Telephonic communications – Diagnostic testing – malfunction indication – or electrical... – Testing of subscriber loop or terminal
Reexamination Certificate
1998-11-02
2002-05-14
Tieu, Binh K. (Department: 2643)
Telephonic communications
Diagnostic testing, malfunction indication, or electrical...
Testing of subscriber loop or terminal
C379S001040, C379S008000, C379S012000, C379S024000, C379S029010
Reexamination Certificate
active
06389111
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method and apparatus for testing telecommunications equipment, and in particular telecommunications equipment over which two-way speech traffic is to be conveyed. The telecommunications equipment in question may be an existing telecommunications network, or part thereof, or individual items of telecommunications equipment not currently in service, for example prototypes of new designs of equipment.
2. Related Art
A number of methods for testing telecommunications equipment have been developed which monitor how the human auditory system responds to a test signal received over the equipment under test, in particular the extent to which distortions introduced by the network are perceptually significant to a listener. In particular the reader is referred to the present applicant's earlier international patent applications, numbers W094100922, W095101011 and W095/15035. In these systems a test signal representative of human speech is transmitted over the system to be tested, and the distortions imposed on the signal by the equipment under test are analysed according to the relative perceptual importance of the distortion imposed. The perceptual distortion depends on such factors as the frequency response of the human auditory system, masking effects (e.g. quiet sounds being less noticeable if louder sounds occur shortly before or after them) and various other factors.
In practical usage most telecommunications systems used for speech carry two-way conversations, in which there are two parties speaking to each other. This affects the way the system responds to the signals input to it. For example, many bidirectional systems use voice activity detection to avoid excessive acoustic noise being transmitted when there is no speech on the respective channel. This results in temporal “clipping”, in which the beginning of a user's utterance is lost because of the response time of the voice activity detector. The simulation of such characteristics would allow a system to be tested under more realistic conditions. However, the simulation of a conversation adds a number of complications to the measurement of signal quality.
Firstly, there are two separate signal paths (from the first user to the second user, and from the second user to the first user) and the signal quality will in general be different on the two lines, although such differences are likely to be relatively small in comparison with the differences between different point-to-point telecommunications links. It is therefore necessary to measure the signal quality of both paths.
Secondly, the perceived quality of each path has an effect on the other, because of the behaviour of the human users of the system. One aspect of human interaction is the natural changes of vocal level that occur between two parties during conversation. The levels at which an individual speaks depend on the level and quality of the speech received from the remote party. This means that during a telephone conversation, predominantly in the first few seconds, there is a subconscious adjustment in levels between users as a result of losses and distortions in the network path. This effect leads to a stable equilibrium for both parties. The users of a telephone line are therefore capable of adjusting their vocal output levels in accordance with the signal quality heard on the return path. Within certain limits, users adjust their vocal level according to this feedback. The level at which a user perceives he has to speak has an effect on the signal quality perceived by that user. The adjustment in vocal level itself also modifies the signal transmitted over the telecommunications system to the listener, and this in turn has an effect on the listening effort required of the other user. For example, if part of the telecommunications system is causing a large attenuation of the signal, then the listener will hear a very quiet received signal. Subconsciously assuming that this attenuation occurs in the return path as well, the listener will himself attempt to compensate by speaking louder. This affects certain characteristics of the voice itself, and the strong signal strength may also introduce distortions, for example ‘clipping’. These effects, and the greater signal strength itself, will be detected by the other user, who will in turn adjust his voice level accordingly.
Thus, the two-way nature of a typical telephone conversation allows users to compensate for some signal quality deficiencies, but this compensation may itself introduce further or different signal quality defects.
SUMMARY OF THE INVENTION
According to the present invention there is provided a method for testing telecommunications equipment over which two-way speech traffic can be carried between a first test point and a second test point, the method comprising the steps of;
a) generating first and second test signals representative of normal conversation, and each having a predetermined vocal level,
b) transmitting the first test signal from the first test point to the second test point,
c) simultaneously transmitting the second test signal from the second test point to the first test point,
d) measuring the quality of the test signals received at the respective test points,
e) determining a vocal level adjustment to be made in response to the quality measured at each test point, and
f) adjusting the vocal levels of the first and second test signals,
the said steps being repeated until a predetermined condition is reached, and an output being generated when said predetermined condition is reached, the output being indicative of the quality measured; wherein the quality measurement uses a perceptual analysis process which measures the extent to which the received signals carry distortions which would be perceptible to a human listener.
According to a further aspect of the invention there is provided apparatus for testing telecommunications equipment over which two-way speech traffic can be carried between a first test point and a second test point, the apparatus comprising;
means for generating first and second test signals representative of normal conversation, each having a predetermined vocal level;
means for supplying the first test signal to the first test point for transmission to the second test point;
means for detecting at the first test point, a signal received from the second test point;
means for measuring the quality of the detected signal by comparison with the second test signal, using a perceptual analysis process in which the extent is measured to which the received signals carry distortions which would be perceptible to a human listener;
means for determining a vocal level adjustment to be made in response to the measured quality;
means for adjusting the vocal level of the first test signal until a predetermined condition is reached; and
means for generating an output indicative of the quality measured when said predetermined condition is reached.
The invention therefore simulates the process by which the participants in a telephone conversation adjust their vocal levels during a telephone call until a predetermined condition, such as an equilibrium, is reached. The perceived signal quality at that equilibrium condition is regarded as the quality of the telecommunications connection which has been established for making the call. This equilibrium may be disturbed, and hence the quality changed, if the characteristics of the connection itself change, for example as a result of changes in radio link quality as a mobile telephone moves relative to its base station, or because of changes in ambient noise, but provided the external conditions remain unchanged the quality of the connection can be regarded as fixed for the duration of a call.
In a preferred arrangement the predetermined equilibrium condition referred to above is that the vocal level of the test signals (or at least one of them) is adjusted in response to the quality measured by less than a predetermined value, indicative that the
Hollier Michael P
Reynolds Richard J
Rix Antony W
Sheppard Philip J
British Telecommunications public limited company
Nixon & Vanderhye P.C.
Tieu Binh K.
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