Method and arrangement for controlling cell change and a terminal of a cellular system

Abstract

The invention relates to an improved method and arrangement for controlling a cell change performed by a terminal of a cellular radio system. In particular the invention relates to a cell change in a situation where the terminal is connected to a special service provided by its current cell, e.g. to the GPRS service (General Packet Radio Service). An essential idea of the invention is that in conjunction with a cell change order a base station sends to the terminal information about whether the terminal is allowed not to carry out the cell change order if the terminal does not know the timing information of the new cell assigned to it. This information is advantageously sent in a signalling message of a certain service, such as the GPRS service. It is an advantage of the invention that a terminal connected to a certain service will not make unnecessary cell change attempts which are doomed to fail. The invention helps direct the cell change in such a manner that the load caused by possible repeated cell change attempts on the terminal and radio signalling is low.

1 .- 15 . (canceled)  
   
   
       16 . A base station (BS,  551 ) in a cellular radio system, comprising means for providing a service (GSM, GPRS) and means for receiving signalling messages from a terminal (MS,  500 ) as well as means for generating signalling messages and sending them to terminals, characterized in that it further comprises means for receiving and processing information obtained from a terminal, which information is arranged so as to convey to the base station the data of those neighbour cells known to the terminal the timing information of which is known to the terminal.  
   
   
       17 . The base station according to  claim 16 , characterized in that said service is the GPRS data packet transmission service.  
   
   
       18 . The base station according to  claim 16 , characterized in that said signalling messages are signalling messages of the GPRS data packet transmission service.  
   
   
       19 . A terminal (MS,  500 ) in a cellular radio system, equipped with means for connecting to a certain service (GSM, GPRS) and comprising means for receiving signalling messages from base stations (BS,  551 ) and means for performing cell specific measurements in order to find a suitable serving cell, characterized in that it is further equipped with means for determining the timing information of neighbour cells and means for sending neighbour information to the base station of the current cell in the case that the timing information of the base station of the new cell assigned to the terminal in a cell change order by the serving base station is unknown to the terminal.  
   
   
       20 . The terminal according to  claim 19 , characterized in that said certain service is the GPRS data packet transmission service.  
   
   
       21 . The terminal according to  claim 19 , characterized in that said signalling messages are signalling messages of the GPRS data packet transmission service.  
   
   
       22 . A cellular radio system comprising base stations (BS,  551 ) and associated cells ( 1 - 11 ) and terminals (MS,  500 ), in which system 
 the base stations are equipped with means for conveying signalling messages between a base station and a terminal, and    the terminals are adapted so as to operate at a certain service level (GSM, GPRS) and to convey signalling messages between a terminal and a base station,    characterized in that it further comprises information, which is known to a terminal, about a set of neighbour cells of said terminal, the timing information of the base stations of which neighbour cells the terminal has determined, whereby said system is adapted so as to convey, after a cell change order addressed to the terminal, said information in a signalling message from the terminal to a base station for the purpose of selecting a new serving cell if the target cell assigned to the terminal in the cell change order is not included in the set of neighbour cells determined by the terminal.    
   
   
       23 . The cellular radio system according to  claim 22 , characterized in that said certain service is the GPRS data packet transmission service.  
   
   
       24 . The cellular radio system according to  claim 22 , characterized in that said signalling messages are signalling messages of the GPRS data packet transmission service.