METHOD FOR DETERMINING RADIO NETWORK HOT SPOT AREA LOCATION, AND TRANSCEIVER FIELD OF THE INVENTION The invention relates to a method for determining radio network hot spot area location, the radio network comprising at least one base station and a plurality of subscriber terminals, the hot spot area having a concentration of subscriber terminals, in which method the base stations form location areas and transmit location code on the basis of which the subscriber terminals are signalling with the base station and identify the base stations belonging to the same location area.

The invention also relates to a transceiver used in a radio network for determining hot spot area location, the radio network comprising at least one base station and a plurality of subscriber terminals, the hot spot area having a concentration of subscriber terminals, and the base stations forming local areas and transmitting location code on the basis of which the subscriber terminals identify the base stations belonging to the local area and are signal- ling with the base station.

BACKGROUND OF THE INVENTION It is previously known to define a concentration of subscriber termi- nals, or hot spot areas, of a radio network, the GSM (Global System for Mobile communication) and the DCS (Digital Cellular System) radio networks in par- ticular. The hot spot areas comprise a plurality of subscriber terminals com- pared with the available radio network capacity in the same area. In the hot spot areas the radio network is overloaded or it is more likely to become over- loaded than any other part of the radio network. Overload could have been detected for example by using a radio network management computer. Over- load can be avoided if a base station is built in the radio network hot spot area and a new cell is formed, for example a microcell. In this way additional ca- pacity is obtained to the radio network. There can be several hot spot areas in the radio network area.

It has previously been known to define the hot spot areas using a receiver located in the radio network area. The receiver has measured the signal strength of subscriber terminals, for example that of mobile phones, lo- cated in the radio network area. The number of subscriber terminals has been determined based on the signal strength. The distance between the subscriber

terminal and the base station has further been determined from the signal strength, the distance having been utilized in the definition of the hot spot area.

However, there have been certain drawbacks in the prior art method. Power control, which is meant for saving the battery in the subscriber terminal, is used in the subscriber terminals. The subscriber terminal power control affects the strength of the transmitted signal. If power control has been used in the subscriber terminals of the radio network and the hot spot area of the radio network has simultaneously been defined, then the exact definition of the hot spot area location has not been successful. Moreover, the precise number of the subscriber terminals located in the hot spot area has not been established by using the method. What has been described above has re- sulted in that e.g. the microcell formed on the basis of the prior art method has arrived at an incorrect position.

SUMMARY OF THE INVENTION An object of the present invention is to implement a method for de- fining precisely a radio network hot spot area and particularly a hot spot area location.

This is achieved with the method set forth in the preamble charac- terized in that a location code not belonging to the location area is transmitted to the subscriber terminals, the number of signalling subscriber terminals is calculated on the basis of said location code and a substantially direct dis- tance that the location code has travelled to the subscriber terminal is calcu- lated using signalling.

The transceiver of the invention is characterized in that the trans- ceiver comprises transmission means for transmitting location code not be- longing to the local area to the subscriber terminals, calculation means for cal- culating the number of signalling subscriber terminals and the calculation means for calculating a distance between the transceiver and the subscriber terminals signalling with the transceiver.

The method of the invention has several advantages. Location code not belonging to the location area is transmitted in the radio network, and based on the signalling code the number of signalling subscriber terminals is calculated. Furthermore, in the method of the invention the substantially direct distance that the location code has travelled to the subscriber terminal is cal-

culated using signalling. Location code is preferably transmitted from various locations of the radio network, whereby a distribution of the subscriber termi- nals can be determined. The precise location of the hot spot area is defined on the basis of the substantially direct distance that the location code has trav- elled to the subscriber terminal. The location of the hot spot area is thus pre- cisely defined using the method, whereby for example a new base station can be located in one go to a preferable terrain.

The preferred embodiments of the method of the invention are also disclosed in the enclosed dependent claims and the preferred embodiments of the transceiver of the invention are disclosed in the enclosed dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS In the following the invention will be described in greater detail with reference to examples in the accompanying drawings, in which Figure 1 shows a radio network in which a transceiver of the inven- tion is used and Figure 2 shows the transceiver of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Figure 1 shows a radio network comprising plural subscriber termi- nals 10, base station 20 and transceiver 30. The radio network is for example a GSM or a DCS network or an equivalent network. Subscriber terminals 10 communicate with base station 20 if necessary. Subscriber terminals in the ra- dio network of the Figure belong to the coverage area of base station 20. The coverage area of base station 20 forms a location area to subscriber terminals 10 located in the area. When subscriber terminal 10 moves outside the loca- tion area, then subscriber terminal 10 updates location information on the ba- sis of which subscriber terminal 10 knows its location. Base station 20 updates information from subscriber terminals 10 located within its coverage area. If subscriber terminal 10 does not leave the coverage area, then the location in- formation of subscriber terminal 10 do not have to be updated. There may be several base stations 20 in the radio network area handling the traffic of the same location area.

Base station 20 comprises antenna 21 using which the base station transmits particular code on the basis of which subscriber terminals 10 located

within the coverage area of base station 20 identify their location. In the exam- ple of the Figure LAC code (Location Area Code) is used for identifying the lo- cation. Different location areas have their own LAC codes. When subscriber terminal 10 updates location information, then subscriber terminal 10 simulta- neously signals with base station 20. Generally the radio network is divided into cells which each one forms its own coverage area.

If there are in the area of base station 20 of the example constantly plural subscriber terminals 10 attempting to establish connections compared with the available capacity of base station 20, then base station 20 eventually becomes overloaded. When overloading occurs a large number of subscriber terminals 10 cannot establish a connection fast enough, for example with an- other subscriber terminal 10. Consequently, a hot spot area has been formed substantially in the area of base station 20. If a new base station 20 or, for ex- ample a microcell, is built in the hot spot area, then the overloading of base station 20 is prevented. However, the coverage area of base station 20 can be extensive in which case it becomes difficult to establish the hot spot area loca- tion.

Figure 2 shows transceiver 30 of the invention. Transceiver 30 comprises transmission means 32 and calculation means 33. Transmission means 32 transmit code indicating location, for example LAC code, to sub- scriber terminals 10. Calculation means 33 calculate the number of subscriber terminals 10 from the signal transmitted by subscriber terminals 10. In addi- tion, transceiver 30 comprises antenna 31 using which transceiver 30 trans- mits for example LAC code to the radio path and receives signal transmitted by subscriber terminal 10. In practice transceiver 30 is e.g. a movable test base station.

Transceiver 30 described in the solution of Figure 1 is used for de- termining the radio network hot spot area. Within the coverage area of base station 20 transceiver 30 is preferably located in the presumed hot spot area or near by. Transmission means 32 of transceiver 30 transmit signalling and LAC code within the coverage area of base station 20. Subscriber terminals 10 receive the signalling and the LAC code transmitted by transmission means 32, subscriber terminals 10 then having a chance to update their location in- formation based on the received LAC code. Subscriber terminals 10 can up- date location information as transmission means 32 transmit different LAC code compared with the LAC code transmitted by base station 20.

When subscriber terminals 10 receive the LAC code of transceiver 30, then subscriber terminals 10 and transceiver 30 are signalling. Calculation means 33 of transceiver 30 calculate the number of subscriber terminals 10 that have tried to update the location position from the signalling between transceiver 30 and subscriber terminal 10. Calculation means 33 calculate the number of subscriber terminals 10 being on standby within the coverage area of subscriber terminals 10. Subscriber terminals 10 on standby are not in speech connection with another subscriber terminal 10. Calculation means 33 also calculate from the signalling a timing advance value on the basis of which calculation means 33 calculate the distance between transceiver 30 and sub- scriber terminal 10. When transceiver 30 transmits location code from various locations of the radio network, it is easy to define the precise location of the hot spot area based on the obtained distance results.

The location information update of subscriber terminals 10 is ended by transmitting a location update reject. If the definition of a hot spot area de- scribed above is performed in various locations of the radio network, then the distribution of subscriber terminals 10 in said area can be calculated from the measuring results. If the distribution of subscriber terminals 10 in some area is substantially larger than the capacity of base station 10 located in the area, then the area probably is a hot spot area. A hot spot area is at least formed when a large number of subscriber terminals 10 located in the area establish connection. Base station 20 has not enough capacity in said situation to si- multaneously serve all subscriber terminals 10 0 located in the area.

Even though the invention has been described above with refer- ence to the example of the accompanying drawings, it is obvious that the in- vention is not restricted to it but can be modified in various ways within the scope of the inventive idea disclosed in the attached claims.