GB2283388A - Telephone network testing - Google Patents

Abstract

The characteristics of a signal between a transmitter and a receiver are tested by a method comprising sending from one to the other two signals comprising: a first transmission in simplex mode at a frequency between 300 Hz and 3000 Hz in order to test the level of audio sound and frequency distortion of the signal, and a second transmission at a lower level in duplex mode using means to detect audio breaks, distortion and noise.

Description

TELEPHONE NETWORK TESTING This invention relates to a method of testing the characteristics of a signal between a transmitter and a receiver, e.g. in a telephone network, and is particularly suitable for testing the quality of a cellular telephone network.

It has previously been proposed to test the audio quality of a cellular network system by the sending of a test programme from a base station to a mobile station and recording the results for analysis but the present invention aims to provide an improved testing method to give more useful and meaningful results.

Accordingly, the invention provides a method of testing the characteristics of a signal between a base transmitter/receiver at a base station and a mobile transmitter/receiver at a mobile station, comprising sending from one to the other two signals comprising: a first transmission in simplex mode at a frequency between 300 Hz and 3000 Hz in order to test the level of audio sound and frequency distortion of the signal, and a second transmission at a lower level in duplex mode using means to detect audio breaks, distortion and noise.

The mobile station will usually be a vehicle in which a portable test unit is carried and the base can conveniently be a fixed location such as a cell site or central office. The test unit at the base can also conveniently be a portable unit. The mobile test unit can conveniently be powered by the vehicle battery or, if desired, a separate isolatable power source. The mobile unit can be arranged to power down automatically after completion of testing or during any pause made to avoid battery drain.

Preferably both test units house audio generation and measurement equipment, call progress tone detectors and a microprocessor to control and record the test sequence, and these may all be of known design. Thus calls may be made either from the base unit to the mobile unit or vice versa.

The method of the invention is designed to combine all required parameter measurements of a call to give a derived result which relates most closely to the user's actual perception of the quality of that call. Thus the first transmission phase of the test can be based on, say, three transmitted frequencies to cover the transmission across the audio band. The second transmission phase is the break test designed for blanket coverage of all parameters simultaneously at both call locations and is particularly suitable for measuring the quality of a cellular connection.

The three frequencies of the first phase may be, for example, 622,1179 and 2410 Hz. These could be transmitted at a typical level of -12dB, but could, for example, usefully be within the range -3 to -18dB The break test of the second phase is performed at a lower level, e.g. typically -22dB, but could, for example, usefully be within the range -15 to -28dB. It conveniently utilises notch filters to detect audio breaks, distortion and noise. For example, for the break test, the mobile unit may transmit a continuous signal of 590 Hz and the base unit a continuous signal of 1000 Hz. Each unit measures the received signal from the other unit, excluding its own transmitted signal. At the end of the break test period, the final voice quality is recorded.

Test measurements may be made continuously e.g. over a programmed period of, e.g. up to 60 minutes, or at regular, predetermined intervals, e.g. 3 or 5 minute cycles selected by the user and are automatically recorded by the microprocessor.

They may be downloaded to the base unit automatically after each test or at intervals, as desired. Thus, a network may be tested automatically and remotely.

Test calls can be made in exactly the same manner as calls by any user with no special support required by the network. The system is very flexible and most of the operations can be controlled by downloaded software.

The base unit may be connected to a PSTN line circuit, e.g. through an RJ11 interface and the mobile unit through an integral cellular phone. If desired, the mobile unit may also be equipped with a satellite location system for precise geographic positioning. The software also conveniently includes means to allocate dates and times for each test call.

The test sequence may be configured through a compatible personal computer, which will normally be located at the base site. The microprocessors automatically control the test call sending programme so that the vehicle driver of the mobile unit can when necessary concentrate solely on driving.

Thus, the system can be programmed to make any desired sequence of cellular or land line-originated calls and all the desired quality tests can be performed during each call. The results can be summarised in a voice quality figure, e.g. starting with a maximum of 100 points, from which points are deducted when quality thresholds are exceeded. The thresholds may all be user configured with default parameters installed for initial user convenience. For example, for the first transmission, two thresholds may be set for each of audio level and frequency for each of the frequency transmissions, i.e. for each of the three frequency transmissions of the above-mentioned embodiment. A drop in audio level will be picked up by the audio level thresholds while noise and co-channel interference, for example, will be picked up by both audio level and frequency thresholds.

Voice quality measurement may be adjusted by adjusting the level and frequency thresholds together with the break level and break frequency settings. Inspection of detail files from previous trials will indicate the usual expected received levels at each of the test frequencies. This can be used in conjunction with observers' notes to adjust the threshold level.

All test results may be stored in battery-backed RAM so that removing power from a unit will not destroy the results.

The invention may, of course, operate known systems for problem diagnosis and for running diagnostic routines.

The results of the test measurements may be provided in a number of reports for analysis and review. These may for example include a Management Summary, Call Summary, Call Detail Report and an ASCII data file for subsequent post processing.

Management Summary Report Is available for any test type and provides a "top level", overview with a breakdown of numbers and percentages, of such items as dropped calls, successful calls, etc.

Call Summary Report Provides a summary of all calls made during a test programme. All significant events such as Hand-off, Release, etc, are clearly displayed on a line of information that includes time stamp, geographic locations, RSSI, Channel number, SAT, Call Quality figures, and response time.

Call Detail Report Provides the in-depth data logged during all test calls. This includes the messages from the Mobile phone data bus (MBus), PSTN progress tones, transmission and noise measurements, channel assignments, geographic locations1 determination of the call quality figure and other data that will assist in identifying network problems.

ASCII File Enables users to post process any of the collected information using standard database programmes. This includes the option of presenting the result graphically on maps.

Typical equipment required by the user comprises a suitable personal computer, e.g. an IBM compatible PC, with approximately 10 mb of hard disc space available, least 500 Kb of RAM, a VGA monitor and DOS at a level of 3.3. or higher. A printer must be must be connected to the PC and a serial port cable between the PC and the base unit. The test procedures can then be commenced and monitored as desired.

Further embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which: Figures IA and IB show a three minute timing diagram for a mobile-unit originated all to a base unit the units and system being code named BUZZARD.

Figure 2 is a circuit diagram of a typical interface to PSTN network for use in the invention; Figure 3 A,B and C is a circuit diagram of the generate and measure section of the system; Figure 4 A,B and C is a circuit diagram of the tone filters and clock generation for use in the system; and Figure 5 is a circuit diagram of the analogue signal selection and measurement stage of the system.

The sequence of numbered steps in Figures 1A and 1 B is as follows: 1) 5 second guard time to allow for out-of synchronisation of the real time clocks.

2) 3.4 seconds to finish on-going unit enquiries and ensure unit is ready for dial command.

3) 4 second wait after dial command, plus up to a maximum of 15 second wait for "ISM" message to say "channel available call going ahead".

4) Length dependent on time for the network to establish the call.

5) Time for PSTN to answer after caller is connected to that PSTN phone.

Minimum of 5.5 seconds, maximum of 13 seconds.

6) 8 second "ON TIME" for called party tone.

7) 1.5 second delay after called party tone off before calling party tone ON.

8) 2 second ON time for calling party tone.

9) 10 second guard time for detection of possible repeat attempts at synchronisation. All test internal timings are made from the end of this guard time.

10) 15.2 seconds for each bi-directional frequency test.

11) Break test length. This will be up to the maximum time set (90 seconds)1 but may be dynamically shortened to ensure that step (15) is 20 seconds.

12) 5 second guard time between each end stopping measuring and stopping generating.

13) 2.5 second delay before line released to ensure calling party releases first.

14) 1 second delay before calling party releases line.

15) 20 second guard time to ensure test completed before end of time slot.

Claims (18)

1. A method of testing the characteristics of a signal between a base transmitter/receiver at a base station and a mobile transmitter/receiver at a mobile station, comprising sending from one to the other two signals comprising: a first transmission in simplex mode at a frequency between 300 Hz and 3000 Hz in order to test the level of audio sound and frequency distortion of the signal, and a second transmission at a lower level in duplex mode using means to detect audio breaks, distortion and noise.

2. A method according to Claim 1, in which the mobile station is a vehicle carrying a portable test unit.

3. A method according to Claim 1 or 2, in which the mobile test unit is arranged to power down automatically after completion of testing.

4. A method according to Claim 1, 2 or 3, in which calls may be made from the base unit to the mobile unit and vice versa.

5. A method according to any preceding Claim1 in which the first transmission is based on three transmitted frequencies to cover transmission across the audio band.

6. A method according to Claim 5, in which the three frequencies are about 622,1179 and 2410 Hz.

7. A method according to any preceding Claim, in which the first transmission is at a level of from about -3dB to -18dB.

8. A method according to any preceding Claim, in which the second transmission is at a level of from about -15dB to -28dB.

9. A method according to any preceding Claim, in which the second transmission utilises notch filters to detect audiobreaks, distortion and noise.

10. A method according to Claim 9, in which the mobile unit transmits a continuous signal of about 590 Hz and the base unit transmits a continuous signal of about 1000 Hz.

11. A method according to any preceding Claim, in which final voice quality is recorded at the end of a break test.

12. A method according to any preceding Claim, in which test measurements are made continuously over a programmed period, or are made at regular predetermined intervals, and are automatically recorded by a microprocessor.

13, A method according to any preceding Claim, in which the mobile unit is equipped with a satellite location system.

14. A method according to any preceding Claim, in which the results are summarised as a voice quality figure which is reached by deducting points from a maximum number when quality thresholds are exceeded.

15. A method according to Claim 14, in which the thresholds are user configured with predetermined default parameters.

16. A method according to Claim 15, in which two thresholds are set for each of audio level and frequency for each frequency transmission.

17. A method according to Claim 16, in which a drop in audio level is identified by the audio level thresholds and noise and co-channel interference are identified by both audio level and frequency thresholds.

18. A method according to any one of Claims 14 to 17, in which voice quality measurement is adjusted by adjusting the level and frequency thresholds together with the break level and break frequency settings.