EP0976274A1

EP0976274A1 - Improvements in, or relating to, measurement of telecommunications connection quality

Info

Publication number: EP0976274A1
Application number: EP97928584A
Authority: EP
Inventors: Erik Bryntse; Ulf Sandberg; Thomas NÖJD; Birgitte Rodger; Bengt Serenius
Original assignee: Telia AB
Current assignee: Telia AB
Priority date: 1996-07-25
Filing date: 1997-06-13
Publication date: 2000-02-02
Also published as: WO1998005179A1; SE9602862L; NO990205D0; SE517413C2; SE9602862D0; NO990205L

Abstract

A method of measuring the quality of a mobile connection, in a mobile telephone system, has the following steps: establishing a mobile connection between a mobile handset and a fixed measurement station; transmitting predetermined test sequences from said mobile handset to said fixed measurement station and vice versa; storing sound signals received by said mobile handset and said fixed measurement station; and analysing said received sound signals to derive a measure of the quality of said mobile connection. A portable measurement briefcase, for use with the method, includes a mobile handset modified for the transmission of predetermined test sequences. A fixed measurement station, for use with the method, includes an ISDN-connected PC equipped with a DSP card.

Description

Improvements in. or Relating to , Measurement of Telecommunications Connection Quality

The present invention relates to a test set for, and a method of, measuring the quality of a connection, established over a mobile telecommunications network.

Modern telecommunications makes it possible for speech, or data, communications to be established on a global basis. In spite of the fact that telecommunications systems and networks are usually very efficient, certain undesired effects, such as echo, can degrade the quality of service provided for telecommunications traffic.

By carrying out quality testing during system/network operation, it is possible to detect the onset of service degradation and system failures before they have a serious adverse effect on quality of service. The ability to anticipate and prevent service degradation, and failure, before complaints are received, has, for many years, been a highly desirable objective for telecommunications operators. A great deal of time, effort and money has been invested by operators into improving their network maintenance systems .

Preventative maintenance can be planned and is invariably cheaper than acute repair of faults.

The speech quality in a modern telecommunications network is harder to supervise than pure data transmission. Furthermore, the speech quality in a telecommunications network is, to a large extent, decided by the analog terminations in the network.

These include electro-acoustical and analog/digital conversion. This creates a problem because telecommunications operators gradually lose control of these parts of the network. However, the installations which exist meet stringent planning criteria and are consequently extensively standardised. This makes their behaviour predictable.

One cause of degradation in quality of service is echo. This is a network specific problem which can substantial degrade speech quality. New network improvements have reduced the attenuation, not only of speech signals, but also of echo. This means that, in modern telecommunications networks, echo is, potentially, a greater problem than it was in older networks. The int odu ti n of star subscriber services, requiring the use of extended control routines and signalling in the telecommunications network, also requires that echo be effectively controlled and methods developed to reduce it.

The subjective reaction to echo depends on the echo delay, i.e. the time between the original signal and the delayed signal. With very short delays the speech sounds "hollow", which is a very unpleasant effect. The effects of echo are made worse by increased echo delay. Echo in a telephone system, therefore, is a phenomenon that needs to be minimised.

In the local network, communication between a subscriber equipment, such as a telephone, and the local telephone exchange, takes place over a two-wire loop. However, for trunk calls the connection is established via microwave, or satellite, links. In this case, the connection is no longer a bidirectional two-wire loop, but two one-way channels, equivalent to two pairs of wires. The device used for conversion from two to four wires is referred to as a hybrid. It is hybrids that are the principle cause echo.

For national connections, the echo losses in hybrids, compared with normal losses in the network, are suppressed. Where longer delays occur, suppression of echo has an unacceptable effect on speech. In order to reduce echo without attenuating speech, it is necessary to utilise an echo cancellation function. Apart from satellite communications, for which echo cancellation is vital, most echo cancellation functions are installed on international connections. Every echo cancellation function is physically associated with a certain country .

Supervision of the quality of service provided by telecommunication networks has been undertaken by telecommunications operators for many years. At the present time there exists, in principle, two methods for network supervision, i.e. quality of service tests are conducted when:

- the network is out of operation; or

the network is in operation.

In the first case a connection is taken out of operation and measurements are performed by introducing signals which are known to behave well in the network. This enables such parameters as attenuation, echo, delay, error probability, etc., to be determined.

In the second case, measurements are performed while the network is operational. A skilled person is connected in both directions on a transmission line, and an estimation of the speech quality is made by listening to a conversation. This method of measurement gives a subjective estimation of speech quality and cannot - - normally be used for continuous control of the network.

It is an object of the present invention to achieve, in relation to known methods of monitoring, and measuring quality of service for a mobile telecommunications network, an improved and simplified measurement set, herein referred to as a measurement briefcase, and a method of performing the measurements.

According to a first aspect of the present invention, there is provided, in a mobile telephone system, a method of measuring the quality of a mobile connection, characterised by:

establishing a mobile connection between a mobile handset and a fixed measurement station;

transmitting predetermined test sequences from said mobile handset to said fixed measurement station and vice versa;

storing sound signals received by said mobile handset and said fixed measurement station; and

analysing said received sound signals to derive a measure of the quality of said mobile connection.

Said fixed measurement station may be connected to an ISDN.

Preferably, said mobile handset is adapted for the transmission of predetermined test sequences.

Said received sound signals may be stored on a DAT recorder .

Preferably, parameters influencing reception quality, including signal strength, channel number, time slot, timing advance and base station identity, are recorded.

Said received sound signals may be stored on a portable computer equipped with a sound card.

Said fixed measurement station may include a PC equipped with a DSP card.

Preferably, echo is simulated in said fixed measurement station by means of an impulse response generated by software on said DSP card.

Sound signals received by said fixed measurement station may be recorded on a hard disc.

Said mobile telephone system may be a GSM system and said mobile handset is a GSM handset.

According to a second aspect of the present invention, there is provided a portable measurement briefcase, for use with the method set forth above, characterised in that said measurement brief case includes a mobile handset modified for the transmission of predetermined test sequences.

Said measurement brief case may include a portable PC equipped with a sound card.

Said measurement brief case may include a DAT recorder adapted to record sound signals received by said modified mobile handset. Preferably, said mobile handset is equipped with a field test display adapted to record parameters affecting reception quality, including signal strength, channel number, time slot, timing advance and base station identity.

Said mobile handset may be a GSM handset.

According to a third aspect of the invention, there is provided a fixed measurement station, for use with the method, as set forth above, characterised in that said fixed measurement station includes an ISDN- connected PC equipped with a DSP card.

Said ISDN-connected PC is arranged to simulate echo by a software generated impulse response.

Said ISDN-connected PC is arranged to store incoming sound signals on a hard disc.

An embodiment of the invention will now be described, by way of example.

The GSM-system offers subscribers the ability to make mobile calls originating from a large number of countries. However, the system has restrictions and is still suffering from early developmental problems, not least due to the rapid extension of the system. In this connection it is important that subscribers really can use their GSM-mobiles abroad without experiencing reduced speech quality. A number of tests with GSM calls between different countries in Europe have been performed. In this context, the routes by which connections are established have been examined. The aim of this exercise is, firstly, to obtain an improved knowledge and understanding of how connection routes are established and, secondly, to make a rough investigation of any quality problems, related to complex connection routes, that occur.

This exercise has shown that there are problems with speech quality. For instance, the following degradations of quality of service have been noted:

varying speech levels (especially between recorded voice messages and mobile originating responses ) ;

echo problems (poor echo cancellation, echo cancellation in tandem); and

other deteriorations of speech quality (distortion) .

It has, however, been difficult to relate these problems to specific elements in the network, or connection routes.

One solution to this problem is to devise a measurement system based on a mobile measurement briefcase, or test set, and a fixed measurement station. The measurement briefcase, includes a GSM-mobile handset. The GSM mobile is used to call the fixed station, which is connected to an ISDN. Measurements can then be performed which, objectively and subjectively, give a measurement of speech quality.

The measurement system enables a better picture of the speech quality on international GSM connections to be obtained and this in turn enables a view of the factors which influence speech quality to be derived.

The measurement briefcase, which is proposed by the present invention, is a tool for the systematic examination of the speech quality of international GSM calls. In addition, the measurement briefcase can also be used to examine the speech quality in an operator's domestic network.

The measurement system is based on a portable measurement briefcase which can easily be transported, and a fixed measurement station located in an operator's domestic network. The measurement briefcase, includes, among other things, a GSM-mobile. The GSM mobile is used to establish a mobile connection with the fixed measurement station by simply making a mobile call to the fixed measurement station.

After the connection between the measurement briefcase and the fixed measurement station has been established, predetermined test sequences can be transmitted and the results stored, for future analysis. The measurement briefcase includes a GSM mobile telephone, modified so that predetermined test sequences can be transmitted, at the same time as received sound signals are stored. This is achieved by means of a portable PC with sound-card, and possibly a DAT- recorder, or the like. Moreover, the telephone is equipped with a field test display, making it possible to read different parameters which may influence reception quality , for instance signal strength, channel number, time slot, timing advance, base station identity , etc..

The fixed station is based on an ISDN-connected PC with a DSP-card. The reason for using an ISDN connection, is that such connections are not subject to echo, because the ISDN uses a four wire connection right up to the subscriber. Echo, which is normally caused by hybrids, which convert from 2-wire to -wire in the local exchange, is instead simulated by an impulse response in software on the DSP (digital signal processing) card. At the same time the incoming sound signals are saved on hard disk and predefined test sequences are transmitted.

Claims

1. In a mobile telephone system, a method of measuring the quality of a mobile connection, characterised by:

establishing a mobile connection between a mobile handset and a fixed measurement station ;

- storing sound signals received by said mobile handset and said fixed measurement station; and

2. A method, as claimed in claim 1, characterised in that said fixed measurement station is connected to an ISDN.

3. A method, as claimed in claim 1, or 2, characterised in that said mobile handset is adapted for the transmission of predetermined test sequences.

4. A method, as claimed in any previous claim, characterised in that said received sound signals are stored on a DAT recorder.

5. A method, as claimed in any previous claim, characterised in that parameters influencing reception quality, including signal strength, channel number, time slot, timing advance and base station identity, are recorded .

6. A method, as claimed in claims and 5, characterised in that said received sound signals are stored on a portable computer equipped with a sound card.

7. A method, as claimed in any previous claim, characterised in that said fixed measurement station includes a PC equipped with a DSP card.

8. A method, as claimed in claim 7, characterised in that echo is simulated in said fixed measurement station by means of an impulse response generated by software on said DSP card.

9. A method, as claimed in either claim 7, or 8, characterised in that sound signals received by said fixed measurement station are recorded on a hard disc.

10. A method, as claimed in any previous claim, characterised in that said mobile telephone system is a GSM system and said mobile handset is a GSM handset.

11. A portable measurement briefcase, for use with the method claimed in any of claims 1 to 10, characterised in that said measurement brief case includes a mobile handset modified for the transmission of predetermined test sequences.

12. A portable measurement briefcase, as claimed in claim 11, characterised in that said measurement brief case includes a portable PC equipped with a sound card.

13. A portable measurement brief case, as claimed in claim 12, characterised in that said measurement brief case includes a DAT recorder adapted to record sound signals received by said modified mobile handset.

14. A portable measurement brief case, as claimed in any of claims 11 to 13, characterised in that said mobile handset is equipped with a field test display adapted to record parameters affecting reception quality, including signal strength, channel number, time slot, timing advance and base station identity.

15. A portable measurement briefcase as claimed in any of claims 11 to 14, characterised in that said mobile handset is a GSM handset.

16. A fixed measurement station, for use with the method claimed in any of claims 1 to 10, characterised in that said fixed measurement station includes an ISDN- connected PC equipped with a DSP card.

17. A fixed measurement station, as claimed in claim

16, characterised in that said ISDN-connected PC is arranged to simulate echo by a software generated impulse response.

18. A fixed measurement station, as claimed in claim

17, characterised in that said ISDN-connected PC is arranged to store incoming sound signals on a hard disc.