WO1999049674A2

WO1999049674A2 - Method and system for monitoring the availability of channels in a telecommunication system

Info

Publication number: WO1999049674A2
Application number: PCT/FI1999/000244
Authority: WO
Inventors: Petri Saarela
Original assignee: Nokia Networks Oy
Priority date: 1998-03-25
Filing date: 1999-03-24
Publication date: 1999-09-30
Also published as: AU3037599A; FI980670L; AR017477A1; FI980670A0; WO1999049674A3; FI107429B

Abstract

Method and system for monitoring the availability of channels in a telecommunication system, a terminal (MS) having a limit mobility area (3) within predetermined cell areas of the wireless communication system so that a call can be set up from within all the cell areas comprised in the mobility area, in which method calls are transmitted via the most suitable cell area, i.e. link cell (1), and a cell adjoining the link cell within the mobility area has been defined as an adjacent cell to the link cell and/or included in its BCCH allocation list. According to the invention, a stand-by cell (2) is defined for the link cell (1), the signal level of the stand-by cell is measured by means of the terminal (MS) and the measurement data are sent from the terminal (MS) to the access node (AN). The access node (AN) monitors the availability of the stand-by cell and executes an alarm function when the measurement data indicate that communication via the stand-by cell (2) is not possible.

Description

METHOD AND SYSTEM FOR MONITORING THE AVAILABILITY OF CHANNELS IN A TELECOMMUNICATION SYSTEM

The present invention relates to a method as defined in the preamble of claim 1 and to a system as defined in the preamble of claim 7 for monitoring the availability of channels in a telecommunication system.

WLL system ( LL, Wireless Local Loop) refers to a system in which the subscriber is connected to a telephone network via a wireless communication system. A subscriber interface is achieved by using a special communication terminal. In principle, the terminal functions like a mobile telephone known in itself, but it can be assigned a limited mobility area within which it can function. The wireless communication system can be implemented using mobile communication technology, e.g. GSM technology (GSM, Global System for Mobile Communications) .

As the communication terminal used by a WLL subscriber is typically a fixed terminal, its ability to function is heavily dependent on the presence of base station coverage. If the base station in the normal coverage area of the terminal is disabled in consequence of a fault or an operating action and the coverage of the adjacent cell is not sufficient to allow connection setup, the result is an interruption in the use of the terminal. Normally, when a call is made from a terminal, it is not possible to select the cell through which the call is to be transmitted. The ter- minal selects the one of the cells that provides the best communication. Thus, measurement results during a call can only be obtained for the cell on which the terminal has been locked.

The object of the present invention is to eliminate the drawbacks described above. A specific object of the present invention is to disclose a new type of method for improving the reliability of a WLL system by using a workable stand-by system.

As for the features characteristic of the invention, reference is made to the claims. The telecommunication system of the invention comprises a local exchange connected to an access node. The access node communicates with a terminal via a wireless communication system. The mobility area of the terminal is limited in accordance with the WLL system, comprising a number of predetermined cell areas. Of the cell areas within the mobility area, the one that provides the best communication is selected as the link cell for the terminal. A list of cells adjacent to the link cell contains the BCCH frequencies (BCCH, Broadcast Control Channel) of those of the adjoining cells which have been defined as adjacent cells to the cell area in question, which are measured by the terminal and to which an ongoing call can be handed over. A BCCH allocation list contains those BCCH frequencies of adjoining cells which are measured by the terminal. No handover is performed on the basis of the BCCH allocation list.

In the method of the invention, a stand-by cell is defined for the link cell, and measurement data relating to the stand-by cell are sent from the terminal to the access node. Stand-by cell means a suitably selected cell through which the call can be transmitted in the event of an interruption or malfunction in the operation of the actual link cell. The link cell may be assigned one or more stand-by cells.

In a preferred embodiment of the invention, a cell area defined as an adjacent cell to the link cell is defined as a stand-by cell. In a preferred embodiment, a cell area comprised in the BCCH allocation list is defined as a stand-by cell.

In a preferred embodiment of the invention, the access node monitors the availability of the stand-by cells by using measurement data sent by the terminal. The purpose of this is to ensure successful communication via a stand-by cell.

In a preferred embodiment of the invention, an alarm function is executed in the access node if the measurement results indicate that communication via a stand-by cell is not possible. The alarm function may consist of e.g. a message issued by the user interface of the telecommunication system or some other corresponding signal to the system operator. Based on the alarm, the operator may take measures to guarantee successful communication even during a service interruption in the actual link cell.

In a preferred embodiment of the present in- vention, the wireless communication system used is based on a digital mobile communication system, preferably the GSM system.

The system of the invention comprises means for defining a stand-by cell for the link cell and for sending measurement data from the terminal to the access node. The cell defined as a stand-by cell in the system is preferably a cell area defined as an adjacent cell to the link cell, or it may be a cell area comprised in the BCCH allocation list of the link cell.

In a preferred embodiment, the system comprises means for monitoring the availability of the stand-by cell in the access node on the basis of measurement data. In a preferred embodiment, the system comprises means for executing an alarm function in the access node when the measurement data indicate that communication via the stand-by cell is not successful. The method of the invention provides the ad- vantage that successful communication can be ensured even when the primary link cell is disabled. During use, wireless communication conditions may change e.g. due to topographic variations so that no information is obtained about the effects of the changes regarding individual subscribers .

In the following, the invention will be de- scribed by the aid of a few examples of its embodiments by referring to the attached drawing, wherein

Fig. 1 is a diagram representing an example of a system in which the method of the invention is applied, Fig. 2 presents an example of the method of the invention,

Fig. 3 is a diagram representing a detail of the system of the invention.

Fig. 1 shows a wireless local loop WLL, in which subscriber terminals MS are connected over a wireless link via a base station BS to an access node AN and from the access node to a wired network local exchange LE using a V5 interface consistent with the ETS 300 347-1 standard. Open interfaces (V5.1 and V5.2) between an access node and a telephone exchange are defined in the ETSI (European Telecommunications and Standards Institute) standards of the ETS 300 324 and ETS 300 347 series. V5 interfaces enable subscribers belonging to a physically separate access network, which may be a wired or a wireless network, to be connected using a standard telephone exchange interface.

In Fig. 2, a mobile station 1 is depicted within its link cell 1. The base station in the link cell 1 is BS1. Base station BS2 is surrounded by cell area 2. Cells 1 and 2 together form a mobility area 3. The mobility area may also consist of a larger number of cells.

Cell area 2 is defined as a stand-by cell for the link cell 1 if it is comprised in the BCCH allocation list for the link cell 1, or if cell 2 has been defined as an adjacent cell to cell 1. In operation, cell 2 corresponds to cell 1, i.e. if measurement results indicate that better communication quality is obtained via cell 2, then a handover to cell 2 is performed, making cell 2 the link cell. A stand-by cell is used in the event of a failure or malfunction in the link cell.

The access node AN comprises means 4 for defining a stand-by cell. This may be done automatically on the basis of a process in the access node. Alterna- tively, a stand-by cell definition may be entered e.g. via the user interface of the telecommunication system by using a MML user interface (MML, Man-Machine Language) , by identifying the LAC and CI (LAC, Location Area Code; CI , Cell Identity) of the cell to be defined as a stand-by cell.

The terminal MS performs measurements during a call to determine whether successful communication via the stand-by cell 2 is possible. The measurement data are transmitted to the access node AN. The access node AN is provided with means 5, e.g. a software process suited for the purpose, for monitoring the measurement data. On the basis of these data, the access node AN can determine the availability of the stand-by cells. In this way, it is possible to ensure that a stand-by cell assumed to be functioning according to the radio network design is actually functional in practice. In case it is detected that a cell defined as a stand-by cell does not meet the conditions for successful communication, the access node AN is provided with means 6 for executing an alarm function. Based on the alarm function, the operator can take measures to correct the situation.

Fig. 3 is a diagram representing a detail of a system according to the invention. Fig. 3 shows a network management system NMS connected to an access node AN. In this example, stand-by cells are defined using means 4 via the network management system NMS. In conjunction with the definition of a stand-by cell, a limit value for the minimum acceptable signal level is also defined. The limit value is transmitted to means 5 analysing stand-by cell availability. If nec- essary, the analysing means transmit a message to alarm means 6. The network management system NMS comprises means for receiving an alarm from the access node AN.

The access node AN is provided with means 7 for sending a cell list to the terminal MS. The terminal MS is provided with means 9 for receiving a cell list, means 10 for measuring the signal level and means 11 for sending measurement data to the access node AN. The access node AN comprises means 8 for re- ceiving measurement data from the terminal MS .

The invention is not restricted to the examples of its embodiments described above, but many variations are possible within the scope of the inventive idea defined by the claims.

Claims

1. Method for monitoring the availability of channels in a telecommunication system, said telecom- munication system comprising a local exchange (LE) , an access node (AN) connected to a local exchange, a wireless communication system connected to the access node, a communication terminal (MS) communicating with the access node (AN) via the wireless communication system, the terminal (MS) having a limited mobility area (3) within predetermined cell areas of the wireless communication system so that a call can be set up from within all the cell areas comprised in the mobility area, in which method calls are transmitted via the most suitable cell area, i.e. link cell (1) , and a cell (2) adjoining the link cell within the mobility area has been defined as an adjacent cell to the link cell and/or included in its BCCH allocation list, charact e ri sed in that a stand-by cell (2) is defined for the link cell (1) , the signal level of the stand-by cell is measured by means of the terminal (MS) and the measurement data are sent from the terminal (MS) to the access node (AN) .

2. Method as defined in claim 1, char - ac t eri sed in that a cell area defined as an adjacent cell to the link cell (1) is defined as a stand-by cell (2) .

3. Method as defined in claim 1 or 2, charac t e ri s ed in that a cell area comprised in the BCCH allocation list of the link cell (1) is defined as a stand-by cell (2) .

4. Method as defined in any one of claims 1 -

3, characteri sed in that the availability of the stand-by cell (2) is monitored in the access node (AN) on the basis of the measurement data.

5. Method as defined in any one of claims 1 -

4 , c h a r a c t e r i s e d in that an alarm function is executed in the access node (AN) when the measurement data indicate that communication via the stand-by cell (2) is not possible.

6. Method as defined in any one of claims 1 - 5, charac t eri s ed in that the wireless communication system is based on a digital mobile communication system.

7. System for monitoring the availability of channels in a telecommunication system, said telecom- munication system comprising a local exchange (LE) , an access node (AN) connected to a local exchange, a wireless communication system connected to the access node, a terminal (MS) communicating with the access node (AN) via the wireless communication system, the terminal (MS) having a limited mobility area (3) within predetermined cell areas of the wireless communication system so that a call can be set up from within all the cell areas comprised in the mobility area, in which system calls are transmitted via the most suitable cell area, i.e. link cell (1), and a cell (2) adjoining the link cell within the mobility area has been defined as an adjacent cell to the link cell and/or included in its BCCH allocation list, charac t e r i s ed in that the system comprises means (4) for defining a stand-by cell (2) for the link cell (1) , means for measuring the signal level of the stand-by cell (2) in the terminal (MS) and means for sending the measurement data from the terminal (MS) to the access node (AN) .

8. System as defined in claim 7, char act eri sed in that the cell area defined in the system as a stand-by cell (2) is a cell area defined as an adjacent cell to the link cell (1) .

9. System as defined in claim 7 or 8, charact er i sed in that the cell area defined in the system as a stand-by cell (2) is a cell area included in the BCCH allocation list of the link cell

(1) ΓÇó

10. System as defined in any one of claims 7

- 9, charac t eri sed in that the system com- prises means (5) for monitoring the availability of the stand-by cell (2) in the access node (AN) on the basis of the measurement data.

11. System as defined in any one of claims 7

- 10, characteri sed in that the system com- prises means (6) for executing an alarm function in the access node (AN) when the measurement data indicate that communication via the stand-by cell (2) is not possible.