Method and arrangement for performing positioning

#The invention relates to an arrangement and a method for performing positioning. In particular, the invention relates to determining the location of desired devices three-dimensionally.

#How to determine the location of various mobile objects is a field under research. Various positioning methods have been developed for different mobile objects. One known solution is satellite positioning. It is based on the idea that orbital satellites transmit detectable and distinguishable signals at known frequencies. When a particular satellite receiver receives a signal from a plurality of satellites, it is able to determine its own location by means of signal transit time delays. One of these satellite positioning methods is known as Global Positioning System (GPS).

#Various radio systems utilize system-specific characteristics in positioning. One positioning method known in cellular radio systems is based on the times of arrival (TOA, Time of Arrival; TDOA, Time Difference of Arrival) of the signals. In general, this method employs an extra receiver placed in connection with the radio system base stations, which receiver listens to mobile station transmission intended for another base station that serves the mobile station. The capacity of the method is limited, because each extra receiver can reliably measure only one mobile station at a time. Another method known in the cellular radio systems is based on the observed time difference (OTD) between the signals. In this method a mobile station measures the time difference between the base stations. The method requires information on the real time difference (RTD) of the base stations, if the base stations are not in synchronization. Positioning is performed on the basis of these data. These methods are only applicable in connection with the cellular radio systems.

#In the following, the invention will be described in greater detail in connection with preferred embodiments, with reference to the attached drawings, in which

#FIG. 1 illustrates one example of an arrangement;

#FIG. 2 is an example of a portable transceiver;

#With reference to FIG. 1, let us study one example of the arrangement. There is a pre-defined area 100, within which positioning is to be performed. For instance, it can be an area, which comprises one or more buildings, any one of which is on fire or there is another similar emergency. The only essential thing is that there are persons or objects moving about the area, whose location is to be monitored. Each person is equipped with a portable transceiver 102 to 108. In different parts of the area there are placed mobile units 110, 112 which include DF stations, i.e. radio direction finding stations 114, 116. In the figure there are only four portable transceivers, but in practice their number may amount to several tens or even hundreds.

#A first mobile unit 110 comprises an antenna 118 and at least one direction finding station 114, which is able to detect the direction, from which the signal of a portable transceiver was transmitted. The unit also comprises a satellite positioning unit 120, for instance a GPS receiver, by means of which the location of the unit can be determined. The unit may also comprise a workstation 122, with which the operation of the unit can be monitored and controlled. The devices of the unit can be interconnected by a local area network, for instance.

#A second mobile unit 112 also comprises an antenna 124 and a direction finding station 116, which is able to detect the direction, from which the signal of a portable transceiver was transmitted. The unit also comprises a satellite positioning unit 126, for instance a GPS receiver. The unit also comprises a control unit or a control transceiver 128, which communicates with the portable transceivers, and a server 130, which controls the operation of the whole arrangement, and a set of workstations 132 to 134, by means of which it is possible to monitor graphically the three-dimensional location of the transceivers. The unit further comprises a reference sensor for calibrating altitude measurements. Typically, but not necessarily, the sensor is located in connection with the control transceiver. The devices of the unit can be interconnected by a local area network, for instance. The first and the second units communicate by means of a wireless local area network or a modem.