A METHOD FOR PROTECTING A LINK IN AN OPTICAL NETWORK

Description

FIELD OF THE INVENTION

[0001] The present invention is in the field of communication technology. In particular, the present invention relates to a fast protection technique realized in the optical transport layer of a network.

BACKGROUND OF THE INVENTION

[0002] Optical networks are usually organized in ring or meshed structures consisting of several nodes connected by unidirectional or, more often, bidirectional links. The usage of reconfigurable optical cross-connects introduces the possibility to reroute traffic and reallocate network resources in a dynamic way.

[0003] Modern optical transport networks for telecommunications rely upon coherent technology to convey information in the amplitude, phase and polarization of light. Whereas the first generation of optical coherent systems usually employed dual polarization QPSK (DP-QPSK) with hard-decision (HD) forward error correction (FEC), state-of-the-art systems support a variety of mQAM modulation formats and coding schemes, where m could e.g. be 16, 32, or 64. In particular, multi-rate multi-format transponders allow to choose coding and modulation according to the characteristics of the link at hand.

[0004] Transport networks are critical telecommunication infrastructures and are therefore subject to strict reliability constraints. An important requirement, often referred to as "survivability", is the ability of the network to provide the committed quality of service (QoS) in several failure scenarios, as regulated by the service level agreement (SLA) between network customers and provider. Although failure protection mechanisms can be realized in different layers of the protocol stack, in this disclosure particular focus is put on implementations at the physical layer.

[0005] Generally, whenever a link failure is detected, the traffic is rerouted onto an available backup link. In some cases a dedicated backup is assigned to some critical links, but typically a shared backup offers a better trade-off between reliability and costs. According to this approach, the network is provided with a certain amount of over-capacity, which is used in the case of failure to establish the required protection paths. At least for single failure scenarios on the most critical links, the protection paths are often preplanned to guarantee the shortest possible service interruption. Note that in the present disclosure, the terms "path" and "link" are used interchangeably.

[0006] In case of link failure, the preplanned or calculated protection link at the optical transport layer might possibly support only a fraction of the bit rate supported by the working link. This happens for instance when the protection path is impaired by stronger noise, nonlinear fiber effects, and/or filtering effects than the designated working path or "given link". This situation is not uncommon, especially when the backup is shared and hence cannot be finely optimized as the working path. However, depending on the SLA, a reduced throughput over the protection link in some fault scenarios is an acceptable option. In this case higher layers must take care of recovering the remaining traffic.

[0007] The flexible nature of multi-rate multi-format transponders offers a convenient way to downgrade the end-to-end throughput, by adapting the coding and modulation schemes. For instance, a 200 Gb/s signal transmitted over the working link using DP-16QAM could be downgraded to a 100 Gb/s signal using DP-QPSK to maintain satisfactory transmission quality over a longer protection link, by discarding the low-priority traffic. The adaptation of the transmission format could either be requested by a central control unit or could be negotiated autonomously between the involved transponders. Unfortunately, both approaches require, besides some signaling overhead, a full reconfiguration of the transponders at the end nodes of the link, which would typically include reprogramming registers of framer and modem devices, tuning analog oscillators and adjusting analog signal levels. This process is, however, extremely time-consuming and results in practice into severe service interruption which will often not be tolerable for high-priority traffic.

[0008] If the long reconfiguration time of the transponders and the additional signaling overhead shall be avoided, the problem could be circumvented, rather than solved, by constraining all protection paths to support at least the same throughput as their respective working path. However, this solution comes at a tremendous cost in terms of required overcapacity in the network. Further, this cost increases with the network size due to the growing number of possible failure scenarios that must be taken into account.

[0009] As an alternative, the throughput on the working path could be artificially lowered below the actual link capacity according to the transmission conditions of the worst-case protection path. Obviously, also this solution comes at a high price, because it sacrifices throughput during normal operation to guarantee a quick failure response.

[0010] According to US 2013/0215942 A1, a transmitter determines a level of error protection of each bit position within symbols of a particular constellation map used for modulation-based communication, and also determines priority levels of application data bits to be placed into a communication frame. Application data bits may then be placed into symbols of the communication frame, where higher priority application data bits are placed into bit positions with greater or equal levels of protection than bit positions into which lower priority application data bits are placed. The communication frame is then transmitted to one or more receivers with an indication of how to decode the placement of the application data bits within the symbols. In another variant, the particular constellation is dynamically selected from a plurality of available constellation maps, such as based on communication channel conditions and/or applications generating the data.

[0011] WO 2010/024619 A2 discloses a symbol mapping apparatus, in which a channel coder outputs a codeword including a plurality of information bits and a plurality of redundancy bits by encoding transmission data. A symbol mapper maps the codeword to the symbol while changing a mapping scheme in the unit of the codeword, including a constellation shift in a constellation diagram.

SUMMARY OF THE INVENTION

[0012] The problem underlying the invention is to provide a method and apparatus for protecting a link in an optical network which allows for avoiding long interruption times but at the same time avoids high overcapacities in the network. This problem is solved by a method according to claim 1 as well as by a control device according to claim 11, a transmitter according to claim 13 and a receiver according to claim 14. Preferred embodiments are defined in the dependent claims.

[0013] According to the method of the invention, the link to be protected is configured for transmitting digital data employing a predetermined modulation format, wherein

• said modulation format uses a constellation diagram comprising a number of symbols,
• each symbol is represented by a point in an n-dimensional Euclidean signal space with n ≥1,
• a binary address is associated with each symbol, and
• said modulation format allows for a constellation distortion, according to which the relative positions of constellation points in the constellation diagram are varied in a predetermined way by a predetermined degree.

[0014] The method further comprises the following steps:

A) partitioning the traffic to be transmitted over the link in two or more priority classes,

B) mapping higher priority traffic to predefined bit positions within the binary symbol addresses,

C) evaluating the quality of a predetermined protection link via which a part of the traffic could be transmitted in case of failure of the given link,

D) determining a degree of distortion of the constellation diagram such that a desired transmission quality for the transmission of the traffic of the highest priority class or classes via said predetermined protection link and a desired transmission quality for the full traffic via said given link are simultaneously ensured, and

E) employing a distorted constellation diagram with the determined degree of distortion for said transmission of digital data over said given link.

[0015] Herein, the n-dimensional Euclidean signal space could e. g. be a two-dimensional plane, such as an I-Q-signal plane. According to the invention, traffic to be transferred over the link is hence partitioned in at least two priority classes. Higher priority traffic is mapped to predefined bit positions within the binary symbol addresses. These would typically be bit positions which even in the modulation format without constellation distortion are better protected, or - in other words - have a lower error probability. Moreover, according to the invention the modulation format allows for a constellation distortion, according to which the relative positions of constellation points in the constellation diagram are varied in a predetermined way by a predetermined degree as compared to a default constellation, which is also referred to as "uniform constellation" herein. As will become more apparent with reference to specific examples, due to a suitable choice of distortion, it becomes possible to further increase the protection of the predefined bit positions to which the priority traffic is mapped.

[0016] According to the invention, it is ensured that at least the higher priority traffic will be safely transmitted in case the traffic is switched from the given link or "working link" to the protection link. Herein, the "higher priority traffic" is the traffic associated with the highest or, if there are more than two priority classes, possibly two or more highest priority classes. For this purpose, in step D) recited above, a degree of distortion of the constellation diagram is determined such that a desired transmission quality for the transmission of the traffic of the highest priority class or classes via said predetermined protection link is ensured. At the same time, the degree of distortion is chosen such that a desired transmission quality for the full traffic via the given link (working link) is simultaneously ensured.

[0017] If a degree of distortion that fulfills both requirements is found, then the corresponding distorted constellation diagram with the determined degree of distortion is used for the transmittal of digital data over the given link. In case of failure value, the traffic can be switched to the protection link without a need for adapting the coding and modulation scheme and the reconfiguration time associated therewith, which allows for an extremely fast recovery of at least the high-priority traffic. If no such degree of distortion can be found, this would indicate that the quality of the protection link is insufficient, and that hence another protection link needs to be considered. However, the skilled person will appreciate that with the method of the invention, due to the possibility to adjust the distortion of the constellation diagram, the available links can be used much more efficiently than in the prior art described above, and that effectively the requirement to the quality of the links is considerably relaxed.

[0018] Note that some of the individual elements of the inventive method are known from prior art but in a different context. Assigning transmitted bits to different priority classes according to some importance criterion is e.g. described in R. Calderbank and N. Seshadri, "Multilevel codes for unequal error protection", IEEE Transactions on Information Theory, vol. 39, no. 4, pp. 1234-1248, July 1993. Further refinements were proposed by R. H. Morelos-Zaragoza, M. P. C. Fossorier, S. Lin and H. Imai in "Multilevel coded modulation for unequal error protection and multistage decoding - Part I: Symmetric constellations", IEEE Transactions on Communications, vol. 48, no. 2, pp. 204-213, February 2000 and by M. Isaka, M. P. C. Fossorier, R. H. Morelos-Zaragoza, S. Lin and H. Imai in "Multilevel coded modulation for unequal error protection and multistage decoding - Part II: Asymmetric constellations", IEEE Transactions on Communications, vol. 48, no. 5, pp. 774-786, May 2000, where also the possibility of distorting constellation diagrams is mentioned. More recent developments are described by C. Shen, and M. Fitz in "On the Design of Modern Multilevel Coded Modulation for Unequal Error Protection Communications," available in the proceedings of the IEEE International Conference on Communications ICC '08 on pp. 1355-1359 and by N. von Deetzen, and W. Henkel in "Unequal error protection multilevel codes and hierarchical modulation for multimedia transmission" included in the proceedings of the IEEE International Symposium on Information Theory ISIT 2008 on pp. 2237-2241. However, none of these documents consider the possibility of these generic techniques in the context of network survivability, or employing any of steps C) to E) above.

[0019] In a preferred embodiment, the method further comprises, in case of failure of said given link, a step F) of rerouting the traffic to said protection path.

[0020] In a preferred embodiment, in step C), the quality of a plurality of alternative predetermined protection links are evaluated, and in step D), the degree of distortion of the constellation diagram is determined such that a desired transmission quality for the worst of said plurality of alternative predetermined protection links is ensured. This way, in case of failure of the working link, it is possible to switch to any one of the alternative predetermined protection links, upon their availability, while still ensuring that at least the high-priority traffic will be safely transmitted. Accordingly, the number of predetermined protection links can be shared with further working links, which allows for a more efficient use of network capabilities.

[0021] In the constellation distortion referred to above, the predetermined way of varying the relative positions of constellation points preferably comprises one or more of

• varying the distances of a subset of adjacent constellation points in said constellation diagram,
• varying the distances of a subset of constellation points from a predefined position in the signal space which does not coincide with a constellation point, or
• rotating the position of a subset of constellation points with respect to an origin of said signal space.

[0022] As will become more apparent from the description below, these types of constellation distortions do in fact allow for further decreasing the error probability of the bit positions to which the higher priority traffic is mapped. Herein, the "predefined position in the signal space" may correspond to the center of mass of a subset of constellation points, or may be chosen such that upon the variation, the average power of the signal remains unchanged, bearing in mind that the power associated with a symbol is proportional to the square of the symbol distance from the origin of the n-dimensional signal space. The "center of mass" of a number of constellation points shall refer to an average position defined by the average of their respective coordinates.

[0023] In a preferred embodiment, the constellation diagram is two-dimensional and comprises four quadrants, and in said binary addresses of said constellation points, there are two predetermined bit positions which have identical values for each constellation point within the same quadrant. Herein, higher priority traffic is mapped to said predetermined two bit positions. This embodiment exploits the fact that even in case of a poor link quality, such as due to higher noise, it will more likely be possible to distinguish symbols from each other that are located in different quadrants and hence comparatively far spaced apart. On the other hand, if symbols within the same quadrant are confused with each other due to a poor signal quality, this does not affect the two bits at the bit positions related to the quadrant, which would hence still be correct. In other words, the error probability for these bits is comparatively low.

[0024] In a preferred embodiment, the modulation format employs a 16QAM constellation, and in said constellation distortion, the predetermined way of varying the relative positions of constellation points comprises reducing the distances between constellation points within the same quadrant while increasing the minimum distance between constellation points of different quadrants, as compared to an even distribution of constellation points. This way, the error probability of bit positions related to the quadrants is further decreased, although at the expense of an increased error probability associated with symbols within a quadrant.

[0025] In another preferred embodiment, the modulation format employs a 32QAM constellation, and in said constellation distortion, the predetermined way of varying the relative positions of constellation points comprises

• for the four constellation points in each quadrant that are closest to the origin of the two-dimensional plane, reducing their respective distance from their center of mass, and
• for the four constellation points in each quadrant that are the farthest from the origin of the two-dimensional plane, increasing their respective distance from the closest one among the four constellation points closest to the origin,

as compared to an even distribution of constellation points. This way, again two bit positions corresponding to the quadrant can be strengthened, and in addition, a further bit position can be strengthened, at the expense of the remaining two bit positions, as will become more apparent from an example of a specific embodiment below.

[0026] In another preferred embodiment, the modulation format employs an 8QAM constellation, and in said constellation distortion, the predetermined way of varying the relative positions of constellation points comprises rotating the four constellation points farthest away from the origin around said origin by an angle, said angle defining said degree of variation. In this embodiment, the error probability of the two bit positions can be decreased at the expense of the error probability of the remaining bit position, as will become more apparent from an example of a specific embodiment below.

[0027] In various embodiments, the traffic to be transmitted over the link corresponds to one of the following:

• 200G traffic transmitted over a single DP-16QAM optical carrier partitioned in two 100 G signals with different priorities,
• 300G traffic transmitted over a super channel consisting of two DP-8QAM carriers, or
• a single carrier 400 G transmission using 32QAM or 64QAM.

[0028] In a preferred embodiment, the method further comprises mapping individual FlexEthernet streams to different bit sets in the binary address of the constellation symbols.

[0029] According to a further aspect of the invention, a control device for controlling the protection of a link in an optical network is provided. Such a control device could e.g. be a network management tool employing suitable software provided for being executed on one or more computers. However, the control device is not limited to any specific type of hardware element, as long as it is capable of carrying out the functions recited below. The control device is configured to be operatively connected to a transmitter and a receiver associated with said link, said transmitter being configured for transmitting digital data employing a predetermined modulation format of the type recited above with reference to the method of the invention. The associated transmitter is further configured for partitioning the data to be transmitted over the link in two or more priority classes, and mapping higher priority traffic to predefined bit positions within the binary symbol addresses.

[0030] The control device is further configured for evaluating the quality of a predetermined protection link via which a part of the traffic could be transmitted in case of failure of the given link, determining a degree of distortion of the constellation diagram such that a desired transmission quality for the transmission of the traffic of the highest priority class or classes via said predetermined protection link and a desired transmission quality for the full traffic via said given link are simultaneously ensured, and instructing said transmitter and said receiver to employ a distorted constellation diagram with the determined degree of distortion for said transmission of digital data over said given link.

SHORT DESCRIPTION OF THE FIGURES

[0031] 

Figure 1

shows a Gray labeled 16QAM constellation diagram without distortion on the left and with distortion on the right,

Figure 2

shows a transmitter and a receiver for use in the method of the invention,

Figure 3

shows the required OSNR at a pre-FEC BER of 2·10^-2 for non-uniform DP-16QAM with a symbol rate of 30.7 GHz,

Figure 4

is a diagram illustrating the derivation of a required degree of distortion of a constellation diagram,

Figure 5

is a diagram showing the reach of the strong bits and the week bits as a function of the degree of distortion of the constellation diagram,

Figure 6

shows a Gray labeled 8QAM constellation diagram without distortion on the left and with distortion on the right,

Figure 7

shows a quasi-Gray labeled 32QAM constellation diagram distorted according to two independent distortion parameters.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] For the purposes of promoting an understanding of the principles of the invention, reference will now be made to a preferred embodiment illustrated in the drawings, and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated apparatus and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur now or in the future to one skilled in the art to which the invention relates.

[0033] For the sake of exemplification we give a detailed description of the method of the invention for the important case that the given link or "working path" carries a payload of about 200 Gb/s, shortly referred to as a "200G client", over a single optical carrier. The modulation format of choice for this application is considered to be DP-16QAM.

[0034] The left side of Fig. 1 shows a uniform 16QAM two-dimensional constellation diagram with Gray labeling: The binary addresses of any two symbols at minimum Euclidean distance differ exactly in one position. In this shown example, the two rightmost bits identify the quadrant, whereas the two leftmost bits determine the symbol in the quadrant on the in-phase (I) - quadrature (Q) plane. With the adopted normalization, the average of the four constellation points in the first quadrant, referred to as "a center of mass" herein and marked by a cross, lies at (2, 2). In each quadrant the distance δ between the projection of every symbol and the projection of the center is equal to 1 both on the I and Q axes. The situation is referred to as the "uniform" or "non-distorted" constellation.

[0035] The right side of Fig. 1 shows a non-uniform, "distorted" 16QAM constellation where δ has been decreased to 0.75. Herein, δ is a geometrical parameter that indicates the "degree of distortion" referred to above, and is also referred to as "distortion parameter" herein. In this case the distance between symbols belonging to different quadrants is enhanced at the expense of the intra-quadrant distances. A reduction of δ hence increases the error resilience on the two rightmost bit positions and degrades that of the two leftmost bit positions in the binary address. Since the two rightmost bits are better protected, they are also referred to as "strong bits" herein, and the two leftmost bits will be referred to as "weak bits". Note that this distortion of the constellation is an example of the "varying of the distances of a subset of constellation points from a predefined position in the signal space which does not coincide with a constellation point" referred to in the introductory portion of the specification, where the predefined position corresponds to the center of mass of the four constellation points in each quadrant. The position of the center of mass could be further shifted such as to keep the average power of the corresponding signal constant.

[0036] In the described example, it shall be assumed that the 200G signal is partitioned in a high-priority and a low-priority 100G client according to step A) referred to above.

[0037] In the following step B), the high-priority traffic is mapped to the strong bits and the low-priority traffic is mapped to the weak bits. This is illustrated in Fig. 2, in which a transmitter 10 and a receiver 12 are shown. As further shown in Fig. 2, the transmitter 10 comprises two identical encoders A and B at reference sign 14, two interleavers A and B at reference sign 16 and a mapper 18. The receiver 12 comprises a demapper 20, de-interleavers A and B at reference sign 22 and decoders A and B at reference sign 24.

[0038] The high-priority and low-priority bit streams, b_A and b_B respectively, are separately encoded by the two identical encoders A and B shown at reference sign 14. Each encoded stream is distributed by the corresponding interleaver 16 between two different inputs of the mapper, corresponding to different bit positions in the binary address. With reference to Fig. 1, the binary positions are numbered from right to left from 1 to 4. The receiver 12 implements the corresponding sequence of inverse operations.

[0039] Further shown in Fig. 2 is a control device 8 which is operatively coupled with the transmitter 10 and the receiver 12. The control device 8 can be realized in software, in hardware or both. In particular, the control device 8 is capable for carrying out the above-mentioned method steps C) and D), and to communicate to the transmitter 10 and the receiver 12 the degree of distortion of the constellation that shall be employed.

[0040] Fig. 3 shows simulation results for DP-16QAM over a DP additive white Gaussian noise (AWGN) channel. A symbol rate of 30.7 GHz is chosen to transport the whole 200G traffic and accommodate for 15% FEC overhead and for pilot symbols employed for non-differential transmission. The required optical signal-to-noise ratio (ROSNR), defined over a noise bandwidth of 12.5 GHz, for a pre-FEC bit error rate (BER) of 2·10^-2, which is assumed to be the FEC threshold, is plotted as a function of the geometry parameter or "distortion parameter" δ both for the strong and the weak bits. The dotted line shows also the ROSNR for a conventional approach with uniform 16QAM when a single FEC code is applied through bit-interleaving to all four bit positions. In Fig. 3, it is seen that by reducing δ, or in other words increasing the degree of distortion, the resilience of the strong bits is increased while sacrificing the performance of the weak bits.

[0041] Next, according to step C) referred to above, the quality of a predetermined protection link via which a part of the traffic could be transmitted in case of failure of the given link or working path is determined. In particular, this comprises determining the available optical signal-to-noise ratio (OSNR) on the working path and the worst-case protection path. Herein, the "worst-case protection path" is the protection path among a set of predetermined alternative protection paths providing the worst transmission quality. For the sake of exemplification it shall be assumed that that these values are 19 dB and 14 dB, respectively, as shown by the additional horizontal lines in Fig. 4.

[0042] Proceeding with step D), the geometry parameter δ, or in other words, the degree of distortion, is determined such as to ensure that the pre-FEC BER is equal or better than the desired threshold both on the working path and the worst protection path. As indicated by the additional vertical lines in Fig. 4, allowed values of the geometry parameter δ range roughly from 0.775 to 0.817. According to step E) the distorted constellation diagram with the determined degree of distortion, i.e. with 0.775 < δ < 0.817, is then employed for the transmission of digital data over the working path. In case of link failure, the traffic is rerouted according to step F) without changing the modulation format, and maintaining the geometry parameter or "degree of distortion" δ. Having chosen the geometry parameter δ in the allowable range, it is ensured that the receiver is still capable of detecting the high-priority traffic with the desired performance without reconfiguration of the coding and modulation scheme.

[0043] Although the proposed solution was exemplified over an idealized AWGN channel model, it works without fundamental modifications also under realistic channel conditions. Fig. 5 shows the performance of non-uniform DP-16QAM over a nonlinear fiber-optic link consisting of several 80 km spans of standard single-mode fiber (SSMF) connected through erbium-doped fiber amplifiers (EDFAs). Again a non-differential transmission and 15% overhead FEC with a BER threshold of 2·10^-2 are assumed. The performance of 96 wavelength division multiplexed carriers with 50 GHz spacing is evaluated, assuming a system margin of 3 dB, an implementation penalty of 2 dB and an EDFA noise figure of 5 dB. The nonlinear interference caused by the fiber is evaluated according to the semi-analytical GN-model described by A. Carena, V. Curri, G. Bosco, P. Poggiolini, and F. Forghieri in the article "Modeling of the impact of non-linear propagation effects in uncompensated optical coherent transmission links", IEEE Journal of Lightwave Technology, volume 30, number 10, pp.1524-1539 (2012). A launch power of ~3 dBm per channel is assumed, which corresponds to optimum performance.

[0044] Fig. 5 shows the maximum reach both for the strong and the weak bits as a function of the geometry parameter δ. Additionally, the dotted line indicates the reach of a conventional transmission system with uniform 16QAM and a single FEC code applied to all four bit positions. It is apparent that the nonlinear fiber effects do not alter the qualitative trend observed in Fig. 3. Once again, by tuning δ one can optimize the performance of strong and weak bits according to the characteristics of protection and working paths.

[0045] Note that after step F), some parameters of the receiver may still need resynchronization or adaptation. In particular the accumulated chromatic dispersion (CD) and the polarization mode dispersion (PMD) over the protection link are typically different from the working link. The resynchronization of the CD compensator (not shown) at the receiver 12 could be either triggered externally together with the reconfiguration of the cross-connects (not shown) or initiated automatically by a locally generated alarm. The PMD compensator is continuously adapted at run-time and therefore reacts automatically to the new channel conditions. The benefit of the approach of the invention stems from the fact that with the current transponder technology, the adaptation of the receiver parameters is much faster (roughly by two orders of magnitude) than a reconfiguration of the coding and modulation scheme.

[0046] According to the invention, in case of link failure, the high-priority client experiences only a short interruption due to failure detection time, reconfiguration of the cross-connects and resynchronization of the receiver: its protection mechanism is completely implemented in the optical layer. On the contrary, the low-priority traffic is dropped at the optical link layer and its protection is fully delegated to the higher layers. As a consequence, low-priority traffic is likely to undergo a longer downtime, consistent with the state of the art.

[0047] In the previous example, the 200G traffic transmitted over a single DP-16QAM optical carrier was partitioned in two 100G signals with different priorities. This application addresses in a natural way the problem of transporting two optical data units 4 (ODU₄), which are standard 100G client signals defined in the optical transport network (OTN) multiplexing hierarchy introduced in the ITU-T recommendation G.709/Y.1331 (02/2012).

[0048] Other advantageous embodiments of the invention relate to

• the transport of 300G traffic over a super-channel consisting of two DP-8QAM carriers,
• single carrier 400G transmission using 32QAM, or
• 400G transmission over a single 64QAM carrier.

[0049] In all these cases, by distorting the symbol constellation, the protection level of distinct ODU₄ (100G) clients can be altered. However, various embodiments of the invention allow also a different granularity of the traffic classes when the transport equipment implements traffic aggregation. This becomes particularly attractive in conjunction with the FlexEthernet project started by the Optical Internetworking Forum (OIF) with the aim of introducing flexible rate connections between routers. Using FlexEthernet-aware transport equipment, in one embodiment one can map individual FlexEthernet streams to different bit-sets in the binary address of the constellation symbols. For example, one can partition 250G traffic transported over a single DP-16QAM carrier into two 125G FlexEthernet clients with different priorities or 150G traffic transported over a single DP-8QAM carrier into a 100G and a 50G client. Further examples are easily conceivable in view of the present disclosure.

[0050] While in the embodiment above, only DP-16QAM modulation formats have been discussed in detail, the invention is by no means limited to this. Square mQAM constellations, like 64QAM, can be treated similarly to 16QAM by clustering their symbols around their center of mass in each quadrant. If necessary, each group of four neighboring points can be further clustered around their respective center of mass, and the center of mass may optionally be shifted.

[0051] According to a further embodiment, the left side of Fig. 6 shows a uniform 8QAM constellation with quasi-Gray labeling. By rotating the outer constellation points in clockwise direction, the constellation on the right side of Fig. 6 is obtained, where the two leftmost bits are strengthened at the expense of the rightmost bit.

[0052] According to a further embodiment, Fig. 7 shows a quasi-Gray labeled 32QAM constellation together with two possible distortion parameters δ₁ and δ₂ that control its geometry. With the adopted normalization, for δ₁=δ₂=1 the uniform constellation is obtained. By decreasing δ₁, for the four constellation points in each quadrant that are closest to the origin of the two-dimensional plane, the respective distance from their center of mass is reduced, which strengthens the quadrant bits 3 and 4 (numbering from right to left) at the expense of the rightmost bits 1 and 2. By increasing δ₂, for the four constellation points in each quadrant that are the farthest from the origin of the two-dimensional plane, the respective distance from the closest one among the four constellation points closest to the origin is increased, which protects the leftmost bit 5 at the expense of all other bits.

[0053] Alternative geometry parameters for the constellations mentioned above and for further symbol constellations can be determined in the framework of alternative embodiments.

[0054] Although a preferred exemplary embodiment is shown and specified in detail in the drawings and the preceding specification, these should be viewed as purely exemplary and not as limiting the invention. It is noted in this regard that only the preferred exemplary embodiment is shown and specified, and the scope of protection of the invention is solely defined by the claims.

Claims

1. A method for protecting a link in an optical network, said link being configured for transmitting digital data employing a predetermined modulation format, wherein

• said modulation format uses a constellation diagram comprising a number of symbols,

• each symbol is represented by a point in an n-dimensional Euclidean signal space with n ≥ 1,

• a binary address is associated with each symbol, and

• said modulation format allows for a constellation distortion, according to which the relative positions of constellation points in the constellation diagram are varied in a predetermined way by a predetermined degree as compared to a non-distorted constellation,

said method comprising the following steps:

A) partitioning the traffic to be transmitted over the link in two or more priority classes,

B) mapping higher priority traffic to predefined bit positions within the binary symbol addresses,

C) evaluating the quality of a predetermined protection link via which a part of the traffic could be transmitted in case of failure of the given link,

D) determining a degree of distortion of the constellation diagram such that a desired transmission quality for the transmission of the traffic of the highest priority class or classes via said predetermined protection link and a desired transmission quality for the full traffic via said given link are simultaneously ensured, and

E) employing a distorted constellation diagram with the determined degree of distortion for said transmission of digital data over said given link.

2. The method of claim 1, wherein said predefined bit positions are bit positions which in the non-distorted constellation have an error probability less than the average error probability of all bit positions.

3. The method according to claim 1 or 2, further comprising, in case of failure of said given link, a step F) of rerouting the traffic to said protection path.

4. The method according to one of the preceding claims, wherein in step C), the quality of a plurality of alternative predetermined protection links are evaluated, and wherein in step D), the degree of distortion of the constellation diagram is determined such that a desired transmission quality for the worst of said plurality of alternative predetermined protection links is ensured.

5. The method according to one of the preceding claims, wherein in said constellation distortion, said predetermined way of varying the relative positions of constellation points comprises one or more of

• varying the distances of a subset of adjacent constellation points in said constellation diagram,

• varying the distances of a subset of constellation points from a predefined position in the signal space which does not coincide with a constellation point,

• rotating the position of a subset of constellation points with respect to an origin of said signal space, and/or

wherein said predefined position in the signal space corresponds to the center of mass of a subset of constellation points, or is chosen such that upon the variation, the average power of the signal remains unchanged.

6. The method according to one of the preceding claims,

wherein said constellation diagram is two-dimensional and comprises four quadrants,

wherein in said binary addresses of said constellation points, there are two predetermined bit positions which have identical values for each constellation point within the same quadrant, and

wherein higher priority traffic is mapped to said predetermined two bit positions.

7. The method according to one of claims 5 to 6, wherein said modulation format employs a 16QAM constellation, and wherein in said constellation distortion, said predetermined way of varying the relative positions of constellation points comprises reducing the distances between constellation points within the same quadrant while increasing the minimum distance between constellation points of different quadrants, as compared to an even distribution of constellation points.

8. The method according to one of claims 5 to 6, wherein said modulation format employs a 32QAM constellation, and wherein in said constellation distortion, said predetermined way of varying the relative positions of constellation points comprises

• for the four constellation points in each quadrant that are closest to the origin of the two-dimensional plane, reducing their respective distance from their center of mass, and

• for the four constellation points in each quadrant that are the farthest from the origin of the two-dimensional plane, increasing their respective distance from the closest one among the four constellation points closest to the origin,

as compared to an even distribution of constellation points.

9. The method according to one of claims 5 to 6, wherein said modulation format employs an 8QAM constellation, and wherein in said constellation distortion, said predetermined way of varying the relative positions of constellation points comprises rotating the four constellation points farthest away from the origin around said origin by an angle, said angle defining said degree of variation.

10. The method of one of the preceding claims, wherein said traffic to be transmitted over the link corresponds to one of the following:

• 200G traffic transmitted over a single DP-16QAM optical carrier partitioned in two 100 G signals with different priorities,

• 300G traffic transmitted over a super channel consisting of two DP-8QAM carriers,

• a single carrier 400 G transmission using 32QAM or 64QAM, and/or wherein said method further comprises mapping individual FlexEthernet streams to different bit sets in the binary address of the constellation symbols.

11. A control device (8) for controlling the protection of a link in an optical network, said control device (8) configured to be operatively connected to a transmitter (10) and a receiver (12) associated with said link, said transmitter (10) being configured for transmitting digital data employing a predetermined modulation format, wherein

• said modulation format uses a constellation diagram comprising a number of symbols,

• each symbol is represented by a point in an n-dimensional Euclidean signal space, wherein n ≥1,

• a binary address is associated with each symbol, and

• said modulation format allows for a constellation distortion, according to which the relative positions of constellation points in the constellation diagram are varied in a predetermined way by a predetermined degree as compared to a non-distorted constellation,

the control device (8) further being configured for

• evaluating the quality of a predetermined protection link via which a part of the traffic could be transmitted in case of failure of the given link,

• determining a degree of distortion of the constellation diagram such that a desired transmission quality for the transmission of the traffic of the highest priority class or classes via said predetermined protection link and a desired transmission quality for the full traffic via said given link are simultaneously ensured, and

• instructing said transmitter and said receiver to employ a distorted constellation diagram with the determined degree of distortion for said transmission of digital data over said given link.

12. The control device (8) of claim 11, wherein said control device is operatively connected to said transmitter (10) and said receiver (12).

13. A transmitter (10) configured for transmitting digital data employing a predetermined modulation format and configured to be operatively connected to the control device (8) of claim 11, wherein

• said modulation format uses a constellation diagram comprising a number of symbols,

• each symbol is represented by a point in an n-dimensional Euclidean signal space, wherein n ≥1

• a binary address is associated with each symbol, and

• said modulation format allows for a constellation distortion, according to which the relative positions of constellation points in the constellation diagram are varied in a predetermined way by a predetermined degree as compared to a non-distorted constellation,

wherein said transmitter (10) is further configured for

• partitioning the data to be transmitted in two or more priority classes,

• mapping higher priority traffic to predefined bit positions within the binary symbol addresses,

• receiving instructions from said control device (8) to employ said distorted constellation diagram with a determined degree of distortion for said transmission of digital data, and

• employing a distorted constellation diagram with the determined degree of distortion for said transmission of digital data.

14. A receiver (12) configured for receiving digital data employing a predetermined modulation format and configured to be operatively connected to the control device (8) of claim 11, wherein

• said modulation format uses a constellation diagram comprising a number of symbols,

• each symbol is represented by a point in an n-dimensional Euclidean signal space, wherein n ≥1

• a binary address is associated with each symbol, and

• said modulation format allows for a constellation distortion, according to which the relative positions of constellation points in the constellation diagram are varied in a predetermined way by a predetermined degree as compared to a non-distorted constellation,

wherein said receiver (12) is further configured for

• receiving instructions from said control device (8) to employ said distorted constellation diagram with a determined degree of distortion for receiving said digital data, and

• employing a distorted constellation diagram with the determined degree of distortion for receiving said digital data.

Ansprüche

1. Verfahren zum Schutz eines Links in einem optischen Netzwerk, wobei der Link für die Übertragung von digitalen Daten unter Verwendung eines vorbestimmten Modulationsformats konfiguriert ist, wobei

- das Modulationsformat ein Konstellationsdiagramm verwendet, das eine Anzahl von Symbolen aufweist,

- jedes Symbol durch einen Punkt in einem n-dimensionalen euklidischen Signalraum mit n ≥1 repräsentiert ist,

- mit jedem Symbol eine binäre Adresse assoziiert ist, und

- das Modulationsformat eine Konstellationsverzerrung zulässt, gemäß der die relativen Positionen von Konstellationspunkten in dem Konstellationsdiagramm auf eine vorbestimmte Weise um einen vorbestimmten Grad im Vergleich zu einer nicht verzerrten Konstellation variiert werden,

wobei das Verfahren die folgenden Schritte aufweist:

A) Aufteilen des über die Verbindung zu übertragenden Verkehrs in zwei oder mehr Prioritätsklassen,

B) Zuordnen von Verkehr höherer Priorität zu vordefinierten Bitpositionen innerhalb der binären Symboladressen,

C) Bewerten der Qualität eines vorbestimmten Schutzlinks, über den ein Teil des Verkehrs im Falle eines Ausfalls des gegebenen Links übertragen werden könnte,

D) Bestimmen eines Verzerrungsgrades des Konstellationsdiagramms, derart, dass eine gewünschte Übertragungsqualität für die Übertragung des Verkehrs der höchsten Prioritätsklasse oder -klassen über den vordefinierten Schutzlink und eine gewünschte Übertragungsqualität für den gesamten Verkehr über den gegebenen Link gleichzeitig gewährleistet sind, und

E) Verwenden eines verzerrten Konstellationsdiagramms mit dem bestimmten Verzerrungsgrad für die Übertragung von digitalen Daten über den gegebenen Link.

2. Verfahren nach Anspruch 1, wobei die vordefinierten Bitpositionen Bitpositionen sind, die in der unverzerrten Konstellation eine Fehlerwahrscheinlichkeit aufweisen, die geringer ist als die durchschnittliche Fehlerwahrscheinlichkeit aller Bitpositionen.

3. Verfahren nach Anspruch 1 oder 2, das ferner bei einem Ausfall der gegebenen Verbindung einen Schritt F) aufweist, bei dem der Verkehr auf den Schutzlink umgeleitet wird.

4. Verfahren gemäß einem der vorhergehenden Ansprüche, wobei in Schritt C) die Qualität einer Vielzahl von alternativen vorbestimmten Schutzlinks ausgewertet wird, und wobei in Schritt D) der Grad der Verzerrung des Konstellationsdiagramms determiniert wird, so dass eine gewünschte Übertragungsqualität für den schlechtesten der Vielzahl von alternativen vorbestimmten Schutzlinks gewährleistet ist.

5. Verfahren gemäß einem der vorhergehenden Ansprüche, wobei in der Konstellationsverzerrung die vorbestimmte Art und Weise, die relativen Positionen der Konstellationspunkte zu variieren, eines oder mehrere der folgenden Merkmale aufweist

- Variieren der Abstände einer Untergruppe von benachbarten Konstellationspunkten in dem Konstellationsdiagramm,

- Variieren der Abstände einer Untergruppe von Konstellationspunkten von einer vordefinierten Position im Signalraum, die nicht mit einem Konstellationspunkt übereinstimmt,

- Drehen der Position einer Untergruppe von Konstellationspunkten in Bezug auf einen Ursprung des Signalraums, und/oder

wobei die vordefinierte Position im Signalraum dem Schwerpunkt einer Untergruppe von Konstellationspunkten entspricht oder so gewählt ist, dass bei der Veränderung die durchschnittliche Leistung des Signals unverändert bleibt.

6. Verfahren nach einem der vorhergehenden Ansprüche,

wobei das Konstellationsdiagramm zweidimensional ist und vier Quadranten aufweist, wobei in den binären Adressen der Konstellationspunkte zwei vorbestimmte Bitpositionen vorhanden sind, die für jeden Konstellationspunkt innerhalb desselben Quadranten identische Werte aufweisen, und

wobei Verkehr mit höherer Priorität auf die beiden vorbestimmten Bitpositionen abgebildet wird.

7. Verfahren nach einem der Ansprüche 5 bis 6, wobei das Modulationsformat eine 16QAM-Konstellation verwendet, und wobei in der Konstellationsverzerrung die vorbestimmte Art und Weise, die relativen Positionen von Konstellationspunkten zu variieren, eine Verringerung der Abstände zwischen Konstellationspunkten innerhalb desselben Quadranten umfasst, während der Mindestabstand zwischen Konstellationspunkten verschiedener Quadranten im Vergleich zu einer gleichmäßigen Verteilung von Konstellationspunkten erhöht wird.

8. Verfahren nach einem der Ansprüche 5 bis 6, wobei das Modulationsformat eine 32QAM-Konstellation verwendet, und wobei in der Konstellationsverzerrung die vorbestimmte Art und Weise, die relativen Positionen der Konstellationspunkte zu variieren, Folgendes umfasst

- für die vier Konstellationspunkte in jedem Quadranten, die dem Ursprung der zweidimensionalen Ebene am nächsten sind, die Verringerung ihres jeweiligen Abstands von ihrem Schwerpunkt, und

- für die vier Konstellationspunkte in jedem Quadranten, die am weitesten vom Ursprung der zweidimensionalen Ebene entfernt sind, erhöhen ihrer jeweiligen Abstände zum nächstgelegenen der vier Konstellationspunkte, die dem Ursprung am nächsten sind,

im Vergleich zu einer gleichmäßigen Verteilung der Konstellationspunkte.

9. Verfahren nach einem der Ansprüche 5 bis 6, bei dem das Modulationsformat eine 8QAM-Konstellation verwendet und wobei bei der Konstellationsverzerrung die vorbestimmte Art und Weise, die relativen Positionen der Konstellationspunkte zu variieren, das Rotieren der vier am weitesten vom Ursprung entfernten Konstellationspunkte um den Ursprung um einen Winkel umfasst, wobei der Winkel den Grad der Variation definiert.

10. Verfahren nach einem der vorhergehenden Ansprüche, wobei der über den Link zu übertragende Verkehr einem der folgenden entspricht:

- 200G-Verkehr, der über einen einzigen optischen DP-16QAM-Träger übertragen wird, der in zwei 100G-Signale mit unterschiedlichen Prioritäten aufgeteilt ist,

- 300G-Verkehr, der über einen aus zwei DP-8QAM-Trägern bestehenden Super-Channel übertragen wird,

- eine 400G-Übertragung auf einem einzigen Träger unter Verwendung von 32QAM oder 64QAM, und/oder

wobei das Verfahren ferner die Zuordnung einzelner FlexEthernet-Ströme zu verschiedenen Bitsätzen in der binären Adresse der Konstellationssymbole aufweist.

11. Steuervorrichtung (8) zur Steuerung des Schutzes eines Links in einem optischen Netzwerk,
wobei die Steuervorrichtung (8) dazu eingerichtet ist, operativ mit einem Sender (10) und einem Empfänger (12) verbunden zu sein, die mit dem Link assoziiert sind, wobei der Sender (10) zum Übertragen digitaler Daten unter Verwendung eines vorbestimmten Modulationsformats eingerichtet ist, wobei

- das Modulationsformat ein Konstellationsdiagramm verwendet, das eine Anzahl von Symbolen aufweist,

- jedes Symbol durch einen Punkt in einem n-dimensionalen euklidischen Signalraum repräsentiert wird, wobei n ≥1 ist,

- mit jedem Symbol eine binäre Adresse assoziiert ist, und

- das Modulationsformat eine Konstellationsverzerrung zulässt, gemäß der die relativen Positionen von Konstellationspunkten in dem Konstellationsdiagramm in einer vorbestimmten Weise um einen vorbestimmten Grad im Vergleich zu einer nicht verzerrten Konstellation variiert werden,

wobei die Steuereinrichtung (8) ferner zu folgendem eingerichtet ist:

- Auswerten der Qualität eines vordefinierten Schutzlinks, über den ein Teil des Verkehrs bei einem Ausfall des gegebenen Links übertragen werden könnte,

- Bestimmen eines Verzerrungsgrades des Konstellationsdiagramms, so dass eine gewünschte Übertragungsqualität für die Übertragung des Verkehrs der höchsten Prioritätsklasse oder -klassen über den vordefinierten Schutzlink und eine gewünschte Übertragungsqualität für den gesamten Verkehr über den gegebenen Link gleichzeitig gewährleistet sind, und

- Anweisen des Senders und des Empfängers, ein verzerrtes Konstellationsdiagramm mit dem bestimmten Verzerrungsgrad für die Übertragung von digitalen Daten über den gegebenen Link zu verwenden.

12. Steuervorrichtung (8) nach Anspruch 11, wobei die Steuervorrichtung operativ mit dem Sender (10) und dem Empfänger (12) verbunden ist.

13. Sender (10), eingerichtet zum Übertragen digitaler Daten unter Verwendung eines vorbestimmten Modulationsformats und dazu eingerichtet, operativ mit der Steuervorrichtung (8) nach Anspruch 11 verbunden zu sein, wobei

- das Modulationsformat ein Konstellationsdiagramm verwendet, das eine Anzahl von Symbolen aufweist,

- jedes Symbol durch einen Punkt in einem n-dimensionalen euklidischen Signalraum repräsentiert wird, wobei n ≥1

- mit jedem Symbol eine binäre Adresse assoziiert ist, und

- das Modulationsformat eine Konstellationsverzerrung zulässt, gemäß der die relativen Positionen von Konstellationspunkten in dem Konstellationsdiagramm in einer vorbestimmten Weise um einen vorbestimmten Grad im Vergleich zu einer nicht verzerrten Konstellation variiert werden,

wobei der Sender (10) ferner zu folgendem eingerichtet ist:

- Aufteilen der zu übertragenden Daten in zwei oder mehr Prioritätsklassen,

- Zuordnen von Verkehr höherer Priorität zu vordefinierten Bitpositionen innerhalb der binären Symboladressen,

- Empfangen von Anweisungen von der Steuervorrichtung (8), das verzerrte Konstellationsdiagramm mit einem bestimmten Verzerrungsgrad für die Übertragung von digitalen Daten zu verwenden, und

- Verwenden eines verzerrten Konstellationsdiagramms mit dem bestimmten Verzerrungsgrad für die Übertragung von digitalen Daten.

14. Empfänger (12), eingerichtet zum Empfangen digitaler Daten, die ein vorbestimmtes Modulationsformat verwenden, und eingerichtet, um operativ mit der Steuereinrichtung (8) des Anspruchs 11 verbunden zu sein, wobei

- das Modulationsformat ein Konstellationsdiagramm verwendet, das eine Anzahl von Symbolen aufweist,

- jedes Symbol durch einen Punkt in einem n-dimensionalen euklidischen Signalraum repräsentiert wird, wobei n ≥1

- mit jedem Symbol eine binäre Adresse assoziiert ist, und

- das Modulationsformat eine Konstellationsverzerrung zulässt, gemäß der die relativen Positionen von Konstellationspunkten in dem Konstellationsdiagramm in einer vorbestimmten Weise um einen vorbestimmten Grad im Vergleich zu einer unverzerrten Konstellation variiert werden,

wobei der Empfänger (12) ferner eingerichtet ist zum

- Empfangen von Anweisungen von der Steuervorrichtung (8), um das verzerrte Konstellationsdiagramm mit einem bestimmten Grad der Verzerrung zum Empfangen der digitalen Daten zu verwenden, und

- Verwenden eines verzerrten Konstellationsdiagramms mit dem bestimmten Verzerrungsgrad zum Empfangen der digitalen Daten.

Revendications

1. Procédé de protection d'une liaison dans un réseau optique, ladite liaison étant configurée de manière à transmettre des données numériques employant un format de modulation prédéterminé, dans lequel :

• ledit format de modulation utilise un diagramme de constellation comprenant un nombre de symboles ;

• chaque symbole est représenté par un point dans un espace de signal euclidien à « n » dimensions, où n ≥ 1 ;

• une adresse binaire est associée à chaque symbole ; et

• ledit format de modulation permet une déformation de constellation, selon laquelle les positions relatives des points de constellation dans le diagramme de constellation sont modifiées, d'une manière prédéterminée, d'un degré prédéterminé par rapport à une constellation non déformée,

ledit procédé comprenant les étapes ci-dessous consistant à :

A) partitionner le trafic à transmettre sur la liaison en deux classes de priorité ou plus ;

B) mettre en correspondance un trafic de priorité plus élevée avec des positions de bits prédéfinies dans les adresses de symboles binaires ;

C) évaluer la qualité d'une liaison de protection prédéterminée par l'intermédiaire de laquelle une partie du trafic pourrait être transmise en cas de défaillance de la liaison donnée ;

D) déterminer un degré de déformation du diagramme de constellation de sorte qu'une qualité de transmission souhaitée pour la transmission du trafic de la ou des classes de priorité la plus élevée par l'intermédiaire de ladite liaison de protection prédéterminée et qu'une qualité de transmission souhaitée pour l'ensemble du trafic par l'intermédiaire de ladite liaison donnée sont garanties simultanément ; et

E) employer un diagramme de constellation déformé avec le degré de déformation déterminé pour ladite transmission de données numériques sur ladite liaison donnée.

2. Procédé selon la revendication 1, dans lequel lesdites positions de bits prédéfinies sont des positions de bits qui, dans la constellation non déformée, présentent une probabilité d'erreur inférieure à la probabilité d'erreur moyenne de toutes les positions de bits.

3. Procédé selon la revendication 1 ou 2, comprenant en outre, en cas de défaillance de ladite liaison donnée, une étape F) consistant à réacheminer le trafic vers ledit chemin de protection.

4. Procédé selon l'une quelconque des revendications précédentes, dans lequel, à l'étape C), la qualité d'une pluralité de liaisons de protection prédéterminées alternatives est évaluée, et dans lequel, à l'étape D), le degré de déformation du diagramme de constellation est déterminé de sorte qu'une qualité de transmission souhaitée pour la pire liaison de ladite pluralité de liaisons de protection prédéterminées alternatives est garantie.

5. Procédé selon l'une quelconque des revendications précédentes, dans lequel, dans ladite déformation de constellation, ladite manière prédéterminée de modifier les positions relatives des points de constellation comprend une ou plusieurs des étapes ci-dessous consistant à :

• faire varier les distances d'un sous-ensemble de points de constellation adjacents dans ledit diagramme de constellation ;

• faire varier les distances d'un sous-ensemble de points de constellation à partir d'une position prédéfinie dans l'espace de signal qui ne coïncide pas avec un point de constellation ;

• faire tourner la position d'un sous-ensemble de points de constellation par rapport à une origine dudit espace de signal ; et/ou

dans lequel ladite position prédéfinie dans l'espace de signal correspond au centre de masse d'un sous-ensemble de points de constellation, ou est choisie de sorte que, suite à la variation, la puissance moyenne du signal reste inchangée.

6. Procédé selon l'une quelconque des revendications précédentes,

dans lequel ledit diagramme de constellation est bidimensionnel et comprend quatre quadrants, dans lequel, dans lesdites adresses binaires desdits points de constellation, il existe deux positions de bits prédéterminées qui présentent des valeurs identiques pour chaque point de constellation dans le même quadrant ; et

dans lequel un trafic de priorité plus élevée est mis en correspondance avec lesdites deux positions de bits prédéterminées.

7. Procédé selon l'une quelconque des revendications 5 à 6, dans lequel ledit format de modulation emploie une constellation 16QAM, et dans lequel, dans ladite déformation de constellation, ladite manière prédéterminée de faire varier les positions relatives des points de constellation comprend l'étape consistant à réduire les distances entre des points de constellation au sein du même quadrant, tout en augmentant la distance minimale entre des points de constellation de différents quadrants, par rapport à une distribution uniforme de points de constellation.

8. Procédé selon l'une quelconque des revendications 5 à 6, dans lequel ledit format de modulation emploie une constellation 32QAM, et dans lequel, dans ladite déformation de constellation, ladite manière prédéterminée de faire varier les positions relatives des points de constellation comprend les étapes ci-dessous consistant à :

• pour les quatre points de constellation dans chaque quadrant qui sont les plus proches de l'origine du plan bidimensionnel, réduire leur distance respective par rapport à leur centre de masse ; et

• pour les quatre points de constellation dans chaque quadrant qui sont les plus éloignés de l'origine du plan bidimensionnel, augmenter leur distance respective par rapport au point le plus proche, parmi les quatre points de constellation les plus proches de l'origine, par rapport à une distribution uniforme des points de constellation.

9. Procédé selon l'une quelconque des revendications 5 à 6, dans lequel ledit format de modulation emploie une constellation 8QAM, et dans lequel, dans ladite déformation de constellation, ladite manière prédéterminée de faire varier les positions relatives des points de constellation comprend l'étape consistant à faire tourner les quatre points de constellation les plus éloignés de l'origine, autour de ladite origine, selon un angle, ledit angle définissant ledit degré de variation.

10. Procédé selon l'une quelconque des revendications précédentes, dans lequel ledit trafic à transmettre sur la liaison correspond à l'un des trafics ci-dessous :

• un trafic de 200 G transmis sur une unique porteuse optique DP-16QAM partitionnée en deux signaux de 100 G avec des priorités différentes ;

• un trafic de 300 G transmis sur un super canal constitué de deux porteuses DP-8QAM ;

• une transmission de 400 G à porteuse unique utilisant une constellation 32QAM ou 64QAM ; et/ou

dans lequel ledit procédé comprend en outre l'étape consistant à mettre en correspondance des flux FlexEthernet individuels avec différents ensembles de bits dans l'adresse binaire des symboles de constellation.

11. Dispositif de commande (8) destiné à commander la protection d'une liaison dans un réseau optique, ledit dispositif de commande (8) étant configuré de manière à être connecté fonctionnellement à un émetteur (10) et à un récepteur (12) associés à ladite liaison, ledit émetteur (10) étant configuré de manière à transmettre des données numériques employant un format de modulation prédéterminé, dans lequel :

• ledit format de modulation utilise un diagramme de constellation comprenant un nombre de symboles ;

• chaque symbole est représenté par un point dans un espace de signal euclidien à « n » dimensions, où n ≥ 1 ;

• une adresse binaire est associée à chaque symbole ; et

• ledit format de modulation permet une déformation de constellation, selon laquelle les positions relatives des points de constellation dans le diagramme de constellation sont modifiées, d'une manière prédéterminée, d'un degré prédéterminé par rapport à une constellation non déformée ;

le dispositif de commande (8) étant en outre configuré de manière à :

• évaluer la qualité d'une liaison de protection prédéterminée par l'intermédiaire de laquelle une partie du trafic pourrait être transmise en cas de défaillance de la liaison donnée ;

• déterminer un degré de déformation du diagramme de constellation de sorte qu'une qualité de transmission souhaitée pour la transmission du trafic de la ou des classes de priorité la plus élevée par l'intermédiaire de ladite liaison de protection prédéterminée et qu'une qualité de transmission souhaitée pour l'ensemble du trafic par l'intermédiaire de ladite liaison donnée sont garanties simultanément ; et

• donner instruction audit émetteur et audit récepteur d'employer un diagramme de constellation déformé avec le degré de déformation déterminé pour ladite transmission de données numériques sur ladite liaison donnée.

12. Dispositif de commande (8) selon la revendication 11, dans lequel ledit dispositif de commande est connecté fonctionnellement audit émetteur (10) et audit récepteur (12).

13. Émetteur (10) configuré de manière à transmettre des données numériques employant un format de modulation prédéterminé, et configuré de manière à être connecté fonctionnellement au dispositif de commande (8) selon la revendication 11, dans lequel :

• ledit format de modulation utilise un diagramme de constellation comprenant un nombre de symboles ;

• chaque symbole est représenté par un point dans un espace de signal euclidien à « n » dimensions, où n ≥ 1 ;

• une adresse binaire est associée à chaque symbole ; et

• ledit format de modulation permet une déformation de constellation, selon laquelle les positions relatives des points de constellation dans le diagramme de constellation sont modifiées, d'une manière prédéterminée, d'un degré prédéterminé par rapport à une constellation non déformée ;

dans lequel ledit émetteur (10) est en outre configuré de manière à :

• partitionner les données à transmettre en deux classes de priorité ou plus ;

• mettre en correspondance un trafic de priorité plus élevée avec des positions de bits prédéfinies au sein des adresses de symboles binaires ;

• recevoir des instructions en provenance dudit dispositif de commande (8) visant à employer ledit diagramme de constellation déformé avec un degré de déformation déterminé pour ladite transmission de données numériques ; et

• employer un diagramme de constellation déformé avec le degré de déformation déterminé pour ladite transmission de données numériques.

14. Récepteur (12) configuré de manière à recevoir des données numériques employant un format de modulation prédéterminé, et configuré de manière à être connecté fonctionnellement au dispositif de commande (8) selon la revendication 11, dans lequel :

• ledit format de modulation utilise un diagramme de constellation comprenant un nombre de symboles ;

• chaque symbole est représenté par un point dans un espace de signal euclidien à « n » dimensions, où n ≥ 1 ;

• une adresse binaire est associée à chaque symbole ; et

• ledit format de modulation permet une déformation de constellation, selon laquelle les positions relatives des points de constellation dans le diagramme de constellation sont modifiées, d'une manière prédéterminée, d'un degré prédéterminé par rapport à une constellation non déformée ;

dans lequel ledit récepteur (12) est en outre configuré de manière à :

• recevoir des instructions, en provenance dudit dispositif de commande (8), visant à employer ledit diagramme de constellation déformé avec un degré de déformation déterminé pour recevoir lesdites données numériques ; et

• employer un diagramme de constellation déformé avec le degré de déformation déterminé, en vue de recevoir lesdites données numériques.

Drawing