Multiplex communications – Communication techniques for information carried in plural... – Combining or distributing information via frequency channels
Patent
1997-07-09
2000-08-22
Ton, Dang
Multiplex communications
Communication techniques for information carried in plural...
Combining or distributing information via frequency channels
370500, 375285, H04B 10155
Patent
active
061083518
DESCRIPTION:
BRIEF SUMMARY
The invention relates to non-linear circuits and more particularly to devices for correcting linearity of such circuits.
It applies for example to the circuits for modulating an optical signal from a laser for the fibre optic transmission of signals. This modulation, carried out with the aid of an external modulator wired to the output of the laser, is a source of non-linearity.
Systems for transmitting a signal are generally sensitive to the non-linearity of the various elements of which they are composed. Although the non-linearity of these elements is imposed by the physics, it is nevertheless possible to add linearizing devices so as to improve the overall performance of the system. It is necessary in this case to have available a means of measuring the residual non-linearities of the system to be corrected so as to be able to optimize the parameters of the linearizing device. If moreover the non-linearities of the system are required to change over time, the measuring device must be incorporated into the system so as to react in real time to the linearizing devices.
A known means of estimating non-linearity consists in the use of one or more pilot signals. FIG. 1 represents such a device according to the prior art.
The pilot signal, usually sinusoidal, is generated by a pilot oscillator or generator 1. This signal is sent to a second input of an adder 2 whose first input is supplied with the signal to be transmitted or useful signal. The non-linear device in respect of which it is sought to correct the disturbing effects due to non-linearity is wired up downstream of the pilot frequency generator, for example at the output of the adder 2. A coupler 4 is wired to the output of the non-linear device so as to tap off, from its coupled output, the intermodulations created by this device. The direct output from the coupler delivers the signal to be harnessed, which will optionally be filtered so as to be rid of the previously added pilot signal. The signal tapped off from the coupled output is transmitted to the input of a path for measuring second-order intermodulation signals or of several paths for measuring intermodulation signals of successive orders, for example two paths in the diagram. Each of the paths consists of a first band-pass filter 5.1, 5.2, whose role is to select the harmonic whose frequency corresponds to the order of intermodulation of the path, followed by a detector 6.1, 6.2, which measures the amplitude or the power of the filtered signal. The detector can be a simple diode or a device which associates a resistor and a temperature measurement such as a bolometer. The output of the detector is linked to a low-pass filter 7.1, 7.2, which eliminates the spurious frequencies. The output of each of the paths (or of the measurement path in the case where it is unique) is linked to a control device 8, itself linked to the non-linear device. This control device transforms the signals received into control signals suitable for the inputs for correcting non-linearity of the non-linear device.
The devices of this type suffer from major drawbacks. They cannot provide information on the phase of the intermodulations and they are rather insensitive, in particular when the device is working in the presence of noise. They are not suitable if the levels of the intermodulation products, that is to say the non-linearities to be measured, are very low.
An improvement in this sensitivity, for devices of this type, runs up against a prohibitive cost. Thus, effective filtering of the intermodulation products would require not only the use of noise filters 5.1, 5.2 of high performance, which are therefore tricky to construct, but also of a perfectly frequency-stable pilot signal.
The purpose of the present invention is to alleviate the aforesaid drawbacks. Its subject is a process for estimating non-linearity of a device consisting in generating one or more pilot signals upstream of the device for measuring components of their intermodulation products at the output of this device, characterized in that the
REFERENCES:
patent: 5323119 (1994-06-01), Powell et al.
patent: 5710653 (1998-01-01), Nemecek et al.
patent: 5720039 (1998-02-01), Lieberman
patent: 5745839 (1998-04-01), Lieberman
patent: 5818544 (1998-10-01), Han
PCT International Office Search Report.
002010054; Bertelsmeier et al- "Linearization of broadband optical transmission systems by adaptive predistortion".
Journal of Lightwave Technology Progress in Externally Modulated AM CATV Transmission Systems--vol. 11, No. 1 Jan. 1993 Nazarathy et al.
Hardy Patrick
Hergault Stephane
Duffy Vincent E.
Ho Tuan Q
Kurdyla Ronald H.
Thomson Broadcast Systems
Ton Dang
LandOfFree
Non-linearity estimation method and device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Non-linearity estimation method and device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Non-linearity estimation method and device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-589527