GB2344489A

GB2344489A - Transmission testing apparatus

Info

Publication number: GB2344489A
Application number: GB9819906A
Authority: GB
Inventors: Michael Henley
Original assignee: Racal Instruments Ltd
Current assignee: Aeroflex Burnham Ltd
Priority date: 1998-09-11
Filing date: 1998-09-11
Publication date: 2000-06-07
Anticipated expiration: 2018-09-11
Also published as: GB9819906D0; GB2344489B

Abstract

The testing apparatus generates reference data defining respective reference levels of r.f. power (P<SB>BT</SB>, P<SB>MT</SB>) to be transmitted by the Base Transceiver Station (BTS) and a mobile station (MS) of a GSM cellular mobile telecommunications system. The BTS is caused to initiate transmissions of r.f. power at these levels and the corresponding power levels (P<SB>MR</SB>,P<SB>BR</SB>) received from the MS and the BTS in response to the transmissions are monitored. The reference levels (P<SB>BT</SB>,P<SB>MT</SB>) and the received levels (P<SB>MR</SB>,P<SB>BR</SB>) are processed to generate test values (T<SB>1</SB>,T<SB>2</SB>,T<SB>3</SB>) which can be used to assist in correcting for power losses in the system.

Description

TESTING APPARATUS AND METHODS This invention relates to apparatus and methods for testing transmission between a basestation and a mobile station of a cellular mobile telecommunications system, such as the GSM system.

Figure 1 of the accompanying drawings shows a schematic representation of a typical GSM cellular mobile telecommunications system. Such systems provide direct-dial telephone service to mobile users using r. f. transmissions.

The service area of the system is divided into discrete regions called cells (C), and each cell (C) has a basestation which processes calls to and from mobile stations (MS) located within the cell.

The basestation of each cell (C) comprises a Base Transceiver Station (BTS) located within the cell and an associated Base Station Control (BSC) common to all the cells. The BSC is connected to the Mobile Switching Centre (MSC) which, in turn, is connected to the Public Telephone Switching Network (PTSN).

The MSC also has access to databases of users. The BTS receives signals from, and transmits signals to a mobile station (MS) via r. f. transmission paths known as the up-link and the down-link respectively. The BSC controls, inter alia, the levels of r. f. power transmitted by the BTS and by the MS. To this end, the BTS and the MS both have calibrated transmission power controls and both also have the capability to measure the levels r. f. power they receive. In use, the BSC signals, via the BTS, the level of r. f. power to be transmitted by the MS, and the BTS signals to the BSC the level of r. f. power it receives from the MS. Similarly, the BSC signals the level of power to be transmitted by the BTS and the MS signals to the BSC, via the BTS, the level of r. f. power it receives from the BTS.

There will, of course, be some attenuation of r. f. power due to so-called"air losses". However, since the physical paths between the antennas of the BTS and MS are identical, the"air loss"on the up-link should be substantially the same as that on the down-link, apart from minor differences attributable to different transmission frequencies used by the BTS and the MS.

RF power loss can also arise for a range of reasons unconnected with"air loss". These additional power losses may occur because of faults or errors associated with the BTS itself; for example, misalignment or faulty connection of a directional antenna on the BTS, installation on the BTS of an antenna poorly suited to a required application (e. g. a sectored cell configuration needs a highly directional antenna), connection of a faulty antenna or occurrence of faults in the BTS power control circuitry.

These additional losses reduce the level of r. f. power transmitted and/or received by the BTS and this may result in impaired quality of communications within the cell. For this reason, it would be desirable reliably to detect for such losses so that remedial action might be taken; however, this presents a significant technical problem.

With a view to alleviating the problem, the present invention provides a method and apparatus for testing r. f. transmission between a basestation and a mobile station of a cellular mobile telecommunications system.

According to one aspect of the invention there is provided a method for testing r. f. transmission between a basestation and a mobile station of a cellular mobile telecommunications system, the method including the steps of generating reference data defining respective reference levels of r. f. power to be transmitted by the basestation and the mobile station, causing the basestation to initiate transmissions of r. f. power by the basestation and by the mobile station according to the respective reference levels defined by the reference data, and monitoring measurement data received from the basestation and being representative of respective levels of r. f. power received by the mobile station and by the basestation in response to said transmissions initiated by the basestation.

According to another aspect of the invention there is provided an apparatus for testing r. f. transmission between a basestation and a mobile station of a cellular mobile telecommunications system, the apparatus comprising means for generating reference data defining respective reference levels of r. f. power to be transmitted by the basestation and the mobile station, means for causing the basestation to initiate transmissions of r. f. power by the basestation and by the mobile station according to the respective reference levels defined by the reference data, and means for monitoring measurement data received from the basestation and being representative of respective levels of r. f. power received by the mobile station and the basestation in response to said transmissions initiated by the basestation.

Embodiments of the invention are now described, by way of example only, by reference to the accompanying drawings of which: Figure 1 shows a schematic representation of a typical GSM cellular mobile telecommunications system; Figure 2 shows an apparatus according to the invention in use in the telecommunications system, and Figure 3 is a block circuit diagram showing the apparatus of Figure 2.

Referring to Figure 2 of the drawings, the test apparatus 10 is being used to test r. f. transmission between a mobile station (MS) and the Base Transceiver Station (BTS) of a cell (C) of a GSM network. The apparatus 10 is directly connected to the BTS thereby by-passing the Base Station Control (BSC) and, in effect, replacing the BSC for the duration of the test procedure.

Referring to Figure 3, the apparatus 10 has a reference level generator 11 arranged to generate reference data defining respective reference levels PBT and Pmof r. f. power to be transmitted by the BTS and the MS.

The reference data is supplied to a radio signalling link 12 (similar to that contained in the BSC) where it is combined with control data to form a data packet which is output to the BTS via an output port 13. The control data is of a form (similar to that produced by the BSC) such as to cause the BTS to initiate r. f. power transmissions by the BTS and the MS, and these transmissions will occur at the power levels PBT and PMT respectively, defined by the reference data generated in the reference level generator 11.

The BTS assembles measurement data representing the levels of r. f. power PMR and PBR received by the MS and the BTS in response to transmissions by the BTS and the MS respectively.

This measurement data is routed to an input port 14 of instrument 10 and is then supplied to a measurement level detector 15 via the radio signalling link 12. The measurement level detector 15 monitors the measurement data and derives therefrom the received power levels PMR and PBR.

The reference levels PBT, PMT and the corresponding received levels PMR, PBR are supplied to a processor 16 which is arranged to evaluate three test values Tl, T2 and T3.

The first test value Tl is given by the expression: T1 = PBT PMR, the second test value T2 is given by the expression T2 = PR ~ PBR and the third test value T3 is given by the expression T3 = T1-T2 The first and second test values T1, T2 represent power loss on the down-link and on the up-link respectively.

If no additional losses are present in the system, the value of T, and T2 would be solely attributable to air losses. In these circumstances, the third test value T3 would be less than a threshold 5 whose value is set to take account of the relatively minor difference between air losses on the up-link and the down-link.

If the value of T3 exceeds the threshold value 5 this will indicate that additional losses are also present in the system. The user will then have the opportunity to take remedial action (e. g. by investigating and correcting for faults, antenna misalignments etc.) with a view to eliminating or reducing the additional losses. To assist in this objective the value of T3 may be displayed on a screen 17 or by alternative user-readable display means. The display means will enable the user to assess the effect of his actions, any improvement being reflected as a reduction in the value of T3.

It will be appreciated that the reference level generator 11 may be set to define an offset to the power level transmitted on the up-link or the down-link to take account of known losses or gains as will occur, for example, when the BTS has different antenna types for transmission and reception.

It will also be appreciated that although the apparatus of Figure 2 is shown as being directly connected to the BTS, the apparatus could alternatively be arranged to interface with the BSC.

Claims

1. A method for testing r. f. transmission between a basestation and a mobile station of a cellular mobile telecommunications system, the method including the steps of generating reference data defining respective reference levels of r. f. power to be transmitted by the basestation and the mobile station, causing the basestation to initiate transmissions of r. f. power by the basestation and by the mobile station according to the respective reference levels defined by the reference data, and monitoring measurement data received from the basestation and being representative of respective levels of r. f. power received by the mobile station and by the basestation in response to said transmissions initiated by the basestation.

2. A method as claimed in claim 1, wherein said reference data is supplied to, and said measurement data is received from the base transceiver station (BTS) of the basestation, and said causing step causes the BTS to initiate said transmissions of r. f. power.

3. A method as claimed in claim 1 or claim 2, including processing said levels of r. f. power respectively transmitted and received by the basestation and the mobile station to generate a first test value, processing said levels of r. f. power respectively transmitted and received by the mobile station and the basestation to generate a second test value, and deriving an output from said first and second test values.

4. A method as claimed in claim 3, wherein the first and second test values are derived from respective differences between the processed levels.

5. A method as claimed in claim 3 or claim 4, wherein the output is derived from a difference between the first and second test values.

6. A method as claimed in claim 5 including using said output to apply corrective action to the basestation to reduce a said difference between the first and second test values.

7. An apparatus for testing r. f. transmission between a basestation and a mobile station of a cellular mobile telecommunications system, the apparatus comprising means for generating reference data defining respective reference levels of r. f. power to be transmitted by the basestation and the mobile station, means for causing the basestation to initiate transmissions of r. f. power by the basestation and by the mobile station according to the respective reference levels defined by the reference data, and means for monitoring measurement data received from the basestation and being representative of respective levels of r. f. power received by the mobile station and the basestation in response to said transmissions initiated by the basestation.

8. An apparatus as claimed in claim 7 operably connectable to the base transceiver station (BTS) of the basestation, whereby, in use, said means for causing supplies said reference data to, and receives said measurement data from, the BTS, and causes the BTS to initiate said transmissions of r. f. power.

9. An apparatus as claimed in claim 7 or claim 8, including processing means for processing said levels of r. f. power respectively transmitted and received by the basestation and the mobile station to generate a first test value, for processing said levels of r. f. power respectively transmitted and received by the mobile station and the basestation to generate a second test value, and for deriving an output from said first and second values.

10. An apparatus as claimed in claim 9, wherein said first and second test values are derived from respective differences between the processed levels.

11. An apparatus as claimed in claim 9 or claim 10, wherein the output is derived from a difference between the first and second test values.

12. An apparatus as claimed in any one of claims 9 to 11 including display means for displaying said output.

13. An apparatus as claimed in claim 12, wherein said display means also displays said first and second test values.

14. A method substantially as herein described with reference to Figures 2 and 3 of the accompanying drawings.

15. An apparatus substantially as herein described with reference to Figures 2 and 3 of the accompanying drawings.