METHOD FOR POSITIONING OF A USER EQUIPMENT OPERATING IN A CELLULAR NETWORK

Abstract

The present invention relates to a method for positioning of a user equipment operating in a cellular network, the user equipment being configured to ascertain location information of base stations of the cellular network. The method comprises the steps of: obtaining cell specific reference signals from a serving base station and at least one other base station, obtaining from the serving base station a synchronization indication relating to time synchronization among the serving base station and the at least one other base station, determining a time difference of arrival of the reference signals of at least two base stations that are time synchronized, and determining a position of the user equipment based on the location information of the respective base stations and the determined time differences of arrival.

Claims

1. Method for positioning of a user equipment operating in a cellular network, the user equipment being configured to ascertain location information of base stations of the cellular network, wherein the method comprises the steps of: obtaining cell specific reference signals from a serving base station and at least one other base station, obtaining from the serving base station a synchronization indication relating to time synchronization among the serving base station and said at least one other base station, determining a time difference of arrival of said reference signals of at least two base stations that are time synchronized, determine a position of the user equipment based on the location information of the respective base stations and the determined time differences of arrival.

2. Method according to claim 1, wherein the exact position is determined by the presence or absence of signals of at least one base station in proximity of said at least two base stations.

3. Method according to claim 1, where the synchronization indication comprises an indication relating to at least one of: activated carrier aggregation, Voice over LTE, CoMIP, MBSFN, TDD, intrafrequency carrier synchronization.

4. Method according to claim 3, wherein the synchronization indication relates to a base station capability the user equipment is incapable of supporting.

5. Method according to claim 1, wherein at least parts of the ascertained location information are stored in a memory unit of the user equipment.

6. Method according to claim 1, wherein in case the user equipment determines that the at least two base stations are equipped with a global navigation satellite system receiver, said determination being at least based on providing a global navigation satellite system time indication in its broadcast information or from information locally stored in the user equipment, then said base stations are acknowledged to be time synchronized.

7. Method according to claim 1, wherein at least parts of the ascertained location information are retrieved on demand from a remote server connectively coupled to the cellular network.

8. User equipment operating in a cellular network, the user equipment being configured to ascertain location information of base stations of the cellular network, wherein the user equipment is configured to: obtain cell specific reference signals from a serving base station and at least one other base station, obtain from the serving base station a synchronization indication relating to time synchronization among the serving base station and said at least one other base station, determine a time difference of arrival of said reference signals of at least two base stations that are time synchronized, determine a position of the user equipment based on the location information of the respective base stations and the determined time differences of arrival.

9. User equipment according to claim 8, configured to determine the exact position by the presence or absence of signals of at least one base station in proximity of said at least two base stations.

10. User equipment according to claim 8, where the synchronization indication comprises an indication relating to at least one of: activated carrier aggregation, Voice over LTE, CoMIP, MBSFN, TDD, intrafrequency carrier synchronization.

11. User equipment according to claim 8, wherein the synchronization indication relates to a base station capability the user equipment is incapable of supporting.

12. User equipment according to claim 8, comprising a memory unit, the user equipment being configured to store at least parts of the ascertained location information in said memory unit.

13. User equipment according to claim 8, configured to determine if the at least two base stations are equipped with a global navigation satellite system receiver, said determination being at least based on providing a global navigation satellite system time indication in its broadcast information or from information locally stored in the user equipment, and in case the determination indicates that the at least two base stations are equipped with a global navigation satellite system receiver, to acknowledge that said base stations are time synchronized.

14. User equipment according to claim 8, configured to retrieve at least parts of the ascertained location information on demand from a remote server connectively coupled to the cellular network.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0078] The following description and the annexed drawings set forth in detail certain illustrative aspects and are indicative of but a few of the various ways in which the principles of the embodiments may be employed. Characteristics and advantages of the present invention will appear when reading the following description and annexed drawings of advantageous embodiments given as illustrative but not restrictive examples.

[0079] FIG. 1 represents a user equipment of the type to which the present invention is applied as an embodiment;

[0080] FIG. 2 shows a sequence diagram of an embodiment of the inventive method;

[0081] FIG. 3 displays a user equipment of the type to which the present invention is applied in another embodiment.

[0082] FIG. 1 schematically shows a user equipment UE of the type to which the present invention is applied as an embodiment in the surrounding of three base stations BS1, BS2, BS3 of a cellular network CN. The user equipment is camping on at least one of the base stations.

[0083] Displayed is a user equipment in the form factor of a smartphone. However other, more simple types of device e.g. for machine-type communication, are mainly addressed by the inventive method. Nonetheless, the inventive method is not exclusive to one or the other category of user equipments.

[0084] The shown base stations BS1, BS2, BS3 are additionally time synchronized. This is in particular the case due to the support of at least one service which requires time synchronized base stations, in particular Coordinated Multi-point Transmission/Reception (CoMIP). With the feature of being time synchronized a base station would be able to send an accurate time stamp, and each receiver would retrieve the same time stamp from two time synchronized base stations, under the condition that the transmission conditions are the same. Further over the air interface the base station transmits information relative to its capabilities. This is in particular happening through a broadcast e.g. via system information blocks (SIBs).

[0085] One of that capabilities is the information relating to the CoMIP support of the base station, and the base stations in proximity.

[0086] For each of the base stations BS1, BS2, BS3 it is known the location, in particular by means of a geographic co-ordination pair (x.sub.1,y.sub.1), (x.sub.2,y.sub.2), (x.sub.3,y.sub.3). Such location information of base stations are stored in the location list LL of the user equipment UE.

[0087] With that the user equipment has the knowledge that signals from each of the base stations which comprise a time indication can be used for position calculation.

[0088] The position calculation is carried out by a time difference of arrival calculation. For each signal retrieved from a base station the user equipment may calculate the time difference T.sub.1, T.sub.2, T.sub.3 between the arrival time and the submitted timestamp of the data transmission over the air interface. From the time difference of arrival (TDOA) a distance is calculated according to the commonly known formula:

d=c*(τ.sub.arrival−τ.sub.sent)

where c is the speed of light.

[0089] With the calculated distance d.sub.1, d.sub.2, d.sub.3 a circle around each base station BS1, BS2, BS3 is derived. The locations of each point of the circle per base station in a two dimensional field is however calculated by the formula:

d=√{square root over ((x.sub.UE−x).sup.2+(y.sub.UE−y).sup.2)}

[0090] For d the measured distance from above can be retrieved, and x, y depict the position of the respective base stations. So the equation only needs to be solved to x.sub.UE resp. y.sub.UE, but this does not retrieve unique results, but define the possible positions in the distance around the base stations location x, y, thus forming a circle.

[0091] The position p where the circles around the base stations intersect, is the determined position in geo-coordinates (x.sub.UE,y.sub.UE) of the user equipment UE.

[0092] FIG. 2 shows in a sequence diagram a process flow of an exemplifying embodiment of the invention. The user equipment UE in this embodiment is communicatively connected to a control application AP, thus the UE is effectively the radio modem or communication unit of the control application. The process flow starts with the user equipment sending at least one message M1 to base station BS1, in order to camp on said base station. After powering up the user equipment UE it requires registration, authentication and a couple of additional steps leading to messages going to and fro between user equipment UE and base station BS1. When the user equipment was actually registered, the message M1 only depicts a reselection, following a suitability check to find the best suitable base station for the user equipment.

[0093] A dedicated response from the base station BS1 is typically carried out, but in this figure omitted out of simplicity reasons. After message M1 was sent, it is assumed that the user equipment is camping on base station BS1.

[0094] Then the user equipment retrieves from two base stations BS1 and BS2 in the proximity of the user equipment a message M2, M3, e.g. via broadcast where the user equipment obtains the reference signals from the received transmissions. Such reference signals are regularly inserted into the downlink signal structure of each LTE based transmission.

[0095] Based on the reference signals the user equipment can derive the time difference of arrival TDOA.

[0096] With message M4 the user equipment retrieves, preferably via a broadcast from the serving base station, a synchronization indication. This is preferably part of the capabilities, i.e. services that can be retrieved from said base station, and informs the user equipment typically indirectly about the fact that the base station is time synchronized with the base stations in the surrounding.

[0097] In step M5 the user equipment then retrieves the location of base station BS1 and BS2, and preferably also from BS3, that is all base stations where the user equipment can decode signals from in the current position. The location is stored in the location list LL available in the memory of the base station. Should the respective base station's location not be available, then a request to a remote server communicatively coupled to the cellular network CN is to be carried out after step M5.

[0098] When all the information are gathered, and the synchronization indication was retrieved, then the user equipment carries out in M6 the distance calculation based on the time difference of arrival and the locations of the base stations. As in this example the reference signals, and consequently the time difference of arrival, is retrieved only from two base stations, the calculation leads to probably two candidate points, at the two intersections of the distance circles, as visible in FIG. 1.

[0099] Hence the user equipment checks with message M7 signals from at least one other base station BS3. This base station does not need to be synchronized with the other base stations BS1, BS2. It only required to know the position of the base station.

[0100] Based on this information from the two possibilities the location can be derived, and provided with message M8—typically on demand—to the control application AP.

[0101] Should the base stations BS1, BS2, and BS3 are all be synchronized and the user equipment UE can derive time difference of arrival for all said base stations, then a position p is unambiguously found out.

[0102] How the calculation with reference signals from only two base stations is carried out is shown in FIG. 3.

[0103] Here the situation is comparable to the one of FIG. 1, except that based on time difference of arrival a distance d1, d2 is determined for only two base stations BS1, BS2.

[0104] The result is, that at the intersections of the resulting circles the candidate positions p1, p2 are determined. For determining the position of the user equipment hence it needs to be decided which of the positions p1, p2 is the correct one.

[0105] This situation is solved by means of base station BS3, for which the location (x.sub.3, y.sub.3) is known from the location list LL.

[0106] For the user equipment, which can retrieve in the exemplifying embodiment strong signals from base station BS3, it is hence clear, that it needs to be located close to the base station BS3. This leads to the result that only the candidate position p2 can be the correct location of the user equipment, as its location is closer to base station BS3 than the candidate position p1.

[0107] This shows that even with a retrieval of the synchronized time difference of arrival from only two base station the position of a user equipment can be determined with sufficient accuracy, and without additional equipment or support from the cellular network.

[0108] In the above detailed description, reference is made to the accompanying drawings that show, by way of illustration, specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. It is to be understood that the various embodiments of the invention, although different, are not necessarily mutually exclusive. For example, a particular feature, structure, or characteristic described herein in connection with one embodiment may be implemented within other embodiments without departing from the scope of the invention. In addition, it is to be understood that the location or arrangement of individual elements within each disclosed embodiment may be. The above detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims, appropriately interpreted, along with the full range of equivalents to which the claims are entitled.