Telephonic communications – Diagnostic testing – malfunction indication – or electrical... – Of hybrid or echo suppressor or canceller
Patent
1985-10-04
1988-02-23
Ng, Jin F.
Telephonic communications
Diagnostic testing, malfunction indication, or electrical...
Of hybrid or echo suppressor or canceller
379410, H04B 346
Patent
active
047275669
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
The present invention relates to a method of testing an apparatus for adaptive echo cancellation and more particularly to a method for testing apparatus included in transmission equipment used for digital communication.
BACKGROUND
An apparatus for adaptive echo cancellation of the kind mentioned above has been previously described in Swedish patent application 8106444-6. As described in the Swedish application, echo cancellation of, for example, an incoming analogue signal is effected by correction signals from an adaptive balance filter, the correction signals being added to the incoming signal and the parameters of the balance filter being continuously or in stepwise fashion updated from a correction unit.
A known method of functionally controlling digital equipment is to loop circuit data flow from a transmitter to a receiver and to carry out a bit error measurement. In this way the transmitter, receiver and four-wire to two-wire junction of the echo cancellation apparatus can be functionally controlled.
SUMMARY OF INVENTION
Verification of the function of the echo canceller included in the apparatus involves certain problems, since a measuring signal must be supplied to the two-wire side of the apparatus in such a case. This means that an access relay must be connected to the two-wire circuit upstream of the hybrid circuit for supplying the measuring signal to the echo canceller. Also, the measuring signal must be line coded in the way employed in the send units of the apparatus with the object of simulating a remote signal. Finally, the echo is changed when the line is interrupted, which makes it theoretically possible for the echo from the measuring equipment to be inhibited, but not the echo from the line.
In the above mentioned apparatus of the prior art, it is of importance to establish that the correction unit and the digital balance filter fulfil their functions within given error margins. This means that the balance filter should supply correction values to a summator, which adds the correction values to incoming signals so that the value of the residue echo falls below a given limit. If the incoming signal is sampled and the correction signal consists of digital values at the addition, these values should be correct within given intervals. Incorrect values for the correction signals give poorer echo cancelling and can thus give rise to incorrect reception. As examples of causes may be mentioned: false supply values to the balance filter, deficient synchronism and fault in the memory cell structure of the balance filter, e.g. a faulty ROM in the storage unit.
The object with the present invention is to provide a method of testing the function of an adaptive echo canceller without using an access relay on the line side.
BREIF DESCRIPTION OF DRAWINGS
The invention will now be described in detail with reference to the accompanying drawing, wherein:
FIG. 1 is a block diagram of an apparatus for adaptive echo cancellation, in which the inventive method is utilized, and
FIG. 2 is a diagram of some signals which occur in the apparatus according to FIG. 1.
DETAILED DESCRIPTION
An apparatus for adaptive echo cancellation is illustrated in the block diagram of FIG. 1, together with a circuit for carrying out the method provided in accordance with the invention.
On the send side, the apparatus includes a send unit A for data with a coding unit B connected to the output of the send unit A for recoding send data to a suitable line code, e.g., a biphase code. The output of the coding unit B is connected to a two-wire to four-wire hybrid circuit F, here exemplified as a voltage bridge including the resistors R1, R2 and R3 as well as an operational amplifier J. In one of the two-wire paths a switch SW1 is connected to one terminal of a line transformer TR.
In the reception path of the apparatus, there is a filter circuit (a lowpass filter) C with its input connected to the ouput of the amplifier J for receiving and filtering the incoming line signal from the two-wire line. The o
REFERENCES:
patent: 4005277 (1977-01-01), Araseki et al.
patent: 4282411 (1981-08-01), Stewart
patent: 4355406 (1982-10-01), Guidoux
patent: 4360712 (1982-11-01), Horna
patent: 4546216 (1985-10-01), Tegethoff
Ng Jin F.
Telefonaktiebolaget LM Ericsson
Vaas R.
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