the position known in which the runtime by statistical methods in particular by weighted averaging after a spe main focus formula is determined.

The object of the present invention is therefore to improve te method for locating an active mobile station in a digital cellular network (especially with a GSM System) in which timing advance measurements imp are lemented.

This is achieved according to the invention by a method according to independent method claim 1 . Furthermore, a computer program product is provided with which a method according to the invention is presented in a machine-readable form and which can be downloaded to base stations or mobile stations of a digital mobile radio network in order to carry out a method according to the invention.

The dependent claims relate to preferred embodiments men of the present invention.

The improvement in the accuracy of the invention proposed method is based on signal evaluation and re processes that take advantage of the fact that individual Bursts transfer energy structured bit by bit. Fiction according to this is used in such a way that for the advance time measurement synchronization bits broadcast on the transmitter side are received be evaluated, and a correlation between received genes signals and individual synchronization bits leads, with characteristic correlation coefficients be evaluated, which is a further estimate for the actual distance between sending and receiving The station.

It can be in a GSM mobile radio system in this Software resources already implemented to carry out ei The timing advance algorithm must be used, such as this is expressed by claims 3 and 4.

The advantages and features of the present invention result also from the exemplary embodiments explained below len in connection with the drawings.

Show it:

Figure 1 shows the relationship between the delay time ("timing advance") and the distance of a Mobilsta tion to a base station.

FIG. 2 shows the construction of an "access burst" in the GSM standard;

Fig. 3 is a block diagram of an embodiment of a method according to the invention a zugrundelie constricting position determination algorithm ( "contest" - algorithm) in a GSM system;

Fig. 4 shows the profile of an interpolated correlation radio tion for the RACH channel in response to a correlation index, as occurs when using the "contest"-Algorithmusses; and

Fig. 5 shows the course of an interpolated Energiesummenfunk tion depending on a correlation index, as occurs when using the "CONTEST" algorithm.

The present invention is exemplified using the GSM Norm explained. However, it is straightforward for the expert understandable that the inventive method also in after other mobile radio standards operated digital mobile radio system men can be used, provided they have synchronization bits structured individual data packets ("bursts") for implementation of timing advance measurements. It is also not absolutely necessary that timing advance measurements only in "uplink" mode (from the mobile station to a base station tion) are carried out, in principle are also mobile communications systems conceivable in which timing advance measurements in the "down link "operation (from the base station to a mobile station) be performed.

Fig. 2 shows an example of the structure of a so-called "Access burst" as it is in the GSM standard 05.02. is specified in section 5.2.7. The access burst consists of 87 bits, namely 7 tail bits ("end bits"), 41 bit training sequence ("synchronization sequence"), 36 bit information and 3 tail bits ("end bits"). It is only used in "uplink" mode (ie from the mobile station to the base station) and in RACH.

An algorithm as described in ei nem inventive method for operating a GSM system tems can be used to determine the location of a Mon to determine bilstation.

The algorithm is to be described with reference to FIGS . 2 to 5 for the RACH channel (random access channel) in a GSM system. However, it can also be applied to "normal bursts" in GSM systems (see GSM 05.02 Section 5.2.3).

The 41 synchronization bits indicated in FIG. 2 in an access burst are essential for the implementation of a location determination algorithm according to the invention in the embodiment explained below.

Fig. 3 shows a block diagram of an embodiment of a a method according to the invention underlying position determination algorithm ( "contest" algorithm = Correlation Energy Threshold Method = correlation energy threshold method) in a GSM system, in which a timing advance measure to replace a timing advance value between the mobile station and Base station is carried out.

In the chain of individual function blocks 2 to 5 shown at the top in FIG. 3, software resources are used, as are already implemented in base stations, and which are combined in FIG. 3 in a block "Timing Advance Algorithm".

Details of such timing advance algorithms are not specifically specified in the GSM standard, but are usually implemented individually by mobile radio operators in their proprietary specifications for the operation of mobile radio base stations. For the purposes of the present invention, it can be assumed that the “timing advance algorithm” function block shown at the top in FIG. 3 is representative of the timing advance algorithms installed in practice by mobile radio operators at the time of registration.

For further explanation it is assumed that there are 156 complex IQ values x _i (in-phase quadrature phase values) from an AD converter 1 (ADC - analog digital converter) in the receiving unit of a base station (ie in "uplink" mode) that correspond to an incoming signal from a mobile station that is connected to the base station and whose distance relative to the base station is to be determined as precisely as possible. The discrete IQ values x _i correspond to the (analog) signal voltage values of an incoming signal at a receiving antenna of a receiving station, that is, in the present example, a GSM base station.

It is assumed that these complex IQ values x _{i are} output in the baseband of the AD converter 1 . The specification 0 <i = 156 results from the GSM 05.02 standard. Section 5.2.2.

The complex values x _i are reduced in a function block 2 by approximately 67,708 kHz, which corresponds to a rotation of 90 ° per symbol duration in the complex plane. This operation is already implemented for the timing advance algorithm, which results in a linear system for the rotated complex values y _i .

The following formula describes this operation:

Then, in function block 3 , there is an example of a correlation of the y _i with the synchronization sequence of the GSM access burst. In another embodiment, the y _i could also be correlated with the synchronization sequence of a GSM normal burst.

For the correlation of the y _i with the synchronization sequence of the GSM access burst, e.g. B. uses the symbols t _i , which are derived from the bits defined in the GSM 05.02 version 4.6.0 section 5.2.7, ie

t _i = BN _{l + 7} .2 - 1 (2)

where applies here

0 <l ≦ 41 (3).

As a general rule for other synchronization sequences, synchronization takes place with bits t _i , a number l _max of synchronization bits being present.

When synchronizing with the synchronization bits of an access burst, e.g. B. 73 (= 68 + 5, namely 68 extended guard bits according to GSM 05.02 Section 5.2.7 and e.g. 5 bits for the duration of the mobile radio channel) Get correlation results c _m in the following way:

As a general rule for other synchronization sequences, correlation results c _{m are obtained} in the following way:

Instead of 5 symbol durations on the basis of equation (5), a different number of symbols can also be assumed for the duration of the mobile radio channel, so that the following generally applies to the number of correlation results obtained:

0 <m ≦ m _max (5 ').

FIG. 4 shows an example of the correlation coefficients c _m in the case of the correlation of the y _i obtained according to equation (1) with the synchronization sequence of the GSM access bursts, where in this representation the discrete values c _{m have been} interpolated so that a results in a continuous envelope as a correlation function.

The correlation index m according to equation (4) is plotted on the horizontal axis, and a correlation function derived from the correlation coefficients c _m by interpolation is plotted on the vertical axis. For the interpolation of the correlation function from the discrete standardized correlation coefficients according to equation (4), any interpolation method can be used.

The location of the maximum of the correlation function is a measure of the distance between the mobile station and the base station. The distance between two successive correlation indices m, m + 1 in FIG. 4 corresponds on a time axis to the duration of a symbol in the GSM standard, that is to say 3.77 μs. If the mobile station moves relative to the base station, the correlation maximum also shifts. A shift in the correlation maximum by the width of an entire symbol corresponds to a change in the distance between the mobile station and base station by approximately 555 m.

In practice, however, it can be seen that the exact position of the correlation maximum in FIG. 4 is often relatively unstable, since there are "flickering" of the correlation maximum due to multiple-run effects and atmospheric disturbances on the signal transmission path, ie the position of the correlation maximum is not stable and therefore not suitable for determining the position of the mobile station in practice.

The method according to the invention now uses a further transformation of the correlation function shown in FIG. 4, preferably effected by software-implemented method steps, into a representation in which there is an increase in the stability of the position of a correlation maximum relative to atmospheric transmission distortions, namely taking advantage of the fact that in the function block timing advance algorithm shown in FIG . B. is already provided that after the execution of the RACH correlation according to equation (4) provided in function block 3 , the energy of adjacent correlation results is added according to the formula (6) given below.

In the block diagram shown in FIG. 3, an evaluation of the energy of the correlation results is already implemented in two function blocks 4 and 5 in the timing advance algorithm.

It is provided that, for. B. with the 73 correlation results from equation (4) energy values e _n can be calculated.

This happens e.g. B. according to the following formula

Here, k is a relatively small number measured from the total number 41 (generalizing m _max ) of the synchronization bits, and c * | n + l-1 is the complex conjugate value to c _{n + l-1} .

In the present case, let k = 5 be implemented as an example.

With k = 5, a total of 73 - 5 + 1 = 69 energy values e _n are obtained according to equation (6). So the following applies:

0 <n ≦ 69 (7).

The values standardized to 1

are called standardized energy values E _n .

In general, the following applies:

0 <n ≦ n _max (7 ').

In a known timing advance algorithm is onsblock 5 z. B. provided that the timing advance value is determined by determining the position with maximum energy e _max .

According to the exemplary embodiment of the present invention considered here as an example for a GSM mobile radio system, the discrete and standardized energy values E _n determined according to equation (8) are now taken as the basis for a continuous energy sum function f (z) which is obtained by interpolation. This is illustrated in FIG. 3 by a branch from the “timing advance algorithm” block into a “location determination algorithm” block provided according to the invention.

In the "location determination algorithm" block, a continuous energy sum function f (z) is first calculated as an envelope for the discrete standardized energy values E _n by interpolation in function block 7 .

FIG. 5 shows an example of the course of such a continuous energy sum function f (z), which is based on the (per se discrete - see equation (4)) correlation results in FIG. 4. In FIG. 5, the distance between two successive energy sum indices n, n + 1 corresponds to the duration of a symbol to be transmitted, ie 3.77 μs.

For the interpolation of the energy sum function f (z) from the discrete standardized energy values according to equation (7) can  use any interpolation method become. The simplest form is linear interpolation.

Now the goal is to determine the position of the maximum of the energy sum function f (z), which corresponds to the maximum of the correlation function shown in FIG. 4 as best as possible. Because of the "Fla ckern" explained in connection with FIG. 4 of the correlation maximum and because of the number taken into account in connection with equation (6) when calculating the energy value, e.g. B. k = 5 adjacent correlation coefficients shows the energy sum function f (z) in FIG. 5 in the area of its maximum the course of a flattened and slowly "moving back and forth" correlation plateau of height 1 over time .

The speed at which the location of the correlation pla Depending on the number k, teaus "wanders" is the one used to form the ener Take into account the casting sum function f (z) in equation (6) neighboring correlation coefficients significantly lower than the speed at which the maximum of the equation (4) or (4 ') determined correlation coefficients "fla ckert ".

With a very slow correlation back and forth onsplateau of the energy sum function f (z) can be z. B. the Estimate the middle of the correlation plateau relatively easily and as an estimate for the maximum of the according to equation (4) or (4 ') assume the correlation coefficients determined.

Frequently, however, the problem arises in practice that a "snapshot" determined at a specific point in time for determining the position of the plateau of the energy sum function f (z) shown in FIG. 5 does not allow a reliable statement as to where a maximum of the equation (4) or (4 ') determined correlation coefficients without distortion effects due to the route would be ideally typical.

A longer observation of the situation of a slowly "moving" correlation plateaus and a temporal Averaging Remedy. With a mobile station, over a sufficiently long observation period their distance relative to a base station is not (noticeable) changes can be made by averaging several correlates determined in successive time intervals onsplateaus an average for the middle of these correlations form plateaus, which in turn is an estimate of the maxi mum the correlates determined according to equation (4) or (4 ') on coefficient serves.

In practice, however, there is the problem that this times are often not available, e.g. B. because the mobile station moves to the base station relatively quickly away, or due to transmission-related interference only a few bursts between a base station and a mo bilstation can be replaced before it becomes an ab break the connection or, if necessary, continue to travel Chen the mobile station from a dedicated base station an adjacent base station comes (so-called "Hando ver ").

In other words, the problem that the current position of the correlation plateau of the energy sum function f (z) shown in FIG. 5 is ultimately not a reliable measure for estimating the distance between a mobile station and a base station is also shown here in practice.

However, it has been shown in practice that the course the edges of the correlation maximum (in the case of a fixed mobile station) is very stable. In a preferred embodiment This fact is expressed in the present invention uses that on the ascending or on the descending Edge of the energy sum function f (z) is checked where the Energy sum function f (z) a predetermined threshold  (e.g. 50%) of the correlation plateau normalized to the value 1 reached.

On the basis of the distortion-free course of an ideal-typical correlation function, which is known from the well-defined properties of the synchronization bits for the ideal case (without interference effects), it can be empirically determined by which "offset distance" z _{0, x} such a threshold value with x.100% of the "ideal""Should be in the middle of the correlation plateau.

If one determines the position z _{0, x of} the threshold value on the rising or falling edge of the correlation maximum, i.e. where x.100% of the maximum value of the `` correlation plateau '' is reached, one can take into account a previously empirically determined offset z _calibrate in Fig . 5, the position for determ men _pos, which would speak to one shown in the diagram in Fig. 4, "i deal typical", not "flickering" due to transmission links related distortions correlation maximum ent. This position corresponds with the greatest possible probability to the exact position of the mobile station.

According to the invention, the exact position of the correlation maximum of the correlation coefficients c _{m is} estimated by means of empirical correction factors by evaluating the position of threshold values on the rising or falling edges of an energy sum function f (z).

In Fig. 5 is illustrated how the value of 0.5 lenwert as smoldering has been selected at the rising edge of the total energy function, ie the location of the rising edge is determined, where f (z _0,5) = 0.5 holds.

A previously empirically determined _calibration constant z _{calibrate must be} subtracted from this value z _0.5 (or added on the falling edge) in order to obtain the best possible estimated value z _pos for the actual position of the correlation maximum, ie in the present example

z _pos = z _0.5 - Z _calibrate . (9).

The distance between the base station and the mobile station can then be calculated in the following way:

Distance = 555 mz _pos (10)

In a generalization of equation (9):

z _pos = z _{0, x} - z _calibrate (9 ').

If z _pos = 0 in equation (9), then z _calibrate = z _{0, x} results. In other words, the desired calibration _constant z _{calibrate is} generally obtained by carrying out a measurement when the distance between the mobile station and base station is zero. From the position of the plateau of the correlation maximum of the energy sum function f (z) and the position of the threshold value z _{0, x} , the calibration _constant z _calibrate can then be determined, which is also valid if the distance between the mobile station and the base station is not equal to zero.

Measurement results of the CONTEST algorithm

A version of the CONTEST algorithm was developed in Feldversu Chen tested. A comparison was made with position sensors instead of GPS receivers (Global Positioning System = Geolocation using geostationary satellites sent location signals). The measurements were very precise with an accuracy better than 50 m, but there were also Measurements with an error of 460 m. The results have to  to be analyzed in more detail. The mistakes could be on Timing errors in the "Layer 1 trace", timing errors in the mobile station or other Ursa not yet understood Chen based. However, the results show that in GSM a Mobile station in principle with an accuracy in the area of 50 m using the CONTEST algorithm locally can be settled.

Claims (5)

1. A method for improving the accuracy of the position determination of a mobile station in a digital mobile radio network, in particular a mobile radio network operated according to the GSM standard, in which the advance measurement method ("timing advance measurement" method) is implemented, in which synchronization bits for synchronization be ver of time slots uses in which sends a transmitting station to be transmitted symbols, and a receiving station receives these, are being calculated between at a receiving station from a sen Denden station incoming signals and predefined Syn chronisationsbits characteristic correlation coefficient and derived from energy coefficients, characterized in that that the position of the maximum of an energy coefficient calculated by interpolation from the correlation coefficients by adding the energy of adjacent correlation coefficients of one at a receiving antenna of the receiving station during a time s incoming signal derived continuous and over the duration of the symbols transmitted energy sum function f (z) is evaluated, and the location of this maximum is used as a measure for a further estimate of the actual distance between the sending and receiving station. 2. The method according to claim 1, characterized in that threshold values are determined on the rising or falling edge of the graph of the energy sum function f (z) plotted over the symbol duration, where the value of the energy sum function f (z) contains a predefined percentage (x .100%) of the normalized maximum of the energy sum function f (z), and a previously empirically determined offset z _calibrate for the time interval between the maximum of the energy sum function f (z) and the threshold value has been determined, so that one by Offset z _calibrate compared to the threshold position z _{0, x} shifted position in the maximum of the energy sum function with the highest possible probability of the ideal-typical position of the maximum corresponds to the correlation coefficient of the incoming signals and the synchronization bits, which would ideally assume the maximum of the correlation function without distortion-related distortions, and whereby au s the estimated ideal-typical position, the maximum of the correlation function, the actual spatial distance between the mobile station and base station is determined. 3. The method according to claim 1 or 2, characterized in that the following steps are carried out as part of a timing advance algorithm performed in a GSM mobile radio system by the base station:

• a) provision of incoming signal values corresponding to complex values x _i in the baseband of an analog-digital converter on the base station receiver side;
• b) lowering the complex values x _i by a frequency value which corresponds to a rotation by 90 ° in the complex plane, as a result of which the x _i in corresponding values
  be transformed;
• c) performing a correlation with the synchronization bits t _{i of} a synchronization sequence of the GSM access bursts or the GSM normal bursts, as a result of which correlation results c _{m are obtained} in the following way:
  
• d) Calculating energy values
  in which
  0 <n ≦ m _max - k + 1,
• e) normalize the values too
  
• f) calculating an enveloping interpolation curve f (z) based on the energy values E _n ;
• g) determining a position z _{0, x of} a predetermined threshold value x.100% of a correlation plateau normalized to the value 1 on the rising or falling edge of the interpolation curve;
• h) Calculating z _pos = z _{0, x} ± z _calibrate with an empirically predetermined _calibration offset value z _{calibrate in} order to obtain the best possible estimate z _pos for a position in the maximum of the energy sum function, which with the greatest possible probability of the position of the maximum of an ideal type corresponds to the correlation function of the incoming signals with the synchronization bits not distorted due to the transmission path;
• i) converting the position of the estimated value z _pos into an an estimate of the distance between the mobile station and the base station according to
  Distance = 555 mz _pos .

4. The method according to claim 1 or 2, characterized in that in step d) a correlation with the synchronization sequence of the GSM access bursts is carried out using the synchronization bits t _e , which che from the in the GSM 05.02 version 4.6.0 section 5.2.7 defined bits can be derived as follows:
t _e = BN _{l + 7} .2 - 1, where 0 <l ≦ 41. 5. Computer program product stored on a computer readable medium, the computer program product being machines readable program means for reading in the computer pro Command steps for implementation contained in the gram product a method according to one of the preceding claims in ei ner base station or a mobile station in a digital Cellular network contains.