CA2245068A1 - Measurement method and device for the evaluation of digital transmission systems - Google Patents
Measurement method and device for the evaluation of digital transmission systems Download PDFInfo
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- CA2245068A1 CA2245068A1 CA002245068A CA2245068A CA2245068A1 CA 2245068 A1 CA2245068 A1 CA 2245068A1 CA 002245068 A CA002245068 A CA 002245068A CA 2245068 A CA2245068 A CA 2245068A CA 2245068 A1 CA2245068 A1 CA 2245068A1
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L43/00—Arrangements for monitoring or testing data switching networks
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L1/00—Arrangements for detecting or preventing errors in the information received
- H04L1/24—Testing correct operation
- H04L1/242—Testing correct operation by comparing a transmitted test signal with a locally generated replica
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- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Testing, Inspecting, Measuring Of Stereoscopic Televisions And Televisions (AREA)
- Arrangements For Transmission Of Measured Signals (AREA)
- Monitoring And Testing Of Transmission In General (AREA)
Abstract
A measurement method and a device for the evaluation of digital transmission systems having a backward channel for transmitting secondary information. A
transmitting test device and a receiving test device access a forward channel, and, controlled by the transmitting test device, record corresponding sequences of the original and output signals in the form of reference and test signals. At the end of recording, the transmitting test device transmits the stored reference signal via the backward channel to the receiving test device, from where the test and reference signals are provided to a common analysis system. Using the method of the invention, natural test signals, in particular segments of real program material, can be used to evaluate digital transmission systems.
transmitting test device and a receiving test device access a forward channel, and, controlled by the transmitting test device, record corresponding sequences of the original and output signals in the form of reference and test signals. At the end of recording, the transmitting test device transmits the stored reference signal via the backward channel to the receiving test device, from where the test and reference signals are provided to a common analysis system. Using the method of the invention, natural test signals, in particular segments of real program material, can be used to evaluate digital transmission systems.
Description
~ CA 0224~068 1998-08-12 [2345/44]
Measurement Method and Device for the Evaluation of Digital Transmission Systems Field of the Invention The present invention relates to a measurement method and device for the evaluation of digital transmission systems.
Related Technology Due to new perception-based data compression methods for audio and video signals, new measurement methods that require knowledge of the signal before andafter transmission are needed for the measurement and evaluation of digital tr~n~mi~ion systems. Perception-based data compression methods use the capabilities of human perception in order to reduce the large volume of data needed for audio and, in particular, video signals. Inforlnation contained in the original signal, such as very high noise frequencies or rapid image movements which are beyond human sensory perception capabilities, are removed from the original signal in data transmission systems by suitable masks and filters on the transmitting side. This reduces considerably the volume of data to be transmitted to the receiving test device, thereby making the entire data tr~n~mi~ion system more powerful, for example by the ability to transmit more video images per second.
Since data tr~n~mi~ion systems with this type of data compression method influence and distort the frequency pattern of the original signal to be transmitted, testing the system with simple test signals such as a simple sine wave or a stationary signal provides very little indication of whether the original signal fully matches the output signal of the data tr~n~mi~ion system on the receiving side with respect to human perception. This quality test can be reasonably carried out only with testsignals that resemble the real program material as closely as possible and also exhibit its great variety. A digital transmission system for broadcasting programs, therefore, should be tested, for example, with voice signals and segments of signals from a wide variety of musical styles as well as various video signals.
CA 0224~068 1998-08-12 In contrast to the use of simple signals as the test signal, the use of such segments from real program material have a disadvantage in that the reference signals, i.e., the test signal before being compressed on the transmitting side and supplied to the tr~n.~mi~ion link, must be provided explicitly on the receiving side. It would otherwise not be possible to compare the test signal to the reference signal in order to determine the quality of the trAn~mi~ion link. This problem does not arise with simple test signals since a sine-wave, for example, is defined by indicating itsfrequency and amplitude, thereby requiring little storage space. Natural test signals, on the other hand, require a considerable amount of storage space in the measurement and analysis equipment. In addition, new test signals can be integrated into themeasurement system only with difficulty.
A further disadvantage in the use of predefined segments of real program material is the fact that measuring the tr~n~mi~ion quality during normal transmission is very difficult, since the contents of predefined test signals do not usually fit into the 1 5 tr~n~mi~ion.
Summary of the Invention An object of the present invention is to provide a measurement method and a corresponding device for the evaluation of digital tr~n~mi~ion systems, which method can be carried out during normal tr~n~mi~ion without interfering with the normaltransmission. A wide variety of test signals relevant for assessing the transmission quality may be used and the storage space needed for storing test and reference signals may be reduced.
The present invention therefore provides a measurement method for the evaluation of digital transmission systems in which measuring instruments on thetransmitting and receiving sides (the transmitting test device and the receiving test device) are able to access the forward channel and record sequences of the original signal on the transmitting side and sequences of the output signal on the receiving side. The transmitting test device initiates and cancels its own data collection and, using control signals, data collection by the receiving test device so that the CA 0224~068 1998-08-12 transmitting test device and receiving test devices record corresponding sequences of the original and output signals in the form of reference and test signals respectively.
In doing so, the control signals are transmitted via the backward channel. At the end of recording, the transmitting test device also transmits the stored reference signal via S the backward channel to the receiving test device, from where the test and reference signals are supplied to a common evaluation system.
The measurement method of the present invention is preferably carried out with a device having a transmitting test device and a receiving test device, with the transmitting test device being used on the transmitting side prior to encoding and transmitting the signals, and the receiving test device being used on the receiving side after decoding. The transmitting test device and the receiving test device are able to record sequences of the original signal (on the transmitting side) and the output signal (on the receiving side) from the forward channel, with these sequences being stored in a segment memory.
The transmitting test device contains a control unit which controls the recording of these sequences on the transmitting and receiving sides. To control the recording action of the receiving test device, the transmitting test device sends control signals via the backward channel in the form of secondary information to the receiving test device, which is able to detect the control signals with a control unit.
The transmitting test device is also able to transmit the sequence recorded on the transmitting side to the receiving test device via the backward channel. In order to transmit information, i.e. the control signals and the recorded sequence, this information must be converted to the data format (user bits) transmittable on the backward channel, which, in the case of the transmitting test device according to the present invention, is accomplished with a converter. After transmitting the secondary information, the signals are decoded in a control unit on the receiving side and the control signals contained in the secondary information and generated by the control unit of the transmitting test device detected. Controlled by these control signals, the receiving test device starts recording a sequence from the forward channel or from the backward channel in the corresponding segment memory for the test or reference CA 0224~068 1998-08-12 slgnal.
According to the present invention, it is possible to select any segment of the transmitted original signal as a test signal. The measurement can therefore be carried out during the regular tr~n~mi~sion of an audio or video program. The selection of the sequence of the original signal used as the test or reference signal is controlled by a transmitting test device positioned on the transmitting side of the tr~n~mi~ion device.
The transmitting test device is able, for example, to automatically identify characteristic sequences of the original signal which then trigger the start of the measurement. The measurement can also be started automatically at regular intervals or in response to manual input.
The measurement method is used according to the present invention in digital tr~n~mi~.~ion systems which transmit the original signals on a forward channel and provide a backward channel for transmitting secondary information. The information transmitted via the forward channel is compressed, for example according to the perception-based method described above, while the secondary information is transmitted uncompressed via the backward channel.
The measurement method according to the present invention can be applied to the known standards for digital transmission such as AES/EBU or DAB. In these types of tr~n~mi~.~ion formats, user-definable data fields are transmitted to the receiver at a low transmission rate. For example, the AES/EBU format provides a user-definable data stream that is 1/32 of the overall tr~n~mi~ion capacity.
According to the present invention, the transmitting test device controls data collection by the receiving test device via this backward channel and synchronizes it with the receiving test device's own data collection. When starting the measurement, the transmitting test device generates a control signal and transmits it to the receiving test device. The control signal is, for example, a predetermined, characterizingnumeric code which is detected by the receiving test device, in particular its control unit.
After emitting this start control signal, the transmitting test device starts collecting data by sampling the original signal from the forward channel. The as yet CA 0224~068 1998-08-12 uncompressed data is recorded and stored on the transmitting side in the form of a reference signal. Likewise, after receiving the start control signal via the backward channel, the receiving test device starts sampling the output signal transmitted via the forward channel and records this data on the receiving side in the form of a test signal.
Since, due to its simple data structure, the start control signal is transmitted via the backward channel at the same speed as the original signal via the forward channel, the transmitting and receiving test devices always record corresponding sequences of the original and output signals.
While recording the reference signal, the transmitting test device preferably emits a continuous control signal, e.g., bit sequence 111.. , which tells the receiving test device to continue collecting data from the test signal. When this control signal is canceled, i.e., after the transmitting test device cancels data collection, the receiving test device also stops recording the data. As a result, corresponding sequences of the original and output signals having the same length are always recorded. If the receiving test device also determines the length of this control signal, e.g., the number of ones transmitted as the bit sequence, this information can be easily converted to information about the length of test and reference signals, simplifying the later evaluation. The segment duration should be transmitted a second time in the form of a number in order to detect tr~n~mis~ion errors.
It is also advantageous if, at the end of data collection, the transmitting testdevice emits a control signal, e.g., bit sequence 000, which ends recording of the test signal by the receiving test device. This stop control signal preferably initiates the transmission of the reference signal stored by the transmitting test device to the receiving test device via the backward channel. When the receiving test device receives the stop control signal, it therefore stops sampling the forward channel to record the test signal and switches over to sampling the backward channel to record the reference signal. However, this step can also be carried out with two control slgnals.
The transmitting test device notifies the receiving test device of the beginning and end of reference signal transmission, using control signals. One of these control CA 0224~068 1998-08-12 signals is preferably identical to the control signal for stopping recording of the test signal. On the receiving side, recording of the reference signal from the backward channel is subsequently started or stopped. It is possible to dispense with the control signal for stopping reference signal recording by the receiving test device if the receiving test device determines the length of the previously stored test signal or the number of test signal values stored and records a corresponding number of values of the reference signal transmitted by the transmitting test device via the backward channel. This avoids possible mism~tched reference and test signal lengths caused by faulty data collection synchronization and provides reference and test signals of the same length for evaluation on the receiving side.
The original data from the forward channel sampled by the transmitting test device is transmitted, for example in bit-serial format, to the receiving test device via the backward channel. Since the data transport capacity of the backward channel is lower than that of the forward channel, transmitting the reference signal via the backward channel takes more time than does transmitting the test signal via the forward channel. However, the number of data points remains the same so that thereceiving test device can assign corresponding data points of the reference and test signals to one another. The time needed to transmit a signal frequency thereforedetermines the maximum repetition rate at which the method can be carried out. Once test and reference signals are present and available for evaluation on the receiving side, the procedure can be restarted by collecting a new segment from the original signal and output signal in the form of reference and test signals. This provides fairly continuous control over transmission quality with a large number of different test slgnals.
When using the method according to the present invention, only the storage space for a signal frequency of a certain length needs to be available on the transmitting side, while the storage space for a sequence pair, namely the test and reference signals, needs to be provided on the receiving side. Furthermore, additional storage space is needed on the receiving side if simultaneous evaluation and collection of a new test signal is to be provided. For this purpose, the test and reference signals CA 0224~068 1998-08-12 can be passed on to an analysis unit, thereby freeing up the segment memory.
Brief Description of the Drawings An embodiment of the present invention is described below with reference to the drawings, in which:
Figure 1 shows a block diagram for applying the method according to the present invention;
Figure 2 shows a block diagram of the transmitting test device of the present invention for demonstrating the generation of a test signal on the transmitting side;
1 0 and Figure 3 shows a block diagram of the receiving test device of the present invention for demonstrating the generation of a test signal on the receiving side.
Detailed Description Figure 1 shows a block diagram for applying the method according to the present invention for the evaluation of digital transmission links. Digital audio and/or video signals from a forward channel 7 are encoded on the transmitting side with a tr~n~mi~ion system 3 and supplied to a tr~n~mi~ion link. Prior to encoding, perception-basedcompression of the original signal may also take place in the tr~n~mi~ion system. On the receiving side, the output signals are decoded again and made available to the user. The compression and tr~n~mi~ion quality of this primary information is checked in the method according to the present invention by comparing a test signal sent by transmission system 3 via forward channel 7 during normal transmission to a reference signal, with the test and reference signals being composed of segments of real program material.
Tr~n~mi~ion system 3 provides the ability to transmit any user-definable secondary information.
Transmitting test device 1 selects the test signals with a central unit 5. This central unit 5 can access forward channel 7 and can record data from this channel. It marks automatically or, in response to manual input, a specific segment of the original signal, which, for example, can have characteristics that are critical to the transmission, CA 0224~068 1998-08-12 and causes transmitting test device and receiving test device 1 and 2 to record this sequence synchronously. The transmitting test device sends the control signals needed to do this to the receiving test device in the form of secondary information. The sequence recording has no effect on normal transmission.
At the end of the sequence recording, the reference signal is present on the transmitting side and the test signal on the receiving side. The test signal is stored in a segment memory 4 in receiving test device 2. Tr~n~mission system 3 then transmits the reference signal via the backward channel, and the receiving test device records it in memory 4, during which process the tr:~n~mis.~ion of secondary information does not interfere with normal operation.
Receiving test device 2 synchronizes the sequences recorded in the form of reference and test signals in the memory and also performs an error check. The sequences of the same length assigned to each other are then evaluated together in order to evaluate the tr~n~mis~ion quality. It is possible to record a new sequence pair during the 1 5 evaluation.
Figures 2 and 3 show a block diagram of the transmitting test device and receiving test device of the present invention in order to demonstrate the generation of the test signal on the transmitting and receiving sides and the control of the measurement procedure on the receiving side.
The method according to the present invention is applied to a transmission system of audio signals according to the AES-3 tr~n~mis~ion standard. The AES-3 format provides a user-definable data stream (user bits) making up 1/32 of the transmission capacity. Referring to Figure 2, this secondary information/user bits is supplied to AES-3 encoder 3.1, which is located at the input of transmission system 3, shown in Figure 1, via a backward channel 8. The primary information, i.e. the original or previously compressed audio signals, reaches AES-3 encoder 3.1 via forward channel 7. AES-3encoder 3.1 converts the information in the known manner to the data format in which it can be transmitted and combines the user bits and primary information from backward and forward channels 8 and 7 by multiplexing.
The reverse procedure is carried out on the receiving side, as shown in Figure 3.
CA 0224~068 1998-08-12 The transmitted data is decoded in the known manner by an A E S-3 decoder 3.2 and distributed on forward and backward channels 7' and 8', respectively, in the form of primary information, i.e., the output audio signal and user bits, by demultiplexing.
The measurement procedure is controlled by the kansmitting test device. For thispurpose, central unit 5 of the transmitting test device has a control unit 5.2 which samples the audio signal from the forward channel. Control unit 5.2 automatically checks to see whether a signal segment critical for assessing the transmission quality is present. The presence of such a sequence can cause the control unit to automatically start the measurement. In addition, control unit 5.2 can start the measurement at regular intervals 10 or in response to manual input.
The start of a test segment is identified by a precisely specified and suitable numeric sequence, for example, the sequence 1010.... This control signal controls data collection by the transmitting test device, with a sequence of the uncompressed audio signal from the forward channel being recorded in a segment memory 5.1. This control signal also controls data collection by the receiving test device. To do this, it must be first converted to the user bit format in a converter 5.3 and supplied to encoder 3.1 via backward channel 8. The signal is transmitted to the receiving test device in the form of secondary information, where it is evaluated with control unit 9 on the receiving side.
This control unit 9 on the receiving side decodes the user bits and detects the control signals of the transmitting test device from this data stream. It initiates the steps corresponding to the control signals.
The duration of the test segment is marked by a further control signal, e.g., a transmission of ones that is uninterrupted during the recording period. While control unit 5.2 is emitting this signal, the transmitting test device and receiving test device each record the corresponding sequence of the audio signal from forward channel 7 or 7' . This sequence is stored in the form of a reference signal in memory 5.1 of the transmitting test device and in the form of a test signal in memory 4.2 of the receiving test device. This type of continuous control signal ensures that corresponding sequences of the same length are always recorded.
The end of the test segment is determined by a further control signal, e.g., by CA 0224~068 1998-08-12 control unit 5.2 setting the user bit to zero. This ends recording of the reference sequence on the transmitting side and recording of the test sequence on the receiving side.
At the end of recording, the transmitting test device sends the reference signalduration to the receiving test device in the form of a number in order to check for errors.
5 If this information does not match the test signal length determined by the receiving test device, a transmission error has occurred and the measurement is discarded.
In the next step, the sampled values of the selected sequence stored in memory 5.1 of the transmitting test device are transmitted in the form of secondary information/user bits. The transmission is initiated by a further control signal of control unit 5.2, e.g., user 10 bit 1. This control signal causes the receiving test device to record the sampled values transmitted in bit-serial format and to store them in memory 4.1, which is the memory for the reference signal. The test signal is already stored in memory 4.2 of the receiving test device.
The reference and test signals are now present on the receiving side and are 15 evaluated together in the known manner in an evaluation unit 10. Transmission of the next test segment can begin during the evaluation.
Measurement Method and Device for the Evaluation of Digital Transmission Systems Field of the Invention The present invention relates to a measurement method and device for the evaluation of digital transmission systems.
Related Technology Due to new perception-based data compression methods for audio and video signals, new measurement methods that require knowledge of the signal before andafter transmission are needed for the measurement and evaluation of digital tr~n~mi~ion systems. Perception-based data compression methods use the capabilities of human perception in order to reduce the large volume of data needed for audio and, in particular, video signals. Inforlnation contained in the original signal, such as very high noise frequencies or rapid image movements which are beyond human sensory perception capabilities, are removed from the original signal in data transmission systems by suitable masks and filters on the transmitting side. This reduces considerably the volume of data to be transmitted to the receiving test device, thereby making the entire data tr~n~mi~ion system more powerful, for example by the ability to transmit more video images per second.
Since data tr~n~mi~ion systems with this type of data compression method influence and distort the frequency pattern of the original signal to be transmitted, testing the system with simple test signals such as a simple sine wave or a stationary signal provides very little indication of whether the original signal fully matches the output signal of the data tr~n~mi~ion system on the receiving side with respect to human perception. This quality test can be reasonably carried out only with testsignals that resemble the real program material as closely as possible and also exhibit its great variety. A digital transmission system for broadcasting programs, therefore, should be tested, for example, with voice signals and segments of signals from a wide variety of musical styles as well as various video signals.
CA 0224~068 1998-08-12 In contrast to the use of simple signals as the test signal, the use of such segments from real program material have a disadvantage in that the reference signals, i.e., the test signal before being compressed on the transmitting side and supplied to the tr~n.~mi~ion link, must be provided explicitly on the receiving side. It would otherwise not be possible to compare the test signal to the reference signal in order to determine the quality of the trAn~mi~ion link. This problem does not arise with simple test signals since a sine-wave, for example, is defined by indicating itsfrequency and amplitude, thereby requiring little storage space. Natural test signals, on the other hand, require a considerable amount of storage space in the measurement and analysis equipment. In addition, new test signals can be integrated into themeasurement system only with difficulty.
A further disadvantage in the use of predefined segments of real program material is the fact that measuring the tr~n~mi~ion quality during normal transmission is very difficult, since the contents of predefined test signals do not usually fit into the 1 5 tr~n~mi~ion.
Summary of the Invention An object of the present invention is to provide a measurement method and a corresponding device for the evaluation of digital tr~n~mi~ion systems, which method can be carried out during normal tr~n~mi~ion without interfering with the normaltransmission. A wide variety of test signals relevant for assessing the transmission quality may be used and the storage space needed for storing test and reference signals may be reduced.
The present invention therefore provides a measurement method for the evaluation of digital transmission systems in which measuring instruments on thetransmitting and receiving sides (the transmitting test device and the receiving test device) are able to access the forward channel and record sequences of the original signal on the transmitting side and sequences of the output signal on the receiving side. The transmitting test device initiates and cancels its own data collection and, using control signals, data collection by the receiving test device so that the CA 0224~068 1998-08-12 transmitting test device and receiving test devices record corresponding sequences of the original and output signals in the form of reference and test signals respectively.
In doing so, the control signals are transmitted via the backward channel. At the end of recording, the transmitting test device also transmits the stored reference signal via S the backward channel to the receiving test device, from where the test and reference signals are supplied to a common evaluation system.
The measurement method of the present invention is preferably carried out with a device having a transmitting test device and a receiving test device, with the transmitting test device being used on the transmitting side prior to encoding and transmitting the signals, and the receiving test device being used on the receiving side after decoding. The transmitting test device and the receiving test device are able to record sequences of the original signal (on the transmitting side) and the output signal (on the receiving side) from the forward channel, with these sequences being stored in a segment memory.
The transmitting test device contains a control unit which controls the recording of these sequences on the transmitting and receiving sides. To control the recording action of the receiving test device, the transmitting test device sends control signals via the backward channel in the form of secondary information to the receiving test device, which is able to detect the control signals with a control unit.
The transmitting test device is also able to transmit the sequence recorded on the transmitting side to the receiving test device via the backward channel. In order to transmit information, i.e. the control signals and the recorded sequence, this information must be converted to the data format (user bits) transmittable on the backward channel, which, in the case of the transmitting test device according to the present invention, is accomplished with a converter. After transmitting the secondary information, the signals are decoded in a control unit on the receiving side and the control signals contained in the secondary information and generated by the control unit of the transmitting test device detected. Controlled by these control signals, the receiving test device starts recording a sequence from the forward channel or from the backward channel in the corresponding segment memory for the test or reference CA 0224~068 1998-08-12 slgnal.
According to the present invention, it is possible to select any segment of the transmitted original signal as a test signal. The measurement can therefore be carried out during the regular tr~n~mi~sion of an audio or video program. The selection of the sequence of the original signal used as the test or reference signal is controlled by a transmitting test device positioned on the transmitting side of the tr~n~mi~ion device.
The transmitting test device is able, for example, to automatically identify characteristic sequences of the original signal which then trigger the start of the measurement. The measurement can also be started automatically at regular intervals or in response to manual input.
The measurement method is used according to the present invention in digital tr~n~mi~.~ion systems which transmit the original signals on a forward channel and provide a backward channel for transmitting secondary information. The information transmitted via the forward channel is compressed, for example according to the perception-based method described above, while the secondary information is transmitted uncompressed via the backward channel.
The measurement method according to the present invention can be applied to the known standards for digital transmission such as AES/EBU or DAB. In these types of tr~n~mi~.~ion formats, user-definable data fields are transmitted to the receiver at a low transmission rate. For example, the AES/EBU format provides a user-definable data stream that is 1/32 of the overall tr~n~mi~ion capacity.
According to the present invention, the transmitting test device controls data collection by the receiving test device via this backward channel and synchronizes it with the receiving test device's own data collection. When starting the measurement, the transmitting test device generates a control signal and transmits it to the receiving test device. The control signal is, for example, a predetermined, characterizingnumeric code which is detected by the receiving test device, in particular its control unit.
After emitting this start control signal, the transmitting test device starts collecting data by sampling the original signal from the forward channel. The as yet CA 0224~068 1998-08-12 uncompressed data is recorded and stored on the transmitting side in the form of a reference signal. Likewise, after receiving the start control signal via the backward channel, the receiving test device starts sampling the output signal transmitted via the forward channel and records this data on the receiving side in the form of a test signal.
Since, due to its simple data structure, the start control signal is transmitted via the backward channel at the same speed as the original signal via the forward channel, the transmitting and receiving test devices always record corresponding sequences of the original and output signals.
While recording the reference signal, the transmitting test device preferably emits a continuous control signal, e.g., bit sequence 111.. , which tells the receiving test device to continue collecting data from the test signal. When this control signal is canceled, i.e., after the transmitting test device cancels data collection, the receiving test device also stops recording the data. As a result, corresponding sequences of the original and output signals having the same length are always recorded. If the receiving test device also determines the length of this control signal, e.g., the number of ones transmitted as the bit sequence, this information can be easily converted to information about the length of test and reference signals, simplifying the later evaluation. The segment duration should be transmitted a second time in the form of a number in order to detect tr~n~mis~ion errors.
It is also advantageous if, at the end of data collection, the transmitting testdevice emits a control signal, e.g., bit sequence 000, which ends recording of the test signal by the receiving test device. This stop control signal preferably initiates the transmission of the reference signal stored by the transmitting test device to the receiving test device via the backward channel. When the receiving test device receives the stop control signal, it therefore stops sampling the forward channel to record the test signal and switches over to sampling the backward channel to record the reference signal. However, this step can also be carried out with two control slgnals.
The transmitting test device notifies the receiving test device of the beginning and end of reference signal transmission, using control signals. One of these control CA 0224~068 1998-08-12 signals is preferably identical to the control signal for stopping recording of the test signal. On the receiving side, recording of the reference signal from the backward channel is subsequently started or stopped. It is possible to dispense with the control signal for stopping reference signal recording by the receiving test device if the receiving test device determines the length of the previously stored test signal or the number of test signal values stored and records a corresponding number of values of the reference signal transmitted by the transmitting test device via the backward channel. This avoids possible mism~tched reference and test signal lengths caused by faulty data collection synchronization and provides reference and test signals of the same length for evaluation on the receiving side.
The original data from the forward channel sampled by the transmitting test device is transmitted, for example in bit-serial format, to the receiving test device via the backward channel. Since the data transport capacity of the backward channel is lower than that of the forward channel, transmitting the reference signal via the backward channel takes more time than does transmitting the test signal via the forward channel. However, the number of data points remains the same so that thereceiving test device can assign corresponding data points of the reference and test signals to one another. The time needed to transmit a signal frequency thereforedetermines the maximum repetition rate at which the method can be carried out. Once test and reference signals are present and available for evaluation on the receiving side, the procedure can be restarted by collecting a new segment from the original signal and output signal in the form of reference and test signals. This provides fairly continuous control over transmission quality with a large number of different test slgnals.
When using the method according to the present invention, only the storage space for a signal frequency of a certain length needs to be available on the transmitting side, while the storage space for a sequence pair, namely the test and reference signals, needs to be provided on the receiving side. Furthermore, additional storage space is needed on the receiving side if simultaneous evaluation and collection of a new test signal is to be provided. For this purpose, the test and reference signals CA 0224~068 1998-08-12 can be passed on to an analysis unit, thereby freeing up the segment memory.
Brief Description of the Drawings An embodiment of the present invention is described below with reference to the drawings, in which:
Figure 1 shows a block diagram for applying the method according to the present invention;
Figure 2 shows a block diagram of the transmitting test device of the present invention for demonstrating the generation of a test signal on the transmitting side;
1 0 and Figure 3 shows a block diagram of the receiving test device of the present invention for demonstrating the generation of a test signal on the receiving side.
Detailed Description Figure 1 shows a block diagram for applying the method according to the present invention for the evaluation of digital transmission links. Digital audio and/or video signals from a forward channel 7 are encoded on the transmitting side with a tr~n~mi~ion system 3 and supplied to a tr~n~mi~ion link. Prior to encoding, perception-basedcompression of the original signal may also take place in the tr~n~mi~ion system. On the receiving side, the output signals are decoded again and made available to the user. The compression and tr~n~mi~ion quality of this primary information is checked in the method according to the present invention by comparing a test signal sent by transmission system 3 via forward channel 7 during normal transmission to a reference signal, with the test and reference signals being composed of segments of real program material.
Tr~n~mi~ion system 3 provides the ability to transmit any user-definable secondary information.
Transmitting test device 1 selects the test signals with a central unit 5. This central unit 5 can access forward channel 7 and can record data from this channel. It marks automatically or, in response to manual input, a specific segment of the original signal, which, for example, can have characteristics that are critical to the transmission, CA 0224~068 1998-08-12 and causes transmitting test device and receiving test device 1 and 2 to record this sequence synchronously. The transmitting test device sends the control signals needed to do this to the receiving test device in the form of secondary information. The sequence recording has no effect on normal transmission.
At the end of the sequence recording, the reference signal is present on the transmitting side and the test signal on the receiving side. The test signal is stored in a segment memory 4 in receiving test device 2. Tr~n~mission system 3 then transmits the reference signal via the backward channel, and the receiving test device records it in memory 4, during which process the tr:~n~mis.~ion of secondary information does not interfere with normal operation.
Receiving test device 2 synchronizes the sequences recorded in the form of reference and test signals in the memory and also performs an error check. The sequences of the same length assigned to each other are then evaluated together in order to evaluate the tr~n~mis~ion quality. It is possible to record a new sequence pair during the 1 5 evaluation.
Figures 2 and 3 show a block diagram of the transmitting test device and receiving test device of the present invention in order to demonstrate the generation of the test signal on the transmitting and receiving sides and the control of the measurement procedure on the receiving side.
The method according to the present invention is applied to a transmission system of audio signals according to the AES-3 tr~n~mis~ion standard. The AES-3 format provides a user-definable data stream (user bits) making up 1/32 of the transmission capacity. Referring to Figure 2, this secondary information/user bits is supplied to AES-3 encoder 3.1, which is located at the input of transmission system 3, shown in Figure 1, via a backward channel 8. The primary information, i.e. the original or previously compressed audio signals, reaches AES-3 encoder 3.1 via forward channel 7. AES-3encoder 3.1 converts the information in the known manner to the data format in which it can be transmitted and combines the user bits and primary information from backward and forward channels 8 and 7 by multiplexing.
The reverse procedure is carried out on the receiving side, as shown in Figure 3.
CA 0224~068 1998-08-12 The transmitted data is decoded in the known manner by an A E S-3 decoder 3.2 and distributed on forward and backward channels 7' and 8', respectively, in the form of primary information, i.e., the output audio signal and user bits, by demultiplexing.
The measurement procedure is controlled by the kansmitting test device. For thispurpose, central unit 5 of the transmitting test device has a control unit 5.2 which samples the audio signal from the forward channel. Control unit 5.2 automatically checks to see whether a signal segment critical for assessing the transmission quality is present. The presence of such a sequence can cause the control unit to automatically start the measurement. In addition, control unit 5.2 can start the measurement at regular intervals 10 or in response to manual input.
The start of a test segment is identified by a precisely specified and suitable numeric sequence, for example, the sequence 1010.... This control signal controls data collection by the transmitting test device, with a sequence of the uncompressed audio signal from the forward channel being recorded in a segment memory 5.1. This control signal also controls data collection by the receiving test device. To do this, it must be first converted to the user bit format in a converter 5.3 and supplied to encoder 3.1 via backward channel 8. The signal is transmitted to the receiving test device in the form of secondary information, where it is evaluated with control unit 9 on the receiving side.
This control unit 9 on the receiving side decodes the user bits and detects the control signals of the transmitting test device from this data stream. It initiates the steps corresponding to the control signals.
The duration of the test segment is marked by a further control signal, e.g., a transmission of ones that is uninterrupted during the recording period. While control unit 5.2 is emitting this signal, the transmitting test device and receiving test device each record the corresponding sequence of the audio signal from forward channel 7 or 7' . This sequence is stored in the form of a reference signal in memory 5.1 of the transmitting test device and in the form of a test signal in memory 4.2 of the receiving test device. This type of continuous control signal ensures that corresponding sequences of the same length are always recorded.
The end of the test segment is determined by a further control signal, e.g., by CA 0224~068 1998-08-12 control unit 5.2 setting the user bit to zero. This ends recording of the reference sequence on the transmitting side and recording of the test sequence on the receiving side.
At the end of recording, the transmitting test device sends the reference signalduration to the receiving test device in the form of a number in order to check for errors.
5 If this information does not match the test signal length determined by the receiving test device, a transmission error has occurred and the measurement is discarded.
In the next step, the sampled values of the selected sequence stored in memory 5.1 of the transmitting test device are transmitted in the form of secondary information/user bits. The transmission is initiated by a further control signal of control unit 5.2, e.g., user 10 bit 1. This control signal causes the receiving test device to record the sampled values transmitted in bit-serial format and to store them in memory 4.1, which is the memory for the reference signal. The test signal is already stored in memory 4.2 of the receiving test device.
The reference and test signals are now present on the receiving side and are 15 evaluated together in the known manner in an evaluation unit 10. Transmission of the next test segment can begin during the evaluation.
Claims (13)
1. A method for evaluating a digital transmission system, the transmission system transmitting an original signal on a forward channel and secondary information on a backward channel between a transmitting side and a receiving side, an output signal associated with the original signal being received at the receiving side, the method comprising:
recording sequences of the original signal on the transmitting side using a transmitting test device and recording the output signal on the receiving side using a receiving test device;
activating and deactivating recording by the receiving test device using controlsignals transmitted by the transmitting test device to the receiving test device so that the transmitting test device and receiving test device record corresponding sequences of the original signal and the output signal as a recorded reference signal and a recorded test signal, respectively, the control signals being transmitted via the backward channel;
transmitting, using the transmitting test device, the recorded reference signal via the backward channel to the receiving test device at the end of recording;
supplying the test and reference signals from the receiving test device to a common evaluation system; and checking the transmission quality by comparing the test signal with the reference signal provided on the receiving side.
recording sequences of the original signal on the transmitting side using a transmitting test device and recording the output signal on the receiving side using a receiving test device;
activating and deactivating recording by the receiving test device using controlsignals transmitted by the transmitting test device to the receiving test device so that the transmitting test device and receiving test device record corresponding sequences of the original signal and the output signal as a recorded reference signal and a recorded test signal, respectively, the control signals being transmitted via the backward channel;
transmitting, using the transmitting test device, the recorded reference signal via the backward channel to the receiving test device at the end of recording;
supplying the test and reference signals from the receiving test device to a common evaluation system; and checking the transmission quality by comparing the test signal with the reference signal provided on the receiving side.
2. The method of claim 1 wherein the original signal includes audio or video signals.
3. The method as recited in claim 1 wherein the control signal transmitted by the transmitting test device to the receiving test device to activate recording by the receiving test device is a predetermined numeric code, the transmitting test device starting recording after transmitting the predetermined numeric code and the receiving test device starting recording after receiving the predetermined numeric code.
4. The method of claim 1 further comprising:
emitting, using the transmitting test device, a continuous control signal which maintains continuous recording by the receiving test device during reference signal recording by the transmitting device, and canceling the control signal to end recording by the receiving test device so that corresponding reference and test signal sequences of the same length are recorded.
emitting, using the transmitting test device, a continuous control signal which maintains continuous recording by the receiving test device during reference signal recording by the transmitting device, and canceling the control signal to end recording by the receiving test device so that corresponding reference and test signal sequences of the same length are recorded.
5. The method of claim 4 wherein the continuous control signal is a bit sequence of ones.
6. The method as recited in claim 1 further comprising, at the end of recording by the transmitting test device, transmitting a control signal for deactivating recording of the test signal by the receiving test device.
7. The method as recited in claim 6 wherein the control signal is a bit sequence of zeros.
8. The method as recited in claim 6 further comprising recording of the reference signal by the receiving test device, and wherein the control signal for deactivating recording of the test signal by the receiving test device initiates the transmission and recording of the reference signal by the transmitting test device and receiving test device, respectively.
9. The method as recited in claim 1 wherein the receiving test device determines a length of the test signal or a number of stored test signal values and records acorresponding number of values of the reference signal transmitted by the transmitting test device so that reference and test signals of the same length are present on the receiving side and can be evaluated.
10. The method as recited in claim 1 further comprising recording of the reference signal by the receiving test device, and wherein the transmitting test device notifies the receiving test device of a beginning and end of reference signal transmission, using control signals, to activate or deactivate reference signal recording by the receiving test device.
11. The method as recited in claim 1 wherein the method is carried out automatically by the transmitting test device at regular intervals or when characteristic original signals detected by the transmitting test device are present or in response to manual input.
12. The method as recited in claim 11 wherein the characteristic original signals are signal sequences predetermined to be critical to the digital transmission system.
13. A device for evaluating a digital transmission system which transmits an original signal on a forward channel and secondary information on a backward channel between a transmitting side and a receiving side, an output signal associated with the original signal being received at the receiving side, the transmission quality being checked on the receiving side by comparing a test signal with a reference signal, the device comprising:
a transmitting test device for recording sequences of the original signal on thetransmitting side in the form of the reference signal, for transmitting the original signal via the forward channel, and for transmitting control signals via the backward channel to control recording by the receiving test device, the transmitting test device having a central unit for controlling the recording of the sequences of original signal, the central unit having a control unit, a segment memory and a converter for converting the control signals and the sequences recorded on the transmitting side to secondary information transmittable to the receiving test device via the backward channel;
a receiving test device for recording the output signal on the receiving side in a segment memory in the form of a test signal, the output signal being transmitted to the receiving test device via the forward channel using the transmitting test device and the receiving test device, the receiving test device having at least one segment memory and a control unit capable of detecting the control signals transmitted in the form of secondary information, thereby starting the recording of a signal sequence from the forward channel or from the backward channel in one of the at least one segment memory; and a common evaluation system for evaluating the test signal and the reference signal, the test signal and the reference signal being supplied by the receiving test device to the common evaluation system;
wherein the control signals transmitted by the transmitting test device activate and deactivate recording by the receiving test device so that the transmitting test device and receiving test device record corresponding sequences of the original signal and the output signal in the form of the reference signal and the test signal, respectively.
a transmitting test device for recording sequences of the original signal on thetransmitting side in the form of the reference signal, for transmitting the original signal via the forward channel, and for transmitting control signals via the backward channel to control recording by the receiving test device, the transmitting test device having a central unit for controlling the recording of the sequences of original signal, the central unit having a control unit, a segment memory and a converter for converting the control signals and the sequences recorded on the transmitting side to secondary information transmittable to the receiving test device via the backward channel;
a receiving test device for recording the output signal on the receiving side in a segment memory in the form of a test signal, the output signal being transmitted to the receiving test device via the forward channel using the transmitting test device and the receiving test device, the receiving test device having at least one segment memory and a control unit capable of detecting the control signals transmitted in the form of secondary information, thereby starting the recording of a signal sequence from the forward channel or from the backward channel in one of the at least one segment memory; and a common evaluation system for evaluating the test signal and the reference signal, the test signal and the reference signal being supplied by the receiving test device to the common evaluation system;
wherein the control signals transmitted by the transmitting test device activate and deactivate recording by the receiving test device so that the transmitting test device and receiving test device record corresponding sequences of the original signal and the output signal in the form of the reference signal and the test signal, respectively.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19735472A DE19735472C2 (en) | 1997-08-16 | 1997-08-16 | Measuring method for evaluating digital transmission systems and device therefor |
| DE19735472 | 1997-08-16 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2245068A1 true CA2245068A1 (en) | 1999-02-16 |
Family
ID=7839112
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002245068A Abandoned CA2245068A1 (en) | 1997-08-16 | 1998-08-12 | Measurement method and device for the evaluation of digital transmission systems |
Country Status (3)
| Country | Link |
|---|---|
| EP (1) | EP0898429B1 (en) |
| CA (1) | CA2245068A1 (en) |
| DE (2) | DE19735472C2 (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE19934622A1 (en) * | 1999-07-23 | 2001-01-25 | Deutsche Telekom Ag | Testing/fault diagnosis of standard fixed connection in telecommunications network involves passing random bit sequence for bit error rate test, evaluating signals received via loop |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2116403B (en) * | 1982-03-01 | 1985-10-23 | British Broadcasting Corp | Improvements relating to digital data transmission |
| DE3723115C1 (en) * | 1987-07-13 | 1989-03-16 | Telefonbau & Normalzeit Gmbh | Test and measuring device for digital signals |
| US5261757A (en) * | 1991-10-03 | 1993-11-16 | The United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration | Shaft mount for data coupler system |
| DE4333953A1 (en) * | 1992-12-04 | 1994-06-09 | Siemens Ag | Unidirectional data channel testing method - sending test data e.g. images to channel, comparing reception frequency with transmission frequency and detecting reference data |
| US5446492A (en) * | 1993-01-19 | 1995-08-29 | Wolf; Stephen | Perception-based video quality measurement system |
-
1997
- 1997-08-16 DE DE19735472A patent/DE19735472C2/en not_active Expired - Fee Related
-
1998
- 1998-07-16 DE DE59813955T patent/DE59813955D1/en not_active Expired - Lifetime
- 1998-07-16 EP EP98113234A patent/EP0898429B1/en not_active Expired - Lifetime
- 1998-08-12 CA CA002245068A patent/CA2245068A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| EP0898429A3 (en) | 2000-12-20 |
| EP0898429A2 (en) | 1999-02-24 |
| DE19735472C2 (en) | 2000-05-31 |
| DE19735472A1 (en) | 1999-02-18 |
| EP0898429B1 (en) | 2007-03-28 |
| DE59813955D1 (en) | 2007-05-10 |
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