Cryptography – Cellular telephone cryptographic authentication
Reexamination Certificate
1999-07-15
2004-01-06
Sheikh, Ayaz (Department: 2132)
Cryptography
Cellular telephone cryptographic authentication
C380S258000, C380S270000, C380S273000, C455S456500
Reexamination Certificate
active
06674860
ABSTRACT:
The invention relates to a method and arrangement for managing a service in a mobile communications system, a mobile station and an intelligent module of a mobile station. The invention is advantageously applied to a location method for a mobile station. The method can be applied to analog and digital mobile communications systems. An example of such a system is the digital, time division based GSM (Global System for Mobile Communications).
Location information of a mobile station can be used for many purposes:
pricing of calls can be performed according to the location of a mobile station, whereby calls made from the home area, for example, can be cheaper;
when an emergency call is made from a mobile station, it is possible to determine the location of the calling mobile station (this function will be required by the authorities in some countries);
the user of a mobile station may need information about his/her location e.g. when traveling,
the authorities can use the location information to locate a stolen mobile station or to trace a missing person, for example.
As the location process involves data traffic in the system, it is necessary that the operator be able to charge for the location service according to use. In addition, the location process has to be secure so that the location information cannot be falsified by the user e.g. in order to be allowed a home area discount while elsewhere than in the home area. Furthermore, the data may be confidential as it is not necessarily in the interests of the operator to impart system-related information to a third party.
The Global Positioning System (GPS) based on the use of signals received from satellites is widely used for location purposes. This arrangement would require that a GPS receiver be added to mobile stations, which would result in considerable additional costs. Therefore, in a location system intended for all mobile phones it is preferable to utilize the cellular system's own signals transferred between the mobile station and base stations to locate a mobile station, even though some mobile station models may also include a GPS receiver.
A method is known from publication [1] WO 92/05672 wherein the distance of a mobile station from a base station is determined on the basis of the propagation delay of a signal transmitted between the mobile station and the base station.
FIG. 1
illustrates the operating principle of such a method. By measuring at a base station
1
the propagation delay of a signal sent by a mobile station
14
, it is obtained an estimated distance d
1
between the mobile station and the base station. Because of a certain measuring accuracy of the distance measurement, the assumed location of the mobile station is a ring-shaped area the width of which depends on the time delay measuring accuracy. A corresponding propagation delay measurement can be performed for a signal between the mobile station and other base stations. The result is one ring-shaped location area per each base station involved in the measurement. In the situation illustrated by
FIG. 1
, the propagation delays between the mobile station and base station
11
, mobile station and base station
12
, and mobile station and base station
13
produce estimated distances d
1
, d
2
and d
3
which correspond to the ring-shaped areas
16
,
17
and
18
. The rings intersect at area
19
, which is the mobile station location area obtained from the three propagation delay measurements. Thus, the location of the mobile station can be determined to be an area the order of dimension of which equals the measuring accuracy. In the method described above, locating is substantially carried out by the system, and no special functions are needed in mobile stations to realize the measurement.
A disadvantage of the method based on the propagation delay measured from a signal between a mobile station and base stations is that the propagation delay cannot be easily measured at such an accuracy that the accuracy of the mobile station location information would be adequate for all the above-mentioned applications. In addition, the mobile station has to establish an uplink connection with every base station for which the propagation delay is to be measured. If the location information has to be continuously updated, the data traffic related to the location information puts a considerable load on the connection capacity of the mobile communications system. Furthermore, the high volume of data communications makes the measuring slow. It is also a problem of the method that errors in the absolute timing accuracy of the mobile station produce errors in the location result obtained.
FIG. 2
illustrates the operating principle of a time difference based measurement in which the measurement can be performed by the mobile station or by the system. Let the mobile station receive signals from a plurality of base stations, in the case depicted by
FIG. 2
from three base stations BTS
1
, BTS
2
and BTS
3
. An estimate for the location of the mobile station is determined by means of the observed time difference (OTD) between the signals received from the base stations, whereby it is possible to calculate by means of the time difference between signals received from two base stations the difference d
1
-d
2
between the distance d
1
between the mobile station and a first base station and the distance d
2
between the mobile station and a second base station. Then those potential location points of the mobile station in which the value of the distance difference equals d
1
-d
2
constitute a hyperbola-shaped curve, which thus represents the potential location points of the mobile station. In
FIG. 2
, this curve is depicted by a dashed line. Since the measurement result has a certain error margin, the location area of the mobile station is in reality a band between two hyperbolas, the width of the band depending on the error margin of the measurement result. When signals are received from at least three base stations BTS
1
, BTS
2
and BTS
3
, the result consists of a plurality of location areas A
12
, A
13
and A
23
such that the mobile station is located at the intersection A
MS
of those areas. Determining a restricted location area requires time difference measurement for signals received from at least three base stations unless other methods such as propagation delay measurement are used in addition to the time difference measurement. If other additional methods are used, it is possible to use the time difference measured for signals received from only two base stations. So, when using the measurement principle depicted in
FIG. 2
, the location of a mobile station can be calculated either by the mobile station or by the system.
From patent document [2] FI 101445 it is known a solution in which a mobile station measures the time differences of signals received from base stations and transmits the measured time difference data to the mobile communications system. The mobile location center in the mobile communications system calculates the location of the mobile station on the basis of the measured time difference data and base station location coordinates and base station real time difference (RTD) data. This solution has the disadvantage that time difference data have to be transmitted from the mobile station to the system, which puts a load on the data transfer capacity in the uplink direction.
In the solutions disclosed in documents [1] and [2], the location of a mobile station is calculated by the cellular system. Then the mobile station location information must be transmitted from the system to the mobile station in a special message if the application requiring the location information is in the mobile station. If the user needs the location information continually, a lot of data transfer will occur in the downlink direction, too. Another disadvantage is that the user receives no real-time location information because the location information has to be first calculated by the system.
A solution is known from
Baum Ronald
Nokia Mobile Phones Ltd.
Perman & Green LLP
Sheikh Ayaz
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