WO2002045312A2

WO2002045312A2 - Method and device for transmitting data via optical waveguides

Info

Publication number: WO2002045312A2
Application number: PCT/DE2001/004289
Authority: WO
Inventors: Alexander Mircescu
Original assignee: Siemens Aktiengesellschaft
Priority date: 2000-11-30
Filing date: 2001-11-15
Publication date: 2002-06-06
Also published as: DE10059559A1; WO2002045312A3

Abstract

The invention relates to a method for transmitting data via optical waveguides that is characterized by combining the methods frequency (or wavelength) division multiplexing, multiplexing, time division multiplexing and code division multiplexing for transmitting data. The invention further relates to an optical transmitter, an optical receiver, an optical multiplexer (1) and an optical demultiplexer (2) for carrying out said method.

Description

description

Method and device for data transmission via optical fibers

The present invention relates to a method for data transmission via optical fibers, an optical transmission device for transmitting data via optical fibers and an optical receiving device for receiving data via optical fibers.

Optical fibers (glass fibers) are particularly well suited for the transmission of large amounts of data with a high data transmission rate over long distances. The possible data transmission rate depends on the transmission bandwidth of the transmission medium (optical fiber). The usable wavelength range for optical data transmission via fiber is between 1.3 and 1.6 μ of the optical carrier. This area results in a theoretical transmission bandwidth of 50 THz. So far, however, it has not been technically possible to fully utilize this theoretical range.

In the prior art, two transmission methods are available for utilizing the transmission bandwidth of optical fibers:

On the one hand, the data is transmitted using the so-called time division multiplex method (TDMA, Time Division Multiple Access). The time axis is continuously divided into sections (so-called frames) with a certain time duration T, the so-called frame duration. Each of these frames consists of a certain number of time slots (ti ... t _n) , each frame having the same number of time slots and the time slots being arranged without overlap. The time slots in a frame are used from 1 to n meriert; the same time slots in the successive frames form a channel for data transmission.

The second transmission method for data transmission via optical fibers is the so-called frequency division multiplexing (FDMA, Frequency Division Multiple Access), also referred to as wavelength division multiplexing (WDM, Wavelength Division Multiplex) in optical communications technology.

With frequency division multiplexing, each channel occupies a certain narrow frequency band in an available frequency range. The individual channels for data transmission are transmitted through different carrier frequencies in different frequency ranges. In optical communication, this means that different channels are transmitted with different wavelengths of light.

The terms “frequency or frequency division multiplex” and “wavelength or wavelength division multiplex” can be used in an equivalent manner since the frequency and the wavelength are inversely proportional to one another. In optical transmission technology, the wavelength of the light with which the data is transmitted is usually specified. However, the frequency is more suitable for displaying a (frequency) spectrum or its broadening and transmission bandwidth.

In theory, it is possible to use a one-dimensional access procedure, i.e. by using only one multiplex method for data transmission over an optical fiber, the entire theoretical transmission bandwidth of 50 THz can be used. However, this exploitation places high demands on the technical implementation of the components used:

Wavelength division multiplex uses very fine-tunable laser diodes for transmission and corresponding photodiodes for Receiving the respective signals of the specific wavelength needed.

In time-division multiplexing, the data or data packets to be transmitted have to be reduced in time in order to increase the spectral utilization of the transmission bandwidth, so that with increasing spectral utilization, higher time requirements are placed on the signal-evaluating components, since the duration of the time slots cannot be made arbitrarily short.

Due to these limits of technical implementation, it has not been possible to fully utilize the entire transmission bandwidth of optical fibers.

In order to be able to make better use of the available transmission bandwidth, the two multiplex methods described are combined with one another in the prior art.

In optical communications technology, data transmission was carried out for a long time using the time division multiplex method and is currently being supplemented by the wavelength division multiplex method. Specifically, this means that several channels for data transmission in time-division multiplexing are transmitted over a common optical fiber at different wavelengths. The spectral efficiency, i.e. the utilization of the available transmission bandwidth is improved as a result, but not yet fully achieved.

With the same procedure, the spectral utilization could also be increased in mobile, radio communication; this was implemented in the GSM system (Global System for Mobile Telecommunica- tion) of the mobile phones.

The object of the present invention is therefore to provide a method and a device with which the spectral efficiency of the data transmission, ie the utilization to further improve the available transmission bandwidth of the optical waveguide.

This object is achieved by a method for transmitting data via optical fibers according to the appended claim 1. Furthermore, this object is achieved by an optical transmission and reception device and by an optical multi- and demultiplexer according to the appended claims 5, 8, 9 and 12.

According to the present invention, a method is used for the transmission of data via optical fibers, which consists of a combination of time division multiplexing (TDMA) and code division multiplexing (CDMA) and is transmitted with a certain wavelength of light via an optical fiber.

The present invention provides an optical transmission device for transmitting data over optical fibers, the data in time and code division multiplexing over one

Optical fiber shipped. In this case, the data from a number of channels for data transmission are converted into code functions by means of the code multiplex method by linking with a code for one channel in each case. In each case several of these code functions are inserted into a time slot by means of the time multiplex method, wherein several time slots result in a frame with a certain duration. These frames are now transmitted by an optical transmitter (e.g. laser diode) with a certain wavelength via an optical waveguide. That way, in everyone

Time slot to transmit data from multiple channels in the form of code functions.

Furthermore, the present invention provides an optical multiplexer for data transmission via optical fibers. This optical multiplexer consists of several of the described optical transmission devices, the optical transmitters each differentiate in the wavelength in which they emit the light. In this way, several frames can be transmitted simultaneously via one optical fiber using the frequency (or wavelength) multiplex method. Feeding several modulated carriers into a common one

Optical waveguide is made by an optical wavelength division multiplexer.

The combination of frequency, time and code division multiplex methods results in a three-dimensional medium access method for data transmission via an optical fiber.

The data is received in exactly the reverse order by an optical receiving device or an optical demultiplexer with the corresponding devices.

The advantage of the combination of the various multiplexing methods according to the invention is that a much better spectral efficiency of the glass fiber can be achieved with the available technical components than in the prior art, i.e. that the utilization of the theoretical transmission bandwidth of 50 THz on glass fibers for data transmission can be better exploited.

Furthermore, the present invention can be implemented relatively easily in existing systems since, compared to the prior art, the transmitting and receiving devices only have to be expanded by the code multiplexing and code demultiplexing devices. Nothing changes in the optical components (e.g. laser transmitters, photodiodes, optical fibers).

Advantageous embodiments of the present invention are given in the respective subclaims.

The number of code functions that are transmitted per time slot depends on the number of channels for data transmission and the number of time slots per frame. With a number of * n channels for data transmission with the same distribution of the code functions, this results in a number of m code functions per time slot.

However, if the channels have different requirements, for example with regard to the data transmission rate, the individual time slots can each also transmit a different number of code functions. The sum of the code functions that are transmitted per frame must then total m * n in order to be able to transmit the data of all channels.

If the data transmission method according to the invention is applied over k wavelengths, the total number of k * m * n channels whose data can be transmitted over an optical fiber is obtained with a uniform distribution of the code functions over the time slots, which is an increase compared to the prior art means by a factor m.

The present invention is explained in more detail below on the basis of a preferred exemplary embodiment with reference to the accompanying drawings, in which:

1 shows the frequency spectrum of a data transmission in frequency division multiplexing,

2 shows the frequency spectrum of a data transmission in time or code division multiplexing,

3 shows the frequency spectrum in the combination of frequency, time and code division multiplexing according to the invention, and

Fig. 4 is a schematic representation of the optical data transmission system according to the invention. As can be seen in FIG. 1, in the case of frequency division multiplexing each signal, ie each carrier fi ... f _k , occupies a narrow frequency band in the frequency space which is available overall for data transmission (transmission bandwidth Δf). The respective spectra (Gaussian signals), which result from the modulation of the respective carriers fi ... f with the data to be transmitted and which can be obtained by a Fourier transformation of the time function, are arranged in this frequency space without overlap, and each have a transmission bandwidth of Δfi ... Δfk The number of carriers fi ... f _k that can be transmitted using frequency division multiplexing is due to the transmission bandwidth Δf of the optical fiber (theoretically up to 50 THz) and the number of Gauss 'shear signals that can be generated with optical transmitters (laser diodes) in this frequency range. The receiver has optical receivers (photodiodes), which can each filter the corresponding frequency, or an optical demultiplexer, which assigns the individual frequencies fi ... f _k to the corresponding receiver circuits in order to recover the transmitted data.

As can be seen from FIG. 1, it is conceivable to maximize the spectral utilization up to the maximum transmission bandwidth Δf by using numerous narrow-band signals which can be transmitted by the carriers f _x ... f _k and generated by laser diodes , However, the technical implementation for utilizing the maximum transmission bandwidth .DELTA.f is extremely difficult since very fine-tunable optical transmitters are required.

For this reason, the 50 THz transmission bandwidth of fiber optic cables has not yet been fully exploited.

Fig. 2 shows the representation of the spectrum of a data transmission in time or code division multiplexing. In time-division multiplexing, a carrier with a single frequency fi is used, in which the data of the individual transmission channels are transmitted successively in overlap-free time slots ti ... t _n . These time slots ti ... t _n are arranged in a so-called frame, the duration of which results from the number of time slots and the respective duration of the individual time slots. After transferring the time slots ti ... _tn starts transmission of time slots ti ... t _n again.

Here, the spectrum fi is broadened, which is determined by a Fourier transformation of time-limited signals, i.e. of the data to be transferred can be determined. Specifically, this means that, just like with frequency division multiplexing, an increase in the data rate of the data to be transmitted or the bandwidth of a signal to be transmitted results in a broadening of the spectrum.

With the time-division multiplex method, it is also theoretically conceivable to achieve full utilization of the available bandwidth Δf. To increase the transmission bandwidth, however, the duration of the time slots must be reduced, since a certain frame duration may not be exceeded for data or voice transmission in order to transmit the data or voice without errors or distortion. This requirement entails a high requirement for the signal processing and evaluating components. For this reason, the full utilization of the available transmission bandwidth has not been possible until now using the time-division multiplex method for data transmission via optical fibers.

Another multiplex method is the so-called code multiplex method (CDMA, Code Division Multiple Access). This multiplex method is a transmission method in which several channels are transmitted at the same time with the same carrier frequency. In this multiplex method, the (digital) data contained in the individual transmission channels are each linked to a different digital code, which has a significantly higher clock rate than the data to be transmitted. The codes used must be as orthogonal as possible to one another, ie the codes differ from one another as much as possible in the mathematical sense, so that the correlation (= relationship) between the codes used is as low as possible (close to 0). The recipient is through the

Knowledge of the respective code for the corresponding channel for data transmission is able to decode the data of the corresponding channel and thus to obtain the corresponding information.

As can be seen from FIG. 2, it is theoretically also possible by means of the code multiplex method to utilize the entire available transmission bandwidth solely by means of this method, in that the data are transmitted only with one transmission frequency (carrier). A number of code functions Ci ... C _{m are} transmitted via this transmission frequency, so that the frequency spectrum is broadened. The data of a transmission channel is transmitted with each code function Ci ... C _m . In this case, however, the technical implementation of so many orthogonal codes that would be necessary to utilize the entire transmission bandwidth Δf is extremely difficult.

In the prior art, to increase the spectral efficiency in the optical waveguide, the time and frequency (or wavelength) multiplexing methods are combined to form a two-dimensional access method. The combination of these two access methods is also known from radio technology. With this method, several sampled transmission channels are transmitted on different carrier frequencies fi and f ₂ (or with different wavelengths, see also FIG. 3a) using the time division multiplex method (TDMA); the time division The method is thus used on every carrier frequency (Fig. 3b).

With k carrier frequencies fi ... f and n time slots ti ... t _π per carrier frequency, the data from k * n transmission channels can be transmitted.

This combination of time and frequency division multiplexing results in a broadening of the frequency spectrum compared to the use of only one multiplexing method (FIG. 3b); thus the spectral efficiency is increased and the usable transmission bandwidth approaches the theoretically available transmission bandwidth of 50 THz.

This combination has proven itself because it means that the technical requirements for the respective components for time and frequency division multiplexing are lower than when using only one multiplexing method with the same transmission bandwidth used. Conversely, this means that when the components currently available for time and frequency division multiplexing are used in combination, the sum of the advantages can be used and thus a higher spectral efficiency (higher utilization of the available transmission bandwidth) can be achieved. The same statements naturally also apply to the other possible two combinations of time and code division multiplex methods and frequency and code division multiplex methods.

According to the present invention, the known two-dimensional access method, ie the combination of time and frequency division multiplex methods, is expanded to a three-dimensional access method. This means that in addition to the time and frequency division multiplex method, the code division multiplex method is used for data transmission in optical fibers. The data of several transmission channels are transmitted on each carrier frequency fi ... fk n every time slot t _x ... t _n . The data of the transmission channels, which are each transmitted in a time slot, are in turn each linked with their own code to form a code function Ci ... C _{m in} accordance with the code division multiplex method. The resulting frequency spectrum is shown in Fig. 3c.

The codes used are based, for example, on so-called Walsh functions, which are periodic, assume the values +1 and -1 and form an orthonormal system. With the help of the Walsh functions and pseudo-random functions, codes can be generated that are orthogonal to each other and can thus be clearly determined by forming the correlation.

Thus, according to the present invention, a total of k * n * m channels (signals) can be transmitted at k transmission frequencies (or k wavelengths of light) with n timeslots per transmission frequency and m code functions per timeslot (see FIG. 3c).

The use according to the invention of a three-dimensional medium access method (FDMA-TDMA-CDMA) for data transmission via optical fibers leads to a further broadening of the frequency spectrum which is used for data transmission, as can be seen in FIG. 3c. The spectral efficiency is thus further increased compared to the prior art.

By combining the technically available components for the respective multiplex processes, analogous to the two-dimensional access process described, the sum of the advantages of the individual multiplex processes can be used. 4 schematically shows an example of an optical data transmission system in which the data transmission takes place by means of the method according to the invention.

For the sake of simplicity, in the example shown, each optical transmission device, each consisting of a code ultiplex device lli ... ll _k , a time-division multiplex device 12χ ... 12 _k and an optical transmitter 13ι ... 13k (eg laser diode) processes the data from a number of n * m channels for data transmission; the same applies to each optical receiving device, each consisting of an optical receiver 23ι ... 23 (eg photodiode), a time demultiplexing device 22ι ... 22 _k and a code multiplexing device 21ι ... 21 _k .

In each case several of the optical transmission devices together with an optical wavelength multiplexer 14 result in the optical multiplexer 1. The same applies to the optical demultiplexer 2, which consists of several optical receiving devices and an optical wavelength demultiplexer 24.

Claims

claims

1. Method for transmitting data via optical fibers (LWL), code functions being generated from data which are transmitted in a multiplicity of channels for data transmission by means of the code multiplex method,

Time slots ti ... t _{n are} generated using the time division multiplex method and the code functions generated are inserted into the time slots, n time slots each forming a frame and the frames having a specific wavelength being transmitted via an optical waveguide (LWL).

2. The method according to claim 1, characterized in that the number of channels is n * m.

3. The method according to claim 1 or 2, characterized in that m code functions Ci ... C _{m are} transmitted in each time slot ti ... t _n .

4. The method according to claim 1, 2 or 3, characterized in that a plurality of frames are transmitted simultaneously with k different wavelengths via a common optical waveguide (LWL) in the wavelength division multiplex method.

5. Optical transmission device for sending data over optical fibers (LWL), with a code division multiplexing device (lli), which generates data functions from the data that are transmitted via a multiplicity of channels for data transmission, code functions by means of the code division multiplexing method, a time division multiplexing device (12χ), the time slots generated by means of time division multiplexing and the generated Inserts code functions into the time slots, where n time slots ti ... t _{n form} a frame, and an optical transmitter (13ι) which sends the frames with a certain wavelength via an optical fiber (LWL).

6. Optical transmission device according to claim 5, characterized in that the number of channels is n * m.

7. Optical transmission device according to claim 5 or 6, characterized in that the time-division multiplexing device (12ι) inserts m code functions Ci ... C _m into each time slot ti ... t _n .

8. Optical multiplexer (1) for sending data over

Optical waveguide (LWL), characterized by a number k optical transmission devices according to claim 5, 6 or 7, wherein the optical transmitter (13ι ... l3 _k ) each differ in the wavelength with which they send the frame, and an optical Wavelength multiplexer (14) for joining and simultaneously sending the frames of the k optical transmitters (13ι ... l3 _k ) over a common optical fiber (LWL), so that the respective frames are transmitted in the wavelength multiplex method over the optical fiber (LWL).

9. Optical receiving device for receiving data via optical waveguides (LWL), with an optical receiver (23ι), the frames that are transmitted at a certain wavelength via an optical waveguide (LWL) in time-division multiplexing, a frame consisting of n time slots ti ... t _n exists, each time slot code functions in code division multiplexing and each co- defunction contains the data of a channel for data transmission, a time demultiplexing device (22ι), which reads out the code functions contained therein from each time slot tι ... t _n , and a code demultiplexing device (21χ), which reads the data from the read code functions in the original Restores channels for data transmission.

10. Optical receiving device according to claim 9, characterized in that the number of channels is n * m.

11. Optical receiving device according to claim 9 or 10, characterized in that the time demultiplexing device (22ι) reads m code functions Ci ... C _m from each time slot ti ... t _n .

12. Optical demultiplexer (2) for receiving data via optical waveguides (LWL), characterized by an optical wavelength demultiplexer (24) for simultaneously receiving frames which are transmitted via a common optical waveguide (LWL) in the wavelength division multiplexing method and for dividing the Frame on optical receiving devices, and a number k optical receiving devices according to claim 9, 10 or 11, wherein the optical receivers (23ι ... 23 _k ) each differ in the wavelength with which they receive the frames.