KR100367814B1 - Method and device for signal repetition - Google Patents

Abstract

The present invention provides a method and apparatus for repeating signals in an electro-optical network with low bit error probability. The method comprises the following steps: receiving an optical signal and converting it into an electrical signal; Applying and / or inverting nonlinearity on the electrical signal; Converting the electrical signal into an optical signal; And transmitting the optical signal.

Description

Signal repetition method and apparatus {METHOD AND DEVICE FOR SIGNAL REPETITION}

Because a complete optical network is limited to having more complex network configurations, there are several forms of electro-optical network configurations in which communication proceeds through fiber optic connections, but at any location for optical purposes for any purpose. Is converted into an electrical signal and processed, after which the electrical signal is reconverted into an optical signal. One such object is for example the repetition of a signal along the length of a connection.

One factor that contributes to determining the transmission capacity of the network is the bit error probability. Many other factors affect the bit error probability, some of which may be named for example noise and variance. Dispersion means that different wavelengths propagate at different speeds through the optical fiber and pulses transmitted through the fiber spread, causing intersymbol interference. Inter-signal interference means that the risk of advancing adjacent pulses towards each other increases the risk of providing incorrect detection of pulses.

The performance of the communication network can be shown in part in the so-called eye opening diagram. Such a diagram is obtained when a digital signal is connected to the oscilloscope's vertical input and its time axis is triggered coincident to the sign. Each sign sweeps over earlier, and they form an eye pattern. As a measure of the performance of the network, the so-called eye opening penalty, hereinafter referred to as EOP, may be defined according to the following equation.

Where B is the vertical opening of the eye in the ideal case where only the attenuation of the network affects the signal, i.e. the distance from level 0 to level 1, and A is the same distance if the signal is also affected by dispersion or the like. If the eye opening is reduced, the margin of allowed noise is reduced, resulting in less margin of error determination. As a result, the lower the EOP, the better the performance of the network.

It is further preferred that the communication network has a high transparency with respect to the bit rate, for example. This means that the communication function for a number of different bit rates, ie the structure of the network, is not too limited to the requirements of the given bit rate. Another aspect, such as transparency, is related to the signal protocol used, e.g., which coding is used. As a result, it is also desirable that the structure of the network does not limit the type of signaling protocol that can be used.

TECHNICAL FIELD The present invention relates to telecommunication methods and apparatus, and more particularly, to a signal processing method and apparatus in an optical or electro-optical network.

In the field of current telecommunications, there are optical networks as well as electrical networks and combinations thereof. Pure optical networks have large transmission capacity for point-to-point transmission, but with more complex network configurations, electrical networks can be superior in some respects. This is because complex networks require repetitive operations such as light distribution, filtering, switching, and the like, as well as overall operations involving loss and noise generation amplification.

A complete optical network is analog, which makes it difficult to overcome repetitive operations such as light distribution, filtering, switching, etc., and the overall operation involving loss and noise generation amplification.

1 shows an apparatus according to a first embodiment of the invention.

2 shows an example of a nonlinear function of a nonlinear unit according to the invention;

3 shows noise accumulation expressed in BER (bit error rate) as a nonlinear function when amplitude noise is significant;

4 shows an apparatus according to a second embodiment of the invention.

FIG. 5 shows inter-symbol interference, expressed in eye-opening-penalty in dB (hereinafter referred to as EOP) as a function of fiber optic splice length in kilometers for different nonlinearities compared to the fully optical case. Drawing.

6 shows an apparatus according to a third embodiment of the invention.

Accumulation of intersymbol interference, as well as noise caused by dispersion in the optical fiber, increases the bit error probability that limits the transmission capacity of the network. This results in some problems with the sizing of the optical network, i.e. the problem of not being able to form the network sufficiently large and complex, and also the problem of having transparency for eg bit rate. In nonlinear circuits, the noise may include time jitter (jitter) and signal level noise (amplitude noise) of the signal flank.

It is an object of the present invention to provide a method and apparatus for reliable signal processing, in particular repetition and transmission of information, in a communication network having a low bit error probability.

It is also an object of the present invention to solve the above problems with scalability, bit rate transparency, noise and inter-signal interference of a communication network.

It is another object of the present invention to solve the above problems with scalability, transparency, noise and dispersion at bit rates of 10 Gb / sec and above.

The above object is achieved with a method and apparatus having the features described in the independent claims. Other features and developments of the invention are provided in the other claims.

The present invention achieves this object by using a simple analog bit rate transparent OEO circuit (opto-electro-optics) comprising an inverter as a repeater and preferably introducing the intended nonlinearity in the electronic device.

According to the present invention, a method is provided for causing a repetitive signal to be inverted and / or nonlinear, and an apparatus comprising an inverter and / or a nonlinear unit.

With the method and apparatus according to the invention, the following advantages are obtained.

The bit error rate (hereafter referred to as BER) accumulates much more slowly through nonlinear pulse shaping when amplitude noise is a predominant bit error source. This is the case, for example, because the increased bandwidth reduces jitter, so the system bandwidth is significantly larger than the maximum allowable bit rate. Inter-signal interference is also accumulated more slowly through nonlinear pulse formation. This reduction in inter-signal interference increases, i.e. the performance of the network is further improved through the inversion of the signal as implemented according to the present invention. This effect lowers the bit error probability during transmission on the communication network. In addition, no clocking of the signal is required. This solution means that because it runs without a clock, it has the added benefit of further savings. In addition, it is easily performed at a higher bit rate without a clock in transmission, and the network's transparency to the bit rate becomes higher.

In addition, using the method and apparatus according to the present invention, both RZ pulses (return to zero) and NRZ pulses (not return to zero) can be used. This increases the transparency of the network to the modulation method.

With regard to the fully optical case, there is also an advantage that an electronic supervisory signal can be used which facilitates monitoring and error detection of the communication.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be described below with reference to the accompanying drawings so that the present invention may be more readily understood and implemented. Similar components in the conducting surface are given the same reference numerals.

1 shows an apparatus 1 according to a first embodiment of the invention. The device 1 comprises an optical input 2 connected to an input 3 on the photoelectric converter 4. The output 5 on the photoelectric converter 4 is connected to the input 6 on the filter 7. The output 8 on the filter 7 is connected to the input 9 on the nonlinear unit 10. The output 11 on the nonlinear unit 10 is connected to the input 12 on the amplifier 13. The output 14 on the amplifier 13 is connected to the input 15 on the electro-optical converter 16. The output 17 on the electro-optical converter 16 is connected to the output 18 on the device 1.

According to this embodiment, the nonlinear unit 10 is arranged between the filter 7 and the amplifier 13, but the nonlinear unit 10 is along the chain in the device 1 in a manner well known in the art. Other embodiments may be contemplated that are arranged at any other location. Other embodiments are also conceivable in which the constituent units are included in each other in different combinations in a manner well known to those skilled in the art. For example, the amplifier 13 and the filter 7 may be included in the same unit. Such amplification may also be divided into several amplifiers, and the amplifier 13 or amplifiers may comprise, for example, automatic adjustment of the amplification factor. Different units may also be cascaded in different orders in a manner well known to those skilled in the art.

According to this embodiment, this non-linear unit is located in the electrical region. In accordance with the inventive concept, it is also conceivable for example that the nonlinearity is located in the optical region. For example, the electro-optical converter 16 may include the functionality of the nonlinear unit 10. Another possibility is to move all the functions of the invention into the optical domain. In this case, the photoelectric converter 4 and the electro-optical converter 16 are removed and the other components are optical.

The device 1 can be used as a repeater in an optical communication network. In this case, the input 2 and the output 18 of the device 1 are connected to an optical fiber connection (not shown), and due to the length of the connection, a signal needs to be relayed along this connection. The optical signal received at the input 2 is converted into an electrical signal by the photoelectric converter 4. The electrical signal is filtered by the filter 7. The filter 7 may be a pure low pass filter, but other types of filters that are well known in the art may also be used. It is also possible to change the relative position between components in the device in a manner well known to those skilled in the art.

The output signal from the output 8 of the filter 7 is supplied to the nonlinear unit 10, in which the signal is provided with the intended nonlinearity. Nonlinear unit 10 has a transfer function f (x) that provides an output signal that is a nonlinear response signal to its input signal, which response may be non-binary but need not be non-binary. This signal is then amplified by the amplifier 13 and converted back into an optical signal by the electro-optical converter 16. The optical signal thus obtained is retransmitted to the optical fiber connection (not shown) through the output 18 of the device 1.

By the method according to an embodiment of the present invention, the effect of reducing the bit error probability is obtained through both suppression of intersymbol interference and noise suppression caused by nonlinear pulse shaping, where amplitude noise is a predominant noise.

2 shows a function of the nonlinear unit 10, where x corresponds to a signal on the input 9 of the nonlinear unit 10 and f (x) corresponds to a signal on the output 11. The straight line with a constant slope in the figure corresponds to the fully linear case, but the pure step function illustrates the fully non-linear case. Thus, this figure shows an example of a partially nonlinear case. The nonlinear factor γ can be defined in the following equation.

Here, γ = 0 corresponds to the fully nonlinear case and γ = 1,0 corresponds to the fully linear case. These equations define γ according to an embodiment of the nonlinear unit 10 according to the invention. Numerous other definitions will be apparent to those skilled in the art, where to a certain extent all of them are based on that γ can be set to correspond to the spatial portion between logic "0" and logic "1", the spatial portion being logic "0". Is occupied by the transition between "and logic" 1 ".

FIG. 3 shows the BER (bit error rate) caused by amplitude noise accumulation for a link having approximately 10 repeaters as a nonlinear function applied to the signal through the nonlinear unit 10. The nonlinearity applied to the signal in accordance with the present invention reduces the effect on the bit error probability through noise suppression when amplitude noise is a likely source of bit error. The result is optimal for complete nonlinearity, ie γ = 0, but even incomplete nonlinearity gives good results. This gives a great advantage since full nonlinearity can be difficult to realize at high bit rates. Therefore, through the present invention, it is possible to use the noise suppression effect of nonlinearity without directly limiting the bit rate. The bit rate transparency of the network is in no way limited.

With the method and apparatus according to the invention, the bit error probability during transmission on the communication network is lowered so that the clocking of the signal is not necessary. This solution means that because it runs without a clock, it has the added benefit of further savings. In addition, it is more simply performed without a clock at a higher bit rate in transmission, and the transparency of the network to the bit rate becomes higher.

4 shows a device 41 according to a second embodiment of the invention. This device 41 comprises the same parts as the device 1 according to the first embodiment of the invention, which is connected in a similar manner except that it also has a difference including the inverter 21. The inverter 21 is connected between the filter 7 and the nonlinear unit 10 according to this embodiment, but other locations may also be considered in a manner well known to those skilled in the art. The input 20 on the inverter 21 is connected to the output 8 of the filter 7, and the output 22 on the inverter 21 is connected to the input 9 of the nonlinear unit 10. For this second embodiment, variations such as those mentioned in connection with the first embodiment can also be considered.

The function of the device 41 is similar to that of the device 1. In addition to the desirable effects of noise suppression on the bit error probability described above, this is further reduced through inversion, further suppressing the dispersion effect of the optical fiber. This further reduces the bit error probability by reducing inter-signal interference.

FIG. 5 shows inter-signal interference, expressed in eye opening penalty in dB (hereinafter referred to as EOP) as a function of the length of the fiber optic connection in kilometers for different nonlinearities of the present invention according to the second embodiment. Optimal results are obtained at complete nonlinearity, but this can be difficult to achieve at high bit rates (10 Gb / sec or more) as described above. However, FIG. 5 shows that when the nonlinear factor γ <= 0.5, the distance between the repeaters is EOP <= 1.5 for a communication connection with an optical fiber length less than 1500 km, which is 30 km. If the nonlinear factor γ <= 0.3, then EOP <= 1.0 dB for a communication connection with a fiber length of less than 1500 km.

6 shows an apparatus 61 according to a third embodiment of the invention. The device 61 is coupled in a similar manner except that the nonlinear unit 10 is removed and the output 22 of the inverter 21 is directly connected to the input 12 of the amplifier 13. It comprises the same parts as the device 41 according to the embodiment. For this third embodiment, variations as mentioned in connection with the first embodiment may also be considered.

Claims (24)

As a method of suppressing distribution in a network, Receiving an optical signal to be repeated, Applying nonlinearity to the received signal using a nonlinear function in a manner to suppress variance; Transmitting the signal to which the nonlinearity is applied, Output from the nonlinear function suppresses variance in accordance with the signal amplitude and the nonlinear function itself. The method of claim 1, The nonlinear application is performed with the aid of a nonlinear non-binary transfer function having a nonlinear factor <= 0.5 (γ <= 0.5). The method of claim 1, The nonlinear application is performed with the aid of a nonlinear non-binary transfer function having a nonlinear factor <= 0.3 (γ <= 0.3). A method of repeating a signal in a signal repeater and reducing the bit error probability, Receiving a signal to be repeated, Applying nonlinearity to the signal with the aid of a nonlinear non-binary transfer function, and Transmitting a signal receiving the nonlinearity; and a method for reducing signal repetition and bit error probability in a signal repeater. A method of repeating a signal in an electro-optical network, Receiving and converting an optical signal into an electrical signal; Applying nonlinearity to the electrical signal; Converting the electrical signal into an optical signal; Transmitting a signal in said electro-optical network. A method of repeating a signal in an electro-optical network, Receiving and converting an optical signal into an electrical signal; Filtering the electrical signal; Inverting the electrical signal; Applying nonlinearity to the signal with the aid of a nonlinear transfer function; Electrically amplifying the signal; Converting the electrical signal into an optical signal; Transmitting a signal in said electro-optical network. A method of repeating a signal in an electro-optical network, Receiving and converting an optical signal into an electrical signal; Filtering the electrical signal; Applying nonlinearity to the signal; Amplifying the signal; Converting the electrical signal into an optical signal; Transmitting the converted optical signal. As a repeater used in communication networks, A repeater used in a communication network having one or more non-linear units that apply nonlinearity to a received signal to be repeated to suppress dispersion in the network. As a repeater for use in photoelectric communication networks, A photoelectric converter for converting the received optical signal into an electrical signal; A filter for filtering the electrical signal; An inverter for inverting the electrical signal; A nonlinear unit having a nonlinear transfer function for applying nonlinearity to the electrical signal; An amplifier for amplifying the electrical signal; A repeater for use in a photoelectric communication network having an electro-optical converter for converting the electrical signal into an optical signal to be transmitted. A photoelectric converter for converting the received optical signal into an electrical signal; A nonlinear unit having a nonlinear transfer function for applying nonlinearity to an electrical signal, An amplifier for amplifying the electrical signal, And an electro-optical converter that converts the electrical signal into an optical signal after nonlinearity is applied to the electrical signal. The method of claim 10, The repeater is arranged to reduce a bit error probability during signal transmission, wherein the nonlinear transfer function has a nonlinear factor different from 1.0 (γ ≠ 1.0). As a method of suppressing distribution in a network, Receiving an optical signal to be repeated, Applying a nonlinearity to the received signal using a nonlinear function after the optical signal is converted into an electrical signal; Transmitting a signal receiving the nonlinearity, And wherein said nonlinear function does not receive a timing signal. The method of claim 12, And wherein said applying step comprises applying nonlinearity to said received signal using said nonlinear function after said received signal has been converted from an optical signal to an electrical signal. As a repeater in a communication network, One or more nonlinear wires connected in series to the amplifier, The nonlinear unit comprises a nonlinear function, the input of which is merely an amplitude of the signal to be repeated. delete delete delete delete delete delete delete delete delete delete