WO2013000771A1

WO2013000771A1 - Method of flexibly processing data for optical networks

Info

Publication number: WO2013000771A1
Application number: PCT/EP2012/061751
Authority: WO
Inventors: Erich Gottwald; Harald Rohde; Sylvia Smolorz
Original assignee: Nokia Siemens Networks Oy
Priority date: 2011-06-30
Filing date: 2012-06-19
Publication date: 2013-01-03

Abstract

A method of processing data for optical networks is provided, the method comprising the steps of mapping a plurality of input data streams into a plurality of output data streams and mapping the plurality output data streams into a plurality of optical carriers, wherein the mapping is realized by means of a look up table.

Description

METHOD OF FLEXIBLY PROCESSING DATA FOR OPTICAL NETWORKS

FIELD OF THE INVENTION

The invention relates to an optical communication system and to a method of processing data for optical network. In particular, the invention relates to a coherent transmission for an Ultra-Dense Wavelength Division Multiplex (UDWDM) network especially for the NSN NGOA (Next Generation Optical Access) system in which a set of densely spaced optical channels is generated from one single laser source.

BACKGROUND OF THE INVENTION

Software defined Optics (SDO) is a growing field in which former hard wired modulation schemes are replaced by soft^¬ ware. In the mobile communication world, software defined transmit frequencies are known as well. However, the carrier frequencies are always generated by means of RF electronic circuits whose frequency can be adjusted by software

The problem to be solved is to overcome the disadvantages stated above and in particular to provide a solution which allows the flexible generation of different modulation schemes and transmission systems. SUMMARY OF THE INVENTION

In order to overcome the above-described need in the art, the present invention discloses a method of processing data for optical networks, comprising the steps of mapping a plurality of input data streams into a plurality of output data streams and mapping the plurality output data streams into a plural- ity of optical carriers, wherein the mapping is realized by means of a look up table.

In a next embodiment, the look up table is programmable by means of a software program.

In a further embodiment, the look up table includes a plural- ity of pulse shaping filters.

It is also an embodiment that the look up table includes a plurality of modulation formats for the optical carriers

In a next embodiment of the invention, the look up table in^¬ cludes a plurality of data rates It is also an embodiment that the look up table includes a plurality of channel spacing.

In a next embodiment, the look up table is programmable by means of a hard wired circuit.

In a next embodiment of the invention, the method further in^¬ cludes the steps of feeding the plurality output data streams to a computation unit. It is also an embodiment that the computation unit is confi^¬ gured to perform Modulation and Digital up-conversion.

In a next embodiment of the invention, the computation unit is a multi purpose computation unit.

The method provided, in particular, bears the following ad^¬ vantages : a) The dynamic reconfiguration of the look up table al^¬ lows the flexible generation of different modulation schemes and transmission systems. b) It has relatively broad applications and they can be easy implemented. c) Remarkable performance improvement can be achieved, (because, for example, the calculations of the trigono^¬ metric functions are done in advance and are available in software writable memory locations therefore allow^¬ ing a faster transmission) . d) The computation unit can be a multi-purpose chip, which can be designed and manufactured before that the mod^¬ ulation scheme has been defined. This is possible be^¬ cause its task is to perform a simple computa^¬ tion/combination of the output signals provided by the look up table. The complexity of the calculation is al^¬ located in the look up table, which can be flexibly and dynamically programmed. BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained by way of example in more detail below with the aid of the attached drawings.

Fig.l is a schematic representation of a flexible Ultra Dense Wavelength-Division Multiplexing (UDWDM) Transmitter according to an embodiment of the invention. Fig.2 is a schematic representation of an OLT at 1 G opera^¬ tion according to an embodiment of the invention.

Fig.3 is a schematic representation of an OLT characterized by mixed operation according to an embodiment of the invention. Fig.4 shows the optical output spectrum for 10 separated 1 G carriers according to an embodiment of the invention.

Fig.5 shows 10 carriers grouped together by adaptation of the up-conversion look up tables to form a 10 G signal, according to an embodiment of the invention. Fig.6 shows 10 1 G carriers grouped together by re- programming the up conversion look up tables to form an Orthogonal Frequency Division Multiplexed (OFDM) signal, ac^¬ cording to an embodiment of the invention. DESCRIPTION OF THE INVENTION

Illustrative embodiments will now be described with reference to the accompanying drawings to disclose the teachings of the present invention. While the present invention is described herein with reference to illustrative embodiments for partic^¬ ular applications, it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recog^¬ nize additional modifications, applications, and embodiments within the scope thereof and additional fields in which the present invention would be of significant utility.

A simple and effective method is provided which allows, in an easy and flexible way, the generation of any combination of data rates from 1G to 10 G with a granularity of 1 G.

Fig.l is a schematic representation of a flexible Ultra Dense Wavelength-Division Multiplexing (UDWDM) Transmitter according to an embodiment of the invention. In particular Fig.l shows a fully digital, flexible carrier generation by means of freely programmable look up tables according to an embodi^¬ ment of the invention. As illustrated in Fig.l, 10 tributary data streams of 1 Gbps each are fed into the digital part of the transmitter 103, pre-processed (e.g. framing, FEC, OAM etc.), fed into the digital modulation stage and are there modulated, e.g. with a DQPSK modulation format. All tributaries are then fed into the digital up-converter block 101 and sent to the Digital to Analog Converters (DAC) 105 and to the IQ modulator 106.

In the digital up-converter block 101 each tributary is digitally multiplied with its according high frequency carrier. If the data signal is D(t) and the carrier frequency is f_n, then the resulting I and Q components for the modulator are formed as :

I (t)=D(t) *sin (2nf_nt) , and

Q (t) =D (t) *cos (2nf_nt) Since it is extremely difficult to calculate the trigonomet^¬ ric functions sine and cosine numerically, this multiplica^¬ tion is done by using look up tables, i.e. the argument of the function is used as an address of a memory and the con^¬ tent of the memory contains the according function value. For the 10 channel multicarrier transmitter, as shown in

Fig.l, 5 look up tables (either consisting of two sub-tables for the sine and cosine or dual ported) are used.

According to one embodiment of the invention, n input data streams are mapped into m output data streams, the m output data streams being mapped to a plurality of carriers (e.g. 1 to 10) within the bandwidth limits, the mapping being realized by means of a look up table configured to flexibly (dy^¬ namically) generate data rate and/or channel spacing and/or modulation formats of the transmitted optical signals. The look up table is suitable to be flexibly programmed by means of an external interface (look up table loading) which can define the different data rates and/or channel spacing and/or modulation formats. The m output data streams are fed to the computation unit 101 ( "Modulation & Digital up-conversion" unit) which combines the m output data streams into two digital data stream (SO and SI ) . In case of symmetric frequency assignment, since the carriers are symmetric on both sides of the optical carrier, two car^¬ riers can share the same lookup table.

In "normal" Next Generation Optical Access (NGOA) operation, the lookup tables can be filled with values for the sine and cosine components such that the carriers are well separated, according to the NGOA frequency plan.

The look up tables can be either hard wired or realized as software-writable memory. In the latter case, the frequency grid of a transmitter is freely programmable, just by software. Either 10 channels at 1 G each or one channel at 10G or any arbitrary combination can be programmed.

Since the up-conversion is realized simply by reading out the memory tables, any pulse shaping filter can be included in these memory tables as well.

In case of asymmetric frequency assignment, i.e. the frequen^¬ cy grid at the negative side of the optical carrier is not equal to that on the positive side, the re-use of look up tables, as in the symmetric case, is not possible and a look up table must be foreseen for each of the tributaries.

The arrangement of 10 lG-channels which can be multiplied with an arbitrary look-up table together with the digital multiplexer can be used to define any function that can be represented with the hardware defined maximum sampling rate, e.g. at least 10G modulation.

Fig.2 is a schematic representation of an OLT at 1 G opera^¬ tion according to an embodiment of the invention. In Fig.2 the All Optical Transceiver Groups (OTG) are configured to 1 G mode .

Fig.3 is a schematic representation of an OLT characterized by mixed operation according to an embodiment of the invention. In particular, Fig 3 shows an OLT in which one of the OTGs 301 is configured to be operated in a 10 G mode.

Fig.4 shows the optical output spectrum for 10 separated 1 G carriers according to an embodiment of the invention.

Fig.5 shows 10 carriers grouped together by adaptation of the up-conversion look up tables to form a 10 G signal, according to an embodiment of the invention.

Fig.6 shows 10 1 G carriers grouped together by re- programming the up conversion look up tables to form an Orthogonal Frequency Division Multiplexed (OFDM) signal, ac^¬ cording to an embodiment of the invention. The present invention is not limited to the details of the above described principles. The scope of the invention is de^¬ fined by the appended claims and all changes and modifica^¬ tions as fall within the equivalents of the scope of the claims are therefore to be embraced by the invention. Mathe- matical conversions or equivalent calculations of the signal values based on the inventive method or the use of analogue signals instead of digital values are also incorporated. List of Abbreviations:

IQ In-phase and Quadrature

LO Local Oscillator

NGOA Next Generation Optical Access

OLT Optical Line Terminal

OTG Optical Transceiver Group

LIC Line Interface Card

ONU Optical Network Unit

PON Passive Optical Network

UDWDM Ultra Dense WDM

OFDM Orthogonal Frequency Division Multiplex

Claims

Claims :

1. Method of processing data for optical networks, compris ing :

- mapping a plurality of input data streams into a plu^¬ rality of output data streams;

- mapping the plurality output data streams into a plu^¬ rality of optical carriers;

- wherein the mapping is realized by means of a look up table .

2. Method according to claim 1, wherein look up table is programmable by means of a software program.

3. Method according to claim 2, wherein the look up table includes a plurality of pulse shaping filters.

4. Method according to claim 2, wherein the look up table includes a plurality of modulation formats for the opti cal carriers .

5. Method according to claim 2, wherein the look up table includes a plurality of data rates.

6. Method according to claim 2, wherein the look up table includes a plurality of channel spacing.

7. Method according to claim 1, wherein the look up table is programmable by means of a hard wired circuit.

8. Method according any of the preceding claims, further comprising :

- feeding the plurality output data streams to a compu^¬ tation unit.

9. Method according to claim 8, wherein the computation

unit is configured to perform Modulation and Digital up- conversion .

10. Method according to claim 8, wherein the computation

unit is a multi purpose computation unit.